Effects of Changes in Arterial Carbon Dioxide and Oxygen Partial Pressures on Cerebral Oximeter Performance

Noninvasive Neuromonitoring Modalities in Children Part I: Pupillometry, Near-Infrared Spectroscopy, and Transcranial Doppler Ultrasonography

BACKGROUND

Noninvasive neuromonitoring in critically ill children includes multiple modalities that all intend to improve our understanding of acute and ongoing brain injury.

METHODS

In this article, we review basic methods and devices, applications in clinical care and research, and explore potential future directions for three noninvasive neuromonitoring modalities in the pediatric intensive care unit: automated pupillometry, near-infrared spectroscopy, and transcranial Doppler ultrasonography.

RESULTS

All three technologies are noninvasive, portable, and easily repeatable to allow for serial measurements and trending of data over time. However, a paucity of high-quality data supporting the clinical utility of any of these technologies in critically ill children is currently a major limitation to their widespread application in the pediatric intensive care unit.

CONCLUSIONS

Future prospective multicenter work addressing major knowledge gaps is necessary to advance the field of pediatric noninvasive neuromonitoring.

The incidence, risk factors and outcomes of impaired cerebral autoregulation in aortic arch surgery: a single-center, retrospective cohort study

BACKGROUND

Impairment of cerebral autoregulation (CA) has been observed in patients undergoing cardiopulmonary bypass (CPB), but little is known about its risks and associations with outcomes. The cerebral oximetry index (COx), which is a moving linear correlation coefficient between regional cerebral oxygen saturation (rScO2) and mean blood pressure (MAP), may reflect CA function. When COx approaches 1, it implies that CA is damaged, whereas the CA is functional when the COx value approaches 0. The objective of this study was to analyze the incidence and risks of impaired CA, based on COx assessment, in patients undergoing total aortic arch replacement under systemic moderate hypothermia and circulatory arrest of the lower body (MHCA). We also evaluated the association between impaired CA and patient outcomes.

METHODS

One hundred and fifty-four adult patients who underwent total aortic arch replacement with stented elephant trunk implantation under MHCA at our hospital were retrospectively analyzed. Patients were defined as having new-onset impaired CA if pre-CPB COx < 0.3 and post-CPB COx > 0.3. Pre- and intraoperative factors were tested for independent association with impaired CA. Postoperative outcomes were compared between patients with normal and impaired CA.

RESULTS

In our 154 patients, 46(29.9%) developed new-onset impaired CA after CPB. Multivariable analysis revealed a prolonged low rScO2 (rScO2 < 55%) independently associated with onset of impaired CA, and receiver operating charactoristic curve showed a cutoff value at 40 min (sensitivity, 89.5%; specificity, 68.0%). Compared with normal CA patients, those with impaired CA showed a significantly higher rates of in-hospital mortality and postoperative complications.

CONCLUSIONS

Prolonged low rScO2 (rScO2 < 55%) during aortic arch surgery was closely related to onset of impaired CA. Impaired CA remained associated with the increased rates of postoperative complications and in-hospital mortality.

TRIAL REGISTRATION

ChiCTR1800014545 with registered date 20/01/2018.

Absolute Versus Relative Near-Infrared Spectroscopy in Pediatric Cardiac Patients

OBJECTIVES

Near-infrared spectroscopy (NIRS) has been increasingly accepted as a noninvasive marker of regional tissue oxygenation despite concerns of imprecision and wide limits of agreement (LOA) with invasive oximetry. New generation absolute monitors may have improved accuracy compared with trend monitors. We sought to compare the concordance with invasive venous oximetry of a new generation absolute NIRS-oximeter (FORESIGHT ELITE; CASMED, Branford, CT) with a modern widely used trend monitor (INVOS 5100C; Medtronic, Minneapolis, MN).

DESIGN

Prospective single-center study.

SETTING

Tertiary pediatric heart center.

