Assessment of Regional Ventilation During Recruitment Maneuver by Electrical Impedance Tomography in Dogs.

BACKGROUND: During protective mechanical ventilation, electrical impedance tomography (EIT) is used to monitor alveolar recruitment maneuvers as well as the distribution of regional ventilation. This technique can infer atelectasis and lung overdistention during mechanical ventilation in anesthetized patients or in the ICU. Changes in lung tissue stretching are evaluated by monitoring the electrical impedance of lung tissue with each respiratory cycle. OBJECTIVE: This study aimed to evaluate the distribution of regional ventilation during recruitment maneuvers based on the variables obtained in pulmonary electrical impedance tomography during protective mechanical ventilation, focusing on better lung recruitment associated with less or no overdistention. METHODS: Prospective clinical study using seven adult client-owned healthy dogs, weighing 25 ± 6 kg, undergoing elective ovariohysterectomy or orchiectomy. The animals were anesthetized and ventilated in volume-controlled mode (7 ml.kg-1) with stepwise PEEP increases from 0 to 20 cmH2O in steps of 5 cmH2O every 5 min and then a stepwise decrease. EIT, respiratory mechanics, oxygenation, and hemodynamic variables were recorded for each PEEP step. RESULTS: The results show that the regional compliance of the dependent lung significantly increased in the PEEP 10 cmH2O decrease step when compared with baseline (p < 0.027), and for the nondependent lung, there was a decrease in compliance at PEEP 20 cmH2O (p = 0.039) compared with baseline. A higher level of PEEP was associated with a significant increase in silent space of the nondependent regions from the PEEP 10 cmH2O increase step (p = 0.048) until the PEEP 15 cmH2O (0.019) decrease step with the highest values at PEEP 20 cmH20 (p = 0.016), returning to baseline values thereafter. Silent space of the dependent regions did not show any significant changes. Drive pressure decreased significantly in the PEEP 10 and 5 cmH2O decrease steps (p = 0.032) accompanied by increased respiratory static compliance in the same PEEP step (p = 0.035 and 0.018, respectively). CONCLUSIONS: The regional ventilation distribution assessed by EIT showed that the best PEEP value for recruitment maintenance, capable of decreasing areas of pulmonary atelectasis in dependent regions promoting less overinflation in nondependent areas, was from 10 to 5 cmH2O decreased steps.

An in vivo image acquisition system for the evaluation of tracheal mechanics in rats.

Mechanical evaluation of tracheal grafts is of great relevance for transplant research. Although there are some publications demonstrating different techniques of tracheal mechanical evaluation, there is still no definitive or preferred protocol available. Here, we present a simple image processing acquisition system that can be used for in vivo experiments. Six male Wistar rats were submitted to orotracheal intubation and a longitudinal incision was made to expose the trachea. Images of tracheae were acquired from a video camera in different scenarios of bronchoconstriction using methacholine (MCh) (Basal, PBS, MCh 30 µg/kg, MCh 300 µg/kg, and postmetabolized) during imposed-inspiration and imposed-expiration. The area variation ratio (the ratio between areas during expiration vs. inspiration) was 1.1× for the Basal group, while the ratio for MCh 300 µg/kg was 6.5×. The area variation of imaged tracheae was statistically significant at the dose of MCh 300 µg/kg for imposed-inspiration versus imposed-expiration (P = .002). Likewise, elastance data of respiratory mechanics indicated a statistically significant difference at the dose of MCh 300 µg/kg for imposed-inspiration versus imposed-expiration (P = .026). Our image processing analysis protocol presented corresponding behavior when compared to mechanical parameters of the respiratory system. In addition, our image acquisition system was able to highlight the differences between imposed-inspiration and imposed-expiration. Image analysis of the tracheal area variation seems to be in agreement with the elastance of the respiratory system. Taken together, these observations may help future studies of tracheal transplantation for in situ assessment of graft patency.