CHEST PAINGeneral Medical Emergencies 535 Establish venous access with an i.v. cannula, send blood for FBC, coagulation
profile and ELFTs, and attach a cardiac monitor and pulse oximeter to the patient.
(i) Only request a D-dimer test after assessing the clinical pre-test
probability as low and one or more PE rule-out criteria (PERC)
are positive. See points 9 to 11 below.
6 Consider a blood gas that may ref lect hypocapnia from hyperventilation, and
less commonly hy poxia, but t hat will be norma l in over 20% patients wit h PE.
(i) Do not perform an arterial blood gas (ABG) routinely, unless
there is an unexplained low pulse oximeter reading on room air.
ABGs rarely help.
7 Perform an ECG, mainly to exclude other diagnoses such as ACS or pericarditis.
(i) It may show a tachycardia alone or possibly right axis deviation,
right heart strain, right bundle branch block (RBBB) or atrial
fibrillation (AF) in PE.
(ii) The well-known ‘S1Q3T3’ pattern is neither sensitive nor specific
for PE.
8 Request a CXR, again mainly to exclude other diagnoses such as pneumonia
or a pneumothorax.
(i) It may be normal in PE, or show a blunted costophrenic angle,
raised hemidiaphragm, an area of linear atelectasis or infarction,
or an area of oligaemia.
9 Determine the clinical pre-test probability now before requesting any
further diagnostic imaging (see Table 2.3).Table 2.3 Estimation of the clinical pre-test probability for suspected pulmonary
embolus (PE)
Feature Score
Clinical signs and symptoms of DVT (minimum of leg swelling and pain
with palpation of the deep veins. See p. 55) 3
Alternative diagnosis less likely than PE 3
Heart rate >100 beats/min 1.5
Immobilization or surgery in previous 4 weeks 1.5
Previous DVT or PE 1.5
Haemoptysis 1
Cancer 1
Low pre-test probability = score < 2 Moderate pre-test probability = score 2–6
High pre-test probability = score > 6
DVT, deep venous thrombosis; PE, pulmonary embolus.
Modified from Wells PS, Anderson DR, Rodger M et al. (2001) Excluding pulmonary
embolism at the bedside without diagnostic imaging: management of patients with
suspected pulmonary embolism presenting to the emergency department by using a
simple clinical model and D-dimer. Ann Intern Med 135:98–107.