PATIENTS

Children undergoing elective cardiac catheterization under general anesthesia. Time-paired venous oximetry samples (jugular and renal) were compared with NIRS-derived oximetry by two monitors using regression and Bland-Altman analysis.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

We enrolled 36 children (19 female, 10 cyanotic) with median age 4.1 years (25-75%, 2.5-7.8 yr) and weight 16.7 kg (12.3-29.1 kg). The absolute difference between NIRS-derived and invasive jugular oximetry was less than 10% in 67% of occasions for both monitors. Correlation was fair (Spearman rs = 0.40; p = 0.001) for the FORESIGHT ELITE and poor ( rs = 0.06; p = 0.71) for the INVOS 5100C. Bias and LOA were +6.7% (+22%, -9%) versus +1.3% (LOA = +24%, -21%), respectively. The absolute difference between NIRS-derived and invasive renal oximetry was less than 10% in 80% of occasions with moderate correlation ( rs = 0.57; p < 0.001) for the FORESIGHT ELITE and in 61% of occasions with moderate correlation ( rs = 0.58; p < 0.001) for the INVOS 5100C; bias and LOA were +3.6% (+19%, -12%) and -1.4 % (+27%, -30%), respectively. NIRS correlation with renal venous oximetry was worse for cyanotic versus noncyanotic patients ( p = 0.02).

CONCLUSIONS

Concordance and LOA of NIRS-derived oximetry with invasive venous oximetry in the cerebral and renal vascular beds was suboptimal for clinical decision-making. Cyanosis adversely affected NIRS performance in the renal site.

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.

Effect of one-lung ventilation on the correlation between left and right cerebral saturation

BACKGROUND

To investigate if the correlation between left and right cerebral tissue oxygen saturation (SctO₂) was affected by one-lung ventilation (OLV) in patients undergoing lung cancer surgery.

METHODS

Patients who underwent surgery for lung cancer were enrolled. Left and right SctO₂ were collected during anesthesia. The primary outcome was the correlation between left and right SctO₂ at 30 min after OLV which was analysed by Pearson correlation and linear regression model. Secondary outcomes included the trend of left-right SctO₂ change over the first 30 min after OLV, correlation of left-right SctO₂ during OLV for each patient; maximal difference between left-right SctO₂ and its relationship with postoperative delirium.

RESULTS

Left-right SctO₂ was moderately correlated at baseline (r = 0.690, P < 0.001) and poorly correlated at 30 min after OLV (r = 0.383, P < 0.001) in the Pearson correlation analysis. Linear regression analysis showed a poor correlation between left and right SctO₂ at 30 min after OLV (r = 0.323, P < 0.001) after adjusting for confounders. The linear mixed model showed a change in left-right SctO₂ over the first 30 min after OLV that was statistically significant (coefficient, -0.042; 95% CI, -0.070--0.014; P = 0.004). For the left-right SctO₂ correlation during OLV in each patient, 62.9% (78/124) patients showed a strong correlation, 19.4% (24/124) a medium correlation, and the rest a poor correlation. The maximal difference between the left and right SctO₂ was 13.5 (9.0, 20.0). Multivariate analysis showed that it was not associated with delirium (odds ratio [OR], 1.023; 95% CI, 0.963-1.087; P = 0.463).

CONCLUSIONS

The correlation between left and right SctO₂ was affected by one-lung ventilation in patients undergoing lung cancer surgery. This result indicates the requirement of bilateral SctO₂ monitoring to reflect brain oxygenation.

TRIAL REGISTRATION

This study was a secondary analysis of a cohort study approved by the Clinical Research Review Board of Peking University First Hospital (#2017-1378) and was registered in the Chinese Clinical Trial Registry on 10/09/2017 ( http://www.chictr.org.cn , ChiCTR-ROC-17012627).

Prehospital monitoring of cerebral circulation during out of hospital cardiac arrest ? A feasibility study

BACKGROUND

About two-thirds of the in-hospital deaths after out-of-hospital cardiac arrests (OHCA) are a consequence of anoxic brain injuries, which are due to hypoperfusion of the brain during the cardiac arrests. Being able to monitor cerebral perfusion during cardiopulmonary resuscitation (CPR) is desirable to evaluate the effectiveness of the CPR and to guide further decision making and prognostication.

