Haemodynamic effects of pressure support and PEEP ventilation by nasal route in patients with stable chronic obstructive pulmonary disease.

BACKGROUND--Intermittent positive pressure ventilation applied through a nasal mask has been shown to be useful in the treatment of chronic respiratory insufficiency. Pressure support ventilation is an assisted mode of ventilation which is being increasingly used. Invasive ventilation with intermittent positive pressure, with or without positive end expiratory pressure (PEEP), has been found to affect venous return and cardiac output. This study evaluated the acute haemodynamic support ventilation by nasal mask, with and without the application of PEEP, in patients with severe stable chronic obstructive pulmonary disease and hypercapnia. METHODS--Nine patients with severe stable chronic obstructive pulmonary disease performed sessions lasting 10 minutes each of pressure support ventilation by nasal mask while undergoing right heart catheterisation for clinical evaluation. In random order, four sessions of nasal pressure support ventilation were applied consisting of: (1) peak inspiratory pressure (PIP) 10 cm H2O, PEEP 0 cm H2O; (2) PIP 10 cm H2O, PEEP 5 cm H2O; (3) PIP 20 cm H2O, PEEP 0 cm H2O; (4) PIP 20 cm H2O, PEEP 5 cm H2O. RESULTS--Significant increases in arterial oxygen tension (Pao2) and saturation (Sao2) and significant reductions in arterial carbon dioxide tension (PaCO2) and changes in pH were observed with a PIP of 20 cm H2O. Statistical analysis showed that the addition of 5 cm H2O PEEP did not further improve arterial blood gas tensions. Comparison of baseline values with measurements performed after 10 minutes of each session of ventilation showed that all modes of ventilation except PIP 10 cm H2O without PEEP induced a small but significant increase in pulmonary capillary wedge pressure. In comparison with baseline values, a significant decrease in cardiac output and oxygen delivery was induced only by the addition of PEEP to both levels of PIP. CONCLUSIONS--In patients with severe stable chronic obstructive pulmonary disease and hypercapnia, pressure support ventilation with the addition of PEEP delivered by nasal mask may have short term acute haemodynamic effects in reducing oxygen delivery in spite of adequate levels of SaO2.     

急性呼吸窘迫综合征患者适应性支持通气的效果

目的 评价适应性支持通气（ASV）模式与间歇正压通气（IPPV）模式在急性呼吸窘迫综合征（ARDS）患者中的效果。方法 ARDS患者30例，年龄19—46岁，男18例，女12例，ASAⅢ或Ⅳ级。先应用IPPV模式，吸入氧浓度60％，PEEP为0，潮气量（VT）10ml／kg，吸呼比（I：E）1：2，维持8h后随机选择换用ASV或继续IPPV通气模式，通气时依次按0、5、10cm H2O增加PEEP，每一PEEP水平的通气时间为60min，在同样的分钟通气量的设置下，4h后更换另一种通气模式，仍按0,5、10cm H2O增加PEEP，每一PEEP水平的通气时间为60min。每个PEEP水平通气50min时，用Swan-Ganz导管、心电监测仪、呼吸机监测记录血液动力学、呼吸力学和氧代谢数据。结果 与IPPV模式比较，ASV模式下气道峰值压降低，肺动态顺应性（Cdyn）、动脉氧分压（PaO2）和氧供（DO2）增加（P〈0．05）。两种通气模式的血液动力学参数比较差异无统计学意义（P〉0．05）。结论 ASV模式比IPPV模式更有利于ARDS患者的通气治疗。     

Functional residual capacity and respiratory mechanics as indicators of aeration and collapse in experimental lung injury

Increased functional residual capacity (FRC) and compliance are two desirable, but seldom measured, effects of positive end-expiratory pressure (PEEP) in mechanically ventilated patients. To assess how these variables reflect the morphological lung perturbations during the evolution of acute lung injury and the morphological changes from altered PEEP, we correlated measurements of FRC and respiratory system mechanics to the degree of lung aeration and consolidation on computed tomography (CT). We used a porcine oleic acid model with FRC determinations by sulfur hexafluoride washin-washout and respiratory system mechanics measured during an inspiratory hold maneuver. Within the first hour, during constant volume-controlled ventilation with PEEP 5 cm H(2)O, FRC decreased by 45% +/- 15% (P = 0.005) and compliance decreased by 35% +/- 12% (P = 0.005). Resistance increased by 60% +/- 62% (P = 0.005). Only the FRC changes correlated significantly to the decreased aeration (R(2) = 0.56; P = 0.01) and the increased consolidation (R(2) = 0.43; P = 0.04) on CT. When the PEEP was changed to either 10 or 0 cm H(2)O, there were larger changes in FRC than in compliance. We conclude that, in our model, FRC was a more sensitive indicator of PEEP-induced aeration and recruitment of lung tissue and that FRC may be a useful adjunct to PaO(2) monitoring. IMPLICATIONS: Lung injury was quantified on computed tomography and related to monitored values of functional residual capacity and mechanical properties of the respiratory system. We found the functional residual capacity to be a more sensitive marker of the lung perturbations than the compliance. It might be of value to include functional residual capacity in the monitoring of acute lung injury.     

