Assessment of acid-base disturbances in hypothermia and their physiologic consequences

Impact of rewarming rate on the mortality of patients with accidental hypothermia: analysis of data from the J-Point registry

BACKGROUND

Accidental hypothermia (AH) is defined as an involuntary decrease in core body temperature to < 35 °C. The management of AH has been progressing over the last few decades, and numerous techniques for rewarming have been validated. However, little is known about the association between rewarming rate (RR) and mortality in patients with AH.

METHOD

This was a multicentre chart review study of patients with AH visiting the emergency department of 12 institutions in Japan from April 2011 to March 2016 (Japanese accidental hypothermia network registry, J-Point registry). We retrospectively registered patients using the International Classification of Diseases, Tenth Revision code T68: 'hypothermia'. We excluded patients whose body temperatures were unknown or ≥ 35 °C, who could not be rewarmed, whose rewarmed temperature or rewarming time was unknown, those aged < 18 years, or who or whose family members had refused to join the registry. RR was calculated based on the body temperature on arrival at the hospital, time of arrival at the hospital, the documented temperature during rewarming, and time of the temperature documentation. RR was classified into the following five groups: ≥2.0 °C/h, 1.5-< 2.0 °C/h, 1.0-< 1.5 °C/h, 0.5-< 1.0 °C/h, and < 0.5 °C/h. The primary outcome of this study was in-hospital mortality. The association between RR and in-hospital mortality was evaluated using multivariate logistic regression analysis.

RESULT

During the study, 572 patients were registered in the J-Point registry, and 481 patients were included in the analysis. The median body temperature on arrival to the hospital was 30.7 °C (interquartile range [IQR], 28.2 °C-32.4 °C), and the median RR was 0.85 °C/h (IQR, 0.53 °C/h-1.31 °C/h). The in-hospital mortality rates were 19.3% (11/57), 11.1% (4/36), 14.4% (15/104), 20.1% (35/175), and 34.9% (38/109) in the ≥2.0 °C/h, 1.5-< 2.0 °C/h, 1.0-< 1.5 °C/h, 0.5-< 1.0 °C/h, and < 0.5 °C/h groups, respectively. Multivariate regression analysis revealed that in-hospital mortality rate increased with each 0.5 °C/h decrease in RR (adjusted odds ratio, 1.49; 95% confidence interval, 1.15-1.94; P_trend < 0.01).

CONCLUSION

This study showed that slower RR is independently associated with in-hospital mortality.

Accidental hypothermia

Accidental hypothermia causes profound changes to the body's physiology. After an initial burst of agitation (e.g., 36-37°C), vital functions will slow down with further cooling, until they vanish (e.g. <20-25°C). Thus, a deeply hypothermic person may appear dead, but may still be able to be resuscitated if treated correctly. The hospital use of minimally invasive rewarming for nonarrested, otherwise healthy patients with primary hypothermia and stable vital signs has the potential to substantially decrease morbidity and mortality for these patients. Extracorporeal life support (ECLS) has revolutionized the management of hypothermic cardiac arrest, with survival rates approaching 100%. Hypothermic patients with risk factors for imminent cardiac arrest (i.e., temperature <28°C, ventricular arrhythmia, systolic blood pressure <90 mmHg), and those who have already arrested, should be transferred directly to an ECLS center. Cardiac arrest patients should receive continuous cardiopulmonary resuscitation (CPR) during transfer. If prolonged transport is required or terrain is difficult, mechanic CPR can be helpful. Intermittent CPR may be appropriate in hypothermic arrest when continuous CPR is impossible. Modern postresuscitation care should be implemented following hypothermic arrest. Structured protocols should be in place to optimize prehospital triage, transport, and treatment as well as in-hospital management, including detailed criteria and protocols for the use of ECLS and postresuscitation care.

Accidental hypothermia-an update : The content of this review is endorsed by the International Commission for Mountain Emergency Medicine (ICAR MEDCOM)

BACKGROUND

This paper provides an up-to-date review of the management and outcome of accidental hypothermia patients with and without cardiac arrest.

METHODS

The authors reviewed the relevant literature in their specialist field. Summaries were merged, discussed and approved to produce this narrative review.

RESULTS

The hospital use of minimally-invasive rewarming for non-arrested, otherwise healthy, patients with primary hypothermia and stable vital signs has the potential to substantially decrease morbidity and mortality for these patients. Extracorporeal life support (ECLS) has revolutionised the management of hypothermic cardiac arrest, with survival rates approaching 100 % in some cases. Hypothermic patients with risk factors for imminent cardiac arrest (temperature <28 °C, ventricular arrhythmia, systolic blood pressure <90 mmHg), and those who have already arrested, should be transferred directly to an ECLS-centre. Cardiac arrest patients should receive continuous cardiopulmonary resuscitation (CPR) during transfer. If prolonged transport is required or terrain is difficult, mechanical CPR can be helpful. Delayed or intermittent CPR may be appropriate in hypothermic arrest when continuous CPR is impossible. Modern post-resuscitation care should be implemented following hypothermic arrest. Structured protocols should be in place to optimise pre-hospital triage, transport and treatment as well as in-hospital management, including detailed criteria and protocols for the use of ECLS and post-resuscitation care.

