Physiological Control Algorithms; Flow Estimation; Ventricular Suction Detection Alarm - HeartWare Ventricular Assist System Instructions For Use Manual

HeartWare

7.3 Physiological Control Algorithms

The "Fixed" mode is used for HVAD
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information about device performance and HVAD

7.3.1 Flow Estimation

Estimated HVAD Pump blood flow is calculated using VAD power, speed parameters, and hematocrit based on a blood sample from the patient. The default hematocrit setting is 30%,
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but for accurate flow estimation, the patient's hematocrit should be entered into the monitor. Adjustments to the hematocrit setting on the monitor should be made for hematocrit
changes 5% or greater.
NOTE: HeartWare recommends that hematocrit be updated in the monitor whenever hematocrit changes by 5% or more.
The valid range of estimated blood flow is -2 to 10 L/min. The table below shows monitor and controller display messages and what they mean.
Monitor and Controller Display
"----"
"< -2 L/min"
"-2 L/min" up to "10 L/min"
"> 10 L/min"
* The error is the maximum of either 1 L/min or 20%, whichever is greater.
Out of range values on the low side (less than -2 L/min), are invalid in terms of estimated flow but could indicate an incorrect hematocrit value used in the flow calculation. Out of range values
on the high side (greater than 10 L/min), may suggest thrombus formation in the HVAD
nOTE: Flow estimation should only be used as a trending tool. Actual flow may differ from readout due to variability of patient's hematocrit.
DO NOT rely only on flow estimation to assess cardiac output. An average estimated flow on the monitor or controller display of less than 2 L/min, or greater than 10 L/min
◗ ◗
may indicate an electrical fault, incorrect hematocrit entry or an occlusion due to thrombus or other materials (e.g., tissue fragments) in the device. Inaccurate assessment
of HVAD Pump flow may lead to less than optimal treatment.
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7.3.2 Ventricular Suction Detection Alarm

A suction condition may occur due to ventricular collapse or inflow occlusion. Ventricular collapse occurs when a continuous flow VAD attempts to pump more blood from the left ventricle
than is available, resulting in considerable reduction in ventricular volume. Left ventricular collapse can be the result of clinical events affecting left ventricular preload including
hypovolemia (bleeding), right heart failure, arrhythmia or pulmonary embolus. An inflow occlusion occurs when an inflow cannula is obstructed by the interventricular septum, also
causing a suction condition. Temporary inflow obstruction can occur as a result of surgical positioning, patient position or during straining (Valsalva).
The ventricular suction detection alarm functions by monitoring the estimated flow for sudden decreases in flow rate. A flow baseline is established by continuously tracking the minimum
flow values. A trigger value is established at 40% below the estimated flow baseline. An indication of suction is obtained when the minimum flow falls below this trigger level. The alarm
will be triggered if this condition is maintained for 10 seconds.
The flow minimum that triggers the suction alarm is also used to define the suction clear limit. The estimated flow baseline is continuously compared to this limit. The suction alarm will
be cleared if the flow baseline is maintained above the trigger level for 20 seconds. This is an indication that the suction condition has cleared.
Figure 12: Suction Detection Alarm
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6 HeartWare Ventricular Assist System
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Pump operation, which means the clinician sets the pump speed (RPM). In addition, the HVAD
® Pump blood flow estimation.
Estimated Flow Range
Invalid
less than -2 L/min
-2 to 10 L/min
greater than 10 L/min
Average Flow Range
less than 0 L/min
0 to 5 L/min
5 to 10 L/min
greater than 10 L/min
Pump or could also be indicative of an incorrect hematocrit value used in the flow calculation.
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warning
Pump control algorithms provide clinicians
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Error*
out of range
1 L/min
20%
out of range