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Effect of Exogenous Surfactant on Total Respiratory System Compliance

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Effect of Exogenous Surfactant on Total Respiratory System Compliance Arch Dis Child: first published as 10.1136/adc.59.8.798-a on 1 August 1984. Downloaded from Archives of Disease in Childhood, 1984, 59, 798-802 Correspondence Effect of exogenous surfactant on total ner's own published data' show that newborn babies do not always accept lung inflation passively and often respiratory system compliance respond with a rejection reflex or an augmented inspira- tion. Both profoundly alter the tidal volume and therefore Sir, the calculation of compliance. Also the expiratory tidal I should like to comment on the paper by Milner et al on volume might be reduced because the inhaled air is the effect of the Cambridge artificial surfactant on lung trapped in the lung as the peripheral airways collapse compliance of intubated preterm babies at birth.' during expiration. Factors like this suggest that the In 1980 Fujiwara' claimed that an 'artificial surfactant' measurement of compliance in this situation may produce dramatically improved the oxygenation of babies with results that are difficult to interpret. Perhaps functional respiratory distress syndrome. Since then there has been residual capacity or thoracic gas volume would be more considerable interest in exogenous surfactant treatment. reliable measurements if they could be made accurately. Four years later, however, there are few published reports (3) Surfactant treated babies received a dose im- with results of clinical trials that can be interpreted with mediately after birth. The 'before treatment' measurement confidence. In most studies there are too few babies and no of compliance was therefore made before the second dose. controls, or unsatisfactory controls.36 Even the careful This fact was not considered to be relevant by the authors study of Halliday7 did not include enough babies to show even though the treated babies had a 'before treatment' conclusive results. compliance on average 50% higher than the control group The publication of Milner's paper' adds another (mean (SD) 0-54 (0-19) v 0-36 (0-22) ml/cm H,O). This, example of tantalisingly inconclusive data to the published like the rest of the compliance data, was not statistically reports. It is such a small study that it is not possible to significant because the numbers are too small for such a make any satisfactory conclusion. The reasons for this large variation in the compliance measurement. study being unsatisfactory are: (4) The babies were not randomised to this particular (1) There is no consideration of the numbers of babies study. They were extracted from a larger randomised trial. copyright. needed in their trial to show a significant difference Four years after Fujiwara's original paper the role of between the compliance measurements of the surfactant exogenous natural or artificial surfactant remains unde- treated babies and the controls. For this trial the way to cided; I believe that it is counterproductive to publish small calculate the number of babies needed is firstly to series of anecdotal data and then draw unsubstantiated determine what change in compliance could be considered conclusions from them. a significant improvement or 'the smallest medically COLIN J MORLEY relevant difference'. Milner mentions that there was no University Clinical 'significant improvement' without defining what he con- of Cambridge School, Addenbrooke's Hospital, http://adc.bmj.com/ sidered to be significant. Obviously this value depends on the accuracy and reproducibility of the compliance Cambridge CB2 2QQ measurements. Compliance varied three to fourfold among the controls before (0-21 to 0-61 ml/cm H,O) and after saline (0-15 to 0-69 mUcm H2O). With this enormous Professor Milner and co-workers comment: variation the smallest acceptable difference would need to be quite large, that is, a 50% change. The mean lung Firstly, Dr Morley criticises the number of babies in our compliance of the controls before saline was 0-36, there- study.' Our aim as stated in the paper was to see whether fore a 50% change would be 0-18. Using the relevant Table artificial surfactant given during resuscitation produced on September 30, 2021 by guest. Protected in 'Statistics in Practice" it can be calculated (using this changes similar to those seen when added to animal value of 0- 18 and the sample's standard deviation of 0.22) models. For this, we considered that small numbers were that a trial size of 70 babies would be needed to detect a adequate, similar indeed to those published by Dr Morley 50% change in compliance at the one per cent'level with an himself."' We also stated that this type of study could not 80% power. Realistically, it might be surprising if surfac- determine when artificial surfactant