Propofol (TIVA / Status epilepticus)

Short-acting sedative-hypnotic injectable anesthetic; potentiates GABA at GABA-A receptors causing chloride influx and hyperpolarization. Rapid IV onset (≈1–2 min) with short duration of action (≈5–7 min after a single induction dose in dogs; 5–12 min in cats) due principally to rapid redistribution from CNS to peripheral tissues. Hepatic glucuronide conjugation is the primary metabolic pathway; clearance exceeds hepatic blood flow, suggesting extrahepatic metabolism.

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Clinical background

Propofol is the most widely used IV anesthetic induction agent in small animals and one of the most useful drugs for total intravenous anesthesia (TIVA) and refractory status epilepticus. It provides rapid, smooth induction with controllable depth, and the short context-sensitive half-life makes recovery predictable after short procedures. The main downsides are dose-dependent cardiorespiratory depression, no analgesia, and, in cats, limited duration tolerance because of slow biotransformation and the risk of Heinz-body anemia with repeated daily dosing.

Pharmacology

Alkylphenol GABA-A receptor positive modulator. Propofol enhances the inhibitory effect of GABA at the GABA-A receptor, producing dose-dependent CNS depression that progresses from sedation to general anesthesia. The drug also has direct sodium-channel effects that contribute to its anticonvulsant activity at higher doses, this is the basis for its use in refractory status epilepticus.

Onset is within 30–60 seconds IV. Distribution is rapid (highly lipophilic) and the early-phase decline in plasma concentration is dominated by redistribution out of the CNS into peripheral tissues. After a single induction bolus, this redistribution is what drives the rapid recovery, not metabolism. With sustained CRI, peripheral tissues saturate and recovery times become more dependent on hepatic clearance, particularly in cats.

Hepatic metabolism is rapid in dogs (high extraction ratio); cats have slower clearance because of limited glucuronidation, which is the basis for the recommendation to limit propofol CRIs in cats to short durations (typically <1 hour) or to use lower doses with extended monitoring.

The product is an oil-in-water emulsion (egg lecithin and soybean oil), which is why it has a milky white appearance and why patients with documented egg or soy allergy are at theoretical risk of allergic reactions. The lipid vehicle also supports bacterial growth, single-use practice and prompt disposal of opened vials are essential.

Indications

Two indication modes are encoded in this calculator:

TIVA maintenance (dogs)

• Total IV anesthesia for procedures where inhalant anesthesia is undesirable (eg, airway procedures, MRI without inhalant capability)
• Anesthesia in patients with severe respiratory disease where inhalants would worsen V/Q matching
• Brief procedures in clinics without inhalant equipment

Refractory status epilepticus (dogs and cats)

• Continued seizure activity after first-line benzodiazepines and second-line agents (levetiracetam, phenobarbital) have been given at appropriate doses
• Used as a CRI for typically up to 24–48 hours, with goal of achieving burst suppression on EEG (where available) or clinical seizure control while concurrent maintenance anticonvulsants reach therapeutic levels

Why this calculator blocks TIVA in cats

Plumb’s documents two species-specific concerns that make sustained propofol infusion in cats problematic:

1. Prolonged recovery. Cats have limited glucuronidation capacity. After repeated boluses or any sustained CRI, peripheral redistribution and slow elimination produce recoveries that can extend hours longer than equivalent dog protocols.
2. Heinz-body anemia. Multi-day propofol administration in cats has been associated with Heinz-body formation, malaise, anorexia, and diarrhea. The mechanism is thought to involve oxidative damage to feline hemoglobin, which is more susceptible to Heinz-body formation than dog hemoglobin.

A single induction bolus in cats is appropriate and well-tolerated. A short (≤30 minute) maintenance infusion in cats is acceptable when clinically indicated. Sustained TIVA in cats is not. This calculator’s TIVA mode is dog-only by design; for refractory status epilepticus in cats, the calculator’s status-epi mode is enabled because the indication is short-duration and the risk-benefit shifts.

Dosing

TIVA maintenance (dogs): 0.1–0.5 mg/kg/min IV CRI. Default 0.1 mg/kg/min, which assumes a premedicated patient, premedications substantially reduce CRI requirements. Maintenance dose sparing was reported as ≈48% with benzodiazepine + opioid premed and ≈37% with phenothiazine + opioid premed (label data); α₂ agonist + opioid combinations reduce the dose by up to 40–60%. Unpremedicated patients may require doses near 0.3 mg/kg/min. Titrate to depth, propofol is fast and forgiving, so move in small steps and wait 1–2 minutes between adjustments.

