Key result
Cardiopulmonary bypass increased the mean apparent clearance of nitroglycerin by 20%, from 0.044 L/kg/min before bypass to 0.052 L/kg/min during bypass (P = .05).
Why the study?
Does cardiopulmonary bypass increase the clearance of nitroglycerin in patients undergoing coronary artery bypass graft surgery?
Observational (n=7)
Does cardiopulmonary bypass increase the clearance of nitroglycerin in patients undergoing coronary artery bypass graft surgery?
Cardiopulmonary bypass slightly increases the clearance of nitroglycerin, which may partially explain the need for increased dosages during bypass.
May warrant closer nitroglycerin monitoring during bypass; leaves open whether clearance changes affect outcomes or require randomized dosing trials.
The effect of cardiopulmonary bypass on the clearance of nitroglycerin (NTG) was studied in seven patients scheduled for coronary artery bypass graft surgery. Intravenous NTG was administered through nonadsorbing tubing at a starting dosage of 5-10 micrograms/min and was adjusted as needed. Blood samples were obtained from the radial artery and antecubital vein before bypass and from the arterial outlet of the oxygenator during bypass at least 30 minutes apart during a constant dosage or at least 30 minutes after a dosage change. Serum concentrations were analyzed for NTG by gas chromatography. Venous NTG concentrations were always lower than concurrent arterial concentrations, with an average arteriovenous extraction of 67.2%. Serum concentrations of NTG were generally within the range associated with a therapeutic response in congestive heart failure patients. Consistent with other reports, NTG concentrations varied widely among patients and considerable intrasubject fluctuations in drug concentrations were seen. The mean +/- SD apparent clearance of NTG before bypass of 0.044 +/- 0.02 L/kg/min increased 20% to 0.052 +/- 0.02 L/kg/min during bypass (P = .05). These results suggest that cardiopulmonary bypass increases the clearance of NTG; however, the magnitude appears to be small and only partially explains the reported increased dosage needed during cardiopulmonary bypass.
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Dasta et al. (1986) conducted an observational in Coronary artery disease requiring bypass graft surgery (n=7). Cardiopulmonary bypass vs. Before bypass was evaluated on Apparent clearance of nitroglycerin (p=.05). Cardiopulmonary bypass increased the mean apparent clearance of nitroglycerin by 20%, from 0.044 L/kg/min before bypass to 0.052 L/kg/min during bypass (P = .05).
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