Airway management

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Dr P A Nee, Whiston Hospital,. Whiston, Prescot, Merseyside. L35 5DR, UK; patrick.nee@sthk. nhs.uk. Accepted 7 June 2007. Airway management is a core skill ...

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Airway management P A Nee, J Benger and R M Walls Emerg Med J 2008 25: 98-102

doi: 10.1136/emj.2005.030635

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Occasional series in critical care in the emergency department

Airway management P A Nee,1 J Benger,2 R M Walls3 1

Whiston Hospital, Prescot, Merseyside, UK; 2 United Bristol Healthcare Trust, Bristol, UK; 3 Brigham and Women’s Hospital, Harvard Medical School, Boston, Massachusetts, USA Correspondence to: Dr P A Nee, Whiston Hospital, Whiston, Prescot, Merseyside L35 5DR, UK; [email protected] nhs.uk Accepted 7 June 2007

Airway management is a core skill of emergency medicine. Physicians in the emergency department must be able to provide definitive resuscitative care to all patients who present with an acute threat to life, including those who need immediate airway management. Some patients present in severe respiratory distress—for example, with airway burns—and require immediate life-saving intervention. Others present with advanced respiratory compromise—for example, in status asthmaticus— when coordinated airway interventions are an essential part of emergency care. Still others present with conditions that appear initially to present no urgent airway threat. However, insidious processes can rapidly create an airway catastrophe. Practitioners must have the skills and knowledge necessary to undertake effective emergency airway management. A methodical approach permits careful evaluation of the patient’s airway for predicted difficulty with intubation, bag-mask ventilation (BMV), surgical airway or all of these. When potential difficulty is identified, the plan must account for the anticipated problems and a back-up plan developed. When airway difficulty is not anticipated, rapid sequence induction using an anaesthetic induction (sedative) drug and a rapidly acting neuromuscular blocker is the preferred approach.

ILLUSTRATIVE CASE A 45-year-old man known to have severe ankylosing spondylitis is brought to the emergency department (ED) having been struck by a car while crossing the road. He has a minor head injury with a well-preserved level of consciousness and a chest injury with an obvious flail segment affecting the left anterolateral chest wall. Paramedics have placed him on a long spine board with his neck immobilised in a semi-rigid collar and head blocks. On arrival in the ED he is alert (Glasgow Coma Score (GCS) 15) and complaining of left chest pain and breathing difficulty. He is reasonably comfortable and not asking to sit up. He has no neck pain and is able to move all limbs. Vital signs are: pulse rate 110, BP 165/110, respiratory rate 38 and shallow. Oxygen saturation is 84% while breathing high-flow oxygen via a face mask with a reservoir bag. An intravenous infusion of normal saline is in progress. BMV, synchronised to the patient’s spontaneous breathing, is instituted and the oxygen saturation improves to 90%. A chest radiograph reveals leftsided rib fractures, pulmonary contusion and possible left haemothorax. There is no pneumothorax. Left tube thoracostomy drains a little blood but does not improve the oxygen saturation. 98

QUESTIONS (1) 1. 2. 3. 4.

What are the indications for tracheal intubation in the ED? What is the best technique to achieve successful tracheal intubation? Describe the essential steps in preparation for intubation. What assessment tools are available to predict intubation difficulty?

DISCUSSION (1) (1) What are the indications for tracheal intubation in the ED? The decision to intubate depends upon: c The patient’s ability to maintain and protect his/her airway. c The adequacy of oxygenation and ventilation. c The predicted clinical course. Intubation is indicated when the risks of intubation are outweighed by the risks of not doing so. Examples include a patient whose condition is expected to deteriorate (eg, asthma with progressive respiratory failure) or when the patient must leave the ED for imaging or be transferred to the operating theatre or another hospital. Similarly, there are circumstances in which delaying intubation might create additional hazard for the patient; for example, when progressive airway swelling can render later intubation more difficult or impossible. This patient has a marginal oxygen saturation (SpO2) of 90%, even with high flow oxygen and assisted ventilation. His work of breathing is increased and he is likely to tire soon. The shape of the oxygen-haemoglobin dissociation curve determines that the SpO2 will fall precipitously if gas exchange deteriorates further and deterioration is highly likely to occur as the pulmonary injury continues to develop. Non-invasive ventilatory support is relatively contraindicated because of the early stage of resuscitation, the likelihood of progression of the pulmonary injury, difficulty with cough and clearance of secretions and the need for opioid analgesics which may suppress spontaneous breathing.

