Capnography the ventilation vital sign
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Capnography : The Ventilation Vital Sign. Mazen Kherallah, MD FCCP Critical Care Medicine and Infectious DIsease. Objectives. Define Capnography Discuss Respiratory Cycle Discuss ways to collect ETCO2 information Discuss Non- intubated vs. intubated patient uses

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Capnography the ventilation vital sign

Capnography: The Ventilation Vital Sign

Mazen Kherallah, MD FCCP

Critical Care Medicine and Infectious DIsease


  • Define Capnography

  • Discuss Respiratory Cycle

  • Discuss ways to collect ETCO2 information

  • Discuss Non-intubated vs. intubated patient uses

  • Discuss different waveforms and treatments of them.

So what is capnograhy
So what is Capnograhy?

  • Capnography- Continuous analysis and recording of Carbon Dioxide concentrations in respiratory gases ( I.E. waveforms and numbers)

  • Capnometry- Analysis only of the gases no waveforms

Respiratory cycle
Respiratory Cycle

  • Breathing- Process of moving oxygen into the body and CO2 out can be passive or non-passive.

  • Metabolism-Process by which an organism obtains energy by reacting O2 with glucose to obtain energy.

    • Aerobic- glucose+O2 = water vapor, carbon dioxide, energy (2380 kJ)

    • Anaerobic- glucose= alcohol, carbon dioxide, water vapor, energy (118 kJ)

Respiratory cycle con t
Respiratory Cycle con’t

  • Ventilation- Rate that gases enters and leaves the lungs

    • Minute ventilation- Total volume of gas entering lungs per minute

    • Alveolar Ventilation- Volume of gas that reaches the alveoli

    • Dead Space Ventilation- Volume of gas that does not reach the respiratory portions ( 150 ml)

Respiratory cycle1
Respiratory Cycle

Oxygen-> lungs -> alveoli -> blood




muscles + organs











Respiratory cycle2
Respiratory Cycle





How is etco2 measured
How is ETCO2 Measured?

  • Semi-quantitative capnometry

  • Quantitative capnometry

  • Wave-form capnography

Semi quantitative capnometry
Semi-Quantitative Capnometry

  • Relies on pH change

  • Paper changes color

    • Purple to Brown to Yellow

Quantitative capnometry
Quantitative Capnometry

  • Absorption of infra-red


  • Gas source

    • Side Stream

    • In-Line

      Factors in choosing device:

  • Warm up time

  • Cost

  • Portability

Waveform capnometry
Waveform Capnometry

  • Adds continuous waveform display to the ETCO2 value.

  • Additional information in waveform shape can provide clues about causes of poor oxygenation.

Interpretation of etco2
Interpretation of ETCO2

  • Excellent correlation between ETCO2 and cardiac output when cardiac output is low.

  • When cardiac output is near normal, then ETCO2 correlates with minute volume.

  • Only need to ventilate as often as a “load” of CO2 molecules are delivered to the lungs and exchanged for 02 molecules

Etco2 values
EtCO2 Values

  • Normal 35 – 45 mmHg

  • Hypoventilation > 45 mmHg

  • Hyperventilation < 35 mmHg


  • Relationship between CO2 and RR

    • RR  CO2 Hyperventilation

    •  RR  CO2 Hypoventilation

Why etco2 i have my pulse ox
Why ETCO2 I Have my Pulse Ox?

Pulse Oximetry


  • Oxygen Saturation

  • Reflects Oxygenation

  • SpO2 changes lag when patient is hypoventilating or apneic

  • Should be used with Capnography

  • Carbon Dioxide

  • Reflects Ventilation

  • Hypoventilation/Apnea detected immediately

  • Should be used with pulse Oximetry

What does it really do for me
What does it really do for me?

Non-Intubated Applications

Intubated Applications

  • Bronchospasms: Asthma, COPD, Anaphlyaxis

  • Hypoventilation: Drugs, Stroke, CHF, Post-Ictal

  • Shock & Circulatory compromise

  • Hyperventilation Syndrome: Biofeedback

  • Verification of ETT placement

  • ETT surveillance during transport

  • Control ventilations during CHI and increased ICP

  • CPR: compression efficacy, early signs of ROSC, survival predictor

Normal capnogram1

  • 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

Normal capnogram2

  • 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


  • Increased Phase III slope

    • Obstructive lung disease

  • Phase III dip

    • Spontaneous resp

  • Horizontal Phase III with large ET-art CO2 change

    • Pulmonary embolism

    •  cardiac output

    • Hypovolemia

  • Sudden  in ETCO2 to 0

    • Dislodged tube

    • Vent malfunction

    • ET obstruction

  • Sudden  in ETCO2

    • Partial obstruction

    • Air leak

  • Exponential 

    • Severe hyperventilation

    • Cardiopulmonary event


  • Gradual 

    • Hyperventilation

    • Decreasing temp

    • Gradual  in volume

  • Sudden increase in ETCO2

    • Sodium bicarb administration

    • Release of limb tourniquet

  • Gradual increase

    • Fever

    • Hypoventilation

  • Increased baseline

    • Rebreathing

    • Exhausted CO2 absorber

Paco 2 petco 2 gradient
PaCO2-PetCO2 gradient

  • Usually <6mm Hg

  • PetCO2 is usually less

  • Difference depends on the number of underperfused alveoli

  • Tend to mirror each other if the slope of Phase III is horizontal or has a minimal slope

