Extracranial contamination in the INVOS 5100C versus the FORE-SIGHT ELITE cerebral oximeter: a prospective observational crossover study in volunteers

Effect of Extracerebral Contamination on Near-infrared Spectroscopy as Revealed during Organ Donation: A Prospective Observational Study in Brain-dead Organ Donors

BACKGROUND

Near-infrared spectroscopy (NIRS) has been utilized widely in anesthesia and intensive care to monitor regional cerebral oxygen saturation (rScO2). A normal oxygenation of extracerebral tissues may overlay and thereby mask cerebral desaturations, a phenomenon known as extracerebral contamination. The authors investigated the effect of a cessation of extracerebral tissue perfusion on rScO2 in patients with anoxic brains.

METHODS

In a single-center, prospective, observational study, brain-dead adults undergoing organ donation were investigated. rScO2 was measured bifrontally using the INVOS 5100C/7100 as well as the ForeSight Elite system. To achieve an efficient conservation of organs and to prevent a redistribution of the perfusion fluid to other tissues, the aorta was clamped before organ perfusion. rScO2 was monitored until at least 40 min after aortic clamping. The primary outcome was the amount of extracerebral contamination as quantified by the absolute decrease in rScO2 after aortic clamping. Secondary outcomes were the absolute rScO2 values obtained before and after clamping.

RESULTS

Twelve organ donors were included. Aortic clamping resulted in a significantly (P < 0.001) greater absolute decrease in rScO2 when comparing the INVOS (43.0 ± 9.5%) to the ForeSight (27.8 ± 7.1%) monitor. Before aortic clamping, near-normal rScO2 values were obtained by the INVOS (63.8 ± 6.2%) and the ForeSight monitor (67.7 ± 6.5%). The rScO2 significantly (P < 0.001) dropped to 20.8 ± 7.8% (INVOS) and 39.9 ± 8.1% (ForeSight) 30 min after clamping, i.e., a condition of a desaturation of both extracerebral and cerebral tissues.

CONCLUSIONS

The abrupt end of extracerebral contamination, caused by aortic clamping, affected both NIRS monitors to a considerable extent. Both the INVOS and the ForeSight monitor were unable to detect severe cerebral hypoxia or anoxia under conditions of normal extracerebral oxygenation. While both NIRS monitors may guide measures to optimize arterial oxygen supply to the head, they should not be used with the intention to detect isolated cerebral desaturations.

EDITOR’S PERSPECTIVE

Differences of cerebral oxygen saturation in dialysis patients: a comparison of three principals of near infrared spectroscopy

PURPOSE

It has been reported that cerebral oxygen saturation (rSO2) measured by near infrared spectroscopy is low in dialysis patients. We compared the rSO2 values of dialysis patients before living donor kidney transplantation and their donors as controls by using three spectroscopes that utilize different principals, the INVOS 5100C (spatially resolved spectroscopy), FORE-SIGHT ELITE (modified Beer-Lambert law) and tNIRS-1 (time-resolved spectroscopy).

METHODS

Before induction of anesthesia, the sensors of one of the three spectroscopes were placed on the forehead and rSO2 values were recorded followed by the same measurement using the other two spectroscopes. The primary objective was to compare the rSO2 values of the dialysis patients and controls using the three spectroscopes by the unpaired t test. Then we compared the rSO2 values among the spectroscopes in both dialysis patients and controls by one-way ANOVA. Finally, we examined the relations between the rSO2 values and the physiological values by using the Pearson correlation coefficient.

RESULTS

Fifteen pairs of dialysis patients and controls were studied. With the INVOS 5100 C, the values of the dialysis patients (59.7 ± 9.7% (mean ± standard deviation) were 13% lower than those of the controls (73.3 ± 6.9%) (P < 0.01). With the tNIRS-1, the values were 57.8 ± 4.8% in the dialysis patients and 63.3 ± 3.5% in the controls (P < 0.01). Almost no differences were observed with the FORE-SIGHT ELITE (71.6 ± 4.9% [dialysis patients] vs. 70.8 ± 4.3% [Controls]) (P = 0.62). Among the spectroscopes, the values were significantly different in both dialysis patients and controls. For the INVOS 5100C and tNIRS-1, correlation coefficients between rSO2 values and blood Hb and serum Alb were more than 0.5.

CONCLUSIONS

The rSO2 values for comparisons between the dialysis patients and the controls were different according to differences of the principles of the near infrared spectroscopes. In the INVOS 5100C and tNIRS-1, rSO2 values may be related to blood Hb and serum Alb.

The Influence of Extracerebral Tissue on Continuous Wave Near-Infrared Spectroscopy in Adults: A Systematic Review of In Vivo Studies