METHODS

Two different devices were used to measure regional cerebral oxygen saturation (rSO2): INVOS™ 5100 (Medtronic, Minneapolis, MN, USA) and Root® O3 (Masimo Corporation, Irvine, CA, USA). At the scene of the OHCA, advanced life support (ALS) was immediately initiated by the Emergency Medical Services (EMS) personnel. Sensors for measuring rSO2 were applied at the scene or during transportation to the hospital. rSO2 values were documented manually together with ETCO2 (end tidal carbon dioxide) on a worksheet specially designed for this study. The study worksheet also included a questionnaire for the EMS personnel with one statement on usability regarding potential interference with ALS.

RESULTS

Twenty-seven patients were included in the statistical analyses. In the INVOS™5100 group (n = 13), the mean rSO2 was 54% (95% CI 40.3-67.7) for patients achieving a return of spontaneous circulation (ROSC) and 28% (95% CI 12.3-43.7) for patients not achieving ROSC (p = 0.04). In the Root® O3 group (n = 14), the mean rSO2 was 50% (95% CI 46.5-53.5) and 41% (95% CI 36.3-45.7) (p = 0.02) for ROSC and no ROSC, respectively. ETCO2 values were not statistically different between the groups. The EMS personnel graded the statement of interference with ALS to a median of 2 (IQR 1-6) on a 10-point Numerical Rating Scale.

CONCLUSION

Our results suggest that both INVOS™5100 and ROOT® O3 can distinguish between ROSC and no ROSC in OHCA, and both could be used in the pre-hospital setting and during transport with minimal interference with ALS.

A comprehensive review of cerebral oximetry in cardiac surgery

BACKGROUND

Patients who undergo cardiac surgery are at increased risk of stroke, postoperative cognitive decline, and delirium. These neurocognitive complications have led to increased costs, intensive care unit stays, morbidity, and mortality. As a result, there is a significant push to mitigate any neurological complications in cardiac surgery patients. Near-infrared spectroscopy to measure regional cerebral oxygen saturations has gained consideration due to its noninvasive and user-friendly nature. Cerebral oximetry desaturations during cardiac surgery have been linked to an array of adverse clinical outcomes. However, the most effective intraoperative interventions to protect this vulnerable patient population have yet to be ascertained.

AIM OF STUDY

To provide a comprehensive summary of the intraoperative management for cerebral oximetry desaturations during cardiac surgery. The review highlights clinical outcomes from cerebral oximetry use to quantify the importance of identifying cerebral desaturations during cardiac surgery. The review then interrogates possible interventions for cerebral oximetry desaturations in an effort to determine which interventions are most efficacious and to enlighten possible areas for further research.

METHODS

A narrative review of randomized controlled trials, observational studies, and systematic reviews with metanalyses was performed through August 2021.

RESULTS

There is significant heterogeneity among patient populations for which cerebral oximetry monitoring has been studied in cardiac surgery. Further, the definition of a clinically significant cerebral desaturation and the assessment of neurocognitive outcomes varied substantially across studies. As a result, metanalysis is challenging and few conclusions can be drawn. Cerebral oximetry use during cardiac surgery has not been associated with improvements in neurocognitive outcomes, morbidity, or mortality to date. The evidence to support a particular intervention for an acute desaturation is equivocal.

CONCLUSIONS

Future research is needed to quantify a clinically significant cerebral desaturation and to determine which interventions for an acute desaturation effectively improve clinical outcomes.

Effects on cerebral blood flow of position changes, hyperoxia, CO2 partial pressure variations and the Valsalva manoeuvre: A study in healthy volunteers

BACKGROUND

Maintaining adequate blood pressure to ensure proper cerebral blood flow (CBF) during surgery is challenging. Induced mild hypotension, sitting position or unavoidable intra-operative circumstances such as haemorrhage, added to variations in carbon dioxide and oxygen tensions, may influence perfusion. Several of these circumstances may coincide and it is unclear how these may affect CBF.