CONCLUSIONS

Based on new evidence, additional clinical experience and clearer management guidelines and documentation, the treatment of accidental hypothermia has been refined. ECLS has substantially improved survival and is the treatment of choice in the patient with unstable circulation or cardiac arrest.

Accidental hypothermia

Accidental hypothermia has produced many cases of intact survival even after prolonged cardiac arrest, but it is also often fatal. In recent years, alterations in resuscitation care that sometimes confused or discouraged resuscitation teams have largely been supplanted by an emphasis on safe, rapid, effective rewarming. Rewarming decisions and even the simple recognition of hypothermia remain challenging. This review seeks to update and demystify some of these challenges.

[Physiologic effects of hypothermia]

Therapeutic use of hypothermia has come to the frontline in the past decade again in the prevention and in mitigation of neurologic impairment. The application of hypothermia is considered as a successful therapeutic measure not just in neuro- or cardiac surgery, but also in states causing brain injury or damage. According to our present knowledge this is the only proven therapeutic tool, which improves the neurologic outcome after cardiac arrest, decreasing the oxygen demand of the brain. Besides influencing the nervous system, hypothermia influences the function of the whole organ system. Beside its beneficial effects, it has many side-effects, which may be harmful to the patient. Before using it for a therapeutic purpose, it is very important to be familiar with the physiology and complications of hypothermia, to know, how to prevent and treat its side-effects. The purpose of this article is to summarize the physiologic and pathophysiologic effects of hypothermia.

National Athletic Trainers' Association position statement: environmental cold injuries

OBJECTIVE

To present recommendations for the prevention, recognition, and treatment of environmental cold injuries.

BACKGROUND

Individuals engaged in sport-related or work-related physical activity in cold, wet, or windy conditions are at risk for environmental cold injuries. An understanding of the physiology and pathophysiology, risk management, recognition, and immediate care of environmental cold injuries is an essential skill for certified athletic trainers and other health care providers working with individuals at risk.

RECOMMENDATIONS

These recommendations are intended to provide certified athletic trainers and others participating in athletic health care with the specific knowledge and problem-solving skills needed to address environmental cold injuries. Each recommendation has been graded (A, B, or C) according to the Strength of Recommendation Taxonomy criterion scale.

Kardiopulmonale Reanimation nach Heroinintoxikation und Hypothermie

We present the case of a 21-year-old female drug addict with severe accidental hypothermia (core body temperature 27.5 degrees C) and cardiorespiratory arrest. After successful cardiopulmonary resuscitation the patient was actively internally rewarmed without the use of extracorporal circulation. Although at the first clinical presentation the patient appeared to be dead, an excellent neurological outcome was achieved. This case report reviews the epidemiology, pathophysiology, prognostic markers and the therapeutic approaches of severe hypothermia.

Metabolic depression in hibernation and major depression: an explanatory theory and an animal model of depression

Metabolic depression, an adaptive biological process for energy preservation, is responsible for torpor, hibernation and estivation. We propose that a form of metabolic depression, and not mitochondrial dysfunction, is the process underlying the observed hypometabolism, state-dependent neurobiological changes and vegetative symptoms of major depression in humans. The process of metabolic depression is reactivated via differential gene expression in response to perceived adverse stimuli in predisposed persons. Behavior inhibition by temperament, anxiety disorders, genetic vulnerabilities, and early traumatic experiences predispose persons to depression. The proposed theory is supported by similarities in the presentation and neurobiology of hibernation in bears and major depression and explains the yet unexplained neurobiological changes of depression. Although, gene expression is suppressed in other hibernators by deep hypothermia, bears were chosen because they hibernate with mild hypothermia. Pre-hibernation in bears and major depression with atypical features are both characterized by fat storage through overeating, oversleeping, and decreased mobility. Hibernation in bears and major depression with melancholic features are characterized by withdrawal from the environment, lack of energy, loss of weight from not eating and burning stored fat, changes in sleep pattern, and the following similar neurobiological findings: reversible subclinical hypothyroidism; increased concentration of serum cortisol; acute phase protein response; low respiratory quotient; oxidative stress response; decreased neurotransmitter levels; and changes in cyclic-adenosine monophosphate-binding activity. Signaling systems associated with protein phosphorylation, transcription factors, and gene expression are responsible for the metabolic depression process during pre-hibernation and hibernation. Antidepressants and mood stabilizers interfere with the hibernation process and produce their therapeutic effects by normalizing the fluctuation of activities in the different signaling systems, which are down-regulated during hibernation and depression and up-regulated during exodus from hibernation and the hypomanic or manic phase of mood disorders. The ways individuals cognitively perceive, understand, communicate, and react to the vegetative symptoms of depression, from downregulation in energy production, and in the absence of known medical causes, produce the other characteristics of depression including guilt, helplessness, hopelessness, suicidal phenomena, agitation, panic attacks, psychotic symptoms, and sudden switch to hypomanic or manic episodes. The presence of one or more of these characteristics depends on the person's neuropsychological function, its social status between the others, and the other's response to the person. Neurobiological changes associated with metabolic depression during entrance, maintenance, and exodus from hibernation in bears is suggested as a natural animal model of human depression and mood disorders.

