Calcium gluconate (membrane stabilization)

Emergency membrane-stabilization therapy for life-threatening hyperkalemia. 10% calcium gluconate 0.5–1.5 mL/kg IV slowly over 10–20 min with continuous ECG. Onset 1–3 min; duration only 30–60 min. Calcium does NOT lower K, it raises the cardiac cell threshold potential, restoring the gradient that hyperkalemia has narrowed. A bridging therapy that buys time for K-lowering treatment (insulin/dextrose, fluid therapy) and definitive correction of the underlying cause.

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Clinical background

Calcium gluconate is the emergency-room drug for hyperkalemic cardiac arrhythmia. It does one thing well: it stabilizes the cardiac cell membrane within minutes, holding the patient out of arrhythmia while the slower-acting K-lowering therapies (insulin/dextrose, fluid therapy) and the definitive treatment of the underlying cause take effect. It does not lower potassium. The duration of action is short, 30 to 60 minutes, and its only role is bridging.

What calcium does at the cardiac cell membrane

Hyperkalemia depolarizes the resting membrane potential of cardiac cells. As resting potential rises closer to threshold, the gradient between the two narrows, voltage-gated Na channels begin to inactivate, and conduction slows. The ECG changes follow a predictable sequence as serum K rises:

1. Peaked T waves (often the first finding, around K 5.5–6.5)
2. Prolonged PR interval as AV conduction slows
3. Loss of P waves as atrial electrical activity fails
4. Widened QRS as ventricular conduction slows
5. Sine-wave QRS as conduction approaches asystole
6. Asystole

Calcium does not change the serum K. It works by raising the cardiac cell threshold potential, which restores the gradient between resting potential and threshold even though the resting potential remains depolarized. The membrane is “stabilized” in the sense that an action potential can be triggered normally and conducted properly. The effect manifests on ECG within 1–3 minutes, peaked T waves flatten, PR interval shortens, QRS narrows.

The mechanism explains the short duration. Calcium does not address the underlying problem (excess K, with or without acidosis); it only buys time by altering the threshold. Once serum calcium falls back to baseline (30–60 min), the protective effect is gone. The patient who was given calcium but no K-lowering or definitive therapy is in the same place at 60 minutes that they were before the calcium.

Indications

Emergency hyperkalemia treatment in any species. The two most common GP scenarios are:

• Feline urethral obstruction: male cats with sudden post-renal hyperkalemia from urine retention, often with concurrent metabolic acidosis driving K extracellularly
• Hypoadrenocorticism (Addisonian crisis) in dogs: mineralocorticoid deficiency causing K retention, often with concurrent hyponatremia, volume depletion, and metabolic acidosis

Other indications include oliguric AKI, tumor lysis syndrome (acute), severe rhabdomyolysis with myoglobin-induced AKI, and rare presentations like β-blocker overdose.

The threshold for using calcium is not the K value alone, it is the K plus the ECG findings. A patient with K of 6.5 and peaked T waves needs calcium; a patient with K of 7.0 about to be deobstructed in the next 10 minutes may not need it if there are no ECG changes. The calculator surfaces this on the page text. In practice, most clinicians give calcium any time K > 7 with ECG changes, or any time the rhythm is overtly abnormal regardless of the exact K.

Calcium gluconate vs calcium chloride

This is a recurring medication-error point worth understanding. Both salts are sold as parenteral 10% solutions; they look similar on the shelf; they treat the same indications. But they are NOT interchangeable on a mL basis.

10% calcium gluconate: - 100 mg/mL of the gluconate salt - 9.3 mg/mL elemental Ca - 0.465 mEq/mL Ca²⁺

10% calcium chloride: - 100 mg/mL of the chloride salt
- 27.2 mg/mL elemental Ca - 1.36 mEq/mL Ca²⁺ (≈3× more potent than gluconate per mL)

Calcium chloride delivers about 3× the elemental calcium per mL. Substituting chloride for gluconate at the gluconate dose triples the calcium load. Even more important, calcium chloride is much more cardiotoxic at equipotent doses (some authors suggest because of the chloride load and the lower pH of the solution) and is severely tissue-toxic on extravasation, necrosis is common.

The IV preparation for hyperkalemia is calcium gluconate. Veterinary references uniformly specify gluconate, not chloride. If you reach into the drug cart and grab a vial labeled “calcium chloride 10%,” put it back. The InfusionFox calculator math is based on the gluconate concentrations.

