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Ann Thorac Surg 2004;77:908-912
© 2004 The Society of Thoracic Surgeons
a Department of Cardiovascular Surgery, Fukuoka, Japan
b Department of Neonatal Cardiology, Fukuoka Children's Hospital, Fukuoka, Japan
Accepted for publication September 5, 2003.
* Address reprint requests to Dr Kado, Department of Cardiovascular Surgery, Fukuoka Children's Hospital, 2-5-1 Tojin-machi, Chuo-ku, Fukuoka 810-0063, Japan
e-mail: kado{at}pluto.dti.ne.jp
| Abstract |
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METHODS: Twenty-seven patients with hypoplastic left heart syndrome who underwent the Norwood procedure from June 1998 to February 2002 were managed with the following low-resistance strategy. Intraoperative high-flow and low-resistance cardiopulmonary bypass was achieved with total avoidance of circulatory arrest and a large dose of chlorpromazine. In weaning from the bypass, pulmonary vascular resistance was maximally decreased by inspired oxygen fraction (100%), inhaled nitric oxide (20 ppm), and nitroglycerin (2 to 4 µg/kg/min). Then pulmonary blood flow was determined by adjusting the systemic to pulmonary shunt. Postoperatively, with continuous infusion of chlorpromazine and nitroglycerin as a systemic and pulmonary vasodilator, the inspired oxygen fraction and inhaled nitric oxide were tapered as the arterial oxygen saturation improved.
RESULTS: In most patients, inhaled nitrous oxide and inspired oxygen fraction were weaned within 3 days. The postoperative course was stable with minimum changes in circulatory and respiratory status for the survivors. Patients were extubated on a median of 6 postoperative days. Early mortality was 11.1% (3 of 27), and none of the patients died of hemodynamic deterioration.
CONCLUSIONS: The low resistance strategy is a simple and useful method for perioperative management of the Norwood procedure, minimizing fluctuation in both pulmonary and systemic vascular resistance and maintaining stable circulatory and respiratory status.
| Introduction |
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| Patients and methods |
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The low resistance strategy
Intraoperative management
A large dose of chlorpromazine (4.6 ± 1.8 mg/kg) was used as an
-blocker during the cardiopulmonary bypass [6, 7]. Pump flow rate was 168.9 ± 12.8 mL/kg/min, and the lowest rectal temperature was 29.5 ± 1.1C°. Thus, high-flow, low-resistance and moderate hypothermia cardiopulmonary bypass was achieved with complete avoidance of deep hypothermic circulatory arrest that contributes to keep systemic vascular resistance low. In addition, dilution ultrafiltration was routinely used during the bypass. In weaning from the cardiopulmonary bypass after peripheral temperature was completely rewarmed, pulmonary vascular resistance was maximally decreased with oxygen (100%), nitric oxide gas inhalation (20 ppm), and nitroglycerin (2 to 4 µg/kg/min). Under these conditions, pulmonary artery flow was adjusted at the target systolic blood pressure of 60 to 65 mm Hg and arterial oxygen saturation (SaO2) of 75% to 80%. In patients with a RV-PA conduit, the conduit was banded or partially clipped (n = 14) to reduce the blood flow or another modified Blalock-Taussig shunt was added (n = 2) to increase the blood flow. In 1 patient with modified Blalock-Taussig shunt, a stitch was placed on the inferior surface of the innominate artery just proximal to the graft anastomosis to reduce the shunt flow. Hematocrit was kept in 45% to 50%. The sternum was left open in all but 1 patients.
Postoperative management
In the intensive care unit, heart rate, systemic blood pressure, right atrial pressure, and pulse oximetry saturation (Spo2) were monitored continuously. Arterial blood gas analysis including pH, Po2, Pco2, SaO2, HCO3-, base excess, hematocrit, electrolytes, blood glucose, and more recently, lactate level were repeated every 30 to 60 minutes for the first 24 hours, and as needed afterwards. Patients were sedated and paralyzed with fentanyl and vecuronium for 2.3 ± 1.9 days. Commonly used inotropic agents were dopamine (3 to 10 µg/kg/min), dobutamine (3 to 10 µg/kg/min), and epinephrine (0.05 to 0.2 µg/kg/min). Chlorpromazine was continuously used as a systemic vasodilator [6]. Inspired oxygen fraction and inhaled nitrous oxide were tapered as SaO2 increased constantly since admission to the intensive care unit. Nitroglycerin was continuously used as a pulmonary vasodilator [8]. In closing the sternum on the median of postoperative day 3, pulmonary artery flow was readjusted by loosening the band or removing the clip from the conduit (n = 6) or tightening the band of the conduit (n = 1). Peritoneal dialysis was applied in 24 patients (88.9%) to correct water balance and electrolytes.
