Evidence Based Practice and Quality Assurance
Background and Goal of Study: The Fencl-Stewart approach to acid-base disorders, simplified by Story et al.,1 estimates the base excess (BE) effects of strong ion, albumin (A) and unmeasured anions (UA). It has been suggested that the UA component of BE is a clinical marker for mortality in an Intensive Care population.1 We examined the importance of each of the BE effects on perioperative complications in a population of elderly trauma patients.
Materials and Methods: Arterial blood gas analysis, plasma albumin and electrolyte levels were measured at hospitalization in consentient consecutive patients aged >70 scheduled for femur fracture repair. BE was determined by a blood gas machine. BE effects were defined as1: Na-CI effect = [Na+]-[Cl−] − 38; A effect = 0.25 × [42-albumin]; UA effect = BE − NA-Cl effect − A effect. Patients were blindly observed during surgery and for 7 postoperative days. Total number of complications (hypotension, cardiac symptoms, respiratory failure, oliguria, anemia [Hb < 10mg/dl], infections and cognitive deterioration) was correlated with each BE effect using linear regressions. Predictive values (PV) of significant BE effects on complications were tested using Chi-square and Fisher's Exact Test.
Results and Discussions: 38 patients (81 ± 7 years, 22 were ASA3, 16 ASA2) were studied. Number of complications significantly correlated with standard BE and UA effect (both p = 0.003) but not with Na-CI or A effects. BE and UA values < −2 were associated with occurrence of >2 complications (both p < 0.01) with similar positive PV (BE: 100%; UA: 85%) and better negative PV for UA (BE: 64%; UA: 75%).
Conclusion(s): In elderly trauma patients, at risk for undetected hypovolemia and hypoperfusion2, a simplified analysis of acid-base balance identifies patients who will develop perioperative complications. The hypothesis that UA effect may guide fluid therapy, leading to improved outcome, requires further evaluation.
1 Story DA, Morimatsu H, Bellomo R. Br J Anaesth
2004; 92: 54-60.
2 Venn R, Richardson P, Ploniecki J et al. Br J Anaesth
2002; 88: 65-71.