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Stage 1 palliation of hypoplastic left heart syndrome: Implications of blood gases
Stage 1 Palliation of Hypoplastic Left Heart Syndrome: Implications of Blood Gases K. M. Strauss, MD, A. Dongas, MD, U. Hein, MD, F. Goelnitz, MD, W-R Thies, MD, PhD, T. Breymann, MD, and K. Inoue, MD, PhD Objective: To estimate ratios of pulmonary-to-systemic blood flows (Qp/Qs) after stage I palliation (Norwood operation) for hypoplastic left heart syndrome and to determine whether early postoperative death can be associated with abnormalities of Qp/Qs ratios. Design: Retrospective. Setting: University hospital. Participants: Patients who underwent stage I palliation (Norwood operation) for hypoplastic left heart syndrome (n ⴝ 76). Interventions: None. Measurements and Main Results: The results of the last intraoperative blood gas analysis were compared between patients who survived the day of operation (58 of 76) and the patients who died intraoperatively or within 4 hours after operation (18 of 76). Qp/Qs ratios were calculated using the
Fick principle from arterial and venous oxygen saturations at estimated pulmonary venous oxygen saturation of 95%. A lower arterial oxygen saturation (SaO2, 69.0 ⴞ 20.5% v 77.3 ⴞ 8.5%; p < 0.05) and more marked metabolic acidosis (pH, 7.244 ⴞ 0.115 v 7.298 ⴞ 0.095; p < 0.05; base excess, ⴚ6.8 ⴞ 4.4 v ⴚ3.0 ⴞ 4.2; p < 0.05) were observed in nonsurvivors. Calculated Qp/Qs ratios ranged between 0.2 and 6.5 in survivors and between 0.6 and 1.9 in nonsurvivors. Conclusions: Postoperative excessive pulmonary blood flow was not implicated as a cause of death based on blood gas data and Qp/Qs ratios. In nonsurvivors, low cardiac output and hypoxemia were assumed to be major problems. Copyright © 2001 by W.B. Saunders Company
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Isoflurane and fentanyl were the main anesthetics in all cases. All patients were nasotracheally intubated. For measurement of arterial blood pressure, the right radial artery and a femoral artery were usually cannulated. Comparisons of blood pressures between both arteries assessed for possible interference of blood flow (stenosis) in the corresponding artery after construction of the neoaorta. A triple-lumen 4.5F central venous catheter was placed in the right or left internal jugular vein. During cardiopulmonary bypass (CPB), isoflurane was administered through the oxygenator. After CPB, isoflurane or fentanyl and midazolam were administered. An arterial oxygen saturation (SaO2) of 75% to 85% was considered optimal in a single ventricle with parallel pulmonary and systemic circulations. By changing minute ventilation and inspiratory oxygen concentration (FIO2) and administering cardiovasoactive drugs, the goal was to keep SaO2 within this range. After surgery, patients were transferred to the intensive care unit with a tracheal tube in place. The surgical repair consisted of creation of a neoaorta, atrial septectomy, and establishment of pulmonary blood flow using a 3.5- or 4-mm polytetrafluoroethylene graft as a modified Blalock-Taussig shunt or central aortopulmonary shunt. The neoaorta was constructed using the proximal pulmonary artery, ascending aorta, and dacron vascular prosthesis. The major part of surgery was performed with deep hypothermic circulatory arrest. Arterial blood gases were obtained at the following times: (1) after induction of anesthesia, (2) immediately after the end of CPB, and (3) before the end of surgery or, in cases of intraoperative death, before the start of resuscitation or circulatory collapse. Venous blood gas analyses were not available in all patients; they were summarized separately. The Qp/Qs ratio was calculated using the Fick principle from arterial and venous SO2 as follows:
YPOPLASTIC LEFT heart syndrome (HLHS) is a group of complex cardiac anomalies in which hypoplasia or atresia of the aortic valve, the ascending aorta, the mitral valve, and the left ventricle are present. Since the early 1980s, it has been possible to perform a palliative procedure in the neonatal period by creation of a single ventricle (stage I palliation, Norwood operation) and later to divide the pulmonary and systemic circulations through the second (bidirectional Glenn shunt or hemi-Fontan procedure) and the third (Fontan procedure) operations. Although the results of these procedures have improved significantly, the operative mortality, especially of the Norwood operation, is still high compared with other cardiac operations in the same age group.1-3 The early postoperative course after the Norwood operation is often characterized by hemodynamic instability and sudden death. An imbalance of blood flow between the pulmonary and systemic circulations, especially an excessive pulmonary blood flow, has been emphasized as a cause of this postoperative instability.4,5 An excessive pulmonary blood flow in a single ventricle with parallel pulmonary and systemic circulation means a decrease of systemic and coronary perfusion. The consequence is circulatory collapse despite high arterial oxygen saturation. As a result, careful anesthetic management is required to optimize the ratio of pulmonary-to-systemic blood flow (Qp/Qs). Qp/Qs ratios are particularly influenced by respiratory settings and administration of cardiovasoactive agents. The purpose of this study is to present the authors’ intraoperative management for the Norwood operation and to delineate the causes of immediate postoperative death from the data on arterial blood gases. The primary question is whether an excessive pulmonary blood flow is the major cause of death. METHODS Data were collected retrospectively on 76 patients who underwent a Norwood procedure between June 1989 and July 1998. The intraoperative and postoperative courses of patients were reviewed from manual anesthetic records, intraoperative automated trend records, surgical notes, and hospital charts.