Hypothermia during reperfusion after asphyxial cardiac arrest improves functional recovery and selectively alters stress-induced protein expression

This study examined whether prolonged hypothermia induced 1 hour after resuscitation from asphyxial cardiac arrest would improve neurologic outcome and alter levels of stress-related proteins in rats. Rats were resuscitated from 8 minutes of asphyxia resulting in cardiac arrest. Brain temperature was regulated after resuscitation in three groups: normothermia (36.8 degrees C x 24 hours), immediate hypothermia (33 degrees C x 24 hours, beginning immediately after resuscitation), and delayed hypothermia (33 degrees C x 24 hours, beginning 60 minutes after resuscitation). Mortality and neurobehavioral deficits were improved in immediate and delayed hypothermia rats relative to normothermia rats. Furthermore, both immediate and delayed hypothermia improved neuronal survival in the CA1 region of the hippocampus assessed at 14 days. In normothermia rats, the 70-kDa heat shock protein (Hsp70) and 40-kDa heat shock protein (Hsp40) were increased within 12 hours after resuscitation in the hippocampus. Delayed hypothermia attenuated the increase in Hsp70 levels in the hippocampus but did not affect Hsp70 induction in the cerebellum. Hippocampal expression of Hsp40 was not affected by hypothermia. These data indicate that prolonged hypothermia during later reperfusion improves neurologic outcome after experimental global ischemia and is associated with selective changes in the pattern of stress-induced protein expression.

Accidental hypothermia

Individuals at extremes of age and those who have certain underlying medical conditions are at greatest risk for hypothermia. Hypothermia may occur during any season of the year and in any climate. Prompt recognition of hypothermia and early institution of the rewarming techniques are imperative for a successful outcome with minimal complications. Several rewarming techniques are available and the decision to use any of them depends on the degree of hypothermia, the condition of the patient, and the rewarming rate possible with the technique chosen.

Experience with prolonged induced hypothermia in severe head injury

BACKGROUND: Recent prospective controlled trials of induced moderate hypothermia (32-34 degrees C) for relatively short periods (24-48 h) in patients with severe head injury have suggested improvement in intracranial pressure control and outcome. It is possible that increased benefit might be achieved if hypothermia was maintained for more periods longer than 48 h, but there is little in the literature on the effects of prolonged moderate hypothermia in adults with severe head injury. We used moderate induced hypothermia (30-33 degrees C) in 43 patients with severe head injury for prolonged periods (mean 8 days, range 2-19 days). RESULTS: Although nosocomial pneumonia (defined in this study as both new chest radiograph changes and culture of a respiratory pathogen from tracheal aspirate) was quite common (45%), death from sepsis was rare (5%). Other findings included hypokalaemia on induction of hypothermia and a decreasing total white cell and platelet count over 10 days. There were no major cardiac arrhythmias. There was a satisfactory neurological outcome in 20 out of 43 patients (47%). CONCLUSION: Moderate hypothermia may be induced for more prolonged periods, and is a relatively safe and feasible therapeutic option in the treatment of selected patients with severe traumatic brain injury. Thus, further prospective controlled trials using induced hypothermia for longer periods than 48 h are warranted.

Prolonged resuscitation in acute deep hypothermia

A case report is described with successful outcome of prolonged cardiopulmonary resuscitation in a 30-year-old man suffering from acute deep hypothermia. His lowest temperature recorded was 23 degrees C. Continuous external cardiac massage was required for a total of 4.5 h whilst rewarming was instituted. The patient eventually left hospital with no permanent sequelae. A review of hypothermia follows, emphasising some important management principals and pitfalls.

Bretylium tosylate and electrically induced cardiac arrhythmias during hypothermia in dogs

The effect of bretylium tosylate on plasma catecholamines and on electrically induced arrhythmias was evaluated in anesthetized hypothermic dogs. Bretylium at a dose of 7.5 mg/kg was administered prior to cooling from 37 degrees C to 27 degrees C. During cooling, the ventricular arrhythmia threshold (VAT) in control animals decreased from 10.1 +/- 1.9 to 4.4 +/- 1.3 impulses, while the VAT in bretylium-treated animals increased from 9.8 +/- 2.9 to 23.2 +/- 2.7 impulses. Catecholamine levels increased during cooling in all animals. In control animals, the epinephrine/norepinephrine ratio was unchanged, but in animals treated with bretylium tosylate, the ratio increased more than 10-fold (from 0.48 +/- 0.1 to 5.49 +/- 0.32 at 29.9 degrees C). The demonstrated increase in catecholamine levels during hypothermia suggests that the protection offered by bretylium tosylate against cardiac arrhythmias is not explained by modification of catecholamine levels, and is more likely due to an alteration of the electrophysiologic properties of cardiac tissues.