In Vitro/In Vivo Evaluation of a Portable Anesthesia Machine with an Oxygen Concentrator for Dogs Under General Anesthesia with Isoflurane

Abstract

This prospective, non-blinded study assessed the performance of a portable anesthesia machine with an oxygen concentrator (PAM_OC) across various oxygen flow rates and vaporizer settings, incorporating both in vitro and in vivo experiments. The oxygen delivery test measured the time required to reach 90% fraction of inspired oxygen (FIO₂) at various flow rates. The vaporizer test assessed the time to stabilize maximum fraction of inspired isoflurane (FIIso) concentration at various oxygen flow rate and vaporizer settings. In the in vivo test, six adult male Beagle dogs (11.4 ± 1.4 kg) were evaluated. The in vivo evaluation included monitoring physiological parameters during isoflurane anesthesia. The higher flow rates significantly reduced the time to plateau for FIO₂ (p < 0.001). Maximum FIIso values were lower than the vaporizer dial settings, and increased oxygen flow rates significantly reduced the time required to reach target values (p < 0.001). Physiological parameters remained stable throughout anesthesia, confirming adequate oxygenation and anesthetic maintenance. The PAMoc, despite its lower pounds per square inch, yielded predictable outcomes consistent with those obtained in conventional anesthesia systems. These results demonstrated the viability of the PAMoc for anesthesia administration in the field and other challenging environments.

Keywords: anesthesia machine; dog; isoflurane; oxygen concentrator; portable.

Figure 1

Schematic diagram of the portable anesthesia machine. (a) Oxygen supply line connected to an oxygen concentrator. (b) Plenum-type vaporizer for isoflurane administration. (c) Breathing circuit utilizing a rebreathing system and a passive scavenging system. (d) A gas sample line connected to the Y connector of the breathing tube, with measurements obtained using a sidestream capnography system.

Figure 2

Oxygen delivery test. (a) The time (min) required to reach 90% FIO₂ depending on the O₂ flow rate (L/min). (b) Change over time (min) of FIO₂ (%) produced by the oxygen concentrator at a flow rate of 5 L/min. Error bars indicate range. FIO₂, fraction of inspired oxygen.

Figure 3

Vaporizer test. (a) The time (min) required to reach the maximum FIIso (%) based on the O₂ flow rate (L/min) using oxygen concentrator. (b) Maximum FIIso (%) based on the O₂ flow rate (L/min) using oxygen concentrator. (c) The time (min) required to reach the maximum FIIso (%) based on the O₂ flow rate (L/min) using oxygen cylinder. (d) Maximum FIIso (%) based on the O₂ flow rate (L/min) using oxygen cylinder. Error bars indicate range. FIIso, fraction of inspired isoflurane.

Figure 3

Vaporizer test. (a) The time (min) required to reach the maximum FIIso (%) based on the O₂ flow rate (L/min) using oxygen concentrator. (b) Maximum FIIso (%) based on the O₂ flow rate (L/min) using oxygen concentrator. (c) The time (min) required to reach the maximum FIIso (%) based on the O₂ flow rate (L/min) using oxygen cylinder. (d) Maximum FIIso (%) based on the O₂ flow rate (L/min) using oxygen cylinder. Error bars indicate range. FIIso, fraction of inspired isoflurane.

Figure 4

In vivo test. (a) The FIIso (%) for the six Beagle dogs over time (min). (b) The FE’Iso (%) for the six Beagle dogs over time (min). The vaporizer dial setting was increased from 0 to 3% and maintained for 10 min, reduced to 2% for the following 20 min, then adjusted to 1% for 10 min, and finally set to 0% for an additional 10 min. Error bars indicate standard deviations. FE’Iso, end-expiratory concentration of isoflurane; FIIso, fraction of inspired isoflurane. Open arrow: vaporizer set (%).