Bedside Snapshot
- Normal (Adult)
- −2 to +2 mEq/L (−2 to +2 mmol/L). Base deficit (BD) is the same number with the sign flipped: BE −8 = BD 8.
- Critical Values
- No universal lab critical value (typical; lab-specific). BD >6 mEq/L (BE below −6): moderate shock. BD >10 mEq/L (BE below −10): critical.
- High Suggests
- Metabolic alkalosis: vomiting or NG suction, diuretics, alkali load (bicarbonate, citrate from transfusion), or compensation for chronic CO₂ retention
- Low Suggests
- Metabolic acidosis: shock with lactic acidosis (hemorrhage, sepsis), DKA, toxic alcohols or salicylate, renal failure, saline-related hyperchloremia, diarrhea
- Act Now If
- BD >6 mEq/L in trauma, or BD rising despite resuscitation: treat as hemorrhagic shock; control bleeding, prepare blood products, check lactate, notify the trauma team or receiving facility
- Watch Out For
- A normal BE does not exclude shock: low albumin or a coexisting alkalosis can hide a lactic acidosis. Check lactate.
Reference & Critical Ranges
Lab-specific ranges: Every lab sets its own range, and it shifts with the analyzer and the population. Trust the range on your lab report. The values below are typical.
Reference ranges
| Population | Conventional | SI | Notes |
|---|---|---|---|
| Adult | −2 to +2 mEq/L | −2 to +2 mmol/L | Same for men and women. Most analyzers report standard base excess (SBE, also labelled BE(ecf)). |
| Children | Same as adult | Same as adult | Beyond the newborn period, interpret with adult values. |
| Neonate (cord or first-hour gas) | — | — | Read against the encephalopathy screening thresholds in Special Populations (base deficit ≥16 mmol/L or pH ≤7.0). |
Severity & critical values
| Level | Conventional | SI | What it means |
|---|---|---|---|
| Normal | BE −2 to +2 mEq/L | −2 to +2 mmol/L | No net metabolic disturbance. Two opposing disorders can still cancel out; check lactate, anion gap and chloride. |
| Mild base deficit | BD >2 to 6 mEq/L (BE −2 to −6) | >2 to 6 mmol/L | Mild metabolic acidosis. Trauma: class II in the BD-based grading of Mutschler 2013 (not an official ATLS table); blood products possible. |
| Moderate base deficit | BD >6 to 10 mEq/L (BE −6 to −10) | >6 to 10 mmol/L | Moderate metabolic acidosis. Trauma: class III in the Mutschler 2013 BD-based grading; blood products likely needed. |
| Critical | BD >10 mEq/L (BE below −10) | >10 mmol/L | Severe metabolic acidosis. Trauma: class IV in the Mutschler 2013 BD-based grading; prepare for massive transfusion. |
| Base excess | BE >+2 mEq/L | >+2 mmol/L | Metabolic alkalosis, or compensation for chronic CO₂ retention. No validated severity grades: judge by pH, bicarbonate and K⁺. |
Critical values: No lab has a universal panic value for BE (typical; lab-specific). Call BD >6 mEq/L (BE below −6) moderate shock. Call BD >10 mEq/L (BE below −10) critical. Watch hardest in trauma or sepsis.
Conversion: For BE, 1 mEq/L equals 1 mmol/L. The same number reads correctly in both unit systems.
Standard base excess (Van Slyke approximation)
SBE ≈ 0.93 × ([HCO₃⁻] − 24.4 + 14.83 × (pH − 7.40))
Normal is −2 to +2 mmol/L. Your analyzer does the math. Use the printed value, and note whether it is SBE or actual BE.
