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The relationship between systemic oxygen uptake and del ivery during moderate hypothermic cardiopulmonary bypass: critical values and effects of vasodilation by hydralazine

Institute of Anaesthesiology and Intensive Care, Catholic University of The Sacred Heart, Rome

A. Gennari

Institute of Anaesthesiology and Intensive Care, Catholic University of The Sacred Heart, Rome

L. Martinelli

Institute of Anaesthesiology and Intensive Care, Catholic University of The Sacred Heart, Rome

R. Zamparelli

Institute of Anaesthesiology and Intensive Care, Catholic University of The Sacred Heart, Rome

R. Schiavello

Institute of Anaesthesiology and Intensive Care, Catholic University of The Sacred Heart, Rome

The relationship between oxygen delivery (DO₂) and uptake (VO₂) has been studied during moderately hypothermic cardiopulmonary bypass (CPB) in 15 patients undergoing myocardial revascularization. As soon as nasopharyngeal temperature was lowered to 32°C, blood flow was decreased from 2.4 to 2.0 l/min/m ². Arterial and mixed venous blood gas analyses were performed five and eight minutes later and DO₂ and VO₂ were calculated; VO₂ stabilized in five minutes after changing blood flow and neither DO₂ nor VO₂ values changed three minutes later (DO ₂: 217 ± 19 versus 215 ± 17 ml/min/m2; VO₂: 63 ± 12 versus 66 ± 14 ml/min/m2). Blood flow then was increased to 2.3 l/min/m² and DO₂ and VO₂ were determined again, five minutes later; they both increased significantly, to 243 ± 20 and 74 ± 13 ml/min/m ², respectively. However, a further blood flow increase to 2.6 l/min/m ² which caused DO₂ to increase to 277 ± 24 ml/min/m ², did not affect VO₂ which was unchanged five minutes later (76 ± 13 ml/min/m²); VO₂ dependence on DO₂ values higher than 243 ± 20 ml/min/m² was consequently ruled out. Ten patients, having a mean arterial pressure higher than 80 mmHg, were eventually vasodilated with hydralazine, 0.1 mg/kg intravenously, and DO₂ and VO₂ were determined after five and ten minutes. As blood flow did not change, DO₂ was unaffected while a slight increase in VO₂ mean values was observed which was not statistically significant (prior to hydralazine: 78 ± 15 ml/min/m²; five minutes later: 82 ± 17 ml/min/m²; 10 minutes later: 76 ± 18 ml/min/m²).

In conclusion, during hypothermic CPB at 32°C, VO₂ plateau ranges between 48 and 102 mi/min/m ² (mean ± 2 SD) in 95% of patients, corresponding to 66 and 141 ml/min/m ² at 37°C; this finding closely matches other literature reports. Consequently, lower VO₂ values suggest inadequate oxygen supply to tissues. Critical DO₂ at 32°C is lower than 283 ml/min/m² in 97.5% of patients. Finally, arterial vasoconstriction does not seem to play a significant role in tissue hypoperfusion.

Perfusion, Vol. 10, No. 5, 315-321 (1995)
DOI: 10.1177/026765919501000506


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