A bench test to confirm the core features of volume-assured non-invasive ventilation.
Volume-assured non-invasive ventilation (NIV) theoretically guarantees minute ventilation with circuit leak compensation unlike other modes of NIV. Bench testing demonstrated that minute ventilation was maintained with varying lung compliance and resistance with minimal effect from circuit leak, confirming for the first time the core features of volume-assured NIV.


OBJECTIVE
Volume-assured non-invasive positive pressure ventilation (va-NIPPV) is a novel mode designed to adapt pressure support (PS) to achieve a target minute ventilation (TgV). This may optimize ventilation; however, no data confirm that va-NIPPV compensates appropriately for the changes in pulmonary mechanics and circuit leak seen in clinical practice. Bench testing assessed these principles.


METHODS
A ventilator featuring a va-NIPPV mode was studied. A test lung with varying compliance and resistance, and pneumotachograph were used. Eight lung model settings were chosen: (i) low resistance and high compliance; (ii) low resistance and low compliance; (iii) high resistance and high compliance; and (iv) high resistance and low compliance, all with and without additional circuit leak. An expiration valve, respiratory rate of 15, inspiratory time of 1 s and PS between 3 and 21 cm H2O were used. Va-NIPPV was tested with varying TgV after establishing the range of minute ventilation possible in a pressure preset mode.


RESULTS
At a TgV of 10 L/min, va-NIPPV delivered minute ventilation of (median (interquartile range) ): 11 (10.9-11, 10.2 (10.2-10.3), 12.4 (12.4-12.4) and 11.2 (10.9-11.2) L/min in test lung settings 1, 2, 3 and 4, respectively. Additional leak between 8-33 L/min had little effect. Similar results were seen at other TgV, within the ventilator's PS capabilities.


CONCLUSIONS
These data confirm that va-NIPPV is able to approximate a preset TgV with varying lung compliance and resistance, and that additional circuit leak has little effect on the delivered minute ventilation.
Oscroft
Nicholas S
NS
Respiratory Support and Sleep Centre, Papworth Hospital NHS Foundation Trust, Papworth Everard, Cambridge, UK. nickoscroft@doctors.net.uk
Smith
Ian E
IE
D000403:Airway Resistance / Q000502:physiology; D006801:Humans; D008168:Lung / Q000502:physiology; D008170:Lung Compliance / Q000502:physiology; D008954:Models, Biological; D011175:Positive-Pressure Respiration / Q000295:instrumentation* / Q000592:standards*; D015656:Respiratory Mechanics / Q000502:physiology