Decrease of Functional Residual Capacity and Ventilation Homogeneity after Neuromuscular Blockade in Anesthetized Young Infants and Preschool Children

Background: Based on age-dependent differences in pulmonary mechanics, the effect of neuromuscular blockade may differ in infants compared with older children. The aim of this study was to determine the impact of neuromuscular blockade and its reversal by positive end-expiratory pressure (PEEP) on functional residual capacity (FRC) and ventilation distribution in young infants and preschool children.

Methods: The authors studied 14 infants (aged 0-6 months) and 25 preschool children (aged 2-6 yr). FRC and lung clearance index were calculated. Measurements were taken (1) after intubation, (2) during neuromuscular blockade, and (3) during neuromuscular blockade plus application of PEEP (3 cm H2O).

Results: Functional residual capacity (mean +/- SD) decreased from 21.3 +/- 4.7 ml/kg to 12.2 +/- 4.8 ml/kg (P < 0.001) during neuromuscular blockade in infants and from 25.6 +/- 5.9 ml/kg to 23.0 +/- 5.3 ml/kg (P < 0.001) in preschool children. With the application of PEEP, FRC increased to 22.3 +/- 5.9 ml/kg (P = 0.4829, compared with baseline) in infants and 28.2 +/- 5.8 ml/kg (P < 0.001) in children. The lung clearance index increased after neuromuscular blockade, whereas baseline values were regained after the application of PEEP. The changes induced by neuromuscular blockade were significantly greater in infants compared with preschool children (P < 0.001).     

The effect of PEEP-ventilation on gas exchange and airway closure in experimental pulmonary emphysema

The benefits of mechanical ventilation with positive end-expiratory pressure (PEEP) are well documented, especially for patients with acute respiratory failure. PEEP increases functional residual capacity (FRC) and reduces closing volume (CV) and ventilation-perfusion mismatching. Little is known about the effects of PEEP in patients with chronic obstructive pulmonary disease, where closing volume and ventilation-perfusion mismatching are increased. We investigated the effects of PEEP in a canine model of panlobular emphysema (PLE). METHODS. After completion of control-period measurements, PLE was induced in eight dogs by intratracheal application of 20 ml aerosolized 16% papain solution. Three weeks later the effects of continuous positive-pressure ventilation (CPPV, PEEP 10 cmH2O) on gas exchange, FRC, and CV were investigated. Conventional intermittent positive-pressure ventilation (IPPV) served as reference. Measurements of CV were done using both the foreign gas bolus method and the single-breath oxygen test. FRC was determined by the nitrogen dilution technique. RESULTS. The papain-induced emphysema produced a deteriation in oxygenation, enlargement of FRC and CV, and an increase in quasi-static lung compliance. CPPV led to a further increase of FRC, but gas exchange was not improved nor was CV reduced. In the PLE period, mean pulmonary arterial pressures (MPAP) were higher during both modes of ventilation. CPPV tended to increase MPAP and pulmonary capillary wedge pressure when compared with IPPV. Systemic hemodynamic conditions were stable throughout the experiment. CONCLUSIONS. The application of PEEP to emphysematous lungs seemed to enlarge FRC, predominantly in the nondependent rather than in the dependent lung regions, which are prone to airway closure. In patients with emphysema, ventilation with PEEP may further deteriorate the impaired distribution of ventilation and thus counteract any improvement of gas exchange.     

The outcome of early pressure-controlled inverse ratio ventilation on patients with severe acute respiratory distress syndrome in surgical intensive care unit

BACKGROUND: Pressure-controlled inverse ratio ventilation (PC-IRV) was used in patients with acute respiratory distress syndrome (ARDS) after failed volume-cycled conventional ratio ventilation (VC-CRV). The aim of this study was to evaluate the outcome of early PC-IRV in severe ARDS. METHODS: Twenty patients with severe ARDS were switched from VC-CRV to PC-IRV if they failed to maintain SaO(2) >90% by the following criteria: peak inspiratory pressure (PIP) >35 cm H(2)O, FIO(2) = 60%, and positive end-expiratory pressure (PEEP) 10 cm H(2)O. RESULTS: The values of PIP, mean airway pressure, minute volumes, and lung injury score in VC-CRV were 43.9 +/- 8.0 cm H(2)O, 19.5 +/- 6.4 cm H(2)O, 11.0 +/- 2.1 L/min, and 2.8 +/- 0.2 respectively. In PC-IRV, the corresponding data were 31.8 +/- 5.1 cm H(2)O, 25.4 +/- 4.6 cm H(2)O, 8.3 +/- 0.9 L/min, and 2.5 +/- 0.4. All of these parameters were significantly different. Fifteen patients (75%) survived their intensive care unit stay. CONCLUSIONS: Early PC-IRV in severe ARDS improves oxygenation, facilitates tapering of high fraction of inspiratory oxygen, and decreases high PEEP or PIP, and then results in the improvement of the patient's outcome.     

