Thoracic epidural anaesthesia combined with general anaesthesia versus general anaesthesia alone for one-lung ventilation

  • Protocol
  • Intervention

Authors


Abstract

This is the protocol for a review and there is no abstract. The objectives are as follows:

To evaluate the effectiveness and safety of thoracic epidural anaesthesia combined with general anaesthesia versus general anaesthesia alone for reducing either the clinical outcomes or shunt fraction consequent from the establishment of OLV.

Background

Description of the condition

One-lung ventilation (OLV) is the process of excluding one lung from ventilation using airways designed for this purpose. It was developed to improve surgical access for certain thoracic procedures such as lung, oesophageal, aortic or mediastinal surgery (Karzai 2009) and to protect the ventilated lung from contamination with blood or pus from the operated side. OLV was first described in 1931 by Gale and Waters (Brodsky 2005) and quickly resulted in the development of increasingly complex lung resection surgery. OLV is now used for almost all thoracic operations in which the lung is operated on, or in which the collapse of the lung improves access to the operation field. However, during OLV, the adequacy of arterial oxygenation is threatened because blood that flows through the non-ventilated lung cannot be oxygenated (Bassi 2008). Thus, the blood flow to the non-ventilated lung is wasted perfusion and blood flowing back to the left heart will be low in oxygen (a right-to-left shunt of deoxygenated blood). In addition, there are other factors that may contribute to hypoxia in OLV such as neuromuscular blockade with positive pressure ventilation that favours preferential ventilation of the non-dependent zones of the lung and inhalational agents that block the hypoxic pulmonary vasoconstriction reflex. Both clinicians and researchers quantify this 'wasted perfusion' as the shunt fraction: the percentage of blood put out by the heart that is not completely oxygenated. There is a normal shunt fraction of about 5% and, theoretically, the right-to-left shunt in the non-ventilated lung plus this normal 5% of blood going through the ventilated lung leads to a shunt fraction in excess of 50% (Lohser 2008) and marked hypoxaemia. On the other hand, both passive and active mechanisms play a role in decreasing the blood flow to the non-ventilated lung. Surgical manipulation and gravity passively reduce the blood flow to the non-ventilated lung, and hypoxic pulmonary vasoconstriction actively increases vascular resistance in the non-ventilated lung, leading to a further decrease in blood flow (Lohser 2008). Multiple reports suggest that hypoxaemia during OLV, defined by a decrease in arterial haemoglobin oxygen saturation (SaO2) to less than 90%, occurs in 5% to 10% of patients (Guenoun 2002; Hurford 1993; Slinger 1988; Slinger 1992). If not appropriately managed in these patients, OLV may result in significant morbidity and mortality from tissue hypoxia.

Description of the intervention

Thoracic epidural anaesthesia is a central neuraxial block technique and involves the use of local anaesthetics injected into the thoracic epidural space to produce a reversible loss of sensation and motor function. It has many benefits, such as reducing the need for intravenous or inhalational analgesia, excellent postoperative analgesia and fast recovery of gastrointestinal function. General anaesthesia refers to the use of a variety of intravenous or inhalational agents (or both) to render the patient unconscious. To date, both thoracic epidural anaesthesia combined with general anaesthesia and general anaesthesia alone have been used for maintaining OLV.

How the intervention might work

Hypoxic pulmonary vasoconstriction (HPV) is an adaptive mechanism unique to the pulmonary circulation that allows redirection of blood flow to alveoli with higher oxygen tension, thereby reducing the blood flow through the non-ventilated lung (known as a ventilation/perfusion mismatching). HPV is of greatest benefit when 30% to 70% of the lung is made hypoxic (Marshall 1980). During OLV, it is well recognized that volatile anaesthetic agents such as ether, halothane and nitrous oxide inhibit HPV in a dose-dependent fashion, whereas most intravenous anaesthetics do not inhibit HPV (Benumof 1985; Eisenkraft 1990; Lohser 2008). Thoracic epidural anaesthesia is frequently used for intraoperative and postoperative analgesia in thoracic surgical patients and its role in OLV remains under debate. In experimental studies, epidural anaesthesia did not inhibit HPV (Ishibe 1996; Pfitzner 2006), which may reduce the right-to-left shunt in OLV.