KEY WORDS: hypoplastic left heart syndrome, Norwood operation, ratio of pulmonary-to-systemic blood flow
From the Departments of Anesthesiology, Pediatric Cardiology, and Thoracic and Cardiovascular Surgery, Heart and Diabetic Center NRW, Ruhr University of Bochum, Bad Oeynhausen, Germany. Address reprint requests to K. M. Strauss, Heart and Diabetic Center NRW, Department of Anesthesiology, Georgstrasse 11, 32545 Bad Oeynhausen, Germany. E-mail: [email protected] Copyright © 2001 by W.B. Saunders Company 1053-0770/01/1506-0013$35.00/0 doi:10.1053/jcan.2001.28318
Journal of Cardiothoracic and Vascular Anesthesia, Vol 15, No 6 (December), 2001: pp 731-735
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Qs ⫽ VO 2 /共systemic artery SO 2 ⫺ mixed venous SO 2 兲共Hb兲 ⫻ 共1.39兲
Table 2. Preoperative Patient Characteristics
(1)
Qp ⫽ VO 2 /共pulmonary venous SO 2 ⫺ pulmonary artery SO 2 兲 Age (d)
⫻ 共Hb兲共1.39兲
(2)
where VO2 is oxygen consumption and Hb is hemoglobin concentration (g/dL). Dissolved oxygen content was neglected. Because systemic SaO2 equals pulmonary artery SO2 in a single ventricle with parallel systemic and pulmonary circulations, equations (1) and (2) can be combined as follows, assuming pulmonary venous SO2 to be 95%: Qp/Qs ⫽ 共arterial SO 2 ⫺ venous SO 2 兲/共95 ⫺ arterial SO 2 兲 Continuous values are expressed as mean ⫾ SD. Comparisons of values between 2 groups were done with Student’s t-test for unpaired data and chi-square test; p values ⬍ 0.05 were considered to be statistically significant. RESULTS
There were 48 patients who showed the typical form of HLHS and 28 patients who had other types of cardiac anomalies but required a Norwood procedure. The patients of the latter group had a variety of anomalies (Table 1). The common characteristic features of these patients were obstruction of the aortic outflow tract, hypoplasia or interruption of the aortic arch, and underdevelopment or hypofunction of the ventricle for systemic circulation. Most importantly, a biventricular repair was not possible in these patients. The patients with the typical form of HLHS were 20 ⫾ 13 days old (median, 15 days old) and 3.6 ⫾ 0.5 kg (median, 3.6 kg), whereas the patients with other types of cardiac anomalies were 75 ⫾ 70 days old (median, 41 days old) and weighed 4.0 ⫾ 0.9 kg (median, 3.8 kg) (Table 2). The former patients were significantly younger (p ⬍ 0.001) and weighed less (p ⬍ 0.05). Of the patients, 71% with the typical form of HLHS and 79% with other types of cardiac anomalies were breathing room air (p ⫽ NS). The trachea was preoperatively intubated in 69% and in 50% of the patients (p ⫽ NS). The patients with the typical form of HLHS were significantly more likely to require prostaglandin E1 inTable 1. Classification of Patients by Anatomic Diagnosis Diagnosis
n
Typical form of hypoplastic left heart syndrome 48 DORV, hypoplastic LV, MA, MS, AS 6 DILV, TGA, hypoplastic RV, hypoplastic aorta 6 VSD, AS, IAA, hypoplastic aortic arch 5 TGA, hypoplastic RV, TCA, IAA, ISTHA, hypoplastic aortic arch 3 AVSD, small LV, AS 2 VSD, IAA, hypoplastic ascending aorta 2 Hypocontractile LV (endocardiofibroelastosis), AS, AA 2 TCA, L-TGA, hypoplastic RV, hypoplastic aortic arch 1 DILV, L-TGA, rudimentary RV, MS, ISTHA, hypoplastic aortic arch 1 Abbreviations: DORV, double-outlet right ventricle; LV, left ventricle; MA, mitral atresia; MS, mitral stenosis; AS, aortic stenosis; DILV, double-inlet left ventricle; TGA, transposition of the great arteries; RV, right ventricle; VSD, ventricular septal defect; IAA, interrupted aortic arch; TCA, tricuspid atresia; ISTHA, coarctation of the aortic isthmus; AVSD, atrioventricular septal defect; AA, aortic atresia.
Weight (kg) Sex (male) FIO2 Room air Mechanical ventilation PGE1 infusion Inotropic support
Hypoplastic Left Heart Syndrome (n ⫽ 48)
Other Complex Anomalies (n ⫽ 28)
15 (4-69) 20 ⫾ 13 3.6 (2.5-4.7) 3.6 ⫾ 0.5 25 (52%) 0.21 (0.21-0.85) 34 (71%) 33 (69%) 46 (96%) 21 (44%)
41 (7-254) 75 ⫾ 70 3.8 (2.6-6.6) 4.0 ⫾ 0.9 17 (61%) 0.21 (0.21-0.80) 22 (79%) 14 (50%) 15 (54%) 4 (14%)
p
⬍0.001 ⬍0.05 NS NS NS ⬍0.001 ⬍0.01
NOTE. Data are shown as median and range, mean ⫾ SD, or number of patients; p value indicates comparison between the typical form of hypoplastic left heart syndrome and other complex anomalies. Abbreviations: NS, not statistically significant; FIO2, inspiratory oxygen concentration; PGE1, prostaglandin E1.
fusion for ductal patency and inotropic support than the patients with other types of cardiac anomalies (96% v 54%; p ⬍ 0.001 and 44% v 14%; p ⬍ 0.01). For induction and maintenance of anesthesia, fentanyl was given in small repetitive doses (3 to 6 g/kg). The total dose of fentanyl was ⬍15 g/kg. The inspiratory concentration of isoflurane was kept between 0.4% and 1.5%. Additionally, 0.1 to 0.3 mg/kg of midazolam or 1 to 2 mg/kg of ketamine or both were administered at induction of anesthesia and intermittently after induction. There were no differences in intraoperative characteristics between patients with the typical form of HLHS and patients with other types of cardiac anomalies, so intraoperative data are considered together. The CPB duration including circulatory arrest time was 197 ⫾ 45 minutes (Table 3). Circulatory arrest lasted 74 ⫾ 22 minutes. Nasopharyngeal and rectal temperatures were 16.2 ⫾ 2.1°C and 19.8 ⫾ 2.2°C before the start of circulatory arrest. After CPB, 99% of patients required inotropic support with dopamine (5 to 10g/kg/min); 86%, epinephrine (0.05 to 0.2 g/kg/min); and 62%, phosphodiesterase III inhibitor (maintenance dose, enoximone, 5 to 15 g/kg/min, or milrinone, 0.25 to 0.75 g/kg/min) (Table 4). Arterial blood gas results and acid-base balance are shown in Table 5 separately for patients who survived the day of operation (survivors, n ⫽ 58) and for those who died intraoperatively or on the day of surgery (nonsurvivors, n ⫽ 18). Of the
Table 3. Surgical Characteristics Operation Time
Total CPB Circulatory arrest
min
Temperature
197 ⫾ 45 Nasopharyngeal 198 (90-329) 74 ⫾ 22 Rectal 77 (26-118)
°C
16.2 ⫾ 2.1 16.2 (11.8-21.4) 19.8 ⫾ 2.2 19.8 (14.4-25.0)
NOTE. Data are shown as mean ⫾ SD and as median and range. The values for temperature refer to those before the start of circulatory arrest. Abbreviation: CPB, cardiopulmonary bypass.
