Arterial oxygenation and one-lung anesthesia

PURPOSE OF REVIEW: In the presence of the obligatory shunt during one-lung ventilation, arterial oxygenation is determined by the magnitude of the shunt in addition to the oxygen content of the mixed venous blood coursing through that shunt. The present discussion aims to heighten awareness of factors determining arterial oxygenation during one-lung anesthesia, other than the magnitude of the shunt and dependent lung low-ventilation perfusion units. RECENT FINDINGS: A convenient way to increase mixed venous and thereby arterial oxygenation is to raise cardiac output. While this approach has achieved some success when increasing cardiac output from low levels, other studies have highlighted limitations of this approach when cardiac output attains very high levels. The effect of anesthesia techniques on the relationship between oxygen consumption and cardiac output could also explain unanswered questions regarding the pathophysiology of arterial oxygenation during one-lung anesthesia. SUMMARY: The effects of anesthesia techniques on oxygen consumption, cardiac output and therefore mixed venous oxygenation can significantly affect arterial oxygenation during one-lung anesthesia. While pursuing increases in cardiac output may, under limited circumstances, benefit arterial oxygenation during one-lung ventilation, this approach is not a panacea and does not obviate the necessity to optimize dependent lung volume.     

全麻下单肺通气对肺功能的影响

目的　探讨单肺通气状况的最佳呼吸方式。方法　 60例 ASA ～ 级开胸病人单肺麻醉时 ,在分钟通气量设定的条件下 ,随着吸气时间相对延长 (通过降低呼吸频率和吸∶呼比值 )的不同通气条件变化 ,对单肺功能和血气分析的影响进行了临床研究。结果　单肺通气时 ,在呼吸频率 =12次 /分 ,吸∶呼比值 =1∶ 1时 ,通气侧肺顺应性、实际分钟通气量和脉搏血氧饱和度明显改善 ,血气结果最佳 ,与双肺通气相比较无显著性差异 ( P>0 .0 5 ) ;气道压力显著降低 ,与单肺通气其它通气条件相比较有显著性降低 ( P<0 .0 5 )。但过分降低呼吸频率 ( RR<10次 /分 )达到的效果会适得其反。结论　在单肺通气使用麻醉呼吸器时 ,相对降低呼吸频率 ( RR=12次 /分 )、相对延长吸气时间 ( I∶ E=1∶ 1.5 ) ,可达到提高肺顺应性和通气量 ,降低气道压力 ,提高血氧和降低二氧化碳分压的良好效果     

瑞芬太尼复合异丙酚靶控输注对单肺通气时血液氧合及肺内分流的影响

目的 探讨瑞芬太尼复合异丙酚靶控输注在食道手术单肺通气下对血流动力学、血液氧合及肺内分流率的影响。方法 45例ASAI～Ⅱ级术中需要单肺通气的择期食道癌手术患者随机分成3组，每组15例：瑞芬太尼和异丙酚靶控组（RP组），芬太尼复合异丙酚靶控组（FP组），异氟醚组（IS组）。通过靶控分别输入瑞芬太尼和异丙酚、芬太尼和异丙酚及吸入异氟烷维持麻醉。连续监测心电图（ECG）、指脉搏氧饱和度（SPO2）、平均动脉压（MAP）、中心静脉压（CVP）、呼气末CO2分压（PETCO2）和HR。分别于清醒仰卧位吸空气时（TO），麻醉双肺通气15min（T1），单肺通气15min（T2）、30min（T3）、60min（T4）、120min（T5）及再次双肺通气30min（T6）等7个时间点分别经桡动脉、颈内静脉采集动脉血和混合静脉血2ml进行血气测定，计算肺内分流率（Qs／Qt）。结果IS组MAP在T01下降大于其余两组（P＜0．05）、在T02上升大于其余两组（P＜0．05），IS组HR在T02增高大于其余两组（P＜0．05）；3组患者PaO2在吸入纯氧后均于T1时达到最高在T3时降至最小，后又逐渐增高；与T0相比，PaO2在麻醉后各时点均显著增加。PO2在麻醉后各时点均有不同程度的增加，但IS组增加更明显（P＜0．05）。Qs／Qt在T3左右达到最高后逐渐降低；IS组在T2～6时点增加更明显。RP组拔管时间明显缩短（P＜0．05）。结论 3种麻醉方法术中均能满足手术要求。瑞芬太尼或芬太尼复合异丙酚靶控输注能维持更稳定的血流动力学，改善动脉血氧和降低肺内分流。瑞芬太尼复合异丙酚靶控输注术毕苏醒迅速且苏醒质量高。     

