Workshop 2012 – Oxygen Safety 1
The Safe Use and Prescription of Medical Oxygen
Luke HowardConsultant Respiratory Physician
Imperial College Healthcare NHS Trust&
Co-Chair, British Thoracic Society Emergency Oxygen Guideline Group
Workshop 2012 – Oxygen Safety 2
Topics to be covered
• Oxygen physiology– How is oxygen delivered and utilised– How is carbon dioxide cleared– How can oxygen delivery be optimised
• Dangers of oxygen• BTS Guidelines
– Monitoring– Delivery
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ATP
O2
O2
What can change?
Gas exchange
FiO2
•Oxygen carrying & buffering capacity•Flow
Oxygen utilisation
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Oxygen Delivery
DO2 = Q x {[SaO2/100 x Hb x 1.3]+ [PaO2 x 0.003 x 10]}
Stagnant Hypoxia Anaemic
HypoxiaHypoxaemicHypoxia
Cytopathic HypoxiaCytopathic Hypoxia
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Resting oxygen consumption remains constant until PaO2falls below 23 mmHg (~3kPa) Anesthesiology 2001;95:A1123
↑Cardiac output↑O2 extraction
↑Cardiac output↑O2 extraction
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O
7
VO
2(m
l/kg/
min
)
OPaO2 (mmHg)
100
14Increased metabolic
demand
Impaired cardiac reserve
AnaemiaTissue oedema
Mitochondrial dysfunction
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Hypoxic Pulmonary Vasoconstriction
Reduces the impact of low VQ unitsReduces the impact of low VQ units
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Impaired respiratory mechanics, eg, COPDImpaired respiratory mechanics, eg, COPD
Acidosis
Coma
Acidosis
Coma
Alveolar hypoventilation Hypercapnia
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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
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Plant et al., Thorax 2000
• 47% 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)
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Risk of Oxygenation in COPD
<7.3
7.3-
10 10-
13.3>
13.3
Plant et al., Thorax 2000, 55: 550-4
Increased risk
of intubation
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Randomised Controlled Trial of Titrated vsHigh -Flow Oxygen
• Pre-hospital setting• Tasmania• 405 patients with presumed exacerbation of COPD• Titrated arm:
– Nasal prongs to achieve SpO2 88-92%• High-Flow arm:
– 8-10 l/min non-rebreathing mask
Austin et al., BMJ 2010
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Danger 2: Alveolar Gas Equation and “Rebound Hypoxia”
• PAO2 = PIO2 – PaCO2/RER
• PAO2 = (100 - PIN2) – PaCO2/RER
• Case study:– COPD exacerbation at home - on air– Seen by ambulance crew – given high flow
oxygen– Brought to ER – oxygen removed
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Oxygen Delivery
DO2 = Q x {[SaO2/100 x Hb x 1.3]
+ [PaO2 x 0.003 x 10]}
Stagnant
Hypoxia Anaemic
HypoxiaHypoxaemic
Hypoxia
Cytopathic Hypoxia
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DO2 = Q x {[SaO2/100 x Hb x 1.3]
+ [PaO2 x 0.003 x 10]}High flow oxygen:
•Decreased cardiac output
•Decreased coronary flow (~20%)
•Increased systemic vascular resistance
High flow oxygen:
•Decreased cardiac output
•Decreased coronary flow (~20%)
•Increased systemic vascular resistance
Circulatory effects of decreasing
oxygen??
Circulatory effects of decreasing
oxygen??
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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 mild-
moderate stroke• Hypoxic lung injury
Harten JM et al J Cardiothoracic Vasc Anaesth 2005; 19: 173-5
Kaneda T et al. Jpn Circ J 2001; 213-8
Frobert O et al. Cardiovasc Ultrasound 2004; 2: 22
Haque WA et al. J Am Coll Cardiol 1996; 2: 353-7
Thomaon aj ET AL. BMJ 2002; 1406-7
Ronning OM et al. Stroke 1999; 30
McNulty, PH et al. JAP 2007; 102; 2040-45.
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Retrospective analysis of ICU mortality• 36,307 patients
in 50 Dutch ICUs
De Jonge et al., CritCare 2008
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Time
Sp
O2
FiO2 0.3
FiO2 1.0
Trigger
Danger 6: High-Flow Oxygen Delays Diagnosis of Deteri oration
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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
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Step up and down through oxygen delivery devicesStep up and down through oxygen delivery devices
To avoid
rebound
hypoxia
In case of
higher
respiratory
rates/flows
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Step up and down through oxygen delivery devicesStep up and down through oxygen delivery devices
Pre-hospital
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Step up and down through oxygen delivery devicesStep up and down through oxygen delivery devices
Once
stable
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Oxygen prescription
Model for oxygen section in hospital prescription c harts cal