1.End tidal carbon dioxide analysis

2.Transcutaneous and carbon dioxide monitors

Introduction

• Capnometry refers to the measurement and quantification of inhaled or exhaled CO2

concentrations at the airway opening.

• Capnography, however, refers not only to the method of CO2 measurement, but also to its graphic display as a function of time or volume.

PHYSIOLOGY OF CAPNOMETRY

Oxygenation and Ventilation

Oxygenation

(oximetry)

Cellular

Metabolism

Ventilation

(capnography)

CO2

O2

Oxygenation and Ventilation

• Oxygenation

– Oxygen for metabolism

– SpO2 measures % of O2 in RBC

– Reflects change in oxygenation within 5 minutes

• Ventilation

– Carbon dioxide from metabolism

– EtCO2 measures exhaled CO2 at point of exit

– Reflects change in ventilation within 10 seconds

CO2 transport

End-tidal CO2 (EtCO2)

• Reflects changes in

– Ventilation - movement of air in and out of the lungs

– Diffusion - exchange of gases between the air-filled alveoli and the pulmonary circulation

– Perfusion - circulation of blood

End-tidal CO2 (EtCO2)

r r Oxygen

O

2CO2

O

2

VeinA te y

Ventilation

Perfusion

Pulmonary Blood Flow

Right

Ventricle

Left

Atrium

End-tidal CO2 (EtCO2)

• Monitors changes in – Ventilation - asthma, COPD, airway

edema, foreign body, stroke

– Diffusion - pulmonary edema, alveolar damage, CO poisoning, smoke inhalation

– Perfusion - shock, pulmonary embolus, cardiac arrest, severe dysrhythmias

PRINCIPLES OF CAPNOGRAPHY

BEER-LAMBERT LAW

Types of sensors

Solid state CO2 sensors

Chopper wheel CO2 sensor

Sidestream vs Mainstream Capnometry

Sidestream/ Diverging• CO2 sensor located away from the

airway gases to be measured.• Incorporate a pump or

compressor.• Tubing length- 6 ft• Gas withdrawal rate 30-

500ml/min• Lost gas volume needs to be

considered in closed circuit anesthesia.

• Gases must pass through various water traps and filters.

• Transport delay time• Associated RISE TIME

Mainstream/ Non- diverting• Sample cell placed directly in the

patients breathing circuit.

• Inspiratory and expiratory gases pass directly through the IR path

• Increase in dead space and is heavy

• Sample cell heated to 40 degrees to minimize condensation.

• Increased risk of facial burns.

• Requires daily calibration.

• No delay time

• RISE TIME is faster

Types of capnometers

CAPNOGRAPHY WAVEFORMS

Interpretation of TIME

Capnographic Waveform

• Normal waveform of one respiratory cycle

• Similar to ECG

– Height shows amount of CO2

– Length depicts time

Capnographic Waveform

• Waveforms on screen and printout may differ in duration

– On-screen capnography waveform is condensed to provide adequate information the in 4-second view.

Capnographic Waveform

• Capnograph detects only CO2

from ventilation

• No CO2 present during inspiration

– Baseline is normally zero

A B

C D

E

Baseline

Capnogram Phase IDead Space Ventilation

• Beginning of exhalation

• No CO2 present

• Air from trachea, posterior pharynx, mouth and nose

– No gas exchange occurs there

– Called “dead space”

Deadspace

Capnogram Phase I Baseline

Beginning of exhalation

AB

IBaseline

Capnogram Phase IIAscending Phase

• CO2 from the alveoli begins to reach the upper airway and mix with the dead space air – Causes a rapid rise in the

amount of CO2

• CO2 now present and detected in exhaled air

Alveoli

Capnogram Phase IIAscending Phase

CO2 present and increasing in exhaled air

II

A B

C

Ascending Phase

Early Exhalation

Capnogram Phase IIIAlveolar Plateau

• CO2 rich alveolar gas now constitutes the majority of the exhaled air

• Uniform concentration of CO2 from alveoli to nose/mouth

Capnogram Phase IIIAlveolar Plateau

CO2 exhalation wave plateaus

A B

C D

III

Alveolar Plateau

Capnogram Phase IIIEnd-Tidal

• End of exhalation contains the highest concentration of CO2

– The “end-tidal CO2”

