The document discusses pulse oximetry and capnography. Pulse oximetry uses light absorption to non-invasively measure arterial oxygen saturation by comparing absorbed and transmitted light through tissues at red and infrared wavelengths. It can detect hypoxemia but is influenced by other factors like skin pigment. Capnography measures exhaled carbon dioxide concentration using infrared absorption, with the capnogram tracing showing phases that can assess ventilation and oxygenation status. Both are important monitoring tools during medical procedures.

3.  Introduction
 Principle
 Hemoglobin absorption spectra
 Parts of oximeter
 Sites
 Mechanism
 Types
 Application
 Sources of error

4.  Oxygenation is measured by pulse oximetry
 The pulse oximeter is a noninvasive device that measures
the oxygen saturation of your patient’s blood (fifth vital
sign).
 Earlier oximetry ,introduced in 1940s to detect hypoxemia
had two short comings
› (a) the transmission of light was influenced by factors
other than hemoglobin (e.g., skin pigments, and the
thickness of the earlobe),
› (b) it was not possible to differentiate between
hemoglobin in arteries and veins.
 pulse oximetry is based on the presence of pulsatile blood
flow(pulsating artery)

5.  Uses spectrophotometry
based on the Beer-Lambert
law.
 Beer’s law: absorbance is
proportional to the
concentration of the
attenuating species in the
material.
 Lambert’s law: absorbance
is directly propertional to its
thickness(path length)

6.  Pulse oximeter combines two
technologies
 Spectrophotometry: measures oxygen
saturation
 Optical plethysmography: measures
pulsatile changes in blood volume and
heart rate.

8.  Differentiates oxy from deoxy Hb by the
differences in absorption of light at 660 nm
and 940 nm
 Minimizes tissue interference by separating
out the pulsatile signal
 Estimates HR by measuring cyclic changes
in light transmission
 Estimates functional Hb by comparing
amounts of oxy and deoxy Hb

9.  Functional oxygen saturation: Functional
O2 saturation (SaO2) refers to the amount of
O2Hb as a fraction of the total amount of
O2Hb and deO2Hb
 Fractional oxygen saturation: The O2Hb
fraction or fractional saturation is defined as
the amount of O2Hb as a fraction of the total
amount of Hb.

10.  The pulse oximeter consists of a probe attached
to the patient's finger or ear lobe which is linked
to a computerized unit.
 One side of probe contains two light emitting
diodes that emit monochromatic light at
wavelength 660 (red) & 940 (infrared).
 Otherside contains photo detector.
 It is connected to AC amplifier that amplifies
pulsatile light waves & blocks nonpulsatile
waves.

12. The sensor measures the ambient light &
subtracts it.
LED turned on & off rapidly.
The absorption of transmitted light is
measured & variation time recorded.
This results a wave form with trough as blood
flows into the finger (more absorption) during
systole & a peak as blood flows into veins in
diastole

13. Monitor analyses the
measurements & splits into two
components i.e fixed & varying.
Above steps repeated sequentially
using light of at least two
wavelengths at 120 Hz.
The monitor requires 8 heart beats
to make calculations & then
assumes the frequency of wave
form is the heart rate.

14.  Transmisson pulse oximetry
 Reflectance pulse oximetry
 Co-oximetry
 Transcutaneous oximetry

16.  Finger ,toes
 Ear
 Forehead
 Thenar ,hypothenar eminence,palm
 penis

17.  Mandatory for any anaesthetic procedure
particularly in
› Pre-existin lung disease
› One lung ventilation
› OSAS & polysomnography
 To control Oxygen administration (to avoid
hyperoxia in premature infants)
 Monitoring vascular volume & peripheral
circulation
 To know adequecy of CPR

19. Source of Error Effect on SpO2 relative to SaO2
Hypotension
Anemia
Polycythemia
Motion
Low SaO2
Methemoglobinemia
Carboxyhemoglobinemia
Cyanmethemoglobin
Sulfhemoglobin
Hemoglobin F
Hemoglobin H
Hemoglobin K
Hemoglobin S
Methylene blue
Indigo carmine
Indocyanine green
Isosulfan blue
Fluorescein
↓
↓
No significant effect
↓
Variable
↓/↑ (SpO2 approaches 85%)
↑
No significant effect
No significant effect
No significant effect
No significant effect
↓
No significant effect
↓
↓
↓
No significant effect/↓
No significant effect

