Vasoconstrictors are combined with local anesthetics for which reasons? (Select all that apply, one, several or none)
To reduce the risk of toxicity
To prevent bradycardia
To prolong anesthesia
To enhance absorption
To shorten the duration of action
Correct Answer : A,C
A. Vasoconstrictors (such as epinephrine) cause local vasoconstriction, which reduces blood flow at the injection site. This slows the rate at which the anesthetic is absorbed into the systemic circulation. As a result, plasma drug levels remain lower, decreasing the likelihood of systemic toxicity (e.g., CNS effects like seizures or cardiovascular effects such as arrhythmias). This is particularly important with potent local anesthetics like lidocaine or bupivacaine, where high systemic levels can be dangerous.
B. Vasoconstrictors do not prevent bradycardia. Instead, they stimulate adrenergic receptors, which can lead to increased heart rate (tachycardia) and elevated blood pressure if absorbed systemically. Therefore, they are used cautiously in clients with cardiovascular disease. Preventing bradycardia is not a therapeutic goal of adding vasoconstrictors.
C. By decreasing local blood flow, vasoconstrictors delay the removal of the anesthetic from the injection site, allowing it to remain in contact with nerve fibers longer. This prolongs the duration of anesthesia, which is beneficial during longer procedures and reduces the need for repeated dosing.
D. Vasoconstrictors actually decrease (not enhance) absorption into systemic circulation. This is the key mechanism behind both reduced toxicity and prolonged action. Enhanced absorption would increase systemic drug levels, which is the opposite of the intended effect.
E. Because vasoconstrictors slow drug absorption and keep the anesthetic localized, they prolong rather than shorten the duration of action. Shortening duration would require faster systemic uptake, which vasoconstrictors specifically prevent.
Nursing Test Bank
Naxlex Comprehensive Predictor Exams
Related Questions
Correct Answer is A
Explanation
A. Neuromuscular blocking agents (NMBAs)act at the neuromuscular junctionto prevent acetylcholine from stimulating muscle contraction. This leads to paralysis of skeletal muscles, including the diaphragm and intercostal muscles, which are critical for breathing. Because these patients cannot breathe independently, mechanical ventilation is requiredwhen NMBAs are used.
B. While some NMBAs can have minor cardiovascular effects, their primary action is muscle paralysis, not slowing of the heart via vagal stimulation. Bradycardia may occur with certain agents like succinylcholine, but this is not the general principle for all NMBAs.
C. NMBAs do not produce unconsciousness or analgesia. They are purely paralytic agents. The patient remains aware unless adequate anesthesia is also provided with inhalation or IV agents.
D. NMBAs do not increase the required dose of inhalation anesthetics. In fact, using NMBAs may allow the anesthesiologist to reduce inhalation anesthetic doses slightly, since muscle relaxation is provided pharmacologically rather than relying solely on deep anesthesia.
Correct Answer is B
Explanation
A. Antithyroid drugs, such as methimazoleand propylthiouracil (PTU), do not directly affect blood glucose levels. While thyroid hormones themselves influence metabolism, the primary effect of antithyroid medications is on thyroid hormone synthesis, not on glucose regulation.
B. One of the most serious adverse effectsof antithyroid drugs is agranulocytosis, which manifests as a significant reduction in white blood cells (particularly neutrophils). This greatly increases the risk of infection, sometimes with minimal warning signs. Patients may present with fever, sore throat, or other early infection symptoms, which should prompt immediate discontinuation of the drug and medical evaluation. Routine monitoring of WBC counts, especially early in therapy, helps detect this rare but life-threatening complication.
C. Antithyroid medications do not increase red blood cell count. Erythropoiesis is unrelated to the mechanism of these drugs. Any changes in RBCs would likely be due to unrelated conditions, not the antithyroid therapy.
D. Platelet counts are not typically affectedby antithyroid drugs. Thrombocytopenia is rare and not a standard laboratory concern for patients taking these medications.
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