Sliding scale insulin for non-critically ill hospitalised adults with diabetes mellitus

Review question

What are the effects of sliding scale insulin compared with other insulin therapies for non-critically ill hospitalised adults with diabetes mellitus?

Background

There are several options to treat people with diabetes who have been admitted to the hospital. Both low glucose levels (hypoglycaemia) and high glucose levels (hyperglycaemia) might increase the risk of death and complications such as infections and longer hospital stay and therefore should be avoided. The most common method to treat hospitalised people with diabetes is sliding scale insulin therapy. The term 'sliding scale' refers to the increasing administration of the pre-meal insulin dose based on the blood sugar level before the meal. For example, if a person has a blood glucose level between 140 mg/dL to 180 mg/dL, a short-acting usual insulin dose could be 4 units insulin, and for a blood glucose level between 181 mg/dL and 220 mg/dL, it could be 6 units insulin. This kind of rigid insulin application usually fixes the amount of carbohydrate to be eaten at each meal but does not deliver insulin in a physiologic manner. It is therefore doubtful whether good glycaemic control (satisfactory blood glucose levels) can be achieved by sliding scale insulin in hospitalised diabetic people and whether this approach results in better outcomes in the long term. There are other insulin strategies like background (basal) insulin doses combined with flexible pre-meal insulin (bolus insulin) according to what and how much people want to eat. Sliding scale insulin means strict adherence to a regular schedule of meals and physical activity, and people must follow a prescribed diet. Intensified insulin therapy (basal-bolus strategy) allows flexible insulin doses according to physical activity, stress, and meal preferences, and under hospital conditions demands well-trained medical staff. Sliding scale insulin is still widely used, and it remains unclear which insulin strategy is best to treat hospitalised diabetic people.

Study characteristics

We found eight randomised controlled trials (studies in which participants are assigned to one of two or more treatment groups in a random manner) where 387 people on sliding scale insulin therapy and 615 on mainly basal-bolus insulin treatment with type 2 diabetes could be analysed. The average length of hospital stay was between five and 24 days. Six studies compared sliding scale insulin with basal-bolus insulin; one study compared sliding scale insulin with basal insulin only; and the remaining study used continuous insulin infusion as the control group. The average age of participants was 44.5 years to 71 years.

The evidence is up to date as of December 2017.

Key results

The main comparison was between sliding scale insulin and basal-bolus insulin therapy with the following results. Of the four studies reporting deaths, one out of 268 participants in the SSI group compared with two out of 334 participants in the basal-bolus group died. Severe hypoglycaemic episodes, defined as blood glucose levels below 40 mg/dL, occurred in 5 per 1000 people in the sliding scale insulin groups compared with 24 per 1000 people in the basal-bolus insulin groups. These data are uncertain because further analyses showed neither a positive nor a negative effect comparing both insulin strategies. The length of hospital stay in the sliding scale insulin groups compared with the basal-bolus insulin groups was 0.5 days longer, again with further analyses indicating that this information is uncertain. The results for adverse events other than hypoglycaemic episodes, such as postoperative infections, did not indicate an advantage or disadvantage of either strategy. The average blood glucose level during hospital stay in the sliding scale groups was 14.8 mg/dL higher compared with the basal-bolus groups. We are uncertain about these data because analyses showed neither a positive nor a negative effect comparing both insulin strategies. No trial reported on deaths caused by diabetes as such or socioeconomic effects like costs of the interventions or absence from work.

Certainty of the evidence

Overall, our confidence in the results for all analysed outcomes was low or very low mainly due to the low number of studies and participants and because the results were not precise, that is they could change in any direction once new studies are published.

Authors' conclusions: 

We are uncertain which insulin strategy (SSI or basal-bolus insulin) is best for non-critically hospitalised adults with diabetes mellitus. A basal-bolus insulin strategy in these patients might result in better short-term glycaemic control but could increase the risk for severe hypoglycaemic episodes. The certainty of the body of evidence comparing SSI with basal-bolus insulin was low to very low and needs to be improved by adequately performed, well-powered RCTs in different hospital environments with well-educated medical staff using identical short-acting insulins in both intervention and comparator arms to compare the rigid SSI approach with flexible insulin application strategies.

