In a postoperative patient with a base excess of –10 mEq/L on the arterial blood gas, what are the likely causes and how should it be managed?

Postoperative Base Excess of -10 mEq/L: Causes and Management

A base excess of -10 mEq/L in a postoperative patient represents moderate-to-severe metabolic acidosis that requires immediate investigation for hemorrhagic shock, tissue hypoperfusion, or iatrogenic hyperchloremic acidosis from excessive normal saline administration, followed by aggressive resuscitation with balanced crystalloids and urgent treatment of the underlying cause. 1, 2

Prognostic Significance

• Base deficit of -10 mEq/L is the threshold that defines "severe" acidosis and independently predicts increased mortality, massive transfusion requirements, and post-traumatic organ failure. 1
• This degree of acidosis indicates significant tissue hypoperfusion and oxygen debt that demands immediate intervention. 1
• In surgical populations, base deficit >-10 mEq/L correlates with substantially increased risk of death and postoperative complications. 1

Immediate Diagnostic Priorities

Measure serum lactate immediately to differentiate tissue hypoperfusion from other causes:

• Lactate >2 mmol/L indicates inadequate tissue perfusion and ongoing shock. 1
• Lactate that fails to normalize within 24 hours is associated with 77.8% survival, dropping to only 13.6% if elevated >48 hours. 1
• Rising lactate despite resuscitation suggests ongoing hemorrhage, unrecognized surgical pathology, or inadequate source control. 3

Calculate the anion gap and corrected chloride to determine the type of acidosis:

• Elevated chloride with normal anion gap indicates iatrogenic hyperchloremic acidosis from excessive normal saline administration during surgery. 1, 2
• Elevated anion gap with elevated lactate suggests tissue hypoperfusion, hemorrhagic shock, or bowel ischemia. 2, 4
• Postoperative metabolic acidosis is most commonly due to either hyperchloremic acidosis from large saline infusions or lactic acidosis from tissue hypoperfusion—often both coexist. 2

Likely Causes in Postoperative Patients

Hemorrhagic shock or ongoing bleeding:

• Inadequate intraoperative resuscitation or unrecognized ongoing blood loss. 1
• Check hemoglobin, coagulation parameters (PT, APTT, fibrinogen, platelets), and consider surgical re-exploration if bleeding is suspected. 1

Iatrogenic hyperchloremic acidosis:

• Excessive normal saline administration during surgery is a leading cause of postoperative metabolic acidosis. 1, 2
• Saline-induced hyperchloremia decreases strong ion difference, causing metabolic acidosis independent of tissue perfusion. 2, 5
• Total volume of saline infused intraoperatively is an independent predictor of postoperative acidosis. 2

Tissue hypoperfusion despite adequate blood pressure:

• Inadequate cardiac output, vasopressor-induced vasoconstriction without adequate volume resuscitation, or microcirculatory dysfunction. 1
• Bowel ischemia or mesenteric hypoperfusion in abdominal surgery patients. 3

Unmeasured anions:

• Colloid solutions (e.g., polygeline) can contribute to acidosis through increased strong ion gap. 6
• Ketoacidosis, uremia, or toxin ingestion (less common postoperatively). 7

Immediate Resuscitation Strategy

Administer balanced crystalloids (lactated Ringer's or Plasma-Lyte), NOT normal saline:

• Give 20 mL/kg bolus of lactated Ringer's solution over 15-30 minutes as initial therapy. 8
• Repeat boluses up to 60 mL/kg total until perfusion improves, monitoring for pulmonary edema. 8
• Avoid normal saline entirely—it will worsen existing metabolic acidosis through hyperchloremic mechanisms. 1, 8
• Balanced crystalloids have a strong ion difference closer to plasma and do not cause hyperchloremic acidosis. 1

Hemodynamic targets:

• Target mean arterial pressure (MAP) ≥65 mmHg. 8, 3
• Target urine output >0.5-1 mL/kg/hour as a marker of adequate tissue perfusion. 8, 3
• If hypotension persists after 40-60 mL/kg fluid resuscitation, start norepinephrine as first-line vasopressor. 8

Monitoring Requirements

Serial arterial blood gas measurements every 1-2 hours initially:

• Monitor pH, PCO2, base excess, and lactate to assess response to therapy. 1, 8
• Failure of lactate to decrease or worsening base deficit indicates inadequate resuscitation or unrecognized pathology requiring surgical intervention. 1, 3

Check electrolytes immediately:

• Measure potassium, magnesium, calcium, and phosphate. 8
• Severe hyperkalemia (K+ >5.5 mmol/L) may accompany acidosis and requires urgent treatment. 8

Surgical Decision-Making

Do not delay surgical re-exploration if surgical pathology is suspected:

• Source control is paramount—medical correction of acidosis will fail if ongoing bleeding, bowel ischemia, or anastomotic leak is present. 8, 3
• Signs requiring urgent surgical intervention include peritonitis, worsening acidosis despite resuscitation, or rising lactate. 3
• Consider damage control surgery if patient develops severe physiologic derangement (pH ≤7.2, lactate ≥5 mmol/L). 3

Additional Supportive Measures

Broad-spectrum antibiotics:

• Administer immediately given high risk of bacterial translocation from gut hypoperfusion or suspected intra-abdominal sepsis. 8, 3

Optimize ventilation:

• Ensure adequate minute ventilation to prevent respiratory acidosis from compounding metabolic acidosis. 1
• Avoid excessive positive pressure ventilation that may impair venous return and worsen tissue perfusion. 1

Analgesia:

• Inadequate pain control can contribute to sympathetic stimulation and impaired tissue perfusion. 1

Common Pitfalls to Avoid

• Do not continue administering normal saline—this is a common iatrogenic cause of worsening acidosis postoperatively. 1, 2
• Do not assume acidosis is purely "dilutional" or benign—base deficit of -10 mEq/L predicts serious complications and requires aggressive investigation. 1
• Do not delay surgical re-exploration while attempting medical correction if surgical pathology is suspected. 8, 3
• Do not rely solely on blood pressure—lactate and base deficit are better markers of tissue perfusion. 1

ICU Length of Stay

• Postoperative metabolic acidosis is associated with significantly longer ICU and hospital length of stay. 2
• Early recognition and aggressive treatment may reduce this morbidity. 2