Capnography

Luft developed the principle of capnography in 1943 from the knowledge that CO2 is

one of the gases that absorbs infra-red (IR) radiation of

a particular wavelength.

In 1978 Hollandwas the first

country to adopt capnography as a standard of monitoring

Capnography, has become an integral part of monitoring for preventing life

threatening events

Incidence of hypoxia is less

Capnography when used in conjunction with pulse oximetry and visual inspection

of chest detected respiratory depression 17 times

more often than without capnography

•Capnography forewarns of impending hypoxia by about 5 to 240

seconds

Capnography triggers early intervention and decreases the

incidence of oxygen desaturation

Monitors use

infrared spectrographymass spectrography

Raman spectrographyphotoacoustic analysers

colorimetric devices

Hypoxia is our primary concern

If uncorrected can lead to

death

Applications of Capnography

                                                                                                                              

                                              

INTENSIVIST

Capnography

A graphic display of instantaneous CO2 concentration (FCO2) versus time or expired

volume during a respiratory cycle (CO2 waveform or capnogram)

Machine that generates a waveform and the capnogram is the actual waveform

CapnographCapnometer

Numerical display of maximum inspiratory and expiratory CO2

concentrations during a respiratory cycle

Capnometry

Capnograms

CO2 waveforms which can be of two types

CO2 expirogramTime capnogram

Infra Red SpectrographyCO2 absorbs Infra red light at 4.3

µm

Factors affecting IR Spectrography

Effect of Atmospheric Pressure

• Use of 4.3 µ m IR light does not affect CO2 measurements

Effect of N2O on CO2 measurements

Effect of N2O on CO2 measurements

Effect of Oxygen on CO2 measurements

Effect of water vaporWater absorbs IR light but minimum at 4.3µ m

Changes in water vapor alter CO2 readings

Water can obstruct sampling tube

Methods for decreasing contamination of sampling tubes by liquids or secretions

Position the sampling vertically upwards

Use water filters at both ends of sampling tube

Response Time of AnalyzerSlow analyzers distort CO2 wave forms

Use of more powerful amplifiers

Minimizing the volume of the sampling chamber and tubes

Use of relatively high sampling flow rates (150 ml-min-l)

Response time can be reduced by

Inhalational agents do not affect CO2 measurement

Chemical method of CO2 measurement

A chemically treated foam

indicator contained in a

plastic container

MAIN STREAM CAPNOGRAPH SIDE STREAM CAPNOGRAPH

Types of Capnographs

Time Capnogram

Volume Capnogram

Time Capnogram

Volume Capnogram

No inspiratory segment in a volume capnogram.

Time capnogram has both inspiratory (0) as well as expiratory segment.

The expiratory segment of a volume capnogram is divided into three phases, phase I, II, and III

• Normal end expiratory CO2 partial pressure ranges between

35 and 45 mmHg

BASIC PHYSIOLOGY

Fast CapnogramA Trend Capnogram

A time capnogram may be recorded at two speeds

High speed capnogram (7mm.sec-1)

Detailed information about each breath

Overall CO2 changes (trend) can be followed at a slow (0.7 mm.sec-1) speed

Fast or regular capnogram

Trend Capnogram

Components of a time capnogramExpiratory segment

Phase I - Anatomical dead space Phase II - Mixture of anatomical and

alveolar dead spacePhase III - Alveolar plateau

Alfa angle - Angle between phase II and phase III (V/Q status of lung)

Nearly 90During rebreathing

beta angle increases

the horizontal baseline of phase 0 and phase I can be elevated above

normal

Beta Angle

Prolonged response time of the capnometer compared to

respiratory cycle time of the patient, particularly in children,

can give same picture

Between phases 11 and IIIIncreases as the slope of phase 111 increases the angle. The alpha angle (primarily linked to variations in time constants within the lung) An indirect indication of V/Q status of the lung

Alpha Angle

Alveolar Plateau (phase III) has positive slope due to Continuous excretion of CO2 from Late

emptying of alveoli with low V/Q ratio containing relatively higher CO2 concentration

