Sodium bicarbonate: indications and application

Sodium bicarbonate makes infrequent appearances in the SAQs. Most of them are limited to older-style "critically evaluate" questions, or invitations to compare bicarbonate to other exogenous buffer systems (such as THAM). The more recent trend towards easily graded data interpretation SAQs has seen little bicarbonate action. For instance, at one stage (2011) the candidates were asked to calculate the dose of bicarbonate replacement.

Bicarbonate-themed SAQs in the ABG interpretation section consist of only Question 6.2 from the first paper of 2011. Question 27 from  the first paper of 2009 asked the candidates to compare and contrast the pharmacology of carbicarb, sodium bicarbonate and THAM; somehow the discussion of THAM has (totally arbitrarly) ended up in the fluids and electrolytes section.

Accepted indications for sodium bicarbonate

• Hyperkalaemia
• Treatment of sodium channel blocker overdose with ECG features (e.g. tricyclic overdose)
• Urinary alkalinisation (salicylate poisoning)
• Normal anion gap metabolic acidosis

Debated indications for sodium bicarbonate

• Cardiac arrest with severe acidosis
• DKA with severe acidosis
• Restoration of completely depleted buffer systems (eg. HCO₃^- level approaching 0)
• Pulmonary hypertension and severe right heart failure

Adverse effects of sodium bicarbonate administration

• Peripheral vein thromobophlebitis
• Hypernatremia
• Volume overload
• Hypokalemia
• Ionised hypocalcemia
• Left shift of oxyhaemoglobin dissociation curve
• Impaired clearance of lactate (by disinhibition of glycolysis)
• Intracellular acidosis (maybe)
• Hypercapnea

Calculation of bicarbonate dose

• body weight in kg × 1
• body weight × 0.3 × SBE
• body weight × 0.3 × (desired HCO₃^- - measured HCO₃^- )
• body weight × ( 0.4 + 2.6 / measured HCO₃^- )