When whole-body perfusion collapses, the body redistributes flow. Brain and heart autoregulate. Kidney, gut, skin, and skeletal muscle get clamped down first.
Interactive · Stage 01
The Triage Game
Case File · ICU Bay 4
Marcus
Age 58 · Septic Shock
"MAP 52 mmHg (70 to 100). Lactate 6 mmol/L (<2). Pressors are rising. The team has one job: restore perfusion pressure for the organs that die fastest."
Stage 02 · Redistribute Flow
Rank the flow order. Every placement reveals the physiology.
1
Protected First
2
Protected Second
3
Sacrificed First
Stage 03 · Pattern Locked
Brain. Heart. Reserve Beds.
Brain glows. Heart stays fueled. Kidney, gut, skin, and skeletal muscle constrict. That is the shock trade: preserve the least ischemia-tolerant tissue first.
Triage Hierarchy
Route
Sympathetic tone squeezes renal, splanchnic, skin, and muscle beds. Organ autoregulation preserves cerebral and coronary flow while MAP is restored to >= 65 mmHg.
Pattern
Creatinine can rise after shock because it lags behind injury and recovery. The resuscitation target is perfusion pressure, not a same-day normal creatinine.
Pearl
Neurons can die after 3 to 5 minutes without ATP. Renal tubules can recover if hypoperfusion is corrected before ischemic ATN locks in.
Cellular · First Event
Na/K Pump: First to Fall
Toggle the pump · watch the cell
Pump Running · Cell Stable
Na+ stays out. K+ stays in. Volume held.
Bedside · Board Traps
Clinical Applications
Permissive AKI
"Creatinine doubled on day 2 of shock. Is the treatment wrong?"
Not by itself. Creatinine lags days behind the perfusion event, so it cannot be the immediate target. Vasopressors and fluids restore perfusion pressure while the kidney declares injury later. Resuscitation target = MAP >= 65 mmHg, not normal creatinine.
Prerenal AKI
"BUN:Cr ratio is 28:1. Why so high?"
The hypoperfused but intact kidney is avidly reabsorbing urea, Na, and water. Urea rises out of proportion to creatinine because the tubules still work. BUN:Cr > 20:1 = prerenal azotemia · the kidney is concentrating what little it has.
Why AKI Reverses, Strokes Don't
"Same ischemia, same duration. Why does one recover?"
Tubular epithelium can regenerate if the basement membrane survives. Mature neurons do not divide, and ATP loss rapidly collapses ion gradients. Brain protection comes first because cytotoxic edema begins when Na/K-ATPase fails.
Earliest Sign of Cell Injury
"Which finding precedes everything else?"
Cellular swelling. The Na/K pump stops, Na+ floods in, water follows. This happens before nuclear changes, before enzyme leak, before any inflammatory marker. Swelling = the first event · not necrosis, not apoptosis, not pyknosis.
Perfusion Target
MAP = (2 x DBP + SBP) / 3. Shock resuscitation targets MAP >= 65 mmHg. Normal MAP is 70 to 100 mmHg.
BUN:Cr Ratio
Normal BUN:Cr is about 10 to 15:1. Prerenal azotemia is > 20:1. BUN normal range is 7 to 20 mg/dL. Cr normal range is 0.6 to 1.2 mg/dL.
FENa
FENa = (UNa x PCr) / (PNa x UCr) x 100. Prerenal is < 1%. ATN is > 2%.
ATN Fingerprint
Intrinsic ATN has BUN:Cr about 10 to 15:1, FENa > 2%, and muddy brown granular casts. Lactate normal range is < 2 mmol/L.
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