Negative Lung Elastance in Mechanically Ventilated Spontaneously Breathing Patient

Abstract

Mathematical modelling of respiratory system can guide clinicians in better monitoring and decision making for mechanically ventilated (MV) patients in intensive care unit (ICU). However, most mathematical models are develop for fully sedated patients and not particularly reliable to be applied for spontaneous breathing (SB) patients. Monitoring respiratory mechanics of SB patients requires invasive clinical protocols and equipment that are clinically too intensive to carry out. Previous study hypothesized that negative elastance occurred in SB patients due to the SB effort produced by the patient. Thus, this paper aims to further investigate the distribution of negative elastance in SB patients by extending the noninvasive time-varying elastance model. By capturing and reviewing the distribution of the negative elastance in SB patient, it can provide more consistent monitoring and decision making particularly for SB patients. Clinical data from 5 MV patients from Christchurch Hospital were used in this study. The area under the curve (AUC) for the time-varying elastance, Edrs, is estimated and analysed in each SB patient. The results are reported as median and interquartile range (IQR) for continuous data with a total of 82 hours. From the result, it was found that all patients have distribution of negative elastance with Patients 1 and 3 have higher distribution of negative elastance due to the SB effort. The median vaue for the negative elastance for all patients’ ranges from -0.66 cmH20.s/l to -2.27 cmH20.s/l. Negative elastance occurs when negative pressure is generated in the patient’s pleural space causing air volume to enter the lung. Thus, by capturing and reviewing the distribution of the negative elastance in SB patient, it can provide more consistent monitoring and decision making particularly for SB patients.