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.

Metabolic impact of shivering during therapeutic temperature modulation: the Bedside Shivering Assessment Scale.

BACKGROUND AND PURPOSE: Therapeutic temperature modulation is widely used in neurocritical care but commonly causes shivering, which can hamper the cooling process and result in increases in systemic metabolism. We sought to validate a grading scale to assist in the monitoring and control of shivering. METHODS: A simple 4-point Bedside Shivering Assessment Scale was validated against continuous assessments of resting energy expenditure, oxygen consumption, and carbon dioxide production as measured by indirect calorimetry. Therapeutic temperature modulation for fever control or the induction of hypothermia was achieved with the use of a surface or endovascular device. Expected energy expenditure was calculated using the Harris-Benedict equation. A hypermetabolic index was calculated from the ratio of resting of energy expenditure to energy expenditure. RESULTS: Fifty consecutive cerebrovascular patients underwent indirect calorimetry between January 2006 and June 2007. Fifty-six percent were women, and mean age 63+/-16 years. The majority underwent fever control (n=40 [80%]) with a surface cooling device (n=44 [87%]) and had signs of shivering (Bedside Shivering Assessment Scale >0, 64% [n=34 of 50]). Low serum magnesium was independently associated with the presence of shivering (Bedside Shivering Assessment Scale >0; OR, 6.8; 95% CI, 1.7 to 28.0; P=0.01). The Bedside Shivering Assessment Scale was independently associated with the hypermetabolic index (W=16.3, P<0.001), oxygen consumption (W=26.3, P<0.001), resting energy expenditure (W=27.2, P<0.001), and carbon dioxide production (W=18.2, P<0.001) with a high level of interobserver reliability (kappa(w)=0.84, 95% CI, 0.81 to 0.86). CONCLUSIONS: The Bedside Shivering Assessment Scale is a simple and reliable tool for evaluating the metabolic stress of shivering.