Performance of electrical impedance tomography in detecting regional tidal volumes during one-lung ventilation

Background: Electrical impedance tomography (EIT) is becoming a new medical imaging modality for continuous monitoring of regional lung function in the intensive care unit or operating room. The aim of our study was to evaluate the performance of EIT in detecting regional tidal volumes in patients during volume-controlled mechanical ventilation of one or both lungs.
Methods: Ten adult patients undergoing elective thoracic surgery were included. EIT measurements were performed with the Goe-MF II EIT system. Data were collected before surgery during ventilation of both, the right and left lungs. Tidal volumes of 800 and 400 ml were applied during bilateral and unilateral ventilation, respectively.
Results: Ventilation-related impedance changes determined in the whole chest cross-section during the right and left lung ventilation did not significantly differ from each other and were equal to 47.6±5.6% and 48.5±7.8% (mean±SD) of the value determined during bilateral ventilation. During unilateral ventilation, EIT clearly separated the ventilated and non-ventilated lung regions; nevertheless, ventilation-related impedance changes were also detected at the non-ventilated sides in areas corresponding to 3.4±4.1% and 12.4±6.9% of the scan halves during ventilation of the left and right lung, respectively. Changes in global tidal volumes were adequately detected by EIT during both bilateral and unilateral lung ventilation.
Conclusion: Although good separation of the ventilated and non-ventilated sides of the chest was possible, the data indicate that reliable quantification of regional tidal volumes during asymmetric or inhomogeneous distribution patterns requires regions-of-interest analysis.     

Effect of positive end-expiratory-pressure on regional ventilation in patients with acute lung injury evaluated by electrical impedance tomography

BACKGROUND AND OBJECTIVE: For the treatment of patients with adult respiratory distress syndrome and acute lung injury bedside measurements of regional lung ventilation should be considered for optimizing ventilatory settings. The aim was to investigate the effect of positive end-expiratory pressure (PEEP) on regional ventilation in mechanically ventilated patients at the bedside by electrical impedance tomography. METHODS: Eight mechanically ventilated patients were included in the study. PEEP levels were increased from 0 to 5, 10, 15 mbar and back to 0 mbar. Regional ventilation in 912 regions of the thorax was investigated at each PEEP by electrical impedance tomography. The obtained regions were divided in four groups: none (none and poorly ventilated regions including chest wall and mediastinum), bad, moderate and well-ventilated regions. RESULTS: Increasing the PEEP stepwise from 0 to 15 mbar decreased the non-ventilated regions (none: 540 regions at PEEP 0 and 406 regions at PEEP 15). In contrast, the other regions increased (bad: 316 regions at PEEP 0 and 380 regions at PEEP 15; moderate: 40 regions at PEEP 0 and 100 regions at PEEP 15; well: 0 region at PEEP 0 and 34 regions at PEEP 15 (median values)) indicating an improvement of regional ventilation. CONCLUSIONS: Increasing PEEP in mechanically ventilated patients reduces none ventilated regions (atelectasis). Furthermore, it leads to a shift from none and bad ventilated regions to moderately and well-ventilated regions. Electrical impedance tomography is a bedside technique and might be an alternative to computed tomography scan to assess aerated lung regions.     

Regional ventilation in cystic fibrosis measured by electrical impedance tomography

BackgroundThe feasibility of electrical impedance tomography (EIT) as an alternative examination tool in cystic fibrosis (CF) was examined.Methods14 CF patients and 14 healthy volunteers were studied. Spirometry and EIT measurements were performed simultaneously. The global inhomogeneity (GI) index was applied to assess the degree of ventilation homogeneity at different levels of maximum inspiratory volume. Ratios of maximum expiratory flow at 25% and 75% of vital capacity (MEF₂₅/MEF₇₅) were calculated for both global lung and regional areas in EIT images.ResultsSignificant differences among GI values at various lung volumes were found in CF patients (P < 0.01) but not in healthy subjects. Global MEF₂₅/MEF₇₅ measured with spirometry and with EIT were highly correlated for all subjects (r² = 0.69, P < 0.01). Significant difference in global MEF₂₅/MEF₇₅ was found between CF patients and healthy volunteers with both spirometer (CF: 0.15 ± 0.09; healthy: 0.46 ± 0.15; P < 0.001) and EIT (CF: 0.14 ± 0.09; healthy: 0.42 ± 0.08; P < 0.001). Regional airway obstruction was identified in the MEF₂₅/MEF₇₅ maps in CF patients.ConclusionsCompared to the global parameters provided by spirometry, EIT is able to deliver both global and regional information to assess the airway obstruction in CF patients.     

