Erin Fuller, MD
Hyperglycemia in critical illness
During critical illness there is increased release of counter-regulatory hormones (e.g. glucagon, growth hormone, catecholamine, and glucocorticoids) and high levels of pro-inflammatory cytokines (e.g. TNFalpha and IL-1). This results in impaired insulin release and sensitivity as well as stimulation of gluconeogenesis and glycogenolysis, all of which contribute to hyperglycemia.
Excessive administration of corticosteroids and dextrose in IV fluids or TPN can further contribute to the problem.
New onset difficult to control hyperglycemia without changes in glucose delivery may indicate developing or unidentified infection
Risks of hyperglycemia in critically ill patients
Perioperative hyperglycemia is an independent predictor of increased mortality, wound infection, anastomotic failure, and need for re-operative interventions in surgical patients. Glycemic control has been shown to improve mortality and decrease hospital length of stay and wound infection rates in critically ill surgical patients.
It is important to note however that much of the existing literature does not truly prove that hyperglycemia itself causes negative outcomes. It may be a marker of degree of illness. In turn it may not be the way you control the glucose that improves outcomes but merely the fact that it can be controlled is a sign of improvement in the patient’s condition.
What should target blood glucose be?
The NICE-SUGAR trial was a large multicenter RCT comparing outcomes of 6000+ ICU patients managed with intensive insulin therapy (target BG 81-108) vs conventional glucose control (target BG < 180). The study found significantly higher 90 day mortality (27.5% vs 24.9, P=0.02) and incidence of severe hypoglycemia (6.8% vs 0.5%, P<0.001) in the intensive group versus the conventional group. Multiple other studies have now shown increased risks of hypoglycemia with an intensive approach.
The paper can be accessed at the NEJM website by clicking on the following link: https://www.nejm.org/doi/full/10.1056/NEJMoa0810625
Also see the following RCT of medical and surgical ICU patients that showed no difference in mortality but more episodes of hypoglycemia with intensive control:
Intensive versus conventional insulin therapy: a randomized controlled trial in medical and surgical critically ill patients. Arabi YM, Dabbagh OC, Tamim HM, Al-Shimemeri AA, Memish ZA, Haddad SH, Syed SJ, Giridhar HR, Rishu AH, Al-Daker MO, Kahoul SH, Britts RJ, Sakkijha MH. Crit Care Med. 2008 Dec;36(12):3190-7.
Glycemic variability
Fluctuations in blood glucose, or glycemic variability, though not universally defined, has been shown to be independently associated with increased risk of mortality in critically ill patients.
Glycemic control
All patients admitted to the SICU should be started on a regular insulin sliding scale with blood glucose checks every 6 hours regardless of history of DM.
If BG maintains > 140, discontinue or reduce glucose-containing IV fluids.
Target BG 110-180. If patients have BG > 180 on 2 consecutive checks, regular insulin infusion should be initiated.
Hypoglycemia
The American Diabetic Association and the American Association of Clinical Endocrinologists define hypoglycemia as glucose less than 70 mg/dL and severe hypoglycemia as less than 40 mg/dL.
Glucose < 70 Consider dextrose
Glucose < 40 Needs urgent dextrose
Investigation should also be done to determine cause of hypoglycemia-hepatic failure, iatrogenic dosing of insulin, abrupt cessation of TPN, tubefeeds.