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Cochrane Database of Systematic Reviews Protocol - Intervention

High concentration versus low concentration sevoflurane for anaesthesia induction

Authors' declarations of interest

Version published: 17 October 2007 Version history

https://doi.org/10.1002/14651858.CD006837

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view the current version 29 June 2016
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Abstract

This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:

We aim to compare the induction time and complication rates between high and low concentration sevoflurane anaesthetic induction techniques in patients who received gas induction for general anaesthesia.

Background

General anaesthesia (GA) may be induced either by intravenous injection (IV induction) or by breathing in a volatile anaesthetic agent along with oxygen through a mask (inhalational induction). Inhalational anaesthetic induction may be the preferred method in children and in some adult patients who refuse intravenous cannulation (Eger II 2003) or have poor venous access. One of the commonly used volatile anaesthetic agents for inhalational induction of anaesthesia is sevoflurane (Ulthane™, Sevorane™). Sevoflurane (2, 2, 2 ‐trifluoro‐1‐[trifluoromethyl] ethyl fluoromethyl ether) was first introduced into clinical practice in Japan in 1990 and is sweet‐smelling, non‐flammable and less irritating to mucous membranes.

Induction of anaesthesia with sevoflurane has been reported to be safe, reliable and well accepted by patients (van den Berg 2005). Its characteristics are: inherent stability; low flammability; non‐pungent odour; limited irritation to airways; low blood or gas anaesthetic solubility, which allows rapid induction of, and emergence from, anaesthesia; minimal cardiovascular and respiratory side effects; and minimal end‐organ effects (Delgado‐Herrera 2001). Sevoflurane's muscle relaxation properties allow the insertion of a laryngeal mask airway (LMA) or endotracheal intubation (Aantaa 2001) without a muscle relaxant.

Inhalational induction of anaesthesia with sevoflurane uses either low or high concentrations of sevoflurane. The low concentration technique involves initially administering a low concentration of sevoflurane, then increasing the concentration until the patient is anaesthetized (Eger II 2003). The high concentration technique involves administering high concentrations of sevoflurane (from 6% to 8 %) from the beginning, continuing until the patient is anaesthetized (Eger II 2003). Both techniques can be carried out using different breathing patterns, either vital capacity or tidal volume breathing. The vital capacity method consists of breathing out the residual volume then taking a maximal breath and holding as long as is comfortable followed by spontaneous respiration; and the tidal volume method involves normal breathing and respiratory rate.

Other interventions or medications can be used to improve the quality of induction of anaesthesia (for example inspiratory pressure support at 15 cm H2O using an anaesthetic ventilator (Banchereau 2005)); priming of the breathing circuit with high concentration sevoflurane in oxygen, with or without nitrous oxide prior induction of anaesthesia (Yurino 1995); use of nitrous oxide with sevoflurane and oxygen (Dubois 1999; O'Shea 2001); use of sufentanil (Meaudre 2004), midazolam (Nishiyama 2002) or clonidine (Watanabe 2006) before induction of anaesthesia. Induction time, the time to loss of eyelash reflex (LOER), is measured to compare the efficacy of the different methods. However, complications during the induction of anaesthesia such as coughing, salivation, failed induction at the first attempt, laryngospasm, breath holding, apnea, severe movement or panic reaction, hypotension, an epileptiform electroencephalogram (EEG) and bradycardia can increase the morbidity (Epstein 1998; Kaisti 1999; Martin‐Larrauri 2004; Roodman 2003; Vakkuri 2001; Yurino 1995).

High concentration volatile anaesthetic induction has been reported to result in a shorter (faster) induction time (Epstein 1998; Martin‐Larrauri 2004). A shorter induction time is the preferred choice. But this may be accompanied by a number of complications such as breath holding, laryngospasm, severe movement and hypotension (Dubois 1999; Epstein 1998; Martin‐Larrauri 2004). More frequent and longer duration apnea after induction (Pancaro 2005) with a high concentration of sevoflurane and a higher incidence of bradycardia (Green 2000) and epileptiform EEG (Constant 2005; Vakkuri 2001) have been reported.