Electrical impedance tomography: changes in distribution of pulmonary ventilation during laparoscopic surgery in a porcine model

Background

Because of the creation of a pneumoperitoneum, impairment of ventilation is a common side-effect during laparoscopic surgery. Electrical impedance tomography (EIT) is a method with the potential for becoming a tool to quantify these alterations during surgery. We have studied the change of regional ventilation during and after laparoscopic surgery with EIT and compared the diagnostic findings with computed tomography (CT) scans in a porcine study.

Materials and methods

After approval by the local animal ethics committee, six pigs were included in the study. Two laparoscopic operations were performed [colon resection (n=3) and fundoplicatio (n=3)]. The EIT measurements (6th parasternal intercostal space) were continuously recorded by an EIT prototype (EIT Evaluation Kit, Dräger Medical, Lübeck, Germany). To verify ventilatory alterations detected by EIT, a CT scan was performed postoperatively.

Results

Ventilation with defined tidal volumes was significantly correlated to EIT measurements (r ²=0.99). After creation of the pneumoperitoneum, lung compliance typically decreased, which agreed well with an alteration of the distribution of pulmonary ventilation measured by EIT. Elevation of positive end-inspiratory pressure reopened non-aerated lung areas and showed a recovery of the regional ventilation measured by EIT. Additionally, we could detect pulmonary complications by EIT monitoring as verified by CT scans postoperatively.

Conclusion

EIT monitoring can be used as a continuous non-invasive intraoperative monitor of ventilation to detect regional changes of ventilation and pulmonary complications during laparoscopic surgery. These EIT findings indicate that surgeons and anesthetists may eventually be able to optimize ventilation directly in the operating theatre.     

Regional ventilation in spontaneously breathing COVID-19 patients during postural maneuvers assessed by electrical impedance tomography

Background

Gravity-dependent positioning therapy is an established concept in the treatment of severe acute respiratory distress syndrome and improves oxygenation in spontaneously breathing patients with hypoxemic acute respiratory failure. In patients with coronavirus disease 2019, this therapy seems to be less effective. Electrical impedance tomography as a point-of-care functional imaging modality for visualizing regional ventilation can possibly help identify patients who might benefit from positioning therapy and guide those maneuvers in real-time. Therefore, in this prospective observational study, we aimed to discover typical patterns in response to positioning maneuvers.

Methods

Distribution of ventilation in 10 healthy volunteers and in 12 patients with hypoxemic respiratory failure due to coronavirus disease 2019 was measured in supine, left, and right lateral positions using electrical impedance tomography.

Results

In this study, patients with coronavirus disease 2019 showed a variety of ventilation patterns, which were not predictable, whereas all but one healthy volunteer showed a typical and expected gravity-dependent distribution of ventilation with the body positions.

Conclusion

Distribution of ventilation and response to lateral positioning is variable and thus unpredictable in spontaneously breathing patients with coronavirus disease 2019. Electrical impedance tomography might add useful information on the immediate reaction to postural maneuvers and should be elucidated further in clinical studies. Therefore, we suggest a customized individualized positioning therapy guided by electrical impedance tomography.     

个体化PEEP对腹腔镜手术后肺部并发症影响的Meta分析

目的 评价术中采用个体化呼气末正压（PEEP）对腹腔镜手术后肺部并发症（PPCs）的影响。

方法 检索PubMed、Embase、Cochrane Library、中国知网、万方数据库、维普,收集腹腔镜手术中使用个体化PEEP的随机对照试验（RCT）,检索时间为建库至2022年1月。采用RevMan 5.4软件进行Meta分析。

结果 共纳入15篇RCT研究,共计患者917例,个体化PEEP组460例,对照组457例。与对照组比较,个体化PEEP组PPCs发生率明显降低（RR=0.27,95%CI 0.14～0.51,P<0.001）,驱动压明显减小（MD=-3.06 cmH₂O,95%CI -3.38～-2.23 cmH₂O,P<0.001）。两组生理无效腔、MAP、血管活性药物、住院时间差异无统计学意义。

结论 与固定PEEP或呼气末零压通气比较,腹腔镜手术中应用个体化PEEP可降低PPCs发生率,同时不增加血流动力学紊乱的风险。     

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.     