Why it is important to do this review

There have been several small randomized controlled trials (RCTs) comparing thoracic epidural anaesthesia combined with general anaesthesia versus general anaesthesia alone for OLV (Garutti 2003; Ozcan 2007; Xu 2010). However, no consistent conclusion has been drawn from these individual studies. We aim to summarize the results of all available data systematically to generate the best evidence for the role of epidural anaesthesia in OLV.

Objectives

To evaluate the effectiveness and safety of thoracic epidural anaesthesia combined with general anaesthesia versus general anaesthesia alone for reducing either the clinical outcomes or shunt fraction consequent from the establishment of OLV.

Methods

Criteria for considering studies for this review

Types of studies

We will include all RCTs that compare thoracic epidural anaesthesia combined with general anaesthesia versus general anaesthesia alone for OLV. We will exclude cross-over studies and cluster RCTs.

Types of participants

We will include all adult patients (18 years of age or older) undergoing OLV, both emergency and elective cases. We will exclude participants who only have one lung.

Types of interventions

The intervention group will be patients undergoing OLV under thoracic epidural anaesthesia combined with general anaesthesia. The control group will be all patients undergoing OLV under general anaesthesia alone, either maintained with intravenous anaesthetics, inhalational anaesthetics or both.

For inclusion, the trial methodology must include confirmation by direct observation that OLV has been successfully established, and confirmation by fibreoptic bronchoscopy that the tracheal tube is correctly positioned.

Types of outcome measures

Primary outcomes
  1. Hospital mortality.

  2. Major morbidity such as cerebral anoxic injury and myocardial infarction, as defined in the individual included studies.

Secondary outcomes
  1. Length of intensive care unit (ICU) stay: measured in days.

  2. Time to extubation: measured in minutes, defined by discontinuation of propofol infusion/inhaled anaesthesia until extubation.

  3. Hypoxaemia: defined as a decrease in arterial haemoglobin oxygen saturation (SaO2) to less than 90%.

  4. Intrapulmonary shunt fraction. We will calculate shunt fraction according to the formula shown in Appendix 1.

  5. Complications associated with the thoracic epidural anaesthesia such as: cardiac arrest, bleeding, infections, postspinal headache and prolonged neurological (medullary or peripheral) injury lasting more than one month.

Outcomes will not form part of the study eligibility assessment so that studies that meet the participant, intervention and comparison criteria will be included in the review even if they report no relevant outcomes.

Search methods for identification of studies

Electronic searches

We will search the following databases: the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library, latest issue), MEDLINE via Ovid SP (1956 to date) and EMBASE via Ovid SP (1980 to present). We will perform electronic searches using exploded Medical Subject Headings and the appropriate corresponding keywords in combination with the sensitivity-maximizing RCT search strategy (Higgins 2011). We will not apply any language restrictions.

We will search MEDLINE using the search strategy described in Appendix 2. We will adopt our MEDLINE search strategy for searching other databases.

Searching other resources

We will search for ongoing trials in the following registers:

  1. WHO International Clinical Trials Registry Platform;

  2. clinicaltrials.gov;

  3. metaRegister of Controlled Trials;

  4. other national trial registries, such as the Centre for Clinical Trials (China), Clinical Trials Registry (India) and The Netherlands National Trial Register.

We will check the reference lists of all eligible trials and reviews. We will also contact experts in this field in order to identify unpublished research and trials still underway.

Data collection and analysis

Selection of studies

We will combine the results of the searches above and exclude duplicate records. Two authors (FW and YW) will independently screen all titles and abstracts for eligibility. The authors will independently record the reason for excluding each trial. A copy of the 'Study selection form' we will use will be can be found in Appendix 3.