Partial liquid ventilation with perfluorodecalin following unilateral canine lung allotransplantation in non-heart-beating donors.

BACKGROUND: The purpose of this study was to evaluate canine lungs obtained from non-heart-beating donors after unilateral lung transplantation subjected to partial liquid ventilation with perfluorodecalin. METHODS: Twelve donor dogs were killed and kept under mechanical ventilation for 3 hours. Heart-lung blocks were harvested after retrograde pulmonary hypothermic flush with Perfadex. Left lung grafts were randomly transplanted into 12 weight-matched recipient animals. Animals were divided into 2 groups: control (standard mechanical ventilation, n = 6) and PLV (partial liquid ventilation, n = 6). Forty-five minutes after transplantation, the animals in the PLV group received perfluorodecalin (15 ml/kg) via orotracheal tube. All animals received volume-controlled ventilation (FIO2) 1.0, PEEP 5 cm H(2)O) over 6 consecutive hours. Thereafter, blood-gas analysis, ventilatory mechanics and hemodynamics were registered at 30-minute intervals. After 6 hours of reperfusion the animals were killed and the transplanted lungs were extracted to obtain the wet/dry weight ratio. RESULTS: There were significant differences in pulmonary arterial pressure, which were higher in control group animals (p < 0.009). The control animals also showed higher arterial PaO(2) than those in the PLV group (p < 0.00001), but lower PaCO(2) (p < 0.008). The peak and plateau pressures were higher in the PLV group (p < 0.00001). Neither static compliance nor wet/dry weight ratios were different in between groups. CONCLUSIONS: PLV with perfluorodecalin yields functional results compatible with life in this model. Nonetheless, pulmonary gas exchange and mechanics were superior after reperfusion in animals given conventional mechanical ventilation up to 6 hours after left lung allotransplantation.     

The effects of nebulized salbutamol, external positive end-expiratory pressure, and their combination on respiratory mechanics, hemodynamics, and gas exchange in mechanically ventilated chronic obstructive pulmonary disease patients

We hypothesized that combined salbutamol and external positive end-expiratory pressure (PEEPe) may present additive benefits in chronic obstructive pulmonary disease (COPD) exacerbation. In 10 anesthetized, mechanically ventilated, and bronchodilator-responsive COPD patients exhibiting moderate intrinsic PEEP (PEEPi), we assessed respiratory system (rs) mechanics, hemodynamics, and gas exchange at (a) baseline (zero PEEPe [ZEEPe]), (b) 30 min after 5 mg of nebulized salbutamol administration (ZEEPe-S), (c) 30 min after setting PEEPe at baseline PEEPi level (PEEPe), and (d) 30 min after 5 mg of nebulized salbutamol administration with PEEPe maintained unchanged (PEEPe-S). Return of determined variable values to baseline values was confirmed before PEEPe application. Relative to ZEEPe, (a) at ZEEP-S, PEEPi (4.8 +/- 0.7 versus 7.0 +/- 1.1 cm H(2)O), functional residual capacity change (115.6 +/- 23.1 versus 202.1 +/- 46.0 mL), minimal rs (airway) resistance (9.3 +/- 1.4 versus 11.8 +/- 2.2 cm H(2)O.L(-1).s(-1)), and additional rs resistance (5.2 +/- 1.4 versus 7.2 +/- 1.3 cm H(2)O.L(-1).s(-1)) were reduced (P < 0.01), and hemodynamics were improved; (b) at PEEPe, PEEPi (3.7 +/- 1.3 cm H(2)O) was reduced (P < 0.01), and gas exchange was improved; and (c) at PEEPe-S, PEEPi (2.0 +/- 1.2 cm H(2)O) was minimized, and rs mechanics (static rs elastance included), hemodynamics, and gas exchange were improved. Conclusively, in carefully preselected COPD patients, bronchodilation/PEEPe exhibits additive benefits.     

