Chapter 33.
Answers A, C and E are true statements, whereas B and D are false.
1. The cholera enterotoxin contains A and B subunits. Subunit A is an enzyme, which enters the enterocyte and irreversibly activates adenylcyclase, whereby a cascade of reactions are triggered. Subunit B links the enterotoxin to the brush borders of the enterocyte, so the effect is persistent. As cAMP is activated in the cell it activates an electrogenic chloride-channel in the brush border membrane. This causes an enormous secretion of NaCl and water into the lumen of the small intestine.
Acute dehydration with loss of base leads to metabolic acidosis and hypovolaemic shock. Therapy is immediate rehydration.
2. The extended ECV is a functional unit consisting of the extracellular fluid volume and the red cell volume. This is the primary compartment in electrolyte and acid-base disturbances. The extended ECV is 75 * 0.2 = 15 kg.
3. The fractional loss of ECV is 1/15 at the start of the disease, because all fluid is lost from the extracellular volume. Soon the cells also lose water and electrolytes. A loss of water from 75 to 60 kg of body weight is life-threatening. The intracellular compartment (ICV) of a 75 kg person is approximately 26 kg. The total water loss from ICV is probably 2/3 or 10 kg, leaving a reduction of ECV to 5 kg (15 is diminished to 10 kg).
4. Rehydration is important because of imminent shock and death.
5. The effect of tetracycline is to eradicate the vibrio and thus their endotoxin production. Hereby, the diarrhoea decreases dramatically, and the patient is cured within days.
6. The base excess is -15 mmol per l of extended ECV. The patient first of all needs a total compensation in a normal 15 l extended ECV, where ( 15 * 15) = 225 mmol is missing. While this compensation takes place, approximately half of these base equivalents are transferred to the body cells, where there is an intracellular acidosis in 26 kg ICV. This is why the base excess was measured to -8 mM and not to zero after two hours of infusion of 225 mmol bicarbonate. This patient probably needs an infusion volume corresponding to 225-450 mmol bicarbonate more in the hours to come. Careful monitoring of the acid-base variables is essential until the compensation is complete in all compartments.
1. The diagnosis is probably cerebral malaria with coma. The malaria prophylaxis is inefficient.
2. A blood film showing malaria parasites inside the red cells confirms 2.Malaria. Plasmodium falciparum was found, and the parasite is most likely resistant to chloroquine.
3. The treatment of choice is to administer quinine intravenously.
1. Pulmonary tuberculosis.
2. Combination therapy with rifampicillin and isoniazid is administered each morning half an hour before breakfast. The standard dose to adults is 600 mg rifampicillin (2 capsules) and 300 mg isoniazid (one capsule). The first months of therapy also pyrazinamide is given in a dose of 2 g a day. isoniazid necessitates supplement with pyridoxine (50-100 mg daily) in order to prevent B6- avitaminosis.
3. Steroids are immuno-suppressors, so they speed-up the progression of the infection, which may prove fatal. This is malpractice.
4. Seemingly healthy persons are chest X-rayed and a tuberculin test is performed. Persons with symptoms or signs must be examined carefully including cultures of gastric juice for 4-8 weeks.