Question 18

Compare and contrast the pharmacology of Hartmann’s solution and 0.9% saline?

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College Answer

This question asked for a comprehensive description of the components and chemical properties of each solution (including pH and calculated and measured osmolarity). A mechanistic description of the different acid base effects was expected. Marks were also allocated for the advantages and disadvantages of each fluid (for example the calcium in Hartmann’s risks causing precipitation when mixed with certain drugs and blood products). Lastly, it was expected that answers would provide situations where one fluid might be preferred over the other (for example saline to treat dehydration and metabolic alkalosis secondary to gastric losses – as in a pyloric obstruction). Descriptions of the physiological handling of each fluid after bolus or infusion was not required.

Discussion

Name Normal saline Hartmann's solution
Class Crystalloid fluid Crystalloid fluid
Chemistry Monovalent cation salt:
0.9% sodium chloride (8.77g/L, or 150 mmol/L)
- pH around 4.6
- calculated osmolality 300 mOsm/kg
- measured osmolality 286 mOsm/kg
"Balanced" crystalloid solution composed of several cation salts:
- Sodium chloride (105 mmol/L)
- Sodium lactate (29 mmol/L)
- Potassium chloride (5 mmol/L)
- calcium chloride (2 mmol/L)
So, in total;, 131 mmol/L sodium, 112 mmol/L chloride, 5 mmol/L potassium and 2mmol/Lcalcium
- pH 5.0
- Calculated osmolality 278 mOsm/kg
- Measured osmolality 260 mOsm/kg
Routes of administration IV, subcutaneously, orally, or as a neb (plus multople others) IV only
Absorption 100% oral bioavailability; well absorbed 100% oral bioavailability; well absorbed
Solubility pKa 3.09; good water solubility pKa of sodium lactate is 3.78; all components have excellent water solubility.
Distribution VOD=0.2L/kg, basically confined to the extracellular fluid
(thus: 25% remains intravascular, 75% becomes interstitial)
VOD=0.2L/kg, basically confined to the extracellular fluid
(thus: 25% remains intravascular, 75% becomes interstitial)
Target receptor As a resuscitation fluid, you could say that the target receptor is the baroreceptor As a resuscitation fluid, you could say that the target receptor is the baroreceptor
Metabolism Not metabolised Only the lactate is metabolised, producing H2O and CO2
Elimination Eliminated renally, where specific reabsorption mechanisms in the renal tubule regulate the rate of sodium and chloride excretion Eliminated renally, where specific reabsorption mechanisms in the renal tubule regulate the rate of sodium and chloride excretion
Time course of action Half life is 20-40 minutes in healthy volunteers, longer in shock states and in mechanically ventilated patients (up to 8 hours) Half life is 20-40 minutes in healthy volunteers, longer in shock states and in mechanically ventilated patients (up to 8 hours)
Mechanism of action Expands the extracellular fluid volume and changes the biochemistry of the body fluids Expands the extracellular fluid volume and changes the biochemistry of the body fluids
Clinical effects Volume expansion:
- by 25% of the infused volume, after 25-30 minutes
- below the circulatory reflex activation threshold
- effect is greater during the infusion (prior to redistribution)
Change in osmolality:
- minimal; unnoticed by osmoreceptors
Change in biochemistry:
- trivial sodium elevation (~0.5-.0 mmol/L)
- nontrivial chloride elevation (up to 3 mmol/L)
- decrease in bicarbonate and base excess (also up to 3 mmol/L)
Volume expansion:
- by 25% of the infused volume, after 25-30 minutes
- below the circulatory reflex activation threshold
- effect is greater during the infusion (prior to redistribution)
Change in osmolality:
- minimal; unnoticed by osmoreceptors
Change in biochemistry:
- trivial sodium depression (~0.5-1.0 mmol/L)
- trivial chloride elevation (up by 1.5 mmol/L for every litre of Hartmanns)
- increase in bicarbonate and base excess (up by 2-3 mmol/L)
Single best reference for further information Griffel and Kaufman (1992) White & Goldhill (2010)

References

White, S. A., and D. R. Goldhill. "Is Hartmann's the solution?." Anaesthesia 52.5 (1997): 422-427.

McLoughlin, P. D., and D. A. Bell. "Hartmann's Solution-osmolality and lactate." Anaesthesia and intensive care 38.6 (2010): 1135.