Effects of PEEP on oxygenation and respiratory mechanics during one-lung ventilation

Effects of positive end-expiratory pressure on regional cerebral oxygen saturation in elderly patients undergoing thoracic surgery during one-lung ventilation: a randomized crossover-controlled trial

BACKGROUND

A significant reduction in regional cerebral oxygen saturation (rSO2) is commonly observed during one-lung ventilation (OLV), while positive end-expiratory pressure (PEEP) can improve oxygenation. We compared the effects of three different PEEP levels on rSO2, pulmonary oxygenation, and hemodynamics during OLV.

METHODS

Forty-three elderly patients who underwent thoracoscopic lobectomy were randomly assigned to one of six PEEP combinations which used a crossover design of 3 levels of PEEP-0 cmH2O, 5 cmH2O, and 10 cmH2O. The primary endpoint was rSO2 in patients receiving OLV 20 min after adjusting the PEEP. The secondary outcomes included hemodynamic and respiratory variables.

RESULTS

After exclusion, thirty-six patients (36.11% female; age range: 60-76 year) were assigned to six groups (n = 6 in each group). The rSO2 was highest at OLV(0) than at OLV(10) (difference, 2.889%; [95% CI, 0.573 to 5.204%]; p = 0.008). Arterial oxygen partial pressure (PaO2) was lowest at OLV(0) compared with OLV(5) (difference, -62.639 mmHg; [95% CI, -106.170 to -19.108 mmHg]; p = 0.005) or OLV(10) (difference, -73.389 mmHg; [95% CI, -117.852 to -28.925 mmHg]; p = 0.001), while peak airway pressure (Ppeak) was lower at OLV(0) (difference, -4.222 mmHg; [95% CI, -5.140 to -3.304 mmHg]; p < 0.001) and OLV(5) (difference, -3.139 mmHg; [95% CI, -4.110 to -2.167 mmHg]; p < 0.001) than at OLV(10).

CONCLUSIONS

PEEP with 10 cmH2O makes rSO2 decrease compared with 0 cmH2O. Applying PEEP with 5 cmH2O during OLV in elderly patients can improve oxygenation and maintain high rSO2 levels, without significantly increasing peak airway pressure compared to not using PEEP.

TRIAL REGISTRATION

Chinese Clinical Trial Registry ChiCTR2200060112 on 19 May 2022.

Effect of permissive hypercarbia on lung oxygenation during one-lung ventilation and postoperative pulmonary complications in patients undergoing thoracic surgery: A prospective randomised controlled trial

BACKGROUND

The effect of hypercarbia on lung oxygenation during thoracic surgery remains unclear.

OBJECTIVE

To investigate the effect of hypercarbia on lung oxygenation during one-lung ventilation in patients undergoing thoracic surgery and evaluate the incidence of postoperative pulmonary complications.

DESIGN

Prospective randomised controlled trial.

SETTING

A tertiary university hospital in the Republic of Korea from November 2019 to December 2020.

PATIENTS

Two hundred and ninety-seven patients with American Society of Anaesthesiologists physical status II to III, scheduled to undergo elective lung resection surgery.

INTERVENTION

Patients were randomly assigned to Group 40, 50, or 60. An autoflow ventilation mode with a lung protective ventilation strategy was applied to all patients. Respiratory rate was adjusted to maintain a partial pressure of arterial carbon dioxide of 40 ± 5 mmHg in Group 40, 50 ± 5 mmHg in Group 50 and 60 ± 5 mmHg in Group 60 during one-lung ventilation and at the end of surgery.

MAIN OUTCOME MEASURES

The primary outcome was the arterial oxygen partial pressure/fractional inspired oxygen ratio after 60 min of one-lung ventilation.

RESULTS

Data from 262 patients were analysed. The partial pressure/fractional inspired oxygen ratio was significantly higher in Group 50 and Group 60 than in Group 40 (269.4 vs. 262.9 vs. 214.4; P  < 0.001) but was not significantly different between Group 50 and Group 60. The incidence of postoperative pulmonary complications was comparable among the three groups.

CONCLUSION

Permissive hypercarbia improved lung oxygenation during one-lung ventilation without increasing the risk of postoperative pulmonary complications or the length of hospital stay.

TRIAL REGISTRATION

NCT04175379.

A structured narrative review of clinical and experimental studies of the use of different positive end-expiratory pressure levels during thoracic surgery

OBJECTIVES

This study aimed to present a review on the general effects of different positive end-expiratory pressure (PEEP) levels during thoracic surgery by qualitatively categorizing the effects into detrimental, beneficial, and inconclusive.

DATA SOURCE

Literature search of Pubmed, CNKI, and Wanfang was made to find relative articles about PEEP levels during thoracic surgery. We used the following keywords as one-lung ventilation, PEEP, and thoracic surgery.

RESULTS

We divide the non-individualized PEEP value into five grades, that is, less than 5, 5, 5-10, 10, and more than 10 cmH₂ O, among which 5 cmH₂ O is the most commonly used in clinic at present to maintain alveolar dilatation and reduce the shunt fraction and the occurrence of atelectasis, whereas individualized PEEP, adjusted by test titration or imaging method to adapt to patients' personal characteristics, can effectively ameliorate intraoperative oxygenation and obtain optimal pulmonary compliance and better indexes relating to respiratory mechanics.

CONCLUSIONS

Available data suggest that PEEP might play an important role in one-lung ventilation, the understanding of which will help in exploring a simple and economical method to set the appropriate PEEP level.

