Sequential changes of arterial oxygen tension in the supine position during one-lung ventilation

To investigate how surgical positions affect the severity and progress of hypoxemia during one-lung ventilation (OLV), we studied 33 adult patients undergoing right thoracotomy with left OLV. The patients were divided into three groups according to the positions during surgery as follows: the supine position (SP) group (n = 11), the left semilateral decubitus position (LSD) group (n = 9), and the left lateral decubitus position (LLD) group (n = 13). Analysis of arterial blood gases was sequentially determined every 5 min for 30 min during OLV (fractional ratio of inspiratory oxygen = 1.0) in each position. OLV was promptly terminated and switched to bi-lung ventilation if Spo2 declined to 90%. Pao2 progressively decreased with time in all three groups (P < 0.01). The incidence of termination of OLV within 30 min was higher in the SP group (82%), compared with that in the LSD (11%) and LLD (8%) groups (P < 0.01). Final Pao2 (65+/-12 mm Hg, mean +/- SD, P < 0.01 versus LLD, P < 0.05 versus LSD) and SaO2 (91%+/-4%, P < 0.01 versus LLD and LSD) at the termination of OLV in the SP group were the lowest. There was no difference between these values in the LSD and LLD groups (128+/-54 mm Hg, 96%+/-2%, and 167+/-69 mm Hg, 97%+/-4%, respectively) 30 min after the start of OLV. The time for Pao2 to decrease to 200 mm Hg calculated from each regression curve was 354 s in the SP group, 583 s in the LSD group, and 798 s in the LLD group. The time for Pao2 to decline to 100 mm Hg was 794 s in the SP group. In the regression curves of the LSD and LLD groups, the Pao2 did not decrease to 100 mm Hg. Heart rate was slow at baseline in the SP group (P < 0.05 versus LSD), but other hemodynamic variables did not differ among the three groups throughout this study. The LSD was as effective as the LLD in avoiding life-threatening hypoxemia during OLV. IMPLICATIONS: Close observation and prompt counteractions including termination of one-lung ventilation (OLV) are crucial for patients under OLV in the supine position, because life-threatening hypoxemia frequently occurs approximately 10 min after starting OLV, even under 100% oxygen inhalation. The left semilateral decubitus position was as effective as the left lateral decubitus position in avoiding life-threatening hypoxemia during OLV.     

Hemodynamic effects of positive end-expiratory pressure during partial liquid ventilation in newborn lambs

BACKGROUND/PURPOSE: The aim of this study was to compare the effect of positive end-expiratory pressure (PEEP) application on hemodynamics, lung mechanics, and oxygenation in the intact newborn lung during conventional ventilation (CV) and partial liquid ventilation (PLV) at functional residual capacity (FRC). CV or PLV modes of ventilation do not affect hemodynamics nor the optimum PEEP for oxygenation. METHODS: Seven newborn lambs (1 to 3 days old) were instrumented to measure pulmonary hemodynamics and airway mechanics. Each lamb was used as their own control to compare different modes of ventilation (CV followed by PLV) under graded variations of PEEP (4, 8, 12, and 16 cm H(2)O) on the influence on pulmonary blood flow and pulmonary vascular resistance. RESULTS: There was a significant drop in pulmonary blood flow (PBF) from baseline (PEEP of 4 cm H(2)O on CV, 1,229 +/- 377 mL/min) in both modes of ventilation on a PEEP of 16 cm H(2)O (CV, 750 +/- 318 mL/min v PLV, 926 +/- 396 mL/min, respectively; P <.05). Peak inspiratory pressure (PIP) was higher on PLV at PEEP states of 4 cm H(2)O (16.5 +/- 1.3 cm H(2)O to 10.6 +/- 2.1 cm H(2)O; P <.05) and 8 cm H(2)O (18.8 +/- 2.2 cm H(2)O to 15.1 +/- 2.6 cm H(2)O; P <.05) when compared with CV. Conversely, PIP required to maintain the pCO(2) was lower on PLV at PEEP states of 12 (22.5 +/- 3.6 cm H(2)O to 24.2 +/- 3.8 cm H(2)O; P <.05) and 16 cm H(2)O (27.0 +/- 1.6 cm H(2)O to 34.0 +/- 5.9 cm H(2)O; P <.05). CONCLUSIONS: Hemodynamically, CO is impaired at a PEEP above 12 cm H(2)O in intact lungs. PFC at FRC does provide an advantage in lung mechanics more than 10 to 12 cm H(2)O of PEEP by decreasing the amount PIP needed to achieve the similar levels of gas exchange and minute ventilation, implying a reduced risk for barotrauma with chronic ventilation. Thus, selection of the appropriate level of PEEP appears to be important if PLV is to be utilized at FRC. The best strategy for PLV, including the selection of PEEP, remains to be determined.     

