Effects of positive end-expiratory pressure on ventilatory and oxygenation parameters during pressure-controlled one-lung ventilation

OBJECTIVES: The purpose of this study was to investigate the effects of PEEP on oxygenation and airway pressures during PCV-OLV. DESIGN: Randomized, crossover, clinical study. SETTING: University hospital. PARTICIPANTS: Twenty-five patients undergoing thoracotomy. INTERVENTIONS: During the first 5 minutes of OLV, all patients were ventilated with VCV (PEEP: 0) (VCV-ZEEP). Afterward, ventilation was changed to PCV with PEEP: 0 (PCV-ZEEP) or PEEP: 4 cmH2O (PCV-PEEP) for 20 minutes. In the following 20 minutes, PCV-PEEP and PCV-ZEEP were applied in reverse sequence. MEASUREMENTS AND MAIN RESULTS: At the end of VCV-ZEEP airway pressures (peak airway pressure, plateau airway pressure, mean airway pressure, and pause airway pressure) were recorded. At the end of PCV-PEEP and PCV-ZEEP airway pressures, PaO2 and Qs/Qt were recorded. Ppeak and Pplat were significantly lower with PCV-PEEP compared with VCV-ZEEP (eg, Ppeak: 33.4+/-4.2, 28.3+/-4.1, and 28.9+/-3.7 cmH2O in VCV-ZEEP, PCV-ZEEP, and PCV-PEEP, respectively; p<0.05 for PCV-ZEEP v VCV-ZEEP and PCV-PEEP v VCV-ZEEP). PCV-PEEP was associated with an increased PaO2 (230.3+/-69.8 v 189.0+/-54.8 mmHg, p<0.05) and decreased Qs/Qt (33.4%+/-7.3% v 38.4%+/-5.7%, p<0.05) compared with PCV-ZEEP (mean+/-SD). Eighty-eight percent of the patients have benefited from PEEP. CONCLUSION: During OLV, PCV with a low level of PEEP leads to improved oxygenation with lower airway pressures.     

The effect of timing of application of positive end-expiratory pressure on oxygenation during one-lung ventilation

Many studies have confirmed that applying positive end-expiratory pressure (PEEP) to the dependent lung during one-lung ventilation (OLV) improves oxygenation. Our purpose was to investigate the best time and level of PEEP application. Thirty patients undergoing thoracic surgery were randomised into three groups. After 20 minutes of two-lung ventilation (TLV) in the lateral position, all patients received OLV for one hour During OLV, 0, 5, 10 cmH2O PEEP were applied in order in group A, with each level sustained for 20 minutes. Group B had 5 cmH2O PEEP applied and maintained for one hour Patients in group C received PEEP with levels set in the opposite order to that of group A. The ventilation model was then converted to TLV. PaO2, PaCO2 and respiratory mechanical variables were compared at five different time points among groups, 20 minutes after TLV (T1), 20 (T2), 40 (T3) and 60 minutes (T4) after OLV and 20 minutes after conversion to TLV (T5). We found that PaO2 was lower in group A than the other two groups at T2 (P <0.05). PaO2 decreased significantly at T5 compared with T1 (P <0.05) in group A only. When PEEP was set to 10 cmH2O, the airway pressure increased significantly (P <0.05). These findings indicate that PEEP applied at the initial time of OLV improves oxygenation most beneficially. Five cmH2O PEEP may produce this beneficial effect without the increase in airway pressure associated with 10 cmH2O PEEP.     

The effect of positive end-expiratory pressure and continuous positive airway pressure on the oxygenation and shunt fraction during one-lung ventilation with propofol anesthesia.