全麻复合硬膜外阻滞对单肺通气期间肺内分流的影响

目的：探讨全麻复合高位硬膜外阻滞对单肺通气期间肺内分流（Qs/Qt )的影响。方法：择期开胸手术病人30例随机分为两组：全麻复合硬膜外组（A组）和全麻组（B组）。两组病人分别于麻醉前、双肺通气20分钟、单肺通气15、30分钟时采动脉血及混合静脉血行血气分析，并计算出Qs/Qt等。结果：单肺通气时，两组病人Qs/Qt较双肺通气时显著增加（P＜0．01），PaO2显著降低（P＜0．05）。单肺通气15、30分钟时，A组病人Qs/Qt显著大于B组（P＜0．01）；PaO2显著低于B组（P＜0．05）。麻醉期间A组病人心率亦显著慢于B组（P＜0．05）。结论：单肺通气期间，全麻复合硬膜0．05）。麻醉期间A组病人心率亦显著慢于B组（P＜0．05）。结论：单肺通气时间，全麻复合硬膜外阻滞可引起Qs/Qt增加，PaO2降低，可能与硬膜外阻滞削弱低氧性肺血管收缩机制（HPV）有关。     

血液稀释对单肺通气麻醉期间脑氧合的影响

目的观察不同程度血液稀释对单肺通气全麻手术中脑氧合的影响。方法30例单纯肺叶切除术行单肺通气的患者,随机均分为血液稀释组和对照组。血液稀释组分别在单肺通气后血液稀释前（T1）、Hct达（30±1）％（T2）和Hct达（26±1）％（T3）三个不同时点,对照组则在相对应的时点同步从动脉和颈内静脉取血作血气分析和乳酸测定,并记算颈内静脉血氧饱和度（SjvO2）、动脉颈内静脉血氧含量差（DA-jvO2）、脑氧摄取率（CERO2）和动脉-颈内静脉血乳酸含量差（DA-jvL）。结果血液稀释组在T2时SjvO2较T1时升高,DA-jvO2和CERO2较T1时降低（P〈0．05）;T3时与T1时比较虽有变化,但差异无统计学意义。与对照组比,m液稀释组Tz时SjvO2升高,DA-jvO2和CERO2降低,差异有统计学意义（P〈0．01）;T3时SjvO2、DA-jvO2和CER02差异无统计学意义。两组患者DA-jvL组内组间差异无统计学意义。结论单肺通气全身麻醉期间血液稀释到Hct达（30±1）％时脑氧合状况较佳,Hct达（26±1）％时不会影响脑氧合状况。     

Arterial oxygenation during one lung ventilation

Purpose  To compare the effects of isoflurane and sevoflurane on artenal oxygenation and middle cerebral artery blood flow velocity during one lung ventilation. Methods  This was a randomized, crossover study in 20 patients undergoing thoracotomy for oesophageal cancer and scheduled for long term one lung ventilation (OLV). They were randomized to one of two groups: group A. firstly isoflurane was administered followed by sevoflurane, and then isoflurane was resumed; group B. the order of the administration was reversed. Artenal blood gas samples were drawn at the start of OLV, 30 and 60 min after the initiation of OLV and the end of OLV (the change of volatile anesthetics was done 30 and 60 min after the start of OLV). Middle cerebral artery (MCA) was monitored continuously with the probe positioned over the temporal bone window. This probe transmitted 2 MHZ wave Doppler signals. Time-averaged MCA blood flow velocity was calculated from the signals. Results  The PaO values decreased 30 min after the start of OLV (364.4 ±33.4 mmHg vs 179.0 ± 19.5, and 338.7 ± 24.8 mmHg vs 139.7 ± 19.9 in groups A and B respectively), but there was no difference between the groups. Blood flow velocity of MCA did not change after the start of OLV (53.1 ± 3.2, 55.9 ± 3.0. 56.4 ± 2.4, and 54.1 ± 1.9 vs 50.8 ± 2.1, 50.7 ± 2.4, 53.7 ± 1.5, 50.8 ± 2.2 cm · sec⁻¹ in groups A and B respectively): there was no difference between the groups. (P < 0.05). Conclusion  In clinical practice, the selection of either isoflurane and sevoflurane for OLV was of no difference in terms of the artena 1 blood oxygenation. With both agents MCA blood flow velocity was maintained during OLV.

