The Safe Use and Prescription of Medical Oxygen. Luke Howard

Transcription

1 The Safe Use and Prescription of Medical Oxygen Luke Howard Consultant Respiratory Physician Imperial College Healthcare NHS Trust & Co-Chair, British Thoracic Society Emergency Oxygen Guideline Group Workshop 2012 Oxygen Safety 1

2 Oxygen physiology Topics to be covered How is oxygen delivered and utilised How is carbon dioxide cleared How can oxygen delivery be optimised Dangers of oxygen BTS Guidelines Monitoring Delivery Workshop 2012 Oxygen Safety 2

3 The Oxygen Cascade Workshop 2012 Oxygen Safety 3

4 The Oxygen Cascade Workshop 2012 Oxygen Safety 4

5 O 2 O 2 The Oxygen Cascade O 2 O 2 ATP Workshop 2012 Oxygen Safety 5

6 Gas exchange O 2 What can change? FiO 2 O 2 Oxygen utilisation ATP Oxygen carrying & buffering capacity Flow Workshop 2012 Oxygen Safety 6

7 Oxygen Delivery DO 2 = Q x {[SaO 2 /100 x Hb x 1.3] + [PaO 2 x x 10]} Stagnant Hypoxia Hypoxaemic Hypoxia Anaemic Hypoxia Cytopathic Hypoxia Workshop 2012 Oxygen Safety 7

8 Resting oxygen consumption remains constant until PaO 2 falls below 23 mmhg (~3kPa) Anesthesiology 2001;95:A1123 Cardiac output O 2 extraction Workshop 2012 Oxygen Safety 8

9 14 7 Increased metabolic demand VO 2 (ml/kg/min) Impaired cardiac reserve Anaemia Tissue oedema Mitochondrial dysfunction O O PaO 2 (mmhg) 100 Workshop 2012 Oxygen Safety 9

10 The Oxygen Cascade Workshop 2012 Oxygen Safety 10

11 Dangers of Oxygen Therapy Workshop 2012 Oxygen Safety 11

12 Hypoxic Pulmonary Vasoconstriction Reduces the impact of low VQ units Workshop 2012 Oxygen Safety 12

13 Impaired respiratory mechanics, eg, eg, COPD Alveolar hypoventilation Hypercapnia Acidosis Coma Workshop 2012 Oxygen Safety 13

14 Ventilation-perfusion matching and oxygen administration Diverts blood flow away from diseased lung Uses low oxygen levels in diseased lung to signal to divert blood away Administering oxygen masks this signal Diseased lung is less efficient at clearing carbon dioxide When respiratory mechanics are impaired, eg COPD, this inefficiency cannot be compensated for by increasing overall ventilation and carbon dioxide retention occurs Workshop 2012 Oxygen Safety 14

15 Plant et al., Thorax % of 982 patients with exacerbation of COPD were hypercapnic on arrival in hospital 20% had Respiratory Acidosis (ph < 7.35) 5% had ph < 7.25 (and were likely to need ICU care) Workshop 2012 Oxygen Safety 15

16 Risk of Oxygenation in COPD < > 13.3 Increased risk of intubation Plant et al., Thorax 2000, 55: Workshop 2012 Oxygen Safety 16

17 Workshop 2012 Oxygen Safety 17

18 Randomised Controlled Trial of Titrated vs High-Flow Oxygen Pre-hospital setting Tasmania 405 patients with presumed exacerbation of COPD Titrated arm: Nasal prongs to achieve SpO % High-Flow arm: 8-10 l/min non-rebreathing mask Austin et al., BMJ 2010 Workshop 2012 Oxygen Safety 18

19 Results Workshop 2012 Oxygen Safety 19

20 Danger 2: Alveolar Gas Equation and Rebound Hypoxia PAO 2 = PIO 2 PaCO 2 /RER PAO 2 = (100 - PIN 2 ) PaCO 2 /RER Case study: COPD exacerbation at home - on air Seen by ambulance crew given high flow oxygen Brought to ER oxygen removed Workshop 2012 Oxygen Safety 20

21 Rebound Hypoxia PaO kpa PaCO kpa Workshop 2012 Oxygen Safety 21

22 Rebound Hypoxia PaO 2 32 kpa PaCO 2 10 kpa Workshop 2012 Oxygen Safety 22

23 Rebound Hypoxia PaO kpa PaCO 2 10 kpa Workshop 2012 Oxygen Safety 23

24 Oxygen Delivery DO 2 = Q x {[SaO 2 /100 x Hb x 1.3] + [PaO 2 x x 10]} Stagnant Hypoxia Hypoxaemic Hypoxia Anaemic Hypoxia Cytopathic Hypoxia Workshop 2012 Oxygen Safety 24

25 DO 2 = Q x {[SaO 2 /100 x Hb x 1.3] + [PaO 2 x x 10]} High flow oxygen: Decreased cardiac output Decreased coronary flow (~20%) Increased systemic vascular resistance Circulatory effects of of decreasing oxygen?? Workshop 2012 Oxygen Safety 25

26 PaO 2 13 kpa PvO 2 6 kpa Capillary PmtO kpa Workshop 2012 Oxygen Safety 26

27 Dangers 3,4,5...: High-Flow Oxygen? Coronary vasoconstriction ( flow by <23%) Increased Systemic Vascular Resistance Reduced Cardiac Index Possible reperfusion injury post MI and mildmoderate stroke Hypoxic lung injury Harten JM et al J Cardiothoracic Vasc Anaesth 2005; 19: Kaneda T et al. Jpn Circ J 2001; Frobert O et al. Cardiovasc Ultrasound 2004; 2: 22 Haque WA et al. J Am Coll Cardiol 1996; 2: Thomaon aj ET AL. BMJ 2002; Ronning OM et al. Stroke 1999; 30 McNulty, PH et al. JAP 2007; 102; Workshop 2012 Oxygen Safety 27

28 Retrospective analysis of ICU mortality 36,307 patients in 50 Dutch ICUs De Jonge et al., Crit Care 2008 Workshop 2012 Oxygen Safety 28

29 J-shaped Relationship in PaO 2 /FiO 2 vs Standardised Mortality Workshop 2012 Oxygen Safety 29

30 Danger 6: High-Flow Oxygen Delays Diagnosis of Deterioration Trigger FiO SpO 2 FiO Time Workshop 2012 Oxygen Safety 30

31 BTS Guidelines Workshop 2012 Oxygen Safety 31

32 How to Approach the Patient on 100% Oxygen in hypercapnic failure Patient conscious: Change to 35% Venturi Device Patient drowsy: Leave the patient on high-flow oxygen then, Start NIV with Oxygen / call ICU Workshop 2012 Oxygen Safety 32

33 Step up and down through oxygen delivery devices To avoid rebound hypoxia In case of higher respiratory rates/flows Workshop 2012 Oxygen Safety 33

34 Step up and down through oxygen delivery devices Pre-hospital Workshop 2012 Oxygen Safety 34

35 Step up and down through oxygen delivery devices Once stable Workshop 2012 Oxygen Safety 35

36 Oxygen prescription Model for oxygen section in hospital prescription charts cal Workshop 2012 Oxygen Safety 36

37 Workshop 2012 Oxygen Safety 37