Case 3 - Wheezing and Cyanosis in a 16-Month Old

The patient is a 16 month old male who presents to the Emergency Department with a one day history of coughing, congestion, and runny nose. His only medications were acetaminophen and a cough syrup. He was seen by his primary physician and instructed to go to the E.D. His mother stated that he had a heart murmur, for which he had been seen by a cardiologist and told that he had a hole in his heart that would close on its own. He had no other medical problems, no previous surgeries, and had been doing well until the current illness.

Exam: VS T37.1R, P170, R48, BP 112/74, oxygen saturation 78% on room air. The patient appeared pale and irritable, with moderate respiratory distress. Peripheral and central cyanosis were present. Diffuse wheezes were heard bilaterally. The precordium was hyperdynamic, and a grade III/VI holosystolic murmur was present, loudest along the left sternal border. The abdomen was soft, with no organomegaly. Peripheral pulses were brisk.

The patient was treated with 100% oxygen, subcutaneous terbutaline, and albuterol aerosols. A peripheral IV was placed. The patient's oxygen saturation decreased to the 50's with crying, but returned to the 70's when he was calmed down. He was placed in the knee-chest position and a dose of morphine was given IV. A 20cc/kg bolus of normal saline was given IV. He continued to have inspiratory and expiratory wheezes. Albuterol and ipratropium bromide aerosols were given. A CXR and an EKG were done.

View EKG.

Determine the axis of QRS in the frontal plane (using the limb leads). Note that several leads are isoelectric (I, AVF, and AVL). Since I and AVF are perpendicular to each other, this represents misplaced leads or the axis is perpendicular to both leads (ie., an anterior or posterior axis). The cardiologist reviewing this EKG noted the axis to be "indeterminate", indicating that the axis of QRS is largely perpendicular to the frontal plane. The cardiologist has re-labeled leads V1-V3. Regardless of this change, it appears that the axis of QRS is anterior since V1 and V2 are greatly positive (large R waves). The large R waves in lead V1, V2, and V3 meet voltage criteria for right ventricular hypertrophy. Although RVH usually has a right axis in the frontal plane (greater than 90 degrees), the right ventricle is anterior; thus, it may have an anterior axis as well. Although RVH is normal for a newborn, RVH is not normal for a 16-month old child.

View CXR image.

This CXR shows a boot-shaped heart with an upturned apex secondary to right ventricular hypertrophy and a concavity of the left upper heart border (pulmonary outflow tract hypoplasia). The aorta may be shifted to the right (it is best seen on the right) versus rotational artifact. The pulmonary vasculature is decreased (hypoperfused lungs appear hyperlucent), and the main pulmonary artery segment is small. Hyperinflation is present, but no acute infiltrates are seen. The CXR and EKG are consistent with the clinical impression of Tetralogy of Fallot (TOF) with a hypercyanotic spell, triggered by an episode of bronchiolitis.

At this point, the patient's clinical condition deteriorated. On 100% O2, the patient's oxygen saturation decreased to the 40's, with increased work of breathing and cyanosis, and decreased level of consciousness. Midazolam and vecuronium were administered in rapid sequence to facilitate intubation with an endotracheal tube. What ET tube size should be selected for this patient?

ET tube size can be estimated in several ways. A commonly used method is the formula:

ETT = Age / 4 + 4

Thus, a two year old would need a 4.5 ETT:

4.5 = 2 / 4 + 4

This formula doesn't work well under this age. Newborns require a 3.0 or 3.5, while an 8-month old would probably require a 4.0 ETT. In the case of our 16-month old patient, a 4.5 ETT was used. ET tube position was confirmed by auscultation and CXR; however, the oxygen saturations remained in the 30's to 50's despite bag ventilation with 100% O2 through the endotracheal tube. Continued wheezes were heard, and albuterol aerosols were given. An ABG showed pH 7.30, pCO2 41, PO2 29, Base Excess -5.9. Another fluid bolus was given, as well as sodium bicarbonate and morphine, without improvement.

A cardiologist was consulted, and a stat echocardiogram done in the E.D. showed Tetralogy of Fallot with severe right ventricular outflow tract obstruction. A dose of phenylephrine (alpha agonist) was given, resulting in a rapid improvement in oxygen saturation to 100%. Repeat ABG showed pH 7.29, pCO2 37, pO2 132, Base Excess -8.3. Shortly thereafter, the patient's oxygen saturation began to drift back down into the 80's, so a phenylephrine infusion was started, with improvement in O2 Sat to the 90's. The patient was admitted to the Pediatric Intensive Care Unit.