STAGE I PALLIATION OF HLHS AND BLOOD GASES
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Table 4. Inotropic Support After Cardiopulmonary Bypass Drug
n
Dopamine Epinephrine Phosphodiesterase III inhibitor
75 (99%) 65 (86%) 47 (62%)
18 nonsurvivors, 10 patients died intraoperatively, and 8 died postoperatively in the intensive care unit within 4 hours after the end of operation. Slight metabolic alkalosis was observed in both groups directly after induction of anesthesia. After CPB, acidosis and low SaO2 developed in both groups. Comparisons between 2 groups showed no difference after induction of anesthesia and directly after CPB, but in the last blood gas analysis, a metabolic acidosis and low SaO2 were more evident in the nonsurvivors. In the last blood gas analysis, arterial blood pH of the nonsurvivors was 7.244 ⫾ 0.115 compared with 7.298 ⫾ 0.095 of the survivors (p ⬍ 0.05), base excess was ⫺6.8 ⫾ 4.4 versus ⫺3.0 ⫾ 4.2 (p ⬍ 0.01), and SaO2 was 69.0 ⫾ 20.5% versus 77.3 ⫾ 8.5% (p ⬍ 0.05). Data from central venous SO2 (assumed to be equivalent to mixed venous SO2) were not available for all patients but were available in 33 of the survivors and in 9 of the nonsurvivors because venous blood was taken for gas analysis at the discretion of anesthesiologists. For these patients, Qp/Qs ratio was calculated assuming pulmonary venous SO2 to be 95%. Calculated Qp/Qs ratio was 0.2 to 6.5 in survivors and 0.6 to 1.9 in nonsurvivors. In 30% (10 of 33) of the survivors, Qp/Qs ratio was ⬎2.0 and in 12% (4 of 33) was ⬍0.5, whereas in all nonsurvivors Qp/Qs ratio was 0.5 to 2.0. A deviation of Qp/Qs ratio was not a major problem in patients who died on the day of operation if Qp/Qs ratio between 0.5 and 2.0 is assumed to be acceptable. Venous SO2 in the last blood gas analysis was 50.0 ⫾ 11.8% in the survivors and 40.2 ⫾ 16.1% in the nonsurvivors (p ⬍ 0.05). DISCUSSION
Because a single ventricle with parallel systemic and pulmonary circulations exists after stage I palliation for HLHS, it is crucial for anesthetic care to optimally balance blood flows in these 2 circulations. According to some authors,4,5 emphasis has been placed on excessive pulmonary blood flow as a cause of postoperative hemodynamic instability. Large pulmonary blood flow results in high SaO2 but diminishes systemic perfusion, including coronary blood flow, which leads to circulatory collapse. Consequently, addition of carbon dioxide into inspiratory gas has been advocated6-8 because carbon dioxide is a strong pulmonary vasoconstrictor with minimal effect on systemic vascular resistance.9-11 The present study shows that frequent problems encountered in nonsurvivors were low arterial and low venous SO2 and metabolic acidosis. The last blood gas analysis in the patients who died showed lower SaO2 (69.0% v 77.3%; p ⬍ 0.05), lower venous SO2 (40.2% v 50.0%; p ⬍ 0.05), and more negative base excess (⫺6.8 v ⫺3.0; p ⬍ 0.01) compared with the patients who survived. A low SaO2 argues against a too high intraoperative Qp/Qs ratio to be a cause of death. Probably, low cardiac output and hypoxemia (pulmonary gas exchange abnormalities or low pulmonary
blood flow or both) played a significant role in the patients who died. The authors could not confirm previous work in which frequent postoperative circulatory problems were attributed to excessive pulmonary blood flow. According to a mathematical model of Barnea et al,12 the optimal Qp/Qs ratio is ⬍1.0. The optimal Qp/Qs ratio is the one at which systemic oxygen availability becomes maximal. The authors studied the effect of varying the Qp/Qs ratio on oxygen availability, systemic SaO2 and mixed venous SO2 at various hypothetical pulmonary venous SO2 and cardiac output values. According to these calculations, oxygen availability increases initially with increasing Qp/Qs ratio, reaches a maximum at the optimal Qp/Qs ratio, then falls. Systemic SaO2 increases with increasing Qp/Qs ratio continuously, first steeply, then gradually, and approaches the upper limit. Systemic SaO2 is not a predictive parameter for oxygen availability. In contrast, changes of mixed venous SO2 correlate well with changes of oxygen availability. Venous SO2 increases first with increasing Qp/Qs ratio, reaches a maximum when the optimal Qp/Qs ratio is reached, then falls. Correlations between venous SO2 and Qp/Qs ratio and between venous SO2 and oxygen availability were shown in an animal experiment.13 In that study, the optimal Qp/Qs ratio was at or slightly ⬎1.0. From clinical experience, optimal Qp/Qs ratio is considered to be 1.0.14,15 Rossi et al5 studied postoperative blood gas analyses in 13 patients who underwent the Norwood operation. Two patients died within 24 hours after operation. Rossi et al5 calculated a Qp/Qs ratio assuming pulmonary venous SO2 to be 96%. In that study, 6 of 13 patients had a Qp/Qs ratio of ⬎2.0 directly after arrival in the intensive care unit. In the patients who survived,
Table 5. Comparison of Arterial Blood Gas Data Between Survivors and Nonsurvivors Study Period
After induction pH PaCO2 (mmHg) PaO2 (mmHg) SaO2 (%) BE Hemoglobin (g/dL) After CPB pH PaCO2 (mmHg) PaO2 (mmHg) SaO2 (%) BE Hemoglobin (g/dL) Last blood gas pH PaCO2 (mmHg) PaO2 (mmHg) SaO2 (%) BE Hemoglobin (g/dL)
Survivors (n ⫽ 58) Nonsurvivors (n ⫽ 18)
p
7.460 ⫾ 0.078 41.4 ⫾ 8.2 109.6 ⫾ 95.9 95.2 ⫾ 5.4 5.1 ⫾ 4.6 12.5 ⫾ 1.6
7.492 ⫾ 0.084 38.7 ⫾ 10.0 109.5 ⫾ 85.7 95.1 ⫾ 5.8 5.2 ⫾ 3.4 13.1 ⫾ 1.5
NS NS NS NS NS NS
7.294 ⫾ 0.091 43.4 ⫾ 9.3 40.1 ⫾ 9.8 72.6 ⫾ 13.5 ⫺5.3 ⫾ 3.3 11.5 ⫾ 1.5
7.278 ⫾ 0.101 41.2 ⫾ 9.4 40.5 ⫾ 14.2 70.0 ⫾ 17.5 ⫺7.1 ⫾ 4.3 11.7 ⫾ 1.8
NS NS NS NS NS NS
7.298 ⫾ 0.095 48.4 ⫾ 9.1 43.5 ⫾ 10.1 77.3 ⫾ 8.5 ⫺3.0 ⫾ 4.2 12.1 ⫾ 2.0
7.244 ⫾ 0.115 47.4 ⫾ 11.5 42.8 ⫾ 15.5 69.0 ⫾ 20.5 ⫺6.8 ⫾ 4.4 12.0 ⫾ 1.6
⬍0.05 NS NS ⬍0.05 ⬍0.01 NS
NOTE. Data are shown as mean ⫾ SD; p value indicates comparison between survivors and nonsurvivors. Abbreviations: NS, not statistically significant; CPB, cardiopulmonary bypass; BE, base excess.
