Hematorheology during deep hypothermia

Enhanced Blood Clotting After Rewarming From Experimental Hypothermia in an Intact Porcine Model

Introduction: Due to functional alterations of blood platelets and coagulation enzymes at low temperatures, excessive bleeding is a well-recognized complication in victims of accidental hypothermia and may present a great clinical challenge. Still, it remains largely unknown if hemostatic function normalizes upon rewarming. The aim of this study was to investigate effects of hypothermia and rewarming on blood coagulation in an intact porcine model. Methods: The animals were randomized to cooling and rewarming (n = 10), or to serve as normothermic, time-matched controls (n = 3). Animals in the hypothermic group were immersion cooled in ice water to 25°C, maintained at 25°C for 1 h, and rewarmed to 38°C (normal temperature in pigs) using warm water. Clotting time was assessed indirectly at different temperatures during cooling and rewarming using a whole blood coagulometer, which measures clotting time at 38°C. Results: Cooling to 25°C led to a significant increase in hemoglobin, hematocrit and red blood cell count, which persisted throughout rewarming. Cooling also caused a transiently decreased white blood cell count that returned to baseline levels upon rewarming. After rewarming from hypothermia, clotting time was significantly shortened compared to pre-hypothermic baseline values. In addition, platelet count was significantly increased. Discussion/Conclusion: We found that clotting time was significantly reduced after rewarming from hypothermia. This may indicate that rewarming from severe hypothermia induces a hypercoagulable state, in which thrombus formation is more likely to occur.

Severe Aortic Thrombosis and Profound Hypothermia: A Case Report

Background

Blood clot formation is a multifactorial process and has been related many times in intensive care units. Here is presented a multiple thrombosis formation in a rewarming patient.

Case description

A 68-year-old patient was admitted to our intensive care unit after lying on the floor for an unknown time. She presented a severe hypothermia at 26° and a severe cardiogenic shock. Because she was confused and was hypoxemic, she had been intubated at her admission. After intravascular warming, we could stop sedative medications. She presented a right hemiparesis and acute left leg ischemia. Computed tomography (CT) scan revealed a constituted left Sylvian stroke and a massive clot along the aorta. She required a surgical embolectomy and fasciotomy. She died after she presented a severe bowel ischemia on the third day after her admission.

Conclusion

Relevant hypothesis for blood clot formation in this patient may include prolonged lying position or blood temperature variation. Hypothermia and rewarming responsibilities may explain multiple thrombosis development.

How to cite this article

Schmitt J, Esnault P, Sartre M, Cungi PJ, Meaudre E. Severe Aortic Thrombosis and Profound Hypothermia: A Case Report. Indian J Crit Care Med 2021;25(5):588-589.

Selective hypothermia: an experimental study on traumatic brain injury in rats

OBJECTIVE: To evaluate the efficiency of selective hypothermia in the treatment of the traumatic brain injury in rats. METHOD: After the trauma produced for the model of cortical impact, a small craniectomy in the right frontoparietal region was carried through; after the procedure the animals had been divided in two groups of 15 each. Group A, without treatment with hypothermia (control group) and group B, treated with selective hypothermia for a period to 5 to 6 hours. After this time all the animals were sacrificed, their brains had been removed and histopathological analysis was carried through. RESULTS: Comparison between both groups was done using the counting of neurons injured for field. Counting in the control group n=15 had an average of 70.80 neurons injured for field against an average of 21.33 neurons injured for field in group B (submitted to the treatment with hypothermia), with n=15 also. The difference was statiscally significant. CONCLUSION: Based in the quantification of the neurons injured for field, the effectiveness of the treatment with selective hypothermia was demonstrated.

Phase II clinical trial of moderate hypothermia after severe traumatic brain injury in children

OBJECTIVE

To determine whether moderate hypothermia (HYPO) (32-33 degrees C) begun in the early period after severe traumatic brain injury (TBI) and maintained for 48 hours is safe compared with normothermia (NORM) (36.5-37.5 degrees C).

METHODS

After severe (Glasgow Coma Scale score < or =8) nonpenetrating TBI, 48 children less than 13 years of age admitted within 6 hours of injury were randomized after stratification by age to moderate HYPO (32-33 degrees C) treatment in conjunction with standardized head injury management versus NORM in a multicenter trial. An additional 27 patients were entered into a parallel single-institution trial of excluded patients because of late transfer or consent (delayed in transfer >6 h but within 24 h of admission), unknown time of injury (e.g., child abuse), and adolescence (e.g., aged 13-18 yr). Assessments of safety included mortality, infection, coagulopathy, arrhythmias, and hemorrhage as well as ability to maintain target temperature, mean intracranial pressure (ICP), and percent time of ICP less than 20 mm Hg during the cooling and subsequent rewarming phases. Additionally, assessments of neurocognitive outcomes were obtained at 3 and 6 months of follow-up.

