Finger pulse oximetry is a standard method of monitoring oxygenation due to its ease of use, widespread availability, and non-invasive nature. However, in certain clinical settings, finger pulse oximetry may be inaccurate, inappropriate, or insufficient. Compromised peripheral perfusion can lead to inaccurate readings, whether due to peripheral vascular disease, shock, hypothermia, or vasoconstriction1–3. In other clinical settings, the fingertip may be unavailable due to trauma or amputation, among other factors. Finally, providers may simply require more information than a finger pulse oximeter can provide. It is also important to note that patient-specific factors such as skin pigmentation and nail polish can affect pulse oximetry readings4. Therefore, clinicians must be aware of alternatives approaches to oxygenation monitoring other than traditional finger pulse oximetry.
When the finger cannot provide clear information on the patient’s oxygenation status, clinicians have a wide range of alternative superficial sites available to them for pulse oximetry. These include the toe, earlobe, and forehead5. Other sites have recently been explored for use in hypoperfusion. The nasal septum2, ear canal6, and penile shaft7 have been demonstrated to be viable alternatives in preliminary studies.
When exploring alternative sites for probe placement, it is important to be aware of the different technologies available. Pulse oximeters typically function by emitting a beam of light that passes through tissue and toward a sensor on the other side (called transmission pulse oximetry). However, certain devices can function through a technique called reflectance pulse oximetry. In this method, a sensor is placed adjacent to the device’s light source, allowing the oximeter to measure beams of light that are reflected rather than transmitted through tissue8. Transmission pulse oximetry works well for thin structures like the fingertip or earlobes. Unfortunately, these sites are vulnerable to inaccurate readings in hypoperfusing states. In this case, reflectance pulse oximetry can be used on more central sites that are too thick for transmission pulse oximetry like the wrist, upper arm9, chest, or forehead.
Another technology which can be used to measure oxygenation is Near Infrared Spectroscopy (NIRS), which measures the oxygen saturation of hemoglobin in the specific tissue region in which the NIRS probes are placed. NIRS has been used most extensively in cardiac surgery for perioperative monitoring of cerebral oxygenation but continues to gain traction in other fields10. Unlike traditional pulse oximetry, NIRS provides information about local tissue oxygenation rather than a global measure of oxygenation; it also measures both venous and arterial oxygenation simultaneously, leading to lower readings than are seen in pulse oximetry.
Clinicians may also consider invasive alternatives to finger pulse oximetry for measuring oxygenation. Arterial blood gas (ABG) analysis provides a reliable assessment of oxygenation and may be helpful in confirming the accuracy of finger pulse oximetry. Mixed venous oxygen saturation and central venous oxygen saturation also allow for invasive monitoring of oxygenation11,12; they are particularly useful in gaining an insight into tissue oxygen delivery and consumption.
Altogether, clinicians have a wide range of alternatives to finger pulse oximetry for monitoring oxygenation. By considering alternative probe sites, embracing new technologies, and integrating data from multiple sources, it is possible to gain a confident assessment of oxygenation status for many patients.
References
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