A ventilator system for delivering drive pressure ventilation to a patient, the ventilator system comprising: a pressure generating system that generates a flow of breathing gas; a ventilation tubing system including a patient interface for connecting the pressure generating system to the patient; one or more non-invasive sensors operatively coupled to at least one of the pressure generating system or the ventilation tubing system , wherein the one or more non-invasive sensors generate output indicative of at least one of flow, volume or pressure; a display for displaying a drive pressure, wherein the drive pressure comprises a pressure for inflating the lungs of the patient against a compliance of the lungs; and a controller configured to collect and analyze the output to determine a condition, in response to the condition, the controller is configured to temporarily switch the ventilator system from a spontaneous breath subtype into a proportional assist (PA) breath subtype for at least one breath, wherein the spontaneous breath subtype does not include the proportional assist (PA) breath subtype, wherein the controller is configured to estimate a respiratory system compliance of the patient during the PA breath subtype based on the output collected during the PA breath subtype; after the at least one breath, the controller is configured to switch the ventilator system from the PA breath subtype back to the spontaneous breath subtype, characterized in that , after a return to the spontaneous breath subtype, the controller is configured to calculate the drive pressure of the patient based on the respiratory system compliance and the output after the return. a pressure generating system that generates a flow of breathing gas; a ventilation tubing system including a patient interface for connecting the pressure generating system to the patient; one or more non-invasive sensors operatively coupled to at least one of the pressure generating system or the ventilation tubing system , wherein the one or more non-invasive sensors generate output indicative of at least one of flow, volume or pressure; a display for displaying a drive pressure, wherein the drive pressure comprises a pressure for inflating the lungs of the patient against a compliance of the lungs; and a controller configured to collect and analyze the output to determine a condition, in response to the condition, the controller is configured to temporarily switch the ventilator system from a spontaneous breath subtype into a proportional assist (PA) breath subtype for at least one breath, wherein the spontaneous breath subtype does not include the proportional assist (PA) breath subtype, wherein the controller is configured to estimate a respiratory system compliance of the patient during the PA breath subtype based on the output collected during the PA breath subtype; after the at least one breath, the controller is configured to switch the ventilator system from the PA breath subtype back to the spontaneous breath subtype, characterized in that , after a return to the spontaneous breath subtype, the controller is configured to calculate the drive pressure of the patient based on the respiratory system compliance and the output after the return. <EOS>