Back to #Basics: When to Use Sodium Bicarb in the ICU
Why Blood pH Matters
The human body tightly regulates blood pH between 7.35 and 7.45. Even slight deviations can disrupt:
Electrolyte balance (especially potassium and calcium)
Membrane potentials
Protein structure and cellular function
Small pH shifts reflect significant changes in H+ ion concentration due to the logarithmic pH scale. That’s why even minor acidosis or alkalosis can be clinically significant.
How the Body Maintains pH
We constantly generate acids through metabolism. The body counteracts this using:
Clinical Consequences of Severe Acidemia
When pH drops significantly:
↓ Cardiac output (↓ contractility + ↑ afterload)
↑ Tachyarrhythmias
↓ Arrhythmia threshold
Hyperkalemia from K⁺ shifting out of cells
→ worsens cardiac instability
What Happens When You Give Sodium Bicarbonate?
One amp = 50mL of 8.4% sodium bicarbonate
Osmolality: ~2000 mOsm/L (extremely hypertonic)
Sodium Effects:
Adds ~2 mEq of Na⁺ to serum
Pulls ~125mL of water from intracellular space to ECF
Can increase serum sodium and dehydrate cells
Bicarbonate Effects:
Mostly converted to CO₂ + H₂O
Residual bicarb diluted by intracellular water shift
If no severe acidosis, kidneys excrete excess bicarb
Importance of Ventilation When Giving Bicarbonate
Bicarbonate administration works by buffering free hydrogen ions:
HCO₃⁻ + H⁺ ⇌ H₂CO₃ ⇌ CO₂ + H₂O
From a purely chemical standpoint, even in a closed system, this reaction consumes protons and raises pH by reducing [H⁺]. So, yes — adding bicarbonate will shift the equilibrium and increase pH, regardless of ventilation, as Ravnit correctly points out.
However, in clinical practice, especially in critically ill or ventilated patients, this isn’t the whole picture.
When bicarbonate is given, it generates CO₂, which must be exhaled. If the patient is unable to increase minute ventilation — due to sedation, muscle fatigue, or lack of an advanced airway — the CO₂ accumulates. This can:
Negate the pH benefit of buffering
Potentially worsen intracellular acidosis
Raise PaCO₂, increasing work of breathing and cerebral blood flow
In these scenarios, bicarbonate might simply exchange one acid (H⁺) for another (CO₂) — not always a net win. This is especially important when:
The patient is not intubated
Minute ventilation is fixed or limited
Severe hypercapnia is already present
Thus, while bicarbonate does increase pH in theory, the clinical effectiveness depends heavily on the patient’s ability to clear CO₂.
TLDR:
Theory: Bicarbonate buffers H⁺ and raises pH (true even in closed systems)
Practice: If CO₂ can't be eliminated, the benefit is limited or lost
Implication: Use caution when giving bicarb to acidemic patients without ventilatory reserve
When to Give Bicarbonate
Strong Indications:
Non-anion gap metabolic acidosis (NAGMA)
Diarrhea
Adrenal insufficiency
Renal tubular acidosis
Hyperkalemia
Drives K⁺ into cells temporarily
Sodium channel blocker overdose
TCAs, local anesthetics, carbamazepine, flecainide
Salicylate toxicity
Used for urinary alkalinization
Controversial or Conditional Use
Lactic Acidosis with pH < 7.1
May improve hemodynamics and perfusion
No proven mortality benefit
Consider as bridge to CRRT
Lactic Acidosis with AKI or Concurrent NAGMA
Supported by BICAR-ICU trial
Cardiac Arrest
AHA recommends against routine use
Some providers give bicarb if pH < 7.1
Risks: hypernatremia, hypocalcemia, post-ROSC alkalosis
When Not to Give Bicarb
Diabetic Ketoacidosis (DKA)
Bicarb doesn’t improve acidosis
Risks:
Cerebral edema
Worsening ketosis
Hypokalemia
Tissue hypoxia
Lactic Acidosis with pH > 7.15
Surviving Sepsis Campaign advises against bicarb to improve hemodynamics (Grade 2B)
How to Dose It
Use isotonic sodium bicarb when possible
Bolus: Calculate using SBE formula or weight-based
Continuous infusion: For slower correction, especially if trending labs
SUMMARY:
| Summary: Bicarbonate in the ICU | ||
|---|---|---|
| Give | Don’t Give | Consider |
| Hyperkalemia** | DKA (especially pediatric) | Lactic acidosis with pH < 7.1 |
| NAGMA | Lactic acidosis with pH > 7.15 | Lactic acidosis + AKI or NAGMA |
| Sodium channel blocker overdose | Cardiac arrest with severe acidemia | |
| Salicylate toxicity (alkalinization) | Uremic acidosis | |
Want More?
Listen to our ABG Podcast Episode
Explore the delta ratio, SBE, and acid-base pearls
Check out our ICU APP Fellowship and educational content at Pulmcast.com
Further reading:
Attributions
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