Source: Waters et al. Anesth Analg 2001; 93: 817-22

Reviewer:  R. Prasad, MD

Summary:

• NS group developed hyperchloremic metabolic acidosis
• NS group got more intraop bicarb, platelets.
• No diff in postop outcomes.
• More blood products (including FFP, platlets, PRBC, albumin) given to NS group

• Need larger numbers to look at individual blood product requirements more closely
• Wonder about the conclusion re: sum of all blood products ... if hetastarch (in NS or LR) were used instead of albumin, would there still be a significant difference?
• Is a temporary hyperchloremic metabolic acidosis really much of a problem?

• 66 open AAA, standard anesthetic (iso/fent/cisatracurium, thoracic epidural bolused with MSO4 and bupiv/fent/epi gtt started after unclamping, when stable)
• Randomized to LR or NS as predominant fluid (started on arrival to OR, ended on arrival to ICU)
• Exclusions: h/o abnl renal fnct, abnl BUN or Cr or Na values, acid-base abnormalities
• PRBC if Hgb<10; FFP, platelets given when evidence of microvascular bleeding, and point-of-care PT/PTT measurements
• Std monitors, a-line, CVC, PAC at anesthesiologists' discretion. Crystalloid given to keep PAOP or CVP within 10% of baseline. Coloid restricted to periods of rapid blood loss. Bicarb only if base balance < -5 ( [body weight kg x base deficit x 0.3] /2).
• Sample size based on changes in BE in prelim study of 25 pts. With 33 pts/group, there is 90% power to detect difference in BE of 5 mEq/L or more from baseline with p>0.05, assuming the std dev of change from baseline was ~3 mEq/L (from prelim study). Posthoc analysis indicated they had 90% power to detect 10% change in values of continuous outcome measures.

• 33 pts per group.
• No differences in demographic data or incidence of chronic disease
• except HTN (NS 85%, LR 58%)
• however, no diff in number of pts being medicated for HTN
• Similar AAA locations, lines (CVC v. PAC)
• Volume crystalloids, EBL, PRBC, FFP, albumin similar (though NS 500ml albumin vs. LR 0 - not significant)
• NS:
• UOP more (1200ml vs. 975ml)
• got more bicarb intraop (40ml vs. 4ml)
• more platelets (552ml vs. 421ml)
• greater overall blood product exposure (including PRBC, FFP, plt, albumin)
• Similar postop complications, vent time, ICU time, hosp stay

• Post hoc power calculation suggests sample size was adequate to detect 10% difference between groups.
• Acidosis after NS resulted in more bicarb administration intraop, but no diff in ICU bicarb requirements - suggests NS-related changes were transient.
• Larger UOP in NS may be b/c they received average of 500ml more crystalloid, 1500ml more total fluid (although differences in each were not significantly different). Interpretation complicated by use of dopamine during surgery.
• No diff in EBL, but fewer blood products given in LR group (plts and FFP,