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Home , Veterinary surgery

Ready, Set, Go to ! Andrea Sundholm, DVM, DACVS-SA

As surgeons, the actual procedure is what we are all looking forward to. However, there is a lot of work that goes in to each patient before we ever even set foot into the operating room. This presentation focuses on the preoperative diagnostics, protocols and patient preparation with specific attention to fracture repair and abdominal for foreign bodies, C-sections and liver biopsy.

Preoperative Work Each patient should have a complete and thorough physical examination. With anesthesia in their future, we are specifically paying attention to things that may change or affect our protocols for bloodwork, anesthesia and type of surgery. Does this patient have a heart murmur? Are they dehydrated? Do they have a systemic disease like diabetes? Chest radiographs are typically recommended in patients over 10 years of age, especially if neoplasia is a differential. Bloodwork should be current and ideally completed within the last 30 days before a procedure. Depending on the surgery, some type of bloodwork may be recommended immediately before the procedure. A complete blood count and chemistry panel is appropriate for any age of patient. Other individual parameters like lactate can be used as a marker of perfusion to help guide fluid and blood product therapy. Liver function tests and coagulation profile are recommended before hepatobiliary surgery. A more abbreviated blood panel may be appropriate in some patients.

Surgical safety check lists have been implemented in many human and veterinary hospitals. Cray et al demonstrated that more perioperative complications occurred when there was not a checklist. One of the biggest advantages from this study was that there was greater confidence in communication among team members. The check list involves dedicated stop points to check multiple patient parameters, anesthesia concerns, equipment, and imaging displays for example.

Anesthesia This is a basic review of common medications used for premedication and induction. Listed doses are personal preference.

The primary use of opioids is analgesia. They can reduce the dose of induction agents as well as inhalant requirements. The most common side effects include ileus, nausea, vomiting, dysphoria, hyperthermia and respiratory depression. The cardiovascular effects are minimal. Some common examples are morphine (0.1 mg/kg), (0.1 mg/kg), methadone (0.25 mg/kg), fentanyl (5 mcg/kg), (0.015 mg/kg) and butorphanol (0.2 mg/kg). Butorphanol is sufficient only for mild pain and therefore its use in surgery is limited as a premedication. Opioids are combined with sedatives/tranquilizers to provide analgesia and muscle relaxation. Opioids can be reversed with naloxone.

Sedatives/tranquilizers are used for narcosis and muscle relaxation. As with opioids, they can reduce the dose of induction medications and inhalants. In young or healthy animals benzodiazepines can cause excitement and anxiety, especially when given as a single agent. There is a wide safety margin and do not cause any significant cardiovascular or respiratory depression. Examples include (0.1 mg/kg) and (0.1 mg/kg). Benzodiazepine’s can be reversed with flumazenil. Phenothiazine’s do not provide any analgesia and cause vasodilation leading to hypotension. There is no reversal and it should be restricted to cardiovascular stable patients. Example includes acepromazine (0.01 mg/kg). Alpha-2 agonists cause profound with bradycardia and a reflex hypertension. They can also cause hyperglycemia, diuresis and respiratory depression. Examples include dexmedetomidine (2 mcg/kg) and . Xylazine is associated with a marked increase in complications and cardiac arrest in and therefore should be avoided. Dexmedetomidine can be reversed with .

Induction agents provide anesthesia and muscle relaxation. The therapeutic index is very narrow which makes anesthesia induction one of the most hazardous times of anesthesia. Preoxygenation for at least 5 minutes is recommended. (4 mg/kg or to effect) causes apnea/respiratory depression and is rapidly metabolized. It can be used as a continuous rate infusion instead of inhalant anesthesia. (1 mg/kg) is a dissociative anesthesthetic that also provides analgesia. (2 mg/kg) is similar to propofol but has a longer duration of action. It can be used in all types of patients including pregnant animals and sick animals. Alfaxalone can also be used as a CRI to maintain anesthesia but may result in a more challenging recovery. Etomidate is induction agent that is typically used in higher risk cardiac patients.

