Comparison of the acute hemodynamic effects of hypertonic or colloid infusions immediately after mitral valve repair

OBJECTIVE

To determine the acute hemodynamic effect of hypertonic saline and/or colloid solutions as volume resuscitation in postoperative mitral valve repair patients.

DESIGN

Prospective, randomized trial.

SETTING

Postoperative cardiac intensive care unit of Broussais Hospital.

PATIENTS

Twenty-six patients who underwent mitral valve repair were prospectively studied. Two patients were excluded during the study.

INTERVENTIONS

During the immediate postoperative period, when wedge pressure decreases to <8 mm Hg, patients were randomly assigned to receive 250 mL of either hypertonic saline 7.2%-hydroxyethyl starch 6% (molecular weight, 200,000; hydroxyethylation ratio, 0.5) solution (HS-HES group), hypertonic saline 7.2% solution (HS group), or hydroxyethyl starch 6% solution (HES group). The infusion was completed within 15 mins. No additional volume was infused throughout the study.

MEASUREMENTS AND MAIN RESULTS

Standard hemodynamic measurements and echocardiographic data demonstrated that HS-HES and HS induced a higher increase in left ventricular end-diastolic area than HES. In the HS-HES and HS groups, systemic vascular resistances decreased significantly and end-systolic area tended to decrease. In the HES group, systemic vascular resistances did not change and end-systolic area tended to increase. Accordingly, ejection fraction increased significantly by 21% and 18% with HS-HES (from 50.5 +/- 5.5 to 61.2 +/- 4.8) and HS (from 49.7 +/- 3.6 to 58.8 +/- 3.3), respectively, and did not change with HES. A major increase in cardiac index was observed after hypertonic solutions infusion, from 2.9 +/- 0.3 to 4.1 +/- 0.4 L/min/m2 in the HS-HES group and from 2.7 +/- 0.3 to 3.8 +/- 0.4 L/min/m2 in the HS group. Then, cardiac index progressively returned to baseline values within the 3 hrs after the infusion. No significant difference was observed between HS-HES and HS. In these groups, plasma sodium increased significantly after the infusion and remained higher than baseline values throughout the study. Adverse events were observed only with hypertonic solution administration: hypotensive episodes, sudden increases in pulmonary capillary wedge pressure, and ventricular arrhythmias. These side effects are likely attributable to a too-high dose and/or rate of infusion. All patients included in the study were discharged from the hospital before the 10th postoperative day.

CONCLUSION

We conclude that in patients who have undergone mitral valve repair, postoperative infusion of hypertonic saline solutions increases left ventricular preload and left ventricular ejection fraction. The use of these hypertonic solutions may be of interest in patients with valvular cardiomyopathy. A titrated dose and a low rate of infusion may substantially improve the safety.

Does aprotinin modify the effects of ischaemia-reperfusion on the myocardial performance of a blood perfused isolated rabbit heart?

Aprotinin has been reported to influence positively or negatively the process of ischaemia-reperfusion. However, it is a complex drug acting on platelets, neutrophils and coagulation, which may also have a direct effect by inhibiting intracellular proteases and free radical generation. The goal of this study was to determine the direct effects of aprotinin on the myocardial performances of an isolated blood perfused rabbit heart preparation after normothermic global ischaemia. Two groups of 10 hearts were studied. The control group (ischaemia) underwent 30 min of global normothermic ischaemia. In the aprotinin group, (aprotinin) 200 KUI mL-1 of aprotinin was added to the perfusate before ischaemia. Measurements were obtained at base-line, 10, 30 and 60 min after reperfusion. Normothermic ischaemia significantly decreased myocardial performance in both groups. After 60 min reperfusion, myocardial contractility significantly recovered in the aprotinin group compared with the ischaemia group. Aprotinin contributes significantly by limiting the consequences of ischaemia on myocardial performances. This effect may be due to a direct action of the drug because leucocytes and plasma proteins were removed in this preparation.

Early extubation after mitral valve surgery: a target-controlled infusion of propofol and low-dose sufentanil

OBJECTIVE

In the current study, the use of a target-controlled infusion of low-dose propofol was combined with a continuous infusion of sufentanil for patients undergoing mitral valve surgery. The purpose of the study was to evaluate the hemodynamic stability, the time to awakening and spontaneous ventilation, and the feasibility in an early extubation setting of a total intravenous anesthetic technique.

DESIGN

Prospective study.

SETTING

University hospital.

PARTICIPANTS

Fifteen patients scheduled for elective mitral valve surgery.

INTERVENTIONS

Induction of anesthesia consisted of sufentanil (1 microgram/kg), propofol (1 microgram/mL) target plasma concentration achieved over 3 minutes, and atracurium (0.5 mg/kg). The propofol target-controlled infusion was maintained at 1 microgram/mL throughout surgery and stopped at skin closure. A continuous infusion of sufentanil at 1.8 micrograms/kg/hr was started after induction and reduced to 0.9 microgram/kg/hr at the start of cardiopulmonary bypass and stopped at the end of bypass. Atracurium was infused at a rate of 0.5 mg/kg/hr up to sternal closure. No inhalation agents were used.

