Reduced potassium following trauma indicative of severe head injury?

Practically all victims of significant trauma will have blood sampled for plasma potassium estimation soon after admission to hospital emergency departments. But what is the frequency and significance of abnormal potassium results at admission for these trauma patients? 

That was the question addressed in design of a recently published retrospective clinical study of trauma victims admitted to the emergency department of a hospital in Hiroshima, Japan. The studied population comprised 520 victims of major trauma (Injury Severity Score, ISS >15) who had sustained their injury within 24 hours of admission. 

Result of admission plasma potassium estimation was retrieved for all study participants along with their clinical record and outcome of the trauma. Three outcomes were considered for this study: death, and two life-saving interventions (LSI); one for severe head injury (craniotomy, i.e. surgical removal of part of the skull bone) and the other for severe bleeding (either massive transfusion or some other operative procedure designed to ameliorate massive hemorrhage). 

Of the 520 study participants, 44 (8.5 %) did not survive their injury and died in hospital, 64 (12.3 %) received life-saving craniotomy and 117 (22.5 %) received one or other LSI for bleeding. The remaining 295 (56 %) survived their trauma without recourse to either LSI.

All 520 patients were categorized to one of six groups according to their admission plasma potassium concentration (<3.0 mmol/L, 3.0-<3.5 mmol/L, 3.5-<4.0 mmol/L, 4.0-<4.5 mmol/L, 4.5-<5.0 mmol/L and >5.0 mmol/L). 

Abnormal potassium was evident at admission in 234 (45 %) patients; reduced plasma potassium (<3.5 mmol/L) was evident in 227 (43.6 %) patients and increased plasma potassium (>5.0 mmol/L) was evident in just 7(1.3 %) patients. Thus an important finding of the study is that hypokalemia at admission is by far the more common abnormality. Hyperkalemia is apparently a rare occurrence among major trauma patients at the time of admission.

Analysis of the relationship between potassium values and first outcome measure, mortality revealed that although mortality rates tended to be highest in those with severe hypokalemia (<3.0 mmol/L) and hyperkalemia (>5.0 mmol/L) adjusted logistic regression analysis revealed no statistically significant difference in mortality between the six groups. 

However, analysis of the relationship between potassium values and second outcome measure, craniotomy did reveal a statistically significant association. Thirty-three percent (33 %) of patients whose plasma potassium was <3.0 mmol/L received craniotomy, and most (77 %) craniotomies were performed on patients whose admission plasma potassium was <4.0 mmol/L. 

Logistic regression analysis confirmed that the lower the plasma potassium the more likely it was that patients required life-saving craniotomy. Since the need for craniotomy is a surrogate marker of severe ( life-threatening) head injury, the authors of this study were able to conclude that the degree of hypokalemia at admission may reflect severity of head injury.