OBJECTIVE

To describe the variation in transcranial Doppler and regional cerebral oxygen saturation (rSO2), as a surrogate of CBF, after cardiac preload and gravitational positional changes.

DESIGN

Observational study.

SETTING

Operating room at Hospital Clínic de Barcelona.

VOLUNTEERS

Ten healthy volunteers, white, both sexes.

INTERVENTIONS

Measurements were performed in the supine, sitting and standing positions during hyperoxia, hypocapnia and hypercapnia protocols and after a Valsalva manoeuvre.

MAIN OUTCOME MEASURES

Cardiac index (CI), haemodynamic and respiratory variables, maximal and mean velocities (Vmax, Vmean) (transcranial Doppler) and rSO2 were acquired. Results were analysed using a generalised estimating equation technique.

RESULTS

CI increases more than 16% after a preload challenge were not accompanied by differences in rSO2 or Vmax - Vmean. With positional changes, Vmean decreased more than 7% (P = 0.042) from the supine to the seated position. Hyperoxia induced a cerebral rSO2 increase more than 6% (P = 0.0001) with decreases in Vmax, Vmean and CI values more than 3% (P = 0.001, 0.022 and 0.001) in the supine and standing position. During hypocapnia, CI rose more than 20% from supine to seated and standing (P = 0.0001) with a 4.5% decrease in cerebral rSO2 (P = 0.001) and a decrease of Vmax - Vmean more than 24% in all positions (P = 0.001). Hypercapnia increased cerebral rSO2 more than 17% (P = 0.001), Vmax - Vmean more than 30% (P = 0.001) with no changes in CI. After a Valsalva manoeuvre, rSO2 decreased more than 3% in the right hemisphere in the upright position (P = 0.001). Vmax - Vmean decreased more than 10% (P = 0.001) with no changes in CI.

CONCLUSION

CBF changes in response to cerebral vasoconstriction and vasodilatation were detected with rSO2 and transcranial Doppler in healthy volunteers during cardiac preload and in different body positions. Acute hypercapnia had a greater effect on recorded brain parameters than hypocapnia.

Effects of different ventilation on cerebral oxygen saturation and cerebral blood flow before and after modified ultrafiltration in infants during ventricular septal defect repair

OBJECTIVE

To analyse the changes of different ventilation on regional cerebral oxygen saturation and cerebral blood flow in infants during ventricular septal defect repair.

METHODS

Ninety-two infants younger than 1 year were enrolled in the study. End-expiratory tidal pressure of carbon dioxide was maintained at 40-45 and 35-39 mmHg in relative low and high ventilation groups. Regional cerebral oxygen saturation and flow velocity of the middle cerebral artery were recorded after anaesthesia (T0), cut pericardium (T1), separation from cardiopulmonary bypass (T2), the end of modified ultrafiltration, (T3) and at the end of operation (T4).

RESULTS

The relative low ventilation group exhibited a significantly high regional cerebral oxygen saturation at each time point except for T2 (T0:77 ± 4, T1:76 ± 5, T3:76 ± 8, T4:76 ± 8, respectively, p < 0.001). Flow velocity of the middle cerebral artery in the relative low ventilation group was higher compared to the relative high ventilation group at each time point except for T2 (T0:53 ± 14, T1:54 ± 15, T3:53 ± 17, T4:52 ± 16, respectively, p < 0.001). Between the two groups, T2 showed the lowest middle cerebral artery flow velocity (relative low ventilation: 39 ± 15, relative high ventilation: 39 ± 11, p < 0.001).

CONCLUSION

The infants' regional cerebral oxygen saturation and middle cerebral artery flow velocity performed better in the range of 40-45 mmHg end-expiratory tidal pressure of carbon dioxide during CHD surgery. Modified ultrafiltration increased cerebral oxygen saturation. It was important to regulate ventilation in order to balance cerebral oxygen in infants.

"Silent" Presentation of Hypoxemia and Cardiorespiratory Compensation in COVID-19

Severe hypoxemia presents variably, and sometimes silently, without subjective complaints of dyspnea. The adequacy of cardiovascular compensation for oxygen delivery to tissues should be a focus in all hypoxemic patients.

