From the Department of Medical Sciences, Clinical Physiology, Uppsala University, Sweden (G.H.) Department of Anesthesia and Intensive Care, Karolinska Hospital, Huddinge, Sweden (L.T.) Department of Morphology, Surgery, and Experimental Medicine, Section of Anesthesia and Intensive Care, University of Ferrara, Italy (G.S.) Department of Intensive Care Medicine, University Hospital (Inselspital), University of Bern, Bern, Switzerland (H.U.R.) Department of Anesthesia and Intensive Care, Västerås Hospital, Västerås, Sweden (L.E.) Uppsala University, Centre for Clinical Research, Hospital of Västmanland, Västerås, Sweden (J.Ö.).
Anesthesiology. 2019 Jul;131(1):46-57. doi: 10.1097/ALN.0000000000002693.
During anesthesia oxygenation is impaired, especially in the elderly or obese, but the mechanisms are uncertain.
Pooled data were examined from 80 patients studied with multiple inert gas elimination technique and computed tomography. Oxygenation was impaired by anesthesia, more so with greater age or body mass index. The key contributors were low ventilation/perfusion ratio (likely airway closure) in the elderly and shunt (atelectasis) in the obese.
Anesthesia is increasingly common in elderly and overweight patients and prompted the current study to explore mechanisms of age- and weight-dependent worsening of arterial oxygen tension (PaO2).
This is a primary analysis of pooled data in patients with (1) American Society of Anesthesiologists (ASA) classification of 1; (2) normal forced vital capacity; (3) preoxygenation with an inspired oxygen fraction (FIO2) more than 0.8 and ventilated with FIO2 0.3 to 0.4; (4) measurements done during anesthesia before surgery. Eighty patients (21 women and 59 men, aged 19 to 69 yr, body mass index up to 30 kg/m2) were studied with multiple inert gas elimination technique to assess shunt and perfusion of poorly ventilated regions (low ventilation/perfusion ratio [(Equation is included in full-text article.)]) and computed tomography to assess atelectasis.
PaO2/FIO2 was lower during anesthesia than awake (368; 291 to 470 [median; quartiles] vs. 441; 397 to 462 mm Hg; P = 0.003) and fell with increasing age and body mass index. Log shunt was best related to a quadratic function of age with largest shunt at 45 yr (r2 =0.17, P = 0.001). Log shunt was linearly related to body mass index (r2 = 0.15, P < 0.001). A multiple regression analysis including age, age2, and body mass index strengthened the association further (r2 = 0.27). Shunt was highly associated to atelectasis (r2 = 0.58, P < 0.001). Log low (Equation is included in full-text article.)showed a linear relation to age (r2 = 0.14, P = 0.001).
PaO2/FIO2 ratio was impaired during anesthesia, and the impairment increased with age and body mass index. Shunt was related to atelectasis and was a more important cause of oxygenation impairment in middle-aged patients, whereas low(Equation is included in full-text article.), likely caused by airway closure, was more important in elderly patients. Shunt but not low(Equation is included in full-text article.)increased with increasing body mass index. Thus, increasing age and body mass index impaired gas exchange by different mechanisms during anesthesia.
麻醉期间氧合作用受损，尤其是在老年人或肥胖患者中，但机制尚不确定。
利用来自 80 名接受多种惰性气体消除技术和计算机断层扫描检查的患者的数据进行了汇总分析。麻醉会导致氧合作用受损，年龄较大或体重指数较高时更为明显。关键的贡献因素是老年人的通气/灌注比（可能是气道关闭）低，肥胖患者的分流（肺不张）。
在老年人和超重患者中，麻醉越来越普遍，这促使当前研究探索年龄和体重依赖性动脉氧分压（PaO2）恶化的机制。
这是对患有以下情况的患者的汇总数据进行的主要分析：（1）美国麻醉师协会（ASA）分类为 1；（2）正常用力肺活量；（3）预充氧时吸入氧分数（FIO2）大于 0.8，通气时 FIO2 为 0.3 至 0.4；（4）在手术前麻醉期间进行测量。80 名患者（21 名女性和 59 名男性，年龄 19 至 69 岁，体重指数高达 30kg/m2）接受了多种惰性气体消除技术检查，以评估分流和通气不良区域的灌注（低通气/灌注比[方程式包含在全文文章中]）和计算机断层扫描评估肺不张。
与清醒时相比，麻醉期间的 PaO2/FIO2 较低（368；291 至 470[中位数；四分位数]与 441；397 至 462mmHg；P=0.003），且随年龄和体重指数增加而下降。对数分流与年龄的二次函数关系最佳，最大分流发生在 45 岁（r2=0.17，P=0.001）。对数分流与体重指数呈线性相关（r2=0.15，P<0.001）。包括年龄、年龄 2 和体重指数的多元回归分析进一步增强了这种关联（r2=0.27）。分流与肺不张高度相关（r2=0.58，P<0.001）。低对数（方程式包含在全文文章中）与年龄呈线性关系（r2=0.14，P=0.001）。
麻醉期间 PaO2/FIO2 比值受损，且这种受损随年龄和体重指数增加而加重。分流与肺不张有关，是中年患者氧合受损的更重要原因，而低（方程式包含在全文文章中），可能是气道关闭引起的，在老年患者中更为重要。随着体重指数的增加，分流而不是低（方程式包含在全文文章中）增加。因此，在麻醉期间，年龄和体重指数通过不同的机制损害气体交换。
