Anesth Analg 2000;91:1375-1380
© 2000 International Anesthesia Research Society
PEDIATRIC ANESTHESIA
Intraoperative Evaluation of Pulmonary Artery Flow During the Fontan Procedure by Transesophageal Doppler Echocardiography
Shinji Kawahito, MD, PhD,
Hiroshi Kitahata, MD, , PhD,
Katsuya Tanaka, MD, PhD,
Junpei Nozaki, MD, and
Shuzo Oshita, MD, PhD
Department of Anesthesiology, Tokushima University School of Medicine, 3-18-15 Kuramoto, Tokushima, 770-8503 Japan
Address correspondence and reprint requests to Shinji Kawahito, MD, PhD, Department of Surgery, Baylor College of Medicine, One Baylor Plaza, Houston, TX 77030. Address e-mail to kawahito @bcm.tmc.edu.
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Abstract
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After the Fontan procedure, pulmonary artery (PA) flow is maintained without right ventricular pump function. We evaluated intraoperative PA flow velocity patterns using transesophageal Doppler echocardiography (TEE) immediately after cardiopulmonary bypass (CPB) in patients during Fontan or hemi-Fontan procedures. We studied 10 patients with single-ventricle physiology (age range, 5 mo to 3 yr 1 mo). Anesthesia was induced and maintained with fentanyl. After induction of anesthesia, a pediatric TEE probe was inserted into the esophagus. All patients had surgical repair involving direct anastomosis of the right atrium to the PA. Immediately after completion of CPB, adequacy of the atriopulmonary anastomosis was assessed and PA flow velocity was recorded. In all patients, the atriopulmonary anastomosis was clearly defined using a single-plane TEE probe, and PA flow recording was completed successfully. Intraoperative PA flow velocities showed two distinct patterns. Biphasic forward flows with peak velocities during systole and diastole were observed in six patients. The remaining four patients showed forward flows with flow reversals. The four patients demonstrating flow reversals showed significantly reduced fractional shortening (26.5 ± 2.1% vs 35.5 ± 6.3%) and larger pressure gradient between the right atrium and left atrium (10.8 ± 1.3 mm Hg vs 8.0 ± 0.9 mm Hg) when compared to those without reverse flow. Two patients with reverse flow required reoperation because of hypotension. Because PA flow is influenced by pulmonary vascular resistance and left ventricular function, TEE assessed intraoperative PA flow should be further evaluated as a useful predictor of surgical outcome after a Fontan procedure.
Implications: We evaluated intraoperative pulmonary artery flow velocity patterns with transesophageal Doppler echocardiography (TEE) in patients during a Fontan procedure. Because pulmonary artery flow is influenced by pulmonary vascular resistance and ventricular function, intraoperative evaluation of pulmonary artery flow using TEE should be further evaluated as a predictor of surgical outcome after a Fontan procedure.
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Introduction
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The first successful right ventricular bypass was performed by Fontan and Baudet in patients with tricuspid atresia by anastomosing the right atrium to the main pulmonary artery using a homograft (1). In recent years, the Fontan procedure, a functional radical repair of tricuspid atresia, univentricular heart, or similar conditions, has improved the long-term outcome of patients. The indications for this procedure have been expanded because of the recognition of peculiar postoperative hemodynamics. After the Fontan procedure, pulmonary artery (PA) flow is maintained without right ventricular pump function. Pulmonary perfusion and, consequently, cardiac output become critically dependent on low pulmonary vascular resistance (PVR) and normal systemic ventricular function (2,3). In particular, just after completion of cardiopulmonary bypass (CPB), even a small reactive increase in PVR may cause deleterious systemic venous hypertension associated with resistant low cardiac output syndrome, despite a technically successful operation.
Postoperative evaluation of PA flow velocity patterns using transthoracic echocardiography, in conjunction with assessment of ventricular function, may predict clinical outcome (4–8). However, there are few reported evaluations of PA flow patterns using intraoperative transesophageal echocardiography (TEE) (9). We evaluated PA flow velocity patterns in patients during Fontan procedures using Doppler TEE immediately after completion of CPB.
