Monitoring ventilation during anesthesia.

In patients under anesthesia, ventilation is often monitored less adequately than circulation. A simple method, neglected in adults, is the use of a precordial or oesophageal stethoscope. Respiratory volumes may be measured directly, or inferred from flowrates or pressure changes. A rough measurement of inspired volumes may be made using a nonrebreathing valve, and controlling fresh gas input to maintain a constant underfilled reservoir bag. Spirometry of expired volumes is difficult and requires sophisticated apparatus. Respiratory volumes are easily inferred from flowrates using the Wright or Dr?ger respirometers. Flowrates may also be inferred from pressure changes, which are easy to record, as in the pneumotachorgraph. Accurate measurements require attention to many details, such as linearity of the transducer response over the flowrates measured. Calibration should be with the anesthetic gases used, at controlled temperature and humidity. Positive pressure ventilation peaks give a high flow artefact, and electronic drift requires regular recalibration. Electrical impedance changes may also be used to infer and record respiratory volumes, with reasonable accuracy if individual calibration is carried out. Anesthesia offers excellent opportunities to measure compliance and resistance, but itself changes these values, so that relation to normal values or changes due to pathology is difficult. Occlusion pressure is also readily measured during anesthesia, as an indication of respiratory drive, but rigid control of all other factors affecting respiratory muscle tensions is necessary.     

Monitoring of vecuronium-induced neuromuscular blockade during one-lung ventilation

Purpose  We investigated the monitoring of neuromuscular blockade caused by vecuronium in patients receiving one-lung ventilation (OLV) anesthesia for lung surgery. Methods  Eighteen adult patients requiring OLV for lung surgery (OLV group) and 18 undergoing two-lung ventilation (TLV) for colon surgery (control group) were enrolled in this study. In the two groups, anesthesia was maintained with sevoflurane, fentanyl, and epidural lidocaine. Time from vecuronium 0.1 mg·kg⁻¹ to the onset of neuromuscular blockade; times to the return of T1, T2, T3, or T4 (the first, second, third, or fourth response of the train-of-four [TOF]); and recovery of T1/control or TOF ratio (T4/T1) were compared between the two groups. Results  Time to the onset of neuromuscular blockade in the OLV group was similar to that in the control group (289 ± 74 vs 270 ± 85 s [mean ± SD]; P = 0.482). Times from vecuronium to the return of T1, T2, T3, or T4 in the OLV group did not significantly differ from those in the control group (21.9 ± 7.0 vs 25.8 ± 6.7 min for T1; P = 0.099). T1/control in the OLV group was significantly higher than that in the control group 50-120 min after vecuronium (P < 0.05). The TOF ratio did not differ significantly between the two groups. Conclusion  During OLV for lung surgery, recovery of T1/control is accelerated in anesthetized patients receiving vecuronium.     

Monitoring equipment induced tachycardia in patients with minute ventilation rate-responsive pacemakers

Minute ventilation-sensing pacemakers enable the paced heart to respond to an increased workload. Two patients with such a pacemaker developed pacemaker-driven tachycardia when connected to an electrocardiogram (ECG) monitor also capable of documenting ventilatory frequency and ECG lead disconnection. This tachycardia stopped when the ECG leads were removed. These pacemakers and monitors emit a low-amplitude electrical current and measure the resultant impedence signal across the chest. When patients are connected to the monitor the pacemaker sensor summates both impedence signals and the paced heart rate is increased as a result.      

Monitoring perioperative changes in distribution of pulmonary ventilation by functional electrical impedance tomography

Background: Electrical impedance tomography (EIT) is a noninvasive technique providing cross-sectional images of the thorax. We have tested an extended evaluation procedure, the functional EIT (f-EIT), to identify the local shifts of ventilation known to occur during the transition between spontaneous, controlled and assisted ventilation modes.
Methods: Ten patients scheduled for elective laparotomy were studied in the surgical ward, operating theatre and ICU during spontaneous and different modes of mechanical ventilation. Sixteen ECG electrodes were placed on the circumference of the thorax and connected with an EIT device (APT System Mark I, IBEES, Sheffield, UK). Measurements lasting 180 s were performed and f-EIT images of regional ventilation computed. The geometrical centre of ventilation was determined to quantify the regional distribution of lung ventilation during individual modes of ventilation.
Results: F-EIT confirmed the differences in the distribution of ventilation associated with various modes of artificial ventilation. Accentuated ventilation of the dependent lung regions was observed during spontaneous breathing, whereas a shift of the centre of ventilation to the nondependent regions was found during controlled ventilation. In the course of assisted ventilation a continuous displacement of the centre of ventilation back towards the dependent lung regions, consistent with an increased proportion of spontaneous breathing, was detected. Unassisted spontaneous breathing after weaning from mechanical ventilation resulted in a similar ventilation distribution as during tidal breathing prior to surgery.
Conclusion: F-EIT determined the redistribution of lung ventilation during different modes of mechanical ventilation. We expect that f-EIT will become a useful noninvasive bedside monitoring technique for imaging regional ventilation in pulmonary diseased patients during mechanical ventilation.     

Monitoring of brainstem function during vertebral basilar aneurysm surgery. The use of spontaneous ventilation.