Splanchnic circulation and regional sympathetic outflow during peroperative PEEP ventilation in humans

The splanchnic organs represent a major target for sympathetic outflow and an important region for haemodynamic effects on cardiovascular homeostasis. We have studied regional haemodynamic and sympathetic changes in the splanchnic bed during standardized circulatory stress from positive end-expiratory pressure ventilation (PEEP). We investigated eight patients undergoing major upper abdominal surgery using a radiotracer method to measure plasma spillover of norepinephrine as an index of sympathetic nerve activity using arterial, portal and hepatic venous blood sampling. Mesenteric and hepatic perfusion were measured by ultrasound transit time flowmetry and blood-gas analyses. Steady state measurements were performed before and during PEEP ventilation at 10 cm H2O. Plasma spillover of norepinephrine in the mesenteric and hepatic organs represented mean 49 (SEM 8)% and 7 (2)%, respectively, of systemic norepinephrine spillover at baseline, and PEEP ventilation did not cause any significant changes. However, PEEP ventilation significantly decreased portal venous blood flow while hepatic blood flow was preserved by a compensatory increase in hepatic arterial blood flow. Mesenteric and hepatic oxygen delivery changed according to blood flow, and there were no changes in regional oxygen consumption. Thus PEEP ventilation altered mesenteric and hepatic perfusion, independent of any change in corresponding sympathetic nerve activity. Regulation of hepatic blood supply, not related to sympathetic activity, maintained liver oxygenation during PEEP ventilation despite a simultaneous decrease in mesenteric perfusion.      

Thoracic electrical impedance and fluid balance during aortic surgery

Indices of fluid balance were evaluated during and after aortic surgery in 16 consecutive patients. Thoracic electrical impedance (TI), heart rate (HR), central venous (CVP), pulmonary artery mean (PAMP), pulmonary wedge (PWP) and mean arterial (MAP) pressure as well as fourteen arterial and venous blood gas variables were followed. Consistent with a reduction of TI by 4.2 (—5.2 to 9.2) Ohm (median and range) during the operation, fluid balance was in excess of 1.8 (—0.1 to 3.3) 1 when evaporation was not taken into account, and it remained elevated by 1.3 (0.0 to 5.4) 1 on the first postoperative morning. The HR, MAP and PWP remained stable, while CVP and PAMP decreased by 6 (-2 to 13) and 6 (-1 to 22) mmHg, respectively. Of the determined variables only TI revealed a meaningful correlation to fluid balance (rho= —0.41; P <0.01). Haemoglobin concentrations increased in proportion to the administered packed erythrocytes, while arterial oxygen saturation, pH and base excess decreased in proportion to the excess fluid. The results indicate that while central venous and pulmonary artery mean pressures gave the impression of a volume deficit, the positive fluid balance was mirrored by thoracic electrical impedance, and that even a minor increase of fluid balance may affect pulmonary function in patients subjected to aortic surgery.     

等比通气对腹腔镜子宫切除术中喉罩通气的影响

目的观察腹腔镜子宫切除术中使用等比通气(equal ratio ventilation,ERV)模式对患者呼吸力学、血流动力学和喉罩通气的影响。方法择期行腹腔镜子宫切除术女性患者80例,年龄29～63岁,BMI 20～30 kg/m~2,ASAⅠ或Ⅱ级。按随机数字表法分为ERV组(E组)和常规通气(conventional ratio ventilation,CRV)组(C组),每组40例。常规静脉麻醉诱导后置入喉罩行机械通气,E组I∶E 1∶1;C组I∶E 1∶2。如果术中气道压力峰值(Ppeak)超过35 cmH_2O或者喉罩发生严重漏气(不能达到设置V_T的80%),则将喉罩更换为气管插管。在麻醉诱导后10 min(T_0)、气腹后30 min(T_1)、气腹后60 min(T_2)、关闭气腹后10 min(T_3)时记录Ppeak、气道平台压力(Pplat)、气道平均压力(Pmean)、P_(ET)CO_2和分钟通气量(MV)等呼吸力学指标;记录酸碱度(pH)、中心静脉氧分压(PcvO_2)、中心静脉二氧化碳分压(PcvCO_2)等中心静脉血气分析指标;记录HR、MAP、心输出量(CO)、心脏指数(CI)、每搏量(SV)、每搏量变异(SVV)等血流动力学指标。记录反流误吸、咽喉痛、喉罩带血、更换气管插管等气道并发症的发生情况。结果 T_1—T_2时E组Ppeak、Pflat明显低于C组(P0.05),Pmean明显高于C组(P0.05)。不同时点两组PcvO_2、CO差异无统计学意义。两组均无一例反流误吸。两组咽喉痛、喉罩带血发生率差异无统计学意义。E组更换气管导管发生率明显低于C组(P0.05)。结论在腹腔镜子宫切除术中使用ERV对CO无明显影响并可降低Ppeak,减少喉罩漏气的发生;但在改善患者PcvO_2方面未见明显效果。     