Near-infrared spectroscopy (NIRS) is a non-invasive technique for measuring regional tissue haemoglobin (Hb) concentrations and oxygen saturation (rSO₂). It may be used to monitor cerebral perfusion and oxygenation in patients at risk of cerebral ischemia or hypoxia, for example, during cardiothoracic or carotid surgery. However, extracerebral tissue (mainly scalp and skull tissue) influences NIRS measurements, and the extent of this influence is not clear. Thus, before more widespread use of NIRS as an intraoperative monitoring modality is warranted, this issue needs to be better understood. We therefore conducted a systematic review of published in vivo studies of the influence of extracerebral tissue on NIRS measurements in the adult population. Studies that used reference techniques for the perfusion of the intra- and extracerebral tissues or that selectively altered the intra- or extracerebral perfusion were included. Thirty-four articles met the inclusion criteria and were of sufficient quality. In 14 articles, Hb concentrations were compared directly with measurements from reference techniques, using correlation coefficients. When the intracerebral perfusion was altered, the correlations between Hb concentrations and intracerebral reference technique measurements ranged between |r| = 0.45-0.88. When the extracerebral perfusion was altered, correlations between Hb concentrations and extracerebral reference technique measurements ranged between |r| = 0.22-0.93. In studies without selective perfusion modification, correlations of Hb with intra- and extracerebral reference technique measurements were generally lower (|r| < 0.52). Five articles studied rSO₂. There were varying correlations of rSO₂ with both intra- and extracerebral reference technique measurements (intracerebral: |r| = 0.18-0.77, extracerebral: |r| = 0.13-0.81). Regarding study quality, details on the domains, participant selection and flow and timing were often unclear. We conclude that extracerebral tissue indeed influences NIRS measurements, although the evidence (i.e., correlation) for this influence varies considerably across the assessed studies. These results are strongly affected by the study protocols and analysis techniques used. Studies employing multiple protocols and reference techniques for both intra- and extracerebral tissues are therefore needed. To quantitatively compare NIRS with intra- and extracerebral reference techniques, we recommend applying a complete regression analysis. The current uncertainty regarding the influence of extracerebral tissue remains a hurdle in the clinical implementation of NIRS for intraoperative monitoring. The protocol was pre-registered in PROSPERO (CRD42020199053).

Associations among preoperative transthoracic echocardiography variables and cerebral near-infrared spectroscopy values at baseline before anesthesia in patients undergoing cardiac surgery: a retrospective observational study

Cerebral tissue oximetry with near-infrared spectroscopy (NIRS) is used to monitor cerebral oxygenation during cardiac surgery. To date, reduced baseline cerebral NIRS values have been attributed to reduced cerebral blood flow primarily based on a significant positive correlation between left ventricular ejection fraction (LVEF) and baseline rSO₂ measured with the INVOS 5100C oximeter. Reportedly, however, rSO₂, but not StO₂ measured with the FORESIGHT Elite oximeter, correlated with LVEF. We, thus, investigated associations among baseline NIRS values measured with three different oximeters before anesthesia for cardiac surgery and preoperative transthoracic echocardiography (TTE) variables, including LVEF, to examine whether there are inter-device differences in associations among baseline NIRS values and TTE variables. Using Spearman's correlation coefficient, we retrospectively investigated associations among 15 preoperative TTE variables, including LVEF, and baseline NIRS values, including rSO₂, StO₂, and TOI with the NIRO-200NX oximeter in 1346, 515, and 301 patients, respectively. Only rSO₂ (p < 0.00001), but not TOI or StO₂ (p > 0.05), positively correlated with LVEF. On the other hand, baseline rSO₂, TOI, and StO₂ consistently, negatively correlated with the left atrial diameter index (LADI), early diastolic transmitral flow velocity (E), E-to-early diastolic mitral annular velocity ratio (E/e'), estimated right ventricular systolic pressure (eRVP), and inferior vena cava diameter index (IVCDI) (p < 0.0005 to p < 0.00001). Because all of these five TTE variables could be positively associated with right as well as left ventricular filling pressure, our results indicated that reduced baseline NIRS values were consistently associated not with reduced LVEF but with TTE findings indicative of elevated biventricular filling pressure. Our data suggest that regional venous congestion greatly contributes to reduced baseline NIRS values in patients undergoing cardiac surgery.

Assessment of a Non-Invasive Brain Pulse Monitor to Measure Intra-Cranial Pressure Following Acute Brain Injury

Background

Intracranial pressure (ICP) monitoring requires placing a hole in the skull through which an invasive pressure monitor is inserted into the brain. This approach has risks for the patient and is expensive. We have developed a non-invasive brain pulse monitor that uses red light to detect a photoplethysmographic (PPG) signal arising from the blood vessels on the brain's cortical surface. The brain PPG and the invasive ICP waveform share morphological features which may allow measurement of the intracranial pressure.

Methods

We enrolled critically ill patients with an acute brain injury with invasive ICP monitoring to assess the new monitor. A total of 24 simultaneous invasive ICP and brain pulse monitor PPG measurements were undertaken in 12 patients over a range of ICP levels.

Results

The waveform morphologies were similar for the invasive ICP and brain pulse monitor PPG approach. Both methods demonstrated a progressive increase in the amplitude of P2 relative to P1 with increasing ICP levels. An automated algorithm was developed to assess the PPG morphological features in relation to the ICP level. A correlation was demonstrated between the brain pulse waveform morphology and ICP levels, R²=0.66, P < 0.001.

Conclusion

The brain pulse monitor's PPG waveform demonstrated morphological features were similar to the invasive ICP waveform over a range of ICP levels, these features may provide a method to measure ICP levels.

Trial Registration

ACTRN12620000828921.

Early outcomes of Sun's procedure in elderly patients with acute aortic dissection: a single-center retrospective study

OBJECTIVE

The effect of patient age on the outcome of Sun's procedure for acute type A aortic dissection (ATAAD) remains controversial. We retrospectively investigated the early outcomes of Sun's procedure in elderly patients with ATAAD in our single center.

METHODS

This study involved 106 patients who underwent Sun's procedure. The patients were divided into the elderly group (≥70 years, n = 17) and younger group (<70 years). Baseline, intraoperative, and postoperative data were compared between the groups.

RESULTS

The mean age in the elderly and younger groups was 75.7 and 50.7 years, respectively. The type of aortic root operations were not significantly different between the groups. Concomitant surgeries were more frequently performed in the elderly group, but without statistical significance. All intraoperative cardiopulmonary bypass variables as well as the in-hospital and 30-day mortality rates were similar between the groups. The incidences of most postoperative complications were also similar except for a higher incidence of sepsis in the elderly group.

