Effect of oxygen content on postoperative cognitive dysfunction in patients undergoing open-heart surgery

Introduction: Brain's decreased oxygen delivery is proposed as a risk factor for postoperative cognitive dysfunction (POCD). This study's objective was to investigate the effect of arterial oxygen content (CaO2) on POCD in patients undergoing open-heart surgery. Subjects and Methods: Adult patients listed for elective open-heart surgery at Cipto Mangunkusumo General Hospital were enrolled. The patients' cognitive function was tested using the Rey Auditory Verbal Learning Test, trail-making test, and digit span test (forward–backward) before and 5 days after surgery. The hemoglobin level, arterial saturation (SaO2), and arterial oxygen partial pressure (PaO2) were measured at the following five time points: before induction, 10 min after the commencement of cardiopulmonary bypass (CPB), 10 min after the cessation of CPB, 6 h postoperatively, and 1 day postoperatively. The CaO2 was calculated as follows: CaO2= 1.36 × hemoglobin × SaO2 + 0.003 × PaO2. Data were compared using Student's t-test or the Mann–Whitney test with SPSS software version 20.0 (IBM Corp., Armonk, NY, USA). Results: POCD was found in nine patients (47.4%). The CaO was significantly lower in patients with POCD than those without POCD at 10 min after the cessation of CPB (12.1 ± 2.6 vs. 14.5 ± 1.7, respectively; P = 0.03). The hemoglobin level appeared to be the cause of the decreased CaO2 in the POCD group (8.5 ± 2.3 vs. 10.2 ± 1.2, P = 0.06). Decreased oxygen content after CPB cessation may impair brain tissue oxygenation that causes POCD. Conclusion: Hemoglobin level may play an important role in POCD development after open-heart surgery.