09 pre hospital capnography

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  • 1.Pre-Hospital Capnography Dr Nick FosterEMICS

2. Early Warning:When do you want the patients parachute to open? Capnography 4-10 minutes Pulse Oximetry Pulse Oximetry 30-60 seconds ECG ECG 10 seconds No monitor = free fall! 3. Physiology Carbon dioxide

  • A Capnograph will show you second by second where you are with the patient by showing you
    • The CO2 reading
    • The CO2 waveform
    • The Respiratory rate
    • The Oxygen saturation
    • The pulse rate
  • Metabolism/Perfusion/Ventilation

4. Capnography An EtCO 2value of e.g..38mm/Hg with a trace i s as diagnostic as an ECG T i m e 5 0 4 0 3 0 2 0 1 0 0 5. Application in clinical practice Objectives How it works Thephysiology involved 6. How it works 7. CO 2monitoring technology

  • Capnometry:the measurement and numerical display of the CO 2level appearing in the airway
  • Capnograpahy:the measurement andgraphical display of the CO 2level appearing in the airway

8. CO 2monitoring technology Compares the amount of infrared light absorbed by a sample of expired CO 2to a chamber with no CO 2 Infrared spectroscopy 9. CO 2monitoring technology Respiratory gases are continuously aspirated by a side port tube connection from the patients airway Sidestream sampling

  • Advantages
  • Able to monitor intubated and non-intubated patients
  • Uses thin tubing therefore less dead space
  • Less likely to become contaminated with moisture because it is away from the airway
  • Uses a zero reference to keep the monitoring calibration

10. CO 2monitoring technology Sidestream sampling

  • Disadvantages
  • There is a lag time between sampling and measurementAdvances: faster response time
  • If the patient is breathing rapidly, there may be contamination of the inhaled and exhaled gases and give a falsely low CO2 reading.Advances: Lower sample rates now used
  • The tubing can get obstructed by water and mucus
  • Pre-hospital use is in its infancy

11. The physiology involved Physiology of Respiration Physiology of Metabolism 12. Physiology of metabolism

  • An acidoisis makes the pH more acidic than usual
  • An alkalosis makes the pH more alkaline than usual

Metabolism Homeostasis.The body tries to maintain a state of equilibrium despite everything we throw at it. Body pH range 71.-7.8, homeostasis is about 7.3 -7.4 A body pH of 7.2 called acidaemia A body pH of 7.5 called alkalaemia 13. Physiology of metabolism

  • There are a number of acids in the body
          • CO2
          • Lactic acid from cell activity if starved of oxygen.

Complex chemical interactions that keep these in balance.

  • These dangerous acids need to be removed
    • Buffers: immediate
    • CO2 production: minutes
    • Renal excretion/Liver breakdown: days

14. Physiology of metabolism

  • A balance exists
  • ACID CO2
  • Tissues Lungs

By looking at what goes into the body via the lungs (Oxygen) and what comes out (Carbon dioxide) you get a picture as to how damaged or ill the body is 15. Physiology of respiration

  • a natural waste product of cellular activity

Carbon dioxide 16. Oxygen-> lungs -> alveoli -> blood muscles + organs Oxygen cells Oxygen Oxygen + Glucose energy CO 2 blood lungs CO 2 breath CO 2 Physiology of respiration Oxygen/Carbon dioxide interaction: Metabolism CO2 produced by cellular metabolism diffuses across the cell membrane into the circulating blood. 5-10% carried in solution 20-30% bound to haemoglobin 60-70% carried as bicarbonate in the red blood cell 17. O 2 CO 2 O 2 CO 2 CO 2 Physiology of respiration Oxygen/Carbon dioxide interaction: Perfusion and Ventilation Ventilation Perfusion 18.