CONCLUSIONS

Emergency performance of Sun's procedure for patients with ATAAD characterized by dissection and/or entry tear in the aortic arch should not be denied on the basis of advanced age alone. Comparable early in-hospital outcomes can be achieved in elderly patients.

Recovery of organ-specific tissue oxygen delivery at restrictive transfusion thresholds after fluid treatment in ovine haemorrhagic shock

Background

Fluid resuscitation is the standard treatment to restore circulating blood volume and pressure after massive haemorrhage and shock. Packed red blood cells (PRBC) are transfused to restore haemoglobin levels. Restoration of microcirculatory flow and tissue oxygen delivery is critical for organ and patient survival, but these parameters are infrequently measured. Patient Blood Management is a multidisciplinary approach to manage and conserve a patient’s own blood, directing treatment options based on broad clinical assessment beyond haemoglobin alone, for which tissue perfusion and oxygenation could be useful. Our aim was to assess utility of non-invasive tissue-specific measures to compare PRBC transfusion with novel crystalloid treatments for haemorrhagic shock.

Methods

A model of severe haemorrhagic shock was developed in an intensive care setting, with controlled haemorrhage in sheep according to pressure (mean arterial pressure 30–40 mmHg) and oxygen debt (lactate > 4 mM) targets. We compared PRBC transfusion to fluid resuscitation with either PlasmaLyte or a novel crystalloid. Efficacy was assessed according to recovery of haemodynamic parameters and non-invasive measures of sublingual microcirculatory flow, regional tissue oxygen saturation, repayment of oxygen debt (arterial lactate), and a panel of inflammatory and organ function markers. Invasive measurements of tissue perfusion, oxygen tension and lactate levels were performed in brain, kidney, liver, and skeletal muscle. Outcomes were assessed during 4 h treatment and post-mortem, and analysed by one- and two-way ANOVA.

Results

Each treatment restored haemodynamic and tissue oxygen delivery parameters equivalently (p > 0.05), despite haemodilution after crystalloid infusion to haemoglobin concentrations below 70 g/L (p < 0.001). Recovery of vital organ-specific perfusion and oxygen tension commenced shortly before non-invasive measures improved. Lactate declined in all tissues and correlated with arterial lactate levels (p < 0.0001). The novel crystalloid supported rapid peripheral vasodilation (p = 0.014) and tended to achieve tissue oxygen delivery targets earlier. PRBC supported earlier renal oxygen delivery (p = 0.012) but delayed peripheral perfusion (p = 0.034).

Conclusions

Crystalloids supported vital organ oxygen delivery after massive haemorrhage, despite haemodilution to < 70 g/L, confirming that restrictive transfusion thresholds are appropriate to support oxygen delivery. Non-invasive tissue perfusion and oximetry technologies merit further clinical appraisal to guide treatment for massive haemorrhage in the context of Patient Blood Management.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40635-022-00439-6.

Experimental near-infrared spectroscopy-guided minimally invasive segmental artery occlusion

OBJECTIVES

Minimally invasive staged segmental artery (SA) coil- and plug embolization is a new method for paraplegia prevention associated with extensive aortic procedures. Near-infrared spectroscopy of the paraspinal collateral network (cnNIRS) has emerged as a non-invasive method for spinal cord monitoring. The aim of this study was to evaluate cnNIRS to guide minimally invasive SA occlusion.

METHODS

In a chronic large animal experiment, 18 juvenile pigs underwent two-stage minimally invasive staged SA coil- and plug embolization for complete SA occlusion. Coil-embolization was performed either by SA main stem occlusion (characteristic of pig anatomy) or separately for the left- and right SA. Lumbar cnNIRS was recorded during and after the procedure. Neurological status was assessed up to 3 days after complete SA occlusion.

RESULTS

Mean time from SA coil embolization to minimum cnNIRS values was 11 ± 5 min with an average decrease from 101 ± 2% to 78 ± 8% of baseline (difference: -23 ± 9, P < 0.001). Lumbar cnNIRS demonstrated significant differences between left and right when SAs were occluded separately in all cases (-7 ± 4%, 1 min after first SA occlusion; P = 0.001). Permanent paraplegia occurred in 2 (11%) and any kind of neurological deficit-temporary or permanent-in 7 animals (39%). Association between lumbar cnNIRS and neurological outcome after minimally invasive staged SA coil- and plug embolization suggests positive correlation (R = 0.5, P = 0.052).

CONCLUSIONS

Lumbar cnNIRS independently reacts to unilateral SA occlusion. cnNIRS-guided SA occlusion is feasible and may become a useful adjunct facilitating adequate and complete vessel occlusion.

Neuromonitoring and Neurocognitive Outcomes in Cardiac Surgery: A Narrative Review

Neurocognitive dysfunction after cardiac surgery can present with diverse clinical phenotypes, which include postoperative delirium, postoperative cognitive dysfunction, and stroke, and it presents a significant healthcare burden for both patients and providers. Neurologic monitoring during cardiac surgery includes several modalities assessing cerebral perfusion and oxygenation (near-infrared spectroscopy, transcranial Doppler and jugular venous bulb saturation monitoring) and those that measure cerebral function (processed and unprocessed electroencephalogram), reflecting an absence of a single, definitive neuromonitor. This narrative review briefly describes the technologic basis of these neuromonitoring modalities, before exploring their use in clinical practice, both as tools to predict neurocognitive dysfunction, and with a bundle of interventions designed to optimize cerebral oxygen supply, with the aim of reducing postoperative delirium and cognitive dysfunction following cardiac surgery.

