Barwing and colleagues have evaluated whether a formula based on the selleck chem Ponatinib measurement from nose to ear lobe to xiphoid process of the sternum (the NEX distance) modified for the EAdi catheter (NEXmod) is adequate for predicting the accurate position of the esophageal probe [51]. They observed in 18 of 25 patients (72%) that at NEXmod the EAdi signal was suitable for running NAVA. The NAVA mode was possible at the optimal position in four patients – the optimal position being defined by checking three criteria: stable EAdi signals, electrical activity highlighted in central leads of the catheter positioning tool, and an absence of the p-wave in the distal lead. The authors thus concluded that positioning the EAdi catheter using NEXmod gives a good approximation in most of the patients.

Moreover, the body position, positive end-expiratory pressure (PEEP) and intra-abdominal pressure are factors known to influence the position of the diaphragm. Barwing and colleagues therefore enrolled 20 patients in order to evaluate the effects of these factors on catheter position [52]. They evaluated six different situations regarding the PEEP, body position and intra-abdominal pressure. Their results demonstrated that these factors may modify the EAdi catheter optimal position, although not compromising a stable signal due to the wide electrode array. One can therefore conclude that the optimal catheter position should be adjusted after major changes in ventilator settings, clinical condition or patient positioning.

Management of patient-ventilator synchronyThe time lag between the neural inspiratory input and the occurrence of a ventilator breath affects all steps of the respiratory cycle (initiation, insufflation, and cycling-off for expiration) [53]. Among the different forms of asynchrony, ineffective triggering (also known as wasted effort) is the most common during invasive MV. During noninvasive ventilation (NIV), leaks at the patient-ventilator interface impair the function of the pneumatic trigger and cycling system [54], thus promoting specific asynchronies (autotriggering and prolonged insufflation) [55].Ineffective efforts are explained both by patients’ characteristics and by ventilator settings. The presence of intrinsic PEEP increases the patient effort required to trigger the ventilator, thereby increasing the likelihood that the patient’s inspiratory effort will fail to trigger a ventilator breath [36,53,56].

A weak inspiratory effort, which may occur during situations of low respiratory drive such as excessive ventilation, is also a risk factor and is common in patients receiving high assist levels [22] or sedation [38]. An excessive level of pressure support is also associated with prolonged insufflation, thus promoting hyperinflation and intrinsic Cilengitide PEEP. Reduction of ineffective efforts is often possible through a careful optimization of ventilator settings, at least in short-term studies.