This document discusses the importance and applications of pre-hospital capnography. Capnography provides real-time information about ventilation, perfusion and metabolism by measuring end-tidal carbon dioxide levels. It can help assess airway placement, effectiveness of CPR, and detect metabolic abnormalities earlier than other vital signs. The document argues that capnography should be considered more important than the traditional ABCs (airway, breathing, circulation) approach in pre-hospital care as it directly measures ventilation and perfusion.

1. Pre-Hospital Capnography Dr Nick Foster EMICS

2. Early Warning: When do you want the patient’s parachute to open? Capnography 4-10 minutes Pulse Oximetry Pulse Oximetry 30-60 seconds ECG ECG 10 seconds No monitor = free fall!

4. Capnography An EtCO 2 value 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 ► The physiology involved

6. ► How it works

8. ► CO 2 monitoring technology Compares the amount of infrared light absorbed by a sample of expired CO 2 to a chamber with no CO 2 Infrared spectroscopy

11. ► The physiology involved Physiology of Respiration Physiology of Metabolism

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

19. METABOLISM PERFUSION VENTILATION So CO 2 levels 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

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 Fever Hypercatabolic states Increased cardiac output Increased blood pressure Hypoventilation by patient Bronchial intubation (reduces the dead space) Rebreathing Inadequate fresh gas flows Poor ventilation by Dr Faulty valves Technical errors Machine faults Reduced Alveolar Ventilation Increased Pulmonary perfusion Increased CO2 output

36. Waveform analysis Hypoventilation Base line at zero, but height is increased gradually Hyperventilation Baseline at zero, but height is reduced gradually

37. Clinical applications

38. Intubated patients Applications

42. Non-intubated patients Applications

47. Applications Worsening asthma This patient needs ventilatory assistance Note the narrow base and tachypnoea and rising CO2 3 patients short of breath Asthma

48. Applications Response to treatment with Terbutaline. Indices return to normal. This patient has asthma: Diagnosis . 3 patients short of breath Asthma

49. Applications COPD Shark fin shaped waveform appearance showing airway obstruction. Wide base (cf asthma which was narrow) Elevated ETCO2 level 50mmHg Pt has COPD In contrast with asthma 3 patients short of breath

57. Applications The unconscious patient Look for hypoventilation i.e. a high endtidal CO2 reading And a low respiratory rate

60. Applications Metabolic states With acidosis, the respiratory rate increases (e.g. diabetic ketoacidosis)

61. METABOLISM PERFUSION VENTILATION Physiology reminder 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

62. Applications Metabolic states: a tale of two patient both with diabetic ketoacidosis Who is the sickest of the two? Patient A Endtidal CO2 30mmHg SpO2 100 RR 30 Pulse 120 Patient B Endtidal CO2 30mmHg SpO2 99 RR 10 Pulse 120

63. Applications Metabolic states A diabetic with a normal ETCO2 is not sick A diabetic with a low ETCO2 is a sick person. An ETCO2 of 6mmHg is bordering on a cardiac arrest

64. Applications Metabolic states 55 year old male collapsed at home Endtidal CO2 24 SpO2 92 RR 10 Pulse 80 Alcoholic, Myxoedema ( had not taken thyroxine for two years) very pale (Hb 2.4) BP 80/-, hepatic encephalopathy, jaundice, hypotensive. He died 3 days later This patient is very ill.

67. Why is Pre-Hospital Capnography important

79. When do you want the parachute to open? Capnography 4-10 minutes Pulse Oximetry Pulse Oximetry 30-60 seconds ECG ECG 10 seconds No monitor = free fall!