MEASUREMENTS AND MAIN RESULTS

Hemodynamic data were within normal limits. Six patients (40%) responded to verbal commands within 15 minutes postoperatively, 10 (67%) within the first hour, and all patients recovered within 2 hours. Four patients (27%) resumed spontaneous ventilation within the first 15 postoperative minutes. The time to successful spontaneous ventilation was 169 +/- 42 minutes. Spontaneous ventilation was associated with a 21% increase in cardiac index. Total sufentanil dose was 328 +/- 28 micrograms (4.6 +/- 0.2 microgram/kg), whereas total propofol dose was 862 +/- 44 mg (13.1 +/- 1.2 mg/kg). No patient required reintubation.

CONCLUSION

The simplicity of the method with only one change in infusion rate is a major advantage. The technique permits predictable recovery and return to spontaneous ventilation in all patients. Its use in patients entering early extubation protocols is appealing for its reproducibility, simplicity, and safety.

Tris-hydroxymethyl aminomethane and sodium bicarbonate to buffer metabolic acidosis in an isolated heart model

Metabolic acidosis induces a decrease in the developed force of cardiac muscle by affecting every step of the excitation--contraction coupling pathway. Due to transient worsening in intracellular acidosis, the value of administering sodium bicarbonate therapeutically during acute acidosis has been questioned. An alternative therapeutic drug, Tris-hydroxymethyl aminomethane (THAM) has the advantage of diffusing into the intracellular space. This study was designed to evaluate the effects of metabolic acidosis on myocardial performance and to determine the effects of alkalinization with sodium bicarbonate, THAM, and their combination. Using a blood-perfused isolated heart preparation, left ventricular contractility and relaxation were measured at normal pH and during metabolic acidosis (pH = 7.0). Acidosis dramatically impaired myocardial contractility and relaxation. After buffering with sodium bicarbonate, although plasma bicarbonate concentration was normalized, pH remained below normal owing to an increased PaCO2. Contractility and relation were initially worsened, then slightly improved to return to control values. THAM uncompletely buffered acidosis but significantly improved contractility and relaxation. The combination of THAM with sodium bicarbonate perfectly buffered acidosis without modifying PaCO2 and significantly improved contractility. The combination of THAM with sodium bicarbonate is based on the ability of THAM to capture the CO2 produced by the sodium bicarbonate buffer. This combination achieves a perfect correction of metabolic acidosis and improves myocardial performance.

[Threshold values of colloid-osmotic pressure, serum albumin or protein during perioperative period]

The water flux across the capillary membrane is directly related to a gradient of hydrostatic and colloid osmotic forces. The membrane is not an absolute barrier to proteins. Any change in the capillary permeability tends to decrease the plasmatic colloid osmotic pressure. The interstitial space includes a perimicrovascular space and a compliant connective tissue space, where oedema accumulates. The lymphatics may easily drain excess filtration, but cannot clear constituted oedema. Primarily, the risk of pulmonary oedema determines the lower limit of the colloid osmotic pressure. During the perioperative period, any extrapolation of the colloid, osmotic pressure from protidaemia or albuminaemia would be approximate. Two major conclusions can be drawn from the results of Guyton and Lindsey. First, in the absence of left ventricular failure, a 50% decrease in colloid osmotic pressure does not increase extravascular lung water. Second, in the case of left ventricular failure, when the left atrial pressure exceeds 10 mmHg, a 50% decrease in colloid osmotic pressure significantly increases the risk of pulmonary oedema. In these experiments, an impairment in capillary membrane permeability is likely. As a result, the threshold at which extravascular water starts to accumulate cannot be precisely defined. However, in the perioperative period, capillary membrane permeability is frequently altered by the acute phase reaction. Finally, in most perioperative clinical situations, a 50% decrease in colloid osmotic pressure may not require any treatment.

Mechanisms of increased myocardial contractility with hypertonic saline solutions in isolated blood-perfused rabbit hearts

Hypertonic saline improves organ perfusion and animal survival during hemorrhagic shock because it expands plasma volume and increases tissue oxygenation. Because both decreased and increased myocardial performance have been reported with hypertonic saline, the effects of hyperosmolarity and the mechanism accounting for it were investigated in isolated blood-perfused rabbit hearts. Coronary blood flow (CBF), myocardial contractility, relaxation, and oxygen consumption were measured during administration of blood perfusates containing 140-180 mmol sodium concentrations ([Na+]). In two other series of experiments, the role of Na(+)-Ca2+ exchange in the inotropic effect of hyperosmolarity (160 mmol sodium concentration) and hypertonicity (sucrose) were also investigated. Hypertonic [Na+] induced a significant increase in contractility and relaxation, combined with a coronary vasodilation. Myocardial oxygen consumption (MVO2) increased at all hypertonic [Na+] without significant change in coronary venous oxygen tension (PVO2) and content (CVO2). Amiloride (0.3 mmol) inhibited the improved contractility observed with 160 mmol sodium. Similar Na(+)-Ca2+ exchanger blockade did not inhibit the inotropic effect of sucrose. These results confirm the positive inotropic effect of hypertonic [Na+]. The inhibition of this improvement by amiloride suggests that calcium influx through the sarcolemna could be the major mechanism of this effect.