In the last several years, a new classification of pneumonias acquired during ICU stay has emerged and reflects the development of non-invasive ventilation and more commonly elderly and frail patients being admitted to the ICU. The new classification expanded hospital-acquired pneumonia (HAP) into ventilated and non-ventilated ICU-acquired pneumonias, while a new diagnosis emerged for ventilator-associated tracheobronchitis (VAT) [6,7,8]. Unlike VAP, patients with ventilated HAP were usually intubated after the onset of infection, and not with a preceding period of 48 h of ventilation. The definition of VAT shares the same criteria as VAP, except without the presence of new pulmonary infiltrates on portable chest radiograph . The absence of lung infiltrates does not exclude the possibility that a percentage of VAT could be actual VAP, if a computed tomography scan is performed. It is thus possible that some reports of “zero VAP” were created artificially by reporting possible VAP as “ventilator-associated tracheobronchitis”, or identifying intubated HAP patients that fulfil VAP criteria, as “ventilated HAP” and not VAP, among other potential explanations.
Old and new challenges
A recurrent issue in VAP is making an accurate diagnosis in patients with a clinical suspicion of pneumonia . In daily ICU practice, clinicians still use the presence of new radiographic infiltrates plus at least two of the classical clinical criteria for VAP diagnosis. Overall these criteria had 70% sensitivity and specificity in a postmortem study . Recent developments in VAP diagnosis include the use of bedside lung ultrasound to detect pulmonary infiltrates compatible with pneumonia, and molecular point-of-care tests of respiratory secretions to identify potential pathogens. In skilled hands lung ultrasound has an important complementary role in VAP diagnosis . The advantage of lung ultrasound is its non-invasive use at the bedside as both a diagnostic tool, and as a method to follow the response of VAP to treatment. The appropriate use of lung ultrasound in the diagnosis and management of VAP is still being defined in terms of patient-centered outcomes. Other unsolved topic in VAP is the use of invasive or non-invasive respiratory sampling for microbiological diagnosis. Potential new randomised controlled trials (RCTs) focusing on comparing each strategy associated with protocols for antibiotic stewardship, or applying molecular diagnostic methods could add to the field . A main challenge still remains defining a gold-standard for VAP diagnosis.
Rapid and accurate microbial diagnosis of VAP is still a matter of debate. Recent advances in molecular tests provide promising tools for identifying pathogens and resistance profiles. A pilot RCT using the polymerase chain reaction (PCR) to detect methicillin-resistant S. aureus (MRSA) in the bronchoalveolar lavage (BAL) of mechanically ventilated patients has demonstrated better diagnostic performance and antibiotic management than with traditional methods . Other multicenter studies show a very good sensitivity and good concordance of rapid molecular tests for both MRSA and Gram-negative bacilli with conventional cultures [13, 14].
In the last decade, the emergence of multi-drug and extensively drug-resistant (MDR and XDR) Gram-negative bacilli has presented a tremendous challenge for clinicians. Experts commissioned by the World Health Organisation (WHO) prioritized carbapenem-resistant Acinetobacter, ESBL-producing Enterobacterales, and carbapenem-resistant Pseudomonas aeruginosa as the major challenges for the future . Importantly, there is a worldwide variability of the prevalence of these microorganisms and their different mechanism of resistance. In the last 5 years, several new antibiotics have been studied and approved for use in VAP . Most of them include the combination of a beta-lactam or a carbapenem with a beta-lactamase inhibitor (ceftazidime–avibactam, ceftolozane-tazobactam, imipenem–relebactam, meropenem–vaborbactam) or beta-lactams with new mechanisms of action (e.g., cefiderocol), some of them with broad activity against almost all MDR/XDR microorganism . Although timely and accurate treatment is fundamental for better outcome, empiric overtreatment is also frequent in VAP and necessitates an organized approach to antibiotic stewardship. Importantly, risk factors and scores for MDR have not been accurate enough so far to better target initial empiric treatment.