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.     

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.     

Biologically variable ventilation improves oxygenation and respiratory mechanics during one-lung ventilation

BACKGROUND: Hypoxemia is common during one-lung ventilation (OLV). Atelectasis contributes to the problem. Biologically variable ventilation (BVV), using microprocessors to reinstitute physiologic variability to respiratory rate and tidal volume, has been shown to be advantageous over conventional monotonous control mode ventilation (CMV) in improving oxygenation during the period of lung reinflation after OLV in an experimental model. Here, using a porcine model, the authors compared BVV with CMV during OLV to assess gas exchange and respiratory mechanics. METHODS: Eight pigs (25-30 kg) were studied in each of two groups. After induction of anesthesia-tidal volume 12 ml/kg with CMV and surgical intervention-tidal volume was reduced to 9 ml/kg. OLV was initiated with an endobronchial blocker, and the animals were randomly allocated to either continue CMV or switch to BVV for 90 min. After OLV, a recruitment maneuver was undertaken, and both lungs were ventilated for a further 60 min. At predetermined intervals, hemodynamics, respiratory gases (arterial, venous, and end-tidal samples) and mechanics (airway pressures, static and dynamic compliances) were measured. Derived indices (pulmonary vascular resistance, shunt fraction, and dead space ventilation) were calculated. RESULTS: By 15 min of OLV, arterial oxygen tension was greater in the BVV group (group x time interaction, P = 0.003), and shunt fraction was lower with BVV from 30 to 90 min (group effect, P = 0.0004). From 60 to 90 min, arterial carbon dioxide tension was lower with BVV (group x time interaction, P = 0.0001) and dead space ventilation was less from 60 to 90 min (group x time interaction, P = 0.0001). Static compliance was greater by 60 min of BVV and remained greater during return to ventilation of both lungs (group effect, P = 0.0001). CONCLUSIONS: In this model of OLV, BVV resulted in superior gas exchange and respiratory mechanics when compared with CMV. Improved static compliance persisted with restoration of two-lung ventilation.     

Prediction of arterial oxygen tension during one-lung ventilation: analysis of preoperative and intraoperative variables

OBJECTIVE: To determine whether currently available preoperative and intraoperative variables related to arterial oxygen tension (PaO(2)) can be used as predictors for low PaO(2) during one-lung ventilation (OLV). DESIGN: A prospective cohort study. SETTING: Primary university hospital. PARTICIPANTS: Adult patients (n = 92) undergoing thoracic surgery requiring OLV. INTERVENTIONS: Preoperative and intraoperative data, including past medical history, physical examination, and usual preoperative and intraoperative tests, were collected and used as explanatory variables for PaO(2) during OLV by univariate and multivariate analysis. A stepwise logistic regression including the same independent variables was used to identify patients who should be expected to develop arterial hypoxemia (PaO(2) <70 mmHg). Arterial blood gas samples were analyzed 15 minutes after the onset of OLV and after thoracotomy to determine the lowest PaO(2) value during OLV. MEASUREMENTS AND MAIN RESULTS: Preoperative (age, hematocrit, relative perfusion of the nondependent lung) and intraoperative (PaO(2) during 2-lung ventilation and mean arterial pressure at the lowest PaO(2)) variables were identified as independent factors affecting PaO(2) in OLV. PaO(2) during 2-lung ventilation was the only independent variable accounting for arterial hypoxemia when multivariate logistic regression was performed. CONCLUSION: The PaO(2) during OLV can be predicted using routinely available preoperative and intraoperative data. From a clinical point of view, this study failed to identify patients at risk of arterial hypoxemia when OLV is instituted because mainly intraoperative independent variables are involved in the decrease of PaO(2) in this situation.     

Halothane and isoflurane do not decrease PaO2 during one-lung ventilation in intravenously anesthetized patients

We examined the effect of the inhalational anesthetics halothane (H) and isoflurane (IF) on arterial oxygenation during one-lung ventilation. Twenty consenting patients who required thoracotomy and one-lung ventilation were initially anesthetized only with the intravenous agents, diazepam, fentanyl, pancuronium, metocurine, and infusions of either ketamine or methohexital. A double lumen endotracheal tube was inserted, and each patient's lungs were mechanically ventilated (two-lung ventilation, step 1) with 100% O2 while the patient was in the lateral decubitus position. After the pleura was opened, the nondependent lung was collapsed while the dependent lung continued to be ventilated with 100% O2. After serial PaO2 measurements indicated achievement of stable one-lung ventilation conditions (step 2), intravenous anesthetic agents were discontinued, and either H (n = 10) or IF (n = 10) was administered (step 3) so that PETH = 7.70 +/- 0.61 mm Hg and PETIF = 9.89 +/- 1.08 mm Hg for more than 15 min; at the end of step 3, PaH/PETH = 0.82 (n = 5), PaIF/PETIF = 0.75 (n = 5), PvH/PETH = 0.64 (n = 3), and PvIF/PETIF = 0.68 (n = 3). The inhalational anesthetics were then discontinued, and intravenous agents were reinstituted, allowing PETH and PETIF to decrease below 0.50 mm Hg (step 4). Two-lung ventilation was resumed at the end of the surgical procedure (step 5). PaO2 decreased from 441 +/- 64 to 252 +/- 70 mm Hg when one-lung ventilation was achieved (steps 1-2), and PaO2 increased from 258 +/- 72 to 395 +/- 65 mm Hg when two-lung ventilation was resumed (steps 4-5).(ABSTRACT TRUNCATED AT 250 WORDS)     

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.     