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.     

VARIATIONS IN LUNG VOLUME AND COMPLIANCE DURING PULMONARY SURGERY

Functional residual capacity (FRC) and breath-by-breath complianceof the ventilatory system (C₁₅) were measured in 10 mechanicallyventilated patients during anaesthesia for lung surgery (pneumonectomy,lobectomy, lung or pleural resections or exploratory thoracotomy).In eight patients not requiring pneumonectomy, FRC of the lowerlung decreased by 8±9% (mean± 1 SD) (P < 0.05)while that of the upper lung increased by 75±24% (P <0.001) when the patient was turned to the lateral position.When the pleura was opened, FRC of the lower lung decreasedby a further 10±10% (P <0.01). One-lung ventilation(OLV), however, increased FRC of the lower lung back to thevalue found in the supine position before surgery. When two-lungventilation was re-established, FRC of the lower lung was aboutthe same as during corresponding stages before OLV. In the twopatients who underwent pneumonectomy, FRC of the remaining lungwas about 30% greater after OLV than at corresponding stagesbefore surgery. In the patients not requiring pneumonectomy,C₁₅ decreased from 29±6ml/cm H₂O to 23±6ml/cmH₂O (P < 0.05) on the lower side when the patient was turnedon his side. The corresponding figures on the upper side were24±8 ml/cm H₂O and 30±5ml/cm H₂O respectively(P < 0.05). There was no further significant change whenthe pleura was opened. After surgery when the patient was turnedto the supine position, C₁₅ of the lung not operated on wasalmost the same as before surgery.     

COPD患者肺叶切除术时低潮气量通气的效果

目的 评价慢性阻塞性肺疾病(COPD)患者行肺叶切除术时低潮气量通气的效果.方法 择期行肺叶切除术的COPD患者28例,年龄65～84岁,ASA Ⅱ或Ⅲ级,随机分为常规潮气量组(TV组,n=14)和低潮气量组(LV组,n=14).均于气管插管后行机械通气,参数设置:TV组潮气量(VT)为10 ml/kg,呼气末正压(PEEP)为0;LV组Vr为5～6 ml/kg,PEEP为0～5 cm H2O.采用旁气流法监测气道峰压(Ppeak)、气道平台压(Pplat)、气道阻力(Raw)及动态肺顺应性(Cd).于平卧位双肺通气10 min(T1)、侧卧位单肺通气90 min(T2)、术毕平卧位双肺通气10 min(T3)及术后24 h(T4)时取桡动脉血样,行血气分析,计算氧合指数(OI)、肺泡.动脉血氧分压差[P(A-a)O2]及呼吸指数(RI);取颈内静脉血样,测定血清肿瘤坏死因子-α(TNF-α)及白细胞介素-6(IL-6)的浓度.结果 与T1时比较,2组T2-4时血清TNF-α及IL-6浓度升高(P<0.05);与TV组比较,LV组T2-4时血清TNF-α及IL-6浓度降低(P<0.05),T1-3时Ppeak及Raw降低,T2.3时Cd升高(P<0.05).T1-4时2组OI、RI及P(A-a)O2差异无统计学意义(P0.05).结论 低VT,通气可通过降低炎性反应,减轻COPD患者肺叶切除术时机械通气诱发的肺损伤.     