Near-infrared spectroscopy device selection affects intervention management for cerebral desaturation during cardiopulmonary bypass surgery

OBJECTIVE

Currently, several near-infrared spectroscopy oximetry devices are used for detecting cerebral ischemia during cardiopulmonary bypass (CPB) surgery. We investigated whether two different models of near-infrared spectroscopy oximetry devices affect the assessment of cerebral ischemia and its management during CPB.

METHODS

From January 2017 to August 2017, 70 adult cardiovascular surgery cases were randomly assigned to 1 of 2 different near-infrared spectroscopy oximetry devices. The devices were INVOS 5100C (Medtronic, Minneapolis, MN, USA) (group I; n = 35) and FORE-SIGHT ELITE (CAS Medical Systems, Branford, CT, USA) (group F; n = 35).

RESULTS

There were no significant differences in patient characteristics. The rSO₂ values were significantly higher for patients in group F than for patients in group I. Scalp-Cortex distance showed negative correlations with the mean rSO₂ values in group I (P = 0.01). Interventions for low rSO₂ during CPB for groups I and F were increase perfusion flow (13:5; P = 0.03), blood transfusion (7:1; P = 0.02), and both (6:1; P = 0.04), respectively. The Scalp-Cortex distance in group I was significantly longer in patients who required intervention than in patients who did not (17.1 ± 2.5 vs 15.1 ± 1.6 mm; P = 0.007).

CONCLUSIONS

It is inappropriate to use the same intervention criteria for different near-infrared spectroscopy oximetry devices. Moreover, brain atrophy influence rSO₂ values depending on device selection. It is important to note that inappropriate device selection may misguide perfusionists into performing unnecessary or excessive intervention during CPB.

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.

Cerebral Tissue Regional Oxygen Saturation as a Valuable Monitoring Parameter in Pediatric Patients Undergoing Extracorporeal Membrane Oxygenation

Objective: Brain function monitoring technology for extracorporeal membrane oxygenation (ECMO) support has been developing quite slowly. Our objective was to explore the data distribution, variation trend, and variability of cerebral tissue regional oxygen saturation (CrSO₂) in pediatric patients undergoing ECMO. Methods: Eight patients who received venoarterial ECMO (V-A ECMO) were included in our study. All of them accepted continuous CrSO₂ monitoring by near-infrared spectroscopy (NIRS) within 12 h of ECMO initiation until ECMO wean. Differences in the CrSO₂ distribution characteristic, the variation trend of daily CrSO₂, and the variability of CrSO₂ for the first 5 days following ECMO initiation were compared between survivors and non-survivors according to pediatric intensive care unit (PICU) mortality. Results: The percentage of time of CrSO₂ <60% against the whole monitoring time was significantly lower in survivors in both hemispheres {right: 4.34% [interquartile range (IQR) = 0.39-8.55%] vs. 47.45% [IQR = 36.03-64.52%], p = 0.036; left: 0.40% [IQR = 0.01-1.15%] vs. 30.9% [IQR = 26.92-49.62%], p = 0.036}. Survivors had significantly higher CrSO₂ on the first 4 days. Root mean of successive squared differences (RMSSD), the variability variable of CrSO₂, was significantly lower in survivors (right: 3.29 ± 0.79 vs. 6.16 ± 0.67, p = 0.002; left: 3.56 ± 1.20 vs. 6.04 ± 1.44, p = 0.039). Conclusion: Lower CrSO₂, CrSO₂ <60% over a longer period of time, and higher fluctuation of CrSO₂ are likely associated with PICU mortality in pediatric patients undergoing V-A ECMO. Clinical Trial Registry: URL: http://www.chictr.org.cn/showproj.aspx?proj=46639, trial registry number: ChiCTR1900028021.

Validation of a Novel NeurOs Cerebral Oximetry Monitor Against the INVOS Monitor During Cardiac Surgery

OBJECTIVES

To compare the performance of a novel NeurOs cerebral oximetry monitor against the INVOS monitor during the entire intraoperative phase of cardiac surgery, including periods of known fluctuation in brain oxygenation, such as preoxygenation, induction, cannulation, and cardiopulmonary bypass.

DESIGN

This study was a prospective, nonrandomized, healthcare-provider and outcome-assessor blinded study.

SETTING

Tertiary care university hospital; single institutional study.

PARTICIPANTS

Twenty-three patients who underwent cardiac surgery with cardiopulmonary bypass.

INTERVENTIONS

Both self-adhesive INVOS sensors and the assembled NeurOs sensors were placed accordingly when the patient arrived in the operating room.

MEASUREMENTS AND MAIN RESULTS

Ten out of 13 cases under the normal mode and eight out of the 10 cases under the high- sensitivity mode showed significant correlations between the NeurOs and INVOS groups (p < 0.05, r value from 0.24-0.88). When all cases were combined, NeurOs demonstrated significant correlation with INVOS (r = 0.5, 95% confidence interval [CI] 0.44-0.56, p < 0.01 for normal mode; r = 0.69, 95% CI 0.64 to 0.74, p < 0.01 for high-sensitivity mode) in both modes. To evaluate the data diversity, the authors performed a cluster analysis and found much less variation existed in the NeurOs normal mode when compared with INVOS (standard deviation [SD] 16.6% in INVOS, 4% in NeurOs normal mode) but similar patterns in the high-sensitivity mode (SD 17.6% in INVOS, 15.2% in NeurOs high-sensitivity mode). Bland-Altman plot analysis showed that most of the data fell between ± 1.96 SD lines, which demonstrated good consistency between these two methods under both modes of NeurOs (-28.8 to 30.8 in the normal mode; -36.6 to 32.7 in high-sensitivity mode). In the normal mode of NeurOs monitoring, receiver operating characteristic analysis suggested a 2% cutoff point was most optimal from the baseline for detecting hyperoxia (sensitivity 73%; specificity 66%) and minus 1% (sensitivity 66%; specificity 67%) for detecting hypoxia. Whereas in the high-sensitivity mode, the optimal cutoff point was 3% from baseline for detecting hyperoxia (sensitivity 75%; specificity 68%), and minus 3% for detecting hypoxia (sensitivity 90%; specificity 45%).

