Update of the Treatment of Nosocomial Pneumonia in the ICU

Rafael Zaragoza; Pablo Vidal-Cortés; Gerardo Aguilar; Marcio Borges; Emili Diaz; Ricard Ferrer; Emilio Maseda; Mercedes Nieto; Francisco Xavier Nuvials; Paula Ramirez; Alejandro Rodriguez; Cruz Soriano; Javier Veganzones; Ignacio Martín-Loeches

Disclosures

Crit Care. 2020;24(383) 

In This Article

Epidemiology

The definitions of hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP) are not homogeneous and may alter the incidences reported.[9] In this document, we will refer to HAP as that which appears as of 48 h from hospital admission, in the ICU or in the hospital ward, whether or not related to mechanical ventilation (MV). We will use the term HAP to talk of that HAP unrelated to MV or intubation, as opposed to VAP, which is what appears after 48 h of MV. When a patient presents symptoms of infection of the lower respiratory tract after more than 48 h under MV and does not present opacities on chest X-ray, the patient is diagnosed with ventilator-associated tracheobronchitis (VAT).

Respiratory infections are the most prevalent nosocomial infection observed in ICUs.[10] In a broad global multicentre study, half the patients presented an infection at the time of the observation, 65% of respiratory origin[11] and HAP and VAP accounted for 22% of all hospital infections in a prevalence study performed in 183 US hospitals.[12] A total of 10 to 40% of patients who underwent MV for more than 48 h will develop a VAP. Marked differences are observed between different countries and kinds of ICU.[13] These variations can be accounted for by diagnostic difficulties, differences in the definition used, the diagnostic methods used and the classification of units because the prevalence of VAP is higher in certain populations (patients with adult respiratory distress syndrome (ARDS),[14] with brain damage,[15] or patients with veno-arterial extracorporeal membrane oxygenation (VA-ECMO).[16]

If we analyse the density of incidence, significant differences between European and US ICUs have been reported. The National Healthcare Safety Network (NHSN) (2013) reported that the average rate of VAP in the USA was 1–2.5 cases/1000 days of MV,[17] substantially lower than in Europe, 8.9 episodes/1000 days of MV according to the European Centre for Disease Prevention and Control (ECDC).[18] In Spain, according to the ENVIN-HELICS 2018 report, the incidence was 5.87 episodes/1000 days of MV.[3] Both in the USA and in Europe, the incidence of VAP has gradually reduced,[19] probably in relation to preventive measures,[20] although a potential bias cannot be ruled out due to not very objective monitoring criteria.

A condition with growing relevance is ventilator-associated tracheobronchitis (VAT). In a prospective and multicentre study, the incidence of VAT and VAP was similar with 10.2 and 8.8 episodes for 1000 days of mechanical ventilation, respectively.[21] Sometimes, it is difficult to differentiate VAT and VAP, and in fact, some authors advocate that the two entities are a continuum and that VAT patients can evolve towards VAP.[22] These authors report a series of reasons in their rationale: higher incidence of VAP in patients with VAT compared to those with VAT, post-mortem findings coexisting in both entities, higher ranges of biomarkers (procalcitonin) or severity scores in VAP compared to VAT and mortality, or a common microbiology.[23]

Non-ventilated ICU patients appear to have a lower risk of developing pneumonia, as reported in a recent study, where 40% of cases of pneumonia acquired in the ICU occurred in patients who had not been ventilated previously.[24] Another study, performed in 400 German ICUs, reports a number of VAP of 5.44/1000 days MV, as opposed to 1.58/1000 days of non-invasive mechanical ventilation (NIMV) or 1.15/1000 HAP patients.[25] The global incidence (including intra- and extra-ICU) of HAP ranges from 5 to more than 20 cases/1000 hospital admissions, being more complex to determine, because of the heterogeneity of definitions and the methodology used. The European Centre for Disease Prevention and Control (ECDC), analysing data from 947 hospitals in 30 countries, reports a prevalence of HAP of 1.3% (95% CI, 1.2 to 1.3%).[26] However, a US study reports a frequency of HAP of 1.6% in hospitalized patients, with a density of incidence of 3.63/1000 patients-day.[27] Moreover, a Spanish multicentre study[28] that analysed 165 episodes of extra-ICU HAP reports an incidence of 3.1 (1.3–5.9) episodes/1000 admissions, variable according to hospital and type of patient.

In the non-ventilated patient's group, when cultures are available, the aetiology is similar to VAP,[24] with a predominance of P. aeruginosa, S. aureus and Enterobacteriaceae spp..[29] This also depends on the patient's severity, individual risk factors and local epidemiology.

Table 1 summarizes the studies published from 2010 to 2019 about the microbiology of ICU-acquired pneumonia (including HAP, VAP and VAT).

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