3.1 Derivation of the study cohort
During the study period, 346 patients with cardiac arrest were admitted to the ICU, including 77 with IHCA and 269 with OHCA. Overall, 17 patients were excluded because of lack of ROSC times, out of which 9 were from the OHCA cohort. The final study cohort that was analysed consisted of 260 OHCA patients (Fig. 1).
3.2 Patient characteristics
The mean age was 58 years (SD = 17), with most patients (156, 60%) being less than 65 years old. Most of the patients were male (178, 68%). There were 109 patients (42%) who survived hospital discharge. Of the 151 patients who died, 145 (96%) died following WLST, including 89 patients (61%) within the first 72 hours of ICU admission—the ‘early’ cohort. Cardiac causes accounted for the majority of OHCA (141/260, 54.5%), with myocardial infarction as the leading cause. Asphyxia and pneumonia were the major non-cardiac causes of OHCA (Table 1 and 2).
The non-shockable cohort accounted for 52% of the 260 patients enrolled in the study. Of these, 26% of PEA patients and 41% of the asystole group underwent WLST. In contrast, most patients from the shockable group (78/125, 68%) did not receive WLST (Table 3).
3.3 Withdrawal of life-sustaining treatment
Patients in whom life-sustaining treatment was withdrawn had higher severity of illness scores on admission than survivors (mean (SD) APACHE II score 35 (7) vs. 29 (8); p < 0.001) (Table 2). They also had longer median arrest times before ROSC than survivors (27 (IQR 19–40) vs. 16 (IQR 11–26) minutes; p = 0.006) (Table 3).
Out of the 260 patients in the study cohort, 161 (62%) received targeted temperature management, of which a target of 32–34°C and 34–36°C were given to 91 (35%) and 70 (27%), respectively. There was no association between WLST and targeted temperature management. However, the median duration of core body temperature >36°C in the first 24 hours post-OHCA was higher in the non-withdrawal group compared to those sustaining WLST (10 (IQR 1–18) vs. 3.5 (IQR 0–12) hours; p < 0.001) (Additional File 1).
Although the overall proportion of WLST remained relatively the same over the study period, the gap between early and late WLST widened (Fig. 2). Interestingly, the trend of hospital death appeared to decline with an increased proportion of survivors, which is both unexpected and challenging to explain (Fig. 3).
3.4 Multivariable analysis for WLST
3.4.1 Total cohort
Out of the study cohort of 260 patients, age (OR 1.03, 95% CI 1.01–1.06; p=0.01), ROSC time (OR 1.04, 95% CI 1.01–1.07; p = 0.003), APACHE II score (OR 1.07, 95% CI 1.02–1.13; p = 0.005), absent brainstem reflexes on day 1 post-OHCA (OR 13.12, 95% CI 4.14–41.54; p < 0.001), non-shockable rhythm (OR 4.10, 95% CI 1.41–11.94; p = 0.01) and status myoclonus (OR 20.86, 95% CI 5.47–79.56; p < 0.001) were independently associated with WLST, adjusting for all other covariates in the model (Table 4).
3.4.2 Early WLST
For patients with ICU length of stay <72 hours, ROSC time (OR 1.05, 95% CI 1.01–1.09; p = 0.01), APACHE II score (OR 1.09, 95% CI 1.01–1.16; p = 0.02), absent brainstem reflexes on day 1 post-OHCA (OR 18.47, 95% CI 3.53–96.64; p = 0.001), status myoclonus (OR 38.9, 95% CI 4.55–332.57; p = 0.001) and non-shockable rhythm (OR 3.22, 95% CI 1.06–9.82; p = 0.04) were independently associated with early WLST, adjusting for all other covariates in the model (Table 4). The factors related to WLST were identical in the total cohort and the early WLST cohort, albeit differences in the effect size (Table 4).
3.4.3 Late WLST
For patients with ICU length of stay ≥72 hours, age (OR 1.06, 95% CI 1.00 - 1.12; p=0.03) and Glasgow Coma Scale (GCS) motor response of <4 (OR 91.59, 95% CI 11.66–719.18; p < 0.001) was independently associated with late WLST, adjusting for all other covariates in the model (Table 4).