Effect of pressures and type of ventilation on aerosol delivery to chronic obstructive pulmonary disease patients

Background

Continuous Positive Airway Pressure (CPAP), BiPhasic Positive Airway Pressure (BiPAP), and high flow nasal cannula (HFNC) show some evidence to have efficacy in COVID-19 patients. Delivery during noninvasive mechanical ventilation (NIV) or HFNC gives faster and more enhanced clinical effects than when aerosols are given without assisted breath. The present work aimed to compare the effect of BiPhasic Positive Airway Pressure (BiPAP) mode at two different pressures; low BiPAP (Inspiratory Positive Airway Pressure (IPAP)/Expiratory Positive Airway Pressure (EPAP) of 10/5 cm water) and high BiPAP (IPAP/EPAP of 20/5 cm water), with HFNC system on pulmonary and systemic drug delivery of salbutamol. On the first day of the experiment, all patients received 2500 μg salbutamol using Aerogen Solo vibrating mesh nebulizer. Urine samples 30 min post-dose and cumulative urinary salbutamol during the next 24 h were collected on the next day. On the third day, the ex-vivo filter was inserted before the patient to collect the delivered dose to the patient of the 2500 μg salbutamol. Salbutamol was quantified using high-performance liquid chromatography (HPLC).

Results

Low-pressure BiPAP showed the highest amount delivered to the lung after 30 min followed by HFNC then high-pressure BiPAP. But the significant difference was only observed between low and high-pressure BiPAP modes (p = 0.012). Low-pressure BiPAP showed the highest delivered systemic delivery amount followed by HFNC then high-pressure BiPAP. Low-pressure BiPAP was significantly higher than HFNC (p = 0.017) and high-pressure BiPAP (p = 0.008). No significant difference was reported between HFNC and high-pressure BiPAP. The ex-vivo filter was the greatest in the case of low-pressure BiPAP followed by HFNC then high-pressure BiPAP. Low-pressure BiPAP was significantly higher than HFNC (p = 0.033) and high-pressure BiPAP (p = 0.008). Also, no significant difference was found between HFNC and high-pressure BiPAP.

Conclusions

Our results of pulmonary, systemic, and ex-vivo drug delivery were found to be consistent. The low BiPAP delivered the highest amount followed by the HFNC then the high BiPAP with the least amount. However, no significant difference was found between HFNC and high BiPAP.

Anesthetic Management for Pulmonary Resection: Current Concepts and Improving Safety of Anesthesia

Increasingly complex procedures are routinely performed using minimally invasive approaches, allowing cancers to be resected with short hospital stays, minimal postsurgical discomfort, and improved odds of cancer-free survival. Along with these changes, the focus of anesthetic management for lung resection surgery has expanded from the provision of ideal surgical conditions and safe intraoperative patient care to include preoperative patient training and optimization and postoperative pain management techniques that can impact pulmonary outcomes as well as patient lengths of stay.

Positive end-expiratory pressure as a novel method to thwart CO2 leakage from capnothorax in robotic-assisted thoracoscopic surgery

Capnography and end tidal CO2 (EtCO2) aids the anaesthesiologist in diagnosing problems during all phases of general anaesthesia. Negative arterial to end-tidal carbon-dioxide gradient during anaesthesia has been reported in various conditions including pregnancy, infants and inadvertent exogenous addition of carbon dioxide (CO2) to the expired gas in case of thoracoscopic procedures with iatrogenic injury to lung parenchyma/bronchial tree. Thus, airway injury or intentional opening of airway as a part of surgical step can be diagnosed using a negative arterial and end tidal CO2 gradient. Higher optimal PEEP can be used as a splint across the bronchial cuff in one-lung ventilation which prevents leak from capnothorax and decrease inadvertent entry of CO2 in to the expired gases which erroneously increase arteriolar to end tidal CO2 gradient.

Comparative effects of open-lung positive end-expiratory pressure (PEEP) and fixed PEEP on respiratory system compliance in the isoflurane anaesthetised healthy dog

This study was performed to assess the effects of open-lung positive end-expiratory pressure (OL-PEEP) following stepwise recruitment manoeuvre (RM) and those of a fixed PEEP of 5 cm H₂O without previous RM on respiratory system compliance (Crs) and selected cardiovascular variables in healthy dogs under general anaesthesia. Forty-five healthy client-owned dogs undergoing surgery were anaesthetised and mechanically ventilated (tidal volume, VT = 10-12 mL/kg; PEEP = 0 cm H₂O) for 1 min (baseline) and randomly allocated into zero positive end-expiratory pressure (ZEEP), PEEP (5 cm H₂O) and OL-PEEP treatment groups. In the OL-PEEP group, a stepwise RM was performed and the individual OL-PEEP was subsequently applied. The Crs, heart rate (HR) and non-invasive mean arterial pressure (NIMAP) were registered at baseline and then every 10 min during 60 min. In the ZEEP group, Crs decreased from baseline. In the PEEP group, Crs was not different from either baseline or ZEEP group values. In the OL-PEEP group, Crs was higher than both baseline and ZEEP group values at all time points as well as of those in the PEEP group during at least 20 min after RM. There were no differences for HR and NIMAP between groups. A clinically relevant hypotension following RM was observed in 40% of dogs. Therefore, an individually set OL-PEEP following stepwise RM improved Crs in anaesthetised healthy dogs, although transient but clinically relevant hypotension was observed during RM in some dogs. Fixed PEEP of 5 cm H₂O without previous RM did not improve Crs, although it prevented it from decreasing.

Intrabronchial Catheter Resuscitation for Respiratory and Cardiorespiratory Arrest

INTRODUCTION

We sought to determine whether intrabronchial oxygenation would provide adequate gas exchange during both anesthesia induced apneic and cardiopulmonary arrest and cardiac massage (CPR).

METHODS

Ten pigs underwent general anesthesia with mechanical ventilation. Blood gases were measured in each animal at 4 min intervals for up to 28 min. An intrabronchial catheter (4 L/min O2) was inserted through an endotracheal tube after respirator cessation. Group A animals (6) were resuscitated with the catheter but without CPR. Group B animals (4) were rendered apneic and cardioplegic and resuscitated by CPR for 28 min using the intrabronchial device.

