Airway management and acute upper-airway obstruction

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Chapter 25 Airway management and acute upper-airway obstruction

The primary objective of airway management is to secure unobstructed gas exchange and protect the lungs from soiling. Because of the critical importance of maintaining gas exchange, upper-airway obstruction is a life-threatening emergency. Upper-airway obstruction results from a wide range of pathophysiological processes, and therefore rapid assessment and establishment of a patent airway must take priority, even in the absence of a specific diagnosis. As no single airway management modality is universally applicable, the intensive care unit (ICU) physician must be capable of performing a variety of airway management techniques and instituting them in a logical and systematic way (Figure 25.1).

Figure 25.1 Difficult airway algorithm (see text). LMA, laryngeal mask airway; iLMA, intubating laryngeal mask airway; TTJV, transtracheal jet ventilation.

AIRWAY MANAGEMENT TECHNIQUES

Airway management techniques are generally classified as non-invasive or invasive, depending on whether instrumentation occurs above or below the glottis, surgical or non-surgical, and definitive (Table 25.1). Definitive techniques secure the trachea and provide some protection from macroscopic aspiration and soiling. While bag-and-mask ventilation and direct laryngoscopic tracheal intubation remain the routine methods of airway management in ICU, the use of fibreoptic bronchoscopy is increasingly common, especially in special circumstances. Management of failed intubation and ventilation by various alternative techniques, particularly the use of the intubating laryngeal mask airway (iLMA) and cricothyroidotomy, is well described.^1,²

Table 25.1 Characteristics of airway management techniques

The technique of choice will depend on each individual situation and is determined by the interaction of patient and clinical factors, which partially determine the appropriate technique (Table 25.2), and the clinician’s experience in applying the chosen technique. Other factors include availability of help, levels of training and supervision and accessibility of equipment. A portable storage unit with a wide choice of equipment appropriate for difficult airway management should be available in every ICU (Table 25.3).

Table 25.2 Commonly recommended applications of described airway management techniques. Examples of common alternatives are given in approximate order of choice

	Difficult direct laryngoscopic intubation	With difficult spontaneous/mask ventilation
Awake	Fibreoptic bronchoscopic intubation Direct laryngoscopic intubation* Blind nasal intubation Retrograde intubation	Percutaneous cricothyroidotomy* Surgical tracheostomy*
Anaesthetised or comatose (empty stomach)	Bag-and-mask ventilation Direct laryngoscopic intubation Different blade Fibreoptic bronchoscopic intubation Intubating LMA/LMA Lighted stylet Blind nasal intubation	Laryngeal mask airway (LMA) Transtracheal jet ventilation Rigid ventilating bronchoscope Percutaneous cricothyroidotomy Surgical tracheostomy
(full stomach)	Maintain cricoid pressure with all techniques Intubating LMA/Proseal LMA Combitube	Percutaneous cricothyroidotomy Surgical tracheostomy Combitube

The technique(s) chosen should also depend on the clinician’s knowledge and ability. Cricoid pressure should be applied with a force of approximately 30 N, but applied force can be temporarily reduced to assist airway manoeuvres.

* Under local anaesthesia.

Masks

Face and nasal masks of differing make and size variety

Airways

Oropharyngeal airways

Nasopharyngeal airways

Airway intubator guide for oral endoscopic intubation

Laryngeal mask airway (LMA) and intubating LMA with appropriate endotracheal tubes

Rigid laryngoscope with a variety of designs and sizes

Short handle or variable angle (Patil-Syracuse) laryngoscope

Curved blades: Macintosh, Bizarri-Guiffrida

Straight blades: Miller

Bent blade: Belscope

Articulating-tip blade: McCoy

Fibreoptic stylet laryngoscope or Bullard laryngoscope

Endotracheal tubes of assorted size

Murphy tubes

Microlaryngoscopy tubes

Endotracheal tube stylets

Gum elastic bougie (Eschmann stylet)

Malleable stylet

Tube changer, hollow tube changer (jet stylet)

Lighted stylet (light wand)

Fibreoptic intubation equipment

Patil endoscopic mask, oral airways or blocks to facilitate oral endoscopic intubation

