Quantitative Analysis of the Effect of Prolonged Mechanical Ventilation on Capnographic Indices

摘要

The monitoring of carbon dioxide pressure through Capnography has been clinically used as a continuous and non-invasive measurement of alveolar ventilation. The patients with lung disease, respiratory and hemodynamic instability and when in mechanical ventilation have a significant alteration in the waveform of the capnogram. In this study, quantitative analysis between capnographic indices of the patients under prolonged mechanical ventilation were obtained and compared to waveforms of spontaneously breathing patients. The measurements were performed at the 10th day of invasive mechanical ventilation and 48 hours after tracheal extubation, totalling 52 capnographic curves. PaCO_2 and PetCO_2 measurements maintained a significant correlation in spontaneously breathing patients (r~2 = 0.97, p<0.001) and a weak correlation in patients during prolonged mechanical ventilation (r~2=0.86). Four waveform parameters (intermediate slope, alpha angle, beta angle and area ratio) were identified as altered. These altered parameters can provide guidance to physicians about the physiological interpretation of capnograms and clinical decision. Proper interpretation of the capnogram can alert a clinician to important changes in mechanical ventilatory parameters in order to obtain a capnographic wave closest to normal thereby improving the lung function of patients.