We will resolve any disagreements by consensus or by consulting with a third author (XD) who will arbitrate on trial inclusion. If further information is required to make a decision about trial inclusion, we will contact the first author of the relevant trial (LT).

We will compile a list of all eligible trials. (See Appendix 4 for a copy of the 'Form for eligible trials').

Data extraction and management

Two authors (FW and YW) will independently extract data using a standardized data extraction form. A copy of the form we will use can be found in Appendix 5. We will resolve any disagreements by discussion and, if necessary, by consulting with a third author (XD). If further information is required, we will contact corresponding authors via email (LT).

Assessment of risk of bias in included studies

Two authors (FW and YW) will independently assess the methodological quality of the eligible trials using the 'Risk of bias' tool described in Chapter 8 of the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). A copy of the form we will use can be found in Appendix 6. We will resolve disagreements by discussion, where necessary, with the help of a third review author (XD).

We will use the following criteria to assess the risk of bias of the included studies: the quality domains of random sequence generation, allocation concealment, blinding of participants and personnel, blinding of outcome assessment, incomplete outcome data, selective reporting and any other potential threats to validity.

We will consider a trial as having a low risk of bias if all domains are assessed as adequate. We will consider a trial as having a high risk of bias if one or more domain is assessed as inadequate or unclear. We will report the 'Risk of bias' table as part of the 'Characteristics of included studies' table and present a 'Risk of bias' summary figure which will detail all of the judgements made for all included studies in the review.

Measures of treatment effect

We will use odds ratio (OR) as a measure of effect for dichotomous outcomes (such as the incidence of hypoxaemia). We will use mean difference (MD) for continuous variables.

Unit of analysis issues

The individual participant in each clinical trial will be the unit of analysis. We will exclude cross-over studies and cluster RCTs.

Dealing with missing data

We will contact the authors of included trials to obtain missing data necessary for meta-analysis (LT). If this fails, we will calculate standard deviations from the standard errors or confidence intervals, as described in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2011). Where standard deviations cannot be calculated, we will impute these using the mean of the reported standard deviations from the other trials.

We will address the impact of missing data in the discussion section of the review.

Assessment of heterogeneity

We will assess the clinical heterogeneity of the included studies according to their clinical and methodological diversity ('Risk of bias' assessment). We will address clinical heterogeneity using subgroup analyses.

We will assess statistical heterogeneity using visual inspection of the forest plot and the I2 statistic. We will consider significant statistical heterogeneity to be present when the I2 value is greater than 50%.

Assessment of reporting biases

We will construct funnel plots to assess any publication bias if more than 10 trials are included in our systematic review.

Data synthesis

If the degree of heterogeneity is not excessive, we will generate a quantitative summary by meta-analysis using Review Manager software (RevMan 5.1). We will use a fixed-effect model if there is no significant heterogeneity among studies. We will use a random-effects model if the P value for the Cochran Q statistic is less than 0.1.

Subgroup analysis and investigation of heterogeneity

We will perform subgroup analysis for different measured time points and agents of general anaesthesia and epidural anaesthesia. We will compare subgroups using an interaction term if appropriate.

Subgroup analysis according to measured time point:

  • 10 minutes after one-lung ventilation

  • 15 minutes after one-lung ventilation

  • 20 minutes after one-lung ventilation

  • 30 minutes after one-lung ventilation

Subgroup analysis according to agents of general anaesthesia:

  • Control patients received intravenous general anaesthesia

  • Control patients received inhalational general anaesthesia

  • Control patients received both intravenous and inhalational general anaesthesia

Subgroup analysis according to agents of epidural anaesthesia:

  • Patients received opiates alone for epidural anaesthesia

  • Patients received local anaesthetics alone for epidural anaesthesia

  • Patients received mixed agents for epidural anaesthesia

Sensitivity analysis

We will perform sensitivity analysis to exclude trials at high risk of bias or trials with significant clinical heterogeneity. We will compare random-effects and fixed-effect estimates of each outcome variable. To assess the influence of the trials which have imputed standard deviation (SD) data, we will perform sensitivity analyses based on the 'borrowed' data. If sensitivity analyses identify particular factors that influence the conclusions of the review, we will explore the potential causes of the uncertainties and interpret the result of the review with caution.