– The number seen on your monitor

• Normal EtCO2 is 35-45mmHg

Capnogram Phase IIIEnd-Tidal

End of the the wave of exhalation

A B

C D End-tidal

Capnogram Phase IVDescending Phase

• Inhalation begins

• Oxygen fills airway

• CO2 level quickly drops to zero

Alveoli

Capnogram Phase IVDescending Phase

Inspiratory downstroke returns to baseline

A B

C D

EIV

Descending Phase

Inhalation

Capnography Waveform

Normal range is 35-45mm Hg (5% vol)

Normal Waveform

45

0

a-A Gradient

r r Alveolus

PaCO2

VeinA te y

Ventilation

Perfusion

arterial to Alveolar Difference for CO2

Right

Ventricle

Left

Atrium

EtCO2

End-tidal CO2 (EtCO2)

• Normal a-A gradient

– 2-5mmHg difference between the EtCO2

and PaCO2 in a patient with healthy lungs

Factors Affecting ETCO2 Levels

45

0

Hyperventilation

RR : EtCO2

45

0

Normal

Hyperventilation

Waveform: Regular Shape, Plateau Below Normal

• Indicates CO2 deficiency

Hyperventilation

Decreased pulmonary perfusion

Hypothermia

Decreased metabolism

• Interventions

Adjust ventilation rate

Evaluate for adequate sedation

Evaluate anxiety

Conserve body heat

Hypoventilation

45

0

45

0

RR : EtCO2

Normal

Hypoventilation

Waveform: Regular Shape, Plateau Above Normal

• Indicates increase in ETCO2

Hypoventilation

Respiratory depressant drugs

Increased metabolism

• Interventions

Adjust ventilation rate

Decrease respiratory depressant drug dosages

Maintain normal body temperature

Bronchospasm Waveform Pattern

• Bronchospasm hampers ventilation– Alveoli unevenly filled on inspiration – Empty asynchronously during expiration– Asynchronous air flow on exhalation dilutes exhaled

CO2

• Alters the ascending phase and plateau– Slower rise in CO2 concentration – Characteristic pattern for bronchospasm– “Shark Fin” shape to waveform

Capnography Waveform Patterns

45

0

Normal

Bronchospasm

45

0

Capnography Waveform Patterns

45

0

Hypoventilation

Normal

45

0

45

0

Bronchospasm

Hyperventilation

45

0

Airway obstruction Cardiogenic oscillations

Curare Cleft Esophageal Intubation

Rebreathing of CO2 Faulty inspiratory valve

Patient with single lung transplant Faulty inspiratory valve

Ruptured/ Leaking ET tube cuff Leak in side stream sample line

Expiratory valve stuck open

Electrical Noise

VOLUME CAPNOGRAM

Volume Capnogram

Acute Bronchospasm

Changes in pulmonary perfusion

Advantages of volume capnogram

• Allows for estimation of the relative contributions of anatomic and alveolar components of Vd.

• More sensitive than the time capnogram in detecting subtle changes in dead space that are caused by alterations in PEEP, pulmonary blood flow, or ventilation heterogeneity.

• Allows for determination of the total mass of CO2 exhaled during a breath and provides for estimation of V˙ CO2.

USES OF CAPNOGRAPHY

Detect ET Tube Displacement

Confirm ET Tube Placement

Capnography in Cardiopulmonary Resuscitation

• Assess chest compressions

• Early detection of ROSC

• Objective data for decision to cease resuscitation

• Use feedback from EtCO2 to depth/rate/force of chest compressions during CPR.

In Laparoscopic Surgeries

1.Non invasive monitor of PaCO2 and can be used to adjust ventilation.2.Detection of accidental intravascular CO2 insufflation.3.Helps to detect complications of CO2 insufflation like pneumothorax.

