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

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

Recruitment maneuvers after a positive end-expiratory pressure trial do not induce sustained effects in early adult respiratory distress syndrome

BACKGROUND: Recruitment maneuvers performed in early adult respiratory distress syndrome remain a matter of dispute in patients ventilated with low tidal volumes and high levels of positive end-expiratory pressure (PEEP). In this prospective, randomized controlled study the authors evaluated the impact of recruitment maneuvers after a PEEP trial on oxygenation and venous admixture (Qs/Qt) in patients with early extrapulmonary adult respiratory distress syndrome. METHODS: After a PEEP trial 30 consecutive patients ventilated with low tidal volumes and high levels of PEEP were randomly assigned to either undergo a recruitment maneuver or not. Data were recorded at baseline, 3 min after the recruitment maneuver, and 30 min after baseline. Recruitment maneuvers were performed with a sustained inflation of 50 cm H2O maintained for 30 s. RESULTS: Compared with baseline the ratio of the arterial oxygen partial pressure to the fraction of inspired oxygen (Pao2/Fio2) and Qs/Qt improved significantly at 3 min after the recruitment maneuver (Pao2/Fio2, 139 +/- 46 mm Hg versus 246 +/- 111 mm Hg, P < 0.001; Qs/Qt, 30.8 +/- 5.8% versus 21.5 +/- 9.7%, P < 0.005), but baseline values were reached again within 30 min. No significant differences in Pao2/Fio2 and Qs/Qt were detected between the recruitment maneuver group and the control group at baseline and after 30 min (recruitment maneuver group [n = 15]: Pao2/Fio2, 139 +/- 46 mm Hg versus 138 +/- 39 mm Hg; Qs/Qt, 30.8 +/- 5.8% versus 29.2 +/- 7.4%; control group: [n = 15]: Pao2/Fio2, 145 +/- 33 mm Hg versus 155 +/- 52 mm Hg; Qs/Qt, 30.2 +/- 8.5% versus 28.1 +/- 5.4%). CONCLUSION: In patients with early extrapulmonary adult respiratory distress syndrome who underwent a PEEP trial, recruitment maneuvers failed to induce a sustained improvement of oxygenation and venous admixture.     

Effect of high-frequency jet ventilation on oxygenation during one-lung ventilation in patients undergoing thoracic aneurysm surgery

Purpose To evaluate the effect of high-frequency jet ventilation (HFJV) and continuous positive airway pressure (CPAP) on oxygenation and the shunt fraction (Qs/Qt) during one-lung ventilation (OLV). Methods Twenty-five patients who were undergoing resection of a descending aortic aneurysm were studied. Arterial oxygenation, Qs/Qt, and hemodynamics were evaluated just before the initiation of OLV (T₁), 15 min after OLV (T₂), and 15 min (T₃) and 30 min (T₄) after the application of HFJV or CPAP to the nondependent lung. Results There were no significant changes in the mean arterial blood pressure (MAP), heart rate (HR), central venous pressure (CVP), or mixed venous partial pressure of oxygen throughout this study. The arterial partial pressure of oxygen (Pa_O2) values after the application of HFJV or CPAP increased significantly, from 173.8 ± 39.6 mmHg (T₂) to 344.1 ± 87.9 mmHg (T₃) and 359.9 ± 82.4 mmHg (T₄) in the HFJV group (P < 0.05), and from 153 ± 38.5 mmHg (T₂) to 243 ± 48.5 mmHg (T₃) and 249.7 ± 55.0 mmHg (T₄) in the CPAP group (P < 0.05). The shunt fraction decreased significantly after the initiation of HFJV or CPAP, from 38.7% ± 8.9% (T₂) to 27.0% ± 8.0% (T₃) and 25.9% ± 8.7% (T₄) in the HFJV group (P < 0.05), and from 44.6% ± 8.6% (T₂) to 34.3% ± 10.2% (T₃) and 32.6% ± 8.5% (T₄) in the CPAP group (P < 0.05). The arterial saturation of oxygen (Sa_O2) increased significantly after the application of either HFJV or CPAP (P < 0.05). Conclusions Both HFJV and CPAP can improve oxygenation during OLV.     

单肺通气期间麻醉期用药对肺内分流的影响

背景 低氧血症是单肺通气(one lung ventilation,OLV)期间最常见的并发症.缺氧性肺血管收缩(hypoxic pulmonary vasoconstriction,HPV)是肺血管对局部低氧分压的反射性收缩,可以减少肺内分流(pulmonary shunt fraction,Qs/Qt)、维持动脉血氧分压(partial pressure of arterial oxygen,PaO2)、防止低氧血症的发生.目的 探讨OLV期间麻醉期用药对Qs/Qt的影响,指导临床应用.内容 综述OLV期间麻醉期用药对机体HPV、Qs/Qt和PaO2的影响.趋向 OLV期间麻醉期用药可以对HPV产生抑制或增强作用,从而影响Qs/Qt和PaO2.临床上要避免使用抑制HPV作用、增加Qs/Qt的药物,防止患者出现低氧血症.     

