Metabolic benefits of surface counter warming during therapeutic temperature modulation

Objective: To determine the impact of counter warming (CW) with an air circulating blanket on shivering and metabolic profile during therapeutic temperature modulation (TTM). Design: A prospective observational study. Setting: An 18-bed neurologic intensive care unit. Patients: Fifty mechanically ventilated patients with brain injury undergoing TTM with automated surface and intravascular devices. Interventions: Fifty indirect calorimetry (IDC) measurements with and without CW during TTM. Measurements and main results: IDC was continuously performed for 10-15 minutes at baseline with CW (phase I), off CW (phase II), and again after the return of CW (phase III). Shivering severity during each phase was scored on a scale of 0-3 using the Bedside Shivering Assessment Scale (BSAS). Resting energy expenditure (REE), oxygen consumption, and carbon dioxide production were determined by IDC; 56% were women, with mean age 61 ± 15 years. At the time of IDC, 72% of patients had signs of shivering (BSAS >0). All measures of basal metabolism increased after removal of the air warming blanket (from phases I and II); REE increased by 27% and oxygen consumption by 29% (both p < 0.002). A one-point increase in baseline BSAS was noted in 55% (n = 23/42) of patients from phase I to phase II. In a multivariate analysis, sedative use (p = 0.03), baseline moderate to severe shivering (p = 0.04), and lower serum magnesium levels (p = 0.01) were associated with greater increases in REE between phase I and phase II of CW. Phase III of CW was associated with a reversal in the increases in all metabolic variables. Conclusions: Surface CW provides beneficial control of shivering and improves the metabolic profile during TTM.