In patients presenting with an exacerbation of COPD can a normal venous blood gas pCO2 rule out arterial hypercarbia?
Date First Published:
August 31, 2012
Last Updated:
March 11, 2015
Report by:
Mark Woods, Consultant in Emergency Medicine (Whiston Hospital, Merseyside, UK and Mersey School of Emergency Medicine, UK)
Search checked by:
David Hodgson, Whiston Hospital, Merseyside, UK and Mersey School of Emergency Medicine, UK
Three-Part Question:
In [patients with an Acute Exacerbation of COPD] can a [normal venous blood gas CO2] [rule out arterial hypercarbia]?
Clinical Scenario:
A 74 year old male patient with known COPD presents acutely breathless with widespread wheeze. He refuses an arterial blood gas (ABG) and complains that last time he was here it took a long time to get the sample and it was very painful. You have already obtained a venous blood gas which has a PaCO2 of 5.5kPa. You wonder if this is sufficient to rule out arterial hypercarbia, and therefore, is an ABG in this patient an unnecessary test?
Search Strategy:
Ovid MEDLINE(R) 1948 to week 4 November 2014. Embase and CINHAL databases via the Athens gateway. Cochrane database of systematic reviews. Date of search is 31/07/2013.
Search Details:
Medline:[chronic obstructive pulmonary disease.ti,ab OR chronic obstructive airway* disease.ti,ab OR COPD.ti OR COAD.ti OR BRONCHITIS OR BRONCHITIS, CHRONIC OR EMPHYSEMA OR PULMONARY EMPHYSEMA] AND [venous blood gas*.ti,ab OR vbg*.ti,ab OR venous co2.ti,ab OR [exp BLOOD GAS ANALYSIS AND VENOUS] OR [hypercarbia.ti,ab AND VEOUS] OR [exp HYPERCAPNIA AND VENOUS] OR [exp CARBON DIOXIDE/bl [bl=Blood] AND VENOUS] LIMIT to English Language
EMBASE: [chronic obstructive pulmonary disease.ti,ab OR chronic obstructive airway* disease.ti,ab OR COPD.ti OR COAD.ti OR BRONCHITIS OR BRONCHITIS, CHRONIC OR EMPHYSEMA OR PULMONARY EMPHYSEMA] AND [venous blood gas*.ti,ab OR vbg*.ti,ab OR venous co2.ti,ab OR [exp BLOOD GAS ANALYSIS AND VENOUS] OR [hypercarbia.ti,ab AND VEOUS] OR [exp HYPERCAPNIA AND VENOUS] OR [exp CARBON DIOXIDE/bl [bl=Blood] AND VENOUS] LIMIT to English Language
EMBASE: [chronic obstructive pulmonary disease.ti,ab OR chronic obstructive airway* disease.ti,ab OR COPD.ti OR COAD.ti OR BRONCHITIS OR BRONCHITIS, CHRONIC OR EMPHYSEMA OR PULMONARY EMPHYSEMA] AND [venous blood gas*.ti,ab OR vbg*.ti,ab OR venous co2.ti,ab OR [exp BLOOD GAS ANALYSIS AND VENOUS] OR [hypercarbia.ti,ab AND VEOUS] OR [exp HYPERCAPNIA AND VENOUS] OR [exp CARBON DIOXIDE/bl [bl=Blood] AND VENOUS] LIMIT to English Language
Outcome:
17 papers where identified in total. 11 were of sufficient quality and relevance for inclusion.