Use of a neck brace minimizes double-lumen tube displacement during patient positioning

PURPOSE: When patients are moved from the supine to the lateral decubitus position, the double-lumen endobronchial tube (DLT) is often displaced. The aim of this study was to determine whether a DLT is displaced when there are no movements of the head and neck. METHODS: One hundred patients scheduled for elective thoracic surgery were randomly divided into control and brace groups. Only a left-sided DLT was used during the study. All patients in the brace group wore a neck collar before the positional change. Using a fibreoptic bronchoscope, the distance from the tracheal opening to the main carina and from the bronchial opening to the bronchial carina was measured in the supine and lateral decubitus positions. RESULTS: Displacement of the DLT (mean +/- SD) during a change from the supine to the lateral decubitus position was greater in the control group (6.3 +/- 5.5 mm in the trachea; 2.4 +/- 3.6 mm in the bronchus) than in the brace group (2.2 +/- 3.9 mm in the trachea; 0.6 +/- 3.1 mm in the bronchus); (P < 0.001). The incidence of clinically significant displacement, greater than 5 mm from the initial correct position, was higher in the control group than in the brace group (48% vs 12%, P < 0.001). CONCLUSION: By restricting head and neck movements with a neck brace, the DLT displacement could be minimized while positioning patients for thoracotomy. The main cause of the DLT displacement during lateral positioning appears to be related to movement of the head and neck.     

Lung recruitment improves the efficiency of ventilation and gas exchange during one-lung ventilation anesthesia

Atelectasis in the dependent lung during one-lung ventilation (OLV) impairs arterial oxygenation and increases dead space. We studied the effect of an alveolar recruitment strategy (ARS) on gas exchange and lung efficiency during OLV by using the single-breath test of CO(2) (SBT-CO(2)). Twelve patients undergoing thoracic surgery were studied at three points in time: (a) during two-lung ventilation and (b) during OLV before and (c) after an ARS. The ARS was applied selectively to the dependent lung and consisted of an increase in peak inspiratory pressure up to 40 cm H(2)O combined with a peak end-expiratory pressure level of 20 cm H(2)O for 10 consecutive breaths. The ARS took approximately 3 min. Arterial blood gases, SBT-CO(2), and metabolic and hemodynamic variables were recorded at the end of each study period. Arterial oxygenation and dead space were better during two-lung ventilation compared with OLV. PaO(2) increased during OLV after lung recruitment (244 +/- 89 mm Hg) when compared with OLV without recruitment (144 +/- 73 mm Hg; P < 0.001). The SBT-CO(2) analysis showed a significant decrease in dead-space variables and an increase in the variables related to the efficiency of ventilation during OLV after an ARS when compared with OLV alone. In conclusion, ARS improves gas exchange and ventilation efficiency during OLV. IMPLICATIONS: In this article, we showed how a pulmonary ventilatory maneuver performed in the dependent lung during one-lung ventilation anesthesia improved arterial oxygenation and dead space.     

Liquid ventilation improves pulmonary function, gas exchange, and lung injury in a model of respiratory failure.

