D. C. SAWYER, E. I. EGER, II AND W. V. LUMB 
763 
allow withdrawal of blood not long after the 
caval tubing occluded. 
Extensive adhesions precluded replacement 
of the portal vein catheter. However, repeated 
studies were possible in animals with functional 
catheters. Also, this instrumentation allowed 
studies to be conducted continuously over a pe- 
riod of days. 
Results of this study indicate that uptake and 
distribution studies at low anesthetic concentra- 
tions cannot necessarily be used to predict 
events at concentrations used clinically. Also, 
metabolic studies of subanesthetic concentra- 
tions cannot be extrapolated with all anesthet- 
ics to predict metabolism during anesthesia. 
Because of their exposure to low concentrations 
of anesthetics which are metabolized, anesthe- 
tists may produce large amounts of metabolites 
relative to those produced by patients. 
SUMMARY 
Miniature swine appear to adapt well to rela- 
tively long term bioinstrumentation procedures. 
Pigs have restricted movement of their head 
and feet and cannot damage external catheters 
secured by bandages. When housed in the same 
or adjacent pens, they will cooperate to remove 
bandages. Therefore implanted animals must be 
separated. To prevent rubbing of catheters im- 
planted dorsal and anterior to the shoulders, 
low overhangs of pen structures must not be 
available. An important factor is precondition- 
ing to the laboratory environment before sur- 
gery and the minimal use of physical restraint. 
Animals, when brought to the laboratory from 
pens, were trained to walk to and from the table 
on a ramp. Pigs do not like to be picked up and 
scream quite vigorously before being placed on 
a table. This procedure is quite helpful when 
working with animals above 30 kg. Also, by 
avoiding excitement, consistent control data can 
be obtained from instrumented animals. 
REFERENCES 
1. Sawyer, D. C, Lumb, W. V., and Stone, H. L. 
Cardiovascular effects of halothane, methoxyflur- 
f/l ane, pentobarbital, and thiamylal. J. Appl. Physiol. 
30:36-43, 1971. 
2. Sawyer, D. C, and Lumb, W. V. Halothane anes- 
thesia in miniature swine. Anesthesia Analgesia Cur- 
rent Res. 49:616-619, 1970. 
3. Sawyer, D. C, and Stone, H. L. Thoracic surgery 
for electromagnetic flow sensor implantation on 
miniature swine. In: Swine in Biomedical Research, 
edited by L. K. Bustad and M. P. Burns. Richland, 
Wash. : Atomic Energy Commission and Pacific 
Northwest Laboratory, 1966, p. 405-409. 
4. Sawyer, D. C, Eger, E. I., II, Bahlman, S. H., 
CuLLEN, B. F., and Impelman, D. M. Concentration 
dependence of hepatic halothane metabolism. Anes- 
thesiology 34:230-235, 1971. 
5. Vetto, R. M., and Boge, C. H. A simplified 
method for constructing a common hepatic vein in 
the dog. Ann. Surg. 155:543-546, 1962. 
6. Halsey, M. J., Sawyer, D. C, Eger, E. L, II, 
Bahlman, S. H., and Impelman, D. M. Hepatic 
metabolism of halothane, methoxyflurane, cyclopro- 
pane, Ethrane, and Forane in miniature swine. 
Anesthesiology 35:43-47, 1971. 
7. Sawyer, D. C, Eger, E. I., II, Bahlman, S. H. 
Halsey, M. J., Cullen, B. F., and Impelman, D. 
M. Metabolism of inhalation anesthetics. In: Cellu- 
lar Toxicity of Anesthetics, edited by B. Raymond 
Fink, the Williams and Wilkins Co., Baltimore, 
1972. 
DISCUSSION 
Ed Jankus, University of Minnesota, St. 
Paul : I thank you for a very fine paper. I'd like 
to ask you a question concerning methoxyflur- 
ane particularly. Would you comment on the de- 
gree of analgesia achieved with that anesthetic 
in the pig in your experience, and would you 
also state the degree of acidosis that resulted 
and the mechanism that produced this ? 
Dr. Sawyer : We never evaluated the analge- 
sia in these animals, so I really cannot com- 
ment. We were never stimulating them after 
anesthesia in the study. We used halothane to 
do the implants. So for that reason I really 
don't know. We were supposed to have some an- 
algesia post-anesthesia and I think that it prob- 
ably occurred, because the concentration of 
anesthetic is still around for a long time. As far 
as the acidosis, I think there is both a metabolic 
and a respiratory acidosis, as the PC02 is ele- 
vated. 
Dr. Jankus : How profound was that in your 
experiment? 
Dr. Sawyer: Not terribly bad. We assisted 
ventilation. Animals were breathing sponta- 
neously, but we assisted them as well. We just 
