title: Perioperative buffered versus non-buffered fluid administration for surgery in adults.
abstract: BACKGROUND
  Perioperative fluid therapy influences clinical outcomes following major surgery. Fluid preparations may be based on a simple non-buffered salt solution, such as normal saline, or may be modified with bicarbonate or bicarbonate precursor buffers, such as maleate, gluconate, lactate or acetate, to better reflect the human physiological state. These latter fluids have theoretical advantages over normal saline in preventing hyperchloraemic acidosis. A number of clinical studies have now compared fluid preparations with and without a buffer to achieve a balanced electrolyte solution for perioperative fluid resuscitation.
  
  
  OBJECTIVE
  To review the safety and efficacy of perioperative administration of buffered versus non-buffered fluids for plasma volume expansion or maintenance in adult patients undergoing surgery.
  
  
  METHODS
  We electronically searched the Cochrane Central Register of Controlled Trials (CENTRAL) (2011, Issue 4), MEDLINE (1966 to May 2011), EMBASE (1980 to May 2011), and CINAHL (1982 to May 2011). We handsearched conference abstracts and where possible, contacted leaders in the field.
  
  
  METHODS
  We only included randomized trials of buffered versus non-buffered intravenous fluids for perioperative fluid resuscitation. The trials with other forms of comparisons such as crystalloids versus colloids and colloids versus different colloids were excluded. We also excluded trials using hypertonic fluids and dextrose-based fluids.
  
  
  METHODS
  Two authors independently extracted data and assessed the methodological quality of clinical trials. We resolved any disagreements by discussion. We contacted the trial authors to provide additional information where appropriate. We presented pooled estimates of the dichotomous outcomes as odds ratios (OR) and on continuous outcomes as mean differences, with 95% confidence intervals (CI). We analysed data on Review Manager 5.1 using fixed-effect models, and when heterogeneity was high (I² > 40%) random-effect models were used.
  
  
  RESULTS
  We identified 14 publications reporting 13 trials or comparisons with a total of 706 participants. For many of the outcomes reported, there was significant clinical and statistical heterogeneity. The primary outcome of mortality at any time was reported in only three studies with a total of 267 patients. The mortality rate was 2.9% for the buffered fluids group and 1.5% for the non-buffered fluids group but this difference was not statistically significant. The Peto OR was 1.85 (95% CI 0.37 to 9.33, P = 0.45, I(2)= 0%). Organ dysfunction was only presented for renal impairment. There was no difference in renal insufficiency leading to renal replacement therapy between the buffered and non-buffered groups (OR 0.61, 95% CI 0.23 to 1.63, P = 0.32, I(2) = 0%). Markers of organ system failure as assessed by urine output, creatinine and its variables (for renal function), PaC0(2) (respiratory function) and postoperative nausea and vomiting (gastro-intestinal function) showed a statistically significant difference only in PaC0(2) levels. The mean difference was 1.18 with lower PaC0(2) levels in the non-buffered fluid group (95% CI 0.09 to 2.28, P = 0.03, I(2) = 0%) compared to the buffered fluid group.There was no difference in intraoperative blood loss nor the volumes of intraoperative red cell or fresh frozen plasma transfused between groups. There was an increase in platelet transfusion in the non-buffered group which was statistically significant after analysing the transformed data (log transformation because the data were highly skewed).A number of metabolic differences were noted. There was a difference in postoperative pH of 0.06 units, lower in the non-buffered fluid group (95% CI 0.04 to 0.08, P < 0.00001, I(2) = 74%). However, this difference was not maintained on postoperative day one. The non-buffered fluid group also had significantly greater base deficit, serum sodium and chloride levels.There was no difference demonstrated in length of hospital stay and no data were reported on cost or quality of life.
  
  
  CONCLUSIONS
  The administration of buffered fluids to adult patients during surgery is equally safe and effective as the administration of non-buffered saline-based fluids. The use of buffered fluids is associated with less metabolic derangement, in particular hyperchloraemia and metabolic acidosis. Larger studies are needed to assess robust outcomes such as mortality.
authors.affiliation: Department of Anaesthesia, UCL Centre for Anaesthesia, London, UK. edwardburdett@gmail.com.
authors.forename: Edward
authors.initials: E
authors.lastname: Burdett
authors.forename: Ahilanandan
authors.initials: A
authors.lastname: Dushianthan
authors.forename: Elliott
authors.initials: E
authors.lastname: Bennett-Guerrero
authors.forename: Suzie
authors.initials: S
authors.lastname: Cro
authors.forename: Tong J
authors.initials: TJ
authors.lastname: Gan
authors.forename: Michael P W
authors.initials: MP
authors.lastname: Grocott
authors.forename: Michael F M
authors.initials: MF
authors.lastname: James
authors.forename: Michael G
authors.initials: MG
authors.lastname: Mythen
authors.forename: Catherine M N
authors.initials: CM
authors.lastname: O'Malley
authors.forename: Anthony M
authors.initials: AM
authors.lastname: Roche
authors.forename: Kathy
authors.initials: K
authors.lastname: Rowan
mesh_terms: D000328:Adult; D002021:Buffers; D005440:Fluid Therapy / Q000009:adverse effects / Q000379:methods* / Q000401:mortality; D006801:Humans; D019990:Perioperative Care / Q000379:methods; D010952:Plasma Substitutes / Q000008:administration & dosage; D016032:Randomized Controlled Trials as Topic; D013514:Surgical Procedures, Operative
chemical_list: D002021:Buffers; D010952:Plasma Substitutes