Cerebral and tissue oximetry

Correlation of Near-Infrared Spectroscopy (NIRS) with Invasive Arterial Pressure Monitoring during Aortic Coarctation Surgery in Pediatric Patients

Aortic coarctation surgery in pediatric patients requires the placement of two arterial cannulas to monitor pressure gradients and surgical correction adequacy. Near-infrared spectroscopy (NIRS) monitoring provides insight into regional blood flow. This study aimed to investigate the correlation between NIRS values and invasive arterial pressures, exploring NIRS monitoring as a potential substitute for arterial cannulation. In a cohort of 21 consecutive pediatric patients undergoing aortic coarctation surgery, recordings of NIRS and invasive arterial pressure values were evaluated at various time intervals. Pearson correlation evaluated the relationship between NIRS values and invasively measured arterial pressures. Moderate to strong correlations were observed between the mean arterial pressure (MAP) of the upper and lower arteries and cerebral (rSO2-C) and somatic (rSO2-S) NIRS values 5 min after cross-clamp placement (r = 0.621, p = 0.003; r = 0.757, p < 0.001). Strong correlations were found 15 min after cross-clamp placement (r = 0.828, p = 0.002; r = 0.783, p = 0.004). Before transfer to the ICU, a strong correlation existed between the upper artery MAP and rSO2-C (r = 0.730, p < 0.001), but there was no correlation between the lower artery MAP and rSO2-S. These findings are promising, but further studies are required to validate it as a reliable substitute for invasive pressure monitoring in this patient population.

Cerebral regional oxygen saturation as a predictive parameter for preoperative heart failure and delayed hemodynamic recovery in transcutaneous aortic valve implantation: a retrospective cohort study

This study aimed to investigate the relationship of perioperative cerebral regional oxygen saturation (rSO2) with various preoperative clinical variables and hemodynamic changes during transfemoral transcatheter aortic valve implantation (TAVI) under general anesthesia. We retrospectively analyzed cerebral rSO2 values from left-hemisphere measurements obtained using near-infrared spectroscopy (O3™ regional oximetry) at five time points: pre-induction, the start of the procedure, the start of valve deployment, time of lowest cerebral rSO2 value during valve deployment, and the end of the procedure. This study included 91 patients (60 with balloon-expandable valves and 31 with self-expandable valves). The baseline cerebral rSO2 values were correlated with B-type natriuretic peptide, hemoglobin, fractional shortening, ejection fraction, left ventricular mass index, left ventricular end-systolic diameter, STS risk of mortality, and STS morbidity or mortality. The patients who took longer to recover their systolic blood pressure to 90 mmHg after valve deployment with a balloon-expandable valve (group B) had lower cerebral rSO2 values during deployment compared to patients with faster recovery with balloon-expandable valve (group A) and with self-expandable valve (group C). Baseline cerebral rSO2 is associated with preoperative variables related to cardiac failure and function, and a significant decline during valve deployment may indicate a risk of prolonged hypotension during TAVI.

Cerebral autoregulation-based mean arterial pressure targets and delirium in critically ill adults without brain injury: a retrospective cohort study

PURPOSE

Cerebral autoregulation (CA) is a mechanism that acts to maintain consistent cerebral perfusion across a range of blood pressures, and impaired CA is associated with delirium. Individualized CA-derived blood pressure targets are poorly characterized in critically ill patients and the association with intensive care unit (ICU) delirium is unknown. Our objectives were to characterize optimal mean arterial pressure (MAPopt) ranges in critically ill adults without brain injury and determine whether deviations from these targets contribute to ICU delirium.

METHODS

We performed a retrospective cohort analysis of patients with shock of any etiology and/or respiratory failure requiring invasive mechanical ventilation, without a neurologic admitting diagnosis. Patients were screened daily for delirium. Cerebral oximetry and mean arterial pressure data were captured for the first 24 hr from enrolment.

RESULTS

Forty-two patients with invasive blood pressure monitoring data were analyzed. Optimal mean arterial pressure targets ranged from 55 to 100 mm Hg. Optimal mean arterial pressure values were not significantly different based on history of hypertension or delirium status, and delirium was not associated with deviations from MAPopt. Nevertheless, the majority (69%) of blood pressure targets exceeded the current 65 mm Hg Surviving Sepsis guidelines.

CONCLUSION

We observed that MAPopt targets across patients were highly variable, but did not observe an association with the incidence of delirium. Studies designed to evaluate the impact on neurologic outcomes are needed to understand the association with individualized mean arterial pressure targets in the ICU.

STUDY REGISTRATION

ClinicalTrials.gov (NCT02344043); first submitted 22 January 2015.

Noninvasive tracking of mixed venous oxygen saturation via near-infrared spectroscopy cerebral oximetry: a retrospective observational study

Although previous studies have shown correlation between regional cerebral oxygen saturation (rScO2) and mixed venous oxygen saturation (SvO2), there is a lack of pragmatic information on the clinical applicability of these findings, such as tracking ability. We retrospectively analyzed continuous intraoperative recordings of rScO2 and SvO2 obtained from a pulmonary artery catheter and either of two near-infrared spectroscopy (NIRS) devices (INVOS 5100C, Medtronic; O3, Masimo) during off-pump cardiopulmonary bypass (OPCAB) surgery in adult patients. The ability of rScO2 to track SvO2 was quantitatively evaluated with 5 min interval changes transformed into relative values. The analysis included 176 h of data acquired from 48 subjects (26 and 22 subjects for INVOS and O3 dataset, respectively). The area under ROC of the left-rScO2 for detecting change of SvO2 ≥ 10% in INVOS and O3 datasets were 0.919 (95% CI 0.903-0.936) and 0.852 (95% CI 0.818-0.885). The concordance rates between the interval changes of left-rScO2 and SvO2 in INVOS and O3 datasets were 90.6% and 91.9% with 10% exclusion zone. rScO2 can serve as a noninvasive tool for detecting changes in SvO2 levels, a critical hemodynamic measurement.

Effects of dexmedetomidine on kidney and brain tissue microcirculation and histology in ovine cardiopulmonary bypass: a randomised controlled trial

Cardiac surgery requiring cardiopulmonary bypass is associated with postoperative acute kidney injury and neurocognitive disorders, including delirium. Intra-operative inflammation and/or impaired tissue perfusion/oxygenation are thought to be contributors to these outcomes. It has been hypothesised that these problems may be ameliorated by the highly selective α2 -agonist, dexmedetomidine. We tested the effects of dexmedetomidine on renal and cerebral microcirculatory tissue perfusion, oxygenation and histology in a clinically relevant ovine model. Sixteen sheep were studied while conscious, after induction of anaesthesia and during 2 h of cardiopulmonary bypass. Eight sheep were allocated randomly to receive an intravenous infusion of dexmedetomidine (0.4-0.8 μg.kg-1 .h-1 ) from induction of anaesthesia to the end of cardiopulmonary bypass, and eight to receive an equivalent volume of matched placebo (0.9% sodium chloride). Commencement of cardiopulmonary bypass decreased renal medullary tissue oxygenation in the placebo group (mean (95%CI) 5.96 (4.24-7.23) to 1.56 (0.84-2.09) kPa, p = 0.001), with similar hypoxic levels observed in the dexmedetomidine group (6.33 (5.33-7.07) to 1.51 (0.33-2.39) kPa, p = 0.002). While no differences in kidney function (i.e. reduced creatinine clearance) were evident, a greater incidence of histological renal tubular injury was observed in sheep receiving dexmedetomidine (7/8 sheep) compared with placebo (2/8 sheep), p = 0.041. Graded on a semi-quantitative scale (0-3), median (IQR [range]) severity of histological renal tubular injury was higher in the dexmedetomidine group compared with placebo (1.5 (1-2 [0-3]) vs. 0 (0-0.3 [0-1]) respectively, p = 0.013). There was no difference in cerebral tissue microglial activation (neuroinflammation) between the groups. Dexmedetomidine did not reduce renal medullary hypoxia or cerebral neuroinflammation in sheep undergoing cardiopulmonary bypass.

Monitoring Changes in Oxygen Muscle during Exercise with High-Flow Nasal Cannula Using Wearable NIRS Biosensors

Exercise increases the cost of breathing (COB) due to increased lung ventilation (V˙E), inducing respiratory muscles deoxygenation (∇SmO2), while the increase in workload implies ∇SmO2 in locomotor muscles. This phenomenon has been proposed as a leading cause of exercise intolerance, especially in clinical contexts. The use of high-flow nasal cannula (HFNC) during exercise routines in rehabilitation programs has gained significant interest because it is proposed as a therapeutic intervention for reducing symptoms associated with exercise intolerance, such as fatigue and dyspnea, assuming that HFNC could reduce exercise-induced ∇SmO2. SmO2 can be detected using optical wearable devices provided by near-infrared spectroscopy (NIRS) technology, which measures the changes in the amount of oxygen bound to chromophores (e.g., hemoglobin, myoglobin, cytochrome oxidase) at the target tissue level. We tested in a study with a cross-over design whether the muscular desaturation of m.vastus lateralis and m.intercostales during a high-intensity constant-load exercise can be reduced when it was supported with HFNC in non-physically active adults. Eighteen participants (nine women; age: 22 ± 2 years, weight: 65.1 ± 11.2 kg, height: 173.0 ± 5.8 cm, BMI: 21.6 ± 2.8 kg·m-2) were evaluated in a cycle ergometer (15 min, 70% maximum watts achieved in ergospirometry (V˙O2-peak)) breathing spontaneously (control, CTRL) or with HFNC support (HFNC; 50 L·min-1, fiO2: 21%, 30 °C), separated by seven days in randomized order. Two-way ANOVA tests analyzed the ∇SmO2 (m.intercostales and m.vastus lateralis), and changes in V˙E and ∇SmO2·V˙E-1. Dyspnea, leg fatigue, and effort level (RPE) were compared between trials by the Wilcoxon matched-paired signed rank test. We found that the interaction of factors (trial × exercise-time) was significant in ∇SmO2-m.intercostales, V˙E, and (∇SmO2-m.intercostales)/V˙E (p < 0.05, all) but not in ∇SmO2-m.vastus lateralis. ∇SmO2-m.intercostales was more pronounced in CTRL during exercise since 5' (p < 0.05). Hyperventilation was higher in CTRL since 10' (p < 0.05). The ∇SmO2·V˙E-1 decreased during exercise, being lowest in CTRL since 5'. Lower dyspnea was reported in HFNC, with no differences in leg fatigue and RPE. We concluded that wearable optical biosensors documented the beneficial effect of HFNC in COB due to lower respiratory ∇SmO2 induced by exercise. We suggest incorporating NIRS devices in rehabilitation programs to monitor physiological changes that can support the clinical impact of the therapeutic intervention implemented.

