APPLICATION OF MINIATURE SWINE 
TO ANESTHETIC STUDIES ON THE 
CARDIOVASCULAR SYSTEM AND 
HEPATIC INHALATION ANESTHETIC METABOLISM 
D. C. Sawyer*, E. I. Eger, II" and W. V. Lumb"* 
Miniature swine were used for studies on the car- 
diovascular effects of anesthetics and hepatic metabo- 
lism of inhalation anesthetics. Hormel swine were 
selected to study effects of halothane, methoxyflurane, 
pentobarbital and thiamylal on cardiac output, stroke 
volume, mean arterial pressure, heart rate and related 
variables. The experimental design was to study each 
anesthetic at 2 week intervals. This provided a maxi- 
mum of 48 periods for 12 pigs. Thirty-eight of 48 runs 
were accomplished. Incomplete periods in the design re- 
sulted from aortic rupture subsequent to flow sensor 
implantation in 3 animals and nonfunctional aortic 
catheters in 3 animals. Duration of instrumentation av- 
eraged 60.6 (25-127) days. Representative and consist- 
ent control data were obtained and compared with data 
recorded during and following anesthesia. Each anes- 
thetic decreased cardiac output and stroke volume. Heart 
rate, mean arterial pressure and peripheral vascular re- 
sistance were variably affected. For metabolism studies, 
catheters were implanted in the aorta, portal vein and 
common hepatic vein of miniature pigs. A common he- 
patic vein was formed to isolate the liver for in vivo 
metabolic studies. Animals were used 34-150 days post- 
implantation. These studies demonstrated that the liver 
extracts (metabolizes) a greater fraction of halothane 
and fluroxene from hepatic blood at lower than at 
higher anesthetic partial pressures. From exposure to 
low subanesthetic concentrations for periods of 20 
hours to 1 week, considerable hepatic metabolism of 
halothane, methoxyflurane and fluroxene was found 
with little or no metabolism of Ethrane and no metabo- 
lism of cyclopropane, nitrous oxide or Forane. 
INTRODUCTION 
When animals are selected as subjects for 
study, 2 major considerations must be made. 
First, from previous investigations, which ani- 
* Associate Professor, Department of Small Animal Surgery & 
Medicine, College of Veterinary Medicine, Michigan State Univer- 
sity, East Lansing, Michigan 48823. 
•* Professor, Department of Anesthesia, University of California, 
San Francisco, California 94122. 
Professor and Director, Surgical Laboratory, Colorado State 
University, Fort Collins, Colorado 80521. 
mal would be the most desirable from a physio- 
logical or pharmacological point of view? 
Second, which animal would be most conducive to 
allow accomplishment of the study? For the in- 
vestigations described in this paper regarding 
the effects of anesthetics, miniature swine were 
selected as research subjects because physiolog- 
ical responses are similar to those found in man 
and other animals. In addition, swine readily 
adapt to the laboratory environment and can be 
used for chronic instrumentation studies. 
Miniature swine were used to study cardio- 
vascular effects of halothane, methoxyflurane, 
pentobarbital and thiamylal. f In a separate 
study, miniature swine were selected to investi- 
gate hepatic metabolism of inhalation 
anesthetics, ft 
METHODS 
Twelve Hormel miniature swine, 30-35 kg 
were surgically instrumented to study cardio- 
vascular effects of anesthetics.^ During general 
anesthesia with halothane,^ a left thoracotomy 
was performed.^ An electromagnetic flow sen- 
sor was placed around the ascending aorta. 
Silicone rubber catheters were placed in the tho- 
racic descending aorta and superior vena cava. 
After a 10-day recovery period, control meas- 
urements were made from unmedicated animals 
at 2-day intervals and immediately prior to 
t This work was conducted at the Surgical Laboratory by Dr. 
Sawyer and Dr. Lumb and was supported by U.S. Public Health 
Service Grant GM-HE-14456-02 and Special Fellowship Award 
B-F2-GM-29, 932-02. 
tt Investigations were conducted at the San Francisco Medical 
Center by Dr. Sawyei-. Dr. Eger and others and was supported by 
U.S. Public Health Service Grants 5T 1 GM-0063-12, 1 PC 1 GM- 
15571-OlAl and 2 FO3-FM-29932-03, the Ayerst Laboratories, and 
Ohio Medical Products, a Division of Air Reduction Company, Inc. 
759 