RESULTS

All group A animals were resuscitated and survived after 24 min of apnea. Mean pO2 decreased from 378 mmHg (95% confidence interval [CI], 288-468) to 292 mmHg (95% CI, 246-339), P = 0.009; pCO2 increased from 52 mmHg (95% CI, 43-61) to 137 mmHg (95% CI, 116-158), P < 0.0001; and pH decreased from 7.32 (7.29-7.36) to 6.98 (6.92-7.03), P < 0.0001. In a control animal bronchial catheter oxygen flow ceased at baseline and pO2 decreased from 268 to 30 mmHg by 20 min. In group B animals mean pO2 decreased from 426 mmHg (95% CI, 273-579) to 130 mmHg (95% CI, 92-168) after 28 min, P < 0.0001; pCO2 increased from 49 mmHg (95% CI, 41-58) to 73 mmHg (95% CI, 61-86), P = 0.03; and pH decreased from 7.34 (7.33-7.35) to 7.07 (6.98-7.16), P < 0.0001. In the control receiving intratracheal oxygen pO2 decreased from 324 to 88 mmHg after 16 minu of CPR.

CONCLUSIONS

Intrabronchial oxygenation provides sustained hyperoxemia during complete apnea and cardiac arrest with CPR.

Physiologic Evaluation of Ventilation Perfusion Mismatch and Respiratory Mechanics at Different Positive End-expiratory Pressure in Patients Undergoing Protective One-lung Ventilation

BACKGROUND

Arterial oxygenation is often impaired during one-lung ventilation, due to both pulmonary shunt and atelectasis. The use of low tidal volume (VT) (5 ml/kg predicted body weight) in the context of a lung-protective approach exacerbates atelectasis. This study sought to determine the combined physiologic effects of positive end-expiratory pressure and low VT during one-lung ventilation.

METHODS

Data from 41 patients studied during general anesthesia for thoracic surgery were collected and analyzed. Shunt fraction, high V/Q and respiratory mechanics were measured at positive end-expiratory pressure 0 cm H2O during bilateral lung ventilation and one-lung ventilation and, subsequently, during one-lung ventilation at 5 or 10 cm H2O of positive end-expiratory pressure. Shunt fraction and high V/Q were measured using variation of inspired oxygen fraction and measurement of respiratory gas concentration and arterial blood gas. The level of positive end-expiratory pressure was applied in random order and maintained for 15 min before measurements.

RESULTS

During one-lung ventilation, increasing positive end-expiratory pressure from 0 cm H2O to 5 cm H2O and 10 cm H2O resulted in a shunt fraction decrease of 5% (0 to 11) and 11% (5 to 16), respectively (P < 0.001). The PaO2/FIO2 ratio increased significantly only at a positive end-expiratory pressure of 10 cm H2O (P < 0.001). Driving pressure decreased from 16 ± 3 cm H2O at a positive end-expiratory pressure of 0 cm H2O to 12 ± 3 cm H2O at a positive end-expiratory pressure of 10 cm H2O (P < 0.001). The high V/Q ratio did not change.

CONCLUSIONS

During low VT one-lung ventilation, high positive end-expiratory pressure levels improve pulmonary function without increasing high V/Q and reduce driving pressure.

Effects of Positive End-Expiratory Pressure on Pulmonary Oxygenation and Biventricular Function during One-Lung Ventilation: A Randomized Crossover Study

Although the application of positive end-expiratory pressure (PEEP) can alter cardiopulmonary physiology during one-lung ventilation (OLV), these changes have not been clearly elucidated. This study assessed the effects of different levels of PEEP on biventricular function, as well as pulmonary oxygenation during OLV. Thirty-six lung cancer patients received one PEEP combination of six sequences, consisting of 0 (PEEP_0), 5 (PEEP_5), and 10 cmH₂O (PEEP_10), using a crossover design during OLV. The ratio of arterial oxygen partial pressure to inspired oxygen fraction (P/F ratio), systolic and diastolic echocardiographic parameters were measured at 20 min after the first, second, and third PEEP. P/F ratio at PEEP_5 was significantly higher compared to PEEP_0 (p = 0.014), whereas the P/F ratio at PEEP_10 did not show significant differences compared to PEEP_0 or PEEP_5. Left ventricular ejection fraction (LV EF) and right ventricular fractional area change (RV FAC) at PEEP_10 (EF, p < 0.001; FAC, p = 0.001) were significantly lower compared to PEEP_0 or PEEP_5. RV E/E’ (p = 0.048) and RV myocardial performance index (p < 0.001) at PEEP_10 were significantly higher than those at PEEP_0 or PEEP_5. In conclusion, increasing PEEP to 10 cmH₂O decreased biventricular function, especially on RV function, with no further improvement on oxygenation compared to PEEP 5 cmH₂O during OLV.

Optimal PEEP during one-lung ventilation with capnothorax: An experimental study

BACKGROUND

One-lung ventilation (OLV) with induced capnothorax carries the risk of severely impaired ventilation and circulation. Optimal PEEP may mitigate the physiological perturbations during these conditions.

METHODS

Right-sided OLV with capnothorax (16 cm H₂ O) on the left side was initiated in eight anesthetized, muscle-relaxed piglets. A recruitment maneuver and a decremental PEEP titration from PEEP 20 cm H₂ O to zero end-expiratory pressure (ZEEP) was performed. Regional ventilation and perfusion were studied with electrical impedance tomography and computer tomography of the chest was used. End-expiratory lung volume and hemodynamics were recorded and.

RESULTS

PaO₂ peaked at PEEP 12 cm H₂ O (49 ± 14 kPa) and decreased to 11 ± 5 kPa at ZEEP (P < 0.001). PaCO₂ was 9.5 ± 1.3 kPa at 20 cm H₂ O PEEP and did not change when PEEP step-wise was reduced to 12 cm H₂ O PaCO_2. At lower PEEP, PaCO₂ increased markedly. The ventilatory driving pressure was lowest at PEEP 14 cm H₂ O (19.6 ± 5.8 cm H₂ O) and increased to 38.3 ± 6.1 cm H₂ O at ZEEP (P < 0.001). When reducing PEEP below 12-14 cm H₂ O ventilation shifted from the dependent to the nondependent regions of the ventilated lung (P = 0.003), and perfusion shifted from the ventilated to the nonventilated lung (P = 0.02).

