Page 407 - Clinical Small Animal Internal Medicine

38 Respiratory Monitoring in Critical Care 375

chronic cardiac or respiratory disease. Tachypnea and hypoxemia. However, in anemic patients, the amount of
VetBooks.ir hyperpnea with exertion are also considered early signs deoxygenated hemoglobin present in the capillary beds
may be too low to result in a color change detectable to
in this same setting. Both tachypnea and hyperpnea are
adaptive responses in most settings, but not all. These
Abnormal or excessive abdominal motion during res-
responses represent the clinically apparent consequences the clinician.
of attempts to maximize alveolar ventilation. However, piration may indicate respiratory distress. Passive
they may be triggered by pain, hypotension, and other abdominal motion and increased abdominal effort are
factors. In patients with upper airway disease, these not the same thing, although they may look similar from
responses are generally maladaptive as they increase the a distance. More pronounced outward motion of the
work of breathing and may promote further airway nar- abdomen on inspiration is passive and caused by
rowing via the Venturi effect. increased contraction of the diaphragm. Active contrac-
Tachypnea must be distinguished from panting which tion of the abdominal muscles (e.g., rectus abdominis)
occurs in hyperthermic (not febrile) animals with the represents recruitment of accessory respiratory muscles
mouth open. Febrile animals have a reset thermoregula- whereas passive displacement of the abdominal contents
tory set‐point and thus the elevation in body tempera- during inspiration does not. The clinician may need to
ture will only result in occasional panting when body palpate the ventral abdominal muscles during exhalation
temperature temporarily exceeds this threshold. to distinguish between the two conditions. Tensing of
Tachypnea does not imply open‐mouth breathing the rectus abdominis during exhalation can usually be
whereas this is a hallmark of panting. Panting does not clearly felt when increased abdominal effort is truly pre-
alter ventilatory status whereas tachypnea may result in sent. Activation of the abdominal muscles during respi-
hyperventilation in some settings but not others. ration actively aids exhalation and passively assists
Respiratory monitoring also includes assessing patients inspiration. Increasing intraabdominal pressure (and
for clinical signs relating to reduced respiratory gas flow thus passively increasing intrathoracic pressure) raises
velocity. Such flow reductions may manifest as prolonga- the pressure driving expiratory gas flows. This increase
tions of the inspiratory (upper airway disease) or expira- in abdominal pressure also serves to place the diaphragm
tory (intrathoracic airway disease) phases of respiration. in a more cranial position prior to the next inspiratory
Both phases of respiration may be affected concurrently effort. This diaphragmatic shift places it in a more
in some disease states. One example is feline asthma. favorable orientation for contraction and thus abdomi-
Bronchoconstriction results in increased resistance to nal muscle activity can enhance diaphragmatic perfor-
both inspiratory and expiratory flows, although the mance. True increased abdominal effort generally
increase is generally more marked during exhalation. An indicates expiratory flow limitation due to intrathoracic
inability to vocalize indicates a severe reduction in expir- airway narrowing or collapse.
atory gas flows and should prompt immediate assess- Some patients may have atypical abdominal wall
ment of upper airway patency. motion. Paradoxical motion (abdomen moving inward
Several clinical signs that manifest in veterinary on inspiration) may be seen with diaphragmatic hernia,
patients with respiratory distress represent adaptive fatigue, or paralysis. A more focal inward movement of
responses that serve to reduce airway resistance. Neck the abdominal wall adjacent to the costal arch is often
extension as discussed above is one example. Flaring of seen in patients with pleural effusion. Any significant
the nares represents recruitment of the dilator naris motion of the soft tissues in the region overlying the
muscle and is stimulated by hypoxemia and hypercap- thoracic inlet may indicate abnormal or increased
nia and inhibited by pulmonary stretch receptor respiratory effort.
activation. Breathing through an open mouth also
reduces respiratory system resistance while foregoing Clinical Signs of Dyspnea
the benefits of gas conditioning (humidification, parti-
cle trapping) by the nasal passage. Animals in respira- Small animal patients may also exhibit clinical signs that
tory distress often breathe with their mouths open one might attribute to the unpleasant sensation of dysp-
although other conditions (pain, hyperthermia) can nea. Such signs include a blunted response to the envi-
also elicit this same response. Animals in respiratory ronment (obtundation) as the patient focuses solely on
distress typically do not hang the mouth passively the act of breathing. An “anxious” facial expression with
open, but rather actively retract the commissures of dilated pupils bilaterally is common. Such patients are
the lips and extend the tongue outward. Activity of the typically not eating, drinking, or sleeping adequately. A
genioglossus muscle may be synchronized with the patient that has been in respiratory distress and is now
respiratory cycle, resulting in cyclic protrusion of the devoting energies to these other needs is likely improv-
tongue outwards. ing. In cats, the absence of grooming behaviors may be
Cyanosis is a severe but unreliable sign of respiratory associated with sensations of dyspnea. Returning to
compromise. When present, it generally indicates severe normal hygiene routines often accompanies a marked