Early postoperative changes in cerebral oxygen metabolism following neonatal cardiac surgery: effects of surgical duration

Abstract

Objective: The early postoperative period following neonatal cardiac surgery is a time of increased risk for brain injury, yet the mechanisms underlying this risk are unknown. To understand these risks more completely, we quantified changes in postoperative cerebral metabolic rate of oxygen (CMRO(2)), oxygen extraction fraction (OEF), and cerebral blood flow (CBF) compared with preoperative levels by using noninvasive optical modalities.

Methods: Diffuse optical spectroscopy and diffuse correlation spectroscopy were used concurrently to derive cerebral blood flow and oxygen utilization postoperatively for 12 hours. Relative changes in CMRO(2), OEF, and CBF were quantified with reference to preoperative data. A mixed-effect model was used to investigate the influence of total support time and deep hypothermic circulatory arrest duration on relative changes in CMRO(2), OEF, and CBF.

Results: Relative changes in CMRO(2), OEF, and CBF were assessed in 36 patients, 21 with single-ventricle defects and 15 with 2-ventricle defects. Among patients with single-ventricle lesions, deep hypothermic circulatory arrest duration did not affect relative changes in CMRO(2), CBF, or OEF (P > .05). Among 2-ventricle patients, total support time was not a significant predictor of relative changes in CMRO(2) or CBF (P > .05), although longer total support time was associated significantly with greater increases in relative change of postoperative OEF (P = .008).

Conclusions: Noninvasive diffuse optical techniques were used to quantify postoperative relative changes in CMRO(2), CBF, and OEF for the first time in this observational pilot study. Pilot data suggest that surgical duration does not account for observed variability in the relative change in CMRO(2), and that more comprehensive clinical studies using the new technology are feasible and warranted to elucidate these issues further.

FIGURE 1

Time profiles of the relative change from preoperative levels in each outcome variable—rCMRO₂ (A), rCBF (B), rOEF (C), and rCaO₂ (D)— after removal from CPB for all patients with single-ventricle lesions. The horizontal line indicates no change from preoperative levels. The x-axis (time) is standardized between patients by setting t = 0 as the time the patient was taken off CPB. rCMRO₂, Relative change in postoperative cerebral metabolic rate of oxygen; rCBF, relative change in postoperative cerebral blood flow; rOEF, relative change in postoperative oxygen extraction fraction; rCaO₂, relative change in postoperative arterial oxygen concentration; CPB, cardiopulmonary bypass.

FIGURE 2

Time profiles of the relative change from preoperative levels in each outcome variable—rCMRIO₂ (A), rCBF (B), rOEF (C), and rCaO₂ (D)— after removal from CPB for all patients with 2-ventricle lesions. The horizontal line indicates no change from preoperative levels. The x-axis (time) is standardized between patients by setting t = 0 as the time the patient was taken off CPB. rCMRO₂, Relative change in postoperative cerebral metabolic rate of oxygen; rCBF, relative change in postoperative cerebral blood flow; rOEF, relative change in postoperative oxygen extraction fraction; rCaO₂, relative change in postoperative arterial oxygen concentration; CPB, cardiopulmonary bypass.