CONCLUSION

Optimal PEEP was 12-18 cm H₂ O and probably relates to capnothorax insufflation pressure. With suboptimal PEEP, ventilation/perfusion mismatch in the ventilated lung and redistribution of blood flow to the nonventilated lung occurred.

The Effects of Secondhand Smoke Exposure on Postoperative Pain and Ventilation Values During One-Lung Ventilation: A Prospective Clinical Trial

OBJECTIVES

To investigate the relationships between secondhand smoke (SHS) exposure and oxygenation during one-lung ventilation (OLV) in lobectomy surgery and between SHS exposure and postoperative analgesic consumption.

DESIGN

Prospective study.

SETTING

University, Faculty of Medicine, operating room.

PARTICIPANTS

Sixty adult patients with American Society of Anesthesiologists score II to III, aged 18 to 65 years, with a body mass index (BMI) <35 kg/m² scheduled for lobectomy surgery by open thoracotomy.

INTERVENTIONS

Patients were divided into 2 groups: the SHS group (n = 30) (urine cotinine level ≥6.0 ng/mL) and the NS (nonsmoker) group (n = 30) (urine cotinine level <6.0 ng/mL and no smoking history). SHS exposure was defined according to a previously published algorithm.

MEASUREMENTS AND MAIN RESULTS

Noninvasive blood pressure, electrocardiography, capnography, and peripheral oxygen saturation were monitored, and intra- and postoperative arterial oxygen tension (PaO₂), arterial carbon dioxide tension (PaCO₂), and intraoperative peak airway pressure were compared between the 2 groups. Postoperative analgesic consumption was calculated. No significant differences in demographics or preoperative data were noted between the 2 groups. PaO₂ values 10 minutes after OLV onset and 10 minutes after the end of OLV were increased significantly in the NS group compared with those in the SHS group (p < 0.05). PaO₂ values after 10 minutes of OLV in the NS and SHS groups were 285.5 ± 90 mmHg and 186.7 ± 66 mmHg, respectively. PaO₂ values after OLV termination in the NS and SHS groups were 365.8 ± 58 mmHg and 283.6 ± 64 mmHg (p < 0.05), respectively. PaCO₂ values 10 minutes after OLV onset, 10 minutes after the end of OLV, at the end of surgery, and upon arrival in the intermediate care unit were significantly different between the 2 groups (p < 0.05).

CONCLUSION

The present study demonstrated that during OLV, patients exposed to SHS exhibited significantly lower arterial oxygen pressure compared with nonsmokers. Arterial carbon dioxide values were increased significantly in SHS-exposed patients. Morphine consumption for postoperative analgesia also was increased in patients exposed to SHS compared with that in nonsmokers.

Oxygenation, inflammatory response and lung injury during one lung ventilation in rabbits using inspired oxygen fraction of 0.6 vs. 1.0

Maintaining adequate oxygenation during one-lung ventilation (OLV) requires high inspired oxygen fraction (FiO₂). However, high FiO₂ also causes inflammatory response and lung injury. Therefore, it remains a great interest to clinicians and scientists to optimize the care of patients undergoing OLV. The aim of this study was to determine and compare oxygenation, inflammatory response and lung injury during OLV in rabbits using FiO₂ of 0.6 vs. 1.0. After 30 minutes of two-lung ventilation (TLV) as baseline, 30 rabbits were randomly assigned to three groups receiving mechanical ventilation for 3 hours: the sham group, receiving TLV with 0.6 FiO₂; the 1.0 FiO₂ group, receiving OLV with 1.0 FiO₂; the 0.6 FiO₂ group, receiving OLV with 0.6 FiO₂. Pulse oximetry was continuously monitored and arterial blood gas analysis was intermittently conducted. Histopathologic study of lung tissues was performed and inflammatory cytokines and the mRNA and protein of nuclear factor kappa B (NF-κB) p65 were determined. Three of the 10 rabbits in the 0.6 FiO₂ group suffered hypoxemia, defined by pulse oximetric saturation (SpO₂) less than 90%. Partial pressure of oxygen (PaO₂), acute lung injury (ALI) score, myeloperoxidase (MPO), tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), mRNA and protein of NF-κB p65 were lower in the 0.6 FiO₂ group than in the 1.0 FiO₂ group. In conclusion, during OLV, if FiO₂ of 0.6 can be tolerated, lung injury associated with high FiO₂ can be minimized. Further study is needed to validate this finding in human subjects.

Severe hypoxemia during carinal resection in the lateral position under one-lung ventilation of a non-dependent lung: a case report

During one-lung ventilation (OLV) in the lateral position, the dependent, ventilated lung receives more blood flow than the non-dependent, non-ventilated lung owing to gravity, improving the match of ventilation and perfusion. Conversely, in the rare clinical situations when OLV is applied to the non-dependent lung, arterial oxygenation can get worse due to considerable shunt flow to the dependent non-ventilated lung. We report a case of severe hypoxemia during carinal resection under OLV of a non-dependent lung. In this case, OLV had to be applied to the non-dependent lung in the lateral position because the bronchus of the non-dependent lung was anastomosed with the trachea, whereas the bronchus of the dependent lung had already been resected for carinal resection. The subsequent hypoxemia resulting from the shunt flow to the dependent non-ventilated lung was treated successfully by ligating the pulmonary artery of the dependent lung.

