Addition of enoximone to adrenergic agents in the management of severe heart failure

Enoximone pharmacokinetics in infants

Enoximone and enoximone sulphoxide concentrations were measured in plasma of 20 infants, median age 6.0 (range 0.6-49.7) weeks, during and after prolonged continuous infusions. Patients were given enoximone 1 mg kg-1 and an infusion at 10 micrograms kg-1 min-1 just before being weaned from cardiopulmonary bypass (CPB). The infusion was stopped when clinically indicated, after a median 97 (range 24-572) h. Arterial blood samples were taken 30 min and 12 h after CPB, every 24 h during the infusion, and then 2, 4, 8, 12 and 24 h after the infusion was stopped. Pharmacokinetic non-compartmental analysis was performed using TOPFIT software. Fourteen patients who retained normal hepatic function had a median (95% confidence intervals) clearance of 9.7 (6.3-14.1) ml min-1 kg-1, elimination half-life of 5.2 (2.4-6.8) h and a volume of distribution of 3.6 (2.0-5.7) litre kg-1. The six patients with significant hepatic dysfunction had a lower clearance, 5.7 (2.4-14.5) ml min-1 kg-1, and significantly longer elimination half-life, 7.6 (6.5-10.9) h (P = 0.02). Enoximone sulphoxide elimination half-life was significantly prolonged in three patients with renal dysfunction, 16.2 (10.5-17.7) h versus 6.9 (6.1-9.4) h (P = 0.03). These results confirm that enoximone pharmacokinetics in infants is similar to that found in adults. The infusion rate of enoximone should be reduced if hepatic or renal dysfunction supervenes.

Vasopressin as an alternative to norepinephrine in the treatment of milrinone-induced hypotension

OBJECTIVE

To determine whether vasopressin could be effective in treating the hypotension associated with phosphodiesterase III inhibition. Phosphodiesterase III inhibitors are cardiotonic agents that increase myocardial contractility and decrease vascular smooth muscle tone. The vasodilatory effect can be profound, and the resulting hypotension frequently requires the administration of catecholamine pressors.

DESIGN

Retrospective analysis of existing data.

SETTING

The medical or surgical intensive care unit of Columbia-Presbyterian Medical Center.

PATIENTS

Three consecutive patients receiving milrinone and requiring catecholamine pressors to maintain systolic arterial pressure of > or =90 mm Hg.

INTERVENTIONS

Vasopressin was administered to the three patients.

MEASUREMENTS AND MAIN RESULTS

Vasopressin (0.03-0.07 units/min) increased systolic arterial pressure from 90+/-4.7 to 130+/-2.3 mm Hg while reducing the administration of catecholamine pressors.

CONCLUSIONS

Vasopressin at very low doses appears to be an effective vasopressor for milrinone-induced hypotension.

Vasorelaxant actions of enoximone, dobutamine, and the combination on human arterial coronary bypass grafts

Enoximone (a type III-selective phosphodiesterase inhibitor) and dobutamine (a beta-receptor agonist) are positive inotropic drugs frequently used in the postoperative management of coronary bypass surgery. The purpose of this study was to characterize their relaxant effects on the human internal mammary artery (IMA) and the gastroepiploic artery (GEA) and to test the hypothesis that their combination may have greater than additive relaxant effects. In organ baths, the relaxant effects of enoximone and dobutamine were tested on rings of IMA (n = 86) precontracted with U46619 (a thromboxane A2 mimetic), norepinephrine (NE), or KCl. The relaxant effects of dobutamine and enoximone also were tested on rings of GEA (n = 42) precontracted with U46619 and NE. The effect of the combination of enoximone and dobutamine were tested on rings of IMA (n = 24) precontracted with U46619 or NE. With respect to maximal relaxations induced by papaverine (10(-4) M), enoximone (< or =10(-3) M) caused full relaxations of IMA precontracted with NE, U46619, or KCI. Dobutamine (< or =10(-3) M) caused full relaxations of IMA precontracted with NE or KCI but only 46% (95% CI, 27-65) relaxation in the rings precontracted with U46619. Similar patterns of relaxation were observed in GEA rings, with dobutamine inducing partial relaxation in GEA precontracted with U46619. The pD2 values of enoximone and dobutamine were both significantly lower in segments precontracted with U46619. The in vitro threshold relaxant concentrations were in the upper limits or over the range of therapeutic plasma concentrations. The relaxant effect of the combination was significantly more important than the theoretic additive effect in IMA contracted with U46619 or NE. Enoximone and dobutamine are potent in vitro vasodilators but exert weak relaxant effects in IMA and GEA at concentrations in the therapeutic range. There is, however, a greater than additive vasorelaxant effect of the combination, suggesting that the vasorelaxant effect of the combination, in addition to the additive inotropic effect, may be beneficial to patients undergoing coronary bypass grafting.

