Influence of a strict glucose protocol on serum potassium and glucose concentrations and their association with mortality in intensive care patients

INTRODUCTION Tight glucose control therapy (TGC) has been implemented to control hyperglycemia in ICU patients. TGC may also influence serum potassium concentrations. We therefore investigated the influence of TGC on both serum glucose and serum potassium concentrations and associated mortality. METHOD We performed a retrospective analysis including all patients admitted to the ICU of a tertiary hospital for 24 hours or more and with at least three serum glucose and serum potassium concentrations between 1999-2001 (conventional period), 2002-2006 (implementation period) or 2007-2009 (TGC period). Segmented regression analysis was used to estimate changes in outcomes that occurred after the intervention controlling for pre-intervention trends. Means and standard deviations (SDs) of serum glucose and serum potassium concentrations, and rate of severe hypoglycemia (≤ 2.2 mmol/L) and hypokalemia (≤ 3 mmol/L), were compared between the TGC and conventional period. RESULTS Although mean serum glucose concentrations dropped 2.1 mmol/L (95% CI =-1.8 to -2.3 mmol/L, p<0.002), mean serum potassium concentrations did not change (absolute increase 0.02 mmol/L; 95% CI = -0.06 to 0.09 mmol/L, p=0.64). The rate of severe hypoglycemia increased with 5.9% (95% CI=-3.0 to -8.9, p<0.002), but the rate of hypokalemia remained equal (absolute reduction 4.8%; 95% CI = -11.1% to 1.5%, p=0.13). The SD of serum glucose concentrations within a patient did not change, while the SD of serum potassium concentrations even decreased 0.04 mmol/L (95% CI = -0.01 to -0.07, p = 0.01). ICU mortality decreased but this decrease was not significant (absolute difference -3.63%; 95% CI = -9.33 to 2.09, p = 0.20). Mean serum glucose concentrations, mean serum potassium concentrations and SDs of both serum glucose and serum potassium concentrations were all independently associated with ICU mortality. Highest mortality rates were seen at both the lowest and highest mean values (U/J-shaped association) and mortality rates increased with increasing variability (SDs) for both serum glucose and serum potassium concentrations. CONCLUSION Our study shows that a TGC was not associated with an increased risk of serum potassium related events. Low and high mean values and high variability of both serum glucose and serum potassium concentrations are predictors for high ICU mortality.