Uses of pulse oximetry

Simple, portable "all-in-one" monitor of oxygenation, pulse rate and rhythm regularity, suitable for "field" use.
As a safe, non-invasive monitor of the cardio-respiratory status of high-dependency patients - in the emergency department, during general and regional anaesthesia, postoperatively and in intensive care. This includes procedures such as endoscopy, where often frail patients are given sedative drugs such as midazolam. Pulse oximeters detect the presence of cyanosis more reliably than even the best doctors when using their clinical judgement.

During the transport of patients - especially when this is noisy - for example in aircraft, helicopters or ambulances. The audible tone and alarms may not be heard, but if a waveform can be seen together with an acceptable oxygen saturation, this gives a global indication of a patient's cardio-respiratory status.

To assess the viability of limbs after plastic and orthopaedic surgery and, for example, following vascular grafting, or where there is soft tissue swelling or aortic dissection. As a pulse oximeter requires a pulsatile signal under the sensor, it can detect whether a limb is getting a blood supply.

As a means of reducing the frequency of blood gas analysis in intensive care patients- especially in paediatric practice where vascular (arterial) access may be more difficult. To limit oxygen toxicity in premature neonates supplemental oxygen can be tapered to maintain an oxygen saturation of 90% - thus avoiding the damage to the lungs and retinas of neonates. Although pulse oximeters are calibrated for adult haemoglobin, HbA, the absorption spectra of HbA and HbF are almost identical over the range used in pulse oximetry, so the technique remains reliable in neonates.

During thoracic anaesthesia - when one lung is being collapsed down - to determine whether oxygenation via the remaining lung is adequate or whether increased concentrations of oxygen must be given.

Fetal oximetry- a developing technique that uses reflectance oximetry, using LEDs of 735nm and 900nm. The probe is placed over the temple or cheek of the fetus, and needs to be sterile and sterilisable. They are difficult to secure and the readings are variable, for physiological and technical reasons. Hence the trend is more useful than the absolute value.

1. Pulse oximeters give non-invasive estimation of the arterial haemoglobin oxygen saturation.
   
   
2. Useful in: anaesthesia, recovery, intensive care (including neonatal), patient transport. 2 principles involved:
   
   
3. Differential light absorption by haemoglobin and oxyhaemoglobin. Identification of pulsatile component of signal.
   
   No direct indication of a patient's ventilation, only of their oxygenation.
   
   
4. Lag monitor - time delay between potentially hypoxic event such as respiratory obstruction and a pulse oximeter detecting low oxygen saturation.
   
   
5. Inaccuracies: ambient light; shivering and vasoconstriction; abnormal haemoglobins; and alterations in pulse rate and rhythm.
   
   
6. Advances in microprocessor have led to improved signal processing.
   
   

Alternatives to pulse oximetry?

Bench CO-oximetry is the gold standard - and is the classic method by which a pulse oximeter is calibrated. The CO-oximeter calculates the actual concentrations of haemoglobin, deoxyhaemoglobin, carboxyhaemoglobin and methaemoglobin in the sample and hence calculates the actual oxygen saturation. CO-oximeters are much more accurate than pulse oximeters - to within 1%, but they give a 'snapshot' of oxygen saturation, are bulky, expensive and require constant maintenance as well as requiring a sample of arterial blood to be taken.

Blood gas analysis - requires an invasive sample of arterial blood. It gives the 'full picture', including arterial partial pressure of oxygen and carbon dioxide, arterial pH, actual and standardised base excess and actual and standardised bicarbonate concentrations. Many blood gas analysers report a calculated saturation which is less accurate than that provided by the pulse oximeter.

2P-Oximeter's new PULOX2000 is an accurate, light weight & affordable pulse oximeter designed for on-the-go spot checking of the saturation of hemoglobin with oxygen–available now.

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