Capnography: The Ventilation Vital Sign

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Capnography The Ventilation Vital Sign

• Mazen Kherallah, MD FCCP
• Critical Care Medicine and Infectious DIsease

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Objectives

• 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.

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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

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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- glucoseO2 water vapor, carbon
  dioxide, energy (2380 kJ)
• Anaerobic- glucose alcohol, carbon dioxide,
  water vapor, energy (118 kJ)

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Respiratory Cycle cont

• 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)

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Respiratory Cycle
Oxygen -gt lungs -gt alveoli -gt blood
Oxygen
breath
CO2
muscles organs
lungs
Oxygen
CO2
cells
energy
blood
Oxygen Glucose
CO2
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Respiratory Cycle
ALL THREE ARE IMPORTANT!
PERFUSION
VENTILATION
METABOLISM
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How is ETCO2 Measured?

• Semi-quantitative capnometry
• Quantitative capnometry
• Wave-form capnography

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Semi-Quantitative Capnometry

• Relies on pH change
• Paper changes color
• Purple to Brown to Yellow

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Quantitative Capnometry

• Absorption of infra-red
• light
• Gas source
• Side Stream
• In-Line
• Factors in choosing device
• Warm up time
• Cost
• Portability

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Waveform Capnometry

• Adds continuous waveform display to the ETCO2
  value.
• Additional information in waveform shape can
  provide clues about causes of poor oxygenation.

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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

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Hyperventilation Kills
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EtCO2 Values

• Normal 35 45 mmHg
• Hypoventilation gt 45 mmHg
• Hyperventilation lt 35 mmHg

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Physiology

• Relationship between CO2 and RR
• ?RR ? ?CO2 Hyperventilation
• ? RR ? ? CO2 Hypoventilation

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Why ETCO2 I Have my Pulse Ox?

• Pulse Oximetry

• Capnography

• 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

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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

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NORMAL CAPNOGRAM
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NORMAL CAPNOGRAM

• 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

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NORMAL CAPNOGRAM

• 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

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ABNORMALITIES

• 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

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ABNORMALITIES

• 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

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PaCO2-PetCO2 gradient

• Usually lt6mm 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

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LIMITATIONS

• 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

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USES

• 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

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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 gt0.6
  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

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Normal Wave Form

• Square box waveform
• ETCO2 35-45 mm Hg
• Management Monitor Patient

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Dislodged ETT

• Loss of waveform
• Loss of ETCO2 reading
• Management Replace ETT

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Esophageal Intubation

• Absence of waveform
• Absence of ETCO2
• Management Re-Intubate

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CPR

• Square box waveform
• ETCO2 10-15 mm Hg (possibly higher) with adequate
  CPR
• Management Change Rescuers if ETCO2 falls below
  10 mm Hg

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Obstructive Airway

• Shark fin waveform
• With or without prolonged expiratory phase
• Can be seen before actual attack
• Indicative of Bronchospasm( asthma, COPD,
  allergic reaction)

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ROSC (Return of Spontaneous Circulation)

• During CPR sudden increase of ETCO2 above 10-15
  mm Hg
• Management Check for pulse

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Rising Baseline

• Patient is re-breathing CO2
• Management Check equipment for adequate oxygen
  flow
• If patient is intubated allow more time to exhale

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Hypoventilation

• Prolonged waveform
• ETCO2 gt45 mm Hg
• Management Assist ventilations or intubate as
  needed

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Hyperventilation

• Shortened waveform
• ETCO2 lt 35 mm Hg
• Management If conscious gives biofeedback. If
  ventilating slow ventilations

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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

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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

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CAPNOGRAM 1
J Int Care Med, 12(1) 18-32, 1997
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CAPNOGRAM 2
J Int Care Med, 12(1) 18-32, 1997
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CAPNOGRAM 3
J Int Care Med, 12(1) 18-32, 1997
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CAPNOGRAM 4
J Int Care Med, 12(1) 18-32, 1997
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CAPNOGRAM 5
J Int Care Med, 12(1) 18-32, 1997
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CAPNOGRAM 6
J Int Care Med, 12(1) 18-32, 1997
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CAPNOGRAM 7
J Int Care Med, 12(1) 18-32, 1997
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CAPNOGRAM 8
J Int Care Med, 12(1) 18-32, 1997
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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