Authors: Larson AC, Jamrogowicz JL, Kulikowicz E, Wang B, Yang ZJ, Shaffner DH, Koehler RC, Lee JK.
After hypoxic brain injury, maintaining blood pressure within the limits of cerebral blood flow autoregulation is critical to preventing secondary braininjury. Little is known about the effects of prolonged hypothermia or rewarming on autoregulation after cardiac arrest. We hypothesized that rewarming would shift the lower limit of autoregulation (LLA), that this shift would be detected by indices derived from near-infrared spectroscopy (NIRS), and that rewarming would impair autoregulation during hypertension. Anesthetized neonatal swine underwent sham surgery or hypoxic-asphyxic cardiac arrest followed by 2h of normothermia and 20h of hypothermia with or without rewarming. Piglets were further divided into cohorts for cortical laser-Doppler flow measurements during induced hypotension or hypertension. We also tested whether indices derived from NIRS could identify the laser-Doppler flow-derived LLA. The LLA did not differ significantly among groups with sham surgery and hypothermia (29±8 mmHg), sham surgery and rewarming (34±7 mmHg), arrest and hypothermia (29±10 mmHg), and arrest and rewarming (38±11 mmHg). The LLA was not affected by arrest (P=0.60), temperature (P=0.08), or interaction between arrest and temperature (P=0.73). The NIRS-derived indices accurately detected the LLA, with the area under the receiver-operator characteristic curves of 0.81-0.96 among groups. In groups subjected to arrest and hypothermia with or without rewarming, the slope of laser-Doppler flow relative to cerebral perfusion pressure during hypertension was not significantly different from zero (P>0.10). In conclusion, rewarming did not shift the LLA during hypotension or affect autoregulation during hypertension after asphyxic cardiac arrest. The NIRS-derived autoregulation indices accurately identified the LLA.
Full text and source: Journal of Applied Physiology
J Appl Physiol. 2013 Sep 5.