D-dimer in diagnosing of PE

There were five trauma cases this morning in the ICU. The ICU 2 was admitted during the weekend. Another polytrauma case (without TBI), who developed acute respiratory failure and required ventilatory support. The injuries are fracture  right ribs from 2nd to 5th, lung contusion, open book fracture and fracture femur. The C-spine was cleared clinically. There were bilateral pulmonary infiltrates on both sides of the lungs. He has moderate increased in A-a gradient. I start to go thru few differential diagnoses in my mind which include fat embolism syndrome, PE, aspiration pneumonia, worsening lung contusions and finally TRALI. Suddenly I was distracted by the MO's comment: Since the D-dimer was positive, this patient has been treated for pulmonary embolism and 'they' have started him on fondaparinux...I asked, what was the next plan? She said, the orthopedic team is planning for ILN once this patient is more 'stable'..Actually, I raised few issues, first of all the safety of fondaparinux in this pelvic injury and secondly since when D-dimer was used as a confirmatory test for PE??

"D-dimer assays for the diagnosis of PE have been extensively studied. They are best characterized as having good sensitivity and negative predictive value but poor specificity and positive predictive value."

Sensitivity: D-dimer levels are abnormal in about 95% of all patients with PE when measured by ELISA, quantitative rapid ELISA or semi-quantitative rapid ELISA. This falls to about 90% when measured by qualitative rapid ELISA or quantitative latex agglutination, 86% measured by semiquantitative latex agglutination and 82% measured by erythrocyte agglutination. Among patients who have subsegmental PE, d-dimer levels are abnormal in only 50% when measured by quantitative latex agglutination.

Specificity: D-dimer levels are normal in only 40-68% of patients without PE, regardless of the assay used. This is a consequence of abnormal D-dimer levels being common among hospitalized patients, especially those with malignancy or recent surgery. The specificity decreases even further in the setting of severe renal dysfunction and increased patient age.

NPV: The ability of a normal or negative D-dimer assay to exclude acute PE  depends on both the type of D-dimer assay and the clinical pretest probability that a patient has acute PE.

Taken together, the evidence indicates that a D-dimer level less than 500ng/ml by quantitative ELISA or semiquantitative latex agglutination is sufficient to exclude PE in patients with a low or moderate pretest probability of PE.
source: uptodate.com



 

BLUNT AORTIC INJURY

Today, during the morning handover, there was a polytrauma case. Very interesting, since he has thoracic aorta dissection,, open book fracture of pelvis, liver laceration and fracture femur. Another striking findings were rhabdomyolysis and acute kidney injury. This is a very interesting case since there are a few possible causes of acute kidney injury which include hypovolemia, contrast induced nephropathy, rhabdomyolisis, and trauma to the genitourinary tract.

I asked the MO, was the dissection due to blunt aortic injury?? Well, she didn't have a clue.

Blunt aortic injury usually occur at the junction between the mobile arch and the fixed descending aorta, just distal to the origin of the left subclavian artery, as a result of severe deceleration injury. Less frequently, the ascending aorta or arch vessels are injured by direct trauma.

It is divided into two:
1. Significant aortic injury: with disruption of the intima and full thickness of the media. There is a high risk of rupture

2. Minimal aortic injury: with laceration limited to the intima and inner media.  Radiologically this manifests as an intimal flap< 1 cm with minimal periaortic hematoma. There is a low risk of rupture

Clinical signs include unequal upper limb pulses, pseudocoarctation or interscapular murmur. The aortic injury should be suspected if the mechanism of injury is suggestive of rapid deceleration such as high speed (greater than 90 km/hr) motor vehicle or motorcycle crashes or a pedestrian hit by a vehicle.
CT and transesophageal echocardiography have been used for screening and diagnostic purposes.
Limitation of TOE : it provides high diagnostic accuracy for aortic injury and also allows examination for blunt cardiac injury. Imaging of distal aorta, proximal arch and major branches are limited.

Chest radiograph signs of blunt aortic injury:
1. Signs of periaortic hematoma:
-Widened mediastinum > 8 cm at the level of aortic knuckle
-Obscured aortic knuckle
-Opacification of aortopulmonary window
-Deviation of trachea, left main bronchus or nasogastric tube
-Thickened paratracheal stripe

2. Indirect signs:
-left haemothorax
-Left pleural cap
-Fractured first or second ribs


Significant aortic injury requires prompt surgical or endoluminal stent repair. Surgery should be deferred sometimes indefinitely if severe associated injuries or comorbidities make the operative risk unacceptably high.
Options for surgery: direct repair (clamp and sew), endoluminal stent repair.
Conservative management includes antihypertensive therapy (B-blockers +/- vasodilators) and serial imaging to assess for expanding pseudoaneurysm that will require intervention.

reference: Oh's intensive care manual 5th edition pg 794