Non-invasive blood pressure14-11Principles of SuperSTAT Noninvasive Blood PressureDeterminationThe oscillometric method of determining NIBP is accomplished by a sensitive transducer whichmeasures cuff pressure and pressure oscillations within the cuff. For the first determinationtaken on a patient, the algorithm stores the pattern of the patient's oscillation size as a functionof the pressure steps. For subsequent manual (determined as such when the previousdetermination is less than 16 minutes old), auto or stat determinations taken of the samepatient,as few as four pressure steps may be necessary to complete the determination process. Whenemploying fewer pressure steps, the system uses the stored information from the previousblood pressure determination to decide the best pressure steps to take. The algorithmmeasures the consistency of pulse size to tell if the oscillations taken at a step are good and ifmore steps are needed.The first determination settles at an initial target pressure of 135 mmHg (adult mode) and 100mmHg (neonate mode), depending on initial target pressure preset. To allow for rapid settlingof cuff pressure, the monitor will momentarily inflate to a higher pressure then immediatelydeflate to the target pressure. After inflating the cuff, the NIBP parameter begins to deflate. Theoscillations versus cuff pressure are measured to determine the mean pressure and calculatethe systolic and diastolic pressures.During an NIBP determination, the parameter deflates the cuff one step each time it detectstwo pulsations of relatively equal amplitude. The time between deflation steps depends on thefrequency of these matched pulses (pulse rate of the patient). However, if the monitor is unableto find any pulse within several seconds, it will deflate to the next step. The process of findingtwo matched pulses at each step provides artifact rejection due to patient movement andgreatly enhances the accuracy of the monitor. In stat mode, some steps may require only onepulse.Figure 14-4 Full NIBP Determination Sequence for AdultAt each step the microprocessor stores cuff pressure, the matched pulse amplitude, and thetime between successive pulses. The stepped deflation and matched pulse detection continuesuntil diastolic pressure is determined or total cuff pressure falls below 8 mmHg. The parameterthen deflates the cuff (to zero detected pressure), analyzes the stored data, and updates thescreen.
