Sedation and Neuromuscular Blockade

Patients received propofol (initial dose 20 µg/kg/min) or intermittent lorazepam (initial dose 2 mg every 4 hours) for sedation during TH, titrated to keep the Sedation-Agitation Scale (SAS) at 1 or 2 [1]. Analgesia was provided by fentanyl infusion (initial dose of 25 µg per hour). During the active cooling phase, shivering was treated with intermittent intravenous doses of pancuronium or vecuronium (0.1 mg/kg) to provide neuromuscular blockade (NMB). Nurses administered additional sedation as needed to keep the post-NMB BIS value less than 50. This value was conservatively derived from data suggesting a BIS less than 60 during normothermic NMB reduces awareness, and that each degree Celsius drop in temperature reduces the BIS value by 1.1 [2-4]. Sedation was continued until temperature returned to 36.5º C, at which point the SAS target was adjusted to 3-4. During the rewarming and therapeutic normothermia periods, shivering was suppressed with focal counterwarming and treated with dexmedetomidine, meperidine, buspirone, and acetaminophen in various combinations. Bladder temperature, sedation level, sedative and NMB doses, and clinical shivering assessment (qualitative yes-no) were recorded hourly on a bedside flowsheet or in a computerized medical record (eCare Manager, VISICU, Baltimore MD).

Hypothermia Protocol

The first 13 subjects were cooled using ice-packs to the groin, neck, and axilla, and a rubber cooling mat (Blanketrol II, Cincinnati SubZero, Cincinnati OH). The next 84 patients were cooled with the Arctic Sun temperature management system (Medivance Corporation, Louisville, CO) targeted to a bladder temperature of 33°C. Cold intravenous fluids were administered to augment the cooling process in some cases. Our protocol evolved during this prospective series. After the first 32 patients, the period of active cooling was increased from 18 to 24 hours, and after 40 patients, the rewarming period was increased from 6 to 12 hours. Following rewarming to 36.5°C, the Arctic Sun was left in place to maintain normothermia and avoid fever until 72 hours after ROSC. Mean arterial blood pressure was maintained > 65 mmHg with vasopressors if necessary, and cefuroxime was administered to reduce early-onset pneumonia [5].

References

1. Riker RR, Picard JT, Fraser GL (1999) Prospective evaluation of the Sedation-Agitation Scale for adult critically ill patients. Crit Care Med 27:1325-9

2. Mathew JP, Weatherwax KJ, East CJ, White WD, Reves JG (2001) Bispectral analysis during cardiopulmonary bypass: the effect of hypothermia on the hypnotic state. Journal of Clinical Anaesthesia 13:301-5.

3. Ekman A, Lindholm ML, Lennmarken C et al. (2004) Reduction in the incidence of awareness using BIS monitoring. Acta Anaesthesiol Scand 48:20-26

4. Myles PS, Leslie K, McNeil J et al. (2004) Bispectral index monitoring to prevent awareness during anaesthesia: the B-Aware randomized controlled trial. Lancet 363:1757-63.

5. Sirvent JM, Torres A, El-Ebiary M, et al. (1997) Protective effect of intravenously administered cefuroxime against nosocomial pneumonia in patients with structural coma. Am J Respir Crit Care Med 155:1729-34.