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ORIGINAL ARTICLE

Crisis management during anaesthesia: difficult intubation

A D Paix, J A Williamson, W B Runciman
...............................................................................................................................
Qual Saf Health Care 2005;14:e5 (http://www.qshc.com/cgi/content/full/14/3/e5). doi: 10.1136/qshc.2002.004135

Background: Anaesthetists may experience difficulty with intubation unexpectedly which may be
associated with difficulty in ventilating the patient. If not well managed, there may be serious consequences
for the patient. A simple structured approach to this problem was developed to assist the anaesthetist in this
difficult situation.
Objectives: To examine the role of a specific sub-algorithm for the management of difficult intubation.
Methods: The potential performance of a structured approach developed by review of the literature and
analysis of each of the relevant incidents among the first 4000 reported to the Australian Incident
Monitoring Study (AIMS) was compared with the actual management as reported by the anaesthetists
involved.
See end of article for Results: There were 147 reports of difficult intubation capable of analysis among the first 4000 incidents
authors’ affiliations reported to AIMS. The difficulty was unexpected in 52% of cases; major physiological changes occurred in
....................... 37% of these cases. Saturation fell below 90% in 22% of cases, oesophageal intubation was reported in
Correspondence to: 19%, and an emergency transtracheal airway was required in 4% of cases. Obesity and limited neck
Professor W B Runciman, mobility and mouth opening were the most common anatomical contributing factors.
President, Australian Conclusion: The data confirm previously reported failures to predict difficult intubation with existing
Patient Safety Foundation,
GPO Box 400, Adelaide, preoperative clinical tests and suggest an ongoing need to teach a pre-learned strategy to deal with
South Australia 5001, difficult intubation and any associated problem with ventilation. An easy-to-follow structured approach to
Australia; research@apsf. these problems is outlined. It is recommended that skilled assistance be obtained (preferably another
net.au
anaesthetist) when difficulty is expected or the patient’s cardiorespiratory reserve is low. Patients should be
Accepted 11 January 2005 assessed postoperatively to exclude any sequelae and to inform them of the difficulties encountered. These
....................... should be clearly documented and appropriate steps taken to warn future anaesthetists.

D
ifficult intubation occurs relatively commonly in It was concluded that, if this algorithm had been correctly
association with general anaesthesia. Its true incidence applied, a functional diagnosis would have been reached
is unknown but is estimated to be 1–3%.1 Approx- within 40–60 seconds in 99% of applicable incidents, and
imately half of all cases are not predicted.1 A difficult that the learned sequence of actions recommended by the
intubation can be anticipated in a number of circumstances COVER portion would have led to appropriate steps being
including a previous history of difficulty with intubation, taken to handle the 60% of problems relevant to this portion
syndromes known to be associated with difficulty to of the algorithm.6 However, this study also showed that the
intubate, and some pathoanatomical states involving the 40% of problems represented by the remainder of the
head and neck region. Less reliable are anatomical hallmarks algorithm, ABCD–A SWIFT CHECK, were not always
which may be sought at preoperative assessment including promptly diagnosed or appropriately managed.6–8 It was
thyromental distance (see Appendix 1)2 and the relative decided that it would be useful, for these problems, to
tongue/pharyngeal size (Mallampati test, see Appendix 2).3 develop a set of specific sub-algorithms in an easy to use
If the anaesthetised patient cannot breathe spontaneously crisis management manual.9 This study reports on the place
or the lungs cannot be otherwise ventilated by mask, then a of the AB COVER CD–A SWIFT CHECK algorithm in the
series of manoeuvres must immediately be undertaken diagnosis and initial management of difficult intubation,
culminating, if necessary, in gaining direct transtracheal provides an outline of a specific crisis management sub-
access to the airway. Such a structured approach is dealt with algorithm for this problem during anaesthesia, and provides
elsewhere in this set of articles.4 an indication of the potential value of using this structured
We concur with the recommendation of the American approach. It examines cases of difficult intubation from the
Society of Anesthesiologists’ Task Force on the management first 4000 reports to AIMS and expands on the report that
of the difficult airway that all anesthesiologists should have a reviewed the data from the first 2000 reports.10
preformed strategy for intubation of the difficult airway.5
In 1993 a core crisis management algorithm, represented METHODS
by the mnemonic COVER ABCD–A SWIFT CHECK, was Information of relevance to difficult endotracheal intubation
proposed as the basis for a systematic approach to crisis was extacted from the first 4000 reports to AIMS. All
management during anaesthesia (the AB precedes COVER incidents with the keywords ‘‘difficult intubation’’, ‘‘failed
for the non-intubated patient) where it is not immediately intubation’’, and ‘‘fibreoptic intubation’’ were analysed with
obvious what should be done or where actions taken have respect to causes, management and outcome. The basis for
failed to remedy the situation.6 This was validated against the the COVER–ABCD algorithm has been described in detail
first 2000 incidents reported to the original Australian elsewhere.6 A specific sub-algorithm was developed (fig 1).
Incident Monitoring Study (AIMS). AIMS is an ongoing
study which involves the voluntary anonymous reporting of RESULTS
any unintended incident which reduced or could have Of the first 4000 incidents reported to AIMS, 160 (4%) dealt
reduced the safety margin for a patient.7 with problems with endotracheal intubation. There was one

