Is it safe to use an adult pulse oximeter on an infant?

Using Adult Pulse Oximeters on Infants

Adult pulse oximeters can be used on infants when pediatric probes are unavailable, but expect significant measurement challenges including frequent signal failures, falsely low readings, and prolonged time to obtain readings—particularly in infants under 1 year of age. 1

Device Performance by Age and Weight

Infants Under 1 Year

• Adult fingertip oximeters fail to obtain readings in approximately 7.5% of attempts in young infants, with success rates improving modestly as age increases. 1
• Time to successful measurement shows a negative correlation with age, meaning younger infants require longer to obtain stable readings with adult devices. 1
• The smallest infants (under 30 kg, median age 2 months) present the greatest technical challenges for adult probes due to finger size mismatch. 1

Children Over 1 Year

• Adult fingertip oximeters perform quite well in larger children with relatively normal oxygen saturations (87-99% range), showing a mean difference of only -0.7% (SD 2.5%) from hospital-grade devices. 1
• The estimated root mean square error (EARMS) for adult devices in older children is 2.5%, which falls within acceptable clinical parameters. 1

Critical Technical Limitations

Probe Fit and Signal Detection

• Pulse oximeters require adequate detection of arterial pulsations to distinguish arterial from venous blood—this pulsatile signal is compromised when probe size doesn't match the measurement site. 2
• Probes that fall off easily lead to inaccurate measurements and false alarms, a particular problem when adult-sized probes are used on infant fingers. 3
• Poor perfusion of the extremity yields falsely low oxygen saturation readings, which is exacerbated by probe mismatch. 2

Accuracy Concerns in Hypoxemic Infants

• Pulse oximetry accuracy is particularly poor in the 76-90% saturation range, which is critically important for infants with respiratory distress or cyanotic heart disease. 3
• In neonates with critical congenital heart disease, pulse oximetry overestimates arterial oxyhemoglobin by a mean of 5.4%, with overestimation >3% in 65.4% of measurements and >10% in 15.3% of measurements. 4
• Standard pulse oximeters have inherent accuracy limitations of ±4-5% even under optimal conditions. 2

Clinical Decision-Making Framework

When Adult Oximeters Are Acceptable

• Use adult fingertip oximeters for children over 1 year old weighing ≥30 kg when oxygen saturations are expected to be relatively normal (>90%). 1
• For intermittent spot-checks in stable infants where trending is more important than absolute values. 2
• When pediatric probes are unavailable and clinical assessment suggests the infant is not critically hypoxemic. 3

When Adult Oximeters Are Inadequate

• Never rely solely on adult pulse oximeter readings in infants with suspected critical hypoxemia, respiratory distress, or cyanotic heart disease—clinical assessment must take priority. 3, 2
• Infants under 1 year old, particularly those under 6 months, where measurement failure rates are highest. 1
• When precise oxygen saturation values are needed for clinical decision-making (e.g., determining need for supplemental oxygen, assessing for critical congenital heart disease). 4

Practical Optimization Strategies

Improving Measurement Success

• Before accepting any reading, verify accuracy by repositioning the probe and repeating the measurement to ensure adequate surface contact. 2
• Actively warm the measurement site before and during measurement to improve peripheral perfusion. 2
• Ensure the infant's extremity is still and not moving, as motion artifact creates additional signal noise and invalid calculations. 2

Alternative Measurement Sites

• Consider using the infant's toe rather than finger if the adult probe provides better fit. 3
• If adequate signal cannot be obtained despite warming and repositioning, obtain arterial blood gas analysis for PaO2 measurement. 2

Understanding Normal Infant Physiology

Transient Desaturations Are Normal

• 60% of healthy infants between 2 weeks and 6 months exhibit transient oxygen desaturation below 90%, to values as low as 83%—this is a normal phenomenon. 3
• During sleep, healthy infants have mean SpO2 of 96.3% with desaturation episodes reaching a nadir of 86%. 3
• False reliance on pulse oximetry may lead to less careful monitoring of actual respiratory status. 3

Age-Specific Hypoxemia Definitions

• For infants under 1 year: hypoxemia is defined as spending 5% of time with SpO2 ≤90%, or three independent measurements ≤90%. 3
• For children 1 year and older: hypoxemia is defined as spending 5% of time with SpO2 ≤93%, or three independent measurements ≤93%. 3

Common Pitfalls to Avoid

Alarm Fatigue and Over-Reliance

• Alarm fatigue is recognized by The Joint Commission as a contributor to in-hospital morbidity and mortality—adult probes on infants generate excessive false alarms. 3
• One study found very poor documentation of hypoxemia alerts by pulse oximetry, indicating clinicians become desensitized to alarms. 3
• Continuous pulse oximetry in infants not requiring oxygen is associated with unnecessarily prolonged hospitalization and increased risk of minor adverse events. 3

Confounding Factors

• Dark skin pigmentation can systematically overestimate oxygen saturation, particularly problematic when combined with probe mismatch. 2
• Peripheral vasoconstriction, hypothermia, anemia, hypotension, and nail polish all adversely affect accuracy. 5
• The presence of intravascular dyes and changes in systemic vascular resistance compromise readings. 5

In summary: adult pulse oximeters can serve as a backup option for older infants and children when pediatric equipment is unavailable, but clinicians must recognize the substantial limitations in accuracy, reliability, and measurement success rates—particularly in infants under 1 year of age where clinical assessment should always supersede oximetry readings. 1, 3, 2