Near-Infrared Spectroscopy to Assess Cerebral Autoregulation and Optimal Mean Arterial Pressure in Patients With Hypoxic-Ischemic Brain Injury: A Prospective Multicenter Feasibility Study

Shining a light on cerebral autoregulation: Are we anywhere near the truth?

The near-infrared spectroscopy (NIRS)-derived cerebral oximetry index (COx) has become popularized for non-invasive neuromonitoring of cerebrovascular function in post-cardiac arrest patients with hypoxic-ischemic brain injury (HIBI). We provide commentary on the physiologic underpinnings and assumptions of NIRS and the COx, potential confounds in the context of HIBI, and the implications for the assessment of cerebral autoregulation.

Post Cardiac Arrest Care in the Cardiac Intensive Care Unit

PURPOSE OF REVIEW

Cardiac arrests constitute a leading cause of mortality in the adult population and cardiologists are often tasked with the management of patients following cardiac arrest either as a consultant or primary provider in the cardiac intensive care unit. Familiarity with evidence-based practice for post-cardiac arrest care is a requisite for optimizing outcomes in this highly morbid group. This review will highlight important concepts necessary to managing these patients.

RECENT FINDINGS

Emerging evidence has further elucidated optimal care of post-arrest patients including timing for routine coronary angiography, utility of therapeutic hypothermia, permissive hypercapnia, and empiric aspiration pneumonia treatment. The complicated state of multi-organ failure following cardiac arrest needs to be carefully optimized by the clinician to prevent further neurologic injury and promote systemic recovery. Future studies should be aimed at understanding if these findings extend to specific patient populations, especially those at the highest risk for poor outcomes.

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.

Are NIRS-derived cerebral autoregulation and ABPopt values different between hemispheres in hypoxic-ischemic brain injury patients following cardiac arrest?

PURPOSE

Near-infrared spectroscopy (NIRS) has been suggested as a non-invasive monitoring technique to set cerebral autoregulation (CA) guided ABP targets (ABPopt) in comatose patients with hypoxic-ischemic brain injury (HIBI) following cardiac arrest. We aimed to determine whether NIRS-derived CA and ABPopt values differ between left and right-sided recordings in these patients.

METHODS

Bifrontal regional oxygen saturation (rSO2) was measured using INVOS or Fore-Sight devices. The Cerebral Oximetry index (COx) was determined as a CA measure. ABPopt was calculated using a published algorithm with multi-window weighted approach. A paired Wilcoxon signed rank test and intraclass correlation coefficients (ICC) were used to compare (1) systematic differences and (2) degree of agreement between left and right-sided measurements.

RESULTS

Eleven patients were monitored. In one patient there was malfunctioning of the right-sided optode and in one patient not any ABPopt value was calculated. Comparison of rSO2 and COx was possible in ten patients and ABPopt in nine patients. The average recording time was 26 (IQR, 22-42) hours. The ABPopt values were not significantly different between the bifrontal recordings (80 (95%-CI 76-84) and 82 (95%-CI 75-84) mmHg) for the left and right recordings, p = 1.0). The ICC for ABPopt was high (0.95, 0.78-0.98, p < 0.001). Similar results were obtained for rSO2 and COx.

CONCLUSION

We found no differences between left and right-sided NIRS recordings or CA estimation in comatose and ventilated HIBI patients. This suggests that in these patients without signs of localized pathology unilateral recordings might be sufficient to estimate CA status or provide ABPopt targets.

Comparison of cerebral metabolic rate of oxygen, blood flow, and bispectral index under general anesthesia

SIGNIFICANCE

The optical measurement of cerebral oxygen metabolism was evaluated.

AIM

Compare optically derived cerebral signals to the electroencephalographic bispectral index (BIS) sensors to monitor propofol-induced anesthesia during surgery.

APPROACH

Relative cerebral metabolic rate of oxygen ( rCMRO 2 ) and blood flow (rCBF) were measured by time-resolved and diffuse correlation spectroscopies. Changes were tested against the relative BIS (rBIS) ones. The synchronism in the changes was also assessed by the R-Pearson correlation.

RESULTS

In 23 measurements, optically derived signals showed significant changes in agreement with rBIS: during propofol induction, rBIS decreased by 67% [interquartile ranges (IQR) 62% to 71%], rCMRO 2 by 33% (IQR 18% to 46%), and rCBF by 28% (IQR 10% to 37%). During recovery, a significant increase was observed for rBIS (48%, IQR 38% to 55%), rCMRO 2 (29%, IQR 17% to 39%), and rCBF (30%, IQR 10% to 44%). The significance and direction of the changes subject-by-subject were tested: the coupling between the rBIS, rCMRO 2 , and rCBF was witnessed in the majority of the cases (14/18 and 12/18 for rCBF and 19/21 and 13/18 for rCMRO 2 in the initial and final part, respectively). These changes were also correlated in time ( R > 0.69 to R = 1 , p - values < 0.05 ).

CONCLUSIONS

Optics can reliably monitor rCMRO 2 in such conditions.

Deviations from PRx-derived optimal blood pressure are associated with mortality after cardiac arrest

AIM

Pressure reactivity index (PRx) provides a surrogate measurement of cerebrovascular autoregulation (CAR). We determined whether deviations from PRx-derived optimal mean arterial pressure (MAPopt) were associated with in-hospital mortality after adult cardiac arrest.

