Differential Ventilation and Selective PEEP During Anaesthesia in the Lateral Decubitus Posture

The potential of differential ventilation (DV) with selective positive end-expiratory pressure (PEEP) has been tested versus conventional ventilation with and without general PEEP. Gas exchange and central haemodynamics were studied in 15 subjects with no clinical or radiological signs of pulmonary disease. The rationale of the method was to ensure ventilation of the well-perfused dependent lung and to counteract airway closure within that lung. The subjects were intubated with a double-lumen catheter prior to scheduled abdominal surgery. During general anaesthesia in the lateral posture, they were given DV. The mean inspired oxygen fraction was 0.32. Fifty per cent ("even" tidal volume (VT) distribution) or 70% ("inverted" VT distribution) of the inspired volume was administered to the dependent lung. Two synchronized ventilators were used. In eight subjects DV was also combined with PEEP applied solely to the dependent lung (selective PEEP). The major findings were that DV with even VT distribution reduced venous admixture by 26% ( P <0.05) and the alveolo-arterial oxygen tension gradient (P(A-a)o2) by 30% ( P <0.05) in comparison with conventional ventilation in the lateral position. The addition of selective PEEP further reduced the P(A-a)o2 by 13%. P(A-a)o2 was consequently 43% lower than during conventional ventilation without PEEP in the lateral posture ( P <0.01). Selective PEEP also had less impact on cardiac output than general PEEP (P<0.05). It is concluded that DV with even distribution of VT and selective PEEP can reduce the P(A-a)o2 in anaesthetized lung-healthy subjects in the lateral position.     

Lung and Chest Wall Mechanics during Differential Ventilation with Selective PEEP

Eight patients free from cardio-pulmonary disease and with a mean age of 46 years were studied during general anaesthesia in the lateral position. Measurements of hemithoracic mechanics were made during four different modes of ventilation: 1. Conventional ventilation (free distribution of ventilation) with no positive end-expiratory pressure (PEEP) (CV), 2. differential ventilation (50% of ventilation to each lung) with no PEEP (DV:0), and 3 and 4. DV with selective PEEP of 0.8 and 1.6 kPa, respectively, to the dependent lung only (DV:8, DV:16). During CV, 60% of ventilation was distributed to the non-dependent lung. Non-dependent hemithoracic compliance was 64% greater and inspiratory resistance 39% lower than those of the dependent hemithorax. No significant differences between the two hemithoraces were noted during DV:0, but on application of selective PEEP the compliance of the dependent hemithorax increased and its resistance decreased. With DV:16, the compliances of the two hemithoraces were essentially equal, as were their resistances. Selective PEEP caused a larger volume increase in the dependent lung than general PEEP. Selective PEEP reduced the volume of the non-dependent lung but only by 1/3 of the simultaneous increase in that of the dependent lung. Oesophageal pressure increased only slightly on selective inflation of the dependent lung, and remained negative within the 21 volume range studied. It is suggested that the altered mechanics of the dependent lung during selective PEEP result in a more even distribution of the inspired gas within that lung.     

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.     

Ventilation-perfusion relationships and atelectasis formation in the supine and lateral positions during conventional mechanical and differential ventilation

Patients without respiratory symptoms were studied awake and during general anesthesia with mechanical ventilation prior to elective surgery. Ventilation-perfusion (VA/Q) relationships, gas exchange and atelectasis formation were studied during five different conditions: 1) supine, awake; 2) supine during anesthesia with conventional mechanical ventilation (CV); 3) in the left lateral position during CV; 4) as 3) but with 10 cm of positive end-expiratory pressure (PEEP) and 5) as 3) but using differential ventilation with selective PEEP (DV + SPEEP) to the dependent lung. Atelectatic areas and increases of shunt blood flow and blood flow to regions with low VA/Q ratios appeared after induction of anesthesia and CV. With the patients in the lateral position, further VA/Q mismatch with a fall in PaO2 and increased dead space ventilation was observed. Atelectatic lung areas were still present, although the total atelectatic area was slightly decreased. Some of the effects caused by the lateral position could be counteracted by adding PEEP. Perfusion of regions with low VA/Q ratios and venous admixture were then diminished, while PaO2 was slightly increased; shunt blood flow and dead space ventilation were essentially unchanged. During CV + PEEP, there was a decrease in cardiac output, compared to CV in the lateral position. DV + SPEEP was more effective than CV + PEEP in decreasing shunt flow and increasing PaO2 in the lateral position; in addition to this, cardiac output was not affected.     