Causes of Abnormal Results
Low (base deficit, BE below −2 mEq/L)
A base deficit is metabolic acidosis. Either acid was gained or bicarbonate was lost. The severity grades sit in Reference & Critical Ranges.
| Mechanism | Common causes | Bedside clue |
|---|---|---|
| Lactic acidosis from hypoperfusion | Hemorrhagic, septic or cardiogenic shock; cardiac arrest; severe hypoxemia; carbon monoxide or cyanide poisoning | Tachycardia, hypotension or high shock index, cool skin, rising lactate |
| Lactic acidosis without hypoperfusion (type B) | Metformin toxicity; seizures; liver failure; malignancy; thiamine deficiency; epinephrine or beta-agonist effect | Normal perfusion and normal or near-normal BP; check metformin and other drug history, and lactate with the same sample |
| Ketoacidosis | Diabetic ketoacidosis (DKA), including euglycemic DKA on SGLT2 inhibitors; alcoholic or starvation ketoacidosis | Deep, rapid breathing; positive ketones; glucose may be near normal |
| Toxic acids | Methanol, ethylene glycol, salicylate; 5-oxoproline, D-lactate (GOLDMARK mnemonic) | High anion gap; osmolal gap early with toxic alcohols; tinnitus and respiratory alkalosis with salicylate |
| Renal failure | Acute kidney injury, advanced chronic kidney disease (CKD) | Rising creatinine, hyperkalemia, low urine output |
| Chloride load | Large volumes of 0.9% saline | Normal anion gap, high chloride, normal lactate |
| Bicarbonate loss (gut) | Diarrhea, pancreatic or small-bowel fistula, ureteral diversion | Normal anion gap, high chloride, history of losses |
| Bicarbonate loss (kidney) | Renal tubular acidosis, acetazolamide | Normal anion gap with no gut losses |
Injured patient with a base deficit: Assume hemorrhage until proven otherwise. Do not blame the saline, the alcohol or the seizure before bleeding is excluded.
High (base excess, BE above +2 mEq/L)
A positive BE is metabolic alkalosis. It can also be the kidneys compensating for chronic CO₂ retention.
| Mechanism | Common causes | Bedside clue |
|---|---|---|
| Gastric acid loss | Vomiting, nasogastric (NG) suction | Volume depletion, low chloride, low K⁺ |
| Diuretics | Loop and thiazide diuretics | Low chloride, low K⁺ |
| Compensation or post-hypercapnia | Chronic CO₂ retention (COPD, obesity hypoventilation); persists after rapid correction of chronic hypercapnia | Chronically high PaCO₂; alkalemia after intubation and brisk ventilation of a CO₂ retainer |
| Alkali load | Sodium bicarbonate; citrate from massive transfusion; calcium carbonate (milk-alkali syndrome) | Recent resuscitation or antacid use; high calcium with milk-alkali |
| Mineralocorticoid excess | Primary aldosteronism, Cushing syndrome, exogenous corticosteroids, villous adenoma (with potassium loss) | Hypertension with low K⁺ |
Interpretation & Bedside Approach
Step-by-step approach
- Is it real? Start with the sample. Delay, air or flush contamination all move BE. Keep the sample type and analyzer the same when you trend.
- How sick is the patient? Read BE beside pH, lactate and perfusion. In trauma, BD >6 mEq/L should prompt early blood-product readiness. At BD >10 mEq/L (class IV in the Mutschler 2013 grading), prepare for massive transfusion.
- Name the primary process. pH says acidemia or alkalemia. PaCO₂ speaks for the lungs. SBE speaks for the metabolism. Because SBE holds steady when PaCO₂ changes acutely, it isolates the metabolic problem.
- Check compensation. Run the SBE rules below. Is PaCO₂ well above the expected value? Then a second, respiratory acidosis is hiding in there: a tiring or oversedated patient.
- Explain a base deficit. Line it up against lactate, the albumin-corrected anion gap, chloride, ketones and creatinine. Lactate unable to account for the BD? Think chloride, ketones, renal failure or a toxin.
- Trend and escalate. Repeat the gas after each big resuscitation step. If the BD stalls or worsens, it points to ongoing bleeding or hypoperfusion. Call the trauma team, the receiving facility or medical control.
