More is not always better. This is notably true when it comes to the treatment of acute hyperkalemia. Emergent treatment of acute hyperkalemia is bread-and-butter emergency medicine. Many of us have order sets that simplify care: maybe calcium, an insulin shifter or two (intravenous (IV) insulin and/or inhaled beta-agonist), coupled with perhaps a diuretic and/or a potassium binder. Intravenous insulin shifts potassium into cells, thereby lowering serum potassium within an hour of administration. Despite the routine nature of hyperkalemia treatment, adverse events from IV insulin are common and largely attributable to overtreatment.
Hypoglycemia following insulin administration for hyperkalemia is common, occurring in approximately one in six patients (about 17 percent).1,2 Some groups are particularly at risk, especially those with renal insufficiency and those who have normal serum glucose levels. One other critical predictor of hypoglycemia is the dose of insulin administered. A meta-analysis found that reduced-dose insulin (either five units or 0.1 unit/kg) was associated with nearly half the odds of hypoglycemia when compared with 10 units of insulin (odds ratio (OR), 0.55; 95 percent CI, 0.43 to 0.69).3 This effect was magnified when restricted to severe hypoglycemia (OR, 0.41; 95% CI, 0.27 to 0.64).3 More insulin equals more hypoglycemia. The critical question is—does a reduced dose of insulin lower potassium as much as a 10-unit dose?
It appears that IV insulin doses between five and 10 units result in roughly similar reductions in serum potassium (somewhere between 0.5 and one mmol/L). A meta-analysis comparing studies using a whopping 20 units of IV insulin over 30 minutes to a 10-unit insulin bolus found no significant difference between dosing strategies; all reduced serum potassium between 0.5 and 1.14 mmol/L.4 Larger observational studies have confirmed these results and extended the findings to even lower doses of IV insulin. The majority of studies examining reduced-dose insulin for hyperkalemia have found no significant difference in potassium reduction compared with 10 units of IV insulin (mean difference, -0.02; 95 percent CI, -0.11 to 0.07). Two studies have touted a “significant” difference between a five-unit strategy and a 10-unit strategy with regard to potassium reduction.5,6 However, the difference between strategies was 0.17 to 0.27 mmol/L, which is unlikely to be clinically significant, especially as most patients returned to near-normal potassium levels. In fact, a consensus statement, Kidney Disease: Improving Global Outcomes on the emergency-department management of acute hyperkalemia, embraces the five-unit strategy.7