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Venous Blood Gases in the ED: EuSEM15

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As presented at EUSEM 2015, this presentation discusses how venous blood gas analysis fits into clinical care in emergency departments. The evidence is correct as of Sept 2015

Veröffentlicht in: Gesundheit & Medizin
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Venous Blood Gases in the ED: EuSEM15

  1. 1. Anne-Maree Kelly Professor and Director Joseph Epstein Centre for Emergency Medicine Research @Western Health, Australia OR Can venous blood gas analysis replace ABG in the ED?
  2. 2. I have not received industry funding for any of my blood gas research.
  3. 3.  I am a ‘woose’ ◦ I dislike needles and am averse to pain  My experience ◦ Late presentation of asthma and DKA because of fear of ABG ◦ More severe illness, that was potentially preventable  Was there another way? ◦ Searched the literature – limited data in paeds for VBG but no data in adults ◦ Decided to generate data to test my clinical questions
  4. 4.  To understand the agreement performance of variables on arterial and venous blood gas analysis  To be aware of how venous blood gas analysis can be safely used in clinical decision-making  To be aware of grey areas and unanswered questions
  5. 5.  Discussion will be limited to comparisons between arterial and peripheral venous samples as these are the most relevant to Emergency Medicine practice
  6. 6.  Establishing acid-base status ◦ Mainly pH; but also bicarbonate  Measuring respiratory function/ ventilation  Mainly pCO2; but also pH  ‘Quick check’ potassium, haematocrit, some electrolytes
  7. 7.  Less pain for patients  Fewer complications, especially vascular and infection  Fewer needle-stick injuries to staff  Easier blood draw  Minimal training requirement
  8. 8. Respiratory Disease Metabolic disease  Is my patient hypoxic?  Does this patient have respiratory failure?  Is this patient a CO2 retainer?  Do I need to provide additional ventilatory support?  Is my treatment working?  Is my patient acidotic/ alkalotic?  What sort of acid-base disturbance do they have?  Is my treatment working?
  9. 9. ELISSA WOULD YOU?  18 year old  Known asthmatic, previous admissions  2 day exacerbation  Arrival by ambulance  Pulse 120, SpO2 on oxygen 93%, able to speak in short phrases, tight wheeze  Obtain an ABG for pO2, pCO2 and pH?  Obtain a VBG for pCO2 and pH?  Obtain a VBG for pH and hypercarbia screen?  Proceed without blood gas based on clinical assessment
  10. 10. Clinical features VBG RESULT  18 year old  Known asthmatic, previous admissions  2 day exacerbation  Arrival by ambulance  Pulse 120, SpO2 on oxygen 93%, able to speak in short phrases, tight wheeze  VBG result ◦ pH 7.35 ◦ pCO2 35mmHg (4.7 kPa)  Is this data enough to guide initial clinical decision- making? ◦ Yes ◦ No ◦ Unsure
  11. 11. TRAN WOULD YOU?  74 year old  Known COPD  Acute respiratory distress  Pulse 118, BP 140  Respiratory rate 35  SpO2 (air) 86%  Obtain an ABG for pO2, pCO2 and pH?  Obtain a VBG for pCO2 and pH?  Obtain a VBG for pH and hypercarbia screen?  Proceed without blood gas based on clinical assessment
  12. 12. Clinical features VBG result  74 year old  Known COPD  Acute respiratory distress  Pulse 118, BP 140  Respiratory rate 35  SpO2 (air) 86%  VBG result ◦ pH 7.16 ◦ pCO2 82.6mmHg (11 kPa) ◦ Bicarbonate 28.8mmmol/l  Is this data enough to guide initial clinical decision- making? ◦ Yes ◦ No ◦ Unsure
  13. 13. Clinical features A different VBG result  74 year old  Known COPD  Acute respiratory distress  Pulse 118, BP 140  Respiratory rate 35  SpO2 (air) 86%  VBG result ◦ pH 7.45 ◦ pCO2 42mmHg (5.6 kPa) ◦ Bicarbonate 28.8mmmol/l  What about this?
