Chapter 17.
I. Answers B, C, and E relate to metabolic alkalosis and are true, whereas A and D are false.
II. Answers A, B and E are true statements, whereas C, and D are false.
1. By the help of Fig. 17-11 the base excess is read (calculated) to be zero. This patient is in a normal state between attacks of dyspnoea.
2. During emergency conditions the base excess is read (calculated) from Fig. 17-11 to be zero.
3. During emergency conditions the patient has developed an acute respiratory alkalosis by hyperventilation. The diagnosis is probably hyperventilatory tetany.
1. PB is 80 kPa and the water vapour pressure at body temperature is 6.26 kPa or 47 mmHg. Atmospheric air has a fractional oxygen content of 0.2093, here corresponding to a
PIO2 of (80 -6.26) 0.2093 = 15.48 kPa or 114 mmHg.
2. The alveolar gas equation states: PIO2 = PAO2 + PACO2 . Accordingly, the PAO2 of the patient is (114 - 60) = 54 mmHg or 7.2 kPa. The chemical respiratory drive is the low oxygen tension combined with the high carbon dioxide tension. The combined respiratory drive is high.
3. The base excess of the extracellular fluid is approximately +10. The base excess is compensatory elevated. The condition is a subacute or chronic respiratory acidosis.
1. pH = 7.40 The arterial H+ concentration = 10-7.40 mol per l = 40 nM.
pH = 7.00 The arterial H+ concentration = 10-7 mol per l = 100 nM.
pH = 7.80 The arterial H+ concentration = 10-7.80 mol per l = 16 nM.
2. Log scales differ from proportional scales. - Logarithms often hide detailed information.
3. Metabolic acidaemia is characterized by H+ excess in the blood. This reduces the base excess (negative values) - an important base deficit. This condition occurs in diabetics and in persons working supramaximally.
Metabolic alkalosis is caused by a primary accumulation of base in the extracellular fluid. Loss of gastric fluid (vomiting with loss of HCl), intake of base, and use of diuretics can cause this form of alkalosis. The low [H+] reduces ventilation and increases bicarbonate, leading to the typical positive base excess. The respiratory compensation raises PaCO2 and pH is reduced. The compensation is never total, since the rise in PaCO2 and the fall in PaO2 in itself limits the fall in ventilation.
