CRNI Infusion-Related Pharmacology 2 — Questions and Answers
Question 1: What is the primary concern when administering vancomycin IV too rapidly?
- Nephrotoxicity
- Red man syndrome (Correct answer)
- Ototoxicity
- Hepatotoxicity
Correct answer: Red man syndrome
Rapid vancomycin infusion causes histamine release resulting in red man syndrome, characterized by flushing, erythema, and hypotension of the upper body.
Red man syndrome (vancomycin flushing syndrome) is a histamine-mediated reaction caused by rapid IV vancomycin infusion. It presents with erythematous flushing of the face, neck, and upper torso, pruritus, and potentially hypotension and tachycardia. It is not a true allergy but a rate-dependent pharmacological effect. Prevention requires infusing vancomycin at no faster than 10 mg/minute (typically each 500 mg over at least 30 minutes, or 1 g over at least 60 minutes). If symptoms occur, the infusion should be stopped, antihistamines administered, and the infusion restarted at a slower rate once symptoms resolve.
Question 2: Which drug-drug interaction is MOST dangerous when co-administering IV heparin and nitroglycerin?
- Increased bleeding risk from potentiated anticoagulation
- Decreased heparin efficacy requiring higher doses (Correct answer)
- Nitroglycerin precipitation in the IV line
- Cardiovascular collapse from synergistic vasodilation
Correct answer: Decreased heparin efficacy requiring higher doses
IV nitroglycerin can decrease heparin's anticoagulant effect, requiring increased heparin doses that may cause bleeding complications when nitroglycerin is discontinued.
IV nitroglycerin interferes with heparin's anticoagulant activity, likely through competitive binding or conformational changes. During co-administration, higher heparin doses are needed to achieve therapeutic aPTT values. The critical danger occurs when nitroglycerin is discontinued - the inhibitory effect is removed, and the elevated heparin dose now exerts full anticoagulant effect, potentially causing serious bleeding. The CRNI must monitor aPTT closely during co-administration, communicate with the pharmacy about dose adjustments, and especially monitor after nitroglycerin discontinuation. Heparin dosing should be reduced when nitroglycerin is stopped.
Question 3: What is the correct method for calculating an IV drug infusion rate when given mg/kg/min dosing?
- Multiply the dose by patient weight, divide by concentration, multiply by 60 (Correct answer)
- Simply multiply the dose by the drip factor
- Use the patient's ideal body weight and round to the nearest 10 mL/hr
- Divide the total bag volume by the desired infusion time
Correct answer: Multiply the dose by patient weight, divide by concentration, multiply by 60
For weight-based infusion calculations: (dose in mg/kg/min multiplied by patient weight in kg divided by drug concentration in mg/mL) multiplied by 60 equals infusion rate in mL/hr.
Weight-based IV infusion calculations require systematic unit conversion. The formula is: Rate (mL/hr) = (Dose [mg/kg/min] x Weight [kg] x 60 [min/hr]) / Concentration [mg/mL]. For example, dopamine 5 mcg/kg/min for a 70 kg patient using 400 mg in 250 mL (1.6 mg/mL): (0.005 mg/kg/min x 70 kg x 60) / 1.6 mg/mL = 13.1 mL/hr. The CRNI must verify: actual patient weight (not estimated), correct drug concentration, appropriate units (mcg vs mg), and use of an infusion pump for all vasoactive drips. Independent double-checks are required for high-alert medications.
Question 4: Which IV medication requires protection from light during infusion?
- Ceftriaxone
- Nitroprusside (Correct answer)
- Metronidazole
- Piperacillin-tazobactam
Correct answer: Nitroprusside
Nitroprusside is highly photosensitive and must be protected from light during preparation and infusion to prevent degradation to cyanide.
Sodium nitroprusside decomposes when exposed to light, releasing cyanide ions that can accumulate to toxic levels. The IV bag and tubing must be wrapped in opaque material (typically amber or foil wrapping) during preparation and throughout infusion. Freshly prepared solutions are brownish in color; a blue, green, or dark red discoloration indicates degradation and the solution must be discarded. Other light-sensitive IV drugs include: amphotericin B, doxorubicin, furosemide, and certain vitamins. The CRNI must identify light-sensitive medications and ensure appropriate light protection measures are in place before initiating infusion.
Question 5: What is the pharmacological rationale for using a 0.22-micron in-line filter during IV infusion?
- To filter out air bubbles only
- To remove particulate matter, microorganisms, and endotoxins (Correct answer)
- To slow the infusion rate
- To prevent drug precipitation visible to the eye only
Correct answer: To remove particulate matter, microorganisms, and endotoxins
A 0.22-micron filter removes particulate matter, bacteria, fungi, and endotoxins from the infusate, providing an additional safety barrier against contamination.
The 0.22-micron filter is a sterilizing-grade filter that removes particles, bacteria, fungi, and air. It serves as the final safety barrier between the infusion solution and the patient's bloodstream. A 0.22-micron pore size is small enough to remove all bacteria (smallest approximately 0.3 microns) while allowing passage of dissolved medications. Some filters also retain endotoxins through charge-based adsorption. Specific filter requirements vary by infusion type: 0.22 micron for crystalloid solutions and most medications, 1.2 micron for lipid-containing solutions (which cannot pass through 0.22 micron), and blood products require 170-260 micron standard blood filters. Certain medications (e.g., albumin, immune globulin) should not be filtered.
Question 6: A patient receiving IV phenytoin develops burning at the peripheral IV site with a pH of the infusate measured at 12. What action should the nurse take?
- Apply a warm compress and continue the infusion
- Stop the infusion, assess for extravasation, and consider central line placement for continuation (Correct answer)
- Dilute the phenytoin further and resume peripherally
- Increase the infusion rate to minimize contact time
Correct answer: Stop the infusion, assess for extravasation, and consider central line placement for continuation
Phenytoin has a pH of approximately 12, making it highly alkaline and irritating to peripheral veins. Burning suggests chemical phlebitis or extravasation requiring IV discontinuation.
IV phenytoin has a pH of approximately 12 (highly alkaline) and contains propylene glycol as a solvent, both of which cause significant venous irritation. Peripheral administration carries risks of chemical phlebitis, tissue necrosis upon extravasation, and purple glove syndrome (distal limb edema with discoloration). When burning occurs, the infusion must be stopped immediately and the site assessed for extravasation. For continued therapy, options include: central venous access for phenytoin, or switching to fosphenytoin (a water-soluble prodrug with pH 8.6-9.0 that can be safely given peripherally). The maximum peripheral infusion rate for phenytoin is 50 mg/min (25 mg/min in elderly).
CRNI Infusion-Related Pharmacology 2
What is the primary concern when administering vancomycin IV too rapidly?