Support-vector classification of low-dose nitrous oxide administration with multi-channel EEG power spectra.

Support-vector machines (SVMs) can potentially improve patient monitoring during nitrous oxide anaesthesia. By elucidating the effects of low-dose nitrous oxide on the power spectra of multi-channel EEG recordings, we quantified the degree to which these effects generalise across participants. In this single-blind, cross-over study, 32-channel EEG was recorded from 12 healthy participants exposed to 0, 20, 30 and 40% end-tidal nitrous oxide. Features of the delta-, theta-, alpha- and beta-band power were used within a 12-fold, participant-wise cross-validation framework to train and test two SVMs: (1) binary SVM classifying EEG during 0 or 40% exposure (chance = 50%); (2) multi-class SVM classifying EEG during 0, 20, 30 or 40% exposure (chance = 25%). Both the binary (accuracy 92%) and the multi-class (accuracy 52%) SVMs classified EEG recordings at rates significantly better than chance (p < 0.001 and p = 0.01, respectively). To determine the relative importance of frequency band features for classification accuracy, we systematically removed features before re-training and re-testing the SVMs. This showed the relative importance of decreased delta power and the frontal region. SVM classification identified that the most important effects of nitrous oxide were found in the delta band in the frontal electrodes that was consistent between participants. Furthermore, support-vector classification of nitrous oxide dosage is a promising method that might be used to improve patient monitoring during nitrous oxide anaesthesia.

A prospective observational study on the effect of emboli exposure on cerebral autoregulation in cardiac surgery requiring cardiopulmonary bypass.

OBJECTIVE: Cerebrovascular autoregulation impairment has been associated with stroke risk in cardiac surgery. We hypothesized that greater arterial emboli exposure in open-chamber surgery might promote dysautoreguation. METHODS: Forty patients underwent closed or open-chamber surgery. Transcranial Doppler detected emboli and measured bilateral middle cerebral artery flow velocities. Cerebral autoregulation was assessed by averaging the mean velocity index ("Mx," a continuous moving correlation between cerebral blood flow velocity and mean arterial pressure) over 30 min before and after aortic cross-clamp removal. RESULTS: Median (interquartile range) emboli counts were 775 (415, 1211) and 2664 (793, 3734) in the closed-chamber and open-chamber groups. Most appeared after the removal of the aortic cross-clamp (open-chamber 1631 (606, 2296)), (closed-chamber 229 (142, 384)), with emphasis on the right hemisphere (open-chamber: 826 (371, 1622)), (closed-chamber 181 (66, 276)). Linear mixed model analyses of mean velocity index change showed no significant overall effect of group (0.08, 95% CI: -0.04, 0.21; p = 0.19) or side (0.01, 95% CI: -0.03, 0.05; p = 0.74). There was an interaction between group and side (p = 0.001), manifesting as a greater increase in mean velocity index in the right hemisphere in the open than the closed group (mean difference: 0.15, 95% CI: 0.02, 0.27; p = 0.03). CONCLUSIONS: Overall, change in mean velocity index before and after cross-clamp removal did not differ between groups. However, most emboli entered the right cerebral hemisphere where this change was significantly greater in the open-chamber group, suggesting a possible association between embolic exposure and dysautoregulation.

A prospective observational study of emboli exposure in open versus closed chamber cardiac surgery.

OBJECTIVE: Exposure to cerebral emboli is ubiquitous and may be harmful in cardiac surgery utilizing cardiopulmonary bypass. This was a prospective observational study aiming to compare emboli exposure in closed-chamber with open-chamber cardiac surgery, distinguish particulate from gaseous emboli and examine cerebral laterality in distribution. METHODS: Forty patients underwent either closed-chamber procedures (n = 20) or open-chamber procedures (n = 20). Emboli (gaseous and solid) were detected using transcranial Doppler in both middle cerebral arteries in two monitoring phases: 1, initiation of bypass to the removal of the aortic cross-clamp; and 2, removal of aortic cross-clamp to 20 minutes after venous decannulation. RESULTS: Total (median (interquartile range)) emboli counts (both phases) were 898 (499-1366) and 2617 (1007-5847) in closed-chamber and open-chamber surgeries, respectively. The vast majority were gaseous; median 794 (closed-chamber surgery) and 2240 (open-chamber surgery). When normalized for duration, there was no difference between emboli exposures in closed-chamber and open-chamber surgery in phase 1: 6.8 (3.6-15.2) versus 6.4 (2.0-18.1) emboli per minute, respectively. In phase 2, closed-chamber surgery cases were exposed to markedly fewer emboli than open-chamber surgery cases: 9.6 (5.1-14.9) versus 43.3 (19.7-60.3) emboli per minute, respectively. More emboli (total) passed into the right cerebral circulation: 985 (397-2422) right versus 376 (198-769) left. CONCLUSIONS: Patients undergoing open-chamber surgery are exposed to considerably higher numbers of cerebral arterial emboli after removal of the aortic cross-clamp than those undergoing closed-chamber surgery, and more emboli enter the right middle cerebral artery than the left. These results may help inform the evaluation of the pathophysiological impact of emboli exposure.

