Pulse oximeters are now commonly included in the medical kits carried by CMC and are a useful adjunct to physical examination skills during clinical assessments. Physical findings like cyanosis and pallor are very difficult to assess in low-light operations and hypoxemia can easily be missed.

Normal pulse oximetry, or pulse ox, values are in the high 90s, unless at altitude, in which case they may be significantly lower. For example, a healthy person at 12,000 feet may have a pulse ox in the high 80s. This is an important point to remember during aeromedical evacuations when cabin altitudes may trigger a decrease in the pulse ox readings. Low saturation levels and trends to lower saturations can be indicative of respiratory compromise and should trigger further assessment to rule out life-threatening conditions.

There are several factors that can affect the pulse oximetry readings. Lowered readings can be caused by shock (where the poor perfusion affects the signal and causes a low reading) and cold temperatures (which cause peripheral vasoconstriction with a similar drop in perfusion). On the other hand, carboxyhemoglobin (seen in carbon monoxide poisoning) can cause a falsely elevated reading. And other conditions can interfere with the readings by altering the perceived intensity of the light signal, like very well-lit environments, nail polish, some skin pigmentations, and motion artifact.

Pulse ox monitoring should be initiated in casualties who are unconscious or who have injuries associated with impaired oxygenation (like blast injuries, chest contusion, and penetrating injuries of the chest). It should also be used to monitor casualties who have TBI, in order to ensure that their oxygen saturations remain above 90%, as hypoxemia will worsen their clinical outcomes.

Keep in mind that saturation levels may not signal impending shock, as good hemoglobin oxygen saturations may be seen in casualties shortly before they go into hypovolemic shock. Also, if a casualty has obvious signs of airway obstruction, tension pneumothorax, or hemorrhage, their treatment should not be delayed to establish pulse oximetry.