capnography the ventilation vital sign n.
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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