OBJECTIVE: The authors evaluated gas exchange, pulmonary function, and lung histology during perfluorocarbon liquid ventilation (LV) when compared with gas ventilation (GV) in the setting of severe respiratory failure. BACKGROUND: The efficacy of LV in the setting of respiratory failure has been evaluated in premature animals with surfactant deficiency. However, very little work has been performed in evaluating the efficacy of LV in older animal models of the adult respiratory distress syndrome (ARDS). METHODS: A stable model of lung injury was induced in 12 young sheep weighing 16.4 +/- 3.0 kg using right atrial injection of 0.07 mL/kg of oleic acid followed by saline pulmonary lavage and bijugular venovenous extracorporeal life support (ECLS). For the first 30 minutes on ECLS, all animals were ventilated with gas. Animals were then ventilated with either 15 mL/kg gas (GV, n = 6) or perflubron ([PFC], LV, n = 6) over the ensuing 2.5 hours. Subsequently, ECLS was discontinued in five of the GV animals and five of the LV animals, and GV or LV continued for 1 hour or until death. MAIN FINDINGS: Physiologic shunt (Qps/Qt) was significantly reduced in the LV animals when compared with the GV animals (LV = 31 +/- 10%; GV = 93 +/- 4%; p < 0.001) after 3 hours of ECLS. At the same time point, pulmonary compliance (CT) was significantly increased in the LV group when compared with the GV group (LV = 1.04 +/- 0.19 mL/cm H2O/kg; GV = 0.41 +/- 0.02 mL/cm H2O/kg; p < 0.001). In addition, the ECLS flow rate required to maintain the PaO2 in the 50- to 80-mm Hg range was substantially and significantly lower in the LV group when compared with that of the GV group (LV = 14 +/- 5 mL/kg/min; GV = 87 +/- 15 mL/kg/min; p < 0.001). All of the GV animals died after discontinuation of ECLS, whereas all the LV animals demonstrated effective gas exchange without extracorporeal support for 1 hour (p < 0.01). Lung biopsy light microscopy demonstrated a marked reduction in alveolar hemorrhage, lung fluid accumulation, and inflammatory infiltration in the LV group when compared with the GV animals. CONCLUSION: In a model of severe respiratory failure, LV improves pulmonary gas exchange and compliance with an associated reduction in alveolar hemorrhage, edema, and inflammatory infiltrate.     

The effects of acute isovolemic hemodilution on oxygenation during one-lung ventilation

Data on the effects of isovolemic hemodilution (IH) on oxygenation during one-lung ventilation (OLV) are lacking. We studied 47 patients with hemoglobin >14 g/dL who were scheduled for lung surgery (17 with normal lung function [group NL], 17 with chronic obstructive pulmonary disease [COPD] [group COPD], and 13 with COPD as control for time/anesthesia effects [group CTRL]). Anesthesia was standardized. The tracheas were intubated with a double-lumen tube. Ventilatory settings and fraction of inspired oxygen remained constant. The study was performed with patients in the supine position before surgery. OLV was initiated for 15 min. Two-lung ventilation was reinstituted, and IH was performed (500 mL); an identical volume of hydroxyethyl starch was administered. Subsequently, OLV was again performed for 15 min. In group CTRL, the same sequences of OLV were performed without IH. At the end of each period of OLV, pulmonary mechanics and blood gases were recorded. Data were analyzed by analysis of variance (mean +/- sd). In group NL and group CTRL, the arterial oxygen partial pressure remained constant, whereas it decreased in group COPD from 119 +/- 21 mm Hg before IH to 86 +/- 16 mm Hg after IH (P <0.01). Mild IH impairs gas exchange during OLV in COPD patients, but not in patients with normal lung function.     

Pulmonary Blood Flow Does Not Redistribute in Dogs with Reposition from Supine to Left Lateral Position

Background: Recent studies have questioned the classical gravitational model of pulmonary perfusion. Because the lateral position is commonly used during surgery, the authors studied the redistribution of pulmonary blood flow in the left lateral decubitus position using a high spatial resolution technique.

Methods: Distributions of pulmonary blood flow were measured using intravenously injected 15-[micro sign]m diameter radioactive-labeled microspheres in eight halothane-anesthetized dogs, which were studied in the supine and left lateral decubitus positions in random order. Lungs flushed free of blood were air-dried at total lung capacity and sectioned into 1,498-2,396 (1.7 cm3) pieces per animal. Radioactivity was measured by a gamma counter, and signals were corrected for piece weight and normalized to mean flow.

Results: Blood flow to the dependent left lung did not increase, and blood flow to the nondependent right lung did not decrease in the lateral position. The left lung received 39.3 +/- 7.0% and 39.2 +/- 8.8% (mean +/- SD) of perfusion in the supine and left lateral positions, respectively. Detailed assessment of the spatial distributions of pulmonary blood flow revealed the lack of a gravitational gradient of blood flow in the lateral position. The distributions of blood flow did not differ in the supine and left lateral decubitus positions.     