STUDY OBJECTIVE: To evaluate the effect of positive end-expiratory pressure (PEEP) and continuous positive airway pressure (CPAP) on the oxygenation and shunt fraction during one-lung ventilation (OLV). DESIGN: Prospective clinical study. SETTING: Inpatient thoracic surgery and anesthesia clinic at an University hospital. PATIENTS: 15 patients with esophageal cancer who were scheduled for radical surgery. INTERVENTIONS: Arterial oxygenation, shunt fraction, and hemodynamics were evaluated at 20 min after the start of operation, at 20 minutes after the initiation of OLV under zero end-expiratory pressure (ZEEP), 20 minutes after the application of 4 cm PEEP to the dependent lung, at 20 minutes after OLV under ZEEP, 20 minutes after the application of 4 cm CPAP to the nondependent lung, and again under ZEEP, and after the combined application of PEEP and CPAP to the dependent and nondependent lungs. MEASUREMENTS AND MAIN RESULTS: There were no significant changes in mean pulmonary artery pressure, mean arterial blood pressure, heart rate, mixed venous partial pressure of oxygen, or arterial and mixed venous saturation of oxygen (SVO(2)) during this study. Arterial partial pressure of oxygen (pO(2)) increased and shunt fraction values decreased significantly after the application of PEEP (pO(2); 197.8 +/- 32.9 mmHg, Qs/Qt; 22.9 +/- 5.6%), CPAP (pO(2); 212.6 +/- 15.9 mmHg, Qs/Qt; 22.8 +/- 5.9%), and combination of PEEP and CPAP (pO(2); 222.0 +/- 42.8 mmHg, Qs/Qt; 24.1 +/- 6.4%) compared with ZEEP (pO(2); 128.1 +/- 37.5 mmHg, Qs/Qt; 33.2 +/- 6.8% ). But there were no significant differences regarding oxygenation and shunt fraction during PEEP, CPAP, or the combination of PEEP and CPAP. CONCLUSIONS: The application of PEEP to the dependent lung, CPAP to the nondependent lung, and the combination of PEEP and CPAP, are useful for improving oxygenation and decreasing Qs/Qt.     

Prospective,randomized, controlled evaluation of the preventive effects of positive end-expiratory pressure on patient oxygenation during one-lung ventilation

BACKGROUND AND OBJECTIVE: This prospective, randomized, controlled study evaluated the effects on oxygenation by applying a selective and patient-specific value of positive end-expiratory pressure (PEEP) to the dependent lung during one-lung ventilation. METHODS: Fifty patients undergoing thoracic surgery under combined epidural/general anaesthesia were randomly allocated to receive zero PEEP (Group ZEEP, n = 22), or the preventive application of PEEP, optimized on the best thoracopulmonary compliance (Group PEEP, n = 28). Patients' lungs were mechanically ventilated with the same setting during two- and one-lung ventilation (FiO2 = 0.5; VT = 9mL kg(-1), inspiratory :expiratory time = 1 : 1, inspiratory pause = 10%). RESULTS: Lung-chest wall compliance decreased in both groups during one-lung ventilation, but patients of Group PEEP had 10% higher values than patients with no end-expiratory pressure (ZEEP) applied--Group ZEEP (P < 0.05). During closed chest one-lung ventilation, the PaO2 : FiO2 ratio was lower in Group PEEP (232 +/- 88) than in Group ZEEP (339 +/- 97) (P < 0.05); but no further differences were reported throughout the study. No differences were reported between the two groups in the need for 100% oxygen ventilation (10 patients of Group ZEEP (45%) and 14 patients of Group PEEP (50%) (P = 0.78)) or re-inflation of the operated lung during surgery (two patients of Group ZEEP (9%) and three patients of Group PEEP (10%) (P = 0.78)). Postanaesthesia care unit discharge required 48 min (25th-75th percentiles: 32-58 min) in Group PEEP and 45 min (30-57 min) in Group ZEEP (P = 0.60). CONCLUSIONS: The selective application of PEEP to the dependent, non-operated lung increases the lung-chest wall compliance during one-lung ventilation, but does not improve patient oxygenation.     

