Sehlin Maria, Brändström Helge, Winsö Ola, Haney Michael, Wadell Karin, Ohberg Fredrik
Department of Surgical and Perioperative Sciences, Anesthesiology and Intensive Care Medicine, Umeå University, Umeå, Sweden.
Aviat Space Environ Med. 2014 Nov;85(11):1092-9. doi: 10.3357/ASEM.4013.2014.
Continuous positive airway pressure (CPAP) is used in air ambulances to treat patients with impaired oxygenation. Differences in mechanical principles between CPAP devices may affect their performance at different ambient air pressures, as will occur in an air ambulance during flight.
Two different CPAP systems, a threshold resistor device and a flow resistor device, at settings of 5 and 10 cm H₂O were examined. Static pressure, static airflow, and pressure during simulated breathing were measured at ground level and at three different altitudes [2400 m (7874 ft), 3000 m (9843 ft), and 10,700 m (35,105 ft)].
When altitude increased, the performance of the two CPAP systems differed during both static and simulated breathing pressure measurements. With the threshold resistor CPAP, measured pressure levels were close to the preset CPAP level. Static pressure decreased 0.71 ± 0.35 cm H₂O at CPAP 10 cm H₂O compared to ground level and 35,105 ft (10,700 m). With the flow resistor CPAP, as the altitude increased, CPAP produced pressure levels increased. At 35,105 ft (10,700 m), the increase was 5.13 ± 0.33 cm H₂O at CPAP 10 cm H₂O.
The velocity of airflow through the flow resistor CPAP device is strongly influenced by reduced ambient air pressure, leading to a higher delivered CPAP effect than the preset CPAP level. Threshold resistor CPAP devices seem to have robust performance regardless of altitude. Thus, the threshold resistor CPAP device is probably more appropriate for CPAP treatment in an air ambulance cabin, where ambient pressure will vary during patient transport.
持续气道正压通气（CPAP）用于空中救护车治疗氧合受损患者。CPAP设备之间机械原理的差异可能会影响其在不同环境气压下的性能，就像空中救护车飞行时会出现的情况一样。
研究了两种不同的CPAP系统，一种是阈值电阻器设备，另一种是流量电阻器设备，设置为5和10厘米水柱。在地面以及三个不同海拔高度[2400米（7874英尺）、3000米（9843英尺）和10700米（35105英尺）]测量静态压力、静态气流和模拟呼吸时的压力。
海拔升高时，两种CPAP系统在静态和模拟呼吸压力测量过程中的性能有所不同。对于阈值电阻器CPAP，测量的压力水平接近预设的CPAP水平。与地面水平和35105英尺（10700米）相比，在CPAP为10厘米水柱时，静态压力降低了0.71±0.35厘米水柱。对于流量电阻器CPAP，随着海拔升高，CPAP产生的压力水平增加。在35105英尺（10700米），CPAP为10厘米水柱时增加了5.13±0.33厘米水柱。
通过流量电阻器CPAP设备的气流速度受环境气压降低的强烈影响，导致输送的CPAP效果高于预设的CPAP水平。阈值电阻器CPAP设备似乎无论海拔如何都具有稳定的性能。因此，阈值电阻器CPAP设备可能更适合在空中救护车舱内进行CPAP治疗，因为在患者转运过程中环境压力会发生变化。