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Methods
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The study protocol was approved by the Ethics Committee on Human Study of Tokushima University School of Medicine, and written informed consent was obtained from family members or guardians of all patients. Ten patients (5 female and 5 male) with single-ventricle physiology were prospectively enrolled. The mean age of the patients was 24 ± 10 months (age range, 5–37 mo), and mean weight was 10.3 ± 2.6 kg (weight range, 4.0 to 12.8 kg). All patients had surgical repair by direct anastomosis of the right atrium to the PA without conduits. Five patients had the conventional Fontan connections and 5 had hemi-Fontan procedures (10). In all patients, an interatrial baffle fenestration (11,12) was created. Three patients had concomitant procedures: total anomalous pulmonary venous connection repair (two patients), Kaye-Damus-Stansel procedure (one patient), and common atrioventricular valve regurgitation repair (one patient). Demographic data, diagnoses, palliations, and surgical procedures are summarized in Table 1. Preoperative conditions were as follows: mean PA pressure, 14.1 ± 4.8 mm Hg; PVR, 3.1 ± 1.8 Wood Units; PA index (the sum of cross-sectional areas of the right and left pulmonary arteries just proximal to the first branches normalized by body surface area) (13), 287.2 ± 129.4 mm2/m2, ejection fraction, 69.6 ± 12.8%; capillary partial pressure of oxygen, 34.0 ± 5.3 mm Hg. All operations were performed via median sternotomy and involved CPB. Aortic cross-clamping and myocardial cardioplegia arrest were also used in all patients. Total operation time, anesthesia time, cardiopulmonary bypass time, and aortic cross-clamping time were 729 ± 94 min, 850 ± 106 min, 316 ± 87 min, and 104 ± 31 min, respectively.
Anesthesia was induced and maintained with sevoflurane in 100% oxygen and increments of fentanyl (total, 100 to 200 µg/kg). Muscle relaxation was achieved with vecuronium. After induction of anesthesia, a TEE probe (6.8-mm diameter, UST-5234S-5TM; Aloka, Tokyo, Japan) was inserted into the esophagus and attached to a color Doppler imaging system (SSD-830TM; Aloka). The patients were ventilated to maintain PaCO2 at 30 to 35 mm Hg, and peak airway pressure was maintained less than 15 cm H2O. Patients were weaned from CPB with dopamine (3 to 7 µg/kg/min), dobutamine (3 to 7 µg/kg/min), and nitroglycerin (0.5 to 2.0 µg/kg/min). After CPB, hyperventilation using 100% oxygen was performed (tidal volume 10 mL/kg, respiratory rate 20–30 bpm, peak airway pressure below 15 cm H2O) in all patients. PaCO2 was maintained at approximately 30 mm Hg. Five to 10 min after completion of CPB, the adequacy of atriopulmonary anastomosis was assessed by TEE, and PA flow velocity was recorded with a pulse wave Doppler technique. The PA was visualized to its bifurcation with TEE by withdrawal and rotation of the transducer at the level of the upper esophagus, varying the degree of anteflexion. The pulsed Doppler sampling volume was carefully placed in the center of the main PA trunk. The following time intervals were used: end of the P wave to peak of the R wave (atrial systole), peak of the R wave to end of the T wave (left ventricular systole), and end of the T wave to end of the P wave (early left ventricular diastole). Ejection fraction and fractional shortening of the main ventricle (right or left) was measured using Teichholz’s method. Transpulmonary pressure gradient (central venous pressure - left atrial pressure) was also measured.
Results are shown as mean ± SD. Statistical analysis was performed using the Mann-Whitney U-test and Fisher’s exact probability test, and P < 0.05 was considered to be significant.
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Results
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The atriopulmonary anastomosis was clearly defined in all patients using a single plane TEE probe, and PA flow recordings were successfully obtained (Fig. 1). Intraoperative PA flow velocities showed two distinct patterns. Biphasic forward flows with peak velocities during systole and diastole (normal flow pattern, Fig. 2) were observed in six patients (patients 2, 5, 6, 7, 9, 10), and the remaining four patients (patients 1, 3, 4, 8) showed forward flows with flow reversals (abnormal flow pattern, Fig. 3).
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Figure 1. Transesophageal echocardiographic image of the right atrium (RA) anastomosed to the pulmonary artery. Pulmonary blood flow is seen from the RA through the anastomosis with no evidence of stenosis. RPA = right pulmonary artery, LPA = left pulmonary artery, MPA = main pulmonary artery, SVC = superior vena cava.
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Figure 2. Pulsed Doppler transesophageal echocardiographic recording (A) and a schematic (B) of the pulmonary artery flow after cardiopulmonary bypass (normal flow pattern). A biphasic forward flow pattern was observed. Flow began at the end of the T wave, peaked at or before the P wave, and returned to baseline by the peak of the R wave (early ventricular diastole and atrial systole). Forward flow recommenced at the peak of the R wave and returned to baseline at the end of the T wave (ventricular systole). RPA = right pulmonary artery, LPA = left pulmonary artery, MPA = main pulmonary artery, SVC = superior vena cava, RA = right atrium, AO = aorta.