Mechanical ventilation with positive end-expiratory pressure preserves arterial oxygenation during prolonged pneumoperitoneum

BACKGROUND: Laparoscopic surgery usually requires a pneumoperitoneum by insufflating the abdominal cavity with carbon dioxide (CO2). Increased intraabdominal pressure causes diaphragmatic displacement resulting in compressed lung areas, which leads to formation of atelectasis, especially during mechanical ventilation. Application of positive end-expiratory pressure (PEEP) can maintain pulmonary gas exchange. The objective of this study was to investigate the effect of abdominal gas insufflation on arterial oxygenation during mechanical ventilation with and without PEEP in rats. METHODS: In experiment 1, two groups of six rats were continuously insufflated with CO2 at 12 mmHg for 180 min. Group 1 was ventilated with 8 cm H2O PEEP and group 2 had 0 cm H2O PEEP. Group 3 served as a control. This group had abdominal wall lifting and was ventilated with 0 cmH2O PEEP. In experiment 2, two groups of six rats had abdominal CO2 insufflation and were ventilated with or without PEEP during 180 min (group 4 and 5). In this experiment, abdomens were desufflated in both groups for 5 min at 60 and 120 min. Blood pressure monitoring and measurement of arterial pO2 was performed by placement of an indwelling carotid artery catheter in both experiments. RESULTS: In both experiments, paO2 values decreased significantly in insufflation groups that were ventilated with 0 cmH2O PEEP (groups 2 and 5). Insufflation groups ventilated with 8 cmH2O PEEP had paO2 values comparable to these of control group. There were no significant differences in mean arterial pressure between insufflation groups ventilated with or without PEEP. CONCLUSION: PEEP preserves arterial oxygenation during prolonged pneumoperitoneum in rats with minimal adverse hemodynamic effects.     

Positive end-expiratory pressure applied to the dependent lung during one-lung ventilation improves oxygenation and respiratory mechanics in patients with high FEV1

BACKGROUND AND OBJECTIVE: The aim of this study was to test the efficacy of positive end-expiratory pressure (PEEP) to the dependent lung during one-lung ventilation, taking into consideration underlying lung function in order to select responders to PEEP. METHODS: Forty-six patients undergoing open-chest thoracic surgical procedures were studied in an operating room of a university hospital. Patients were randomized to receive zero end-expiratory pressure (ZEEP) or 10 cmH2O of PEEP to the dependent lung during one-lung ventilation in lateral decubitus. The patients were stratified according to preoperative forced expiratory volume in 1 s (FEV1) as an indicator of lung function (below or above 72%). Oxygenation was measured in the supine position, in the lateral decubitus with an open chest, and after 20 min of ZEEP or PEEP. The respiratory system pressure-volume curve of the dependent hemithorax was measured in supine and open-chest lateral decubitus positions with a super-syringe. RESULTS: Application of 10 cmH2O of PEEP resulted in a significant increase in PaO2 (P < 0.05). This did not occur in ZEEP group, considered as a time matched control. PEEP improved oxygenation only in patients with high FEV1 (from 11.6+/-4.8 to 15.3+/-7.1 kPa, P < 0.05). There was no significant change in the low FEV1 group. Dependent hemithorax compliance decreased in lateral decubitus, more in patients with high FEV1 (P < 0.05). PEEP improved compliance to a greater extent in patients with high FEV1 (from 33.6+/-3.6 to 48.4+/-3.9 mLcmH2O(-1), P < 0.05). CONCLUSIONS: During one-lung ventilation in lateral decubitus, PEEP applied to the dependent lung significantly improves oxygenation and respiratory mechanics in patients with rather normal lungs as assessed by high FEV1.     

呼气末正压通气对二氧化碳气腹病人动脉血氧合的影响

目的观察腹腔镜手术期间呼气末正压通气(PEEP)对二氧化碳气腹病人动脉血氧合及血液动力学的影响。方法20例ASAⅠ～Ⅱ级经腹腔镜肾上腺肿块、输尿管上段结石及肾切除的病人,随机均分为P组和C组。50%氧气混合空气机械通气,P组予以5cmH2O的PEEP,C组无PEEP。观察建立二氧化碳气腹前(T0)、气腹后10min(T1)、30min(T2)、1h(T3)和2h(T4)的PaO2、PaCO2、HR及MAP。结果P组气腹期间PaO2有上升趋势,而C组呈下降趋势,气腹后1hC组显著低于P组(P<0.05)。两组MAP和HR波动均未超过11%。结论腹腔镜手术期间PEEP能促进动脉血氧合,对循环影响较小。     

Mechanics of ventilation with positive end-expiratory pressure.

