Monitoring critical small-animal patients (Proceedings)


Monitoring critical small-animal patients (Proceedings)

Aug 01, 2010

For a technician, the daily assessment of their critical care patients often begins with rounds. After receiving a brief verbal history and synopsis of presentation, diagnostics, and treatments a tech is ready to take over the care of that patient. Of primary importance is an initial hands on assessment. Only then will a tech be ready to monitor each patient according to its individual needs.

Recently there has been a list generated that discusses monitoring 20 items to assess critical patients each day. Many of those parameters will be included, but the primary body systems of cardiovascular, respiratory, neurologic, metabolic, and urologic systems will be discussed. Due to limited time, this presentation will highlight these systems since each one would require a book chapter to adequately cover the material. It is difficult to put these items in order of priority as the nature of a critical care patient is to change moment by moment. Rather a technician has to maintain an eye on the global patient to assess for not only the primary complaint, but also remote area body systems not directly related to the illness or injury.

Cardiovascular monitoring

Each patient should be evaluated for heart rate, pulse rate and quality, mucous membrane color, and capillary refill time.
     • Both bradycardia & tachycardia diminish cardiac output
     • If bradycardia <40-60 bpm- perform a blood pressure to ensure adequate tissue perfusion
     • Causes of bradycardia-drugs, pain, vagal reflexes, AV blocks, hyperkalemia
     • Tachycardia rates >180 big dogs, >200 little dogs, >240 cats
     • Causes of tachycardia-shock, hypovolemia, pain, hypoxemia, hyperthermia, sepsis, heart disease
     • Palpate pulse rate & quality while ausculting the heart
     • Pulse deficit indicates heart arrhythmia
     • Estimate appropriate stroke volume
     • Thready pulse indicates poor cardiac output
     • Bounding pulse may indicate septic shock (vasodilation conditions)
     • MM should be pastel pink color and moist
     • Red injected color can indicate sepsis, hyperthermia, hypertension, carbon monoxide poisoning
     • Pale/white indicates varying degrees of anemia or vasoconstriction
     • Blue (cyanotic) equals lack of oxygen saturated hemoglobin and cannot be seen until PaO2<50
     • Brown indicates acetaminophen toxicity
     • Yellow indicates liver disease, bile duct obstruction, hemolysis, prior oxyglobin transfusion
     • Dry/tacky membranes equal dehydration
     • Prolonged CRT (>2seconds) can occur from hypovolemia, hypothermia, poor cardiac output, pain
     • Rapid CRT can occur during sepsis, hyperthermia, or drugs (inhalation anesthesia)

An electrocardiogram is a staple of critical care monitoring and technicians should become accustomed to evaluating every ECG tracing for abnormal heart rhythms. Any patient that exhibits irregular rhythm and increased or decreased heart rate upon physical exam should be monitored several times a day.
     • ECG does not assess patient for myocardial performance, cardiac output, or blood pressure
     • Perform tracings on still patient in right lateral recumbancy and evaluate in same systematic steps
     • Determine heart rate
     • Evaluate rhythm as regular, regularly irregular, or irregularly irregular
     • Identify the P, QRS, & T waveforms
     • Evaluate the PR and QT intervals and inspect ST segment for elevation or depression
     • Rhythm disruptions commonly caused by electrolyte abnormalities, hypoxemia, effusions, and pain

Arterial blood pressure should be monitored several times a day on critical patients by either indirect or direct methods as appropriate for the severity of disease. Arterial blood pressure is the product of cardiac output, vascular capacity, and blood volume. If one of those factors is abnormal, neurohumeral reflexes will alter the others to maintain normal pressure.
     • Indirect measurements include sphygmomanometer, Doppler, or oscillometric methods
     • Width of cuff should equal 40% circumference of patient limb and fit snugly
     • If cuff is too loose pressure will be erroneously high, and vise versa- too tight will be erroneously low
     • First audible return of sound is systolic pressure using a Doppler
     • Oscillometric method uses mathematical calculations and interpretations of intracuff and limb blood volume changes to determine systolic, diastolic, and mean pressures
     • All indirect methods are least accurate when pressures are low and during vasoconstriction
     • Direct measurement is most accurate and requires catheterization of an artery
     • Measuring devices can be common supplies or manufacturer ready transducer
     • Transducer must be at heart level to set zero reading
     • Normal systolic, diastolic, and mean ABP are 100-160, 60-100, and 80-120mmHg respectively; variations between dog and cat and pressures between animal to animal will vary
     • Hypotension causes, systolic < 60 -hypovolemia, poor cardiac output, or vasodilation
     • Hypertension, mean pressure > 140mmHg, can cause retinal detachment, excessive cardiac work, and increased intracranial pressure

Central venous pressure is a critical monitoring tool especially useful for assessing a patient's response to fluid therapy, possible fluid overload, or in conditions such as renal, cardiac, or pulmonary disease and during septic shock.
     • CVP's require a central venous catheter placement
     • Catheter should terminate in cranial vena cava proximal to right atrium
     • Measuring devices may be common supplies or manufacturer ready transducer
     • Transducer must be at right atrium level to set zero reading
     • Normal value in dogs and cats is 0-5 cmH20 and trends are ultimately important
     • Readings of <0, or negative numbers, reflect hypovolemia
     • Values of 12-15 cmH20 indicate varying degrees of fluid overload, approaching 20 indicates heart failure, with values >20 present with cardiac tamponade

Cardiac output monitoring requires sophisticated catheters and devices as well as monitoring true oxygen delivery and oxygen consumption. These procedures are not commonly performed. More typically monitored is respiratory function and assessment of lung perfusion and ventilation. These will be discussed next.