V-Series Nerve Agents (VX Gas) – Effects, Symptoms, Treatment, Antidote

Chemical weapons are a serious concern as some of these agents can be deadly in very small doses and do not need to be dispersed with specialized equipment. One such chemical weapon that has gained recent public attention is the VX nerve agent. It should not be confused with another well known chemical agent, sarin, which is a G-series agent. The V-series nerve agents like VX are said to be 10 times more deadly than sarin.

What is the VX nerve agent?

The VX nerve agent, also sometimes referred to as VX nerve gas, is an extremely toxic and highly deadly organophosphate  produced for the purposes of warfare.  It is part of the V-series of nerve agents where the V stands for venomous. The VX nerve agent is the most well known and more important of the V-series agents. Less is known about the others such as Ve, Vg and Vm. Therefore the focus on V-series agents usually revolves around the VX agent specifially.

VX is not as volatile as sarin (G-series nerve agents). Therefore inhalation of VX is not the most common route of exposure. Instead the VX liquid can more easily enter the system by being absorbed through the skin. The severity of symptoms and lethality depends on the dose of VX that a person is exposed to as well as the thickness of the skin at the exposed area. However, even a very small dose of VX can be deadly within minutes to hours. V-series nerve agents are similar to organophosphate pesticides but are much more toxic.

What are the effect of VX gas?

It is important to first understand how nerves work in order to understand the effect of V-series nerve agents, and specifically VX, on the body. Nerves are the body’s “transmission cables” carrying messages to different parts of the body. These “messages” are known as impulses and control just about every action and function in the body, from regulating the heart beat and breathing to controlling muscles and facilitating senses such as sight, odor and taste.

The impulses are chemical and electrical in nature. Simply, as the impulse travels through a nerve cell then it is an electrical in nature but when this impulse moves from one nerve cell to another then it is a chemical in nature. VX affects this chemical aspect of the impulse. One of the chemicals that carries the signal from one nerve ending to the other or from the nerve ending to the target tissue like muscle is known as acetylcholine (ACh).

Aceytlcholine is released from one nerve and binds to receptors on the other nerve. It binds specifically to muscarinic and nicotinic receptors. Once acetylcholine has completed its action then it has to be neutralized. If not, the acetylcholine would keep acting by stimulating the receptor and this can cause a host of disruptions. Acetylcholine is therefore neutralized by an enzyme known as acetylcholinesterase (AChE) which degrades it into acetic acid and choline.

V-series nerve agents work by binding to this enzyme, acetylcholinesterase (AChE), thereby preventing it from neutralizing acetylcholine. Therefore acetylcholine continues to act on its target receptors and keeps stimulating the target tissue. Eventually the V-series nerve agent forms an irreversible bond with acetylcholinesterase (AChE) rendering it useless. Either more acetylcholinesterase (AChE) has to be produced by the body or  it has to be administered.

In this regard, the V-series nerve agents are similar to certain type of insectides, specifically the organophosphate and carbamate insecticides. However, the V-series nerve agent does differ from these insecticides in that it binds more strongly with acetylcholinesterase (AChE). Furthermore there is a point where the binding with acetylcholinesterase (AChE) becomes irreversible with V-series nerve agents (this is known as “aging”) while it is largely reversible with the insecticides.

Read more about pesticide poisoning symptoms.

Signs and Symptoms of VX Exposure

The severity of signs and symptoms depends on the dose and area of contact. This may also determine the onset of symptoms. Therefore not all of the signs and symptoms of VX exposure discussed below may be immediately evident. Death can occur even before some of these signs and symptoms are noticed.

  • Shortness of breath
  • Difficulty breathing
  • Chest tightness
  • Slow breathing and eventually breathing stops (apnea)
  • Muscle twitches, initially in and around the area of contact and eventually throughout the body
  • Paralysis
  • Sweating
  • Abnormalities of heart rate – very slow (bradycardia) or very rapid (tachycardia)
  • Eye pain
  • Dim or blurred vision
  • Runny nose (if vapor is inhaled)
  • Abdominal cramps
  • Paleness
  • Excessive salivation and tearing
  • Anxiety and depression
  • Confusion
  • Loss of consciousness
  • Seizures

How does VX kill a person?

The VX nerve agent causes nerves to become dysfunctional and for muscles to go into spasm. This can affect the nerves and muscles throughout the body. However, in terms of its lethal effects, it is the disruption of the nerves responsible for breathing and the spasm of the muscles of the airways and respiration that are most significant. Most cases of death from V-series nerve agents occur when the muscles of respiration become paralyzed and/or the there is depression of the nerve centers in the brain. In simple terms, VX kills by causing asphyxiation or respiratory failure.

Read more about poisoning symptoms.

Treatment of VX Exposure

The treatment of VX exposure involves decontamination, oxygen therapy and the administration of an antidote if exposure can be confirmed. However, if exposure is only suspected then decontamination and observation for at least 18 hours is advisable to monitor for any symptoms before other measures are instituted. Decontamination involves thoroughly washing the area of contact with soap and water. In the event of vapor exposure, a person must be removed from the contaminated area and exposed to fresh air. Oxygen therapy should be commenced immediately.

The drugs used for treating VX exposure includes:

  • Atropine is an anticholinergic that blocks acetylcholine (ACh) at muscarinic receptors but not at nicotinic receptors.
  • Pralidoxime is an oxime that reactivates acetylcholinesterase (AChE) before there is irreversible binding (“aging”) with VX.
  • Diazepam is a benzodiazepine that is used for seizures and prevention of seizures which arises with VX exposure.

None of these drugs are administered if VX exposure is suspected unless symptoms arise. Atropine is used for mild, moderate and severe cases of VX exposure. Pralidoxime is used for moderate to severe cases but may be used in low doses in mild cases if breathing symptoms do not improve. Diazepam is used in moderate to severe cases even if seizures are not present.

What is the antidote for VX nerve agents?

Atropine and pralidoxime are used as antidotes against V-series nerve agent exposure. It may be available as two separate antidotes or as a combination in a single antidote. Antidote Treatment Nerve Agent Autoinjector (ATNAA) kits containing both atropine and pralidoxime are commercially available. This combination antidote is available as a single auto-injector. It is not usually available over-the-counter (OTC) and a prescription is therefore required.

References:

  1. emedicine.medscape.com/article/831760
  2. emergency.cdc.gov/agent/vx/basics/facts.asp

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