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:
     a)  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.
     b)  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.
     c)  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. 
     d)  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.
     e)  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.
     f)  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.