Management of the Patient with a bidirectional Glenn, by Melissa Jones.
My name is Melissa Jones.
I'm a nurse practitioner in the cardiac intensive care unit at Children's National Medical Center
in Washington DC and today we will briefly discuss the bidirectional Glenn patient and
post-operative management.
So the objectives of this talk are to briefly describe the history and the purpose of the
bidirectional Glenn procedure, we'll review relevant pre-operative data, discuss post-operative
physiology and complications, and review the challenges associated with mechanical support.
So, briefly, a history of the cavopulmonary anastamosis.
Dr. Carlyn was an Italian surgeon who first described the anastamosis in eight dogs.
There were surgeons in Italy, the United States, and Russia who continued to work on this procedure.
Dr. Shoemaker in the United States described two patients who underwent a cavopulmonary
anastamosis in 1954 and one had transposition of the great arteries and the other had truncus
arteriousus.
Both had elevated pulmonary vascular resistance and unfortunately both died.
In 1956, Dr. Meshalkin reports 24 cases of cavopulmonary anastamosis in patients in Russia.
One of them had pulmonary atresia, the other 23 had Tetralogy of Fallot.
And 21 out of 24 of those patients survived, suggesting that this was a potential benefit
to patients with cyanotic disease.
In 1958, Dr. Glenn completed the first successful cavopulmonary anastamosis on a 7 year old
with transposition of the great arteries and that patient survived.
So the bidirectional Glenn is now the standard second stage of the single ventricle palliation
pathway.
It's an anastamosis between the superior vena cava and the right pulmonary artery.
This physiology provides completely passive pulmonary blood flow.
It reduces the volume load on the single ventricle, it preserves the myocardial and AV valve function,
it improves distribution of pulmonary blood flow and the growth of the pulmonary vascular
bed, and it provides a predictable QPQS.
It's oftentimes a very stable circulation for high risk single ventricle patients.
These two diagrams illustrate the fact that there are many variations of single ventricle
anatomy that will undergo a bi-directional Glenn procedure.
On the left is a patient with hypoplastic left heart syndrome and on the right is a
patient with truncus arteriosus in complete AV canal, with bad AV valve disease.
So what is the information that we need to gather before the bi-directional Glenn procedure?
So we want to know about the pulmonary artery pressure and anatomy, the pulmonary vascular
resistance, the condition of the aortic arch, specifically if the patient had an Norwood
as the stage one procedure.
We want to know the function of the AV valves, the caval anatomy, the ventricular compliance,
and pulmonary vein sats.
The goal of post-operative management is to reduce the transpulmonary gradient.
Important cardiopulmonary interactions to consider are the effects of positive pressure
ventilation and spontaneous breathing.
Spontaneous breathing leads to negative intrathoracic pressure, a rise in the RA transmural pressure,
and a decrease in the right atrial pressure, improving pulmonary and systemic venous return.
Positive pressure ventilation, on the other hand, creates positive intrathoracic pressure,
a decrease in the right atrial transmural pressure, and a rise in the right atrial pressure,
decreasing pulmonary and systemic venous return.
Maintaining low atrial pressure is important to promoting systemic and pulmonary venous
return and optimizing hemodynamics.
This slide illustrates a patient that was extubated shortly after returning from the
operating room.
On the x-axis is time and the y-axis is the NIRS monitoring.
You can see that, after the patient was extubated, they had a rise in their NIRS, suggesting
improved oxygen delivery.
This is a study out of China that looked at 24 patients after the bidirectional Glenn
procedure.
They used standard monitoring plus cerebral and mesenteric NIRS and ultrasound monitoring
of the ascending aorta to derive the cardiac index.
They looked at three specific time points, 30 minutes prior to extubation, 30 minutes
after extubation, and 12 hours after extubation.
The top two graphs depict the cerebral and mesenteric NIRS.
You can see that, after extubation at points two and three, the NIRS rise.
The graph on the lower left shows the central venous pressure after extubation, which, as
you can see, falls.