  14. 14. JANE WOULD YOU?  26 year old  Insulin dependent diabetic  2 days of vomiting and diarrhoea  Pulse 125, BP 100  Bedside glucose ‘Hi’  Obtain an ABG for pO2, pCO2 and pH?  Obtain a VBG for pCO2 and pH?  Obtain a VBG for pH and hypercarbia screen?  Proceed without blood gas based on clinical assessment
  15. 15. Clinical features VBG result  26 year old  Insulin dependent diabetic  2 days of vomiting and diarrhoea  Pulse 125, BP 100  Bedside glucose ‘Hi’  VBG result: ◦ pH: 7.26 ◦ pCO2 16mmHg (2.1 kPa) ◦ Bicarbonate 7.1 mmol/l ◦ Potassium 3.8 mmol/l ◦ Base excess -14  Is this data enough to guide initial clinical decision- making? ◦ Yes ◦ No ◦ Unsure
  16. 16.  Outcome of interest is how closely venous and arterial values agree, not how well they correlate  Weighted mean difference gives an estimate of the accuracy between the methods  95% limits of agreement give information about precision Arterial value Venous value 95% LoA
  17. 17.  There is limited data about the tolerance clinicians have with respect to agreement between arterial and venous values of blood gas parameters  Depending on this tolerance, the degree of agreement may be acceptable or unacceptable ◦ There is considerable variation between clinicians regarding this tolerance!
  18. 18.  A number of relatively small studies  Patient cohorts are highly varied  Patient groups of interest are those at high risk of acidosis or hypercarbia ◦ Reporting does not always provide this detail ◦ Data is often dominated by patients with normal pH, pCO2 and blood pressure
  19. 19.  13 studies ◦ Range from 44 to 346 patients  Various conditions ◦ DKA (3), COAD (4), trauma (1)  2009 patients  Weighted mean difference of 0.033 pH units  95% limits of agreement generally within +/- 0.1 pH units
  20. 20.  COAD ◦ 5 studies (643 patients) ◦ Weighted mean difference= 0.034 pH units ◦ 95% limits of agreement generally +/- 0.1
  21. 21.  DKA ◦ 3 studies (265 patients) ◦ Weighted mean difference = 0.02 pH units ◦ 95% limits of agreement = -0.009 to 0.02 pH units (1 study)
  22. 22.  In patients without severe circulatory compromise, agreement between arterial and venous values for pH in both metabolic and respiratory conditions is close.  Level of a agreement is probably clinically acceptable to most clinicians.
  23. 23.  8 studies  965 patients  Various conditions ◦ COAD 4  Weighted mean difference = 6.2 mmHg  95% limits of agreement: up to -17.4 to +23.9 mmHg ◦ 5/7 studies reporting LoA report LoA band >20mmHg
  24. 24.  4 studies  452 patients  Weighted man difference = 7.26 mmHg  95% limits of agreement: up to -14 to +26mmHg ◦ All 3 studies that report LoA have LoA band >20mmHg
  25. 25.  Agreement between venous and arterial pCO2 is NOT good enough for clinical inter-changeability BUT WAIT ......
  26. 26. Author, year No. Screening cut-off Sens. Spec. NPV %ABG avoided Kelly, 2002 196 45 100 57 100 43 Kelly, 2005 107 45 100 47 100 29 Ak, 2006 132 45 100 * 100 33 McCanny, 2011 94 45 100 34 100 23 POOLED DATA 529 45 100 (95% CI 97- 100) 53 (95% CI 57-58) 100 (95% CI 97- 100) 35% (95% CI 32-41) Data limited to studies in cohorts with respiratory disease
  27. 27.  1 study  Average difference between change in pH (v-a) was 0.001 (LoA -0.7 to +0.7).  Average difference between change in pCO2 (v-a) was 0.04mmHg (LoA -17.3 to +18.2).  For both pH and pCO2, in the majority of cases the direction of change was the same although the magnitude was variable.
