The rational selection of inotropic drugs in cardiac surgery

Hemodynamic responses to dobutamine during acute normovolemic hemodilution

The effects of dobutamine (DOB) on myocardial performance, systemic hemodynamics, and oxygen delivery during acute normovolemic hemodilution in anesthetized rats were studied. Forty-two Sprague Dawley rats (body weight 375 to 425 g) were divided into six equal groups. Hemodynamic and cardiac indices were measured or calculated at baseline, 30 minutes after the initiation of hemodilution (HD), and 15 minutes after DOB or saline infusion. Myocardial performance in response to acute pressure or volume loads was studied in all groups of animals. HD to a hematocrit (Hct) value of 20% resulted in no change in heart rate (HR), increased CI, SVI, and LV dP/dt, and decreased MAP, SVRI, and oxygen delivery index (O2DI). HD increased peak SV and CI after preload stress while the left ventricular developed pressure (LVDP) was unchanged. Infusion of DOB as 7.5 or 15 micrograms/kg/min increased HR, CI, and LV dP/dt as well as LVDP. At the same time, DOB decreased MAP and SVR, whereas the SVI remained unchanged. In non-HD animals both doses of DOB increased LVDP, but only the larger dose increased CI, whereas peak SV decreased with the smaller dose. Arterial carbon dioxide tension (PaCO2) increased, whereas pH and arterial oxygen tension (PaO2) decreased; however, O2DI remained unchanged. Concomitant hemodilution and DOB infusion resulted in attenuation of HR response to DOB, exaggerated the drop in MAP and SVR, and increased LV dP/dt. Only the larger dose of DOB increased the CI, whereas neither dose could alter the SVI in HD animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Early intervention of inotropic support in facilitating weaning from cardiopulmonary bypass: the New England Deaconess Hospital experience

The current article reviews the therapeutic advantages and disadvantages of early inotropic intervention prior to separation from cardiopulmonary bypass (CPB). Background information is provided on predictors of failure to wean as well as the multiple etiologies and consequences of the "failed wean" from CPB. Advantages of early inotropic intervention include (1) increased contractility, (2) resolution/prevention of ischemia, (3) attainment of therapeutic levels of drug, (4) minimization of inotropic side effects while on CPB, (5) avoidance of mechanical intervention (intra-aortic balloon pump), (6) dilatation of the internal mammary artery, and (7) prevention of the "failed wean". Disadvantages of early inotropic intervention include (1) unnecessary drug usage, (2) tachycardia/arrhythmias, (3) hyper/hypotension, (4) metabolic disturbances (hyperglycemia), (5) coagulation disorders, (6) need for additional drugs to treat side effects, (7) possible myocardial damage, and (8) additional costs. A brief review of this institution's preference for amrinone follows, including its pharmacology, side effects, and dosing prior to separation from CPB. Due to the large percentage of patients with diabetes mellitus undergoing cardiac surgery at our institution (approximately 30% to 40%) a synopsis of special inotropic considerations for this patient population is included.

Inotropic support of the heart that fails to successfully wean from cardiopulmonary bypass: the Montreal Heart Institute experience

The selection of an appropriate therapeutic regimen, especially in patients with preexisting cardiac dysfunction prior to surgery, is a crucial element for successful separation from cardiopulmonary bypass (CPB). At the present time there are no definitive studies to determine which treatment modality, or combination of treatments, is optimal in this patient population. A brief review of the literature is presented to answer the following questions: (1) Should inotropic support be administered in anticipation of failure to wean from CPB? and (2) Which inotrope or combination of drugs is best? There is no evidence at present that the prophylactic administration of inotropes to assist separation from CPB may result in damaging effects to the myocardium in humans. Inasmuch as tachycardia is avoided and coronary perfusion pressure is maintained within the normal range, prophylactic inotropes may be of benefit to patients with preexisting myocardial dysfunction during weaning from CPB by allowing a smoother separation and a shorter time on CPB. While no specific drug has been proven superior, the use of phosphodiesterase inhibitors as part of the regimen to provide inotropic support in these patients may exert a beneficial effect on myocardial ischemia and reperfusion injury. Prophylactic support of the circulation during separation from CPB, especially with phosphodiesterase inhibitors, may be indicated in this specific patient population as part of the strategy to ensure maximal preservation of myocardial function.