The effect of graded increments in positive end-expiratory pressure (PEEP) on arterial oxygen partial pressure (PaO2) and shunt fraction (Qs/QT), oxygen delivery, and respiratory mechanics and work required to ventilate 8 critically ill patients is reported. The work required to ventilate the patients increases markedly with the application and progressive increase in the level of PEEP. However, improvement in lung mechanics lowers the net work of ventilating the lungs. At 20 cm H2O PEEP, the mean value for the work of ventilation in this group of patients is twice the mean value without PEEP. The increase in work of ventilation with PEEP is critical in the use of PEEP when patients are breathing spontaneously with or without intermittent mandatory ventilation.     

Pulmonary wedge catheterization during positive end-expiratory pressure ventilation in the dog.

In ten supine anesthetized dogs, recordings of left atrial (LA) and pulmonary-artery wedge (PW) pressures were simultaneously obtained at several levels of positive end-expiratory pressure (PEEP) ventilation with the thorax either open or closed. Lateral roentgenograms were taken to determine the relative vertical positions of the LA and PW catheter tips. When the wedge catheter tip was vertically above the left artrial catheter tip, mean PW followed airway pressure at PEEP of more that 5 cm H20. For PEEP 5 cm H20 or less, and for PW catheter tip positions vertically below the LA catheter tip at all levels of PEEP, mean wedge catheter pressure was close to left atrial pressure. Thus, it appears the LA pressure can best be estimated by PW catheter positions vertically below the left atrium during positive end-expiratory pressure ventilation.     

七氟醚和丙泊酚在小潮气量联合低呼气末正压对单肺通气时肺内分流、氧合和炎性因子的影响比较

目的 比较单肺通气过程中,七氟醚和丙泊酚对实施小潮气量联合低呼气末正压通气(positive end-expiratorypressure,PEEP)患者肺内分流、氧合和炎性因子的影响.方法 择期行右侧开胸手术的食管癌患者76例,美国麻醉医师协会(ASA)分级Ⅰ～Ⅲ级,采用随机数字表法将患者分为丙泊酚组(P组)和七氟醚组(S组),每组38例.P组持续输注丙泊酚,S组持续吸入七氟醚,维持脑电双频指数(bispectal index,BIS)40～50,其他用药两组相同.分别在手术开始前(T0)和单肺通气后30(T1)、60(T2)、90 min(T3)以及膨肺后双肺通气30(T4)、60 min(T5),采集颈内静脉和桡动脉血样进行血气分析,计算肺内分流率(Qs/Qt)、相邻两个时间点动脉血氧分压(arterial partial pressure of oxygen,PaO2)和Qs/Qt的变化值(△PaO2和△Qs/Qt),并测定白细胞介素(interleukin,IL)-8、IL-10和肿瘤坏死因子(tumor necrosis factor,TNF)-α的浓度.结果 与T0比较:两组T1～T5时Qs/Qt、IL-8、IL-10、TNF-α均升高,PaO2降低(P＜0.05).与T1比较:两组T4、T5时PaO2明显升高,Qs/Qt明显降低(P＜0.05);P组IL-8、IL-10、TNF-α在T3～T5时升高,而S组在T2～T5时升高(P＜0.05).两组间比较:△PaO2[P组(-1.3±7.7)、(-1.9±6.0),S组(-4.3±4.3)、(-3.1±5.3)]和△Qs/Qt[P组(0.06-±0.57)、(0.07±0.34),S组(0.71±0.86)、(0.72±0.95)]在T1～T2、T2～T3时间段比较差异均有统计学意义(P＜0.05),S组IL-8、IL-10、TNF-α在T2～T5时均高于P组(P＜0.05).结论 单肺通气期间实施小潮气量联合低PEEP时,丙泊酚比七氟醚对肺内分流和氧合影响更小,产生炎性因子少.     