The perioperative antibiotic choice depends on the type of surgery. It is recommended to have given the antibiotic 30 minutes prior to skin incision and is then repeated every 90 minutes intraoperatively. Cefazolin (22 mg/kg) and ampicillin sulbactam (30 mg/kg) are examples.

Patient Preparation The purpose is to remove hair, dirt and microbes from the skin. Clipping immediately prior to surgery is associated with the lowest risk. A “rough” prep is performed in the induction area and then repeated again in the operating room. The skin scrub is typically a chlorhexidine or iodine based solution that is alternated with alcohol. Chlorhexidine has a longer residual activity. Iodine based solutions should always be used for procedures around the eye. Iodine generally causes more skin irritation. It is recommended to read the manufacturers recommendations for dilutions and contact time but in general five minutes of contact time is recommended.

Fracture Repair Radiographs should be available in the operating room and have been recently obtained. What could go wrong during the procedure that you want to be prepared for? Sometimes these procedures take

longer than expected so be diligent about antibiotics. Hemorrhage can be iatrogenic or be present due to a large hematoma or unstable fracture. Does this patient need a blood transfusion? If conversion to an is possible, make sure your skin prep and draping reflects that. A purse string can be considered for pelvic limb/pelvic procedures to decrease the risk of fecal contamination. Open fractures are special in that early administration of broad spectrum antibiotics is one of the most important factors to decrease the infection risk. These fracture need rigid stabilization, copious lavage, adequate soft tissue coverage, and antibiotics.

Example anesthesia protocol: Premedication: carprofen (subcutaneous injection), opioid, dexmedetomidine/benzodiazepine, antibiotic Induction: Propofol or alfaxalone Regional anesthesia: epidural (morphine +/- bupivacaine), Nocita Maintenance: opioid CRI +/- ketamine CRI

Nocita is a long acting that provides up to 72 hours of postoperative pain relief by releasing bupivacaine over time. It is FDA approved for TPLO in dogs and in .

For patient preparation we are commonly using a hanging leg prep. This can also be used for , pelvic fractures, and digit amputations.

Foreign Body Animals with foreign bodies often have distended stomachs, are nauseated and vomit. Therefore, a swift induction and is imperative. An orogastric tube can be passed immediately after induction of anesthesia to decompress the stomach to limit the risk of regurgitation while under anesthesia. I frequently pass an orogastric tube in surgery while I’m doing the explore to limit expulsion of liquid orally. Hypotension is frequently encountered due to fluid losses and dehydration. It’s important to correct fluid imbalances prior to surgery. With an obstruction, secretion of fluid into the intestinal lumen is increased and absorption of fluid is decreased. Electrolyte derangements are common especially with potassium, sodium and chloride. Treatment consists of intravenous infusions of balanced crystalloid solutions starting with a bolus (10-20 mls/kg). Intraoperative assessments should be made due to the ongoing losses.

Example anesthesia protocol: Premedication: benzodiazepine/dexmedetomidine, maropitant/ondansetron, opioid, antibiotic Induction: Propofol or alfaxalone Fluid rate: crystalloids 5-10 mls/kg/hr, opioid CRI or intermittent opioid injections I avoid NSAIDS in all gastrointestinal cases and typically do not extend antibiotics past the perioperative doses. Extended use of antibiotics does not prevent and increases the incidence of resistant bacteria. Cefazolin remains one of the most effective choices. The is clipped and prepped

from the xyphoid to pubis with wide lateral margins. The prepuce is flushed with dilute chlorhexidine (especially if staying within the surgical field). In male dogs, the prepuce can be diverted from the surgical field using a penetrating towel clamp.

C-section C-section requires special attention not only to the dam but fetuses as well. The dam should be fully clipped before she is induced. The goal should be to remove all fetuses within 15-20 minutes of induction. If the fetal heart rate is low before surgery, premedicate the dam with atropine (0.22 mg/kg IM). There can be large fluid shift especially if she is spayed at the same time therefore be prepared to give a fluid bolus for hypotension. Opioids are given after the last fetus is removed therefore anesthesia is either maintained with a propofol/alfaxalone CRI or inhalant anesthesia.

