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Comparison of effectiveness between gas flow 1 and 2 L.min-1 for general anesthesia in infants and children |
Suraseranivongse S, Chowvanayotin S, Pirayavaraporn S, Valairucha S, Arunpruksakul N, Areewatana S |
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Record Status This is a critical abstract of an economic evaluation that meets the criteria for inclusion on NHS EED. Each abstract contains a brief summary of the methods, the results and conclusions followed by a detailed critical assessment on the reliability of the study and the conclusions drawn. Health technology The use of fresh gas flow (FGF), at rates of 1 and 2 litres per minute (L/min), for general anaesthesia in infants and children.
Economic study type Cost-effectiveness analysis.
Study population The study population comprised infants and children aged between 1 month and 8 years with ASA physical status I or II, who had undergone surgery that lasted at least 1 hour.
Setting The setting was secondary care. The economic study was carried out in Bangkok, Thailand.
Dates to which data relate The dates when the effectiveness and resource use data were collected were not reported. The price year was not reported.
Source of effectiveness data The effectiveness data were derived from a single study.
Link between effectiveness and cost data The same patients provided the effectiveness data and the cost data. It would appear that the costing was carried out prospectively.
Study sample Power calculations were reported. Twenty-four patients in each group would be needed to detect a statistical difference of 10% (one-sided test with alpha error of 0.05) at a power of 0.90. The 77 paediatric patients included in the analysis were randomly assigned to two groups. Thirty-eight patients received FGF 1 L/min (study group) and 39 received FGF 2 L/min (control group). The patients in the study group had a median age of 2 years (interquartile range: 0.775 - 3.5) and a mean body weight of 11.31 (+/- 3.93) kg The patients in the control group had a median age of 1.5 years (interquartile range: 0.83 - 2) and a mean body weight of 10.67 (+/- 4.18) kg. Initially, all patients received a high flow of gas of 6 L/min for 15 minutes, after which the total gas flow was reduced. Each group was stratified into three strata according to age, type of anaesthesia and type of ventilator used.
Study design The study was a prospective, randomised clinical trial that was conducted in a single centre. Random number table were used for the study design. Blinding of the outcome assessment was not reported. The clinical outcomes were assessed until recovery.
Analysis of effectiveness The analysis was conducted on an intention to treat basis. The primary health outcomes assessed were:
the success rate,
the necessity of using a capnometer,
the need of a larger endotracheal tube,
the time elapsed from the cessation of isoflurane until recovery, and
low flow duration.
The secondary health outcomes were:
leakage in the system;
changes in arterial oxygen saturation, end tidal carbon dioxide, temperature, inspired oxygen concentration, and inspired and expired concentration nitrous oxide; and
isoflurane dial setting.
There were no statistically significant differences between the two groups at baseline in terms of age, ratio of infants and children, body weight, anaesthetic technique, type of ventilator used, type of surgery, anaesthetic time and operation time.
Effectiveness results The success rate was 100% (39 out of 39) in the control group versus 92% (35 out of 38) in the study group. The difference was not statistically significant.
All failure cases were due to system leakage.
The time elapsed from termination of isoflurane until recovery was significantly longer in the study group (5 minutes) than in the control group (12 minutes), (p=0.010). However, the duration from cessation of low flow until recovery was no different.
There were no statistically significant differences in the other health outcomes between the two groups.
Clinical conclusions The success rate of using FGF 1 and 2 L/min was found to be equivalent. A lower FGF (i.e. 1 L/min) did not result in a hypoxic FGF mixture, nor did it lead to significant re-breathing of carbon dioxide in comparison with the higher FGF (i.e. 2 L/min).
Measure of benefits used in the economic analysis The effectiveness analysis indicated equal efficacy of the two interventions. Therefore, only the costs were considered in the economic analysis. No summary measure of health benefits was derived.
Direct costs The authors did not report the perspective from which the costing was carried out. The direct costs included in the analysis were the costs of isoflurane mass consumed, soda lime and FGF. The cost of anaesthetic gas and agent analysers, including a capnometer, were not included in the analysis. Discounting was not carried out as the costs were incurred during less than 2 years. The costs were taken from the authors' setting. The dates and price year were not reported. The quantities were reported in detail. Only the average costs per minute were reported.
