Algorithms for unanticipated difficult endotracheal intubation in adults

Difficulties in endotracheal intubation, proper ventilation and oxygenation of a patient are the commonest cause of CNS hypoxaemic injuries and anaesthesia-related deaths. The prevalence may even be higher than the official data. Moreover, difficult endotracheal intubation may cause traumatic complications, i.e. severe damage to soft tissues (larynx, oral cavity) and resulting remote consequences, e.g. airway obstruction. Therefore, management of the unanticipated difficult intubation should focus on the maintenance of oxygenation and prevention of upper airway damage, including aspiration of gastric contents to the airways.
The present guidelines for “difficult intubation” are based on the Difficult Airway Society guidelines (www.das.uk.com; Henderson JJ, M.T. Popat MT, Latto IP, Pearce AC: Difficult Airway Society guidelines for management of the unanticipated difficult intubation. Anaesthesia 2004, 59: 675–694) modified by the Section of Instrumental Management of Difficult Airways of the Polish Society of Anaesthesiology and Intensive Therapy. The knowledge of instrumental provision of patent airways was updated and supplemented with the authors` experiences. The survey substantiates the choice of techniques and describes alternative methods for difficult intubation management. The guidelines do not include paediatric or obstetric patients and anticipated difficult intubations, which should be managed using the scenarios individually adjusted to a given patient.
The algorithms mainly regard the cases in which the glottis cannot be visualized at direct laryngoscopy. Even if visualization is possible, the placement of the endotracheal tube may be difficult. It should be stressed that the use of a proper rigid guide or insertion of the Eschmann flexible introducer (bougie) into the larynx followed by sliding of the endotracheal tube into the larynx is recommended only when at least a part of the laryngeal opening is visualized. “Blind” insertions of the endotracheal tube are not recommended.
The essence of guidelines are algorithms (scenarios) of management. They are based on a series of alternative plans used once initially planned techniques have failed. None of the methods is reliable; alternative, ”rescue” plans of management are necessary. The effective method of airway management requires careful planning in situations when the initial plan (plan A) fails and its “rescue” versions should be implemented (plans B, C, D). Prior to endotracheal intubation, anaesthetists should always consider its possible failure. Routine, haste, mindless faith in one’s skills, lack of prepared devices or management plans in case of difficulties are common causes of potential failures and complications.  When difficulties occur, the assistance of another anaesthetist or anaesthetic nurse and suitable equipment should be available. Seeking assistance is the first and basic step in the management algorithm for difficult intubation. If more experienced anaesthetists are not available, next attempts to provide patent airways should be made by another anaesthetist, even less experienced. The fresh hand approach is recommended.
The approach to everyday practice of provision of patent airways should be changed. The maintenance of tissue oxygenation takes priority during each stage of “rescue” options. Provision of patent airways, including endotracheal intubation, is only one of the methods to accomplish the goal.

I. Algorithm 1 shows the main rules of management. It contains the „rescue” and key techniques required as well as possible outcomes of each plan stage. The successive plans of management are denoted by letters A-D:
– plan A - initial (routine) intubation plan;
– plan B - when plan A fails;
– plan C - maintenance of oxygenation and ventilation of lungs, postponement of surgery, awakening the patient when plans A and B have failed;
– plan D - rescue techniques for “can`t intubate, can`t ventilate” (CICV) cases.
The outcome of each plan determines progression to subsequent plans. In some cases, progress depends on clinical factors, such as the best visualization of the larynx. The subdivision of Cormack-Lehane grade 3 into 3a (the epiglottis can be elevated) and 3b (the epiglottis cannot be elevated from the posterior pharyngeal wall) markedly affects the choice and  success of flexible bougie and fiberoscopic techniques. In specific situations when “full stomach” patients must be anaesthetized, the management plans ought to be modified (algorithm 3).
The main stages of “rescue” plans and individual techniques for provision of patent airways are discussed thoroughly in the guidelines. Their full description, however, should be sought in suitable textbooks and scientific literature. The techniques discussed should be practised under competent supervision during routine intubations or on manikins. Periodic trainings of the personnel and verification of their skill are recommended. The entire staff should be familiar with the guidelines; the suitable charts should be placed in operating theatres and guidelines put into practice in the form of legally settled hospital documents. The procedures may modify the guidelines accounting for the specificity of the workplace. The difficult intubation kits should be prepared.  

II. Algorithm for unanticipated difficult endotracheal intubation during routine general anaesthesia in an adult patient after induction of anaesthesia with non-depolarising neuromuscular blocking agents (algorithm 2).