Perioperative lung protective ventilation in obese patients

The perioperative use and relevance of protective ventilation in surgical patients is being increasingly recognized. Obesity poses particular challenges to adequate mechanical ventilation in addition to surgical constraints, primarily by restricted lung mechanics due to excessive adiposity, frequent respiratory comorbidities (i.e. sleep apnea, asthma), and concerns of postoperative respiratory depression and other pulmonary complications. The number of surgical patients with obesity is increasing, and facing these challenges is common in the operating rooms and critical care units worldwide. In this review we summarize the existing literature which supports the following recommendations for the perioperative ventilation in obese patients: (1) the use of protective ventilation with low tidal volumes (approximately 8 mL/kg, calculated based on predicted -not actual- body weight) to avoid volutrauma; (2) a focus on lung recruitment by utilizing PEEP (8–15 cmH₂O) in addition to recruitment maneuvers during the intraoperative period, as well as incentivized deep breathing and noninvasive ventilation early in the postoperative period, to avoid atelectasis, hypoxemia and atelectrauma; and (3) a judicious oxygen use (ideally less than 0.8) to avoid hypoxemia but also possible reabsorption atelectasis. Obesity poses an additional challenge for achieving adequate protective ventilation during one-lung ventilation, but different lung isolation techniques have been adequately performed in obese patients by experienced providers. Postoperative efforts should be directed to avoid hypoventilation, atelectasis and hypoxemia. Further studies are needed to better define optimum protective ventilation strategies and analyze their impact on the perioperative outcomes of surgical patients with obesity.

Is small tidal volume with low positive end expiratory pressure during one-lung ventilation an effective ventilation method for endoscopic thoracic surgery?

Background

The present study will focus on the rationale for the use of small tidal volume with 6 cmH₂O positive end expiratory pressure (PEEP) with the changes of arterial oxygen tension, plateau airway pressure, and static lung compliance during one lung ventilation for endoscopic thoracic surgery.

Methods

Forty-three patients were intubated with a double-lumen endobronchial tube. After positioning the patients in the lateral decubitus, one-lung ventilation was started with 100% oxygen, tidal volume 10 ml/kg without PEEP; arterial oxygen tension, plateau airway pressure, and static compliance were checked as baseline values (T0). Fifteen minutes later, same parameters were measured (T15). The tidal volume had changed to 6 ml/kg with 6 cmH₂O PEEP. Fifteen minutes later, the same parameters were measured (T30).

Results

Oxygen tension had decreased at T15 (282.1 ± 83.4 mmHg) compared to T0 (477.2 ± 82.4 mmHg) (P < 0.0001), but was maintained at T30 (270.4 ± 81.9 mmHg). There was no difference in peak inspiratory pressure at T15 or T30 compared to T0, plateau airway pressure was increased at T15 and T30 (P < 0.05) and static lung compliance was decreased at T15 and T30 (P < 0.0001).

Conclusions

In carrying out one-lung ventilation for thoracic surgery using an endoscope, the addition of a PEEP of 6 cmH₂O in the dependent lung, while reducing the tidal volume of 6 ml/kg, both oxygen tension and lung compliance are maintained without increasing the plateau airway pressure. Protective lung ventilation is useful for one lung ventilation.

High-frequency jet ventilation using the Arndt bronchial blocker for refractory hypoxemia during one-lung ventilation in a myasthenic patient with asthma

A novel method in the management of refractory severe hypoxemia during one-lung ventilation (OLV) in a patient who presented with myasthenia gravis, asthma, a symptomatic mediastinal mass, hiatal hernia, and a moderate pericardial effusion is presented. The patient was scheduled for excision of a large anterior mediastinal mass and creation of a pericardial window through a left thoracotomy. One-lung ventilation was achieved using an Arndt bronchial blocker. High-frequency jet ventilation (HFJV) was applied to the surgical nondependent lung through the lumen of the Arndt endobronchial blocker with titration of positive end-expiratory pressure to the dependent lung. Oxygenation improved significantly. The use of HFJV through the Arndt blocker offers an effective method for treatment of refractory hypoxemia during OLV.

Current ventilation practice during general anaesthesia: a prospective audit in Melbourne, Australia

Background

Recent evidence suggests that the use of low tidal volume ventilation with the application of positive end-expiratory pressure (PEEP) may benefit patients at risk of respiratory complications during general anaesthesia. However current Australian practice in this area is unknown.

Methods

To describe current practice of intraoperative ventilation with regard to tidal volume and application of PEEP, we performed a multicentre audit in patients undergoing general anaesthesia across eight teaching hospitals in Melbourne, Australia.

Results

We obtained information including demographic characteristics, type of surgery, tidal volume and the use of PEEP in a consecutive cohort of 272 patients. The median age was 56 (IQR 42–69) years; 150 (55%) were male. Most common diagnostic groups were general surgery (31%), orthopaedic surgery (20%) and neurosurgery (9.6%). Mean FiO₂ was 0.6 (IQR 0.5-0.7). Median tidal volume was 500 ml (IQR 450-550). PEEP was used in 54% of patients with a median value of 5.0 cmH₂O (IQR 4.0-5.0) and median tidal volume corrected for predicted body weight was 9.5 ml/kg (IQR 8.5-10.4). Median peak inspiratory pressure was 18 cmH₂O (IQR 15–22). In a cohort of patients considered at risk for respiratory complications, the median tidal volume was still 9.8 ml/kg (IQR 8.6-10.7) and PEEP was applied in 66% of patients with a median value of 5 cmH₂0 (IQR 4–5). On multivariate analyses positive predictors of tidal volume size included male sex (p < 0.01), height (p = 0.04) and weight (p < 0.001). Positive predictors of the use of PEEP included surgery in a tertiary hospital (OR = 3.11; 95% CI: 1.05 to 9.23) and expected prolonged duration of surgery (OR = 2.47; 95% CI: 1.04 to 5.84).

Conclusion

In mechanically ventilated patients under general anaesthesia, tidal volume was high and PEEP was applied to the majority of patients, but at modest levels. The findings of our study suggest that the control groups of previous randomized controlled trials do not closely reflect the practice of mechanical ventilation in Australia.