The graph on the bottom right shows the cardiac index, which also rises after extubation.
Cyanosis is one of the common post-operative problems after a bidirectional Glenn.
One simple way to think about the potential etiology of cyanosis, or treatment interventions
to treat cyanosis after a bidirectional Glenn procedure, is to think about the blood flow
that makes up the aortic sat.
So we must consider a low mix venous sat, potentially from anemia, increased oxygen
consumption, or low cardiac output.
Another consideration is pulmonary vein desaturation.
We also must consider that there is a potential for a restrictive atrial septum that's precluding
oxygenated blood from getting to the right side of the heart and out to the body.
There is a potential for decreased pulmonary blood flow, which may be the result of elevated
pulmonary vascular resistance, anatomic obstruction to the bidirectional Glenn, poor ventricular
function, or AV valve regurgiation.
Finally, we must consider VV collaterals, collaterals that bypass the lungs and go directly
to the heart from the venous system.
We know that PVR is lowest at FRC, so an anesthetic plan that allows for early extubation is key.
Premature extubation in an oversedated patient could lead to atelectasis and therefore a
rise in PVR and poor hemodynamics.
On the other end of the spectrum is the patient who must stay intubated.
If a patient must stay intubated, then minimizing the mean airway pressure will help to improve
hemodynamics and oxygenation.
In the setting of a cyanotic patient after a bidirectional Glenn procedure, allowing
for permissive hypercarbia, mild permissive hypercarbia, might help to improve cerebral
blood flow and then subsequently pulmonary blood flow.
This is a patient who had a DKS, along with their bidirectional Glenn procedure.
The green line is the PO2 and the blue is the PCO2.
The patient's PO2s were hovering around the high 20s.
We allowed for a rise in the CO2 and subsequently the PO2 rose to the mid 30s.
Another post-operative problem that we see often in the bidirectional Glenn is hypertension.
The etiology is unclear, perhaps from pain, catecholamine surge, or intracranial hypertension.
Perhaps this hypertension is needed for cerebral perfusion or perhaps the ventricle is hyperdynamic
after acute removal of volume load.
It's important to remember that these patients are often not narcotic naive.
This is a recent review of NPC QIC database, characterizing factors that lead to increased
length of stay after the bidirectional Glenn procedure.
They looked at 448 patients after the stage two.
Those patients all went home after the stage one.
The median length of stay was eight days.
If there is an early Glenn, between the ages of two to four months, then there was an additional
three days of hospitalization noted.
Factors associated with a prolonged length of stay after the bidirectional Glenn was
the need for a reoperation or cardiac cath after the stage two, the use of non-oral forms
of nutrition, or the development of post-operative complications.
Moving on to the challenges of mechanical support with a bidirectional Glenn, this is
an evaluation of the ELSO database to characterize the differences between survivors and non-survivors
of ECMO after the bidirectional Glenn procedure.
They looked at 103 infants, ranging in age from 3 months to 1 years.
The predictors of mortality are listed.
41% of these patients survived to hospital discharge and 14% of those had subsequent
neurologic injury.
We know there's not a lot of experience with bidirectional Glenn patients requiring VAD
support.
This is a retrospective review of patients supported on the Berlin Heart after a cavopulmonary
shunt.
They reviewed 4 patients and 3 out of 4 of those patients survived a transplant.
What they found is that ventricular cannulation was facilitated by the excision of trabeculae
and chords, often from the right ventricle.
So in summary, the bidirectional Glenn reduces the volume load on the single ventricle and
preserves myocardial function, AV valve function, and provides a predictable QpQs.
Spontaneous breathing is best for reducing the transpulmonary gradient and optimizing
hemodynamics.
Cyanosis and hypertension are common post-operative problems.
The anatomy of the bidirectional Glenn presents challenges for mechanical support.
However, ECMO and VAD are both options if medical management is not enough.
Thank you for listening to this talk and I hope it's provided you with useful information
to help you take care of patients after the bidirectional Glenn procedure.
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