Atypical Plasma Cholinesterase

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What are two other names for plasma cholinesterase?

Pseudocholinesterase and butyrocholinesterase

In patients who have low concentrations of normal (typical) plasma cholinesterase, how much is the duration of neuromusclar blockage prolonged?

With low concentrations of normal (typical) plasma cholinesterase, the duration of neuromuscular blockade by succinylcholine is doubled or tripled (slighly prolonged)

Identify the incidence of heterozygous atypical plasma cholinesterase in the general population. Identify the incidence of homozygous atypical plasma cholinesterase in the general population.

The incidence of heterozygous atypical plasma cholinesterase in the general population is about 1:25, or 4%. The incidence of homozygous atypical plasma cholinesterase in the general population is about 1:2800, or 0.04%.

What agents have prolonged action in patients who have atypical pseudocholinesterase?

Succinylcholine, mivacurium, and ester-type local anesthetics

Distinguished between common and atypical plasma cholinesterase.

The common type of plasma cholinesterase is able to hydrolyze succinylcholine while abnormal variety is unable to hydrolyze succinylcholine at concentrations that occur in the blood of anesthetized patients.

What lab test assesses plasma pseudocholinesterase activity?

Dibucaine test.

How is dibucaine used to test for pseudocholinesterase activity? what is the normal range for the dibucaine number?

Dibucaine depresses the activity of pseudocholinesterase. If pseudocholinesterase is normal, dibucaine will depress that activity of pseudocholinesterase by 70-80%. The percent of dibucaine depresses pseudocholinesterase is called the dibucaine number. The normal dibucaine number is usually said to be 80%.

If a patient has one normal and one abnormal gene for plasma cholinesterase (the patient is a heteozygote), what dibucaine number is expected? How long will succinylcholine neuromuscular block be prolonged?

Heterozygotes have dibucaine numbers for atypical plasma cholinesterase that range from 30-70 (Morgan and Mikhail states that 40-60 is the range). Neuromuscular block in heterozygotes is slightly prolonged by succinylcholine.

What does it mean if the dibucaine number is between 30-70?

The individual is a heterozygote for the abnormal pseudocholinesterase.

If a patient has two abnormal genes for plasma cholinesterase (the patient is a homozygote), what dibucaine number is expected? How long will succinylcholine neuromuscular block by prolonged?

Homozygotes have a dibucaine number for atypical cholinesterase of about 20. Neuromuscular block with succinylcholine is quite prolonged 6-8hrs in homozygotes.

Does the dibucaine number reflect the quantity or concentration of pseudocholinesterase present?

No. The dibucaine number reflects the effectiveness of the enzymes for hydrolyzing succinylcholine, not the quantity or concentration of the enzymes in the plasma.

If the patient who has received succinylcholine (or mivacurium) remains paralyzed several (2-8) hours later, what is the patient's dibucaine number? Is the concentration of plasma cholinesterase of this patient normal or abnormal?

The patient who remains paralyzed several hours (2-8hr) after receiving succinylcholine or (mivacurium) has a dibucaine number of 20 (the patient is homozygous for atypical plasma cholinesterase), and the concentration of plasma cholinesterase is normal.

How does a patient who is homozygous for atypical plasma cholinesterase eliminate succinylcholine?

Succinylcholine will be eliminated by the kidneys. With renal elimination, the duration of action of succinylcholine is prolonged, possibly for greater than two hours after an intubating dose.

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