Method for manipulating peak flow measurements producing falsely raised readings.

Methods by which patients can artificially produce raised peak flow measurements have been described. We recently observed a patient manipulating the peak flow meter in a way that had not been described before. A study was therefore undertaken to determine if this technique could repeatedly produce clinically significant changes in peak flow readings. Fifteen adults, using a mini-Wright peak flow meter, made five measurements using the correct technique followed by five manipulated measurements under observation. Significant increases in peak flow measurements were observed in 14 of the 15 subjects. The mean increase in peak flow rate using the incorrect technique was 56% (range -4% to 86%). Clinicians should be aware that patients might employ this technique to manipulate measurements which could have consequences for management.

The use of pulse oximetry in the prevention of hyperoxaemia in preterm infants.

UNLABELLED: When deciding an appropriate upper limit for pulse oxygen saturation (SpO2) in preterm infants the usefulness of current data is limited by the fact that previous studies have examined a population of more mature infants and children or have applied various exclusion criteria which produce results unrepresentative of clinical practice. We tested the hypothesis of previous workers that maintaining the SpO2 below 98% would ensure an arterial oxygen tension (PaO2) less than 12kPa. A total of 477 simultaneous measurements of PaO2 and SpO2 were made using Ohmeda Biox oximeters on 43 infants who were less than 33 weeks gestation and receiving supplementary oxygen. Of 435 measurements performed when the SpO2 was 97% or less, 26 (6%) had a PaO2 greater than 12kPa. Further examination of the data showed that of 108 estimations performed when the SpO2 was less than 94%, none had a PaO2 greater than 12kPa. CONCLUSION: When using Ohmeda Biox pulse oximeters an upper limit of 97% for SaO2 is not effective in preventing hyperoxaemia; however, a limit of 93% is likely to maintain the PaO2 below 12kPa.

The relationship of pulmonary interstitial emphysema to subsequent type of chronic lung disease.

Chronic lung disease of prematurity (CLD) can be classified using the chest radiograph taken on day 28 into type 1 (homogeneous opacification) or type 2 (the presence of cystic change) and it has been suggested that the presence of pulmonary interstitial emphysema (PIE) leads to the development of type 2 CLD. To further study this relationship we examined the chest radiographs taken on days 1-7, 14, 21 and 28, of 202 infants treated at Liverpool Maternity Hospital between January 1980 and December 1989 who developed CLD. 39% (54/137) of infants who developed type 1 CLD had suffered from PIE compared with 78% (51/65) with type 2 CLD (p < 0.001). There was no difference in the incidence of PIE in infants who developed CLD and subsequently died compared with those who survived. In the infants who survived there was no significant difference in length of oxygen dependency between those who suffered from PIE (median 99 days oxygen dependent) and those who had no PIE (median 105 days). We conclude that the presence of PIE is associated with subsequent development of type 2 CLD but is not a prerequisite for this radiographic type of chronic lung disease. Of those infants who survive to develop CLD, the presence of PIE does not alter prognosis in terms of duration of oxygen dependency or mortality.