Comment on Mankowska et al. Critical Flicker Fusion Frequency: A Narrative Review. Medicina 2021, 57, 1096.

We have read with great interest the review by Mankowska et al. [...].

An Electroencephalogram Metric of Temporal Complexity Tracks Psychometric Impairment Caused by Low-dose Nitrous Oxide.

BACKGROUND: Nitrous oxide produces non-γ-aminobutyric acid sedation and psychometric impairment and can be used as scientific model for understanding mechanisms of progressive cognitive disturbances. Temporal complexity of the electroencephalogram may be a sensitive indicator of these effects. This study measured psychometric performance and the temporal complexity of the electroencephalogram in participants breathing low-dose nitrous oxide. METHODS: In random order, 20, 30, and 40% end-tidal nitrous oxide was administered to 12 participants while recording 32-channel electroencephalogram and psychometric function. A novel metric quantifying the spatial distribution of temporal electroencephalogram complexity, comprised of (1) absolute cross-correlation calculated between consecutive 0.25-s time samples; 2) binarizing these cross-correlation matrices using the median of all channels as threshold; (3) using quantitative recurrence analysis, the complexity in temporal changes calculated by the Shannon entropy of the probability distribution of the diagonal line lengths; and (4) overall spatial extent and intensity of brain complexity, was quantified by calculating median temporal complexity of channels whose complexities were above 1 at baseline. This region approximately overlay the brain's default mode network, so this summary statistic was termed "default-mode-network complexity." RESULTS: Nitrous oxide concentration correlated with psychometric impairment (r = 0.50, P < 0.001). Baseline regional electroencephalogram complexity at midline was greater than in lateral temporal channels (1.33 ± 0.14 bits vs. 0.81 ± 0.12 bits, P < 0.001). A dose of 40% N2O decreased midline (mean difference [95% CI], 0.20 bits [0.09 to 0.31], P = 0.002) and prefrontal electroencephalogram complexity (mean difference [95% CI], 0.17 bits [0.08 to 0.27], P = 0.002). The lateral temporal region did not change significantly (mean difference [95% CI], 0.14 bits [-0.03 to 0.30], P = 0.100). Default-mode-network complexity correlated with N2O concentration (r = -0.55, P < 0.001). A default-mode-network complexity mixed-effects model correlated with psychometric impairment (r2 = 0.67; receiver operating characteristic area [95% CI], 0.72 [0.59 to 0.85], P < 0.001). CONCLUSIONS: Temporal complexity decreased most markedly in medial cortical regions during low-dose nitrous oxide exposures, and this change tracked psychometric impairment.

Visualization of Intracranial Pressure Insults After Severe Traumatic Brain Injury: Influence of Individualized Limits of Reactivity.

Cerebral perfusion pressure (CPP) lower limits of reactivity can be determined almost continuously after severe traumatic brain injury (TBI), and deviation below the lower limit carries important prognostic information. In this study, we used a recently derived coloured contour method for visualizing intracranial pressure (ICP) insults to describe the influence of having a CPP above the CPP lower limits of reactivity after severe TBI. In a cohort of 729 patients, we examined the relationship between ICP insults and the 6-month Glasgow Outcome Scale score, using colour-coded plots, as described previously. We then assessed this relationship when ICP insults were above or below the CPP lower limit of reactivity. We found a curvilinear relationship whereby even prolonged durations of low-intensity ICP insults were not associated with poor outcomes but short durations of high-intensity insults were. When only ICP insults with a CPP below the CPP lower limit of reactivity were considered, a much lower intensity of ICP insults could be tolerated. A CPP above the lower limits of reactivity exerts a protective effect, whereas a CPP below the lower reactivity limits renders the patient vulnerable to increased morbidity from intracranial hypertension.