Selective PEEP in Acute Bilateral Lung Disease. Effect on Patients in the Lateral Posture

Seven patients with acute respiratory failure due to diffuse and fairly uniform lung disease were studied during mechanical ventilation in the lateral decubital position with: (a) zero end-expiratory pressure (ZEEP) through a double-lumen oro-bronchial tube to permit a recording of the ventilation to each lung; (b) bilateral positive end-expiratory pressure (PEEP) of 1.2 kPa, with maintenance of ventilation distribution between lungs as observed during ZEEP; (c) selective PEEP of 1.2 kPa, applied to the dependent lung only, with ventilation as during ZEEP; and (d) conventional PEEP of 1.2 kPa applied to both lungs through a single-lumen tube, with free distribution of ventilation between the lungs. During ZEEP, 69% of ventilation was distributed to the non-dependent and 31% to the dependent lung; cardiac output was 6.51 X min-1, venous admixture (QS/QT) 40% and arterial oxygen tension (PaO2) 8.3 kPa. With bilateral PEEP, functional residual capacity (FRC) increased by 0.331, cardiac output was reduced to 5.11 X min-1 and venous admixture to 32%. PaO2 increased to 10.1 kPa. With selective PEEP the dependent lung FRC increased by 0.211 and the FRC of the non-dependent lung decreased by 0.081. Cardiac output increased to 6.11 X min-1, which was no longer significantly different from that during ZEEP. Venous admixture remained at the same level as with bilateral PEEP.(ABSTRACT TRUNCATED AT 250 WORDS)     

Regional Differences in Lung Function during Anaesthesia and Intensive Care: Clinical Implications

Anaesthesia and most frequently acute respiratory failure are accompanied by a lowered functional residual capacity (FRC). This lowering promotes airway closure in dependent lung units and forces ventilation to non-dependent regions. Perfusion, on the other hand, is forced towards dependent lung units. A ventilation-perfusion mismatch is created and hypoxaemia may develop. General PEEP counters airway closure, but impedes cardiac output and forces perfusion further to dependent regions. In addition, barotrauma may occur. Improved matching of ventilation and perfusion can be achieved by: (1) positioning the subject in the lateral posture; (2) ventilating each lung separately in proportion to its perfusion (differential ventilation); and (3) applying PEEP only to the dependent lung (selective PEEP). Because of less overall intrathoracic pressure and lung expansion, interference with the total lung blood flow and the danger of barotrauma should be less than with general PEEP. Improved gas exchange with a 50-100% increase in PaO2 has been observed in a limited number of patients with acute bilateral lung disease studied so far during differential ventilation and selective PEEP.     

One-lung ventilation with high tidal volumes and zero positive end-expiratory pressure is injurious in the isolated rabbit lung model

We tested the hypothesis that one-lung ventilation (OLV) with high tidal volumes (VT) and zero positive end-expiratory pressure (PEEP) may lead to ventilator-induced lung injury. In an isolated, perfused rabbit lung model, VT and PEEP were set to avoid lung collapse and overdistension in both lungs, resulting in a straight pressure-time (P-vs-t) curve during constant flow. Animals were randomized to (a) nonprotective OLV (left lung) (n = 6), with VT values as high as before randomization and zero PEEP; (b) protective OLV (left lung) (n = 6), with 50% reduction of VT and maintenance of PEEP as before randomization; and (c) control group (n = 6), with ventilation of two lungs as before randomization. The nonprotective OLV was associated with significantly smaller degrees of collapse and overdistension in the ventilated lung (P < 0.001). Peak inspiratory pressure values were higher in the nonprotective OLV group (P < 0.001) and increased progressively throughout the observation period (P < 0.01). The mean pulmonary artery pressure and lung weight gain values, as well as the concentration of thromboxane B(2), were comparatively higher in the nonprotective OLV group (P < 0.05). A ventilatory strategy with VT values as high as those used in the clinical setting and zero PEEP leads to ventilator-induced lung injury in this model of OLV, but this can be minimized with VT and PEEP values set to avoid lung overdistension and collapse. IMPLICATIONS: One-lung ventilation with high tidal volumes and zero positive end-expiratory pressure (PEEP) is injurious in the isolated rabbit lung model. A ventilatory strategy with tidal volumes and PEEP set to avoid lung overdistension and collapse minimizes lung injury during one-lung ventilation in this model.     

