The autonomic =vegetative nervous system works without the control of our consciousness.
It is divided into the sympathetic and parasympathetic nervous systems.
The
sympathetic nervous system influences the organs and the metabolism resulting in an
increase in efficiency:
- Cardiovascular stimulation
- Mobilisation of metabolic reserves
- Inhibition of digestive activities
The
parasympathetic nervous system influences the organs and the metabolism resulting in
regeneration:
- Decreased cardiac and circulatory functions
- Limitation of energy consumption
- Increase in resorption and digestion
The peripheral transmitters of the sympathetic system are norepinephrine (noradrenaline) and epinephrine (adrenaline).
The transmitter of the parasympathetic system is acetylcholine.
The target organs possess different receptors:
α, β
1, β
2
| Organ |
α |
β1 |
β2 |
| Heart |
|
Heart rate ↑Contractility ↑Excitability ↑Conductibility↑ |
|
| Bronchi |
|
|
Dilatation |
| Vessels |
Contraction
(skin, kidney) |
|
Dilatation
(muscle, liver) |
| Gastrointestinal tract |
Contraction of sphincters |
|
Inhibition of peristalsis |
| Skeletal muscles |
|
|
Glycogenolysis |
| Fat tissue |
|
Lipolysis |
|
The effect of sympathetic stimulation depends on the receptor distribution of the given organ.
Adrenaline is a sympathomimetic agent, i.e. it stimulates the sympathetic nervous system.
It stimulates all types of receptors: α, β
1, β
2
Topical administration:
Vessels in skin and mucous membranes react with vasoconstriction.
Systemic effects:
- Increase in all cardiac functions (tachycardia)
- Increased resistance of peripheral vessels (predominance of α receptors) resulting in an increase in blood pressure
- Marked bronchial dilatation
- Predisposition for hyperglycaemia secondary to glycogenolysis
The following adrenaline concentrations are commonly used in dentistry:
- 1:100,000 =0.01 mg/mL
- 1:200,000 =0.005 mg/mL
Conversion of the maximum dose of 0.25 mg adrenaline:
| 1:200,000 means: | 1g/200,000 mL |
| Equivalent to: | 1,000 mg/200,000 mL |
| | =1 mg/200 mL |
| | =0.25 mg/50 mL |
| | =0.005 mg/mL |
Noradrenaline is a sympathomimetic agent that preferably stimulates α receptors, and only to a lesser extent β1 receptors.
It leads to pronounced vasoconstriction (α).
The systemic effects of this vasoconstriction are a reflectory reduction in the heart rate.
In contrast to adrenaline, noradrenaline has more side effects, such as:
Headaches, strong hypertension, and bradycardia.
The side effect ratio of noradrenaline compared to adrenaline is 9:1; therefore, adrenaline should be preferred!
All local anaesthetics (LAs) cause vasodilatation that has a longer-lasting effect than analgesia.
Vasoconstrictors are frequently used as additives to prevent rapid absorption of LA solution from the site of injection and action.
Advantages:
- Increased duration and effectivity of anaesthesia
- Reduced maximum concentration in serum
- Less blood in area of surgery
- Total LA dose can be reduced
- Antagonistic effect to vasodilatation
Use of added vasoconstrictor in case of cardiovascular disorders
A strong sympathetic activation may be induced by higher amounts of a vasoconstrictor within a short period of time, or by accidental intravascular injection.
However, heavy strain or pain may lead to a strongly increased release of endogenous adrenaline which may then exceed the by far lower amount of adrenaline given during dental treatment (Little 2000).
Therefore, the advantages of local anaesthesia with a vasoconstrictor exceed the presumed or potential dangers and disadvantages.
If local anaesthetics containing adrenalin are used, the quantity of added adrenaline should be as low as possible (1:200,000).
The maximum dose of adrenaline as a vasoconstrictor for patients with cardiovascular disorders, however, should not exceed 40 micrograms (8mL of a solution of 1:200,000).
22.5 microgram adrenaline as addition to local anaesthetics (4.5mL of a solution of 1:200,000) were tolerated well by patients with cardiovascular disorders of different degrees (Niwa, 2001).
1:200,000 equals 0.005mg adrenaline/mL, or 5µl/mL.
But: No topical use of vasoconstrictors
Vasoconstrictors should not be used for local haemostasis in patients with cardiovascular hypertensive agents, neither should adrenaline-containing retraction cords be used.
Symptoms
- Increased blood pressure
- Tachycardia
- Hypoxia of myocardium (angina pectoris)
- Heterotopic excitation stimulus (extra systoles, ventricular tachycardia, ventricular fibrillation)
- Diabetogenic effect (increased blood sugar level)
- Vegetative symptoms (paleness, agitation, cold sweat)
- Occasional paroxysmal opposite reactions (bradycardia, vasovagal syncope)
Measures
- Administer oxygen via a nasal tube
- Monitor blood pressure and pulse
A mild intoxication is transient because of the short duration of action (1-2 minutes).
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