Extravasation is the inadvertent leakage of a vesicant drug from a blood vessel into the surrounding subcutaneous tissue. This complication is serious, especially when involving vasoconstrictive agents like norepinephrine or dopamine. These drugs cause intense constriction of local blood vessels, leading to severe localized tissue damage, including blistering and tissue death. Phentolamine mesylate is the specific pharmacological antidote used to counteract these tissue-damaging effects.
Phentolamine’s Role in Counteracting Extravasation
Phentolamine is an alpha-adrenergic blocking agent that inhibits the effects of the extravasated vasopressor drugs. When a vasopressor leaks, it binds to alpha-receptors on local blood vessel cells, causing intense constriction. This sustained vasoconstriction severely limits blood flow, leading to localized tissue ischemia (lack of oxygen and nutrients).
If blood flow is not restored promptly, the cellular injury can quickly progress to necrosis (tissue death). Phentolamine reverses this by competitively blocking the alpha-1 and alpha-2 adrenergic receptors. This blockade causes the contracted blood vessels to relax and widen, a process called vasodilation.
Immediate vasodilation increases local blood flow, serving two protective functions. It allows the extravasated drug to be reabsorbed or significantly diluted within the tissue. Crucially, it restores oxygen and nutrient delivery to the compromised tissue, counteracting ischemia and preventing necrosis. Phentolamine is the first-line treatment and is most effective when administered within the first hour, though it can be beneficial up to twelve hours later.
Preparation of the Injection Site and Medication
Management begins by immediately stopping the infusion of the offending drug. The intravenous catheter should be left in place temporarily to attempt aspiration of the residual drug and surrounding fluid. Aspiration is performed gently using a small syringe to remove as much of the leaked substance as possible before the antidote is introduced.
Following aspiration, the phentolamine antidote must be prepared precisely. The standard adult dose is 5 to 10 milligrams of phentolamine mesylate, diluted in 10 milliliters of 0.9% sodium chloride (normal saline). This dilution creates the solution ready for local infiltration into the affected tissue.
Before injection, assess the affected area to define the extent of the injury. The site should be marked to outline the boundaries of the extravasation, which often appears cold, blanched, or pale. A small-gauge needle (25-gauge or smaller) is selected to ensure minimal trauma during the multiple-site infiltration.
Step-by-Step Injection Technique
Phentolamine administration involves local infiltration, distributing the medication throughout the entire affected area. The diluted 10 mL solution is divided and infiltrated into the tissue using multiple subcutaneous or intradermal injection sites. The goal is to encircle the area where the vesicant drug leaked, avoiding injection directly into the center of the injury.
The extravasation site is often mentally divided into quadrants to ensure comprehensive coverage. At each injection point, only a small volume (0.5 to 1.0 milliliter) of the diluted solution is administered. This small volume maximizes the spread of the antidote and minimizes the risk of increasing tissue pressure, which could compromise local circulation.
The needle is inserted around the periphery of the marked area, and the small amount of medication is gently injected. After each injection, the needle is withdrawn, and the process is repeated at adjacent sites until the entire 10 mL dose is evenly distributed. The total dose depends on the size of the extravasation, with the maximum adult dose being 10 mg.
Monitoring for Resolution and Potential Side Effects
After phentolamine infiltration, the site requires continuous observation for signs of resolution. The expected positive response is a rapid reversal of blanching and paleness, often within minutes, as local vasodilation restores blood flow. The skin should return to a normal color, the temperature should increase, and any hardness or swelling should begin to decrease.
If signs of ischemia (blanching or coldness) persist or return, a second dose of phentolamine may be necessary after 60 minutes. Although phentolamine is administered locally, systemic absorption can occur, requiring monitoring for side effects. Common systemic effects include a drop in blood pressure and an increase in heart rate (reflex tachycardia).
To ensure patient safety, vital signs, especially blood pressure, should be monitored frequently, often every five minutes for the first hour. Comprehensive documentation is mandatory. This includes recording the details of the extravasated drug, the time of the event, the phentolamine dose, the injection sites, and the patient’s immediate response.