Department of Respiratory Diseases, Aalborg Hospital, Århus University Hospital, Denmark.
COPD. 2013 Aug;10(4):405-10. doi: 10.3109/15412555.2013.771161. Epub 2013 Mar 28.
International guidelines recommend that when changing FIO2 in patients with COPD receiving Long-Term Oxygen Therapy (LTOT), 30 minutes should be waited for steady state before measurement of arterial blood gasses. This study evaluates whether 30 minutes is really necessary, as a smaller duration might improve the logistics of care, potentially reducing the time spent by patients at the out-patient clinic.
12 patients with severe to very severe COPD according to the GOLD guidelines were included. Patients had a median FEV1% of 23% of the predicted value (range 15-64%), median FEV1/FVC 0.43 (range 0.26-0.63), and chronic respiratory failure necessitating LTOT, 1-4 liters/minute, minimum 16 hours/day. Following a FIO2 reduction (wash out), arterial blood gases were measured at 0, 1, 2, 4, 8, 12, 17, 22, 32 and 34 minutes. FIO2 was then increased to baseline levels (wash in) and blood gasses measured at 0, 1, 2, 4, 8, 12, 17, 22, 32, and 34 minutes. Data were analyzed to examine the dynamics of arterial PO2 and saturation (SO2) wash out and wash in by calculating the time constants, tau (ô), and to evaluate the time required to reach values which might be considered clinically stable, defined as PO2 within 0.5 kPa and SO2 within 1% of equilibrium values.
For arterial PO2 values of time constants were about 3 minutes and similar for both wash out and wash in. A median of 5 minutes was required to reach clinically stable values of PO2 in both wash out and wash in, with 7-8 minutes sufficient in 75% of patients, and in the worst case 14 minutes. For SO2, values of the time constant were 4.5 and 1.4 minutes for wash out and wash in, respectively. The time required to reach clinically stable values was different in the two phases. For wash out the median time was 7.4 minutes, and in the worst case 15.6 minutes. For wash in the median time was 2.6 minutes and in worst case 6.8 minutes. No significant changes in PCO2 or pH were seen during FIO2 changes.
DISCUSSION/CONCLUSION: This study shows that oxygen equilibration relevant for clinical interpretation requires only 10 minutes following an increase and 16 minutes following a decrease in FIO2. over the range studied.
国际指南建议，在接受长期氧疗（LTOT）的 COPD 患者中改变 FIO2 时，应等待 30 分钟达到稳定状态，然后再测量动脉血气。本研究评估 30 分钟是否真的有必要，因为较短的时间可能会改善护理的后勤工作，潜在地减少患者在门诊就诊的时间。
纳入了 12 名根据 GOLD 指南患有严重至非常严重 COPD 的患者。患者的中位 FEV1%预测值为 23%（范围 15-64%），中位 FEV1/FVC 为 0.43（范围 0.26-0.63），慢性呼吸衰竭需要 LTOT，1-4 升/分钟，最低 16 小时/天。在 FIO2 降低（冲洗）后，在 0、1、2、4、8、12、17、22、32 和 34 分钟测量动脉血气。然后将 FIO2 增加到基线水平（冲洗入），并在 0、1、2、4、8、12、17、22、32 和 34 分钟测量血气。通过计算时间常数τ（ô）来分析动脉 PO2 和饱和度（SO2）冲洗和冲洗出的动力学，以评估达到可能被认为临床稳定的值所需的时间，定义为 PO2 在 0.5 kPa 内和 SO2 在平衡值的 1%内。
对于动脉 PO2 值，时间常数约为 3 分钟，冲洗出和冲洗入的时间常数相似。冲洗出和冲洗入达到临床稳定 PO2 值分别需要中位数 5 分钟，75%的患者 7-8 分钟即可，最差情况下需要 14 分钟。对于 SO2，冲洗出和冲洗入的时间常数分别为 4.5 和 1.4 分钟。在两个阶段达到临床稳定值所需的时间不同。冲洗出的中位数时间为 7.4 分钟，最差情况下为 15.6 分钟。冲洗入的中位数时间为 2.6 分钟，最差情况下为 6.8 分钟。在 FIO2 变化期间，PCO2 或 pH 没有明显变化。
讨论/结论：本研究表明，在研究范围内，增加 FIO2 后需要 10 分钟，降低 FIO2 后需要 16 分钟即可达到与临床解释相关的氧气平衡。