Hyperbaric oxygen for decompression sickness.

Decompression sickness (DCS, "bends") is caused by formation of bubbles in tissues and/or blood when the sum of dissolved gas pressures exceeds ambient pressure (supersaturation). This may occur when ambient pressure is reduced during any of the following: ascent from a dive; depressurization of a hyperbaric chamber; rapid ascent to altitude in an unpressurized aircraft or hypobaric chamber; loss of cabin pressure in an aircraft; and during space walks.

Examining Collaborative Processes for Climate Change Adaptation in New Brunswick, Canada.

Collaboration is a proposed strategy to address super wicked environmental problems, such as climate change. Yet, understanding how it works for climate change adaptation is nascent. This research aims to advance the understanding of this by a cross-case analysis of three cases in New Brunswick, Canada. We sought to illuminate the inner workings of multiparty collaboration in the context of community climate change adaptation; identify important qualities of the process and outcomes from it, and probe their relationships; and, explore how they come about in practice. A questionnaire was sent to individuals involved in cases and key informant interviews were conducted. Results reveal case-specific variations, but more importantly, common qualities and outcomes across the cases. They offer key insight into elements which may be important in collaborative settings. These are informative for influencing the uptake of collaborative strategies in climate change adaptation and offer the opportunity to better understand their functional effectiveness.

Emerging indications for hyperbaric oxygen.

PURPOSE OF REVIEW: To identify and discuss emerging trends in the therapeutic use of hyperbaric oxygen. RECENT FINDINGS: There has been a maturing of the clinical evidence to support the treatment of sudden hearing loss, a wide range of problematic chronic wound states and the prevention and treatment of end-organ damage associated with diabetes mellitus. On the other hand, the controversy continues concerning the use of hyperbaric oxygen therapy (HBOT) to treat sequelae of mild traumatic brain injury. HBOT remains poorly understood by many medical practitioners despite more than 50 years of clinical practice. Pharmacological actions arise from increased pressures of oxygen in the blood and tissues. Most therapeutic mechanisms identified are not the simple result of the reoxygenation of hypoxic tissue, but specific effects on immunological and metabolic pathways by this highly reactive element. HBOT remains controversial despite biological plausibility and a solid clinical evidence base in several disease states. SUMMARY: Multiple proposals for new indications for HBOT continue to emerge. Although many of these will likely prove of limited clinical importance, some show significant promise. Responsible practitioners remain acutely aware of the need for high-quality clinical evidence before introducing emerging indications into routine practice.

Consensus guideline: Pre-hospital management of decompression illness: expert review of key principles and controversies.

(Mitchell SJ, Bennett MH, Bryson P, Butler FK, Doolette DJ, Holm JR, Kot J, Lafère P. Pre-hospital management of decompression illness: expert review of key principles and controversies. Diving and Hyperbaric Medicine. 2018 March;48(1):45е.doi.10.28920/dhm48.1.45-55.) Guidelines for the pre-hospital management of decompression illness (DCI) had not been formally revised since the 2004 Divers Alert Network/Undersea and Hyperbaric Medical Society workshop held in Sydney, entitled "Management of mild or marginal decompression illness in remote locations." A contemporary review was initiated by the Divers Alert Network and undertaken by a multinational committee with members from Australasia, the USA and Europe. The process began with literature reviews by designated committee members on: the diagnosis of DCI; first aid strategies for DCI; remote triage of possible DCI victims by diving medicine experts; evacuation of DCI victims; effect of delay to recompression in DCI; pitfalls in management when DCI victims present at hospitals without diving medicine expertise and in-water recompression. This was followed by presentation of those reviews at a dedicated workshop at the 2017 UHMS Annual Scientific Meeting, discussion by registrants at that workshop and, finally, several committee meetings to formulate statements addressing points considered of prime importance to the management of DCI in the field. The committee placed particular emphasis on resolving controversies around the definition of "mild DCI" arising over 12 years of practical application of the 2004 workshop's findings, and on the controversial issue of in-water recompression. The guideline statements are promulgated in this paper. The full workshop proceedings are in preparation for publication.

Microbiological Contamination of Drugs during Their Administration for Anesthesia in the Operating Room.

