In the emergency department I had partial toe numbness; the physician said perfusion was normal despite a stroke volume index of 23.69 mL/m² and pulse‑oximeter saturations of 99‑100 % on both finger and big toe. Is this physiologically plausible?

Is This Scenario Physiologically Plausible?

Yes, this scenario is entirely plausible and represents a common clinical situation where peripheral numbness occurs despite adequate arterial perfusion and oxygen saturation. Your stroke volume index of 23.69 mL/m² is significantly low (normal range 33-47 mL/m²), but pulse oximetry readings of 99-100% on both finger and toe accurately reflect arterial oxygen saturation, not perfusion adequacy.

Understanding the Disconnect Between Symptoms and Measurements

Pulse Oximetry Measures Oxygenation, Not Perfusion

• Pulse oximetry measures the percentage of hemoglobin saturated with oxygen in arterial blood, not the volume or adequacy of blood flow to tissues 1
• Even with reduced cardiac output or stroke volume, as long as the blood reaching the extremity is well-oxygenated, pulse oximetry will read 99-100% 2
• The device requires only minimal pulsatile flow to generate a reading—it does not quantify perfusion adequacy 3, 4

Low Stroke Volume Index Does Not Preclude Normal Oxygen Saturation

• Your SVI of 23.69 mL/m² indicates reduced cardiac output per heartbeat, but this doesn't necessarily mean tissue hypoxia if compensatory mechanisms (increased heart rate, peripheral vasoconstriction) maintain oxygen delivery 1
• Pulse oximetry can remain accurate even in patients with abnormal cardiac index, though it may overestimate saturation by up to 7% in some cases with severely abnormal hemodynamics 2

Why Toe Numbness Can Occur with Normal Pulse Oximetry

Multiple Non-Ischemic Causes of Numbness

• Peripheral neuropathy (diabetic, metabolic, or other causes) is the most common reason for toe numbness with normal perfusion 1, 5
• Nerve compression or radiculopathy can cause sensory changes without affecting arterial flow 5
• Metabolic disturbances or electrolyte abnormalities may cause paresthesias independent of perfusion 1

Clinical Assessment of Perfusion

• The physician's assessment of "normal perfusion" likely included:
  • Palpable pedal pulses (dorsalis pedis and posterior tibial) 1, 5
  • Normal capillary refill time
  • Absence of dependent rubor, elevation pallor, or trophic skin changes 1, 5
  • Warm skin temperature
• The presence of palpable foot pulses does not completely rule out peripheral artery disease, but makes significant flow-limiting stenosis less likely 1

Limitations of Pulse Oximetry in Assessing Perfusion

What Pulse Oximetry Cannot Tell You

• Pulse oximetry provides no information about tissue perfusion adequacy, blood flow volume, or oxygen delivery to tissues 1, 3
• It cannot detect early circulatory compromise if arterial oxygen content remains normal 1
• Low perfusion states may affect signal quality but can still yield accurate saturation readings if a signal is obtained 3, 4

When Additional Testing Is Needed

If there were genuine concern about arterial perfusion to your toes, appropriate testing would include 1, 5:

• Ankle-brachial index (ABI) as the initial diagnostic test for peripheral artery disease 1, 5
• Toe-brachial index (TBI) if ABI is >1.40 (suggesting noncompressible vessels from calcification) or if clinical suspicion remains high 1, 5
• Toe pressures with a threshold of <30 mmHg suggesting impaired perfusion 1
• Doppler waveform analysis to assess arterial flow patterns 1

Clinical Bottom Line

The physician's demonstration with toe pulse oximetry was appropriate to show you that arterial oxygen saturation was normal, but this does not comprehensively assess perfusion. The combination of normal pulse oximetry, clinical examination findings suggesting adequate perfusion, and your symptom of numbness (rather than pain, coldness, or tissue breakdown) makes a non-vascular cause most likely 1, 5. Your low stroke volume index is concerning from a cardiac standpoint but does not contradict the local assessment of adequate toe perfusion 1.

Common Pitfall to Avoid

• Do not equate normal pulse oximetry with normal tissue perfusion—they measure different physiological parameters 1, 3
• If symptoms progress to include pain, color changes, temperature changes, or tissue breakdown, formal vascular assessment with ABI/TBI would be indicated 1, 5