GE HEALTHCARE B20, User'S Reference Manual

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Non-invasive blood pressure
14-11
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 of 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 to decide the best pressure steps to take. 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 patient movement and
greatly enhances the accuracy of the monitor. In stat mode, some steps may require only one
pulse.
Figure 14-4 Full NIBP Determination Sequence for Adult
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.