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Pre‐procedural considerations

Equipment

Pulse oximeter

A pulse oximeter is a device that measures the amount of haemoglobin saturation in the tissue capillaries (Blows [21]). The probe consists of two light‐emitting diodes (one red and one infra‐red) on one side of the probe and a photo detector on the other side (Appadu and Lin [6]). The device projects light through the tissue to the detector and measures absorption in pulsatile blood by saturated haemoglobin (visible red) and desaturated haemoglobin (infra‐red wavelength) (Appadu and Lin [6]). This is translated by the receiver into a percentage of oxygen saturation of the blood, symbolized as SpO₂.

In order to achieve a successful reading, the sensor of the pulse oximeter should be placed on an appropriate site with an adequate pulsating vascular bed (the probe must be designed for use on the chosen site) (Blows [21]). Therefore, the sensor may be attached to the patient's fingers (most common), ears, toes or nose (Goodell [71], Johnson et al. [89]).

Pulse oximeters are vital in all areas where oxygen is administered and form part of any acute medical department's essential equipment (O'Driscoll et al. [147]). They should be checked, calibrated, maintained and stored as per the manufacturer's recommendations to ensure accurate and reliable results (Peate and Wild [157]).

Specific patient preparation

Appropriate positioning of the patient can help to ease any respiratory distress and facilitate the assessment and observation of their breathing (Cleave [45]). The patient should have rested and not have engaged in any strenuous physical activity prior to the assessment (Bickley [18]). If this is not contraindicated, the patient should be positioned upright or lying in bed with the head section elevated to an angle of 45–60° to allow good lung expansion; pillows can help to support the patient in this position (Peate and Wild [157]). With the patient's consent (RCN [169]), it may be useful to remove clothing from their thorax to aid with observation of breathing (Bickley [18]). Positioning can also help to relax the patient and therefore potentially reduce the distress resulting from breathlessness (Adam et al. [2]).

The patient should give their consent to the assessment and remain still while pulse oximetry is being performed so that an accurate result can be obtained (Blows [21]). As mentioned previously, non‐invasive blood pressure measurement should not be performed while pulse oximetry recording is underway, and nail polish should be removed from the probe site (Peate and Wild [157]).

Procedure guideline 14.4

Respiratory assessment and pulse oximetry

Table 14.7 Prevention and resolution (Procedure guideline 14.4)

Problem	Cause	Prevention	Action
Unable to turn on the pulse oximeter	Low battery	Ensure the pulse oximeter is left on continuous charge when not in use.	Connect the pulse oximeter to mains electricity. It should function once it is connected to a power supply.
The pulse oximeter is working but the heart rate and saturations display is blank	Loose connection	Carefully store the cables after use to prevent damage.	Check that the probe is securely connected to the machine.
Poor trace or inconsistent reading	Movement from shivering, seizures or tremors can affect the accuracy of the reading ( Blows [21])	Encourage the patient to keep as still as possible. If still unable to obtain an accurate reading, try to use a site that is less affected by movement, for example an ear lobe.	If the finger has been used, compare the pulse rate as given by the oximeter with the palpated radial pulse. If there is a difference then the oxygen saturation reading will not be accurate and arterial blood gases may be required to monitor the patient's oxygen saturation, if accurate pulse oximetry cannot be obtained from an alternative site ( Adam et al. [2]).
Unexpectedly low result that does not correlate with the patient's clinical condition	The site chosen may not have an adequate blood supply	Check for perfusion by palpating for a pulse and checking the area is warm, with good capillary refill.	Reposition the sensor on a new site. If the result remains low, arterial blood gases may need to be considered ( Adam et al. [2]).
Pulse oximetry heart rate does not correlate with palpated pulse	Not all pulsations are being detected	Check for perfusion by palpating for a pulse and checking the area is warm, with good capillary refill.	Obtain a replacement probe and/or monitor ( Peate and Wild [157]).