Rapid and selective cerebral hypothermia achieved using a cooling helmet

The Effect of Hypothermia and Hyperthermia on Acute Brain Injury

The brain is extraordinarily susceptible to changes in temperature. Hyperthermia has been shown to exacerbate the biochemical cascade of secondary brain injury. Inversely, hypothermia limits the damaging effects of secondary brain injury. There has been a great deal of investigation regarding the detrimental effects of hyperthermia and the neuroprotection of hypothermia in animal studies. Within the last decade, clinical trials have begun to establish how the brain reacts to both temperature extremes. In the future, studies of hypothermia will continue in the quest of the optimal timing and degree of hypothermia. Hyperthermia will be examined in depth for its detrimental effects on an injured brain. Interventions for the prevention and treatment of hyperthermia will be explored. Nurses will implement cooling strategies to induce hypothermia, applying interventions to prevent complications, and they will also diagnose hyperthermia, deciding when and if to intervene pharmacologically and therapeutically. These advanced nursing actions will be guided by knowledge and understanding of available evidence. This article presents the pathophysiology of secondary brain injury and how it is affected by both hypothermia and hyperthermia. A review of the research leading up to clinical trials is explored, as well as a discussion of the future of temperature modulation for the brain injury patient. This information will help healthcare providers understand the effect that both hypothermia and hyperthermia have on the acutely injured brain.

The role of hypothermia in neurosurgical patients

PURPOSE OF REVIEW

Interest in the therapeutic use of mild hypothermia was rekindled in the 1980s by the publication of promising animal studies. The results of several large clinical trials have become known in the last few years. This paper examines the recent evidence supporting the use of intraoperative hypothermia for neurosurgical patients.

RECENT FINDINGS

This article will cover advances made in three key areas: evidence for a clinical benefit from intraoperative hypothermia, advances in cerebral temperature monitoring, and new techniques for cooling the brain.

SUMMARY

There is currently insufficient evidence to support the use of mild intraoperative hypothermia for protection against focal cerebral ischaemia. Future investigations should focus on specific patient subgroups, and make use of recent advances in selective brain hypothermia and intracranial temperature monitoring.

Innovations in the management of cerebral injury

During the past decade, brain tissue oxygen monitoring has been studied predominantly in Europe. Cerebral oxygenation monitoring was implemented in many intensive care units and correlations of intracranial pressure, cerebral perfusion pressure, end-tidal carbon dioxide monitoring, fever and partial pressure of brain tissue oxygenation (Pbto2) have been described (Crit Care Nurse. 2003;23[4, pt 1]:17-27). The monitoring of brain tissue oxygen is now being done and researched in the United States. This article will discuss the history of treatment of traumatic brain injury and how treatment interventions are changing with the latest technological advances in monitoring of cerebral oxygen levels and suggested interventions and factors that affect brain tissue oxygenation. It is clear that by understanding the causes of hypoxia and ischemia--along with the interventions to treat them--the critical care team will be better able to prevent low oxygen states in the brain and optimize treatment, thus improving patient outcome.

[Therapeutic hypothermia after cardiac arrest]

The use of therapeutic hypothermia following different hypoxic-ischaemic insults has played an important role in various concepts of non-specific protection of cells for a long time. Although the use of deep therapeutic hypothermia after cardiac arrest in the last century did not lead to an improved outcome, recent data have demonstrated very positive effects of mild therapeutic hypothermia. The data from the European multicenter trial as well as those from Australia have clearly demonstrated a decrease in mortality and a better neurological outcome for patients being cooled to 32-34 degrees C for 12 or 24 h. In 2003, this led to the implementation of mild therapeutic hypothermia (32-34 degrees C) into the International Liaison Committee on Resuscitation (ILCOR) recommendations and guidelines for the treatment of unconscious patients after prehospital cardiac arrest. This article gives an overview on existing concepts and future perspectives of therapeutic mild hypothermia.

Locally induced hypothermia for treatment of acute ischaemic stroke: a physical feasibility study

During the treatment of stroke by local intra-arterial thrombolysis (LIT) it is frequently possible to pass the blood clot with a micro-catheter, allowing perfusion of brain tissue distally to the occlusion. This possibility allows for new early treatments of ischaemic brain tissue, even before the blood clot has been removed. One potential new approach to preserve brain tissue at risk may be locally induced endovascular hypothermia. Physical parameters such as the required micro-catheter input pressure, output velocity and flow rates, and a heat exchange model, applicable in the case of a micro-catheter placed within a guiding catheter, are presented. Also, a simple cerebral temperature model is derived that models the temperature response of the brain to the perfusion with coolant fluids. Based on this model, an expression has been derived for the time needed to reach a certain cerebral target temperature. Experimental in vitro measurements are presented that confirm the usability of standard commercially available micro-catheters to induce local hypothermia of the brain. If applied in vivo, the model predicts a local cooling rate of ischaemic brain tissue of 300 g of approximately 1 degrees C in 1 min, which is up to a factor 30-times faster than the time-consuming systemic hypothermia via the skin. Systemic body temperature is only minimally affected by application of local hypothermia, thus avoiding many limitations and complications known in systemic hypothermia.

A new method for inducing hypothermia during cardiac arrest

OBJECTIVE

It has been shown that hypothermia induced after successful resuscitation of comatose survivors of ventricular fibrillation cardiac arrest improves survival and neurologic function. Recent studies also suggest that earlier induction of hypothermia may yield even more improvement. We sought to determine if a new pump system, in addition to vigorous external chest compression, could rapidly induce hypothermia during cardiopulmonary resuscitation in a porcine model of cardiac arrest.

METHODS

Nine pigs (25-37 kg) were instrumented with micromanometers and thermocouple probes. Two 8-Fr catheters were placed into the femoral veins. Cardiac arrest was induced with 60-Hz current. After 5 mins of no support, chest compression was performed by a circumferential pneumatic bladder (vest-cardiopulmonary resuscitation). Blood was withdrawn from one catheter by a pump system that maximized flow by servo-control of inlet pressure, was cooled, and was returned through the other catheter. Four dogs were instrumented similarly, and cooling was performed during normal circulation.

RESULTS

In the pigs, baseline temperatures were (mean +/- SEM) 37 +/- 1 degree C. With blood cooling in the external chiller to 10 degrees C, cerebral and right atrial temperatures were reduced by 0.49 +/- 0.09 and 0.67 +/- 0.21 degrees C/min, respectively, for 10 mins. With blood cooling in the external chiller to 4 degrees C, cerebral and right atrial temperatures were reduced by 0.61 +/- 0.18 and 1.56 +/- 0.33 degrees C/min, respectively. Cerebral cooling lagged behind right atrial cooling. There was a strong correlation between coronary perfusion pressure (aortic to right atrial mean decompression-phase pressure) and cerebral cooling rate (r = .79; p < .022). Rates of cooling during normal circulation in dogs were similar.

CONCLUSIONS

Rapid induction of mild hypothermia is feasible with a system that uses venous access, standard access techniques, and external chest compression. Induction of mild hypothermia during cardiac arrest in the field appears feasible and may allow the benefit of very early induction of hypothermia to be determined in patients.