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Figure 3. Pulsed Doppler transesophageal echocardiographic recording (A) and a schematic (B) of the pulmonary artery flow after cardiopulmonary bypass (abnormal flow pattern). A reverse flow pattern was observed in four patients. Reverse flow was detected between the end of the T wave and the end of the P wave (early ventricular diastole). RPA = right pulmonary artery, LPA = left pulmonary artery, MPA = main pulmonary artery, SVC = superior vena cava, AO = aorta.
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There were no significant differences in sex or preoperative variables including mean PA pressure, PVR, PA index, ejection fraction, or capillary partial pressure of oxygen among patients demonstrating a normal flow pattern and patients demonstrating an abnormal flow pattern. However, the 4 patients showing flow reversal were significantly younger and weighed significantly less than those without reverse flow (Table 2). There were no significant differences in operation time, anesthesia time, CPB time, or cross-clamping time among the patients with normal flow patterns and the patients with abnormal flow patterns. However, the four patients showing flow reversals had a significantly decreased fractional shortening and an increased transpulmonary pressure gradient compared with those without reverse flow. They also tended to have a decreased ejection fraction (Table 3). Two patients with reverse flow required reoperation because of hypotension (patients 1 and 8). Because inadequate fenestration was observed in patient 1, a larger fenestration was created during cardiopulmonary bypass. Patient 8, who had severe atrioventricular valve insufficiency, required atrioventricular valvuloplasty. This patient died of heart failure, however, on postoperative day 10. The remaining two patients (patients 3 and 4) showing reverse flow also showed chronic low cardiac output postoperatively and had prolonged tracheal intubation, intensive care unit stay, and hospitalization. All patients showing normal PA flow were symptom-free and required no reoperation.
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Discussion
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This study demonstrates that TEE can provide unique anatomic and physiologic information during Fontan procedures in small children and, thus, may have a significant impact on patient management. PA flow just after completion of the CPB during the Fontan procedure was biphasic in some patients and appeared to be related to both active (atrial systole) and passive events. However, 4 of our patients demonstrated reverse flow and all 4 had a poor outcome.
Since its introduction in 1971, the Fontan procedure (1) with its many variants, collectively referred to as "orthoterminal correction," has become the ultimate surgical treatment for patients with only one functional ventricle. However, certain anatomic and physiologic factors mitigate against a successful outcome with the Fontan procedure. Though the surgical techniques for Fontan procedures have been described in detail, reports of its anesthetic management are uncommon (14,15). It is very difficult to estimate anatomical correction, ventricular function, and PVR intraoperatively. Although echocardiography is most useful, clear echocardiographic definition of the result of the Fontan procedures is not easily obtained in the operating room under transthoracic echocardiography or epicardial examination because of the posterior position of the atriocavopulmonary anastomoses. However, TEE may overcome these problems. The development of small pediatric TEE probes has opened new possibilities for imaging cardiovascular structures in children (16,17). Fyfe et al. (9) reported the atriocavopulmonary connection to be clearly defined in all cases using TEE. O’Leary et al. (18) reported that intraoperative biplane TEE had a significant impact most frequently in patients during the Fontan procedure. However, there has been no detailed report of PA flow patterns obtained by TEE recorded just after CPB.
After the Fontan operation, PA flow is maintained in the absence of right ventricular pump function. Several investigators have demonstrated postoperative flow velocity patterns in the PA in patients who have undergone the Fontan operation (4–9). Almost all note that PA flow profiles after Fontan procedures appear to be uniform and unrelated to the basic anomaly or type of repair. Our TEE findings are in agreement with transthoracic echocardiography findings of previous investigators. PA forward flow is biphasic; the initial forward flow begins at the end of the T wave, peaks at or before the P wave, and returns to baseline by the peak of the R wave, i.e., during early left ventricular diastole and atrial systole. The secondary forward flow begins at the peak of the R wave and returns to baseline at the end of the T wave, i.e., left ventricular systole. During initial forward flow, the left atrium is simultaneously emptying into its ventricle and being filled as a result of pulmonary venous return. Initial forward flow is probably initiated by blood passing from central pulmonary to peripheral pulmonary arteries, then into the pulmonary venous bed. This forward flow of pulmonary blood flow is augmented by atrial systole. The secondary forward flow may be caused by two events. Right atrial relaxation results in forward flow from the cava to the right atrium and PA. During this period, the left atrium is filled from the pulmonary venous bed, and there is passage of blood from the PA into the emptying pulmonary venous pool.