Administration

Slow IV with continuous ECG monitoring throughout. Per Silverstein Ch. 122 / DiBartola Ch. 5: 0.5–1.5 mL/kg of 10% calcium gluconate over 10–20 minutes. The calculator defaults to 1.0 mL/kg over 15 minutes (mid-range).

The “continuous ECG” piece is not optional. The classic mistake, and a documented cause of veterinary CPR scenarios, is giving calcium too fast in a patient whose membrane is already maximally depolarized. Hypercalcemia from too-rapid IV calcium can itself cause arrhythmias and arrest. The rule: stop the infusion immediately if bradycardia worsens, PR interval lengthens further, or QRS widens. Resume at half the rate after rhythm stabilizes.

The infusion rate matters more than the precise dose. A 5 mL bolus over 30 seconds is much more dangerous than a 10 mL bolus over 15 minutes. When in doubt, slow down.

Never IM or SC. Calcium causes severe tissue necrosis subcutaneously. If extravasation occurs during IV administration, stop the infusion immediately, attempt to aspirate from the catheter before removing it, and apply warm compresses. Hyaluronidase infiltration has been described for severe extravasation.

Line compatibility

Calcium precipitates with several common concurrent infusions. Two that matter most:

• Sodium bicarbonate: calcium carbonate precipitates. NEVER co-infuse, never share a line, flush thoroughly between drugs.
• Potassium phosphate (KPhos): calcium phosphate precipitates. NEVER co-infuse.

In practice, hyperkalemia patients are often on multiple concurrent infusions. The safest approach: a separate IV line for any calcium-incompatible therapy. If you only have one IV line, flush thoroughly with saline before and after every drug, and do not run anything in parallel during the calcium infusion.

LRS contains 3 mEq/L of calcium. At standard CRI rates this is not clinically meaningful and LRS is a fine carrier fluid for a hyperkalemic patient. Do not, however, mix calcium gluconate boluses INTO the LRS bag, you’d raise the calcium concentration enough to cause local precipitation issues at the line interface.

What the patient needs next

Calcium alone cannot save the patient. Within minutes of the calcium infusion finishing, you should be:

• Drawing up insulin and dextrose for the K-shifting bolus (see /insulin-dextrose-hyperK)
• Starting or continuing aggressive fluid therapy
• Mobilizing the resources for definitive treatment of the underlying cause:
  • Feline UTO: decompressive cystocentesis if not already done, sedation + urinary catheter placement
  • Addisonian crisis: dexamethasone 0.1–0.2 mg/kg IV (does not interfere with cortisol assay), aggressive fluid resuscitation with 0.9% NaCl, ACTH stim test for confirmation
  • AKI: address the inciting cause; mannitol or furosemide if oliguria persists despite fluid therapy

The hyperkalemia emergency hub at /hyperkalemia-emergency lays out the full workflow.

Repeat dosing

Calcium dosing can be repeated if bradyarrhythmias recur during the bridging window, this is not uncommon when serum K is very high or when insulin/dextrose has not yet kicked in. The same dose and infusion duration apply. Continuous ECG continues.

If repeated calcium dosing is required and K-lowering therapy is in progress, reassess: are you actually correcting the K? Is fluid therapy adequate? Is the underlying cause being addressed? Repeated calcium doses without clinical improvement is a sign that the bridging therapy alone is not enough.

Adverse effects

In addition to the bradyarrhythmia and extravasation risks above:

• Hypotension with rapid administration (calcium-induced vasodilation; transient)
• Vomiting during the infusion (uncommon but documented)
• Hypercalcemia with overdosing or repeated dosing in a patient with chronic kidney disease (Ca clearance is partly renal)
• Soft tissue mineralization with prolonged or excessive supplementation (not a concern for emergency dosing)

The drug is generally well-tolerated when given correctly. The danger is in administration speed, not in the drug itself.

Sources

• Cooper ES. Urethral Obstruction. In: Silverstein DC, Hopper K, eds. Small Animal Critical Care Medicine. 3rd ed. Elsevier; 2023. Chapter 122 (cites the 0.5–1.5 mL/kg dose range and the slow-administration ECG-monitored protocol).
• DiBartola SP. Disorders of Potassium. In: Fluid, Electrolyte, and Acid-Base Disorders in Small Animal Practice. 4th ed. Elsevier; 2012. Chapter 5 (overview of hyperkalemia mechanisms, ECG progression, and the calcium-gluconate-vs-chloride distinction).