Prevention of atelectasis formation during the induction of general anesthesia in morbidly obese patients

Atelectasis caused by general anesthesia is increased in morbidly obese patients. We have shown that application of positive end-expiratory pressure (PEEP) during the induction of anesthesia prevents atelectasis formation in nonobese patients. We therefore studied the efficacy of PEEP in morbidly obese patients to prevent atelectasis. Twenty-three adult morbidly obese patients (body mass index >35 kg/m(2)) were randomly assigned to one of two groups. In the PEEP group, patients breathed 100% oxygen (5 min) with a continuous positive airway pressure of 10 cm H(2)O and, after the induction, mechanical ventilation via a face mask with a PEEP of 10 cm H(2)O. In the control group, the same induction was applied but without continuous positive airway pressure or PEEP. Atelectasis, determined by computed tomography, and blood gas analysis were measured twice: before the induction and directly after intubation. After endotracheal intubation, patients of the control group showed an increase in the amount of atelectasis, which was much larger than in the PEEP group (10.4% +/- 4.8% in control group versus 1.7% +/- 1.3% in PEEP group; P < 0.001). After intubation with a fraction of inspired oxygen of 1.0, PaO(2) was significantly higher in the PEEP group compared with the control group (457 +/- 130 mm Hg versus 315 +/- 100 mm Hg, respectively; P = 0.035) We conclude that in morbidly obese patients, atelectasis formation is largely prevented by PEEP applied during the anesthetic induction and is associated with a better oxygenation. IMPLICATIONS: Application of positive end-expiratory pressure during induction of general anesthesia in morbidly obese patients prevents atelectasis formation and improves oxygenation. Therefore, this technique should be considered for anesthesia induction in morbidly obese patients.     

移动CT监测肺不张的临床应用

目的应用电子计算机体层摄影(CT)观察全身麻醉诱导前后肺不张的变化。方法8例择期行神经外科手术的患者,于麻醉前、麻醉诱导插管后行全肺CT扫描,选择肺尖、肺门、右膈顶上1cm三个层面的CT图像分析观察肺不张的变化。结果三个层面中,右膈顶上1cm层面的图像麻醉前后变化最明显,麻醉诱导插管后监测到明显的肺不张。结论全麻导致患者肺不张的面积和百分比增加,围术期肺部CT扫描能有效地监测到肺不张的发生,有助于优化术中机械通气,减少肺损伤。     

Catecholamine crisis during induction of general anesthesia

Catecholamine crises associated with pheochromocytoma may cause life-threatening cardiovascular conditions. We report the case of a 75-year-old male who developed a hypertensive crisis during induction of general anesthesia for elective resection of a cervical neuroma due to an undiagnosed pheochromocytoma. Hemodynamic instability occurred immediately after the injection of fentanyl, propofol and rocuronium, prior to laryngoscopy and in the absence of any manipulation of the abdomen. In this case report, we present the management of this incident and discuss the underlying pathophysiology triggering a catecholamine crisis.     

Optimal oxygen concentration during induction of general anesthesia

BACKGROUND: The use of 100% oxygen during induction of anesthesia may produce atelectasis. The authors investigated how different oxygen concentrations affect the formation of atelectasis and the fall in arterial oxygen saturation during apnea. METHODS: Thirty-six healthy, nonsmoking women were randomized to breathe 100, 80, or 60% oxygen for 5 min during the induction of general anesthesia. Ventilation was then withheld until the oxygen saturation, assessed by pulse oximetry, decreased to 90%. Atelectasis formation was studied with computed tomography. RESULTS: Atelectasis in a transverse scan near the diaphragm after induction of anesthesia and apnea was 9.8 +/- 5.2 cm2 (5.6 +/- 3.4% of the total lung area; mean +/- SD), 1.3 +/- 1.2 cm2 (0.6 +/- 0.7%), and 0.3 +/- 0.3 cm2 (0.2 +/- 0.2%) in the groups breathing 100, 80, and 60% oxygen, respectively (P < 0.01). The corresponding times to reach 90% oxygen saturation were 411 +/- 84, 303 +/- 59, and 213 +/- 69 s, respectively (P < 0.01). CONCLUSION: During routine induction of general anesthesia, 80% oxygen for oxygenation caused minimal atelectasis, but the time margin before unacceptable desaturation occurred was significantly shortened compared with 100% oxygen.     

