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Three Part Question

In an [acute exacerbation of COPD] can a [venous blood gas] reliably assess [ventilatory function]?

Clinical Scenario

A 65 year old female presents to the Emergency Department acutely short of breath. You diagnose an acute exacerbation of COPD. You take an arterial blood gas, but wonder whether a venous one would have sufficed.

Search Strategy

Databases searched included:
Embase Classic + Embase 1947–May 2013;
Medline 1946– May 2013;
Cochrane Database;
CINAHL and
TRIP.
Web sites searched included Google Scholar


A comprehensive literature search was conducted using the following search strategy:

[(arterial blood gas or abg).mp OR exp arterial gas/]
AND
[(exp venous blood/ and exp blood gas analysis/) OR (venous adj4 gas*).mp.]
AND
[(copd or chronic obstructive pulmonary disease).mp OR exp chronic obstructive lung disease/]

Search Outcome

Using all search methods, a total of 43 papers were found. 8 papers were directly relevant to the three part question. The review article by Kelly 2010 merely provided a summary of the primary research papers and offered no new evidence, therefore was not included.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Dilber H, Polat G, Büyüksirin M, Karadag Polat S, Tibet G. 2005 Turkey	100 patients presenting with exacerbation of COPD and acute respiratory failure as diagnosed by history, examination, CXR, ECG, spirometry and ABG.	Single centre prospective observational study. Level 3 evidence	Venous blood gases can be used instead of arterial gases when looking at pH, pCO2 and HCO3	r>0.7 for correlation of arterial and venous pH, pCO2 and HCO3	Not generalisable to UK based population: 83% male, 17% female. No power calculation. Convenience sample. No mean differences or Bland Altman analysis performed between arterial and venous values. Incorrect conclusion based on statistical analyses used.
Kelly AM, Kerr D, Middleton P. 2005 Australia	107 patients presenting with COPD as judged by the treating clinician	Single centre prospective observational validation study. Level 3 evidence	A venous cut-off value of pCO2<45mmHg will rule out arterial hypercarbia	Bland Altman testing showed little agreement between venous and arterial pCO2. 100% sensitivity, 47% specificity and NPV 100% for vdetecting arterial hypercarbia when a venous pCO2<45mmHG cut-off used	No demographic data other than age available. No power calculation. Convenience sample. Wide confidence intervals for all documented statistics.
Ak A, Ogun CO, Bayir A, Kayis SA, Koylu R 2006 Turkey	132 patients presenting with exacerbations of COPD as defined by the Acute Exacerbation of COPD Criteria (Burge & Wedzicha)	Single centre prospective observational study. Level 3 evidence	Venous blood gases can reliably predict the arterial values of pH, pCO2 and HCO3. A venous screening cut-off of 45mmHg will reliably detect arterial hypercarbia	r>0.9 for correlation of arterial and venous pH, PCO2 and HCO3. r<0.3 for pO2 values. 100% sensitivity, NPV 100% and PPV 62% for vernous pCO2 <46mmHg cut-off in detecting arterial hypercarbia	Not generalisable to UK based population: 70% male; 30% female. No power calculation. Exclusion criteria not adhered to. No confidence intervals given for sensitivity, PPV or NPV.
Razi E, Moosavi GA 2007 Iran	Single centre prospective observational study. Level 3 evidence	107 patients presenting with exacerbations of COPD associated with hypercarbia and a pCO2>45mmHg	Despite a strong correlation, venous blood gases cannot be used as a substitute for arterial gases as the correlation was not close or excellent.	r>0.7 for correlation of arterial and venous pH, pCO2, pO2 and HCO3. At higher venous oxygen saturations (≥70%) there is an increased number of patients with venous to arterial pCO2<5mmHg compared to when venous oxygen saturations are lower	Not generalisable to a UK based population: 74% male, 26% female. Selected patients mean that a complete range of presentations have not been explored therefore limiting applicability. Convenience sample. No power calculation. No relevance given to post hoc analysis regarding pCO2 level at different venous oxygen saturations. Mean difference between arterial and venous parameters given but not interpreted. No Bland Altman analysis performed.
Lim BL, Kelly AM 2010 Australia	Meta-analysis to identify the utility of venous blood gases in exacerbations of COPD.	Meta-analysis of prospective observational studies. SIGN 50 1-	pH and HCO3 parameters for venous blood gases are clinically interchangeable with arterial blood gases.	Weighted average differences of pH, pCO2 and HCO3. Range of LOA for pH, pCO2 and HCO3	Inclusion criteria not adhered to. Clinically heterogeneous papers. Statistically flawed results. No evidence levels assigned.
Novovic M, Topic V. 2012 Serbia	47 patients presenting with COPD as defined by an increased sputum production, purulent sputum and dyspnoea	Single centre prospective observational study	pH, pCO2 and HCO3 values from venous blood gases can be used as a substitute for an arterial blood gas	r>0.7 for correlation of arterial and venous pH, pCO2 and HCO3; r<0.6 for pO2 values	Small sample size. No power calculation. Incorrect conclusion based on statistical analyses. Mean difference between arterial and venous parameters given but not interpreted
McCanny P, Bennett K, Staunton P, McMahon G. 2012 Australia	89 patients with a previously documented diagnosis of COPD presenting with an acute exacerbation	Single centre prospective observational study	A venous blood gas can accurately determine arterial hypercarbia. There is insufficient evidence for a venous blood gas to replace an arterial one.	Bland Altman shows good agreement and narrow LOA's between arterial and venous pH, but little agreement and wide LOA's between pCO2 values. 100% sensitiviity, 34% specificity given for a pCO2 cut-off of venous pCO2<45mmHg. r>0.8 for correlation of arterial and venous pH and HCO3.	Smaller than required sample size. Convenience sample. Statistical techniques not uniformly applied to data No definition f arterial hypercarbia.

