Exhaustion of an ABEK nitric oxide absorber Costs of sevoflurane and propofol anaesthesia

Editor,—The ABEK HgCO NO-P3 filter (Drager) has been Editor,—We read with interest the article by Smith and colleagues on the costs of sevoflurane and propofol anaesthesia. In today’s described as an effective method of scavenging nitric oxide and nitrogen dioxide. The filter contains microglass fibres coated with cost-conscious climate, cost analyses such as the one published recently by Smith and colleagues are worthwhile. The authors copper and chromium salts, and the catalysts, manganese dioxide and copper oxide. This article describes its use with an Evita 2 have shown that induction and maintenance of anaesthesia with propofol is more expensive than induction and maintenance with ventilator with a minute volume of 6.1 litre min. Proximal nitric oxide concentrations of 55–70 ppm were maintained in 100% sevoflurane. However, we are concerned with some of their conclusions and would like to make a few general comments. oxygen. Measurement of environmental nitrogen dioxide concentrations over a 170-h period peaked at 0.4 ppm. The First, we were disappointed that, contrary to their claims, the authors had not included all direct and indirect costs. Rowe recommendation was that this filter could be used safely for up to 1 week. recently published a cost comparison of propofol and inhalation anaesthesia and we were surprised that this article, which Since this report, we have successfully used this filter. Readings taken close to the filter are usually undetectable, with a maximum contained a more comprehensive cost analysis, was not cited. The most glaring cost that the authors ignored was that of overnight recorded concentration of nitrogen dioxide 0.4 ppm. If a patient remains on nitric oxide for longer than 7 days, the filter is changed admission. We accept that their admission rate was low and unlikely to alter overall costs significantly, but it would have been routinely. However, we would like to describe a case in which the filter became exhausted within 72 h. helpful to include some estimate of the additional costs associated with the admission of the two patients who received inhalation A 16-yr-old was admitted to the PICU with respiratory failure after bone marrow transplantation. A presumed diagnosis of anaesthesia only. Notwithstanding the costs arising from i.v. infusion pumps, other costs that should have been mentioned pneumocystitis pneumonia was made and he was treated with oxygen via facial mask CPAP and high-dose co-trimoxazole. His include the capital and maintenance costs of sevoflurane vaporizers and the scavenging apparatus. condition deteriorated and an open lung biopsy was undertaken after which he required mechanical ventilation. He continued to Second, we believe that the use of nitrous oxide for all groups was a flaw in the study design. The environmental problems deteriorate rapidly and nitric oxide 20 ppm was commenced. His lungs were ventilated at a minute volume of 16 litre min, FIO2 associated with the use of nitrous oxide were ignored completely. 3 Furthermore, nitrous oxide is known to increase the incidence of 100%, tidal volume 800 ml, ventilatory frequency 20 bpm and I:E ratio 1:1. Airway pressures were 40/10 cm H2O. Expired nitrogen nausea and vomiting, 4 5 and this has made interpretation of the results more difficult. There was already a significantly lower dioxide concentrations were measured using an electrochemical sensor (with PTFE membrane). Concentrations remained less than incidence of nausea and vomiting in patients who received propofol, but omission of nitrous oxide may have resulted in an 2 ppm at all times. After 72 h there was a sudden increase in the environmental nitrogen dioxide level. After replacement of the even lower incidence. Ventilation with oxygen and air would probably have increased propofol use and cost, but this has to be scavenging filter, environmental nitrogen dioxide concentrations decreased rapidly to zero. balanced against the benefit of emesis-free recovery. Treatment of PONV comprised only one drug administration in the propoful Our report demonstrates the need to measure environmental nitrogen dioxide concentrations, particularly in the vicinity of the group, whereas 21 doses of different drugs were required to treat patients in the sevoflurane nitrous oxide group. filter, as the filter may become exhausted more quickly than reported previously. Compared with the results of Squire, Knightley Third, in the discussion, the authors present their study as confirming that sevoflurane ‘is an acceptable day-case anaesthetic’. and Petros, this patient was receiving a lower inspired nitric oxide concentration but had a much greater minute volume. The Later they assert that propofol was associated with ‘few clinical benefits in terms of speed or quality of recovery’. Sevoflurane, manufacturers estimate that the filter will take 4–5 litre of nitric oxide with a flow rate of 8 litre min. However, our patient had however, was associated with a six-fold higher incidence of nausea and a 12-fold higher incidence of vomiting than induction and twice this flow rate. We suggest that when patients have such a high minute volume while using nitric oxide, the ABEK filter maintenance of anaesthesia with propofol. Given that postoperative emesis is a concern patients have before surgery, it is difficult to should be changed at least every 72 h. see how induction and maintenance of anaesthesia with sevoflurane can be considered ‘acceptable’. Surely this markedly lower C. G. Stack incidence of nausea and vomiting associated with propofol is ‘a M. Gibbons significant clinical benefit’? In fact, one in 10 patients in the J. A. Nuttall sevoflurane group did not wish to receive the same anaesthetic M. Quinton during future surgery. In the analysis of ‘cost’, should not the cost Paediatric Intensive Care to the individual patient in terms of personal comfort also rate? Sheffield Children’s Hospital Finally, it is worth pointing out that anaesthesia where nitrous Western Bank oxide is used is, by definition, not ‘total i.v. anaesthesia’, as Sheffield, UK mentioned in the last paragraph of the article.