Statistical analysis of costs No statistical analysis of the costs was carried out.
Indirect Costs The indirect costs were not included.
Sensitivity analysis No sensitivity analysis was reported.
Estimated benefits used in the economic analysis See the 'Effectiveness Results' section.
Cost results The total average cost per minute was THB 1.5418 for the study group and THB 2.4799 for the control group.
A FGF of 1 L/min could save 39.6% in isoflurane costs (THB 1.4526 versus 2.405) and 50% in fresh gas (THB 0.03122 versus 0.06245), but 78.4% more could be spent on soda lime (THB 0.0575 versus 0.0124). The overall saving from using an FGF of 1 L/min was 37.8%.
Synthesis of costs and benefits Authors' conclusions A fresh gas flow (FGF) of 1 litre per minute (L/min) could be safely used, if there is no system leakage, at a lower cost than that for an FGF of 2 L/min. Should system leakage occur, it is readily corrected by increasing the FGF to 2 L/min.
CRD COMMENTARY - Selection of comparators The authors did not explicitly justify the choice of the comparators. It was unclear if FGFs of 1 and 2 L/min represented arbitrary low flow gas levels, or whether they reflected recommended low flow levels in the physicians' community. You should judge whether those comparators are relevant in your setting.
Validity of estimate of measure of effectiveness The analysis was based on a prospective randomised clinical trial, which was appropriate given the study question. The study had several strengths. First, power calculations were carried out to prove statistical significance in health outcomes. Second, an appropriate statistical analysis was conducted to compare the groups at baseline. Finally, the study sample appears to have been representative of the study population. Hence, this will allow the authors' findings to be generalised to other patients. The main drawback of the study was that the outcome assessment was not performed blind. Therefore, some biases might have affected the results of the analysis.
Validity of estimate of measure of benefit The analysis of benefits was based upon the clinical equivalence of the interventions. Therefore, the economic analysis only included the costs.
Validity of estimate of costs Although the perspective adopted was unclear, it appears that the cost categories relevant to a hospital perspective have been included. The authors reported that some costs were excluded from the analysis. Capnometer costs were excluded because they were similar in both groups, whereas the costs of the anaesthetic gas were excluded because they could be safely adjusted by clinical prediction. These omissions are unlikely to have affected the authors' conclusions. The quantities were reported separately from the costs, which will help the generalisability of the results to other settings. The resource use quantities were taken from the clinical trial. No statistical or sensitivity analysis of the quantities was carried out. The unit costs were not reported, but average costs per minute were estimated using data from the authors' setting. No statistical or sensitivity analysis of the prices was carried out, which limits the interpretation of the results. No price year was reported, which will prevent any possible inflation exercises. Discounting was not relevant, as all the costs were incurred during a short time, and hence was not performed.
Other issues The authors did not compare their results with those from other studies. The issue of generalisability to general practice was addressed. The authors suggested that in general practice where a special ventilator is not available, a lower FGF of 1 L/min was safe in most cases with both pressure- and volume-limited ventilators. The authors do not appear to have presented their results selectively and their conclusions reflected the scope of the analysis. The authors did not report any limitations of their study.
Implications of the study The authors recommended the use of a capnometer in both types of FGF, whereas inspired oxygen and inspired isoflurane concentrations could be clinically adjusted.
Source of funding Supported by the Sisiraj Research Development Fund and the Thailand Research Fund.
Bibliographic details Suraseranivongse S, Chowvanayotin S, Pirayavaraporn S, Valairucha S, Arunpruksakul N, Areewatana S. Comparison of effectiveness between gas flow 1 and 2 L.min-1 for general anesthesia in infants and children. Journal of the Medical Association of Thailand 2004; 87(11): 1343-1348 Indexing Status Subject indexing assigned by NLM MeSH Anesthesia, Inhalation /methods; Anesthetics, Inhalation /administration & Child; Child, Preschool; Cost-Benefit Analysis; Dose-Response Relationship, Drug; Humans; Infant; Oximetry; Volatilization; dosage /economics AccessionNumber 22005000342 Date bibliographic record published 31/01/2006 Date abstract record published 31/01/2006 |
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