Sunday, July 24, 2011
Notes from July 2011 St. Louis AVMA Conference-Anesthesia and the Heart
These are papers from the July 2011 St. Louis AVMA conference. I’ve edited them to delete some of the vet only jargon and for space considerations. If you see (…) that means that information has been deleted due to these considerations. The ones listed here include HCM, and other heart related papers, treatments, papers on x-rays and echos, thrombosis, kidney disease, idiopathic cystitis, pain management, anesthesia and cardiac disease, supplements and other hazards for pets, and some other basic information I hope is helpful.
ANESTHESIA AND CARIDAC DYSFUNCTION
Donna M.Sisak, CVT, VTS (Anesthesia)
Seattle Veterinary Specialists
The heart is the organ that supplies blood and oxygen to all parts of the body. It is a pump
composed of muscle which pumps blood throughout the body. The blood carries vital materials
necessary to maintain life and removes waste products that are not needed. The heart controls
the supply of oxygenated blood and the elimination of carbon dioxide. When the heart is not
functioning properly all organs can be compromised putting the body’s function in jeopardy.
Anesthetizing a patient with cardiac dysfunction presents quite a challenge to the anesthetist.
Arrhythmia, fluid overload and significant cardiovascular depression can occur depending on the
type of cardiovascular dysfunction. Understanding the type of cardiac dysfunction the patient
suffers from can give us a great deal of insight and direction in our anesthetic approach. Signs
of cardiac disease may include increased heart rate, irregular pulse, respiratory problems,
syncope, cyanosis, ascites.
Types of Cardiac Dysfunction
Impaired cardiac output…
CO is an important factor in determining the effectiveness of the heart to deliver blood to the rest
of the body. Cardiomyopathies (hypertrophic cardiomyopathy), valvular cardiac disease (mitral
insufficiency) and periacardial disease (pericardial tamponade) are all diseases that impair CO.
General anesthetic considerations for these patients would be the following: preoxygenate prior
to induction to support the patient’s oxygen status and avoid potential hypoxia, avoid drugs that
can promote tachycardia (anticholinergics, dissociatives).
Consider the use of opioids in all stages of the anesthetic protocol. Opioids are necessary for analgesia and cause minimal effects to the myocardium (can cause bradycardia which may be beneficial in some of these
patients). If negative cardiovascular effects are noted, opioids can be reversed.
Consider sedation vs. general anesthesia for theses patients depending on involvement of the procedure.
Avoid if possible and minimize the use of alpha-2 drugs, these drugs depress the myocardium
and may encourage arrhythmias.
Congenital Heart Disease-Congenital heart disease is a defect or malformation of the heart of blood vessel that occurs before birth…General anesthetic considerations for these patients would be the following: these patients are
young and require additional support regarding heart rate, blood glucose, body temperature
during surgery, consider pain associated with a thoracotomy, manipulation around the
myocardium may cause ectopic beats to appear. A decrease in heart rate and blood pressure
may occur once the PDA is ligated.
Persistent Right Aortic Arch-This is a vascular anomaly, an abnormal development of blood vessels that arise from the aoric arch in the fetus. In PRAA abnormal blood vessel forms a ring which entraps the esophagus
(and sometimes the trachea) causing regurgitation. Unthriftiness and aspiration pneumonia
may also be present. General anesthetic consideration for these patients would be similar to PDA. The patients are
young and will require a pediatric approach. These patients may be suffering from aspiration
pneumonia due to the entrapped esophagus so prepare to support respiratory compromise.
Any manipulation around the myocardium may exacerbate ectopic beats.
Hypotension or Hypovolemia-A constant focus for the anesthetist is maintaining adequate peri-op blood pressure in the patient. Many anesthetic agents we use can affect blood pressure either by vasodilatation,
myocardial depression or bradycardia. The volume status of the patient should be assessed
and stabilized prior to anesthesia either with crystalloids, colloids or blood products. Blood
pressure measurement is a valuable tool in determining or patients perfusion status.
Anemia-Patients that are anemic have decreased oxygen carrying capacity of their blood. These
patients are more at risk for hypoxemia and hypotension…Many anesthetic agents are protein bound. In hypoprotemic patients, there is less protein for the drugs to bind to leaving a lot more of the active form of the drug in
circulation causing a more pronounced anesthetic effect. General anesthetic considerations for these patients would be: preoxygenate prior to induction to support O2 status of the patient. A preoperative PCV/TP should be performed to determine if a transfusion is warranted. Serial PCV /TP should be considred through the anesthetic event
(depending or duration), and in recovery supplemental O2 may be beneficial to these patients.
Anesthetic Agents and Cardiac Dysfunction
A knowledge and understanding of anesthetic agents is a critical factor in appropriate
management and recovery of these patients.
Opioids – hydromorphone, oxymorphone, methadone, fentanyl, buptorphanol, buprenorphine
These are valuable anesthetic agents. Their primary function is to provide the patients with
analgesia. Their use is warranted for all patients at some level depending on the magnitude of
pain…Opioids are cardiovascular sparing…less chance for cardiac depression…
Tranquilizers-Benzodiazepines (diazepam, midozolam) are mild sedatives used for sedation or general
anesthesia. These drugs have minimal cardiovascular effects. They are usually used in
combination with other drugs (opioids) during induction and maintenance because of their
Phenothiazines (acepromazine) are potent sedatives usually incorporated into the premed or
recovery period…They can be used in patients with cardiac dysfunction though low doses are advised.
Alpha-2 agonist (dexmedetomdine) is a potent sedative advised to use on young, healthy
cardiovascular stable patients…
Propofol: Propofol is a hypnotic agent that depressed the CNS and produces sedation. It is
commonly used as an induction agent for short procedures. It is a potent vasodilator that can
produce a transient hypotension. In patients with cardiac dysfunction it is advised to use with
caution due to its dose dependent vasodilation…
Etomidate: A short acting hypnotic IV anesthetic used for induction of General Anesthesia and
sedation. It is considered a good agent for “sick” hearts since it is associated with minimal
riskt of SVR or heart rate and it has minimal myocardial depressant effects with little change in CO.
It is always used in combination with other drugs (opioids, tranquillizers) since it is emetic and is
associated with increased nausea and vomiting.
Ketamine is a dissociative agent than can produce anesthesia, analgesia and amnesia…causes
an increase in heart rate, CO and blood pressure and a rise in myocardial O2 consumption.
Inhalants-Isoflurane is a non-arrythomgenic, potent vasodilator. In patients with heart disease, it is
important to devise a “balance” anesthetic technique to avoid vasodilation and hypotension. By
incorporating injectible anesthetics perioperatively to the patient, the amount of inhalant needed
is lessened. Sevoflurane is also a potent vasodilator with cardiovascular effects similar to those
of isoflurane. It is less soluble than Isoflurane promoting a faster induction and recovery.
Mckelvay Diane, Hollingshead K. Wayne, Veterinary Anesthesia and Analgesia, ed3, St. Louis, 2003
Paddleford Robert, Manual of Small Anesthesia, ed2, Philadephia, 1999, Saunders
Greene, Stephen A., Veterinary Anesthesia and Pain Management Secrets, Philadelphia, 2002,
Hanley and Belfus, Inc
Lumb William V., Jones E.Wynn, Lumb and Jones’ Veterinary Anestheia, ed3, Baltimore, 1996,
Williams and Wilkins
Additional References available upon request.