Anesthesia for a senior or sick animal: opioid premedication, induction with midazolam and propofol
Opioid premedication, IM or slow IV; then IV induction with midazolam and propofol, slowly, to effect. For short anesthesia in senior, sick or debilitated animals, or before an inhalant.1,2
This page is an educational reference for veterinarians and veterinary students. It does not replace a thorough examination, clinical judgment, or the attending veterinarian's final decision. Doses are for adult animals, per kilogram; the amount and volume of each drug for a patient, and the doses for neonates and seniors, are calculated in the tool itself.
Step by step
per kilogram of body weight
1 Preanesthetic preparation Before the injection
Healthy animal: allow free access to water; withhold food for 4–6 hours before anesthesia.3
Animal under 8 weeks or under 2 kg: withhold food for no more than 1–2 hours, monitor blood glucose before, during and after induction, and schedule it as the first patient of the day.3
Animal with a history or risk of regurgitation: withhold food and water for 6–12 hours.3
After IM injection, its effect begins within 10–20 minutes and lasts 2–4 hours.2
Does not release histamine and causes little or no vomiting.1,2
Like morphine, it may slow the heart rate and depress breathing.2
On its own it may cause restlessness in a young, healthy animal; it is given with a sedative.1
3 Wait and prepare 15–30 minutes
Premedication is usually given 15–30 minutes before induction.1
These 15–30 minutes are for IM injection. If you gave the opioid IV, induce once it has taken effect: methadone and morphine 1–5 minutes, buprenorphine 20–45 minutes.1,2
Methadone and morphine start to work 10–20 minutes after IM injection and 1–5 minutes after IV injection; buprenorphine after 20–45 minutes.2
Watch the animal closely in a quiet place; sedation needs monitoring and support just as anesthesia does. Monitor breathing, heart rate and mucous membrane color.2
Place an IV catheter in the meantime.
Preoxygenate with 100% oxygen for 3 minutes before induction; this provides an oxygen reserve for about 6 minutes.2
Inject slowly IV and watch the animal. In young, healthy animals, midazolam may cause excitement; this protocol is for senior, sick or debilitated animals.1,4,5
Slowly IV, just before propofol; midazolam lowers the propofol dose needed.1,2
In dogs, you can give about 1 mg/kg of propofol first, then midazolam, and then the rest of the propofol in small increments to effect; in this order there is less excitement and less propofol is needed.5
Effects of this drug
On its own it produces little sedation; with an opioid, it sedates senior or debilitated animals better.1
Given with propofol, it lowers the propofol dose and makes post-induction apnea less likely or shorter.1,2
In young, healthy animals it may cause excitement and restlessness instead of calming.1,4,6
Brief apnea and hypotension at induction are very common: inject slowly, and have intubation equipment, oxygen and assisted ventilation ready.2,8
Prepare the syringe with the volume of the range, but you need not inject it all: inject slowly IV to effect, until the depth of anesthesia is enough for intubation.2,8
Give the induction dose over about 10–40 seconds; injecting very slowly may not produce enough depth.8
Start at the low end. After the first portion, allow time for the drug to act and assess the animal; if needed, give further portions in small increments. Do not make the first portion too small, because a very small dose may cause excitement.2,4
If the animal is moderately sedated after premedication or its disease is moderate, expect the low end of the range; in a deeply sedated, obtunded or very sick animal, even less than the low end may be enough.2
Effects of this drug
Produces rapid, short anesthesia with a rapid recovery.8
Its effect starts quickly and is short, so it is easy to give to effect, and it can be repeated during the same anesthetic.2
Depresses breathing and circulation in a dose-dependent way. Brief apnea and mild hypotension at induction are very common; rapid injection causes apnea, bradycardia and hypotension.2,8
It relaxes muscle more than ketamine and midazolam; paddling, muscle twitching or nystagmus are sometimes seen at induction.1,8
6 Intubation, oxygen and eye protection Immediately after induction
Place the endotracheal tube as soon as possible and give oxygen.2,8
If breathing stops or is weak, provide assisted ventilation with oxygen.1,8
Apply a corneal lubricant ointment or drops and repeat every 2–4 hours.2
In cats, the larynx goes into spasm when stimulated: before intubation, drip no more than 0.2 mL of 2% lidocaine without epinephrine onto the arytenoid cartilages from a 1 mL syringe without a needle, and wait 60–90 seconds with oxygen. A spray with a nozzle may damage the laryngeal mucosa.4
In cats, if laryngospasm occurs, stop, give oxygen and check the depth of anesthesia; wait 60–90 seconds before trying again. Laryngospasm usually resolves on its own.4
7 Anesthesia 5–10 minutes
A single dose of propofol provides about 5–10 minutes of anesthesia.1
For a few more minutes, inject one-third to one-half of the induction dose again, slowly, to effect.1,2
For a longer procedure, maintain anesthesia with an inhalant.1
In cats, do not continue propofol for more than 30 minutes; cats eliminate it more slowly, and longer use prolongs recovery.4,8
8 Recovery and reversal After anesthesia ends
Recovery from propofol is rapid: the animal wakes as the drug redistributes from the brain to other tissues.8
Continue monitoring and supporting the animal until full recovery, and maintain body temperature.2
A sick or debilitated animal benefits from oxygen during recovery, especially if its body temperature is low. Measure blood pressure periodically during this period as well.1
Both drugs are reversible. If sedation is excessive or prolonged, or breathing is weak, reverse midazolam with flumazenil: 0.01–0.2 mg/kg IV, starting with the lowest amount and repeating as needed until effect.1,4
Methadone and morphine are reversed by naloxone: 0.002–0.02 mg/kg IV or IM; the lowest amount for partial reversal and the highest for full reversal. As the opioid is reversed, its analgesia also decreases or disappears; reassess pain.1,4
The percentage on each side is not a measurement but a qualitative grade from the sources: full 100, good 75, partial 50, low 25, none zero. It refers to the peak effect after induction, not the whole duration.