Two-lung and one-lung ventilation in patients with chronic obstructive pulmonary disease: the effects of position and F(IO)2

We compared the effects of position and fraction of inspired oxygen (F(IO)2) on oxygenation during thoracic surgery in 24 consenting patients randomly assigned to receive an F(IO)2 of 0.4 (eight patients, Group 0.4), 0.6 (eight patients, Group 0.6), or 1.0 (eight patients, Group 1.0) during the periods of two-lung (TLV) and one-lung ventilation (OLV) in the supine and lateral positions. TLV and OLV were maintained while the patients were first in the supine and then in the lateral position for 15 min each. Thereafter, respiratory mechanical data were obtained, and arterial blood gas samples were drawn. Pao2 decreased during OLV compared with TLV in both the supine and lateral positions. In all three groups, Pao2 was significantly higher during OLV in the lateral than in the supine position: 101 (72-201) vs 63 (57-144) mm Hg in Group 0.4; 268 (162-311) vs 155 (114-235) mm Hg in Group 0.6; and 486 (288-563) vs 301 (216-422) mm Hg in Group 1.0, respectively (P < 0.02, Wilcoxon's signed rank test). We conclude that, compared with the supine position, gravity augments the redistribution of perfusion as a result of hypoxic pulmonary vasoconstriction, when patients are in the lateral position, which explains the higher Pao2 during OLV. IMPLICATIONS: This study compares oxygenation during thoracic surgery during periods of two-lung and one-lung ventilation with patients in the supine and lateral positions when using three different fraction of inspired oxygen values. Arterial oxygen tension was decreased in all three groups during one-lung ventilation in comparison with the two-lung ventilation values, but the decrease was significantly less in the lateral, compared with the supine position.     

The effects of head and body positioning on upper airway collapsibility in normal subjects who received midazolam sedation

STUDY OBJECTIVE: To test the hypothesis that the change of body and head position affects upper airway patency during midazolam sedation. DESIGN: Clinical study using 30 healthy subjects. SETTING: Research unit for sleep study. INTERVENTIONS: We used a pressure-flow relationship to evaluate critical closing pressure (Pcrit) and upper airway resistance (Rua) in different condition of body and head position. A pressure-flow relationship was obtained in 3 body postures (supine, 15 degrees elevation, and 30 degrees elevation) and was obtained in 3 head positions (supine with the head in the neutral, supine with head extension, and supine position with head rotated). MEASUREMENTS: The pressure and inspiratory flow at subjects' nose mask were recorded. Polysomnographic parameters (electroencephalograms, electrooculograms, submental electromyograms, upper esophageal pressure, and plethysmogram) were also recorded. MAIN RESULTS: In experiment 1, 30 degrees elevation of the body significantly decreased Pcrit (P < 0.05) to -13.3 +/- 1.3 cm H(2)O compared with -8.2 +/- 1.4 cm H(2)O in supine condition without changing the slope (1/Rua). In experiment 2, head extension significantly decreased Pcrit (-12.5 +/- 1.3 cm H(2)O) (P < 0.05) compared with the value (-8.2 +/- 1.0 cm H(2)O) in supine condition without changing the slope (1/Rua). CONCLUSIONS: Our findings indicate that 30 degrees body elevation and head extension significantly decreased upper airway collapsibility during midazolam sedation and established the relative potency of maneuvers that maintain upper airway patency.     

Effects of sevoflurane compared with those of isoflurane on arterial oxygenation and hemodynamics during one-lung ventilation