Plan A: initial (routine) plan of endotracheal intubation
In the routine approach to endotracheal intubation, the typical equipment is recommended, i.e. the laryngoscope with a curved blade of a suitable size. The key element of patients` safety is to ensure appropriate oxygen saturation during attempts of endotracheal intubation by substituting oxygen for nitrogen in order to prolong the period of safe apnoea. This is accomplished by preoxygenation for at least 3 min and 90% oxygen in the air expired. Another relevant issue is proper sequence of anaesthetics:  the supply of an anaesthetic, an attempt to ventilate lungs through the facial mask followed by administration of relaxants once such ventilation has been found feasible. The use of relaxants according to the timing principle is not recommended.
The first endotracheal intubation attempt should be performed under optimal conditions after adequate muscle relaxation (a suitable dose of a neuromuscular blocker) and in the appropriate position of the head and neck (the “sniffing” position). In some groups of patients, other positions are used, e.g. in severely obese patients, the head elevated laryngoscopy position (HELP) is recommended, i.e. with the rolled cushions placed under the shoulders. External laryngeal manipulation is recommended, e.g. backward, upward, rightward pressure (BURP) on the thyroid cartilage. If, despite these measures, the visualization of the glottis is still a grade 3 or 4 (Cormack), alternative techniques (devices) ought to be used, i.e. the Eschmann bougie and/or other blades. Alternative devices of proven clinical value for direct laryngoscopy include laryngoscopes with the straight blade (Miller) and blade with a mobile  tip lifting the epiglottis (McCoy). The choice depends on the skills of anaesthetists in an individual technique. Proper oxygenation should be maintained by facial mask ventilation between the attempts. Each should not exceed 30 sec. The decision about the technique change or progress to the next plan should be prompt without endangering the patient to become hypoxic and without further, prolonged attempts of intubation with force, which may lead to traumatic complications and injuries. Eschmann bougies are not expensive and should be included in each intubation kit. There is evidence that Eschmann bougies are more useful than endotracheal tubes on rigid guides when visualization of the larynx is a Cormack grade 3. Rigid guides cause more laryngeal and tracheal injuries.
Alternative laryngoscopy techniques of recognized clinical value may be used by those experienced in their application – thus trainings are necessary. Our observations confirm that even the best equipment in the hands of inexperienced anaesthetists is useless and in many cases further attempts of intubation with the techniques and devices the attending anaesthetist is familiar with are more beneficial.
The most commonly mentioned devices of verified and high efficacy include:
–flexible fiberoscopes
–fibre optic guides, e.g. Levitan FPS Scope, OptiFelx, SenSaScope, Bonfils;
–video laryngoscopes, e.g. Berci-Kaplan, Glidescope, McGrath;
–optical laryngoscopes, e.g. AirTraq, Pentax AWS;
–magnifying laryngoscopes, e.g. Truview Evo2.
The ‘golden standard’ for anticipated and unanticipated difficulties in glottis visualization is a fiberoscope. Unfortunately, there are at least several inconveniences associated with its use:
1.The endotracheal tube runs ‘blindly’ through the glottis, which is likely to injure the epiglottis or vocal cords.
2.High skills are required; therefore, periodic trainings should be provided.
3.The majority of fiberoscopes is expensive on purchase and operation and requires special devices and rooms for sterilization.
4.Fiberoscopes are damage-sensitive, including biting by patients.
5.Secretions limit the visual field; in the majority of cases, special anti-fog liquids are necessary.
The other devices for intubation under visual control are divided into the following groups:
1.Fibre optic guides, e.g. Bonfils, Sikani, Levitan, SensaScope.
2.Video laryngoscopes with standard or similar to typical blades, e.g. Glidescope, Berci-Kaplan, McGrath.
3.Video laryngoscopes with endotracheal tube canals, e.g. AirTraq, Pentax AWS.
The assets of the first group devices include: high percentages of successful intubations, lesser force needed to visualize the superior laryngeal aperture – lower percentages of traumatic complications, smaller mouth opening required for intubation, shorter time to become skilful and retention of these skills for a long time (compared to fiberoscopes).
The drawbacks of such devices are limited visual field, secretions and blood limit the view, intubations through the nose are infeasible.
The second group devices can be divided into two subgroups:
2.1.Video laryngoscopes with the Macintosh blade: LaryFlex, Berci-Kaplan.
2.2.Video laryngoscopes with differently bent blades: McGrath, Berci-Kaplan Dorges.
Their advantages include better visual field (with a „normal” laryngoscope – about 15o whereas with a video laryngoscope – even 80o), high percentages of successful intubations, a good learning curve, lesser force needed to visualize the laryngeal opening, better ”lightening”, smaller mobility of the cervical spine required.  
The inconveniences are associated with the necessity to use the guide and the fact that visibility may be limited by the fog or secretions and blood in the oral cavity.
The third group includes the devices with a special canal for the endotracheal tube. Compared to the second group, the devices cause less severe haemodynamic reactions to attempts to visualize the laryngeal opening. The examples are AirTraq and Pentax AWS.
Video-optic guides (Levitan, Bonfils) should be used with a laryngoscope.  The endotracheal tube railroaded over the guide is laryngoscopy-guided to the region of laryngeal  opening and inserted into the trachea under visual control through the viewfinder. Video laryngoscopes are used in a similar way.
Multiple and prolonged attempts of intubation increase the number of complications and deaths. The extent of laryngeal oedema may be clinically undetectable until extubation or fiberoscopy. Therefore, the essential part of plan A is to limit the number and time of intubation attempts to prevent traumatic complications (of the larynx, in particular), which may make lung ventilation impossible. It is difficult to justify more than two attempts with the same size of the blade. Four laryngoscopies at most are acceptable. However, the third attempt should be carried out by another anaesthetist. If such techniques and manoeuvres fail, plan B should be implemented.
According to the ESA guidelines presented in Copenhagen in 2008, guides for endotracheal tubes should be used in each case of anticipated intubation. Moreover, video laryngoscopes are recommended for routine use in each patient undergoing anaesthesia and endotracheal intubation, as they reduce the incidence of traumatic complications.