  28. 28.  Agreement between venous and arterial pCO2 is NOT good enough for clinical inter-changeability  pCO2 on VBG is a reliable screening test for clinically relevant hypercarbia  In combination with clinical assessment, change in venous pH and pCO2may be useful to monitor progress but requires validation
  29. 29.  8 studies  1211 patients  Various conditions ◦ COAD =2  Weighted mean difference = -1.3mmol/l  95% limits of agreement : up to +/- 5mmol/l
  30. 30.  COAD ◦ 2 studies (643 patients) ◦ Weighted mean difference= -1.34 mmol/l ◦ 95% limits of agreement: none reported
  31. 31.  DKA ◦ 1 study (21 patients) ◦ Weighted mean difference = -1.88 mmol/l ◦ 95% limits of agreement = -2.8 to 0.9 mmol/l
  32. 32.  Limited data shows good agreement  Evidence regarding 95% limits of agreement is sparse  Probably close enough agreement for classification as high, low or normal  Clinical acceptability may be context specific
  33. 33.  Two studies only ◦ In a sample of 103 patients (various conditions), they report:  mean difference of 0.089  95% limits of agreement -0.974 to +0.552 ◦ In 326 trauma patients  mean difference -0.3 BE units  95% limits of agreement -4.4 to +3.9 BE units  20% did not fall within pre-defined clinical equivalence threshold Current view: Agreement unclear. If accuracy is needed in critically ill, need ABG.
  34. 34.  2 studies in DKA comparing BG vs serum K+  In both studies serum K+ is usually higher than BG K+.  Fu et al. ◦ 95% limits of agreement -0.96 to +1.19mmol/l ◦ 80% of patients had agreement within +/- 0.5mmmol/L  Roblas et al. ◦ Mean difference 1.13mmol/l (serum higher) ◦ 34% of patients had agreement within +/- 0.5 mmol/L.
  35. 35.  Conflicting data  No data in mixed acid-base disorders  Limited data in toxicological conditions
  36. 36.  Clinical decision-making isn’t just about the numbers  Clinical aspects of assessment are also important  Particularly the case in acute respiratory disease
  37. 37. ELISSA VBG RESULT  18 year old  Known asthmatic, previous admissions  2 day exacerbation  Arrival by ambulance  Pulse 120, SpO2 on oxygen 93%, able to speak in short phrases, tight wheeze  VBG result ◦ pH 7.35 ◦ pCO2 35mmHg (4.7 kPa)  Is this data enough to guide initial clinical decision- making? ◦Yes ◦ No ◦ Unsure
  38. 38. TRAN VBG result  74 year old  Known COPD  Acute respiratory distress  Pulse 118, BP 140  Respiratory rate 35  SpO2 (air) 86%  VBG result ◦ pH 7.16 ◦ pCO2 82.6mmHg (11 kPa) ◦ Bicarbonate 28.8mmmol/l  Is this data enough to guide initial clinical decision- making? ◦ Yes ◦ No ◦ Unsure
  39. 39. TRAN A different VBG result  74 year old  Known COPD  Acute respiratory distress  Pulse 118, BP 140  Respiratory rate 35  SpO2 (air) 86%  VBG result ◦ pH 7.45 ◦ pCO2 42mmHg (5.6 kPa) ◦ Bicarbonate 28.8mmmol/l  Is this data enough to guide initial clinical decision- making? ◦ Yes ◦ No ◦ Unsure
  40. 40. JANE VBG result  26 year old  Insulin dependent diabetic  2 days of vomiting and diarrhoea  Pulse 125, BP 100  Bedside glucose ‘Hi’  VBG result: ◦ pH: 7.26 ◦ pCO2 16mmHg (2.1 kPa) ◦ Bicarbonate 7.1 mmol/l ◦ Potassium 3.8 mmol/l ◦ Base excess -14  Is this data enough to guide initial clinical decision- making? ◦ Yes ◦ No ◦ Unsure
  41. 41.  pH and bicarbonate ◦ probably close enough agreement for clinical purposes in DKA, acute respiratory failure, isolated metabolic acidosis ◦ More work needed in toxicology, shock, mixed disease  pCO2 ◦ NOT enough agreement for clinical purposes, either as one-off or to monitor absolute change ◦ Data suggests venous pCO2 is useful as a screening test  Base excess ◦ Agreement unclear  Potassium ◦ Beware the error margin at the extremes of the normal range
  42. 42. Questions?Questions

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