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
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
O 2 CO 2 O 2 CO 2 CO 2 Physiology of respiration Oxygen/Carbon dioxide interaction: Perfusion and Ventilation Ventilation Perfusion
CO 2 elimination = CO 2 -> blood -> lungs -> exhalation
Physiology of respiration Ventilation Perfusion
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
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
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
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
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
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.
Capnography measurements The waveform Phase I Represents the CO2-free gas from the airways (anatomical and apparatus dead space).
Capnography measurements The waveform Phase II Consists of a rapid upswing on the tracing (due to mixing of dead space gas with alveolar gas).
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
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
Normal waveform: Capnography measurements The waveform
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
Causes for a fall in end tidal CO 2 Hypothermia Hypocatabolic state (eg gross myxoedema)
Applications The shape is a shark fin Width of the shape gets smaller as the patient gets worse
Applications Worsening asthma This patient needs ventilatory assistance Note the narrow base and tachypnoea and rising CO2 3 patients short of breath Asthma
Applications Response to treatment with Terbutaline. Indices return to normal. This patient has asthma: Diagnosis . 3 patients short of breath Asthma
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
Applications Endtidal CO2 27% SpO2 91 RR 30 Pulse 120 Seen by GP 5 days before and diagnosed flu. Fever for 6 days. Temp 104F, Left side chest sign, creps ++, increased breathsounds, Whisp pect, Diagnosis left pneumonia in fact Legionella developed empyema 4 days later.
Applications Endtidal CO2 38 SpO2 99 on air RR 14 Pulse 80 Chest pain, pleuritic. 4 hours. ECG normal. Chest examination normal, normal percussion, normal breath sounds. Tender chest wall. Calves normal and no tenderness
Applications Endtidal CO2 22 SpO2 – on 99% oxygen RR 23 Pulse 98 24 year old male, driver RTA car fire. Had to be pulled from the car by passers by. Airway open, no carbonaceous material around mouth, nares clear. Breathing spontaneous, good A/E. Cap refill <2 radial pulse 110/80 GCS 14/15. No focal neurology. No obvious fracture
Applications Metabolic states With acidosis, the respiratory rate increases (e.g. diabetic ketoacidosis)
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
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
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
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.