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the Qp/Qs ratio changed during the postoperative course and was between 0.5 and 2.0 at 24 hours postoperatively. At the same time, arteriovenous SO2 difference was ⱕ25%. Mixed venous SO2 was ⱖ50%. From these data, the authors defined as acceptable a Qp/Qs ratio of ⬍2.0 and an arteriovenous SO2 difference of ⬍25%. For the present results, the authors defined an acceptable range of Qp/Qs ratio based on their data. In the present study, high Qp/Qs ratios were observed in the patients who survived the day of operation. Although Qp/Qs ratio ideally should be 1.0, it is conceivable that a wide range of Qp/Qs ratios can be tolerated. Evidence can be found in the report of Chang et al.16 They performed cardiac catheterization in patients who had undergone a Norwood operation shortly before stage II palliation and found the Qp/Qs ratio to be 0.5 to 3.5. Another explanation for this discrepancy between estimated Qp/Qs ratio and patient outcome is error in calculation of the Qp/Qs ratio. For the calculation of Qp/Qs ratio, the authors considered pulmonary venous SO2 to be 95%. At diagnostic cardiac catheterization, pulmonary venous SO2 is assumed to be equal to systemic SaO2. This assumption does not apply to patients with right-to-left shunt. A hypothetical value (95%) of pulmonary venous SO2 was used in this study. Pulmonary venous SO2 might be lower than 95% after CPB, however, because of ventilation-perfusion inequality or diffusion impairment or both. If a true pulmonary venous SO2 is lower than the theoretical value of 95%, Qp/Qs ratio will be underestimated with the above-mentioned calculation. When pulmonary venous SO2 is ⬎95%, Qp/Qs ratio will be overestimated. Determination of Qp/Qs ratio might be difficult in the clinical setting. The application of another marker for oxygen delivery, venous SO2, has been emphasized.5,13,17 Because venous SO2 correlates well with oxygen availability, therapy should be aimed to increase venous SO2. Positive inotropic drugs were administered in all but one patient. Dopamine was the drug of the first choice (75 of 76 patients). Most patients also received epinephrine (65 of 76) or phosphodiesterase III inhibitor (47 of 76). The Children’s Hospital of Phil-
adelphia group reported that positive inotropic drugs were rarely necessary after the Norwood operation.14,18 According to Hansen and Hickey,19 however, 70% of patients needed positive inotropic drugs. The University of Michigan group advised the administration of dopamine for high pulmonary blood flow to raise pulmonary vascular resistance.20 According to Jonas et al,4 high doses of positive inotropic drugs should not be given in cases of increased pulmonary blood flow because positive inotropic drugs increase systemic vascular resistance, which results in a further increase of systemic-to-pulmonary shunt. Riordan et al21 studied the effects of dopamine, dobutamine, and epinephrine on Qp/Qs ratio in an animal model of univentricular circulation. The 3 drugs increased cardiac output but had different effects on Qp/Qs ratio and oxygen delivery. Although dopamine (5 and 15 g/kg/min) had no effects on Qp/Qs ratio, epinephrine (0.05 and 0.1 g/kg/min) increased oxygen delivery with decline of Qp/Qs ratio. Dobutamine (5 and 15 g/kg/min) caused an increase of Qp/Qs ratio and concomitantly a decrease of oxygen delivery. It is questionable if these results are transferable to humans, but they indicate at least that positive inotropic drugs may not work similarly on the Qp/Qs ratio. Knowledge of venous SO2 is important for judgment of the effects of drugs on oxygen delivery. One of the crucial points in the anesthetic management for the Norwood operation lies in maintenance of maximal oxygen delivery by optimally balancing Qp/Qs ratio. In a clinical setting, the goal should be achievement of optimal arterial and venous SO2 via manipulation of respiratory parameters or administration of cardiovasoactive drugs. The authors considered an SaO2 of 75% to 85%, a mixed venous SO2 of ⬎50%, and an arteriovenous SO2 difference of ⬍25% as target values. In the present study, excessive postoperative pulmonary blood flow was not implicated as a cause of death from blood gas data and Qp/Qs ratios derived from arterial and venous SO2. In nonsurvivors, low cardiac output and hypoxemia (pulmonary gas exchange abnormalities or low pulmonary blood flow or both) are assumed to be major problems.
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8. Gullquist SD, Schmitz ML, Hannon GD, et al: Carbon dioxide in the inspired gas improves early postoperative survival in neonates with congenital heart disease following stage I palliation. Circulation 86: I360, 1992 (suppl 1) 9. Morray JP, Lynn AM, Mansfield PB: Effect of pH and PCO2 on pulmonary and systemic hemodynamics after surgery in children with congenital heart disease and pulmonary hypertension. J Pediatr 113: 474-479, 1988 10. Viitanen A, Salmenpera¨ M, Heinonen J, Hynynen M: Pulmonary vascular resistance before and after cardiopulmonary bypass: The effect of PaCO2. Chest 95:773-778, 1989 11. Mora GA, Pizzaro C, Jacobs ML, Norwood WI: Experimental model of single ventricle: Influence of carbon dioxide on pulmonary vascular dynamics. Circulation 90:II43-II46, 1994 (part 2) 12. Barnea O, Austin EH, Richman B, Santamore WP: Balancing the circulation: Theoretic optimization of pulmonary/systemic flow ratio in hypoplastic left heart syndrome. J Am Coll Cardiol 24:1376-1381, 1994 13. Riordan CJ, Randsbaek F, Storey JH, et al: Balancing pulmonary and systemic arterial flows in parallel circulations: The value of monitoring systemic venous oxygen saturation. Cardiol Young 7:7479, 1997
STAGE I PALLIATION OF HLHS AND BLOOD GASES