Application of PEEP using the i-gel during volume-controlled ventilation in anesthetized, paralyzed patients

Purpose

This prospective, randomized trial was designed to assess whether the i-gel supraglottic airway device is suitable for volume-controlled ventilation while applying positive end-expiratory pressure (PEEP) of 5 cmH₂O under general anesthesia. It was believed that this device might improve arterial oxygenation.

Methods

Forty adult patients (aged 20–60 years) scheduled for elective orthopedic surgery were enrolled in this study. Twenty patients were ventilated without external PEEP [zero positive end-expiratory pressure (ZEEP) group], and the other 20 were ventilated with PEEP 5 cmH₂O (PEEP group) after placing an i-gel device. Volume-controlled ventilation at a tidal volume (TV) of 8 ml/kg of ideal body weight, leak volume, and arterial blood gas analysis were investigated.

Results

The incidences of a significant leak were similar in the ZEEP and PEEP groups (3/20 and 1/20, respectively; P = 0.605), as were leak volumes. No significant PaO₂ difference was observed between the two groups at 1 h after satisfactory i-gel insertion (215 ± 38 vs. 222 ± 54; P = 0.502).

Conclusions

The use of an i-gel during PEEP application at 5 cmH₂O did not increase the incidence of a significant air leak, and a PEEP of 5 cmH₂O failed to improve arterial oxygenation during controlled ventilation in healthy adult patients.     

Preoperative special tests and intraoperative arterial oxygen partial pressure during one-lung ventilation

The value of preoperative lung function tests was examined in 11 patients as a method to predict changes in intraoperative PaO2 (dPaO2) during one-lung ventilation in pulmonary surgery. Ventilation (Kr-81m and Xe-133) and perfusion (Tc-99m microspheres) to the lung to be operated upon significantly predicted the intra-operative decrease in PaO2. The correlation between ventilation percentage to the diseased lung and dPaO2 was 0.87 (SEE = 9.99) and between perfusion and dPaO2 0.84 (SEE = 9.51).     

急性高容量血液稀释对单肺通气犬肺水的影响

目的探讨急性高容量血液稀释(AHHD)对单肺通气犬通气侧和非通气侧肺水的影响。方法32只健康成年杂种犬,雌雄各半,体重12-21kg,随机分为4组(A、B、C和D组),A组行单肺通气,B、C、D组在单肺通气基础上行AHHD,每组8只。各组麻醉诱导后气管插管,游离左侧总支气管后结扎行单肺通气。B、C、D组在单肺通气10 min时经头静脉或股静脉以80 m1·kg-1·h-1的速率输注6%中分子羟乙基淀粉行AHHD,分别将红细胞比容(Hct)降至25%、20%、15%。分别记录双肺通气10 min(双肺通气时)、单肺通气10 min(单肺通气时)和AHHD至预定值(血液稀释时)心率(HR)、收缩压(BP)、舒张压(DP)、平均动脉压(MAP)、心输出量(CO)、每搏输出量(SV)、射血分数(EF)、外周血管阻力(SVR)、中心静脉压(CVP)。A组在单肺通气10min、B、C、D组Hct降至预定值后10 min处死犬。测定肺水参数:肺湿重(W)、肺干重(D)、肺水系数(Qw)、血管内肺水(IVLW)、血管外肺水(EVLW)、总肺水(TLW)、肺含水百分数(H2O%)、肺湿干重比(W/D)。结果D组1只犬出现双侧肺水肿;与A组比较,B、C、D组双侧肺IVLW、TLW、IVLW/D增加,C、D组双侧肺H2O%、W/D和,TLW/D增加,D组双侧肺EVLW、Qw增加(P<0.05或0.01);双侧肺TLW与EVLW的相关系数分别为0.761和0.824(P<0.01)。通气侧、非通气TLW(X)与EVLW(Y)直线回归方程分别为Y=-0.56 0.88X、Y= -4.08 1.62X,r2分别为0.58、0.68(P<0.01)。结论单肺通气犬应用6%羟乙基淀粉行AHHD时, 在Hct降至20%以上时主要是增加了IVLW和TLW,EVLW增加相对较少;而Hct降至15%时,有发生肺水肿的危险。     

Arterial oxygen desaturation during one-lung ventilation in a patient with segmental pulmonary infarction

A left thoracotomy for decortication of an infected haemothorax was performed on a 52-year-old man with a partially infarcted left lower lobe that occurred as a rare complication of a pulmonary venous embolus. Before the completion of surgery, after an uncomplicated 40 minutes of one-lung ventilation, the left lung was temporarily re-expanded to assess air leak. On the resumption of one-lung ventilation the SpO2 fell rapidly to 85%, despite apnoeic oxygenation of the non-ventilated lung. In the absence of evidence of double-lumen tube displacement, intra-pulmonary shunting as a consequence of impaired hypoxic pulmonary vasoconstriction in the newly expanded markedly pathological lung is considered the most likely mechanism.     

