A balanced view of balanced solutions

Abstract

The present review of fluid therapy studies using balanced solutions versus isotonic saline fluids (both crystalloids and colloids) aims to address recent controversy in this topic. The change to the acid-base equilibrium based on fluid selection is described. Key terms such as dilutional-hyperchloraemic acidosis (correctly used instead of dilutional acidosis or hyperchloraemic metabolic acidosis to account for both the Henderson-Hasselbalch and Stewart equations), isotonic saline and balanced solutions are defined. The review concludes that dilutional-hyperchloraemic acidosis is a side effect, mainly observed after the administration of large volumes of isotonic saline as a crystalloid. Its effect is moderate and relatively transient, and is minimised by limiting crystalloid administration through the use of colloids (in any carrier). Convincing evidence for clinically relevant adverse effects of dilutional-hyperchloraemic acidosis on renal function, coagulation, blood loss, the need for transfusion, gastrointestinal function or mortality cannot be found. In view of the long-term use of isotonic saline either as a crystalloid or as a colloid carrier, the paucity of data documenting detrimental effects of dilutional-hyperchloraemic acidosis and the limited published information on the effects of balanced solutions on outcome, we cannot currently recommend changing fluid therapy to the use of a balanced colloid preparation.

Figure 1

Representation of the Stewart model. Charge balance in blood plasma. Any difference between apparent strong ion difference (SID_a) and effective strong ion difference (SID_e) is the strong ion gap (SIG) and presents unmeasured anions. The SIG should not be confused with the anion gap (AG). A corrected AG can be calculated to account for variations in albumin concentration. Adapted from Stewart [6].

Figure 2

Plasma bicarbonate concentration versus relative haemoglobin after acute haemodilution in different patient groups. Plasma bicarbonate (HCO₃^-) concentration (mmol/l) versus relative haemoglobin (Hb) (%) after acute normovolaemic haemodilution in different patient groups. Comparison is shown for predicted (open squares) and reported (filled circles) values [18] of the actual HCO₃^- concentration (top curve), composed of the calculated HCO₃^- values (filled triangles) from plasma dilution, plus the increments from the plasma proteins (Pr), the erythrocytes (E), and the interstitial fluid (ISF) with corresponding buffers. Adapted from Lang and Zander [12].

Figure 3

Chloride load and base excess in elderly patients undergoing abdominal surgery. Chloride load in the three groups of patients - Ringer's lactate group (filled circles), isotonic saline group (filled squares), and HES 130/0.4 plus Ringer's lactate (open triangles) - was calculated. The variations in base excess for the three groups are shown graphically. It is remarkable that there is no difference between the Ringer's lactate group and the HES 130/0.4 plus Ringer's lactate group. *P < 0.05. POD, postoperative day. Adapted from Boldt and colleagues [24].

Figure 4

Hospital mortality associated with type of metabolic acidosis. Mortality associated with the major ion contributing to the metabolic acidosis. Hospital mortality associated with the various causes of metabolic acidosis (standard base excess (SBE) <-2). Mortality percentage is mortality within each subgroup, not a percentage of overall mortality. Lactate indicates that lactate contributes to at least 50% of the SBE; SIG, strong ion gap contributes to at least 50% of SBE (and not lactate); hyperchloraemic, absence of lactate or SIG acidosis and SBE <-2; none, no metabolic acidosis (SBE ≥-2 mEq/l). P < 0.001 for the four-group comparison. Adapted from Gunnerson and colleagues [47].