14. Nicolson SC, Steven JM, Jobes DR: Hypoplastic left heart syndrome, in Nichols DG, Cameron DE, Greely WJ, et al (eds): Critical Heart Disease in Infants and Children. St Louis, MO, Mosby, 1995, pp 863-884 15. Norwood WI: Hypoplastic left heart syndrome, in Sabiston DC Jr, Spencer FC (eds): Surgery of the Chest. Philadelphia, PA, Saunders, 1995, pp 1659-1666 16. Chang AC, Farrell PE Jr, Murdison KA, et al: Hypoplastic left heart syndrome: Hemodynamic and angiographic assessment after initial reconstructive surgery and relevance to modified Fontan procedure. J Am Coll Cardiol 17:1143-1149, 1991 17. Tweddell JS, Hoffman GM, Fedderly RT, et al: Patients at risk for low systemic oxygen delivery after the Norwood procedure. Ann Thorac Surg 69:1893-1899, 2000
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18. Jacobs ML, Rychik J, Murphy JD, et al: Results of Norwood’s operation for lesions other than hypoplastic left heart syndrome. J Thorac Cardiovasc Surg 110:1555-1562, 1995 19. Hansen DD, Hickey PR: Anesthesia for hypoplastic left heart syndrome: Use of high-dose fentanyl in 30 neonates. Anesth Analg 65:127-132, 1986 20. Iannettoni MD, Bove EL, Mosca RS, et al: Improving results with first-stage palliation for hypoplastic left heart syndrome. J Thorac Cardiovasc Surg 107:934-940, 1994 21. Riordan CJ, Randsbaek F, Storey JH, et al: Inotropes in the hypoplastic left heart syndrome: Effects in an animal model. Ann Thorac Surg 62:83-90, 1996
Fick principle from arterial and venous oxygen saturations at estimated pulmonary venous oxygen saturation of 95%. A lower arterial oxygen saturation (SaO2, 69.0 ⴞ 20.5% v 77.3 ⴞ 8.5%; p < 0.05) and more marked metabolic acidosis (pH, 7.244 ⴞ 0.115 v 7.298 ⴞ 0.095; p < 0.05; base excess, ⴚ6.8 ⴞ 4.4 v ⴚ3.0 ⴞ 4.2; p < 0.05) were observed in nonsurvivors. Calculated Qp/Qs ratios ranged between 0.2 and 6.5 in survivors and between 0.6 and 1.9 in nonsurvivors. Conclusions: Postoperative excessive pulmonary blood flow was not implicated as a cause of death based on blood gas data and Qp/Qs ratios. In nonsurvivors, low cardiac output and hypoxemia were assumed to be major problems. Copyright © 2001 by W.B. Saunders Company
H
Isoflurane and fentanyl were the main anesthetics in all cases. All patients were nasotracheally intubated. For measurement of arterial blood pressure, the right radial artery and a femoral artery were usually cannulated. Comparisons of blood pressures between both arteries assessed for possible interference of blood flow (stenosis) in the corresponding artery after construction of the neoaorta. A triple-lumen 4.5F central venous catheter was placed in the right or left internal jugular vein. During cardiopulmonary bypass (CPB), isoflurane was administered through the oxygenator. After CPB, isoflurane or fentanyl and midazolam were administered. An arterial oxygen saturation (SaO2) of 75% to 85% was considered optimal in a single ventricle with parallel pulmonary and systemic circulations. By changing minute ventilation and inspiratory oxygen concentration (FIO2) and administering cardiovasoactive drugs, the goal was to keep SaO2 within this range. After surgery, patients were transferred to the intensive care unit with a tracheal tube in place. The surgical repair consisted of creation of a neoaorta, atrial septectomy, and establishment of pulmonary blood flow using a 3.5- or 4-mm polytetrafluoroethylene graft as a modified Blalock-Taussig shunt or central aortopulmonary shunt. The neoaorta was constructed using the proximal pulmonary artery, ascending aorta, and dacron vascular prosthesis. The major part of surgery was performed with deep hypothermic circulatory arrest. Arterial blood gases were obtained at the following times: (1) after induction of anesthesia, (2) immediately after the end of CPB, and (3) before the end of surgery or, in cases of intraoperative death, before the start of resuscitation or circulatory collapse. Venous blood gas analyses were not available in all patients; they were summarized separately. The Qp/Qs ratio was calculated using the Fick principle from arterial and venous SO2 as follows:
YPOPLASTIC LEFT heart syndrome (HLHS) is a group of complex cardiac anomalies in which hypoplasia or atresia of the aortic valve, the ascending aorta, the mitral valve, and the left ventricle are present. Since the early 1980s, it has been possible to perform a palliative procedure in the neonatal period by creation of a single ventricle (stage I palliation, Norwood operation) and later to divide the pulmonary and systemic circulations through the second (bidirectional Glenn shunt or hemi-Fontan procedure) and the third (Fontan procedure) operations. Although the results of these procedures have improved significantly, the operative mortality, especially of the Norwood operation, is still high compared with other cardiac operations in the same age group.1-3 The early postoperative course after the Norwood operation is often characterized by hemodynamic instability and sudden death. An imbalance of blood flow between the pulmonary and systemic circulations, especially an excessive pulmonary blood flow, has been emphasized as a cause of this postoperative instability.4,5 An excessive pulmonary blood flow in a single ventricle with parallel pulmonary and systemic circulation means a decrease of systemic and coronary perfusion. The consequence is circulatory collapse despite high arterial oxygen saturation. As a result, careful anesthetic management is required to optimize the ratio of pulmonary-to-systemic blood flow (Qp/Qs). Qp/Qs ratios are particularly influenced by respiratory settings and administration of cardiovasoactive agents. The purpose of this study is to present the authors’ intraoperative management for the Norwood operation and to delineate the causes of immediate postoperative death from the data on arterial blood gases. The primary question is whether an excessive pulmonary blood flow is the major cause of death. METHODS Data were collected retrospectively on 76 patients who underwent a Norwood procedure between June 1989 and July 1998. The intraoperative and postoperative courses of patients were reviewed from manual anesthetic records, intraoperative automated trend records, surgical notes, and hospital charts.