Summary of findings

We will use the principles of the GRADE system (Guyatt 2008) to assess the quality of the body of evidence associated with the specific outcomes intrapulmonary shunting, hypoxaemia, time to extubation, hospital mortality, length of ICU stay and complications associated with thoracic epidural anaesthesia in our review and construct a 'Summary of findings' (SOF) table using the GRADE software. The GRADE approach appraises the quality of a body of evidence based on the extent to which one can be confident that an estimate of effect or association reflects the item being assessed. The quality of a body of evidence considers the study methodological quality, the directness of the evidence, heterogeneity of the data, precision of the effect estimates and the risks of publication bias.

Acknowledgements

We would like to thank Mike Bennett (content editor), Marialena Trivella (statistical editor), Javier Eslava-Schmalbach and Joanne Guay (peer reviewers) for their help and editorial advice during the preparation of this protocol for the systematic review.

We also want to thank Jane Cracknell (Manager Editor, Cochrane Anaesthesia Review Group (CARG)) for her assistance in the preparation of this protocol.

Appendices

Appendix 1. Shunt fraction

The shunt fraction (Qs/Qt) will be calculated from the formula:

  1. Qs/Qt = (CcO2 - CaO2)/(CcO2 - CvO2)

  2. CcO2 = (Hb * 1.34) + (PAO2 * 0.0031)

  3. C (a or v) O2 = (Hb * 1.34 * %Saturation) + (0.0031 * PO2)

  4. PAO2 = FiO2 (Pb - PH2O) - (PaCO2/0.8)

Qs means the amount of shunted blood (blood not participating in gas exchange). 

Qt means the total cardiac output.

CcO2 means the oxygen content of pulmonary capillary blood.

CaO2 means oxygen content of arterial blood.

CvO2 means oxygen content of mixed venous blood.

PAO2 means partial pressure of oxygen in alveolar air.

PaO2 means partial pressure of oxygen in arterial blood.

PvO2 means partial pressure of oxygen in mixed venous blood.

Hb = haemoglobin.  

%Saturation = % oxygen saturation in arterial blood or mixed venous blood.

FiO2 = fraction of inspiration O2.

Pb = pressure of atmosphere.

PaCO2 = partial pressure of carbon dioxide in arterial blood.

Appendix 2. OVID MEDLINE search strategy

1 exp Respiration, Artificial/ or exp One-Lung Ventilation/ or ((one or single) adj3 lung*).af.
2 ((thoracic or epidural) adj3 an?esth*).ti,ab. or exp Anesthesia, Epidural/ or exp Anesthesia, General/ or exp Anesthesia, Inhalation/ or exp Anesthesia, Intravenous/
3 1 and 2
4 ((randomized controlled trial or controlled clinical trial).pt. or randomized.ab. or placebo.ab. or clinical trials as topic.sh. or randomly.ab. or trial.ti.) not (animals not (humans and animals)).sh.
5 3 and 4

Appendix 3. Study selection form

Thoracic epidural anaesthesia combined with general anaesthesia versus general anaesthesia alone for one-lung ventilation

Study selection form

1. General information

First author Year Publication type Reviewer Review date Title reviewed Abstract reviewed Full text reviewed
        

 2. Study selection guidelines

Study characteristics Eligibility criteria Result
YesNoUnclear
Types of studiesRCT   
Types of participantsAdult patients (18 years of age or older) undergoing an elective one-lung ventilation surgical procedure   
Types of intervention

The control group will be all patients undergoing general anaesthesia, either intravenous anaesthesia or inhalational anaesthesia

The intervention group will be all patients undergoing thoracic epidural anaesthesia combined with general anaesthesia

   
Types of outcome measuresRelevant outcomes (intrapulmonary shunting, hospital mortality, time to extubation, length of ICU stay, hypoxaemia, complications associated with thoracic epidural anaesthesia)   
          Included                                      Excluded
Reason for exclusion 