Purpose. This study was designed to compare the effects of sevoflurane and isoflurane on Pao₂ and hemodynamic variables during one-lung ventilation (OLV) in surgical patients. Methods. Twelve patients undergoing an esophageal procedure with thoracotomy for which a long period of OLV was required were studied using a randomized crossover design. Group 1 received 1.2% isoflurane from the induction of anesthesia until 30 min after starting OLV, and then received 1.7% sevoflurane during the remaining period. In group 2, the order of the anesthetics was reversed. All experimental procedures were performed in the left lateral decubitus position with the chest opened. Arterial and mixed venous blood gases and cardiac outputs were analyzed immediately before OLV, during OLV, and after resumption of two-lung ventilation (TLV). Results. OLV produced lower Pao₂ and higher venous admixture (Q _s/Q _t) values than TLV. However, there was no significant difference between sevoflurane and isoflurane in Pao₂ or Q _s/Q _t during OLV. Other hemodynamic variables except for Pvˉo₂ showed no significant differences between the anesthetics. Conclusion. The effects of sevoflurane on Pao₂ and the hemodynamic variables were similar to those of isoflurane during TLV and OLV in the lateral decubitus position. Received for publication on January 29, 1999; accepted on August 6, 1999     

Effects of posture on carbon dioxide responsiveness in patients with obstructive sleep apnoea.

BACKGROUND--It is well known that upper airway resistance increases with postural change from a sitting to supine position in patients with obstructive sleep apnoea (OSA). It is not known, however, how the postural change affects the ventilatory and occlusion pressure response to hypercapnia in patients with OSA when awake. METHODS--The responses of minute ventilation (VE) and mouth pressure 0.1 seconds after the onset of occluded inspiration (P0.1) to progressive hypercapnia (delta VE/delta PCO2, delta P0.1/delta PCO2) both in sitting and supine positions were measured in 20 patients with OSA. The ratio of the two (delta VE/delta P0.1) was obtained as an index of breathing efficiency. The postural changes in response to carbon dioxide (CO2) after uvulopalatopharyngoplasty (UPPP) were also compared in seven patients with OSA. RESULTS--There were no significant changes in the resting values of end tidal PCO2, P0.1, or VE between the two positions. During CO2 rebreathing, delta VE/delta PCO2 did not differ between the two positions, but delta P0.1/delta PCO2 was significantly higher in the supine than in the sitting position (supine, mean 0.67 (SE 0.09) cm H2O/mm Hg; sitting, mean 0.57 (SE 0.08) cm H2O/mm Hg), and delta VE/delta P0.1 decreased significantly from the sitting to the supine position (sitting, 4.6 (0.4) l/min/cm H2O; supine, 3.9 (0.4) l/min/cm H2O). In seven patients with OSA who underwent UPPP, delta VE/delta P0.1 improved significantly in the supine position and postural change in delta VE/delta P0.1 was eliminated. CONCLUSIONS--These results suggest that in patients with OSA the inspiratory drive in the supine position increases to maintain the same level of ventilation as in the sitting position, and that the postural change from sitting to supine reduces breathing efficiency. Load compensation mechanisms of patients with OSA appear to be intact while awake in response to the rise in upper airway resistance.     

A comparative evaluation of transcutaneous and end-tidal measurements of CO2 in thoracic anesthesia

We performed this study to assess the accuracy of transcutaneous CO(2) (PTCCO(2)) monitoring compared with end-tidal CO(2) (PETCO(2)) in thoracic anesthesia. Twenty-six patients undergoing pneumonectomy with thoracotomy for which a long period of one-lung ventilation (OLV) was required were studied. The lungs were mechanically ventilated in the lateral decubitus position. PTCCO(2), PETCO(2), and arterial CO(2) (PaCO(2)) were simultaneously measured during two-lung ventilation (TLV) and during OLV at intervals of 15 min. All patients completed the study protocol. Bland-Altman analysis revealed a bias of -0.4 mm Hg with a precision of +/-2.5 mm Hg during OLV and 1.4 mm Hg with +/-4.3 mm Hg during TLV when PTCCO(2) and PaCO(2) were compared and revealed a bias of -5.8 mm Hg with a precision of +/-4.1 mm Hg during OLV and -7.1 mm Hg with +/-4.6 mm Hg during TLV when PETCO(2) and PaCO(2) were compared. We conclude that PTCCO(2) monitoring is accurate for evaluating CO(2) levels during thoracic anesthesia.     