KEY WORDS: hypoplastic left heart syndrome, Norwood operation, ratio of pulmonary-to-systemic blood flow
From the Departments of Anesthesiology, Pediatric Cardiology, and Thoracic and Cardiovascular Surgery, Heart and Diabetic Center NRW, Ruhr University of Bochum, Bad Oeynhausen, Germany. Address reprint requests to K. M. Strauss, Heart and Diabetic Center NRW, Department of Anesthesiology, Georgstrasse 11, 32545 Bad Oeynhausen, Germany. E-mail: [email protected] Copyright © 2001 by W.B. Saunders Company 1053-0770/01/1506-0013$35.00/0 doi:10.1053/jcan.2001.28318
Journal of Cardiothoracic and Vascular Anesthesia, Vol 15, No 6 (December), 2001: pp 731-735
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Qs ⫽ VO 2 /共systemic artery SO 2 ⫺ mixed venous SO 2 兲共Hb兲 ⫻ 共1.39兲
Table 2. Preoperative Patient Characteristics
(1)
Qp ⫽ VO 2 /共pulmonary venous SO 2 ⫺ pulmonary artery SO 2 兲 Age (d)
⫻ 共Hb兲共1.39兲
(2)
where VO2 is oxygen consumption and Hb is hemoglobin concentration (g/dL). Dissolved oxygen content was neglected. Because systemic SaO2 equals pulmonary artery SO2 in a single ventricle with parallel systemic and pulmonary circulations, equations (1) and (2) can be combined as follows, assuming pulmonary venous SO2 to be 95%: Qp/Qs ⫽ 共arterial SO 2 ⫺ venous SO 2 兲/共95 ⫺ arterial SO 2 兲 Continuous values are expressed as mean ⫾ SD. Comparisons of values between 2 groups were done with Student’s t-test for unpaired data and chi-square test; p values ⬍ 0.05 were considered to be statistically significant. RESULTS
There were 48 patients who showed the typical form of HLHS and 28 patients who had other types of cardiac anomalies but required a Norwood procedure. The patients of the latter group had a variety of anomalies (Table 1). The common characteristic features of these patients were obstruction of the aortic outflow tract, hypoplasia or interruption of the aortic arch, and underdevelopment or hypofunction of the ventricle for systemic circulation. Most importantly, a biventricular repair was not possible in these patients. The patients with the typical form of HLHS were 20 ⫾ 13 days old (median, 15 days old) and 3.6 ⫾ 0.5 kg (median, 3.6 kg), whereas the patients with other types of cardiac anomalies were 75 ⫾ 70 days old (median, 41 days old) and weighed 4.0 ⫾ 0.9 kg (median, 3.8 kg) (Table 2). The former patients were significantly younger (p ⬍ 0.001) and weighed less (p ⬍ 0.05). Of the patients, 71% with the typical form of HLHS and 79% with other types of cardiac anomalies were breathing room air (p ⫽ NS). The trachea was preoperatively intubated in 69% and in 50% of the patients (p ⫽ NS). The patients with the typical form of HLHS were significantly more likely to require prostaglandin E1 inTable 1. Classification of Patients by Anatomic Diagnosis Diagnosis
n
Typical form of hypoplastic left heart syndrome 48 DORV, hypoplastic LV, MA, MS, AS 6 DILV, TGA, hypoplastic RV, hypoplastic aorta 6 VSD, AS, IAA, hypoplastic aortic arch 5 TGA, hypoplastic RV, TCA, IAA, ISTHA, hypoplastic aortic arch 3 AVSD, small LV, AS 2 VSD, IAA, hypoplastic ascending aorta 2 Hypocontractile LV (endocardiofibroelastosis), AS, AA 2 TCA, L-TGA, hypoplastic RV, hypoplastic aortic arch 1 DILV, L-TGA, rudimentary RV, MS, ISTHA, hypoplastic aortic arch 1 Abbreviations: DORV, double-outlet right ventricle; LV, left ventricle; MA, mitral atresia; MS, mitral stenosis; AS, aortic stenosis; DILV, double-inlet left ventricle; TGA, transposition of the great arteries; RV, right ventricle; VSD, ventricular septal defect; IAA, interrupted aortic arch; TCA, tricuspid atresia; ISTHA, coarctation of the aortic isthmus; AVSD, atrioventricular septal defect; AA, aortic atresia.
Weight (kg) Sex (male) FIO2 Room air Mechanical ventilation PGE1 infusion Inotropic support
Hypoplastic Left Heart Syndrome (n ⫽ 48)
Other Complex Anomalies (n ⫽ 28)
15 (4-69) 20 ⫾ 13 3.6 (2.5-4.7) 3.6 ⫾ 0.5 25 (52%) 0.21 (0.21-0.85) 34 (71%) 33 (69%) 46 (96%) 21 (44%)
41 (7-254) 75 ⫾ 70 3.8 (2.6-6.6) 4.0 ⫾ 0.9 17 (61%) 0.21 (0.21-0.80) 22 (79%) 14 (50%) 15 (54%) 4 (14%)
p
⬍0.001 ⬍0.05 NS NS NS ⬍0.001 ⬍0.01
NOTE. Data are shown as median and range, mean ⫾ SD, or number of patients; p value indicates comparison between the typical form of hypoplastic left heart syndrome and other complex anomalies. Abbreviations: NS, not statistically significant; FIO2, inspiratory oxygen concentration; PGE1, prostaglandin E1.
fusion for ductal patency and inotropic support than the patients with other types of cardiac anomalies (96% v 54%; p ⬍ 0.001 and 44% v 14%; p ⬍ 0.01). For induction and maintenance of anesthesia, fentanyl was given in small repetitive doses (3 to 6 g/kg). The total dose of fentanyl was ⬍15 g/kg. The inspiratory concentration of isoflurane was kept between 0.4% and 1.5%. Additionally, 0.1 to 0.3 mg/kg of midazolam or 1 to 2 mg/kg of ketamine or both were administered at induction of anesthesia and intermittently after induction. There were no differences in intraoperative characteristics between patients with the typical form of HLHS and patients with other types of cardiac anomalies, so intraoperative data are considered together. The CPB duration including circulatory arrest time was 197 ⫾ 45 minutes (Table 3). Circulatory arrest lasted 74 ⫾ 22 minutes. Nasopharyngeal and rectal temperatures were 16.2 ⫾ 2.1°C and 19.8 ⫾ 2.2°C before the start of circulatory arrest. After CPB, 99% of patients required inotropic support with dopamine (5 to 10g/kg/min); 86%, epinephrine (0.05 to 0.2 g/kg/min); and 62%, phosphodiesterase III inhibitor (maintenance dose, enoximone, 5 to 15 g/kg/min, or milrinone, 0.25 to 0.75 g/kg/min) (Table 4). Arterial blood gas results and acid-base balance are shown in Table 5 separately for patients who survived the day of operation (survivors, n ⫽ 58) and for those who died intraoperatively or on the day of surgery (nonsurvivors, n ⫽ 18). Of the
Table 3. Surgical Characteristics Operation Time
Total CPB Circulatory arrest
min
Temperature
197 ⫾ 45 Nasopharyngeal 198 (90-329) 74 ⫾ 22 Rectal 77 (26-118)
°C
16.2 ⫾ 2.1 16.2 (11.8-21.4) 19.8 ⫾ 2.2 19.8 (14.4-25.0)
NOTE. Data are shown as mean ⫾ SD and as median and range. The values for temperature refer to those before the start of circulatory arrest. Abbreviation: CPB, cardiopulmonary bypass.