Example anesthesia protocol: Premedication: none Induction: propofol (6-8 mg/kg) or alfaxalone (3-4 mg/kg) Maintenance: propofol CRI (0.05 mg/kg/min) or inhalant anesthesia Systemic opioids and antibiotics given after last fetus is removed. No NSAIDS!

The “puppy resuscitation” team and station should be set before anesthesia starts. If you do use a benzodiazepine or opioid for premedications have flumazenil and naloxone available to administer sublingual to the puppies. If the dam is having a rough recovery, you can administer dexmedetomidine but avoid acepromazine.

Liver Biopsy Obtaining liver biopsies can help guide treatment plans for a hepatopathy. Fine needle aspirate is the least invasive however the diagnostic accuracy using cytologic evaluation is poor. There are studies that report only 30% agreement between cytology and histopathology in dogs. Tru-Cut biopsies are obtained with ultrasound guidance and have a complication rate of 6-22%. Laparoscopic biopsies are a great way to provide a minimally invasive option but can be challenging with ascites or bleeding complications. Traditional open biopsy can be performed using a guillotine technique or a skin punch biopsy instrument with gelfoam for hemostasis. The incision needs to extend to the xyphoid in order to have good visualization of the liver and adequate control of hemostasis. The presence of hepatic disease can increase the risk for hemorrhage or thrombosis. Hypoglycemia is uncommonly associated with end stage liver disease but can be a factor in small or debilitated patients. Consider which of your medications are metabolized through the liver. In patients with liver shunts (congenital or acquired), increased endogenous benzodiazepines can contribute to hepatic encephalopathy signs therefore it may be reasonable to avoid this drug class. Special bloodwork considerations would include pre and post prandial bile acids, coagulation profile and blood type/cross match if the patient has had a blood transfusion previously.

Example anesthesia protocol: Premedication: dexmedetomidine/benzodiazepine, opioid, antibiotic Induction: propofol or alfaxalone Maintenance: intermittent opioid injections, opioid CRI

Brachycephalic Dogs Based on a study by Greunheid et al, we know that brachycephalic breeds that undergo surgery are at a higher risk of peri or postanesthetic complications. Therefore, we have to treat them differently than our average canine patients. Costa et al implemented a standardized perianesthetic protocol to attempt to reduce incidence of postoperative regurgitation, pneumonia and respiratory distress. Their protocol involved preoperative administration of metoclopramide, famotidine, restrictive use of opioids and recovery in the ICU. The postoperative regurgitation decreased from 35% to 9%. If the has any history of regurgitation, I recommend chest radiographs immediately before anesthesia and then start with metoclopramide (0.3 mg/kg SQ) and maropitant (1 mg/kg IV).

Example anesthesia protocol: Premedication: dexmedetomidine/benzodiazepine, methadone, antibiotic, +/- NSAID depending on procedure Induction: propofol or alfaxalone

Although this discussion essentially stops before the patient even has surgery, I’m always trying to think one step ahead to recovery or procedures that are easier performed with the patient still under anesthesia. If we are expecting prolonged recovery would an indwelling urinary catheter be helpful? Is there widespread ileus at the time of surgery or is the pet unlikely to eat that a feeding tube is warranted? Regardless of the procedure but especially with upper airway surgery I essentially put every brachycephalic in oxygen after surgery.

The preoperative work is so important to the success of your surgery and patient! As always, we are here for questions and cases!

References

Costa R., Abelson A., Lindsey J., et al. Postoperative regurgitation and respiratory complications in brachycephalic dogs undergoing airway surgery before and after implementation of a standardized perianesthetic protocol. JAVMA 2020; 256: 899-905

Cray M, Selmic L, McConnell B, et al. Effect of implementation of a surgical safety checklist on perioperative and postoperative complications at an academic institution in North America. VetSurg 2018; 47(8):1052-1065

Gruenheid M, Aarnes TK, McLoughlin MA et al. Risk of anesthesia-related complications in brachycephalic dogs. JAVMA 2018; 253:301-306

Tobias and Johnston Veterinary Surgery Small Animal 2012

Personal experience of Dr. Cheryl Lopate DVM, DACT, Dr. Rachel Hector DVM, DACVAA, Dr. Heidi Shafford DVM, DACVAA