Plan B: secondary endotracheal intubation plan
The basis of this plan is to use alternative supraglottic devices to maintain airway patency. Alternative techniques allow lung ventilation and oxygenation both during and between intubation attempts. This is best achieved by using a dedicated airway device which maintains airway patency while facilitating tracheal intubation.  Although the classic laryngeal mask airway (LMA) has been recommended as a ventilation and intubation device, it was not designed as a conduit for tracheal intubation and has clear limitations when used for this purpose without a fiberoscope. Instead of LMA, other supraglottic airway devices could be used, i.e. laryngeal tube, Cobra PLA, I-Gel, etc. However, only the intubating laryngeal mask airway (ILMA) (FastTrach) enables endotracheal intubation while maintaining ventilation. The device was designed specifically for “blind” intubation. Other available supraglottic devices allowing intubation through their lumen include Cobra PLA, Air-Q and I-Gel. However, due to their design and lower percentages of successful „blind” tracheal intubations, their use with fibre optic guides or fiberoscope is recommended.
To increase the effectiveness of ILMA, the TrachLight technique may be used, yet ILMA intubation with a flexible fiberoscope under direct visual control is more beneficial. The essence of ILMA (or other supraglottic device) use is maintenance of oxygenation and lung ventilation until suitable equipment for endotracheal intubation under visual control is prepared (provided); the fiberoscope is recommended. If such a device is not quickly available, blind intubation attempts through the lumen of supraglottic devices may be undertaken. Only ILMA, however, provides over 90% effectiveness. The use of ILMA requires training and practice yet a learning curve is extremely favourable – the plateau is obtained after about 20 intubations; in the endotracheal intubation – at least 50. ILMA should be removed once proper tube position has been confirmed.  ILMA may also be left and the lungs ventilated through the endotracheal tube after deflating the ILMA sealing cuff.
Intubation with a bronchofiberoscope may be carried out through the classic LMA. The use of  laryngeal masks as fiberoscope guides substantially improves the effectiveness of intubation. Fiberoscopic intubation requires training and practice. In many cases, it is necessary to use the laryngoscope to lift the tongue base to facilitate the insertion of the fiberscope.  The laryngeal mask ventilation canal is used as a guide for the fiberoscope and the “difficult place”, i.e. the tongue base, is omitted; the fiberoscope tip is placed in the laryngeal opening and with slight manoeuvres, the tube may be inserted into the trachea. This also reduces the effects of secretions on the visibility. LMA may be left in place, provided it does not interfere with the procedure.
If two attempts using the rescue emergency secondary plan techniques fail, the surgery should be postponed and the patient awakened – plan C ought to be implemented.
If endotracheal intubation is not necessary for further safe anaesthesia and surgery, the continuation of anaesthesia using the supraglottic device may be considered.  
LMA Supreme is of interest. It is the only laryngeal mask designed for elective use during anaesthesia in 1 and 2 degree obesity and for short laparoscopic procedures. LMA Supreme is characterized by better sealing and easy insertion, yet it is not suitable for  transluminal intubation attempts.  