(2) What is the best technique to achieve successful tracheal intubation? If the patient is not in cardiorespiratory arrest, rapid sequence induction of anaesthesia (RSI) followed by tracheal intubation is the procedure of choice in the ED. RSI has a higher success and lower complication rate than alternative techniques in the ED.1 It requires the administration of a precalculated dose of induction drug and neuromuscular blocker following maximal pre-oxygenation. Pre-oxygenation is achieved by administering 100% oxygen for 3 min or eight vital capacity breaths (although this latter Emerg Med J 2008;25:98–102. doi:10.1136/emj.2005.030635

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Occasional series in critical care in the emergency department Table 1 Summary of the four commonly used induction drugs in adults Induction drug

Dose (mg/kg)

Onset of anaesthesia (s)

Recovery (min)

Cardiovascular depression

Thiopental

2–7

5–15

5–15

++

Cerebroprotective action Useful in isolated head injury Effective anticonvulsant

Etomidate

0.3

5–15

5–15

+

Myoclonic movements on induction Adrenal suppression

Propofol

1.5–2.5

20–40

5–10

+++

Marked hypotension in cardiovascular compromise Induction drug most commonly used in elective anaesthesia Pain on injection Involuntary movements on induction Anticonvulsant properties

Ketamine

1–2

15–30

15–30

Minimal

Dissociative state Potent analgesic Emergence phenomena e.g. agitation, hallucinations Bronchodilator Useful in acute asthma, hypovolaemic trauma and burns

option is rarely practical in the ED). Optimal pre-oxygenation will ensure that a healthy adult patient with normal cardiorespiratory function will tolerate several minutes of apnoea after sedation and paralysis. During RSI no assisted breaths are given between drug administration and laryngoscopy, to reduce the risk of gastric inflation and aspiration. However, in circumstances where oxygenation is inadequate at the onset of RSI or deteriorates after induction, ventilation may be used to maintain adequate oxygen saturation. Sellick’s manoeuvre (cricoid pressure) is used to reduce the risk of aspiration. Intubation may be facilitated by the use of an intubating stylet or bougie, and correct placement must be confirmed by capnography. There are several alternative induction drugs, each with their own advantages and disadvantages; a key factor when selecting a drug for anaesthetic induction is therefore familiarity. The properties of the most commonly used induction drugs are summarised in table 1. Suxamethonium (succinylcholine) is a depolarising (non-competitive) neuromuscular blocker producing profound paralysis within 30–45 s of an intravenous injection of 1.5–2 mg/kg. Suxamethonium remains the most important—and most commonly used—neuromuscular blocker for RSI in the ED. There are a number of important contraindications to its use.2 Bradycardia can occur in children under 10 years of age who are particularly sensitive to the muscarinic effects of suxamethonium, and atropine pretreatment (0.02 mg/kg) may be used in this age group. Bradycardia can also occur in adults, usually after a second dose of suxamethonium, and atropine should be immediately available to counteract this. Pretreatment with a short-acting opioid (usually fentanyl or alfentanil) will reduce the sympatheticmediated hypertensive response to laryngoscopy and intubation, particularly when a rise in intracranial pressure (ICP) would be harmful. Some North American authorities also recommend pretreatment with lidocaine (for reactive airways or raised ICP) or a defasciculating dose of a non-depolarising neuromuscular blocker (for raised ICP). However, neither of these are used routinely in UK practice. Emerg Med J 2008;25:98–102. doi:10.1136/emj.2005.030635

Specific effects

(3) Describe the essential steps in preparation for intubation Preparation for RSI requires that the patient is in an appropriate clinical area with an experienced airway practitioner and assistants available. Practitioners without training in emergency airway management should call for help from a clinician with the appropriate range of emergency airway skills. The necessary equipment and drugs (drawn-up in labelled syringes) must be immediately to hand. The Association of Anaesthetists of Great Britain and Ireland has defined minimum recommended standards of monitoring which are required wherever anaesthesia is administered.3 These include the monitoring of: c Pulse oximetry c Capnometry c Non-invasive blood pressure c Continuous ECG An assessment of potential difficulty with a primary plan for intubation and fallback plan (‘‘plan B’’) should be formulated during this preparatory phase.