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Résumé Objectif  Comparer les effets de l’isoflurane et du sévoflurane sur l’oxygénation arténelle et la vélocité du débit de l’artère cérébrale moyenne pendant la ventilation unipulmonaire. Méthodes  Cette étude aléatoire avec croisement regroupait 20 sujets thoracotomisés pour un cancer de l’oesophage et programinés pour une ventilation unipulmonaire (VUP) prolongée. Ils ont été répartis au hasard en deux groupes: le groupe A recevait de l’isoflurane suivi du sévoflurane et de l’isoflurane à nouveau; dans le groupe B, l’ordre des agerts était inversé. Des échantillons de sang étaient prélevés pour la gazométne arténelle au début de la VUP, 30 et 60 min plus tard, et à la fin de la VUP (l’échange d’anesthésique volatil survenait 30 et 60 min après l’initiation de la VUP) Un capteur placé sur l’os temporal permettait de monitorer l’artère cérébrale moyenne (ACM) en continu par la transmission d’ondes Doppler de 2 MHZ Ces signaux ont servi au calcul de la moyenne de la vélocité du débit de l’ACM en fonction du temps. Résultats  Les valeurs de la PaO₂ ont diminué 30 min après le début de la VUP (respectivement dans les groupes A et B; 364,4 ± 33,4 mmHg à 179,0 ± 19,5 et 338,7 ± 24,8 mmHg à 139,7 ± 19,9) mais sans différence intergroupe La vélocité sanguine de l’ACM n’a pas changé après la mise en marche de la VUP (respectivement dans les groupes A et B; 53,1 t 3,2; 55,9 ± 3,0: 56,4 ± 2,4 et 54,1 ± 1,9 vs 50,8 ± 2,1; 50,7 ± 2,4; 53,7 ± 1,5: 50,8 ± 2,2 cm · s⁻¹); il n’y a pas eu de différence entre les groupes (P < 0,05). Conclusion  En clinique, le choix de l’isoflurane ou du sévoflurane pour la VUP n’influence pas l’oxygénation artérielle Le débit sanguin de l’ACM se maintient pendant la VUP avec l’un et l’autre des agents.

     

Biologically variable ventilation improves oxygenation and respiratory mechanics during one-lung ventilation

BACKGROUND: Hypoxemia is common during one-lung ventilation (OLV). Atelectasis contributes to the problem. Biologically variable ventilation (BVV), using microprocessors to reinstitute physiologic variability to respiratory rate and tidal volume, has been shown to be advantageous over conventional monotonous control mode ventilation (CMV) in improving oxygenation during the period of lung reinflation after OLV in an experimental model. Here, using a porcine model, the authors compared BVV with CMV during OLV to assess gas exchange and respiratory mechanics. METHODS: Eight pigs (25-30 kg) were studied in each of two groups. After induction of anesthesia-tidal volume 12 ml/kg with CMV and surgical intervention-tidal volume was reduced to 9 ml/kg. OLV was initiated with an endobronchial blocker, and the animals were randomly allocated to either continue CMV or switch to BVV for 90 min. After OLV, a recruitment maneuver was undertaken, and both lungs were ventilated for a further 60 min. At predetermined intervals, hemodynamics, respiratory gases (arterial, venous, and end-tidal samples) and mechanics (airway pressures, static and dynamic compliances) were measured. Derived indices (pulmonary vascular resistance, shunt fraction, and dead space ventilation) were calculated. RESULTS: By 15 min of OLV, arterial oxygen tension was greater in the BVV group (group x time interaction, P = 0.003), and shunt fraction was lower with BVV from 30 to 90 min (group effect, P = 0.0004). From 60 to 90 min, arterial carbon dioxide tension was lower with BVV (group x time interaction, P = 0.0001) and dead space ventilation was less from 60 to 90 min (group x time interaction, P = 0.0001). Static compliance was greater by 60 min of BVV and remained greater during return to ventilation of both lungs (group effect, P = 0.0001). CONCLUSIONS: In this model of OLV, BVV resulted in superior gas exchange and respiratory mechanics when compared with CMV. Improved static compliance persisted with restoration of two-lung ventilation.     