根据静态压力-容量曲线指导开胸手术病人保护性单肺通气的效果

目的 评价根据静态压力.容积曲线(P-V曲线)设置开胸手术病人的呼气末正压(PEEP)行单肺通气(OLV)的效果.方法 择期行肺叶切除术病人120例,性别不限,年龄20～60岁,体重40～ 80 kg,ASA分级Ⅱ或Ⅲ级.双肺通气(TLV)3 min后,描绘准静态P-V曲线,确定P-V曲线低位拐点对应的压力(PLIP).采用随机数字表法,将病人随机分为5组(n＝24):对照组(C组)和不同保护性OLV方式组(P1～4组).C组PEEP为0,vT为10 ml/kg;P1组PEEP为0,vT为6ml/kg; P2组PEEP为PLIP,-2 cm H2O,VT为6ml/kg;P3组PEEP为PLIP,VT为6 ml/kg;P4组PEEP为PLIP+2 cmH2O,VT为6 ml/kg.分别于TLV和OLV呼吸力学指标平稳后,记录气道峰压、气道平台压、气道阻力和肺顺应性.分别于麻醉诱导前、TLV 20 min和OLV 20 min时,取动脉血样,进行血气分析,计算肺内分流率.分别于OLV开始时和OLV结束时采集动脉血样,采用酶联免疫吸附法测定血浆II-6和TNF-α的浓度.结果 与C组比较,P4组TLV和OLV呼吸力学指标平稳后气道峰压和气道平台压升高,气道阻力降低,OLV结束时血浆IL-6浓度降低,P1组、P2组、P3组和P4组PaC02升高(P<0.05或0.01);P1组、P2组和P3组各呼吸力学指标、血气分析指标和血浆IL-6和TNF-α的浓度比较差异无统计学意义(P＞0.05).与P1组、P2组和P3组比较,P4组气道峰压和气道平台压升高,OLV结束时血浆IL-6浓度降低(P<0.05或0.01).结论 VT为6 ml/kg,根据PLIP+2 cm H2O确定PEEP,有助于改善开胸手术病人的氧合,抑制炎性反应,是保护性OLV的有效手段.     

Differential ventilation in bilateral lung disease

General anaesthesia and many types of acute respiratory failure are accompanied by a decrease in functional residual capacity (FRC). This reduction promotes closure of dependent airways and alveolar collapse, thus impeding ventilation of these regions. Perfusion, on the other hand, is forced towards dependent regions by lowered pulmonary vascular pressure and increased alveolar pressure. Ventilation-perfusion (V/Q) inequality develops, impairing gas exchange and arterial oxygenation. Application of general positive end-expiratory pressure (PEEP) increases FRC and may improve gas exchange but cannot restore V/Q to normal. Differential ventilation, with equal distribution of ventilation between the lungs, and the application of PEEP solely to the dependent lung (selective PEEP) with the patient in the lateral position, improve V/Q matching and gas exchange with less impedance of cardiac output and less danger of barotrauma. This ventilation technique has proved successful in short-term experiments and in a small number of patients treated over several days.     

Hemodynamic effects of high-frequency jet ventilation

The hemodynamic effects of high-frequency jet ventilation (HFJV) and conventional ventilation were compared in normovolemic and functionally hypovolemic dogs. In normovolemic animals, no differences in hemodynamic function were found among spontaneous ventilation, conventional ventilation, and HFJV. When venous return was impaired by 15 cm H2O PEEP, cardiac index and stroke index were 25% higher with HFJV than with conventional ventilation (P less than 0.05). In another study with PEEP, conventional ventilation was compared to spontaneous ventilation, HFJV synchronized to five different parts of the cardiac cycle, and asynchronous HFJV. Heart rate was 15% lower and mean arterial pressure was 26% lower with conventional ventilation than with HFJV modes (P less than 0.05). There were no differences between synchronous and asynchronous HFJV. These results indicate that hemodynamic dysfunction may be less likely with HFJV than conventional ventilation. No advantage of synchronizing jet pulsations to a specific part of the cardiac cycle could be demonstrated.     

