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 during thoracic anesthesia]

Aim of the study was to test individual mechanical and functional responses to open chest lateral decubitus during one lung ventilation. We measured dependent lung pressure volume (P-V) curves of 19 patients during supine and lateral decubitus. We found that patients characterized by high FEV1 developed greater changes in P-V curve shape than those characterized by low FEV1. Based on these results we decided to test a ventilation strategy characterized by the use of ZEEP or PEEP = 10 cm H2O applied to the dependent lung. In a preliminary set of patients stratified by FEV1 we found that PEEP deteriorated PaO2/FiO2 in patients with low FEV1, while there was a trend towards improvement in patients with high FEV1. It is possible that dependent lung PEEP counteracts atelectasias in normal lungs, while it may divert blood flow or create dead space in patients with sick and stiff lungs. We conclude that during one lung ventilation in open chest lateral decubitus, ventilatory setting need to be individually tailored.     

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.     

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.     

Alveolar recruitment improves ventilatory efficiency of the lungs during anesthesia

PURPOSE: The goal of this study was to analyze the effect of positive end-expiratory pressure (PEEP), with and without a lung recruitment maneuver, on dead space. METHODS: 16 anesthetized patients were sequentially studied in three steps: 1) without PEEP (ZEEP), 2) with 5 cm H(2)O of PEEP and 3) with 5 cm H(2)O of PEEP after an alveolar recruitment strategy (ARS). Ventilation was maintained constant. The single breath test of CO(2) (SBT-CO(2)), arterial oxygenation, end-expiratory lung volume (EELV) and respiratory compliance were recorded every 30 min. RESULTS: Physiological dead space to tidal volume decreased after ARS (0.45 +/- 0.01) compared with ZEEP (0.50 +/- 0.07, P < 0.05) and PEEP (0.51 +/- 0.06, P < 0.05). The elimination of CO(2) per breath increased during PEEP (25 +/- 3.3 mL.min(-1)) and ARS (27 +/- 3.2 mL.min(-1)) compared to ZEEP (23 +/- 2.6 mL.min(-1), P < 0.05), although ARS showed larger values than PEEP (P < 0.05). Pa-etCO(2) difference was lower after recruitment (0.9 +/- 0.5 kPa, P < 0.05) compared to ZEEP (1.1 +/- 0.5 kPa) and PEEP (1.2 +/- 0.5 kPa). Slope II increased after ARS (63 +/- 11%/L, P < 0.05) compared with ZEEP (46 +/- 7.7%/L) and PEEP (56 +/- 10%/L). Slope III decreased significantly after recruitment (0.13 +/- 0.07 1/L) compared with ZEEP (0.21 +/- 0.11 1/L) and PEEP (0.18 +/- 0.10 1/L). The angle between slope II and III decreased only after ARS. After lung recruitment, PaO(2), EELV, and compliance increased significantly compared with ZEEP and PEEP. CONCLUSION: Lung recruitment improved the efficiency of ventilation in anesthetized patients.     

Sevoflurane anaesthesia for one-lung ventilation with PEEP to the dependent lung in sheep: effects on right ventricular function and oxygenation

This study was undertaken to examine the effect of sevoflurane on right ventricular junction, the safety of sevoflurane for onelung ventilation and the effects of PEEP (positive end-expiratory pressure) to the dependent lung in this model using 12 openchest sheep. Haemodynamic variables, including cardiac output, mean arterial blood pressure, right ventricular pressure and pulmonary arterial pressure, and right ventricular segment shortening (sonomicrometry) were measured. First, animals received 2.0, 3.0 or 4.0% sevoflurane for 20 min each, respectively, during two-lung ventilation to measure the dose-dependent haemodynamic effects of sevoflurane. Then one-lung ventilation was performed with a randomized sequence of 0 (ZEEP), 5 and 10 cm H₂O PEEP to the dependent lung under 2.0% sevoflurane anaesthesia after one-hour stabilization. A decrease in systolic segment shortening along with increases in both the end-diastolic and end-systolic lengths of the right ventricle were observed at 3.0 and 4.0% sevoflurane, while global right ventricular function remained substantially unchanged during twolung ventilation. During one-lung ventilation the PaO₂ was greater with 5 cm H₂O PEEP 198 mmHg (± 25 SEM) than with ZEEP 138 mmHg (± 22) or with 10 cm H₂O PEEP 153 mmHg (± 23) (P < 0.05). No differences in haemodynamic variables or segment shortening between ZEEP and PEEPs during one-lung ventilation were observed. We conclude that although sevoflurane causes a dose-dependent depression of right ventricular function, sevoflurane anaesthesia can be safely applied to one-lung ventilation, and that 5 cm H₂O PEEP to the dependent lung can improve arterial oxygenation without causing changes in right ventricular function.     