Effects of permissive hypercapnia on intraoperative cerebral oxygenation and early postoperative cognitive function in older patients with non-acute fragile brain function undergoing laparoscopic colorectal surgery: protocol study

BACKGROUND

Perioperative brain protection in older patients has been the focus of research recently; meanwhile, exploring the relationship between regional cerebral oxygen saturation (rSO2) and brain function in the perioperative period has been an emerging and challenging area-the difficulties related to the real-time monitoring of rSO2 and the choice of feasible interventions. As an advanced instrument for intraoperative rSO2 monitoring, the clinical application of near-infrared spectrum (NIRS) cerebral oxygen monitoring has gradually increased in popularity and is being recognized for its beneficial clinical outcomes in patients undergoing cardiac and noncardiac surgery. In addition, although sufficient evidence to support this hypothesis is still lacking, the effect of permissive hypercapnia (PHC) on rSO2 has expanded from basic research to clinical exploration. Therefore, monitoring intraoperative rSO2 in older patients with NIRS technology and exploring possible interventions that may change rSO2 and even improve postoperative cognitive performance is significant and clinically valuable.

METHODS

This study is a single-center randomized controlled trial (RCT). 76 older patients are enrolled as subjects. Patients who meet the screening criteria will be randomly assigned 1:1 to the control and intervention groups. PHC-based mechanical ventilation will be regarded as an intervention. The primary outcome is the absolute change in the percent change in rSO2 from baseline to the completion of surgery in the intervention and control groups. Secondary outcomes mainly include observations of intraoperative cerebral oxygenation and metabolism, markers of brain injury, and assessments of patients' cognitive function using scale through postoperative follow-up.

DISCUSSION

The findings of this RCT will reveal the effect of PHC on intraoperative rSO2 in older patients with nonacute fragile brain function (NFBF) and the approximate trends over time, and differences in postoperative cognitive function outcomes. We anticipate that the trial results will inform clinical policy decision-makers in clinical practice, enhance the management of intraoperative cerebral oxygen monitoring in older patients with comorbid NFBF, and provide guidance for clinical brain protection and improved postoperative cognitive function outcomes.

TRIAL REGISTRATION

ChiCTR, ChiCTR2200062093, Registered 9/15/2022.

Intraoperative application of regional cerebral oxygen saturation monitoring for geriatric patients in China: a survey

Background

Regional cerebral oxygen saturation (rSO2) monitoring is a real-time and non-invasive technique for estimating the balance of regional cerebral oxygen supply and consumption. Despite the growing popularity of this monitoring technique, data regarding outcome benefits remain sparse and contradictory. This study was conducted to explore the popularity and understanding of cerebral oxygen saturation monitoring during anesthesia in geriatric patients.

Methods

An online self-report questionnaire was distributed in March 2021 to various hospitals in China for dissemination to anesthesiologists. Questions surveyed cerebral oximetry equipment and utilization, demographics, and clinical practice of participants.

Results

In total, 447 anesthesiologists responded. Of these, 301 (67.3%) respondents reported that their hospitals were equipped with cerebral oximetry, which 274 anesthesiologists use during anesthesia. A high percentage of anesthesiologists chose to monitor rSO2 during cardiac surgery (77.4%, n = 212) and neurosurgery (40.5%, n = 111). Most anesthesiologists agreed that a 30% reduction from the rSO2 baseline requires intervention to avoid cerebral ischemia, mainly via elevating arterial pressure and fraction of inspired oxygen (FiO2). Of those without cerebral oximetry, 138 of 146 (94.5%) anesthesiologists were willing to monitor rSO2. In addition, 291 respondents believed that cerebral oxygen monitoring would help prevent postoperative cognitive dysfunction.

Conclusion

Our survey indicated that the prevalence of cerebral oximetry remains relatively low, while almost all anesthesiologists expressed their willingness to use rSO2 monitoring in geriatric anesthesia. Heterogeneity in clinical practice was identified, indicating relevant knowledge gaps that should encourage further clinical research to optimize treatment.

Cerebral tissue oximeter suitable for real-time regional oxygen saturation monitoring in multiple clinical settings

Maintenance of adequate blood perfusion and oxygen delivery is essential for cerebral metabolism. Cerebral oximeters based on near-infrared spectroscopy (NIRS) have been used for noninvasive, continuous, real-time monitoring of cerebral oxygen saturation and management of cerebral oxygen adequacy perioperatively and intraoperatively in various clinical situations, such as cardiac surgery, anesthesia, and cerebral auto-regulation. In this study, a portable and modular cerebral tissue oximeter (BRS-1) was designed for real-time detection of regional oxygen saturation over the brain, finger, or other targeted body tissues, as well as for wireless cerebral oxygenation monitoring. The compact and lightweight design of the system makes it easy to use during ambulance transport, in an emergency cart, or in an intensive care unit. The system performance of the BRS-1 oximeter was evaluated and compared with two US FDA-cleared cerebral oximeters during a controlled hypoxia experiment. The results showed that the BRS-1 oximeter can be used for real-time detection of cerebral desaturation with an accuracy similar to the two commercial oximeters. More importantly, the BRS-1 oximeter is capable of capturing cerebral oxygen saturation wirelessly. The BRS-1 cerebral oximeter can provide valuable insights for clinicians for real-time monitoring of cerebral/tissue perfusion and management of patients in prehospital and perioperative periods.

Traumatic Brain Injury: Intraoperative Management and Intensive Care Unit Multimodality Monitoring

Traumatic brain injury is a devastating event associated with substantial morbidity. Pathophysiology involves the initial trauma, subsequent inflammatory response, and secondary insults, which worsen brain injury severity. Management entails cardiopulmonary stabilization and diagnostic imaging with targeted interventions, such as decompressive hemicraniectomy, intracranial monitors or drains, and pharmacological agents to reduce intracranial pressure. Anesthesia and intensive care requires control of multiple physiologic variables and evidence-based practices to reduce secondary brain injury. Advances in biomedical engineering have enhanced assessments of cerebral oxygenation, pressure, metabolism, blood flow, and autoregulation. Many centers employ multimodality neuromonitoring for targeted therapies with the hope to improve recovery.

Regional oxygen saturation measured by two different oximetry monitors in infants and children undergoing living donor liver transplantation with bilirubin measurements: A prospective observational study

BACKGROUND

Tissue oximetry devices use wavelengths in the 680-870 nm range to separate between oxygenated/deoxygenated hemoglobin. Conjugated bilirubin has an absorption peak at 730 nm.

AIMS

We hypothesized that ForeSight Elite using 5 wavelengths reduces interference from bilirubin and shows higher regional tissue oxygen saturation (rSO₂ ) than INVOS 5100C incorporating 2 wavelengths.

METHODS

Infants and children undergoing living donor liver transplantation were included between March 2019 and September 2020. Cerebral and somatic rSO₂ were measured, and real-time simultaneous data were collected. Additionally, measurements were collected at (1) baseline, (2) beginning of dissection phase, (3) beginning of anhepatic phase, (4) reperfusion phase, and (5) skin closure. Bilirubin level was available at baseline and at reperfusion. Hyperbilirubinemia was defined as bilirubin level ≥1.0 mg/dl.

RESULTS

Thirty-three patients with median age of 27 months and median weight of 12 kg were included. Baseline bilirubin levels were higher compared to values at reperfusion (p = .021). A linear mixed effects model considering bilirubin as fixed and patient as random effect showed that there was a statistically significant difference in cerebral rSO₂ readings in function of time (p = .031), device (p < .001), and bilirubin concentrations (p = .007) but not for hemoglobin (p = .347), SpO₂ (p = .882), and arterial partial pressure of CO₂ (P_a CO₂ ) (p = .146). The model showed that there was a statistically significant difference in somatic rSO₂ readings in function of device (p < .001) and bilirubin concentrations (p = .023) but not for time (p = .074), hemoglobin (p = .954), SpO₂ (p = .108), and P_a CO₂ (p = .775). Bland-Altman plot analyzing cerebral and somatic rSO₂ between both devices showed respectively a mean absolute bias and 95% limits of agreement of 21.73% (-10.21 to 53.67) and 19.52% (-29.51 to 68.54).

CONCLUSIONS

Oximetry devices emitting light at >2 wavelengths may overcome interference from hyperbilirubinemia providing higher rSO₂ readings.