Adaptive servo-ventilation therapy using an innovative ventilator for patients with chronic heart failure: a real-world, multicenter, retrospective, observational study (SAVIOR-R)

Adaptive servo-ventilation (ASV) therapy using an innovative ventilator—originally developed to treat sleep-disordered breathing (SDB)—is a novel modality of noninvasive positive pressure ventilation and is gaining acceptance among Japanese cardiologists in expectation of its applicability to treat patients with chronic heart failure (CHF) based on its acute beneficial hemodynamic effects. We conducted a multicenter, retrospective, real-world observational study in 115 Japanese patients with CHF, who had undergone home ASV therapy for the first time from January through December 2009, to examine their profile and the effects on their symptoms and hemodynamics. Medical records were used to investigate New York Heart Association (NYHA) class, echocardiographic parameters including left ventricular ejection fraction (LVEF), cardiothoracic ratio (CTR), brain natriuretic peptide (BNP), and other variables. Most of the patients were categorized to NYHA classes II (44.4 %) and III (40.7 %). SDB severity was not determined in 44 patients, and SDB was not detected or was mild in 27 patients. In at least 71 patients (61.7 %), therefore, ASV therapy was not applied for the treatment of SDB. CHF was more severe, i.e., greater NYHA class, lower LVEF, and higher CTR, in 87 ASV-continued patients (75.7 %) than in 28 ASV-discontinued patients (24.3 %). However, SDB severity was not related to continuity of ASV. The combined proportion of NYHA classes III and IV (P = 0.012) and LVEF (P = 0.009) improved significantly after ASV therapy. CTR and BNP did not improve significantly after ASV therapy but showed significant beneficial changes in their time-course analysis (P < 0.05, respectively). Improvements in LVEF and NYHA class after ASV therapy were not influenced by SDB severity at onset. The present study suggests that ASV therapy would improve the symptoms and hemodynamics of CHF patients, regardless of SDB severity. A randomized clinical study to verify these effects is warranted.

Respiratory function during anesthesia: effects on gas exchange

Anaesthesia causes a respiratory impairment, whether the patient is breathing spontaneously or is ventilated mechanically. This impairment impedes the matching of alveolar ventilation and perfusion and thus the oxygenation of arterial blood. A triggering factor is loss of muscle tone that causes a fall in the resting lung volume, functional residual capacity. This fall promotes airway closure and gas adsorption, leading eventually to alveolar collapse, that is, atelectasis. The higher the oxygen concentration, the faster will the gas be adsorbed and the aleveoli collapse. Preoxygenation is a major cause of atelectasis and continuing use of high oxygen concentration maintains or increases the lung collapse, that typically is 10% or more of the lung tissue. It can exceed 25% to 40%. Perfusion of the atelectasis causes shunt and cyclic airway closure causes regions with low ventilation/perfusion ratios, that add to impaired oxygenation. Ventilation with positive end-expiratory pressure reduces the atelectasis but oxygenation need not improve, because of shift of blood flow down the lung to any remaining atelectatic tissue. Inflation of the lung to an airway pressure of 40 cmH2O recruits almost all collapsed lung and the lung remains open if ventilation is with moderate oxygen concentration (< 40%) but recollapses within a few minutes if ventilation is with 100% oxygen. Severe obesity increases the lung collapse and obstructive lung disease and one-lung anesthesia increase the mismatch of ventilation and perfusion. CO2 pneumoperitoneum increases atelectasis formation but not shunt, likely explained by enhanced hypoxic pulmonary vasoconstriction by CO2. Atelectasis may persist in the postoperative period and contribute to pneumonia.

Anesthesia for thoracic surgery: a survey of middle eastern practice

Purpose:

The main objective of this survey is to describe the current practice of thoracic anesthesia in the Middle Eastern (ME) region.

Methods:

A prospective online survey. An invitation to participate was e-mailed to all members of the ME thoracic-anaesthesia group. A total of 58 members participated in the survey from 19 institutions in the Middle East. Questions concerned ventilation strategies during one-lung ventilation (OLV), anesthesia regimen, mode of postoperative analgesia, use of lung isolation techniques, and use of i.v. fluids.

Results:

Volume-controlled ventilation was favored over pressure-controlled ventilation (62% vs 38% of respondents, P<0.05); 43% report the routine use of positive end-expiratory pressure. One hundred percent of respondents report using double-lumen tube (DLT) as a first choice airway to establish OLV. Nearly a third of respondents, 31.1%, report never using bronchial blocker (BB) in their thoracic anesthesia practice. Failure to pass a DLT and difficult airway are the most commonly cited indications for BB use. Regarding postoperative analgesia, the majority 61.8% favor thoracic epidural analgesia over other techniques (P<0.05).

Conclusions:

Our survey provides a contemporary snapshot of the ME thoracic anesthetic practice.

Sudden generalized lung atelectasis during thoracotomy following thoracic lavage in 3 dogs

OBJECTIVE

To describe sudden onset of generalized pulmonary atelectasis following thoracic lavage in 3 dogs.

SERIES SUMMARY

Thoracic lavage was performed following ligation of a patent ductus arteriosus in case 1, prior to closure of a large traumatic full thickness wound in the chest wall in case 2, and during investigation of an idiopathic spontaneous pneumothorax in case 3. In each case anesthesia and surgery were uneventful until thoracic lavage was performed, after which sudden generalized pulmonary atelectasis was observed. The atelectasis was visualized and was associated with oxyhemoglobin desaturation, decreased end-tidal carbon dioxide partial pressure (ETCO(2)), and a marked increase in the peak inspiratory pressure (PIP) required to achieve visible lung inflation. Occlusion of the endotracheal tube and cervical trachea was directly eliminated as the cause of atelectasis in cases 1 and 2, and indirectly eliminated in case 3. Improvement in pulmonary function occurred in all cases in response to increased PIP ± positive end expiratory pressure (PEEP).

NEW OR UNIQUE INFORMATION PROVIDED

Generalized atelectasis should be considered a possible complication of thoracic lavage performed during thoracotomy. In the cases presented here, it is suspected that pre-existing reduction in lung volume (due to inadequate ventilation, surgical compression, absorption atelectasis) was exacerbated by the addition of the lavage fluid to the thoracic cavity. This pre-existing lung collapse is believed to have resulted in reduction of lung volume and that further reduction below the critical closing volume occurred following instillation of saline into the thorax resulting in the subsequent development of generalized atelectasis. The performance of regular arterial blood gas analyses and different ventilation protocols may have prevented the marked atelectasis that was observed in these cases.

