|EVIDENCE BASED DATA
|Year : 2008 | Volume
| Issue : 1 | Page : 96
Rapid Sequence Induction
Senior Prof. & Head, Department of Anaesthesiology, R.N.T.Medical College, Udaipur (Raj.), India
|Date of Web Publication||19-Mar-2010|
25, Polo Ground, Udaipur (Raj.)
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Bajaj P. Rapid Sequence Induction. Indian J Anaesth 2008;52:96
The term "rapid sequence induction" (RSI) usually applies when tracheal intubation must be performed in a patient who is suspected of having a full stomach and who is at risk for pulmonary aspiration of gastric contents. The goal is to secure the airway without producing any regurgitation and vomiting. The procedure involves three objectives : 1) preventing hypoxia during the induction- intubation sequence ; 2) minimizing the time between induction and tracheal intubation, when the airway is unprotected by the patient's reflexes or by the cuffed tracheal tube;and 3) applying measures to decrease the chances of pulmonary aspiration of gastric contents. The first of these objectives is normally met by preoxygenation. Typically, breathing 100% oxygen for 3-5 min before induction of anaesthesia allows the patient to sustain apnea for a period of 5-8 min without hypoxia.  The second objective involves minimization of the induction -intubation interval, which means that a short acting hypnotic agent should be administered with a neuromuscular blocking agent with a rapid onset of action. Finally, the chance of aspiration is diminished by applying cricoid pressure, by refraining from positive pressure ventilation before tracheal intubation is accomplished, and by waiting until neuromuscular blockade is complete to perform tracheal intubation.
All these steps have their detractors. Preoxygenation has been associated with atelectasis.  , but this is a minor problem compared with the added protection afforded by an increase in oxygen contents in the lungs. Application of cricoid pressure has been criticized  , and positive pressure ventilation has been advocated by some. The role of alternate airway devices, such as the ProSeal laryngeal mask airway in patients with a full stomach is debated by some. In addition, there is uncertainty regarding which patients should be considered as having a full stomach and who should undergo RSI. The effectiveness of the whole procedure in preventing aspiration of gastric contents has not been evaluated. However, the approach is logical and widely applied. Emergency cases and poor muscle relaxation at the time of intubation have been identified as predisposing factors for pulmonary aspiration.
| Current problems and controversies|| |
Between 1982 and September 2005, there has not been a single study in which RSI was applied to patients scheduled for emergency surgery. All studies dealing with the problem of neuromuscular blockade and intubating conditions during the course of a RSI have used elective patients in whom RSI was simulated. Most of these studies have focused on neuromuscular profile and intubating conditions comparing succinylcholine and nondepolarizing agents. After the demise of rapacuronium, the most interesting of the nondepolarizing agent remains rocuronium, introduced in the 1990s. Still, the dose required to match the intubating qualities of succinylcholine appears to be 1.0 mg.kg -1 , at least in elective patients  , and that dose of rocuronium is associated with a long duration of action.
The introduction of propofol and remifentanil into clinical practice had the theoretical advantage of modifying the practice of RSI because of the ability of these drugs to improve intubating conditions. Unfortunately, most of the evidence comes from elective patients rather than emergency surgery patients. The difference might not be trivial. Early pharmacokinetics are modified by cardiac output, and the study of this phenomenon has been termed "front-end pharmacokinetics"  . If cardiac output is decreased, as may happen in emergency patients, the early plasma concentration of drug is increased because the dose is diluted in a smaller volume.
The question of dose was fuelled by another controversy. A major concern with RSI is what to do if intubation is not possible. The margin of safety is increased if the neuromuscular blocking agent has a duration of action that is shorter than the duration of apnea after proper preoxygenation. Although it was widely believed that such protection could be afforded by succinylcholine 1mg.kg -1 , recent evidence suggests that this might not be true, and some authors recommend a dose reduction.  In children, the use of succinylcholine has been questioned because of cases of hyperkalemia and cardiac arrest that are frequently resistant to resuscitative efforts.  Finally, RSI has been used outside the operating room. Not surprisingly, most studies in the emergency literature suggest that success at intubation is greater if neuromuscular blocking agents are used.  This means that recommendations have to be formulated for their optimal use.
| Do we need neuromuscular blocking agents|| |
With the introduction of propofol as a hypnotic agent and the rapidly acting opioid drugs alfentanil and remifentanil, the need for neuromuscular blocking agents for intubation has been questioned. However, the quality of intubating conditions is less predictable and tracheal intubation becomes frequently impossible if neuromuscular blocking agents are omitted. In elective patients, heavy doses of alfentanil (60mcg.kg -1 ) or remifentanil (4mcg.kg -1 ) are required to produce conditions that approach those produced by succinylcholine.  These doses are associated with hypotension, and logic dictates that the occurrence of such hypotensive episodes is likely to be greater in emergency patients. Intubation was impossible in 20% of patients who received alfentanil,30mcg.kg -1 or less, or remifentanil, 3mcg.kg -1 or less. 
The need for neuromuscular blocking agents seems obvious when one considers the results obtained by emergency physicians. A review of four studies indicated that failure to intubate occurred in 0% -1.3 % in patients in whom RSI with muscle paralysis was applied compared with 8.6 % -28 % when intubation was performed under sedation only  Three attempts were required in 2%-3% of paralyzed patients compared with a 10.7%-24% incidence with sedation only. Intense neuromuscular blockade can increase the chance of success at tracheal intubation, but it can also benefit the patient. Aspiration is less likely with profound neuromuscular blockade.  Also, the incidence of laryngeal injuries is less if intubating conditions are excellent, and this situation is more frequent if neuromuscular blocking agents are used. 
There is limited evidence on the best drug and dose of neuromuscular blocking agent indicated in RSI. Data have to be extrapolated from simulated RSI in elective patients and studies on patients requiring intubation in the emergency room. The use of neuromuscular blocking agents improves intubating conditions, and probably the risk of aspiration, over any induction technique using only opioids and hypnotic agents. Succinylcholine remains the "gold standard" and should be administered unless there are contraindications to its use. The dose of 1mg.kg -1 without precurarization or 2mg.kg -1 with precurarization appears to be optimal, providing adequate intubating conditions without prolonged duration. However, protection against hypoxia cannot be guaranteed. Precurarization should be limited to rocuronium 0.03mg.kg -1 or equivalent. The optimal intubating dose of rocuronium is 1mg.kg -1.
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