For the diagnosis of ventilator-associated pneumonia, the most common clinical criteria that are used are fever, worsening gas exchange, new onset or increasing bradycardia (<80/min) or tachycardia (>200/min), new onset or increasing tachypnea (<60/min) or apnea (>20 s), new onset or increasing dyspnea (retractions, nasal flaring, grunting), and purulent secretions. Unfortunately, those criteria are non-specific. Apisarnthanarak et al. [15] reported that hypothermia (79%) and new-onset tachypnea (63%) were the most common clinical symptoms in extremely preterm neonates. In their study, Khattab et al. [16] conducted a comparison between newborns with and without ventilator-associated pneumonia (VAP). They found that 80% of the neonates with VAP exhibited chest auscultation abnormalities and mucopurulent endotracheal tube discharge.

The most common radiologic criteria used to diagnose VAP in neonates are the presence of new or progressive infiltrate, adhesions or fluid in lobar fissures/pleura, or cavitations, pneumatocele, or air bronchograms on chest X-ray. In comparison to infiltrates, the presence of air bronchograms shows a higher sensitivity (58–83%) [17]. In complicated instances, including infants with underlying cardiac or pulmonary disease, sequential chest X-rays (days 0, 2, 3, and 7) aid in the confirmation of VAP. VAP is known to exhibit a wide range of non-specific radiographic abnormalities that can mimic other lung conditions, such as respiratory distress syndrome (RDS) brought on by a surfactant deficiency which can further complicate an accurate diagnosis [18].

Currently, there are two techniques—invasive (bronchoscopic) and minimally invasive (tracheal aspirate)—to obtain a sample for microbiologic examination. Bronchoalveolar lavage (BAL) is the most reliable method for sampling in the neonate population and is highly specific but difficult to employ in all cases and requires experienced specialists due to the small diameter of the endotracheal tube (ETT) [19]. On the other hand, the minimally invasive method for collection of specimens through tracheal aspirates (TA) is easy to use but there is a risk of over-diagnosing VAP, which can lead to the overuse of antibiotics [20]. Baltimore [13] acknowledged the challenges associated with diagnosing ventilator-associated pneumonia (VAP) in the neonatal intensive care unit (NICU) population, namely regarding the interpretation of endotracheal tube (ETT) cultures. The colonization of the endotracheal tube by both Gram-positive and Gram-negative organisms usually happens after 48 h of intubation and MV. This is also the time when the diagnosis of VAP is initially evaluated [21,22]. Hence, distinguishing between colonization and infection is challenging, and the reliability of tracheal aspirate cultures is uncertain.

In order to find out how different professional opinions and criteria can affect the identification of VAP cases, Cordero et al. [23] undertook a study. Using the CDC classification and a positive tracheal aspirate, 37 newborns hospitalized in the NICU were diagnosed with VAP by designated infection control practitioners (ICPs). Of the 37 patients recognized by the ICPs as VAP cases, seven were diagnosed with VAP by the NICU’s neonatologists. Additionally, radiologists were also asked to examine the X-rays of the 37 patients and in 8 of the 11 patients with equivocal signs of infection, they stated that there were radiographic changes suggestive of VAP. These authors came to the conclusion that a single positive tracheal aspirate does not differentiate between airway colonization and VAP, and radiography findings without conclusive clinical and laboratory evidence may be erroneous.

The signs and symptoms that most of the available definitions for VAP use are subjective and this can lead to variabilities in the reported cases between researchers [24,25]. This might be the possible explanation why the CDC introduced the so-called ventilator-associated episode (VAE) definitions to better capture the wide range of complications that might occur during mechanical ventilation [26]. VAEs are brought on by persistent rises in ventilator settings following a period of stable or declining ventilator settings. Pediatric VAE (PedVAE) is defined as an increase in the daily minimum mean airway pressure of 4 cmH₂O that is sustained for 2 calendar days after 2 days of stable or decreasing daily minimum mean airway pressure, or an increase in the FiO₂ of 25 points that is sustained for 2 days after 2 days of stable or decreasing daily minimum FiO₂s in children and neonates [27]. This type of definition and classification is not routinely implemented by NICUs but can help in the future to better differentiate the different complications that might occur in this fragile population during mechanical ventilation.

Despite improvements in other NICU care practices that have considerably increased the survival of extremely low birth weight (ELBW) (<1000 g) infants, the diagnosis and management of VAP in the NICU setting have not evolved over the past few decades. Therefore, there is an urgent need to enhance the diagnostics of VAP in this population of patients through research that emphasizes establishing more sensitive and accurate diagnostic techniques and biomarkers [28].