Is calcium or ephedrine superior to placebo for emergence from cardiopulmonary bypass?

To determine whether ephedrine or CaCl2 improves hemodynamics in cardiac surgery patients emerging from cardiopulmonary bypass, three sequential doses of either CaCl2 (200 mg/dose; n = 12), ephedrine (5 mg/dose; n = 12), or placebo (n = 12) were administered in a prospective, randomized, double-blind fashion. Thermodilution volumetric catheters were used to calculate right ventricular (RV) volumes and ejection fraction. The first dose of ephedrine improved RV stroke volume from 57 +/- 3 to 63 +/- 4 mL/beat (P < 0.05) and ejection fraction from 44 +/- 2% to 49 +/- 2% (P < 0.05). Subsequent doses maintained this improvement but without further change. In contrast, placebo and CaCl2 had minimal effects on RV end-systolic volume, stroke volume, and ejection fraction. After the third injection of ephedrine, mean arterial pressure had significantly increased from 78 +/- 2 to 93 +/- 4 mmHg (P < 0.05) in contrast to insignificant increments with placebo and CaCl2. Serum ionized calcium increased by 6% to 8% after each CaCl2 bolus but remained stable in the ephedrine and placebo groups. CaCl2 failed to improve RV performance in mildly hypocalcemic patients during separation from cardiopulmonary bypass. In patients with normal preoperative ventricular function, ephedrine more effectively improved RV performance and arterial blood pressure than placebo or CaCl2, and is a suitable short-acting drug to assist separation from cardiopulmonary bypass.

Calcium inhibits the cardiac stimulating properties of dobutamine but not of amrinone

To contrast the effect of increasing blood calcium concentrations on the cardiovascular actions of intravenous beta-adrenergic agonists and phosphodiesterase inhibitors, 46 patients recovering from aortocoronary bypass surgery received either dobutamine or amrinone both in the presence and absence of a calcium infusion. Cardiac output, systemic arterial pressure, pulmonary arterial pressure, central venous pressure, pulmonary artery occlusion pressure, heart rate, and blood ionized calcium concentration were measured before and during infusions of dobutamine (2.5 and 5.0 micrograms/kg/min) and amrinone (0.75 mg/kg bolus + 10 micrograms/kg/min or 2.25 mg/kg bolus + 20 micrograms/kg/min). After the initial dobutamine infusion period, patients were randomly and blindly assigned to receive either a calcium or placebo infusion, and the dobutamine infusions were repeated. Because of the long duration of amrinone's actions, the amrinone maintenance infusion was continued while randomized, blinded infusion of either calcium or placebo was added. Dobutamine (5 micrograms/kg/min) increased cardiac output from 7.1 +/- 0.3 L/min to 9.1 +/- 0.4 L/min, and increased heart rate from 93 +/- 4 beats/min to 107 +/- 4 beats/min. Systemic vascular resistance decreased and stroke volume increased. Dobutamine had no significant effects on other hemodynamic values. Amrinone (2.25 mg/kg bolus + 20 micrograms/kg/min) increased cardiac output from 5.6 +/- 0.4 L/min to 6.9 +/- 0.5 L/min, and increased heart rate from 87 +/- 3 beats/min to 98 +/- 3 beats/min. Amrinone decreased mean arterial pressure, systemic vascular resistance, pulmonary artery occlusion pressure, central venous pressure, and pulmonary artery pressure. Calcium infusion increased arterial pressure (8 to 13 percent) but had no significant effects on any other hemodynamic parameters. Calcium reduced the increase in cardiac output produced by dobutamine by 30 percent, but it did not alter the cardiotonic actions of amrinone. Thus, calcium inhibits the cardiotonic actions of certain beta-adrenergic agonists, most likely by interfering with signal transduction through the beta-adrenergic receptor complex.