Brain Protection in Aortic Arch Surgery: An Evolving Field

Despite advances in cardiac surgery and anesthesia, the rates of brain injury remain high in aortic arch surgery requiring circulatory arrest. The mechanisms of brain injury, including permanent and temporary neurologic dysfunction, are multifactorial, but intraoperative brain ischemia is likely a major contributor. Maintaining optimal cerebral perfusion during cardiopulmonary bypass and circulatory arrest is the key component of intraoperative management for aortic arch surgery. Various brain monitoring modalities provide different information to improve cerebral protection. Electroencephalography gives crucial data to ensure minimal cerebral metabolism during deep hypothermic circulatory arrest, transcranial Doppler directly measures cerebral arterial blood flow, and near-infrared spectroscopy monitors regional cerebral oxygen saturation. Various brain protection techniques, including hypothermia, cerebral perfusion, pharmacologic protection, and blood gas management, have been used during interruption of systemic circulation, but the optimal strategy remains elusive. Although deep hypothermic circulatory arrest and retrograde cerebral perfusion have their merits, there have been increasing reports about the use of antegrade cerebral perfusion, obviating the need for deep hypothermia. With controversy and variability of surgical practices, moderate hypothermia, when combined with unilateral antegrade cerebral perfusion, is considered safe for brain protection in aortic arch surgery performed with circulatory arrest. The neurologic outcomes of brain protection in aortic arch surgery largely depend on the following three major components: cerebral temperature, circulatory arrest time, and cerebral perfusion during circulatory arrest. The optimal brain protection strategy should be individualized based on comprehensive monitoring and stems from well-executed techniques that balance the major components contributing to brain injury.

Improving the safety of shoulder arthroscopy in the beach chair position: a prospective randomized trial investigating the effect of compression stockings on cerebral desaturation events in obese patients

BACKGROUND

Devastating transient and permanent postoperative neurocognitive complications in previously healthy, low-risk patients have been observed after elective shoulder arthroscopy in the beach chair position (BCP). Continuous monitoring of cerebral oxygen saturation has been recommended to identify cerebral desaturation events (CDEs) and improve patient safety. However, the relatively high cost and limited availability of monitoring may not be cost-effective. More cost-effective and available measures, including the use of thigh-high compression stockings (CS), have been investigated. However, efficacy data of CS usage is limited, especially for obese patients, who have been shown to be at increased risk for CDEs. The purpose of this was study was to determine if the intraoperative addition of thigh-high compression stockings decreases the incidence, frequency, and magnitude of CDEs in obese patients undergoing shoulder arthroscopy in the BCP.

METHODS

Thirty-three patients in the treatment group wore both thigh-high compression stockings (CS) and sequential compression devices (SCDs), and the remaining 33 patients in the control group wore SCDs alone. Cerebral oximetry was monitored during surgery using near-infrared spectroscopy.

RESULTS

The incidence of CDEs was equal between groups, with 9 patients (27%) in each experiencing desaturation events. The median number of CDEs per patient was 3 for the control group and 1 for patients wearing CS (P = .29). There was no difference between groups in terms of median time from induction of anesthesia to onset of CDE (P = .79), median time from upright positioning to onset of CDE (P = .60), mean CDE duration per patient (P = .22), and median cumulative CDE duration (P = .19). The median maximal desaturation from baseline was also not different between groups: 27.6% in the control group and 24.3% in the treatment group (P = .35).

CONCLUSION

The combination of thigh-high CS and SCDs did not decrease the incidence, frequency, or magnitude of CDEs in patients undergoing shoulder arthroscopy in the BCP. Twenty-seven percent of patients undergoing shoulder arthroscopy in the BCP demonstrated CDEs with or without the use of CS. Therefore, further research is required to identify cost-effective, minimally invasive, and universally available methods of decreasing the incidence of CDEs during this common surgical procedure.

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.