Monitoring of cardiovascular, respiratory, and evoked potential parameters has been advocated during posterior fossa surgery to detect brainstem ischemia that may result from surgical manipulations. We report here our retrospective and smaller prospective experience of spontaneous ventilation as a monitor in patients undergoing vascular surgical procedures in the posterior fossa. Forty patients' charts were reviewed retrospectively, and 10 patients were studied prospectively. Respiratory changes in the retrospectively studied group occurred in 9 patients. Four patients developed apnea during temporary occlusion of the vertebral artery. These respiratory changes were associated with simultaneous cardiovascular changes in only 2 patients, and of the 13 patients monitored with evoked potentials, only 2 had simultaneous evoked potential changes. In the prospectively studied group, respiratory changes occurred in 4 patients. Three patients (2 with apnea during temporary occlusion) had a simultaneous change in evoked potentials but no cardiovascular changes. One patient had a change in all three parameters. Allowing our patients to breathe spontaneously provided an early and rapid indication of brainstem ischemia, especially during the temporary occlusion of the vertebral basilar artery system.     

肥胖患者单肺通气期间的通气策略

背景 肥胖人群比例不断升高,肥胖影响正常生理功能,给麻醉带来不少问题,尤其在单肺通气(one-lung ventilation,OLV)过程中. 目的 减少肥胖患者OLV过程对预后转归的影响,降低肥胖患者围手术期呼吸系统并发症的发生率. 内容 探讨肥胖患者围手术期OLV期间的通气策略,包括通气模式的选择、保护性通气策略、高碳酸血症、肺泡复张策略和吸氧浓度的选择. 趋向 肥胖患者OLV期间采用小潮气量联合呼气末正压通气(positive end-expiratory pressure, PEEP)、间断肺泡复张和低到中度Fi02等通气策略有助于改善氧合、降低肺不张发生率,高碳酸血症在无肺部疾病患者中是否具有肺保护作用尚待研究.     

术侧肺部分通气法与单肺通气的比较研究

Objective The purpose of this study was to compare oxygenation and airway pressure during partial ventilation of the independent lung( PLV) with one-lung ventilation(OLV). Methods 16 patients undergoing thoracotomy for esophageal carcinoma were randomized divided into two groups and a self -controlled cross -over study was used. Two types of ventilation was used in different sequence after two-lung ventilation(TLV), oxygenation index( OI) and airway pressure was compared between groups. Results OI was significantly lower during OLV and PLV than TLV, while it was significantly higher during PLV than OLV (PLV391±112, OLV134±53, TLV530±92,P<0.05). Airway pressure was also significantly lower during PLV than OLV[Ppeak: (19±3) cm H20 vs(27±5) cm H2O,Pplat: (17±2) cm H2O vs (23±3) cm H20, P<0.05 ]. Conclusion PLV significantly improve oxygenation and respiratory mechanics.     

术侧肺部分通气法与单肺通气的比较研究

目的 与单肺通气(one-lung ventilation,OLV)比较术侧肺部分通气(partial ventilation of independent lung,PLV)情况下的氧合与气道压力.方法 16例接受食道手术的患者随机分为两组,进行自身对照交叉研究.在双肺通气后按不同顺序接受OLV和术侧肺PLV,比较3种通气时氧合指数(oxygen index,OI)及气道压力的变化.结果 两种通气方式下OI均显著低于双肺通气(two-lung ventilation,TLV),但PLV时显著高于OLV(PLV391±112,OLV134±53,TLV530±92,P<0.05);气道压力值在PLV时也显著低于OLV[Ppeak:(19±3)cm H2O vs(27±5)cm H2O,Pplat:(17±2)cm H2O vs(23±3)cm H2O,P<0.05](1 cm H2O=0.098 kPa). 结论PLV显著改善了氧合和呼吸力学指标.     

术侧肺部分通气法与单肺通气的比较研究

Objective The purpose of this study was to compare oxygenation and airway pressure during partial ventilation of the independent lung( PLV) with one-lung ventilation(OLV). Methods 16 patients undergoing thoracotomy for esophageal carcinoma were randomized divided into two groups and a self -controlled cross -over study was used. Two types of ventilation was used in different sequence after two-lung ventilation(TLV), oxygenation index( OI) and airway pressure was compared between groups. Results OI was significantly lower during OLV and PLV than TLV, while it was significantly higher during PLV than OLV (PLV391±112, OLV134±53, TLV530±92,P<0.05). Airway pressure was also significantly lower during PLV than OLV[Ppeak: (19±3) cm H20 vs(27±5) cm H2O,Pplat: (17±2) cm H2O vs (23±3) cm H20, P<0.05 ]. Conclusion PLV significantly improve oxygenation and respiratory mechanics.     

Noninvasive ventilation

Endotracheal intubation and mechanical ventilation have traditionally been employed in patients with acute respiratory insufficiency. However, this form of management can have serious adverse effects, mainly infections and barotrauma. Noninvasive ventilation (NIV) has been shown to be an effective alternative, as it reduces both the frequency of complications and cost of care. In fact, NIV is currently the first choice treatment for acute respiratory insufficiency in patients who have chronic obstructive pulmonary disease or who are immunocompromised. It is also commonly applied in patients with asthma, pneumonia, and acute cardiogenic pulmonary edema. Correct indication and training in use of NIV equipment is necessary to ensure success and facilitate patient tolerance.