and stethoscope.

2. The sphygmomanometer uses a pneumatic cuff to

encircle the upper arm or leg and a pressure gauge

(manometer) to register the pressure in the cuff.

3. There are two types of manometers

a. Mercury (mercury column)

b. Aneroid (mechanical air gauge)

4. The encircling pneumatic cuff is inflated to a pressure

higher than the estimated systolic pressure in the

underlying artery. The cuff pressure compresses the

artery and stops blood flow.

5. A stethoscope placed distal to the cuff, over the

occluded artery, will pick up the Korotkoff sounds as

the cuff is deflated and the pressure of the cuff decreases

to the point at which blood flow resumes through the

artery.

6. Korotkoff sounds are the noise generated by blood flow

returning to the compressed artery and originate from a

combination of turbulent blood flow and oscillations of

the arterial wall. The sounds have been classified into

five phases:

a. Phase I: Appearance of clear tapping sounds corresponding to the appearance of a palpable pulse

b. Phase II: Sounds become softer and longer

c. Phase III: Sounds become crisper and louder

d. Phase IV: Sounds become muffled and softer

e. Phase V: Sounds disappear completely. The fifth

phase is thus recorded as the last audible sound.

7. An 8- to 9-MHz Doppler device can be used in place of

a stethoscope. This device will detect only systolic BP

levels.

B. Indications

1. Measurement of BP in larger 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 muffle

the Korotkoff sounds.

2. Decreased perfusion, ischemia, infiltrate or injury in

limb

3. Peripheral venous/arterial catheter in limb

D. Limitations

1. Provides only intermittent BP measurements

2. Manual measurement cumbersome or impossible in

small infants

3. Accuracy depends on ability to recognize Korotkoff

sounds and may be user-dependent.

4. Pressure may not be detectable in low-perfusion states

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

problem; use clinical correlation.

5. Pressure is not detectable or is inaccurate when the

baby is actively moving or agitated.

6. Measures only systolic and diastolic BP; mean BP measurement not available

Chapter 9 ■ Blood Pressure Monitoring 57

7. Can be used only to measure pressure in the upper arm

or thigh

8. The Korotkoff sound method tends to give values for

systolic pressure that are lower than the true intra-arterial pressure, and diastolic values that are higher.

9. Inaccurate measurements (Table 9.1)

E. Equipment

1. Neonatal cuff (Table 9.2). Select a cuff that will fit

comfortably around the upper arm or thigh; the inflatable bladder should completely encircle the extremity

without overlapping. The width should be 90% of the

limb circumference at the midpoint (5).

2. Mercury manometer or aneroid-type gauge

3. Appropriate-sized stethoscope with diaphragm or

Doppler system

F. Precautions (Table 9.1)

1. Carefully select the appropriate cuff size, because incorrect size can significantly alter the BP recorded (6).

a. Cuff too small: BP will be higher than actual BP.

b. Cuff too large: BP will be lower than actual BP.

2. Check functional integrity of manometer

3. Check integrity of cuff for leaks

4. Check speed of cuff deflation: If deflation is too rapid,

accuracy may be compromised.

5. Patient must be quiet and still during measurements.

6. For optimal infection control, use disposable cuff for

each patient.

G. Technique

1. Place the infant supine, with the limb fully extended

and level with the heart.

2. Measure the limb circumference and select the appropriate size cuff for the limb.

a. Neonatal cuffs are marked with the size range

(Table 9.2).

b. When the cuff is wrapped around the limb, the

end of the cuff should line up with the range mark

(Fig. 9.1).

c. If the end of the cuff falls short of the range mark,

the cuff size is too small.

d. If the end of the cuff falls beyond the range mark,

the cuff size is too large.

3. Apply the cuff snugly to the bare limb, above the elbow

or knee joint.

Table 9.1 Sources of Error in Indirect Blood Pressure Measurements

Problem Effect on Blood Pressure Precaution

Defective manometer

1. Air leaks

2. Improper valve function

3. Dry, degraded or cracked tubing

4. Loss of mercury

Falsely low values 1. Check level of mercury at zero cuff pressure

2. Check for cleared definition of meniscus

3. Verify that pressure holds when tightened. Check

tubing for cracks

Inappropriate cuff size Verify appropriately sized cuff

1. Too narrow

2. Too wide

1. Falsely high values

2. Falsely low values

Cuff applied loosely Falsely high values owing to ballooning of bag and

narrowing of effective surface

Apply cuff snugly

Cuff applied too tightly Inaccurate reading owing to impedance of flow

through artery

Apply cuff snugly without undue pressure

Rapid deflation of cuff 1. Falsely low values owing to inaccurate detection

of beginning of sounds or

2. Falsely high values owing to inadequate equilibration

between cuff pressure and manometer pressure

Deflate cuff at rate of 2–3 mm Hg/s

Active or agitated patient Variable Recheck when patient is quiet

Table 9.2 Neonatal Cuff

Cuff No. (Size) Limb Circumference (cm)

1 3–6

2 4–8

3 6–11

4 7–13

5 8–15

From American Academy of Pediatrics Task Force Pressure Control: Report.

Pediatrics. 1977;59:797, with permission.

58 Section II ■ Physiologic Monitoring

4. Place the stethoscope or Doppler over the brachial

artery for the upper arm or above the popliteal artery for

the thigh.

5. Inflate the cuff rapidly to a pressure 15 mm Hg above

the point at which the brachial pulse disappears.

6. Deflate the cuff slowly.

7. The pressure at which a sound is first heard is the systolic

pressure (Korotkoff I). The pressure at which silence

begins corresponds to the diastolic pressure (Korotkoff V).

The pressure should be measured to the nearest 2 mm Hg.

In patients in whom the sounds do not disappear, the

point at which the sounds change abruptly to a muffled tone

can be accepted as an approximation of the diastolic pressure but will be slightly higher than true diastolic pressure.

H. Complications

1. Perfusion in the limb may be compromised if the cuff is

not completely deflated.