Introduction: Initial blood pH after ROSC has been considered to be a strong indicator of both the duration of the cardiac arrest as well as the quality of the cardiopulmonary resuscitation. However, to date, there are still conflicting data with regards to its predictive value for survival and neurological recovery.
Hypothesis: Initial blood pH after return of spontaneous circulation (ROSC) does not solely relate to the final neurological outcome in survivors of a cardiac arrest (CA).
Methods: We retrospectively analyzed consecutive CA patients (pts) admitted at our center between September 2006 and March 2017 and aimed to determine the association between pH levels on admission and survival/neurological outcome.
Results: A total of 398 pts were included, of which 190 (47%) had a good neurological outcome (CPC 1-2), while the remaining 208 (53%) had severe cerebral disability or died (CPC 3-5). Pts with a CPC 3-5 were older in age (59.2 ± 15.5 vs 65.5 ± 14.4 years, p <0.01); predominantly male sex (n=150, 72.1%), and had previous history of type 2 diabetes mellitus (30 vs 66 patients, p<0.03). As expected, they had a less frequently witnessed CA (183 (96.3%) vs 181 (87%), p<0.01), a more prolonged time to ROSC (19.6 ± 12.5 vs 32.2 ± 20.6 min, p<0.01) and asystole was registered as initial rhythm in a higher proportion of pts (18 (9.4%) vs 75 (36%), p<0.001). In matter of their blood gas parameters, pH was significantly lower (7.2 ± 0.1 vs 7.1 ± 0.2, p<0.01) with concomitant higher levels of lactate (5.2 ± 5.8 vs 7.4 ± 4.8 mg/dl, p<0.02) and pCO2 (52.1 ± 16.1 vs 57.3 ± 18.6 mmHg, p<0.03). Rates of survival and neurological recovery tend to be lower as pH decreased (Figure 1). Nevertheless, even with critical values of pH defined as levels under 7, more than 20% of pts survived with good neurological outcome.
Conclusion: Initial low blood pH should not be used as an isolated predictor of neurological outcome as it may be affected by the etiology of the CA and underlying condition of each pt.