Radial To Dorsalis Pedis Arterial Pressure Gradient During Cardiopulmonary Bypass

Objective: To observe the radial to dorsalis pedis arterial pressure gradient during cardiopulmonary bypass,and discuss its potential mechanism.Methods:Thirty-four patients undergoing cardiac surgery were studied. Surgical procedures include aortic and mitral valve replacements, and combinations of these. Patients with arteriosclerosis obliterans were excluded. Anesthesia was induced and maintained with 10μg (k g?h) fentanyl and 0.2 mg (k g? h) diazepam with vecuronium for muscle relaxation. After CPB, a 1:l dopamine-dobutamine mixture was administered to all patients at a rate of 5-10μg (k g?min) to maintain cardiac index (CI). The perfusion flow during CPB was nonpulsatile and was regulated to between 2.2 and 2.4 L.min-1.m-2. The mean radial arterial pressure was maintained between 50 and 70 mm Hg by using single injections of 0.05 mg norepinephrine as necessary. Moderate hypothermia (rectal temperature [RT] 32°C) and a-stat blood gas management were used. The ventilatory rate was adjusted to maintain Paco2, between 35 and 40 mmHg, and the inspired oxygen concentration was fixed at 100%.Pressures in the left radial and left Dorsalis Pedis arteries were measured through two 5-cm, 20-gauge plastic cannulae, which were connected to a transducer via three-way stopcocks and a 160-cm rigid pressure monitoring line. The midaxillary level was used as the zero point, and transducers were zeroed prior to each measurement. Radial arterial pressure and dorsalis pedis arterial pressure were recorded at seven time points before, during, and after the CPB procedure: T1) pre-bypass, after anesthesia induction; T2) at initiation of CPB; T3) 5min after weaning from CPB support T4) 10 min after weaning from CPB support; T5) 20 min after weaning from CPB support; T6) 30 min after weaning from CPB support; and T7) at sternal closure. We definedΔP as the radial to dorsalis pedis artery mean pressure gradient. All patients were divided into two subgroups according toΔP at T4: High-P (pressure gradient≥10 mm Hg) or Low-P (pressure gradient <10 mm Hg). Additional variables measured concomitantly with blood pressure were RT, hematocrit (Hct), cardiac output (CO), and central venous pressure. Skinsurface temperatures were also monitored on the palm of the same hand on which the radial artery pressure was monitored. There were no intravenous infusion catheters in this arm.Results: The doses of the dopamine/dobutamine mixture were not different between the two groups. There was no linear correlation between the pressure gradient and the dose of dopamine/dobutamine mixture after CPB. After induction of anesthesia and during partial CPB,ΔP values were not different. In High-P, a significantΔP developed just after weaning from CPB support (13.1±8.01 vs 3.25±5.15 mm Hg in Low-P,P≤0.05) and remained high until sternal closure (12.1±5.38 vs -3±12.0 mm Hg,P≤0.05).There were no significant RT or room temperature differences between the two groups throughout the study, but the palm temperature was significantly lower in High-P patients than in Low-P patients at T4,T5,T6,T7. Furthermore, there was a significant, positive, linear correlation betweenΔP at sternal closure and rectal to palm temperature (r =0.70,P≤0.05). There were no significant and differences between the two groups with regard to Hct throughout the operation, and the dose of norepinephrine used during CPB (0.20±0.23,median 0.1 mg vs 0.23±0.22, median 0.15 mg in the High-p and Low-P groups, respectively).Conclusion: The radial to dorsalis pedis arterial pressure gradient has been observed after cardiopulmonary bypass. Arterial vasodilation and vasoconstriction have been considered as causes for this gradient.