Optimize Ventilation

• Use capnography to titrate EtCO2 levels in patients sensitive to fluctuations

• Patients with suspected increased intracranial pressure (ICP)

– Head trauma

– Stroke

– Brain tumors

– Brain infections

Optimize Ventilation

• High CO2 levels induce cerebral vasodilatation– Positive: Increases CBF to

counter cerebral hypoxia

– Negative: Increased CBF, increases ICP and may increase brain edema

• Hypoventilation retains CO2

which increases levels

CO2

Optimize Ventilation

• Low CO2 levels lead to cerebral vasoconstriction– Positive: EtCO2 of 25-30mmHG causes a

mild cerebral vasoconstriction which may decrease ICP

– Negative: Decreased ICP but may cause or increase in cerebral hypoxia

• Hyperventilation decreases CO2 levels CO2

The Non-intubated Patient Capnography Applications

• Identify and monitor bronchospasm

– Asthma

– COPD

• Assess and monitor

– Hypoventilation states

– Hyperventilation

– Low-perfusion states

Capnography in Bronchospastic Conditions

• Air trapped due to irregularities in airways

• Uneven emptying of alveolar gas

– Dilutes exhaled CO2

– Slower rise in CO2 concentration during exhalation

Alveoli

Capnography in Bronchospastic Diseases

• Uneven emptying of alveolar gas alters emptying on exhalation

• Produces changes in ascending phase (II) with loss of the sharp upslope

• Alters alveolar plateau (III) producing a “shark fin”

A B

C D

EII

III

Capnography in Bronchospastic Conditions

AsthmaCase

Initial

After therapy

Capnography in Bronchospastic Conditions

Pathology of COPD

• Progressive

• Partially reversible

• Airways obstructed

– Hyperplasia of mucous glands & smooth muscle

– Excess mucous production

– Some hyper-responsiveness

Capnography in Bronchospastic Conditions

Capnography in COPD

• Arterial CO2 in COPD

– PaCO2 increases as disease progresses

– Requires frequent arterial punctures for ABGs

• Correlating capnograph to patient status

– Ascending phase and plateau are altered by uneven emptying of gases

Capnography in Hypoventilation States

• Altered mental status– Sedation

– Alcohol intoxication

– Drug Ingestion

– Stroke

– CNS infections

– Head injury

• Abnormal breathing

• CO2 retention – EtCO2 >50mmHg

Capnography Applicationson Non-intubated Patients

• New applications now being reported

– Pulmonary emboli

– CHF

– DKAr r O xy g e n

O 2

V e inA te y

PULMONARY EMBOLUS

TRANSCUTANEOUS AND CARBON DIOXIDE MONITORS

• Transcutaneous measurements of PO2 (Ptco2) and Pco2 (Ptcco2) are monitoring methods that aim to provide noninvasive estimates of arterial O2 and CO2, or at least trends associated with these variables.

• Transcutaneous monitoring can be applied when expired gas sampling is limited.

• The measurements are based on the diffusion of O2 and CO2 through the skin.

• Used successfully in neonates and infants

• Applied when expired gas sampling is limited

• Measurements are based on the diffusion of CO2and O2 through the skin.

• Warming is used to facilitate gas diffusion.

• Such an increase in temperature promotes increased O2 and CO2 partial pressure at skin surface.

• Ptco2 is usually lower than PaO2, and Ptcco2 is higher than Paco2.

• A transducer using a pH electrode to measure the Pco2 (Stow-Severinghaus electrode) is used.

• A change in pH is proportional to the logarithm of the Pco2 change. For CO2

monitors

• A temperature correction factor is used to estimate Paco2 from Ptcco2.

Uses of Ptcco2

1. Assess the efficacy of mechanical ventilation in respiratory failure.

2. Laparoscopic surgery with prolonged pneumoperitoneum.

3. Deep sedation for ambulatory hysteroscopy in healthy patient.

4. Weaning from mechanical ventilation after off pump CABG.

Uses of Ptco2

• Detect hyperoxia in neonates

• Adults:

1. Wound management

2. peripheral vascular disease

3. hyperbaric medicine.

Limitations

• Poor cutaneous blood flow

• Frequent calibration

• Slow response time

• Skin burns with prolonged application

References

• Understanding anesthesia equipment, 5th

edition Dorsch and Dorsch

• Miller’s Anesthesia 8th edition

• Care fusion capnography handbook

• www.capnography.org

THANK YOU

THE END