全麻中低潮气量机械通气对病人肺泡不张发生的影响

目的 探讨全麻中低潮气量（VT）机械通气对病人肺泡不张发生的影响。方法 择期全麻下行开颅手术病人16例。ASAⅠ级或Ⅱ级，心功能Ⅰ级或Ⅱ级，年龄20-50岁，随机分为2组，每组8例，常规VT（10 ml／kg）组（TV组）和低VT（6 ml／kg）组（LV组）。分别于气管插管后10 min和手术结束后10min采用移动CT行全肺扫描，计算膈上1 cm层面肺不张面积和百分比，同时行动脉血气分析，记录动脉血二氧化碳分压（PaCO2），并计算肺泡．动脉血氧分压差[P（A-a），O2]、氧合指数（PaO2／FiO2）及呼吸指数（RI）。结果 气管插管后10 min和手术结束后10 min时2组病人肺泡不张的发生率、面积、百分比、P（A-a）O2、PaCO2、PaO2／FiO2及RI组内、组间差异均无统计学意义（P〉0．05）。结论 低VT （6 ml／kg）机械通气不增加全麻下开颅手术病人肺泡不张的发生。     

Memory formation during general anesthesia for emergency cesarean sections

BACKGROUND: Occurrence of explicit memory (i.e., conscious recall) has been reported especially after surgical procedures in which anesthesia is considered to be "light." In addition, previous research has shown that implicit memory (e.g., improved memory test performance in absence of conscious recall) decreases with increasing hypnotic state. The current study investigated explicit and implicit memory during emergency cesarean sections with consistently light levels of hypnotic state. METHOD: Words were presented via headphones, and the bispectral index was recorded throughout surgery. Memory for the presented words was tested after recovery with a word-stem completion test. Using both parts of the process dissociation procedure allowed separation of explicit and implicit memory. In the "inclusion" part of the process dissociation procedure, patients are asked to complete word stems, if possible, with the corresponding words recalled from the intraoperative presentation. In the "exclusion" part, patients are instructed to avoid the words presented intraoperatively and to use other words instead. In the absence of recall, patients are asked to use the first word that comes to mind. RESULTS: The mean bispectral index during word presentation was 76.3 (+/-3.0). On average, the 24 patients were able to make correct inclusion-exclusion decisions: In the inclusion part, hit rates (i.e., the probability of responding with a word presented during surgery) were higher than base rates (0.37 vs. 0.31), whereas in the exclusion part hit rates were lower (0.23 vs. 0.28). Importantly, the patients made these inclusion-exclusion decisions without being able to consciously recall the words presented during surgery. CONCLUSIONS: This study shows that if words are presented at relatively light levels of anesthesia, patients are able to control their inclusion-exclusion decisions. This weak form of explicit memory can occur in the absence of conscious recall.     

No sex differences in memory formation during general anesthesia

BACKGROUND: Women respond differently to anesthesia than men, initially recovering more rapidly, but having more postoperative morbidity. Studies on surgical patients report evidence of memory formation during anesthesia. However, sex differences in memory formation have not been explored. Therefore, the authors investigated sex differences in the implicit and explicit memory formation during general anesthesia. METHODS: With ethics committee approval, 120 consenting adult patients scheduled to undergo surgery during general anesthesia were recruited. Intraoperatively, 16 target words were presented to patients via headphones, and the Bispectral Index was recorded. Postoperatively, memory for presented words was tested using a word stem completion test. The test was divided into inclusion and exclusion parts, to delineate implicit and explicit memory contributions. RESULTS: Target and distracter hit rates were similar in men and women. For the whole study group, there was a significant difference between inclusion target hit rate (0.42) and base hit rate (0.39) (P = 0.01). Buchner's model suggested that this memory formation was attributable to both implicit and explicit memory. A Bispectral Index value greater than 50 was the only significant predictor of inclusion target hit rate. None of the patients were able to consciously recall the words presented during surgery. CONCLUSIONS: Patients showed greater memory performance for words presented during general anesthesia than for words not presented. However, sex differences in memory formation were not observed. A relation between hypnotic state and memory during sevoflurane anesthesia was also established, suggesting that memory formation is possible even at hypnotic depths considered to be adequate anesthesia.     