Comment(s)

Venous pH and HCO3 can be used interchangeably with arterial values in patients with COPD. Using Bland Altman analysis, there is insufficient agreement between arterial and venous pCO2 for them to be used interchangeably. However, if venous pCO2 is less than 45mmHg it can confidently be said that the patient will not have arterial hypercarbia, therefore does not need an ABG.

Clinical Bottom Line

In patients with acute exacerbations of COPD, a venous blood gas can be used to assess ventilatory function.

References

1. Dilber H, Polat G, Büyüksirin M, Karadag Polat S, Tibet G. Comparison of venous and arterial blood values in cases of COPD with acute respiratory failure. Izmir Pulmonary Diseases Journal 2005;19(1):7-13
2. Kelly AM, Kerr D, Middleton P. Validation of venous pCO2 to screen for arterial hypercarbia in patients with chronic obstructive airways disease. J Emerg Med 2005;28(4):377-9
3. Ak A, Ogun CO, Bayir A, Kayis SA, Koylu R Prediction of arterial blood gas values from venous blood gas values in patients with acute exacerbation of chronic obstructive pulmonary disease Tohoku J Exp Med 2006;210(4):285-90
4. Razi E, Moosavi GA Comparison of arterial and venous blood gases analysis in patients with exacerbation of chronic obstructive pulmonary disease Saudi Med J 2007;28(6):862-5
5. Lim BL, Kelly AM A meta-analysis on the utility of peripheral venous blood gas analyses in exacerbations of chronic obstructive pulmonary disease in the emergency department Eur J Emerg Med 2010;17(5):246-248
6. Novovic M, Topic V. Correlation between arterial and venous blood gas analysis parameters in patients with acute exacerbation of chronic obstructive pulmonary disease Srp Arh Celok Lek 2012;140(7-8):436-440
7. McCanny P, Bennett K, Staunton P, McMahon G. Venous vs arterial blood gases in the assessment of patients presenting with an exacerbation of chronic obstructive pulmonary disease Am J Emerg Med 2012;30(6):896-900