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Updated: Jun 12, 2026
Monitoring Lung Function with Electrical Impedance Tomography in the Intensive Care Unit
Published on: September 6, 2024
In vitro assessment of proportional assist ventilation
Deena-Shefali Patel1, Gerrard F Rafferty, Simon Hannam
1Division of Asthma, Allergy and Lung Biology, MRCAsthma UK Centre in Allergic Mechanisms of Asthma, King's College London, London, UK.
Objective:
During proportional assist ventilation (PAV) the timing and frequency of inflations are controlled by the patient and the patient's work of breathing may be relieved by elastic and/or resistive unloading. It is important and the authors' objective to determine whether ventilators delivering PAV function well in situations mimicking neonatal respiratory conditions.
Design:
In vitro laboratory study.
Setting:
Tertiary neonatal ICU.
Interventions:
Dynamic lung models were developed which mimicked respiratory distress syndrome, bronchopulmonary dysplasia and meconium aspiration syndrome to assess the performance of the Stephanie neonatal ventilator.
Main Outcome Measures:
The effects of elastic and resistive unloading on inflation pressures and airway pressure wave forms and whether increasing unloading was matched by an 'inspiratory' load reduction.
Results:
During unloading, delivered pressures were between 1 and 4 cm H(2)O above those expected. Oscillations appeared in the airway pressure wave form when the elastic unloading was greater than 0.5 cm H(2)O/ml with a low resistance model and 1.5 cm H(2)O/ml with a high resistance model and when the resistive unloading was greater than 100 cm H(2)O/l/s. There was a time lag in the delivery of airway pressure of at least 60 ms, but increasing unloading was matched by an inspiratory load reduction.
Conclusions:
During PAV, unloading does reduce inspiratory load, but there are wave form abnormalities and a time lag in delivery of the inflation pressure. The impact of these problems needs careful evaluation in the clinical setting.
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