每日一题_2022.08.18

A gravida 3, para 2 woman at 33weeks’ gestation is evaluated in the emergency department in acute hypoxic respiratory failure. She reports subjective fevers and chills and a productive cough. Physical examination shows her to be in acute distress with tachypnea and accessory muscle use. Vital signs include blood pressure of 197/92 mm Hg and oxyhemoglobin saturation of 86% on a nonrebreather face mask. Auscultation of her lung fields elicits shallow breaths, bilateral crackles, and focal rhonchi throughout the right middle and upper lobes. As part of the preparation for intubation, she is placed on high-flow nasal cannula oxygenation throughout the intubation procedure to allow for apneic oxygenation.

Which of the following is a relevant concept regarding the use of apneic oxygenation?

A. It is contraindicated in pregnancy.

B. It decreases the incidence of hypercapnia.

C. It delays time to desaturation throughout the intubation.

D. It decreases the incidence of anoxic brain injury in the fetus.

答案解析：

充分的胎儿氧合需要母体动脉血氧分压 (PaO2) 大于70 mmHg，这相当于通过脉搏血氧测定法测量的血氧饱和度为95%。妊娠患者的低氧血症对母亲和胎儿有双重影响，应立即补氧逆转。妊娠可引起解剖变化，包括膈肌升高和胸腔直径增加。妊娠导致功能残气量下降，每分钟通气量增加。气道管理过程中的低氧血症有可能是发病和死亡的严重原因，储备功能有限的缺氧妊娠患者更是如此。即使预氧合，储备很少的患者在气道操作期间也可能发生快速去饱和事件。鼻导管在大多数医疗保健环境中普遍存在。简单干预是在任何计划的气道操作下以 10-15 L/min 开始高流量氧合。即使诱导和/或麻痹，氧气仍将向下梯度进入肺泡，并扩散到通过的乏氧血流中。已证实呼吸暂停氧合可延迟去饱和时间，并在整个插管过程中维持较高的PaO2。

事实上，这种技术常被用于脑死亡检查时，以防止低氧血症。二氧化碳继续从血流扩散到肺泡中，但不会进一步扩散（导致扩散减少和循环血液中蓄积增加）。呼吸暂停氧合不能预防高碳酸血症或呼吸性酸中毒，与脑死亡检查诱导的结果相似。尚无数据表明呼吸暂停氧合可降低胎儿缺氧性脑损伤的发生率。

正确答案：C