VASCULAR RESUSCITATION
Vascular resuscitation is a neglected aspect of neonatal resuscitation.
Those who are premature and asphyxiated near the end of labor are especially likely
to be hypovolemic.
If the neonate's condition does not improve rapidly with ventilation
and tactile stimulation, an umbilical artery catheter should be inserted to measure
blood gases and pH, to measure arterial blood pressure, to expand blood volume, and
to administer drugs. Most preterm neonates weighing less than 1250 g at birth and
1% to 3% of term neonates require an umbilical artery catheter during resuscitation.
It also may be helpful to insert an umbilical venous line whose tip is in the superior
vena cava or the right atrium to determine the adequacy of blood volume replacement.
Insertion of Intravascular Catheters
Umbilical Artery Catheterization
A stopcock should be attached into one end of a 3.5F or 5.0F umbilical
artery catheter, and the catheter and stopcock should be flushed with sterile saline.
The stump of the umbilical cord is grasped with a clamp and the cord held straight
up in the air. The abdomen and umbilical cord are sterilized with an iodine-containing
solution, and the abdomen is sterilely draped. Next, a sterile umbilical tape is
tied loosely around the cord, and the cord is cut cleanly with a scalpel, leaving
2 cm of stump. The stump is firmly grasped with the gloved fingers of one hand,
and one of the two thick-walled umbilical arteries is dilated with a curved iris
forceps. With the stopcock filled with fluid, a 3.5F umbilical artery catheter is
inserted into the artery if the neonate weighs less than 1500 g, or a 5F catheter
is used if the neonate weighs 1500 g or more. After the catheter is inside the vessel,
the stopcock should be partially opened. Some resistance may be encountered when
the catheter has been advanced 3 to 5 cm into the vessel, but this resistance can
usually be overcome by applying steady downward pressure on the catheter. If the
catheter cannot advance, a second catheter can be inserted into the other artery
while leaving the first catheter in place. This maneuver often causes one or the
other vessel to relax and permits one of the catheters to be advanced into the aorta.
When blood appears in the catheter, the stopcock should be closed, and the catheter
should be advanced 1 to 2 cm, depending on the size of the neonate. Blood should
be withdrawn from the catheter, and all air should be removed from the system. (The
accidental injection of small amounts of air [<0.1 mL] may obstruct blood flow
to the legs for several hours.) The catheter should be attached to a pressure transducer
and the arterial pressure measured.
Umbilical Venous Catheterization
The stump of the umbilical cord is prepared, grasped, and tied
as described previously. The single, large, thin-walled
umbilical vein is grasped with iris forceps, and the air-free catheter is inserted
3 to 5 cm into the vessel with a twisting motion. The stopcock must be closed to
prevent aspiration of air through the catheter if the patient takes a deep breath.
The catheter is connected to a pressure transducer, and the intravascular pressure
is displayed on an oscilloscope. When the catheter tip enters the thoracic vena
cava, the pressure tracing deflects negatively with each spontaneous inspiration.
When the catheter tip is in an intra-abdominal vein, the deflection is positive
during inspiration. After the catheter tip is in the intrathoracic vena cava, the
catheter should be fixed in place and the PO2
of the blood measured. If the PO2
exceeds
40 mm Hg, the catheter tip is probably in the left atrium and should be withdrawn
into the right atrium or the intra-thoracic inferior vena cava. It is imperative
that no air be injected through venous catheters because the air may enter the systemic
circulation through the foramen ovale and occlude a coronary or cerebral artery.
If it does, the neonate may die or suffer CNS damage. If the catheter "tickles"
the atrial septum, the neonate may suffer arrhythmias. Withdrawal of the catheter
a short distance can solve the problem.
