The outcome of many illnesses for which patients are treated in intensive care units (ICUs) has not improved dramatically over the past decades, despite the development of high-tech monitors and sophisticated mechanical and pharmacological support of vital organ systems. Indeed, critically ill patients requiring intensive care for more than five days have a 20 percent risk of death and substantial morbidity. Recently, however, evidence from a few randomized controlled clinical studies has shown a reduction in mortality and morbidity in the ICU, simply by rethinking and fine-tuning some of the basic interventions utilized by intensive care medicine, such as mechanical ventilation, fluid administration, inotropic support, and metabolic control.
Results published in 2001 of a prospective randomized trial that evaluated tight glycemic control (TGC) in a surgical ICU has been extremely influential in changing standard of care in ICUs, and as well as generating new studies evaluating TGC in other hospital populations. In that 2001 study, where only 13 percent of patients had a history of diabetes, maintenance of normoglycemia with insulin infusions reduced mortality in patients remaining in the ICU for more than 5 days by 48 percent. It also greatly decreased the incidence of acute renal failure, septicemia, and critical illness polyneuropathy.
While there is ongoing debate and research on what level of blood glucose is optimal, and whether the benefits to patients result solely from lower blood glucose, or from the broad physiological effects of insulin, or from both, glycemic control protocols are being instituted in hospital ICUs. Concerns that arise during protocol implementation include worry about hypoglycemia, accuracy of glucose meters, and increased nursing work-load. Clinicians in units with TGC report that with close monitoring symptomatic hypoglycemia is rare, and recommend choosing a glucome ter that has the highest correlation with lab values in the euglycemic range to help prevent hypoglycemia.
Continuous glucose monitors will be the optimal solution for avoiding hypoglycemia and decreasing workload in the ICU. Many research groups have been working on their development. There is an approved device for detecting glycemic excursions in outpatients with diabetes that has shown promise in monitoring critically ill patients. The Continuous Glucose Monitoring System (CGMS, Medtronic MiniMed) utilizes a subcutaneous sensor implanted in the abdomen. However, in its current format, the CGMS does not provide real-time monitoring. GluCath (GluMetrics, Inc.) is a catheter device in the development pipeline for continuous monitoring of hospitalized patients. The device consists of an optical fiber to which an optical glucose sensor is applied. The sensor is a fluorescent chemical complex immobilized in a thin-film hydrogel that is permeable to glucose.
FDA approved glucose monitoring systems for the ICU include the HemoCue Glucose 201 DM System, LifeScan SureStepFlexx Professional Blood Glucose Management System, and Roche Diagnostics Accu-Chek Inform System. All 3 systems have handheld devices that provide quantitative glucose measurement of capillary, venous, arterial and neonatal whole blood, and yield plasma calibrated results. TELCOR provides connectivity for the 3 systems, and RALS-Plus provides connectivity for Roche and LifeScan.
The HemoCue Glucose 201 DM System provides the glucose analyzer, docking station, microcuvettes, and 201 DM software. The glucose test system is based on the glucose dehydrogenase method and consists of the analyzer and a unique disposable microcuvette, which serves as pipette, reaction vessel, and measuring cuvette. Approximately 5 l blood is drawn into the cuvette cavity by capillary action and spontaneously mixed with dried reagents on the inner walls. The cuvette is then placed into the analyzer, the absorbance is measured, and the glucose level is displayed in 40 to 240 seconds, depending on concentration. Accurate results are claimed for the whole measurement range of 0-444 mg/dl. Quality control (QC) must be performed with the HemoCue control cuvette and commercially available glucose controls. The analyzer has both power adapter and batteries, built-in barcode scanner, infrared transmitter, and memory of 4000 Patient/STAT tests, 500 QC tests and 500 analyzer logs.
The LifeScan SureStepFlexx Professional Blood Glucose Management System is available with all DataLink connectivity options. A drop of blood is applied to the SureStep test strip, which contains a hydrophilic foam that reduces potential for contamination. Plasma from the sample flows through the pad to the reagent membrane, where glucose undergoes the glucose oxidase reaction. The test strip is inserted into the meter, and results appear in approximately 30 seconds. The measurement range is 0-500 mg/dl and is reported by one researcher to be highly accurate in the low ranges. There is an internal verification system and QC must be performed using SureStepPro glucose control solutions. The meter is battery powered, has an optional barcode scanner, and memory of 4000 user IDs and 1500 tests results.
The Roche Accu-Chek Inform System utilizes the DataCare POC information management system and Accu-Chek Comfort CurveTest Strips. The glucose test system is based on the glucose dehydrogenase method, and results appear in 26 seconds. Studies have shown that the Accu-Chek meter is accurate over a wide range of glucose concentrations. QC tests include a linearity kit, and glucose control solutions that come with the test strips. The meter has a rechargeable battery, barcode scanner, and memory of 4000 measurements.
- Helen Londe, MD
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