important that type-specific alarm limits are set (16).

 To avoid hyperoxemia, a minimal sensitivity of at

least 95% is required.

10. Pulse oximeters rely on detecting pulsatile flow in body

tissues; therefore, a reduction in peripheral pulsatile

blood flow produced by peripheral vasoconstriction

results in an inadequate signal for analysis.

11. Pulse oximeters average their readings over several seconds depending on oximeter type and internal settings.

Oximeters with a long averaging time may not be able

to detect acute and transient changes in SpO2.

12. Venous congestion may produce venous pulsations,

which can produce low readings.

13. The pulse oximeter only provides information about

oxygenation. It does not give any indication of the

patient’s carbon dioxide elimination.

In summary, it is optimal to make some correlation

between SpO2 and PaO2 throughout a reasonable range of

SpO2 (lower, 85% to 88%; higher, 95% to 97%) before relying completely on SpO2 for oxygen and/or respirator management (14,16).

E. Equipment

1. Manufacturer-specific sensor and monitor (Fig. 10.5) with

a. Display of SpO2 and pulse rate and a pulse indicator

b. Adjustable alarm limits for SpO2 and pulse rate

c. Battery-powered operation

2. Neonatal sensor, either disposable or reusable

a. Disposable sensors have become the standard for

infection and quality control.

68 Section II ■ Physiologic Monitoring

b. Disposable neonatal sensors are available in different sizes, depending on the site to be used.

F. Precautions

1. Use only with detectable pulse.

 Cardiopulmonary bypass with nonpulsating flow,

inflated blood pressure cuff proximal to the sensor,

tense peripheral edema, hypothermia, low-perfusion

state secondary to shock or severe hypovolemia, and significant peripheral vasoconstriction may interfere with

obtaining accurate readings (9)

2. Assess the sensor site every 8 hours to be certain that the

adherent bandage is not constricting the site and that

the skin is intact.

3. Whenever possible, the SpO2 sensor should not be on

the same extremity as the blood pressure cuff.

 When the cuff is inflated, the SpO2 sensor will not

detect a pulse, will not update SpO2 values, and will

alarm. Use of ace bandages on the extremities to

increase central venous return may also interfere with

the function of the sensor.

4. Malpositioned sensor: When a probe is not placed symmetrically, it can allow some light from the LED emitters to reach the photodetector in the sensor without

going through the tissue at the monitoring site and will

therefore produce falsely low readings. This is called

the penumbra effect.

5. To avoid possible transfer of infection, do not share

pulse oximetry probes between patients.

G. Technique

1. Familiarize yourself with the system before proceeding.

2. Select an appropriate sensor and apply it to the patient.

a. Finger, toe, lateral side of the foot, or across the

palm of the hand. (Placing the sensor in a position

matching that of the peripheral arterial line, if present, may avoid discrepancies caused by intracardiac

or ductal shunts when trying to correlate SpO2 with

arterial PO2.)

b. For neonates 500 g to 3 kg, anter