Incompatibilities

In case of intolerance to a local anesthetic, various symptoms can occur. Itching and reddening often occur, so that there is always the danger of an allergy. In the case of an allergic reaction, severe systemic reactions are sometimes to be expected, which can range from a drop in blood pressure to complete anaphylactic shock.

General, physiology and effect

The first local anesthetic used as such was cocaine in the 19th century. However, unlike the drugs commonly used today, cocaine has addictive properties. Nowadays, it is rarely used in medicine, especially for ear, nose and throat procedures.

Over the years, derivatives of cocaine have been developed. There are two groups of cocaine. Those of the ester type, which include cocaine, procaine and tetracaine, and those of the amide type.

These include lidocaine, prilocaine and mepivacaine. They differ in their chemical and physiological properties. All local anaesthetics act by blocking voltage-dependent sodium channels.

In the nociceptive system (i.e. the system of pain detection and transmission) this leads to a blockage of the transmission of the action potential. The pain is thus absorbed by receptors in the periphery – for example in the hand – but then blocked in its transmission to the central nervous system. This means that local anesthetics do not inhibit the registration or absorption of the pain stimulus, but its transmission.

Thus, the perception of pain does not reach the consciousness and the person concerned does not perceive any pain. The disadvantage of local anesthetics is that the sodium channels they block are not only present in the nociceptive system. They are also found in the heart and central nervous system.

By inhibiting the transmission of excitation in the heart, they can lead to cardiac arrhythmia and even cardiac arrest, and dangerous side effects can occur in the central nervous system. Therefore, as the name suggests, the substances may only be used locally. Procaine Injection If the dosage or application is wrong, however, it is possible that the local anaesthetic is distributed further in the body than intended, so that complications can arise.

There are several factors that can prevent this. Firstly, the local application mentioned above, which makes a large-area distribution unlikely. On the other hand, by using substances that are unstable, i.e. they are quickly broken down and then lose their effect.

A third factor that avoids the unintentional distribution of the local anesthetic in the body is the addition of vasoconstrictive substances, i.e. drugs that constrict the blood vessels. The applied local anesthetic thus reaches the tissue, but due to vasoconstriction of the surrounding vessels, it cannot diffuse away from the place where its effect is desired in large quantities. However, vasoconstrictive substances such as adrenaline or noradrenaline must not be used in procedures on the acres.

This includes fingers, toes and also the nose.In this case, a vasoconstriction would increase the risk of a permanent undersupply of blood and thus of tissue death. Lidocaine, which belongs to the amide-type local anesthetics, is not only used for local anesthesia, but is also used as an antiarrhythmic agent. Thus, it acts against cardiac arrhythmia by interfering with the function of the sodium channel.

This may sound paradoxical at first, since – as mentioned above – local anesthetics can trigger cardiac arrhythmias, as can lidocaine. In this respect, it can be used for the therapy of cardiac arrhythmias, but its contrary proarhythmic potential must not be disregarded. Nerve fibers react differently to local anesthetics.

For example, impulse transmission is inhibited earlier in the thinner sensitive fibers than in thicker motor nerve fibers. This is the reason why the sensation of pain can be switched off while maintaining motor function. The different sensitive qualities are also switched off at different speeds.

First the sensation of pain decreases, then the sensation of temperature and even later the sensation of touch and pressure. Often patients who have been administered a local anesthetic do feel the pressure of the scalpel or other instruments, but no longer feel pain. Due to their chemical properties, local anaesthetics have a significantly reduced effectiveness if the pH value is too low (i.e.

too acidic) or too high (i.e. too alkaline). This means that local anesthesia will be significantly less effective or not effective at all in inflamed tissue with a lower pH value. This must be considered before application.