Proper dosage of fentanyl for open heart surgery performed under CPB without cardioplegia

Objective To determine the proper dosage of fentanyl for open heart surgery performed under cardiopulmonary bypass (CPB) without aortic cross-clamping and cardioplegia.Methods Twenty-seven ASA Ⅰ -H patients (10 male, 17 female) with fairly good cardiac function (NYHA Ⅰ - Ⅱ) scheduled for surgical repair of atrioseptal defect ( ASD) or ventricular septal defect (VSD) or mitral valve replacement (MVR) were studied. Age ranged from 18 to 44 years and body weight from 35 to 58 kg. The patients were randomly divided into three fentanyl dosage groups: group Ⅰ 10μkg ; group II 30 μg kg-1 and group Ⅲ 50 μg kg-1. Premedication consisted of intramuscular pethidine 1-2 mg kg-1 and scopolamine 0.05-0.06 mg kg-1 . Anesthesia was induced with midazolam 0.2 mg kg-1 and fentanyl 5 μg kg-1 . Tracheal intubation was facilitated with vecuronium 0.15 mg g-1 . The patients were mechanically ventilated (Vr 8-10 ml kg-1 ,F 10-12 bpm,FiO2 100% ). The rest of the total dose of fentanyl (5 μg kg-1 in group I , 25 μg kg-1 in group II , 45 μg kg-1 in group III) was infused after induction of anesthesia until the initiation of CPB, supplemented with inhalation of 0.6 % isoflurane. During CPB propofol was infused at 5 mg kg-1 h-1 . after discontinuation of CPB, again 0.6% isoflurane was inhaled until the end of surgery. Vecuronium 0.05 mg kg was given every 25-30 min during operation. EGG, HR, BP, CVP, SpO2, PET CO2 and body temperature (naso-pharyngeal and rectal) were continuously monitored during operation. Arterial blood samples were obtained before anesthesia (T0), 5 min after tracheal intubation (T, ) , immediately after thoracotomy (T2) , immediately before CPB (T3), 15 min after CPB was initiated (T4) , 10 min after termination of CPB (T5) and 5 min after chest was closed (T6) for blood gas analyses and determination of blood electrolytes and acid-base balance and blood concentrations of glucose, ACTH, angiotensin Ⅱ (A- Ⅱ ) and cortisol. Time of emergence from anesthesia and extubation were recorded.Results The demographic data, including age and body weight, CPB time and duration of surgery were comparable among the three groups. There were no significant changes in SpO2 , PETCO2 , body temperature, blood gases and electrolytes during operation in the three groups. MAP decreased significantly during CPB. The blood glucose, ACTH, A- Ⅱ and cortisol concentrations increased significantly during and after CPB as compared with the preanesthetic baseline (T0 ) ( P 0.05) and were higher in group Ⅰ than those in group II and Ⅲ ( P 0.01) . Time of emergence from anesthesia and extubation were significantly shorter in group Ⅰ than those in group Ⅱand H ( P 0.05) Conclusion Fentanyl 30 μg · kg -1 is appropriate for cardiac surgery performed under CPB without cardioplegia according to the hemodynamic and stress responses induced and recovery from anesthesia.