2. Prolonged or repeated cuff inflation has been associated with ischemia, purpura, and/or neuropathy.

3. Cuff inflation will interfere with pulse oximetry measurement in the same limb.

4. Nosocomial infection may result from using the same

cuff for more than one patient.

Oscillometric Measurement of Arterial Blood

Pressure (Automatic Noninvasive)

A. Background

The oscillometric or noninvasive blood pressure (NIBP)

monitoring technique offers a method for measuring all

arterial blood pressure parameters (systolic, diastolic,

mean, heart rate) (7–15). The underlying principle of this

method is that the arterial wall oscillates when blood flows

in pulsatile fashion through a vessel. These oscillations are

transmitted to a cuff placed around the limb. As the pressure within the cuff is reduced, the pattern of oscillations

changes (Fig. 9.2). When arterial pressure is just above the

cuff pressure, there is a rapid increase in the amplitude of

the oscillations and this is taken as systolic pressure. The

point at which the amplitude of the oscillations is maximal

coincides with the mean arterial pressure. Diastolic pressure is recorded when there is a sudden decrease in oscillations. Although many types of monitors use the same basic

technique, the integration of the oscillometric method

within an NIBP algorithm may differ substantially between

manufacturers.

1. This technique employs a BP cuff interfaced to a computerized BP monitor.

2. A pneumatic cuff is used in the same fashion as with

the auscultatory technique.

3. The monitor employs a miniature computer-controlled

air pump and a bleed valve to control inflation and

deflation of the cuff.

4. A pressure transducer interfaced to the cuff tubing

senses the inflation pressure of the cuff and oscillations transmitted to the cuff by the underlying

artery.

Fig. 9.1. Cuff of correct size applied to upper arm.

Fig. 9.2. Determination sequence for oscillometric measurement.

Chapter 9 ■ Blood Pressure Monitoring 59

5. The system will inflate the cuff to a level above the

point at which no pulsations are detected.

6. As the cuff is being deflated to the level of the systolic

pressure, oscillations from the arterial wall are transmitted to the cuff. A transducer measures static pressure

and pressure oscillations received and transmitted by

the cuff

7. The systolic pressure is assigned the value of the cuff

pressure at the time oscillations were initially detected.

8. Mean arterial pressure is generally the lowest cuff pressure with the greatest average oscillation amplitude.

The diastolic value is determined by the lowest cuff

pressure when there is a sudden decrease in oscillations.

9. Heart rate values are calculated by computing the

mean value of the time interval between pulsations.

10. Higher detection sensitivity allows this technique to be

used on parts of the extremities where auscultatory

methods are not possible (i.e., forearm and lower leg).

B. Indications

1. Measurement of BP in stable infants or when invasive

BP measurement is not required or is unavailable

2. When only intermittent BP measurements are required

C. Contraindications

1. Severe edema in the limb to be measured; will affect result

2. Decreased perfusion, ischemia, infiltrate or injury in

limb

3. Peripheral venous/arterial catheter in place in limb

D. Limitations

1. Provides only intermittent BP measurements

2. Pressure may not be detectable in low-perfusion state

or shock. Do not assume that it is simply an equipment

problem; use clinical correlation.

3. Pressure is not detectable or may be inaccurate in neonates who are restless or having seizures.

4. Inaccurate measurements (Table 9.1)

E. Equipment

1. Neonatal NIBP monitor—display should include systolic, diastolic, mean, and heart rate values (Fig. 9.3)

2. Neonatal cuff (designed for use with the specific

monitor)—cuff may be single-tube or double-tube type,

provided the appropriate adapter is used. Neonatal cuff

sizes range from 1 to 5 (Table 9.2).

F. Precautions

1. Incorrect cuff size can significantly alter the BP value

obtained; therefore, careful selection of cuff size is very

important.