SYSTEMIC EFFECTS OF VASOCONSTRICTORS

-Unintentional injection of LA into a blood vessel can cause systemic effects, as can the rapid absorption of large amounts of LA (occasionally).

-Anesthesiologist must take special precautions against systemic toxicity. Time is critical for tx of systemic toxicity. Must have CPR training and working oxygen source, along with other equipment, including a defibrillator and suction device. Drugs such as succinylcholine, diazepam or thiopental, vasopressors, and atropine should be in syringes with needles attached. Pulse and BP should be taken before the block.

-the administration of LA requires 3 precautions to avoid systemic toxicity:
1) aspiration,
2) adequate test doses,
3) slow administration of full dose in fractional amounts.

-If blood is found on aspiration, move the needle to another place, but a clear aspiration does not necessarily ensure a safe injection. The possibility of systemic toxicity still exists.

-Epinephrine response consists of an increase in BP and pulse, circumoral pallor, palpitations and nervousness. Pts on beta-adrenergic blocking drugs may not respond to epinephrine with increased HR, but will usually have an increased BP.

-Slow injection technique while monitoring the pt is essential for the quick detection of systemic effects, also you must be careful not to move the needle into a blood vessel after a safe aspiration.

-Systemic toxicity after an intravascular injection will usually occur within 1-2 minutes, 5 or more minutes may elapse if rapid tissue absorption is the cause of systemic effects (for spinal block specifically, or also for dental injections? I don’t know… )

-If untreated, convulsions with hypoxia, hypercarbia and acidosis may result. Respiratory abnormalities including apnea may occur. The hypoxia and acidosis cause myocardial contractions from the direct effects of the LA, and may result in cardiac arrhythmias, asystole, or ventricular fibrillation. Prior to convulsions, the pt may display any or all of a plethora of signs: slurred or incoherent speech, restlessness, nervousness, dizziness, blurred vision, tinnitis, and or drowsiness.

-Pts with LA-induced convulsions developed rapid hypoxia, hypercarbia, and acidosis within a minute. Oxygen consumption and carbon dioxide production are greatly increased during LA convulsions, thus immediate and effective ventilation with oxygen is essential to avoid cardiac arrest.

-Tx of systemic toxicity:
1.) Establish and maintain an airway;
2) immediately administer 100% oxidation (may prevent convulsions);
3) if necessary, use drugs to control convulsions;
4) if cardiac arrest occurs despite other procedures, CPR must be initiated and continued as necessary.

Category: Pharmacology Notes