INTRODUCTION

Ventilator Associated Pneumonia (VAP) is the most common health care-associated infection in intensive care units (ICU). Its appearance causes an increase in stay, mortality and economic costs [1].

The traditional diagnostic criteria are clinical, radiological and microbiological [2]. Around them there have been growing controversies; thus, for example, the poor reliability of radiological criteria has been recognized in ICU patients where there may be other situations (such as atelectasis or pulmonary edema), other than an inflammatory condensation and that share radiological signs. For this reason the Center for Disease prevention and Control (CDC) of the United States, implemented in 2013 a system for monitoring events associated with ventilation where the VAP was one of them [3]. In order to decrease the subjectivity and variability of the traditional radiological criteria, the chest radiograph was rejected as a diagnostic criterion. The major criteria are related to objective parameters of the type of end-expiration positive pressure values and fraction of oxygen in the inspired air. An interesting study by Ego et al. [4] demonstrated the variability in the diagnosis of VAP according to the criteria used. The authors report incidence rates from 4% to 42% according to the use of six of the most popular definations and variations from 0% to 44% modeling up to 89 combinations of criteria. At present there is no universalization of the criteria of the CDC and the absence of reliable and universal diagnostic criteria, continues as an unresolved problem.

Computed tomography although it is cited as gold standard radiological criteria, is a diagnostic method that requires the transfer of the patient usually at risk, in addition to the cost and exposure to ionizing radiation therefore, in the opinion of the authors, it should not be the study of choice for radiological diagnosis of VAP in the ICU.

Since a few years ago, a method discarded at the beginning for the imaging study of the lung and its covers, has been gaining a vital place in the diagnostic arsenal of intensive medicine: pulmonary ultrasound [5-7]. Alzahrani et al. [8] published a systematic review and meta-analysis on the use of pulmonary ultrasound in the diagnosis of pneumonia and concluded that it was an accurate tool, easily available, low cost and free of radiological risk.

Materials and Methods

In non-pathological pulmonary ultrasound, the pulmonary glide and A lines are visualized. The first corresponds to the sliding of the visceral pleura against the parietal pleura and the A lines are repetative artifacts of horizontal reverberation parallel to the pleural line and generated by the sub pleural air normally present in the alveoli (Figure 1A).

The B lines are comet-like, hyper echoic artifacts that arise from the pleural line and propagate vertically erasing the A lines and moving when the pulmonary slip is present (Figure 1B). They indicate partial loss of pulmonary aeration and represent the thickening of sub pleural septa by deposition of fibrous tissue, inflammatory cells, or pulmonary edema.