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Capnography
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Capnography

  1. 1. CAPNOGRAPHY
  2. 2. • History • Terminology • Why capnography • Physics • Types • Basic physiology • Components of capnography • Clinical application • Carry home
  3. 3. • History • Terminology • Why capnography • Physics • Types • Basic physiology • Components of capnography • Clinical application • Carry home
  4. 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. 5. • History • Terminology • Why capnography • Physics • Types • Basic physiology • Components of capnography • Clinical application • Carry home
  6. 6. terminology • Capnometry • Capnometer • Capnography • Capnogram • Capnograph
  7. 7. • History • Terminology • Why capnography • Physics • Types • Basic physiology • Components of capnography • Clinical application • Carry home
  8. 8. Oxygenation • Measured by pulse 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. 9. • Capnography provides information about CO2 production, pulmonary perfusion, alveolar ventilation, respiratory patterns, and elimination of CO2 from the anesthesia circuit and ventilator.
  10. 10. Ventilation • Measured by the 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. 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. 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. 13. • Capnography and pulse 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. 14. Case Scenario • 61 year 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. 15. Why Measure Ventilation— Non-Intubated Patients • Objectively assess acute respiratory disorders – Asthma – COPD • Possibly gauge response to treatment
  16. 16. Why Measure Ventilation— Non-intubated Patients • 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. 17. • History • Terminology • Why capnography • Basic physiology • Physics • Types • Components of capnography • Clinical application • Carry home
  18. 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. 19. End-tidal CO2 (EtCO2) r r Oxygen O 2 CO2 O 2 VeinA te y Ventilation Perfusion Pulmonary Blood Flow Right Ventricle Left Atrium
  20. 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. 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. 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. 23. a-A Gradient r r Alveolus PaCO2 VeinA te y Ventilation Perfusion Arterial to Alveolar Difference for CO2 Right Ventricle Left Atrium EtCO2
  24. 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. 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. 26. • History • Terminology • Why capnography • Basic physiology • Physics • Types • Components of capnography • Clinical application • Carry home
  27. 27. Raman effect • Electromagnetic radiation 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. 28. Absorption of radiation depends on the wavelength of radiation
  29. 29. • Energy of radiation 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. 30. Raman spectrography • Raman Spectrography 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
  31. 31. Mass spectrograpy
  32. 32. Chemical method of CO2 measurement - pH sensitive chemical indicator
  33. 33. Effect of atmospheric pressure • 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%
  34. 34. Influence of water vapour 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
  35. 35. 2. Effect of water 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
  36. 36. • History • Terminology • Why capnography • Basic physiology • Physics • Types • Components of capnography • Clinical application • Carry home
  37. 37. Volume capnography Time capnography
  38. 38. Time capnography Advantages • Simple and convenient • Monitor non-intubated patients • Monitor dynamics of inspiration and expiration Disadvantages • Poor estimation of V/Q status of lungs • Physiologic space dead space
  39. 39. Sidestream
  40. 40. Side-stream Capnographs advantages Easy to connect 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
  41. 41. Sampling of CO2 from nasal cannulae
  42. 42. Adequacy of spontaneous respiration Sampling of CO2 from oxygen mask
  43. 43. mainstream
  44. 44. Mainstream • Advantages No sampling tube 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.