On the crucial ventilatory setting adjustment from two- to one-lung ventilation

Lung mechanics, histology, oxygenation and type-III procollagen (PCIII) mRNA were studied aiming to evaluate the need to readjust ventilatory pattern when going from two- to one-lung ventilation (OLV). Wistar rats were assigned to three groups: the left lung was not ventilated while the right lung received: (1) tidal volume (V(T))=5 ml/kg and positive end-expiratory pressure (PEEP)=2 cm H(2)O (V5P2), (2) V(T)=10 ml/kg and PEEP=2 cm H(2)O (V10P2), and (3) V(T)=5 ml/kg and PEEP=5 cm H(2)O (V5P5). At 1-h ventilation, V5P2 showed hypoxemia, alveolar collapse and impaired lung function. Higher PEEP minimized these changes and prevented hypoxemia. Although high V(T) prevented hypoxemia and maintained a higher specific compliance than V5P2, a morphologically inhomogeneous parenchyma and higher PCIII expression resulted. In conclusion, the association of low V(T) and an adequate PEEP level could be useful to maintain arterial oxygenation without inducing a possible inflammatory/remodeling response.

Cardiac output estimation using pulmonary mechanics in mechanically ventilated patients

The application of positive end expiratory pressure (PEEP) in mechanically ventilated (MV) patients with acute respiratory distress syndrome (ARDS) decreases cardiac output (CO). Accurate measurement of CO is highly invasive and is not ideal for all MV critically ill patients. However, the link between the PEEP used in MV, and CO provides an opportunity to assess CO via MV therapy and other existing measurements, creating a CO measure without further invasiveness.

This paper examines combining models of diffusion resistance and lung mechanics, to help predict CO changes due to PEEP. The CO estimator uses an initial measurement of pulmonary shunt, and estimations of shunt changes due to PEEP to predict CO at different levels of PEEP. Inputs to the cardiac model are the PV loops from the ventilator, as well as the oxygen saturation values using known respiratory inspired oxygen content. The outputs are estimates of pulmonary shunt and CO changes due to changes in applied PEEP. Data from two published studies are used to assess and initially validate this model.

The model shows the effect on oxygenation due to decreased CO and decreased shunt, resulting from increased PEEP. It concludes that there is a trade off on oxygenation parameters. More clinically importantly, the model also examines how the rate of CO drop with increased PEEP can be used as a method to determine optimal PEEP, which may be used to optimise MV therapy with respect to the gas exchange achieved, as well as accounting for the impact on the cardiovascular system and its management.

Protective ventilation to reduce inflammatory injury from one lung ventilation in a piglet model

OBJECTIVES

To test the hypothesis that protective ventilation strategy (PVS) as defined by the use of low stretch ventilation (tidal volume of 5 ml x kg(-1) and employing 5 cm of positive end expiratory pressure (PEEP) during one lung ventilation (OLV) in piglets would result in reduced injury compared to a control group of piglets who received the conventional ventilation (tidal volume of 10 ml x kg(-1) and no PEEP).

BACKGROUND

PVS has been found to be beneficial in adults to minimize injury from OLV. We designed the current study to test the beneficial effects of PVS in a piglet model of OLV.

METHODS

Ten piglets each were assigned to either 'Control' group (tidal volume of 10 ml x kg(-1) and no PEEP) or 'PVS' group (tidal volume of 5 ml x kg(-1) during the OLV phase and PEEP of 5 cm of H2O throughout the study). Experiment consisted of 30 min of baseline ventilation, 3 h of OLV, and again 30 min of bilateral ventilation. Respiratory parameters and proinflammatory markers were measured as outcome.

RESULTS

There was no difference in PaO2 between groups. PaCO2 (P < 0.01) and ventilatory rate (P < 0.01) were higher at 1.5 h OLV and at the end point in the PVS group. Peak inflating pressure (PIP) and pulmonary resistance were higher (P < 0.05) in the control group at 1.5 h OLV. tumor necrosis factor-alpha (P < 0.04) and IL-8 were less (P < 0.001) in the plasma from the PVS group, while IL-6 and IL-8 were less (P < 0.04) in the lung tissue from ventilated lungs in the PVS group.

CONCLUSIONS

Based on this model, PVS decreases inflammatory injury both systemically and in the lung tissue with no adverse effect on oxygenation, ventilation, or lung function.

Update on one-lung ventilation: the use of continuous positive airway pressure ventilation and positive end-expiratory pressure ventilation--clinical application

PURPOSE OF REVIEW

The purpose of this review is to examine the evidence for and the clinical use of continuous positive airway pressure (CPAP) and positive end-expiratory pressure (PEEP) for the management of one-lung ventilation during thoracic surgery. CPAP and PEEP use are important as we are increasingly challenged with patients with less respiratory reserve and greater comorbidity leading to the need for greater clinical management and more interventions during one-lung ventilation for thoracic surgery to prevent perioperative complications.

RECENT FINDINGS

The focus of this article is on the most recent literature with selected classic articles. First, the supportive literature and rationale for application of PEEP, CPAP or both during thoracic surgery are reviewed, relative to the threats of hypoxemia, hyperoxia and mechanical lung injury. The second part of the article focuses on the clinical use of PEEP and CPAP. Algorithms for the application of CPAP and PEEP to patients both at risk and not at risk of acute lung injury are presented.

SUMMARY

CPAP and PEEP are useful not only to treat hypoxia and atelectasis as the consequence of one-lung ventilation, perhaps more importantly, also as part of a protective lung-ventilation strategy to ameliorate mechanical stress and prevent acute lung injury.

