GE B20 User Manual page 98

Principles of SuperSTAT Noninvasive Blood Pressure
Determination
The oscillometric method of determining NIBP is accomplished by a
sensitive transducer which measures cuff pressure and pressure
oscillations within the cuff. For the first determination taken on a
patient, the algorithm stores the pattern of the patient's oscillation
size as a function of the pressure steps. For subsequent manual
(determined as such when the previous determination is less than 16
minutes old), auto or STAT determinations taken on the same
patient,
as few as four pressure steps may be necessary to complete the
determination process. When employing fewer pressure steps, the
system uses the stored information from the previous blood
pressure determination and picks the best of the pressure steps. The
algorithm measures the consistency of pulse size to tell if the
oscillations taken at a step are good and if more steps are needed.
The first determination settles at an initial target pressure of 135
mmHg (adult mode) and 100 mmHg (neonate mode), depending on
initial target pressure preset. To allow for rapid settling of cuff
pressure, the monitor will momentarily inflate to a higher pressure
then immediately deflate to the target pressure. After inflating the
cuff, the NIBP parameter begins to deflate. The oscillations versus
cuff pressure are measured to determine the mean pressure and
calculate the systolic and diastolic pressures.
During an NIBP determination, the parameter deflates the cuff one
step each time it detects two pulsations of relatively equal
amplitude. The time between deflation steps depends on the
frequency of these matched pulses (pulse rate of the patient).
However, if the monitor is unable to find any pulse within several
seconds, it will deflate to the next step. The process of finding two
matched pulses at each step provides artifact rejection due to
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patient movement and greatly enhances the accuracy of the
monitor. In stat mode, some steps may require only one pulse.
At each step the microprocessor stores cuff pressure, the matched
pulse amplitude, and the time between successive pulses. The
stepped deflation and matched pulse detection continues until
diastolic pressure is determined or total cuff pressure falls below 8
mmHg. The parameter then deflates the cuff (to zero detected
pressure), analyzes the stored data, and updates the screen.
The operating cycle is composed of four parts: inflation time,
deflation time, evaluation time, and wait time. Wait time, which
varies from mode to mode, is affected by the cycle time (auto mode)
or operator intervention (manual mode).
Troubleshooting
• Measurement does not work or values seem unstable:
−
Check that cuff tubings are not bent, stretched, compressed
or loose.
−
When using hoses without identification, make sure that you
have selected the inflation limits in the NIBP Setup menu.
−
Prevent motion artifacts.
−
Use cuffs of correct size.