Influence of positive end-expiratory pressure on extravascular lung water during the formation of experimental hydrostatic pulmonary oedema

The influence of positive end-expiratory pressure (PEEP) on extravascular lung water measured with the double-indicator dilution technique (EVLWi) has been studied during formation of hydrostatic pulmonary oedema in a canine model. The oedema was created by elevating the mean pulmonary artery pressure (PAP) to 30 mmHg (4.0 kPa) by inflation of a left atrial balloon, and a simultaneous intravenous saline infusion of 15 ml.kg-1.h-1. All dogs were ventilated with zero end-expiratory pressure (ZEEP) until the initial EVLWi had increased by 50%. In one group (n = 5) a PEEP of 10 cmH2O (1.0 kPa) was applied and the dogs were studied for a further 4 h and in the other group (n = 5) ZEEP was maintained throughout the study. During the first 2 h after ZEEP/PEEP application EVLWi increased from 13.7 +/- 2.1 to 20.2 +/- 1.2 ml.kg-1 with ZEEP ventilation and from 13.6 +/- 1.2 to 18.6 +/- 1.9 ml.kg-1 with PEEP ventilation. EVLWi remained unchanged during the last 2 h in both groups. The gas exchange improved with PEEP, arterial oxygen tension increased from 30.4 +/- 8.9 kPa to 38.6 +/- 2.5 kPa (P less than 0.01), and the shunt fraction decreased from 6.0 +/- 3.8% to 1.2 +/- 0.8% (P less than 0.001). There were significant differences (P less than 0.01) in both PaO2 and shunt fraction between the ZEEP and PEEP groups throughout the study. In conclusion, positive end-expiratory pressure improves gas exchange but does not protect against increasing extravascular lung water during the creation of hydrostatic pulmonary oedema.     

Positional hypoxaemia following post-traumatic pulmonary insufficiency.

The effect of body position on ventilatory function was evaluated in a patient with unilateral lung disease. The patient's pulmonary dynamics were examined in the supine, right, and left decubitus positions under conditions of positive pressure ventilation with zero end-expiratory pressure (ZEEP) and 5 cm H2O (0.9 KPa) positive end expiratory pressure (PEEP). When the patient was positioned so that the "diseased" lung was dependent, there was a marked decrease in PaO2 and increase in venous admixture when compared to the values in the supine position. These changes were relatively greater in the ZEEP, than the PEEP situation. When the "diseased* lung was not dependent, there was an increase in PaO2 and a decrease in venous admixture. This was most pronounced when PEEP was applied. Changes in body position may result in clinically significant alterations in pulmonary gas exchange, especially in patients with pre-existing pulmonary dysfunction.     

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.     

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 (PaO(2)) 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 gases were measured during two-lung ventilation and one-lung ventilation before, during, and after the application of 5 cm H(2)O 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) PaO(2) 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 H(2)O PEEP. The mean plateau end-expiratory pressure increased from 4.2 to 6.8 cm H(2)O with the application of 5 cm H(2)O PEEP and decreased to 4.5 cm H(2)O when 5 cm H(2)O PEEP was removed. Six patients showed a clinically useful (> 20%) increase in PaO(2) with 5 cm H(2)O PEEP, and nine patients had a greater than 20% decrease in PaO(2). The change in PaO(2) with the application of 5 cm H(2)O 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 PaO(2) 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 PaO(2) when 5 cm H(2)O PEEP was applied. CONCLUSIONS: The effects of the application of external 5 cm H(2)O PEEP on oxygenation during one-lung ventilation correspond to individual changes in the relation between the plateau end-expiratory pressure and the inflection point of the static compliance curve. When the application of PEEP causes the end-expiratory pressure to increase from a low level toward the inflection point, oxygenation is likely to improve. Conversely, if the addition of PEEP causes an increased inflation of the ventilated lung that raises the equilibrium end-expiratory pressure beyond the inflection point, oxygenation is likely to deteriorate.     