Expected compensation (SBE rules)
| Primary disorder | Expected change | Example |
|---|---|---|
| Metabolic acidosis | PaCO₂ ≈ 40 + SBE | SBE −10 → PaCO₂ about 30 mmHg |
| Metabolic alkalosis | PaCO₂ ≈ 40 + 0.6 × SBE | SBE +10 → PaCO₂ about 46 mmHg |
| Acute respiratory acidosis or alkalosis | SBE unchanged (about 0) | Acute PaCO₂ 70 mmHg → SBE still about 0 |
| Chronic respiratory acidosis or alkalosis | SBE ≈ 0.4 × (PaCO₂ − 40) | Chronic PaCO₂ 60 mmHg → SBE about +8 |
Base deficit and lactate together
| Pattern | Suggests |
|---|---|
| High BD, high lactate | Lactic acidosis from shock or hypoperfusion; resuscitate and find the source |
| High BD, normal lactate | Non-lactate acidosis: saline-related hyperchloremia, ketoacidosis, renal failure, toxic alcohol, diarrhea |
| High lactate, BE near normal | A coexisting alkalosis hides the acidosis: low albumin, vomiting or NG suction, diuretics, recent bicarbonate or citrate |
| Lactate falling, BD persists | Hyperchloremia from saline, renal failure or other unmeasured acids; reassess before chasing more fluid |
Lactate first: The 2023 European trauma bleeding guideline names blood lactate as a sensitive test to estimate and monitor bleeding and tissue hypoperfusion. With no lactate result, base deficit may be a suitable alternative (Recommendation 10, Grade 1B). The BD-based shock classes are not an official ATLS table, and methodologists have challenged them on method. Read them next to the clinical picture, not instead of it.
Field & Transport Considerations
Point-of-care testing
Handheld cartridge blood-gas analyzers read pH and PCO₂, then calculate bicarbonate and BE (usually the extracellular form). Each device works only inside its temperature range. A peripheral venous sample is acceptable for BD, and the initial venous BD predicts mortality in hemorrhagic shock. Venous PCO₂ and PO₂ still do not stand in for arterial values. EtCO₂ from the waveform tracks ventilation, not BE. A spontaneously breathing patient with a large BD often shows a low EtCO₂, and that is compensation.
Before and during interfacility transport
- Hand over: BE, lactate, pH and PaCO₂ with time stamps, the sample type and the resuscitation given (blood products, crystalloid volume, bicarbonate).
- Expect change en route: Blood products, bicarbonate and big saline volumes all shift BE. Watch a BD that worsens in transit: it suggests ongoing bleeding or hypoperfusion. Call the receiving team and medical control.
- Ventilated patients (Paramedic/RN/CCT): After you intubate a patient with a large BD, their compensation now depends on your ventilator settings. Set minute ventilation to hold PaCO₂ near the pre-intubation compensated value. A "normal" PaCO₂ of 40 mmHg can drop the pH sharply. Confirm with EtCO₂ and a repeat gas, per local protocol.
- Re-check: repeat a gas after major resuscitation steps and ventilator changes, on the same sample type and analyzer.
Special Populations
| Population | What changes | Clinical implication |
|---|---|---|
| Neonates & infants | Cord or first-hour gas (umbilical, arterial, venous or capillary) within 60 min of birth screens for hypoxic-ischemic encephalopathy (HIE) | pH ≤7.0 or BD ≥16 mmol/L: evaluate for therapeutic hypothermia. pH 7.01–7.15 or BD 10–15.9 mmol/L counts only with an acute perinatal event plus ventilation ≥10 min or 10-min Apgar ≤5. Call a cooling center early. |
| Children & adolescents | Same reference range as adults | Admission BD predicts mortality in pediatric as well as adult trauma. The ATLS BD classes were derived in adults; use pediatric vital signs and perfusion alongside them (see pediatric shock). |
| Pregnancy | Respiratory alkalosis of pregnancy with renal compensation | A mildly negative BE can be a normal compensation; a true BD with low perfusion still means maternal shock, which also endangers the fetus. |
| Older adults | No clinically meaningful difference in range | Baseline BE may be shifted by CKD or diuretics; compare with prior results. |
