Engineering education in health care technology and industry

1. Basic
Intensive
Care Unit
Equipment
(MT 6204)
TUTOR: ERICK KANYIKI (BMET)
MUST_2022

2. PULSE
OXIMETER

3. CONTENTS
▪ Introduction
▪ Meaning of pulse oximeter
▪ Uses of pulse oximeter
▪ Construction of pulse oximeter
▪ Parts of pulse oximeter
▪ Working principle of pulse oximeter
▪ Errors in pulse oximeter
▪ Planned Preventive Maintenance (PPM)
▪ Troubleshooting and repair of pulse oximeter

5. INTRODUCTION

6.  HEMOGLOBIN(Hb)
• Hemoglobin is a protein in red blood cells that contains a compound
known as heme, which in turn contains iron, which is what transports
oxygen in the bloodstream
• Hemoglobin transports oxygen from lungs to the rest of the body
where it releases oxygen for the cell use.
• Assessment of oxygen saturation is necessary in clinical management
of patients in all hospital settings

7. MEANING

8.  PULSE OXIMETER
• Is a device used to measure oxygen saturation (SpO2) in the body, i.e.
How much hemoglobin in the blood is carrying oxygen.
• (SpO2)- Saturation of Peripheral Oxygen: is a measure of the
percentage of hemoglobin saturated with oxygen.
• The pulse oximeter measures oxygen saturation non invasively.

9. Types of pulse oximeters
• Fixed pulse oximeter (as a part of anesthesia machine)
• Hand held pulse oximeter (portable)
• Finger clip oximeter

11. USES

12. ▪ Helps to determine the severity of illness by evaluating if (SpO2) is
low and if respiratory support is needed.
▪ To assess the success of treatment and determine a need for decreasing
respiratory interventions to achieve target SpO2.
▪ Continuous reading of patient vital signs undergoing surgical
procedures under general anesthesia
▪ Continuous reading of patient vital signs undergoing surgical
procedures under conscious sedation
▪ After surgery during recovery period

13. CONSTRUCTION

14. ***SELF READ ON THIS***
Pulse oximeter is constructed based on two laws:
 BEER’S LAW
 LAMBERT’S LAW

15. PARTS

18. ▪ LCD
• A typical pulse oximeter displays the oxygen saturation, heart rate and
the waveform of measured pulses. Some additional features may
include battery power, alarms and visible/ audible warning lights and
indicators.
 PROBE
• The probe is made up of a sensor, cable and attachment head and is the
first point of failure for most pulse oximeters.

19. • The pulse oximeter probe sensor has two main components: a
photodiode and a pair of LEDs that emit red and infrared light
(typically in wavelengths of 660 nm and 940 nm, respectively).
• A photodiode is a light-sensitive semiconductor diode. It produces
current when it absorbs photons

20. • These components may be arranged with the LEDs and photodetector
arranged opposite to each other, with the body measurement site in
between
• OR with the LEDs and photodetector arranged next to each other,
along the body. In this, the photodetector collects light signals bounced
back from the body tissue. When attached to the peripheral tissue (ear,
finger or foot), oxyhemoglobin partially absorbs the infrared light (at a
940 nm wavelength) and deoxyhemoglobin (venous and capillary)
absorbs red light (at a 660nm wavelength).
• The non-absorbed transmitted or reflected light signals are then
detected by the photo detector.

21. ▪ CONTROL CIRCUIT BOARD
• Located internally, the control circuit board mainly consists of memory
circuits, multiplexers, current to voltage converters, filters and a
microprocessor.
• The control PCB identifies and isolates the absorbance of the pulsatile
fraction of arterial blood component light signals from the absorbance
due to non-pulsatile light signals from capillary blood. These signals
then undergo amplification, filtration and artefacts rejection. The
microprocessor determines the percent of oxygen in the blood by
comparing the concentration of oxyhemoglobin to deoxyhemoglobin at
two different light wavelengths using the formula below.

23. Question
• Why we use two types of lights in pulse oximeter

24. WORKING PRINCIPLE

25. • Oxygen is carried in the bloodstream by binding to hemoglobin in red
blood cells. Each hemoglobin can carry four oxygen molecules and at
that point becomes 100% saturated. The colour of blood depends on how
much hemoglobin is saturated with oxygen. Hemoglobin that is carrying
oxygen (oxyhemoglobin) and appears bright red, while deoxygenated
hemoglobin (deoxyhaemoglobin) appears dark red
• A probe consisting of a red LED, an infrared LED, and a photodetector.
• A timing control circuit sequences the LEDs and synchronize them with
the photodetector. There are three phases in one timing cycle: Red “on”
and IR “off,” Red “off” and IR “on,” and both LEDs “off.” The latter is
to measure the dark signal to eliminate the effects of the ambient light.

26. • Analog and digital electronics amplifies and process the signal
• A processor computes the transmitted red and infrared light intensity
ratio and match the %SaO2 from the lookup table. It can also derive
the heart rate from the pulsating waveform and compares the measured
values (heart rate, %SaO2) to the alarm settings
• A display shows the %SaO2 values, the alarm limits, and the heart rate.

28. ERRORS

29. Poor perfusion
• A patient suffering from poor perfusion usually has lower than normal
blood pressure. A lack of blood in the capillaries will decrease the
signal to noise ratio and therefore increase the error of the
measurement.
Excessive signal attenuation
• Patients with dark skin pigment or too thick tissue (e.g., skin) at the
measurement site will decrease the signal penetration (decrease the
detector signal level) and increase measurement error.

30. External interference
• Ambient light can introduce errors in measurement. There were
reported incidents that flashing light and fluorescent light sources were
misinterpreted by machines as pulsating red or IR signals. To avoid
external light interference, pulse oximeter probes are usually designed
with a cover to block external light from reaching the sensor.
Motion
• Motion will cause changes in the optical path length, which will
produce measurement errors

31. Substances in blood
• Some substances in the bloodstream may affect the absorption of the
light sources. A high level of dyshemoglobin in carbon monoxide
poisoning, low hematocrit counts of an anemic patient, and artificial
dyes in a patient’s blood can all affect the accuracy of the
measurement.