Thu18November0303AM 4

Which one of the following haematology results is associated with least risk of vertebral canal haematoma, if a central neuraxial block is performed in a patient?

(Please select 1 option)

An Internationlised normalised ratio (INR) of 1.4 Correct

An aPPT of 80 seconds

A thromboelastogram with a K of 8 minutes and an a-angle of 25 degrees

A platelet count of 49×109/L

A bleeding time of 11 minutes

Explanation

Following the third National Audit Project (NAP3) conducted on behalf of the Royal College of Anaesthetists, the incidence of vertebral canal haematoma after neuraxial blockade was 0.85 per 100 000 (95% CI 0-1.8 per 100 000). Whilst unquantifiable, the incidence of vertebral canal haematoma following neuraxial blockade in coagulopathic patients is likely to be higher. For that reason, a coagulopathy remains a relative contraindication for conducting a spinal or epidural and only performed by experienced personnel having weighed up the balance of risk.

The relative risk of performing central neuraxial blockade in obstetric patients are as follows:

Normal risk INR = 1.4

Increased risk INR 1.4-1.7

High risk 1.7-2.0

The bleeding time is used to measure the primary phase of haemostasis, which involves platelet adherence the injured capillary wall, and subsequent platelet activation and aggregation. The bleeding time can be abnormal when the platelet numbers are low or the platelets are dysfunctional. An expansion of the circulation associated with pregnancy reduces the platelets count. A normal bleeding time is 1-9 minutes.

The threshold for thrombocytopenia varies from 150 ×109/L -100 x 109/L and levels between these thresholds are common in mothers at delivery. Provided that a low count is stable, maternal health is good, and there are normal fibrinogen levels, INR and APTT, then expert opinion is that neuroaxial blockade can be justified provided the platelet count is 50×109/L or above.

Normal values for a thromboelastography include:

Initiation phase (R): 4-8 min

Amplification (K): 1-4 min

Propagation (a-Angle): 47-74°

Maximal amplitude (MA): 55-73mm

Clot stability (LY) 30%: 0-8%

A Prolonged K/Reduced a-Angle indicates the presence of Fibrinogen deficiency (i.e. DIC).

The activated partial thromboplastin time (aPTT) is a test of clotting function that focuses on the 'intrinsic' and 'common' pathways of the in vitro coagulation cascade model. Coagulation factors and cofactors within each pathway integrate to generate a fibrin clot end-point, the time taken to form the clot being the aPTT. The reference range of the aPTT is 30-40 seconds.

A prolonged APTT can result from vitamin K deficiency, liver disease, disseminated intravascular coagulation and anticoagulant therapy with vitamin K antagonists, UFH, LMWH, fondaparinux, direct thrombin inhibitors, direct-FXa inhibitors.

References:

Cook TM, Counsell D, Wildsmith JAW. Major complications of central neuraxial block: report on the Third National Audit Project of the Royal College of Anaesthetists. British Journal of Anaesthesia 2009; 102: 179-90.

Regional Anaesthesia and Patients with Abnormalities of Coagulation. The Association of Anaesthetists of Great Britain & Ireland The Obstetric Anaesthetists' Association (November 2013)

Regional Anaesthesia UK

Answer Statistics

1

67%

2

6%

3

13%

4

10%

5

5%

Times answered: 270