Monitoring of rectal, epidural, and intraventricular temperature in neurosurgical patients

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 2: physiological measurements

In this, the second of four historical reviews on human thermoregulation during exercise, we examine the research techniques developed by our forebears. We emphasise calorimetry and thermometry, and measurements of vasomotor and sudomotor function. Since its first human use (1899), direct calorimetry has provided the foundation for modern respirometric methods for quantifying metabolic rate, and remains the most precise index of whole-body heat exchange and storage. Its alternative, biophysical modelling, relies upon many, often dubious assumptions. Thermometry, used for >300 y to assess deep-body temperatures, provides only an instantaneous snapshot of the thermal status of tissues in contact with any thermometer. Seemingly unbeknownst to some, thermal time delays at some surrogate sites preclude valid measurements during non-steady state conditions. To assess cutaneous blood flow, immersion plethysmography was introduced (1875), followed by strain-gauge plethysmography (1949) and then laser-Doppler velocimetry (1964). Those techniques allow only local flow measurements, which may not reflect whole-body blood flows. Sudomotor function has been estimated from body-mass losses since the 1600s, but using mass losses to assess evaporation rates requires precise measures of non-evaporated sweat, which are rarely obtained. Hygrometric methods provide data for local sweat rates, but not local evaporation rates, and most local sweat rates cannot be extrapolated to reflect whole-body sweating. The objective of these methodological overviews and critiques is to provide a deeper understanding of how modern measurement techniques were developed, their underlying assumptions, and the strengths and weaknesses of the measurements used for humans exercising and working in thermally challenging conditions.

Prediction of Intracranial Temperature Through Invasive and Noninvasive Measurements on Patients with Severe Traumatic Brain Injury

The brain's temperature measurements (TB) in patients with severe brain damage are important, in order to offer the optimal treatment. The purpose of this research is the creation of mathematical models for the TB's prediction, based on the temperatures in the bladder (TBL), femoral artery (TFA), ear canal (TΕC), and axilla (TA), without the need for placement of intracranial catheter, contributing significantly to the research of the human thermoregulatory system.The research involved 18 patients (13 men and 5 women), who were hospitalized in the adult intensive care units (ICU) of Larissa's two hospitals, with severe brain injury. An intracranial catheter with a thermistor was used to continuously measure TB and other parameters. The TB's measurements, and simultaneously one or more of TBL, TFA, TEC, and TA, were recorded every 1 h.To create TB predicting models, the data of each measurement was separated into (a) model sample (measurements' 80%) and (b) validation sample (measurements' 20%). Multivariate linear regression analysis demonstrated that it is possible to predict brain's temperature (PrTB), using independent variables (R2 was TBL = 0.73, TFA = 0.80, TEC = 0.27, and TA = 0.17, p < 0.05). Significant linear associations were found, statistically, and no difference in means between TB and PrTB of each prediction model. Also, the 95% limits of agreement and the percent coefficient of variation showed sufficient agreement between the TB and PrTB in each prediction model.In conclusion, brain's temperature prediction models based on TBL, TFA, TEC, and TA were successful. Its determination contributes to the improvement of clinical decision-making.

Report of a consensus meeting on human brain temperature after severe traumatic brain injury: its measurement and management during pyrexia

Temperature disturbances are common in patients with severe traumatic brain injury. The possibility of an adaptive, potentially beneficial role for fever in patients with severe brain trauma has been dismissed, but without good justification. Fever might, in some patients, confer benefit. A cadre of clinicians and scientists met to debate the clinically relevant, but often controversial issue about whether raised brain temperature after human traumatic brain injury (TBI) should be regarded as "good or bad" for outcome. The objective was to produce a consensus document of views about current temperature measurement and pyrexia treatment. Lectures were delivered by invited speakers with National and International publication track records in thermoregulation, neuroscience, epidemiology, measurement standards and neurocritical care. Summaries of the lectures and workshop discussions were produced from transcriptions of the lectures and workshop discussions. At the close of meeting, there was agreement on four key issues relevant to modern temperature measurement and management and for undergirding of an evidence-based practice, culminating in a consensus statement. There is no robust scientific data to support the use of hypothermia in patients whose intracranial pressure is controllable using standard therapy. A randomized clinical trial is justified to establish if body cooling for control of pyrexia (to normothermia) vs moderate pyrexia leads to a better patient outcome for TBI patients.

