WILLIAM J. DONAWICK AND JAMES W. BUCHANAN 
291 
0.05 to 0.1 mg/kg of atropine sulfate 30 min- 
utes before surgery. 
Barbiturates, even the very short-acting ones, 
are unsafe in the calf because they cause pro- 
longed depression and high mortality.^ The ad- 
ministration of halothane and nitrous oxide 
through a face mask offers a safe, rapid alter- 
nate method for the induction of anesthesia. 
For induction, a conical face mask was fash- 
ioned from a plastic detergent bottle with a 
foam rubber seal at the muzzle end and an 
adaptor for attaching it to the anesthetic ma- 
chine at the spout. With the calf standing, anes- 
thesia was begun with halothane (4% ) , nitrous 
oxide (71%), and oxygen (25%). The calf was 
placed in lateral recumbency when it was no 
longer able to stand even with assistance. This 
prevented the involuntary movements of the ex- 
citatory stage. Approximately 5 minutes were 
required before the laryngeal reflex was abol- 
ished sufficiently to permit intubation. 
Inability to see the larynx because of the 
length of the calf's muzzle and the thickness of 
the base of the tongue made endotracheal intu- 
bation difficult. It was most easily accomplished 
by blind placement of the endotracheal tube 
with the calf lying on its right side, the head 
hyperextended and the tongue pulled forward 
as far as possible. A mental stylet was placed in 
the endotracheal tube to aid in the manipula- 
tions to get past the epiglottis. 
Moderate to severe respiratory acidosis oc- 
curred during inhalation anesthesia in calves 
that were breathing spontaneously even though 
they were kept in the first stage of surgical 
anesthesia."!" Oxygenation during sponta- 
neous ventilation before thoracotomy was ade- 
quate with 40 % oxygen in the gas mixture. 
Large tidal volume-high pressure (30 to 33 
cm of HoO) ventilation was necessary to pro- 
vide adequate oxygenation during thoracotomy. 
The tidal volume required was approximately 2 
liters with a minute-ventilation of 40 liters. An 
undesirable side-effect of hyperventilation was 
respiratory alkalosis, but it was inevitable if 
adequate oxygenation were to be assured. The 
failure to maintain adequate oxygenation dur- 
ing thoracotomy without large tidal volume- 
high pressure ventilation was probably caused 
by a combination of factors, including the ana- 
tomic structure of the bovine lung and the lat- 
eral positioning of the calf during thoracotomy. 
Mechanical damage was not seen in the lungs of 
calves ventilated continuously at a high pres- 
sure. Small tidal volume-low pressure ventila- 
tion during the thoracotomy, even with 100% 
oxygen, resulted in hypoxemia, hypercapnia, 
atelectasis, and increased alveolar-arterial oxy- 
gen gradient. 
The thymus gland occupies a large part of the 
cranial thorax in young calves. If thymectomy 
is attempted, care must be taken during dissec- 
tion because the phrenic and vagus nerves 
course through it and the gland is supplied by 
one or more blood vessels easily torn from the 
brachiocephalic trunk. 
The brachiocephalic trunk is the only branch 
arising from the ascending aortic arch. The calf 
has a left azygos vein which empties into the 
coronary sinus ; for this reason coronary sinus 
blood does not give a true reflection of my- 
ocardial metabolism. 
A median sternotomy is easy to perform and 
provides access to both sides of the thorax. 
However, the calf has a deep thorax and acces- 
sibility to the heart is poor. Postoperatively, 
infection of the incision line often occurs since 
calves spend much of their time in sternal re- 
cumbency and contamination of the incision is 
unavoidable. 
A lateral thoracotomy without rib resection 
in the left 3rd intercostal space provides good 
exposure of the brachiocephalic trunk and the 
cranial aspect of the main pulmonary artery. 
The left 4th space is preferable for approaching 
the pulmonic valve and cannulating the right 
atrium. The left 5th space is preferable for ap- 
proaching the mitral valve. The skin incision 
was always made over the 6th intercostal 
space. If placed further forward it often be- 
came infected and healed slowly. 
Frequently after operation, the calves were 
anorectic. At the commencement of the opera- 
tion we administered an electrolyte solution^ in- 
travenously at the rate of 80 ml/kg/24 hr. The 
fluids were given until the calf was able to 
drink sufficient water (approximately 10% of 
body weight in water/day) . 
^ Normosol R and M, Abbott Laboratories, North Chicago, Illinois 
60064. 