The influence of body position and differential ventilation on lung dimensions and atelectasis formation in anaesthetized man

The effects of body position and anaesthesia with mechanical ventilation on thoracic dimensions and atelectasis formation were studied by means of computerized tomography in 14 patients. Induction of anaesthesia in the supine position reduced the cross-sectional area for both lungs and caused atelectasis formation in dependent lung regions in 4/5 patients. Conventional ventilation with positive end-expiratory pressure (PEEP) increased thoracic dimensions and reduced, but did not eliminate, the atelectatic areas. The vertical diameters of both lungs were smaller in the lateral position as compared to the supine position (16.7 vs 10.4 cm in the left lung and 17.3 vs 12.8 cm in the right lung). The lateral positioning also caused a large reduction of the atelectatic area in the non-dependent lung. Differential ventilation with selective PEEP to the dependent lung eliminated (3/8 patients) or reduced (5/8 patients) dependent lung atelectasis. It can be concluded that lung geometry is altered in the lateral position: the shape of the lung makes the vertical diameter of each lung less in the lateral position, compared to the supine position. The atelectatic areas are mainly located in the dependent lung in the lateral position, and these atelectatic areas could be further reduced by selective PEEP to this lung.     

Comparison between conventional and protective one-lung ventilation for ventilator-assisted thoracic surgery

Recent papers suggest protective ventilation (PV) as a primary ventilation strategy during one-lung ventilation (OLV) to reduce postoperative pulmonary morbidity. However, data regarding the advantage of the PV strategy in patients with normal preoperative pulmonary function are inconsistent, especially in the case of minimally invasive thoracic surgery. Therefore we compared conventional OLV (VT 10 ml/kg, FiO2 1.0, zero PEEP) to protective OLV (VT 6 ml/kg, FiO2 0.5, PEEP 5 cmH2O) in patients with normal preoperative pulmonary function tests undergoing video-assisted thoracic surgery. Oxygenation, respiratory mechanics, plasma interleukin-6 and malondialdehyde levels were measured at baseline, 15 and 60 minutes after OLV and 15 minutes after restoration of two-lung ventilation. PaO2 and PaO2/FiO2 were higher in conventional OLV than in protective OLV (P<0.001). Interleukin-6 and malondialdehyde increased over time in both groups (P<0.05); however, the magnitudes of increase were not different between the groups. Postoperatively there were no differences in the number of patients with PaO2/FiO2<300 mmHg or abnormalities on chest radiography. Protective ventilation did not provide advantages over conventional ventilation for video-assisted thoracic surgery in this group of patients with normal lung function.     

Lung collapse and gas exchange during general anesthesia: effects of spontaneous breathing, muscle paralysis, and positive end-expiratory pressure

Lung densities (atelectasis) and pulmonary gas exchange were studied in 13 supine patients with no apparent lung disease, the former by transverse computerized tomography (CT) and the latter by a multiple inert gas elimination technique for assessment of the distribution of ventilation/perfusion ratios. In the awake state no patient had clear signs of atelectasis on the CT scan. Lung ventilation and perfusion were well matched in most of the patients. Three patients had shunts corresponding to 2-5% of cardiac output, and in one patient there was low perfusion of poorly ventilated regions. CT scans after 15 min of halothane anesthesia and mechanical ventilation showed densities in dependent lung regions in 11 patients. A shunt was present in all patients, ranging from 1% in two patients (unchanged from the awake state) to 17%. Ventilation of poorly perfused regions was noted in nine patients, ranging from 1-19% of total ventilation. The magnitude of the shunt significantly correlated to the size of dependent densities (r = 0.84, P less than 0.001). Five patients studied during spontaneous breathing under anesthesia displayed both densities in dependent regions and a shunt, although of fairly small magnitude (1.8% and 3.7%, respectively). Both the density area and the shunt increased after muscle paralysis. PEEP reduced the density area in all patients but did not consistently alter the shunt. It is concluded that the development of atelectasis in dependent lung regions is a major cause of gas exchange impairment during halothane anesthesia, during both spontaneous breathing and mechanical ventilation, and that PEEP diminishes the atelectasis, but not necessarily the shunt.     

