• etCO2 level [ Time Frame: 30-60 seconds ]
  to find a threshold value of etCO2 collected when the NGT is well positioned in trachea
• pH [ Time Frame: 30-60 seconds ]
  to find a threshold value of pH collected when the NGT is positioned in the esophagus and in the stomach.

• etCO2 level in chronic obstructive pulmonary disease (COPD) patients [ Time Frame: 30-60 seconds ]
  subanalysis for the threshold value in the group with chronic obstructive pulmonary disease (COPD)
• pH in patients taking proton pump inhibitors (PPIs) [ Time Frame: 30-60 seconds ]
  identify patients taking proton pump inhibitors (PPIs) and perform a sub-subanalysis for the threshold value in the group with already diagnosed gastro-esophageal reflux disease.

Numerous methodologies have been evaluated to recognize the correct positioning of NGT at the gastric level, including different clinical techniques (such as gastric auscultation, aspiration of the NGT), ultrasound techniques, etc. Actually, the diagnostic gold standard is the thoraco-abdominal anterior-posterior radiography, which is considered the only non-invasive method capable to confirm the correct pose of the NGT at intra-diaphragmatic level. This method, however, even if it is non-invasive, requires the use of ionizing radiation (4 micro-Sievert (uSv) for radiography) which could be repeated multiple time for the same patient; NGT may need to be repositioned several times during the same hospital stay, increasing patient exposure to ionizing radiation and, potentially, also the health workers exposure.

The aim is to identify into the group A the threshold value between tracheal and esophageal etCO2 and into the group B the theshold value between gastric and esophageal pH.

Phase A: etCO2 measurement will be collected 1. after intubation, when the tube is inserted into the endotracheal tube, before proceeding with the aspiration of secretions and 2. once the NGT has been inserted, by a probe located at the end of the tube.

Phase B: pH measurement will be collected at the end of the procedure, once the NGT is inserted, at 1.a distance of 25 cm from the mouth (oesophageal site) and at 2. a distance of 40 cm (gastric site), aspirating the gastric contents and measuring on specific litmus paper.

• Gastric Feeding Tube
• Blood Gas Monitoring, Transcutaneous
• pH

• Other: etCO2
  At the end of the procedure, therefore, for each patient two values of etCO2 are acquired which will allow to obtain two "populations of values" of the etCO2: the values at the endotracheal level and the esophageal level values. The authors will find the "threshold value" of etCO2 collected when the NGT is well positioned in trachea. The study manager is not directly involved in the measurement and recording of etCO2 values.
  Other Name: Group A
• Other: pH
  At the end of the procedure, for each patient two values of pH are acquired which will allow to obtain two pH "value populations": a value at esophageal level and a value at the gastric level. The authors will find the "threshold value" of pH collected when the NGT is positioned in the esophagus and in the stomach. The study manager is not directly involved in the measurement and recording of pH values.
  Other Name: Phase B

• Group A - etCO2

  At the end of the anaesthesia , as usual, the secretions are aspirated with a suction tube of 18 Fr of caliber (diameter 6 mm). When the tube is inserted into the endotracheal tube, before proceeding with the aspiration of the secretions, a capnometer is attached to its outer end, measuring the etCO2 value for 10-15 seconds. At the end of the measurement, authors proceed with the aspiration of the secretions as usual.

  Authors then proceed with the laying of a NGT according to local protocols. Also in this case, once the NGT has been inserted, the etCO2 is measured at the end of the probe for 10-15 seconds. At the end of the measurement, the capnometer can be detached, as a standard procedure, and the NGT can be used as usual.

  At the end of the procedure, therefore, for each patient, two values of etCO2 are acquired which will allow to obtain two "populations of values" of the etCO2: the values recorded at the endotracheal level and the one recorded at the oesophageal level.

  Intervention: Other: etCO2
• Group B - pH

  At the end of the anaesthesia , once the NGT is inserted, the pH is measured by aspirating the gastric contents and measuring on specific litmus paper the pH values, both at a distance of 25 cm from the mouth (oesophageal site) and at a distance of 40 cm (gastric site).

  At the end of the procedure, for each patient two values of pH are acquired which will allow to obtain two pH "value populations": a value at oesophageal level and a value at the gastric level.

  Intervention: Other: pH

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Inclusion criteria:

• Adult patients (> 18 years)
• Patients male and female
• Patients intubated by oro- or naso-tracheal way
• Post-induction curarized patients
• Fasting patients (from at least 6 hours)

Exclusion criteria:

• Patient refusal
• Patients with known bleeding diathesis / ongoing bleeding
• Patients at risk of bleeding (defined as thrombocytes <50 G/l, fibrinogen <1.0 g/l, international normalized ratio (INR) > 2.5, activated partial thromboplastin time (aPTT) > 70 sec)
• Patients with traumatic brain injury / Polytrauma
• Patients with esophagus-tracheal fistulas or malformations of the ear, nose, and throat (ENT) sphere
• Patients with current or previous radiotherapy of the ENT sphere
• Patients unable to give their informed consent due to language barriers
• Women who are pregnant