Ron Mandsager, DVM, DACVA
4/24/03

Gastrointestinal disease

• Variety of disease processes...
• Preoperative stabilization of fluid balance, electrolyte balance important, if possible...

Gastric Dilitation/Volvulus (GDV)

• Surgical emergency
• Present with:
  • Respiratory compromise
  • Cardiovascular compromise
  • Cardiac dysrhythmias (PVC's, V tach, tachycardia)
  • Hypotension
  • Hypoxemia
  • Acid/base disturbances
• If possible, decompress stomach prior to anesthesia
• Large volumes of IV fluids rapidly (multiple large bore catheters)
• Acid/base evaluation helpful
• Monitor & treat cardiac dysrhythmias as they present - lidocaine usually first line of defense
• Anesthetic managment
  • Preanesthetic: opioids +/- benzodiazepines
  • Induction:
    • rapid induction to gain control of airway quickly is preferable, initiate positive pressure ventilation
    • may be able to intubate w/ neuroleptanalgesic combination (eg oxymorphone + diazepam)
    • propofol my drug of choice
    • low dose thiopental may be used - but cautiously - potential for aggravating arrhythmias
    • mask induction w/ isoflurane/sevoflurane may be used - but it is slower
  • Maintenance
    • isoflurane/sevoflurane
    • supplemental opioids (eg oxymorphone, hydromorphone, fentanyl) IV to reduce inhalant concentration
  • IPPV usually needed
  • Monitor cardiovascular system closely
    • ECG
    • Blood pressure

Equine Colic

• One of our most common emergency surgical procedures
• Patients present in a variety of conditions, from minimally to severely compromised
  • Respiratory compromise
  • Cardiovascular compromise
  • Dehydration
  • Hypotension
  • Hypoxemia
  • Electrolyte imbalances
  • Acid/Base disturbances
• Again, stabilize if possible
  • Large volumes of fluids IV rapidly (multiple large bore catheters)
  • Bicarbonate if acidotic
  • Pain managment (usually w/ alpha-2)
• Our current anesthetic protocol
  • premedicate w/ xylazine + butorphanol or xylazine + fentanyl
  • induce w/ diazepam + ketamine
  • maintain w/ sevoflurane +/- fentanyl infusion or supplemental butorphanol
  • Monitor
    • airway gases
    • invasive blood pressure
    • ECG
    • pulse oximetry
  • IPPV
  • Multiple IV lines for rapid fluid administraion
  • Dobutamine
  • Calcium supplementation
  • Colloids
  • The kitchen sink if you think it will help...
• Recovery often slow - postoperative pain management should be considered

Neurological Disease

Patient w/ siezure disorders

• Many patients present for anesthesia w/ a history of epilepsy
• Medical management consists of a variety of drugs, most commonly phenobarbital
• Represent low risk for anesthesia, uncommon to see problems w/ siezure disorders during the perianesthetic period
• However, a few points to remember:
  • Maintain antiepileptic medications throughout the perianesthetic period
  • Avoid anesthetic agents that may exacerbate siezure disorders
    • Phenothiazines
    • Dissociatives

Patient w/ cranial mass/CNS dysfunction/head trauma

• Potentially difficult cases to manage - may be high risk
• Preoperative evaluation of CNS function important - may present in a semiconcious or unconcious state
• Minimize increases in intracranial pressure are an important goal of anesthetic management
  • Careful monitoring of fluid balance
  • Medical therapy - mannitol, furosemide, corticosteroids
  • Hyperventilation
    • ICP increases linearly with P_aCO₂
    • Cerebral blood flow increases by ~ 2 ml/min/100 g of brain tissue for every 1 mmHg increase in P_aCO₂ from 20 - 80 mmHg
    • As cerebral blood flow increases, so does ICP
    • Maintain P_aCO₂ around 25 - 30 mmHg
• Anesthetic management
  • Preanesthetize w/ opioid +/- benzodiazepine if needed
  • Rapid induction w/ propofol or thiopental
  • Maintenance w/ isoflurane
  • Initiate IPPV immediately, and maintain throughout the anesthetic period
  • Moderate fluid therapy

Patient w/ spinal cord disease

• Another of our most common emergency cases
• Intervertebral disc disease common - present w/ rapid onset of pain & paralysis
• Usually middle aged, healthy otherwise
• Anesthetic management usually not difficult, however must consider that a myelogram is usually part of the diagnostic workup
  • Myelograms potentially cause siezures during the recovery period
  • Avoid anesthetic agents that may potentiate siezure disorders
  • Be prepared to treat seizures during recovery
    • Post-myelographic siezures usually present initially w/ twitching around the eyes & lips, then spread throughout the body
    • Rapid administration of diazepam IV at the onset of a siezure is the first line of defense
    • If siezures persist, then pentobarbital or phenobarbital is the next in line...
• Movement of the patient during anesthesia must be done carefully!
  • While awake, the patient uses muscle rigidity to 'splint' the affected area of the spine, and limit further damage
  • Under anesthesia, the muscle relaxation we produce removes this mode of self protection
  • Critical to move the patients carefully, with minimal twisting or flexing of the spine
  • Potential exists to exacerbate the condition, produce more cord trauma

Patient requiring EEG analysis

• Need a short period of general anesthesia to minimize movement artifacts from the EEG
• All anesthetics produce changes in the EEG
• Standardize anesthetic management to limit variability between patients
• Our standard anesthetic protocol is a light level of thiobarbiturate anesthesia
• propofol has also been advocated as a useful drug for EEG analysis

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© 1996-2003, Oklahoma State University College of Veterinary Medicine, all rights reserved Last modified October 19, 2007 by Ron Mandsager, DVM, DACVA Questions? Comments? Contact me at aerrane@okstate.edu

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