Anesthetic management of a parturient with uncorrected tetralogy of Fallot for Cesarean section.

Tetralogy of Fallot is the most common cyanotic congenital heart disease. We report the anesthetic management of a patient with uncorrected Fallot's tetralogy for Cesarean section.

INTRODUCTION

Tetralogy of Fallot (TOF) is the most common cyanotic congenital heart disease. It accounts for 5-6% of cases of congenital heart disease.[1] Uncorrected cyanotic heart disease carries a high risk in pregnancy for both mother and fetus. A review of 57 pregnancies in women with uncorrected TOF showed a fetal mortality of 22% and a maternal mortality of 7%.[2] We report a case of a 29-year-old parturient with uncorrected TOF managed successfully under general anesthesia (GA) for Cesarean section.

CASE REPORT

A 29-year-old gravida 4, para 0, at 34 weeks gestation, was admitted in our obstetric ward with bad obstetric history and with complaint of breathlessness on routine work. Patient was a known case of heart disease since childhood who was advised surgery, but she had not undergone the same. She was not taking any medications at home. In the past, she had had three abortions and had undergone curettage twice. The anesthesia details were not known, but they were uneventful.

On examination, she had cyanosis [Figure 1], peripheral as well as central, and grade 2 clubbing [Figure 2]. Her pulse rate was 92 beats/min and her blood pressure was 144/90 mm of Hg. There was no variation of pulse and blood pressure in the extremities. When sitting, her SpO2 on room air was 86%. Pedal edema was present. Cardiovascular system revealed a pansystolic murmur of grade 3 in the pulmonary as well as aortic areas, radiating all over the precordium. Rest of the examination was unremarkable. Her hemoglobin was 16.5 gm% and packed cell volume (PCV) was 60%. Echocardiography showed a large subaortic ventricular septal defect with predominant right to left shunt. There was 40-50% overriding of the aorta. Right ventricular cavity was predominant with right ventricular hypertrophy. Biventricular function was within normal limits. There was moderate to severe pulmonary stenosis which was infundibular and valvular type. The pulmonary gradient was 68 mm. ECG showed sinus tachycardia with P pulmonale with poor R wave progression. Arterial blood gas analysis further confirmed shunting (pH 7.376, pO2 54.9 mmHg, pCO2 30.2 mmHg, SO2 86.8%, HCO3 17.3 mmol/l, base deficit 6.2 mmol/l). Chest X-ray showed boot-shaped heart [Figure 3].

Figure 1

Cyanosis

Figure 2

Clubbing

Figure 3

Chest radiograph showing boot-shaped heart

After obtaining cardiologist's opinion, she was posted for an elective Cesarean section. High risk consent was taken. Infective endocarditis prophylaxis was administered. On the operation table, her SpO2 on room air in the supine position was 84%, with O2 polymask it was 89%, and with 100% O2 it improved to 90%. She was premedicated with intravenous (IV) ranitidine 50 mg and metoclopramide 10 mg. Intramuscular glycopyrrolate 0.2 mg was administered since we had planned GA for her. The right internal jugular vein was cannulated under local anesthesia under strict asepsis. We preloaded the patient with 500 ml of lactated ringer's solution before the start of surgery. After preoxygenation with 100% O2, anesthesia was induced with IV ketamine 80 mg, 1.25% thiopentone sodium 75 mg, and IV succinylcholine 100 mg, and the trachea was intubated. 100% O2 was administered till the birth of baby. IV fentanyl 60 mcg was given after the delivery of the baby. We administered IV methargin diluted slowly as the uterus had not contracted after the birth of the baby. SpO2 was maintained around 93-94%. 0.4-0.8% Isoflurane was then started and IV vecuronium was administered so as to control the ventilation. We then administered 50% N2O in O2. The O2 saturation dropped; however, it did not drop beyond 90%. Central venous pressure was monitored throughout the surgery and maintained within normal limits. At the end of surgery, neuromuscular blockade was reversed with IV neostigmine 2.5 mg and glycopyrrolate 0.5 mg. The trachea was then extubated once the patient became fully conscious, was obeying oral commands, and could hold her head. IV paracetamol 1 g was then administered for postoperative analgesia. BP throughout was maintained between 144/92 and 136/90 mmHg and pulse rate which was 104/min before the induction of anesthesia came down to 86/min at the end of the procedure. Intraoperatively, the patient received about 250 ml of Ringer's lactate. There were no cyanotic spells or any fall in BP intraoperatively. The patient was closely monitored in the immediate postoperative period in the ICU. The postoperative period was uneventful and she was discharged on the 7th postoperative day with the advice to undergo surgical intervention.

