Thoratec HeartMate II LVAS, Руководство пользователя

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Pump Parameters
The system-provided parameters of speed, power, flow, and pulsatility index (PI), in
conjunction with echocardiography, serve as the primary indicators of device func-
tion. Once baseline values representing a satisfactory level of patient support are
established, the degree of change in a parameter usually has more clinical signifi-
cance than its absolute value. No single parameter is a surrogate for monitoring the
clinical status of the patient, and changes in all parameters should be considered
when assessing a situation.
Flow
Flow is directly related to speed and power. As the fixed speed is increased, flow will
increase. Pump flow is not directly measured but is an estimated value based on
pump power. Any increase in power will result in an increase in estimated flow. Any
condition that causes an increase in pump power not related to increase flow, such
as thrombus on the bearings or obstruction of the rotor, will display an erroneously
high flow.
Power
The amount of power used by the pump is determined by pump speed and blood
flow through the pump. Under normal conditions, the power increases with either
pump speed or flow. Gradual power increases (over hours or days) may signal a
deposition of thrombus inside the pump. Depending on the speed, power values
greater than 10 to 20 watts may also indicate the presence of a thrombus. Abrupt
changes in power, more than 2 watts, not accompanied by a change in pump speed
should also be evaluated.
Pulsatility Index (PI)
The pulse index, or “PI,” is a measure of the magnitude of the flow pulse through
the pump during the cardiac cycle. It is measured and averaged over a 15-second
interval and displayed on the monitor.
PI = Max Flow - Min Flow X 10
Average Flow
Factors that affect PI are LV preload or contractility and pump speed. When preload
increases in the native left ventricle, the Starling Curve is affected (i.e., increased
contractility) and pulsatility increases. When preload decreases, PI decreases. Pump
speed is inversely related to PI. As pump speed is increased, the LV is unloaded with
a decrease in preload, resulting in a lower PI value. Conversely, decreasing pump
speed increases LV preload, resulting in a higher PI value.
Note : Even a severely depressed heart has some residual rhythmic contraction; and,
any contraction will create a pressure pulse. Thus, under most circumstances, sys-
temic flow is pulsatile. It takes a completely flaccid heart or one in fibrillation to
have no ventricular contribution to the pulse at all.
CLINICAL OPERATION AND PATIENT MANAGEMENT
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