Clinical and Technical Limitations of Cerebral and Somatic Near-Infrared Spectroscopy as an Oxygenation Monitor

Cerebral and somatic near-infrared spectroscopy monitors are commonly used to detect tissue oxygenation in various circumstances. This form of monitoring is based on tissue infrared absorption and can be influenced by several physiological and non-physiological factors that can induce error in the interpretation. This narrative review explores those clinical and technical limitations and proposes solutions and alternatives in order to avoid some of those pitfalls.

Cerebral oxygen desaturation in patients with totally thoracoscopic ablation for atrial fibrillation: A prospective observational study

BACKGROUND

Epicardial radiofrequency ablation for stand-alone atrial fibrillation under total video-assisted thoracoscopy has gained popularity in recent years. However, severe cardiopulmonary disturbances during the surgery may affect cerebral perfusion and oxygenation. We therefore hypothesized that regional cerebral oxygen saturation (rSO2) would decrease significantly during the surgery. In addition, the influencing factors of rSO2 would be investigated.

METHODS

A total of 60 patients scheduled for selective totally thoracoscopic ablation for stand-alone atrial fibrillation were enrolled in this prospective observational study. The rSO2 was monitored at baseline (T0), 15 min after anesthesia induction (T1), 15 minute after 1-lung ventilation (T2), after right pulmonary vein ablation (T3), after left pulmonary vein ablation (T4) and 15 minute after 2-lung ventilation (T5) using a near-infrared reflectance spectroscopy -based cerebral oximeter. Arterial blood gas was analyzed using an ABL 825 hemoximeter. Associations between rSO2 and hemodynamic or blood gas parameters were determined with univariate and multivariate linear regression analyses.

RESULTS

The rSO2 decreased greatly from baseline 65.4% to 56.5% at T3 (P < .001). Univariate analyses showed that rSO2 correlated significantly with heart rate (r = -0.173, P = .186), mean arterial pressure (MAP, r = 0.306, P = .018), central venous pressure (r = 0.261, P = .044), arterial carbon dioxide tension (r = -0.336, P = .009), arterial oxygen pressure (PaO2, r = 0.522, P < .001), and base excess (BE, r = 0.316, P = .014). Multivariate linear regression analyses further showed that it correlated positively with PaO2 (β = 0.456, P < .001), MAP (β = 0.251, P = .020), and BE (β = 0.332, P = .003).

CONCLUSION

Totally thoracoscopic ablation for atrial fibrillation caused a significant decrease in rSO2. There were positive correlations between rSO2 and PaO2, MAP, and BE.

Impact of CPAP on Forehead Near-infrared Spectroscopy Measurements in Patients With Acute Respiratory Failure: Truth or Illusion

BACKGROUND

Critically ill patients with acute respiratory failure admitted to an intensive care unit are at high risk for cerebral hypoxia. We investigated the impact of continuous positive airway pressure (CPAP) therapy on regional cerebral tissue oxygenation (rSO2).

MATERIALS AND METHODS

In total, 40 extubated surgical intensive care unit patients requiring classic oxygen therapy (COT) for acute respiratory failure were examined. Near-infrared spectroscopy (INVOS 5100C, Covidien) was used for 30 minutes to detect bilateral rSO2 during COT via facemask (6 L/min) and CPAP therapy (40% fraction of inspired oxygen, 8 cm H2O CPAP) using a randomized crossover study design. Patients served as their own control. Continuous hemodynamic routine monitoring and blood gas analysis were performed. The effect of CPAP therapy on rSO2 and influence of assessed covariables were investigated using a mixed linear model.

RESULTS

Median rSO2 increased from 57.9% (95% confidence interval [CI], 54.2-61.5) during COT to 62.8% (95% CI, 59.2-66.5) during CPAP therapy (P<0.0001). The estimated difference from the mixed model between COT and CPAP is -5.0 (95% CI, -6.3 to -3.7). Median arterial partial pressure of carbon dioxide decreased from 47.8±5.1 mm Hg during COT to 43.1±5 mm Hg during CPAP (P<0.001), whereas arterial partial pressure of oxygen remained unchanged (P=0.329). In total, 23% of patients had SO2 levels <50%, with a higher prevalence under COT.

