The Relationship between the Ratio of Urine Osmolality to Serum Osmolality and Neurological Outcomes in Out-of-hospital Cardiac Arrest Patients

Abstract

Background: Progressive ischemic brain injury after cardiac arrest can cause damage to the hypothalamic-pituitary axis, particularly the pituitary gland. This may impact serum osmolality (SOsm) and urine osmolality (UOsm) in patients who have experienced out-of-hospital cardiac arrest (OHCA). We assumed that a low ratio of UOsm to SOsm (USR) is related to poor outcomes among OHCA patients. Therefore, the present study was designed to evaluate the association between the USR within 72 h after the restoration of spontaneous circulation (ROSC) and 6-month neurological outcomes in OHCA patients.

Methods: This prospective, observational study included OHCA patients with targeted temperature management at Chonnam National University Hospital in Gwangju, Korea, between January 2016 and December 2022. We collected SOsm and UOsm data at admission (T0) and 24 (T1), 48 (T2), and 72 h (T3) after ROSC. The primary outcome was a poor neurological outcome at 6 months defined by cerebral performance categories 3, 4, or 5.

Results: This study included 319 patients. The mean UOsm and USRs at T0, T1, T2, and T3 of patients with poor outcomes were lower than those of patients with good outcomes. Multivariable analysis indicated that the USRs at T1 (odds ratio [OR], 0.363; 95% confidence interval [CI], 0.221-0.594), T2 (OR, 0.451; 95% CI, 0.268-0.761), and T3 (OR, 0.559; 95% CI, 0.357-0.875) were associated with a poor outcome. The areas under the receiver operating characteristic curves of USRs at T0, T1, T2, and T3 for predicting poor outcomes were 0.615 (95% CI, 0.559-0.669), 0.711 (95% CI, 0.658-0.760), 0.724 (95% CI, 0.671-0.772), and 0.751 (95% CI, 0.699-0.797), respectively.

Conclusions: The USRs within 72 h of ROSC were associated with poor neurological outcomes at 6 months in OHCA patients.

Keywords: cardiac arrest; prognosis; serum osmolality; targeted temperature management; urine osmolality.

Fig. 1.

Flow diagram of patient inclusion. OHCA, out-of-hospital cardiac arrest; SOsm, serum osmolality; UOsm, urine osmolality; TTM, targeted temperature management; CPC, cerebral performance category; ROSC, restoration of spontaneous circulation.

Fig. 2.

CDI occurrence time after ROSC. Among CDI cases, 61.7% occured within 3 days, and 38.3% occured more than 3 days after ROSC. CDI, central diabetes insipidus; ROSC, restoration of spontaneous circulation.

Fig. 3.

AUCs for SOsm (A), UOsm (B), and USR (C) for predicting poor outcomes. The AUC for USR at 72 h after ROSC was significantly different from those for SOsm and UOsm at the same time point. AUCs, areas under the receiver operating characteristic curves; SOsm, serum osmolality; UOsm, urine osmolality; USR, ratio of urine osmolality to serum osmolality; ROSC, restoration of spontaneous circulation.