2. LOCAL ANESTHESIA - The principle of local anesthesia is infiltration of the tissue with a local anesthetic drug derived from procaine. They are generally available in 0.5, 1 and 2% solution, with or without adrenaline or noradrenaline as a vasoconstrictor. In the young pregnancy vasoconstrictors should not be used. There is no danger of bleeding and theoretically they may cause ischaemia. But in the advanced pregnancy they largely reduce blood loss and ischaemia in the pregnant uterus never occurs (Finks 1972) because of the abundant blood supply. Noradrenaline (nor-epinephrine) instead of adrenaline is recommended since it has the same vasoconstrictive properties but it does not cause tachycardia.

Of the different procaine derivates, LIGNOCAINE is least toxic and has a very rapid action. It is readily available in most countries, but the combination with adrenaline or noradrenaline seems to exist only in the form of 1.8 ml dental cartridges. Therefore this combination must be made by adding noradrenaline to the plain solution.

Infiltration of a local anesthetic is improved if the concentration is low, the temperature is high, and the pH is high. Best results are obtained by diluting a 2% solution with an equal volume of isotonic (1.4%) sodium bicarbonate solution and allowing the mixture to warm up before use. The maximum dose of lignocaine is 3 mg per kg bodyweight, or 6 mg if solution contains (nor)adrenaline. The maximum dose of (nor-)adrenaline for an adult is .5 mg. A concentration of 1:100 000 (1 mg per 100 ml fluid) gives best results.

The effective dose is much lower, about half the maximum dose. This leads to the following recommendation:

1. Keep in stock (all solutions are available in 20 ml bottles):

- Lignocaine 2 % solution plain,

- Sodium bicarbonate 4 % solution,

- Water for injection.

- (Nor-)adrenaline amp l ml = 1mg.

2. Prepare 60 ml of (nearly) isotonic sodium bicarbonate by adding 40 ml of water for injection to 20 ml of 4% sodium bicarbonate solution.

3. Prepare another 60 ml and add 1.5 mg (1l/2 amp) of (nor)adrenaline to obtain a 1:40 000 solution .

4. Mix equal volumes of 2% lignocaine and one of the diluting fluids to obtain 1% lignocaine plain and 1% lignocaine with (nor-)adrenaline 1:80 000 respectively.

For a young pregnancy 10 ml of 1% plain lignocaine is given in two injections of 5 ml on both sides of the cervix, giving a total of 100 mg of lignocaine. In an advanced pregnancy 20 ml of 1% lignocaine with (nor-)adrenaline is given in four injections, two on each side of the cervix, totalling to 200 mg of lignocaine and .25 mg of (nor-)adrenaline. This covers practically every bodyweight. Only for very light patients (under 30 kg) the dose must be diminished.

To avoid the great uterine vessels, inject at 10 and 2 o'clock positions (and 4 and 8 o'clock in the advanced pregnancy). It is very important to withdraw the plunger before injecting to check that the needle did not enter a vessel. Intravenous injection has a toxic effects on the CZS. Mild effects are dizziness and a pricking sensations in tongue and lips. More severe effects are muscle movements like an epileptiform insult. A very severe form with arrest of breathing is rare but may be fatal. Immediate IV injection of 10 mg of diazepam is indicated.

In a (no longer existing) hospital in Amsterdam a patient died after injection of 30 ml of a local anaesthetic because of coma and respiratory arrest. It is not known if diazepam was given. Rare as this complication may be, it is wise to have a syringe of diazepam ready.

In Utrecht a 15 year old Marrocan patient incidently was given an injection with a ten times higher concentration of the local anesthetic. A convulsion followed by death was the sad result.

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last reviewed spring 2010