Muscle relaxants are given as part of a rapid-sequence induction to facilitate tracheal intubation. Among all the muscle relaxants available, succinylcholine is the only one with a fast (≅1 min) onset and a fast recovery. Therefore it is still the most frequently used muscle relaxant for rapid-sequence induction despite its well-known side-effects. The short duration of action of succinylcholine is, however, no substitute for aggressive airway management in the case of an unexpectedly difficult intubation in order to prevent life-threatening hypoxia. A preoperative assessment of the airway is mandatory in any patient and may indicate the need for using intubation techniques without a muscle relaxant. Rocuronium in large doses (i.e. ≥1 mg kg−1) is an alternative to succinylcholine in a classical rapid-sequence setting under relatively light anaesthesia. With respect to rapid tracheal intubation, the timing and priming principles offer little advantage over the use of rocuronium in doses of 0.6 mg kg−1 in combination with an appropriate induction technique (i.e. including an opioid) or over the use of larger doses of rocuronium (≥1.0 mg kg−1) under relatively light anaesthesia, and may even be potentially harmful.

In contrast to rocuronium, the use of rapacuronium in a rapid-sequence setting has been associated with dose-dependent respiratory side-effects that limit its usefulness in doses higher than 1.5 mg kg−1 for this indication.

The choice of hypnotics and opioids for rapid-sequence induction, and the use of premedication, is influenced by the choice of the muscle relaxant. Anaesthetic agents have a major influence on the quality of intubation when rapid-sequence induction is achieved without a muscle relaxant. Premedication is important, along with a high dose of propofol (2.5 mg kg−1 or more) and a short-acting opioid such as alfentanil (30–40 μg kg−1) or remifentanil (up to 4 μg kg−1). It has also been demonstrated that i.v. lidocaine can improve intubating conditions. When a muscle relaxant is used, the choice of the anaesthetic agents depends on the onset of action of the relaxant. With a rapid-acting compound such as rocuronium at a dose of 0.6 mg kg−1, the hypnotic agents need to be supplemented with only a small dose of opioids, e.g. alfentanil 10–20 μg kg−1. When succinylcholine, rocuronium 1.0 mg kg−1 or rapacuronium 1.5 mg kg−1 are used, excellent intubating conditions may be obtained by relatively smaller doses of hypnotic agents even without opioids; however, haemodynamic and intraocular pressure changes are better controlled when small doses of opioids are administered.