| Results |
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| Comment |
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Deep hypothermic circulatory arrest is widely used in the Norwood procedure, but this procedure has been reported to cause an increase in pulmonary vascular resistance [1113] postoperatively. In addition, Tweddell and coworkers [14] found that systemic vascular resistance was also elevated after the Norwood procedure using deep hypothermic circulatory arrest. Moreover, Tokunaga and coworkers [15] demonstrated that sympathetic nerve activity and systemic vascular resistance significantly increased immediately after deep hypothermic circulatory arrest in an animal model. We have developed a new cardiopulmonary bypass technique that enables us to completely avoid deep hypothermic circulatory arrest, and we have been using this technique with the Norwood procedure [4, 5]. In this perfusion technique, high-flow, low-resistance, and moderate hypothermic perfusion can be achieved with a high dose of chlorpromazine as a systemic vasodilator [6]. We also adopt routine use of dilution ultrafiltration during the bypass and peritoneal dialysis after the operation expecting their beneficial effects on removing inflammatory substances from the blood, which may increase vascular resistance [16, 17].
Several reports have acknowledged the beneficial effects of systemic vasodilator on postoperative management of the Norwood procedure [10, 18, 19]. Phenoxybenzamine was reported to be useful in reducing and stabilizing systemic vascular resistance as well as improving systemic oxygen delivery [14, 18]. We have been using chlorpromazine as a systemic vasodilator for its
-blocking effect as well as a sedative in neonatal open-heart surgery. Administration of chlorpromazine during the operation effectively decreases systemic vascular resistance in an arterial switch operation [6]. After the Norwood procedure, we also recognized the beneficial effects of continuous infusion of chlorpromazine on keeping low and less variable systemic vascular resistance and reducing afterload of the volume-overloaded right ventricle. Tweddell and coworkers [18] reported that phenoxybenzamine effectively decreased systemic vascular resistance to achieve stable Qp/Qs after the Norwood operation. However, we aim to achieve more invariable Qp/Qs by stabilizing pulmonary vascular resistance in addition to systemic vascular resistance in our low resistance strategy.
In patients with HLHS, pulmonary vascular resistance is elevated due to high pulmonary blood flow and high pulmonary artery pressure preoperatively, and long-lasting cardiopulmonary bypass can contribute the further elevation of pulmonary vascular resistance [2022]. The recovery from this elevated pulmonary vascular resistance alters the balance between Qp and Qs very easily in a single ventricle physiology early after the operation. In order to reduce the range for pulmonary vascular resistance to fluctuate, pulmonary vasculature was dilated maximally at weaning from cardiopulmonary bypass with inhaled nitrous oxide and a high concentration of inspired oxygen as potent pulmonary vasodilators [23]. Under this condition, pulmonary blood flow was determined by adjusting systemic to pulmonary shunt. This is a totally opposite conception to the conventional management, in which pulmonary vascular resistance has to be kept high in order to prevent pulmonary overcirculation. After all, postoperative management in the intensive care unit was simply to taper inhaled nitrous oxide and inspired oxygen fraction as SaO2 improved, with continuous drip of chlorpromazine to keep systemic vascular resistance low. This one-directional treatment facilitated postoperative management of the Norwood procedure. Frequent ventilator manipulation was rarely required.
We tapered inhaled nitrous oxide and inspired oxygen fraction as SaO2 steadily improved after the operation. However, in a parallel circulation, SaO2 does not reflect Qp/Qs [24]. The rise in SaO2 may indicate two situations: one is when the value of Qp/Qs is high because of decreasing pulmonary vascular resistance or increasing systemic vascular resistance that results in pulmonary overcirculation and systemic hypoperfusion. In this situation, weaning of pulmonary vasodilators is the right way to keep Qp/Qs balanced. The other is when total cardiac output increases with Qp/Qs well-balanced. In this situation, tapering of pulmonary vasodilators does not make sense, but we did not observe significant hemodynamic changes or progress in metabolic acidosis during the postoperative course, suggesting that there was no negative influence of tapering pulmonary dilators on the Norwood circulation in our series.
Currently, some institutions adopt continuous mixed venous saturation monitoring in post-Norwood management [18, 24]. With a value of mixed venous saturation, Qp/Qs, cardiac output, and vascular resistances can be assumed, and they seem to make post-Norwood management easier.
In conclusion, the low resistance strategy is a simple and useful method for perioperative management of the Norwood procedure, minimizing fluctuation in both pulmonary and systemic vascular resistance and maintaining stable circulatory and respiratory status.
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