How to assess pre and post ductal SpO2 during pre-anaesthesia checkup?

Assessment of Pre-ductal and Post-ductal SpO2 During Pre-anesthesia Checkup

During pre-anesthesia checkup, pre-ductal and post-ductal SpO2 should be measured with pulse oximeter probes placed on the right hand (pre-ductal) and either foot (post-ductal), with a normal value being ≥95% in both measurements. 1

Technique for Measurement

• Place a pulse oximeter probe on the right hand or right upper limb (pre-ductal measurement) and another probe on either foot (post-ductal measurement) 1, 2
• Ensure proper probe placement with good contact and adequate perfusion to avoid false readings 3
• Allow sufficient time for readings to stabilize and record both values 2
• Document baseline values in the pre-anesthesia record for reference during and after the procedure 1

Normal Values and Interpretation

• The lower limit of acceptable oxygen saturation should be ≥95% in both pre-ductal and post-ductal measurements 1
• A difference of >3% between pre-ductal and post-ductal measurements may indicate right-to-left shunting through a patent ductus arteriosus, suggesting possible congenital heart disease 1, 4
• In healthy newborns, it may take 12-14 minutes after birth to reach SpO2 of 95% (pre-ductal and post-ductal respectively), with some taking up to 55 minutes 2

Factors Affecting SpO2 Readings

• Peripheral vasoconstriction can lead to inaccurate readings, especially in the extremities 3, 5
• Anemia can affect the accuracy of pulse oximetry readings 5
• Dark skin tone and skin discoloration may impact readings 5
• Irregular breathing patterns can cause technical issues with SpO2 monitoring 6
• Changes in blood flow can significantly affect the accuracy of pulse oximetry 3

Special Considerations

• For patients with sickle cell disease, document baseline oxygen saturation pre-operatively as these patients may have lower baseline values 1
• For patients with Duchenne muscular dystrophy, SpO2 should be measured in room air, and if SpO2 is ≤95%, measurement of blood and/or end-tidal carbon dioxide level should be performed 1
• For patients at risk of hypercapnic respiratory failure, be aware that the target SpO2 range should be 88-92% rather than 94-98% 7, 6
• Position the patient appropriately during measurement - a semi-sitting position with head elevated at 25-30° may provide more accurate readings, especially in obese patients 1, 6

Clinical Implications

• SpO2 level less than 90% should be considered a clinical emergency 5
• If SpO2 level is below 94%, assume the patient is hypoxic until proven otherwise 5
• For patients with SpO2 below 85% (not at risk of hypercapnic failure), be prepared to administer oxygen via reservoir mask at 15 L/min 7, 6
• Significant differences between pre-ductal and post-ductal measurements may indicate congenital heart disease requiring further evaluation 1, 4

Documentation Requirements

• Record both pre-ductal and post-ductal SpO2 values 1
• Document the patient's position during measurement 1
• Note any supplemental oxygen being administered 1
• Record any significant difference between pre-ductal and post-ductal measurements 1