do not adequately hold these devices in place.
Drug‐facilitated intubation
Drug‐facilitated intubation is the use of intravenous sedative and/or neuromuscular blocking agents to facilitate ETI of patients with intact protective airway reflexes [75].
Rapid sequence intubation
Rapid sequence intubation (RSI) denotes the use of a neuromuscular blocking (paralytic) agent combined with a sedative or induction agent to facilitate ETI of a patient with intact protective reflexes. The salient goals of RSI are to facilitate rapid sedation and paralysis of the patient and insertion of the endotracheal tube while effecting minimum physiological disturbances (heart rate, blood pressure, intracerebral pressure, etc.). Current prehospital RSI practices closely parallel emergency department practices. The general clinical indications for prehospital RSI include the need for airway and ventilatory control in patients with intact protective airway reflexes: for example, victims of traumatic brain injury.
RSI technique
The main elements of prehospital RSI include:
Insertion of an intravenous line.
Attachment of continuous monitors (electrocardiogram, blood pressure, and pulse oximetry).
Preoxygenation of the patient (nonrebreather mask or BVM ventilation).
Rapid administration of pretreatment, sedative/induction, and neuromuscular blocking agents.
Performance of laryngoscopy and tube placement.
Verification of tube placement and securing of the endotracheal tube.
Pretreatment agents may be administered prior to attempting RSI, for example, intravenous lidocaine to attenuate the intracerebral pressure response to laryngoscopy. Because there are only limited data supporting the effectiveness of pretreatment regimens, protocols often exclude the use of these agents during prehospital RSI.
Sedation
A wide range of sedative/induction and neuromuscular blocking agents exist. The most popular sedative/induction agent for RSI is etomidate. Most clinicians favor this agent because of its minimal effect upon blood pressure, heart rate, and intracerebral pressure. The typical induction dose for etomidate is 0.3 mg/kg intravenously (20 mg in a typical 70‐kg patient). Some studies have raised concern regarding the clinical consequences of adrenal suppression resulting from etomidate administration [76, 77]. Limited data describe the link between etomidate’s adrenocortical suppression and patient outcomes [77].
Another commonly used agent for sedation/induction is midazolam 0.1 mg/kg. However, because midazolam and other benzodiazepines may cause clinically significant hypotension, and because many prehospital patients requiring RSI have significant hemodynamic compromise, many EMS physicians prefer not to use these agents for prehospital RSI.
While not truly a sedative agent, ketamine has emerged as another potential agent for facilitating RSI. Ketamine is a dissociative agent. In the absence of neuromuscular blockade use, ketamine maintains airway reflexes. Ketamine is also not associated with significant hypotension. Side effects of ketamine include increased secretions and potential increase of intracranial pressure. While the latter could be harmful in patients with traumatic brain injury, the association of ketamine use with outcomes in these patients is unclear. Ketamine is typically dosed at 1 to 2 mg/kg intravenously, or 2 to 4 mg/kg if given intramuscularly.
Paralysis
The most commonly used neuromuscular blocking agent for RSI is succinylcholine, typically administered at a dose of 1.0–2.0 mg/kg intravenously (70–140 mg in a typical 70‐kg patient). Succinylcholine’s rapid onset and short duration of action are ideal for RSI. The rationale for using a rapid‐acting paralytic is to achieve intubating conditions as quickly as possible. The rationale for using a short‐acting paralytic is to facilitate rapid recovery of the patient’s spontaneous airway reflexes in the event of unsuccessful laryngoscopy and intubation efforts.
Relative contraindications to succinylcholine include conditions with known hyperkalemia, such as acute renal failure or rhabdomyolysis. Succinylcholine‐induced hyperkalemia in these settings may cause cardiopulmonary arrest. While burn injuries can cause hyperkalemia, this complication usually does not occur until 2 or 3 days after the acute injury. Succinylcholine can be safely used for the acute management of burn victims. Other relative contraindications to succinylcholine include muscular‐wasting diseases (which can cause hyperkalemia) and pseudocholinesterase deficiency that prolongs the neuromuscular blockade due to slower drug metabolism.
Nondepolarizing agents such as rocuronium and vecuronium may be used as alternatives to succinylcholine for RSI. Rocuronium, dosed at 1 mg/kg, has a rapid onset (1–3 minutes), although its duration of action (30–45 minutes) is longer than succinylcholine (5–9 minutes). Vecuronium, dosed at 0.1 mg/kg, has a slightly longer onset of action (2–4 minutes), and duration of 25–40 minutes. “High‐dose” vecuronium (0.15–0.28 mg/kg) has an even longer duration of action (60–120 minutes). Clinicians should anticipate prolonged recovery time from vecuronium in obese patients, elderly patients, and those with hepatorenal dysfunction. Both rocuronium and vecuronium can be reversed by sugammadex (2–4 mg/kg).
After successful RSI, it is essential to administer additional medications to maintain sedation and paralysis. Therefore, EMS clinicians performing RSI should carry longer‐acting paralytics (for example, vecuronium) and longer‐acting sedative agents (for example, lorazepam, midazolam, or diazepam).
Pediatric practices for RSI often vary slightly from adult protocols. The pediatric literature raises concern regarding the possibility of unrecognized muscular myopathies, which would result in hyperkalemia with administration of succinylcholine [78]. Therefore, many specialty pediatric transport teams use nondepolarizing agents to facilitate paralysis. The use of etomidate for children remains unresolved. Prehospital RSI protocols vary between the use of etomidate and midazolam for sedation. Because of paradoxical bradycardia with RSI agents in children, clinicians may pretreat patients with intravenous atropine.
Sedation‐assisted endotracheal intubation
Sedation‐assisted intubation is intubation using a sedative agent only, without concurrent neuromuscular blocking agents [7579–83]. Medications used to facilitate intubation in this manner include benzodiazepines (midazolam or diazepam), etomidate, and ketamine. Sedation‐assisted intubation historically resulted from the belief that intubation is safer without than with the use of neuromuscular blockade. However, critics of the technique note that incomplete ablation of the gag reflex can potentiate the threat of vomiting and aspiration. Also, first‐pass intubation success is optimized with the use of neuromuscular blockade. Consequently, most EMS medical directors strongly discourage the use of sedation‐assisted intubation.
Other drug‐facilitated techniques
Safe RSI requires meticulous preparation and preoxygenation to avoid peri‐intubation adverse events. Adequate preoxygenation for RSI may require application of 100% oxygen for at least 3 minutes. However, proper preparation for RSI may not be possible with a combative or agitated patient. Delayed sequence intubation involves the initial delivery of a sedative to facilitate patient positioning, preparation, and preoxygenation, and subsequent delayed administration of paralytic and intubation [84]. The time interval between sedative and paralytic may be 5‐10 minutes or even longer. Delayed sequence intubation may be accomplished using any induction agent. EMS experience with this technique is limited [85].
Conclusion
Airway management is one of the most important elements of prehospital emergency care. Prehospital airway management involves numerous clinical, educational,