In our Doppler studies, evidence of reverse flow based on TEE recording of intraoperative PA flow velocities was found in 4 patients. Reverse flow was detected between the end of the T wave and the end of the P wave (early ventricular diastole). Investigators have described reverse flow (4,5,7,9). Hagler et al. (5) reported that an abnormal PA flow pattern was most frequently associated with reduced ventricular function. Fyfe et al. (9) reported the Fontan operation to be eventually unsuccessful in patients with reverse flow, and pulmonary blood flow reversal may prove to be a new indicator of inadequate hemodynamics after the Fontan operation. Frommelt et al. (7) reported patients with reverse flow to have a significantly decreased ejection fraction and a poor outcome. With the decreased ventricular function, atrial systolic filling pressures are likely increased; the ventricular suction effect is decreased, and PA flow is diminished or absent in systole and early diastole. Our patients with flow reversal also had significantly decreased fractional shortening and increased transpulmonary pressure gradient in comparison to those without reverse flow.
Reverse flow suggests elevated PVR and/or reduced left ventricular function. Patients with abnormal flow had diastolic reverse PA flow. Postoperative morbidity and mortality after Fontan procedures are mainly related to decreased cardiac output associated with increased PVR and systemic ventricular dysfunction. Preoperatively, PVR did not differ significantly among patients with a normal flow pattern and those with an abnormal pattern. It would seem that just a few more patients in this study might have revealed that a significant difference did exist between the two groups. During surgery, PVR is most labile immediately after CPB because of pulmonary endothelial dysfunction (19). Thus, even a minor increase in PVR may result in severe impairment of pulmonary perfusion and, consequently, in decreased cardiac output syndrome.
The influence of ventilation and valve regurgitation in PA flow must also be considered. After the Fontan operation, hyperventilation with 100% oxygen is generally performed to decrease PVR. However, aggressive mechanical ventilation may further decrease pulmonary perfusion (20). Frommelt et al. (7) showed that forward PA flow was augmented during inspiration in all Fontan patients but that the pattern of flow was not influenced by ventilation. However, Fyfe et al. (9) reported that decreasing peak inspiratory pressure eliminated flow reversal in a patient. Although inspiratory pressure may influence the PA flow pattern during the Fontan procedure, all measurements in our study were performed under exactly the same ventilatory conditions after the completion of CPB. Therefore, we believe there were no remarkable differences between the normal PA flow patients and the abnormal PA flow patients in terms of ventilatory factors. In addition, valve regurgitation can influence PA flow pattern. Frommelts et al. (7) reported abnormal PA flow in a patient with severe aortic and atrioventricular insufficiency. Reverse flow is probably related to severe aortic and atrioventricular valve insufficiency with resulting alterations in left ventricular diastolic and left atrial systolic pressures. Among our patients, one with reverse flow had severe atrioventricular valve insufficiency.
In recent years, the Fontan operation and its modifications have been used in progressively younger patients for the surgical treatment of complex congenital heart defects. Patient selection is an important factor in the outcome of Fontan operations. The initial recommendation for a Fontan procedure between 4 and 15 years of age was based upon concerns that surgery at an earlier age resulted in increased mortality rates secondary to an immature pulmonary vascular bed and consequent increased PVR. In our study, the four patients showing reverse flow were significantly younger and weighed significantly less than those without reverse flow. This definitive operation has been made relatively safe by intervening staging strategies. The shunting from right to left after a staging operation may also influence the PA flow pattern. Another factor of influence may be the CPB. The duration of CPB in our series was close to 5 hours. This is very long for a Fontan procedure, and it might have been responsible in part for the pulmonary hypertension.
In conclusion, the atriopulmonary anastomosis was clearly defined in all patients, and the PA flow patterns were successfully recorded using the single plane TEE probe for infants. Because PA flow is influenced by PVR and left ventricular function, intraoperative PA flow seems to be a useful predictor for surgical outcome in patients during a Fontan procedure. However, use of single-plane pediatric TEE cannot be applied to the widely used lateral tunnel-type total cavopulmonary operation. Also, because PA flow velocity after Fontan procedures has multifactorial determinants and is influenced by several pathological and procedural factors, findings cannot be extrapolated from one study population to another. The importance of biphasic forward PA flow and reverse PA flow in the various subsets of patients and the long-term clinical implications are important questions for further investigation in a larger study group.
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Footnotes
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Presented, in part, at the annual meeting of the American Society of Anesthesiologists, Dallas, Texas, October 11, 1999.
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Accepted for publication August 21, 2000.
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Abstract
Introduction
