Chris Cameron Clinical pharmacologist & General Physician CCDHB Oxygen- A prescribing Blindspot?
Ms J, 70yo Lives with partner, who has a recent diagnosis of breast cancer Works 3 days a week Weight 46kg Smoker (80 pack year history) Ex tol about 500m on flat Recent admission (May 17) for IECOPD
PMHx Severe COPD ICU admission July 2012. Spirometry Sept 2014: FEV1 0.66 litres (31%), FVC 61%, FEV1/FVC 42% Last seen by Resp Sept 2014 CT chest (2014) Moderate centrilobular emphysematous change with hyperinflation of the lungs
RxHx Bezafibrate 400mg PO nocte Omeprazole 20mg PO mane Salbutamol 100mcg 2 puffs inh BD and PRN q4h Seretide 125/25 2 puffs inh bd Spiriva 18mcg 1 puff inh od Aspirin E.C. 100mg PO od Cholecalciferol 1.25mg PO monthly Dermol ointment, apply to psoriasis occasionally Ensure liquid 1.5kcal/mL - chocolate, 1 BD
ICU admission 2012 Not known to be a CO2 retainer Slow respiratory wean - intubated for 12 days Trial of BiPAP resulted in increased agitation and intolerance and so was stopped. Hypercapnic on further ABG's. Documented ICU note that Ms J has significant respiratory disease (COPD with FEV1 0.77). While she was successfully, though slowly, weaned from mechanical ventilation, her underlying lung pathologies are likely to worsen, especially if she continues to smoke. As such, she would be a poor candidate for ICU therapy if she presented to hospital in a number of months time; although they would be happy to discuss this further if the situation does arise.
Blood gases in recent admissions Date & time O2 given pco2 PO2 ph 23 June 2012 0722 4L 44 (A) 74 7.34 1245 6L 67 (A) 108 7.18 Trial of BiPAP unsuccessful Transferred to ICU, intubated and ventilated 1430 2L 54 (A) 56 7.27 5 July 2012 Extubated 5 July 2012 Date & time O2 given pco2 po2 ph 13 May 2017 unknown 47 (?V) 55 7.4 15 May 2017 unknown 55 (?V) 40 7.36
Final admission 14-17 July PC: Cough, fever, SOB IECOPD, new paf VBG: ph 7.382, pco2 49.9, HCO3 29.6 Bloods: CRP 9, WCC 8.1, Neuts 6.5 ECG: Sinus tachycardia (132)with frequent PACs/PAF. No acute ischaemic changes. CXR: Heart not enlarged. Significant hyperinflation of the chest but no focal consolidation/evidence of failure. Plan: 1) Admit Gen Med 2) Q2H obs - EWS adjusted 3) Further IVF 4) Continue IV Cefuroxime given Penicillin allergy 5) Prophylactic Clexane 6) Monitor heart rate but if does not settle with ABs and further fluid may need rate control - oral short acting metorpolol tartrate. 7) Ca/PO4 and Mg added to bloods. (Unable to add TFTs - repeat bloods mane with TFTs). 8) NRF form signed in discussion with patient.
Progress 14-16 July Ms J was steadily improving HR settling, still some paf SW discussions re care for partner Date & time O2 given pco2 po2 ph 14 July 2017 18.51 (ED) 45% 50 (V) 21 7.38 (HCO3 29.6)
Then suddenly..
What happened? Ms J was started on 2L/min O2 in the early hours of 16 July when her O2 sats were 92% RA After about 4 hours she became restless and HR (AF) She then had a seizure Transferred to HDB Date & time O2 given pco2 po2 ph 16 July 2017 2L/min 120 (A) 70 6.99
Time O2 given pco2 po2 ph 0709? 114 (A) 65 7.08 0816 4L 105 (A) 71 7.08
Lessons to be learned No-one appreciated that Ms J was a CO2 retainer This was not on her problem list No O2 therapy was prescribed for her VBGs were used to guide therapy No O2 therapy documented on VBG No Venturi mask was used Signs of CO2 retention not appreciated
ABG vs. VBG in COPD Values from VBG: ph ABG=VBG po2 ABG bears no relation to VBG Low po2 can predict CO2 retention pco2 If VBG pco2 <46, then ABG <46 usually If VBG pco2 >46, the ABG pco2 is high, but?how high In COPD patients and others at risk of T2RF, ABGs need to be used to guide O2 therapy. Get some practice. VBGs are not useful in this setting.
PML Guidance
x 14 July 2017 Venturi Mask 2L-4L/min
Do not administer oxygen unless discussed with registrar/smo x
Supplemental O2 is an FiO2 > 21% and is a drug (remember RA=21% O2) Type of device Litres O2/minutes FiO2 inhaled When to use Nasal prongs 1L/min 2L/min 3L/min 4L/min 6L/min 24% (0.24) 28% 33% 41% 45% When low flow O2 needed in a patient without CO2 retention. If >4L/min humidification is recommended Hudson mask Venturi mask Non-rebreather mask 4L/min 6L/min 8L/min 2-4L/min 2-4L/min 4-6L/min 6-8L/min 9-10L/min 10-12L/min 12-15L/min 24-28% 31% 35-40% 24% 26% 28% 30% 35% 40% 50% In hypoxic patients without CO2 retention In hypoxic patients with known CO2 retention, or at risk of CO2 retention Upto 15L/min 60-90% In hypoxic patients without CO2 retention
Signs of hypercapnia Sedation, comatose Altered mental status, confusion, paranoia, seizures Muscle twitches Vasodilatation of the skin flushed face, strong, bounding pulse Papilloedema Asterixis an easy sign to elicit
What did we learn? Supplementary O2 is a drug Supplementary O2 must be prescribed All COPD patients are potential CO2 retainers Education of nursing and junior medical staff is needed