Many variables affect anesthesia including the patient, the sedative and anesthetic agents used and the anesthetist. Veterinary
patients pose a greater anesthetic challenge than human patients because of weight and breed variables, monetary limitations
and often the lack of a comprehensive anesthetic history. Preanesthetic testing helps identify pre-existing conditions thus
improving anesthetic safety but also providing valuable baseline data for future comparison. Furthermore, not offering preanesthetic
testing can open your practice to liability issues and create anesthetic nightmares.
History of Preanesthetic Testing at Metzger Animal Hospital
Preanesthetic profiling young patients was a new concept in the 1980's and emerged as more common occurrence in the late 1990's.
Client compliance is frequently an issue with new programs and preanesthetic testing is a good example.
To overcome these challenges, Metzger Animal Hospital developed a client consent form for preanesthetic testing in 1996.The
original form explained the purpose of the tests, likening them to tests a physician would run if the client were to undergo
surgery. Clients would choose among three Pet Health Screens, based on the animal's age and health status, and then sign the
form which resulted in client compliance of approximately 65-70% (Form #1).
In 1997, compliance increased to over 80 percent after the hospital started mailing the form before the scheduled surgery
or dental date with a cover letter emphasizing the importance and advantages of testing. In addition, the letter served as
a reminder and included a pre-surgery checklist (Form#2).
In 1998 Metzger Animal Hospital instituted mandatory preanesthetic testing for all surgical and dental procedures. Tests include
the CBC, biochemical profile with electrolytes for all patients and adding thyroid testing (total T4) for all patients over
7 years of age. Advantages include a more comprehensive testing protocol, less client confusion and better team member efficiency.
Improved preanesthetic patient care
Comprehensive laboratory profiling allows for a more thorough evaluation of organ systems including hematopoetic, renal, hepatic
and endocrine systems. Proper evaluation of testing parameters frequently depends on one another, for example evaluating calcium
and albumin or amylase with renal function. Hematology is a very important preanesthetic test because anemia, polycythemia,
leucopenia, Leukocytosis and thrombocytopenia may contribute to adverse anesthetic events (ref_Guide to hematology). Pre-existing
renal or hepatic disease may interfere with anesthetic metabolism and excretion especially in anesthetics requiring biotransformation
and elimination. Undetected hypoglycemia may result in serious cerebral dysfunction and death. Electrolyte abnormalities such
as hyperkalemia may predispose the patient to life-threatening cardiac arrhythmias.
Client confusion is eliminated with mandatory preanesthetic testing because no forms or signatures are required and a consistent
unified message is communicated that the practice believes the testing is important. Preanesthetic testing is analogous to
pain management-you either believe in it or you don't.
Front office and technician team members welcome mandatory testing because once again, no forms or signatures are required.
Front office staff can focus on clients instead of answering questions about the cost and forms. With mandatory testing technicians
no longer need to review forms to see which patients receive the needed testing.
Mandatory preanesthetic testing is becoming the standard of care and the veterinary team needs to explain the safety benefits
to patients and visually review the results with owners when the patient is discharged.
Risk versus benefit
The cost of testing must be weighed against the benefits. Statistically speaking anesthetic complications and abnormalities
detected on preanesthetic testing are uncommon. A recent study of nearly 1,000,000 patients (254,530 cats with an average
age of 8 months and 738,276 dogs averaging 10 months of age )undergoing pre-anesthetic profiling, reported 9% of patients
had one or more laboratory parameters outside of the normal reference range. Preanesthetic testing included a CBC and a 12
chemistry biochemical profile. Table 1 shows results of various preanesthetic abnormalities and their relative incidence in
patients presented for ovariohysterectomy, castration or dental procedures. Note that electrolytes were not part of the preanesthetic
protocol included in the study which would undoubtedly increase the % of patients with results deviating from the reference
range. Also note that every abnormality may not significantly affect anesthesia or surgery, however other parameters like
HCT, platelet count and creatinine might significantly affect patient recovery and survival.