Effect of isoflurane on gas exchange and systemic and pulmonary hemodynamics in man during single lung ventilation]

OBJECTIVE. We studied the effect of 1.5% isoflurane end expiratory fraction on arterial oxygenation and on systemic and pulmonary hemodynamics during nonsurgical single lung ventilation. MATERIAL AND METHODS. The study includes 6 patients undergoing surgical thoracotomy. In all cases a double lumen endotracheal tube was inserted and pulmonary ventilation was performed with a FiO2 = 1. Patients were placed on lateral decubitus position. The following variables were measured: mean arterial pressure (MAP), mean pulmonary artery pressure (MPAP), central venous pressure (CVP), capillary pulmonary pressure (CPP), cardiac output (CO), and Qs/Qt. Measurements were taken at three different situations. The first was done under bilateral pulmonary ventilation and intravenous anesthesia with thiopental, fentanyl, and diazepam. The nondependent lung was collapsed by means of a selective ventilation of the dependent lung, and the second series of measurements was done 20 min after intravenous anesthesia. The third block of data was obtained after 15 min of respiratory ventilation with 1.5% isoflurane. RESULTS. Single lung ventilation induced a significant decrease of Pa O2 (379 +/- 96 mmHg vs 208 +/- 93 mmHg) and a significant increase in Qs/Qt (20 +/- 8% vs 30 +/- 10%). However, during isoflurane ventilation there were no significant changes in PaO2 (208 +/- 93 mmHg vs 204 +/- 94 mmHg) nor in Qs/Qt (30 +/- 10 vs 28 +/- 8). Isoflurane elicited a significant decrease of the CO, whereas MPAP, RVS, and PvO2 did not show significant variations. CONCLUSIONS. We conclude that 1.5% isoflurane end expiratory concentrations did not significantly affect pulmonary oxygenation during single lung ventilation.     

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.     

Intrapulmonary shunting during deliberate hypotension with nifedipine, diltiazem and labetalol in dogs

Pulmonary shunt (Qs/Qt) was calculated in 49 mongrel dogs weighing 18-20 kg during mechanical ventilation, before and during deliberate hypotension with either nifedipine (group N), diltiazem (group D), labetalol (group L), or ethyl alcohol and polyethylene glycol (group E). A 30 per cent decrease in mean arterial blood pressure occurred after two minutes of nifedipine infusion, two minutes after diltiazem, and three minutes after labetalol; these effects lasted two hours after nifedipine administration, 90 minutes after diltiazem and three hours after labetalol. There was an accompanying significant decrease in systemic and pulmonary vascular resistance. Qs/Qt and cardiac output increased significantly after nifedipine infusion. Shunt increased (mean +/- S.E.) from 9.7 +/- 0.8 to 18.25 +/- 1.05 per cent at two minutes (p less than 0.0005); 19.05 +/- 1.2 per cent at 30 minutes (p less than 0.005); 17.5 +/- 1.6 per cent at two hours (p less than 0.01); and 12 +/- 1.1 per cent at three hours (p less than 0.025). No increase in shunt occurred after the administration of diltiazem, labetalol or polyethylene glycol and ethyl alcohol. Arterial oxygen tension (PaO2) decreased significantly after nifedipine infusion from 146 +/- 11.5 to 105 +/- 3.5 mmHg two minutes after infusion; to 89.5 +/- 3 mmHg 30 minutes after; 115 +/- 4.75 mmHg two hours after; and 130 +/- 10.75 mmHg three hours later. PaO2 was not significantly different after diltiazem, labetalol, or polyethylene glycol and ethyl alcohol administration. With nifedipine cardiac output increased from 2.25 +/- 0.3 to 3.95 +/- 0.25 after two minutes (p less than 0.005) to 3.85 +/- 0.35 after 30 minutes (p less than 0.005), 3.7 +/- 3 after two hours (p less than 0.01) to 2.9 +/- 1.1 after three hours. No significant increase in cardiac output occurred in groups D or L. These results suggest that only nifedipine infusion significantly alters oxygenation in dogs and therefore its use warrants caution in the presence of a preexisting abnormal Qs/Qt.     

