Back to basics for basal rates?

When insulin pump therapy was first introduced it offered the potential to vary basal insulin delivery in a way that could not be achieved with conventional subcutaneous injection. Now insulin pumps offer at least 24 basal rates over a 24-hour period, and some twice this number. Furthermore, all offer the pump user the potential to store several different basal rate profiles. Is the ability to vary basal rates through the day the key to optimising outcomes for insulin pump therapy, or is it perhaps the reliability of absorption of the much smaller insulin depot that is more important to the efficacy of pump therapy?

Two recent publications (summarised alongside) address different aspects of pump basal insulin delivery. Chow and colleagues reviewed insulin pump data in patients with either type 1 or type 2 diabetes who had been on pump therapy for over 3 months and had an HbA_1c ≤58 mmol/mol (7.5%). Their aim was to determine which method of determining a starting basal rate best approximated the stable basal rate achieved once pump therapy had been optimised. They concluded that the safest starting basal rate for those with type 1 diabetes was one calculated on the basis of the existing total daily dose of insulin, giving 75% of this dose as the pump total daily dose and 50% of this as the basal rate. Whist this was no better than a weight-based method (using 0.5 unit/kg/day) or an empirical 0.8 unit/hour, it was more likely to underestimate the final basal rate and therefore less likely to put the user at increased risk of hypoglycaemia. The authors did formulate an algorithm based on weight and total daily basal insulin dose pre-pump, which was significantly better at predicting the final basal rate, but not to the extent that we should be advocating a move away from the commonly used method for determining starting basal rates.

Laimer and colleagues report an observational study of data from 5545 adults with type 1 diabetes entered into a German–Austrian database between 1995 and 2014. The average age of the cohort was just over 33 years and the duration of diabetes over 17 years. The average total daily insulin dose was surprisingly high at 71.77 units. The authors devised a basal rate variability index and assessed the correlation between the basal rate variability and complications. By considering the hourly variation of the basal rate from the lowest hourly basal rate, the authors found that the mean variability in basal rate was 27.8±12.9%. After logistical regression analysis, greater basal rate variability was positively associated with an increased risk of severe hypoglycaemia and diabetic ketoacidosis. It is possible, as the authors discuss, that the basal rate variability reflects the difficulty of managing their diabetes for these particular pump users, and that basal rate changes have been made in response to episodes of hypoglycaemia or ketoacidosis, rather than predisposing the user to these acute complications. However, it seems reasonable to conclude that minimising unnecessary basal rate variability should be a consideration when optimising insulin pump therapy regimens.

Finally, though, a note of caution against over-simplification of basal rates. Ruan and colleagues (summarised alongside) report data from 1564 total days – and 1918 nights – of free-living closed-loop insulin delivery in 32 adults with type 1 diabetes. They found that the coefficient of variation of overnight insulin delivery was 31%, compared to 17% for total daily insulin requirements. The authors discuss the variety of factors that may contribute to this overnight variability, which include evening meal composition, activity levels the previous day and prior hypoglycaemia. Thus, we can conclude that whilst the standard basal insulin rate profile may need to be kept simple, pump users need to be cognisant of factors that alter their overnight insulin requirements and be prepared to make temporary basal rate adjustments to mitigate the effect of these factors.

To read the article summaries, please download the PDF