  • Oxygenation= oxygen->lungs ->alveoli ->blood
  • Metabolism= oxygen is converted to energy +CO 2
  • CO 2elimination = CO 2 ->blood ->lungs ->exhalation

Physiology of respiration Ventilation Perfusion 19. METABOLISM PERFUSION VENTILATION So CO 2levels provide evidence of three parameters going on the body Physiology What's happening at the cellular level How well the circulation is performing How well the lungs are working 20. METABOLISM PERFUSION VENTILATION Physiology If metabolism fails, acid forms (metabolic acid).With severe shock, the patient becomes very acidic and very ill Metabolic acidosis This may be tolerated if circulation and oxygenation are maintained. The acid is converted to CO2 and this is blown off by the lungs 21. METABOLISM PERFUSION VENTILATION Physiology If the circulation is failing, this acid cannot be transported to the lungs and the patient becomes iller Metabolic acidosis CO2 cannot be removed from the lungs as it cannot get there. Your only hope is to get the circulation working more effectively 22. METABOLISM PERFUSION VENTILATION Physiology Carbon dioxide If the breathing is inadequate, CO2 accumulates in the blood and is converted to acid Respiratory acidosis By ventilating the patient, we can get rid of the excessive CO2 and thereby reduce the damage the acid in the blood is doing to the tissues 23. Physiology

  • Metabolic acidosis
  • Acid builds up (anaerobic metabolism)
  • Tissue hypoxia(anaemia, shock, severe infection, diabetic ketoacidosis)
  • Renal failure
  • Loss of body salts(severe diarrhoea)
  • Respiratory acidosis
  • Hypoventilation: CO2 builds up
  • Airway obstruction
  • Central neuro : brain injury, stroke, opiates
  • Periph neuro : spinal cord, MND
  • Chest wall disease(muscle, flail chest, trauma, pneumothorax
  • COPD
  • Pneumonia ,
  • Respiratory alkalosis
  • Hyperventilation: CO2 blown off
  • Anxiety states
  • Asthma-low O2, low CO2
  • PE- low O2, low CO2
  • BUT as exhaustion sets in
  • -low O2 with rising CO2
  • Metabolic alkalosis
  • Acid is lost
  • Severe vomiting(acid lost from stomach)

24. Capnography measurements 25. Normal waveform: Capnography measurements The waveform I just want you to look at the display first for a minute and then I will break the wave down into its constituent parts 26. Capnography measurements The waveform The lungs are composed of tissue involved in gas exchange (alveoli) and tubes connecting them to the outside world (bronchi, trachea). These tubes ARE NOT involved in gas exchange and is called dead space. 27. Capnography measurements The waveform Phase I Represents the CO2-free gas from the airways (anatomical and apparatus dead space). 28. Capnography measurements The waveform Phase II Consists of a rapid upswing on the tracing(due to mixing of dead space gas with alveolar gas). 29. Capnography measurements The waveform Phase III Consists of an alveolar plateau representing CO2-rich gas from the alveoli. It almost always has a positive slope, indicating a rising PCO2 30. Capnography measurements The waveform Phase 0 Is the inspiratory phase where normal air is breathed in. There is only 0.36mmHg of CO2 in the air compared to 40mmHg in expired air 31. Capnography measurements The waveform 32. Normal waveform: Capnography measurements The waveform 33. Causes for a rise in end tidal CO 2 FeverHypercatabolic states Increased cardiac outputIncreased blood pressure Hypoventilation by patient Bronchial intubation (reduces the dead space) Rebreathing Inadequate fresh gas flows Poor ventilation by Dr Faulty valves Technical errorsMachine faults Reduced Alveolar Ventilation Increased Pulmonary perfusion Increased CO2 output 34. Causes for a fall in end tidal CO 2 Hypothermia Hypocatabolic state (eg gross myxoedema)

  • Reduced cardiac output
  • Hypotension
  • Hypovolaemia
  • Pulmonary embolism
  • Cardiac arrest

HyperventilationApnoea Airway blocked: obstruction, ET tube extubated Circuit disconnectionSampling tube leak Technical errorsMachine faults Increased Alveolar Ventilation Reduced Pulmonary perfusion Reduced CO2 output 35.

  • Look for five characteristics of the waves,
  • Height (normal = 38mmHg. Tall = high CO2, small = low CO2)
  • Rate
  • Rhythm (regular, getting bigger (or smaller)
  • Base line (how wide it is)
  • Shape of the wave

Waveform analysis 36. Waveform analysis HypoventilationBase line at zero, but height is increased gradually Hyperventilation Baseline at zero, but height is reduced gradually 37. Clinical applications 38. Intubated patients Applications 39.

  • Intubation
  • Verification of tube placement and monitoring ET placement during transport AND its dynamic (cf to a CO2 disc)
  • 5-20% of tubes are misplaced either at the time of intubation or during transfer.

Applications In