DISCUSSION

The four components of TOF are malaligned ventricular septal defect (VSD), obstruction to right ventricular (RV) outflow, aortic overriding of VSD, and right ventricular hypertrophy (RVH) due to the RV seeing aortic pressure via large VSD. These four characteristics were first described by Fallot in 1888. The relationship between resistance of blood flow from ventricles into aorta and into the pulmonary vessels plays a major role in determining the hemodynamic and clinical picture. When the obstruction to pulmonary vessels is severe, the pulmonary blood flow is reduced markedly and a large volume of desaturated systemic venous blood is shunted from right to left across VSD. Severe cyanosis and erythrocytosis occur and symptoms of systemic hypoxemia are prominent.[3]

In pregnant patients with TOF, the decrease in peripheral resistance that accompanies pregnancy augments right to left shunt and may exaggerate maternal cyanosis, which poses risks for both mother and fetus.[4] Women who had undergone repair and in whom cyanosis did not reappear do well in pregnancy.[5] Any disease complicated by severe maternal hypoxemia is likely to lead to miscarriage, preterm delivery, or fetal death. When hypoxemia is intense enough to stimulate a rise in hematocrit above 65%, pregnancy wastage is 100%.[5] Patients with TOF have an increased risk of fetal loss, and their offspring are more likely to have congenital anomalies than offspring in the general population. Adverse maternal events, although rare, may be associated with left ventricular dysfunction, severe pulmonary hypertension, and severe pulmonic regurgitation with RV dysfunction.

With uncorrected TOF, pregnancy presents serious risks, including maternal mortality. Preexisting pulmonary hypertension is a concern. In addition, elevated cardiac output leads to increased venous return to hypertrophic right ventricle. These changes, together with decreased systemic vascular resistance increase the right to left shunt. Oxygenation decreases, hematocrit rises, and cyanosis worsens, further stressing an already compromised system. Risk factors worsening the prognosis include prepregnancy hematocrit exceeding 65%, history of cardiac failure or syncope, cardiomegaly, RV pressure exceeding 120 mm Hg or strain pattern of ECG or saturation less than 80%.[6]

The magnitude of right to left intracardiac shunt can be increased by (1) decreased systemic vascular resistance, (2) increased pulmonary vascular resistance, and (3) increased myocardial contractility.[7]

Our goal during anesthesia was to maintain systemic vascular resistance and to avoid any decrease in peripheral vascular resistance as any of these changes would result in increased right to left shunt. Hence, we opted for GA. We induced our patient with ketamine and administered 75 mg of 1.25% thiopentone. Though intermittent positive pressure ventilation can decrease pulmonary blood flow by increasing pulmonary vascular resistance, we controlled ventilation of the patient's lungs avoiding excessive positive airway pressure. 100% O2 was given till the birth of baby, and after delivery, N2O 50% in O2 was given, keeping a close watch on oxygen saturation. N2O increases pulmonary vascular resistance, but this potentially adverse effect is more than offset by its beneficial effects on systemic vascular resistance (no change or modest increase). The principal disadvantage of using N2O is decrease in inspired O2 concentration, hence one has to limit the inspired concentration of N2O to 50%.[7] We preloaded our patient with 500 ml of lactated ringer's solution so as to maintain intravascular volume during surgery as acute hypovolemia tends to increase right to left intracardiac shunt. We did not administer the bolus dose of syntocinon as that would affect peripheral vascular resistance; however, we did administer intravenous methergin diluted and very slowly as the uterus had not contracted. There was no adverse intraoperative event or any fall in blood pressure or decrease in oxygen saturation below 90% in the intraoperative period, though we had kept the adrenergic agonist phenylephrine ready.