  45. 45. • History • Terminology • Why capnography • Physics • Types • Basic physiology • Components of capnography • Clinical application • Carry home
  46. 46. Capnographic Waveform • Normal waveform of one respiratory cycle • Similar to ECG – Height shows amount of CO2 – Length depicts time
  47. 47. 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 – Printouts are in real-time – Observe RR on device
  48. 48. Capnographic Waveform • Capnograph detects only CO2 from ventilation • No CO2 present during inspiration – Baseline is normally zero A B C D E Baseline
  49. 49. Phase I Dead space ventillation Beginning of exhalation A B IBaseline
  50. 50. Phase II Ascending Phase Alveoli CO2 present and increasing in exhaled air II A B C Ascending Phase Early Exhalation
  51. 51. Phase III Alveolar Plateau CO2 exhalation wave plateaus A B C D III Alveolar Plateau
  52. 52. Capnogram Phase III End-Tidal End of the the wave of exhalation contains the highest concentration of CO2 - number seen on monitor A B C D End-tidal
  53. 53. Capnogram Phase IV Descending Phase • Inhalation begins • Oxygen fills airway • CO2 level quickly drops to zero Alveoli
  54. 54. Capnogram Phase IV Descending Phase Inspiratory downstroke returns to baseline A B C D E IV Descending Phase Inhalation
  55. 55. Inspiratory segment • Phase 0: Inspiration • Beta Angle - Angle between phase III and descending limb of inspiratory segment
  56. 56. Expiratory segment • Phase I - 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
  57. 57. Capnography Waveform Normal range is 35-45mm Hg (5% vol) Normal Waveform 45 0
  58. 58. Capnography Waveform Patterns 0 45 Hypoventilation RR : EtCO2 45 0 Hyperventilation RR : EtCO2 45 0 Normal
  59. 59. • History • Terminology • Why capnography • Physics • Types • Basic physiology • Components of capnography • Clinical application • Carry home
  60. 60. Capnography-3 sources of information • No. – PEtCO2 values • Shapes of capnogram • (a-ET)PCO2 differences
  61. 61. (a-ET)PCO2 differences • (a-ET)PCO2 difference is a gradient of alveolar dead space. increase decrease Age Emphysema Low cardiac output states Hypovolemia Pulmonary embolism Pregnancy and Children
  62. 62. Five characteristics of capnogram 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
  63. 63. Resuscitation- trend
  64. 64. • A terminal upswing at the end of phase 3, known as phase 4, can occur in pregnant subjects, obese subjects and low compliance states
  65. 65. The slope the expiratory plateau is increased as a normal physiological variation in pregnancy
  66. 66. Prolonged inspiratory descending limb • 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
  67. 67. Base line elevated in • Inadequate fresh gas flow • Accidental administration of CO2 • Rebreathing • Insp / exp valve malfunction • Exhausted CO2 absorber
  68. 68. Elevation of base line
  69. 69. Contamination of CO2 monitor • sudden elevation of base line and top line
  70. 70. Expiratory valve malfunction • Expiratory valve malfunction can result in prolonged abnormal phase 2 and phase 0
  71. 71. Inspiratory valve malfunction • Elevation of the base line, prolongation of down stroke, prolongation of phase III
  72. 72. Bain circuit • Inspiratory base line and phase I are elevated above the zero due to rebreathing. Note the rebreathing wave during inspiration.
  73. 73. Hypoventilation • Gradual elevation of the height of the capnogram, base line remaining at zero
  74. 74. hyperventillation • Gradual decrease in the height of the capnogram, base line remaining at zero
  75. 75. Oesophageal intubation
  76. 76. Cardiogenic oscillations. • Ripple effect, superimposed on the plateau and the descending limb, resulting from small gas movements produced by pulsations of the aorta and heart.
  77. 77. Airway obstruction (eg., bronchospasm). Phase II and phase III are prolonged and alpha angle (angle between phase II and phase III) is increased
  78. 78. bronchospasm during After relief
  79. 79. Curare effect
  80. 80. Malignant hyperpyrexia
  81. 81. hypothermia • A gradual decrease in end tidal carbon dioxide hypothermia, reduced metabolism, hyperventilation, leaks in the sampling system
  82. 82. Kyphoscoliosis • The CO2 waveform has two humps. resulted in a compression of the right lung
  83. 83. • Capnogram during spontaneous ventilation in adults
  84. 84. • Sampling problems such air or oxygen dilution during nasal or mask sampling of carbon dioxide in spontaneously breathing patients.
  85. 85. Detection of pulmonary air 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.
  86. 86. Effective circulating blood volume can reduce the height of capnograms
  87. 87. • History • Terminology • Why capnography • Physics • Types • Basic physiology • Components of capnography • Clinical application • Carry home
  88. 88. Phases of the Capnogram 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
  89. 89. Hyperventilation Progressively lower plateau (phase II) segment Baseline remains at zero Decreasing CO2 levels
  90. 90. Hypoventilation Steady increase in height of Phase II Baseline remains constant
  91. 91. Spontaneous Ventilation Short Alveolar plateau Increased frequency of waveforms
  92. 92. Cardiogenic Oscillations Ripples during Phase II and Phase III Due to changes in pulmonary blood volume and ultimately CO2 pressure as a result of cardiac contractions
  93. 93. Curare Cleft Shallow dips in phase II plateau Can occur when patient is in a light plane of anesthesia Represent patient attempts to breathe independent of mechanical ventilation
  94. 94. Bronchospasm Airway Obstruction COPD Sloping of inspiratory and expiratory segments Prolonged Phase II and Phase III
  95. 95. Rebreathing of Soda Lime 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
  96. 96. Bain System Smaller wave form represents rebreathing of CO2
  97. 97. Slow ventilation Incompetent inspiratory valve Prolongation of Phase 0
  98. 98. • Capnography provides another objective data point in making a difficult decision
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