Splenic contraction and cardiovascular responses are augmented during apnea compared to rebreathing in humans

The spleen contracts during apnea, releasing stored erythrocytes, thereby increasing systemic hemoglobin concentration (Hb). We compared apnea and rebreathing periods, of equal sub-maximal duration (mean 137 s; SD 30), in eighteen subjects to evaluate whether respiratory arrest or hypoxic and hypercapnic chemoreceptor stimulation is the primary elicitor of splenic contraction and cardiovascular responses during apnea. Spleen volume, Hb, cardiovascular variables, arterial (SaO₂), cerebral (ScO₂), and deltoid muscle oxygen saturations (SmO₂) were recorded during the trials and end-tidal partial pressure of oxygen (P_ETO₂) and carbon dioxide (P_ETCO₂) were measured before and after maneuvers. The spleen volume was smaller after apnea, 213 (89) mL, than after rebreathing, 239 (95) mL, corresponding to relative reductions from control by 20.8 (17.8) % and 11.6 (8.0) %, respectively. The Hb increased 2.4 (2.0) % during apnea, while there was no significant change with rebreathing. The cardiovascular responses, including bradycardia, decrease in cardiac output, and increase in total peripheral resistance, were augmented during apnea compared to during rebreathing. The P_ETO₂ was higher, and the P_ETCO₂ was lower, after apnea compared to after rebreathing. The ScO₂ was maintained during maneuvers. The SaO₂ decreased 3.8 (3.1) % during apnea, and even more, 5.4 (4.4) %, during rebreathing, while the SmO₂ decreased less during rebreathing, 2.2 (2.8) %, than during apnea, 8.3 (6.2) %. We conclude that respiratory arrest per se is an important stimulus for splenic contraction and Hb increase during apnea, as well as an important initiating factor for the apnea-associated cardiovascular responses and their oxygen-conserving effects.

Near-infrared spectroscopy in the medical management of infants

Near-infrared spectroscopy (NIRS) is a technology that is easy to use and can provide helpful information about organ oxygenation and perfusion by measuring regional tissue oxygen saturation (rSO2) with near-infrared light. The sensors can be placed in different anatomical locations to monitor rSO2 levels in several organs. While NIRS is not without limitations, this equipment is now becoming increasingly integrated into modern healthcare practice with the goal of achieving better outcomes for patients. It can be particularly applicable in the monitoring of pediatric patients because of their size, and especially so in infant patients. Infants are ideal for NIRS monitoring as nearly all of their vital organs lie near the skin surface which near-infrared light penetrates through. In addition, infants are a difficult population to evaluate with traditional invasive monitoring techniques that normally rely on the use of larger catheters and maintaining vascular access. Pediatric clinicians can observe rSO2 values in order to gain insight about tissue perfusion, oxygenation, and the metabolic status of their patients. In this way, NIRS can be used in a non-invasive manner to either continuously or periodically check rSO2. Because of these attributes and capabilities, NIRS can be used in various pediatric inpatient settings and on a variety of patients who require monitoring. The primary objective of this review is to provide pediatric clinicians with a general understanding of how NIRS works, to discuss how it currently is being studied and employed, and how NIRS could be increasingly used in the near future, all with a focus on infant management.

Validation of photoacoustic/ultrasound dual imaging in evaluating blood oxygen saturation

Photoacoustic imaging (PAI) was performed to evaluate oxygen saturation (sO₂) of blood-mimicking phantoms, femoral arteries in beagles, and radial arteries in humans at various sO₂ plateaus. The accuracy (root mean square error, RMSE) of PAI sO₂ compared with reference sO₂ was calculated. In blood-mimicking phantoms, PAI achieved an accuracy of 1.49% and a mean absolute error (MAE) of 1.09% within 25 mm depth, and good linearity (R = 0.968; p < 0.001) was obtained between PAI sO₂ and reference sO₂. In canine femoral arteries, PAI achieved an accuracy of 2.16% and an MAE of 1.58% within 8 mm depth (R = 0.965; p < 0.001). In human radial arteries, PAI achieved an accuracy of 3.97% and an MAE of 3.28% in depth from 4 to 14 mm (R = 0.892; p < 0.001). For PAI sO₂ evaluation at different depths in healthy volunteers, the RMSE accuracy of PAI sO₂ increased from 2.66% to 24.96% with depth increasing from 4 to 14 mm. Through the multiscale method, we confirmed the feasibility of the hand-held photoacoustic/ultrasound (PA/US) in evaluating sO₂. These results demonstrate the potential clinical value of PAI in evaluating blood sO₂. Consequently, protocols for verifying the feasibility of medical devices based on PAI may be established.

Correlation and agreement of regional cerebral oxygen saturation measured from sensor sites at frontal and temporal areas in adult patients undergoing cardiovascular anesthesia

Background

The function and viability of the brain depend on adequate oxygen supply. A decrease in cerebral blood supply causing cerebral desaturation may lead to many neurological complications. Direct measurement of regional cerebral oxygen saturation (rScO₂) assists in early detection and management. Near-infrared spectroscopy (NIRS) has been introduced for measuring rScO₂. A pair of sensors are attached to the right and left forehead. However, there are some situations where the forehead of the patient is not accessible for sensor attachment (e.g., neurosurgery involving the frontal area; a bispectral index (BIS) sensor already attached, or a wound to the forehead); therefore, alternate sites for sensor attachment are required. The temporal area was proposed as an alternate site. The objective of this study was to assess the correlation and agreement of rScO₂ measured at the forehead vs. the temporal area.

Methods

Adult patients undergoing cardiothoracic or vascular surgery were monitored for rScO₂ using two pairs of ForeSight sensors. The first pair (A1 and A2) were attached to the right and left forehead, while the second pair (B1 and B2) were attached to the right and left temporal area. The rScO₂ values measured from A1 vs. B1 and A2 vs. B2 were assessed for correlation and agreement using the Bland-Altman analysis.

Results

Data from 19 patients with 14,364 sets of data were analyzed. The data from A1 vs. B1 and A2 vs. B2 showed moderate positive correlation (r = 0.627; P < 0.0001 and r = 0.548; P < 0.0001). The biases of A1 vs. B1 and A2 vs. B2 were -2.3% (95% CI [-2.5 to -2.2]; P < 0.0001) and 0.7% (95% CI [0.6-0.8]; P < 0.0001). The lower and upper limits of agreement of A1 vs. B1 were -17.5% (95% CI [-17.7 to -17.3]) and 12.8% (95% CI [12.6-13.0]). The lower and upper limits of agreement of A2 vs. B2 were -14.6% (95% CI [-14.8 to -14.4]) and 16.0% (95% [CI 15.8-16.3]).

Conclusions

The rScO₂ values measured from sensors at the frontal and temporal areas show a moderate correlation with sufficiently good agreement. The temporal area may be an alternative to the frontal area for cerebral oximetry monitoring.

Influence of moderate-hypothermia on renal and cerebral haemodynamics and oxygenation during experimental cardiopulmonary bypass in sheep

AIM

Cardiac surgery requiring cardiopulmonary bypass (CPB) can result in renal and cerebral injury. Intra-operative tissue hypoxia could contribute to such organ injury. Hypothermia, however, may alleviate organ hypoxia. Therefore, we tested whether moderate-hypothermia (30^o C) improves cerebral and renal tissue perfusion and oxygenation during ovine CPB.

METHODS

Ten sheep were studied while conscious, under stable anaesthesia and during 3 hours of CPB. In a randomised within-animal cross-over design, 5 sheep commenced CPB at a target body temperature of 30 ^o C (moderate-hypothermia). After 90 minutes, body temperature was increased to 36 ^o C (standard-procedure). The remaining 5 sheep were randomised to the opposite order of target body temperature.

RESULTS

Compared with the standard-procedure, moderately-hypothermic CPB reduced renal oxygen delivery (-34.8 ± 19.6%, P = 0.003) and renal oxygen consumption (-42.7 ± 35.2%, P = 0.04). Nevertheless, moderately-hypothermic CPB did not significantly alter either renal cortical or medullary tissue PO₂ . Moderately-hypothermic CPB also did not significantly alter cerebral perfusion, cerebral tissue PO₂ , or cerebral oxygen saturation compared with the standard-procedure. Compared with anaesthetised state, standard-procedure reduced renal medullary PO₂ (-21.0 ± 13.8 mmHg, P = 0.014) and cerebral oxygen saturation (65.0 ± 7.0 to 55.4 ± 9.6%, P = 0.022) but did not significantly alter either renal cortical or cerebral PO₂ .

CONCLUSION

Ovine experimental CPB leads to renal medullary tissue hypoxia. Moderately-hypothermic CPB did not improve cerebral or renal tissue oxygenation. In the kidney, this is probably because renal tissue oxygen consumption is matched by reduced renal oxygen delivery.

Combined Non-Invasive Optical Oximeter and Flowmeter with Basic Metrological Equipment

Optical non-invasive diagnostic methods and equipment are used today in many medical disciplines. However, there is still no generally accepted and unifying engineering theory of such systems. Today, they are developed most empirically and do not always have the desired effectiveness in clinics. Among reasons for their insufficient clinical efficiency, we can claim the limited set of measured parameters, the poorly substantiated technical design parameters, and the lack of metrological certification, which all together lead to large uncertainties and inaccuracies in diagnostic data. The purpose of this study is to develop a new instrument for non-invasive optical oximetry by means of substantiating and creating amore informative tissue oximeter with an enhanced number of measured parameters and equipped with the basic metrological tools—imitational measures. The combination of two related optical diagnostic techniques—a tissue oximetry, including a cerebral one, and a fluctuation flowmetry on a single hardware platform—was used. Theoretical modeling of light transport in tissues was applied to substantiate the main technical design parameters of the device. For each measuring channel, relevant imitation measures for metrological verification and adjustment have been proposed. Some common principles for the operation of such equipment are described in the article, as well.

Significant neonatal intraoperative cerebral and renal oxygen desaturation identified with near-infrared spectroscopy

INTRODUCTION

Near-infrared spectroscopy (NIRS) was used to monitor intraoperative regional oxygen saturation (rSO₂) during open (Op) and minimally invasive (MI) surgery performed in neonates (N) and children.

MATERIALS AND METHODS

NIRS sensors were applied to the forehead and flanks for cerebral rSO₂ (C-rSO₂) and renal rSO₂ (R-rSO₂), respectively. MI included laparoscopy (La), retroperitoneoscopy (Re) and thoracoscopy (Th). In children, Op and MI were major operations taking at least 3 h (MOp; MMI). Pathological desaturation (PD) was defined as > 20% deterioration in rSO₂.

