A systematic performance evaluation of brain and body temperature sensors using ultra-stable temperature references

NPL contributions to the standardisation and validation of contemporary medical thermometry methods

Since the advent of reliable mercury-in-glass thermometers in the latter part of the 19th century the practice of clinical thermometry was thought to be a solved issue. However with advances in technology there has, in recent decades, been a proliferation of temperature measurement methods applied to medical science. Many of these have been introduced because of the clinical benefit they confer, nevertheless, in some cases the metrological foundation and infrastructure to ensure sound measurement was not in place. This paper will focus on the standardisation activity undertaken by the UK's National Physical Laboratory (NPL) to support reliable temperature measurement, using a number of innovative methods, in a clinical setting.

Regional pressure and temperature variations across the injured human brain: comparisons between paired intraparenchymal and ventricular measurements

INTRODUCTION

Intraparenchymal, multimodality sensors are commonly used in the management of patients with severe traumatic brain injury (TBI). The 'gold standard', based on accuracy, reliability and cost for intracranial pressure (ICP) monitoring is within the cerebral ventricle (external strain gauge). There are no standards yet for intracerebral temperature monitoring and little is known of temperature differences between brain tissue and ventricle. The aim of the study therefore was to determine pressure and temperature differences at intraparenchymal and ventricular sites during five days of continuous neuromonitoring.

METHODS

Patients with severe TBI requiring emergency surgery.

INCLUSION CRITERIA

patients who required ICP monitoring were eligible for recruitment. Two intracerebral probe types were used: a) intraventricular, dual parameter sensor (measuring pressure, temperature) with inbuilt catheter for CSF drainage: b) multiparameter intraparenchymal sensor measuring pressure, temperature and oxygen partial pressure. All sensors were inserted during surgery and under aseptic conditions.

RESULTS

Seventeen patients, 12 undergoing neurosurgery (decompressive craniectomy n = 8, craniotomy n = 4) aged 21-78 years were studied. Agreement of measures for 9540 brain tissue-ventricular temperature 'pairs' and 10,291 brain tissue-ventricular pressure 'pairs' were determined using mixed model to compare mean temperature and pressure for longitudinal data. There was no significant overall difference for mean temperature (p = 0.92) or mean pressure readings (p = 0.379) between tissue and ventricular sites. With 95.8 % of paired temperature readings within 2SD (-0.4 to 0.4 °C) differences in temperature between brain tissue and ventricle were clinically insignificant. For pressure, 93.5 % of readings pairs fell within the 2SD range (-9.4756 to 7.8112 mmHg). However, for individual patients, agreement for mean tissue-ventricular pressure differences was poor on occasions.

CONCLUSIONS

There is good overall agreement between paired temperature measurements obtained from deep white matter and brain ventricle in patients with and without early neurosurgery. For paired ICP measurements, 93.5 % of readings were within 2SD of mean difference. Whilst the majority of paired readings were comparable (within 10 mmHg) clinically relevant tissue-ventricular dissociations were noted. Further work is required to unravel the events responsible for short intervals of pressure dissociation before tissue pressure readings can be definitively accepted as a reliable surrogate for ventricular pressure.

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.