Basic Concepts of Fluid and Electrolyte Therapy

The blood buffering system, which is dependent upon
the relative proportions of carbonic acid from carbon dioxide (CO 2
)
and of bicarbonate (HCO 3 – ) defined by the Henderson-Hasselbach
equation. Note that the pH is determined by the ratio of HCO 3 – to
CO 2
.
pH = 6.10 + log
[ HCO 3– ]
0.03pCO 2
haemoglobin
phosphate (organic and inorganic)
bone and its calcium salts
The kidney buffering system which
controls hydrogen (H + ) and bicarbonate (HCO 3–
) excretion or reabsorption
as well as the conversion of ammonia (NH 3
) to ammonium
(NH 4+
) in the urine.
The lung buffering system which controls
the carbon dioxide (CO 2
) in the blood, increasing expired CO 2
when
more is produced or to compensate for metabolic acidosis.
The liver buffering system which
removes and recycles the large amounts of lactate produced by
anaerobic respiration (the Cori cycle).
Disease states can disrupt this finely balanced system resulting in a
dangerously low (pH 7.6). Specific
patient management will depend upon the clinical status of the
patient and correction of the underlying cause. This chapter will pro-
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