CONCLUSIONS

Our results reveal that CPAP therapy compared with COT may influence rSO2 in patients with acute respiratory failure. However, the cause of the rSO2 increase following CPAP application remains to be elucidated, and the accuracy of cerebral oximetry during CPAP therapy in patients with acute respiratory failure remains questionable.

Animal models of emphysema

OBJECTIVE

Chronic obstructive pulmonary disease (COPD) is a common chronic respiratory disease of human beings characterized by not fully reversible airflow limitation. Emphysema is the main pathological feature of COPD which causes high mortality worldwide every year and consumes a large amount of medical expenses. This paper was to review the establishment and evaluation methods of animal models of emphysema or COPD, and put forward some new ideas on animal selection, method of modeling, and model evaluation.

DATA SOURCES

The author retrieved information from the PubMed database up to July 2019, using various combinations of search terms, including emphysema, model, and animal.

STUDY SELECTION

Original articles, reviews, and other articles were searched and reviewed for animal models of emphysema.

RESULTS

This review summarized animal models of emphysema from the perspectives of animal selection, emphysema mechanism, modeling method and model evaluation, and found that passive smoking is the classic method for developing animal model of emphysema, mice are more suitable for experimental study on emphysema. Compared with pulmonary function indicators, airway inflammation indicators and oxidative stress indicators, pathomorphological indicators of lung tissue are the most important parameters for evaluating the establishment of the animal model of emphysema.

CONCLUSIONS

Mice model induced by passive smoking is the classic animal model of emphysema. Pathomorphological indicators are the most important parameters for evaluating the establishment of the animal model of emphysema.

Cerebral Oximetry Fails as a Monitor of Brain Perfusion in Cardiac Surgery: A Case Report

Cerebral oximetry is commonly being advocated as a monitor for regional cerebral tissue oxygenation during cardiac surgery. We have increasing concern about the accuracy of this monitor, including the current systems entering the market, with new probes and algorithms. We present 2 cases where cerebral oximetry failed to accurately portray cerebral oxygenation. In the current form, cerebral oximetry may at best be an expensive tool without any benefit on outcomes. In addition, it may contribute to misleading and confusing clinical data.

Is cerebrovascular autoregulation associated with outcomes after major noncardiac surgery? A prospective observational pilot study

BACKGROUND

Studies have identified multiple risk factors for development of cognitive decline after surgery. Impaired cerebrovascular autoregulation may be a contributor to postoperative cognitive decline.

METHODS

One hundred and forty patients admitted for major elective noncardiac surgery were recruited. Near-infrared spectroscopy was used to calculate the tissue oxygenation index of dynamic autoregulation (TOx). The primary endpoint was Day 3 cognitive recovery as assessed using the Postoperative Quality of Recovery Scale. The secondary endpoint was a combined major adverse event of death, acute myocardial infarction, cardiac arrest, stroke, pulmonary embolism, sepsis, and acute kidney injury at Day 30.

RESULTS

Higher optimal TOx values, signifying impaired autoregulation, were associated with worse outcomes. Patients who cognitively recovered at Day 3 (n = 47) had lower optimal TOx values (TOx_opt ) than patients who did not recover (n = 22): 0.06 (0.24) vs 0.18 (0.16) (mean [SD]), P = 0.02. Patients who did not suffer a major adverse event (n = 102) had lower TOx_opt than patients who did (n = 17): 0.09 (0.21) vs 0.20 (0.27), P = 0.04. When dichotomized as having impaired or intact autoregulation based on TOx_opt levels, a value of TOx_opt ≥0.1 correctly identified 72.7% of patients who did not cognitively recover, OR 3.3 (1.1-9.9) (Odds ratio, [95% CI]), P = 0.03. TOx_opt ≥0.1 correctly identified 82.4% of patients who suffered a major adverse event, OR 4.7 (1.3-17.2), P = 0.02.

CONCLUSIONS

In older and higher risk patients having major noncardiac surgery, impaired cerebrovascular autoregulation was associated with failure of cognitive recovery in the early postoperative period and with 1-month mortality and morbidity.