65 year old female presents with collapse and sudden onset SOB

Metabolic Acidosis – pH7.08

Compensation – Expected pCO2 = 1.5x HCO3+8 = 35mmHg (actual pCO2 61mmHg)

AG = Na -(Cl+HCO3) =20

Delta Gap =(AG-12)/(24-HCO3)=1.3

Expected pAO2 =(713xFiO2)-(PCO2x1.25)=351

A-a gradient =283 (normal =age/4+4=20)

Description:The ABG of this patient shows a metabolic acidaemia with inadequate respiratory compensation or underlying respiratory acidosis. The acidosis is a pure HAGMA, with a delta gap of 1.3.  There is a markedly raised A-a gradient. There are no electrolyte abnormalities but the patient has a moderately high lactate.

Interpretation: In this clinical context the underlying HAGMA is most likely secondary to a lactic acidosis caused by hypoxia and shock.  With the history of collapse and shortness of breath, together with a clear CXR and markedly raised A-a gradient, the most likely diagnosis would be a PE.

Classification of PE by severity and management:

Massive PE – pulseless or sustained hypotension (BP<90mmHg) not due to arrhythmia, hypovolaemia, sepsis, or LV dysfunction. Treated with thrombolysis or embolectomy

Submassive -right ventricular dysfunction or myocardial necrosis, with no hypotension. Treatment – anticoagulation with HDU admission. There is debate around if there is long term benefit to thrombolysis or embolectomy in these patients

Low Risk- absence of hypotension, RV dysfunction and myocardial necrosis. Treatment -anticoagulation.

Prognostic Scores

PESI and Geneva prognostic scores have been used to define low risk groups. The PESI score was originally designed to predict patients mortality and morbidity from PE’s. It has since been validated in a large randomized trial confirming safety in some patients with PE for home therapy.  See MDCalc. All patients social and individual circumstances need to be taken into account prior to applying these scores for outpatient treatment.