Methods for achieving equilibration during expiration in a modified Rapid-O2 oxygen insufflation device

Article information

Korean J Anesthesiol. 2025;78(6):601-602

Publication date (electronic) : 2025 August 1

doi : https://doi.org/10.4097/kja.25396

Darhae Eum, Hyun Joo Kim, Wyun Kon Park

Department of Anesthesiology and Pain Medicine, and Anesthesia and Pain Research Institute, Yonsei University College of Medicine, Seoul, Korea

Corresponding author: Wyun Kon Park, M.D., Ph.D. Department of Anesthesiology and Pain Medicine, and Anesthesia and Pain Research Institute, Yonsei University College of Medicine, 50-1 Yonsei-ro, Seodaemun-gu, Seoul, Korea Tel: +82-2-2228-2420 Fax: +82-2-312-7185 Email: wkp7ark@yuhs.ac

Received 2025 May 12; Revised 2025 June 20; Accepted 2025 July 31.

Dear Editor,

Rapid-O2 oxygen insufflation device^TM (Rapid-O2) (Meditech Systems Inc.) [1] was designed primarily for rescue oxygenation in “cannot intubate, cannot oxygenate” events; thus, hypercarbia is inevitable. To address this limitation, we modified Rapid-O2 (Supplementary Fig. 1) to provide actively enhanced expiration, and demonstrated effective ventilatory support [2]. When using modified Rapid-O2, it is essential to adjust the duration of insufflation and expiration to prevent hyperinflation or lung collapse. Considering that the vital capacity of adults is approximately 5 L, a certain amount of hyperinflation may not be an issue. However, if more gas expires than is insufflated, lung collapse or even negative-pressure pulmonary edema may develop after a short period of actively assisted expiration [3]. Therefore, as a safety measure, we attached a T-type thumb-control connector with a hole to the oxygen supply line (Supplementary Fig. 1A). If the hole is opened when excessive gas expires, the modified Rapid-O2 is functionally switched off [2]. Despite its advantages, this system has some drawbacks. Firstly, the driving pressure in the oxygen supply line is quite high, approximately 1600 cmH₂O [2], which makes it somewhat hard to occlude the hole with a thumb during insufflation. Secondly, the user must use one thumb to open or close the end of the silicone tubing while simultaneously using the other thumb to manage the hole. This dual requirement makes it difficult to immobilize the main body of the modified Rapid-O2, which is connected to a transtracheally mounted catheter. If there is a hole in the main body, the user can cover it with the thumb while wrapping their index finger around the body, providing a secure grip. To address these issues, we removed the thumb-control connector and made an opening in the body (Fig. 1). We assessed whether this modification enables proper equilibration of intrathoracic pressure with the atmosphere through manipulation of the opening. Additionally, we evaluated the convenience of using this feature.

Fig. 1.

Modified Rapid-O2 oxygen insufflation device with a hole in the body. A straight connector with a drilled hole was connected between the T-connector and Luer lock connector. Insufflation was performed by occluding the end of the silicone tubing while keeping the hole closed. Expiration was achieved by opening the end of the silicone tubing while keeping the hole closed.

The diameter of the holes tested ranged from 3.0 mm to 8.0 mm. A 14 G angiocatheter (Becton Dickinson) was used as the insufflating catheter. A pressure-compensated oxygen flow meter (Ohio Medical) was used, and the oxygen flow rate was set at 15 L/min during the assessment. Two methods were used to assess equilibration during expiration. First, at a certain point during expiration, the end of the silicone tubing was occluded and the hole was opened simultaneously. Second, the hole was opened during expiration. The insufflating pressures, gas flows, and volumes were measured when the end of the silicone tubing was occluded for insufflation while simultaneously opening the hole (with the tubing closed and the hole opened). The expiratory pressures and flows were measured when the hole was opened, while the end of the silicone tubing was opened for expiration (with both the hole and tubing opened). The pressures, along with gas flows, were measured using a VT Plus HF Gas Flow Analyzer (VT Plus Analyzer) (BioTek). The insufflating volume was measured using a trachea-lung model equipped with a test lung (SmartLung2000; IMT Analytics AG) [2].

Statistical analysis was not performed on the measurements using the VT Plus Analyzer (n = 4) and trachea-lung model (n = 6) because of the limited number of experiments and the similarity of the measured values within each group. The results were presented as mean ± SD.

With the tubing closed and the hole opened: At a 3.0 mm hole, insufflating pressures were 7 ± 0 cmH₂O which decreased gradually as the diameter increased. The pressure reached approximately 0 cmH₂O at 7.0 mm diameter. The insufflating flow and volume were 43 ± 0 ml/s and 22 ± 1 ml with a 3.0 mm hole. Beyond the 3.0 mm opening, no insufflating flow or volume was detected. With both the hole and tubing opened: At a 3.0 mm hole, the expiratory pressure and flow were −36 ± 0 cmH₂O and 111 ± 1 ml/s, respectively. As the diameter of the hole increased, both the pressure and flow decreased gradually. At an 8.0 mm hole, the pressure and flow dropped to −5 ± 0 cmH₂O and −35 ± 1 ml/s, respectively.

With the tubing closed and the hole opened, the insufflating pressures were less than 2 cmH₂O for holes larger than 3.0 mm. Additionally, both insufflating flows and volumes were 0 ml/s for holes larger than 3.0 mm. This suggests that the lungs remain static in that position during expiration for holes greater than 3.0 mm. Meanwhile, with both the hole and tubing opened, the expiratory pressure and flow were −5 ± 0 cmH₂O and −35 ± 0 ml/s, respectively, with an 8.0 mm hole. This indicates that, even with an 8.0 mm diameter, a small amount of gas is slowly and continuously expelled from the lungs due to the negative pressure created by the 14 G angiocatheter. Meanwhile, an expulsion rate of 35 ml/s would be acceptable for a short duration. The pressure required to occlude the hole in the thumb-control connector was approximately 1600 cmH₂O [2], while the insufflating pressure through the 14 G angiocatheter was about 170 cmH₂O [2]. Therefore, maintaining a seal with a thumb in an 8 mm hole in the body of the modified Rapid-O2 posed no difficulties. Following the previous report on the modified Rapid-O2 [2], we presented a further modification to improve its usability and safety in clinical settings. Simplifying the operation of the device during emergency situations could help reduce delays in oxygenation.

In conclusion, a more effective method for equilibration is opening the hole while occluding the end of the silicone tubing, rather than opening the hole during expiration. Although opening the hole during expiration is somewhat less effective, it remains a practical alternative. In terms of usability, opening the hole during expiration may feel more straightforward and natural for the user. We recommend using an 8.0 mm hole for optimal performance in both configurations.