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Three Part Question

In [a patient suspected of having an acute pulmonary embolism] can [a normal Po2 in room air] [rule out PE]?

Clinical Scenario

A 24 year-old girl attended the Emergency department with a history of pleuritic chest pain, she smokes and takes the pill but otherwise is fit and well. Blood gases in room air were normal to exclude pulmonary embolus. You wonder whether normal Pa O2 in room air is sufficient to rule out PE.

Search Strategy

1950 – November week 3 2008 using the OVID interface.
{[exp pulmonary embolism/ or pulmonary embol$.mp. or PE.mp. or exp thromboembolism/ or pulmonary infarct$.mp.} and [(sensitiv: or diagnos:).mp. or accuracy.tw.] and [oxygen.mp. or exp Oxygen or pO2.mp]}

Search Outcome

403 papers were found of which 7 were relevant.

Relevant Paper(s)

Author, date and country	Patient group	Study type (level of evidence)	Outcomes	Key results	Study Weaknesses
Stein PD et al, 1996, USA	768 patients, those enrolled to the PIOPED study and patients referred by GP for angiography with suspected PE.	Prospective cohort	% patients with PE and pO2 >80mmHg	53/277 19%	Cohort made up of study patients and GP referrals. Demographics not described.
Rodger MA et al, 2000, Canada	246 patients referred for PE imaging. Only 155 had ABG sampling.	Prospective Cohort	% patients with PE and pO2 >80mmHg	21/49 42%	20 patients had an ABG taken while breathing supplemental oxygen.
Stein PD et al, 2007, USA	824 patients investigated for PE in a multicentre study. Only 260 of this group had an ABG.	Prospective cohort	% patients with PE who had pO2 >80mmHg	24/74 32%	A minority of patients had an ABG taken. These may have been the sicker patients.
Metafratzi et al, 2006, Greece	78 patients with a high probability of PE who had been referred for CT pulmonary angiogram.	Prospective Cohort	pO2 range for those diagnosed with PE	63.9 ± 14.1mmHg	Patient group does not represent that of the ED. All patients high probability and presence of hypoxia may have prompted referral for CT.
Hlavac et al, 2005, New Zealand	149 patients age 18-60 with suspected PE. All had pO2 >80mmHg, normal D-dimer and no major risk factor.	Prospective cohort	Follow up at 3 months and one year	140/149 followed up at 3 months, 0/140 had been diagnosed with PE. 126/149 followed up at a year. 0/126 had been diagnosed with PE.	Arterial oxygen level used in combination with D-dimer result and clinical probability. Follow up did not include DVT episodes.
Masotti et al, 2000, Italy	118 medical inpatients over age 65 investigated for PE	Prospective Cohort	% patients with PE and pO2 >75mmHg	2/75 2.5%	Select population.
Egermayer et al, 1998, New Zealand	471 patients referred for PE imaging who also had ABG sampling.	Prospective Cohort	% patients with PE and pO2 >80mmHg	5/39 13%

Comment(s)

This analysis examines only whether a normal pO2 can exclude pulmonary embolism, not the A-a gradient or other blood gas parameters.

Clinical Bottom Line

A normal arterial pO2 does not exclude pulmonary embolic disease in a patient.

References

1. Stein PD. Goldhaber SZ. Henry JW. Miller AC. Arterial blood gas analysis in the assessment of suspected acute pulmonary embolism Chest 109(1):78-81, 1996 Jan.
2. Rodger MA. Carrier M. Jones GN. Rasuli P. Raymond F. Djunaedi H. Wells PS Diagnostic value of arterial blood gas measurement in suspected pulmonary embolism. American Journal of Respiratory & Critical Care Medicine. 162(6):2105-8, 2000 Dec.
3. Stein P, Beemath A, Matta F et al. Clinical Characteristics of Patients with Acute Pulmonary Embolism: Data from PIOPED II. Am J Med 2007; 120:871-879.
4. Metafratzi Z, Vassiliou M, Maglaras G et al. Acute Pulmonary Embolism: Correlation of CT Pulmonary Artery Obstruction Index with Blood Gas Values. AJR 2006; 186:213–219.
5. Hlavac M, Cook J, Ojala R et al. Latex-enhanced immunoassay D-dimer and blood gases can exclude pulmonary embolism in low-risk patients presenting to an acute care setting. Chest 2005; 128:2183-2189.
6. Masotti L, Ceccarelli E, Cappelli R et al. Arterial blood gas analysis and alveolar-arterial oxygen gradient in diagnosis and prognosis of elderly patients with suspected pulmonary embolism. J Geront 2000; 55(12):M761-4.
7. Egermayer P, Town G, Turner J et al. Usefulness of D-dimer, blood gas, and respiratory rate measurements for excluding pulmonary embolism. Thorax 1998; 53:830–834.