What's new with fever control in the ICU

Hypothesis: Fever control, a niche for alpha-2 agonists in the setting of septic shock and severe acute respiratory distress syndrome?

During severe septic shock and/or severe acute respiratory distress syndrome (ARDS) patients present with a limited cardio-ventilatory reserve (low cardiac output and blood pressure, low mixed venous saturation, increased lactate, low PaO2/FiO2 ratio, etc.), especially when elderly patients or co-morbidities are considered. Rescue therapies (low dose steroids, adding vasopressin to noradrenaline, proning, almitrine, NO, extracorporeal membrane oxygenation, etc.) are complex. Fever, above 38.5-39.5°C, increases both the ventilatory (high respiratory drive: large tidal volume, high respiratory rate) and the metabolic (increased O2 consumption) demands, further limiting the cardio-ventilatory reserve. Some data (case reports, uncontrolled trial, small randomized prospective trials) suggest that control of elevated body temperature ("fever control") leading to normothermia (35.5-37°C) will lower both the ventilatory and metabolic demands: fever control should simplify critical care management when limited cardio-ventilatory reserve is at stake. Usually fever control is generated by a combination of general anesthesia ("analgo-sedation", light total intravenous anesthesia), antipyretics and cooling. However general anesthesia suppresses spontaneous ventilation, making the management more complex. At variance, alpha-2 agonists (clonidine, dexmedetomidine) administered immediately following tracheal intubation and controlled mandatory ventilation, with prior optimization of volemia and atrio-ventricular conduction, will reduce metabolic demand and facilitate normothermia. Furthermore, after a rigorous control of systemic acidosis, alpha-2 agonists will allow for accelerated emergence without delirium, early spontaneous ventilation, improved cardiac output and micro-circulation, lowered vasopressor requirements and inflammation. Rigorous prospective randomized trials are needed in subsets of patients with a high fever and spiraling toward refractory septic shock and/or presenting with severe ARDS.

Respective impact of lowering body temperature and heart rate on mortality in septic shock: mediation analysis of a randomized trial

PURPOSE

We previously showed that external cooling decreases day 14 mortality in febrile septic shock. Because cooling may participate in heart rate control, we studied the respective impact of heart rate and temperature lowering on mortality.

METHODS

Post hoc analysis of the Sepsiscool randomized controlled trial database (NCT00527007). Cooling was applied to maintain normothermia (36.5-37 °C) during 48 h. We assessed the time spent below different thresholds of temperature and heart rate on day 14 mortality. The best threshold was selected by AUC-ROC and tested as a potential mediator of mortality reduction. Mediation analysis was adjusted for severity and treatments influencing temperature and heart rate evolution. Sensitivity analysis was done using only patients with appropriate antimicrobial therapy.

RESULTS

A total of 197/200 patients with adequate heart rate and temperature monitoring were analyzed. The best threshold differentiating survivors and nonsurvivors was 38.4 °C for temperature and 95 b/min for heart rate. During the 48 h of intervention, cooling significantly increased the time spent with a temperature below 38.4 °C, p = 0.001, and with a heart rate below 95 b/min, p < 0.01. The longer was the time spent with a temperature below 38.4 °C, the lower was the mortality [adjOR 0.17 (0.06-0.49), p = 0.001]. The time spent with a heart rate below 95 b/min was similar in survivors and nonsurvivors [adjOR 0.68 (0.27-1.72), p = 0.42]. Mediation analysis showed that the time spent with a temperature below 38.4 °C was a significant mediator of mortality.

CONCLUSION

The time spent with a temperature below 38.4 °C was independently associated with patient's outcome and explained 73% of the effect of the randomization on the day 14 mortality. Heart rate lowering was not a mediator of mortality.