Three-Level Ventilation: the First Clinical Experience
<i>Background</i>. By taking into account the problems of artificial ventilation (AV) in inhomogeneous pulmonary processes (acute lung injury (ALI), acute respiratory distress syndrome (ARDS), pneumonia, etc.), the authors used 3-level ventilation (3LV) in 11 patients with inhomogeneous lung lesion. 3LV is defined as an AV mode (modification), the basic ventilation level is CMV, positive continuous ventilation (PCV), or pressure support (PS) (ASB) and set-up features; the so-called ventilation is produced by two positive end-expiratory pressures (PEEP): PEEP (continuous) and PEEP high (PEEPh) at variable frequency and duration (alternation) of transfer between the individual levels of PEEP. <i>Objective</i>: to investigate whether 3 LV can improve gas distribution into the so-called slow bronchoalveolar compartments in the presence of obviously inhomogeneous gas distribution, by reducing the volume load of the so-called rapid compartments, and to improve pulmonary gas exchange, by observing the nontrauma-tizing ventilation rules. <i>Results</i>. 3LV was introduced in 11 patients with severe inhomogenous lung lesion (atypical pneumonia and ARDS/ALI) after ineffective PCV following a recruitment maneuver (PaO<sub>2</sub> (kPa) / FiO<sub>2</sub> = 5-6). Pronounced positive changes occurred in pulmonary gas exchange within 1-4 hours after introducing 3LV at the frequency fPCV = 26±4 breaths/min and PEEPh at the frequency fPEEPh = 7±2 breaths/min with the minute ventilation (MV) = 12±4 l/min. Comparison of post-3LV changes indicated a reduction in short pulmonary failure from 50±5 to about 30±5%. There was an increase in CO<sub>2</sub> elimination with a fall of PaCO<sub>2</sub> to the values below 6±0.3 kPa, as well as a rise in PaO<sub>2</sub> up to 7.5±1.2 kPa with a decrease in FiO<sub>2</sub> to 0.8-0.4. Under the influence of PEEP = 1.2±0.4 kPa, lung recruitment, appearing also as an increase in the static compliance from 0.18±0.02 to 0.3±0.02 l/kPa and later to 0.38±0.05 l/Pa, contributed to the improvement of gas exchange. Airway resistance decreased by more than 30%. Improved lung aeration is regarded by the authors as a manifestation of gas distribution in the region with a longer time constant. Following 5±1 days were transferred for the PS mode, by gradually lowering ventilation support, switched from the ventilation, and taken to the basic unit. <i>Conclusion</i>. The authors conclude that despite a small sample that has been a reason for no statistical assessment, as a last resort the clinical findings support the results of theoretical mathematical simulation of 3 LV on mathematical and physical models. They also note that 3 LV improved pulmonary gas exchange as compared with PCV used within the first 2-4 hours of AV and that it may be a promising ventilation mode for the lung affected with a diffuse inhomogeneous pathological process.