Neuromuscular+Blockers+in+Children

__**Neuromuscular Blockers in Pediatrics**__

//Depolarizing Muscle Relaxants (Succinylcholine)//
 * only short acting muscle relaxant that can be given IM reliably (5 mg/kg in infants, 4 mg/kg in children older than 6 mo.)
 * IV Dose is also higher in infants (2 mg/kg v 1 mg/kg) as total body water content is higher in infants. Succinlycholine is highly water soluble and rapidly redistributes into the extracellular fluid volume.
 * IM dose achieves reliable relaxation in 3-4 min and can last up to 20 min.

Complications of Succinylcholine
 * 1) Cardiac Arrhythmias: common with succ, especially under halothane anesthesia
 * Sinus arrest usually happens with repeated bolus of Succ IV, but can occur after first dose.
 * Some argue that atropine should be given IV prior to Succinylcholine to avoid bradycardia or asystole.

2. Rhabdomyolysis and Hyperkalemia
 * This is of concern particularly in Boys < 8 yrs of age who may have undiagnosed muscular dystrophy.

3. Masseter Spasm 4. Malignant Hyperthermia

Due to these serious potential complications, Succinylcholine should not generally be given routinely to children. It's use, however, should not be altogether avoided because of it's utility to provide rapid, reliable muscle relaxation. It is therefore, generally reserved for children with full stomachs or to treat laryngospasm

//NonDepolarizing Muscle Relaxants//
 * Infants are generally more sensitive to nondepolarizing muscle relaxants as they do not have a fully mature hepatic of renal system.
 * GFR = 15-30% nml @ birth
 * As mentioned earlier, children have greater volume of distribution, and this also contributes to prolonged effect.

Rocuronium
 * Similar profile to Vecuronium, Atracurium, Cisatracurium, however, it can be given IM
 * Studies show that onset time with conditions acceptable for intubation are similar to IM doses of succinylcholine (Rocuronium can be given IM 1 mg/kg in infants and 1.8 mg/kg in children over a yr and produce favorable conditions in 3-4 min). Only caveat is duration (60 min)

|| * || **†**
 * Table 82-4** **-- Commonly Used Muscle Relaxants and Reversal Agents in Pediatrics **
 * ~ Drug ||~ Average Intubation Dose (mg/kg) ||~ Category ||~ Approximate Duration ||
 * Muscle Relaxants[|*] ||
 * Pancuronium || 0.1 || Long acting || ∼45-60 min ||
 * Cisatracurium || 0.1 || Intermediate acting || ∼30 min ||
 * Vecuronium || 0.1 || Intermediate acting || ∼30 min ||
 * Rocuronium ||  || Dose related: ||   ||
 * || 0.3 || Short acting || ∼15-20 min ||
 * || 0.6 || Intermediate acting || ∼30-45 min ||
 * || 1.2 || Long acting || ∼45-75 min ||
 * **Reversal Agents**[|[†]] ||
 * Edrophonium || 0.3-1.0 mg/kg + atropine, 0.02 mg/kg ||  ||   ||
 * Neostigmine || 0.02-0.06 mg/kg + atropine, 0.02 mg/kg ||  ||   ||
 * The response of preterm and term neonates (who may be more sensitive to the drugs) to muscle relaxants varies greatly from patient to patient. Therefore, all doses should be titrated to response. The recommended intubation doses may be reduced 30% to 50% in the presence of a potent inhaled agent. ||
 * The dose of reversal agent given to antagonize nondepolarizing neuromuscular blockade should be determined by the degree of residual neuromuscular blockade (i.e., the dose should be titrated to clinical effect). ||

Reversal
 * Some argue that all small infants and neotates should receive antagonism, regardless if they appear to be clinically recovered because respiratory failure could ensue from increased work of breathing/fatigue. Anatomically, children have less efficient accesory muscles as their ribs extend horizontally instead of caudally and have are mostly cartilage. Small infants are also most likely to be fatigued because they only have 25% type I slow twitch muscle fibers whereas adults usually have 50% (type I have high oxidative capacity)

References: Miller: Miller's Anesthesia, 7th ed. 2009 Miller: Basics of Anesthesia, 6th ed. 2011