A nurse is caring for a patient on mechanical ventilation who suddenly develops severe respiratory distress with decreased oxygen saturation, asymmetrical chest movement, and absent breath sounds on the right side. The ventilator alarm is sounding with high peak pressures. What is the nurse's immediate priority action?

Suspect tension pneumothorax in any mechanically ventilated patient who develops acute deterioration with the classic triad: severe respiratory distress, asymmetrical chest movement, and absent breath sounds on one side. The ventilator will alarm for high peak airway pressures as the machine encounters resistance pushing against the trapped air. Tracheal deviation away from the affected side is a late sign of mediastinal shift. Immediate decompression is required to prevent cardiac arrest from obstructed venous return.

• Priority: Prepare for immediate needle decompression. Assemble a large-bore angiocatheter (14-16 gauge) and antiseptic. The insertion site is the second intercostal space at the midclavicular line on the affected side. A rush of air confirms the diagnosis.
• Simultaneously: Call for the physician or rapid response team. Do not wait for a chest x-ray; this is a clinical diagnosis.
• Support: Increase FiO2 to 100% as a temporizing measure while preparing equipment, but recognize that oxygenation will not improve until the pressure is relieved.
• Post-Decompression: A chest tube will be inserted for definitive management. Ensure the underwater seal drainage system is ready and functional.

Do not confuse tension pneumothorax with endotracheal tube obstruction or mainstem intubation. While both cause high pressures and asymmetrical sounds, a right mainstem intubation typically presents with absent sounds on the left and the tube advanced too far on assessment. Suctioning or withdrawing the tube may resolve it, but in tension pneumothorax, these maneuvers will fail and delay life-saving decompression.