Mechanical ventilation as a life-sustaining procedure is a benefit to medicine and usually safe for the patient. When performed over extended periods, it is known to cause lung injury. Various methods of assessing lung injury have been utilized. An objective measure, lactate dehydrogenase (LDH) isozyme profiles, changed significantly after ventilation in lung-healthy rats. Human studies using LDH 4/5 ratio in bronchoalveolar lavage (BAL) have assisted in diagnosing pulmonary infection. We hypothesized that BAL LDH isozymes would relate to lung changes induced by mechanical ventilation.
With IRB approval and individual signed consent, 30 patients with healthy lungs undergoing elective surgery were enrolled in a prospective non-randomized trial to determine levels of LDH isozymes in BAL fluid, and to correlate these levels to time on mechanical ventilation. Bronchoscopy was performed and a BAL was obtained at intubation. After surgery a second BAL was done in the contralateral lung. Total LDH and LDH isozymes were measured by protein electrophoresis on BAL concentrates. Using pre-surgical BAL LDH isozymes as individual baseline, change in each LDH isozyme as a function of time on mechanical ventilation was plotted.
Mechanical ventilation averaged 2 hr 20 minutes (range: 15-509 minutes). All 5 LDH isozymes increased in the post-surgical BAL, isozyme 4 significantly so (p=0.05). Ventilator time was compared with the change in each LDH isozyme; no statistical significance was found.
This study demonstrated an elevated LDH isoenzyme 4 in BAL fluid during surgical mechanical ventilation with an average time of approximately 2 hours. LDH isozyme measurements, which have historically emphasized cardiac and skeletal muscle metabolism, showed that isozyme 4 is usually remarkably stable, with exercise and training affecting the other isozymes.
The significant increase in BAL isozyme 4 in the present study suggests a potential target for investigating lung injury in patients who are subjected to prolonged mechanical ventilation.
Gregory Howell, University grant monies We work for the University of Missouri-Kansas City. The study was funded by the University.