If the patient is in severe respiratory distress or has an upper airway obstruction, it may be necessary to secure an airway by intubating with an endotracheal tube (Figure 7). This will allow more cranial obstructions (oropharyngeal, laryngeal, majority of the trachea) to be bypassed if the tube can be placed through the obstructing area. It will also allow for supplementation with 100% oxygen if required and mechanical ventilation for patients with severe pulmonary disease or an inability to ventilate because of neuromuscular causes. These patients require constant supervision and monitoring while intubated.
If being provided for more than a few hours, oxygen should be humidified (ie, saturated with water vapor) to prevent desiccation of the airways, especially if the turbinates are bypassed with nasal or tracheal oxygen catheters. Specially designed units that heat and humidify inspired air are available for placement in anesthetic and ventilator circuits, but nasal or cage oxygen humidification can be accomplished by bubbling the oxygen through a chamber of distilled water.
Related Article: Acute Respiratory Distress: The Blue Patient
Patients receiving oxygen therapy should be monitored closely using physical examination parameters such as respiratory rate and effort, mucous membrane color, and heart rate, as hypoxemia can cause tachycardia. Pulse oximetry or arterial blood gas analysis can be used to confirm the patient is oxygenating at an acceptable level with oxygen supplementation. Pulse oximetry is the easiest, least invasive method. The lowest oxygen concentration that maintains the patient at SpO2 >93% or PaO2 >80 mm Hg should be used. As the underlying condition improves, oxygen supplementation should be slowly decreased while ensuring adequate oxygenation. If adequate oxygenation cannot be attained with supplemental oxygen at an acceptable or attainable level, intubation and positive pressure ventilation with positive end-expiratory pressure should be considered. Long-term therapy with high concentrations of oxygen (100% O2 for >24 hours or 60% O2 for >48 hours) is associated with lung damage (ie, oxygen toxicity).8 Inflammatory injury is caused by toxic metabolites of oxygen, including oxygen free radicals and superoxide molecules. Clinically, oxygen toxicity is difficult to diagnose, but changes in the lungs are similar to those seen in acute respiratory distress syndrome.8 The oxygen concentration used to maintain critical patients should always be minimized to the lowest the patient can tolerate.