High–frequency jet ventilation vs continuous positive airway pressure for differential lung ventilation in patients undergoing resection of thoracoabdominal aortic aneurysm

Twenty patients, scheduled for surgical resection of thoracoabdominal aortic aneurysm were divided into two groups according to the type of differential lung ventilation used during graft replacement of the descending thoracic aorta. In the high–frequency jet ventilation (HFJV) group of ten patients, HFJV was applied to the left lung once collapsed and retracted by the surgeon, the patient lying in the right lateral decubitus and being intubated by a Carlens' tube. In the continuous positive airway pressure (CPAP) group of ten patients, CPAP was applied to the left lung at the same mean airway pressure as HFJV (1 kPa). Before anaesthetic induction, an arterial and a Swan–Ganz catheter were inserted for cardiovascular monitoring. The same anaesthetic technique using fentanyl 6 μg·kg^-1, flunitrazepam 0.02 mg kg^-1 and pancuronium 0.1 mg kg^-1 was used for each patient. Haemodynamic and respiratory measurements were made: 15 min after positioning the patients in the right lateral decubitus using two–lung ventilation; 15 min after collapse and retraction of the left lung using one–lung ventilation and 15 min after using differential lung ventilation with CPAP or HFJV. Left lung collapse with conventional one–lung ventilation induced a dramatic decrease in arterial oxygenation: Pao₂/Fio₂ ratio decreased from 43 6 kPa to 20 8 kPa, alveolo–arterial oxygen difference increased from 24 7 kPa to 72 11 kPa and pulmonary shunt increased from 17 2% to 37 3%. Whereas differential lung ventilation with CPAP did not improve any of the respiratory parameters measured, differential lung ventilation with HFJV, significantly increased Pao₂/Fio₂ ratio to 41 14 kPa. Therefore, since HFJV improves gas exchange without altering the conditions of surgical comfort, different lung ventilation with HFJV appears to be superior to differential lung ventilation with CPAP.