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Unmeasured anions in children after cardiac surgery
Deirdre Murray1, David Grant, N Murali
1Paediatric Intensive Care Unit, Royal Children's Hospital, Melbourne, Australia. d.murray@ucc.ie
Insights
Increased unmeasured anions and lactate levels after cardiac surgery predict major adverse events. The highest risk was observed in children with elevated levels of both, indicating their critical role in post-operative outcomes.
Area of Science:
- Pediatric Cardiology
- Critical Care Medicine
- Biochemistry
Background:
- Metabolic acidosis is common post-cardiac surgery.
- The significance of increased unmeasured anions, a frequent cause of acidosis, is not fully understood.
- Predicting major adverse events in pediatric cardiac surgery patients is crucial.
Purpose of the Study:
- To evaluate the predictive value of unmeasured anions and lactate for major adverse events after pediatric cardiac surgery.
- To investigate the combined role of lactate and unmeasured anions in low cardiac output states.
Main Methods:
- Prospective enrollment of pediatric patients undergoing cardiac surgery.
- Arterial blood gas analysis and Stewart method calculations for excess acid and unmeasured anions at multiple time points.
- Definition of major adverse events as low cardiac output states requiring intervention.
Main Results:
- Major adverse events occurred in 7.1% of patients.
- Patients with major adverse events had significantly higher admission unmeasured anion levels (10.6 mEq/L vs. 4.8 mEq/L).
- Lactate levels did not differ between groups, but combined elevated lactate and unmeasured anions identified the highest risk.
Conclusions:
- Elevated unmeasured anion levels are significantly associated with major adverse events post-cardiac surgery.
- The combination of increased lactate and unmeasured anions on admission is the strongest predictor of major adverse events.
Objectives:
Acidosis caused by increased unmeasured anion levels occurs frequently after cardiac surgery, with uncertain significance. We examined the ability of unmeasured anions and lactate to predict major events after cardiac surgery, in addition to lactate/increased unmeasured anion levels during low cardiac output states.
Methods:
In the initial 6 months, all patients admitted after cardiac surgery were enrolled. Arterial samples were taken at 0, 4, 8, 12, 24, and 36 hours postoperatively. The Stewart method was used to calculate excess acid and unmeasured anion levels. Major adverse events were defined as low cardiac output states requiring cardiac massage or mechanical support. In the second 6-month period, data were collected from a further 8 infants during cardiac arrest/extracorporeal membrane oxygenation cannulation.
Results:
One hundred thirteen patients were analyzed. Major adverse events occurred in 8 (7.1%) of 113 patients. On admission, metabolic acidosis occurred in 94 of 113 samples: lactate alone (n = 25); mixed lactate and unmeasured anions (n = 44); and unmeasured anions alone (n = 25). All of the patients who experienced major adverse events had unmeasured anion levels of greater than 3 mEq/L on admission. Initial unmeasured anion levels were significantly higher in those infants with major adverse events (10.6 mEq/L [standard deviation, 8.2 mEq/L] vs 4.8 mEq/L [standard deviation, 6.6 mEq/L], P = .024). Lactate levels did not differ between the 2 groups. In the 16 patients sampled during major adverse events, metabolic acidosis occurred in 15 of 16, with a mean excess acid level of 14.9 mEq/L (standard deviation, 8.3 mEq/L). Although unmeasured anions made a significant contribution, lactate was the predominant acid.
Conclusions:
After cardiac surgery, unmeasured anion levels were significantly higher in those children with major adverse events. The greatest risk of major adverse events was found in children with both increased lactate levels and increased unmeasured anion levels on admission.
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