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Advanced Trauma Life Support ATLS Student Course Manual 2018

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38<br />

CHAPTER 2 n Airway and Ventilatory Management<br />

Because changes in oxygenation occur rapidly and<br />

are impossible to detect clinically, pulse oximetry must<br />

be used at all times. It is invaluable when difficulties<br />

are anticipated in intubation or ventilation, including<br />

during transport of critically injured patients. Pulse<br />

oximetry is a noninvasive method of continuously<br />

measuring the oxygen saturation (O 2<br />

sat) of arterial<br />

blood. It does not measure the partial pressure of<br />

oxygen (PaO 2<br />

) and, depending on the position of the<br />

oxyhemoglobin dissociation curve, the PaO 2<br />

can vary<br />

widely (n TABLE 2-2). However, a measured saturation of<br />

95% or greater by pulse oximetry is strong corroborating<br />

evidence of adequate peripheral arterial oxygenation<br />

(PaO 2<br />

>70 mm Hg, or 9.3 kPa).<br />

Pulse oximetry requires intact peripheral perfusion<br />

and cannot distinguish oxyhemoglobin from carboxyhemoglobin<br />

or methemoglobin, which limits its<br />

usefulness in patients with severe vasoconstriction<br />

and those with carbon monoxide poisoning. Profound<br />

anemia (hemoglobin

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