Neuromuscular blocking agents are drugs that paralyze all of the muscles, including the muscles of breathing. These drugs only affect movement, they do not cause sedation or pain control. Patients will be unable to move when these drugs are used, and will be completely dependent upon the breathing machine. Hearing is not affected by these drugs.

Paralysis is a word used to describe the inability to move. Patients with brain or nerve damage may be unable to move the affected areas of their body. Neuromuscular Blocking Agents are drugs that prevent messages from moving from the nerve to the muscle. This causes a temporary, but widespread paralysis called a "drug induced paralysis". This type of paralysis will go away when the drug wears off.

Because it would be very scary to be paralyzed and on a breathing machine, these drugs are always used with a steady infusion of sedatives and pain medications. Although the patient is most likely asleep, we should always speak to a patient who is receiving a Neuromuscular Blocking Agent as though they can hear us.

These drugs are only used when absolutely needed. They can increase the risk for developing pneumonia and Polyneuropathy of Critical Illness. They can however be life-saving, if they help us to ventilate a patient with severe lung failure.

Because Neuromuscular Blocking Agents stop muscle activity, they also decrease heat production. This makes them useful if we need to dramatically reduce body temperature.

We try to use these drugs for as short a time as possible, and use the lowest drug needed to produce the desired effect (e.g., successfully ventilate the patient). We adjust the dose of these drugs to a Peripheral Nerve Stimulator.

A Peripheral Nerve Simulator is a device that is used to stimulate a nerve for the purpose of producing a muscle contraction. Two electrodes are placed along the nerve and used to deliver the stimulus.

A Train of Four is the method used to test for a response. Also called a "TOF", four consecutive stimulations are applied to the nerve, and the number of muscle twitches are counted. The nerve in the wrist is used the most frequently. To avoid using higher doses of drug than necessary, we try to deliver a dose of Neuromuscular Blocking Agent that will produce 1-2 twitches out of 4 stimulations (described as a Train of Four of 2/4). Unfortunately, very ill patients often do not respond to any stimulation, even though the amount of drug being used is actually less than needed to correct their breathing distress. We do not have an ideal method for adjusting the dose of these drugs.


Image 1: Nurse performing a "Train of Four" test with a Peripheral Nerve Stimulator.