The provider’s order reads: Give mannitol 0.5 g/kg IV now, over 2 hours. The client weighs 165 lb and you have a 100-mL vial of 20% mannitol. How many grams will the client receive? How many milliliters of mannitol will you prepare for this infusion?

Hydrochlorothiazide is a benzothiadiazide derivative inhibiting the Na+/Cl- symporter in the distal convoluted tubule. This thiazide diuretic increases distal sodium delivery, facilitating obligatory potassium excretion and volume reduction. It manages hypertension and edema but is contraindicated in anuria or sulfonamide hypersensitivity. Adverse effects include hypokalemia, hyperuricemia, and hyperglycemia, requiring frequent monitoring of metabolic parameters and renal function to prevent systemic toxicity.

Rationale for correct answers

B. Thiazide diuretics promote the renal excretion of potassium into the tubular lumen. To maintain a serum level between 3.5 and 5.0 mEq/L, potassium supplements are frequently prescribed. This pharmacological intervention prevents hypokalemia, which could otherwise trigger lethal cardiac arrhythmias. Consistent replacement is vital for patients with high-dose therapy.

C. Hydrochlorothiazide consistently causes significant depletion of serum potassium levels during active diuresis. Simultaneously, it competes with uric acid for secretion in the proximal tubule, leading to hyperuricemia. Monitoring these specific laboratory values is essential to identify metabolic disturbances or potential gouty flares. Nurses must track these biochemical shifts regularly.

D. The primary therapeutic objective of hydrochlorothiazide is the reduction of systemic blood pressure through volume depletion. Baseline and serial assessments of pressure are mandatory to evaluate drug efficacy. This prevents the administration of the drug in cases of hypotension, which would compromise vital organ perfusion. It ensures the patient remains hemodynamically stable.

E. Oliguria, defined as urine output < 400 mL per 24 hours, indicates significant renal impairment or severe dehydration. Thiazide diuretics lose their efficacy when the glomerular filtration rate falls below 30 mL/min. Notifying the health care provider is critical because anuria is a strict contraindication for diuretic use. Immediate intervention prevents further acute kidney injury.

Rationale for incorrect answers

A. Thiazide diuretics are well-documented to interfere with pancreatic insulin release and peripheral glucose uptake. This physiological mechanism leads to hyperglycemia rather than decreased blood sugar. Assessing for hypoglycemia is clinically inappropriate as it does not align with the known metabolic side effects of this class. Diabetic patients must monitor for elevated glucose.

F. Clinical studies indicate that thiazide diuretics can cause a transient increase in low-density lipoproteins. They are associated with hyperlipidemia, not a reduction in serum lipids. Expecting to see decreased cholesterol levels is scientifically incorrect based on the drug's metabolic profile. These medications often negatively impact the lipid panel during long-term use.

Test-taking strategy

• Identify the drug class: Recognize hydrochlorothiazide as a thiazide diuretic and recall its primary effects on electrolytes and fluid balance.
• Determine wasting vs. retaining: Thiazides waste potassium (options 2 and 3) but retain calcium and uric acid (option 3).
• Assess clinical priorities:
  • Safety first: Always check the vital sign the drug is intended to treat (blood pressure, option 4).
  • Contraindications: Recall that diuretics require functioning kidneys; thus, low urine output (option 5) is a major red flag.
• Evaluate metabolic "highs": Use the mnemonic "Hyper-GLUC" (Glycemia, Lipidemia, Uricemia, Calcemia) to remember what goes up.
  • This allows you to rule out option 1 (hypoglycemia) and option 6 (decreased lipids) because both glucose and lipids are expected to increase, not decrease.
• Select all that apply: Treat each option as a true/false statement based on the established side effect profile of benzothiadiazides.

Take home points

• Serum potassium and uric acid must be monitored to prevent hypokalemia-induced arrhythmias and hyperuricemia-induced gout.
• Blood pressure should always be assessed prior to administration to prevent severe hypotension and ensure therapeutic efficacy.
• Oliguria or anuria are clinical indicators that thiazide therapy should be withheld and the provider notified immediately.
• Patients with diabetes must monitor for hyperglycemia because thiazides can impair insulin sensitivity and glucose tolerance.

Mannitol is an osmotic diuretic that remains in the extracellular compartment to create an osmotic gradient across the blood-brain barrier. It facilitates the passive movement of water from the parenchyma into the intravascular space to reduce intracranial pressure. Clinical indications include cerebral edema and intraocular pressure reduction. Contraindications include established anuria from severe renal disease, pulmonary edema, or active intracranial bleeding.

Rationale for correct answer

The nurse must first convert the weight from pounds to kilograms.

This is by dividing 165 by 2.2.
Resulting in 75 kg.

Next step is multiplying the weight by the ordered dose (0.5 g/kg)

This determines that the client requires 37.5 g of mannitol.

Since a 20% solution contains 20 g per 100 mL, the nurse divides the desired 37.5 g by 0.20 to calculate the infusion volume.

Correct answer: 187.5 mL

This mathematical process ensures the precise administration of the prescribed osmotic load.

Test-taking strategy

• Convert weight first: Always convert pounds to kilograms (lb / 2.2) before performing dosage calculations in medical math.
  • 165 lb / 2.2 = 75 kg.
• Determine total grams needed: Multiply the kg by the ordered g/kg dose.
  • 75 kg x 0.5 g/kg = 37.5 g.
• Understand percentage concentrations: Recall that percent (%) in medications means grams per 100 mL.
  • 20% mannitol = 20 g in 100 mL (or 0.2 g per 1 mL).
• Calculate final volume: Divide the required grams by the concentration per mL.
  • 37.5 g / 0.2 g/mL = 187.5 mL.
• Verify the logic: Since the dose (37.5 g) is nearly double the amount in one 100 mL vial (20 g), the answer must be nearly double the volume of one vial.
• Avoid unit confusion: Ensure the final answer is in mL as requested by the second part of the question.

Take home points

• Mannitol requires the use of an in-line filter during administration because the solution is prone to crystallization at room temperature.
• Osmotic diuretics act by increasing the osmolality of the glomerular filtrate, which prevents the tubular reabsorption of water.
• Neurological status, hourly urine output, and serum osmolality must be monitored strictly to evaluate the effectiveness of the therapy.
• Rapid administration of high-dose mannitol can cause a transient increase in blood volume, which may exacerbate heart failure or pulmonary congestion.