Effect of Topically-applied Milrinone or Nitroglycerin on Internal Mammary Artery Free Flow

Fifty consecutive patients undergoing elective primary coronary artery bypass grafting were enrolled in this study. Patients were randomly assigned to receive the topical application of one of three agents: milrinone (Baxter Pharmaceuticals, Ahmedabad, India) 10 mg in 20 ml of dextrose 5%, nitroglycerin (Caspian Tamin Pharmaceutical, Guilan, Iran) 10 mg in 20 ml of normal saline, or normal saline (0.9% sodium chloride solution) as control.

All surgical procedures and measurements were carried out by a single surgeon who was blinded to the topical agent which was applied. Each patient enrolled in the study gave a written informed consent, and the study protocol conforms to the ethical guidelines of the 1975 Declaration of Helsinki as reflected in a priori approval by the local human research committee.

Operative Technique After sternal incision, the skeletonized left IMA was harvested from the subclavian artery to its bifurcation with low-powered electrocautery, and major collaterals were ligated with hemoclips. Following systemic heparinization (300 units/kg to achieve an activated clotting time target of 480 seconds), the IMA was divided proximal to its bifurcation. The first IMA flow (flow 1) was measured by reading the volume of blood ejected from the tip of the freely bleeding IMA through a one-minute period. Heart rate, mean arterial pressure and central venous pressure were documented at the same time. The tip of the artery was occluded with a bulldog clamp, and a swab which was soaked with the selected vasodilator at room temperature (18.0 to 20.0 degrees C) was wrapped around the IMA, and was left undisturbed until the second set of measurements.

Cannulation for cardiopulmonary bypass was carried out, and the pump was used to transfuse or drain blood from the patient in order to restore the mean arterial and central venous pressures as nearly as possible to the previous values. Systemic vasopressors or vasodilators were not used. The IMA was then unwrapped and the second IMA flow (flow 2) was measured in the same way. Time, heart rate, and mean arterial and central venous pressures were also recorded.