Read the full abstract...
Background: 

Diabetes mellitus is a metabolic disorder resulting from a defect in insulin secretion, function, or both. Hyperglycaemia in non-critically ill hospitalised people is associated with poor clinical outcomes (infections, prolonged hospital stay, poor wound healing, higher morbidity and mortality). In the hospital setting people diagnosed with diabetes receive insulin therapy as part of their treatment in order to achieve metabolic control. However, insulin therapy can be provided by different strategies (sliding scale insulin (SSI), basal-bolus insulin, and other modalities). Sliding scale insulin is currently the most commonly used method, however there is uncertainty about which strategy provides the best patient outcomes.

Objectives: 

To assess the effects of SSI for non-critically ill hospitalised adults with diabetes mellitus.

Search strategy: 

We identified eligible trials by searching MEDLINE, Embase, LILACS, and the Cochrane Library. We searched the World Health Organization International Clinical Trials Registry Platform (WHO ICTRP) and ClinicalTrials.gov trial registers. The date of the last search for all databases was December 2017. We also examined reference lists of identified randomised controlled trials (RCTs) and systematic reviews, and contacted trial authors.

Selection criteria: 

We included RCTs comparing SSI with other strategies for glycaemic control in non-critically ill hospitalised adult participants of any sex with diabetes mellitus.

Data collection and analysis: 

Two review authors independently extracted data, assessed trials for risk of bias, and evaluated the overall certainty of evidence utilising the GRADE instrument. We synthesised data using a random-effects model meta-analysis with 95% prediction intervals, if possible, or descriptive analysis, as appropriate.

Main results: 

Of 720 records screened, we included eight trials that randomised 1048 participants with type 2 diabetes (387 SSI participants and 615 participants in comparator groups were available for final analysis). We included non-critically ill medical and surgical adults with the diagnosis of diabetes mellitus. The mean follow-up time was measured by the mean length of hospital stay and ranged between five and 24 days. The mean age of participants was 44.5 years to 71 years.

Overall, we judged the risk of bias on the trial level as unclear for selection bias, high for outcome-related performance and detection bias with regard to hypoglycaemic episodes, other adverse events, and mean glucose levels, and low for all-cause mortality and length of hospital stay. Attrition bias was low for all outcome measures.

Six trials compared SSI with a basal-bolus insulin scheme, three of which investigating 64% of all participants in this category also applying an SSI approach in the bolus comparator part. One trial had a basal insulin-only comparator arm, and the remaining trial used continuous insulin infusion as the comparator. For our main comparison of SSI versus basal-bolus insulin, the results were as follows. Four trials reported mortality data. One out of 268 participants in the SSI group (0.3%) compared with two out of 334 participants in the basal-bolus group (0.6%) died (low-certainty evidence). Severe hypoglycaemic episodes, defined as blood glucose levels below 40 mg/dL (2.2 mmol/L), showed a risk ratio (RR) of 0.22, 95% confidence interval (CI) 0.05 to 1.00; P = 0.05; 5 trials; 667 participants; very low-certainty evidence. The 95% prediction interval ranged between 0.02 and 2.57. All nine severe hypoglycaemic episodes were observed among the 369 participants on basal-bolus insulin (2.4%). The mean length of hospital stay was 0.5 days longer for the SSI group, 95% CI -0.5 to 1.4; P = 0.32; 6 trials; 717 participants; very low-certainty evidence. The 95% prediction interval ranged between -1.7 days and 2.7 days. Adverse events other than hypoglycaemic episodes, such as postoperative infections, showed a RR of 1.16, 95% CI 0.25 to 5.37; P = 0.85; 3 trials; 481 participants; very low-certainty evidence. The mean blood glucose levels ranged across basal-bolus groups from 156 mg/dL (8.7 mmol/L) to 221 mg/dL (12.3 mmol/L). The mean blood glucose level in the SSI groups was 14.8 mg/dL (0.8 mmol/L) higher (95% CI 7.8 (0.4) to 21.8 (1.2); P < 0.001; 6 trials; 717 participants; low-certainty evidence). The 95% prediction interval ranged between -3.6 mg/dL (-0.2 mmol/L) and 33.2 mg/dL (1.8 mmol/L). No trial reported on diabetes-related mortality or socioeconomic effects.

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