CONCLUSIONS

In conclusion, the novel NeurOs system was found to correlate with INVOS cerebral oximetry measurements during cardiac surgery.

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.

Comparison of Broadband and Discrete Wavelength Near-Infrared Spectroscopy Algorithms for the Detection of Cytochrome aa3 Reduction

BACKGROUND

Cytochrome aa3, the terminal component of the electron transport chain, absorbs near-infrared radiation (NIR) differentially depending on its oxidation state (Cytox), which can in theory be measured using near-infrared spectroscopy (NIRS) by relating light absorption at specific wavelengths to chromophore concentrations. Some NIRS algorithms use discrete wavelengths, while others analyze a band of NIR (broadband NIRS). The purpose of this study was to test the ability of discrete wavelength and broadband algorithms to measure changes in Cytox (primary outcome), and to determine whether or not a discreet wavelength NIRS algorithm could perform similarly to a broadband NIRS algorithm for the measurement of Cytox in a staged hypoxia-cyanide model (hypoxia and cyanide have oppositional effects on tissue saturation, but both cause cytochrome reduction).

METHODS

Twenty Sprague-Dawley rats were anesthetized with isoflurane, intubated, and instrumented. Blood pressure, end-tidal carbon dioxide, and arterial oxygen saturation were measured. A halogen light source transmitted NIR transcranially. NIR from the light source and the skull was transmitted to 2 cooled charge-coupled device spectrometers. Rats were subjected to anoxia (fraction of inspired oxygen, 0.0) until arterial oxygen saturation decreased to 70%. After recovery, 5 mg/kg sodium cyanide was injected intravenously. The cycle was repeated until cardiac arrest occurred. Relative concentrations of hemoglobin and cytochrome aa3 were calculated using discreet wavelength and broadband NIRS algorithms.

RESULTS

Hypoxia led to an increase in calculated deoxyhemoglobin (0.20 arbitrary units [AUs]; 95% confidence interval [CI], 0.17-0.22; P < .0001), a decrease in calculated oxyhemoglobin (-0.16 AUs; 95% CI, -0.19 to -0.14; P < .0001), and a decrease in calculated Cytox (-0.057 AUs; 95% CI, -0.073 to 0.0040; P < .001). Cyanide led to a decrease in calculated deoxyhemoglobin (-0.037 AUs; 95% CI, 0.046 to -0.029; P < .001), an increase in calculated oxyhemoglobin (0.053 AUs; 95% CI, 0.040-0.065; P < .001), and a decrease in calculated Cytox (-0.056 AUs; 95% CI, -0.064 to -0.048; P < .001). The correlations between "discreet" wavelength algorithms (using 4, 6, 8, and 10 wavelengths) and the broadband algorithm for the measurement of calculated Cytox were 0.54 (95% CI, 0.52-0.56), 0.87 (0.87-0.88), 0.88 (0.88-0.89), and 0.95 (0.95-0.95), respectively.

CONCLUSIONS

The broadband and 10 wavelength algorithm were able to accurately track changes in Cytox for all experiments.

Effect of End-Tidal Carbon Dioxide on Cerebral Dynamics in Infants With Ventricular Septal Defect: A Comparison Between Sevoflurane and Intravenous Anesthetics

OBJECTIVES

The primary aim was to compare the changes in regional cerebral oxygen saturation (rSO₂) and cerebral blood flow velocity (CBFV) during sevoflurane and intravenous anesthesia when the end-tidal carbon dioxide partial pressure (P_ETCO₂) changed in infants undergoing ventricular septal defect (VSD) repair.

DESIGN

Prospective, observational study.

SETTING

Tertiary care hospital.

PARTICIPANTS

Patients younger than 6 months with VSDs.

INTERVENTIONS

End-tidal carbon dioxide was increased by decreasing tidal volume or respiratory rate.

MEASUREMENTS AND MAIN RESULTS

The infants were randomly assigned to receive either sevoflurane (SA group) or midazolam-sufentanil based intravenous anesthesia (IA group). P_ETCO₂ levels of 30 mmHg (T1), 35 mmHg (T2), 40 mmHg (T3), or 45 mmHg (T4) were obtained by adjusting the tidal volume and respiratory rate. There were no significant intergroup differences in rSO_2. In the SA group, as P_ETCO₂ increased from T1 to T4, rSO₂ increased significantly from 68.8% ± 5.9% to 76.4% ± 6.0% (p < 0.001). CBFV increased linearly, whereas the pulsatility index and resistance index decreased linearly from T1 to T4 (p < 0.001). In the IA group, rSO₂ showed a significant increase from 68.6% ± 4.6% to 76.1% ± 6.2% with the change in P_ETCO₂ from T1 to T4 (p < 0.001). CBFV increased linearly, whereas the pulsatility index and resistance index decreased linearly from T1 to T4 (p < 0.001).

CONCLUSION

Cerebrovascular response to different P_ETCO₂ levels was preserved and similar during clinically relevant doses of sevoflurane anesthesia and midazolam-sufentanil based intravenous anesthesia in infants younger than 6 months old undergoing VSD repair.

