Positive End-Expiratory Pressure and Variable Ventilation in Lung-Healthy Rats under General Anesthesia

Abstract

ObjectivesVariable ventilation (VV) seems to improve respiratory function in acute lung injury and may be combined with positive end-expiratory pressure (PEEP) in order to protect the lungs even in healthy subjects. We hypothesized that VV in combination with moderate levels of PEEP reduce the deterioration of pulmonary function related to general anesthesia. Hence, we aimed at evaluating the alveolar stability and lung protection of the combination of VV at different PEEP levels.DesignRandomized experimental study.SettingAnimal research facility.SubjectsForty-nine male Wistar rats (200–270 g).InterventionsAnimals were ventilated during 2 hours with protective low tidal volume (VT) in volume control ventilation (VCV) or VV and PEEP adjusted at the level of minimum respiratory system elastance (Ers), obtained during a decremental PEEP trial subsequent to a recruitment maneuver, and 2 cmH2O above or below of this level.Measurements and Main ResultsErs, gas exchange and hemodynamic variables were measured. Cytokines were determined in lung homogenate and plasma samples and left lung was used for histologic analysis and diffuse alveolar damage scoring. A progressive time-dependent increase in Ers was observed independent on ventilatory mode or PEEP level. Despite of that, the rate of increase of Ers and lung tissue IL-1 beta concentration were significantly lower in VV than in VCV at the level of the PEEP of minimum Ers. A significant increase in lung tissue cytokines (IL-6, IL-1 beta, CINC-1 and TNF-alpha) as well as a ventral to dorsal and cranial to caudal reduction in aeration was observed in all ventilated rats with no significant differences among groups.ConclusionsVV combined with PEEP adjusted at the level of the PEEP of minimal Ers seemed to better prevent anesthesia-induced atelectasis and might improve lung protection throughout general anesthesia.

Variable ventilation from bench to bedside

“…Similarly, respiratory system elastance increased during conventional mechanical ventilation but to a smaller amount during variable ventilation without significant effects on ventral‐dorsal and craniocaudal reduction of aeration or lung tissue cytokine concentrations [ 26 , 27 ].…”

Effects of anaesthesia techniques and drugs on pulmonary function

“…There are indications that too high FiO 2 or PaO 2 targets are harmful. [ 18 ] Variable ventilation with PEEP adjusted at the level of the PEEP of minimal elastance seems to prevent anaesthesia-induced atelectasis and might improve lung protection throughout GA.[ 19 20 ] PEEP at 10 cm H 2 O is necessary to maintain lung function if low VT ventilation is used. [ 21 22 ]…”

Titulação de PEEP por manobra rápida versus lenta utilizando tomografia de impedância elétrica, e estabilidade da função pulmonar com estratégia ventilatória protetora em modelo suíno de síndrome do desconforto respiratório agudo

“…Poucos estudos que usaram recrutamento máximo em combinação com titulação da PEEP resultaram em melhorias significativas e sustentadas na oxigenação, bem como na mecânica pulmonar (61) . No entanto, outros estudos também relataram queda na complacência respiratória ao longo do tempo durante a ventilação mecânica monótona (64,70,71) . Em pacientes com SDRA, esta queda na complacência respiratória e PaO2 após 1 hora, durante VM monótona com PEEP ótima titulada por oxigenação, pode ser minimizada através da estratégia VM com PEEP ótima associada à suspiro (64) .…”

“…Em pacientes com SDRA, esta queda na complacência respiratória e PaO2 após 1 hora, durante VM monótona com PEEP ótima titulada por oxigenação, pode ser minimizada através da estratégia VM com PEEP ótima associada à suspiro (64) . Em um estudo experimental em pulmões saudáveis, a associação da ventilação variável com a PEEP ótima também evitou a deterioração da mecânica pulmonar (71) .…”