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DIFFICULT INTUBATION
REMEMBER, PATIENTS DO NOT DIE FROM FAILED NOTES:
INTUBATION – ONLY FAILED VENTILATION (1) Techniques will vary with the experience and familiarity with the techniques
of the individual anaesthesiologist.
Always have skilled assistance, preferably another anaesthetist, Avoid multiple attempts at laryngoscopy/intubation, as this may cause
when difficulty is expected or the patient's cardiorespiratory bleeding and laryngeal oedema, worsening the situation.
reserve is low. (2) This may require 2 assistants:
one to apply pressure to the larynx and/or the back of the neck,
MANAGEMENT the second to lift the head up.
Call for skilled assistance (3) BURP refers to Backward Upward Rightward Pressure, as described by
Call for the difficult intubation trolley Knill (7). Knill, RL. Difficult laryngoscopy made easy with a “BURP”, Can
Maintain oxygenation at all times J Anaesth 1993; 40: 279–82.
Have someone feel the pulse and call out the SpO2. (4) The most common aid to facilitate successful intubation in the AIMS series
If you cannot ventilate the lungs → page 14* was the gum elastic bougie (46%), followed by a stylet (23%).
(5) The LMA is easy to insert and works well in about 95% of cases. It does
If you can ventilate by face mask, consider not provide airway protection.
waking up the patient OR (6) Airway trauma
maintaining anaesthesia and trying to intubate (1)** Pulmonary aspiration
Post-obstructive pulmonary oedema
Try basic manoeuvres first: Cardiovascular signs and symptoms.
Optimise the head and neck position (2) (7) Provide written advice and document this in the medical record.
Try laryngeal manipulations such as “BURP” (3) (8) Document the problem in the case notes and give the patient a letter to
Try a well-lubricated gum elastic bougie or stylet (4) warn future anaesthetists. If a particular precipitating event was significant,
Try different laryngoscope blades or a particular action was useful in resolving the crisis, this should be
If these fail: clearly explained and documented. Consideration should also be given to
Consider inserting an LMA (5) a hazard alert device such as a Medic-alertTM bracelet.
Consider other techniques: Blind nasal
Retrograde These notes comprise a reverse side of a page of the
Lighted stylet Crisis Management Manual28.
If an LMA is in place consider whether to proceed and whether steps
should be taken to secure endotracheal intubation (5)
Confirm correct placement of endotracheal tube.

FURTHER CARE
Review the situation
Exclude other complications (6)
There is a risk of awareness:
Go and see the patient in the ward
Explain again and reassure them (7)
Advise them to warn future anaesthesiologists (8).

The sub-algorithm forms a facing page of the

Crisis Management Manual28.
* Page references refer to the Crisis Management Manual28.
** Numbers in brackets refer to Notes in the right hand panel.

