Oxygenation of hemoglobin
Most oxygen transported to the tissues is carried on the hemoglobin molecule. Hemoglobin travels through the blood in two
forms: oxyhemoglobin and reduced hemoglobin. Pulse oximetry measures oxygen saturation via light absorption of arterial hemoglobin
through pulsating blood vessels.
Oxygen saturation in an anesthetized dental patient should be maintained between 95 percent and 100 percent, particularly
if the animal is breathing 100-percent oxygen. Saturation readings of 90 percent or less indicate marked desaturation, hypovolemia,
shock or anemia. Possible causes include decreased oxygen flow rate, hypoventilation, diffusion impairment or shunt.
Figure 5: An anesthetized patient's oxygen saturation and heart rate.
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The pulse oximeter reading (Figure 5) denotes only the level of oxygen saturation and heart rate, which may be elevated when the patient hyperventilates in response
to discomfort. A hyperventilating patient also may inhale excessive anesthetic gas leading to hypovolemia. Unfortunately,
oximetry is an unreliable sentinel for hypovolemia, because pulse oximeters do not measure how forcefully the heart is beating.
A patient with an abnormal reading may have an underlying cause that should be determined and corrected by increasing the
flow rate of oxygen delivery and/or mechanically ventilating the patient until the concentration returns to normal. Moreover,
pulse oximetry results are unreliable if the animal has poor perfusion, irregular heart rhythm or anemia.
Because excessive pigmentation and hair usually preclude accurate readings on the pulse oximeter, one of the most effective
placements of the oximeter probe is on the tongue. However, dental procedures, by their nature, involve movement and instruments
in the mouth, which often dislodge the tongue oximeter probe. So other areas for probe placement include the pinna, toe, prepuce,
vulva, metacarpus (tarsus), digits and tail. Rectal probes also are available
Temperature
An anesthetized dental patient loses body heat to the environment because of the procedure's length, exposure to room air
conditioning and use of cold irrigation solutions. Small patients are at the greatest risk, due in large part to their smaller
body-surface-to-mass ratio. Some Nordic breeds (e.g., Samoyed, Siberian Husky, Alaskan Malamute) may become hyperthermic.
This is why temperature control and monitoring are important for dental patients.
Figure 6: Temperature readings for an anesthetized dental patient.
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As the patient's temperature decreases, so does the blood pressure and heart rate. Temperature monitoring (Figure 6) can be as straightforward as a technician inserting a rectal thermometer every 10 to 15 minutes and recording results. Most
multiparameter monitors allow for real-time constant digital evaluation.
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