Airway occlusion pressure to titrate positive end-expiratory pressure in patients with dynamic hyperinflation

BACKGROUND: Although the use of external positive end-expiratory pressure (PEEP) is recommended for patients with intrinsic PEEP, no simple method exists for bedside titration. We hypothesized that the occlusion pressure, measured from airway pressure during the phase of ventilator triggering (P0.1t), could help to indicate the effects of PEEP on the work of breathing (WOB). METHODS: Twenty patients under assisted ventilation with chronic obstructive pulmonary disease were studied with 0, 5, and 10 cm H2O of PEEP while ventilated with a fixed level of pressure support. RESULTS: PEEP 5 significantly reduced intrinsic PEEP (mean +/- SD, 5.2 +/- 2.4 cm H2O at PEEP 0 to 3.6 +/- 1.9 at PEEP 5; P < 0.001), WOB per min (12. 6 +/- 6.7 J/min to 9.1 +/- 5.9 J/min; P = 0.003), WOB per liter (1.2 +/- 0.4 J/l to 0.8 +/- 0.4 J/l; P < 0.001), pressure time product of the diaphragm (216 +/- 86 cm H2O. s-1. min-1 to 155 +/- 179 cm H2O. s-1. min-1; P = 0.001) and P0.1t (3.3 +/- 1.5 cm H2O to 2.3 +/- 1.4 cm H2O; P = 0.002). At PEEP 10, no further significant reduction in muscle effort nor in P0.1t (2.5 +/- 2.1 cm H2O) occurred, and transpulmonary pressure indicated an increase in end-expiratory lung volume. Significant correlations were found between WOB per min and P0.1t at the three levels of PEEP (P < 0.001), and between the changes in P0.1t versus the changes in WOB per min (P < 0.005), indicating that P0.1t and WOB changed in the same direction. A decrease in P0.1 with PEEP indicated a decrease in intrinsic PEEP with a specificity of 71% and a sensitivity of 88% and a decrease in WOB with a specificity of 86% and a sensitivity of 91%. CONCLUSION: These results show that P0.1t may help to assess the effects of PEEP in patients with intrinsic PEEP.     

Airway Occlusion Pressure to Titrate Positive End-expiratory Pressure in Patients with Dynamic Hyperinflation

Background: Although the use of external positive end-expiratory pressure (PEEP) is recommended for patients with intrinsic PEEP, no simple method exists for bedside titration. We hypothesized that the occlusion pressure, measured from airway pressure during the phase of ventilator triggering (P0.1t), could help to indicate the effects of PEEP on the work of breathing (WOB).

Methods: Twenty patients under assisted ventilation with chronic obstructive pulmonary disease were studied with 0, 5, and 10 cm H2O of PEEP while ventilated with a fixed level of pressure support.

Results: PEEP 5 significantly reduced intrinsic PEEP (mean +/- SD, 5.2 +/- 2.4 cm H2O at PEEP 0 to 3.6 +/- 1.9 at PEEP 5;P < 0.001), WOB per min (12.6 +/- 6.7 J/min to 9.1 +/- 5.9 J/min;P = 0.003), WOB per liter (1.2 +/- 0.4 J/l to 0.8 +/- 0.4 J/l;P < 0.001), pressure time product of the diaphragm (216 +/- 86 cm H2O [middle dot] s-1 [middle dot] min-1 to 155 +/- 179 cm H2O [middle dot] s-1 [middle dot] min-1;P = 0.001) and P0.1t (3.3 +/- 1.5 cm H2O to 2.3 +/- 1.4 cm H2O;P = 0.002). At PEEP 10, no further significant reduction in muscle effort nor in P0.1t (2.5 +/- 2.1 cm H2O) occurred, and transpulmonary pressure indicated an increase in end-expiratory lung volume. Significant correlations were found between WOB per min and P0.1t at the three levels of PEEP (P < 0.001), and between the changes in P0.1tversus the changes in WOB per min (P < 0.005), indicating that P0.1t and WOB changed in the same direction. A decrease in P0.1 with PEEP indicated a decrease in intrinsic PEEP with a specificity of 71% and a sensitivity of 88% and a decrease in WOB with a specificity of 86% and a sensitivity of 91%.     

Pulmonary Blood Flow Redistribution with Low Levels of Positive End-expiratory Pressure

Background: Recent studies have questioned the importance of the gravitational model of pulmonary perfusion. Because low levels of positive end-expiratory pressure (PEEP) are commonly used during anesthesia, the authors studied the distribution of pulmonary blood flow with low levels of PEEP using a high spatial resolution technique. They hypothesized that if hydrostatic factors were important in the distribution of pulmonary blood flow, PEEP would redistribute flow to more dependent lung regions.