RESULTS

Mean ages at surgery were N: 5.2 ± 8.2 days, MOp: 2.4 ± 2.9 years, and MMI: 3.8 ± 4.3 years. Despite significantly shorter operative times in N (169 ± 94 min; p < 0.0001), PD was significantly worse; PD(C-rSO₂): N = 14/35 (40.0%) versus MOp = 3/36 (8.3%) and MMI = 7/58 (12.1%); p = 0.0006, and PD(R-rSO₂): N = 27/35 (77.1%) versus MOp = 6/36 (16.7%) and MMI = 7/58 (12.1%); p < 0.0001, respectively. PD(R-rSO₂) occurred immediately with visceral reduction in NOp (Fig. 1) and PD was frequent during NMI(Th) (Fig. 2). rSO₂ was stable throughout MOp and MMI (Fig. 3). Fig. 1 Pathological desaturation in renal rSO₂ after visceral reduction for gastroschisis. Renal rSO₂ deteriorated immediately after viscera were returned to the abdominal cavity rSO₂ regional oxygen saturation Fig. 2 Fragility of tissue perfusion during thoracoscopic lung lobectomy in a neonate. Pathological desaturation occurred frequently during neonatal thoracoscopic surgery rSO₂ regional oxygen saturation Fig. 3 Changes in cerebral and renal rSO₂ according to operative time. Cerebral and renal rSO₂ did not appear to change according to operative time during major open and major minimally invasive surgery in children. rSO₂ regional oxygen saturation CONCLUSIONS: NIRS is a non-invasive technique for monitoring rSO₂ as an indicator of intraoperative stress and vascular perfusion. PD was so significant in neonates that intraoperative NIRS is highly recommended during thoracoscopy and procedures requiring visceral manipulation.

Perspectives: Regional brain oxygen saturation: beyond the brain there is also life

Abstract:

Some procedures, such as cardiovascular surgery, may compromise brain perfusion and require careful management to preserve the integrity of the central nervous system. In this setting, regional cerebral oxygen saturation [rSO2] emerges as an alternative, minimally invasive, monitoring system. The mechanism by which regional oxygen is measured is based on the refraction and absorption of a signal with a specific wavelength. Diagnostic and therapeutic algorithms for these settings. This would allow for a more rational use of goal-directed therapies that reduce morbidity and mortality in these patients.

Cerebral oximetry monitoring using near-infrared spectroscopy during adult procedural sedation: a preliminary study

BACKGROUND AND OBJECTIVES

We sought to evaluate the effect of adult procedural sedation on cerebral oxygenation measured by near-infrared spectroscopy (rSo₂ levels), and to assess whether respiratory depression occurring during procedural sedation was associated with decreases in cerebral oxygenation.

METHODS

We performed a prospective, observational preliminary study on a convenience sample of adult patients (>18 years) undergoing unscheduled procedural sedation in the ED from August 2017 to September 2018 at Hennepin County Medical Center in Minneapolis, Minnesota. The primary outcome measures were rSo₂ values by level of sedation achieved and the incidence of cerebral hypoxaemia during procedural sedation (absolute rSo₂ ≤60 or decrease ≥20% from baseline). The secondary outcome is the decrease in rSo₂ during episodes of respiratory adverse events (AEs), defined by respiratory depression requiring supportive airway measures.

RESULTS

We enrolled 100 patients (53% female). The median (IQR) rSo₂ values (%) by each level of sedation achieved on the Observer Assessment of Alertness and Sedation (OAAS) scale 1-5, respectively, were 74 (69-79), 74 (70-79), 74 (69-79), 75 (69-80), 72 (68-76). The incidence of cerebral hypoxaemia at any point within the sedation (absolute rSo₂ <60%) was 10/100 (10%); 2 out of 10 had rSo₂ reduction more than 20% from baseline value; the median (IQR) observed minimum rSo₂ in these patients was 58 (56-59). We observed respiratory depression in 65 patients via standard monitoring; of these, 39 (60%) required at least one supportive airway measure, meeting the definition of a respiratory AE. During these AEs, 15% (6/39) demonstrated cerebral hypoxaemia with a median (IQR) minimum rSo₂ of 58 (57-59). Four patients (4%) had cerebral hypoxaemia without a respiratory AE.

CONCLUSION

Cerebral oximetry may represent a useful tool for procedural sedation safety research to detect potential subclinical changes that may be associated with risk, but appears neither sensitive nor specific for routine use in clinical practice.

Cerebral oximetry-guided pulmonary artery banding for end-stage heart failure in a child with left ventricular noncompaction cardiomyopathy: a case report

Pulmonary artery banding (PAB) may reduce the need for left ventricular assist devices and heart transplantation in children with end-stage heart failure. However, excessive banding may increase the right ventricular afterload, leading to worsening of heart failure. The estimated right ventricular pressure and the shifting of the interventricular septum by transesophageal echocardiography (TEE), pulmonary artery pressure, right atrial and ventricular pressure, percutaneous oxygen saturation, and mixed venous oxygen saturation are utilized to determine the optimal circumference for PAB. Here, we report the case of a 5-month-old patient with end-stage heart failure due to left ventricular noncompaction cardiomyopathy (LVNC), with a gene mutation of MYH7, who underwent successful PAB. The exact PAB placement was additionally guided by using cerebral regional oxygen saturation (rSO₂) measurement to achieve a tolerable and optimal PAB effect. We monitored rSO₂ and other hemodynamic parameters while surgeons banded the pulmonary artery to achieve both highest rSO₂ levels and stable hemodynamics. rSO₂ was 68% before banding, and increased and remained at over 90% after the banding at same FiO₂. Patient's heart failure improved gradually, and the child was discharged home at 6 months after PAB. The rSO₂ is a simple and non-invasive monitor for the measurement of oxygen delivery to the brain tissue. rSO₂ alone would not be able to guide PAB placement in the vulnerable DCM patients, but it may be of one further monitoring value for the optimal pulmonary artery circumference while patients are undergoing PAB.

Measurement of Tissue Oximetry in Standing Unsedated and Sedated Horses

Near infrared spectroscopy (NIRS) noninvasively measures peripheral tissue oxygen saturation (StO₂) and may be useful to detect early changes in StO₂ in anaesthetized and critically ill horses. This study aimed to identify the muscle belly that provided the highest percentage of successful StO₂ readings and the highest mean StO₂ value. Fifty adult horses were enrolled in a prospective controlled study. StO₂ was measured at six different muscles in each horse, for each intervention: hair overlying the muscle was clipped (post clipping: PC), clipped skin was cleaned with chlorhexidine (post-surgical prepping: PP) and medetomidine was administered intravenously (post medetomidine: PM). Mean StO₂ values were calculated for each muscle, and a linear effects model was used to assess the effect of muscle group and intervention on StO₂. The sartorius muscle gave the highest percentage of successful StO₂ values (p < 0.001) and the highest mean (90% CI) StO₂ values for the PC, PP and PM interventions. Surgical prepping of the skin increased the success for measurement of StO₂ values. For all muscles, administration of medetomidine was associated with lower StO₂ values (p < 0.001). In conclusion, of the muscles examined, the sartorius muscle may be the preferred muscle to measure StO₂ in horses, and clipping and cleaning of the probe placement site is recommended.

Cerebral Perfusion and Brain Oxygen Saturation Monitoring with: Jugular Venous Oxygen Saturation, Cerebral Oximetry, and Transcranial Doppler Ultrasonography

Accumulating evidence indicates that cerebral desaturation in the perioperative period occurs more frequently than recognized. Combining monitoring modalities that reflect different aspects of cerebral perfusion status, such as near-infrared spectroscopy, jugular bulb saturation, and transcranial Doppler ultrasonography, may provide an extended window for prevention, early detection, and prompt intervention in ongoing hypoxic/ischemic neuronal injury and, thereby, improve neurologic outcome. Such an approach would minimize the impact of limitations of each monitoring modality, while individual components complement each other, enhancing the accuracy of acquired information. Current literature has failed to demonstrate any clear-cut clinical benefit of these modalities on outcome prognosis.

Near-Infrared Spectroscopy (NIRS) for Cerebral and Tissue Oximetry: Analysis of Evolving Applications

THE USE OF NEAR-INFRARED SPECTROSCOPY (NIRS) has increased significantly worldwide in the past decade. This technology, first described more than 40 years ago, is based on the fact that near-infrared light is able to penetrate biologic tissue and can obtain real-time, noninvasive information on tissue oxygenation and metabolism. In the clinical setting, NIRS has been able to provide clinicians potentially valuable information in patients with impaired microcirculations (systemic and cerebral). Near-infrared spectroscopy has progressed beyond assessment of brain oxygenation to monitor local tissue and muscle oxygenation and perfusion. This review analyzes the published data and provides the clinician a comprehensive account of the perioperative utility of NIRS in cardiac, vascular and thoracic surgery, as well as its increasing role in tissue/muscle oxygenation monitoring.

Trans-Ocular Brain Impedance Indices Predict Pressure Reactivity Index Changes in a Porcine Model of Hypotension and Cerebral Autoregulation Perturbation

BACKGROUND

Cerebrovascular autoregulation (CA) is a protective mechanism that enables the cerebral vasculature to automodulate tone in response to changes in cerebral perfusion pressure to ensure constant levels of cerebral blood flow (CBF) and oxygen delivery. CA can be impaired after neurological injury and contributes to secondary brain injury. In this study, we report novel impedance indices using trans-ocular brain impedance (TOBI) during controlled systemic hemorrhage and hypotension to assess CA in comparison with pressure reactivity index (PRx).