We aim to compare the induction times and the risk of complications between two the induction methods, low concentration and high concentration of sevoflurane induction of anaesthesia. A technique having a shorter induction time and lower complication rate may help us to choose the optimum volatile anaesthetic induction technique using sevoflurane.

Objectives

We aim to compare the induction time and complication rates between high and low concentration sevoflurane anaesthetic induction techniques in patients who received gas induction for general anaesthesia.

Methods

Criteria for considering studies for this review

Types of studies

We will include all published and unpublished randomized controlled trials (RCTs) comparing high concentration gas induction versus low concentration gas induction. Any studies reported only in abstract form will be included in the studies awaiting assessment category.

Types of participants

We will include patients of all ages receiving an sevoflurane induction technique for general anaesthesia.

Types of interventions

We will include two sevoflurane induction techniques for general anaesthesia.

  1. High concentration sevoflurane (control): equal to or more than a 4% concentration of sevoflurane, including vital capacity and tidal volume breath induction.

  2. Low concentration sevoflurane induction (experimental): starting concentration less than 4% sevoflurane.

Types of outcome measures

Primary outcomes

Our primary outcome is: induction time (time to loss of eyelash reflex (LOER), assessed in seconds (beginning from inhalation of gas until loss of eyelash reflex); or time to drop a weighted object, assessed in seconds (beginning from inhalation of gas until weighted object dropped, for example a syringe).

Secondary outcomes

Our secondary outcomes are:

  1. patient satisfaction (numeric rating scale);

  2. failed gas induction in the first attempt (yes or no);

  3. complications

We will define complications as:

  • cough during induction period;

  • laryngospasm;

  • breath‐holding;

  • apnea;

  • severe movement or panic reaction during induction (such as grabbing the mask, trying to slip off the operating table etc.);

  • hypotension (more than 20% of baseline blood pressure);

  • other rare complications (epileptiform EEG, bradycardia (below 20% of baseline heart rate)).

Search methods for identification of studies

Electronic searches

We will search the current issue of the Cochrane Central Register of Controlled Trials (CENTRAL) (The Cochrane Library), MEDLINE (1950 to present), EMBASE (1980 to present) and LILACS (1982 to present).

We will develop a specific strategy for each database on that developed for MEDLINE (Appendix 1). (Please see: Appendix 2 (CENTRAL); Appendix 3 (EMBASE); Appendix 4 (LILACS)).

Searching other resources

We will also identify trials by:

  1. searching specialist journals such as Anaesthesia and Analgesia; Anesthesiology; Anaesthesia; Acta Anesthesiologica Scandinavica; British Journal of Anaesthesia; Canadian Journal of Anaesthesia; European Journal of Anaesthesia;

  2. searching conference proceedings and abstracts. (The American Society of Anesthesiologists (ASA); International Anaesthesia Research Society (IARS); European Society of Anaesthesiologists (ESA));

  3. contacting known trialists, experts and medical or pharmaceutical companies for unpublished trials;

  4. searching grey literature (such as SIGLE);

  5. checking the reference list of relevant articles.

We will not apply a language restriction.

Data collection and analysis

We will use the standardized methods for conducting a systematic review as described by The Cochrane Collaboration in the Cochrane Handbook for Systematic Reviews of Interventions. (Higgins 2005).

Selection of trials

Two authors (PB and SB) will independently scan the titles and abstracts of reports identified by searching the electronic databases and hand searching journals. We will obtain and assess the full article of any possibly and definitely relevant trials according to the definitions provided in the criteria for considering studies for this review. We (PB and SB) will resolve any disagreement by consensus or, if necessary, by consulting a third author (WK or PP). If we can not resolve differences then we will add the publication reference to those awaiting assessment and contact the study authors for clarification.