Alveolar Plateau

Lower part of the lung is also better

perfused

Lower part of the lung is better

ventilated

If a low V/Q contaninig high CO2 have long time constant, they will contribute to late part of phase III leadig to positive deflection of that

phase

Positive slope of phase IIIdue to late emptying of low v/Q alveoli that

contain high CO2.alpha angle is an indirect incication of V/Q

status of the lungs

Simple and convenient

Monitor non-intubated patients

Monitors dynamics of inspiration as well as expiration

Advantages of time capnography

Poor estimation of V/Q status of the lung

Can not be used to estimate components of physiological deadspace

Disadvantages of time capnography

Components of the tidal volume with capnograph

Increased (a-ET)PCO2

COPDOLD AGE

Hypovolemia Pulmonary embolism

(a-ET)PCO2 decreases

Low frequency ventilationHigh tidal volume

ChildrenPregnant ladies

Decreased COP will increase alveolar dead space and increase

(a-ET)PCO2

How is a capnogram related to a tidal volume

Determination of components of tidal volume using a capnogram

Physiological dead spacesub-divided into anatomical and alveolar dead space

Ventilation/perfusion in thelungs

Any factor that affects V/Q ratio can affects the slope and the height of

phase III

CARDIAC OUTPUTFUNCTIONAL RESIDUAL CAPACITY

CO2 PRODUCTIONAIRWAY RESISTANCE

Ventilation/perfusion in the lungs

Cardiac output and capnograms

Encyclopedia of capnograms

Normal Capnogram

Capnogram recorded during general anesthesia for cesarean section

The slope of the phase III is increased. This is a normal physiological variation.

Airway obstruction can result in an increase in the phase III as well.

Depending on the severity of airway obstruction, phase II can also be prolonged

Occasionally, a phase IV can also occur in pregnant subjects

Capnogram with increased phase III slope

Capnogram with phase IV

Capnograms in pregnancy

Airway obtruction / Bronchospasm

Phase II and phase III are prolonged

Most commonly seen capnograms

Spontaneous ventilationShort alveolar plateau

HyperventilationonBaseline at zero,

but height is reduced gradually

HypoventilationBase line at zero, but height is

increased gradually

IMV ventilationIMV breaths interposed with

spontaneous ventilation

ApneaSelf explanatory

Apnea, or Respiratory obstructionA flat line indicates that there is apnea, or total respiratory

obstruction. It may also indicate disconnection of the CO2 sampling system,

or inability to sample the expired air

Ripples on the alveolar plateau and

descending limb due to movement of gas in the airway as a result

of cardiogenic oscillations

Ripple effect Cardiogenic Oscillations

Curare Cleft

Rebreathing capnograms

Exhausted Soda lime

• Gradual elevation of baseline and the height of the capnograms

Hyperventilation• Baseline is elevated,

• but height can remain the same due to hyperventilation

Rebreathing

• Baseline is elevated, there is an inspiratory wave due to rebreathing of CO2, the height of the capnogram is gradually increasing.

Inspiratory valve defects

• The inspiratory valve is not closing properly resulting in a flip in the plateau at the beginning of

inspiration.

Inspiratory valve malfunction

• valve displaced or totally incompetent

Plateau is prolonged due to rebreathing

Expiratory valve defects

• Prolonged phase II, slanting of descending limb of inspiration, baseline elevation

Malignant Hyperpyrexia• The height of the capnograms is increased. Baseline

at zero until soda lime exhaustion.

Hypotherm

• Hypothermia/reduced metabolism

• The height of the capnograms is decreased.

Sampling leaks

• Sampling tube leaks, Sampling via oxygen face mask, nasal cannula

Break in the sampling tube system or loose connections at sampling tube end of the monitor

Sampling leaks

• Breakage in the sampling filter • Dual plateau capnogram

Sampling leaks

Partial disconnection of main stream sensor (like curare cleft)

Contamination of CO2 sensor

• Sudden rise of base line and height of the waveform

Esophageal intubation

• Flat line as no carbon dioxide

Presence of CO2 in the stomach can give rise to fluctuations in the base line

• Occasionally enough alveolar gas can be forced down the esophagus into the stomach during mask ventilation resulting transiently in few

capnograms as below

Esophageal intubation

• Carbonated beverages in the stomach can result in significant CO2 in expired gases during six breaths.

• However, the shape of capnograms should alert to a non tracheal intubation.