Appendix 4. Eligible trials form

Thoracic epidural anaesthesia combined with general anaesthesia versus general anaesthesia alone for one-lung ventilation

Eligible trials form

Unique ID ISDN Author(s) Publication type Year
1    
2    
3    

Appendix 5. Data extraction form

Thoracic epidural anaesthesia combined with general anaesthesia versus general anaesthesia alone for one-lung ventilation

Data extraction form

Unique ID       ISDN  First author    Year Reviewer Review date
      

 Study methods and details

Trial characteristics Details
Country/countries 
Participant inclusion criteria 
Participant exclusion criteria 
Mean or median age of participants 
Gender of participants 
Baseline imbalances 
Surgery information 
How many participants were randomized? 

Number of participants allocated to:

Combined anaesthesia

General anaesthesia alone

 

Number of participants analysed:

Combined anaesthesia

General anaesthesia alone

 
Combined anaesthesia method 
General anaesthesia alone method 
Outcome definition 

Outcomes

For continuous data

Outcome Combined anaesthesia group General anaesthesia alone group
n Mean SD n Mean SD
Qs/Qt (10 minutes)      
Qs/Qt (15 minutes)      
Qs/Qt (20 minutes)      
Qs/Qt (30 minutes)      
PaO2 (10 minutes)      
PaO2 (15 minutes)      
PaO2 (20 minutes)      
PaO2 (30 minutes)      
Length of ICU stay      
Time to extubation      
Length of hospital stay      
Vasopressin requirement      

 For dichotomous data

Outcome Combined anaesthesia General anaesthesia alone
Number with event Number without event Number with event Number without event
Hypoxia    
Bleeding    
Infections    
Postspinal headache    
Pneumonia    
Hospital mortality    

Appendix 6. Quality assessment form

Thoracic epidural anaesthesia combined with general anaesthesia versus general anaesthesia alone for one-lung ventilation

Quality assessment form

Unique ID       ISDN  First author    Year Reviewer Review date
      
Domain Describe Risk of bias
1. Adequate sequence generation  Low/High/Unclear
2. Allocation concealment  Low/High/Unclear
3. Blinding of participants and personnel  Low/High/Unclear
Blinding of outcome assessment  Low/High/Unclear
4. Incomplete outcome data  Low/High/Unclear
5. Selective outcome reporting  Low/High/Unclear
6. Other potential threats to validity  Low/High/Unclear

Contributions of authors

Fei Wang (FW), Youping Wu (YW), Lu Tang (LT), Chengjie Gao (CG), Jinbao Li (JL) and Xiaoming Deng (XD)

FW, YW and LT contribute equally and they are all first authors. JL and XD are co-corresponding authors.

Conceiving the review: FW, YW, LT, CG, JL, XD

Co-ordinating the review: JL, XD

Undertaking manual searches: FW, YW

Screening search results: FW, YW

Organizing retrieval of papers: LT

Screening retrieved papers against inclusion criteria: FW, YW

Appraising quality of papers: FW, YW

Abstracting data from papers: FW, YW

Writing to authors of papers for additional information: FW, YW

Providing additional data about papers: FW, YW

Obtaining and screening data on unpublished studies: FW, YW

Data management for the review: LT, CG

Entering data into Review Manager (RevMan 5.1): FW, YW, LT, CG

RevMan statistical data: FW, YW, LT, CG

Other statistical analysis not using RevMan: FW, YW, LT, CG

Interpretation of data: FW, YW

Statistical inferences: FW, YW

Writing the review: FW, YW, LT, JL, CG, XD

Securing funding for the review: JL, XD

Performing previous work that was the foundation of the present study: FW, YW, LT, CG, JL, XD

Guarantor for the review (one author): FW

Person responsible for reading and checking the review before submission: FW

Declarations of interest

Fei Wang: none known

Youping Wu: none known

Lu Tang: none known

Chengjie Gao: none known

Jinbao Li: none known

Xiaoming Deng: none known

Ancillary