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.     

Changes in muscle sympathetic nerve activity, venous plasma catecholamines, and calf vascular resistance during mechanical ventilation with PEEP in humans

The sympathetic reflex response to mechanical ventilation with PEEP was studied in conscious human volunteers (n = 8). Muscle sympathetic nerve activity (MSNA) was measured from the peroneal nerve, calf blood flow, forearm venous plasma catecholamines, blood pressure, heart rate, airway pressure, and end-tidal CO2 (%) during spontaneous breathing and during mechanical ventilation with 0-20 cmH2O PEEP. MSNA increased (P less than 0.01) during PEEP ventilation, from 22 bursts.min-1 at spontaneous breathing to 39 bursts.min-1 at 20 PEEP. This increase in MSNA was accompanied by an increase (P less than 0.01) in calf vascular resistance (CVR) from 35 PRU100 at spontaneous breathing to 48 PRU100 at 15 PEEP with no further increase at 20 PEEP. Venous plasma norepinephrine concentrations increased (P less than 0.01) during PEEP ventilation from 0.19 ng.ml-1 at spontaneous breathing to 0.31 ng.ml-1 at 20 PEEP, whereas plasma epinephrine and dopamine were less than 0.03 ng.ml-1 during the experiment. Blood pressure and heart rate were not affected by PEEP ventilation except at 20 PEEP, where blood pressure and heart rate increased (P less than 0.01). The results show that PEEP ventilation induces a considerable reflex increase of MSNA, reflected also by an increase in CVR and venous plasma norepinephrine. It is proposed that the main mechanism responsible for these reflex adjustments is caused by a decreased activity of the cardiopulmonary low-pressure baroreceptors, in turn resulting from a decrease in cardiac transmural pressures due to PEEP ventilation.     

"Closing volume" during high–frequency ventilation in anesthetized dogs

Airway closure, mean airway pressure, gas exchange and different modes of artificial ventilation were investigated in anesthetized and paralyzed dogs with clinically healthy lungs. The animals were ventilated with either intermittent positive pressure ventilation (IPPV), continuous positive pressure ventilation (GPPV, positive end-expiratory pressure (PEEP) = 0.49 kPa) or high-frequency jet ventilation (HFJV, open system) of 2 and 30 Hz with an inspiratory to expiratory (I/E) - ratio of 30/70 and 60/40. Closing volume (CV) was determined by a modified technique, submitting the lung to constant subatmospheric pressure after an inspiratory vital capacity of oxygen. Two different tests for CV were used: the foreign gas bolus (FGB) with helium as nonresident gas and the single breath nitrogen dilution technique (SBO2). During conventional mechanical ventilation, CV decreased significantly (P less than 0.05) after establishing a PEEP of 0.49 kPa. During HFJV, CV increased significantly (P less than 0.01). This effect was predominantly dependent on I/E duration time ratio and to a lesser extent on ventilatory frequency. There were significant differences between CV obtained by the FGB-method (CV(helium] and CV derived from the SBO2-test (CV(SBO2], although both tests revealed the same proportional changes of CV during the different modes of ventilation. The elevated CV was associated with a decreasing Pao2 and increasing Aa-Do2 and Paco2, indicating substantial hypoventilation and mismatching of ventilation and perfusion. Mean airway pressure increased with both CPPV and HFJV, revealing a dissociation between airway pressure and regional FRC distribution during HFJV. It is concluded that certain modes of high-frequency ventilation lead to impaired distribution of inspired gas to dependent lung regions.(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