Compressing the non-dependent lung during one-lung ventilation improves arterial oxygenation, but impairs systemic oxygen delivery by decreasing cardiac output

Purpose  

We have previously found that compression of the non-dependent lung improves arterial oxygenation during one-lung ventilation (OLV) in patients undergoing esophagectomy. The purpose of this study was to investigate the effects of compression of the non-dependent lung on hemodynamic indices and oxygen delivery using a minimally invasive cardiac output (CO) monitor.     

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

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

急性等容血液稀释对犬单肺通气期间肺分流与氧合的影响

目的 观察犬单肺通气期间，不同程度急性等容血液稀释对肺分流和氧供、氧耗等的影响。方法 12只健康杂种犬，基础麻醉后插入双腔气管导管，股动、静脉置管。稳定30分钟（HD0）后，以血定安等速置换全血，分别达到轻度（HD1）、中度（HD2）、重度（HD3）和极重度（HD4）血液稀释四个阶段。每阶段均分为双肺通气（TLV）和单肺通气（ OLV），分别于各阶段TLV、OLV15分钟后测量分流（Qs/Qt)及氧供（DO2）、氧耗（VO2）等各指标变化。结果 随着HD程度的加深，平均动脉压、心输出量、肺血管阻力（PVR）、平均肺动脉压（MPAP）、氧分压、DO2等趋于降低，氧摄取率（EPO2）、血乳酸、Qs/Qt趋于增加，到HD3、HD4时已出现DO2－VO2依赖性降低及无氧酵解征象。与TLV时相比，OLV期间HD0、HD1及HD2组PVR、MPAP增高明显（P＜0．01）。而HD3、H4D4组变化不大（P＞0．05） ；OLV时QS／Qt增加更为明显，HD2、HD3及HD4组分别较基值增加74％、164％及177％（P＜0．01） 。结论 缺氧、ANHD均为影响Qs/Qt与氧合的重要因素，OLV时ANHD应以不低于中度为准。     

异丙酚和氯胺酮对单肺通气犬肺内分流的影响

目的 对比观察异丙酚和氯胺酮对单肺通气犬肺内分流的影响,探讨异丙酚对缺氧性肺血管收缩反应(HPV)的影响程度。方法 杂种犬12只,随机分为异丙酚组、氯胺酮组。两组均于单肺通气(OLV)前30 min开始静滴异丙酚或氯胺酮6 mg·kg-1·h-1,后行单肺通气,于双肺通气(TLV)30 min、单肺通气2、10、30、60 min同时采集动脉血及混合静脉血行血气分析,并计算分流率(Qs/Qt)。结果 两组TLV 30 min Qs/Qt差异无显著性(P>0.05),OLV 2 min时Qs/Qt均较TLV时明显增高(P<0.01),但两组间无明显差异(P>0.05)。OLV 10、30及60 min时两组间Qs/Qt差异有显著性(P<0.05),组内不同时间Qs/Qt差异也有显著性(P<0.05)。结论 异丙酚与氯胺酮相比轻度增加单肺通气时肺内分流。     

急性等容血液稀释对单肺通气期间组织氧合的影响

目的 观察急性等容血液稀释(ANHD)对组织氧合的影响.方法 60例ASA Ⅰ或Ⅱ级择期单肺通气(OLV)胸科手术患者随机均分为三个ANHD组:HD_1组,目标Hct为35%;HD_2组,目标Hct为30%;HD_0组不进行ANHD.连续监测ECG、BP、中心静脉压(CVP)及心输出量(CO),于ANHD前(T_1)、ANHD后30 min(T_2)、OLV 15 min(T_3)、OLV 30 min(T_4)测量动静脉血气及血乳酸(Lac),并计算心脏指数(CI),氧供(DO_2)、氧耗(VO_2)、氧摄取率(ERO_2).结果 三组各时点Na~+、K~+、Ca~(2+)、pH及BE无明显改变.ANHD后CI明显增加,OLV后CI继续增加(P<0.05).ANHD后DO_2增加;ERO_2于OLV时均有增加(P<0.05).结论 适度ANHD(Hct>25%)在OLV胸科手术中能保证机体代谢的氧合需要,维持血流动力学及内环境的稳定.