Padrões de ventilação em anestesia: estudo retrospectivo

Joaquim Edson Vieira, Basílio Afonso Ribeiro Silva, Daniel Garcia Júnior

Lung mechanics impairment, Functional Residual Capacity decrease and atelectasis have been described during general anesthesia. This study aimed at retrospectively evaluating ventilation standards in place at the Central Institute, Hospital das Clinicas, Medical School, University of São Paulo (HCFMUSP). Data on 240 patients under general anesthesia, neuromuscular block and mechanical ventilation were recorded. Ventilation standards - tidal volume in ml (VT), respiratory rate per minute, airway pressure in cmH2O, fresh gas flow in L.min-1, SpO2 and P ET CO2 - were recorded, as well as gender, age, weight and height. Body mass index (BMI) was calculated and patients were distributed in four groups: BMI < 20; 20-25; 25-30 and > 30 kg/m(2). There has been a linear correlation between tidal volume (VT) and weight (r=0.640), and BMI (r=0.467). VT by body mass (ml.kg-1) has shown to be inversely related to BMI: BMI < 20 with 10.74 +/- 1.39; BMI 20-25 with 9.67 +/- 1.08; BMI 25-30 to 8.54 +/- 1.09; BMI > 30 to 7.86 +/- 1.26 (p < 0.001, ANOVA). There have been no differences among groups in respiratory rate. During data collection, males (n = 123) and females (n = 117) had similar SpO2 and P ET CO2, as well as BMI. Positive end-expiratory pressure (PEEP) was installed in 78 procedures (33%). These descriptive data allow us to state that mechanical ventilation standards in anesthesia at HCFMUSP use a tidal volume close to 9 ml.kg-1 and a respiratory rate of 10 incursions per minute. PEEP is not widely applied, but when installed it is approximately 4 cmH2O. Weight and BMI had a positive correlation with VT, and VT/weight (ml.kg-1) ratio was inversely related to BMI.