Positive end-expiratory pressure optimization using electric impedance tomography in morbidly obese patients during laparoscopic gastric bypass surgery

BACKGROUND: Morbidly obese patients have an increased risk for peri-operative lung complications and develop a decrease in functional residual capacity (FRC). Electric impedance tomography (EIT) can be used for continuous, fast-response measurement of lung volume changes. This method was used to optimize positive end-expiratory pressure (PEEP) to maintain FRC. METHODS: Fifteen patients with a body mass index of 49 +/- 8 kg/m(2) were studied during anaesthesia for laparoscopic gastric bypass surgery. Before induction, 16 electrodes were placed around the thorax to monitor ventilation-induced impedance changes. Calibration of the electric impedance tomograph against lung volume changes was made by increasing the tidal volume in steps of 200 ml. PEEP was titrated stepwise to maintain a horizontal baseline of the EIT curve, corresponding to a stable FRC. Absolute FRC was measured with a nitrogen wash-out/wash-in technique. Cardiac output was measured with an oesophageal Doppler method. Volume expanders, 1 +/- 0.5 l, were given to prevent PEEP-induced haemodynamic impairment. RESULTS: Impedance changes closely followed tidal volume changes (R(2) > 0.95). The optimal PEEP level was 15 +/- 1 cmH(2)O, and FRC at this PEEP level was 1706 +/- 447 ml before and 2210 +/- 540 ml after surgery (P < 0.01). The cardiac index increased significantly from 2.6 +/- 0.5 before to 3.1 +/- 0.8 l/min/m(2) after surgery, and the alveolar dead space decreased. P(a)O2/F(i)O2, shunt and compliance remained unchanged. CONCLUSION: EIT enables rapid assessment of lung volume changes in morbidly obese patients, and optimization of PEEP. High PEEP levels need to be used to maintain a normal FRC and to minimize shunt. Volume loading prevents circulatory depression in spite of a high PEEP level.     

经胸腔镜肺大泡切除术中应用单肺通气对血气及血液动力学的影响

目的　观察胸腔镜手术中单肺通气时应用不同水平的呼气末正压通气 (PEEP)对血气及血液动力学的影响。方法　随机选择胸腔镜肺大泡切除术病人 36例 ,均分为三组 :A组为单肺间歇正压通气 (IPPV)通气 ;B组为单肺IPPV加PEEP 5cmH2 O通气 ;C组为单肺IPPV加PEEP10cmH2 O通气。分别记录平卧位双肺通气、侧卧位双肺通气、单肺通气 10min和 30min四个时点的血气和血液动力学参数。结果　各组病人SpO2 始终维持在 99%～ 10 0 %。动脉血氧分压 (PaO2 )也在正常范围 ,但B、C组明显高于A组 (P <0 .0 5 )。其余血气指标无明显变化。三组病人HR、MAP、左心室射血时间 (LVET)及体循环血管阻力 (SVR)均无明显变化。B、C组在单肺通气 10min及 30min后 ,每搏量 (SV)及心输出量 (CO)下降明显 ,但均在正常范围 ,且无组间差异。体位改变时血液动力学稳定。结论　经胸腔镜肺大泡切除术中单肺IPPV、PEEP 5cmH2 O均能维持满意的PaO2 和动脉血二氧化碳分压 (PaCO2 ) ,血液动力学变化不显著 ;但PEEP 5cmH2 O较IPPV能进一步提高PaO2 ,PEEP 10cmH2 O不能较PEEP 5cmH2 O进一步提高PaO2 。