STAGE I PALLIATION OF HLHS AND BLOOD GASES
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Table 4. Inotropic Support After Cardiopulmonary Bypass Drug
n
Dopamine Epinephrine Phosphodiesterase III inhibitor
75 (99%) 65 (86%) 47 (62%)
18 nonsurvivors, 10 patients died intraoperatively, and 8 died postoperatively in the intensive care unit within 4 hours after the end of operation. Slight metabolic alkalosis was observed in both groups directly after induction of anesthesia. After CPB, acidosis and low SaO2 developed in both groups. Comparisons between 2 groups showed no difference after induction of anesthesia and directly after CPB, but in the last blood gas analysis, a metabolic acidosis and low SaO2 were more evident in the nonsurvivors. In the last blood gas analysis, arterial blood pH of the nonsurvivors was 7.244 ⫾ 0.115 compared with 7.298 ⫾ 0.095 of the survivors (p ⬍ 0.05), base excess was ⫺6.8 ⫾ 4.4 versus ⫺3.0 ⫾ 4.2 (p ⬍ 0.01), and SaO2 was 69.0 ⫾ 20.5% versus 77.3 ⫾ 8.5% (p ⬍ 0.05). Data from central venous SO2 (assumed to be equivalent to mixed venous SO2) were not available for all patients but were available in 33 of the survivors and in 9 of the nonsurvivors because venous blood was taken for gas analysis at the discretion of anesthesiologists. For these patients, Qp/Qs ratio was calculated assuming pulmonary venous SO2 to be 95%. Calculated Qp/Qs ratio was 0.2 to 6.5 in survivors and 0.6 to 1.9 in nonsurvivors. In 30% (10 of 33) of the survivors, Qp/Qs ratio was ⬎2.0 and in 12% (4 of 33) was ⬍0.5, whereas in all nonsurvivors Qp/Qs ratio was 0.5 to 2.0. A deviation of Qp/Qs ratio was not a major problem in patients who died on the day of operation if Qp/Qs ratio between 0.5 and 2.0 is assumed to be acceptable. Venous SO2 in the last blood gas analysis was 50.0 ⫾ 11.8% in the survivors and 40.2 ⫾ 16.1% in the nonsurvivors (p ⬍ 0.05). DISCUSSION
Because a single ventricle with parallel systemic and pulmonary circulations exists after stage I palliation for HLHS, it is crucial for anesthetic care to optimally balance blood flows in these 2 circulations. According to some authors,4,5 emphasis has been placed on excessive pulmonary blood flow as a cause of postoperative hemodynamic instability. Large pulmonary blood flow results in high SaO2 but diminishes systemic perfusion, including coronary blood flow, which leads to circulatory collapse. Consequently, addition of carbon dioxide into inspiratory gas has been advocated6-8 because carbon dioxide is a strong pulmonary vasoconstrictor with minimal effect on systemic vascular resistance.9-11 The present study shows that frequent problems encountered in nonsurvivors were low arterial and low venous SO2 and metabolic acidosis. The last blood gas analysis in the patients who died showed lower SaO2 (69.0% v 77.3%; p ⬍ 0.05), lower venous SO2 (40.2% v 50.0%; p ⬍ 0.05), and more negative base excess (⫺6.8 v ⫺3.0; p ⬍ 0.01) compared with the patients who survived. A low SaO2 argues against a too high intraoperative Qp/Qs ratio to be a cause of death. Probably, low cardiac output and hypoxemia (pulmonary gas exchange abnormalities or low pulmonary
blood flow or both) played a significant role in the patients who died. The authors could not confirm previous work in which frequent postoperative circulatory problems were attributed to excessive pulmonary blood flow. According to a mathematical model of Barnea et al,12 the optimal Qp/Qs ratio is ⬍1.0. The optimal Qp/Qs ratio is the one at which systemic oxygen availability becomes maximal. The authors studied the effect of varying the Qp/Qs ratio on oxygen availability, systemic SaO2 and mixed venous SO2 at various hypothetical pulmonary venous SO2 and cardiac output values. According to these calculations, oxygen availability increases initially with increasing Qp/Qs ratio, reaches a maximum at the optimal Qp/Qs ratio, then falls. Systemic SaO2 increases with increasing Qp/Qs ratio continuously, first steeply, then gradually, and approaches the upper limit. Systemic SaO2 is not a predictive parameter for oxygen availability. In contrast, changes of mixed venous SO2 correlate well with changes of oxygen availability. Venous SO2 increases first with increasing Qp/Qs ratio, reaches a maximum when the optimal Qp/Qs ratio is reached, then falls. Correlations between venous SO2 and Qp/Qs ratio and between venous SO2 and oxygen availability were shown in an animal experiment.13 In that study, the optimal Qp/Qs ratio was at or slightly ⬎1.0. From clinical experience, optimal Qp/Qs ratio is considered to be 1.0.14,15 Rossi et al5 studied postoperative blood gas analyses in 13 patients who underwent the Norwood operation. Two patients died within 24 hours after operation. Rossi et al5 calculated a Qp/Qs ratio assuming pulmonary venous SO2 to be 96%. In that study, 6 of 13 patients had a Qp/Qs ratio of ⬎2.0 directly after arrival in the intensive care unit. In the patients who survived,
Table 5. Comparison of Arterial Blood Gas Data Between Survivors and Nonsurvivors Study Period
After induction pH PaCO2 (mmHg) PaO2 (mmHg) SaO2 (%) BE Hemoglobin (g/dL) After CPB pH PaCO2 (mmHg) PaO2 (mmHg) SaO2 (%) BE Hemoglobin (g/dL) Last blood gas pH PaCO2 (mmHg) PaO2 (mmHg) SaO2 (%) BE Hemoglobin (g/dL)
Survivors (n ⫽ 58) Nonsurvivors (n ⫽ 18)
p
7.460 ⫾ 0.078 41.4 ⫾ 8.2 109.6 ⫾ 95.9 95.2 ⫾ 5.4 5.1 ⫾ 4.6 12.5 ⫾ 1.6
7.492 ⫾ 0.084 38.7 ⫾ 10.0 109.5 ⫾ 85.7 95.1 ⫾ 5.8 5.2 ⫾ 3.4 13.1 ⫾ 1.5
NS NS NS NS NS NS
7.294 ⫾ 0.091 43.4 ⫾ 9.3 40.1 ⫾ 9.8 72.6 ⫾ 13.5 ⫺5.3 ⫾ 3.3 11.5 ⫾ 1.5
7.278 ⫾ 0.101 41.2 ⫾ 9.4 40.5 ⫾ 14.2 70.0 ⫾ 17.5 ⫺7.1 ⫾ 4.3 11.7 ⫾ 1.8
NS NS NS NS NS NS
7.298 ⫾ 0.095 48.4 ⫾ 9.1 43.5 ⫾ 10.1 77.3 ⫾ 8.5 ⫺3.0 ⫾ 4.2 12.1 ⫾ 2.0
7.244 ⫾ 0.115 47.4 ⫾ 11.5 42.8 ⫾ 15.5 69.0 ⫾ 20.5 ⫺6.8 ⫾ 4.4 12.0 ⫾ 1.6
⬍0.05 NS NS ⬍0.05 ⬍0.01 NS
NOTE. Data are shown as mean ⫾ SD; p value indicates comparison between survivors and nonsurvivors. Abbreviations: NS, not statistically significant; CPB, cardiopulmonary bypass; BE, base excess.
