The document discusses pulse oximetry and capnography, emphasizing their importance in non-invasive monitoring of oxygen saturation and carbon dioxide levels, respectively. It outlines the principles and technology behind pulse oximeters and capnometers, including their applications in anesthesia and critical care, as well as common limitations and alternatives to these monitoring methods. The text also highlights the significance of integrating both techniques to enhance patient safety and reduce anesthesia-related mishaps.

1. PULSE OXIMETRY
&
CAPNOGRAPHY
Chairperson:DR H V Airani
Moderator:DR Dharanish
Presenter:DR Dharmaraj

2. Pulse oximetry sometimes also called as fifth vital sign.
It is a non-invasive method of measuring haemoglobin
saturation with light signal transmitted through the tissue.
Until 1980s, large, cumbersome and expensive ear oximeters
were used.
Limitation of such oximeters included difficulty in
differentiating light absorbance of arterial blood (pulsatile
component) from venous blood and tissues (static component).
INTRODUCTION

3. Pulse oximeters are available as
• Stand alone devices
• Incorporated into multiparameter
monitors
Technical advances- LEDs, photodetectors and microprocessors-
used to make small, less expensive and easy-to-use oximeters.
These differentiate light absorbance of pulsatile arterial
component from static components, hence called Pulse
Oximeters.

4. Pulse oximetry works on the principle of spectral analysis for
measurement of oxygen saturation, i.e. the detection and
quantification of components in solution by their unique light
absorption characteristics.
Pulse oximeters combine the principle of spectrophotometry and
plethysmography to noninvasively measure the oxygen saturation
in arterial blood.
OPERATING PRINCIPLE

5. PLETHYSMOGRAPHY

6. SPECTROPHOTOMETRY

7. Beer-Lambert law
It states that if a light of known intensity illuminates a chamber of
known dimension, then the concentration of the dissolved substance
can be determined if the incident and transmitted light are measured.
It = Ii e –dCα
Solved for C,
C= (1/dα) ln(Ii/It )
Where,
It - intensity of transmitted light
Ii- intensity of incident light
α - absorption
d- distance the light travels through the
liquid
C- concentration of hemoglobin
e- extinction coefficient of the solute (a
constant for a given solute at a specified
wavelength). It is a measure of tendency of a
substance to absorb light.

8. Beer-Lambert law
Beer's law
Intensity of transmitted light
decreases exponentially as the
concentration of the substance
increases.
Lambert's law
Intensity of transmitted light
decreases exponentially as the
distance travelled through the
substance increases.

9. AC component, represents absorption of light by the pulsating
arterial blood.
DC (baseline) component represents absorption of light by the tissue bed,
including venous, capillary, and nonpulsatile arterial blood.
R = (AC 660 / DC 660) / (AC 940/DC 940)

10. EXTINCTION COEFFICIENT:
It is a measure of tendency of a substance to absorb light.
Adult blood usually contains four types of hemoglobin:
• Oxyhemoglobin (O2hb)
• Reduced hemoglobin (rhb)
• Methemoglobin (methb)
• Carboxyhemoglobin (CO Hb)
Fractional Hb saturation (O2Hb%) is defined as the ratio of oxyhaemoglobin
to total haemoglobin species present.
O2Hb%= HbO2/ (HbO2 + Hb + metHb + COHb) *100
Functional saturation (SaO2) is defined as the ratio of oxyhaemoglobin to
reduced haemoglobin
SaO2 = HbO2/ (HbO2 + Hb ) *100

12. O2 content of arterial blood is,
CaO2 = Oxygen bound to hemoglobin + O2 dissolved in plasma
CaO2 = [1.36 × Hb × HbO % (SpO2)] + [0.003 × PaO2].
Pulse oximeter provides a non
invasive measurement of
arterial hemoglobin saturation,
a variable that is directly
related to oxygen content of
arterial
blood..

13. PaO2 mmHg SpO2%
120 100
110 98
92 97
80 96
74 95
69 94
66 93
63 92
60 91
58 90
56 89
51 86
47 83
40 75
27 50
Normal PaO2 is
80-100 mmHg

14. Each pulse oximeter probe contains :
• LED, which emit two wavelengths of light (red and near infrared)
• A photodetector on the other side measures the intensity of
transmitted light at each wavelength
Pulse Oximeter

15. Transmission Pulse Oximetry
• Light beam is transmitted through a
vascular bed and is detected on
opposite side of that bed
• LED and photodetector on opposite
sides
• Most common type
TYPES OF PULSE OXIMETRY

16. Reflectance Pulse Oximetry
• Light reflected or backscattered.
• LED and photodetector on same side.
• Advantage - its signal in low perfusion is
better
Limitations
 weaker signals
 probe design must eliminate light that is
passed directly
 Photodiode needs to be large
 Vasoconstriction causes overestimation