Effects of lung recruitment maneuver and positive end-expiratory pressure on lung volume,respiratory mechanics and alveolar gas mixing in patients ventilated after cardiac surgery

BACKGROUND: It is unclear whether positive end-expiratory pressure (PEEP) is needed to maintain the improved oxygenation and lung volume achieved after a lung recruitment maneuver in patients ventilated after cardiac surgery performed in the cardiopulmonary bypass (CPB). METHODS: A prospective, randomized, controlled study in a university hospital intensive care unit. Sixteen patients who had undergone cardiac surgery in CPB were studied during the recovery phase while still being mechanically ventilated with an inspired fraction of oxygen (FiO2) 1.0. Eight patients were randomized to lung recruitment (two 20-s inflations to 45 cmH2O), after which PEEP was set and kept for 2.5 h at 1 cmH2O above the pressure at the lower inflexion point (14+/-3 cmH2O, mean +/-SD) obtained from a static pressure-volume (PV) curve (PEEP group). The remaining eight patients were randomized to a recruitment maneuver only (ZEEP group). End-expiratory lung volume (EELV), series dead space, ventilation homogeneity, hemodynamics and PaO2 (oxygenation) were measured every 30 min during a 3-h period. PV curves were obtained at baseline, after 2.5 h, and in the PEEP group at 3 h. RESULTS: In the ZEEP group all measures were unchanged. In the PEEP group the EELV increased with 1220+/-254 ml (P<0.001) and PaO2 with 16+/-16 kPa (P<0.05) after lung recruitment. When PEEP was discontinued EELV decreased but PaO2 was maintained. The PV curve at 2.5 h coincided with the curve obtained at 3 h, and both curves were both steeper than and located above the baseline curve. CONCLUSIONS: Positive end-expiratory pressure is required after a lung recruitment maneuver in patients ventilated with high FiO2 after cardiac surgery to maintain lung volumes and the improved oxygenation.     

利用动态肺顺应性设定呼气末正压在胸腔镜肺叶切除术中的运用

目的 探讨单肺通气利用动态肺顺应性设定呼气末正压通气(positive end-expiratory pressure,PEEP)的优势及可行性. 方法 选择预行右侧肺叶切除患者80例,完全随机分为A组和B组,每组40例:A组,单肺通气实施肺膨胀(sustained inflation,SI)复张后加用20 cmH2O(1 cmH2O=0.098 kPa)的PEEP并递减滴定,随后以得到最大肺顺应性的PEEP值通气,直到恢复双肺通气;B组,通气PEEP值固定为5 cmH2O,其他通气方法同A组.记录患者血气、呼吸等参数. 结果 两组设定的PEEP值[A组(9.2±1.2) cmH2O,B组5 cmH2O]差异有统计学意义(P＜0.05);在单肺通气1 h(T3)、手术结束(T4)时,两组动脉血氧分压(partial pressure of oxygen,PaO2)比较,差异有统计学意义(P＜0.05);B组的PaO2在T3～T4逐步降低,差异有统计学意义(P＜0.05),而A组则维持较好(P＞0.05);T3、T4时刻A组的动态肺顺应性[(30.8±5.9)、(30.7±6.4) ml/cmH2O]与B组[(26.6±5.5)、(26.4±5.2) ml/cmH2O]比较,差异有统计学意义(P＜0.05). 结论 胸腔镜肺叶切除术中的单肺通气,利用动态肺顺应性设定的PEEP值通气能够得到更好的氧合及呼吸参数,并且维持较好.     

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.     

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.     

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)     

Effects of pleural fluid and positive end-expiratory pressure on the measurement of extravascular lung water by the double-indicator dilution technique

The reliability of the double-indicator dilution technique (dye/cold) for measuring extravascular lung water (EVLW) has been studied in lung-healthy dogs after pleural fluid injection of saline (up to 20 ml/kg) during mechanical ventilation at zero and 10 cmH2O (1.0 kPa) end-expiratory pressure (ZEEP and PEEP, respectively). Pleural fluid injection had no effect on EVLW at either ZEEP or PEEP. PEEP induced changes in cardiac output, and reduced both the intravascular (dye) and the thermal indicator volumes, but with no effect on the calculated EVLW. It is concluded that pleural fluid up to 20 ml/kg and ventilation with PEEP of 10 cmH2O (1.0 kPa) do not affect the reliability of the double-indicator dilution technique for measuring extravascular lung water in the dog.     