altered outcome and tant treatment at this stage altered compliance by as much entirely agree that for this, vastly larger numbers would be as 50%. To detect a smaller difference, however, a trial required. with many more babies would be needed. Milner's study In his second point, he claims that our measurements with only 16 babies has a power of less than 20%, that is might be inaccurate due to respiratory efforts by the only a 20% chance of detecting a significant difference at a babies. We were, of course, very careful to exclude one per cent level and not much more at the level of five inflations where the baby made any respiratory efforts per cent. whatsoever. Also we know of no conclusive evidence that (2) The paper concentrates on the acute effect of air is trapped in the lungs during expiration immediately surfactant treatment on static lung compliance without after delivery and would be grateful to receive a reference discussing why it was an appropriate measurement. Mil- on this. 798 Arch Dis Child: first published as 10.1136/adc.59.8.798-a on 1 August 1984. Downloaded from Correspondence 799 Thirdly, as stated in our paper, it is possible that some terms, is readily recognised by the usual criteria of of the first dose remains in the upper airway before inappropriate attention span, impulse control, restlessness, resuscitation. We think this unlikely as the babies had not and rule governed behaviour developing in late infancy breathed and were 'sucked out' during the resuscitation and not associated with gross neurological, sensory, or period. The differences in the initial compliances were motor impairment or severe emotional disturbance. It is more likely due to the fact that the control group had more prevalent in two to three per cent of the child population, very immature babies. predominantly in boys.2-3 Our open trial showed initial Fourthly, the babies were randomised as stated in the improvement in 30 of 35 (86%) children after exclusion paper, certainly to a greater extent than in Dr Morley's diet and challenge testing. As most of this was due to the previous publication.3 removal of food colouring, the eventual diet was neither Finally, we consider that the studies were not anecdotal harmful not irksome, but a good dietician is needed to and that investigating the physiological response to forms work out the details. of treatment are valid, even if they do not measure I fully accept the placebo effect but do not think this whether a particular form of treatment alters the long term explains all the benefits of the diet. Some children outcome. continued to react to the additives over an 18 month period while many others did not (the 'diet' responders), but the mechanism is not clear. Psychometric testing, using ele- References ments of the Stanford Binet test under 4 years of age and Milner AD, Vyas H, Hopkin IE. Effect of exogenous surfactant the Wechsler intelligence scale for school aged children, on total respiratory system compliance. Arch Dis Child serially at six month intervals over a year (three assess- 1984;59:369-7 1. ments) showed significant improvement in two of four 2 Fujiwara T. Chida S, Watabe Y, Maeta H. Morita T. Abe T. preschool and six of eight school aged children on diet Artificial surfactant therapy in hyaline membrane discasc. alone-two of the latter increased their overall 10 by 15 Lancet 1980;i:55-9. and 20 points respectively over a six month period and this 3 Morley C, Bangham A, Miller N, Davis J. Dry artificial lung was maintained. A comparison may be made with two surfactant and its effect on very premature babies. Lanc et recent papers in Clinical Allergy on the effect of house dust 1981 ;i:64-8. 4 Smythe J, Metcalfe I, Dufty P, Possmayer F, Bryan M, mite hyposensitisation, where the beneficial effect was Enhorning G. Hyaline membrane disease treated with bovine clearly seen clinically but no in vitro immunological change surfactant. Pediatrics 1983;71:913-7. could be found to support the effect scientifically.5 copyright. 5 Hallman M, Merritt T, Schneider H, et al. Isolation of human Again I take issue on the subject of allergy. Several surfactant from amniotic fluid and a pilot study of its efficacy in writers agree (as I do myself) that hyperactive children and respiratory distress syndrome. Pediatrics 1983;71:473-82. their families show more signs of allergy to a wide range of 6 Wilkinson A, Jeffery A, Jenkins P. Controlled trials of dry foods than normal children; but that does not make surfactant in preterm infants (abstract). Arch Dis Chiild hyperactivity an allergic condition." Even the late Ben 1982;57:802. 7 Halliday H, McClure G, McC.Reid M, Lappin T, Meban C, Feingold denied that this was an allergic response,7 and Dr Thomas B. Controlled trial of artificial surfactant to prevent Collins-Williams in Toronto was unable to find a signifi- respiratory distress syndrome.
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