Effects of thoracic epidural anaesthesia on pulmonary venous admixture and oxygenation during one-lung ventilation

BACKGROUND: In this clinical randomized study, the effects of four anaesthesia techniques during one-lung ventilation [total intravenous anesthesia (TIVA) with or without thoracic epidural anaesthesia (TEA) (G-TIVA-TEA and G-TIVA), isoflurane anaesthesia with or without TEA (G-ISO-TEA and G-ISO)] on pulmonary venous admixture (Qs/Qt) and oxygenation (OLV) were investigated. METHODS: In 100 patients (four groups, 25 patients in each) undergoing thoracotomy, a thoracic epidural catheter was inserted pre-operatively. In G-TIVA-TEA and G-ISO-TEA, bupivacaine 0.1% + 0.1 mg/ml morphine was administered intra-operatively (10 ml of first bolus + 7 ml/h infusion). Propofol infusion or isoflurane concentration was adjusted to keep a bispectral index (BIS) of between 40 and 50 in all groups. FiO(2) was 0.8 during OLV and 0.5 before and after OLV. Partial arterial and central venous oxygen pressures (PaO(2) and PvO(2)), arterial and venous oxygen saturations and Qs/Qt values were recorded before, during and after OLV. RESULTS: During OLV, PaO(2) was significantly higher and Qs/QT significantly lower in G-TIVA-TEA and G-TIVA compared with G-ISO-TEA and G-ISO (PaO2: 188 +/- 36; 201 +/- 39; 159 +/- 33; 173 +/- 42 mmHg, respectively; Qs/Qt: 31.2 +/- 7.4; 28.2 +/- 7; 36.7 +/- 7.1; 33.7 +/- 7.7%, respectively). No statistical changes were observed in patients with TEA compared with without TEA in any measurement. CONCLUSION: During OLV, TEA does not significantly affect the oxygenation and Qs/Qt and can be used safely regardless of whether TIVA or inhalation techniques are used.     

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.     

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.     

Application of continuous positive pressure to the uppermost lung in patients ventilated through a single lung]

We have studied the oxygenation process in a series of 20 patients who underwent thoracic surgery and were ventilated through a single lung. There were 19 men and one woman with a mean age (+/- SD) of 63 +/- 10.5 years, a mean height of 166 +/- 37.9 cm and a mean weight of 67 +/- 14.1 kg. Premedication and anesthesia were comparable among all patients. Endotracheal intubation was performed with a double lumen Robersthaw cannula. After anesthetic induction the radial and pulmonary arteries were catheterized to obtain samples for gasometric investigation in arterial and venous mixed blood before and after exclusion of one lung with continuous positive pressure (CPAP). Gasometric analysis was also performed during the immediate postoperative period. All patients were ventilated with 100% oxygen concentration 20 min before blood sampling in order to remove the alveolar nitrogen. During single lung ventilation and during application of CPAP (5 cm H20) to the upright sided lung we observed a 50% increase in arterial p02 (Pa02) (p less than 0.001) without any change in mean alveolar p02 (PA02). There was also a 17% decrease in alveolo-arterial oxygen difference (D[A-a]02) (p less than 0.001) and a 16.6% reduction in the intrapulmonary shunt (Qs/Qt) (p less than 0.001). Improvement of oxygenation was attributed to a beneficial effect of CPAP applied to the upright sided lung while intermittent positive pressure was maintained in the recumbent lung.     

Recruitment Maneuvers after a Positive End-expiratory Pressure Trial Do Not Induce Sustained Effects in Early Adult Respiratory Distress Syndrome

Background: Recruitment maneuvers performed in early adult respiratory distress syndrome remain a matter of dispute in patients ventilated with low tidal volumes and high levels of positive end-expiratory pressure (PEEP). In this prospective, randomized controlled study the authors evaluated the impact of recruitment maneuvers after a PEEP trial on oxygenation and venous admixture (Qs/Qt) in patients with early extrapulmonary adult respiratory distress syndrome.

Methods: After a PEEP trial 30 consecutive patients ventilated with low tidal volumes and high levels of PEEP were randomly assigned to either undergo a recruitment maneuver or not. Data were recorded at baseline, 3 min after the recruitment maneuver, and 30 min after baseline. Recruitment maneuvers were performed with a sustained inflation of 50 cm H2O maintained for 30 s.

