Aims Administering intravenous (IV) glucose is common on the Neonatal Intensive Care Unit. Bedside preparation of glucose solutions is often necessary, usually through addition of concentrated 50% glucose to a commercially available bag. Accuracy in the glucose concentration of locally prepared bags will be influenced by a number of factors: variable overages in IV fluid bags, method of preparation and imprecision of measurement during preparation. We aimed to assess the accuracy of three different methods of preparation which had been identified through a national survey.
Methods Bags of 12.5%, 15% and 25% glucose were manufactured through the addition of 50% glucose solution to commercially available bags of 10% or 20% glucose. Three bags of each concentration, were manufactured by each of the methods below:
Removal of fluid from base bag prior to addition of 50% glucose, taking into account published overage.
Removal of fluid from base bag prior to addition of 50% glucose, not taking into account published overage.
Addition of 50% glucose, without prior removal of fluid from base bag.
Three 5 mL samples were then taken from each prepared bag and sent for analysis. Glucose concentration was measured using a quantitative spectrophotometric method. As a control, three 5 mL samples were taken from three bags each of commercially available 5%, 10% and 20% glucose infusion solutions and assayed as above.
Results A total of 81 ‘test’ samples were sent for analysis along with 27 control samples. One 20% glucose control sample was lost in transport meaning that 80 samples were analysed. The median result for each concentration and method was calculated. For method a) where the intended final glucose concentration was 12.5%, 15% and 25%, the actual concentrations obtained were 11.2%, 13.3% and 22.9% respectively. For method b) where the intended final glucose concentration was 12.5%, 15% and 25%, the actual concentrations obtained were 12.4%, 13.4% and 22.0% respectively. For method c) where the intended final glucose concentration was 12.5%, 15% and 25%, the actual concentrations obtained were 12.1%, 13.8% and 20.3% respectively. For the 5%, 10% and 20% control solutions the median reported glucose concentrations were 5.1%, 10.3% and 19.9% respectively.
Conclusions Irrespective of method used and the intended strength, the measured glucose concentration was lower than that being aimed for. In some cases, the glucose concentration was only 80% of that intended. It is not possible to conclude that one method is superior in terms of accuracy. Although it might be possible from our results to suggest the most accurate method for each concentration, this is unlikely to be predictable as manufacturers quote overages as a range rather than an absolute value. In clinical practice, preparation of a glucose solution with a lower concentration than that expected may result in prolonged hypoglycaemia with potential neurological sequelae. An alternative to bedside manufacture of glucose infusion solutions is needed. This could include pharmacy compounding of glucose strengths not commercially available or ‘piggy-backing’ of 50% glucose onto an infusion of a commercially available strength, ideally supported by a glucose load calculator.
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