Protective lung strategy using independent pulmonary ventilation

Background

Independent pulmonary ventilation was introduced in the 1930s and allows the utilization of different ventilatory strategies for each lung to improve gas exchange, respiratory mechanics or both in patients with heterogeneous lung diseases.

Objectives

To evaluate the utilization of independent pulmonary ventilation with protective lung strategies and recruitment maneuvers in patients with acute unilateral lung diseases caused by pneumonia and chest trauma.

Patients and methods

Five critically ill patients, four men and a woman, with a medium age of 47 years (18–81 years) and diagnosis of pneumonia with unilateral lung injury (etiologic agents, Streptococcus pneumoniae and Staphylococccus aureus) and one chest trauma patient with contusion and contralateral bronchopleural fistulae. The mean APACHE II score was 21. They were ventilated in the Siemens Servo 300 Ventilator initially in volume controlled ventilation (VCV) with: tidal volume (Vt) 7.5 ml/kg, respiratory frequency (RF) 22 bpm, positive end expiratory pressure (PEEP) 5 cmH₂O, FiO₂ 100%. The mean static compliance (Cst) and PaO₂/FiO₂ ratio were 32.2 and 162.8, respectively. Augmenting PEEP to 10 cmH₂O, both the mean Cst and mean PaO₂/FiO₂ ratio reduced to 19.4 (40.8% reduction) and116 (29.2% reduction), respectively.

A thoracic computed tomography (CT) scan confirmed unilateral lung affection: three patients with left lung disease and two with right lung disease. After that, a left Robertshaw tube was inserted by laryngoscopy and finally positioned by bronchoscopy in all patients. They were submitted to recruitment maneuver on the side of disease with a continuous positive airway pressure of 40 cmH₂O and then 50 cmH₂O for 40 s. Four patients had recruitment maneuvers guided by CT scan with each step guided by serial 5 mm CT scan slices at the level of the carina. To evaluate the best PEEP (defined as the less visually collapsed area measured by Hounsfield Units on CT scan), a 2 cmH₂O descending PEEP curve was built from 25 cmH₂O until collapsed lung appeared. Then a new recruitment maneuver was performed and the best PEEP was set at 2 cmH₂O above the level of collapse.

The contralateral lung was ventilated with VCV, half of the ideal Vt calculated to the ideal body weight of each patient (3.5 ml/kg), mean PEEP of 8 cmH₂O, plateau pressure lower than 30 cmH₂O and RF of 22 bpm.

Oxygenation, individual lung mechanics and hemodynamic parameters were measured pre and post recruitment maneuvers, as well as at final outcome.

Results

Three 41 Fr and two 39 Fr Robertshaw tubes were inserted, one of the patients presenting a difficult airway. The mean Cst of the diseased lungs were lower than their contralaterals: 12.4 versus 37.4. The mean Cst and PaO₂/FiO₂ ratio increased after the recruitment maneuver increased from 116 to 287 and 12.4 to 23.6, respectively. Sodium bicarbonate was administered as a buffer to three patients who presented severe respiratory acidosis (mean pH 7.05). There was no hemodynamic instability related to the recruitment maneuver. Two patients died, one presented a refractory septic schock and another with gas emboli already on conventional orotracheal tube during the weaning process. Three patients were discharged from hospital.