Thread by @DrNikhilMD

🧵 LACTATE & LACTIC ACIDOSIS: The Complete ICU Breakdown
If you truly understand this thread, you will stop reacting to lactate and start interpreting it like an intensivist.
#MedTwitter #CriticalCare #ICU #FOAMed

1️⃣ Lactate is a survival molecule, not a toxin ⚡
When cells are stressed, lactate rises to help generate ATP quickly.
So a high lactate is not “bad”. It’s the body saying:
“Either oxygen is low, mitochondria are blocked, or my clearance is impaired.”
Your job is to find which one.

2️⃣ Lactate vs Lactic Acid: Stop mixing them up 🧪
• Lactic acid releases H⁺ and lowers pH
• Lactate is the conjugate base that buffers
This is why Lactated Ringer helps acidosis instead of worsening it.
You’re treating physiology, not numbers.

3️⃣ True lactic acidosis needs two things 📉
• Lactate above 2
• pH below 7.35
Lactate alone does not define acidosis.
pH is what predicts hemodynamic collapse, vasoplegia and mortality.

4️⃣ Why clinicians worry about lactic acidosis ❤️‍🔥
At very low pH, the heart weakens, vessels lose tone and enzymes malfunction.
Shock worsens, perfusion falls further, lactate rises more.
This is how metabolic acidosis becomes a vicious spiral.

5️⃣ The metabolic fork in the road 🔬
Under normal oxygen: Pyruvate → Acetyl-CoA → Mitochondria → ATP
Under hypoxia or mitochondrial blockade: Pyruvate → Lactate
RBCs make lactate nonstop because they have no mitochondria at all.
Understanding this explains almost every cause of lactate elevation.

6️⃣ Lactate depends on two forces ⚖️
📌 Production
📌 Clearance
Clearance organs: Liver 70 percent, kidneys 20 percent, muscle 10 percent
Cirrhosis and renal failure don’t just raise lactate. They slow its fall.
That’s why “trend” is sometimes more meaningful than the value.

7️⃣ Type A Lactic Acidosis: The perfusion failure 🚨
Occurs when oxygen delivery cannot meet demand.
Think:
• Septic, cardiogenic, hypovolemic, obstructive shock
• Severe anemia
• Severe hypoxemia
• Mesenteric or limb ischemia
• Seizures, rigors, fever (↑ consumption)
This is the lactate that improves with resuscitation.

8️⃣ Type B Lactic Acidosis: Mitochondria offline ⚡
Oxygen is present but unusable.
Common causes:
• Beta agonists like epinephrine or albuterol
• Propofol infusion syndrome
• Cyanide or nitroprusside toxicity
• Alcohol increasing NADH
• Metformin (rare but classical)
• Thiamine deficiency blocking PDH
These patients need metabolic correction, not liters of fluid.

9️⃣ Type D Lactic Acidosis: The invisible one 🧫
Hospital assays measure L-lactate only.
But gut bacteria produce D-lactate.
Clues:
• High anion gap
• Normal L-lactate report
• Confusion, ataxia
• Short bowel or bacterial overgrowth
Diagnosis requires a special test.

🔟 The most dangerous habit: The “Lactobolo reflex” 💧
High lactate ≠ always fluids.
Fluids worsen:
• Cardiogenic shock
• Propofol toxicity
• Beta-agonist driven lactate
• Thiamine deficiency

Treat physiology, not numbers.

1️⃣1️⃣ The Lactated Ringer myth busted 🧴
LR contains lactate, not acid.
It converts to bicarbonate in the liver and improves acidosis.
But drawing lactate from a line where LR is infusing will falsely elevate results.
Always use a fresh venipuncture.

1️⃣2️⃣ Lactate can be sky-high in normal physiology 🏃‍♂️🔥
Elite rowers reach lactate 25 to 30 with pH as low as 6.8 during competition…
…and remain completely healthy.
Moral: Lactate must always be interpreted in context.

1️⃣3️⃣ The A B D approach makes lactate simple 🧠
A → Oxygen delivery problem
B → Metabolic block or mitochondrial dysfunction
D → Rare bacterial isomer
This 3-step lens solves 90 percent of diagnostic confusion.

1️⃣4️⃣ Management is cause-directed, not lactate-directed 🛠️
Fix the underlying issue:
• Shock → improve perfusion
• Cyanide → hydroxocobalamin
• Thiamine deficiency → thiamine
• Seizures → control
• Toxins → stop the source
A falling lactate confirms your physiology is improving.

1️⃣5️⃣ Final Pearl ✨
Lactate is one of the smartest metabolic alarms in critical care.
It rises early, responds to intervention and tells you exactly where the physiology is failing.
Master lactate, and you master resuscitation.

#MedEd #CriticalCare #Lactate #ICU #FOAMed