Figure 1 Difficult intubation.

cardiac arrest which was successfully resuscitated. No deaths Thirteen reports contained insufficient information for
were reported. Sixty reports (37%) involved emergency further analysis, leaving 147 reports that were analysed with
procedures and there were 43 ‘‘out of hours’’ incidents, respect to cause, management and outcome. Difficulties in
mainly involving trainee anaesthetists. Further information intubation were not predicted in 77 cases (52%). It was
is shown in table 1. judged that preoperative assessment of the airway was
In 42 reports (26%) there was an initial failure to intubate inadequate in 15 of these cases (table 2), and in one case
(table 1). This included 16 cases where a consultant had to be fatigue was felt to be a significant co-factor. Omission of
summoned from another location. In 14 of these 42 cases simple bedside tests such as checking for mouth opening and
intubation was subsequently achieved, so endotracheal neck extension was commonly reported. There were 10
intubation was not achieved in 28 cases (17%). There were reports of errors of judgement despite appropriate preopera-
12 instances of an emergency airway procedure being tive assessment, nine of which involved trainees.
performed. These included five tracheostomies (table 1) and Drug errors were the primary cause of difficulty in 13
successful placement of a laryngeal mask airway (LMA) in reports. This involved ‘‘failure’’ due to drug remaining in the
five patients who could not be ventilated. line dead space (two reports) or decomposition following a
There was difficulty with ventilation via a face mask in 23 prolonged period between preparation and usage (four
reports (14%), including eight of the 12 in which an reports), the wrong dose (four reports), and injection of the
emergency airway procedure was employed. In only two of wrong drug (three reports). This information is summarised
these reports was difficulty with ventilation anticipated. in table 2.

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Table 1 Difficult (including unsuccessful) endotracheal intubations from the first 4000 incidents reported to AIMS
Difficult (failed) Difficult face mask Booked as
Planned surgery intubation ventilation Emergency airway emergency cases

General surgery 50 (17) 12 2 (tracheostomy; LMA) 26

Otorhinolaryngological 25 (5) 5 2 (tracheostomy) 2
Dental 14 (1) 1 1 (tracheostomy) 1
Orthopaedic 13 (3) 1 – 8
Obstetric 10 (3) 1 2 (LMA) 7
Urological 9 (3) 1 – 4
Gynaecological 8 (3) 1 1 (LMA) 1
Plastic surgery 8 (2) 1 1 (cricothyroid puncture) 4
Neurosurgery 8 (2) – – 3
Cardiothoracic 7 (0) Not attempted 1 (sternotomy for ruptured trachea) 2
Vascular 3 (1) – 1 (LMA) 1
Ophthalmological 2 (1) – – –
Others 3 (1) – 1 (semi-elective tracheostomy) 1
Total 160 (42) 23 12 60

LMA, laryngeal mask airway.

Table 3 summarises the reported intubation aids in the 132 thorough preoperative assessment of the airway will fail to
reports where endotracheal intubation was achieved. In detect some difficult intubations, every anaesthetist should
addition, simple manoeuvres alone such as repositioning have a predetermined strategy for dealing with this situation.
the patient, correctly applied cricoid pressure, and the use of Protocols for the management of difficult intubations
‘‘BURP’’ (backward, upward, right (‘‘ward’’) pressure on the previously published by AIMS10 and by the American Society
larynx) enabled intubation in 16 cases (11%).11 for Anesthesiologists’ Task Force on the Management of the
Table 4 shows the perceived contributing factors among Difficult Airway5 recommend a pre-learned strategy and
the difficult intubations reported to AIMS. The three most emphasise the importance of maintaining ventilation;
common factors were obesity (24 cases), limited neck patients do not die from a failure to intubate but from a
mobility, and limited mouth opening. These were also the failure to ventilate.
most commonly reported factors in the analysis of the first In this series the most common remediable cause of
2000 reports to AIMS.10 unpredicted difficulty with intubation occurred in the setting
The reported complications are shown in table 5. The two of inadequate preoperative assessment. The existing bedside
most commonly reported complications were desaturation tests that look for anatomical indicators of difficulty—such as
,90% (22%) and oesophageal intubation (19%). Three the Patil measurement of thyromental distance,2 the
unrecognised oesophageal intubations were reported, all in Mallampati test,3 and the Wilson scoring system12 (see
association with failure to confirm endotracheal tube place- Appendices 1 and 2)—appear, from our data, to lack
ment by capnography in the presence of ‘‘normal’’ breath sensitivity and specificity, making their usefulness limited.
sounds upon auscultation. There were nine reports of gastro- However, performing such tests would have detected the 32
oesophageal reflux with aspiration, two of which were in cases with limited mouth opening and/or neck extension and
association with a failure to intubate. There were two reports might have prevented unexpected difficulties in these cases.
of awareness in the series, although the true incidence may It has been suggested that combining these tests improves
be considerably higher. Epistaxis during attempts at blind the predictive power, with one group of investigators
nasal intubation occurred in two reports, making intubation claiming 100% accuracy in their series.13 More recently,
even more difficult. Minor physiological changes, such as Naguib and colleagues identified four clinical risk factors that
coughing and bucking, or desaturation not less than 90% correlate with difficult laryngoscopy and intubation (positive
were reported in 65 cases (44%). In 18 cases (12%) there were predictive value (PPV) 87.5%): thyromental distance, thyro-
no significant changes in physiology. Sequelae were not sternal distance, neck circumference, and Mallampati class.14
recorded in 10 of the 147 cases (7%). Combining these with a series of radiological measurements
increased the PPV to 95.8%.
DISCUSSION Simultaneous difficulty with ventilation via a face mask
Airway management and endotracheal intubation are funda- occurred in 14% of reports. Emergency airways were required
mental skills for the safe conduct of anaesthesia. The true in nearly half of these (43%). Five emergency tracheotomies
incidence of difficult intubation in anaesthetic practice is were performed, two involving patients with supraglottic
unknown, but is typically estimated at being between 1% and tumours. Another patient required a cricothyroid puncture.
3%.1 Difficult intubation often arises unexpectedly, as was the Reports of the use of laryngeal masks in this setting occurred
case in 52% of incidents in this series. As even the most in five cases. The previous analysis of 2000 incidents in 1993

