A 62-year-old male patient with end-stage emphysema undergoes left-sided single-lung transplantation. He arrives at the ICU after his surgery and is mechanically ventilated on volume assist control mode. The initial ventilator settings are FiO2 of 0.4, PEEP of 10 cm H2O, tidal volume of 380 mL, and respiratory rate of 20 breaths/minute. A few hours later, arterial blood gas reveals hypoxia with hypercapnia. In response, his ventilator settings are changed to FiO2 of 0.5, PEEP of 12 cm H2O, and respiratory rate of 26 breaths/min. One hour later, he has a HR of 120/min, BP of 80/60 mm Hg and SpO2 of 89%. Chest examination reveals bilateral air entry with coarse breath sounds on the left. Arterial blood gas shows worsening hypoxia and hypercapnia. He is started on norepinephrine, and FiO2 is further increased to 0.6.
What is the next best step in management of this patient?A. Chest tube insertion on the right side
Correct Answer: C
The clinical picture in this patient is suggestive of clinically significant acute native lung hyperinflation. Recipients of single lung transplantation for emphysema are prone to develop native lung hyperinflation. The native lung is highly compliant when compared to the graft lung in patients with COPD. It has severe expiratory airflow limitation that can lead to dynamic hyperinflation and air trapping and hence will improve by decreasing the respiratory rate and PEEP (C). The patient has breath sounds bilaterally and hence does not need a chest tube (A). Increasing PEEP and respiratory rate (B) in this situation can worsen dynamic hyperinflation. Obtaining a CT scan will not help in the acute hemodynamic instability that this patient is in because it does not offer any additional information about his mechanical ventilation (D).
Acute hyperinflation with mediastinal shift to the opposite site can compromise hemodynamic and respiratory functions. The increase in intrathoracic pressure impairs venous return and causes hypotension, often requiring vasopressors. Marked compression of the graft lung results in atelectasis, hypoxia, and hypercapnia.
Positive pressure ventilation in such cases must be tailored to the characteristics of the native lung. The best approach to mechanical ventilation in these patients is to maximize the expiratory time by having a shorter inspiratory time and a lower respiratory rate with minimal PEEP. Acute symptomatic hyperinflation has also been treated by temporarily disconnecting the endotracheal tube from ventilator to allow deflation of the native lung. Ventilation can be very challenging if the graft lung develops edema or PGD. Severe respiratory or hemodynamic compromise in such patients can be treated with differential lung ventilation by placing a double-lumen tube. This allows for independent ventilation of the native and graft lungs with suitable ventilator settings.