Fibreoptic endoscopes with light source, adult and paediatric-sized

Combitube

Emergency surgical airway access

Percutaneous cricothyroidotomy set

Transtracheal jet ventilation – cannula and high-pressure O₂ source connectors

Regulated central wall O₂ pressure (Sanders-type injector)

Unregulated central wall O₂ pressure device

Exhaled carbon dioxide monitor

Capnometer/capnograph

Chemical indicators

NON-INVASIVE TECHNIQUES

BAG-MASK VENTILATION

Mask ventilation, using a bag-mask resuscitator, is a basic skill that requires time and experience to master. It should be learned using mannekins, simulators and practice in the controlled environment of the operating theatre so that when used in the emergency setting in ICU the skill is already well established. The manually squeezed bag is self-inflating, usually with a simple reservoir bag in series, which, if kept inflated, ensures that a consistent high oxygen concentration can be delivered. The addition of a positive end-expiratory pressure (PEEP) valve may improve arterial oxygenation in patients with lung pathology and help overcome airway obstruction due to laryngospasm. Transparent face masks are recommended as they allow observation of misting during exhalation, assessment of the position of adjunct artifical airways and early observation of gross airway soiling.

Some considerations when performing mask ventilation include the following:

1 Inadequate ventilation. Good airway positioning by head tilt and chin lift, or if necessary the jaw thrust manoeuvre, is essential to maintain an open airway. The seal of the mask against the face is important and technically good hand positioning must be learned and practised. A beard may be covered with a large adhesive plastic dressing with a hole cut out for the mouth, or smeared with petroleum jelly or water-based lubricant. Ventilation of edentulous patients may be aided by improving hand position or special masks. Two operators are recommended if a mask face leak is excessive, one to hold the mask and the other to manipulate the bag-mask resuscitator.

2 Gastric insufflation is common if high tidal volumes are used and increases the risk of vomiting and aspiration (aim for 300–500 ml). Severe distension may occasionally cause cardiovascular compromise. Carefully applied cricoid may prevent gastric gas insufflation.

3 Pulmonary aspiration. In the emergency situation with a full stomach, mask ventilation with cricoid pressure is recommended until the airway can be secured. Passage of a nasogastric tube to aspirate gastric contents can be attempted, but with caution as vomiting may be induced.

ORO- AND NASOPHARYNGEAL AIRWAYS

In the unconscious patient, functional obstruction is primarily caused by loss of muscular tone and subsequent inspiratory airway narrowing at the soft palate, epiglottis and tongue base. An oropharyngeal airway can help establish an adequate airway for spontaneous or bag-mask ventilation when proper head positioning is insufficient. It is inserted with the concavity facing the palate and then rotated 180° into the proper position as it is advanced. Complications include mucosal trauma, worsening the obstruction by pressing the epiglottis against the laryngeal outlet if the tongue displaces posteriorly, and occasionally laryngospasm. The following sizes (length from flange to tip) are recommended: large adult: 100 mm (Guedel size 5); medium-sized adult: 90 mm (Guedel size 4); small adult; 80 mm (Guedel size 3).

A nasopharyngeal airway is a soft rubber or plastic tube inserted into the nostril and advanced along the floor of the nose (in the direction of the occiput). Correctly positioned, the tube traverses the posterior pharynx. It is better tolerated by semiconscious patients than the oropharyngeal airway. Complications include epistaxis, aspiration and, rarely, laryngospasm or oesophageal placement.

LARYNGEAL MASK AIRWAY (LMA) AND INTUBATING LMA

The LMA is a reusable device that consists of a silicone rubber tube connected to a distal elliptical spoon-shaped mask with an inflatable rim, which is positioned blindly into the pharynx to form a low-pressure seal against the laryngeal inlet.³ LMAs are useful to achieve non-definitive airway patency in many emergency situations (see Figure 25.1), and can be used to provide positive-pressure ventilation.² Once positioned the LMA has been used to guide the passage of stylets, bougies, the bronchoscope and an endotracheal tube into the trachea, but with difficulty.^2,⁴ The iLMA or FasTrach is a modification of the LMA with several features to facilitate intubation once the iLMA is placed.⁵ There is a guiding ramp and epiglottic elevating bar at the aperture to direct the endotracheal tube to the glottis. It also has an anatomically curved, rigid shaft and handle to allow easy and firm manipulation during placement and when the endotracheal tube is passed.⁶ The iLMA is the laryngeal mask of choice if intubation is required, as is frequently the case in ICU patients.

