local anesthesia for hair restoration
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Local anesthesia for hair restoration

Historically speaking, local anesthesia was used as early as Inca civilization by chewing coco leaves and dribbling the enriched saliva in the surgical wounds. It was in 1884 that Karl Koller used coco leaves to extract cocaine which he used as a local anesthesia during glaucoma surgery. This surgery saw the introduction of anesthesia in modern medicine. Halstead in the same year used cocaine as an injection to create blocks in the nerves. Until 1904 when the first chemical anesthesia procaine was synthesized, cocaine was the only practical anesthesia option. In 1943 Lidocaine, the first amide anesthesia was synthesized and to date this is the most popular of all the different types of anesthesia available.

Types of local anesthesia:

Local anesthesia can be broadly classified into caine and non-caine anesthetics. The caine anesthetics have a lipophilic aromatic ring, intermediate chain and a hydrophilic ionizable amine group. Depending on the chemical linkages between the aromatic ring and the intermediate chain, the caine anesthetics are classified as ionized or non-ionized. The ionized form blocks the nerve impulses by attaching itself to the sodium channel receptors on cells while the non-ionized form diffuse through the cell membrane.

When an anesthetic with an ester group, such as cocaine, procaine and tetracaine is used, it has been observed that their effect is of very short duration due to which their analgesic effect is less and poses a risk of hypersensitivity in patients. This group of anesthetics is hydrolyzed in the plasma by an enzyme called pseudocholinesterase. Patient’s who are deficient in this enzyme show toxic symptoms when these drugs are administered in normal doses. Because of these disadvantages, the ester group containing caine anesthetics are not used in hair transplantation procedures.

The amide containing caine anesthetics are the most popularly used agents in hair transplants. This group includes lidocaine, bupivacaine, prilocaine, etidocaine, mepivacaine and ropivocaine out of which lidocaine and bupivacaine are extensively used. These are metabolized in the liver and expelled out of the system by the kidneys. Hence patients with problems in their liver and kidneys are administered this anesthesia with caution.

Lidocaine, the most commonly used anesthesia, has varying effects in different locations in the human body. Its effect is better in parts of the body other than in the face and this effect may be attributed to the body vasculature. It is used extensively in ring blocks because of the early onset of anesthetic effect and when administered as infiltration anesthesia, the effect is immediate. Best of all, it does not affect the cardiovascular system.

Bupivacaine is also used by many surgeons since it has a longer anesthetic effect, that is 4-8 times longer than lidocaine. One fourth the amount of bupivacaine in weight as compared to lidocaine is enough to produce the same anesthetic effect. But in ring blocks, bupivacaine is slow to produce effect and infiltration is very painful. Although bupivacaine has certain advantages, one of the main drawbacks of this agent is that it affects the cardiovascular system. The main effects are arrhythmic heart [irregular heart beats] and fibrillation [muscular twitching without coordination]. It also has a profound effect on the potassium and calcium channels in cells. While it blocks sodium channels rapidly, it takes longer time to unblock them and this can also be one of the factors for causing arrhythmia.

In the non-caine category of anesthesia, only a few agents such as 1% diphenhydramine, 0.9% benzyl alcohol, metoclopramide and tramadol have been studied. Although they are generally considered to cause less pain during infiltration, diphenhydramine seems to be more painful and also leads to localized skin mortification. All the above studied agents have effect lasting for short durations of up to 15 mins and hence they are not used in hair transplantation procedures.

Along with local anesthesia, vasoconstrictors [an agent that causes narrowing of blood vessels] such as epinephrine and ornipressin are used to prolong the effect of anesthesia. A vasoconstrictor not only prolongs anesthetic effect but also limits the absorption of anesthesia thereby lowering toxicity and improving hemostasis. A 2% lidocaine solution has effect for 1-3 hrs while the same when mixed with epinephrine in the ratio 1: 200,000 has an effect lasting 5-8 hrs. The mixing of local anesthesia with epinephrine results in oxidation of epinephrine due to which the pH of the solution turns acidic. To prevent this problem, sodium bisulfate or meta-bisulfate is added to increase the pH. Since epinephrine in heavy doses can affect the heart rate and blood pressure, it must be cautiously used in patients who have hypertension and other cardio related problems.

Just as epinephrine is widely used in US, ornipressin is used in Europe and Australia. Anesthetists of these regions claim that the effect of ornipressin is greater than epinephrine and less toxic to the cardio system. A higher dose of ornipressin however causes dilation of the vessels. It is also found that during vasoconstriction, there is decreased blood flow and higher blood pressure. Hence ornipressin should be administered with caution in patients with heart related anomalies.

Maximum permissible amount of anesthesia –

For a man who weighs 70 kg, a maximum of 50ml of 1% lidocaine with epinephrine can be administered. 1% lidocaine has 10mg of lidocaine per ml of the solution. Similarly 90 ml of 0.25% of bupivacaine with epinephrine in the ratio of 1:100,000 is the permissible limit.