Status epilepticus (dogs and cats): loading bolus 2–8 mg/kg IV slowly to control the seizure, then 0.1–0.25 mg/kg/min CRI. Default 0.15 mg/kg/min. Maximum recommended duration ≈48 hours. Slow the bolus to minimize apnea. Plumb’s notes that bolus speed correlates directly with apnea risk.

The induction-dose reference table on the calculator page reproduces Plumb’s induction ranges for both species; those are intended as bedside reminders, not a calculator input.

Administration

Propofol is given by IV bolus or CRI. The drug is incompatible with most other medications in the same line, flush before and after co-administering anything else. Dedicated lines are common practice. Compatible carriers for dilution (when dilution is needed) are 5% dextrose and 0.9% sodium chloride; lactated Ringer’s is compatible per Plumb’s.

The lipid emulsion supports bacterial growth. Open vials must be discarded within 6 hours per Plumb’s; many institutions follow stricter local rules. Single-patient use is the safest default. Some commercial preparations include a preservative (benzyl alcohol, EDTA), read the label to be sure of which preparation is in front of you, and avoid preservative-containing products in cats where applicable.

Drug interactions

• Premedications (opioids, α₂ agonists, benzodiazepines, phenothiazines), substantial dose-sparing effect on the CRI rate. The 0.1 mg/kg/min default assumes premedication.
• Inhalant anesthetics: additive cardiorespiratory depression; reduce inhalant requirements and propofol CRI rate accordingly.
• Lidocaine: propofol’s hypotensive effect is increased; lidocaine does not reliably reduce propofol requirements in dogs.
• Fentanyl, ketamine, dexmedetomidine: common in TIVA combinations; reduce propofol dose substantially.
• Aminophylline can antagonize propofol’s anticonvulsant action.

Adverse effects

• Apnea: particularly with rapid bolus administration; brief support is usually sufficient. Slow the bolus rate to mitigate.
• Hypotension: dose-dependent, predominantly via reduced vascular resistance. Worsened in volume-depleted patients. Treat with fluid bolus and reduction of the infusion rate before reaching for vasopressors.
• Bradycardia: occasional; usually responsive to anticholinergics or rate reduction.
• Pain on injection: well documented in awake patients given peripheral IV propofol; reduced by injecting into a larger vein or with lidocaine pretreatment.
• Excitatory phenomena during induction or recovery: myoclonus, paddling, opisthotonos. Usually self-limiting; misinterpreted as seizures occasionally.
• Heinz-body anemia in cats with repeated daily dosing.
• Increased ICP risk in head-trauma patients only with rapid bolus (the resulting hypotension drops cerebral perfusion pressure); slow administration is generally well-tolerated and propofol is otherwise neuroprotective.
• Bacterial growth in opened vials, propofol-related sepsis has been reported in human medicine when single-use practice was not followed.

Monitoring

• Respiratory rate, effort, ETCO₂, SpO₂, apnea is the most common acute adverse effect
• Continuous ECG and blood pressure
• Anesthetic depth (jaw tone, palpebral reflex, eye position)
• Body temperature, sustained CRI patients lose heat readily
• For status-epi cases: electrolytes, glucose, periodic CK to watch for propofol-related infusion syndrome (lipemia, metabolic acidosis, rhabdomyolysis) at sustained higher doses
• Cats receiving any propofol CRI, periodic CBC if duration extends beyond a single short procedure, watching for Heinz bodies

Recovery and weaning

After a short TIVA, recovery is typically complete within 5–15 minutes in dogs once the CRI is stopped. After sustained CRIs (>30–60 minutes), peripheral tissue saturation extends recovery; plan for an extended recovery period. Cats recovering from propofol take longer than dogs at any duration.

For status epilepticus, wean slowly once the patient has been seizure-free for the planned interval (often 12–24 hours) and concurrent maintenance anticonvulsants have reached therapeutic levels. Halve the rate every 1–2 hours; if seizures recur, return to the previous effective rate and extend the suppression interval before trying again.

Sources

• Plumb’s Veterinary Drugs, propofol monograph (current edition).