17. EQUIPMENTS
Probes
• The probe (sensor, transducer) comes in
contact with the patient.
• One or more LEDs that emit light at specific
wavelengths and a photodetector.
• LEDs provide monochromatic light.
• Reusable or disposable.
• Self-adhesive probes are less likely to come off
if the patient moves.
• Probes are available in different sizes.
•The photocell should be aligned with the probe
•Contamination should be reduced..
PROBE

18. Cable -The probe is connected to the oximeter by an electrical cable.
Console
•A microcomputer that monitors and controls signal levels , calculations,
activates alarms and messages.
•Panel displays pulse rate, Spo2, and alarm limits.
• Most instruments provide an audible tone whose pitch changes with
the saturation.
• Alarms are commonly provided for low and high pulse rates and for
low and high saturation.
ASA standards for Basic Anaesthetic Monitoring require that the
variable pitch pulse tone and low threshold alarm be audible.

19. Sites of probe placement
• Fingers
• Toe
• Ear
• Nose
• Tongue
• Cheek
• Esophagus
• Forehead
• Penis
DIFFERENT SITES

20. FINGER
• Most common, Convenient, Accurate
• Used even in Burns
• Motion artifacts less frequent
Disadvantages
• Dark nail polish or synthetic nails; Onychomycosis, dirt under
nails can interfere with readings – probe reorientation.
• Resaturation, desaturation detection slower than centrally
placed probes.
• Poor function may be observed when same side as I.V.Fluids-
due to local hypothermia, vasoconstriction
• Same side as Intra-Arterial catheter, BP cuff - ↓ SPO2
TOE
Reliable signal in Epidural Block.-↑ Pulse amplitude
Delay in detection of Hypoxemia

22. USES OF PULSE OXIMETRY
Monitoring oxygenation in :
• Operation theatres
• PACU
• Critical care
• Transport
• Mechanical ventilation

23. • Monitoring peripheral circulation
• Determining systolic blood pressure
• Locating vessels
• Avoidance of hyperoxaemia
• Monitoring vascular volume
• Judicious usage of O2
• Care in NICU
• Fetal oximetry

24. PITFALLS AND LIMITATIONS
Dyshemoglobinemias
COHb and MetHb also absorb light at the pulse oximeter's two
wavelengths, and this leads to error in estimating the percentages
of reduced and oxyhemoglobins.
When the presence of either of these dyshemoglobins is
suspected, pulse oximetry should be supplemented by
multiwavelength co-oximetry.

25. DELAYED DETECTION OF HYPOXIC EVENTS
•Significant delay between a change in alveolar oxygen tension and a
change in the oximeter reading.
•Arterial oxygen reach dangerous levels before the pulse oximeter alarm is
activated.
•Lag time will be increased with poor perfusion and a decrease in blood
flow to the site monitored.
•Lag monitor : Partial pressure of oxygen can have fallen a great deal
before the oxygen saturation starts to fall.
•Response delay due to signal averaging: The signal is averaged out over 5
to 20 seconds. This may result in “frozen” Spo2 values (values being
displayed while the true saturation is rapidly changing) .

26. Electrical interference
• Electrical interference from an electrosurgical unit can cause the
oximeter to give an incorrect pulse count (usually by counting extra
beats) or to falsely register decrease in oxygen saturation.
•Increased in patients with weak pulse signals.
•The effect is transient and limited to the duration of the cauterization.

27. Steps to minimize electrical interference include
• Electrosurgery grounding plate as close to surgical field as possible
• Cable of the sensor to the oximeter away from the electrosurgery
apparatus
• Keeping the pulse oximeter sensor and console as far as possible from
the surgical site and the electrosurgery grounding plate and table
• Operating the unit in a rapid response mode
• Plug to different power source.

28. METHODS TO IMPROVE THE SIGNAL
• Warming cool extremities
• Application of vasodilating cream. Eg. GTN cream, EMLA
• Placing a gloves filled with warm water over patient hand.
• Try an alternative probe site
• Try a different probe.
• Administration of intra-arterial vasodilators.
• Try a different machine
• Digital nerve blocks.

29. 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.
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.

30. CAPNOGRAPHY

31. INTRODUCTION
The presence of CO2 in exhaled gas reflects the fundamental
physiologic processes of ventilation, pulmonary blood flow
and aerobic metabolism.
Its continuous monitoring assures the Anaesthesiologist of
correct placement of EndoTracheal tube or Laryngeal Mask
Airway as well as integrity of a breathing circuit.