BACKGROUND: The aseptic techniques of anesthesiologists in the preparation and administration of injected medications have not been extensively investigated, but emerging data demonstrate that inadvertent lapses in aseptic technique may be an important contributor to surgical site and other postoperative infections. METHODS: A prospective, open, microbiological audit of 303 cases in which anesthesiologists were asked to inject all bolus drugs, except propofol and antibiotics, through a 0.2-µm filter was performed. The authors cultured microorganisms, if present, from the 0.2-µm filter unit and from the residual contents of the syringes used for drawing up or administering drugs. Participating anesthesiologists rated ease of use of the filters after each case. RESULTS: Twenty-three anesthesiologists each anesthetized up to 25 adult patients. The authors isolated microorganisms from filter units in 19 (6.3%) of 300 cases (3 cases were excluded), including Staphylococcus capitis, Staphylococcus warneri, Staphylococcus epidermidis, Staphylococcus haemolyticus, Micrococcus luteus/lylae, Corynebacterium, and Bacillus species. The authors collected used syringes at the end of each case and grew microorganisms from residual drug in 55 of these 2,318 (2.4%) syringes including all the aforementioned microorganisms and also Kocuria kristinae, Staphylococcus aureus, and Staphylococcus hominus. Participants' average rating of ease of use of the filter units was 3.5 out of 10 (0 being very easy and 10 being very difficult). CONCLUSIONS: Microorganisms with the potential to cause infection are being injected (presumably inadvertently) into some patients during the administration of intravenous drugs by bolus during anesthesia. The relevance of this finding to postoperative infections warrants further investigation.

Breath alcohol of anesthesiologists using alcohol hand gel and the "five moments for hand hygiene" in routine practice.

PURPOSE: Appropriate hand hygiene reduces hospital-acquired infections. Anesthesiologists work in environments with numerous hand hygiene opportunities (HHOs). In a prospective observational study, we investigated the potential for an anesthesiologist to return a positive alcohol breath test during routine practice when using alcohol hand gel. METHODS: We observed ten volunteer anesthesiologists over four hours while they implemented the World Health Organization (WHO) "five moments for hand hygiene" using our hospital's adopted standard 70% ethanol hand gel. We measured the expired alcohol concentration at shift start and every fifteen minutes thereafter with a fuel cell breathalyzer calibrated to measure the percentage of blood alcohol concentration (BAC). Blood alcohol specimens (analyzed with gas chromatography) were collected at shift start and, when possible, immediately after a participant's first positive breathalyzer test. RESULTS: Of the 130 breathalyzer tests obtained, there were eight (6.2%) positive breath alcohol results from six of the ten participants, all within two minutes of a HHO. The highest value breathalyzer BAC recorded was 0.064%, with an overall mean (SD) of 0.023 (0.017)%. Five (62.5%) of the positive breathalyzer tests returned to zero in less than seven minutes. All of three blood specimens obtained immediately after a positive breathalyzer reading tested negative for alcohol. CONCLUSION: Anesthesia practitioners using alcohol hand gel in a manner that conforms with recommended hand hygiene can test positive for alcohol on a breathalyzer assay. Positive tests probably arose from inhalation of alcohol vapour into the respiratory dead space following gel application. If workplace breath testing for alcohol is implemented, it should be completed more than 15 min after applying alcohol hand gel. Positive results should be verified with a BAC test.

Clinical evaluation of emboli removal by integrated versus non-integrated arterial filters in new generation oxygenators.

OBJECTIVE: To compare the emboli filtration efficiency of five integrated or non-integrated oxygenator-filter combinations in cardiopulmonary bypass circuits. METHODS: Fifty-one adult patients underwent surgery using a circuit with an integrated filtration oxygenator or non-integrated oxygenator with a separate 20 µm arterial line filter (Sorin Dideco Avant D903 + Pall AL20 (n=12), Sorin Inspire 6 M + Pall AL20 (n=10), Sorin Inspire 6M F (n=9), Terumo FX25 (n=10), Medtronic Fusion (n=10)). The Emboli Detection and Classification quantifier was used to count emboli upstream and downstream of the primary filter throughout cardiopulmonary bypass. The primary outcome measure was to compare the devices in respect of the median proportion of emboli removed. RESULTS: One device (Sorin Inspire 6 M + Pall AL20) exhibited a significantly greater median percentage reduction (96.77%, IQR=95.48 - 98.45) in total emboli counts compared to all other devices tested (p=0.0062 - 0.0002). In comparisons between the other units, they all removed a greater percentage of emboli than one device (Medtronic Fusion), but there were no other significant differences. CONCLUSION: The new generation Sorin Inspire 6 M, with a stand-alone 20 µm arterial filter, appeared most efficient at removing incoming emboli from the circuit. No firm conclusions can be drawn about the relative efficacy of emboli removal by units categorised by class (integrated vs non-integrated); however, the stand-alone 20 µm arterial filter presently sets a contemporary standard against which other configurations of equipment can be judged.

