A new drug is trialled for the treatment of lung cancer. Drug A is given to 500 people with early stage non-small cell lung cancer and a placebo is given to 450 people with the same condition. After 5 years 300 people who received drug A had survived compared to 225 who received the placebo.
What is the number needed to treat to save one life?
Correct Answer C: NNT = 1 / Absolute Risk Reduction.
The question asks about the number needed to treat to save one life. The 'event' is therefore survival.
Numbers needed to treat and absolute risk reduction:
Numbers needed to treat (NNT) is a measure that indicates how many patients would require an intervention to reduce the expected number of outcomes by one It is calculated by 1/(Absolute risk reduction) and is rounded to the next highest whole number Experimental event rate (EER) = (Number who had particular outcome with the intervention) / (Total number who had the intervention).
Control event rate (CER) = (Number who had particular outcome with the control/ (Total number who had the control).
Absolute risk reduction = CER-EER or EER-CER?
The absolute risk reduction (ARR) may be calculated by finding the absolute difference between the control event rate (CER) and the experimental event rate (EER). You will often find both versions of the above listed in different sources. In some ways in doesn't matter which you use as you will end up with the same answer but from a technical point of view:
*this may be more accurately termed absolute benefit increase, rather than absolute risk reduction
A 34-year-old man is climbing Mount Kilimanjaro. For the past two days he has complained of nausea and a headache. The climbing team is now at an altitude of 4,500m when he develops shortness of breath and a pink frothy cough. Examination reveals bibasal crackles.
What is the most appropriate treatment, other than descent?
Correct Answer A: This man has developed high altitude pulmonary oedema (HAPE) and should to be treated with prompt descent, oxygen and nifedipine if it is available. Other options for treating HAPE include dexamethasone, acetazolamide and phosphodiesterase type V inhibitors.
Altitude related disorders: There are three main types of altitude related disorders: acute mountain sickness (AMS), which may progress to high altitude pulmonary edema (HAPE) or high altitude cerebral edema (HACE). All three conditions are due to the chronic hypobaric hypoxia which develops at high altitudes.
Acute mountain sickness is generally a self-limiting condition. Features of AMS start to occur above 2,500 - 3,000m, developing gradually over 6-12 hours and potentially last a number of days:
Prevention and treatment of AMS:
A minority of people above 4,000m go onto develop high altitude pulmonary oedema (HAPE) or high altitude cerebral oedema (HACE), potentially fatal conditions:
Management of HACE:
Management of HAPE:
*the relative merits of these different treatments has only been studied in small trials. All seem to work by reducing systolic pulmonary artery pressure.
What is the main mechanism by which vitamin B12 is absorbed?
Correct Answer D: Vitamin B12 is actively absorbed in the terminal ileum.
A small amount of vitamin B12 is passively absorbed without being bound to intrinsic factor.
Vitamin B12 deficiency: Vitamin B12 is mainly used in the body for red blood cell development and also maintenance of the nervous system. It is absorbed after binding to intrinsic factor (secreted from parietal cells in the stomach) and is actively absorbed in the terminal ileum. A small amount of vitamin B12 is passively absorbed without being bound to intrinsic factor.
Causes of vitamin B12 deficiency:
Features of vitamin B12 deficiency:
Management:
For a patient undergoing an elective splenectomy, when is the optimal time to give the pneumococcal vaccine?
Correct Answer A: The current British National Formulary recommends giving the vaccine at least 2 weeks before elective splenectomy. Therefore 4 weeks is the best response from the given options.
Splenectomy:
Following a splenectomy patients are particularly at risk from pneumococcus, Haemophilus, meningococcus and Capnocytophaga canimorsus* infections.
Vaccination:
Antibiotic prophylaxis:
*usually from dog bites
A 20-year-old man is admitted to the Emergency Department with chest pain. He confides that he has snorted 'a large amount' of cocaine in the previous hours.
Which one of the following features is his cocaine use most likely to cause?
Correct Answer B:
Cocaine: Cocaine use may cause a wide variety of adverse effects.
Cardiovascular effects:
Neurological effects:
Psychiatric effects:
Others:
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