|When non-depolarising agents are used for endotracheal intubation, intubation cannot be accomplished satisfactorily, which prevents its routine use, whenever rapid intubation is desired.
In such conditions suxamethonium is used, despite its several side effects viz. muscle pains, increased intraocular and intracranial pressures, arrhythmias etc.
In order to facilitate rapid endotracheal intubation with non-depolarising agents, the priming principle has been used in the recent past. The Priming principle refers to administration of a small dose (priming dose) of a nondepolarising relaxant, which when followed by the larger intubating dose, after 2-4 minutes, produces relatively rapid and profound blockade to ensure a suitable condition for endotracheal intubation.
Based on the theory that a small dose of nondepolarising relaxant can block large numbers of ACh receptors at the NMJ before appreciable clinical reduction in neuromuscular transmission.
The second larger dose blocks the remaining receptors and effects more rapid onset of intubation conditions.
Optimal priming dose
Atracurium - 0.08-0.09 mg/kg
Vecuronium - 0.01-0.012 mg/kg
Some patients will experience muscle weakness at these doses.
There is potential for loss of airway protection, regurgitation etc.