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STRAUSS ET AL
the Qp/Qs ratio changed during the postoperative course and was between 0.5 and 2.0 at 24 hours postoperatively. At the same time, arteriovenous SO2 difference was ⱕ25%. Mixed venous SO2 was ⱖ50%. From these data, the authors defined as acceptable a Qp/Qs ratio of ⬍2.0 and an arteriovenous SO2 difference of ⬍25%. For the present results, the authors defined an acceptable range of Qp/Qs ratio based on their data. In the present study, high Qp/Qs ratios were observed in the patients who survived the day of operation. Although Qp/Qs ratio ideally should be 1.0, it is conceivable that a wide range of Qp/Qs ratios can be tolerated. Evidence can be found in the report of Chang et al.16 They performed cardiac catheterization in patients who had undergone a Norwood operation shortly before stage II palliation and found the Qp/Qs ratio to be 0.5 to 3.5. Another explanation for this discrepancy between estimated Qp/Qs ratio and patient outcome is error in calculation of the Qp/Qs ratio. For the calculation of Qp/Qs ratio, the authors considered pulmonary venous SO2 to be 95%. At diagnostic cardiac catheterization, pulmonary venous SO2 is assumed to be equal to systemic SaO2. This assumption does not apply to patients with right-to-left shunt. A hypothetical value (95%) of pulmonary venous SO2 was used in this study. Pulmonary venous SO2 might be lower than 95% after CPB, however, because of ventilation-perfusion inequality or diffusion impairment or both. If a true pulmonary venous SO2 is lower than the theoretical value of 95%, Qp/Qs ratio will be underestimated with the above-mentioned calculation. When pulmonary venous SO2 is ⬎95%, Qp/Qs ratio will be overestimated. Determination of Qp/Qs ratio might be difficult in the clinical setting. The application of another marker for oxygen delivery, venous SO2, has been emphasized.5,13,17 Because venous SO2 correlates well with oxygen availability, therapy should be aimed to increase venous SO2. Positive inotropic drugs were administered in all but one patient. Dopamine was the drug of the first choice (75 of 76 patients). Most patients also received epinephrine (65 of 76) or phosphodiesterase III inhibitor (47 of 76). The Children’s Hospital of Phil-
adelphia group reported that positive inotropic drugs were rarely necessary after the Norwood operation.14,18 According to Hansen and Hickey,19 however, 70% of patients needed positive inotropic drugs. The University of Michigan group advised the administration of dopamine for high pulmonary blood flow to raise pulmonary vascular resistance.20 According to Jonas et al,4 high doses of positive inotropic drugs should not be given in cases of increased pulmonary blood flow because positive inotropic drugs increase systemic vascular resistance, which results in a further increase of systemic-to-pulmonary shunt. Riordan et al21 studied the effects of dopamine, dobutamine, and epinephrine on Qp/Qs ratio in an animal model of univentricular circulation. The 3 drugs increased cardiac output but had different effects on Qp/Qs ratio and oxygen delivery. Although dopamine (5 and 15 g/kg/min) had no effects on Qp/Qs ratio, epinephrine (0.05 and 0.1 g/kg/min) increased oxygen delivery with decline of Qp/Qs ratio. Dobutamine (5 and 15 g/kg/min) caused an increase of Qp/Qs ratio and concomitantly a decrease of oxygen delivery. It is questionable if these results are transferable to humans, but they indicate at least that positive inotropic drugs may not work similarly on the Qp/Qs ratio. Knowledge of venous SO2 is important for judgment of the effects of drugs on oxygen delivery. One of the crucial points in the anesthetic management for the Norwood operation lies in maintenance of maximal oxygen delivery by optimally balancing Qp/Qs ratio. In a clinical setting, the goal should be achievement of optimal arterial and venous SO2 via manipulation of respiratory parameters or administration of cardiovasoactive drugs. The authors considered an SaO2 of 75% to 85%, a mixed venous SO2 of ⬎50%, and an arteriovenous SO2 difference of ⬍25% as target values. In the present study, excessive postoperative pulmonary blood flow was not implicated as a cause of death from blood gas data and Qp/Qs ratios derived from arterial and venous SO2. In nonsurvivors, low cardiac output and hypoxemia (pulmonary gas exchange abnormalities or low pulmonary blood flow or both) are assumed to be major problems.
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8. Gullquist SD, Schmitz ML, Hannon GD, et al: Carbon dioxide in the inspired gas improves early postoperative survival in neonates with congenital heart disease following stage I palliation. Circulation 86: I360, 1992 (suppl 1) 9. Morray JP, Lynn AM, Mansfield PB: Effect of pH and PCO2 on pulmonary and systemic hemodynamics after surgery in children with congenital heart disease and pulmonary hypertension. J Pediatr 113: 474-479, 1988 10. Viitanen A, Salmenpera¨ M, Heinonen J, Hynynen M: Pulmonary vascular resistance before and after cardiopulmonary bypass: The effect of PaCO2. Chest 95:773-778, 1989 11. Mora GA, Pizzaro C, Jacobs ML, Norwood WI: Experimental model of single ventricle: Influence of carbon dioxide on pulmonary vascular dynamics. Circulation 90:II43-II46, 1994 (part 2) 12. Barnea O, Austin EH, Richman B, Santamore WP: Balancing the circulation: Theoretic optimization of pulmonary/systemic flow ratio in hypoplastic left heart syndrome. J Am Coll Cardiol 24:1376-1381, 1994 13. Riordan CJ, Randsbaek F, Storey JH, et al: Balancing pulmonary and systemic arterial flows in parallel circulations: The value of monitoring systemic venous oxygen saturation. Cardiol Young 7:7479, 1997
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14. Nicolson SC, Steven JM, Jobes DR: Hypoplastic left heart syndrome, in Nichols DG, Cameron DE, Greely WJ, et al (eds): Critical Heart Disease in Infants and Children. St Louis, MO, Mosby, 1995, pp 863-884 15. Norwood WI: Hypoplastic left heart syndrome, in Sabiston DC Jr, Spencer FC (eds): Surgery of the Chest. Philadelphia, PA, Saunders, 1995, pp 1659-1666 16. Chang AC, Farrell PE Jr, Murdison KA, et al: Hypoplastic left heart syndrome: Hemodynamic and angiographic assessment after initial reconstructive surgery and relevance to modified Fontan procedure. J Am Coll Cardiol 17:1143-1149, 1991 17. Tweddell JS, Hoffman GM, Fedderly RT, et al: Patients at risk for low systemic oxygen delivery after the Norwood procedure. Ann Thorac Surg 69:1893-1899, 2000
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18. Jacobs ML, Rychik J, Murphy JD, et al: Results of Norwood’s operation for lesions other than hypoplastic left heart syndrome. J Thorac Cardiovasc Surg 110:1555-1562, 1995 19. Hansen DD, Hickey PR: Anesthesia for hypoplastic left heart syndrome: Use of high-dose fentanyl in 30 neonates. Anesth Analg 65:127-132, 1986 20. Iannettoni MD, Bove EL, Mosca RS, et al: Improving results with first-stage palliation for hypoplastic left heart syndrome. J Thorac Cardiovasc Surg 107:934-940, 1994 21. Riordan CJ, Randsbaek F, Storey JH, et al: Inotropes in the hypoplastic left heart syndrome: Effects in an animal model. Ann Thorac Surg 62:83-90, 1996