Relevant Paper(s):
| Study Title | Patient Group | Study type (level of evidence) | Outcomes | Key results | Study Weaknesses |
|---|---|---|---|---|---|
| Non-arterial assessment of blood gas status in patients with chronic pulmonary disease. Elborn JS, Finch MB, Stanford CF. 1991 Ireland | 48 Inpatients with COPD | Single centre prospective study | Difference between arterial and venous CO2 values | No significant difference between the arterial and venous CO2 tensions (PaCO2 41+/- 9.5mmHg, PvCO2 42+/-10.6mmHg), with the two being closely related (r=0.84, p<0.001) | Small sample. No power calculation. Single centre. No inclusion or exclusion criteria stated. |
| Can peripheral venous blood gases replace arterial blood gases in emergency department patients? Rang LCF, Murray HE, Wells GA, MacGougan CK. 2002 Canada | 218 patients presenting to a single centre requiring blood gas analysis for any reason. | Single centre prospective convenience study | Correlation between arterial and venous CO2 | r=0.921 | Small cohort. Single centre. Cohort not limited to COPD. |
| Venous pCO2 and pH can be used to screen for significant hypercarbia in emergency patients with acute respiratory disease Kelly AM, Kyle E, McAlpine R. 2002 Australia | 201 patients presenting with 'acute respiratory illness or potential ventilatory compromise' | Single centre prospective convenience study | Sensitivity and specificity of venous pCO2 to detect arterial normocarbia with a cut off value of 6kPa | Sensitivity 100%. Specificity 57.1% | Single centre. No power calculation. Population not limited to patients with COPD. |
| Validation of venous pCO2 to screen for arterial hypercarbia in patients with chronic obstructive airways disease Kelly AM, Kerr D, Middleton P. 2005 Australia | 107 patients presenting to a single centre with COPD | Single centre prospective validation study | Sensitivity of venous pCO2 to detect arterial normocarbia with a cut off value of 6kPa | Sensitivity 100%. 95% CI; 91-100% | Single centre. Small sample size. No power calculation. Limited demographics available for interrogation. |
| Prediction of arterial blood gas values from venous blood gas values in patients with acute exacerbation of chronic obstructive pulmonary disease Ak A, Ogun CO, Bayor A et al. 2006 Turkey | 132 patients presenting with AECOPD | Single centre prospective observational study using convenience sampling. | Correlation between arterial and venous CO2 | r=0.908 | Single centre. No power calculation. No CI provided for statistics. Cohort limited to COPD but not excluding other metabolic disorders. Possible confounders: high altitude and skewed populations towards men. |
| Equation to estimate arterial pCO2 from venous pCO2 using linear regression | Arterial pCO2 = 0.873 x venous pCO2 | ||||
| utility of venous pCO2 to detect arterial hypercarbia (>46mmHg) | 100% sensitivity and NPV. 47% specifity | ||||
| Comparison of arterial and venous blood gases analysis in patients with exacerbation of chronic obstructive pulmonary disease Razi E, Moosavi GA. 2007 Iran | 107 patients presenting with COPD and type 2 respiratory failure (pCO2 > 45mmHg). Convenience sampling used. | Single centre prospective observational study. | Correlation between arterial and venous CO2 | r=0.761 | Single centre. No power calculation. Cohort limited to hypercarbic COPD patients. Excessive exclusion criteria. Skewed population towards men. |
| A meta-analysis on the utility of peripheral venous blood gas analysis in exacerbations of chronic obstructive pulmonary disease in the emergency department Lim BL, Kelly AM. 2010 Australia | Meta-analysis of the literature on the use of peripheral VBGs in ED patients with COPD. | Meta-analysis of prospective observational studies | The weighted average difference for pCO2 | 5.92mmHg | Limits of heterogenous individual studies included in analysis. Only 6 studies. 3 of which not limited to COPD population. 1 author of meta-analysis is also author of 2 of included studies. |