Differential ventilation and selective positive end-expiratory pressure: effects on patients with acute bilateral lung disease

Eleven patients with acute respiratory failure due to diffuse, bilateral lung disease were treated according to a new ventilation concept. The patients were intubated with a double-lumen catheter and positioned in the lateral decubital posture. With two synchronized ventilators, each lung received half of the tidal volume (VT), in accordance with its presumed perfusion (differential ventilation--DV), and the end-expiratory pressure was increased locally in the dependent lung (selective PEEP). DV with and without selective PEEP was compared with conventional ventilation with free distribution of VT, with and without PEEP applied to both lungs. The major findings were that DV with a selective PEEP of 12 cmH2O to the dependent lung decreased venous admixture by 38% (P less than 0.01) in comparison with conventional ventilation with no PEEP. Furthermore, it was found that selective PEEP, in contrast to general PEEP, had no deleterious effect on cardiac output. Consequently, DV with selective PEEP increased arterial oxygen tension by 23% (P less than 0.05) compared with general PEEP and by 46% (P less than 0.001) in comparison with conventional ventilation with no PEEP.     

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.     

Gas exchange impairment and pulmonary densities after cardiac surgery

In 11 patients with impaired respiratory function after coronary artery revascularization surgery, thoracic computed tomography (TCT) and cardiopulmonary profile were obtained. The patients were haemodynamically stable without clinical or radiological signs of lung oedema. Oxygenation was reduced in all patients (alveolo-arterial PO2-difference (PA-aO2) = 37.3 +/- 10.39 kPa, venous admixture (QVA/QT) = 26.4 +/- 4.4%) during mechanical ventilation with positive end-expiratory pressure (PEEP = 5 cmH2O) (0.5 kPa). TCT-scan analysis revealed considerable amounts of crest-shaped bilateral densities in dependent lung regions. There were no differences between the right and left hemithorax. Atelectatic lung tissues were defined as areas presenting with attenuation values of -200 to +20 Hounsfield Units. The magnitude of non-ventilated areas correlated with QVA/QT (r = 0.875, P < or = 0.01), but not with the duration of either extracorporeal circulation, surgical procedure or general anaesthesia. It is concluded that atelectasis in dependent lung areas contributes to impaired gas exchange after cardiac surgery.     

Inspiratory pressure–volume curves at different positive end-expiratory pressure levels in patients with ALI/ARDS

BACKGROUND: In lung protective strategy, positive end-expiratory pressure (PEEP) slightly higher than the Pflex (the airway pressure corresponding to the lower inflection point (LIP) on the inspiratory pressure-volume (P-V) curve measured with ZEEP) is generally recommended. However, this method to determine optimal PEEP lacks a theoretical background and there is no clinical report that investigated how the P-V relationship would be with such PEEP. Therefore, we measured inspiratory P-V curves at different PEEP levels to increase our knowledge about the inspiratory P-V curve with PEEP. METHODS: In eight consecutive patients with ALI/ARDS, inspiratory P-V curves were repeatedly measured at different PEEP levels by low flow inflation technique and LIP was assessed in all inspiratory P-V curves. Afterwards, the minimum PEEP level at which LIP was not identifiable (PEEP(LIP)(-)) was determined and the relationship between Pflex and PEEP(LIP)(-) was investigated. RESULTS: Pflex and PEEP(LIP)(-) could be determined in all patients. Pflex was 9.4+/-2.0 cmH2O (range: 7 to 12 cmH2O) and PEEP(LIP)(-) was 7.9+/-1.6 cmH2O (range: 5 to 10 cmH2O) (mean+/-SD, P=0.0877). PEEP(LIP)(-) was lower than the Pflex in five patients, and significantly lower than the Pflex + 2 cmH2O (P=0.0024). CONCLUSION: From the analysis of inspiratory P-V curves at different PEEP levels, PEEP 2 cmH2O higher than the Pflex may not be necessary to prevent cyclic collapse and reopening of alveoli, at least in some ALI/ARDS patients. Further studies are needed to confirm this preliminary result.