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22 Section I: Diagnostics and Planning

in ventilation and perfusion (V/Q mismatch) and further diagnostics
including thoracic radiographs are warranted.
Lesions of the glossopharyngeal and vagus nuclei or nerves can
depress the swallowing reflex (gag reflex) and result in movement
of contents from the oral cavity into the lungs. This can lead to
pneumonitis or pneumonia. Risks for aspiration pneumonia are
compounded in patients with depressed levels of consciousness
with intracranial disease [4]. Intracranial lesions may lead to abnor-
mal sensorium through direct involvement of the ascending reticu-
lar activating system (ARAS) or indirect involvement of the ARAS
associated with prosencephalic lesions, intracranial hypertension,
and secondary brainstem compression. Careful attention should be
paid to auscultation when evaluating the mentally altered patient.
Further respiratory evaluation is considered in patients with
abnormal respiratory rates or effort, a cough of unknown etiology,
Figure 3.1 Sheltie with anisocoria and absent pupillary light reflexes as a or abnormal lung sounds on auscultation. Cyanotic mucous mem-
result of transtentorial herniation. branes may be indicative of poor gas exchange at the alveolar level
and should be investigated prior to any anesthetic event. Cough
during tracheal palpation is most commonly associated with tra-
hypertension; brain herniation and death may be imminent if cheal collapse or tracheitis. Significant respiratory signs reported by
appropriate therapy is not instituted (Figure 3.1). the owner such as a honking cough that interferes with daily activi-
Identification and treatment of increased ICP is extremely ties may prompt the need for cervicothoracic radiographs to evalu-
important prior to anesthesia to avoid neurological decompensa- ate the intrathoracic and extrathoracic trachea for collapse. Tracheal
tion. Although not directly a part of the neurological evaluation, collapse may be made transiently worse by intubation and respira-
noninvasive blood pressure evaluation is indicated in patients tory depression. If infectious tracheitis is suspected other diagnos-
who have suspected increased ICP to identify a Cushing’s reflex. tics may be indicated. In people with pulmonary disease, both an
A Cushing’s reflex occurs when the brain is receiving too little abnormal chest radiograph and spirometry are risk factors for anes-
oxygen and glucose as a result of life‐threatening increases in ICP thetic complications. However, the strongest predictor of anesthetic
and cerebral vascular compromise. In an effort to maintain cere- outcome in humans with pulmonary disease is serum albumin con-
bral blood flow, the sympathetic centers discharge to increase centration less than 3.5 g/dL [6].
blood pressure and drive up cerebral perfusion pressure. This
increase in blood pressure is usually obvious (>180 mmHg). The Cardiovascular System
carotid and aortic body baroreceptors respond to this by trigger- Cardiovascular disease can be a significant risk factor for anesthe-
ing a reflex bradycardia [5]. sia. In patients undergoing anesthesia for intracranial surgery,
If neuroimaging is done under a separate anesthetic episode to hemodynamic stability is critical. Additionally, intracranial disease
allow for surgical planning, a complete neurological examination may lead to arrhythmias via an ischemic phenomenon known as
should be performed and documented prior to induction of brain-heart or cerebro‐cardiac syndrome; these arrhythmias may
anesthesia for the intended neurosurgical procedure. Ideally the be fatal [5].
examination is done the morning of the procedure. This will allow Initial cardiac evaluation includes assessment of cardiac rate and
for assessment of any changes that have occurred since imaging or rhythm, pulse quality, and capillary refill time. Presence of a mur-
previous evaluation, as well as provide a baseline for postoperative mur not previously documented or one that has recently changed in
comparison. quality or character should prompt cardiac consultation and echo-
cardiography. ECG, electrolyte panel, and packed cell volume
Physical Examination and Extraneural (PCV) should be performed in patients with arrhythmias. Cardiac
Systems Functions evaluation including ECG and thoracic radiographs should be per-
Respiratory System formed in all patients over 7 years of age and in recumbent patients,
Basic respiratory evaluation includes resting respiratory effort, rate trauma victims, and patients with suspected neoplasms [7]. The
and rhythm, auscultation of lung quadrants, evaluation of mucous presence of abnormalities on any of these tests may need additional
membrane color, and palpation of the trachea. Patients with pri- evaluation of the patient by a cardiologist. In breeds at risk for
mary lesions in the medulla or craniocervical junction may develop developing life‐threatening cardiac diseases, such as dilated cardio-
respiratory ataxia, particularly after trauma or surgery. More myopathy in Doberman Pinschers and arrhythmogenic right ven-
severe injury to the brainstem respiratory centers could result in tricular cardiomyopathy in Boxers, Holter monitoring prior to
either respiratory arrest or the need for mechanical ventilation or surgical admission may identify abnormal rhythms and determine
death. Concurrent diseases of the lower cervical spine may risk category [8,9]. Cavalier King Charles Spaniels are the most fre-
interfere with phrenic nerve integrity and decrease chest expansion quent patients undergoing surgery for Chiari‐like malformation
through paresis or paralysis of the diaphragm. Arterial blood and also have a very high incidence of genetically influenced mitral
gas evaluation will provide the best assessment of ventilation. valve disease. In patients with stable cardiac disease, current tho-
If hypoventilation from neurological disease is diagnosed racic radiographs may be valuable in evaluating cardiac size and
[Pao < 60 mmHg, Paco > 60 mmHg, normal alveolar–arterial pulmonary changes but are not always indicated.
2
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(AA) gradient], mechanical ventilation is indicated. An AA gradi- In people, specific indices have been developed that predict mor-
ent below 5 mmHg or greater than 10 mmHg is indicative of mismatch tality rates of cardiac patients undergoing noncardiac procedures.