The effect of venous blood stream cooling on survival of bacterially infected rabbits

Mild induced hypothermia and coagulation and platelet function in patients with septic shock: Secondary outcome of a randomized trial

Coagulation abnormalities and microthrombi contribute to septic shock, but the impact of body temperature regulation on coagulation in patients with sepsis is unknown. We tested the hypothesis that mild induced hypothermia reduces coagulation and platelet aggregation in patients with septic shock. Secondary analysis of randomized controlled trial. Adult patients with septic shock who required mechanical ventilation from eight intensive care units in Denmark were randomly assigned to mild induced hypothermia for 24 h or routine thermal management. Viscoelastography and platelet aggregation were assessed at trial inclusion, after 12 h of thermal management, and 24 h after inclusion. A total of 326 patients were randomized to mild induced hypothermia (n = 163) or routine thermal management (n = 163). Mild induced hypothermia slightly prolonged activated partial thromboplastin time and thrombus initiation time (R time 8.0 min [interquartile range, IQR 6.6-11.1] vs. 7.2 min [IQR 5.8-9.2]; p = .004) and marginally inhibited thrombus propagation (angle 68° [IQR 59-73] vs. 71° [IQR 63-75]; p = .014). The effect was also present after 24 h. Clot strength remained unaffected (MA 71 mm [IQR 66-76] with mild induced hypothermia vs. 72 mm (65-77) with routine thermal management, p = .9). The proportion of patients with hyperfibrinolysis was not affected (0.7% vs. 3.3%; p = .19), but the proportion of patients with no fibrinolysis was high in the mild hypothermia group (8.8% vs. 40.4%; p < .001). The mild induced hypothermia group had lower platelet aggregation: ASPI 85U (IQR 50-113) versus 109U (IQR 74-148, p < .001), ADP 61U (IQR 40-83) versus 79 U (IQR 54-101, p < .001), TRAP 108 (IQR 83-154) versus 119 (IQR 94-146, p = .042) and COL 50U (IQR 34-66) versus 67U (IQR 46-92, p < .001). In patients with septic shock, mild induced hypothermia slightly impaired clot initiation, but did not change clot strength. Platelet aggregation was slightly impaired. The effect of mild induced hypothermia on viscoelastography and platelet aggregation was however not in a range that would have clinical implications. We did observe a substantial reduction in fibrinolysis.

Induced hypothermia in patients with septic shock and respiratory failure (CASS): a randomised, controlled, open-label trial

BACKGROUND

Animal models of serious infection suggest that 24 h of induced hypothermia improves circulatory and respiratory function and reduces mortality. We tested the hypothesis that a reduction of core temperature to 32-34°C attenuates organ dysfunction and reduces mortality in ventilator-dependent patients with septic shock.

METHODS

In this randomised, controlled, open-label trial, we recruited patients from ten intensive care units (ICUs) in three countries in Europe and North America. Inclusion criteria for patients with severe sepsis or septic shock were a mean arterial pressure of less than 70 mm Hg, mechanical ventilation in an ICU, age at least 50 years, predicted length of stay in the ICU at least 24 h, and recruitment into the study within 6 h of fulfilling inclusion criteria. Exclusion criteria were uncontrolled bleeding, clinically important bleeding disorder, recent open surgery, pregnancy or breastfeeding, or involuntary psychiatric admission. We randomly allocated patients 1:1 (with variable block sizes ranging from four to eight; stratified by predictors of mortality, age, Acute Physiology and Chronic Health Evaluation II score, and study site) to routine thermal management or 24 h of induced hypothermia (target 32-34°C) followed by 48 h of normothermia (36-38°C). The primary endpoint was 30 day all-cause mortality in the modified intention-to-treat population (all randomly allocated patients except those for whom consent was withdrawn or who were discovered to meet an exclusion criterion after randomisation but before receiving the trial intervention). Patients and health-care professionals giving the intervention were not masked to treatment allocation, but assessors of the primary outcome were. This trial is registered with ClinicalTrials.gov, number NCT01455116.

FINDINGS

Between Nov 1, 2011, and Nov 4, 2016, we screened 5695 patients. After recruitment of 436 of the planned 560 participants, the trial was terminated for futility (220 [50%] randomly allocated to hypothermia and 216 [50%] to routine thermal management). In the hypothermia group, 96 (44·2%) of 217 died within 30 days versus 77 (35·8%) of 215 in the routine thermal management group (difference 8·4% [95% CI -0·8 to 17·6]; relative risk 1·2 [1·0-1·6]; p=0·07]).

INTERPRETATION

Among patients with septic shock and ventilator-dependent respiratory failure, induced hypothermia does not reduce mortality. Induced hypothermia should not be used in patients with septic shock.

FUNDING

Trygfonden, Lundbeckfonden, and the Danish National Research Foundation.

Role of fever in disease

Infection, trauma, and injury result in a stereotypical response that includes loss of food appetite, increased sleepiness, muscle aches, and fever. For thousands of years fever was considered a protective response, and fevers were induced by physicians to combat certain infections. But with the advent of antipyretic drugs, physicians started to reduce fevers, and fever therapy was virtually abandoned. As a result of (1) studies on the evolution of fever, (2) further understanding of just how tightly the process of fever is regulated, and (3) detailed studies on how fever affects host morbidity and mortality, the view of fever as a host defense response has reemerged. However, data indicate that not all fevers are protective and that high fevers are maladaptive. These issues are discussed in the context of the evolution of host defense responses versus modern medical technology. In short, we speculate that patients who would not have survived severe sepsis in the past are now being kept alive and that the occasionally high fevers seen in these patients may be maladaptive.

The adaptive value of fever

There is overwhelming evidence in favor of fever being an adaptive host response to infection that has persisted throughout the animal kingdom for hundreds of millions of years. As such, it is probable that the use of antipyretic/anti-inflammatory/analgesic drugs, when they lead to suppression of fever, results in increased morbidity and mortality during most infections; this morbidity and mortality may not be apparent to most health care workers because fever is only one of dozens of host defense responses. Furthermore, most infections are not life-threatening and subtle changes in morbidity are not easily detected.