Table 2 Unpredicted difficult intubation

Grade of anaesthetist

Primary cause No Consultant Trainee

No obvious cause 38 25 13
Inadequate preoperative assessment 15 9 6
Drug errors 13 6 7
Errors of judgement/experience 10 1 9
Fatigue 1 0 1
Total 77 41 36

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Table 3 Reported usage of commonly used aids to difficult endotracheal intubation in the first 4000 incidents reported to AIMS
Gum elastic Fibreoptic Change of
Type of surgery bougie Introducer endoscope laryngoscope* Magill forceps Rigid bronchoscope

General surgical 13 8 3 3 1 1
Otorhinolaryngological 3 2 2 2 – –
Dental 3 1 3 1 2 –
Orthopaedic 7 1 1 1 – –
Obstetric 1 1 – – – –
Urological 1 – – 1 – –
Gynaecological 3 2 – – – –
Plastic and reconstructive 3 1 2 – – –
Others 3 2 2 – – –
Total (n = 80) 37 18 13 8 3 1

*This included the use of long, Miller and Bellscope blades.

had no reports of the use of this device.10 Its appearance now success of this simple tool has quietly but radically altered anaesthetic
probably reflects greater application of—and familiarity practice, as all that is now required is a view of the epiglottis…’’.17
with—the laryngeal mask airway and its potentially life Weiss18 has described an endoscopic system which allows
saving role in this situation. There were only two reports in visualisation by substitution of the gum elastic bougie with a
this series where difficulties in intubation and mask flexible endoscope. It provides assistance where direct
ventilation were predicted. Both were managed with an laryngoscopic view of the vocal cords is impaired. Further
awake fibreoptic intubation technique. experience is necessary in adults as it dealt only with
Time honoured methods of managing the difficult intuba- simulated difficult paediatric airways. It has the potential
tion are being supplanted by the use of fibreoptic intubating advantage of converting a blind technique (bougie assisted
techniques where difficulty is predicted, and the laryngeal intubation) into a visualised one.
mask airway where it is not. Mention of the use of blind Several devices are available which were not mentioned in
nasal intubation (six reports), Magill’s forceps (three any of the incident reports in our series. All may have a role
reports), and of the rigid bronchoscope (one report) was to play, but experience in their use and an understanding of
infrequent. More recently, several laryngoscope blades for their suitability for different airway problems is essential
difficult intubation such as the Bellhouse15 and McCoy16 before considering their use in what can be a stressful
blades and the Bullard laryngoscope have been described. situation.
They give the anaesthetist more choice in managing these The cuffed oropharyngeal airway (COPA) may be of
problems. However, trainee anaesthetists may lack apprecia- assistance where problems with ventilation occur. A French
tion of simple and effective techniques, as there were a group19 have reported its use in conjunction with both the
number of instances where consultants rapidly dealt with gum elastic bougie and the fibreoptic laryngoscope to aid
problems by repositioning the patient (‘‘sniffing the morning intubation.
air’’), using laryngeal manipulations such as ‘‘BURP’’,9 or by The intubating laryngeal mask airway (ILMA) is a device
the use of stylets or blind nasal intubation as well as other designed specifically to aid in blind intubation. Clinical trials
laryngoscope blades. confirm its ease of rapid insertion and reliable ventilation in
The use of the gum elastic bougie was widespread in this almost all patients.20 Furthermore, (blind) intubation rates of
series and successfully aided intubation in 46% of cases. A 93–99% are reported.20 A Canadian group20 21 has reported
stylet was successful in a further 23%. These two simple aids multiple attempts at intubation being necessary in some
allowed most problems to be solved and so should be patients, and concluded that experience in the technique
considered early, as soon as difficulties arise. In an editorial would improve the success rate. We advise caution in viewing
in 1993 on the gum elastic bougie, Wilson17 wrote: ‘‘… the
Table 5 Complications reported in association
with difficult intubation from the first 4000
Table 4 Factors identified by reporters as incidents reported to AIMS
contributing to intubation difficulty from the first Complication No of reports
4000 incidents reported to AIMS
Arterial desaturation ,90% 33
Contributing factor No of reports Oesophageal intubation 28
Central cyanosis 10
Obesity 24 Regurgitation 9
Limited neck mobility 17 Bronchospasm 9
Limited mouth opening 15 Laryngospasm 7
Inexperience of laryngoscopist 14 Dental damage 4
Inadequate assistance 13 Cardiac arrhythmias* 3
Drug errors 13 Endobronchial intubation 3
Poor/prominent dentition 11 Epistaxis 2
Equipment deficiencies 8 Pharyngeal trauma 2
Laryngeal tumour 8 Awareness 2
Recent traumatic intubation 8 Masseter spasm 2
Neck mass 3 Others
4
Beard 2 Total 118
Masseter spasm 2
Others* 5 *There were two reports of bigeminy and one of
supraventricular tachycardia.
*Cervical spine instability, facial carcinoma, congenital
Electrocardiographic signs of ischaemia, cardiac arrest, a
microsomia, ruptured trachea, and hair in a ‘‘bun’’ were lacerated tongue, and an oesophageal tear were each
each reported on one occasion. recorded on one occasion.

