Editor’s Note

Drs. Pelletier and Jacobs have given us a beautiful series of drawings illustrating the technique for these two Stage II operations for patients with a single ventricle.  It is very interesting that the results of the two different techniques, as shown in Table 1, are nearly identical.

The hemi-Fontan operation, as illustrated in these drawings, has been perfected by Dr. Jacobs.  His original description of this operation was published in 1996 in the Annals of Thoracic Surgery in a classic paper.  These illustrations show the culmination of over 10 years’ experience with this operation perfecting its techniques.

Of interest, our service at Children’s Memorial Hospital has preferred the bidirectional Glenn technique.  I thought I would comment on some technical differences that we have utilized.  One of the main differences is the use of direct caval cannulation of the superior vena cava with either an 8-Fr or 10-Fr cannula (Edwards Lifesciences Research Medical RMI cannula, Irvine, CA).  This allows continuous cardiopulmonary bypass without maneuvering a cannula in and out of the orifice of the superior vena cava during the anastomosis.

Another technical difference is that we have routinely ligated the azygos vein during the performance of the bidirectional Glenn.  This, of course, prevents steal of blood from the superior cavopulmonary anastomosis circuit to the inferior vena cava.  Often the inferior vena caval pressure is less than the pressure in the cavopulmonary circuit after a bidirectional Glenn or hemi-Fontan and steal through the azygos vein can lead to progressive desaturation.  We have used the site of the ligated and divided azygos vein as a posterior landmark for beginning the anastomosis in the mid-portion of the posterior right pulmonary artery.

A third technical difference is that we use interrupted suture (7-0 PDS; Ethicon, Inc, Somerville, NJ) technique for the entire cavopulmonary anastomosis.  Using this suture technique, we have now performed 118 bidirectional Glenn procedures with a 6% mortality (7/118) and no reoperations or requirement for augmentation of the anastomosis because of stenosis at the time of the extracardiac Fontan.

Another point that I would like to emphasize regarding these operations is the postoperative management of these patients.  In general, postoperative cardiac surgical patients are frequently hyperventilated by the ICU staff in order to prevent pulmonary hypertensive crises and decrease the pulmonary vascular resistance.  Many physicians have the impression that after the bidirectional Glenn or hemi-Fontan procedure, hyperventilation will result in elevation of the peripheral oxygen saturation.  However, some very elegant studies performed by Dr Scott Bradley at the Medical University of South Carolina have demonstrated that this is actually not the case and that in fact a counter-intuitive phenomenon is occurring that all physicians who care for these patients should be aware of [1].  That phenomenon is that elevation of the CO2 to the high 40-to-low 50 mm Hg range actually increases the patient’s peripheral oxygen saturation and O2 delivery.  This counter-intuitive effect occurs because decreasing the ventilation with result of increase in CO2 increases cerebral blood flow.  This increase in cerebral blood flow greatly outweighs any increase in pulmonary vascular resistance caused by hypoventilation.  The increased cerebral blood flow results in increased blood returning to the jugular venous system to the superior vena cava, to the lungs, through the bidirectional superior cavopulmonary anastomosis.  Hence the patient who is having trouble with desaturation following the bidirectional Glenn or hemi-Fontan will respond to allowing the CO2 level to increase as a mechanism to increase their peripheral oxygen saturation rather than hyperventilating them to try to accomplish this goal.  This postoperative management detail should be familiar to any surgeon or intensivist who cares for these patients following bidirectional superior cavopulmonary anastomosis.  Of course, the goal, as mentioned by Drs Jacobs and Pelletier, is to extubate these patients early, which is a way of preventing hyperventilation through the ventilator circuit.

In summary, different institutions appear to prefer either the hemi-Fontan or the bidirectional Glenn, both resulting in a bidirectional superior cavopulmonary anastomosis.  The interesting point here is that different surgeons using very different techniques achieve very similar results with complex cardiac pathology.  It will take further long-term follow-up comparing the results of the lateral tunnel with the extracardiac Fontan with regard to arrhythmias, ventricular function, and complications of the Fontan operation such as protein-losing enteropathy, to determine which of these strategies provides the best outcome for children with functionally single ventricle.

References

1. Bradley SM, Simsic JM, Mulvihill DM.  Hyperventilation impairs oxygenation after bidirectional superior cavopulmonary connection.  Circulation 1998;98:II-372-7.