Anaphylaxis is more common with rocuronium and succinylcholine than with atracurium.

BACKGROUND: Intraoperative anaphylaxis is a rare but serious occurrence, often triggered by neuromuscular-blocking drugs (NMBDs). Previous reports suggest that the rates of anaphylaxis may be greater for rocuronium than for other NMBDs, but imprecise surrogate metrics for new patient exposures to NMBDs complicate interpretation. METHODS: This was a retrospective, observational cohort study of intraoperative anaphylaxis to NMBDs at two hospitals between 2006 and 2012. Expert anesthetic and immunologist collaborators investigated all referred cases of intraoperative anaphylaxis where NMBDs were administered and identified those where a NMBD was considered responsible. New patient exposures for each NMBD were extracted from electronic anesthetic records compiled during the same period. Anaphylaxis rates were calculated for each NMBD using diagnosed anaphylaxis cases as the numerator and the number of new patient exposures as the denominator. RESULTS: Twenty-one patients were diagnosed with anaphylaxis to an NMBD. The incidence of anaphylaxis was 1 in 22,451 new patient exposures for atracurium, 1 in 2,080 for succinylcholine, and 1 in 2,499 for rocuronium (P < 0.001). CONCLUSIONS: In Auckland, the rate of anaphylaxis to succinylcholine and rocuronium is approximately 10-fold higher than to atracurium. Previous estimates of NMBD anaphylaxis rates are potentially confounded by inaccurate proxies of new patient exposures. This is the first study to report anaphylaxis rates using a hard denominator of new patient exposures obtained directly from anesthetic records.

Perspective on Cerebral Microemboli in Cardiac Surgery: Significant Problem or Much Ado About Nothing?

From the time an association was perceived between cardiac surgery and post-operative cognitive dysfunction (POCD), there has been interest in arterial microemboli as one explanation. A succession of studies in the mid-1990s reported a correlation between microemboli exposure and POCD and there followed a focus on microemboli reduction (along with other strategies) in pursuit of peri-operative neuroprotection. There is some evidence that the initiatives developed during this period were successful in reducing neurologic morbidity in cardiac surgery. More recently, however, there is increasing awareness of similar rates of POCD following on and off pump cardiac operations, and following many other types of surgery in elderly patients. This has led some to suggest that cardiopulmonary bypass (CPB) and microemboli exposure by implication are non-contributory. Although the risk factors for POCD may be more patient-centered and multifactorial than previously appreciated, it would be unwise to assume that CPB and exposure to microemboli are unimportant. Improvements in CPB safety (including emboli reduction) achieved over the last 20 years may be partly responsible for difficulty demonstrating higher rates of POCD after cardiac surgery involving CPB in contemporary comparisons with other operations. Moreover, microemboli (including bubbles) have been proven harmful in experimental and clinical situations uncontaminated by other confounding factors. It remains important to continue to minimize patient exposure to microemboli as far as is practicable.

Teamwork, communication, formula-one racing and the outcomes of cardiac surgery.

Most cardiac units achieve excellent results today, but the risk of cardiac surgery is still relatively high, and avoidable harm is common. The story of the Green Lane Cardiothoracic Unit provides an exemplar of excellence, but also illustrates the challenges associated with changes over time and with increases in the size of a unit and the complexity of practice today. The ultimate aim of cardiac surgery should be the best outcomes for (often very sick) patients rather than an undue focus on the prevention of error or adverse events. Measurement is fundamental to improving quality in health care, and the framework of structure, process, and outcome is helpful in considering how best to achieve this. A combination of outcomes (including some indicators of important morbidity) with key measures of process is advocated. There is substantial evidence that failures in teamwork and communication contribute to inefficiency and avoidable harm in cardiac surgery. Minor events are as important as major ones. Six approaches to improving teamwork (and hence outcomes) in cardiac surgery are suggested. These are: 1) subspecialize and replace tribes with teams; 2) sort out the leadership while flattening the gradients of authority; 3) introduce explicit training in effective communication; 4) use checklists, briefings, and debriefings and engage in the process; 5) promote a culture of respect alongside a commitment to excellence and a focus on patients; 6) focus on the performance of the team, not on individuals.