Although preparation and patient positioning techniques for placement of a LMA and iLMA are similar, the insertion technique is quite different. The mask airway is prepared for insertion by deflating and smoothing out the cuffed rim to be wrinkle-free, and the posterior surface and patient hard palate are lubricated with water soluble jelly. The patient is positioned as for endotracheal intubation, with slight flexion of the neck and extension of the atlanto-occipital joint (sniffing-the-morning-air position). The LMA is inserted with the tip of the cuff continuously applied to the hard palate, and with the right index finger guiding the tube to the back of the tongue until a firm resistance is encountered. The cuff is then inflated with 20–40 ml of air (adult sizes) before attachment of the breathing circuit.

To begin insertion of an iLMA, ensure the curved metal tube is in close proximity to the chin (the metal handle points to the toes) and the mask tip flat against the palate prior to insertion. The mask is inserted and positioned with a circular motion, maintaining contact pressure between the posterior aspect of the mask and the palate and posterior pharynx, until some resistance in the hypopharynx is felt. A laryngoscope can be used to assist placement. Once gas exchange is established, an attempt at intubation can be made. The well-lubricated endotracheal tube is passed down the iLMA tube, rotating gently to distribute the lubricant until the 15-cm marker (or the transverse line on the proprietary LMA Fastrach endotracheal tube). The endotracheal tube tip is now positioned through the epiglottic elevating bar. Gently lift the iLMA about 2–5 cm with the metal handle while the endotracheal tube is advanced into the trachea. Inflate the endotracheal tube cuff and confirm tracheal intubation (see later). Remove the endotracheal tube connector, and position the stabiliser rod on the endotracheal tube opening – this is needed to maintain the tube position in the trachea as the mask is removed. Lastly, gently remove the iLMA over the endotracheal tube/stabiliser assembly. Remove the stabiliser rod, reconfirm tube position and secure.

The successful use of an iLMA requires some familiarity with the equipment and technique, and at least simulated exposure is strongly recommended. Contraindications for using an ILMA or LMA include inability to open the mouth, pharyngeal pathology, airway obstruction at or below the larynx, low pulmonary compliance or high airway resistance. Complications include aspiration, gastric insufflation, partial airway obstruction, coughing, laryngospasm, postextubation stridor and kinking of the shaft of the LMA.

COMBITUBE (OESOPHAGEAL–TRACHEAL DOUBLE-LUMEN AIRWAY)

The oesophageal–tracheal Combitube is a double-lumen tube that is blindly inserted into the oropharynx up to the indicated markings.⁷ The oesophageal lumen is blocked at the distal end and has side perforations at the pharyngeal level whereas the tracheal lumen has a hole at the distal end. It has two balloon cuffs, a distal one and a proximal pharyngeal balloon. The patient is ventilated through the oesophageal lumen initially as the Combitube usually enters the oesophagus,⁷ with the distal cuff sealing the oesophagus and the proximal balloon sealing the proximal pharynx. Gas exits the perforations and enters the pharynx and larynx. In the event of failure of ventilation, tracheal intubation may have occurred and then the tracheal lumen is ventilated while the distal cuff seals the trachea. Although demonstrated to be a useful airway management adjunct, its role in resuscitation and management of the difficult airway in the ICU environment is yet to be established. Barotrauma, especially oesophageal rupture, has been reported.

INVASIVE TECHNIQUES

ENDOTRACHEAL INTUBATION

Endotracheal intubation remains the ‘gold standard’ of definitive airway management, allowing for spontaneous and positive-pressure ventilation, with good macroscopic protection from aspiration. Indications include acute airway obstruction, facilitation of tracheal suctioning, protection of the airway in those without protective reflexes, and respiratory failure requiring ventilatory support with high inspired concentrations of oxygen and PEEP.