| Point-of-care bedside gas analyzer: limited use of venous pCO2 in emergency patients Ibrahim I, Ooi SBS, Huak CY, Sethi S. 2011 Singapore | 122 patients requiring ABG analysis as decided by treating physician | Single centre cross-sectional study | Sensitivity and negative predictive value of excluding arterial hypercarbia with a venous PCO2 of below 30mmHg | 100% sensitivity and 100% NPV | Single centre. No power calculation. Cohort not limited to COPD. Possible interpreter bias – pCO2 threshold calculated retrospectively. |
| Venous vs. arterial blood gases in the assessment of patients presenting with an exacerbation of chronic obstructive pulmonary disease McCanny P, Bennett K, Staunton P, McMahon G. 2012 Australia | 89 patients presenting with COPD. Paired arterial and venous blood gas analyses. | Single centre prospective observational study | Sensitivity of venous pCO2 to detect arterial normocarbia with a cut off value of 6kPa | 100% sensitivity | Single centre. Underpowered sample size. Small cohort. Convenience sampling used. |
| Agreement between arterial and venous blood gases in emergency medical care: a systematic review Kelly AM. 2013 Australia | 529 Patients presenting with COPD across 4 studies | Systematic review | Sensitivity of venous pCO2 to detect arterial normocarbia with a cut off value of 45mmHg | 100% sensitivity | Reliance on validity of included studies. |
| COPD: is it all in the vein? Sur, E 2013 Scotland | Patients presenting with an acute exacerbation of COPD to a Scottish urban ED had arterial and venous blood gas analyses. 68 paired samples were compared over a 2 month period. | Prospective observational study | Correlation between arterial and venouspCO2 | Pearson's r=0.973, but 95% LOA -4.94 to 14.26 mmHg | Results presented as a poster. Blood gas analysis performed at physician's discretion rather that according to preset criteria. |
| Detection of arterial hypercarbia, pCO2>45 mmHg | 31 patients (46%), all cases detected by venous pCO2>45 mmHg. Sensitivity 100% (95% CI 89-100%), specificity 86% (95% CI 71-95%). |
Author Commentary:
Arterial blood gas analysis is conventionally a routine test in the assessment of patients with AECOPD. One has to question this practice. Arterial blood gas analysis has many complications including severe pain, failure of procedure, haematoma formation, aneurysm formation, arterial laceration, sepsis and rarely loss of limb. This must be weighed up with the benefit of the procedure, and the principle of 'first do no harm' born into mind. These studies demonstrate that if the venous pCO2 is within range then this excludes arterial hypercarbia. One may argue an arterial sample is still required to assess the pO2, however, the BTS guidelines support using transcutanous oxygen saturations to titrate O2 therapy.
Bottom Line:
In patients presenting with AECOPD, if they have a normal pCO2 on a VBG they do not need an ABG to exclude hypercarbia.
References:
- Elborn JS, Finch MB, Stanford CF.. Non-arterial assessment of blood gas status in patients with chronic pulmonary disease.
- Rang LCF, Murray HE, Wells GA, MacGougan CK.. Can peripheral venous blood gases replace arterial blood gases in emergency department patients?
- Kelly AM, Kyle E, McAlpine R.. Venous pCO2 and pH can be used to screen for significant hypercarbia in emergency patients with acute respiratory disease
- Kelly AM, Kerr D, Middleton P.. Validation of venous pCO2 to screen for arterial hypercarbia in patients with chronic obstructive airways disease
- Ak A, Ogun CO, Bayor A et al.. Prediction of arterial blood gas values from venous blood gas values in patients with acute exacerbation of chronic obstructive pulmonary disease
- Razi E, Moosavi GA.. Comparison of arterial and venous blood gases analysis in patients with exacerbation of chronic obstructive pulmonary disease
- Lim BL, Kelly AM.. A meta-analysis on the utility of peripheral venous blood gas analysis in exacerbations of chronic obstructive pulmonary disease in the emergency department
- Ibrahim I, Ooi SBS, Huak CY, Sethi S.. Point-of-care bedside gas analyzer: limited use of venous pCO2 in emergency patients
- 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
- Kelly AM.. Agreement between arterial and venous blood gases in emergency medical care: a systematic review
- Sur, E. COPD: is it all in the vein?