RESULTS

Moderate HYPO after severe TBI in children was found to be safe relative to standard management and NORM in children of all ages and in children with delay of initiation of treatment up to 24 hours. Although there was decreased mortality in HYPO in both studies, there was an increased potential for arrhythmias with HYPO, although they were manageable with fluid administration or rewarming. Additionally, there was a reduction in mean ICP during the first 72 hours after injury in both studies, although rebound ICP elevations in HYPO compared with those in NORM were noted for up to 10 to 12 hours after rewarming. Although functional outcome at 3 or 6 months did not differ between treatment groups, functional outcome tended to improve from the 3- to 6-month cognitive assessment in HYPO compared with NORM, although the sample size was too small for any definitive conclusions.

CONCLUSION

HYPO is likely a safe therapeutic intervention for children after severe TBI up to 24 hours after injury. Further studies are necessary and warranted to determine its effect on functional outcome and intracranial hypertension.

Pancytopenia induced by hypothermia

Hypothermia has been demonstrated to induce pancytopenia in animals, but whether this association exists in humans is unknown. The authors report the case of an 8-year-old girl in whom hypothermia (temperature 33 degrees C-35 degrees C) is the cause of pancytopenia. The patient developed thermoregulatory dysfunction subsequent to surgical resection of a craniopharyngioma. Her recurrent cytopenias could not be explained by any etiology except chronic hypothermia. The pancytopenia improved upon rewarming the patient to a temperature of 36 degrees C. This association between hypothermia and pancytopenia has rarely been reported in humans and may be underdiagnosed especially in cases of transient or milder presentations. The authors recommend careful hematologic monitoring of patients with thermoregulatory dysfunction.

Therapeutic hypothermia in traumatology

Despite its proven clinical application for protection-preservation of the brain and heart during cardiac surgery, hypothermia research has fallen in and out of favor many times since its inception. Since the 1980s, there has been renewed research and clinical interest in therapeutic hypothermia for resuscitation of the brain after cardiac arrest or TBI and for preservation-resuscitation of extracerebral organs, particularly the abdominal viscera in low-flow states such as HS. Although some of the fears regarding the side effects of hypothermia are warranted, others are not. Without further laboratory and clinical studies, the significance of these effects cannot be determined and ways to overcome these problems cannot be developed. Currently, at the turn of the century, there are significant data demonstrating the benefit of mild-to-moderate hypothermia in animals and humans after cardiac arrest or TBI and in animals during and after HS. The clinical implications of uncontrolled versus controlled hypothermia in trauma patients and the best way to assure poikilothermia for cooling without shivering are still unclear. It is time to consider a prospective trial of therapeutic, controlled hypothermia for patients during traumatic HS and resuscitation. The authors believe that the new millennium will witness remarkable advantages of the use of controlled hypothermia in trauma. Starting in the prehospital phase, mild hypothermia will be induced in hypovolemic patients, which will not only decrease the immediate mortality rate but perhaps also will protect cells and reduce the likelihood of secondary inflammatory response syndrome, multiple organ failure, and late deaths. The most futuristic applications will be hypothermic strategies to achieve prolonged suspended animation for delayed resuscitation in traumatic exsanguination cardiac arrest.

Systemic hypothermia in treatment of severe brain injury: a review and update

Laboratory studies of moderate hypothermia (30-33 degrees C) after injury show diminished neuronal loss after ischemia, diminished excessive neurotransmitter release after ischemia, prevention of blood-brain barrier disruption after ischemia and brain injury, and behavioral improvement after brain injury. Clinical literature suggests that brief periods of moderate hypothermia (> or = 30 degrees C) in humans are not associated with cardiovascular, hematologic, metabolic, or neurological toxicity. Clinical studies were, therefore, organized to investigate the potential application of moderate systemic hypothermia in patients after severe brain injury. A study of 21 elective craniotomy patients and 11 patients with severe brain injury led to the conclusion that 32 to 33 degrees C was the lowest safe temperature in patients with severe brain injury. A randomized study of moderate hypothermia in 46 patients with Glasgow Coma Score (GCS) 4-7 gave an indication of improved neurologic outcome in the hypothermia group. A multicenter, randomized protocol to test the effect of moderate systemic hypothermia in patients with severe brain injury is in progress. Funded by the National Institutes of Health, The National Acute Brain Injury Study: Hypothermia tests the hypothesis that systemic hypothermia to 32-33 degrees C if rendered within 6 h of injury improves Glasgow Outcome Scores (GOS) at 6 months after injury in patients with severe brain injury (GCS 3-8).

