Implementation of a human mainstream capnograph to rats using 3D-printed adapter

Abstract

Introduction: Changes in ventilation/perfusion matching can be assessed by mainstream (MS) or sidestream (SS) capnography. While MS capnography is more accurate than SS, the instrumental dead space of MS airway adapters prohibits their use in rats. Therefore, we aimed to adapt a human-use MS capnograph sensor in rats by 3D printing.

Methods: A new MS airway adapter was designed and 3D printed for a commercially available human capnography sensor (Capnostat 3™) with an instrumental dead space fitting for rats. The device was validated in ventilated rats (n=6) and compared to a rodent-use SS capnograph (Harvard Apparatus Type 340) using different PEEP levels and respiratory rates. Shape factors (2nd and 3rd phase slopes: S2, S3), end-tidal CO₂ (ETCO₂), and average expiratory CO₂ levels (PECO₂) were determined from time and volumetric domains. The arterial partial pressure of CO₂ (PaCO₂) was used as a reference.

Results: MS capnography using the 3D printed adapter detected ETCO₂‑PaCO₂ gradients of ‑4.6 mmHg [95%CI: ‑5.59–‑3.66] compared to ‑13.5 mmHg [‑14.96–‑12.02] of the SS approach. The MS and SS methods showed a significant (p<0.001 for all), strong correlation regarding the main shape factors in both the time (ETCO₂ r=0.75; S2 r=0.73), and volumetric domains (S2 r=0.70; PECO₂ r=0.72).

Conclusions: The 3D printed MS airway adapter resulted in an ETCO₂‑PaCO₂ gradient closer to the physiological ‑10­ to ‑5 mmHg compared to the SS method in rats. The 3D printed adapter also enables the determination of shape factors of the capnogram, demonstrating the benefits of 3D printing in adapting human-use devices to experimental settings.

Funding: OTKA-NKFIH FK134274, NTP-NFTO-20-B-0301