纳美芬预防全麻诱导时舒芬太尼诱发呛咳的临床效果

目的观察纳美芬对全麻诱导时舒芬太尼诱发呛咳、术中丙泊酚用量以及术后镇痛效果的影响。方法选取拟行乳腺癌根治术的全麻患者300例,年龄18~60岁,BMI 18~30kg/m~2,ASAⅠ—Ⅲ级,根据随机数字表法将患者随机分为4组,每组75例:C组(生理盐水)、L组(利多卡因1mg/kg),N1组(纳美芬0.1μg/kg)和N2组(纳美芬0.2μg/kg)。各组分别给予相应的药物2min后开始全麻诱导:靶控输注丙泊酚3.5μg/ml、静推舒芬太尼0.3μg/kg(时间5s)2min后,静推罗库溴铵0.6mg/kg,90s后插管。术毕静注氟比洛芬酯50mg镇痛。记录呛咳发生率及严重程度,记录术中丙泊酚用量,记录术毕、术后6h及24h的VAS疼痛评分。结果 C、L、N1及N2组患者呛咳发生率分别为37.3%、21.3%、5.3%及1.3%。N1组和N2组呛咳发生率明显低于C组和L组(P0.01或P0.05),N1组和N2组差异无统计学意义。C、L组术中丙泊酚用量明显少于N2组(P0.05)。四组术后VAS疼痛评分差异无统计学意义。结论纳美芬0.1μg/kg可有效预防全麻诱导时舒芬太尼引起的呛咳,且不影响术中丙泊酚用量及术后的镇痛效果。     

全身麻醉诱导时咪唑安定与氯胺酮催眠相互作用的研究

目的 以等辐射分析法研究全身麻醉诱导时咪唑安定与氯胺酮之间催眠相互作用.方法 将90例择期上腹部手术患者随机分为:咪唑安定组(M组)、氯胺酮组(K组)、咪唑安定与氯胺酮复合组(C组),每组30例.麻醉诱导前各组以序贯方式给予不同剂量的咪唑安定、氯胺酮及两药复合药物(咪唑安定与氯胺酮剂量的数值比为1:10),给药2 min后开始催眠末点评估,患者对言语指令失去反应即进入催眠末点,对已进入催眠状态的患者进行麻醉末点评估,以序贯法测定三组催眠、麻醉末点半数有效剂量(ED50),以等辐射分析法分析两者之间催眠、麻醉相互作用.结果 在催眠末点:M组ED50为0.18 mg/kg(95%CI 0.09～0.31 mg/kg);K组ED50为0.50 nag/kg(95%CI 0.38～0.61 mg/kg);C组ED50为0.038/0.38 mg/kg(95%CI 0.024/0.24～0.073/0.73mg/kg),在催眠末点,C组ED50偏离相加线无统计学意义.结论 经等辐射分析法证实,咪唑安定与氯胺酮催眠效应上呈现相加作用.     

