Abstract 64: Therapeutic Hypothermia Does Not Affect Tissue Oxygenation, Metabolism or Microvascular Reactivity in Peripheral Muscle
Introduction: Therapeutic hypothermia (TH) is thought to benefit patients by down-regulating the metabolism of tissue. Dynamic Near-infrared Spectroscopy (NIRS) non-invasively measures changes in tissue hemoglobin oxygen saturation. We sought to determine the effects of TH on NIRS variables, hypothesizing that post-cardiac arrest patients undergoing TH would have higher muscle tissue oxygenation (mtO2) but lower muscle tissue oxygen metabolism (mtOM) and microvascular reactivity (mtMR) compared to post-TH period.
Methods: This prospective, observational study included a convenience sample of 28 patients hospitalized in the ICU of a university hospital and treated with TH between 10/09 and 05/10. Thenar tissue oxygen saturations were measured using a tissue spectrometer. A vaso-occlusive test was performed by rapid inflation of pneumatic cuff for 3 minutes within the first 24 hours of post-arrest care and following re-warming with calculation of occlusion and reperfusion slopes (%/minute) for mtOM and mtMR, respectively. For our primary outcome, we used Mann-Whitney U test to compare differences in NIRS variables between groups (TH, post-TH).
Results: TH resulted in a lower core temperature 33.3 (32.7 to 34.3) compared to post-TH core temperature 36.2 (35.1 to 37.1); p<0.001. Skin temperature, heart rate, systolic blood pressure and pulse oximetry were mathematically similar between the TH and post-TH period. TH did not globally affect NIRS variables (Fig 1). Active use of vasopresors resulted in higher baseline mtO2 ((85 (77 to 88) versus 78 (70 to 83); p=0.01) but did not result in higher systolic blood pressure (p=0.3), mtOM (p=0.9) or mtMR (p=0.8).
Conclusions: Muscle tissue oxygenation, oxygen consumption and microvascular reactivity were unaltered by therapeutic hypothermia in post-cardiac arrest patients. However, muscle tissue oxygenation is elevated by the use of vasopressors in the early post-arrest period independent of macrohemodynamics.
- © 2010 by American Heart Association, Inc.