(4) What assessment tools are available to predict intubation difficulty? In all but the most exceptional circumstances, an assessment of potential difficulty in securing a definitive airway is an essential part of the preparation for RSI. There are three areas of difficulty that should be considered: c Difficult BMV c Difficult laryngoscopy (poor view) or difficult intubation c Difficult surgical airway The patient may have physical features that prevent an adequate view of the vocal cords at laryngoscopy such as poor mouth opening, large tongue, prominent teeth or receding jaw. Limited neck mobility, as in the present case, will prevent the alignment of the oral, pharyngeal and laryngeal axes which greatly facilitates orotracheal intubation. The LEMON mnemonic (table 2) is a validated method of assessment in the ED setting.4 The UK Training in Emergency Airway Management 99

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Occasional series in critical care in the emergency department Table 2 LEMON mnemonic for evaluation of potential difficulty in orotracheal intubation L

E

M

O

N

Look externally small mandible large tongue large teeth short neck etc. Evaluate 3-3-2 mouth opening (3 fingers) thyromental distance (3 fingers) surface marking of base of tongue to top of thyroid cartilage use patient’s finger size (2 fingers) Mallampati score16 class I–IV visibility of post-pharyngeal structures on mouth opening not validated in the supine patient Obstruction of upper airways masses stridor difficulty swallowing Neck mobility

Adapted from Walls et al.4

(TEAM) course proposes a similar assessment: HAVNOT (table 3). However, no assessment tool will predict or exclude a difficult airway with 100% certainty, and significant difficulty with laryngoscopy, BMV or both can occur unexpectedly.5

DISCUSSION (2) (1) What are the options for achieving a definitive airway in a patient who is predicted to be difficult to intubate? RSI may be the preferred method of airway management, even in patients with features predictive of difficulty, unless the difficulty is sufficient to make intubation unlikely or if there are barriers to successful BMV. The assistance of an experienced emergency airway practitioner must always be sought. An ‘‘awake look’’ using one-third to one-half the intubating dose of a drug such as etomidate or ketamine, titrated to response, is recommended by some North Amercian experts and may be informative. However, it can be hazardous in inexperienced hands and is not commonly used in the UK. Many anaesthetists prefer to use an inhalational anaesthetic drug such as sevofluorane, provided there is access to an anaesthetic machine. Additionally, topical application of 4% lidocaine spray to the pharynx and larynx may improve patient comfort and compliance. A vasoconstrictor drug such as epinephrine or phenylephrine may be added to the topical anaesthetic to help dry the mucous membranes and inhibit contact bleeding. Laryngoscopy may be accomplished with a standard (Macintosh, Miller) laryngoscope blade, a fibreoptic scope (where available) or any of a series of newer video laryngoscopes or fibreoptic intubating stylets. Whichever approach is chosen, the practitioner must be experienced in its use: an emergency situation is the wrong time to try out novel intubation techniques.

(2) How is a ‘‘failed airway’’ defined? CASE PROGRESSION The patient is deemed to require intubation because of his hypoxic respiratory failure and predicted clinical course. Airway assessment predicts that the patient will be difficult to intubate, based on his immobile (and vulnerable) cervical spine. A senior emergency airway practitioner is called and decides to proceed with RSI, but also prepares to proceed to an immediate surgical airway should this be required. Full pre-oxygenation is carried out and etomidate 0.3 mg/kg is given, followed immediately by suxamethonium 1.5 mg/kg. Cricoid pressure is applied by an experienced assistant. Apnoea and fasciculations occur over the next 30 s and the patient is fully relaxed by 45 s. Laryngoscopy is performed using a size 4 Macintosh blade, and tracheal intubation is attempted with a size 8.0 cuffed tube over an intubating bougie.

QUESTIONS (2) 1. 2. 3.

What are the options for achieving a definitive airway in a patient who is predicted to be difficult to intubate? How is a ‘‘failed airway’’ defined? What action should be taken in the event of a failed airway in the ED?

Table 3 HAVNOT mnemonic for evaluation of potential difficulty in orotracheal intubation H A V N O T

100

History – including previous airway problems Anatomy – features of the face, mouth and teeth that may suggest intubation will be difficult Visual clues – obesity, facial hair, age Neck mobility and accessibility, including the presence of in-line stabilisation Opening of the mouth – less than 3 fingers suggests potential difficulty with intubation Trauma – the possibility of anatomical disruption and blood in the airway

