Tidal volume delivery from ICU ventilators at BTPS conditions: a bench study

Area of Science:

• Mechanical Ventilation
• Respiratory Therapy
• Biomedical Engineering

Background:

• External filters on breathing circuits are not common but may protect expiratory valves.
• Potential benefits include protection from nebulization water saturation and environmental pathogens (e.g., multi-drug-resistant organisms, H1N1 influenza).

Purpose of the Study:

• To evaluate the impact of external filters on tidal volume (VT) delivery accuracy in intensive care unit (ICU) ventilators.
• To compare VT error across different ICU ventilator models with and without external filters.

Main Methods:

• Six ICU ventilators were tested: two with built-in filters and four without.
• External filters (Hygrobac, Sterivent S) were added to the expiratory limb of ventilators without built-in filters.
• Tidal volume delivery was measured under Body Temperature and Pressure Saturated (BTPS) conditions using a lung model in a neonatal incubator.
• Volume error (% set VT) was calculated at various nominal VT settings (300-800 mL).

Main Results:

• Significant differences in volume error were observed across ICU ventilators even without external filters (range: 90-108%).
• Addition of Hygrobac or Sterivent filters resulted in further significant changes in volume error for most tested ventilators (range with filters: 93-112%).
• Volume errors varied considerably between ventilator models and filter types.

Conclusions:

• ICU ventilators exhibit substantial variability in tidal volume delivery accuracy under BTPS conditions.
• The addition of filters to the distal expiratory limb significantly alters VT delivery accuracy.
• Clinical use of external filters requires careful consideration of their impact on ventilator performance.