| CKD / dialysis | Chronic metabolic acidosis lowers baseline BE | Judge an acute change against the patient's usual value; BE rises after dialysis. |
| Liver disease | Low albumin raises BE; lactate clearance is slower | A near-normal BE can hide a lactic acidosis; check lactate and the albumin-corrected anion gap. |
| Other | Alcohol intoxication | Makes lactate a less reliable shock marker in trauma; do not let intoxication explain away a BD. |
Interfering Factors & Pitfalls
Collection & handling
| Factor | Effect | Why | Avoid / fix |
|---|---|---|---|
| Delayed analysis | ↓ pH, ↑ PCO₂ and lactate over time | Blood cells keep metabolizing; faster with very high WBC or platelet counts | Analyze promptly. Up to 30 min at room temperature in a plastic syringe per traditional CLSI C46 guidance; some studies support up to 60 min. Follow your lab policy. |
| Air in the syringe | False PO₂ and PCO₂ | Sample equilibrates with room air | Expel bubbles, cap and mix gently |
| Arterial-line flush in the sample | All values diluted | Flush fluid mixed with blood | Clear enough dead space before sampling, per policy |
Medications & treatments
| Factor | Effect | Why | Avoid / fix |
|---|---|---|---|
| Sodium bicarbonate | ↑ BE | Adds base | A better BE after bicarbonate does not mean perfusion improved; follow lactate |
| Large-volume 0.9% saline | ↓ BE | Hyperchloremic acidosis | Check chloride; the Surviving Sepsis Campaign 2021 suggests balanced crystalloids over saline in sepsis |
| Massive transfusion | ↑ BE later | Citrate is metabolized to bicarbonate | Expect a later alkalosis; do not read it as recovery alone |
| Acetazolamide | ↓ BE | Kidney wastes bicarbonate | Note the drug before searching for another cause |
Physiologic & assay factors
| Factor | Effect | Why | Avoid / fix |
|---|---|---|---|
| Low albumin | ↑ BE (masks acidosis) | Fewer weak acids in plasma | Check lactate and the albumin-corrected anion gap |
| Hypothermia or fever | Analyzer reports values at 37 °C; actual temperature changes pH and PCO₂ | Trauma and arrest patients are often cold; the gas reflects the analyzer temperature setting | Follow local policy on temperature-corrected values; record the patient temperature with the gas |
| Severe anemia or polycythemia | Actual BE is distorted | Hemoglobin changes the buffer capacity of blood; SBE corrects for hemoglobin about 5 g/dL | Use SBE where the analyzer reports it, and say which value you are reading |
| Actual BE vs SBE | Values differ | Different hemoglobin assumptions; analyzers offer several BE formulas | Know which one your analyzer reports; trend on the same device |
Common misinterpretations
- "BE is measured." It is calculated from pH and PCO₂. A bad sample means a bad BE.
- "Every BD is lactate." Not true. Saline, ketones, renal failure and toxins all lower BE with no hypoperfusion involved.
Physiology & Test Basics
What it measures
This page is about base excess (BE) and base deficit (BD). Both are the calculated metabolic part of a blood gas. pH, PaCO₂ and bicarbonate have their own pages. BE is the strong acid, in mmol, needed to drive 1 L of fully oxygenated blood to pH 7.40 at a PCO₂ of 40 mmHg and 37 °C (98.6 °F). Flip a negative BE and you have the base deficit: the base you would need instead.
Physiology & regulation
- Buffers: Bicarbonate, hemoglobin, albumin and phosphate are the buffers. They soak up added acid, and BE tallies every one of them.
- Acid gain or base loss: Add acid or lose base and BE drops. Lactate, ketones, toxins, a chloride load or bicarbonate loss all do it.
- Lungs: PaCO₂ moves within minutes. Bicarbonate shifts with it, but SBE stays put.
- Kidneys: Days, not minutes. They excrete acid and rebuild bicarbonate. That slow compensation is what moves BE.
- Actual BE vs SBE: Actual BE describes the blood alone. CO₂ changes, though, spread through all the extracellular fluid. So SBE models blood diluted with two parts of its own plasma (hemoglobin about 5 g/dL). That is why SBE stays steady when PaCO₂ changes acutely.
