Acid Base Balance Cases Dr Svitlana Zhelezna Clinical Teaching Fellow UHCW NHS Trust 2013/2014 academic year

Acid-base balance Maintenance of normal ECF [H + ] (pH) depends on the balance between: carbon dioxide production and excretion hydrogen ion production and excretion Imbalances are dealt with by buffering Compensation But reversed usually only by correction of the underlying disorder

Case 1 73 yr old man, known COPD Acute exacerbation, SOB, fever Baseline Normal Range pH pCO kPa pO kPa Bicarb mmol/L

Respiratory acidosis Cause hypoventilation leading to CO 2 retention Correction restore normal gas exchange Compensation increased renal acid excretion Features acutely: low pH, n [HCO 3 - ], high pCO 2 chronically: low/normal pH, high [HCO 3 - ], high pCO 2

Case 2 49 y. o. woman T1DM at A&E 2/7 drowsiness O/E: dehydrated, rapid deep breathing pH 7.12 ( ) pCO2 2.2 kPa ( ) pO kPa (12-15) bicarb 12 mmol/L (22-28 )

Case 3 62 yr old woman T2DM 2/7 increasing drowsiness, breathing rapidly and deeply Sodium146mmol/L Potassium6.1mmol/L Chloride109mmol/L Bicarbonate12mmol/L22-28 Urea14mmol/L Creatinine256umol/L pH pCO kPa pO kPa Bicarb mmol/L

Metabolic acidosis Causes increased acid formation acid ingestion bicarbonate loss/AKI reduced metabolism/excretion Correction primary cause increased renal acid excretion Initial Compensation: hyperventilation, hence low pCO 2 Features Acutely: low pH, low [HCO 3 - ], low pCO 2 Chronically: low/normal pH, low [HCO 3 - ], Normal pCO 2

Case 4 47-year old woman – vomiting persistently Previously treated for DU, dehydrated, hypotensive, RR 9 Sodium142mmol/L Potassium2.9mmol/L Chloride85mmol/L Bicarbonate44mmol/L Urea24.3mmol/L Creatinine150mmol/L pH pCO kPa pO kPa Bicarb mmol/L

Metabolic alkalosis (1) Cause loss of gastric acid increased renal H + excretion e.g. in hypokalaemia Correction primary cause increased renal bicarbonate excretion Compensation hypoventilation with CO 2 retention Features high pH, low [H + ], high [HCO 3 - ], N/high pCO 2

Metabolic alkalosis (2) Limit to compensation CO 2 is respiratory stimulant Limits to correction Hypochloraemia thus increased bicarbonate reabsorption with sodium Hypovolaemia thus increased distal sodium reabsorption but potassium depletion (GI loss) so increased acid excretion (paradoxically acid urine)

Thank you! Any questions?