Pneumothorax after Insertion of Nasogastric Tube

DISCUSSION

NGT insertion is frequently ordered with little thought and is routinely performed “blind ” in the ICU. The use of a misplaced NGT is considered a “Never Event ” in the United Kingdom's National Health Service. However, misplacement into the lungs is surprisingly common (0.3%-15%).^[1,2] The significant complications which may then ensue include pneumonia, pneumothorax, respiratory failure, and even death.^[1,2] Misplacement is more common in mechanically ventilated patients.^[1,2] In one series, 60% of misplacements after blind NGT placement occurred in patients receiving mechanical ventilation. ^[2] Risk factors include reduced level of consciousness, absence of a gag reflex, presence of an endotracheal tube, supine position, and head and neck surgery.^[2]

Auscultation of the abdomen while insufflating air and the appearance of the aspirate are often used to exclude NGT misplacement. That these techniques are completely unreliable has been highlighted and guidelines state that these tests should never be used.^[3] However, the same guidelines strongly advocate testing the pH of the aspirate from the NGT.^[3] This is because pH values under 5.5 are thought to confirm that the tip of the NGT is within the stomach. However, gastric pH is increased by continuous enteral feeding and medications that suppress gastric acid secretion.^[3,4] More dangerous, however, is the fact that although the pH of secretions in healthy lungs is 7.38-7.42^[3] infection decreases the pH of pleural fluid and bronchial secretions.^[5] Furthermore, inappropriately “flushing ” the NGT before testing the pH falsely lowers the pH of the aspirate.^[3] Hence, bronchopulmonary NGT misplacement can be masked by reliance on these techniques alone.

The current gold standard investigation to confirm correct NGT placement is X-ray. The sensitivity of this investigation can be increased by the use of radiographic contrast. While this does provide definitive confirmation of the position of the NGT it is expensive, time-consuming, and exposes patients to radiation.^[4] However, mistakes have occurred because previous X-rays in the same patient have erroneously been reviewed. Magnet-tracking systems enable real-time tracking of NGT progression. However, tracheal misplacement cannot be excluded while the tip of the NGT remains in the midline above the diaphragm.^[6]

Hence, these techniques only detect NGT misplacement after it has happened. Thus, although the risk of administering enteral feed into the lung can be reduced, the risks of pneumothorax, and microbial contamination of the lung remain unchanged.^[6] Only real-time visualization of placement of either a guide for NGT placement or the NGT itself can prevent bronchopulmonary misplacement.^[7–9] However, visualization of NGT placement with fluoroscopy, laryngoscopy, or endoscopy is technically challenging, expensive, and time-consuming.^[7–9]

A disposable NGT with a small camera at the distal end is now available (Kangaroo Feeding Tube with IRIS Technology; IRIS, Medtronic, USA).^[9] This allows anatomical landmarks (e.g., larynx, esophagus, folds of the gastric mucosa, and pylorus) to be seen during NGT placement.^[9] It also allows periodic reconfirmation that the NGT remains within the stomach by inspection of the gastric mucosa. A recent prospective, single-center, single-arm case series of ICU patients reported that the success rate of this technology was comparable to endoscopic placement of NGT.^[9] However, this technique is significantly less invasive, cheaper, and quicker than endoscopy.

The authors' current practice for ICU patients with impaired airway protective reflexes is to insert all NGT under direct vision (i.e., with laryngoscopy, endoscopy, fluoroscopy, or NGT camera). Unless a NGT has been inserted under direct vision, an X-ray must be performed and reported (by an appropriately trained clinician) to show that the tip of the NGT is projected over the stomach before it can be used.^[4]