Results: Compared with baseline the ratio of the arterial oxygen partial pressure to the fraction of inspired oxygen (Pao2/Fio2) and Qs/Qt improved significantly at 3 min after the recruitment maneuver (Pao2/Fio2, 139 +/- 46 mm Hg versus 246 +/- 111 mm Hg, P < 0.001; Qs/Qt, 30.8 +/- 5.8% versus 21.5 +/- 9.7%, P < 0.005), but baseline values were reached again within 30 min. No significant differences in Pao2/Fio2 and Qs/Qt were detected between the recruitment maneuver group and the control group at baseline and after 30 min (recruitment maneuver group [n = 15]: Pao2/Fio2, 139 +/- 46 mm Hg versus 138 +/- 39 mm Hg; Qs/Qt, 30.8 +/- 5.8% versus 29.2 +/- 7.4%; control group: [n = 15]: Pao2/Fio2, 145 +/- 33 mm Hg versus 155 +/- 52 mm Hg; Qs/Qt, 30.2 +/- 8.5% versus 28.1 +/- 5.4%).     

Inhalation administration of nitric oxide during selective pulmonary ventilation decreases the intrapulmonary shunt]

OBJECTIVE: To assess the effects of inhaled nitric oxide (NO) on oxygenation and hemodynamics in patients undergoing lung resection surgery during one-lung ventilation (OPV). PATIENTS AND METHODS: Prospective study of 16 patients aged 62 +/- 10 years scheduled for chest surgery under combined general and epidural anesthesia. During ventilation of only one lung, NO was administered for 15 minutes. Arterial blood and mixed venous blood samples were taken for analysis of blood gases and the calculation of intrapulmonary shunt. Pulmonary and systemic hemodynamic variables were also recorded using a Swan-Ganz catheter at three times: baseline (ventilation of both lungs), OLV, and with OLV plus NO (OLV NO). RESULTS: The most relevant data consisted of a significant decrease in shunt after start of NO inhalation in comparison with the level during OLV (31.1 +/- 0.5% versus 36 +/- 0.6%; p < 0.05). Arterial oxygen pressure decreased significantly during OLV and increased after start of NO (118.9 +/- 53.6 versus 155.4 +/- 78.5 mmHg; p < 0.05). Mean pulmonary artery pressure, pulmonary and systemic vascular resistances, and cardiac index did not change with inhalation of NO. CONCLUSIONS: Inhalational administration of NO during OLV significantly improves arterial oxygenation and decreases intrapulmonary shunt during OLV, without causing hemodynamic or systemic effects.     

The effects of remifentanil and thoracic epidural on oxygenation and pulmonary shunt fraction during one-lung ventilation

OBJECTIVE: To compare the effects of remifentanil and thoracic epidural analgesia on the hemodynamic changes and pulmonary shunt fraction during one-lung ventilation (OLV) for thoracotomy. DESIGN: Prospective, single crossover design. SETTING: Tertiary care hospital. PARTICIPANTS: Thirty-four patients undergoing OLV for thoracic surgery. INTERVENTIONS: During general anesthesia with 2-lung ventilation, one-lung ventilation with remifentanil infusion, and one-lung ventilation with thoracic epidural anesthesia (TEA), hemodynamic parameters and arterial and mixed venous blood gases were taken from the radial and pulmonary artery catheters. During these 3 study periods, cardiac index (CI) was measured using thermodilution technique while shunt fraction (Qs/Qt), alveolar arterial oxygen gradient (A-a O(2)), and systemic (SVRI) and pulmonary vascular resistances indices (PVRI) were calculated. A p value <0.05 was taken to be statistically significant. MEASUREMENTS AND MAIN RESULTS: When OLV was instituted, there was a significant decrease in mean arterial blood pressure. Arterial oxygenation decreased, whereas CI and Qs/Qt increased during OLV, but there was no significant difference between remifentanil infusion and thoracic epidural analgesia. CONCLUSIONS: Both remifentanil infusion and TEA are suitable for analgesia during thoracic surgery when OLV is used. There was no significant difference in PaO(2) and Qs/Qt during each administration.     

Effects of continuous positive pressure ventilation and superimposed high frequency oscillation on pulmonary edema following endotracheal injection of hydrochloric acid in dogs

Pulmonary gas exchange was investigated in dogs with pulmonary edema following endotracheal injection of hydrochloric acid during superimposed high frequency oscillation (HFO) and continuous positive pressure ventilation (CPPV) using six inert gas elimination method. When ventilatory condition was changed from IPPV to HFO during pulmonary edema, PaO2 decreased from 61 +/- 4 mmHg to 49 +/- 9 mmHg and Qs/Qt increased from 73 +/- 8% to 77 +/- 9%. However, no change appeared in the perfusion distribution. When ventilatory condition was changed from IPPV to CPPV during pulmonary edema, PaO2 increased from 61 +/- 9 mmHg to 113 +/- 45 mmHg. Qs/Qt showed a tendency to decrease from 62 +/- 7% to 51 +/- 9%, and perfusion shifted toward the low VA/Q region. During HFO, a PEEP-like effect was not generated and mean airway pressure did not increase. Therefore, Qs/Qt was not decreased and PaO2 was not improved. During CPPV, an increase in PaO2 was the result of a decrease in true shunt rather than an improvement in the ventilation-perfusion maldistribution.     