32. • Capnometry is measurement and quantification of inhaled
or exhaled CO2 concentrations at the airway opening.
• Capnometer is a device that measures CO2 concentrations.
• Capnography is a method of measurement and graphical
display of CO2 as a function of time or volume.
• Capnograph is a device that records and displays CO2
concentrations, usually as a function of time.
• Capnogram refers to a graphical display that capnograph
generates; CO2 waveform.
TERMINOLOGY

33. • Changes in respired CO2 may reflect alterations in metabolism,
circulation, respiration and breathing system. Monitoring CO2
gives indication of patient’s metabolic rate.
• Assessment of CO2 production, pulmonary perfusion, alveolar
ventilation, respiratory patterns, and elimination of CO2 from the
anaesthesia circuit and ventilator.
•Capnography and pulse oximetry together could have helped in
the prevention of 93% of avoidable anesthesia mishaps
according to ASA closed claim study.
SIGNIFICANCE

34. METHODS
• Infrared Spectrography
• Mass Spectrometry
• Raman Spectrometry
• Gas Chromatography
• Photoacoustic spectrography

35. • A beam of infrared light is passed through
a gas sample, and the resulting intensity of
the transmitted light is measured by a
photodetector. The infrared light received is
compared to the infrared light transmitted.
The difference is then converted by
calculations into either partial pressure or
percentage of total gas concentration that
we see on the monitor.
• Gaseous CO2 absorbs light over a very
narrow bandwidth centered around 4.26
μm.
Infra-red Spectrography
Normal ETCO2 35-45mmHg

36. TWO TYPES CAPNOMETERS
MAIN STREAM
CAPNOMETER
SIDE STREAM
CAPNOMETER

37. CAPNOGRAM
• Time Capnogram (CO2 versus time)
• Volume Capnogram (CO2 versus volume )

38. Two segments: Inspiratory segment
and Expiratory segment,
•The Inspiratory segment: also
designated as phase 0.
•The Expiratory segment: further
divided into phase I, II and III, and
occasionally phase IV, which
represents the terminal rise in C02
concentration
Two angles: alpha and beta.

39. Phase 0
• Is the inspiratory phase where
normal air is breathed in.
• There is only 0.36mmHg of CO2 in
the inspired air compared to
expired air.

40. Phase I
 Latter part of Inspiration.
 Corresponds to the exhalation of dead space gas from
central conducting airways or any equipment distal to
sampling site, which ideally should have no detectable CO2,
i.e PCO2
~0

41. Phase II (Expiratory
upstroke)
• A sharp rise in PCO2
to a plateau.
• Indicates the sampling of
transitional gas between the
airways and alveoli

42. Phase III (Alveolar Plateau)
• Corresponds to PCO2
in alveolar compartment
• For a lung with relatively homogenous ventilation, Phase III is
almost flat throughout expiration.
• It almost always has a positive slope,
indicating a rising PCO2 .
• Last point of phase III- End tidal Point CO2 at its Maximum.
• 5-5.5 % or 35-40 Torr in normal individuals

43. ANGLES
Alpha angle- between phase II and III. which
increases as slope of phase III increases.
• Normally it is about 100 -110°.
• Decreased- obstructive lung disease
Beta angle-between phase III and phase 0
• Normally about 90°.
• Increased-During rebreathing, children

44. Basic Physiology of a Capnogram
• At end of inspiration - CO2-free gases.
• Carbon dioxide diffuses in alveoli and equilibrates with end-alveolar
capillary blood (PACO2 = PcCO2 = 40 mm Hg).
• The actual concentration of CO2 in the alveoli is determined by the
extent of ventilation and perfusion into the alveoli (V/Q ratio).
• Well ventilated areas of lung ( well matched V/Q regions) – Lower
PCO2
• Less well ventilated areas (poorly matched V/Q regions) have higher
PCO2
• As one moves proximally in the respiratory tract, the concentration
of CO2 decreases gradually to zero at some point - respiratory dead
space

45. APPLICATIONS
• ETCO2 as an estimate of PaCO 2
Measurements of ETCO2 constitute a useful non-invasive tool to
monitor PaCO2 and hence, the ventilatory status of patients during
anesthesia, or in the intensive care unit. In normal individuals, the (a-ET)
PCO2 may vary from 2-5 mmHg.
• Adequacy of spontaneous ventilation & Ventilator malfunction
• Integrity of anaesthetic apparatus
• Warning- Apnoea, extubation, disconnection, obstruction
• Adjustments of fresh gas flow rates in rebreathing systems
• Accidental oesophageal intubation
• Metabolic states
• Changes in lung Compliance/Resistance
• Cardiopulmonary resuscitation

46. ABNORMAL CAPNOGRAM AND
CLINICAL CONSIDERATIONS
To analyze the abnormal capnogram, five
characteristics should be inspected:
• Size (height)
• Shape
• Frequency
• Rhythm
• Baseline

56. REFERENCES
•Miller’s anaesthesia 7th edition
•Textbook of anaesthesia by Cullen and Barash
•Dorsch and dorsch anaesthesia equipments 4th edition

57. THANK YOU