Download Oxygen - Acute Medicine | Warwick Hospital

Emergency Oxygen Therapy
Is there a problem?
Tom Heaps
CONSULTANT ACUTE PHY SICIAN
Clinical Case No. 1
• 79-year-old female, diabetic, morbidly obese
• Admitted with ‘LVF’
• Overnight ‘Reduced GCS ?cause’
• 15L oxygen via non-rebreathe in situ
• ABG showed pH 6.9, pCO2 15.9kPa normal range 4.5-6.0kPa
• Woke up when oxygen removed!
• Oxygen prescribed with target SpO2 88-92%, documented in notes
• Following morning on AMU GCS 3/15 and 15L NRB back in situ!
• Not a candidate for NIV → RIP
Clinical Case No. 2
• 75-year-old male, cervical myelopathy (cord compression due to OA)
• Admitted with reduced GCS (9/15)
• pH 7.1, pCO2 9.6kPa (respiratory acidosis)
• Improved with controlled O2 24-28%
• Treated for pneumonia
• Became drowsy again with rising pCO2 and low RR
• Miotic (small) pupils
• Covered in fentanyl patches
• Improved once patches removed and naloxone given!
Clinical Case No. 3
• 86-year-old female from RH, osteoporosis
• Admitted with pneumonia
• Asked to see on AMU because of ‘fitting’
• Hypotensive, myoclonic jerks, bounding pulse
• On 10L O2 via NRB since admission
• ABG showed pH 7.23, pCO2 12.9kPa
• Minimal improvement with reduced FiO2
• Not a candidate for HDU or NIV on the respiratory ward
→ RIP
Oxygen —there is a problem!
Published national audits have shown;
• Doctors and nurses have a poor understanding of how
oxygen should be used
• Oxygen is often given without any prescription
• If there is a prescription, it is unusual for the patient to
receive what is specified on the prescription
• Monitoring of oxygen administration is often poor
→OXYGEN IS DANGEROUS NPSA alert 2009
Emergency Oxygen Use in Adult Patients
BTS Guideline 2009
• Prescribing by target oxygen saturation
• Keeping SpO2 within normal limits
• Target SpO2 94-98% for most patients 92-98% if >70
• Target SpO2 88-92% (pO2 6.7-10kPa) for those with or at risk
of hypercapnic (high CO2) respiratory failure
Aims of Emergency Oxygen Therapy
1. To correct or prevent potentially harmful hypoxaemia
2. To alleviate breathlessness only if hypoxaemic
Increasing FiO2 (inspired oxygen concentration) is only one way
of increasing overall O2 carrying capacity of blood:
– Protect airway
– Enhance circulating volume and cardiac output
– Correct severe anaemia
– Avoid or reverse respiratory depressants e.g. morphine
– Treat underlying cause e.g. LVF, asthma
Indications for Emergency Oxygen
1. SpO2 <94% <88% if risk of hypercapnia
2. Critical illness e.g. septic shock, major trauma,
anaphylaxis, acute LVF during initial ABCDE
3. Carbon monoxide poisoning irrespective of SpO2
Too much O2 can be harmful…
• Risk of hypercapnia (high CO2) in selected patients
– some patients with chronic hypercapnia are dependent on
hypoxaemia to maintain respiratory drive
• Constriction of coronary arteries
– high O2 levels INCREASED mortality in survivors of cardiac
arrest
• Constriction of cerebral arteries
– high O2 levels INCREASED mortality in non-hypoxic patients
with mild-moderate stroke
Patients at risk of hypercapnia?
• COPD not all patients with COPD —elevated HCO3- on
ABG is a useful clue to chronic CO2 retention
• Morbid obesity OHS and OSA
• Neuromuscular weakness MND, myasthenia, GBS
• Chest wall deformity kyphoscoliosis
• Reduced conscious level
• Morphine and other respiratory sedatives
How should oxygen be delivered to…
Critically unwell / severely hypoxaemic patients?
• high-concentration reservoir / nonrebreathe mask
• delivers 60-80% O2 at 10-15L/min
• SHORT-TERM use only
• ensure bag is filled with oxygen
before attaching to patient
• DO NOT turn down oxygen flow
below 10L/min
How should oxygen be delivered to…
Most other patients?
• nasal cannulae / specs
• comfortable, well-tolerated, lowcost and no risk of re-breathing
• 2-6L/min gives ~24-50% oxygen
• concentration actually delivered
also depends on patient’s:
– tidal volume
– respiratory rate
patients with COPD tend to
breath disproportionately
more oxygen than air with
every breath → risk of
hypercapnia
How should oxygen be delivered to…
Patients at risk of hypercapnic respiratory failure?
• Venturi / fixed performance masks
• accurate between 24-40%
• increasing oxygen flow does NOT
• 60% venturi delivers ~50%
increase FiO2
oxygen
• less affected by tidal
volume and respiratory
rate (useful in COPD)
Monitoring and Titration of O2
ALWAYS
NEVER
• question whether oxygen is
• leave patients on high-
actually required and if so, what is
the target saturation range
• monitor oxygen saturations
frequently / continuously
• titrate flow rate and / or device up
or down until target saturations
achieved
• use minimum flow rate required
• seek to wean off oxygen as soon as
possible
concentration O2 without
repeating ABGs
• use non-rebreathe masks with flow
rates <10L/min
• adjust the flow rate through a
Venturi device without changing
the mask
• suddenly stop high-concentration
oxygen in a hypercapnic patient
without titrating down first (35%)
BTS National Oxygen Audits
Audit Year
2008
2009
2010
2011
2012
2013
2015
Oxygen prescribed with a
target range?
10%
40%
41%
43%
46%
51%
53%
Percent of drug rounds on
which oxygen was signed
for on the drug chart?
5%
27 %
16 %
20%
20%
21%
28%
Percentage of patients within target range where this was prescribed
69%
9% of patents at risk of iatrogenic hypercapnia due to being >2% above their
target range (despite recognised hypercapnic risk)
How can we improve?
Nurse-led and delivered process —ask yourself these key questions:
1. Does this patient actually need oxygen?
– check saturations on air oxygen won’t help unless hypoxaemic
– only give oxygen if patient is outside of their target range
– if in doubt, ask somebody!
2. Is oxygen prescribed on the drug chart?
– immediately ask a clinician to prescribe if not
3. Which device is best for my patient
– nasal cannulae for majority, Venturi mask if risk of hypercapnia
4. What is the target saturation range and is this being achieved?
– titrate oxygen up or down until target SpO2 is achieved
Key Learning Points
• Oxygen is a drug —if it’s not prescribed, DON’T GIVE IT except in an
emergency —like most drugs, oxygen has the potential to kill
• Consider risk of CO2 retention not just COPD patients
• Select best device for delivery nasal cannulae > Venturi > non-rebreathe
• Frequent monitoring of SpO2 is required in all patients on oxygen
• Titrate O2 up or down to achieve target SpO2 94-98% 88-92% if high risk
• Avoid hyperoxaemia risk of hypercapnia and adverse cerebral / coronary effects
• Wean down oxygen at the earliest opportunity once stable
• NEVER leave patients on high-concentration O2 for prolonged periods