Page 449 - Clinical Small Animal Internal Medicine

42 Cardiogenic Shock 417

pericardial effusion and will likely correctly identify tam- As with all forms of shock, oxygen administration
VetBooks.ir ponade if present. Additionally, with a small amount of should be started immediately upon recognition of the
shock state in an effort to maximize arterial oxygen con-
focused training, the emergency clinician can recognize
acute systolic failure (e.g., dilated cardiomyopathy).
ety of methods. The use of flow‐by oxygen with a mask
Evaluation of ventricular function and filling pressures in tent as far as possible. Oxygen can be provided by a vari-
patients with chronic valvular disease requires more train- is easy to perform but requires constant restraint of the
ing and is complicated by the fact that ventricular systolic patient. This method of oxygen supplementation is rela-
and diastolic function changes with age and disease sever- tively inefficient unless a tight‐fitting mask is used.
ity in dogs. The recognition of chordae tendinae rupture, Unfortunately, animals in shock are often intolerant of
mild to moderate valvular insufficiency, caval syndrome having a mask held over their muzzles and they may
or pulmonary hypertension will likely require evaluation struggle or resist. Holding a tube attached to an oxygen
by a veterinary cardiologist. Echocardiography can also source in front of an animal’s face is an extremely inef-
be used to identify rare causes of cardiogenic shock such ficient method of providing oxygen but, recalling that
as intracardiac tumors. perfect is the enemy of good, is probably better than not
The use of biomarkers in veterinary medicine is an providing any supplemental oxygen. Occasionally, ani-
area of active investigation. While many biomarkers have mals will tolerate placement of nasal prongs similar to
been studied and show promise for distinguishing car- those used in human medicine. Due to the large size
diac disease from respiratory disease or for stratifying of the prongs, this is most feasible in large‐breed,
severity of cardiac disease (NT‐proBNP, troponin‐I), no‐brachycephalic dogs.
most are not available as point‐of‐care (POC) tests, lim- A less labor‐intensive way of providing oxygen is
iting the clinical usefulness of these assays for evaluation through the use of an oxygen chamber or cage. Purpose‐
of the patient in cardiogenic shock. The exception to this built oxygen cages are available but require a significant
is troponin‐I, which is available as a POC test (iStat by financial investment and utilize large amounts of oxygen.
IDEXX) and has been shown in several veterinary stud- A less expensive alternative is a plexiglass door with a
ies to correlate with myocardial injury. A high troponin‐I gasket attached to a standard cage that allows introduc-
level in a patient presenting for shock should prompt the tion of oxygen through a port. While this method is less
clinician to further explore the possibility of an underly- expensive than installing purpose‐made cages, the clini-
ing cardiac cause. It should be noted, however, that tro- cian has little control of the oxygen content and limited
ponin‐I levels have been shown to increase in dogs with ability to reduce carbon dioxide accumulation within the
gastric dilation and volvulus and may be elevated in any cage. The amount of oxygen used in these cages is usu-
patient that has cardiovascular instability. The degree of ally higher than in purpose‐made oxygen cages due to
troponin‐I elevation is likely greater in dogs with myo- leakage through imperfect seals.
cardial injury than in those with shock of noncardiac ori- When providing supplemental oxygen in the acute set-
gin. Therefore, the true utility of troponin‐I may be in its ting, the highest achievable F i O 2 should be used. Once
ability to rule out myocardial injury in the acute setting. the patient begins to stabilize, the F i O 2 can be reduced to
Determination of cardiac output would provide strong below 60% to decrease the likelihood of oxygen toxicity
support for a diagnosis of cardiogenic shock, especially in developing.
the absence of other possible causes of shock. While car- Animals with confirmed or suspected pulmonary
diac output monitoring technology exists in veterinary edema and cardiogenic shock should be given loop diu-
medicine, its clinical use remains limited at this time. retics upon presentation. Loop diuretics are rapidly act-
ing, effective diuretics that can quickly improve the
clinical condition of patients with pulmonary edema.
Therapy Furosemide (2 mg/kg) should be administered intramus-
cularly and repeated every 30–60 minutes as needed
Cardiogenic shock is a unique form of shock that is not until clinical signs improve. Attempts at IV catheter
generally responsive to traditional treatments for other placement or IV administration of diuretics can be con-
types of shock, (i.e., volume expansion and vasopres- sidered but patient safety must always be kept in mind.
sor support). In fact, intravascular volume expansion Sometimes it becomes apparent that without more
and vasopressor therapy can be detrimental or even aggressive intervention (i.e., IV administration of medica-
fatal when administered to a patient with cardiogenic tions), the patient’s condition will continue to deteriorate.
shock. Rather, cardiogenic shock must be treated pri- If, in the clinician’s mind, the patient is progressing irre-
marily by improving cardiac performance and second- versibly toward cardiopulmonary arrest unless such inter-
arily by altering vasomotor tone (usually reduction of vention is undertaken, all attempts should be made to
vasomotor tone). minimize the stress and duration of restraint by carefully