Perioperative medications

This chapter is an overview of the drugs that may be needed prior to surgery. Sedatives, analgesics and potentially antibiotics are required for standing surgery. If we are going to use general anesthesia for recumbent surgery, we will add induction agents and maintenance agents, as well. See the later chapters for details on the drug types and for species specific recommendations.

Sedatives

Sedatives and calming agents are often necessary prior to procedures. Excited animals do not respond well to general anesthesia and it is important to ensure animals are calm or sedated before attempting general anesthesia.

Sedatives also need time to work. If an animal is constantly stimulated (talked to, patted, poked), it may not sedate at all. Generally ask everyone to step back and stay calm and quiet for several minutes after administering a sedative or calming agent. Avoid pain or trauma while the sedative is working.

Most sedatives will work quickly.  IV (intravenous) medications will usually take effect within 2-3 minutes while IM (intramuscular) injections take 5-10 minutes if not longer.  Acepromazine is a calming agent (anti-anxiolytic agent) that can take at least 20 minutes to take effect regardless of administration route. Some animals (pigs, mean horses, needle shy animals, +/- camelids) typically need intramuscular medication initially. Horses can be given dexmedetomidine gel orally by the owner before you even arrive on the farm; it does take awhile (30-60 min) to have an effect. Once you have some sedation in the animal, intravenous administration of drugs may now be an option.

Analgesics

Analgesics (opioids, NSAIDs) should be given prior to any pain stimulus whenever possible. Once pain starts, the nerves become upregulated and hypersensitive (“wind-up”). To prevent wind-up, we provide “preemptive analgesia” through preoperative medication. We want the analgesics on board before we cause pain. Again, iv agents will work more quickly than im or sq agents. Orally administered drugs are generally cheaper but oral medications need 1-2 hours to take effect. Plan ahead!

NSAIDs have long durations of action (12-24 hours) while narcotics may need redosing during longer procedures.

Typically, surgical inflammation will continue for at least three days.  This means we need to control inflammation for three days so that healing can occur. 

Antibiotics

Antibiotics should be used only when necessary. Antibiotics change the gut flora, affect the immune system and can actually increase complication rates. However, when contamination risk is high or unknown, we do typically use antibiotics prophylactically, starting before surgery and continuing no longer than 24 hours.  Preoperative antibiotics that are at high levels at the time of any “surprise” are more effective than trying to treat after the fact. This is considered prophylactic use. Prophylactic use of antibiotics is typically restricted to the preoperative +/- surgery period and does not include postoperative care. Preoperative antibiotics tend to be used in most cases of abdominal, respiratory or urogenital surgery due to the risk of contamination. The human guidelines say to use prophylactic antibiotics if the risk of infection is > 5% without antibiotics. They may also be used if infection would be devastating (eg with implants.).

Timing of drugs depends on the route. You want the peak levels to be when you are doing the stuff (surgery) that might lead to contamination. This often begins at least 10 minutes after you anesthetize your patient and continues until incisional closure.

The timing needed to achieve peak levels during surgery varies by drug and route. General guidelines:

• Oral: ~ Two hours after drug is administered
• IV: ~ 15 minutes after injection/infusion
• Intramuscular (IM): ~30 minutes after injection (does depend on the drug formulation with some taking much longer)
• Subcutaneous administration – variable; avoid the subcutaneous route for preoperative medications if possible

Some antibiotics need to be re-administered during longer surgeries to maintain peak levels. However, metabolism under anesthesia is slower so antibiotics tend to stay at higher levels longer.  Example : Potassium penicillin persists 332 min above the MIC in anesthetized horses; it only lasts 199 min in conscious standing horses.

Postoperative antibiotic therapy is generally not needed unless the animal is immunocompromised or you are actually treating an infection.

When we don’t know what sort of surprises we will encounter, we err on the side of broad spectrum bactericidal drugs. We typically pick  first line drugs, rather than those saved for cases of resistance.

If antibiotic therapy is indicated postoperatively, it is often continued for 3-14 days. One common rule is to treat three days past the resolution of clinical signs (fever, signs of inflammation, etc). In hospitalized cases, a blood count is often checked prior to discontinuing antibiotics to ensure no further signs of infection.

Sample protocols for surgical procedures

*In lactating cattle, ceftiofur sodium is typically our first choice due to the limited withholding time required for milk. Ceftiofur acid can be used for longer duration therapy (one injection lasts 72 hours).

#Narcotics are commonly added to all protocols

%Aminoglycosides have been reclassified by WHO (world health organization) as critically important antimicrobials and we should reconsider their use in this schema. Quinolones, other cephalosporins, macrolides, and rifampin should not be used for prophylaxis as they are considered highest priority critically important.

Resources

Perioperative analgesics

The Efficacy of Preemptive Analgesia for Acute Postoperative Pain Management: A Meta-Analysis,  Anesthesia and analgesia 100 3 (2005): 757-73- human work but nice overview

Equine NSAIDs and analgesics chapter

Food animal NSAIDs and analgesics chapter

Perioperative antibiotics

Surgical antimicrobial prophylaxis: Current standards of care. Equine Vet Educ. 2023;35:607–616. – excellent review

Principles of Antimicrobial Therapy: What Should We Be Using? Vet Clin Equine 22 (2006) 279–296- good review of surgical use of antibiotics

Randomized prospective trials to study effects of reduced antibiotic usage in abdominal surgery in cows. J. Dairy Sci. 101:8217–8223. With careful attention, maybe we can pick which cases get preop antibiotics.

Equine antibiotics chapter

Food animal antibiotics chapter