Alveolar recruitment strategy increases arterial oxygenation during one-lung ventilation

BACKGROUND: Deterioration of gas exchange during one lung ventilation (OLV) is caused by both total collapse of the nondependent lung and partial collapse of the dependent lung. A previous report demonstrated that an alveolar recruitment strategy (ARS) improves lung function during general anesthesia in supine patients. The objective of this article was to study the impact of this ARS on arterial oxygenation in patients undergoing OLV for lobectomies. METHODS: Ten patients undergoing open lobectomies were studied at three time points: (1) during two-lung ventilation (TLV), (2) during OLV before, and (3) after ARS. The ARS maneuver was done by increasing peak inspiratory pressure to 40 cm H2O, together with a positive end-expiratory pressure (PEEP) of 20 cm H2O for 10 respiratory cycles. After the maneuver, ventilation parameters were returned to the settings before intervention. RESULTS: During OLV, PaO2 was statistically lower before the recruitment (data as median, first, and third quartile, 217 [range 134 to 325] mm Hg) compared with OLV afterwards (470 [range 396 to 525] mm Hg) and with TLV (515 [range 442 to 532] mm Hg). After ARS, PaO2 values during OLV were similar to those during TLV. During OLV, the degree of pulmonary collapse in the nondependent lung, the hemodynamic status, and the ventilation parameters were similar before and after ARS. CONCLUSIONS: Alveolar recruitment of the dependent lung augments PaO2 values during one-lung ventilation.     

不同浓度布比卡因胸段硬膜外阻滞对单肺通气期间动脉氧合的影响

目的观察不同浓度布比卡因胸段硬膜外阻滞对单肺通气(OLV)期间动脉氧合的影响。方法择期行经左胸食管癌根治术患者120例,年龄50~65岁,随机数字表法均分为四组:A、B、C组采用静脉全麻复合硬膜外阻滞,硬膜外分别给予0.5%、0.25%、0.125%布比卡因,D组为单纯静脉全麻,每组30例。A、B、C三组患者诱导前硬膜外注入5ml相应浓度布比卡因,术中以3~5ml/h持续硬膜外泵入。分别于OLV前(T0)、OLV 15min(T1)、OLV 30min(T2)抽取桡动脉血和混合静脉血行血气分析。结果 T1、T2时A组Qs/Qt明显高于其他三组(P0.05),PaO2明显低于其他三组(P0.05)。T0~T2时A、B组SBP、DBP均明显低于D组(P0.05)。与D组比较,A、B、C组术中阿片类药物和丙泊酚的用量均明显减少(P0.05)。结论静脉全麻复合0.125%和0.25%布比卡因胸段硬膜外阻滞在OLV期间不会增加肺内分流和降低动脉氧合。     

硬膜外阻滞复合全麻对单肺通气期间气体交换的影响

目的 观察胸段硬膜外阻滞复合全麻对单肺通气期间气体交换的影响.方法 随机选择ASA Ⅰ～Ⅱ级择期开胸手术病人80例,将病人随机分为两组,全麻复合硬膜外麻醉组(A组)和全麻组(B组),每组40例.两组病人在开胸前双肺通气20 min(T1)时及开胸后单肺通气(OLV)30 min(T2)、60 min(T3)、120 min(T4)时,分别采动脉血及混合静脉血,观察病人动静脉血气情况并计算肺内分流率(Qs/Qt)值、肺泡-动脉血氧分压差(A-aDO2)和无效腔量/潮气量(Vd/Vt)值.结果 与T1相比,两组T2-4时Paw均升高(P<0.01),T2-4时Qs/Qt均增加(P<0.01),A-aDO2增加(P<0.01),PaO2降低(P<0.01),而Vd/Vt,血压、心率变化无统计学差异(P>0.05);与B组相比,A组T2-4时的Qs/Qt增加(P<0.01),A-aDO2增加(P<0.01),PaO2,降低(P<0.01),而Vd/Vt,血压、心率变化无统计学差异(P>0.05).结论 单肺通气期间硬膜外阻滞复合全麻对肺换气功能有影响,使Qs/Qt增加,PaO2下降,A-aDO2增大;对肺泡通气功能指标Vd/Vt影响甚微.     

Changes in SpO2 during total intravenous anesthesia combined with propofol and SpO2 during one-lung anesthesia ventilation

We retrospectively examined SpO2 during one-lung anesthesia (OLA). One hundred and fifty patients of ASA 1 or 2 for thoracoscopic surgery were anesthetized with propofol and fentanyl (n = 93) or pentazocine (n = 57) and mechanically ventilated with FIO2 = 0.6 in the lateral decubitus position. Twelve patients (8%) developed SpO2 < or = 95% in the first 20 minutes of OLA. It has been reported that hypoxemia during OLA occurs in 13-40% of patients under inhalation anesthesia with FIO2 = 1.0. Our results show the total intravenous anesthesia using propofol is useful to maintain SpO2 during OLA. SpO2 during OLA tended to fall in the patients for right side operation, with lower SpO2 during two-lung ventilation and higher body mass index (BMI). However BMI has never been reported as a predictor of hypoxemia during OLA. A gravity-dependent mechanism is considered to be more responsible for the dependent regional volume reduction during OLA in patients in the lateral decubitus position.