Regional cerebral oximetry is consistent across self-reported racial groups and predicts 30-day mortality in cardiac surgery: a retrospective analysis

Darker skin pigmentation appears to cause underestimation of regional oxygen saturation (rSO₂) for certain cerebral oximetry devices. This presents a risk of triggering unindicated interventions and may limit its utility for predicting adverse outcomes. Our goal was to quantify the impact of self-reported race on oximetry measurements during cardiac surgery and elucidate whether race has a mediating role in the association of rSO₂ with mortality. Data was extracted from our department's data warehouse for adult patients who underwent on-pump cardiac surgery between June 2014 and June 2018. Intraoperative rSO₂ was recorded every 15 s throughout all cases. After grouping patients by self-reported race, multiple linear regression modeling was utilized to assess the association between race and mean pre-bypass rSO₂ while controlling for various perioperative variables. The role of mean pre-bypass rSO₂ for predicting 30-day mortality was evaluated via multiple logistic regression, and the threshold for rSO₂ was selected by maximizing F1 score. There were 4267 patients included. Compared to Caucasian patients, the unadjusted difference in mean pre-bypass rSO₂ was - 0.6% (95% CI - 1.3 to 0.04) for African American patients, - 1.8% (- 2.7 to - 0.9) for Asian patients, 0.1% (- 0.8 to 1.0) for Hispanic patients, - 1.6% (- 3.0 to - 0.4) for Indian/South Asian patients, and - 1.4% (- 3.7 to 0.9) for Pacific Islander patients. After adjusting for perioperative variables, differences in rSO₂ readings less than 2% were observed between racial groups. Mean pre-bypass rSO₂ under 63% was an independent predictor of higher 30-day mortality risk (OR: 2.86, CI 1.39 to 5.53, p = 0.003), and the interaction variable between rSO₂ and race was not statistically significant (p = 0.299). Cerebral oximetry measurements are more consistent across racial groups than previously reported, supporting its utility for intraoperative monitoring and risk stratification. Pre-intervention rSO₂ is associated with increased 30-day mortality at a higher threshold than previously reported and was not significantly impacted by self-reported race.

Effects of relative low minute ventilation on cerebral haemodynamics in infants undergoing ventricular septal defect repair

BACKGROUND

Ventilation-associated changes in blood carbon dioxide levels are associated with various physiological changes in infants undergoing surgery. Studies on the effects of mechanical ventilation on cerebral haemodynamics especially for infants with CHD are scarce.

AIM

This study was done to compare the changes in regional cerebral oxygen saturation and cerebral blood flow velocity when the end-tidal carbon dioxide partial pressure changed during different minute ventilation settings in infants undergoing ventricular septal defect repair.

METHODS

A total of 67 patients less than 1 year old with ventricular septal defect were enrolled, and 65 patients (age: 6.7 ± 3.4 months, weight: 6.4 ± 1.5 kg) were studied. After anaesthesia induction and endotracheal intubation, the same mechanical ventilation mode (The fraction of inspired oxygen was 50%, and the inspiratory-to-expiratory ratio was 1:1.5.) was adopted. The end-tidal carbon dioxide partial pressure of 30 mmHg (T1), 35 mmHg (T2), 40 mmHg (T3), or 45 mmHg (T4) were obtained, respectively, by adjusting tidal volume and respiratory rate. Minute ventilation per kilogram was calculated by the formula: minute ventilation per kilogram = tidal volume * respiratory rate/kg. Regional cerebral oxygen saturation was monitored by real-time near-infrared spectroscopy. Cerebral blood flow velocity (systolic flow velocity, end-diastolic flow velocity, and mean flow velocity), pulsatility index, and resistance index were measured intermittently by transcranial Doppler. Systolic pressure, diastolic pressure, stroke volume index, and cardiac index were recorded using the pressure recording analytical method.

RESULTS

As the end-tidal carbon dioxide partial pressure increased from 30 to 45 mmHg, regional cerebral oxygen saturation increased significantly from 69 ± 5% to 79 ± 4% (p < 0.001). Cerebral blood flow velocity (systolic flow velocity, end-diastolic flow velocity, and mean flow velocity) increased linearly, while pulsatility index and resistance index decreased linearly from T1 (systolic flow velocity, 84 ± 19 cm/second; end-diastolic flow velocity, 14 ± 4 cm/second; mean flow velocity, 36 ± 10 cm/second; pulsatility index, 2.13 ± 0.59; resistance index, 0.84 ± 0.12) to T4 (systolic flow velocity, 113 ± 22 cm/second; end-diastolic flow velocity, 31 ± 6 cm/second; mean flow velocity, 58 ± 11 cm/second; pulsatility index, 1.44 ± 0.34; resistance index, 0.72 ± 0.07) (p < 0.001). There were significant differences in changes of systolic flow velocity, end-diastolic flow velocity, mean flow velocity, pulsatility index, and resistance index as the end-tidal carbon dioxide partial pressure increased from 30 to 45 mmHg between subgroups of infants ≤6 and infants >6 months, while the changes of regional cerebral oxygen saturation between subgroups were not statistically different. Regional cerebral oxygen saturation and cerebral blood flow velocity (systolic flow velocity, end-diastolic flow velocity, and mean flow velocity) were negatively correlated with minute ventilation per kilogram (r = -0.538, r = -0.379, r = -0.504, r = -0.505, p < 0.001). Pulsatility index and resistance index were positively related to minute ventilation per kilogram (r = 0.464, r = 0.439, p < 0.001). The diastolic pressure was significantly reduced from T1 (41 ± 7 mmHg) to T4 (37 ± 6 mmHg) (p < 0.001). There were no significant differences in systolic pressure, stroke volume index, and cardiac index with the change of end-tidal carbon dioxide partial pressure from T1 to T4 (p = 0.063, p = 0.382, p = 0.165, p > 0.05).