Dynamics of re-expansion of atelectasis during general anaesthesia

A major cause of impaired gas exchange during general anaesthesia is atelectasis, causing pulmonary shunt. A 'vital capacity' (VC) manoeuvre (i.e. inflation of the lungs up to 40 cm H2O, maintained for 15 s) may re-expand atelectasis and improve oxygenation. However, such a manoeuvre may cause adverse cardiovascular effects. Reducing the time of maximal inflation may improve the margin of safety. The aim of this study was to analyse the change over time in the amount of atelectasis during a VC manoeuvre in 12 anaesthetized adults with healthy lungs. I.v. anaesthesia with controlled mechanical ventilation (VT 9 (SD 1) ml kg-1) was used. For the VC manoeuvre, the lungs were inflated up to an airway pressure (Paw) of 40 cm H2O. This pressure was maintained for 26 s. Atelectasis was assessed by analysis of computed x-ray tomography. The amount of atelectasis, measured at the base of the lungs, was 4.0 (SD 2.7) cm2 after induction of anaesthesia. The decrease in the amount of atelectasis over time during the VC manoeuvre was described by a negative exponential function with a time constant of 2.6 s. At an inspired oxygen concentration of 40%, PaO2 increased from 17.2 (4.0) kPa before to 22.2 (6.0) kPa (P = 0.013) after the VC manoeuvre. Thus in anaesthetized adults undergoing mechanical ventilation with healthy lungs, inflation of the lungs to a Paw of 40 cm H2O, maintained for 7-8 s only, may re-expand all previously collapsed lung tissue, as detected by lung computed tomography, and improve oxygenation. We conclude that the previously proposed time for a VC manoeuvre may be halved in such subjects.      

“微创”插管技术在甲状旁腺切除术全身麻醉诱导阶段的应用

目的 观察“微创”插管技术在甲状旁腺切除术气管插管全身麻醉诱导阶段的应用效果. 方法 选取拟在全身麻醉下行甲状旁腺切除术的患者100例,ASA分级Ⅲ、Ⅳ级,按随机数字表法分为微创组(L组)和对照组(C组),每组50例.麻醉诱导均采用咪达唑仑、依托咪酯、舒芬太尼、顺式阿曲库铵.L组于诱导后2.5 min用可视喉镜暴露声门,借助一次性喉麻管向喉头周围及声门内喷射2％利多卡因3 ml,继续面罩加压给氧2 min后插入7.0号超滑镇痛气管导管;C组在诱导后4.5 min应用普通喉镜插入7.5号普通气管导管.麻醉维持均采用持续泵入瑞芬太尼、丙泊酚,间断静脉注射顺式阿曲库铵.记录麻醉诱导前(T0)、插管前(T1)、插管时(T2)、插管后1 min(T3)、插管后3 min(T4)时的SBP、DBP、HR、SpO2,并分别于T1和插管后10 min(T5)抽取静脉血检测促肾上腺皮质激素(adrenocortical hormone,ACTH)和皮质醇(corticosteroid,CORT)含量(因CORT有日分泌节律,参与试验手术均安排上午). 结果 围插管期C组SBP、DBP、HR较L组明显升高,差异有统计学意义(P＜0.05),C组血中ACTH和CORT含量均较L组明显增加,差异有统计学意义(P＜0.05). 结论 “微创”插管技术可有效减少甲状旁腺切除术气管插管时心血管反应的发生,减少血液中应激激素释放,增加麻醉安全性.     

舒芬太尼在老年患者全麻诱导中对血液动力学的影响

目的 研究舒芬太尼在老年患者全麻诱导中对血液动力学的影响。方法 择期全麻下手术治疗的老年患者40例,随机分为两组,每组20例。观察组诱导时加用舒芬太尼,对照组则加用芬太尼。分别记录麻醉前（T0）、插管时（T1）、插管后2min（T2）、5min（T3）、10min（T4）各时点的平均动脉压（MAP）、心率（HR）、心输出量（CO）及心脏指数（CI）。结果 MAP、CO、CI在T2、T3、T4时点观察组较对照组低（P〈0．05）,HR在T3、T4时点观察组较对照组低（P〈0．05）,而观察组的MAP、CO、CI、HR在组内T0与T2、T3、T4时点比差异无显著意义。结论 舒芬太尼在老年患者全麻诱导过程中不但对MAP、CO、CI、HR等血液动力学指标无影响,而且能更好地保持循环系统的稳定。     

