Cardiovascular monitoring (Proceedings)

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Cardiovascular monitoring (Proceedings)

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Apr 01, 2010

Cardiovascular (ECG, CVP, blood pressure) monitoring is essential to detect patient changes and to direct therapy and supportive care. Veterinary technicians are expected to have the mechanical ability to understand and operate these monitoring systems, the creativity to adapt a single piece of equipment to serve both a 3 pound Chihuahua and a 200 pound mastiff, the technical ability to prepare the patient for monitoring (placement of central IV lines, arterial lines etc..), and the knowledge to interpret and respond to results as they are collected.

Until normal perfusion is restored frequent serial values can be obtained for:
          • Mucous membrane color and capillary refill time
          • Packed cell volume and total solids
          • Urine output
          • ECG
          • Heart rate and pulse equality
          • Respiratory rate and effort
          • Arterial blood pressure
          • Central venous pressure
          • Cardiac output by Swann Gantz Catheter (not practical in most hospital settings)

ECG/heart rate and pulse equality

The ECG is an important monitoring tool for the critical patient, not just for the conduction abnormalities it detects, but for electrolyte abnormalities and changes in heart rate. Coupled with other monitoring devices, the changes in heart rate may give vital diagnostic information. For example, when tachycardia (rapid heart rate) occurs concurrently with hypotension (decreased blood pressure) the patient may be suffering from hypovolemia (lack of sufficient circulating fluids) while patients with tachycardia occurring concurrently with hypertension (increased blood pressure) may be experiencing extreme pain. Auscultation of heart rate and simultaneous palpation of peripheral pulses yields more information that either alone. Pulse quality, and synchronicity with heart rate are major indicators of perfusion.

Arterial blood pressure physiology and measurement

Arterial blood pressure (ABP) describes the force exerted on blood vessel walls, over a cardiac cycle, by the amount of blood being pumped through them. ABP is a summation measurement of cardiac output (the heart's ability to effectively pump the volume of fluid presented to it), vascular resistance (the elasticity of the vessel walls) and blood volume (the quantity of circulating fluid). Changes in any of these factors can have profound effects on ABP.

The overall goal of the cardiovascular system is to provide oxygen and nutrients to all body tissue as well as to remove metabolic waste products. ABP must be normal to insure adequate blood volume is reaching vital organs.

Increased ABP (hypertension) may be caused by hypervolemia, excessive NaCl retention or increased circulating vasopressors such as cathecholamines and can result in edema formation, arteriole damage, hemorrhage and damage to "target organs" such as the eye, kidney, heart and brain. Because ABP is not routinely measured in veterinary patients hypertension is often first detected because of changes in these target organs. Hypertension is corrected by treating the underlying disease or condition and with the use of antihypertensive agents such as diuretics, vasodilators and/or calcium channel blockers.

Decreased ABP (hypotension) may result from hypovolemia poor blood vessel tone or any condition that diminishes cardiac output. After prolonged periods of hypotension the patient is in danger of developing tissue ischemia, brain damage, renal failure, cardiovascular collapse and death. Hypotension can usually be corrected by aggressive fluid volume support, using both crystalloid and colloid solutions, but may require blood pressure supporting (i.e. inotropic and/or vasoactive drugs as well.

Physiology

Blood pressure is the measurement of tension within the arterial vessel walls at varies points in a cardiac cycle. Systolic blood pressure represents the maximal pressure created by ventricular contraction. Diastolic blood pressure represents the minimal pressure at rest just prior to the next contraction. Mean arterial pressure (MAP or MABP) is the average driving pressure over the entire cardiac cycle and is the major determinant of perfusion to most organs MAP is not a mathematical average of systolic and diastolic pressures because the diastolic phase is approximately twice as long as the systolic phase. Therefore, MAP is derived by the following formula: