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Capnography
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- 2. • History • Terminology •Why capnography • Physics • Types • Basic physiology • Components of capnography • Clinical application • Carry home
- 3. • History • Terminology •Why capnography • Physics • Types • Basic physiology • Components of capnography • Clinical application • Carry home
- 4. • 1943- luft–CO2 absorbs infrared light • Ramwell – proved it beyond doubt • 1978- holland the first country to adopt • 1999 – ISA ‗desirable standard‘ in anaesthesia monitoring standards
- 5. • History • Terminology •Why capnography • Physics • Types • Basic physiology • Components of capnography • Clinical application • Carry home
- 6. terminology • Capnometry • Capnometer •Capnography • Capnogram • Capnograph
- 7. • History • Terminology •Why capnography • Physics • Types • Basic physiology • Components of capnography • Clinical application • Carry home
- 8. Oxygenation • Measured bypulse oximetry (SpO2) – Noninvasive measurement – Percentage of oxygen in red blood cells – Changes in ventilation take minutes to be detected – Affected by motion artifact, poor perfusion and some dysrhythmias
- 9. • Capnography providesinformation about CO2 production, pulmonary perfusion, alveolar ventilation, respiratory patterns, and elimination of CO2 from the anesthesia circuit and ventilator.
- 10. Ventilation • Measured bythe end-tidal CO2 – Partial pressure (mmHg) or volume (% vol) of CO2 in the airway at the end of exhalation – Breath-to-breath measurement, provides information within seconds – Not affected by motion artifact, poor perfusion or dysrhythmias
- 11. 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
- 12. Why Capnography ? •Capnography, an indirect monitor helps in the differential diagnosis of hypoxia to enable remedial measures to be taken before hypoxia results in an irreversible brain damage • Capnography has been shown to be effective in the early detection of adverse respiratory events.
- 13. • Capnography andpulse oximetry together could have helped in the prevention of 93% of avoidable anesthesia mishaps according to ASA closed claim study. • Capnography has also been shown to facilitates better detection of potentially life-threatening problems than clinical judgment alone
- 14. Case Scenario • 61year old male • C/O: ―short-of-breath‖ and ―exhausted‖ • H/O: > 45 years of smoking 2 packs a day, 3 heart attacks, high blood pressure • Meds: ―too expensive to take every day ‖ • Exam: HR 92, RR 18, 160/100, 2+ pitting edema, wheezing, crackles What other information would help in making assessment of this pt.?
- 15. Why Measure Ventilation— Non-IntubatedPatients • Objectively assess acute respiratory disorders – Asthma – COPD • Possibly gauge response to treatment
- 16. Why Measure Ventilation— Non-intubatedPatients • Gauge severity of hypoventilation states – Drug intoxication – Congestive heart failure – Sedation and analgesia – Stroke – Head injury • Assess perfusion status • Noninvasive monitoring of patients in DKA
- 17. • History • Terminology •Why capnography • Basic physiology • Physics • Types • Components of capnography • Clinical application • Carry home
- 18. CO2 transport • 60%as bicarbonate ion • 10-20% binds to amino group of proteins mostly hemoglobin HALDANE EFFECT • 5-10% directly dissolved in plasma
- 19. End-tidal CO2 (EtCO2) rr Oxygen O 2 CO2 O 2 VeinA te y Ventilation Perfusion Pulmonary Blood Flow Right Ventricle Left Atrium
- 20. End-tidal CO2 (EtCO2) •Carbon dioxide can be measured • Arterial blood gas is PaCO2 – Normal range: 35-45mmHg • Mixed venous blood gas PeCO2 – Normal range: 46-48mmHg • Exhaled carbon dioxide is EtCO2 – Normal range: 35-45mmHg
- 21. 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
- 22. 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
- 23. a-A Gradient r rAlveolus PaCO2 VeinA te y Ventilation Perfusion Arterial to Alveolar Difference for CO2 Right Ventricle Left Atrium EtCO2
- 24. End-tidal CO2 (EtCO2) •Normal a-A gradient – 2-5mmHg difference between the EtCO2 and PaCO2 in a patient with healthy lungs – Wider differences found • In abnormal perfusion and ventilation • Incomplete alveolar emptying • Poor sampling
- 25. Negative a-A gradient •Pregnancy • Infants and children • During and after bypass • after coming of cardiac bypass • Low frequency high tidal volume ventilation
- 26. • History • Terminology •Why capnography • Basic physiology • Physics • Types • Components of capnography • Clinical application • Carry home
- 27. Raman effect • Electromagneticradiation and molecule • The transfer of energy affects the vibration energy associated with bonds between the atoms in a molecule • Absorption of radiation at a particular wave length is associated with the specific type of bond between atoms in a molecule.
- 28. Absorption of radiationdepends on the wavelength of radiation
- 29. • Energy ofradiation is proportional to the frequency of radiation • the transfer of energy between the radiation and molecule results in a change in the wavelength of radiation
- 30. Raman spectrography • RamanSpectrography uses the principle of "Raman Scattering" for CO2 measurement. • The gas sample is aspirated into an analyzing chamber, where the sample is illuminated by a high intensity monochromatic argon laser beam. • The light is absorbed by molecules which are then excited to unstable vibrational or rotational energy states (Raman scattering). • The Raman scattering signals (Raman light) are of low intensity and are measured at right angles to the laser beam. • The spectrum of Raman scattering lines can be used to identify all types of molecules in the gas phase
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- 33. Chemical method ofCO2 measurement - pH sensitive chemical indicator
- 34. Effect of atmosphericpressure • FEtCO2=partial pressure(atmospheric pressure-water vapour pressure)*100 • At atm pressure of 760mmHg, FEtCO2=38(760-47)*100 =5% at atm pressure of 500mmHg FEtCO2=38(500-47)*100 =8%
- 35. Influence of watervapour 1. Effect of condensed water: Water vapor may condense on the window of the sensor cell and absorb IR light, thereby produce falsely high C02 readings
- 36. 2. Effect ofwater vapor. The temperature of the sampling gases may decrease during the passage from the patient to the unit, resulting in a decrease in the partial pressure of water vapor. This can cause an apparent increase in C02 concentration of about 1.5-2% FEtCO2=partial pressure(atmospheric pressure-water vapour pressure)*100
- 37. • History • Terminology •Why capnography • Basic physiology • Physics • Types • Components of capnography • Clinical application • Carry home
- 38. Volume capnography Timecapnography
- 39. Time capnography Advantages • Simpleand convenient • Monitor non-intubated patients • Monitor dynamics of inspiration and expiration Disadvantages • Poor estimation of V/Q status of lungs • Physiologic space dead space
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- 41. Side-stream Capnographs advantages Easy toconnect No problems with sterilization Can be used in awake patients Easy to use when patient is in unusual positions such as in prone position Can be used in collaboration with simultaneous oxygen administration via a nasal prong disadvantages Delay in recording due to movement of gases from the ET to the unit Sampling tube obstruction Water vapor pressure changes affect CO2 concentrations Pressure drop along the sampling tube affects CO2 measurements
- 42. Sampling of CO2from nasal cannulae
- 43. Adequacy of spontaneousrespiration Sampling of CO2 from oxygen mask
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- 45. Mainstream • Advantages No samplingtube No obstruction No affect due to pressure drop No affect due to changes in water vapor pressure No pollution No deformity of capnograms due to non dispersion of gases No delay in recording Suitable for neonates and children • Disadvantages weight of the sensor, (the newer sensors are light weight minimizing traction on the endotracheal tube) Long electrical cord, but it is lightweight. Sensor windows may clog with secretions( they can be replaced easily as they are disposable) Difficult to use in unusual patient positioning such as in prone positions.
- 46. • History • Terminology •Why capnography • Physics • Types • Basic physiology • Components of capnography • Clinical application • Carry home
- 47. Capnographic Waveform • Normalwaveform of one respiratory cycle • Similar to ECG – Height shows amount of CO2 – Length depicts time
- 48. Capnographic Waveform • Waveformson screen and printout may differ in duration – On-screen capnography waveform is condensed to provide adequate information the in 4-second view – Printouts are in real-time – Observe RR on device
- 49. Capnographic Waveform • Capnographdetects only CO2 from ventilation • No CO2 present during inspiration – Baseline is normally zero A B C D E Baseline
- 50. Phase I Deadspace ventillation Beginning of exhalation A B IBaseline
- 51. Phase II AscendingPhase Alveoli CO2 present and increasing in exhaled air II A B C Ascending Phase Early Exhalation
- 52. Phase III AlveolarPlateau CO2 exhalation wave plateaus A B C D III Alveolar Plateau
- 53. Capnogram Phase III End-Tidal Endof the the wave of exhalation contains the highest concentration of CO2 - number seen on monitor A B C D End-tidal
- 54. Capnogram Phase IV DescendingPhase • Inhalation begins • Oxygen fills airway • CO2 level quickly drops to zero Alveoli
- 55. Capnogram Phase IV DescendingPhase Inspiratory downstroke returns to baseline A B C D E IV Descending Phase Inhalation
- 56. Inspiratory segment • Phase0: Inspiration • Beta Angle - Angle between phase III and descending limb of inspiratory segment
- 57. Expiratory segment • PhaseI - Anatomical dead space • Phase II - Mixture of anatomical and alveolar dead space • Phase III - Alveolar plateau • Alfa angle - Angle between phase II and phase III (V/Q status of lung
- 58. Capnography Waveform Normal rangeis 35-45mm Hg (5% vol) Normal Waveform 45 0
