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- Dr Puneet Goyal, New Delhi, India (25 August 2006)
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INHALATIONAL NITROGLYCERINE AND PULMONARY HYPERTENSION
- K.R RAMANATHAN, PRINCE CHARLES HOSPITAL, MERTHYR TYDFIL, U.K. (8 August 2006)
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Dr Puneet Goyal, Cardiac-anaesthesiologist Senior Resident, Cardio-Thoracic centre, All India Institute of medical Sciences, New Delhi, India
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Reply- We thank Dr Ramanathan for his interest in our article on efficacy of nitroglycerin inhalation in reducing pulmonary arterial hypertension and for his kind comments. We have demonstrated only the acute effects of nitroglycerin inhalation on pulmonary and systemic haemodynamics in children with pulmonary arterial hypertension secondary to congenital heart disease. We did not study the duration of effect of inhaled nitroglycerin, to avoid multiple blood sampling and to avoid undue prolongation of cardiac catheterization time in these small children, which we have already mentioned as a limitation of our study. This drawback can be minimized by titrating the drug doses and frequency to the desired response. Nitroglycerin inhalation may not be considered useful for long term therapy of pulmonary arterial hypertension because of shorter duration of action and development of tachyphylaxis, where drugs with longer half life (such as inhaled prostanoids) will be more acceptable. But nitroglycerin inhalation can be effectively utilized for acute reduction of pulmonary artery pressure during pulmonary hypertensive crisis. We do not agree with Dr Ramanathan’s opinion that inhaled nitroglycerin will have a side effect profile similar to inhaled NO, because toxicity of inhaled NO is mostly related to formation of reactive products or metabolites like NO2 or peroxynitrites, which is not the case with inhaled nitroglycerin, though we have not studied the pulmonary and systemic (side) effects of long term inhalation of nitroglycerin. Further studies are needed to address issue of nitrate tolerance, rebound pulmonary hypertension and to demonstrate the effects of repeated nitroglycerin inhalation on pulmonary and systemic circulation. We do agree with Dr Ramanathan’s view that combination of other potential NO donor drugs like sildenafil with inhaled nitroglycerin can prove to be a more effective alternative for the management of pulmonary arterial hypertension. None of the patients in group II of our study (who responded to inhaled nitroglycerin but not to oxygen) had absolute contraindication to surgical repair of the defect. Out of 8 patients in this group, 6 patients have already undergone surgical repair of the ventricular septal defect with an uneventful peri-operative course. Dr Puneet Goyal Conflict of Interest:None declared |
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K.R RAMANATHAN DEPARTMENT OF ANESTHESIOLOGY,, PRINCE CHARLES HOSPITAL, MERTHYR TYDFIL, U.K.
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Dear Editor, I read with great interest, the article on inhaled nitro-glycerine [iNTG] and its effects on the pulmonary circulation. Its true that it might prove out to be a cheap alternative to inhaled nitric oxide [iNO] therapy and might be handy in centres where the iNO delivery system is not available. Infact we do not have much randomised trials comparing the relative potencies of iNTG, with iNO and inhaled prostaglandins as pulmonary vasodilators, though all of them have been used for the treatment of severe pulmonary hypertension and hence we will not be able to reach conclusions as to which is the best. It would be prudent to know the duration of action of iNTG since it would help in scheduling the dosage in patients with persistent pulmonary hypertension but long-term therapy with NTG is prone to tachyphyllaxis and systemic side effects like methemoglobinemia. Though the authors observed that the systemic side effects of iNTG were not significant, the pulmonary side effects of iNTG should be the same as that of iNO since its after all a potential NO donor. Hence doing away with the side effects of iNO like formation of free radicals, pulmonary cytotoxicity in the form of immune pulmonary fibrosis or even rebound pulmonary hypertension after withdrawal, does not seem to be a logical possibility even with NTG inhalation though I could not find any literature supporting the same. Another thing of interest would be to note whether reversibility of pulmonary hypertension with iNTG could be used as a standard to decide the operability though we have been using O2 as the gold standard in cath labs. I do agree with the authors’ concerns that the response to surgical correction may not be predictable albeit the fact that their pulmonary vasculature is still reactive and has not undergone irreversible changes. There are articles quoting the use of oral sildenafil , which is also a potential NO donor , in the treatment of secondary pulmonary hypertension especially after initial stabilisation with iNO. The relative pulmonary vascular specificity and its low cost gives it an added advantage like inhaled NTG and a combination of both may logically provide the cheapest alternative to iNO in the long term management of pulmonary hypertension. It will be interesting if the authors have followed up the group 2 patients who responded to NTG but not to O2 as to whether they were subjected to palliative or definitive surgeries at all, and if so, how these children behave intraoperatively and postoperatively. However,it is nice to note that alternatives to iNO do exist and these can be carried out with cost effectiveness especially in centres with no back up for special delivery devices for the administration of iNO. Dr.Ramanathan K.R krramanathan@gmail.com Conflict of Interest:None declared |
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