Methods: The effects of zero cm H2 O PEEP and 5 cm H2 O PEEP on pulmonary gas exchange were studied using the multiple inert gas elimination technique; the distribution of pulmonary blood flow, using fluorescent-labeled microspheres, was also investigated in mechanically ventilated, pentobarbital-anesthetized dogs. The lungs were removed, cleared of blood, dried at total lung capacity, and then cubed to obtain approximately 1,000 small pieces of lung ([approximately] 1.7 cm3).

Results: Positive end-expiratory pressure increased the partial pressure of oxygen by 6 +/- 2 mmHg (P < 0.05) and reduced all measures of ventilation and perfusion heterogeneity (P < 0.05). By reducing flow to nondependent ventral lung regions and increasing flow to dependent dorsal lung regions, PEEP increased (P < 0.05) the dorsal-to-ventral gradient. Redistribution of blood flow with PEEP accounted for 7 +/- 3%, whereas structural factors accounted for 93 +/- 3% of the total variance in blood flow.     

Pulmonary effects of body position, PEEP, and surfactant depletion in dogs

The influence of position (sphinx, lateral, supine), surfactant depletion, and different positive end-expiratory pressure (PEEP) on functional residual capacity (FRC), series dead space (VdS) and compliance of the respiratory system (Crs) were evaluated in five dogs. Ventilation homogeneity as measured by an index (multiple breath alveolar mixing efficiency), oxygenation, and cardiovascular hemodynamics were additionally examined. The dogs were anesthetized with halothane, paralyzed, and mechanically ventilated. FRC and VdS were found to be notably large in dogs, 45 +/- 8 ml/kg and 6 +/- 1 ml/kg, respectively. FRC and ventilation homogeneity were improved in the sphinx position (prone position with upright head). Surfactant depletion by lung lavage with 37 degrees C saline caused an immediate and stable decrease in FRC, Crs, and oxygenation (P less than 0.05, respectively) for about 5 h without marked effects on the circulatory system. FRC and VdS increased with increasing PEEP. At the highest PEEP, 10 cmH2O (1 kPa), Crs decreased (P less than 0.05) and ventilation became more uneven, indicating alveolar overdistension.     

Lung inflation or mechanical ventilation in extracorporeal circulation?

Extracorporeal circulation (ECC), with its shock-like pulmonary perfusion, leads to pathomorphologic and functional pulmonary changes, the postperfusion syndrome. This study investigated the effects of different types of ventilation during ECC on postoperative pulmonary function and the resulting pulmonary blood gas changes. METHOD. Thirty patients scheduled for aortocoronary bypass surgery were studied. Patients with pre-operative left ventricular end-diastolic pressures exceeding 15 mmHg or signs of right ventricular failure, pulmonary hypertension, or pre-existing pulmonary disease were excluded. The patients were randomly assigned to one of the following three groups: Group 1 (n = 10): static pulmonary inflation during ECC, PEEP 5-10 cm H2O, F1O2 1.0; Group 2 (n = 10): low-frequency ventilation during ECC, rate 10/min, PEEP 5 cm 5H2O, F1O2 1.0; Group 3 (n = 10): medium-frequency ventilation during ECC, rate 120/min, PEEP 5 cm 5H2O, F1O2 1.0. The measurements were made under relative steady-state conditions before the start of surgery and postoperatively after an equilibrium phase of at least 15 min. During ECC using a bubble oxygenator (Bentley BOS 10 S) in moderate hypothermia, blood was aspirated from the pulmonary artery during inflation of the wedge balloon and blood gases were analyzed. Postoperative changes in pulmonary function were evaluated by venous admixture (QVA/Qt); changes in pulmonary vascular resistance after ECC were determined using the pulmonary pressure-flow relationship. RESULTS. In group 1, QVA/Qt rose significantly from 9.6 +/- 2.9% preoperatively to 13.6 +/- 3.5% postoperatively (P less than 0.05, t-test for paired samples). In groups 2 and 3, postoperative QVA/Qt was significantly lower than preoperative QVA/Qt (P less than 0.05; group 2: preoperative 11.9 +/- 3.5%, postoperative 8.1 +/- 2.6%; group 3: preoperative 11.9 +/- 3.0%, postoperative 7.8 +/- 3.2%; Fig. 1). The postoperative pulmonary pressure-flow relationship changed similarly in all three groups (Fig. 2). During ECC, blood aspirated from the pulmonary artery during inflation of the wedge balloon was fully oxygenated with a hematocrit approximating that of arterial blood. In ventilated patients, pO2 during ECC was higher in pulmonary arterial blood than in arterial blood. Pulmonary ventilation during ECC did not lead to pulmonary arterial alkalosis. CONCLUSIONS. Pulmonary ventilation during ECC can prevent a post-operative increase in venous admixture. ECC-related pulmonary vascular changes were not affected by ventilation. Middle-frequency ventilation offers no advantage over low-frequency ventilation during ECC, except that the operating field is more quiet.     