METHODS

Yorkshire swine were instrumented to record intracranial pressure (ICP), mean arterial pressure (MAP), and CBF. TOBI was recorded using electrocardiographic electrodes placed on the closed eyelids. Impedance changes (dz) were recorded in response to introducing an alternating current (0.4 mA) through the electrodes. MAP, ICP, and CBF were also measured. Animals were subjected to a controlled hemorrhage to remove 30-40% of each animal's total blood volume over 25-35 min. Hemorrhage was titrated to reach an MAP of approximately 35 mm Hg and end-tidal carbon dioxide above 28 mm Hg. PRx was calculated as a moving Pearson correlation between MAP and ICP. TOBI indices were calculated as the amplitude of the respiratory-induced changes in dz. DZx was calculated as a moving Pearson correlation between dz and MAP. TOBI indices (dz and DZx) were compared with hemodynamic indicators and PRx.

RESULTS

dz was shown to be highly correlated with MAP, ICP, cerebral perfusion pressure, and CBF (r =  - 0.823, - 0.723, - 0.813, and - 0.726), respectively (p < 0.0001). During hemorrhage, cerebral perfusion pressure and CBF had a mean percent decrease (standard deviation) from baseline of - 54.2% (12.5%) and - 28.3% (14.7%), respectively, whereas dz increased by 277% (268%). Receiver operator characteristics and precision-recall curves demonstrated high predictive performance of DZx when compared with PRx with an area under the curve above 0.82 and 0.89 for receiver operator characteristic and precision-recall curves, respectively, with high sensitivity and positive predictive power.

CONCLUSIONS

TOBI indices appear to track changes in PRx and hemodynamics that affect CA during hemorrhage-induced hypotension. TOBI may offer a suitable, less invasive surrogate to PRx for monitoring and assessing CA.

Cerebral oximetry and preventing neurological complication post-cardiac surgery: a systematic review

OBJECTIVES

This systematic review aims to provide an up-to-date summary of the current literature examining the relationship between intraoperative regional cerebral oxygen saturation and neurological complications after cardiac surgery.

METHODS

Observational and interventional studies investigating the link between regional cerebral oxygen saturation and postoperative delirium, cognitive dysfunction and stroke were included. After database searching and study screening, study characteristics and major findings were extracted.

RESULTS

Twenty-seven studies were identified. Of the observational studies (n = 17), 8 reported that regional cerebral oxygen desaturations were significantly associated with neurological complications after cardiac surgery. Of the interventional studies (n = 10), 3 provided evidence for monitoring cerebral oximetry during cardiac surgery as a means of reducing incidence of postoperative cognitive dysfunction or stroke. There was significant heterogeneity in the tools and rigor used to diagnose neurological complications.

CONCLUSIONS

Studies to date show an inconsistent relationship between regional cerebral oxygen saturation and neurological outcomes after cardiac surgery, and lack of clear benefit of targeting cerebral oximetry to minimize neurological complications. Standardized assessments, definitions of impairment and desaturation thresholds will help determine the benefits of cerebral oximetry monitoring during cardiac surgery.

Intraoperative cerebral oximetry in open heart surgeries reduced postoperative complications: A retrospective study

Cardiothoracic surgeries are life-saving procedures but often it results in various complications. Intraoperative cerebral oximetry monitoring used to detect regional cerebral oxygen saturation (rScO2) is a non-invasive method that provides prognostic importance in cardiac surgery. The main aim of the present study was to evaluate the association of intraoperative cerebral oxygen monitoring during cardiac surgery on postoperative complications. This was a case-controlled retrospective study conducted on adult patients, who underwent open-heart surgery in National Heart Institute, Malaysia. The case group comprised patients on protocolized cerebral oximetry monitoring. They were treated using a standardized algorithm to maintain rScO2 not lower than 20% of baseline rScO2. The control group comprised patients with matched demographic background, preoperative risk factors, and type of surgical procedures. Propensity score stratification was utilized to contend with selection bias. Retrospective analysis was performed on 240 patients (case group) while comparing it to 407 patients (control group). The non-availability of cerebral oximetry monitoring during surgery was the prominent predictor for all outcome of complications; stroke (OR: 7.66), renal failure needing dialysis (OR: 5.12) and mortality (OR: 20.51). Postoperative complications revealed that there were significant differences for risk of mortality (p<0.001, OR = 20.51), renal failure that required dialysis (p<0.001, OR = 5.12) and stroke (p <0.05, OR = 7.66). Protocolized cerebral oximetry monitoring during cardiothoracic surgeries was found to be associated with lower incidence of stroke, renal failure requiring dialysis and mortality rate.

The role of non-invasive brain oximetry in adult critically ill patients without primary brain injury

A primary objective in intensive care and perioperative settings is to promote an adequate supply and delivery of oxygen to tissues and organs, particularly to the brain. Cerebral near infrared spectroscopy (NIRS) is a non-invasive, continuous monitoring technique, that can be used to assess cerebral oxygenation. Using NIRS to monitor cerebral oximetry is not new, and has been in widespread use in neonates and cardiac surgery for decades. In addition, it has become common to see NIRS being used in adult and pediatric cardiac surgery, acute neurological diseases, neurosurgical procedures, vascular surgery, severe trauma and other acute medical diseases. Furthermore, recent evidence suggests a role for NIRS in the perioperative settings; detecting and preventing episodes of cerebral desaturation aiming to reduce the development of post-operative delirium. NIRS is not without its limitations; these include the risk of extra-cranial contamination, spatial limitations and skin blood flow/volume changes, as well being a measure of localized blood oxygenation underneath the sensor. However, NIRS is a non-invasive technique and can, therefore, be used in those patients without indications or justification for invasive brain monitoring; non-neurosurgical procedures such as liver transplantation, major orthopedic surgery and critically illness where the brain is at risk. The aim of this manuscript was to discuss the physical principles of NIRS and to report the current evidence regarding its use in critically ill patients without primary non-anoxic brain injury.

Cerebral oxygen saturation (rSO2) during cardiopulmonary bypass (CPB) measured using the INVOS oximeter closely correlates with baseline rSO2

Baseline cerebral regional saturation (rSO₂) measured using the INVOS 5100C (Medtronic, MN, USA) varies widely among patients with cardiac and/or renal diseases. To identify significant correlates of baseline rSO₂ and to investigate intraoperative rSO₂ changes, we conducted a retrospective study in 494 patients undergoing on-pump cardiovascular surgery. Correlations between preoperative blood laboratory test variables and baseline rSO₂ before anesthesia were examined. Intraoperative rSO₂ changes were analyzed. Of all the variables examined, log-transformed B-type natriuretic peptide (BNP) most significantly and negatively correlated with baseline rSO₂ (r = - 0.652, p < 0.0001). Intraoperatively, rSO₂ showed the lowest value during cardiopulmonary bypass (CPB) (median rSO₂: 56.2% during CPB vs. 63.9% at baseline, p < 0.0001). Although rSO₂ during CPB correlated positively with hemoglobin concentration and oxygen delivery during CPB (r = 0.192, p < 0.0001; and r = 0.172, p = 0.0001, respectively), it correlated much more closely with baseline rSO₂ (r = - 0.589, p < 0.0001). Thus, patients showing low baseline rSO₂ primarily associated with preoperatively high BNP continued to show low rSO₂ even during CPB independent of hemodynamics artificially controlled by CPB. Our findings suggest that low baseline rSO₂ in patients with high BNP due to cardiac and/or renal diseases is more likely to result from tissue edema causing alterations in optical pathlength and thus in calculated rSO₂ values, not readily modifiable with CPB, rather than actual cerebral hemodynamic alterations readily modifiable with CPB. These may partly explain why the INVOS oximeter is a trend monitor requiring baseline measures.

Neuromonitoring After Cardiac Arrest: Can Twenty-First Century Medicine Personalize Post Cardiac Arrest Care?

Cardiac arrest survivors comprise a heterogeneous population, in which the etiology of arrest, systemic and neurologic comorbidities, and sequelae of post-cardiac arrest syndrome influence the severity of secondary brain injury. The degree of secondary neurologic injury can be modifiable and is influenced by factors that alter cerebral physiology. Neuromonitoring techniques provide tools for evaluating the evolution of physiologic variables over time. This article reviews the pathophysiology of hypoxic-ischemic brain injury, provides an overview of the neuromonitoring tools available to identify risk profiles for secondary brain injury, and highlights the importance of an individualized approach to post cardiac arrest care.

Cerebrovascular autoregulation and arterial carbon dioxide in patients with acute respiratory distress syndrome: a prospective observational cohort study

BACKGROUND

Early hypercapnia is common in patients with acute respiratory distress syndrome (ARDS) and is associated with increased mortality. Fluctuations of carbon dioxide have been associated with adverse neurological outcome in patients with severe respiratory failure requiring extracorporeal organ support. The aim of this study was to investigate whether early hypercapnia is associated with impaired cerebrovascular autoregulation during the acute phase of ARDS.

METHODS

Between December 2018 and November 2019, patients who fulfilled the Berlin criteria for ARDS, were enrolled. Patients with a history of central nervous system disorders, cerebrovascular disease, chronic hypercapnia, or a life expectancy of less than 24 h were excluded from study participation. During the acute phase of ARDS, cerebrovascular autoregulation was measured over two time periods for at least 60 min. Based on the values of mean arterial blood pressure and near-infrared spectroscopy, a cerebral autoregulation index (COx) was calculated. The time with impaired cerebral autoregulation was calculated for each measurement and was compared between patients with and without early hypercapnia [defined as an arterial partial pressure of carbon dioxide (PaCO2) ≥ 50 mmHg with a corresponding arterial pH < 7.35 within the first 24 h of ARDS diagnosis].

RESULTS

Of 66 patients included, 117 monitoring episodes were available. The mean age of the study population was 58.5 ± 16 years. 10 patients (15.2%) had mild, 28 (42.4%) moderate, and 28 (42.4%) severe ARDS. Nineteen patients (28.8%) required extracorporeal membrane oxygenation. Early hypercapnia was present in 39 patients (59.1%). Multivariable analysis did not show a significant association between early hypercapnia and impaired cerebrovascular autoregulation (B = 0.023 [95% CI - 0.054; 0.100], p = 0.556). Hypocapnia during the monitoring period was significantly associated with impaired cerebrovascular autoregulation [B = 0.155 (95% CI 0.014; 0.296), p = 0.032].