METHODS

Retrospective analysis of post-cardiac arrest patients who had continuously recorded intracranial pressure (ICP) and MAP. PRx was calculated as a moving, linear correlation between ICP and MAP. Impaired CAR was defined as PRx ≥ 0.3. MAPopt was calculated using a multi-window weighted algorithm. The burdens of MAP < 5 mmHg below MAPopt (MAPopt-5) and > 5 mmHg above MAPopt (MAPopt + 5) were calculated by integrating the area between MAP and MAPopt-5 or MAPopt + 5 curves, respectively. Univariate logistic regression tested the association between burden of MAP < MAPopt-5 and outcome.

RESULTS

Twenty-two patients were analyzed. Thirteen (59%) patients died before hospital discharge. Time (median [IQR]) between ROSC and monitoring initiation was 16 [14, 21] hours and duration of monitoring was 35 [22, 48] hours; neither differed between survivors and non-survivors. Median MAPopt was 89 [85, 97] mmHg and did not differ between survivors and non-survivors (89 [83, 94] vs. 91 [85, 105] mmHg, p = 0.64). Burden of MAP < MAPopt-5 was greater for non-survivors compared to survivors (OR 3.6 [95% CI 1.2-15.6]). Range of intact CAR (upper-lower limit) was narrower for non-survivors when compared to survivors (5 [0, 22] vs. 24 [7, 36] mmHg, p = 0.03).

CONCLUSION

A greater burden of MAP below PRx-derived MAPopt-5 was associated with mortality after cardiac arrest. Non-survivors had a narrower range of intact CAR than survivors.

Individualized cerebral perfusion pressure in acute neurological injury: are we ready for clinical use?

PURPOSE OF REVIEW

Individualizing cerebral perfusion pressure based on cerebrovascular autoregulation assessment is a promising concept for neurological injuries where autoregulation is typically impaired. The purpose of this review is to describe the status quo of autoregulation-guided protocols and discuss steps towards clinical use.

RECENT FINDINGS

Retrospective studies have indicated an association of impaired autoregulation and poor clinical outcome in traumatic brain injury (TBI), hypoxic-ischemic brain injury (HIBI) and aneurysmal subarachnoid hemorrhage (aSAH). The feasibility and safety to target a cerebral perfusion pressure optimal for cerebral autoregulation (CPPopt) after TBI was recently assessed by the COGITATE trial. Similarly, the feasibility to calculate a MAP target (MAPopt) based on near-infrared spectroscopy was demonstrated for HIBI. Failure to meet CPPopt is associated with the occurrence of delayed cerebral ischemia in aSAH but interventional trials in this population are lacking. No level I evidence is available on potential effects of autoregulation-guided protocols on clinical outcomes.

SUMMARY

The effect of autoregulation-guided management on patient outcomes must still be demonstrated in prospective, randomized, controlled trials. Selection of disease-specific protocols and endpoints may serve to evaluate the overall benefit from such approaches.

Deviations from NIRS-derived optimal blood pressure are associated with worse outcomes after pediatric cardiac arrest

AIM

Evaluate cerebrovascular autoregulation (CAR) using near-infrared spectroscopy (NIRS) after pediatric cardiac arrest and determine if deviations from CAR-derived optimal mean arterial pressure (MAP_opt) are associated with outcomes.

METHODS

CAR was quantified by a moving, linear correlation between time-synchronized mean arterial pressure (MAP) and regional cerebral oxygenation, called cerebral oximetry index (COx). MAP_opt was calculated using a multi-window weighted algorithm. We calculated burden (magnitude and duration) of MAP less than 5 mmHg below MAP_opt (MAPopt - 5), as the area between MAP and MAPopt - 5 curves using numerical integration and normalized as percentage of monitoring duration. Unfavorable outcome was defined as death or pediatric cerebral performance category (PCPC) at hospital discharge ≥3 with ≥1 change from baseline. Univariate logistic regression tested association between burden of MAP less than MAPopt - 5 and outcome.

RESULTS

Thirty-four children (median age 2.9 [IQR 1.5,13.4] years) were evaluated. Median COx in the first 24 h post-cardiac arrest was 0.06 [0,0.20]; patients spent 27% [19,43] of monitored time with COx ≥ 0.3. Patients with an unfavorable outcome (n = 24) had a greater difference between MAP and MAPopt - 5 (13 [11,19] vs. 9 [8,10] mmHg, p = 0.01) and spent more time with MAP below MAPopt - 5 (38% [26,61] vs. 24% [14,28], p = 0.03). Patients with unfavorable outcome had a higher burden of MAP less than MAPopt - 5 than patients with favorable outcome in the first 24 h post-arrest (187 [107,316] vs. 62 [43,102] mmHg × Min/Hr; OR 4.93 [95% CI 1.16-51.78]).

CONCLUSIONS

Greater burden of MAP below NIRS-derived MAPopt - 5 during the first 24 h after cardiac arrest was associated with unfavorable outcomes.

Monitoring and modifying brain oxygenation in patients at risk of hypoxic ischaemic brain injury after cardiac arrest

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2021. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2021 . Further information about the Annual Update in Intensive Care and Emergency Medicine is available from https://link.springer.com/bookseries/8901 .