Rocuronium is a non-depolarizing neuromuscular blocker which is widely used to produce muscle relaxation to help facilitate surgery and ventilation of the lungs in elective and emergent situations. It is one of the many non-depolarizing neuromuscular blockers that is used but has the distinct advantage of being fast acting and one that is reversible. The major indications for its use are:
It is vital to ensure that the patients who receive a muscle relaxant like rocuronium are adequately sedated to prevent the risk of awareness where a patient can be paralyzed but awake and cannot show the motor signs of awareness.
Non-depolarizing neuromuscular blockers work at the site of nicotinic neuromuscular junction by acting on the synapse. A synapse is a specialized area where the prejunctional nerve ending interacts with a highly folded postjunctional part of the skeletal membrane. Both of these pre and postjunctional sites have a higher concentration of acetylcholine (Ach) and nicotinic acetylcholine receptors (nAchR) respectively. Normally when an electrical impulse reaches the prejunctional nerve terminal, calcium influx causes a release of Ach ligands which then interacts at the nicotinic acetylcholine receptors located at the postjunctional membrane to cause changes in the electrical permeability of the membrane specifically sodium and potassium. This rapid movement of ions causes a decrease in the transmembrane potential to reach threshold potential leading to the generation of an action potential that travels across the muscle membrane and causes muscular contraction.
Nondepolarizing drugs like rocuronium are quaternary ammonium compounds which are intermediately acting, highly ionized drugs administered intravenously under controlled conditions by anesthesiologists and other critical care providers after ensuring that the patient is under the effects of anesthesia. The dose of administration can be decided based on the clinical indication versus patient characteristics. Rocuronium does not undergo metabolism into active metabolites and has very limited lipid solubility. Therefore these drugs do not pass the blood-brain barrier, placental barrier, and other lipid membrane barriers. Thus rocuronium has no effects on the central nervous system, effects on the fetus, minimal renal reabsorption as well as ineffective absorption if given orally. Rocuronium is largely excreted unchanged in bile and has around 30 % renal excretion. Factors like hypothermia, hypovolemia, concomitant volatile agents as well as renal and hepatic diseases prolong the effects of rocuronium.
Rocuronium is an intermediate-acting nondepolarizing neuromuscular blocker with ED95 of 0.3 mg/kg. At a dosing range of 0.6 to 1.2 mg/kg, intubating conditions can be reached in 1 to 2 min with effects lasting until 20 to 35 min. Higher doses like 1.0 to 1.2 mg/kg can be used to provide intubating conditions similar to succinylcholine in a short onset of time like 1 min. However, that comes with a duration of action similar to longer acting nondepolarizing drugs like pancuronium.
The absolute contraindication to using rocuronium would be a documented allergic reaction to the drug. Rocuronium should also not be given to any patient who is not sedated or one who is not under the influence of anesthesia to avoid the risk of awareness. It is advisable not to use rocuronium as an infusion to prevent critical illness myopathy as well as polyneuropathy. Rocuronium should not be used in patients with renal or hepatic dysfunction as it will prolong its effects by delaying elimination. Although with the use of sugammadex, rocuronium can be used in these clinical situations too with caution.
The effects of neuromuscular blockade are assessable by evaluation of a mechanically evoked response to an electrical stimulation using a peripheral nerve stimulator. Routine use of peripheral nerve stimulator is strongly encouraged by the Anesthesia Patient Safety Foundation (APSF) to monitor the depth of neuromuscular blockade during surgery as well as after reversal by the reversal agent to confirm and rule out any residual neuromuscular blockade.
Routinely two sites are used for peripheral nerve stimulation - the distal forearm where ulnar nerve is stimulated using two electrodes placed on the anatomical path of ulnar nerve to stimulate the adductor pollicis muscle of the hand and around the eyes on the forehead to stimulate the facial nerve and orbicularis oculi muscle. The peripheral nerve stimulator can provide an electrical current of specific strength and duration to create a pattern of stimulation. Most commonly a train of four (TOF) is used to evaluate the amount of muscle contraction. Other types of stimulation include a single twitch response, double burst stimulation, tetany, and post-tetanic stimulation. In a TOF stimulation, four electrical stimulations at 2Hz are delivered every 0.5 sec and twitch height response of the fourth twitch is compared to the first twitch. In patients under the effect of rocuronium and other nondepolarizing neuromuscular blocking drugs, the fourth twitch response is smaller than the first due to the depletion of Ach released on successive stimulation. This leads to the calculation of TOF ratio and fade and is a hallmark of nondepolarizing neuromuscular blockade. Loss of 2 twitches out of four is considered adequate for surgical anesthesia, and if all four twitches are lost, one should not administer any more muscle relaxant until there is a recovery of some twitches. A TOF ratio of >0.7-0.9 is considered adequate for complete reversal.
Reversal of rocuronium-induced paralysis is possible with the use of two subgroups of drugs.
Proper use of neuromuscular blocking agents by the anesthesiologist, emergency department physician, intensivist, anesthesia nurse and critical care specialists is of paramount importance. Residual neuromuscular weakness is recognized to be a common problem in the post-anesthesia care unit (PACU) where at least 20 to 40% of patients can be shown to have objective evidence of residual weakness. Current evidence suggests that routine monitoring of neuromuscular blockades are not performed regularly on each patient and subjective assessment of muscle strengths like sustained head-lift as well as hand grips are unreliable markers of a complete reversal of neuromuscular blockade. The only objective method to ensure patient safety and ensure complete reversal is the TOF ratio greater than 0.9. Suggamadex since introduced in 2008 worldwide and 2015 in the USA, there is reliable and consistent literature supporting the safety and reliability of complete reversal of neuromuscular blockade.
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