Pressure control inverse ratio ventilation in the treatment of adult respiratory distress syndrome in patients with blunt chest trauma.

The objective of this study was to evaluate the efficacy of pressure control inverse ratio ventilation (PCIRV) in improving oxygenation in trauma patients with adult respiratory distress syndrome (ARDS) and to assess the potential risks associated with this form of treatment. This was a cohort study assessing the trends in hemodynamic and ventilatory parameters after the initiation of PCIRV, conducted at a community Level I trauma center intensive care unit. The study comprised 15 trauma patients developing severe, progressive ARDS [two or more of the following criteria: positive end-expiratory pressure (PEEP) >10 cm H2O; arterial partial pressure of oxygen divided by fraction of inspired oxygen (PaO2:FiO2) ratio <150; and peak inspiratory pressure (PIP) >45 cm H2O]: ten due to blunt chest injuries, three due to sepsis, and two due to fat emboli syndrome. PCIRV was initiated. Main outcome measures were PIP, PEEP (total, auto), oxygen saturation, cardiac index, oxygen delivery, PaO2:FiO2 ratio, compliance, evidence of complications of PCIRV, and mortality. Within 24 hours of conversion to PCIRV, the patients stabilized and the mean PaO2:FiO2 ratio rose from 96.3+/-57.8 to 146.8+/-91.1 (P<0.05) and PIP fell from 47.9+/-13.8 to 38.8+/-8.4 cm H2O; auto-PEEP increased from 0.5+/-1.9 to 7.5+/-5.6 cm H2O (P<0.05); oxygen delivery index remained stable (563+/-152 to 497+/-175 mL/min/m2); three patients developed evidence of barotrauma, one patient developed critical illness polyneuropathy, and two patients died (13%). PCIRV is an effective salvage mode of ventilation in patients with severe ARDS, but it is not without complications. Auto-PEEP levels and cardiac index should be monitored to ensure tissue oxygen delivery is maintained.     

Relation of the Static Compliance Curve and Positive End-expiratory Pressure to Oxygenation during One-lung Ventilation

Background : Positive end-expiratory pressure (PEEP) is commonly applied to the ventilated lung to try to improve oxygenation during one-lung ventilation but is an unreliable therapy and occasionally causes arterial oxygen partial pressure (Pao2) to decrease further. The current study examined whether the effects of PEEP on oxygenation depend on the static compliance curve of the lung to which it is applied.

Methods : Forty-two adults undergoing thoracic surgery were studied during stable, open-chest, one-lung ventilation. Arterial blood gasses were measured during two-lung ventilation and one-lung ventilation before, during, and after the application of 5 cm H2O PEEP to the ventilated lung. The plateau end-expiratory pressure and static compliance curve of the ventilated lung were measured with and without applied PEEP, and the lower inflection point was determined from the compliance curve.

Results : Mean (+/- SD) Pao2 values, with a fraction of inspired oxygen of 1.0, were not different during one-lung ventilation before (192 +/- 91 mmHg), during (190 +/- 90), or after ( 205 +/- 79) the addition of 5 cm H2O PEEP. The mean plateau end-expiratory pressure increased from 4.2 to 6.8 cm H2O with the application of 5 cm H2O PEEP and decreased to 4.5 cm H2O when 5 cm H2O PEEP was removed. Six patients showed a clinically useful (> 20%) increase in Pao2 with 5 cm H2O PEEP, and nine patients had a greater than 20% decrease in Pao2. The change in Pao2 with the application of 5 cm H2O PEEP correlated in an inverse fashion with the change in the gradient between the end-expiratory pressure and the pressure at the lower inflection point (r = 0.76). The subgroup of patients with a Pao2 during two-lung ventilation that was less than the mean (365 mmHg) and an end-expiratory pressure during one-lung ventilation without applied PEEP less than the mean were more likely to have an increase in Pao2 when 5 cm H2O PEEP was applied.     