CONCLUSION

Our results suggest that moderate permissive hypercapnia during the acute phase of ARDS has no adverse effect on cerebrovascular autoregulation and may be tolerated to a certain extent to achieve low tidal volumes. In contrast, episodes of hypocapnia may compromise cerebral blood flow regulation. Trial registration ClinicalTrials.gov; registration number: NCT03949738; date of registration: May 14, 2019.

Monitoring tissue oxygenation index using near-infrared spectroscopy during pre-hospital resuscitation among out-of-hospital cardiac arrest patients: a pilot study

Background

Tissue oxygenation index (TOI) using the near infrared spectroscopy (NIRS) has been demonstrated as a useful indicator to predict return of spontaneous circulation (ROSC) among out-of-hospital cardiac arrest (OHCA) patients in hospital setting. However, it has not been widely examined based on pre-hospital setting.

Methods

In this prospective observational study, we measured TOI in pre-hospital setting among OHCA patients receiving cardio-pulmonary resuscitation (CPR) during ambulance transportation between 2017 and 2018. Throughout the pre-hospital CPR procedure, TOI was continuously measured. The study population was divided into two subgroups: ROSC group and non-ROSC group.

Results

Of the 81 patients included in the final analysis, 26 achieved ROSC and 55 did not achieve ROSC. Patients in the ROSC group were significantly younger, had higher ∆TOI (changes in TOI) (5.8 % vs. 1.3 %; p < 0.01), and were more likely to have shockable rhythms and event witnessed than patients in the non-ROSC group. ∆TOI cut-off value of 5 % had highest sensitivity (65.4 %) and specificity (89.3 %) for ROSC. Patients with a cut-off value ≤-2.0 % did not achieve ROSC and while all OHCA patient with a cut-off value ≥ 8.0 % achieved ROSC. In addition, ROSC group had stronger positive correlation between mean chest compression rate and ∆TOI (r = 0.82) than non-ROSC group (r = 0.50).

Conclusions

This study suggests that ∆ TOI could be a useful indicator to predict ROSC in a pre-hospital setting.

Monitoring of cerebral oximetry in patients with postural orthostatic tachycardia syndrome

AIMS 

Postural orthostatic tachycardia syndrome (POTS) is a disorder of unknown aetiology characterized by orthostatic intolerance and tachycardia with diverse other symptoms, including neurocognitive deficits. Cerebral oximetry non-invasively measures cerebral tissue saturation (SctO2) and has been shown to be informative in syncope evaluation. We aimed to assess SctO2 in POTS patients and those with normal response to orthostatic provocation, relative to haemodynamic parameters and symptoms.

METHODS AND RESULTS 

Thirty-four patients with POTS (29.1 ± 9.5 years; 26 females) and 34 age-/sex-matched controls with normal head-up tilt tests (HUTs) were included. SctO2 at rest and during HUT were compared between POTS and controls. The relation between SctO2, systolic blood pressure (SBP), and heart rate (HR) during HUT was linearly assessed. SctO2 values were related to dizziness or syncope during HUT. The minimum SctO2-value during HUT was lower (65.4 ± 5.6 vs. 68.2 ± 4.2%, P = 0.023) and changes in SctO2 from supine to minimum HUT value were more pronounced in POTS patients (-5.7 ± 2.9% vs. -4.3 ± 2.1%, P = 0.028). Decrease in SBP from supine to minimum HUT value (P = 0.004) and increase in HR from supine to HUT value at 3 min (P = 0.022) correlated with more pronounced SctO2 decrease in POTS but not controls. SctO2 did not predict syncope or dizziness during HUT.

CONCLUSION 

Postural orthostatic tachycardia syndrome patients have lower cerebral tissue saturation during orthostatic provocation compared with those subjects having normal haemodynamic response to tilt. Orthostatic decrease in cerebral saturation only weakly correlates with HR increase and does not predict vasovagal reflex in POTS. Other hitherto unknown factors may affect cerebral tissue saturation in POTS.

Trans-ocular brain impedance index for assessment of cerebral autoregulation in a porcine model of cerebral hemodynamic perturbation

Cerebrovascular autoregulation (CA) is often impaired following traumatic brain injury. Established technologies and metrics used to assess CA are invasive and conducive for measurement, but not for continuous monitoring. We developed a trans-ocular brain impedance (TOBI) method that may provide non-invasive and continuous indices to assess CA. In this study, we monitored impedance metrics such as respiratory-induced impedance amplitude changes (dz) as well as a novel impedance index (DZx), which is a moving Pearson correlation between mean arterial pressure (MAP) and dz. Yorkshire swine were instrumented to continuously record ICP, MAP, and cerebral blood flow (CBF). TOBI was recorded by placement of standard ECG electrodes on closed eyelids and connected to a data acquisition system. MAP, ICP and CBF were manipulated utilizing an intravenous vasopressor challenge. TOBI indices (dz and DZx) were compared to the hemodynamic indicators as well as pressure reactivity index (PRx). During the vasopressor challenge, dz was highly correlated with ICP, CPP, and CBF (r =  < - 0.49, p < 0.0001). ICP, CPP, and CBF had a mean percent increase (standard deviation) from baseline of 29(23.2)%, 70(25)%, and 37(72.6)% respectively while dz decreased by 31(15.6)%. Receiver operator curve test showed high predictive performance of DZx when compared to PRx with area under the curve above 0.86, with high sensitivity and specificity. Impedance indices appear to track changes in PRx and hemodynamics that affect cerebral autoregulation. TOBI may be a suitable less invasive surrogate to PRx and capable of tracking cerebral autoregulation.

Assessment of a Non Invasive Brain Oximeter in Volunteers Undergoing Acute Hypoxia

INTRODUCTION

Research in traumatic brain injury suggests better patient outcomes when invasive oxygen monitoring is used to detect and correct episodes of brain hypoxia. Invasive brain oxygen monitoring is, however, not routinely used due to the risks, costs and technical challengers. We are developing a non-invasive brain oximeter to address these limitations. The monitor uses the principles of pulse oximetry to record a brain photoplethysmographic waveform and oxygen saturations. We undertook a study in volunteers to assess the new monitor.

PATIENTS AND METHODS

We compared the temporal changes in the brain and skin oxygen saturations in six volunteers undergoing progressive hypoxia to reach arterial saturations of 70%. This approach provides a method to discriminate potential contamination of the brain signal by skin oxygen levels, as the responses in brain and skin oxygen saturations are distinct due to the auto-regulation of cerebral blood flow to compensate for hypoxia. Conventional pulse oximetry was used to assess skin oxygen levels. Blood was also collected from the internal jugular vein and correlated with the brain oximeter oxygen levels.

RESULTS

At baseline, a photoplethysmographic waveform consistent with that expected from the brain was obtained in five subjects. The signal was adequate to assess oxygen saturations in three subjects. During hypoxia, the brain's oximeter oxygen saturation fell to 74%, while skin saturation fell to 50% (P<0.0001). The brain photoplethysmographic waveform developed a high-frequency oscillation of ~7 Hz, which was not present in the skin during hypoxia. A weak correlation between the brain oximeter and proximal internal jugular vein oxygen levels was demonstrated, R2=0.24, P=0.01.

CONCLUSION

Brain oximeter oxygen saturations were relatively well preserved compared to the skin during hypoxia. These findings are consistent with the expected physiological responses and suggest skin oxygen levels did not markedly contaminate the brain oximeter signal.

Regional thigh tissue oxygen saturation during cardiopulmonary bypass predicts acute kidney injury after cardiac surgery

Cardiopulmonary bypass-associated acute kidney injury may appear postoperatively, but predictive factors are unclear. We investigated the potential of regional tissue oxygen saturation as a predictor of cardiopulmonary bypass-associated acute kidney injury. We analyzed the clinical data of 150 adult patients not on dialysis who underwent elective cardiac surgical procedures during January 2015-March 2017. Near-infrared spectroscopy was used to measure regional oxygen saturation. Sensors were placed on the patients' forehead, abdomen, and thigh. The incidence of acute kidney injury was 2% at the end of surgery, 13% at 24 h, and 9% at 48 h, with the highest at 24 h after surgery. The multiple regression analysis revealed that the thigh regional oximetry during cardiopulmonary bypass, oxygen delivery index, and neutrophil count at the end of cardiopulmonary bypass and surgery were independent risk factors for acute kidney injury. The receiver-operating characteristic curve analysis suggested that a cutoff of regional oxygen saturation at the thigh of ≤ 67% was predictive of acute kidney injury within 24 h after surgery. In conclusion, the regional oxygen saturation at the thigh during cardiopulmonary bypass is a crucial marker to predict postoperative acute kidney injury in adults undergoing cardiac surgery.

Randomised controlled trial to investigate the relationship between mild hypercapnia and cerebral oxygen saturation in patients undergoing major surgery

OBJECTIVES

The effects of hypercapnia on regional cerebral oxygen saturation (rSO₂) during surgery are unclear. We conducted a randomised controlled trial to investigate the relationship between mild hypercapnia and rSO₂. We hypothesised that, compared with targeted normocapnia (TN), targeted mild hypercapnia (TMH) during major surgery would increase rSO₂.

DESIGN

A prospective, randomised, controlled trial in adult participants undergoing elective major surgery.

SETTING

A single tertiary centre in Heidelberg, Victoria, Australia.

PARTICIPANTS

40 participants were randomised to either a TMH or TN group (20 to each).

INTERVENTIONS

TMH (partial pressure of carbon dioxide in arterial blood, PaCO₂, 45-55 mm Hg) or TN (PaCO₂ 35-40 mm Hg) was delivered via controlled ventilation throughout surgery.