- 59. Capnography Waveform Patterns 0 45 HypoventilationRR : EtCO2 45 0 Hyperventilation RR : EtCO2 45 0 Normal
- 60. • History • Terminology •Why capnography • Physics • Types • Basic physiology • Components of capnography • Clinical application • Carry home
- 61. Capnography-3 sources ofinformation • No. – PEtCO2 values • Shapes of capnogram • (a-ET)PCO2 differences
- 62. (a-ET)PCO2 differences • (a-ET)PCO2difference is a gradient of alveolar dead space. increase decrease Age Emphysema Low cardiac output states Hypovolemia Pulmonary embolism Pregnancy and Children
- 63. Five characteristics ofcapnogram should be evaluated The shape of a capnogram is identical in all humans with healthy lungs. Any deviations in shape must be investigated to determine a physiological or a pathological cause of the abnormality • Frequency • Rhythm • Height • Baseline • Shape
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- 65. • A terminalupswing at the end of phase 3, known as phase 4, can occur in pregnant subjects, obese subjects and low compliance states
- 66. The slope theexpiratory plateau is increased as a normal physiological variation in pregnancy
- 67. Prolonged inspiratory descendinglimb • due to dispersion gases in the sampling line or as well as prolonged response time of the analyzer. Seen in children who have faster respiratory rates
- 68. Base line elevatedin • Inadequate fresh gas flow • Accidental administration of CO2 • Rebreathing • Insp / exp valve malfunction • Exhausted CO2 absorber
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- 70. Contamination of CO2monitor • sudden elevation of base line and top line
- 71. Expiratory valve malfunction •Expiratory valve malfunction can result in prolonged abnormal phase 2 and phase 0
- 72. Inspiratory valve malfunction •Elevation of the base line, prolongation of down stroke, prolongation of phase III
- 73. Bain circuit • Inspiratorybase line and phase I are elevated above the zero due to rebreathing. Note the rebreathing wave during inspiration.
- 74. Hypoventilation • Gradual elevation ofthe height of the capnogram, base line remaining at zero
- 75. hyperventillation • Gradual decrease inthe height of the capnogram, base line remaining at zero
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- 79. Cardiogenic oscillations. • Rippleeffect, superimposed on the plateau and the descending limb, resulting from small gas movements produced by pulsations of the aorta and heart.
- 80. Airway obstruction (eg.,bronchospasm). Phase II and phase III are prolonged and alpha angle (angle between phase II and phase III) is increased
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- 84. hypothermia • A gradualdecrease in end tidal carbon dioxide hypothermia, reduced metabolism, hyperventilation, leaks in the sampling system
- 85. Kyphoscoliosis • The CO2waveform has two humps. resulted in a compression of the right lung
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- 87. • Sampling problems suchair or oxygen dilution during nasal or mask sampling of carbon dioxide in spontaneously breathing patients.
- 88. Detection of pulmonaryair embolism • A rapid decrease of PETCO2 in the absence of changes in blood pressure, central venous pressure and heart rate indicates an air embolism without systemic hemodynamic consequences. • as the size of air embolism increases, a reduction in cardiac output occurs which further decreases PETCO2 measurement. A reduced cardiac output by itself can decrease PETCO2.
- 89. Effective circulating bloodvolume can reduce the height of capnograms
- 90. • History • Terminology •Why capnography • Physics • Types • Basic physiology • Components of capnography • Clinical application • Carry home
- 91. Phases of theCapnogram Phase I Expiration Represents anatomical dead space Phase II Expiration Mixture of anatomical and alveolar dead space Phase III Expiration Plateau of alveolar expiration Phase 0 Inspiration Rapid fall in CO2 concentration Phase IV Exhalation Compromised thoracic compliance
- 92. Hyperventilation Progressively lower plateau(phase II) segment Baseline remains at zero Decreasing CO2 levels
- 93. Hypoventilation Steady increase inheight of Phase II Baseline remains constant
- 94. Spontaneous Ventilation Short Alveolarplateau Increased frequency of waveforms
- 95. Cardiogenic Oscillations Ripples duringPhase II and Phase III Due to changes in pulmonary blood volume and ultimately CO2 pressure as a result of cardiac contractions
- 96. Curare Cleft Shallow dipsin phase II plateau Can occur when patient is in a light plane of anesthesia Represent patient attempts to breathe independent of mechanical ventilation
- 97. Bronchospasm Airway Obstruction COPD Slopingof inspiratory and expiratory segments Prolonged Phase II and Phase III
- 98. Rebreathing of SodaLime Contamination with CO2 Elevation of Phase II segment and baseline Elevation of baseline and Phase II, smaller inspiratory efforts Progressive elevation of Phase II and baseline
- 99. Bain System Smaller waveform represents rebreathing of CO2
- 100. Slow ventilation Incompetent inspiratoryvalve Prolongation of Phase 0
- 102. • Capnography provides anotherobjective data point in making a difficult decision