Effects of end-inspiratory and end-expiratory pressures on alveolar recruitment and derecruitment in saline-washout-induced lung injury -- a computed tomography study

BACKGROUND: Lung protective ventilation using low end-inspiratory pressures and tidal volumes (VT) has been shown to impair alveolar recruitment and to promote derecruitment in acute lung injury. The aim of the present study was to compare the effects of two different end-inspiratory pressure levels on alveolar recruitment, alveolar derecruitment and potential overdistention at incremental levels of positive end-expiratory pressure. METHODS: Sixteen adult sheep were randomized to be ventilated with a peak inspiratory pressure of either 35 cm H2O (P35, low VT) or 45 cm H2O (P45, high VT) after saline washout-induced lung injury. Positive end-expiratory pressure (PEEP) was increased in a stepwise manner from zero (ZEEP) to 7, 14 and 21 cm of H2O in hourly intervals. Tidal volume, initially set to 12 ml kg(-1), was reduced according to the pressure limits. Computed tomographic scans during end-expiratory and end-inspiratory hold were performed along with hemodynamic and respiratory measurements at each level of PEEP. RESULTS: Tidal volumes for the two groups (P35/P45) were: 7.7 +/- 0.9/11.2 +/- 1.3 ml kg(-1) (ZEEP), 7.9 +/- 2.1/11.3 +/- 1.3 ml kg(-1) (PEEP 7 cm H2O), 8.3 +/- 2.5/11.6 +/- 1.4 ml kg(-1) (PEEP 14 cm H2O) and 6.5 +/- 1.7/11.0 +/- 1.6 ml kg(-1) (PEEP 21 cm H2O); P < 0.001 for differences between the two groups. Absolute nonaerated lung volumes during end-expiration and end-inspiration showed no difference between the two groups for given levels of PEEP, while tidal-induced changes in nonaerated lung volume (termed cyclic alveolar instability, CAI) were larger in the P45 group at low levels of PEEP. The decrease in nonaerated lung volume was significant for PEEP 14 and 21 cm H2O in both groups compared with ZEEP (P < 0.005). Over-inflated lung volumes, although small, were significantly higher in the P45 group. Significant respiratory acidosis was noted in the P35 group despite increases in the respiratory rate. CONCLUSION: Limiting peak inspiratory pressure and VT does not impair alveolar recruitment or promote derecruitment when using sufficient levels of PEEP.     

Pulmonary air trapping during two-lung and one-lung ventilation

OBJECTIVE: Evaluation of the magnitude of pulmonary air trapping during routine thoracic surgery and single-lung transplantation. DESIGN: Prospective study on consecutive patients. SETTING: Single institution, university hospital. PARTICIPANTS: Sixteen patients with no or moderate obstructive lung disease undergoing routine thoracic surgery (group 1), six patients with severe emphysema (group 2), and six patients with severe fibrosis (group 3) undergoing single-lung transplantation. INTERVENTIONS: Occlusion maneuver timed at the end of expiration to measure auto-positive end-expiratory pressure (auto-PEEP) and trapped volume (delta FRC). The maneuver was performed during two-lung ventilation in supine (2LV supine) and lateral decubitus (2LV lateral) positions and during one-lung ventilation (OLV) in lateral decubitus position. At the same time, airway pressures and PaO2 measurements were performed. MEASUREMENTS AND MAIN RESULTS: In group 1, consistent values of auto-PEEP and delta FRC occurred only during OLV: 4.8 +/- 2.5 cm H2O and 109 +/- 61 mL (mean +/- standard deviation). In group 2, auto-PEEP and delta FRC values were 11.7 +/- 6.9 cm H2O and 355 +/- 125 mL during 2LV supine, 8.8 +/- 5.7 cm H2O and 320 +/- 122 mL during 2LV lateral, and 15.9 +/- 3.9 cm H2O and 284 +/- 45 mL during OLV. In group 3, pulmonary air trapping was low. For the three groups together, auto-PEEP and delta FRC (p < 0.0001) related inversely to the ratio of forced expired volume in 1 second (FEV1) to forced vital capacity (FVC) expressed in percent (FEV1/FVC%) during OLV. In contrast, there was no correlation between PaO2 and auto-PEEP or delta FRC. CONCLUSION: Pulmonary air trapping must be suspected in patients with no or moderate obstructive lung disease during OLV and in those with severe obstructive disease as soon as 2LV is initiated.     

Arterial and mixed venous blood acid-base balance during hypoperfusion with incremental positive end-expiratory pressure in the pig

The authors sought to determine how hypoperfusion influences acid-base balance in arterial and mixed venous blood. In anesthetized, ventilated pigs (n = 12), we determined hemodynamics, O2 uptake, CO2 output, dead-space ventilation, arterial and mixed venous blood acid-base balances, and lactate concentrations during graded reductions in cardiac output by incremental positive end-expiratory pressure (PEEP, 0-20 cm H2O). Cardiac output decreased from 3.2 +/- 0.2 (mean +/- SEM) to 1.2 +/- 0.1 L/min at 20 cm H2O PEEP. Oxygen delivery declined more than O2 uptake did by 60% +/- 2% and 27% +/- 2%, respectively. The decrease in CO2 output (by 21% +/- 2%) was less than that in O2 uptake. Fractional dead-space ventilation increased. At a slight increase in carbon dioxide tension (PCO2) of 4 +/- 1 mm Hg, pH decreased in arterial blood from 7.54 +/- 0.01 to 7.47 +/- 0.02 mmol/L, and standard bicarbonate decreased from 30.3 +/- 0.5 to 27.5 +/- 0.6 mmol/L. The decrease in standard bicarbonate exceeded the increase in blood lactate concentrations. At a similar decrease in standard bicarbonate, the decrease in pH was larger (P less than 0.005) in mixed venous blood than in arterial blood owing to a larger increase in PCO2 (from 40 +/- 2 to 50 +/- 2 mm Hg, P less than 0.005). The changes were reversed after discontinuing PEEP. The authors conclude that ischemia after incremental PEEP results in tissue metabolic acidosis with superimposed respiratory acidosis.(ABSTRACT TRUNCATED AT 250 WORDS)     