Immediate postoperative care of cardiac surgical patients

Anesthetic care of the cardiac surgery patient is a continuum, beginning with the preoperative visit and ending when the patient is ambulatory and breathing well on the postoperative floor. Anesthesiologists are well-suited to provide postoperative care because the respiratory and cardiovascular management techniques are an extension of OR management. Attention to details is as important in the ICU as in the OR and offers the opportunity to forestall or reduce morbidity.

Levosimendan potentiates the inotropic actions of dopamine in conscious dogs

We examined the hemodynamic and left ventricular (LV) functional actions of dopamine with and without levosimendan in dogs chronically instrumented for measurement of aortic and LV pressure, +dP/dtmax, subendocardial segment length, and cardiac output (CO). On different experimental days, dogs were randomly assigned to receive dopamine (2.5, 5.0, and 10.0 micrograms kg-1 min-1) in the absence and presence of levosimendan (0.125, 0.25, and 0.5 microgram kg-1 min-1) or levosimendan alone. Dopamine increased heart rate (HR), CO, stroke volume (SV), and pressure-work index (PWI) and decreased systemic vascular resistance (SVR). Dopamine also increased LV systolic and end-diastolic pressures (LVSP and LVEDP) and mean arterial pressure (MAP). Dopamine caused dose-related positive inotropic [increases in preload recruitable stroke work (Mw) and + dP/ dtmax] and lusitropic effects [decreases in the time constant of isovolumic relaxation (tau) and increases in maximum segment-lengthening velocity (dL/dtmax)]. Dopamine also increased the regional chamber thickness constant (Kp) concomitant with increases in LVEDP. In the presence of levosimendan, dopamine-induced increases in HR, PWI, CO, and SV and decreases in SVR were enhanced. Increases in MAP, LVSP, and LVEDP observed with dopamine alone were attenuated by the addition of levosimendan. Dopamine-induced increases in Mw and +dP/dtmax were enhanced by levosimendan. Reductions in tau and increases in dL/dtmax produced by dopamine were similar with and without levosimendan. However, levosimendan abolished increases in Kp caused by dopamine alone. Levosimendan alone caused dose-related improvements in indices of LV systolic and diastolic function. The results indicate that levosimendan potentiates the positive inotropic effects of dopamine in conscious, unsedated dogs, while attenuating the deleterious action of dopamine on chamber compliance.

Acute circulatory support

Numerous drugs can increase cardiac output, thereby improving tissue oxygen delivery, but often they do this at the expense of increasing myocardial oxygen demand. This may be critical when cardiac function is substantially impaired or ischaemia is the precipitating cause. Using polypharmacy to substantially improve cardiovascular status requires detailed knowledge of the pharmacodynamics and interactions of the available agents so that they may be tailored to the individual patient. In some settings combinations of inotropes and vasodilators may be desirable to minimise cardiac workload. In other instances vasopressors may be necessary to urgently restore a minimum perfusion pressure. This paper reviews the use of this group of drugs as well as the mechanical assist devices that may be used when drugs fail.

Pathophysiology and management of self-poisoning with beta-blockers

The prognosis of self-poisoning with beta-blockers is excellent, especially if medical management is started immediately but the wide variety of clinical symptoms and proposed treatments complicate the therapeutic strategy. Beta-blockers that are liposoluble or have marked anti-arrhythmic activity are more lethal (e.g. propranolol, sotalol). Similarly, pre-existing cardiac pathology or co-ingestion of psychotropic or cardioactive drugs increases mortality. The first-line symptomatic treatment is administration of atropine and volume-expanding fluids to treat bradycardia and hypotension, respectively. However atropine is often unsuccessful in reversing beta-blocker-induced bradycardia and repeated doses can provoke atropine poisoning. If symptomatic treatment fails, then antidotes should be administered in a precise order: first, high doses of glucagon, followed by isoproterenol, epinephrine, and the new inhibitors of phosphodiesterases. Mechanical ventilation should be started at the same time as pharmacological treatment in cases of severe collapse or prolonged QRS.