Decompression illness: a comprehensive overview.

Decompression illness is a collective term for two maladies (decompression sickness [DCS] and arterial gas embolism [AGE]) that may arise during or after surfacing from compressed gas diving. Bubbles are the presumed primary vector of injury in both disorders, but the respective sources of bubbles are distinct. In DCS bubbles form primarily from inert gas that becomes dissolved in tissues over the course of a compressed gas dive. During and after ascent ('decompression'), if the pressure of this dissolved gas exceeds ambient pressure small bubbles may form in the extravascular space or in tissue blood vessels, thereafter passing into the venous circulation. In AGE, if compressed gas is trapped in the lungs during ascent, pulmonary barotrauma may introduce bubbles directly into the pulmonary veins and thence to the systemic arterial circulation. In both settings, bubbles may provoke ischaemic, inflammatory, and mechanical injury to tissues and their associated microcirculation. While AGE typically presents with stroke-like manifestations referrable to cerebral involvement, DCS can affect many organs including the brain, spinal cord, inner ear, musculoskeletal tissue, cardiopulmonary system and skin, and potential symptoms are protean in both nature and severity. This comprehensive overview addresses the pathophysiology, manifestations, prevention and treatment of both disorders.

The first deep rebreather dive using hydrogen: case report.

Bounce diving with rapid descents to very deep depths may provoke the high-pressure neurological syndrome (HPNS). The strategy of including small fractions of nitrogen in the respired gas to produce an anti-HPNS narcotic effect increases the gas density which may exceed recommended guidelines. In 2020 the 'Wetmules' dive team explored the Pearse Resurgence cave (New Zealand) to 245 m breathing trimix (approximately 4% oxygen, 91% helium and 5% nitrogen). Despite the presence of nitrogen, one diver experienced HPNS tremors beyond 200 m. The use of hydrogen (a light yet slightly narcotic gas) has been suggested as a solution to this problem but there are concerns, including the potential for ignition and explosion of hydrogen-containing gases, and accelerated heat loss. In February 2023 a single dive to 230 m was conducted in the Pearse Resurgence to experience hydrogen as a breathing gas in a deep bounce dive. Using an electronic closed-circuit rebreather, helihydrox (approximately 3% oxygen, 59% helium and 38% hydrogen) was breathed between 200 and 230 m. This was associated with amelioration of HPNS symptoms in the vulnerable diver and no obvious adverse effects. The use of hydrogen is a potential means of progressing deeper with effective HPNS amelioration while maintaining respired gas density within advised guidelines.

Brachial arterial temperature as an indicator of core temperature: proof of concept and potential applications.

There is potential for heat loss and hypothermia during anesthesia and also for hyperthermia if heat conservation and active warming measures are not accurately titrated. Accurate temperature monitoring is particularly important in procedures in which the patient is actively cooled and then rewarmed such as during cardiopulmonary bypass surgery (CPB). We simultaneously measured core, nasopharyngeal, and brachial artery temperatures to investigate the last named as a potential peripheral temperature monitoring site. Ten patients undergoing hypothermic CPB were instrumented for simultaneous monitoring of temperatures in the pulmonary artery (PA), aortic arterial inflow (AI), nasopharynx (NP), and brachial artery (BA). Core temperature was defined as PA temperature before and after CPB and the AI temperature during CPB. Mean deviations of BA and NP temperatures from core temperature were calculated for three steady-state periods (before, during, and after CPB). Mean deviation of BA and NP temperatures from AI temperature was also calculated during active rewarming. A total of 1862 measurements were obtained and logged from eight patients. Mean BA and NP deviations from core temperature across the steady-state periods (before, during, and after CBP) were, respectively: .23 +/- .25, -.26 +/- .3, and -.09 +/- .05 degrees C (BA), and .11 +/- .19, -.1 +/- .47, and -.04 +/- .3 degrees C (NP). During steady-state periods, there was no evidence of a difference between the mean BA and NP deviation. During active rewarming, the mean difference between the BA and AI temperatures was .14 +/- .36 degrees C. During this period, NP temperature lagged behind AI and BA temperatures by up to 41 minutes and was up to 5.3 degres C lower than BA (mean difference between BA and NP temperatures was 1.22 +/- .58 degrees C). The BA temperature is an adequate surrogate for core temperature. It also accurately tracks the changing AI temperature during rewarming and is therefore potentially useful in detecting a hyperthermic perfusate, which might cause cerebral hyperthermia.