CONCLUSION

A relative low minute ventilation strategy increases regional cerebral oxygen saturation and cerebral blood flow, which may improve cerebral oxygenation and brain perfusion in infants undergoing ventricular septal defect repair.

Electroencephalography and Brain Oxygenation Monitoring in the Perioperative Period

Maintaining brain function and integrity is a pivotal part of anesthesiological practice. The present overview aims to describe the current role of the 2 most frequently used monitoring methods for evaluation brain function in the perioperative period, ie, electroencephalography (EEG) and brain oxygenation monitoring. Available evidence suggests that EEG-derived parameters give additional information about depth of anesthesia for optimizing anesthetic titration. The effects on reduction of drug consumption or recovery time are heterogeneous, but most studies show a reduction of recovery times if anesthesia is titrated along processed EEG. It has been hypothesized that future EEG-derived indices will allow a better understanding of the neurophysiological principles of anesthetic-induced alteration of consciousness instead of the probabilistic approach most often used nowadays.Brain oxygenation can be either measured directly in brain parenchyma via a surgical burr hole, estimated from the venous outflow of the brain via a catheter in the jugular bulb, or assessed noninvasively by near-infrared spectroscopy. The latter method has increasingly been accepted clinically due to its ease of use and increasing evidence that near-infrared spectroscopy-derived cerebral oxygen saturation levels are associated with neurological and/or general perioperative complications and increased mortality. Furthermore, a goal-directed strategy aiming to avoid cerebral desaturations might help to reduce these complications. Recent evidence points out that this technology may additionally be used to assess autoregulation of cerebral blood flow and thereby help to titrate arterial blood pressure to the individual needs and for bedside diagnosis of disturbed autoregulation.

Cerebral Near-Infrared Spectroscopy in Adult Patients Undergoing Veno-Arterial Extracorporeal Membrane Oxygenation

BACKGROUND

Acute cerebral complications (ACC) of veno-arterial extracorporeal membrane oxygenation (VA-ECMO) are associated with poor long-term neurologic outcome. We described the role of rSO₂ monitoring in detecting ACC and desaturations and their relationship with poor outcome when employing VA-ECMO.

METHODS

Retrospective analysis of patients monitored by cerebral frontal near-infrared spectroscopy (NIRS) (CAS Medical Systems Inc., Branford, CT, USA) during VA-ECMO (November 2008-December 2015). ACC was defined as the presence of stroke and/or brain death, while cerebral desaturation as cortical oxygen tissue saturation (rSO₂) < 60%.

RESULTS

Fifty-six of 159 VA-ECMO patients (age 55 [36-60] years) were included; 18 (32%) developed ACC and 36 died (64%). Cerebral desaturation occurred in 43 (74%) patients, who had a higher mortality than those without cerebral desaturation (74 vs. 31%). A high sequential organ failure assessment (SOFA) score on the first day of ECMO (OR 1.40 [95% CIs 1.06-1.84]) and the minimum ECMO blood flow during the first 4 days of therapy (OR 3.05 [1.01-9.17]) were independently associated with the occurrence of cerebral desaturation. Cerebral desaturation occurred more frequently in patients with ACC than others (94 vs. 68%); patients with ACC also had a lower minimal rSO₂ over time (49 vs. 54%) and more frequently had high right-left rSO₂ differences (33 vs. 8%), which were both independent predictors of ACC. The occurrence of cerebral desaturation (OR 7.93 [1.62-38.74]) and high lactate concentrations during the first 4 days of ECMO support (OR 1.22 [1.03-1.46]) was independently associated with hospital mortality.

CONCLUSIONS

Monitoring of rSO₂ could be considered as an interesting tool to monitor the brain of patients on VA-ECMO.

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.

Ultrasound-tagged near-infrared spectroscopy does not disclose absent cerebral circulation in brain-dead adults

BACKGROUND

Near-infrared spectroscopy, a non-invasive technique for monitoring cerebral oxygenation, is widely used, but its accuracy is questioned because of the possibility of extra-cranial contamination. Ultrasound-tagged near-infrared spectroscopy (UT-NIRS) has been proposed as an improvement over previous methods. We investigated UT-NIRS in healthy volunteers and in brain-dead patients.

METHODS

We studied 20 healthy volunteers and 20 brain-dead patients with two UT-NIRS devices, CerOx™ and c-FLOW™ (Ornim Medical, Kfar Saba, Israel), which measure cerebral flow index (CFI), a parameter related to changes in cerebral blood flow (CBF). Monitoring started after the patients had been declared brain dead for a median of 34 (range: 11-300) min. In 11 cases, we obtained further demonstration of absent CBF.

RESULTS

In healthy volunteers, CFI was markedly different in the two hemispheres in the same subject, with wide variability amongst subjects. In brain-dead patients (median age: 64 yr old, 45% female; 20% traumatic brain injury, 40% subarachnoid haemorrhage, and 40% intracranial haemorrhage), the median (inter-quartile range) CFI was 41 (36-47), significantly higher than in volunteers (33; 27-36).

CONCLUSIONS

In brain-dead patients, where CBF is absent, the UT-NIRS findings can indicate an apparently perfused brain. This might reflect an insufficient separation of signals from extra-cranial structures from a genuine appraisal of cerebral perfusion. For non-invasive assessment of CBF-related parameters, the near-infrared spectroscopy still needs substantial improvement.