Set positive end-expiratory pressure during protective ventilation affects lung injury

BACKGROUND: The most appropriate method of determining positive end-expiratory pressure (PEEP) level during a lung protective ventilatory strategy has not been established. METHODS: In a lavage-injured sheep acute respiratory distress syndrome model, the authors compared the effects of three approaches to determining PEEP level after a recruitment maneuver: (1) 2 cm H(2)O above the lower inflection point on the inflation pressure-volume curve, (2) at the point of maximum curvature on the deflation pressure-volume curve, and (3) at the PEEP level that maintained target arterial oxygen partial pressure at a fraction of inspired oxygen of 0.5. RESULTS: Positive end-expiratory pressure set 2 cm H(2)O above the lower inflection point resulted in the least injury over the course of the study. PEEP based on adequate arterial oxygen partial pressure/fraction of inspired oxygen ratios had to be increased over time and resulted in higher mRNA levels for interleukin-8 and interleukin-1beta and greater tissue inflammation when compared with the other approaches. PEEP at the point of maximum curvature could not maintain eucapneia even at an increased ventilatory rate. CONCLUSION: Although generating higher plateau pressures, PEEP levels based on pressure-volume curve analysis were more effective in maintaining gas exchange and minimizing injury than PEEP based on adequate oxygenation. PEEP at 2 cm H(2)O above the lower inflection point was most effective.     

Autocycling and increase in intrinsic positive end-expiratory pressure during mechanical ventilation

Modern ventilators are complicated electronic instruments with microprocessors and software, with the possibility of technical errors and problems such as autocycling. Despite autocycling being recognized as a problem in textbooks and reviews, there are few reports about autocycling in the literature. We report a case where a sudden increase in respiratory frequency due to autocycling resulted in a dangerous increase in intrinsic positive end-expiratory pressure (intrinsic PEEP, PEEPi). We think our case illustrates that autocycling does occur, but that the exact underlying mechanism may be hard to document and understand for clinicians. To remedy this situation, we suggest that manufacture-independent technical expertise should be established to evaluate incidents and suggest improvements.     

Intrinsic positive end-expiratory pressure during one-lung ventilation of patients with pulmonary hyperinflation. Influence of low respiratory rate with unchanged minute volume

Background. We measured lung mechanics and gas exchange duringone-lung ventilation (OLV) of patients with chronic obstructivepulmonary disease, using three respiratory rates (RR) and unchangedminute volume. Methods. We studied 15 patients about to undergo lung surgery,during anaesthesia, and placed in the lateral position. Ventilationwas with constant minute volume, inspiratory flow and FI_O2.For periods of 15 min, RR of 5, 10, and 15 bpm were appliedin a random sequence and recordings were made of lung mechanicsand an arterial blood gas sample was taken. Data were analysedwith the repeated measures ANOVA and paired t-test with Bonferronicorrection. Results. Pa_O2 changes were not significant. At the lowest RR,Pa_CO2 decreased (from 42 (SD 4) mm Hg at RR 15–41 (4)mm Hg at RR 10 and 39 (4) mm Hg at RR 5, P<0.01), and end-tidalcarbon dioxide increased (from 33 (5) mm Hg at RR 15 to 35 (5)mm Hg at RR 10 and 36 (6) mm Hg at RR 5, P<0.01). Intrinsicpositive end-expiratory pressure (PEEPi) was reduced even withlarger tidal volumes (from 6 (4) cm H₂O at RR 15–5 (4)cm H₂O at RR 10, and 3 (3) cm H₂O at RR 5, P<0.01), mostprobably caused by increased expiratory time at the lowest RR. Conclusion. A reduction in RR reduces PEEPi and hypercapniaduring OLV in anaesthetized patients with chronic obstructivelung disease. Br J Anaesth 2002; 88: 56–60