Mastering Vasopressors – Part 6
The Critical Care Decision Tree: Choosing the Right Pressor in Under 60 Seconds
"The best critical care clinicians don't memorize drugs—they recognize physiology."
Imagine you arrive to find a patient with a blood pressure of 72/40.
What do you do?
Many providers immediately think:
"I need Levophed."
Or...
"Let's start epinephrine."
But experienced critical care clinicians don't think about medications first.
They think about physiology.
The medication is simply the tool.
The diagnosis determines which tool comes out of the toolbox.
If you remember one lesson from this entire series, let it be this:
Every pressor should answer one physiologic question.
Step One
Is The Tank Empty?
This is always your first question.
Does the patient have enough circulating volume?
Examples:
-
Hemorrhage
-
Dehydration
-
GI losses
-
Burns
-
Third spacing
-
Massive diarrhea
No vasopressor replaces blood.
No vasopressor replaces volume.
If the tank is empty...
Fill it.
Clues
Flat neck veins.
Collapsed IVC.
Dry mucous membranes.
Narrow pulse pressure.
Cold skin.
History of fluid loss.
Treatment
Blood.
Fluids.
Hemorrhage control.
Source control.
Only after adequate volume should pressors become part of the conversation.
Step Two
Is The Pump Broken?
If volume is adequate...
Can the heart actually move it?
Examples:
Massive MI.
Cardiomyopathy.
Myocarditis.
Valve failure.
Heart failure.
Clues
Pulmonary edema.
Weak pulses.
Cold extremities.
Poor LV squeeze.
Elevated JVP.
Low ETCO₂.
Narrow pulse pressure.
Think
Dobutamine.
Sometimes norepinephrine.
Sometimes epinephrine.
Mechanical support.
Step Three
Are The Pipes Too Relaxed?
This is distributive shock.
Examples:
Sepsis.
Neurogenic shock.
Medication overdose.
Anaphylaxis.
Clues
Warm skin.
Bounding pulses.
Wide pulse pressure.
Flushed appearance.
Low SVR.
Think
Norepinephrine.
Add vasopressin.
Epinephrine if appropriate.
Step Four
Is Something Blocking Circulation?
Examples:
Massive PE.
Tamponade.
Tension pneumothorax.
Auto-PEEP.
Clues
Jugular venous distention.
Sudden hypotension.
Poor ETCO₂.
Right ventricular enlargement.
Absent breath sounds.
Treatment
Not another pressor.
Fix the obstruction.
Step Five
Why Isn't The Pressor Working?
If you're already escalating doses...
Pause.
Ask:
Am I treating the right diagnosis?
Consider
Severe acidosis.
Hypocalcemia.
Adrenal insufficiency.
Persistent hemorrhage.
Persistent sepsis.
Occult cardiogenic shock.
The Pump-Pipes-Tank Rule
Every patient fits somewhere.
Empty Tank
Fill it.
Weak Pump
Support it.
Relaxed Pipes
Squeeze them.
Blocked Flow
Remove the blockage.
Everything else follows.
The Flight Medic Scan
Before you ever touch the pump:
Look.
Touch.
Listen.
Think.
Warm?
Cold?
Bounding?
Weak?
Wide pulse pressure?
Narrow?
Cap refill?
Mental status?
ETCO₂?
Neck veins?
One glance tells an incredible story.
Matching Physiology to Medication
Septic Shock
Problem:
Low SVR.
Medication:
Norepinephrine.
Cardiogenic Shock
Problem:
Low cardiac output.
Medication:
Dobutamine ± norepinephrine.
Bradycardia
Problem:
Poor rate.
Medication:
Epinephrine.
Anaphylaxis
Problem:
Everything.
Medication:
Epinephrine.
Refractory Vasoplegia
Problem:
Catecholamine resistance.
Medication:
Add vasopressin.
Think Like A Flight Medic
Instead of saying:
"I need Levophed."
Start saying:
"My patient has vasoplegia."
Instead of saying:
"I need Dobutamine."
Think:
"My patient has poor forward flow."
Instead of saying:
"The blood pressure is low."
Think:
"Why?"
That one word changes everything.
The 60-Second Decision Tree
Question 1: Is the tank empty?
↓
Yes → Replace volume.
↓
No
↓
Question 2: Is the pump failing?
↓
Yes → Improve contractility.
↓
No
↓
Question 3: Are the pipes too relaxed?
↓
Yes → Vasopressor.
↓
No
↓
Question 4: Is something blocking circulation?
↓
Yes → Fix the obstruction.
↓
No
↓
Reassess.
Reconsider.
Repeat.
The Master Formula
Every shock patient can be understood using one simple equation:
Perfusion = Pump + Pipes + Volume
If any one of those three fails...
The patient fails.
Your job is identifying which one broke first.
Final Thoughts
Critical care medicine isn't about having the most medications.
It's about asking the best questions.
The monitor gives you numbers.
The patient gives you physiology.
The medications simply support the answer.
If this series taught you anything, let it be this:
Never ask...
"Which pressor should I use?"
Instead ask...
"What physiology am I trying to fix?"
Because when you understand the physiology...
The medication almost always chooses itself.