During the last years the number of reports on complications associated with the long term use of neuromuscular blocking agent (NMBA) in the critically ill patient in intensive care unite (ICU) has increased considerably, by providing skeletal muscle relaxant, neuromuscular blocking agents are useful in anesthesia to facilitate intubation, and allow safe abdominal and thoracic surgery. They may also be recommended in ICU to decrease oxygen consumption and improve mechanical ventilation efficacy. The ideal agent or at lest ideal dose regime of existing agents should combine fast onset to increase quickly the relaxation if necessary and rapid recovery. The currently available neuromuscular blocking agents all are under tow category. The first are depolarizing agents that act as acetylcholine analogs that bind to nicotinic receptor. The second broad category of neuromuscular blocking agents is the non- depolarizing agents that competitively bind to nicotinic receptors. Among the non-depolarizing agents, there are two broad pharmaceutical classes amino steroid and the bisquaternary nitrogen compound. The principal mechanism of action of neuromuscular blocking agents is blockade of nicotinic acetylcholine receptors at the neuromuscular junction. However, they may have additional peripheral action .The main peripheral non relaxant actions of muscle relaxants are from either blockade or stimulation of autonomic ganglia and muscurinic acetylcholine receptors at the sino-arterial node, the release of histamine. The level of relaxation required is quite well defined and could be assessed by neuromuscular monitoring, usually no response visible to TOF for intubation and no more than one response fore surgery. Quantitative assessment is available based on the response force following a standardized stimulation, EMG or acceleration.