Prevention of ventilator-induced lung injury with partial liquid ventilation

BACKGROUND/PURPOSE: Pulmonary injury from mechanical ventilation has been attributed to application of excess alveolar pressure (barotrauma) or volume (volutrauma). The authors questioned whether partial liquid ventilation (gas ventilation of the perfluorocarbon filled lung, PLV) would reduce ventilator-induced lung injury. METHODS: A tracheostomy tube and carotid artery catheter were placed in anesthetized Sprague-Dawley rats (500 +/- 50 g). Bovine serum albumin (BSA) labeled with Iodine (I) 125 was administered intraarterially. Ventilation with tidal volume (TV) of 5 mL/kg was initiated. The rats were then selected randomly to a 30-minute experimental period of one of the following ventilation protocols: continued atraumatic gas ventilation (GV, TV, 5 mL/kg; n = 10); atraumatic gas ventilation combined with intratracheal administration of 10 mL/kg perfluorocarbon (GV-PLV, TV, 5 mL/kg, n = 10); barotrauma (BT, peak inspiratory pressure [PIP], 45 cm H(2)O; n = 10); barotrauma with PLV (BT-PLV, PIP, 45 cm H(2)O; n = 8); volutrauma (VT, TV, 30 mL/kg; n = 8); or volutrauma with PLV (VT-PLV, TV, 30 mL/kg; n = 10). Animals were killed and the amount of radiolabeled BSA in both lungs was measured and normalized to the counts in 1 mL of blood from that animal (injury index). Data were analyzed by analysis of variance (ANOVA) with post-hoc t test comparison between groups. RESULTS: There was a significant difference in the (125)I-BSA injury index when all groups were compared (P <.001 by ANOVA). Post-hoc analysis showed a significant decrease in the injury index when comparing BT versus BT-PLV (P =.024) and VT versus VT-PLV (P =.014). CONCLUSION: (125)I-BSA leak produced during high-pressure or high-volume mechanical ventilation is reduced by partial liquid ventilation.     

Effect of rate and inspiratory flow on ventilator-induced lung injury

BACKGROUND: We examined the effects of decreasing respiratory rate (RR) at variable inspiratory times (It) and reducing inspiratory flow on the development of ventilator-induced lung injury. METHODS: Forty sheep weighing 24.6+/-3.2 kg were ventilated for 6 hours with one of five strategies (FIO2 = 1.0, positive end-expiratory pressure = 5 cm H2O): (1) pressure-controlled ventilation (PCV), RR = 15 breaths/min, peak inspiratory pressure (PIP) = 25 cm H2O, n = 8; (2) PCV, RR = 15 breaths/min, PIP = 50 cm H2O, n = 8; (3) PCV, RR = 5 breaths/min, PIP = 50 cm H2O, It = 6 seconds, n = 8; (4) PCV, RR = 5 breaths/min, PIP = 50 cm H2O, It = 2 seconds, n = 8; and (5) limited inspiratory flow volume-controlled ventilation, RR = 5 breaths/min, pressure-limit = 50 cm H2O, flow = 15 L/min, n = 8. RESULTS: Decreasing RR at conventional flows did not reduce injury. However, limiting inspiratory flow rate (LIFR) maintained compliance and resulted in lower Qs/Qt (HiPIP = 38+/-18%, LIFR = 19+/-6%, p < 0.001), reduced histologic injury (HiPIP = 14+/-0.9, LIFR = 2.2+/-0.9, p < 0.05), decreased intra-alveolar neutrophils (HiPIP = 90+/-49, LIFR = 7.6+/-3.8,p = 0.001), and reduced wet-dry lung weight (HiPIP = 87.3+/-8.5%, LIFR = 40.8+/-17.4%,p < 0.001). CONCLUSIONS: High-pressure ventilation for 6 hours using conventional flow patterns produces severe lung injury, irrespective of RR or It. Reduction of inspiratory flow at similar PIP provides pulmonary protection.