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

BACKGROUND

Cerebral oximetry (cerebral oxygen saturation; ScO2) is used to noninvasively monitor cerebral oxygenation. ScO2 readings are based on the fraction of reduced and oxidized hemoglobin as an indirect estimate of brain tissue oxygenation and assume a static ratio of arterial to venous intracranial blood. Conditions that alter cerebral blood flow, such as acute changes in PaCO2, may decrease accuracy. We assessed the performance of two commercial cerebral oximeters across a range of oxygen concentrations during normocapnia and hypocapnia.

METHODS

Casmed FORE-SIGHT Elite (CAS Medical Systems, Inc., USA) and Covidien INVOS 5100C (Covidien, USA) oximeter sensors were placed on 12 healthy volunteers. The fractional inspired oxygen tension was varied to achieve seven steady-state levels including hypoxic and hyperoxic PaO2 values. ScO2 and simultaneous arterial and jugular venous blood gas measurements were obtained with both normocapnia and hypocapnia. Oximeter bias was calculated as the difference between the ScO2 and reference saturation using manufacturer-specified weighting ratios from the arterial and venous samples.

RESULTS

FORE-SIGHT Elite bias was greater during hypocapnia as compared with normocapnia (4 ± 9% vs. 0 ± 6%; P < 0.001). The INVOS 5100C bias was also lower during normocapnia (5 ± 15% vs. 3 ± 12%; P = 0.01). Hypocapnia resulted in a significant decrease in mixed venous oxygen saturation and mixed venous oxygen tension, as well as increased oxygen extraction across fractional inspired oxygen tension levels (P < 0.0001). Bias increased significantly with increasing oxygen extraction (P < 0.0001).

CONCLUSIONS

Changes in PaCO2 affect cerebral oximeter accuracy, and increased bias occurs with hypocapnia. Decreased accuracy may represent an incorrect assumption of a static arterial-venous blood fraction. Understanding cerebral oximetry limitations is especially important in patients at risk for hypoxia-induced brain injury, where PaCO2 may be purposefully altered.

Brain natriuretic peptide (BNP) may play a major role in risk stratification based on cerebral oxygen saturation by near-infrared spectroscopy in patients undergoing major cardiovascular surgery

Purpose

A previous study reported that low baseline cerebral oxygen saturation (ScO₂) (≤50%) measured with near-infrared spectroscopy was predictive of poor clinical outcomes after cardiac surgery. However, such findings have not been reconfirmed by others. We conducted the current study to evaluate whether the previous findings would be reproducible, and to explore mechanisms underlying the ScO₂-based outcome prediction.

Methods

We retrospectively investigated 573 consecutive patients, aged 20 to 91 (mean ± standard deviation, 67.1 ± 12.8) years, who underwent major cardiovascular surgery. Preanesthetic baseline ScO₂, lowest intraoperative ScO₂, various clinical variables, and hospital mortality were examined.

Results

Bivariate regression analyses revealed that baseline ScO₂ correlated significantly with plasma brain natriuretic peptide concentration (BNP), hemoglobin concentration (Hgb), estimated glomerular filtration rate (eGFR), and left ventricular ejection fraction (LVEF) (p < 0.0001 for each). Baseline ScO₂ correlated with BNP in an exponential manner, and BNP was the most significant factor influencing ScO₂. Logistic regression analyses revealed that baseline and lowest intraoperative ScO₂ values, but not relative ScO₂ decrements, were significantly associated with hospital mortality (p < 0.05), independent of the EuroSCORE (p < 0.01). Receiver operating curve analysis of ScO₂ values and hospital mortality revealed an area under the curve (AUC) of 0.715 (p < 0.01) and a cutoff value of ≤50.5% for the baseline and ScO₂, and an AUC of 0.718 (p < 0.05) and a cutoff value of ≤35% for the lowest intraoperative ScO₂. Low baseline ScO₂ (≤50%) was associated with increases in intubation time, intensive care unit stay, hospital stay, and hospital mortality.

Conclusion

Baseline ScO₂ was reflective of severity of systemic comorbidities and was predictive of clinical outcomes after major cardiovascular surgery. ScO₂ correlated most significantly with BNP in an exponential manner, suggesting that BNP plays a major role in the ScO₂-based outcome prediction.

A validation method for near-infrared spectroscopy based tissue oximeters for cerebral and somatic tissue oxygen saturation measurements

We describe the validation methodology for the NIRS based FORE-SIGHT ELITE^® (CAS Medical Systems, Inc., Branford, CT, USA) tissue oximeter for cerebral and somatic tissue oxygen saturation (StO₂) measurements for adult subjects submitted to the United States Food and Drug Administration (FDA) to obtain clearance for clinical use. This validation methodology evolved from a history of NIRS validations in the literature and FDA recommended use of Deming regression and bootstrapping statistical validation methods. For cerebral validation, forehead cerebral StO₂ measurements were compared to a weighted 70:30 reference (REF CX_B) of co-oximeter internal jugular venous and arterial blood saturation of healthy adult subjects during a controlled hypoxia sequence, with a sensor placed on the forehead. For somatic validation, somatic StO₂ measurements were compared to a weighted 70:30 reference (REF CX_S) of co-oximetry central venous and arterial saturation values following a similar protocol, with sensors place on the flank, quadriceps muscle, and calf muscle. With informed consent, 25 subjects successfully completed the cerebral validation study. The bias and precision (1 SD) of cerebral StO₂ compared to REF CX_B was −0.14 ± 3.07%. With informed consent, 24 subjects successfully completed the somatic validation study. The bias and precision of somatic StO₂ compared to REF CX_S was 0.04 ± 4.22% from the average of flank, quadriceps, and calf StO₂ measurements to best represent the global whole body REF CX_S. The NIRS validation methods presented potentially provide a reliable means to test NIRS monitors and qualify them for clinical use.