Chapter 10 – Drugs for Airway Management

Abstract

Correct choice and use of drugs is fundamental to airway management success and safety. This is true for both elective and emergency anaesthesia and at the start and end of anaesthesia. This chapter describes the key elements of drug selection for safe, effective airway management in both the awake and anaesthetised patient. Drugs can importantly facilitate airway management and influence conditions for tracheal intubation or inserting a supraglottic airway. Depression of reflexes and muscle tone can be provided by several hypnotics, but propofol is usually most effective. Neuromuscular blocking agents are not needed for many forms of airway management but can optimise conditions when necessary. The anaesthetist must be familiar with dosing and timing and with quantitative monitoring during reversal. Local anaesthesia may be the only safe choice in managing the difficult airway and sedation can enhance patient tolerance but maintaining adequate spontaneous ventilation is sometimes a challenge.

Chapter 10 Drugs for Airway Management

Lars S. Rasmussen

Difficulties in airway management can be related to anatomical factors, airway pathology and poor positioning but we should not forget the importance of the anaesthetist. Experience and manual skills are essential and the anaesthesia provider can have an important impact on the ability to manage the airway by administering drugs, which in turn can significantly increase the chance of securing the airway on first attempt. The optimal choice, timing and dosage of anaesthetic drugs for airway management will be described in this chapter.

The first step is always to have an airway management strategy, including alternatives if the primary plan fails. Anaesthetic drugs are used to optimise conditions according to that strategy. The results of the airway assessment and the anaesthetist’s experience will guide decision whether to manage the airway with general anaesthesia or with local anaesthesia with or without sedation.

General anaesthesia can be managed with the intention to maintain spontaneous ventilation or with controlled ventilation. Airway tone will be reduced by most anaesthetics and this facilitates insertion of devices by jaw relaxation and depression of reflexes. Tracheal intubation is facilitated when the vocal cords are fully abducted and there is no vocal cord movement or coughing. This likely creates less laryngeal morbidity, including hoarseness and sore throat. The possible drawback is that it may not be possible to maintain spontaneous ventilation or an open airway.

Local anaesthesia for airway management may be combined with sedation. Sedation is used to ameliorate anxiety and discomfort in order to facilitate the airway management, but it carries the risk of overdosing with a transition to general anaesthesia. Sedation is a drug-induced alteration of consciousness during which patients should be able to respond purposefully to verbal commands. Variation in patient response to sedative agents and delayed onset of action may make titration of sedative drugs to obtain a desired level of sedation challenging.

Rapid reversal (to restore spontaneous ventilation and airway tone) is sometimes possible, particularly for opioids and benzodiazepines, for which there are direct antagonists. That is not the case for propofol or barbiturates. For some neuromuscular blocking drugs (NMBDs), sugammadex may also provide rapid reversal of effect.

Where No Airway Management Difficulty Is Anticipated

Hypnotics and Opioids

The most important aspect in this situation is to optimise conditions by giving enough drug with optimal timing in an attempt to secure the airway on first attempt. Subsequent attempts will have lower success rates and the risk of complications increases dramatically, including hypoxaemia, aspiration, dental injury and oesophageal intubation. All anaesthetics depress the level of consciousness and most impair spontaneous ventilation, but they have differential effects on airway reflexes and airway muscle tone. The anaesthetist must carefully assess whether bag-mask ventilation will be possible or not and also what the secondary plan is in case of an inability to ventilate after induction of general anaesthesia.

Bag-mask ventilation, laryngoscopy and insertion of airway devices are all procedures that require decreased muscle tone and the anaesthetist should not attempt any of these without being confident that the desired depth of anaesthesia has been achieved. Inadequate depth of anaesthesia is a common reason for the inexperienced anaesthetist to encounter difficult airway management. This is especially common in patients who consume large doses of opioids or alcohol and in children. Large doses of propofol are effective in depressing reflexes and reducing muscle tone, especially if combined with a rapid-onset opioid such as remifentanil. Other hypnotics (e.g. barbiturates, etomidate and benzodiazepines) are less potent in reducing muscle tone, and an NMBD may be necessary to facilitate airway management. Spontaneous ventilation may be maintained with ketamine and upper airway obstruction is also less common with this hypnotic although secretions can be a problem. An NMBD can create optimal conditions but the anaesthetist must be familiar with the onset time and appropriate dose (Table 10.1).