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Three Part Question

In [patients with clinical diagnosis of pulmonary embolus] do [arterial blood gases] aid in [making a definite diagnosis]?

Clinical Scenario

A 28 year old woman presents with acute suspected pulmonary embolus (PE). You wonder whether normal arterial blood gases are sufficient to rule out pulmonary embolus.

Search Strategy

Medline OVID1966- 2005 Feb week 1
Embase OVID 1980-2005 week 7
(exp pulmonary embolism/ OR pulmonary embolus.mp.) AND (exp embolism/ OR embol$.mp. OR exp thromboembolism/ OR thromboembol$.mp.) AND (exp blood gas analysis/ OR arterial blood gas$.mp.)

Search Outcome

459 papers were found of which 6 directly addressed the question

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Cvitanic et al 1989 USA	78 patients with angiographically proven PE, and no cardiopulmonary disease.	Retrospective cohort	Sensitivity of hypoxaemia	76%,	Excluded all patients with cardiopulmonary disease
Stein PD 1995 USA	768 patients age>18, with clinical diagnosis of PE (Part of Prospective Investigation Of Pulmonary Embolism Diagnosis - PIOPED study)	Prospective Randomized Control trial (PRCT)	Negative predictive value	pCO2=65%; pO2=68%	Recruitment bias -only those with written consent were recruited (APPX half of all suitable patients)
			Specificity	pCO2=50%; pO2=24%
			Positive predictive value	pCO2=37%; pO2=37%
			Sensitivity	pCO2=51%; pO2=81%
Jones S 1997 USA	197 emergency department patients who underwent pulmonary angiography for presumed diagnosis of acute PE	Retrospective Cohort	Negative Predictive Value	pCO2>35 (61%); pO2>80 (66%)	-Seriously ill patients possibly excluded because they were on oxygen -Selection bias as only patients with angiography were recruited
			Specificity	pCO2>35 (51%); pO2>80 (25%)
Prediletto R 1999 Italy	773 consecutive patients with suspected PE (Part of PISAPED study)	PRCT	PE present with normal pO2	14%	Not all patients had gold standard (Angiogram)
			PE present with normal pCO2	35%
			PE absent with normal pO2	13%
			PE absent with normal pCO2	55%
Masotti L 2000 Italy	118 patients aged over 65years who had VQ scan for suspected PE	Retrospective Cohort	Blood gases in patients with and without PE	No significant differences	-No gold standard -Minimal data and statistics given
Rodger MA 2000 Canada	293 consecutive patients referred for imaging (VQ or Pulmonary Angiography)	Prospective Cohort	Unpaired t-test for PE/non PE	No significant differences	Not all patients got gold standard

Comment(s)

Pulmonary angiography, the gold standard diagnostic tool in Pulmonary Embolism,has an unacceptibly high mortality and morbidity rate. It cannot presently be used routinely in clinical practice. A reliable, cost effective, non invasive test if identified would be of great use.

Clinical Bottom Line

Arterial blood gas analysis alone is of very limited diagnostic utility in suspected pulmonary embolism.

References

1. Cvitac, O Improved use of Arterial Blood Gas Analysis in Suspected Pulmonary Embolism Chest 1989;95:48-51
2. Stein PD Arterial blood Gas Analysis in the Assessment of Suspected Acute Pulmonary Embolism Chest 1996;109:78-81
3. Jones J S Use of the Alveolar-Arterial Oxygen Gradient in the Assessment of Acute Pulmonary Embolism American Journal of Emergency Medicine July 1998; 16:333-337
4. Prediletto R Diagnostic value of gas exchange tests in patients with clinical suspicion of pulmonary embolism Critical Care 1999; 3:111-116
5. Masotti L Arterial Blood Gas Analysis and Alveolar-Arterial Oxygen Gradient in Diagnosis and Prognosis of Elderly Patients With Suspected Pulmonary Embolism Journal of Gerontology 2000; 55A:M761-M764
6. Rodger MA Diagnostic Value of Arterial Blood Gas Measurement in Suspected Pulmonary Embolism American Journal of Respiratory and Critical Care Medicine 2000; 162: 2105-2108