Alveolar recruitment strategy increases arterial oxygenation during one-lung ventilation

BACKGROUND: Deterioration of gas exchange during one lung ventilation (OLV) is caused by both total collapse of the nondependent lung and partial collapse of the dependent lung. A previous report demonstrated that an alveolar recruitment strategy (ARS) improves lung function during general anesthesia in supine patients. The objective of this article was to study the impact of this ARS on arterial oxygenation in patients undergoing OLV for lobectomies. METHODS: Ten patients undergoing open lobectomies were studied at three time points: (1) during two-lung ventilation (TLV), (2) during OLV before, and (3) after ARS. The ARS maneuver was done by increasing peak inspiratory pressure to 40 cm H2O, together with a positive end-expiratory pressure (PEEP) of 20 cm H2O for 10 respiratory cycles. After the maneuver, ventilation parameters were returned to the settings before intervention. RESULTS: During OLV, PaO2 was statistically lower before the recruitment (data as median, first, and third quartile, 217 [range 134 to 325] mm Hg) compared with OLV afterwards (470 [range 396 to 525] mm Hg) and with TLV (515 [range 442 to 532] mm Hg). After ARS, PaO2 values during OLV were similar to those during TLV. During OLV, the degree of pulmonary collapse in the nondependent lung, the hemodynamic status, and the ventilation parameters were similar before and after ARS. CONCLUSIONS: Alveolar recruitment of the dependent lung augments PaO2 values during one-lung ventilation.     

A comparison of enflurane and propofol in thoracic surgery

Comparisons between propofol and inhalational anesthetics for maintenance of anesthesia are limited. The purpose of our prospective study was to examine differences between enflurane and propofol during pulmonary resections with one-lung ventilation (1LV). METHOD. 28 patients, ASA risk group II-III, gave written informed consent for inclusion in this institutionally approved study. The patients were randomly allocated to one of the following groups: A: propofol 10 mg kg-1 h-1, B: 1 MAC enflurane, for maintenance of anesthesia. In both groups analgesia was achieved by fentanyl and muscle relaxation, by pancuronium. Ventilation via a double-lumen tube was controlled (FiO2 = 1.0, PaCO2 35-40 mmHg). Measurements, including hemodynamics and arterial and mixed venous blood gases, were obtained before induction (I), during two-lung ventilation (2LV) 15 min after induction in the supine position (II) and 20 min after surgical opening of the chest in the lateral decubitus position (III), 20 min after starting 1LV (IV), and after extubation (V). RESULTS. No significant differences between the two groups were found before induction (I), during 2LV (II, III), or after extubation (V). The only significant differences between the two groups were observed during 1LV (IV): the shunt fraction was 33.9 +/- 2.5% in A and 38.5 +/- 2.6% in B (P less than or equal to 0.05). Hypoxic pulmonary vasoconstriction was not inhibited in A, but was inhibited by 21.5% in group B during 1LV. Since no case of hypoxemia occurred in group A during 1LV (range of PaO2: 75.2-417.0 mmHg), but four patients developed hypoxemia in group B (Range of PaO2: 46.6-431.0 mmHg), regimen A might be of value in high-risk patients during thoracic surgery when 1LV is planned.     

Effects of isoflurane on oxygenation during one-lung ventilation in pulmonary emphysema patients

Background: Hypoxic pulmonary vasoconstriction has an important role in human one-lung ventilation (OLV) in the lateral decubitus position under general anesthesia. During OLV, inhalational anesthesia may inhibit hypoxic pulmonary vasoconstriction and the decrease in arterial oxygenation. We studied the effect of isoflurane administration on arterial oxygen tension in chronic obstructive pulmonary disease patients.
Methods: Ten patients who had thoracoscopic laser ablation of bullous emphysema were studied. Patients received 2% isoflurane in oxygen from induction until the first 20 min of OLV in the lateral decubitus position, then were switched to 1% isoflurane lasting 20 min and next were switched to 0.5% isoflurane lasting 20 min. After each 20-min inhalation, pulmonary and hemodynamic parameters were measured. The given concentrations for isoflurane were merely vapor meter concentrations.
Results: PaO₂/FIO₂, Qs/Qt respiratory rate peak inspiratory pressure and PaCO₂ showed no significant changes at each point of isoflurane. Expiratory tidal volume significantly decreased (P<0.05) with 0.5% isoflurane compared to that with 2% isoflurane. Cardiac output, mean arterial pressure, mean pulmonary arterial pressure, systemic vascular resistance and pulmonary vascular resistance showed no significant changes at each point of isoflurane.
Conclusions: In patients with pulmonary emphysema, arterial oxygenation is not affected by low isoflurane concentration during OLV in the lateral decubitus position.     