Teaching Points:

1. Tetralogy of Fallot includes four congenital heart abnormalities: (1) a ventricular septal defect (VSD), (2) right ventricular outflow tract obstruction, (3) right ventricular hypertrophy, and (4) overriding of the aorta. The right ventricular outflow tract obstruction may be in the form of infundibular stenosis (50%), pulmonary valve stenosis (10%), or a combination of the two (30%). In the most severe form of the anomaly, the pulmonary valve is atretic (10%).
2. Tetralogy of Fallot was suspected in this patient because of cyanosis and hypoxemia out of proportion to the degree of wheezing and respiratory distress. He had previously been followed with the diagnosis of VSD without confirmation by echocardiogram.
3. The possibility of foreign body aspiration should also be considered in any child this age with wheezing and cyanosis. In this case, the CXR findings supported the diagnosis of TOF. If the CXR had instead shown findings consistent with foreign body aspiration, such as asymmetric atelectasis, consolidation, or air trapping, bronchoscopy should be performed. Comparison of inspiratory and expiratory films may aid in making the diagnosis of foreign body aspiration.
4. In TOF, the large nonrestrictive VSD results in identical systolic pressures in the right and left ventricles. Depending on the degree of the right ventricular outflow tract obstruction, either a left-to-right or a right-to-left shunt is present. In acyanotic TOF, mild pulmonary stenosis results in a left-to-right shunt. In cyanotic TOF, more severe degrees of pulmonary stenosis result in a right-to-left shunt. Children with the acyanotic form of TOF gradually develop the cyanotic form by 1-3 years due to worsening pulmonary hypertension.
5. The classic CXR of cyanotic TOF shows a "boot-shaped" heart caused by enlargement of the right ventricle and concavity of the upper left heart border (caused by hypoplasia of the main pulmonary artery segment). Heart size is usually normal, and pulmonary vascular markings are decreased. The CXR of acyanotic TOF is indistinguishable from that of a small to moderate VSD, and may show increased heart size and increased pulmonary vascular markings because of the left-to-right shunt.
6. Episodes of paroxysmal hypoxemia, also called hypercyanotic or tetralogy spells ("Tet Spells") are seen commonly in infants and children with TOF. They are caused by lowering of the systemic vascular resistance or increasing resistance to right ventricular pulmonary outflow, resulting in increased right-to-left shunting at the level of the VSD. Increased cyanosis stimulates the respiratory center to produce hyperpnea. This in turn results in an increase in systemic venous return, increasing the right-to-left shunt through the VSD. This creates a vicious cycle with worsening cyanosis. The spells are usually self-limited, but severe spells may be fatal.
7. Treatment of a hypercyanotic spell includes the following:
   1. Place the child in the knee-chest position. This increases the systemic vascular resistance by compressing the arterial circulation of the lower extremities. This should decrease the amount of right-to-left shunting and favor pulmonary blood flow.
   2. Administer oxygen; however, realize that this has limited benefit, since the problem is reduced pulmonary blood flow, not the ability to deliver oxygen to the lungs.
   3. Administer morphine sulfate 0.1 mg/kg IV or IM. The benefit of morphine sulfate may be in suppressing the respiratory center and decreasing hyperpnea.
   4. Treat the metabolic acidosis with sodium bicarbonate, 1 mEq/kg IV. This reduces the respiratory stimulation by metabolic acidosis, and may diminish the increase in pulmonary vascular resistance caused by hypoxia and acidosis.
   5. Administer phenylephrine 5-20 mcg/kg IV every 10-15 minutes as needed. Phenylephrine increases the systemic vascular resistance, forcing more blood flow to the lungs (i.e., decreasing the degree of right to left shunting across the VSD). Our patient did not respond to the knee-chest position, oxygen, morphine sulfate, or sodium bicarbonate, but showed dramatic improvement after phenylephrine administration. He ultimately required a continuous phenylephrine infusion to maintain adequate pulmonary blood flow to keep oxygen saturations in the 90's. A phenylephrine drip may be run at 0.1-0.5 mcg/kg/min, titrated to desired effect. Phenylephrine is a potent vasoconstrictor that will result in reduced renal and mesenteric perfusion as well.
   6. Administer propranolol, 0.1 mg/kg slow IV push. The dose may be repeated in 15 minutes. By decreasing cardiac contractility, propranolol may decrease infundibular obstruction of right ventricular outflow. Propranolol may also be given orally at 2-4 mg/kg/day PO to prevent hypercyanotic spells. When used chronically, propranolol may also have the beneficial effect of stabilizing peripheral vascular reactivity. Propranolol is a beta blocker and this may induce bronchospasm in patients prone to this.

References:

1. Neches WH and Ettedgui JA. Tetralogy of Fallot. In Oski FA ed. Principles and Practice of Pediatrics. Philadelphia, J.B. Lippincott Co., 1990, pp. 1402-1405.
2. Park MK. The Pediatric Cardiology Handbook. St. Louis, Mosby-Year Book Inc., 1991, pp. 92-98.
3. van Roekens CN, Zuckerberg AL. Emergency Management of Hypercyanotic Crisis in Tetralogy of Fallot. Annals of Emergency Medicine 1995;25:256-258.