Continuous glucose sensors for glycaemic control in the ICU: have we arrived?

Tiered protocol implementation improves treatment of hypoglycaemia in a neurosciences critical care and surgical intensive care unit

BACKGROUND

Although studies demonstrate techniques to limit hypoglycaemia in critically ill patients, there are limited data supporting methods to improve management of existing hypoglycaemia.

OBJECTIVE

Assess the impact and sustainability of a computerised, three tiered, nurse driven protocol for hypoglycaemia treatment.

DESIGN

Retrospective pre and post protocol study.

SETTING

Neurosciences and surgical intensive care units at a tertiary academic medical centre.

MEASUREMENTS

Patients with a hypoglycaemic episode were included during a pre-protocol or post-protocol implementation period. An additional six-month cohort was evaluated to assess sustainability.

RESULTS

Fifty-four patients were included for evaluation (35 pre- and 19 post-protocol); 122 patients were included in the sustainability cohort. Hypoglycaemia treatment significantly improved in the post-protocol cohort (20% vs. 52.6%, p=0.014); with additional improvement to 79.5% in the sustainability cohort. Time to follow-up blood glucose was decreased after treatment from 122 [Q1-Q3: 46-242] minutes pre-protocol to 25 [Q1-Q3: 9-48] minutes post protocol (p<0.0001). This reduction was maintained in the sustainability cohort [median of 29min (Q1-Q3: 20-51)].

CONCLUSION

Implementation of a nurse-driven, three-tiered protocol for treatment of hypoglyacemia significantly improved treatment rates, as well as reduced time to recheck blood glucose measurement. These benefits were sustained during a six-month period after protocol implementation.

Glucose management in critically ill adults and children

Blood glucose management in people with acute myocardial infarction and critical illness has always attracted controversy. Compared with the era before 2001 when no attention was given to blood glucose management, DIGAMI-1 in 1995 and the first Leuven study in 2001 showed improved outcomes with strict control of blood glucose, thereby suggesting a causal association between hyperglycaemia and mortality risk. These landmark trials have set the standard in clinical practice that excessive hyperglycaemia is not acceptable. Multicentre trials contradicted the benefits of tight control of patients' blood glucose and results showed that different standard operating procedures for blood glucose control (eg, blood glucose meters or algorithms), divergent concomitant feeding strategies, and varying patient populations are important confounders. The general consensus now is that excessive hyperglycaemia (>10 mmol/L) and severe hypoglycaemia (<2·2 mmol/L) should be avoided in critically ill adults. If adequate blood glucose meters and clinically validated protocols for insulin-dosing are available, targeting of blood glucose concentrations to less than 8 mmol/L (moderate glycaemic control), while avoiding mild hypoglycaemia (<3·9 mmol/L), is a reasonable strategy in adult patients who are critically ill. This recommendation is not based on findings from randomised controlled trials, but merely represents a very common, pragmatic approach by physicians at the bedside. As a result of the few properly validated technologies for tighter blood glucose control, targeting blood glucose concentrations to less than 6 mmol/L is not recommended, because its risk-to-benefit ratio becomes questionable. Because blood glucose control in the target of adult ranges does not improve patient outcomes for children in the intensive care unit, glucose management in this patient population should be limited to avoid excessive hyperglycaemia (>10 mmol/L).

Using skin for drug delivery and diagnosis in the critically ill

Skin offers easy access, convenience and non-invasiveness for drug delivery and diagnosis. In principle, these advantages of skin appear to be attractive for critically ill patients given potential difficulties that may be associated with oral and parenteral access in these patients. However, the profound changes in skin physiology that can be seen in these patients provide a challenge to reliably deliver drugs or provide diagnostic information. Drug delivery through skin may be used to manage burn injury, wounds, infection, trauma and the multisystem complications that rise from these conditions. Local anaesthetics and analgesics can be delivered through skin and may have wide application in critically ill patients. To ensure accurate information, diagnostic tools require validation in the critically ill patient population as information from other patient populations may not be applicable.

Modeling of effect of glucose sensor errors on insulin dosage and glucose bolus computed by LOGIC-Insulin

BACKGROUND

Effective and safe glycemic control in critically ill patients requires accurate glucose sensors and adequate insulin dosage calculators. The LOGIC-Insulin calculator for glycemic control has recently been validated in the LOGIC-1 randomized controlled trial. In this study, we aimed to determine the allowable error for intermittent and continuous glucose sensors, on the basis of the LOGIC-Insulin calculator.

METHODS

A gaussian simulation model with a varying bias (0%-20%) and CV (-20% to +20%) simulated blood glucose values from the LOGIC-1 study (n = 149 patients) in 10 Monte Carlo steps. A clinical error grid system was developed to compare the simulated LOGIC-Insulin-directed intervention with the nominal intervention (0% bias, 0% CV). The severity of error measuring the clinical effect of the simulated LOGIC-Insulin intervention was graded as type B, C, and D errors. Type D errors were classified as acutely life-threatening (0% probability preferred).

RESULTS

The probability of all types of errors was lower for continuous sensors compared with intermittent sensors. The maximum total error (TE), defined as the first TE introducing a type B/C/D error, was similar for both sensor types. To avoid type D errors, TEs <15.7% for intermittent sensors and <17.8% for continuous sensors were required. Mean absolute relative difference thresholds for type C errors were 7.1% for intermittent and 11.0% for continuous sensors.

CONCLUSIONS

Continuous sensors had a lower probability for clinical errors than intermittent sensors at the same accuracy level. These simulations demonstrated the suitability of the LOGIC-Insulin control system for use with continuous, as well as intermittent, sensors.

Glycemic control in critically ill: A moving target

Glycemic control targets in intensive care units (ICUs) have three distinct domains. Firstly, excessive hyperglycemia needs to be avoided. The upper limit of this varies depending on the patient population studied and diabetic status of the patients. Surgical patients particularly cardiac surgery patients tend to benefit from a lower upper limit of glycemic control, which is not evident in medically ill patient. Patient with premorbid diabetic status tends to tolerate higher blood sugar level better than normoglycemics. Secondly, hypoglycemia is clearly detrimental in all groups of critically ill patient and all measures to avoid this catastrophe need to be a part of any glycemic control protocol. Thirdly, glycemic variability has increasingly been shown to be detrimental in this patient population. Glycemic control protocols need to take this into consideration and target to reduce any of the available metrics of glycemic variability. Newer technologies including continuous glucose monitoring techniques will help in titrating all these three domains within a desirable range.