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Increased plasma potassium – a demographic study
Summarized from Phillips B, Milner S, Zouwail S et al. Severe hyperkalaemia: demographics and outcome. Clin Kidney J 2014; 7: 127-33.
Potassium, the most frequently measured electrolyte in clinical practice is, in health, maintained at a blood serum concentration within the approximate reference range of 3.5 to 5.2 mmol/L. Physiological control of this potassium concentration depends crucially on the ability of the healthy kidney to regulate potassium excretion in urine.
Abnormality of serum potassium concentration may thus be attributable to kidney disease, although there are other, less common, possible causes. If sufficiently severe, increase in serum potassium (hyperkalemia) causes abnormal cardiac rhythms that can result in cardiac arrest. The condition is thus a life-threatening emergency that demands urgent medical intervention.
But how common is severe hyperkalemia in adults, and to what extent is it associated with acute or chronic renal failure? These are the principal questions addressed by a recently published retrospective study conducted by renal physicians (nephrologists) at a UK teaching hospital. Interrogation of their hospital laboratory database was used to identify all potassium results relating to those aged more than 18 years during a one-year period (2011).
Of the 383,422 serum potassium results retrieved, 433 indicated severe hyperkalemia defined for the purposes of this study as serum potassium >6.5 mmol/L. Overall then, the prevalence of severe hyperkalemia in this adult population, derived from in-hospital, outpatient, and primary care clinical settings, was found to be just 0.11 %.
The 433 episodes of severe hyperkalemia involved 365 patients, the vast majority (93 %) of whom were hospital inpatients. The rest were outpatients (29 cases) and primary care GP patients (just three cases).
In 90 % of cases severe hyperkalemia occurred in the context of renal disease (either chronic kidney disease CKD, acute kidney injury AKI, or AKI on a background of CKD), although in only 36 % these cases was the patient under the care of nephrologists.
The authors provide evidence that the clinical response to severe hyperkalemia in terms of urgent repeat measurement of potassium was superior in those patients under the care of nephrologists compared with those under the care of other specialty doctors. A questionnaire of non-nephrology trainee physicians revealed significant gaps in the knowledge required for optimal clinical management of severe hyperkalemia.
Outcome in terms of death within 48 hours following an episode of severe hyperkalemia was found to be worse among those not under the care of nephrologists. Just three deaths occurred among the nephrology cared for cohort, which translates to a mortality rate of 2.2 %. This compared with 36 deaths and a mortality rate of 15 % among the cohort not cared for by nephrology specialists.
As the authors concede, the higher death rate among those not cared for by nephrologists may in part be due to factors unrelated to severe hyperkalemia and its management; for example this cohort of patients were sicker due to higher rate of serious non-renal co-morbidity than those cared for by nephrologists.
In summary this study reveals evidence that severe hyperkalemia is a rare condition (rarer than previous studies suggest) and that it most frequently occurs among hospitalized patients with renal failure.
The study also provides some evidence to suggest that junior non-nephrology doctors currently lack the knowledge base to deliver optimal care to patients with severe hyperkalemia, and that such patients might fare better when under the care of specialist nephrologists, who are necessarily better versed in the intricacies of the role of kidneys in potassium homeostasis.
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