New content quiz February 2014

Light transmission aggregometry is considered the gold standard of platelet function testing, however is complex, time consuming and results are not rapidly available. Flow cytometry is used in the investigation of Glanzmann thrombasthenia, Bernard–Soulier Syndrome and Scott syndrome, as well as to investigate abnormalities in the collagen (GpVI and GpIa/IIa) and thrombin receptors, but is not a test of global platelet function. The skin bleeding time is a global test of coagulation, in which platelet function plays an important part, however is no longer recommended as it is highly dependent on operator technique, influenced by age, gender, haematocrit, vascular pattern, skin thickness and skin temperature, hence has poor reproducibility, sensitivity and specificity. The P2Y12 receptor occupancy assay only tests the efficacy of anti-platelet agents that bind that receptor.

Administration of beta blockers within 24 hours reduces infarct size, reinfarction and mortality by 50% when used alone, however there are less convincing data to support their use in the first few hours following STEMI when other standard therapies are used. As a result, oral administration is usually recommended within the first 24 hours in STEMI. However, the randomised, blinded METOCARD-CNIC trial published in 2013 demonstrated about a 5% reduction in infarct size in anterior MI when beta blockers were used pre PCI and within 6 hours of symptom onset (in selected patients). Beta blockers also decrease the rate of cardiac rupture (ISIS 1) and may worsen symptoms in patients with LVF but probably reduce mortality (ISIS 3), rather than increasing it..(Link)

Indications for immediate antibiotics for patients with sore throat include: patients 2-25 years of age in areas of high incidence of rheumatic fever; patients with history of rheumatic heart disease at any age; when any one of the features of the FeverPAIN score are present (Fever during previous 24 hours, Purulence, Attend rapidly (within three days), Inflamed tonsils, No cough/coryza); scarlet fever; systemically unwell; peritonsillar cellulitis or abscess; and a positive throat culture or rapid antigen test. (Link)

IV antibiotics should be administered as soon as immediate cultures (peripheral blood, other easily obtainable site) have been collected and not delayed whilst whilst waiting for MSU or vascular access catheter cultures. This should be within 30 minutes of arrival if systemically unwell or within 1 hour if clinically well. Suitable regimens include (ticarcillin 3g + clavulinic acid 0.1g (Timentin 3.1g) (50mg/kg in children) + gentamicin 7 mg/kg IV once daily OR
piperacillin 4g + tazobactam 0.5g (Tazocin 4.5g) (100mg/kg in children) 6-8 hourly OR a 3rd/4th generation cephalosporin (ceftazidime 1 g + aminoglycoside). Gentamicin may be omitted if the patient appears systemically well. Vancomycin 1.5g (20mg/kg in children) should be added if: the patient is hypotensive or in shock; there is suspected vascular line infection; or known MRSA carriage. Metronidazole 500mg IV 12 hourly should also be added if abdominal or perineal infection suspected. (Link)

The most common causes of an isolated thrombocytopenia are ITP and drug induced thrombocytopenia. Thrombocytopenia of pregnancy does not cause counts of < 70 and Dengue and portal hypertension rarely do.  (Link)

Expected investigation findings in ITP include: isolated thrombocytopenia; an increased IPF; a normal peripheral blood film; a normal extended coagulation profile; and the presence of platelet bound antibodies in about 50% of cases (i.e. a negative test does not exclude the diagnosis) (Link)

The Rapid Rhino nasal balloon must be removed within 24 hours of insertion due to the risk of mucosal damage. (Link)

A single, immediate defibrillation will revert approximately 95% of cases of VF. The reversion rate drops substantially with each passing minute. (Link)

PEA is defined as the presence of spontaneous organized cardiac electric activity in the absence of blood flow sufficient to maintain consciousness and the absence of a rapid spontaneous return of adequate organ perfusion and consciousness (otherwise it would be syncope!). The proportion of out of hospital cardiac arrests due to PEA is increasing in frequency compared to VF/pulseless VT and now accounts for approximately 40% of cases. Approximately half of all cases of PEA are thought to have been caused by a primary cardiac event and approximately 30% of survivors of PEA have acute coronary occlusions. There is a higher incidence in patients with underlying pulmonary disease, women and increasing age. (Link)

The percentage of survivors of out of hospital cardiac arrest who are subsequently able to live independently is approximately 85%. (Link)

Effective chest compression is the single most important aspect of BLS as it aims to maintain neurological and cardiac function whilst awaiting arrival of AED or ALS capability. Interruption of chest compression should be minimised at all costs as aortic pressure (hence coronary perfusion pressure) drops rapidly after cessation and recovers progressively more slowly after each interruption. Also, the right ventricle progressively dilates with interruption of chest compressions, making defibrillation less effective. Compression rates > 120 are associated with a reduction in compression depth. (Link)

The normal frontal plane p wave axis is 0 – 75 degrees. An abnormal axis associated with abnormal cardiac chamber size and position, and increased mortality due to cardiac or respiratory disease. The p wave axis is often abnormal in COPD. (Link)

Elemental iron doses of < 20 mg/kg have little risk of toxicity, 20-60 mg/kg moderate risk of toxicity, > 60-90 mg/kg have a high risk of toxicity, < 130 mg/kg is potentially fatal and 200 mg/kg is the approximate median fatal dose. (Link)

Carbonyl iron is non-ionic and associated with lower toxicity, due to lack of directly corrosive properties. Although it contains 100% elemental iron, there have been no cases of serious toxicity following ingestion reported yet. (Link)

Vomiting is the most sensitive indicator of toxicity. It usually occurs within 20 minutes of ingestion, occurs within 80 minutes in 90% of cases and the absence of vomiting by 6 hours essentially rules out serious toxicity. (Link)