A failed airway may be defined as an inability to maintain the SpO2 .90% with BMV in the situation where intubation cannot be achieved. In addition, a failed airway exists when an experienced practitioner has not been able to achieve tracheal intubation with three attempts. The chances of successful intubation are greatest with the first attempt, but intubation may still be achieved with subsequent attempts provided that technical adjustments are made and conditions are optimised between attempts. Optimisation may include adjustment of the patient’s position, external laryngeal manipulation, use of a bougie, a change of laryngoscope blade or a change of practitioner. There is no point attempting further laryngoscopy after an initial failure unless something is changed between attempts. If three laryngoscopic attempts have been performed by an experienced practitioner, intubation is very unlikely to be achieved in subsequent attempts. When a failed airway occurs it may or may not be possible to oxygenate the patient successfully with a bag and mask. When BMV is not initially successful, attention must be directed to achieving the best possible technique using a two-handed twoperson technique with both nasopharyngeal and oropharyngeal airways. If oxygenation is still not achieved, a ‘‘can’t intubate, can’t oxygenate’’ failed airway exists. The failed airway therefore occurs in all grades of urgency from the direst emergency demanding immediate intervention to a situation where successful oxygenation by bag and mask permits a more considered approach.

(3) What action should be taken in the event of a failed airway in the ED? A definitive airway is defined as the successful placement of a cuffed tube in the trachea, permitting ventilation of the patient. If the patient cannot be intubated after induction of anaesthesia and paralysis, effective BMV will be required to maintain Emerg Med J 2008;25:98–102. doi:10.1136/emj.2005.030635

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Occasional series in critical care in the emergency department Figure 1 UK TEAM course algorithm, rapid sequence induction (RSI) and failed airway management. LMA, laryngeal mask airway; CXR, chest x ray; NMB, neuromuscular blocking drug.

adequate oxygenation. Oxygenation is the paramount concern, not successful intubation. BMV may be difficult if the patient is obese, has facial hair (or other features precluding a good mask seal), is elderly or edentulous, or has poor lung compliance. If optimal BMV fails to achieve adequate oxygenation, the practitioner must be prepared to proceed to cricothyroidotomy as delay will worsen the hypoxia and increase the likelihood of patient harm. However, the successful insertion of a laryngeal mask airway (LMA) may permit oxygenation and avoid the need for immediate cricothyroidotomy. The LMA is quickly and easily inserted, and most UK authorities identify it as the rescue device of Emerg Med J 2008;25:98–102. doi:10.1136/emj.2005.030635

choice.6–8 The LMA can be successfully placed by clinicians of all grades after a short period of training9 10 and has been shown to be effective in various clinical situations including cardiac arrest,11 trauma12 and prehospital care.13 14 The LMA is not a definitive airway as the orifice sits above the laryngeal inlet and there is no cuffed tube in the trachea. In addition, excessive leakage may occur, preventing successful ventilation and oxygenation when resistance to ventilation is high (eg, in obese patients or those with chronic obstructive pulmonary disease). When the LMA also fails to maintain adequate oxygenation, a surgical airway is immediately indicated. In children under 101

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Occasional series in critical care in the emergency department 12 years this is accomplished using a needle cricothyroidotomy, while in adults a surgical cricothyroidotomy is preferred—either by a prompt open procedure or percutaneous technique. Both methods are relatively easily learned and have similar rates of success and complications.15 The main cause of poor patient outcome after a surgical airway is excessive delay in undertaking the procedure.

Acknowledgements: Tables 1 and 3 and fig 1 are drawn from the UK Training in Emergency Airway Management (TEAM) course and used with permission. The UK TEAM course is approved by the College of Emergency Medicine, details can be found at: http://www.emergencymed.org.uk/CEM/Academic%20Courses/Courses%20 Approved%20by%20CEM.asp. Table 2 is adapted with permission from the Difficult Airway Course and Walls et al.4 Competing interests: None declared.

REFERENCES CASE OUTCOME RSI proves successful. A Cormack and Lehane grade II view is achieved and the tube is passed into the trachea using an intubating bougie. Oxygen saturation never falls below 90% during the procedure. The patient is given a paralysing dose of vecuronium (8 mg) and an infusion of propofol is commenced at 10 ml/h. The patient is transferred to the radiology department for CT scanning of the cervical spine, thorax and abdomen and then to the critical care unit for further management.

CONCLUSIONS This case illustrates the principles of emergency airway management in the ED. A systematic approach is required to initial airway management, airway assessment and preparation for intubation (fig 1). Rapid sequence induction of anaesthesia and tracheal intubation is the technique of choice in the vast majority of patients, but requires a combination of knowledge, skills and judgement that are best achieved through structured training and supervised practice. All emergency airway practitioners must work within their scope of competence, using techniques, drugs and equipment with which they are familiar. A clear plan of immediate action is required in the case of difficult or failed intubation and if both intubation and oxygenation fail.

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1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

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Emerg Med J 2008;25:98–102. doi:10.1136/emj.2005.030635