Beware the airway filter: deadspace effect in children under 2 years

Area of Science:

• Pediatric Anesthesiology
• Respiratory Physiology
• Medical Device Engineering

Background:

• Breathing circuit filters enhance gas humidification and prevent contamination.
• However, filters can significantly increase anatomical deadspace, particularly in pediatric patients with small tidal volumes.

Purpose of the Study:

• To quantify the impact of airway filter deadspace on ventilation requirements in young children.
• To evaluate the accuracy of end-tidal carbon dioxide (P(E)CO(2)) measurements when sampled from different points in the breathing circuit.

Main Methods:

• 20 healthy children under 2 years undergoing tracheal intubation were studied.
• Ventilation was adjusted to maintain P(E)CO(2) at 4.6 kPa (35 mmHg) at the tracheal tube adapter.
• An airway filter was introduced, and respiratory rate was adjusted to maintain target P(E)CO(2).

Main Results:

• A mean increase in ventilation of 1.42 L/min was required to maintain normal P(E)CO(2).
• Airway pressure and respiratory rate increased significantly.
• P(E)CO(2) and partial pressure of inspired carbon-di-oxide (PiCO(2)) were higher when sampled at the tracheal tube adapter compared to the filter port.

Conclusions:

• Increased deadspace from airway filters necessitates greater ventilation in young children to maintain normal P(E)CO(2).
• Sampling P(E)CO(2) and PiCO(2) from the filter port leads to underestimation of the deadspace effect.
• A mathematical model may help predict the impact of this increased deadspace.