Ventilatory management during routine general anaesthesia

Intraoperative hypoxaemia and postoperative respiratory complications remain the challenges of modern anaesthetic practice. Anaesthesia causes both depression of respiratory centres and profound changes of respiratory mechanics. Most anaesthetized patients consequently require mechanical ventilation and supplemental oxygen. Recent data suggest that intraoperative respiratory management of a patient can affect postoperative outcome. In this review, we briefly describe the mechanisms responsible for the impairment of intraoperative gas exchange and provide guidelines to prevent or manage hypoxaemia. Moreover, we discuss several aspects of mechanical ventilation that can be employed to improve patients' outcome.

Physiological effects of a lung-recruiting strategy applied during one-lung ventilation

BACKGROUND

One-lung ventilation (OLV) affects respiratory mechanics and ventilation/perfusion matching, reducing functional residual capacity of the ventilated lung. While the application of a lung-recruiting manoeuvre (RM) on the ventilated lung has been shown to improve oxygenation, data regarding the impact of RM on respiratory mechanics are not available.

METHODS

Thirteen patients undergoing lung resection in lateral decubitus were studied. During OLV, a lung-recruiting strategy consisting in a RM lasting 1 min followed by the application of positive end-expiratory pressure 5 cmH(2)O was applied to the ventilated lung. Haemodynamics, gas exchange and respiratory mechanics parameters were recorded on two-lung ventilation (TLV(baseline)), OLV before and 20 min after the RM (OLV(pre-RM), OLV(post-RM), respectively) and TLV(end). Haemodynamics parameters were also recorded during the RM.

RESULTS

The PaO(2)/FiO(2) ratio was 358+/-126 on TLV(baseline); it decreased to 235+/-113 on OLV(pre-RM) (P<0.01) increased to 351+/-120 on OLV(post-RM) (P<0.01 vs. OLV(pre-RM)), and remain stable thereafter. During the RM, CI decreased from 3.04+/-0.7 l/m(2) OLV(pre-RM) to 2.4+/-0.6 l/m(2) (P<0.05), and returned to baseline on OLV(post-RM) (3.1+/-0.7 l/m(2), NS vs. OLV(pre-RM)). The RM resulted in alveolar recruitment and caused a significant decrease in static elastance of the dependent lung (16.6+/-8.9 cmH(2)O/ml OLV(post-RM) vs. 22.3+/-8.1 cmH(2)O/ml OLV(pre-RM)) (P<0.01).

CONCLUSIONS

During OLV in lateral decubitus for thoracic surgery, application to the dependent lung a recruiting strategy significantly recruits the dependent lung, improving arterial oxygenation and respiratory mechanics until the end of surgery. However, the transient haemodynamic derangement occurring during the RM should be taken into account.

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 (TL V) in the lateral position, all patients received OL V 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 TL V (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.

Anesthesia for thoracic surgery in morbidly obese patients

PURPOSE OF REVIEW

This review considers the anesthetic management of obese patients undergoing thoracic surgery. Extremely or morbidly obese patients differ from patients of normal weight in several ways. Obese patients have altered anatomy and physiology, and usually have associated comorbid medical conditions that may complicate their operative course and increase their risks for postoperative complications.

RECENT FINDINGS

During anesthetic induction and laryngoscopy for tracheal intubation the morbidly obese patient should be in the reverse Trendelenburg position with the head and neck elevated above the table. Placement of a double-lumen tube should be no more difficult in an obese patient than in a normal-weight patient. There are no clear advantages for any of the commonly available inhalational anesthetic agents and each can be used for general anesthesia.

SUMMARY

With proper attention to their special needs, the morbidly obese patient can safely undergo thoracic surgery and one-lung ventilation.

Prise en charge anesthésique de l'œsophagectomie: avancées et perspectives

Oesophagectomy is still characterized by a high postoperative mortality and respiratory morbidity. Nevertheless, epidemiological, medical and surgical advances have improved the management of this surgical procedure. The anaesthesiologist influence is present at each level, from the preoperative evaluation to the management of postoperative complications. The preoperative period is improved by the use of assessment scores, the better knowing of respiratory risk factors and of the neoadjuvant therapy adverse effects. The main objective of the operative period is to ensure a rapid weaning procedure and stability of the respiratory and haemodynamic functions, warranting the anastomotic healing. The interest of the association between respiratory rehabilitation and thoracic epidural analgesia is highlighted in the postoperative period. The management of postoperative complications, mainly represented by respiratory failure and anastomotic leakages, requires a multidisciplinary analysis. The potential interest of non-invasive ventilation and of the modulation of postoperative inflammatory response needs further investigation.

Histochemical Alterations in One Lung Ventilation

BACKGROUND

One lung ventilation is a commonly performed surgical procedure. Although there have been several reports showing that one-lung ventilation can cause pathophysiological alterations such as pulmonary hypoxic vasoconstriction and intrapulmonary shunting, there have been virtually no reports on the effects of one-lung ventilation on lung histology.

MATERIALS AND METHODS

Yorkshire pigs (11-17 kg) were anesthetized, a tracheotomy performed and a tracheal tube inserted. The chest was opened and one lung ventilation (OLV), was induced by clamping of the right main bronchus. OLV was continued for 60 min before the clamp was removed and two lung ventilation (TLV) started. TLV was continued for 30 to 60 min. Blood and lung biopsies were taken immediately before OLV, 30 min and 60 min of OLV and after restoration of TLV.

RESULTS

Histological analyses revealed that the non-ventilated lung was totally collapsed during OLV. On reventilation, there was clear evidence of vascular congestion and alveolar wall thickening at 30 min after TLV. At 60 min of TLV, there was still vascular congestion. Serum nitrite levels (as an index of nitric oxide production) showed steady decline over the course of the experimental period, reaching a significantly low level on reventilation (compared with baseline levels before OLV). Lung MPO activity (marker of neutrophil sequestration) and serum TNFalpha levels were not raised during the entire experimental period.

CONCLUSIONS

These results suggest that there was lung vascular injury after OLV, which was associated with reduced levels of nitric oxide production and not associated with an inflammatory response.