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this device as a universal panacea to the problem of difficult A number of avoidable factors other than inadequate
intubation. Our series confirms that problems arise from preoperative assessment resulted in difficulties. Drug errors
repeated attempts at intubation. A blind technique cannot be occurred in 13 cases and, in all of them, correction of the
recommended where there is abnormal upper airway error allowed intubation to be achieved. Equipment deficien-
anatomy such as tumours, abscesses, or previous deforming cies—largely due to ‘‘failure to check’’ such as no introducer
surgery or trauma. in the theatre and failure of the laryngoscope light—occurred
The Combitube is another airway management device, well in six cases. Inadequate or poorly trained assistants were
established in the emergency medicine setting, that anaes- judged to be a contributing factor in 10 cases. The
thetists may use.22 23 It can be sited without the need for responsibility in all of these instances clearly rests with the
direct laryngoscopy. Its use is associated with a higher anaesthetist.
incidence of complications than the laryngeal mask airway The sequelae of difficult/failed intubation range from the
but it can prevent gastric aspiration. Pharyngeal trauma is trivial to loss of life. In this series no deaths occurred, but
common,22 23 probably due to the 85 ml pharyngeal cuff. major physiological sequelae occurred in 54 reports (37%).
Valve-like upper airway obstruction by the aryepiglottic folds Arterial desaturation less than 90% as measured by pulse
has been described.23 The use of this device should perhaps be oximetry occurred in 22% of reports, and in a further 10 cases
restricted to emergency situations but, again, familiarity is central cyanosis without specific oximetry measurement was
essential. reported. The incidence of oesophageal intubation in this
The previous series, which looked at difficult intubation in series was 19% (28 reports). Of more concern was the failure
1993,10 highlighted the problem of the inexperienced and/or to detect oesophageal intubation in three cases where a
lone anaesthetist having to cope with a difficult intubation. capnograph was not used. All these patients had apparently
In nearly one third of cases (n = 50) the anaesthetist was a normal breath sounds on chest auscultation. Detection in
trainee with 60% of these incidents occurring out of hours. In these cases was from persistent severe desaturation. The
25% of cases serious difficulty occurred despite the pre- capnograph is the only monitor that will reliably detect
operative prediction of a difficult airway. It would appear that oesophageal intubation within a few breaths. The Australian
a pre-considered approach to difficult intubation continues to and New Zealand College of Anaesthetists has recommended
be lacking. A plan of management is shown in fig 1; it that a ‘‘carbon dioxide monitor should be exclusively
discourages prolonged or traumatic attempts at intubation available for every intubated and/or ventilated patient’’.25
which may create additional problems. Always have skilled Difficulty with intubation is a relatively common occur-
assistance, preferably another anaesthetist, when difficulty is rence with general anaesthesia and is often unpredicted, so
expected or the patient’s cardiorespiratory reserve is low.24 every anaesthetist should have a pre-learned strategy for
dealing with this problem.26 27 The data collected in this series
Key messages confirm that early assistance and use of simple measures
such as repositioning the head, trying laryngeal pressure, and
the use of simple aids such as a well lubricated bougie or
N All anaesthetists should have a pre-formed strategy for
stylet will enable resolution of the problem in most cases. The
intubation of the difficult airway.
structured approach presented in fig 1 reflects this, empha-