Hypothermia in acute blunt head injury

Mild to moderate hypothermia has been employed since the 1940s in the treatment of acute blunt head trauma. The utility of hypothermia in ischemic injury has been confirmed, by both animal studies and clinical experience, in cardiovascular and neurological surgery. In blunt injury, though, only one prospective, randomized study has shown a statistically significant improvement in long term outcome. Clinical experience, animal data, proposed mechanisms, technical considerations, and potential risks are reviewed. Hypothermia remains controversial in the setting of blunt head injury but may prove to be a useful treatment modality.

A phase II study of moderate hypothermia in severe brain injury

Forty-six patients with severe nonpenetrating brain injury [Glasgow Coma Scale (GCS) 4-7] were randomized to standard management at 37 degrees C (n = 22) and to standard management with systemic hypothermia to 32 to 33 degrees C (n = 24). The two groups were balanced in terms of age (Wilcoxon's rank sum test, p > 0.95), randomizing GCS (chi-square test, p = 0.54), and primary diagnosis. Cooling was begun within 6 h of injury by use of cooling blankets. Metocurine and morphine were given hourly during induction and maintenance of hypothermia. Rewarming was at a rate of 1 degree C per 4 h beginning 48 h after intravascular temperature had reached 33 degrees C. Muscle relaxants and sedation were continued until core temperature reached 35 degrees C. There were no cardiac or coagulopathy-related complications. Seizure incidence was lower in the hypothermia group (Fisher's exact text, p = 0.019). Sepsis was seen more commonly in the hypothermia group, but difference was not statistically significant (chi-square test). Mean Glasgow Outcome Scale (GOS) score at 3 months after injury showed an absolute increase of 16% (i.e., 36.4-52.2%) in the number of patients in the Good Recovery/Moderate Disability (GR/MD) category as compared with Severe Disability/Vegetative/Dead (SD/V/D) (chi-square test, p > 0.287). Based on evidence of improved neurologic outcome with minimal toxicity, we believe that phase III testing of moderate systemic hypothermia in patients with severe head injury is warranted.

Recurrent hypothermia and thrombocytopenia after severe neonatal brain infection

Two children with multiple severe disabilities due to brain destruction by neonatal infection had recurrent hypothermia (less than 34 degrees C) with associated thrombocytopenia (less than 50,000), and clinical hemorrhage. They also had milder, less consistent erythroid and myeloid cell line abnormalities. The hypothermia was presumed to be due to hypothalamic dysfunction. Rewarming was always followed by correction of hematologic problems, but normal temperature was difficult to maintain. Recognition of this entity may improve long-term management of some severely disabled children.

Effects of circulatory arrest and rewarming on regional blood flow during surface-induced hypothermia

Regional blood flow and distribution of cardiac output (CO) were evaluated by the radioactive microsphere technique in rhesus monkeys during surface rewarming following the induction of deep hypothermia (20 degrees C.) under deep ether anesthesia. A comparison of animals subjected to 30 minutes of circulatory arrest and those not arrested revealed cerebral, coronary, and renal vascular resistance and flow patterns consistent with a hyperemic response to circulatory arrest at 20 degrees C. Throughout rewarming cerebral and coronary absolute flows tended to be at or above the flows noted at comparable cooling temperatures in a previous study. Renal flow fraction (% Qt) were well preserved during rewarming to 30 degrees C., but a decrease was observed thereafter. Carcass (muscle, skin, bone) %Qt was also reduced following rewarming, especially in arrested animals. CO appeared to be similar to those noted at comparable cooling temperatures until 30 degrees C. during rewarming; thereafter, CO did not fully recover to awake control levels. These data suggest that regional flow is redistributed from the carcass and renal circulations to cerebral and coronary circulations in response to hemodynamic alterations during surface rewarming. It was concluded that autoregulative responses to both circulatory arrest and hemodynamic factors are elicited during surface rewarming from deep hypothermia to 20 degrees C. with the method described.