P_ETCO₂ measured by a new lightweight mainstream capnometer with very low dead space volume offers accurate and reliable noninvasive estimation of PaCO₂

Daijiro Takahashi, Takehiko Hiroma, Tomohiko Nakamura
Division of Neonatology, Nagano Children’s Hospital, Nagano, Japan

Objective: Although capnometers are widely used in adult and pediatric intensive care units, they are not widely used in neonatal intensive care units due to issues such as the weight of sensors, dead space, and leakage from tracheal intubation tubes. These authors developed a light and low dead space airway adaptor of end-tidal carbon dioxide pressure (P_ETCO₂) and evaluated the correlations between P_ETCO₂ and partial CO₂ pressure (PaCO₂) in rabbits while changing tidal volume and leakage volume.
Methods: Firstly, Japanese rabbits weighing 2 kg were divided into three tidal volumes (6 mL/kg, 10 mL/kg, or 15 mL/kg), and P_ETCO₂ and PaCO₂ were measured. Secondly, the respiratory apparatus was set to a tidal volume/body weight ratio of 10 mL/kg, leakage rates were divided into seven groups, and P_ETCO₂  and PaCO₂ were measured.
Results: P_ETCO₂ and PaCO₂ were significantly correlated (r² = 0.9099, P < 0.0001) when there was no leakage in the tracheal intubation tubes. No significant differences were observed between PaCO₂ and P_ETCO₂ (P_a-ETCO₂) in the three tidal volume/body weight groups or for groups in which leakage rate was <60%, but significant deviations in P_a-ETCO₂ were noted in groups with leakage rate 60%.
Conclusion: There was a strong correlation between P_ETCO₂ and PaCO₂ when tidal volume/body weight ratio was 6–15 mL/kg with leakage rate <60%. Lightweight mainstream capnometer with a low amount of dead space airway adaptor might be useful in very low birth weight infants with small tidal volume.

Keywords: capnography, mainstream, neonate