N 160 (4%) of the first 4000 AIMS reports dealt with sising simple methods and avoidance of repeated attempts at
endotracheal intubation problems. There were no intubation that may create additional problems.26 These
deaths. patients should be assessed postoperatively to exclude any
N In 28 reports (17%) endotracheal intubation was not sequelae and to inform them of the difficulties encountered.
achieved despite more than one attempt. The problem should be documented clearly in the case notes
N An emergency airway procedure was performed in 12 and the patient given a letter to warn future anaesthetists. If
instances (five tracheostomy, five laryngeal mask a particular precipitating event was significant, or a particular
airway). action was useful in resolving the crisis, this should also be
N Difficult face mask ventilation occurred in 23 reports clearly explained and documented.24 Finally, a hazard alert
device such as a Medic-alertTM bracelet should also be
(14%), eight requiring an emergency airway proce-
dure; in 21 of these 23 reports ventilation difficulty was considered.
not anticipated.
N Intubation difficulties were not predicted in 52% of the ACKNOWLEDGEMENTS
The authors would like to thank all the anaesthetists in Australia and
147 reports capable of full analysis. Omission of
New Zealand who contributed to the 4000 incident reports upon
simple bedside tests beforehand was commonly which this and the other 24 papers in the Crisis Management Series
reported. are based. The coordinators of the project also thank Liz Brown for
N Drug errors were the primary cause in 13 cases. preparing the draft of the original Crisis Management Manual;
N Simple manoeuvres alone (positioning, correct cricoid Loretta Smyth for typing; Monica Bullock RN for earlier coding and
classifying of data; Dr Charles Bradfield for the electronic version of
pressure, ‘‘BURP’’) enabled intubation in 16 cases the algorithms; Dr Klee Benveniste for literature research; and Drs
(11%). Klee Benveniste, Michal Kluger, John Williamson and Andrew Paix
N The most useful aids were a gum elastic bougie and an for editing and checking manuscripts.
introducer.
.....................
N The three most common contributing factors were
Authors’ affiliations
obesity, limited neck mobility, and limited mouth A D Paix, Consultant Anaesthetist, Princess Royal University Hospital,
opening. Orpington, Kent, UK
N Desaturation and oesophageal intubation were the J A Williamson, Consultant Specialist, Australian Patient Safety
most common complications. Foundation; Visiting Research Fellow, University of Adelaide and Royal
N Inadequate preoperative assessment was the most Adelaide Hospital, Adelaide, South Australia, Australia
W B Runciman, Professor and Head, Department of Anaesthesia and
common remediable cause.
Intensive Care, University of Adelaide and Royal Adelaide Hospital,
Adelaide, South Australia, Australia

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This study was coordinated by the Australian Patient Safety Foundation, 2 Patil VU, Stehling LC, Zauder HL. Fiberoptic endoscopy in anesthesia.
GPO Box 400, Adelaide, South Australia 5001, Australia. Chicago: Year Book Medical Publishers, 1983.
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to the larynx which determines how easily the laryngeal and Anesthesiology 1993;78:597–602.
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N head and neck movement; endotracheal intubation with the Macintosh laryngoscope. Anaesth Intensive
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N The mouth is opened as widely as possible and the tongue

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N The observer sits opposite at eye level and inspects the
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28 Australian Patient Safety Foundation. Crisis Management Manual: COVER
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