A mathematical model approach quantifying patients’ response to changes in mechanical ventilation: Evaluation in volume support

Abstract

This paper presents a mathematical model-approach to describe and quantify patient-response to changes in ventilator support. The approach accounts for changes in metabolism (V˙O2, V˙CO2) and serial dead space (VD), and integrates six physiological models of: pulmonary gas-exchange; acid–base chemistry of blood, and cerebrospinal fluid; chemoreflex respiratory-drive; ventilation; and degree of patients’ respiratory muscle-response.The approach was evaluated with data from 12 patients on volume support ventilation mode. The models were tuned to baseline measurements of respiratory gases, ventilation, arterial acid–base status, and metabolism. Clinical measurements and model simulated values were compared at five ventilator support levels.The models were shown to adequately describe data in all patients (χ2, p > 0.2) accounting for changes in V˙CO2, VD and inadequate respiratory muscle-response. F-ratio tests showed that this approach provides a significantly better (p < 0.001) description of measured data than: (a) a similar model omitting the degree of respiratory muscle-response; and (b) a model of constant alveolar ventilation. The approach may help predict patients’ response to changes in ventilator support at the bedside.