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.     

Continuous positive airway pressure versus positive end-expiratory pressure in respiratory distress syndrome.

The hemodynamic and respiratory effects of spontaneous ventilation with continuous positive airway pressure (CPAP) and mechanical ventilation with positive end-expiratory pressure (PEEP) were compared in nine patients who had adult respiratory distress syndrome. These patients were capable of maintaining spontaneous ventilation (tidal volume above 300 ml. and PaCO2 below 45 torr). Arterial and mixed venous blood gases, cardiac output, oxygen delivery and consumption, pulmonary artery pressure, and pulmonary wedge pressure were measured in 11 instances, with each patient on 5 or 10 cm. H2O CPAP or PEEP, and in nine instances, with each patient on the ventilator but without PEEP (O PEEP). During CPAP, when compared to PEEP at the same level of end-expiratory pressure, mean PaO2 increased significantly (p less than 0.05) and mean physiological shunt decreased (p less than 0.05). In nine of 11 instances, cardiac output was higher on CPAP than on a corresponding level of PEEP. Thus CPAP was more effective than the same amount of PEEP in improving arterial oxygenation by the lung without adversely affecting cardiac output.     

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.     

Evaluation of 2 techniques for ventilation support during single-lung ventilation]

In a group of 22 patients undergoing thoracotomy we compared two techniques of ventilatory assistance to the nondependent lung during single lung ventilation. We simultaneously administered a 0.5% FiO2 to the dependent lung. We used a CPAP system with continuous O2 flow limited by an underwater valve at a pressure of +5 cmH2O. We performed 33 ventilatory assistances: in 15 cases to the nondependent lung (CPAP group) and in 18 patients to the lower lobe of the nondependent lung (lobar CPAP group). Evaluation of both techniques was performed by means of arterial blood gas measurement and the mean values were compared using the student's t test. During single lung ventilation the PaO2 in CPAP group increased from 85.86 +/- 22.28 mmHg to 155.52 +/- 59.54 mmHg (p less than 0.001) and in the lobar CPAP series it increased from 88.75 +/- 24.34 mmHg to 122.36 +/- 43.21 mmHg (p less than 0.01). In 11 out of the 22 patients we firstly applied the lobar CPAP and thereafter the CPAP to the whole lung in order to compare the efficacy of both techniques in the same patient. The PaO2 during single lung ventilation was 86.9 +/- 22.7 mmHg and it increased to 111.1 +/- 37.9 mmHg after lobar CPAP (p less than 0.01) ant to 163.3 +/- 64 mmHg after total lung CPAP ventilation (p less than 0.001). Our results confirm the usefulness of both techniques and they indicate that CPAP to the whole nondependent lung is the most effective.     

The effect of hypocapnia on arterial oxygenation in thoracotomized dogs

The effect of hypocapnia on arterial oxygenation was investigated in unilaterally thoracotomized patients (N = 11) and dogs (N = 9) anesthetized with N2O-O2-enflurane. In patients, a change in PaCO2 from 39.7 +/- 1.4 to 28.2 +/- 1.7 mmHg produced a significant fall in PaO2 from 146 +/- 32 to 126 +/- 27 mmHg. In dogs, the change in PaCO2 from 38.7 +/- 0.8 mmHg (normocapnia) to 22.4 +/- 0.9 mmHg (hypocapnia) produced a significant decrease in PaO2 from 94 +/- 6 to 77 +/- 5 mmHg and a significant increase in pulmonary shunt (Qs/Qt) from 13.5 +/- 1.6 to 19.4 +/- 1.7%. Hypocapnia induced significant decreases in cardiac output and pulmonary arterial pressure; from 3.6 +/- 0.4 to 3.1 +/- 0.3 l.min-1, and from 20.8 +/- 1.3 to 17.5 +/- 1.0 mmHg, respectively. After the thoracotomy, the end-expiratory volume of the lung of the thoracotomized side became smaller. Therefore, a large fraction of low VA/Q regions might have existed in the lung of the studied patients and animals. Since hypocapnia induces an attenuation of hypoxic pulmonary vasoconstriction (HPV), an attenuation of HPV by hypocapnia might have occurred in the present study, which in turn produced a disproportionate increase in perfusion to low VA/Q regions, leading to the increase in Qs/Qt as observed in the present study.