The TOBY Study. Whole body hypothermia for the treatment of perinatal asphyxial encephalopathy: a randomised controlled trial

Background

A hypoxic-ischaemic insult occurring around the time of birth may result in an encephalopathic state characterised by the need for resuscitation at birth, neurological depression, seizures and electroencephalographic abnormalities. There is an increasing risk of death or neurodevelopmental abnormalities with more severe encephalopathy. Current management consists of maintaining physiological parameters within the normal range and treating seizures with anticonvulsants.

Studies in adult and newborn animals have shown that a reduction of body temperature of 3–4°C after cerebral insults is associated with improved histological and behavioural outcome. Pilot studies in infants with encephalopathy of head cooling combined with mild whole body hypothermia and of moderate whole body cooling to 33.5°C have been reported. No complications were noted but the group sizes were too small to evaluate benefit.

Methods/Design

TOBY is a multi-centre, prospective, randomised study of term infants after perinatal asphyxia comparing those allocated to "intensive care plus total body cooling for 72 hours" with those allocated to "intensive care without cooling".

Full-term infants will be randomised within 6 hours of birth to either a control group with the rectal temperature kept at 37 +/- 0.2°C or to whole body cooling, with rectal temperature kept at 33–34°C for 72 hours. Term infants showing signs of moderate or severe encephalopathy +/- seizures have their eligibility confirmed by cerebral function monitoring. Outcomes will be assessed at 18 months of age using neurological and neurodevelopmental testing methods.

Sample size

At least 236 infants would be needed to demonstrate a 30% reduction in the relative risk of mortality or serious disability at 18 months.

Recruitment was ahead of target by seven months and approvals were obtained allowing recruitment to continue to the end of the planned recruitment phase. 325 infants were recruited.

Primary outcome

Combined rate of mortality and severe neurodevelopmental impairment in survivors at 18 months of age. Neurodevelopmental impairment will be defined as any of:

• Bayley mental developmental scale score less than 70

• Gross Motor Function Classification System Levels III – V

• Bilateral cortical visual impairments

Trial Registration

Current Controlled Trials ISRCTN89547571

Brain temperature and outcome after severe traumatic brain injury

INTRODUCTION

In humans, raised body temperature is linked to poor outcome after brain injury. Because deviations between brain and body temperature have been reported after severe traumatic brain injury (TBI), the aim of this study was to explore the relationship between initial and mean brain temperature and survival at 3 months.

METHODS

Intraparenchymal temperature was measured 3 - 4 cm within white matter. Logistic regression was used to explore linear and quadratic relationships between initial and average brain temperature and survival at 3 months.

RESULTS

In 36 patients, initial brain temperatures ranged from 33.5 to 39.2 degrees C (median 37.4 degrees C). There was no evidence of an association between initial brain temperature and risk of death, either linear (odds ratio [OR] 95% confidence interval [CI] = 1.3 [0.68 to 2.5], p = 0.42) or quadratic ( p = 0.26). Assuming a linear relationship, patients with higher mean brain temperatures were less likely to die: OR (95% CI) for death per 1 degrees C was 0.31 (0.09 to 1.1), p = 0.06. However, by fitting the quadratic relationship, there was a suggestion that both high and low temperatures were associated with increased risk of death: p = 0.06.

CONCLUSION

Initial brain temperature measured shortly after admission did not predict outcome. There is a suggestion that patients with "middle range" temperatures were less likely to die.