PRIMARY AND SECONDARY OUTCOME MEASURES

The primary endpoint was the absolute difference between the two groups in percentage change in rSO₂ from baseline to completion of surgery. Secondary endpoints included intraoperative pH, bicarbonate concentration, base excess, serum potassium concentration, incidence of postoperative delirium and length of stay (LOS) in hospital.

RESULTS

The absolute difference between the two groups in percentage change in rSO₂ from the baseline to the completion of surgery was 19.0% higher in both hemispheres with TMH (p<0.001). On both sides, the percentage change in rSO₂ was greater in the TMH group than the TN group throughout the duration of surgery. The difference between the groups became more noticeable over time. Furthermore, postoperative delirium was higher in the TN group (risk difference 0.3, 95% CI 0.1 to 0.5, p=0.02). LOS was similar between groups (5 days vs 5 days; p=0.99).

CONCLUSION

TMH was associated with a stable increase in rSO₂ from the baseline, while TN was associated with a decrease in rSO₂ in both hemispheres in patients undergoing major surgery. This resulted in a clear separation of percentage change in rSO₂ from the baseline between TMH and TN over time. Our findings provide the rationale for larger studies on TMH during surgery.

TRIAL REGISTRATION NUMBER

The Australian New Zealand Clinical Trials Registry (ACTRN12616000320459).

Acute Kidney Injury and Renal Regional Oxygen Saturation During Pediatric Liver Transplantation

Background

Kidney injury is a complication among children undergoing liver transplantation (pLTx). Cystatin C serum concentration seems to be superior to creatinine-based determination of kidney injury in adults and children. Near-infrared spectroscopy (NIRS) technology provides non-invasive and real-time measurement of renal tissue oxygenation. Here, we compared renal tissue oximetry (rSrO₂) with conventional diagnostic criteria cystatin C and creatinine concentration in children undergoing pLTx.

Material/Methods

rSrO₂ was measured intraoperatively in children undergoing pLTx over the left kidney, and was statistically compared with pre- and postoperative serum creatinine and cystatin C concentrations.

Results

rSrO₂ was affected by hemoglobin concentration, bilirubin concentration, and FiO₂. Statistical analysis demonstrated that rSrO₂ was significantly reduced in children with preoperative pathologic increased cystatin C concentrations compared to children without (63.7±4.3 vs. 53.4±4.9, p<0.05). We did not detect a significant difference in rSrO₂ between children who developed postoperative renal impairment, either determined by increased postoperative cystatin C concentration, creatinine concentration, or the pRIFLE criteria. Intraoperative increase or decrease in rSrO₂ did not predict the development of postoperative kidney injury.

Conclusions

In children with liver failure undergoing pLTx, a preoperative decrease in rSrO₂ indicates compromised renal function. However, intraoperative rSrO₂ is not predictive of postoperative kidney injury.

Comparing the response of pulse oximetry and regional cerebral oxygen saturation to hypoxia in preschool children

Pulse oximetry and measurement of regional cerebral oxygen saturation (rcSO₂) are used to monitor peripheral and cerebral oxygenation, respectively. However, the response of rcSO₂ and pulse oxygen saturation (SpO₂) to hypoxia in preschool children has not been previously assessed. A total of 36 preschool patients who had undergone a tonsillectomy [age, 4-6 years, American Society of Anesthesiologists grade I or II] were screened and prospectively enrolled in the present study. Hemodynamics, including rcSO₂, SpO₂, non-invasive blood pressure, heart rate, electrocardiogram and capnography, were continuously monitored throughout the study. Following pre-oxygenation, pressure-controlled ventilation with 100% oxygen was administered through a mask with a flow rate of 6 l/min, under total intravenous anesthesia, and the end-tidal carbon dioxide partial pressure was maintained between 30 and 40 mmHg. Tracheal intubation was then performed and ventilation was paused until SpO₂ decreased to 90% or rcSO₂ decreased by >10% of the baseline level. The duration from pausing of mechanical ventilation to the start of the rcSO₂ decline was shorter than that of SpO₂ (80.2±23.6 sec vs. 124.4±20.5 sec; P<0.001). Subsequent to the recovery of ventilation, the duration from the starting point to the increasing point of the baseline of rcSO₂ was longer than that of SpO₂ (84.8±24.3 sec vs. 15.2±6.8 sec; P<0.001). From the point where mechanical ventilation was paused to when rcSO₂/SpO₂ began to decrease, the rcSO₂ and SpO₂ values decreased and a significant correlation of them was observed (Pearson's correlation coefficient=0.317; P=0.027). From the time-point where mechanical ventilation was recovered to the time-point where rcSO₂ or SpO₂ began to increase, rcSO₂ and SpO₂ values decreased and a significant correlation of them was observed (Spearman's correlation coefficient=0.489; P=0.006). From the baseline to the minimum value, compared with the SpO₂, the rcSO₂ declined at a decreased rate (9.7±0.5% vs. 5.3±2.7%; P<0.001). The present clinical trial was registered at http://www.chictr.org.cn on 14th March 2016 (registration no. ChiCTR-OOC-16008095).

Assessment of a Non-Invasive Brain Oximeter in a Sheep Model of Acute Brain Injury

Introduction

Evidence suggests treatments guided by brain oxygen levels improve patient outcomes following severe traumatic brain injury; however, brain oxygen levels are not routinely monitored as an effective non-invasive method has not been established. We undertook a study, in a sheep model of acute brain injury, to assess a new non-invasive brain oximeter. The monitor uses the principles of pulse oximetry to record a pulse and oxygen levels.

Methods

We studied 8 sheep. An acute increase in intracranial pressure was induced with an injection of blood into the cranial vault. The temporal changes in the brain oximeter, intracranial pressure and cerebral perfusion pressure were recorded. Simultaneous conventional skin pulse oximetry was also recorded to assess the possible influence of skin blood flow on the brain oximeter signal.

Results

At baseline, a pulsatile waveform consistent with the brain circulation was obtained in 7 animals. The baseline brain pulse was quite distinct from the simultaneous conventional skin pulse and similar in shape to a central venous pressure waveform. Injection of blood into the cranial vault triggered an immediate increase in intracranial pressure and fall in cerebral perfusion pressure, by 60-s cerebral perfusion pressure recovered. The brain oximeter oxygen levels demonstrated similar changes with an immediate fall and recovery by 60 s. Periods of high intracranial pressure were also associated with high-frequency oscillations in the brain pulse waveform; there was, however, no change in the conventional skin pulse oximeter pulse waveform.

Conclusion

The brain oximeter detected acute changes in both oxygen levels and the brain pulse waveform following an increase in intracranial pressure levels. The brain oximeter could assist clinicians in the management of acute brain injury.

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Near-Infrared-Based Cerebral Oximetry for Prediction of Severe Acute Kidney Injury in Critically Ill Children After Cardiac Surgery

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Cerebral oximetry by near-infrared spectroscopy is used frequently in critically ill children but guidelines on its use for decision making in the PICU are lacking. We investigated cerebral near-infrared spectroscopy oximetry in its ability to predict severe acute kidney injury after pediatric cardiac surgery and assessed its additional predictive value to routinely collected data.

Cerebral Oximetry in Syncope and Syndromes of Orthostatic Intolerance

Cerebral autoregulation is crucial for maintaining cerebral blood flow and perfusion. In recent years, the importance of cerebral oxygenation in syncope and orthostatic intolerance (OI) has received increased attention. Cerebral tissue oxygenation can be measured by using near-infrared spectroscopy (NIRS), which determines the ratio of oxygenated hemoglobin to total hemoglobin in cerebral tissue. NIRS is non-invasive technology using near-infrared light, which displays real-time cerebral tissue oxygenation. Normal values of cerebral tissue oxygenation in healthy subjects are 60 to 80%. Head-up tilt test (HUT) offers the opportunity to observe the haemodynamic changes precipitating syncope and is, today, the standard method for the evaluation of syncope and orthostatic intolerance syndromes. In previous studies where NIRS was applied during HUT, a significant decrease in cerebral tissue oxygenation both prior to and during loss-of-consciousness in vasovagal syncope (VVS) has been observed. Interestingly, cerebral tissue oxygenation appears to decrease even before haemodynamic changes can be observed. Apart from VVS, cerebral tissue oxygenation decreases during orthostatic provocation in patients with orthostatic hypotension (OH) and postural orthostatic tachycardia syndrome (POTS), in the latter even in the absence of hypotension. Importantly, decline of cerebral tissue oxygenation in VVS and POTS during HUT may not correlate with hemodynamic changes. In this mini review, we summarize the current knowledge of the application of cerebral oximetry in syncope and orthostatic intolerance syndromes, discuss its likely value as a clinical diagnostic tool and also emphasize its potential in the understanding of the relevant pathophysiology.

Agreement between frontal and occipital regional cerebral oxygen saturation in infants during surgery and general anesthesia an observational study

BACKGROUND

Advances in perioperative pediatric care have resulted in an increased number of procedures requiring anesthesia. During anesthesia and surgery, the patient is subjected to factors that affect the circulatory homeostasis, which can influence oxygenation of the brain. Near-infrared spectroscopy (NIRS) is an easy applicable noninvasive method for monitoring of regional tissue oxygenation (rScO₂%). Alternate placements for NIRS have been investigated; however, no alternative cranial placements have been explored.

AIM

To evaluate the agreement between frontal and occipital recordings of rScO₂% in infants using INVOS^TM during surgery and general anesthesia.

METHOD

A standard frontal monitoring of rScO₂% with NIRS was compared with occipital rScO₂% measurements in fifteen children at an age <1 year, ASA 1-2, undergoing cleft lip and/or palate surgery during general anesthesia with sevoflurane. An agreement analysis was performed according to Bland and Altman.