Esophageal intubation

Biphasic capnogram Lung transplant

• Biphasic capnogram following single lung transplant suggesting characteristic differential

emptying of each lung

Biphasic capnogram kyphoscoliosis

• Biphasic capnogram in a patient with severe

kyphoscoliosis. • Differential emptying of lungs

Endobronchial intubation Biphasic capnogram

• Biphasic capnogram as a result of endotracheal tube in right main bronchus

Endotracheal tube pulled back above tracheal carina

Downward sloping phase III• The slope of phase III can be reversed in patients with emphysema where there is

marked destruction of alveolar capillary membranes and reduced gas exchange

CARDIAC ARREST

Air Embolism

Thrombo Embolism

Capnography during laparoscopic surgery

Adjust ventilationD

etection of accidental intravascular CO2

insufflationDetection of pneumothorax, and

hemorrhage

Hemodynamic and ventilatory changes during CO2 insufflation

Carbon dioxide Embolism

Capnography

• Five characteristics should be inspected:

height, frequency, rhythm, baseline, and shape

Metabolism

• An increase in end-tidal CO2 is a reliable indicator of increased metabolism

• only in mechanically ventilated patients

• In spontaneously breathing patients, PET CO2 may not increase as a result of

hyperventilation

Increased temperature Shivering

Convulsions Excessive production of catecholaminesAdministration of blood or bicarbonate

Release of an arterial clamp or tourniquet with reperfusion of ischaemic areas

Glucose in the intravenous fluid

Parenteral hyperalimentation

CO2 used to inflate the peritoneal cavity during laparoscopy, the pleural cavity during thoracoscopy or a joint during

arthroscopy.

Metabolic causes of increases in expired CO2 include

Malignant hyperthermia

Hypermetabolic state Massive increase in CO2

production before the rise in temperature

• Early detection through monitoring CO2

Malignant hyperthermia

• Capnography can be monitored for the effectiveness of treatment.

• CO2 production falls with decreased temperature, increased muscle relaxation, and

increased depth of anaesthesia.

During good CPR{ 10 – 15 mmHg }

if you keep PETCO2 up in that 25 range

then there's circulation still going on. ...

That's where you're going to get a positive outcome

Capnograms during spontaneous ventilation

When oxygen is being administered via face mask can be different due to dilution of expired CO2 by oxygen

or room air

COPD V/Q perfusion abnormalities result in a sloping phase II and

phase III

Capnograms during Conscious sedation in spontaneous ventilation

Look for three important changes from baseline capnograms

•Respiratory rate A decreased rate indicates respiratory

depression. Increased rate suggests stimulation from the

procedure

If the PETCO2 increases, it suggests hypoventilation

If the PETCO2 decreases, it suggests hyperventilation, hypoventilation, or upper

airway obstruction depending on the cause.

Observe the patient carefully for evidence of respiratory obstruction.

If present, give jaw thrust, PETCO2 increases as obstruction is relieved.

If there is no improvement in PETCO2, it most likely suggests a central

depression.

Hyperventilation is indicated by an increased respiratory rate.

Over sedation Height of the capnogram

PETCO2 decreased

Hypoventilation Height of the capnogram (PETCO2) is increased

VENTILATOR CIRCUIT

CO2 can highlight derangement in each circuit

Raman spectrography

infraredSpectrography

Methods to measure CO2 level

Photoacoustic spectrography

Mass spectrography

Chemical colorimetricanalysis.

• Capnogram recorded during the use of Bain anesthetic system / Mapelson D.

• The base line is elevated from zero. • During inspiration, there a small rebreathing wave

due to inhalation of carbon dioxide. • The extent of CO2 rebreathing depends FGF, tidal

volume, and respiratory frequency. • Red indicates inspiration.

• A similar capnogram has been reported during closed circuit anesthesia and IPPV where soda lime was totally exhausted

• The only difference observed between the two capnograms is that the signature wave during inspiration in the case of exhausted CO2 absorbent is closer to the expiratory waveform than that during bain circuit

• Curare cleft capnogram (if the second peak occurred during expiration)

Rebreathing capnogram (if the second peak occurred during inspiration).

• Capnographs do not have a device yet for marking inspiration and expiration on the time capnogram,

thereby delaying the diagnosis of the problem.