  • Decreased cardiac output will increase the gradient

  • The gradient can be negative when healthy lungs are ventilated with high TV and low rate

  • Decreased FRC also gives a negative gradient by increasing the number of slow alveoli


  • Critically ill patients often have rapidly changing dead space and V/Q mismatch

  • Higher rates and smaller TV can increase the amount of dead space ventilation

  • High mean airway pressures and PEEP restrict alveolar perfusion, leading to falsely decreased readings

  • Low cardiac output will decrease the reading


  • Metabolic

    • Assess energy expenditure

  • Cardiovascular

    • Monitor trend in cardiac output

    • Can use as an indirect Fick method, but actual numbers are hard to quantify

    • Measure of effectiveness in CPR

    • Diagnosis of pulmonary embolism: measure gradient

Pulmonary uses

  • Effectiveness of therapy in bronchospasm

    • Monitor PaCO2-PetCO2 gradient

    • Worsening indicated by rising Phase III without plateau

  • Find optimal PEEP by following the gradient. Should be lowest at optimal PEEP.

  • Can predict successful extubation.

    • Dead space ratio to tidal volume ratio of >0.6 predicts failure. Normal is 0.33-0.45

  • Limited usefulness in weaning the vent when patient is unstable from cardiovascular or pulmonary standpoint

  • Confirm ET tube placement

Normal wave form
Normal Wave Form

  • Square box waveform

  • ETCO2 35-45 mm Hg

  • Management: Monitor Patient

Dislodged ett
Dislodged ETT

  • Loss of waveform

  • Loss of ETCO2 reading

  • Management: Replace ETT

Esophageal intubation
Esophageal Intubation

  • Absence of waveform

  • Absence of ETCO2

  • Management: Re-Intubate


  • Square box waveform

  • ETCO2 10-15 mm Hg (possibly higher) with adequate CPR

  • Management: Change Rescuers if ETCO2 falls below 10 mm Hg

Obstructive airway
Obstructive Airway

  • Shark fin waveform

  • With or without prolonged expiratory phase

  • Can be seen before actual attack

  • Indicative of Bronchospasm( asthma, COPD, allergic reaction)

Rosc return of spontaneous circulation
ROSC (Return of Spontaneous Circulation)

  • During CPR sudden increase of ETCO2 above 10-15 mm Hg

  • Management: Check for pulse

Rising baseline
Rising Baseline

  • Patient is re-breathing CO2

  • Management: Check equipment for adequate oxygen flow

  • If patient is intubated allow more time to exhale


  • Prolonged waveform

  • ETCO2 >45 mm Hg

  • Management: Assist ventilations or intubate as needed


  • Shortened waveform

  • ETCO2 < 35 mm Hg

  • Management: If conscious gives biofeedback. If ventilating slow ventilations

Patient breathing around ett
Patient breathing around ETT

  • Angled, sloping down stroke on the waveform

  • In adults may mean ruptured cuff or tube too small

  • In pediatrics tube too small

  • Management: Assess patient, Oxygenate, ventilate and possible re-intubation

Curare cleft
Curare cleft

  • Curare Cleft is when a neuromuscular blockade wears off

  • The patient takes small breaths that causes the cleft

  • Management: Consider neuromuscular blockade re-administration

Capnogram 1

J Int Care Med, 12(1): 18-32, 1997

Capnogram 2

J Int Care Med, 12(1): 18-32, 1997

Capnogram 3

J Int Care Med, 12(1): 18-32, 1997

Capnogram 4

J Int Care Med, 12(1): 18-32, 1997

Capnogram 5

J Int Care Med, 12(1): 18-32, 1997

Capnogram 6

J Int Care Med, 12(1): 18-32, 1997

Capnogram 7

J Int Care Med, 12(1): 18-32, 1997

Capnogram 8

J Int Care Med, 12(1): 18-32, 1997

Now what does all this mean to me
Now what does all this mean to me?

  • ETCO2 is a great tool to help monitor the patients breath to breath status.

  • Can help recognize airway obstructions before the patient has signs of attacks

  • Helps you control the ETCO2 of head injuries

  • Can help to identify ROSC in cardiac arrest