Abstracts of Posters Presented at the International Anesthesia Research Society; 72nd Clinical and Scientific Congress; Orlando, FL; March 7-11, 1998: Cardiovascular Anesthesia
INTRODUCTION: The limit of hemodilution compatible with adequate tissue perfusion is still a debate . Gastric tonometry and evaluation of systemic indicators of oxygen transport are the two methods used to measure tissue oxygenation in the clinical setting, although certain limitations exist in both . The aim of this prospective controlled study was to determine the effects of low hemoglobin (Hb) on tissue oxygenation during cardiac surgery including CPB and to compare the results of these two methods.
METHODS: After IRB approval, informed consent was obtained from 25 patients undergoing elective CABG. Patients were allocated according to preoperative Hb concentrations; Group A (n:12) Hb:<or=to12g/dl, Group B(control) (n:13) Hb>12g/dl. Preoperative ventricular function was good in all patients (EF>50%). Anesthetic protocol: IV fentanyl (20 [micro sign]g/kg total), midazolam (10 mg total) and vecuronium, blood pressure controlled by inhaled isoflurane and/or IV nitroglycerine. Gastric tonometer; (Tonometrics Inc.) was introduced after intubation (equilibration period 30 min). Standard CPB technique and nonpulsatile flow was used. Evaluated parameters were; Hb, hematocrit (Htc %), cardiac index (CI), mixed venous oxygen content (CvO2), systemic oxygen consumption (VO2), systemic oxygen delivery (DO2), oxygen extraction ratio (ERO2), gastric intramucosal pH (pHim). Data were obtained; 1) before sternotomy (baseline), 2) during CPB at 30[degree sign]C (rectal), 3) 30 min. after CPB, 4) 1 hr postoperatively, 5) 6 hr postoperative. Demographic data were analyzed by Student's t-test, others by repeated measures ANOVA and posthoc Tukey's HSD test. Results are expressed as mean +/- SE.
RESULTS: Group A and B were similar in demographic data and operation characteristics. Hb and Htc were lower in Group A at all intervals (p<0.05). No significant change was detected in CI. CvO2 was higher in Group B at all intervals (p<0.05). Other data are shown in Table 1.
DISCUSSION: Low Hb level resulted in a decrease in pHim after CPB which was not observed in normal Hb patients due to an increase in DO2. Lowest Hb concentrations were measured during CPB, however both methods showed no deterioration in tissue oxygenation, supporting each other during cardiac surgery.
1. Anesth Analg 1996; 82: 681-6.
2. Intensive Care Med 1997; 23:3-6.