Arterial-venous PCO2 gradient in early postoperative hours following myocardial revascularization
Cavaliere, F.; Martinelli, L.; Guarneri, S.; Varano, C.; Rossi, M.; Schiavello, R.
Journal of Cardiovascular Surgery 37(5): 499-503
1996
ISSN/ISBN: 0021-9509 PMID: 8941692 Document Number: 461324
Objective. To investigate the utility of the arterial-venous PCO-2 gradient (P-a-vCO-2) as a marker of the increased risk of postoperative complications in the early postoperative hours following myocardial revascularization. Experimental design. Prospective study. Setting. The Postoperative intensive Care Unit (ICU) of a University Hospital. Patients. Thirty patients (28 males and 2 females; aged 39-70) that consecutively underwent myocardial revascularization. Interventions. None. Measures. Thirty minutes following arrival at the ICU the hemodynamic parameters were recorder; the arterial and mixed venous hemogasanalyses were obtained, the mixed venous blood hemoglobin saturation (SvO-2) and the O-2 consumption (VO-2) were calculated; and plasma lactate was determined. The arterial and mixed venous hemogasanalyses were determined again 90 minutes after the admission to the ICU. Results. P-a-vCO-2 at 30 minutes was 8.1+-2.3 mmHg and was only slightly lower at 90 minutes (7.5+-2.3 mmHg) so that any significant influence of patient transport to the ICU could be ruled out. P-a-vCO-2 did not significantly relate with cardiac index, mixed venous blood O-2 saturation, and blood lactate. Twenty-one patients (70%) showed P-a-vCO-2 values higher than 7 mmHg at 30 minutes: in comparison with the others they were characterized by higher arterial blood PCO-2 (PACO-2) (37+-5 vs 32+-3 mmHg; P lt 0.05) in spite of similar ventilatory variables, by higher mixed venous blood PCO-2 (PVCO-2) (47+-6 vs 37+-3 mmHg p lt 0.01), and by lower cardiac index values (2.0+-0.3 vs 2.3+-0.6 1/min/m-2; p lt 0.05). The patients that presented abnormally high P-a-vCO-2 values showed a higher rate of postoperative complications, including inadequate cardiac performance, cardiac arrhythmias, prolonged mechanical ventilation, increased plasma creatinine, and jaundice (11 patients out of 21 vs 1 patient out of 9; p lt 0.05). Finally P-a-vCO-2 was related with arterial-mixed venous O-2 content difference (regarded as an index of O-2 consumption), hematocrit, blood temperature and PACO-2 by multiple linear regression (R=0.74; p lt 0.01). The coefficients of all factors but hematocrit were significant; hence, apart from the cardiac index, P-a-vCO-2 was influenced by the metabolic rate, the body temperature (possibly because of CO-2 release during rewarming), and the impaired CO-2 elimination through the lungs. Conclusions. P-a-vCO-2 represents a useful even if aspecific parameter to monitor patients during the early postoperative period after myocardial revascularization.