Authors: Steck D T et al.
Journal of Clinical Anesthesia, 2026, Article 112157
This multicenter cohort study evaluated how often phosphate abnormalities occur after cardiac surgery with cardiopulmonary bypass (CPB) and whether those abnormalities are associated with severe lactic acidosis. Using data from the Multicenter Perioperative Outcomes Group, the authors analyzed nearly 35,000 adult patients across 45 centers who had both phosphate and lactate levels measured within six hours after surgery.
Phosphate abnormalities were common. About 20% of patients developed hypophosphatemia (phosphate <2.5 mg/dL), while 14% developed hyperphosphatemia (>4.5 mg/dL) in the early postoperative period. This means more than one-third of patients had some degree of phosphate disturbance shortly after CPB.
Both low and high phosphate levels were independently associated with an increased risk of severe lactic acidosis (defined as lactate ≥4 mmol/L), even after adjusting for confounders. Hypophosphatemia carried a higher risk (odds ratio 1.46) than hyperphosphatemia (odds ratio 1.30). The most striking finding was in patients with severe hypophosphatemia (<1.0 mg/dL), where the odds of severe lactic acidosis more than doubled (OR 2.53).
The physiologic link is clinically relevant. Phosphate plays a central role in cellular energy metabolism, particularly ATP production. Low phosphate levels can impair oxidative phosphorylation, forcing cells toward anaerobic metabolism and increasing lactate production. On the other hand, hyperphosphatemia may reflect underlying cellular injury, renal dysfunction, or metabolic stress, all of which are also associated with elevated lactate levels.
This study stands out because it moves beyond single-center observations and confirms these associations in a large, diverse, real-world population. While it does not establish causation, it strongly suggests that phosphate abnormalities are not benign lab findings in the immediate postoperative cardiac surgery period.
Key Points
- Phosphate abnormalities occur in over one-third of patients after cardiac surgery with CPB
- Hypophosphatemia (20%) is more common than hyperphosphatemia (14%)
- Both low and high phosphate levels are associated with increased risk of severe lactic acidosis
- Severe hypophosphatemia (<1.0 mg/dL) more than doubles the risk of significant lactic acidosis
- Phosphate likely plays a mechanistic role through impaired cellular energy metabolism
What You Should Know
This study should change how you view early postoperative labs after cardiac surgery. Phosphate is often overlooked compared to potassium or calcium, but it clearly carries meaningful physiologic implications. If you see rising lactate, checking phosphate should be part of your reflex. More importantly, severe hypophosphatemia is not just a number—it may be contributing directly to metabolic failure. While we still lack definitive evidence that correction improves outcomes, ignoring phosphate abnormalities is no longer defensible in high-risk cardiac patients.
We want to thank the Journal of Clinical Anesthesia for allowing us to summarize and share this important work with the anesthesia community.