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Ann Thorac Surg 1995;60:306
© 1995 The Society of Thoracic Surgeons
DR LESLIE HAMILTON (Newcastle-Upon-Tyne, United Kingdom): I am pleased to see that the search for the ``Holy Grail'' of a selective pulmonary vasodilator continues, and I congratulate Goldman and associates on what is obviously another step down this road. I do not have access to nitric oxide at the moment, so I am limited to prostacyclin, and you have demonstrated very well the difficulty with systemic hypotension. There have been some suggestions in the literature recently of giving prostacyclin via the endotracheal tube. Do you have any comments on that?
Second, I still have major concerns about the safety, both in the short term (although you have commented on that) and in the long term regarding the use of nitric oxide. Do you have any comments on toxicity, and do you feel comfortable recommending nitric oxide for prophylactic use in patients you would consider at high risk of pulmonary hypertension postoperatively?
DR LUDWIG K. VON SEGESSER (Zurich, Switzerland): You have told us that hypoxia is one of the vasoconstrictor agents too, and therefore I wanted to know if there was any difference between groups with regard to hypoxia before application of the specific agent.
DR HILLEL LAKS (Los Angeles, CA): I very much enjoyed this report documenting your extensive experience. Some people have postulated that there may be a rebound phenomenon seen after stopping nitric oxide administration, resulting in an acute pulmonary hypertensive crisis. Have you seen that? You had one death in which this may have happened. Do you recommend therefore that one proceeds to a more long-acting, more conventional pulmonary vasodilator after you have stopped nitric oxide administration?
DR GOLDMAN: I thank the discussants for their questions.
In response to Dr Hamilton's first question with regard to the inhalational administration of prostacyclin (PC), there are at present only sporadic reports on the administration of PC by this route. The clinical potential in the management of children with postoperative pulmonary hypertension has yet to be tested. Although we had originally considered comparing inhaled nitric oxide (INO) with inhaled PC, this appeared premature. In addition, a personal communication with one of the authors who has administered inhaled PC revealed that severe coughing was a major side effect in a number of the awake adults studied. This side effect may, however, be abolished by the use of deep sedation and the administration of PC via a jet nebulizer to keep the inhaled particle size down to a minimum. It also remains to be seen whether the acute benefits described from the inhalational administration of PC are sustained with continuous administration and whether there will be accumulation in the lung with systemic absorption resulting in similar side effects to those observed with the intravenous route of administration.
With respect to Dr Hamilton's second question on nitric oxide toxicity, I think the potential long-term side effects of INO are of concern to everybody administering this therapy. At the present time the safe administration of INO requires the monitoring of nitrogen dioxide and methemoglobin. Although we meticulously monitor NO2, we do not, however, know what the toxic dose of NO2 is for sick children-we only have safety guidelines for healthy adults working in industry. It is for this reason that we have moved toward administering the lowest effective dose of INO by conducting regular reverse dose–response studies.
As far as Dr Hamilton's third question on the potential prophylactic use of INO for high-risk patients is concerned, I would personally recommend against this for two reasons: First, there may be unknown toxic side effects of INO, and second, we have noticed that a number of patients do become extremely dependent on the INO during the first few days of therapy. This may lengthen their ventilatory and intensive care course.
The dependence on INO brings me to Dr Laks' question of a possible rebound phenomenon when the INO administration is stopped. Patients in whom a dependence on INO develops during its early course of administration would obviously be at risk of a serious rebound effect and an acute crisis if this therapy was suddenly withdrawn. In our experience such a situation can be avoided by gradually weaning the dose of INO as is tolerated. In this way most patients should be able to be successfully weaned from the INO within a week. In the patient in question who died 2 days after the discontinuation of INO administration, a secondary pneumonia had developed in the interim, which had precipitated her late-onset pulmonary hypertensive crisis. This was therefore not thought to be a rebound crisis caused by stopping INO administration 2 days earlier.
Related Article
Ann. Thorac. Surg. 1995 60: 300-305.
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