Les variations thermiques modifient les paramètres des gaz du sang : quelles conséquences en pratique clinique ?

Accidental hypothermia in severe trauma

Hypothermia, along with acidosis and coagulopathy, is part of the lethal triad that worsen the prognosis of severe trauma patients. While accidental hypothermia is easy to identify by a simple measurement, it is no less pernicious if it is not detected or treated in the initial phase of patient care. It is a multifactorial process and is a factor of mortality in severe trauma cases. The consequences of hypothermia are many: it modifies myocardial contractions and may induce arrhythmias; it contributes to trauma-induced coagulopathy; from an immunological point of view, it diminishes inflammatory response and increases the chance of pneumonia in the patient; it inhibits the elimination of anaesthetic drugs and can complicate the calculation of dosing requirements; and it leads to an over-estimation of coagulation factor activities. This review will detail the pathophysiological consequences of hypothermia, as well as the most recent principle recommendations in dealing with it.

Brain temperature: physiology and pathophysiology after brain injury

The regulation of brain temperature is largely dependent on the metabolic activity of brain tissue and remains complex. In intensive care clinical practice, the continuous monitoring of core temperature in patients with brain injury is currently highly recommended. After major brain injury, brain temperature is often higher than and can vary independently of systemic temperature. It has been shown that in cases of brain injury, the brain is extremely sensitive and vulnerable to small variations in temperature. The prevention of fever has been proposed as a therapeutic tool to limit neuronal injury. However, temperature control after traumatic brain injury, subarachnoid hemorrhage, or stroke can be challenging. Furthermore, fever may also have beneficial effects, especially in cases involving infections. While therapeutic hypothermia has shown beneficial effects in animal models, its use is still debated in clinical practice. This paper aims to describe the physiology and pathophysiology of changes in brain temperature after brain injury and to study the effects of controlling brain temperature after such injury.

[Experts' recommendations for stroke management in intensive care: intracranial hypertension]

This article aims to describe the arguments underlying the experts' recommendations for management of stroke patients in the intensive unit, focusing on intracranial hypertension. This article describes the pathophysiology, diagnostic methods and therapeutic options for intracranial hypertension after stroke, including medical and surgical management.

Oxygen blood transport during experimental sepsis: effect of hypothermia*

OBJECTIVES

The aim of this study was to highlight the link between induced hypothermia and increased survival duration as observed in the septic model developed by the laboratory. To reach this objective, survival duration and blood oxygen transport capacity were measured at two temperatures-38 °C (induced normothermia) and 34 °C (induced hypothermia)-in septic rats.

DESIGN

A prospective, randomized, experimental animal study.

SETTING

University laboratory.

SUBJECTS

Forty-four male Sprague-Dawley rats (median weight, 232 g; range, 200-303 g).

INTERVENTIONS

After anesthesia and obtention of the temperature goal, sepsis was induced by cecal ligation and perforation.

MEASUREMENTS AND MAIN RESULTS

Sepsis induction led to death 5 hrs 11 mins ± 0 hr 36 mins after cecal ligation and perforation at 38 °C. At this temperature, significant changes in blood oxygen transport capacity were observed in septic rats; Hill number decreased from 2.36 ± 0.10 (baseline group) to 1.99 ± 0.17 (septic group) (p = .008) and oxygen-hemoglobin affinity decreased and P50 increased from 41.40 ± 2.4 Torr (baseline group) to 51.17 ± 14.07 Torr (septic group). Furthermore, in normothermia, a significant increase of creatinine and albumin plasmatic concentrations was observed 4 hrs after sepsis induction. Survival duration was significantly higher in induced hypothermia (7 hrs 22 mins ± 0 hr 12 mins at 34 °C) compared with induced normothermia. At 34 °C, no significant change in blood oxygen transport capacity was observed. In the same way, exposure to 34 °C induced no change in measured plasmatic parameters except an increase in albumin concentration in septic rats compared with the baseline group.

CONCLUSIONS

Sepsis led to a decrease of both oxygen hemoglobin cooperativity and affinity at 38 °C. By contrast, no change in these parameters was observed when sepsis was induced during hypothermia. Taken together, these results could be interpreted in normothermia septic rats as an adaptive mechanism that could enhance the release of oxygen at the tissue level. Hypothermia by slowing down sepsis evolution could increase survival duration.

[Therapeutic hypothermia]

The benefit of therapeutic hypothermia after severe head injury is highly controversial. However, hypothermia is still used and studied in this context for multiple reasons. Efficacy of hypothermia is demonstrated after cerebral ischemia in numerous animal studies and after cardiac arrest in human studies. Hyperthermia is a major independent factor of outcome after cerebral ischemic or traumatic brain injury. Moreover, ICP is related to core temperature, and hypothermia may be used to decrease intracranial hypertension. However, many questions are still unresolved and can explain discrepancies between clinical studies: direct measurement of cerebral temperature, relationship between ICP, temperature and PaCO(2), level and duration of hypothermia and precise methods for cooling and particularly for rewarming.