RESULTS

Mean values of frontal and occipital rScO₂% at baseline were largely similar (70.7 ± 4.77% and 69.40 ± 5.04%, respectively). In the majority of the patients, the frontal and occipital recordings of rScO₂ changed in parallel. There was a moderate positive correlation between frontal and occipital rScO₂% INVOS™ readings (rho[ρ]: 0.513, P < .01). The difference between frontal and occipital rScO₂ ranged from -31 to 28 with a mean difference (bias) of -0.15%. The 95% limit of agreement was -18.04%-17.74%. The error between frontal and occipital rScO₂ recordings was 23%.

CONCLUSION

The agreement between frontal and occipital recordings of brain rScO₂% in infants using INVOS^TM during surgery and general anesthesia was acceptable. In surgical procedures where the frontal region of the head is not available for monitoring, occipital recordings of rScO₂% could be an option for monitoring.

Assessment of muscle oxygenation in children with congenital heart disease

BACKGROUND

Adaptive responses to congenital heart disease result in altered muscle perfusion and muscle metabolism. Such changes may be detectable using noninvasive spectroscopic monitors.

AIMS

In this study we aimed to determine if resting muscle oxygen saturation (MOx) is lower in children with acyanotic or cyanotic congenital heart disease than in healthy children and to identify differences in muscle oxygen consumption in children with cyanotic and acyanotic congenital heart disease.

METHODS

Using a custom fiber optic spectrometer system, optical measurements were obtained from the calf or forearm of 49 patients (17 with acyanotic congenital heart disease, 18 with cyanotic congenital heart disease, and 14 control). Twenty additional control patients were used to develop the analytic model. Spectra were used to determine MOx at baseline, during arterial occlusion, and during reperfusion. The rate of muscle desaturation during arterial occlusion was also evaluated. Two-sample t-tests were used to compare each heart disease group with the controls.

RESULTS

Patients with acyanotic and cyanotic congenital heart disease had lower baseline MOx than controls. Baseline MOx was 91.3% (CI 85.9%, 96.7%) for acyanotic patients, 91.1% (CI 86.3%, 95.9%) for cyanotic patients, and 98.9% (CI 96.7%, 101.1%) for controls. Similarly, MOx was lower in the acyanotic and cyanotic groups than the controls after reperfusion (84.6% [CI 74.1%, 95.1%] and 82.1% [CI 74.5%, 89.7%] vs 98.9% [96.5%, 101.3%]). The rate of decline in oxygenation was significantly greater in cyanotic patients versus controls (0.46%/s (CI 0.30%, 0.62%/s) vs 0.17%/s (0.13%, 0.21%/s)).

CONCLUSION

This study demonstrates that muscle oxygenation is abnormal in children with both cyanotic and acyanotic congenital heart disease. This suggests that noninvasive monitoring of muscle oxygenation may provide valuable information in situations where children with congenital heart disease may be at risk of hemodynamic compromise.

Changes in cerebral oxygen saturation and cerebral blood flow velocity under mild +Gz hypergravity

We previously reported that cerebral blood flow (CBF) was reduced by even mild +Gz hypergravity. Regional cerebral oxygen saturation as measured by near-infrared spectroscopy (C-rSO₂) has been widely used to detect cerebral ischemia in clinical practice. For example, decreases in C-rSO₂ reflect reduced CBF or arterial oxygen saturation. Thus it was hypothesized that C-rSO₂ would decrease in association with reduced CBF during mild hypergravity. To test this hypothesis, we measured CBF velocity by transcranial Doppler ultrasonography and C-rSO₂ during mild +Gz hypergravity while participants were in a sitting position. Among 17 male participants, 15 completed 21 min of exposure to +1.5 Gz generated by short-arm centrifuge. C-rSO₂ and mean CBF velocity in the middle cerebral artery (MCBFV_MCA) during centrifugation were averaged every 5 min and compared with pre-hypergravity (+1.0 Gz). C-rSO₂ did not change significantly throughout centrifugation, although MCBFV_MCA gradually decreased from the beginning (−1.2% at 0–5 min), and significantly decreased at 5–10 min (−4.8%), 10–15 min (−6.7%), and 15–20 min (−7.4%). Contrary to our hypothesis, decreases in C-rSO₂ were not detected, despite reductions in CBF velocity during hypergravity. Since some assumptions, such as unaltered arteriovenous volume ratio, hemoglobin concentration, extracranial blood flow, and brain activity, need to be satisfied to monitor cerebral ischemia by C-rSO₂, the present results suggest that these necessary assumptions for near-infrared spectroscopy are not always applicable, and that cerebral oxygenation may not precisely reflect decreases in CBF under mild +Gz hypergravity.

NEW & NOTEWORTHY To our knowledge, this is the first study to evaluate simultaneously cerebral oxygenation monitored by near-infrared spectroscopy and cerebral blood flow (CBF) monitored by transcranial Doppler under +1.5 Gz hypergravity. Contrary to our hypothesis, there was no significant correlation between CBF velocity and regional cerebral oxygen saturation (C-rSO₂). However, an incomplete case nearly involving syncope suggests the possibility that C-rSO₂ can detect a remarkable decrease in CBF with development of presyncope during +Gz hypergravity.

A Pilot Randomized Controlled Study of Mild Hypercapnia During Cardiac Surgery With Cardiopulmonary Bypass

OBJECTIVES

To test whether targeted therapeutic mild hypercapnia (TTMH) would attenuate cerebral oxygen desaturation detected using near-infrared spectroscopy during cardiac surgery requiring cardiopulmonary bypass (CPB).

DESIGN

Randomized controlled trials.

SETTING

Operating rooms and intensive care unit of tertiary hospital.

PARTICIPANTS

The study comprised 30 patients undergoing cardiac surgery with CPB.

INTERVENTIONS

Patients were randomly assigned to receive either standard carbon dioxide management (normocapnia) or TTMH (target arterial carbon dioxide partial pressure between 50 and 55 mmHg) throughout the intraoperative period and postoperatively until the onset of spontaneous ventilation.

MEASUREMENTS AND MAIN RESULTS

Relevant biochemical and hemodynamic variables were measured, and cerebral tissue oxygen saturation (SctO₂) was monitored with near-infrared spectroscopy. Patients were followed-up with neuropsychological testing. Patient demographics between groups were compared using the Fisher exact and Mann-Whitney tests, and SctO₂ between groups was compared using repeated measures analysis of variance. The median patient age was 67 years (interquartile range [IQR] 62-72 y), and the median EuroSCORE II was 1.1. The median CPB time was 106 minutes. The mean intraoperative arterial carbon dioxide partial pressure for each patient was significantly higher with TTMH (52.1 mmHg [IQR 49.9-53.9 mmHg] v 40.8 mmHg [IQR 38.7-41.7 mmHg]; p < 0.001) as was pulmonary artery pressure (23.9 mmHg [IQR 22.4-25.3 mmHg] v 18.5 mmHg [IQR 14.8-20.7 mmHg]; p = 0.004). There was no difference in mean percentage change in SctO₂ during CPB in the control group for both hemispheres (left: -6.7% v -2.3%; p = 0.110; right: -7.9% v -1.0%; p = 0.120). Compliance with neuropsychological test protocols was poor. However, the proportion of patients with drops in test score >20% was similar between groups in all tests.

CONCLUSIONS

TTMH did not increase SctO₂ appreciably during CPB but increased pulmonary artery pressures before and after CPB. These findings do not support further investigation of TTMH as a means of improving SctO₂ during and after cardiac surgery requiring CPB.

Tissue oximetry during cardiac surgery and in the cardiac intensive care unit: A prospective observational trial

Background:

Cerebral oximetry using near-infrared spectroscopy (NIRS) has well-documented benefits during cardiac surgery. The authors tested the hypothesis that NIRS technology can be used at other sites as a tissue oximeter during cardiac surgery and in the Intensive Care Unit (ICU).

Aims:

To establish feasibility of monitoring tissue oximetry during and after cardiac surgery, to examine the correlations between tissue oximetry values and cerebral oximetry values, and to examine correlations between oximetry values and mean arterial pressure (MAP) in order to test whether cerebral oximetry can be used as an index organ.

Settings and Designs:

A large, single-center tertiary care university hospital prospective observational trial of 31 patients undergoing cardiac surgery with cardiopulmonary bypass was conducted.

Materials and Methods:

Oximetry stickers were applied to both sides of the forehead, the nonarterial line forearm, and the skin above one paraspinal muscle. Data were collected from before anesthesia induction until extubation or for at least 24 h in patients who remained intubated.

Statistical Analysis:

Categorical variables were evaluated with Chi-square or Fisher's exact tests, while Wilcoxon rank-sum tests or student's t-tests were used for continuous variables.

Results:

The correlation between cerebral oximetry values and back oximetry values ranged from r = 0.37 to 0.40. The correlation between cerebral oximetry values and forearm oximetry values ranged from r = 0.11 to 0.13. None of the sites correlated with MAP.

Conclusions:

Tissue oximetry at the paraspinal muscle correlates with cerebral oximetry values while at the arm does not. Further research is needed to evaluate the role of tissue oximetry on outcomes such as acute renal failure, prolonged need for mechanical ventilation, stroke, vascular ischemic complications, prolonged ICU and hospital length of stay, and mortality in cardiac surgery.

Non-Invasive Tissue Oximetry-An Integral Puzzle Piece

Non-invasive tissue oximetry is a monitoring method for continuous assessment of tissue oxygenation, which may aid in detection of hemodynamic instability and otherwise unnoticed hypoxia. Numerous studies focused on using non-invasive tissue oximetry intraoperatively, proposing its predictive value in relation to clinical outcome. Tissue oximetry may be part of standard monitoring practice for brain monitoring during cardiac surgery in many clinical centers; however, the monitoring method can be deployed in numerous clinical settings. This succinct overview aims to determine the role of non-invasive tissue oximetry in current clinical practice.