Page 323 - Clinical Small Animal Internal Medicine

29 A Respiratory Pattern‐Based Approach to Dyspnea 291

bronchi collapse, contributing to common clinical signs, are unable to expand normally. As a result, intrapleural
VetBooks.ir most notably coughing. Definitive diagnosis is made via pressure increases and ultimately exceeds the intrapul-
monary pressure, effectively reducing tidal volume.
imaging that may include thoracic and cervical radiogra-
phy, fluoroscopy, and/or tracheobronchoscopy.
Clinicians should follow a standard and consistent Accordingly, a patient must breathe rapidly to maintain
adequate minute ventilation. Classically, affected patients
protocol for assessing and hopefully stabilizing a patient manifest a restrictive breathing pattern characterized by
suspected of having lower airway disease, focusing ini- shallow tachypnea. With reduced tidal volume, alveoli
tially on performing an efficient primary survey. Patients progressively collapse to cause hypoventilation and
should be given appropriate sedation and supplemental hypoxemia due to ventilation–perfusion mismatch.
oxygenation as soon as possible in an effort to reduce the Thoracic auscultation varies depending on the nature
work of breathing and anxiety. Minimal handling is of the pleural disease. Pneumothorax may develop sec-
advocated, as the stress of manipulation may be lethal. ondary to blunt or penetrating thoracic trauma, but may
The least stressful method of supplemental oxygen pro- also occur spontaneously due to primary pulmonary
vision should be employed, and viable options include parenchymal disease. A patient with pneumothorax has
flow‐by, facemask, oxygen cage, nasal cannulation, lung sounds that are most audible ventrally. Pleural effu-
modified Elizabethan collar (i.e., Crowe collar), and tran- sion may occur secondary to accumulation of blood
stracheal catheterization. (hemothorax), infectious exudate (pyothorax), neoplasia,
A commonly used sedative protocol for cardiovascu- chyle (chylothorax), and heart failure; hypervolemia and
larly unstable patients is the combination of a pure mu hypovolemia are rare causes of pleural effusion. A patient
opioid (i.e., fentanyl 2–4 μg/kg IV; oxymorphone 0.05– with pleural effusion commonly has dull ventral lung
0.1 mg/kg IV/IM; methadone 0.2–0.5 mg/kg IV; hydro- sounds with audible and possible increased lungs sounds
morphone 0.1–0.2 mg/kg IV) with a benzodiazepine (i.e., dorsally. Borborygmi may be heard in those patients with
diazepam 0.1–0.5 mg/kg IV; midazolam 0.2–0.4 mg/kg a congenital or traumatic pleuroperitoneal diaphragmatic
IV). Acetylpromazine (0.02–0.1 mg/kg IV/IM) and hernia. A cardiac murmur and/or dysrhythmia may be
butorphanol (0.1-0.2 mg/kg IV/SQ) may be appropriate auscultated in those living with heart disease.
for cardiovascularly stable patients. Inhaled albuterol Patients with pleural disease should be provided sup-
(90–180 μg), a rapidly acting beta‐2 agonist, should be plemental oxygenation as soon as possible via the least
administered; terbutaline (0.01 mg/kg SC) is a reasonable stressful method. Sedation should also be administered,
alternative if a metered‐dose inhaler is not available. ideally prior to thoracocentesis; this is not always feasible
Corticosteroids are commonly used for chronic manage- if imminent respiratory arrest is anticipated. A com-
ment of feline asthma and canine chronic bronchitis, but monly used sedative protocol for cardiovascularly unsta-
their use is not necessarily warranted in the initial man- ble patients is the combination of a pure mu opioid
agement of these diseases; a brief (i.e., 7–10 days) taper- (i.e., fentanyl 2–4 μg/kg IV; oxymorphone 0.05–0.1 mg/
ing regime of antiinflammatory corticosteroid may be kg IV/IM; methadone 0.2–0.5 mg/kg IV; hydromorphone
beneficial in the acute management of tracheobron- 0.1–0.2 mg/kg IV) with a benzodiazepine (i.e., diazepam
chomalacia to help break the cycle of coughing com- 0.1–0.5 mg/kg IV; midazolam 0.2–0.4 mg/kg IV).
monly present in affected patients. Diuretic therapy is not indicated for the emergency man-
Once stable, a thorough physical examination should agement of pleural space disease.
be performed in an effort to determine the underlying Thoracocentesis should generally be performed prior
cause of the lower airways signs. High‐quality, three‐ to thoracic radiography if pleural space disease is sus-
view thoracic radiographs are an essential part of the pected. A thoracocentesis is typically performed at the
diagnostic investigative process. Indirect visualization seventh to ninth intercostal space. If a pneumothorax is
via fluoroscopy and/or direct visualization of the lower suspected, the site of pleural puncture is perpendicular
airways via tracheobronchoscopy may be invaluable, and to the body wall just ventral to the thoracic hypaxial
lower airway cytology and culture should be pursued to musculature; the level of the costochondral junction is
rule out infectious diseases. the site of pleural puncture for those patients with sus-
pected or confirmed pleural effusion. If available, tho-
racic focused assessment with sonography for trauma,
Pleural Space triage and tracking (tFAST ) may be used to confirm
3
pneumothorax and pleural effusion, help determine site
The pleural cavity is the potential space between the of pleural puncture, and may be performed in lateral or
parietal pleura associated with the body wall and visceral sternal recumbency. Thoracocentesis has been uncom-
pleura associated with lungs. When this potential space monly associated with hemorrhage, pulmonary paren-
is occupied by air, fluid, masses and/or viscera, the lungs chymal injury, and iatrogenic infectious disease