Preparation

Prior to proceeding with any attempts at intubation, regardless of the technique chosen, preparation and checking of all relevant equipment are essential. Tracheal intubation should be preceded by adequate preoxygenation, particularly in ICU patients who frequently have pulmonary or cardiac pathology. Difficult airway management equipment (see Table 25.3) should also be accessible within a few minutes. Food, vomitus, blood or sputum may obstruct the airway and therefore suction, able to generate at least 300 mmHg (40 kPa) and a flow rate of 30 l/min, should always be available. Excessively vigorous suctioning should be avoided as it can cause laryngospasm, vagal stimulation, mucosal injury and bleeding.

Direct laryngoscopy

Although an essential skill for all intensivists, direct laryngoscopy and intubation is difficult to master.⁸ It can be learned by simulation, exposure to patients in a controlled environment such as the operating room and subsequently practised under supervision in the ICU setting. A detailed description of the technique is beyond the scope of this chapter; however certain problems and complications commonly encountered in ICU patients should be anticipated and prevented.

Cricoid pressure is usually required as few ICU patients can be adequately starved prior to intubation. ICU patients are at high risk for severe hypotension following the use of hypnotic or sedative agents used to facilitate intubation. Mechanisms include, but are not limited to, direct drug effects causing myocardial depression and decreases in peripheral vascular resistance, a reduction in venous return and preload following the increase in intrathoracic pressure with positive-pressure ventilation and the removal of sympathetic stimulation once anxiety disappears. It is therefore useful to ensure adequate hydration, availability of inotrope and vasopressor drugs, judicial use of positive ventilatory pressures and close haemodynamic monitoring before and during the intubation period.

Because intubation is often more difficult in ICU patients (see later), excellent technique is needed. All first attempts at intubation should incorporate proper head position, the use of techniques such as BURP (backward, upward, rightward pressure) that may be helpful to bring the vocal cords into the field of vision, and, if necessary, the use of a gum elastic bougie or equivalent. A difficult-to-visualise ‘anterior larynx’ can often be more easily intubated if a gum elastic bougie is advanced in the midline and directed anteriorly into the trachea. The endotracheal tube is then advanced over the guide from an initial 90° anticlockwise-rotated position. Clinical signs of correct tracheal placement of the guide include coughing (in incompletely paralysed patients), a resistance felt before the guide is fully advanced (usually at 45 cm or less from the lips because of resistance at the carina or bronchus) and a sensation of clicks from the tracheal rings. A number of alternative intubating guides are available, including the hollow endotracheal tube changer, which can be attached to a side-stream capnometer, or to an oxygen source. The lighted stylet is less commonly used and has a light at the distal end that results in a characteristic midline transillumination appearance when the light enters the larynx.

If multiple intubation attempts are required, the maximum interruption to ventilation should be about 30 s and adequate ventilation and oxygenation must be provided between attempts. Minimum monitoring should consist of continuous-pulse oximetry, electrocardiogram (ECG) and blood pressure. In ICU patients the largest reasonable endotracheal tube should be chosen to facilitate optimal sputum clearance, access for fibreoptic bronchoscopy and to reduce airway resistance in difficult-to-ventilate patients. Sizes of 8.0–9.0 mm in adult males and 7.0–8.0 mm in adult females are generally used.

The route of intubation may be orotracheal or nasotracheal. The orotracheal route is preferred because it has fewer complications. Nasotracheal intubation is contraindicated in the presence of fracture of the base of skull. Other complications include epistaxis, turbinate cartilage and nasal septal damage, and in the long-term an increased risk of nosocomial pneumonia and sinusitis.⁹

Confirmation of tracheal tube placement

Confirming correct intratracheal tube placement is essential. Direct visualisation and measurement of expired CO₂ by capnography are the most reliable methods.¹⁶ Capnography may produce false-positive results with the first few breaths after oesophageal intubation (i.e. detectable end-tidal PCO₂), if gastric insufflation from mask ventilation has occurred. A false-negative (decreased PCO₂, despite correct position) may occur with cardiac arrest and low-cardiac-output states. Position can also be reliably confirmed by fibreoptic confirmation and the use of oesophageal detectors or self-inflating bulbs.¹ Other clinical signs, such as auscultation of breath sounds over both sides of the chest and epigastrium, visualisation of condensed water vapour in the tube and chest wall movement, are less reliable.