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Arterial Blood Gas Analysis and Alveolar-Arterial Oxygen Gradient in Diagnosis and Prognosis of Elderly Patients With Suspected Pulmonary Embolism

^a Institute of Internal Medicine and Geriatrics, University of Siena, Italy
^b Department of Quantitative Methods, University of Siena, Italy

Correspondence: L. Masotti, Istituto di Medicina Interna e Geriatria, Policlinico Le Scotte, Viale Bracci 1 53100 Siena, Italy E-mail: images{at}unisi.it.

Decision Editor: John E. Morley, MB, BCh

Background. Arterial blood gas analysis (BGA) remains a first-step diagnostic approach in patients with suspected pulmonary embolism (PE). The aim of this study was to evaluate BGA parameters in elderly patients with suspected pulmonary embolism for diagnosis and 14-day prognosis.

Methods. We performed a retrospective cohort observational study of 6 years (1994–1999) in a 60-bed acute geriatric ward of University Hospital in Siena, Italy. Room air arterial oxygen partial pressure (pO₂), arterial carbon dioxide partial pressure (pCO₂), pH, arterial oxyhemoglobin saturation (SO₂), and alveolar-arterial oxygen gradient [D(A-a)O₂] were performed on hospital admission of 75 patients with confirmed PE (CPE) and were compared with data from 43 patients with unconfirmed PE (UCPE). The same parameters of 54 CPE surviving patients were compared with 21 CPE nonsurviving patients.

Results. Significantly lower pO₂ and SO_2, and higher DA-aO₂ were found in CPE patients. Respiratory alkalosis was found in one third of the patients in both groups (no significant difference). In the CPE group, there was a significantly lower SO₂ in nonsurviving patients, without significant differences for the other parameters. Metabolic acidosis was significantly more frequent in nonsurviving patients.

Conclusion. More severe hypoxemia, oxyhemoglobin hyposaturation, and higher D(A-a)O₂ are associated with the diagnosis of PE in elderly patients. Respiratory alkalosis is less frequent than in younger patients, and metabolic disorders are negative prognostic indicators.