Pulse oximeter

PULSEOXIMETRY- OPERATING PRINCIPLE-ADVANTAGES AND DISADVANTAGES

1. PULSE OXIMETRY NIRESH DEPARTMENT OF ANAESTHESIOLOGY KG HOSPITAL AND POST GRADUATE MEDICAL INSTITUTE

2. INTRODUCTION OPERATING PRINCIPLES PHYSIOLOGY OXIMETER STANDARDS USE SITE FIXATION STABILISING AND REUSING DISPOSABLE PROBES TESTING APPLICATIONS ADVANTAGES LIMITATIONS & DISADVANTAGES PATIENT COMPLICATIONS CARBON MONOXIDE POISONING

3. INTRODUCTION Pulse oximetry, sometimes called as the fifth vital sign is a non-invasive method of measuring haemoglobin saturation by using a light transmitted through tissue. A low SpO2 can provide warning of hypoxemia before other signs such as cyanosis or other change in heart rate.

4. The ASA and American Association of nurse anaesthetists have made assessment of oxygenation a standard for intra-op and post-op monitoring .

5. OPERATING PRINCIPLES TRANSMISSION PULSE OXIMETRY REFLECTANCE PULSEOXIMETRY

6. OPERATING PRINCIPLES Pulse oximetry consists of Red(R) and a Infrared (IR) light emitting LEDs and a photo detector. Oxygenated and deoxygenated haemoglobin have a different light absorption rate. Oxygenated haemoglobin absorbs more infrared light Deoxygenated haemoglobin absorbs more of red light

7. TRANSMISSION PULSE OXIMETRY The most commonly used is transmission pulse oximetry A light beam is transmitted through a vascular bed and is detected on the opposite side of the bed.

8. REFLECTANCE PULSE OXIMETERY This relies on the light that is reflected to determine oxygen saturation. The probe has both LED and a Diode. The tissue must be well perfused to obtain a strong signal. LIMITATIONS Vasoconstriction can cause over estimation of oxygen satruation level The probe design must eliminate light that is passed directly to the probe or is scattered in the outer surface of the skin.

9. EQUIPMENT The probe ( sensor,transducer ) is a part that comes in contact with the patient. It contains one or more LEDs that emit light at specific wavelengths and a photo detector. The light partially absorbed and modulated as it passes through the tissue is converted into an electronic signal by the photo detector.

10. Types of probes Probes may be reusable or disposable. Reusable probes are either clip-on or attached by using a Velcro Disposable probes are attached by using a adhesive. CABLE the probe is connected by the means of an electric cable. Cables from different manufactures are not interchangeable. CONSOLE Most of the oximeters used in operating rooms are a part of physiologic monitor. The panel usually displays percent saturation, pulse rate, and alarm limits.

11. Most instruments provide an audible tone whose pitch changes with the saturation. In this way we can be aware of the changes in SpO2. ASA standards for basic anaesthetic monitoring require that the variable pitch pulse tone and low threshold alarm be audible.

12. OXIMETER STANDARDS There must be a means to limit the duration of the contionous operation at the temperature above 41^C. If manufacturer claims certain things – the test methods used must be disclosed in the instructions of use. The accuracy must be stated over the range of 70%-100% of SpO2. If manufacturer claims Accuracy during motion If the manufacturer claims accuracy during conditions of low perfusion Alarm limits An indication of signal inadequacy must be provided if SpO2 or PR value displayed is potentially incorrect Variable tone pitch

13. DISPOSABLE OXIMETERS NASAL OXIMETERS

14. FOOT PULSE OXIMETERS REUSABLE OXIMETERS

15. STABILISING THE SIGNAL The search goes through when a pulse oximeter is initially applied. Once a pulse is found, there is usually a delay of few seconds while the SpO2 values for several pulses are averaged. Appearance of a satisfactory waveform is an indication that the readings are reliable. Comparison of the SpO2 PR and ECG is an indication that saturation readings are reliable.

16. APPLICATIONS MONITORING OXYGENATION Anaesthetizing areas – Desaturation can occur at anytime during anaesthesia. Pediatric patients are especially risk. Most severe desaturation occur during induction or emergence. pulse oximetry helps to detect inadvertent bronchial intubation. Oximetry is useful in managing one-lung anaesthesia, for patients undergoing regional and MAC. Problems that can cause a drop in oxygen saturation are fat embolism, amniotic fluid embolism, pulmonary edema , breathing system disconnection and leaks, aspiration, tracheal tube obstruction, O2 delivery failure, bronchospasm, pneumothorax, malignant hyperthermia.

17. PACU – another location where desaturation is common. TRANSPORT – unrecognized desaturation may occur while the patient is being transported. Portable pulse oximeters can be used. OTHER AREAS – patients frequently experience hypoxic episodes in post-op period after leaving PACU. Useful in ICU and helpful during weaning from artificial ventilation. More useful in cardio-pulmonary resuscitation. More useful in primary respiratory arrest

18. CONTROLLING OXYGEN ADMISTRATION MONITORING PERIPHERAL CIRCULATION DETERMINING SYSTOLIC BLOOD PRESSURE. LOCATING ARTERIES AVOIDING HYPEROXEMIA. MONITORING VASCULAR VOLUME AND SYMPATHETIC TONE OTHER USES- High frequency jet ventilation, effectiveness of therapeutic bronchoscopy.

19. ADVANTAGES ACCURACY INDEPENDENCE FROM GASES AND VAPOURS- Readings are not affected by anaesthetic gases NON-INVASIVE CONTIONOUS MEASUREMENTS SEPARATE RESPIRATORY AND CIRCULATORY VARIABLES CONVINIENCE FAST START TIME. TONE MODULATION USER FRIENDLY LIGHT-WEIGHT & COMPACTNESS PROBE VARIETY

20. LIMITATIONS AND DISADVANTAGES FAILURE TO DETERMINE OXYGEN SATURATION POOR FUNCTION WITH POOR PERFUSION DELAYED HYPOXIC EVENT DETECTION ERRACTIC PERFORMANCE WITH DYSRHYTHMIAS

21. INACCURACY Different hemoglobins Bilirubinemia Low saturations – dark skin, cyanotic heart disease Mal positioned probe Venous pulsations Mixing probes- one manufacturers probe used with another manufacturers instrument. Severe anemia Skin pigmentation Dyes Optical interference Nail polish and covering Pressure on probe Hyperemia False alarms

22. FAILURE TO DETECT HYPO-VENTILATION - Hypoventilation and hypercarbia may occur without a decrease in hemoglobin oxygen saturation, especially if the patient is receiving supplemental oxygen. PROBLEMS WITH SOUND RECOGNTION LACK OF USER KNOWLEDGE.

23. OXYGEN DESATURATION Saturation is defined as ratio of oxygen content to oxygen capacity of haemoglobin expressed as a percentage. Desaturation leads to hypoxemia – a relative deficiency of oxygen in arterial blood. Oxygen saturation will not decrease until PaO2 is below 85mmhg SaO2 <than 76% is life threatening.

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