Administration of drugs during cardiopulmonary bypass. An analysis of the fate of a bolus injected through different routes using radio-active technetium

Cardiopulmonary Bypass Emergencies and Intraoperative Issues

Cardiopulmonary bypass (CPB) is a complex biomechanical engineering undertaking and an essential component of cardiac surgery. However, similar to all complex bioengineering systems, CPB activities are prone to a variety of safety and biomechanical issues. In this narrative review article, the authors discuss the preventative and intraoperative management strategies for a number of intraoperative CPB emergencies, including cannulation complications (dissection, malposition, gas embolism), CPB equipment issues (heater-cooler failure, oxygenator issues, electrical failure, and tubing rupture), CPB circuit thrombosis, medication issues, awareness during CPB, and CPB issues during transcatheter aortic valve replacement.

The pharmacokinetics of anesthetic drugs and adjuvants during cardiopulmonary bypass

The institution of cardiopulmonary bypass during cardiac surgery has profound effects on the plasma concentration of drugs and thus their therapeutic effectiveness. These changes occur through acute hemodilution, altered plasma protein binding, hypotension, as well as the use of hypothermia and heparin administration. Isolation of the lungs from the circulation and the possible sequestration of drugs in the bypass circuit also affect drug plasma concentrations on bypass. The individual characteristics of the drug in question are also important in determining the final plasma concentration: Lipid soluble drugs with a high volume of distribution may be more readily taken up by bypass equipment, but the initial fall in concentration at the start of cardiopulmonary bypass may be more readily counteracted by back diffusion into plasma, if large tissue stores have accumulated. The extent of the drug's plasma protein binding is of importance as the effective free fraction in plasma for highly bound drugs will be sensitive to changes in plasma protein binding brought on by factors such as hemodilution, heparin administration as well as alpha, acid-glycoprotein binding. Clearly the fate of drugs administered before or on bypass is complex and can only be accurately determined by specific studies evaluating drug plasma concentrations. This review updates the available data on anesthetics and drugs used during cardiac surgery in order that anesthetists may predict better the likely effect of drugs administered before or during cardiopulmonary bypass.

Propofol sequestration within the extracorporeal circuit

Various drugs administered during cardiac anaesthesia are sequestered in the extracorporeal circuit in vitro, but it is uncertain whether this sequestration phenomenon affects plasma drug concentration in vivo. The present study was undertaken to evaluate (1) in vitro sequestration of propofol in the extracorporeal circuit and (2) whether the change in plasma propofol concentration induced by initiation of cardiopulmonary bypass in vivo can be explained by haemodilution. For the in vitro evaluation, three separate experiments with a closed circuit (membrane oxygenator, reservoir, and tubings) were performed. The pH and PCO2 of the circulating solution (a mixture of Ringer's acetate and whole blood) were maintained within the normal physiological range, and the temperature of the solution was 28 degrees C. The solution was circulated at a flow of 4 L.min-1 and propofol was added to the solution to achieve a concentration of 2 micrograms.ml-1. Serial samples were taken from the circulating solution for measurement of propofol concentration by high performance liquid chromatography. In the in vivo part of the study, 14 patients received a continuous infusion of propofol, and samples for the determination of plasma propofol concentration and blood haematocrit were taken before and five and ten minutes after initiation of cardiopulmonary bypass. In vitro, at 5 and 120 min after addition of propofol into the circulating solution, approximately 65% and 25%, respectively, of the predicted propofol level was measurable in the solution.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of propofol on mean arterial pressure and systemic vascular resistance during cardiopulmonary bypass

This study was designed to evaluate the effects of propofol on mean arterial pressure (MAP) and systemic vascular resistance (SVR) during cardiopulmonary bypass (CPB). Twenty patients were divided randomly for administration of 2 mg.kg-1 propofol (group Propofol, n = 10) or 0.9% saline solution (group Control, n = 10) during CPB. The two groups were comparable with respect to sex, age, height, type of surgery (valvular or coronary), arterial hypertension and preoperative antihypertensive treatment. Only their weight and body surface area were significantly different (control group vs propofol group, respectively: 78.5 +/- 14.4 vs 64.7 +/- 7.7 kg, P < 0.05; and 1.85 +/- 0.2 vs 1.68 +/- 0.13 m2, P < 0.05). MAP, SVR and SVR index were significantly lower in the propofol group than in the control group at 10, 15 and 20 min of study, suggesting that the hypotensive effect of a bolus injection of propofol is due, at least in part, to a direct decrease in the SVR.

Influence of cardiopulmonary bypass on nitroglycerin clearance

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.