20. Source of Error Effect on SpO2 relative to SaO2
Nail polish Black, dark blue, purple
Acrylic fingernails
Henna Red:
Skin pigmentation At SaO2 >80%,
At SaO2 <80%,↑Jaundice
Ambient light
Sensor contact
IABP
↓
No significant effect
No significant effect/↓
no significant effect
No significant effect
no significant effect
↓
↑

21.  Capnography is defined as continuous
monitoring of CO2 concentration vs time in a
gas mixture.
 Capnogram is the tracings of waveforms
obtained on the monitor.
 Capnograph is the machine that generates
the wave form.
 Capnometer is the device that performsthe
measurement & displays the readings in
numerical form.

22.  Infrared Absorption Photometry
 Colorimetric Devices
 Mass Spectrometry
 Raman Scattering

23.  First developed in 1859.
 Based on Beer-Lambert law: Pa = 1 - e-  DC
› Pa is fraction of light absorbed
›  is absorption coefficient
› D is distance light travels though the gas
› C is molar gas concentration
 The higher the CO2 concentration, the higher the
absorption.
 CO2 absorption takes place at 4.25 µm
 N2O, H2O, and CO can also absorb at this wavelength
 Two types: side port and mainstream

25.  Gas is sampled through a small tube
 Analysis is performed in a separate chamber
 Very reliable
 Time delay of 1-60 seconds
 Less accurate at higher respiratory rates
 Prone to plugging by water and secretions
 Ambient air leaks

26.  Sensor is located in the airway
 Response time as little as 40msec
 Very accurate
 Difficult to calibrate without disconnecting (makes
it hard to detect rebreathing)
 More prone to the reading being affected by
moisture
 Larger, can kink the tube.
 Adds dead space to the airway
 Bigger chance of being damaged by mishandling

28.  Contains a pH sensitive dye which undergoes a
color change in the presence of CO2
 The dye is usually metacresol purple and it
changes to yellow in the presence of CO2
 Portable and lightweight.
 Low false positive rate
 Higher false negative rate
 Acidic solutions, e.g., epi, atropine, lidocaine, will
permanently change the color
 Dead space relatively high for neonates, so don’t
use for long periods of time on those patients.

31. A B
C D
E
I

32. A B
C D
E
II

33. A B
C D
E
III

34. A B
C D
E
End-Tidal

35. A B
C D
E
IV

36.  Phase I is the beginning of exhalation
 Phase I represents most of the anatomical
dead space
 Phase II is where the alveolar gas begins to
mix with the dead space gas and the CO2
begins to rapidly rise
 The anatomic dead space can be calculated
using Phase I and II
 Alveolar dead space can be calculated on
the basis of : VD = VDanat + VDalv
 Significant increase in the alveolar dead
space signifies V/Q mismatch

37.  Phase III corresponds to the elimination of
CO2 from the alveoli
 Phase III usually has a slight increase in the
slope as “slow” alveoli empty
 The “slow” alveoli have a lower V/Q ratio and
therefore have higher CO2 concentrations
 In addition, diffusion of CO2 into the alveoli is
greater during expiration. More pronounced
in infants
 ET CO2 is measured at the maximal point of
Phase III.
 Phase IV is the inspirational phase
 Normal range 35-45 mm Hg

48.  To confirm correct position of ET tube (presence of
>3 successive breaths)
 Determines if tip of fibroscope is in trachea
 Diagnosis of malignant hyprethermia
 Detects pulmonary embolism
 Indicates
› Apnoea
› Disconnection of circuit
› Leakage in ETT/circuit
› Ventilator malfunction
› Incompetent inspiratory /expiratory valve
› Assesment of sodalime canister function
 Confirms placement of needle in cricothyroidotomy.

49.  Miller 8th edition (1331-1334 & 1544-1556)
 Morgan &mikhail clinical anaesthesiology 5th
edition (124-127)
 Smith & aitkinhead anaesthesilogy (339-
345)
 The icu book 4th edition (409-426)