小潮气量联合PEEP对单肺通气时胸外科手术患者血管外肺水的影响

目的 探讨小潮气量联合呼气末正压(PEEP)对单肺通气时胸外科手术患者血管外肺水的影响.方法 食道癌手术患者40例,年龄45～80岁,体重48～83kg,性别不限,ASA分级Ⅰ或Ⅱ级,随机分为2组(n=20):传统模式单肺通气组(Ⅰ组)机械通气模式为间歇正压通气(IPPV),VT9 ml/kg,通气频率12次/min;小潮气量联合PEEP单肺通气组(Ⅱ组)机械通气模式为IPPV联合PEEP5 cm H2O,VT6 ml/kg,通气频率15次/min.于麻醉诱导前(T0)、双肺通气30 min(T1)、单肺通气30 min(T2)、单肺通气1 h(T3)、恢复双肺通气拔管前(T4)和术后18 h(T5)时,记录血管外肺水(EVLW)、血管外肺水指数(EVLWI)、肺血管通透性指数(PVPI)和心输出量(CO),于T1～4时记录气道峰压(Ppeak);取股动脉血样,进行血气分析,并计算氧合指数(OI).结果 与Ⅰ组比较,Ⅱ组单肺通气期间EVLWI和.PVPI升高(P＜0.05),其余指标比较差异无统计学意义(P＞0.05);两组各时点OI、CO和Poeak比较差异无统计学意义(P＞0.05);与T0时比较,Ⅰ组T1时PVPI升高(P＜0.05),其余时点PVPI、EVLW和EVLWI差异无统计学意义(P＞0.05),Ⅱ组T2时EVLW、T1～4时EVLWI和T1.2时PVPI升高(P＜0.05);与T1时比较,Ⅰ组T2～5时EVLW、EVLWI和PVPI差异无统计学意义,Ⅱ组T5时PVPI降低(P＜0.05).结论 采用VT6 ml/kg、PEEP 5 cm H2O的单肺通气可增加患者血管外肺水,未对肺功能产生有利作用.     

High frequency ventilation with a conventional respiratory following heart surgery interventions

This study was designed to compare the effects of Continuous Positive-Pressure Ventilation (CPPV) and, by using the same unmodified conventional ventilator, High-Frequency Positive-Pressure Ventilation (HFPPVkonv). First, CPPV and HFPPVkonv were studied in a lung model with both normal (R = 5 mbar/1/second) and elevated (R = 20 mbar/1/second) resistance. Our results indicate that in HFPPVkonv the large compressible volume of the conventional ventilator did not influence lung model ventilation at normal resistance. The adjusted (300 ml) tidal volume (VT) and the measured volume of actual expiration (270 ml) were about the same (Fig. 1). However, with elevated resistance air trapping occurred. The large compressible volume influenced model ventilation during both CPPV and HFPPVkonv (Fig. 2). As a second step we evaluated the effects of HFPPVkonv on gas exchange, airway pressure, and hemodynamics in 12 patients (aged 43-69) postoperatively after elective cardiac surgery. After a period of stabilization at the intensive care unit every patient was first ventilated with CPPV. The ventilator settings were: VT = 10-12 ml/kg, inspiratory: expiratory ratio (I:E) = 1:2, frequency (F) = 12/min, V = 60 1/min, PEEP = 5 cm, FiO2 = 40%. After 20 min of CPPV baseline measurements were made (series I). Then the initial ventilator settings of CPPV were switched to HFPPVkonv, the conventional ventilator remaining unmodified. The settings were changed as follows: I:E = 1:3, F = 60/min, V = 120 1/min, PEEP = 5 cm, FiO2 = 40%. During 60 min of HFPPVkonv variables were measured first after 20 min (series II) and again after another 40 min (series III). Minute volume had to be doubled after changing from CPPV to HPFFVkonv to achieve eucapnia. As a result of the new ventilatory settings, VT and hold showed a significant decrease (P less than 0.01) (Table 2).(ABSTRACT TRUNCATED AT 250 WORDS)     

Selective positive end–expiratory pressure and right ventricular function in dogs

Differential ventilation with selective positive end–expiratory pressure (PEEP) has been shown to reduce cardiac output less than general PEEP. In previous studies we have demonstrated that during selective PEEP left ventricular preload is better maintained than during general PEEP. The present study was designed to determine whether the different haemodynamic responses to selective and general PEEP also might be due to different effects on RV preload. The study was performed on nine acutely instrumented dogs, in which extraventricular pressure was measured by pericardial balloon transducers. Measures of RV preload were obtained by the use of ultrasonic segment length transducers as well as end–diastolic transmural pressure (RVEDP_TM). The study showed reductions in RVEDP _TM during general and selective right (R) PEEP, accompanied by moderate reductions in RV inflow tract segment lengths. These changes were most marked with general PEEP. Selective LPEEP did not change RV preload significantly. Therefore, better maintained cardiac output with selective PEEP than with general PEEP is partly due to less impairment of right ventricular filling.