How it is measured
Draw whole blood into a pre-heparinized blood gas syringe: arterial, peripheral venous or capillary. The analyzer reads pH and PCO₂ and works out bicarbonate and BE. Point-of-care and lab analyzers both give you the result within minutes. Fasting is not needed.
Why it matters
One fast number tells you how big the metabolic disturbance is, and acute breathing changes leave it alone. In trauma, BE grades hemorrhagic shock and the blood you will need. In the ICU, a BD that lactate can't explain points to a second acid-base problem.
Clinical Pearls
Match the ventilator to the compensation: With a BD of 15, a spontaneously breathing patient is already working to hold PaCO₂ near 25 mmHg. Once intubated, the machine has to do that job. Dial in the minute ventilation, then confirm with EtCO₂ and a gas. Miss it and the pH falls.
Trend BD with lactate: Record BE and lactate together, on the same sample type, after every bolus, blood product or vasopressor change. Lactate falling while the BD sits still? Usually it is chloride, not ongoing shock.
BD >6 in trauma should prompt early blood-product readiness: The TraumaRegister DGU derivation data show transfusion need climbing with each BD class. Order blood early, and stop reaching for more crystalloid.
Look for the alactic BD: Take the lactate rise away from the BD. A big remainder is a second acid (ketones, chloride, renal failure, toxic alcohol). Each one needs its own treatment.
A CO₂ retainer's positive BE is expected: A chronic PaCO₂ of 60 mmHg gives an SBE of about +8. That is normal compensation, not a primary metabolic alkalosis.
Do not treat the number with bicarbonate: Go after the cause (bleeding, perfusion, insulin for DKA, dialysis). Bicarbonate to improve hemodynamics in lactic acidemia? The 2021 Surviving Sepsis Campaign suggests against it. It suggests bicarbonate only for septic shock with pH ≤7.2 and acute kidney injury (AKIN stage 2–3). Specific indications such as sodium-channel blocker toxicity and hyperkalemia are on the sodium bicarbonate page.
References
- Rossaint, R., Afshari, A., Bouillon, B., et al. (2023). The European guideline on management of major bleeding and coagulopathy following trauma: sixth edition. Critical Care, 27, 80. https://doi.org/10.1186/s13054-023-04327-7
- Evans, L., Rhodes, A., Alhazzani, W., et al. (2021). Surviving Sepsis Campaign: international guidelines for management of sepsis and septic shock 2021. Intensive Care Medicine, 47(11), 1181–1247. https://doi.org/10.1007/s00134-021-06506-y
- Zanelli, S. A., Wusthoff, C. J., Lucke, A. M., Kaufman, D. A., & American Academy of Pediatrics Committee on Fetus and Newborn. (2026). Therapeutic hypothermia for neonatal hypoxic-ischemic encephalopathy: clinical report. Pediatrics, 157(2), e2025073627. https://doi.org/10.1542/peds.2025-073627
- Heldeweg, M. L. A., Langer, T., & Duška, F. (2024). Guiding resuscitation in shock: base excess or lactate? Critical Care, 28, 249. https://doi.org/10.1186/s13054-024-05039-2
- Berend, K. (2018). Diagnostic use of base excess in acid–base disorders. New England Journal of Medicine, 378(15), 1419–1428. https://doi.org/10.1056/NEJMra1711860
- Mutschler, M., Nienaber, U., Brockamp, T., et al. (2013). Renaissance of base deficit for the initial assessment of trauma patients: a base deficit-based classification for hypovolemic shock developed on data from 16,305 patients derived from the TraumaRegister DGU. Critical Care, 17(2), R42 (landmark derivation study). https://doi.org/10.1186/cc12555
- Kellum, J. A. (2000). Determinants of blood pH in health and disease. Critical Care, 4(1), 6–14 (landmark review; source of the SBE compensation rules). https://doi.org/10.1186/cc644
- Çuhadar, S., Özkanay-Yörük, H., Köseoğlu, M., & Katırcıoğlu, K. (2022). Detection of preanalytical errors in arterial blood gas analysis. Biochemia Medica, 32(2), 020708. https://doi.org/10.11613/BM.2022.020708
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