Plan C: Maintenance of oxygenation and ventilation, postponement of surgery and awakening the patients if plans A and B have failed.
If plan B fails, the priority is to avoid airway trauma (which may lead to complete obstruction due to laryngeal oedema) and to maintain ventilation and oxygenation  using appropriate devices (e.g. LMA). Elective surgery should be postponed and patent airways should be instrumentally maintained (LMA) until complete recovery, complete reversal of neuromuscular block and restoration of protective reflexes. An alternative plan of anaesthesia may be considered if the surgery can be performed under regional anaesthesia; the airways are most safely secured with the patient awakened. If adequate ventilation and oxygenation cannot be achieved, ventilation should be carried out using the face mask. If adequate ventilation is impossible and severe hypoxaemia develops, plan D should be implemented i.e. rescue techniques for can’t ventilate can’t intubate situations. Plan D involves conicotomy or conicopuncture. Tracheatomy is not considered a rescue technique due to its duration.

III. Algorithm for unanticipated difficult endotracheal intubation during rapid induction (without active oxygenation before intubation) – algorithm 3.

Plan A: initial (routine) intubation plan
In such a case, contrary to the one described earlier, the risk of regurgitation, vomiting and aspiration of gastric contents to the lungs is higher. The detailed preparation plans and scenarios of management and treatment of complications are described in the available literature. Modifications of the intubation technique (for this scenario) involve the use of adequately long preoxygenation and the Sellick manoeuvre. It ought to be remembered that preoxygenation (lung nitrogen substituted with oxygen) is essential for apnoea tolerance. At least 3-minute passive oxygenation or 8 deep breaths are recommended. The Sellick manoeuvre is pivotal for prevention of gastric contents aspiration to the lung and is an integral element of rapid sequence intubation (RSI). However, the manoeuvre may hinder the insertion of the laryngoscope blade, placement of the endotracheal tube or even cause obstruction of airways. The cricoid force of 3 kg (30 N) provides good protection against aspiration yet may shift the laryngeal opening and make rapid intubation impossible. Therefore, the force during the Sallick manoeuvre should be reduced to 1 kg if the laryngeal opening is poorly visualized. The main measures to optimize the intubation technique and use of the Eschmann guide or other blades at initial attempts are analogical to those in plan A for patients anaesthetized for elective surgery. If the intubation fails at three attempts, plan C should be implemented (maintenance of oxygenation and awakening the patient).
Deep anaesthesia and excellent relaxation during RSI are essential for provision of good intubation conditions and prevention of regurgitation. Good intubation conditions are achieved during 30-60 sec using rocuronium, 1-1.2 mg kg-1. Rocuronium does not induce muscle fasciculation and possible pressure increases in the peritoneal cavity, which with suxamethonium predisposes to regurgitation. Additionally, immediate reversal of rocuronium effects is possible by supplying sugammadex. Sugammadex should be included in the pharmacological “difficult” intubation kit.

Plan C: Maintenance of oxygenation and ventilation and postponement of surgery, if possible
For two relevant reasons, Plan B is neglected in patients undergoing RSI. The risk of regurgitation and vomiting is much higher compared to patients undergoing induction of anaesthesia for elective surgeries; further attempts of intubation in those patients would enhance the risk. Short action of suxamethonium increases the risk of laryngospasm and may cause difficulties in laryngoscopy when neuromuscular conduction is restored; therefore, further attempts of intubation would only cause additional unnecessary risks. When the initial intubation attempts in this scenario fail, awakening the patient is the safest method of conduit; if possible, the surgery should be postponed.
Plan C is divided into two sub-scenarios, in which the urgency of proceedings with surgery differs. The risk of delaying the surgery vs the risk of proceeding with  the lack of optimal airways protection against aspiration should be balanced. If it is essential to proceed with the surgery, lungs should be ventilated using the face mask and the Sellick manoeuvre maintained.
At present, the use of laryngeal masks is considered a standard, although it is not always effective. It is recommended to use supraglottic devices enabling decompression of the stomach (additional canal for the gastric probe), such as LMA ProSeal or LMA Supreme. LMA ProSeal provides better protection against gas leak (better seal of the larynx) and against aspiration than classic LMA. Unfortunately, compared to classic LMA, the technique of ProSeal LMA placement is more complicated. A new device, LMA Supreme, ensures better seal and is much easier to insert. The device is a good alternative for LMA ProSeal.  MRI in cadavers showed that only LMA Supreme provides complete obturation of the oesophageal aperture and thus prevents potential regurgitation. Additionally, gastric decompression through the gastric probe canal reduces the risk of regurgitation-related complications. The Sellick manoeuvre hinders proper placement of the laryngeal mask and lung ventilation. When the mask is inserted in an emergency, the cricoid pressure may be reduced.
The surgery should be postponed and the patient awakened, if possible; further plan and equipment for “difficult intubation” ought to be prepared. Maintenance of ventilation and oxygenation using the face mask is permissible in such cases, despite increased risk of gastric air distension. If lung ventilation is not possible and life-threatening hypoxia is developing – plan D (the rescue technique for can`t intubate, can`t ventilate situations) should be immediately implemented.  

