A pediatric patient with profound anemia may have a normal oxygen saturation level and still be hypoxemic.
Pulse oximetry provides a noninvasive, accurate estimate of arterial oxygen saturation. Hemoglobin (Hgb) saturated with oxygen absorbs light differently than unsaturated Hgb, and the pulse oximeter measures the amount of absorption and uses it in the calculation of the ratio of saturated Hgb to total Hgb (Figure 1). The pulse oximeter monitor displays the ratio as a percentage.
The patient's oxygenation status depends on the amount of Hgb and on how well it moves throughout the body and how easily oxygen leaves the Hgb and enters the cells. Normal pulse oximetry values vary by age and condition. The generally accepted range is more than 94% unless the patient has anemia.undefined#ref3">3 Probes come in infant, pediatric, and adult sizes. Clip-on probes are primarily used for spot checks, and circumferential tape probes are primarily used for continuous monitoring (Figure 2).
Inaccurate readings can occur in these patients:1
The dynamics of the oxyhemoglobin dissociation curve (ODC) include (Figure 3):
Pulse oximetry readings are altered by:1
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Rationale: Site selection can affect the accuracy of pulse oximeter readings. For instance, in pediatric patients with cyanotic heart disease, a preductal saturation can be obtained in the right arm, and a postductal saturation may be obtained in the left arm or in either foot.
Avoid sites distal to arterial lines and noninvasive blood pressure cuffs and sites on the same side as a Blalock-Taussig shunt.
Rationale: For accurate saturation measurement, the light source and the photodetector must be directly opposite each other.
Do not apply the probe so tightly that it interrupts blood flow to or from the site. Tissue perfusion can be impaired by circumferential restriction of arterial flow. Venous return and venous congestion may lead to venous pulsations and false readings.
Plug portable pulse oximeters into an electrical outlet to keep the battery charged.
For spot-checking saturations, allow the oximeter several minutes to average and obtain a reliable saturation reading.
Rationale: Setting the appropriate alarm parameters decreases the number of false alarms.
Rationale: Correlating the reading with the patient’s heart rate ensures the accuracy of the pulse oximeter value. The patient’s measured electrocardiogram or palpated heart rate should match the heart rate displayed by the pulse oximeter.
If the oximeter displays the pulse wave graphically, the pulse waveform should resemble an arterial waveform without a dicrotic notch. If the pulsatile flow past the probe is sluggish, the waveform may be dampened, and the reading may be incorrect.
At the completion of the procedure, ensure that all choking hazards (e.g., probe wrappers) are removed from the patient’s linens and placed in the appropriate receptacle.
Rationale: Pulse oximetry provides only one piece of information. The patient's physiologic status must be considered to gain a complete understanding of the patient's condition.
Reportable conditions: Hypoxia, including decreased level of consciousness; tachypnea and tachycardia; increased work of breathing; cyanosis; decreased oxygen saturation level
Rationale: Skin probes can cause skin injury. Certain conditions, such as low perfusion states, norepinephrine and other vasoconstrictive infusions, hypoxia, hypotension, prolonged probe contact, and hypothermia, can increase the likelihood of injury.
Reportable conditions: Skin discoloration, decreased capillary refill time, skin breakdown at or distal to the probe site
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