HypnosisLoss of consciousness — 100% (Full)
Propofol produces rapid, predictable, short anesthesia and is given to effect.1,8
The opioid premedication and midazolam co-induction lower the propofol dose needed.1,2,8
In senior or sick animals, short anesthesia is less stressful and better controlled than heavy sedation.2
Anesthetic drugs are not analgesics: if the procedure is painful, the animal will feel the pain after it wakes.9
The opioid is the only analgesic in this protocol; for surgery, also use local anesthesia wherever possible.2
NSAIDs are contraindicated in dehydration, hypovolemia, hypotension, liver disease, uncontrolled gastrointestinal disease and coagulation disorders.9
Muscle relaxationRelaxed muscle tone — 75% (Good)
Propofol relaxes muscle well, and midazolam adds to the relaxation.1
Paddling, muscle twitching or nystagmus are sometimes seen at induction.8
Blood pressure: Falls at induction
The opioid and midazolam have little effect on blood pressure; propofol lowers blood pressure in a dose-dependent way, and hypotension at induction is common. A lower dose and avoiding rapid injection reduce the fall.2,7,8
Propofol ↓ Lowers: Lowers blood pressure in a dose-dependent way; rapid injection increases hypotension and bradycardia.2,8
Midazolam – Little effect: Has little effect on the heart and circulation.7
Before you start: contraindications
Contraindication Do not give propofol to an animal hypersensitive to propofol or to the components of its emulsion.8
Cautions and notes
Caution Stabilize the animal as far as possible before anesthesia: correct dehydration and hypovolemia with IV fluids and control pain. Anesthesia and surgery may worsen existing problems, and propofol lowers blood pressure.2,8
Caution This protocol is for senior, sick or debilitated animals. In a young, healthy animal, an opioid alone may cause restlessness and midazolam may cause excitement; use another protocol for it.1,4
Caution If the premedication does not sedate enough, more propofol is needed, and cardiovascular and respiratory side effects increase.2
Caution Use caution in heart, lung, liver or kidney disease, hypovolemia, hypoproteinemia and hyperlipidemia, and in very thin, debilitated or senior animals; a lower dose may be enough.2,8
Caution An opioid with propofol may markedly depress breathing and slow the heart rate; monitor breathing and heart rate and have oxygen ready. For bradycardia, give atropine after weighing the risks and benefits.8
Caution Midazolam is metabolized in the liver; in liver disease, give the low end of the range and monitor the animal more closely.1,6
Caution Not suitable for calming fractious or aggressive animals.1
Caution Propofol contains no antimicrobial preservative: draw it up aseptically, use it immediately after opening, and discard the remainder. Do not use it if the emulsion stays separated after gentle shaking.8
Caution In sighthounds (such as Greyhounds), propofol is eliminated more slowly and recovery may be slightly longer.1,8
Note Do not mix propofol with another drug in one syringe; it is compatible only with dextrose or saline solutions.8
Note Chloramphenicol, ketoconazole and loperamide slow the elimination of propofol and prolong recovery.8
Caution In cats, repeated propofol anesthetics may lead to red cell damage (Heinz body anemia), anorexia, diarrhea and prolonged recovery; if the cat must be anesthetized again, an interval of more than 48 hours reduces this risk.8
Reversal and emergency drugs
FlumazenilReverses midazolam
Ampoule 0.5 mg in 5 mL (0.1 mg/mL)
First dose, starting from the lowest amount — Intravenous (IV): 0.01 mg/kg1
If sedation is excessive or prolonged, or breathing is weak. If needed, repeat the same amount until effect; up to 0.2 mg/kg in total.1,4
The lowest amount is for partial reversal and the highest for full reversal. As the opioid is reversed, its analgesia also decreases or disappears; reassess pain.1,4
AtropineBradycardia
Ampoule 0.5 mg in 1 mL; do not confuse it with the 10 mg/mL ampoule