Early and late-onset pneumonia in post-cardiac arrest patients: are they truly distinct entities?

Based on a subjective temporal criterion, pneumonia in cardiac arrest survivors has been classified as early-onset pneumonia (EOP), when it is diagnosed within first 72 hours, or late-onset pneumonia (LOP) when it appears > 72 hours (3–7 days). EOP is generally associated with resuscitation-related factors, such as bronchoaspiration and chest compressions, while LOP is linked to invasive mechanical ventilation.

This study aims to determine whether microbiological isolates (i.e. an objective criterion) differ between EOP and LOP, supporting this classification.

We conducted a retrospective observational study based on a prospective registry of patients who were admitted with recovered cardiac arrest to the Intensive Cardiac Care Unit (ICCU) of a tertiary hospital in Spain from September 2006 to April 2022. Pneumonia diagnosis followed the Centers for Disease Control and Prevention (CDC) criteria, January 2023 version.

A total of 588 patients were analysed, excluding 13 patients who died within ≤24 hours (for insufficient data). Baseline characteristics of the study population and cardiac arrest events are summarized in Table 1. The overall incidence of pneumonia was 41% (235 cases). Of the 161 patients with EOP (≤72 hours), microbiological isolates were identified in 39 cases (52.7%). Gram-negative bacteria were the most frequently isolated family of microorganisms in the cultures from respiratory samples in both EOP and LOP. In EOP, H. influenzae, Klebsiella spp., and E. coli were predominant, while in LOP, Klebsiella spp., Serratia spp., Stenotrophomonas spp., and other nosocomial organisms were more common. Furthermore, in LOP, the most frequently isolated pathogen was S. aureus (Figure 1).

The percentage of microbiological isolates was similar to that described in other series. In both EOP and LOP the most frequently isolated family was Gram-negative bacteria, although in LOP a higher percentage of Gram-negative bacilli typical of the hospital environment was found. In addition, in LOP the most frequently isolated microorganism was S. aureus. These findings support that there are differences between these two entities (EOP and LOP) and that the time of diagnosis may aid in selecting appropriate antibiotic treatment.Table 1Figure 1