全麻诱导期血流动力学管理的研究进展

患者在全麻诱导期易出现血流动力学的改变,主要包括气管插管后高血流动力学反应和诱导后低血压两种情况。气管插管后高血流动力学反应可导致患者发生恶性心律失常、心脑血管意外等并发症;诱导后低血压也可引发缺血性脑卒中、心肌缺血等严重的麻醉相关不良事件。因此,维持全麻诱导期的血流动力学稳定非常重要。本文主要从麻醉药物种类的选择、神经阻滞的应用、容量的监测与治疗、诱导药物顺序的优化等方面对全麻诱导期血流动力学管理要点进行综述,为全麻诱导及管理提供参考。     

Echocardiographic monitoring during induction of general anesthesia with a miniaturized esophageal probe

Standard transesophageal echocardiography (TEE) does not allow cardiac monitoring during the induction of anesthesia because standard probes would limit the oropharyngeal space and impair mask ventilation and tracheal intubation. We hypothesized that a prototype, miniaturized TEE probe could be safely introduced transnasally in awake patients and that mask ventilation and orotracheal intubation could be performed while continuously monitoring left ventricular (LV) function during the induction of anesthesia. Forty-five patients were studied prospectively. The transnasal TEE probe was introduced through one of the nares and advanced until a transverse plane image of the LV at the level of the papillary muscles was seen. Anesthesia was induced, and the patients were ventilated with a mask that had previously been threaded over the TEE probe via a central perforation. Probe insertion was successful in 12 patients under local anesthesia alone and in an additional 31 patients with a combination of local anesthesia and mild sedation. In two cases, probe placement was unsuccessful. Overall, hemodynamic variables did not change significantly during insertion. No case of significant mucosal bleeding was seen. In one patient, regurgitation of gastric contents occurred without affecting the perioperative outcome. The two-dimensional echocardiogram image quality of the LV during the induction of anesthesia was good or acceptable in 95% of patients. We conclude that transnasal TEE can effectively be used for cardiac monitoring during the induction of general anesthesia. IMPLICATIONS: This study demonstrates that it is feasible and generally safe to introduce a miniaturized transesophageal echocardiography probe transnasally in awake cardiac risk patients to monitor cardiac performance during the induction of general anesthesia.     

Hemodynamic effects of a combination of general and peridural anesthesia during anesthesia induction in geriatric patients

For major operative procedures in the lower abdomen and many orthopedic procedures such as total hip replacement, a combination of general and epidural anesthesia is used. In order to investigate the hemodynamic effects of such a combination in 14 geriatric patients aged 63-80 years who were undergoing total hip replacement, cardiovascular monitoring was established by an arterial line and a pulmonary artery catheter. The epidural anesthesia was achieved with bupivacaine 0.5% in a dose calculated to obtain a block up to Th 6. General anesthesia was then induced and maintained with midazolam, fentanyl, pancuronium bromide, and a 2:1 nitrous oxide-oxygen mixture. Hemodynamic measurements were established before and 30 min after induction of the epidural anesthesia and 20 min after the induction of general anesthesia. After bupivacaine was injected the loss of sympathetic tone produced a systolic arterial blood pressure decrease from 174 +/- 22 to 136 +/- 28 mmHg (p less than 0.05) and a decrease in heart rate from 73 +/- 12 to 66 +/- 10 min-1 (p less than 0.05). The cardiac index did not change, but the peripheral vascular resistance decreased significantly. Because intravenous fluids were given simultaneously, preload could be maintained. Oxygen delivery and oxygen extraction did not change. During general anesthesia a significant drop in cardiac output was observed from 3.0 +/- 0.6 l/min.m2 to 2.3 +/- 0.4 l/min.m2 (p less than 0.05). The systolic arterial blood pressure decreased to as low as 95 +/- 17 mmHg (p less than 0.05) and oxygen delivery decreased from 500 +/- 125 ml/min.m2 to 323 +/- 84 ml/min.m2 (p less than 0.05).