IV. Failed intubation, increasing hypoxaemia and difficult ventilation in the paralysed and anaesthetized patients (algorithm 4)
Plan D: rescue technique for can`t intubate can`t ventilate  situations.
This scenario may develop rapidly but often occurs after repeated unsuccessful attempts of intubation due to traumatization of airways. It is highly likely that patients after prolonged intubation will develop hypoxaemic CNS damage of various degrees. Before using the invasive rescue techniques to provide airway patency, all other manoeuvres enabling ventilation of lungs should be applied; e.g. tight placement of the face mask, head tilting, insertion of the supraglottic device. However, the decision about cricothyroidotomy should not be much postponed. Facing the risk of complications related to hypoxaemic CNS damage, is it better to perform conicotomy or conicopuncture without waiting too long for qualified assistance or suitable equipment. The risk and complications associated with invasive ventilation techniques should be continually balanced with the risk and complications of hypoxaemic CNS damage or even death of the patient. Rapidly developing hypoxia, especially combined with bradycardia, is an indication for immediate interventions using invasive techniques. At present, the devices  enabling rescue ventilation for about one hour are available, which saves time to undertake other advanced attempts of provision of airway patency. Such devices include the Portex Cricoidotomy Kit (PCK) with a 6-mm tube and ManuJet kit enabling jet ventilation. Classical surgical emergency tracheostomy may be difficult to carry out and induce severe complications. Only a few operators are capable of performing it over less than 3 min. The majority requires more time. Unfortunately, delay in the procedure with increasing hypoxaemia virtually means the patient`s death.  Therefore, rescue tracheotomy is not recommended.
All currently known guidelines of management in CICV situations recommend conicopuncture (percutaneous catheter) and endotracheal jet ventilation (e.g. using the ManuJet) or surgical conicotomy. Both techniques are a standard. Both may be performed successfully within less than 30 sec and do not require much experience or skills compared to tracheotomy.
Conicotomy may be particularly difficult in obese patients. The PCKs are recommended as thanks to the Veres needle the risk of tracheal puncture and oesophageal perforation is markedly reduced. Another advantage of PCK for obese patients is its suitably long catheter and tube. The invasive access to airways is the immediate measure to restore oxygenation. Permanent airway control is necessary by e.g.  tracheotomy; in some patients, intubation may also be feasible.  
Another intubation technique using the cricothyroidotomy is retrograde intubation. This intubation may be performed using the Touchy needle or central intravenous access needle. After identification of the trachea, the epidural catheter or metal guide is inserted cephalad until visible in the oral cavity. The endotracheal tube is railroaded over it and inserted  to airways. Unfortunately, this method is time-consuming and is not recommended in CICV situations. It may be used when endotracheal intubation is necessary, the surgery cannot be postponed, and the suitable equipment for difficult intubation is unavailable provided that ventilation with the face mask is feasible.
The Difficult Airway Society guidelines rely on experience and scientific knowledge. The two main principles are to maintain oxygenation and prevent upper airway injuries. Oxygenation in difficult intubation is mainly maintained by ventilation of lungs using the face mask or supraglottic devices.
The recommended techniques should be an integral part of the initial and further stages of trainings in airway management. Learning of the entire process should be started from the theory followed by implementation of the theoretical knowledge into practice using manikins and finally transferred to clinical settings.
The recommendations in questions generate certain equipment needs. One of them is equipment for regular trainings. Another one is a special kit which should include all instruments needed for management once difficult intubation is faced and should be quickly available whenever procedures under general anaesthesia are carried out.
Suitable scenarios of reporting and informing the patient about difficulties in intubation should be implemented. Events should be recorded not only in anaesthesia protocols but also in discharge cards. Patients should become aware of the necessity to inform the anaesthetist if further general anaesthesias are needed.

Aknowledgements
The authors wish to thank Dr Chris Fretka – the Chairman of the Difficult Airway Society for his permission to use DAS materials while designing the guidelines of the Section of Instrumental Management of Difficult Airways of the Polish Society of Anaesthesiology and Intensive Therapy.

Received: 20.07.2009
Accepted: 20.08.2009

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*Tomasz Gaszynski
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