In scalp infiltrations, it has been observed that the level of lidocaine in plasma differs with the rate of absorption in the subcutaneous infiltration. Except for one study conducted by Maloney et.al in 1982 involving punch grafts, in which they found a correlation between the dosage and concentration of lidocaine in the plasma, further detailed study could reveal its toxicity and maximum dosage applicable to hair transplants.

The toxic effects of local anesthesia –

As mentioned above, the concentration of anesthesia in plasma indicates the degree of toxicity. Local anesthesia is toxic to the neuro and cardio systems. When lidocaine is administered, a concentration of 4 mg/L has anticonvulsant effect and as little as 3 mg/L has neurological effects. The initial symptoms of neurological effect are drowsiness, light headedness, incoherence in speech, sight and taste. With increase in concentration, these symptoms also increase and at 7.5 mg/L concentration a patient can experience seizures. The toxicity increases when the brain is deprived of oxygen and the carbondioxide level in the blood is high due to which the acidity of the blood increases. To prevent neurological damage, benzodiazepines are administered but they mask cardiovascular toxicity.

Bupivacaine can cause central nervous system toxicity at 1 mg/L concentration. Bupivacaine is four times more potent than lidocaine in its anesthetic effect, but its lethal effect in neuro system is four times and cardio system is nearly nine times its anesthetic effect.

The toxicity of local anesthesia can be prevented if the anesthetist follows the patient’s needs methodically by keeping records of the patient’s health conditions, preparing the anesthesia according to need and monitoring it continuously during the surgery. An anesthetist can easily recognize symptoms related to anesthesia such as dizziness, paling of skin, sweating, nausea, differences in blood pressure and fainting. These can be immediately attended to by positioning the patient with his legs slightly elevated and applying cool compressions and reassuring the patient. In patients who have no cardiac problems, 0.4 mg atropine is administered intramuscularly. Rebreathing masks and different medications such as benzodiazepines, flumazenil, hydralazine, naloxone and intravenous fluids are used to prevent toxicity during hair transplantation. Benzodiazepines also cause respiratory depression and is controlled by use of flumazenil. Since local anesthesia can cause cardio vascular collapse, it is usually mandatory that the clinic has all equipment for cardio life support ready.

Some patients may react to vasoconstrictors and such patients are given beta-blockers and nitroglycerin with continuous monitoring of pulse, blood pressure and electrocardiogram. When allergic reactions occur, the patients are treated with epinephrine and antihistamines.

Local anesthesia in hair transplants –

Ring blocks are used to anesthetize the donor area while nerve blocks are used for the recipient areas of the crown and front of the head. Very fine needles are used for infiltrating the solutions to avoid damage of the vessels and distension of tissues.

In a hair transplant procedure, any pain is from the initial local anesthesia injections. To reduce this pain, the following methods are used:-

1. Conscious sedation – administering anesthesia with the patient being comfortable and in a conscious state with normal breathing, continuous monitoring of the patients well being with respect to breathing, pulse, blood pressure, electrocardiogram and keeping cardio life support handy collectively form the conscious sedation procedure. When the sedation is in effect, ring and nerve blocks can be simultaneously administered.

2. Topical local anesthesia – A mixture of 2.5% prilocaine and 2.5% lidocaine when applied to the skin 90-120 mins before injecting local anesthesia reduces the pain of the initial injection. This however does not reduce the actual local anesthesia penetration pain and hence finds limited usage in hair transplantation.

3. Injecting without needles – is done by using injectors that create a weal on the skin so that subsequent injections can be performed using needles. This procedure does not eliminate infiltration pain.

4. Use of ice packs or chilled metal plates has been recommended to numb the skin before injecting the local anesthesia. A combination of ice packs with other methods to lessen pain can be effective.

5. Scratching the skin or vigorously rubbing the area before injection lessens pain.

6. Tumescence – using very dilute and large amounts of local anesthesia increases the turgidity of the tissues and also helps in easier dissection.

7. Temperature and pH control of the local anesthesia – warming the solution to body temperature and increasing the pH of the solution using buffers lessens infiltration pain.

8. Iontophoresis of lidocaine – by transferring lidocaine ions across a membrane to the skin relives pain.

Of all the above mentioned techniques, use of conscious sedation coupled with ice packs is the most helpful in lessening pain.

Local anesthesia for hair restoration references

  • Seager DJ, Simmons C. Local anesthesia in hair transplantation. Dermatol Surg. 2002 Apr;28(4):320-8. Review. PMID: 11966789
  • Nusbaum BP. Techniques to reduce pain associated with hair transplantation: optimizing anesthesia and analgesia. Am J Clin Dermatol. 2004;5(1):9-15. Review. PMID: 14979739
  • Swinehart JM. Local anesthesia in hair transplant surgery. Dermatol Surg. 2002 Dec;28(12):1189. No abstract available. PMID: 12472507
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