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Glucometers are one of the most common medical devices in use today. They cost about $20 or $30 to buy at the drugstore and every nursing station and doctor’s office has one. Most of the time, they work great and are very accurate to measure the blood glucose level by pricking the skin to obtain a drop of capillary blood to put into the glucometer.
In 2001, a study published in New England Journal of Medicine showed that tight glucose control in critically ill patients resulted in improved ICU outcomes. In this study, blood was drawn every 1-4 hours and glucose levels were checked on a laboratory chemistry analyzer. In response, ICUs across the country started practicing “tight glucose control” in critically ill patients and this often meant an insulin drip with glucose checks every hour.
But over the next 10 years, outcomes in most ICUs did not improve with tight glucose control and a lot of patients actually did worse. As a consequence, critical care physicians backed off on the tight glucose control strategy. One of the reasons patients did worse may be that in the original study, blood was drawn up in regular blood tubes and sent to the hospital lab but in normal clinical practice, most of the time, the blood to be tested is not in tubes sent to the hospital lab but instead is from a drop of capillary blood tested with a point-of-care glucometer after pricking the skin on a finger.
It turns out that in our sickest patients, glucometers using capillary blood often don’t work. Because of this, the FDA has not approved glucometers for use in critically ill patients with capillary stick specimens and in 2013, the FDA advised against using glucometers in these patients. The problem is that patients with edema, low blood pressure, and poor capillary filling can have inaccurate results from that drop of capillary blood and it may not truly reflect the real blood glucose level. These patients must have regular arterial or venous blood specimens drawn rather than a skin prick capillary blood specimen.
This means that blood must be obtained from a intravenous line, arterial line, or venipuncture. This is a problem for patients who are on insulin drips because they need glucose measurements as frequently as every hour. Since the FDA does not approve glucometers to be used on capillary blood specimens in critically ill patients, their use in these patients is considered “off label” which poses medical-legal risk for using them. The FDA and CMS did not define what “critically ill” means and left this up to individual hospitals to define; at our medical center, we developed the BRAVE criteria to identify those critically ill patients in whom the capillary blood specimens are inaccurate and should not be used:
Blood Pressure: systolic blood pressure < 80 mm Hg or mean arterial pressure < 55 mm Hg.
Reduced capillary refill rate at collection site: capillary refill > 3 seconds
Acidosis from diabetic ketoacidosis or non-ketotic hyperosmolar acidosis
Vasopressors: norepinephrine, phenylephrine, vasopressin, or dopamine (> 5 mcg/kg/min)
Edema: pitting edema at the capillary stick site
For these patients, you need to get regular blood, commonly from a central venous line or an arterial line. In the past, nurses would need to draw a 5-10 ml blood discard to clear the central line or arterial line of saline or other fluids and this would result in a lot of discarded blood (you could waste an entire unit of blood in 3-4 days in patients needing hourly glucose checks). We now use the VAMP system manufactured by Edwards Lifesciences that allows the “discard” blood to be re-infused into the patient.
For documentation purposes in our electronic medical record, our nurses now have to select whether BRAVE criteria are met when documenting glucometer use and then they have to documents what type of blood specimen they are using. If there is a mismatch in the two selections, then the result is flagged by our point-of-care software. Weekly, our point-of-care staff notify the nurses and nurse managers that have mismatches to provide regular feedback to the nurses. We now have data showing a nice weekly improvement in the number of events since inception of the BRAVE program.
If blood was sent to the lab for a regular glucose check, this would require a full blood tube (another 5 ml). In 2014, the FDA approved one brand of glucometer, the Nova StatStrip Glucose Hospital Meter System, to be used on venous or arterial blood in critically ill patients. This is now the glucometer that we use in our ICU. It permits nurses to just draw up less than 1 ml of blood to put in the point-of-care glucometer (rather than filling up a blood tube to go to the lab) and this has greatly cut down on wasted blood.
In medicine, as with many other disciplines, bad data is often worse than no data. By using BRAVE, we can improve the data on glucose measurement in critically ill patients. Going forward, this may allow us to re-think the advisability of tight glucose control in the ICU for critically ill patients by ensuring that we are accurately measuring glucose levels.
December 1, 2016