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Aspirin is the agent with the shortest half life and a relatively low concentration at therapeutic doses. Prasugrel and clopidogrel have long elimination half lives, so platelets are inhibited as soon as they are transfused. Ticagrelor is a reversible platelet antagonist with a short half life, however it is administered at supratherapeutic doses (to ensure full platelet inhibition between daily doses), so  is also usually present at concentrations that immediately inhibit transfused platelets.

Assay variation between samples may be up to 20%, and biological variation up to 80%. Level changes of < 50% are usually clinically insignificant. As the change drops from 50%, sensitivity for ischaemia increases, at the expense of specificity. An increase of >100% nearly always indicates ischaemia.

A level of  ≥ 1000 ng/L (not 100 ng/L) is highly specific for acute myocardial damage. A value of 0.10 mg/L in the old assay equals 100 ng/ L(not 1000ng/L) for hsTrop. There is no suitable  high sensitivity test for Troponin I

Traumatic SAH tends to be peripheral and patchy in nature, and often contiguous with areas of contusion. More centrally located haemorrhage may be difficult to differentiate from primary SAH (with associated LOC and head trauma) so cerebral CT angiography should be performed in doubtful cases. No treatment is usually required for adult patients with isolated traumatic SAH and a normal neurological exam who are not currently taking anticoagulants or antiplatelet agents. Neurosurgical evaluation or transfer to a trauma centre are not usually necessary. (Link)

Lithium is one of the few anti-depressants associated with a substantial reduction (60% in one analysis) in the rate of suicide compared to placebo for unipolar and bipolar depression. It may also decrease aggression and impulsivity, but has not been shown to be superior to TCADs or to reduce episodes of non fatal self harm.(Link)

In a single study in high risk Chinese patients (ABCD2 score ≥ 4 or stroke and NIHSSS ≤ 3) clopidogrel (300mg loading dose, 75mg/day) and aspirin (variable loading dose, 75mg/day) combined for the first 21 days was associated with a 3% reduced risk of stroke recurrence at 90 days compared to aspirin alone (11% vs 8%) and a 1% increase in bleeding complications.
In lower risk patients, there is a significant increased risk of ICH so this combination therapy should not be used. Aspirin reduces stroke risk by about 10% and is usually not started until 24 hours following thrombolytic therapy.(Link)

A RBC count of > 100,000 RBCs in the final tube suggests SAH, > 10,000 RBCs has LR+ 6 and a finding of < 100 RBCs is rare. A change of < 65% in counts between 1st and 3rd tube has a LR+ 3.6 and a > 65% change in counts LR- 0.10. (Link)

Contraindications to tPA in stroke include an INR > 1.7 and patients taking aspirin and clopidogrel (or similar) therapy. Although there is limited information known about tPA in patients taking NOACs,  some patients with potential high benefit from tPA may be considered for tPA if the APTT is normal for dabigatran or the anti Xa activity is normal for rivaroxiban or apixaban. (Link)

All of the following items are risk factors for haemorrhagic transformation: cardioembolic strokes, ICA occlusion, treatment with tPA, clopidogrel and aspirin therapy, anticoagulation, hypertension and hyperglycaemia. Treatment with tPA confers the highest risk. (Link)

Like many promising treatments, the NNT increases as more patients are studied in more realistic practice situations. The initial NNT from NINDs was quoted as 7 (or potentially as 3 by some thrombo-zealots). It is approximately 11 for treatment within 3 hours, but is 25 in patients treated within 4.5 hours (primarily because there is little/no treatment benefit after 3 hours). (Link)

Statins are generally well tolerated but increase the risk of diabetes by 10%. Simavastatin and pravastatin have the lowest adverse effect rates. Muscle disease occurs in approximately 2% of patients and is most commonly associated with atorvastatin, although it does not appear to be dose related .It usually takes the form of an asymptomatic increase in CK or mild myalgia / myositis and rhabdomyolysis is rare.

Elevation of transaminases is increasingly frequent with higher doses. The highest risk is from fluvastatin and is least common with pravastatin.(Link)

One third of the fetal blood volume is in the placenta at birth and delaying clamping for 2-3 minutes or until the cord no longer pulses significantly increases fetal Hb and Fe stores, but is associated with a mild increased risk of jaundice. Placental transfusion is more rapid if the baby is held below the level of the placenta for the first few minutes, as flow to the fetus after delivery is mostly through the umbilical veins. Non delayed clamping is associated with double the risk of Fe deficiency between 3-6 months of age and this Fe deficiency is associated with specific deficits in cognitive processing in children, not just anaemia or lethargy. (Link)

CT following abdominal stab wound is less sensitive and specific than serial examinations, but is of most use in patients with altered mental state, where serial examinations are unreliable. In the haemodynamically unstable patient it does not provide useful additional pre-operative information and should not be performed prior to laparotomy.  CT does not appear to save time as most of these patients require at least 24 hours of observation.(Link)

The years of life lost (YLL) is the measure of premature mortality and the years lived with disability (YLD) is the measure of the number of years lived with disability. Disability adjusted life years (DALYs) are a summary measurement of population health that measure a population’s health compared to the ideal goal of all individuals living the standard life expectancy in full health and are the sum of YLLs and YLDs. (Link)

Fat has an attenuation of -80 – 120 HU and usually appears dark grey on CT. Bone usually appears white, soft tissue grey and water light grey.(Link)

Subfalcine herniation is the least severe and can sometimes be minimally symptomatic. Alar / sphenoid herniation is more severe as it is nearly always associated with other forms of herniation. Uncal herniation may become central herniation, if both sides are involved – but either carry a worse prognosis than subfalcine herniation. (Link)

The secondary effects of transtentorial herniation tend to occur in the following order as the process progresses, with Duret haemorrhages having the most serious sequelae:

• tissue necrosis and haemorrhage
• compression of ipsilateral posterior cerebral artery
• compression of the oculomotor nerve (III)
• compression of crus cerebri (cerebral peduncle)
• occlusion of the Sylvian aqueduct
• Duret haemorrhages (Link)