Whiteboard Medicine Emergency And Critical Care

LACTATE: BEYOND TISSUE HYPOPERFUSION

One of the most common misconceptions in critical care is that elevated lactate automatically means tissue hypoxia.

In reality, lactate can rise through several different mechanisms.

🔹 Adrenergic stimulation

Catecholamines accelerate glycolysis and increase pyruvate production.

When pyruvate production exceeds mitochondrial processing capacity, excess pyruvate is converted to lactate.

This can occur despite adequate oxygen delivery.

Examples include:

• Septic shock
• Severe asthma receiving beta-agonists
• Seizures
• Post-cardiac arrest states

🔹 Impaired clearance

The liver clears the majority of circulating lactate.

Patients with hepatic dysfunction may therefore develop elevated lactate levels even without increased production.

🔹 Microcirculatory dysfunction

Global oxygen delivery may appear adequate while regional tissue perfusion remains abnormal.

This is particularly important in septic shock.

🔹 True tissue hypoperfusion

This remains an important cause of hyperlactatemia—but it is only one of several mechanisms.

🔹 Why this matters

A persistently elevated lactate does not automatically mean the patient needs more fluid.

Lactate should always be interpreted alongside:

• Physical examination
• Capillary refill
• Urine output
• Bedside ultrasound
• Overall hemodynamics

KEY TAKEAWAYS

✅ Lactate is not synonymous with tissue hypoxia

✅ Adrenergic stimulation commonly elevates lactate

✅ Impaired clearance may contribute substantially

✅ Lactate should never be interpreted in isolation

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Cheers,
WBM

1 day ago | [YT] | 6

Whiteboard Medicine Emergency And Critical Care

VENOUS CONGESTION: THE PHYSIOLOGY BEHIND VExUS

When we think about organ perfusion, we often focus on arterial pressure.

But organ perfusion depends on BOTH arterial inflow and venous outflow.

🔹 Why venous pressure matters

The kidneys, liver, and other organs depend on a pressure gradient.

As central venous pressure rises, the gradient driving blood flow through organs decreases.

This means a patient can have a normal MAP and still develop organ dysfunction from venous congestion.

🔹 CVP isn't useless

CVP performs poorly as a predictor of fluid responsiveness.

However, it can be very useful as a marker of venous congestion.

A CVP of 15 mmHg may tell you little about whether fluids will increase cardiac output, but it may tell you a lot about renal venous hypertension.

🔹 This is where VExUS helps

VExUS evaluates the downstream effects of elevated right-sided pressures.

As congestion worsens:

• Hepatic vein flow becomes abnormal
• Portal vein pulsatility increases
• Intrarenal venous flow becomes increasingly discontinuous

🔹 Why this matters

Some patients with AKI don't need more fluid.

They may need less.

Recognizing venous congestion can completely change your management strategy.

KEY TAKEAWAYS

✅ Organ perfusion depends on arterial and venous pressures

✅ Elevated venous pressure can contribute to AKI

✅ VExUS evaluates the consequences of venous congestion

✅ Not all oliguria should trigger more fluid administration

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Cheers,
WBM

1 week ago | [YT] | 9

Whiteboard Medicine Emergency And Critical Care

Epinephrine can increase lactate—even when patients are improving.

This is one of the most commonly misunderstood ICU findings.

---

Epinephrine:
• Increases cardiac output
• Improves perfusion

But also:
• Stimulates beta-2 receptors
• Increases glycolysis
• Drives lactate production

---

So what happens?

You start epinephrine →
Lactate rises →
But perfusion may actually be better

---

This creates a clinical trap:

Rising lactate is often interpreted as worsening shock.

But in this case, it may reflect:
• Increased metabolic activity
NOT
• Tissue hypoxia

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How to approach it:

Look at the full picture:
• Blood pressure
• Urine output
• Mental status
• Skin perfusion

---

If everything else is improving, the lactate rise may be expected.

---

Takeaway:
Not all lactate elevation is bad—context matters, especially with epinephrine.

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2 weeks ago | [YT] | 7