Human versus Computer Controlled Selection of Ventilator Settings: An Evaluation of Adaptive Support Ventilation and Mid-Frequency Ventilation

Abstract

Background. There are modes of mechanical ventilation that can select ventilator settings with computer controlled algorithms (targeting schemes). Two examples are adaptive support ventilation (ASV) and mid-frequency ventilation (MFV). We studied how different clinician-chosen ventilator settings are from these computer algorithms under different scenarios. Methods. A survey of critical care clinicians provided reference ventilator settings for a 70 kg paralyzed patient in five clinical/physiological scenarios. The survey-derived values for minute ventilation and minute alveolar ventilation were used as goals for ASV and MFV, respectively. A lung simulator programmed with each scenario's respiratory system characteristics was ventilated using the clinician, ASV, and MFV settings. Results. Tidal volumes ranged from 6.1 to 8.3 mL/kg for the clinician, 6.7 to 11.9 mL/kg for ASV, and 3.5 to 9.9 mL/kg for MFV. Inspiratory pressures were lower for ASV and MFV. Clinician-selected tidal volumes were similar to the ASV settings for all scenarios except for asthma, in which the tidal volumes were larger for ASV and MFV. MFV delivered the same alveolar minute ventilation with higher end expiratory and lower end inspiratory volumes. Conclusions. There are differences and similarities among initial ventilator settings selected by humans and computers for various clinical scenarios. The ventilation outcomes are the result of the lung physiological characteristics and their interaction with the targeting scheme.

Figure 1

Clinician-selected settings, adaptive support ventilation and mid-frequency ventilation applied to lung simulator. (a) Respiratory rate; (b) tidal volume as registered by the lung simulator; (c) set inspiratory pressure above PEEP needed to deliver target tidal volume; (d) mean airway pressure; (e) peak inspiratory pressure; (f) auto PEEP; (g) inspiratory time; (h) duty cycle or percent time in inspiration; (i) exhaled minute ventilation (MV) and calculated alveolar minute ventilation (MV_A). Values measured by the lung simulator: (b, d, e, g, h, and i). *Value within the range obtained from the clinician survey.

Figure 2

Lung volumes and ventilator settings. End inspiratory and expiratory volumes are total volumes normalized by weight as measured from the baseline. Baseline is 0 mL in the lung simulator; hence, end expiratory volume is a reflection of PEEP and aPEEP and the end inspiratory volume is a manifestation of PEEP, aPEEP, and tidal volume. Tidal volume was measured as the excursion of the simulator piston; however, it can also be estimated by subtracting the end expiratory from the end inspiratory volumes.