Assessing quality of trials

Two authors (PB and SB) will assess the methodological quality of each trial following the guidelines described in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2005). Our assessment criteria are:

  1. randomizations and allocation concealment: adequate, unclear, or inadequate, not used;

  2. blinding of treatment: adequate, unclear, or inadequate;

  3. blinded outcome assessment: adequate, unclear, or inadequate;

  4. description of dropouts and withdrawals: adequate, unclear, or inadequate;

  5. use of intention‐to‐treat analysis: yes, no, no information.

We will define a trial as: A (low risk of bias, all quality criteria met); B (moderate risk of bias, one or more of the quality criteria only partly met); and C (high risk of bias, one or more criteria not met).
We will resolve any conflicts in assessment through discussion and, if necessary, through evaluation by a third author (WK or PP).

Data extraction

We will use a data extraction form to obtain data from individual studies. This will be performed by two authors (PB and SB). We will use five studies previously chosen as fulfilling the review selection criteria to pilot the form to ensure the data obtained is adequate for the review's purposes. We will obtain or clarify missing or unclear data by contacting authors.
We will obtain data as follows: study characteristics (study authors; authors of the report; MEDLINE journal ID; year of publication; language; country where study performed; source of funding; study design; method of allocation; study population inclusion or exclusion criteria; blinding of patients, operator and assessor; participants (number of participants recruited, completing trial and withdrawing, gender, age, overall sample size); intervention description; statistical methods; use of intention‐to‐treat analysis), outcomes (LOER, time to drop a weighted object, patient satisfaction, failed gas induction in the first attempt, complications (cough during induction period, laryngospasm, breath holding, apnea, severe movement, hypotension, other rare complications). Following data extraction, we will perform double data entry and the database will be screened for inconsistencies as a quality assurance measure.

Statistical analysis

We will analyse data and display it using Review Manager (RevMan 4.2) software distributed by The Cochrane Collaboration.

We will analyse continuous data results, time to LOER, time to drop a weighted object and patient satisfaction as weighted mean differences. We will analyse dichotomous data of failed gas induction in the first attempt and complications (cough, laryngospasm, breath holding, apnea, severe movement, hypotension, bradycardia and epileptiform EEG) as relative risk. We will review the data from included studies qualitatively and then, if possible, combine the data quantitatively by population, intervention and outcome.

We will assess heterogeneity among studies by:

  1. inspection of individual 95% confidence interval in the forest plot;

  2. I2 statistic (Higgins 2002); heterogeneity is suspected if it is more than 50%.

If we cannot detect the sources of heterogeneity then we will use the random‐effects method of DerSimonian and Laird (DerSimonian 1986) to estimate an overall effect of the treatment. If heterogeneity among the trial results is not be detected we will conduct meta‐analysis using the fixed‐effect model.

If heterogeneity is detected the effect of factors that may influence the outcome will be investigated. Subgroup analysis will be performed, where data are available in each subgroup, and the 95% confidence intervals will be examined. Non‐overlap of the intervals will be taken to indicate a statistically significant difference between subgroups. We will compare:

  1. breathing technique (vital capacity, tidal volume);

  2. supplement drug (fentanyl, morphine, lidocaine, midazolam, nitrous oxide);

  3. anaesthetic circuit type (Mapleson system, circle circuit);

  4. different age groups (infant or toddler (0 to 2 years), child (3 to 12 years) and adolescent (more than 13 years).

We will perform sensitivity analyses for missing data and study quality. In the case of missing data, we will employ sensitivity analysis using different approaches to imputing missing data. The best‐case scenario will assume that none of the originally enrolled patients missing from the primary analysis in the treatment group had the negative outcome of interest whilst all those missing from the control group did. The worst‐case scenario will be the reverse. We will also conduct sensitivity analysis by study quality based on the risk of bias (presence or absence of a reliable random allocation method, concealment of allocation and blinding of participants or outcome assessors).

We will test publication bias using funnel plots.