Effects of thoracic epidural meperidine on arterial oxygenation during one-lung ventilation in thoracic surgery

OBJECTIVE: To compare the effects that the use of general intravenous anesthesia (propofol-fentanyl) (GA) or general anesthesia combined with thoracic epidural anesthesia with meperidine (TEA-M) may have on arterial oxygenation during one-lung ventilation (OLV). DESIGN: Prospective. SETTING: Tertiary care hospital. PARTICIPANTS: Seventy-two patients undergoing OLV for thoracic surgery. INTERVENTIONS: Patients were prospectively randomized into two groups: GA (n = 37) fentanyl, propofol, rocuronium anesthesia was used; and group TEA-M (n = 35) were anesthetized with propofol, rocuronium and thoracic epidural meperidine (2 mg/kg in 10-12 mL) administered before anesthetic induction. A double-lumen endotracheal tube was inserted, and mechanical ventilation with 100% oxygen was used during study. Mean arterial pressure, heart rate and arterial and venous blood gases were recorded with the patients in the lateral decubitus position in three phases: during two-lung ventilation (TLV), 15 and 30 minutes after beginning OLV (OLV + 15 and OLV + 30 respectively). The authors measured arterial and venous central oxygen tension, arterial and venous central oxygen saturation, arterial and venous central oxygen content and venous admixture percentage (Qs/Qt%). MEASUREMENTS AND MAIN RESULTS: There were no statistical differences between the two groups for PaO(2) during OLV + 15 (GA = 165 mmHg, TEA-M = 153 mmHg) and OLV + 30 (GA = 176 mmHg, TEA-M = 158 mmHg); and with values for Qs/Qt%. CONCLUSIONS: It is concluded that GA combined with TEA-M (2 mg/kg) do not affect arterial oxygenation during OLV in thoracic surgery.     

Gravity is an important determinant of oxygenation during one‐lung ventilation

Background: The role of gravity in the redistribution of pulmonary blood flow during one‐lung ventilation (OLV) has been questioned recently. To address this controversial but clinically important issue, we used an experimental approach that allowed us to differentiate the effects of gravity from the effects of hypoxic pulmonary vasoconstriction (HPV) on arterial oxygenation during OLV in patients scheduled for thoracic surgery. Methods: Forty patients with chronic obstructive pulmonary disease scheduled for right lung tumour resection were randomized to undergo dependent (left) one‐lung ventilation (D‐OLV; n=20) or non‐dependent (right) one‐lung ventilation (ND‐OLV; n=20) in the supine and left lateral positions. Partial pressure of arterial oxygen (PaO₂) was measured as a surrogate for ventilation/perfusion matching. Patients were studied before surgery under closed chest conditions. Results: When compared with bilateral lung ventilation, both D‐OLV and ND‐OLV caused a significant and equal decrease in PaO₂ in the supine position. However, D‐OLV in the lateral position was associated with a higher PaO₂ as compared with the supine position [274.2 (77.6) vs. 181.9 (68.3) mmHg, P<0.01, analysis of variance (ANOVA)]. In contrast, in patients undergoing ND‐OLV, PaO₂ was always lower in the lateral as compared with the supine position [105.3 (63.2) vs. 187 (63.1) mmHg, P<0.01, ANOVA]. Conclusion: The relative position of the ventilated vs. the non‐ventilated lung markedly affects arterial oxygenation during OLV. These data suggest that gravity affects ventilation–perfusion matching independent of HPV.