Anemia in ICU 

1️⃣ Why Anemia in ICU Is Different

Anemia in the ICU is not just low hemoglobin — it is a complex, multifactorial, inflammation-driven, iatrogenic, and outcome-modifying condition.

• 🔴 > 60–80% of ICU patients develop anemia
• 🔴 ~40–50% receive at least one RBC transfusion
• 🔴 Associated with ↑ mortality, ↑ ventilator days, ↑ LOS

Unlike OPD anemia, ICU anemia is usually:

• Normocytic normochromic
• Inflammation-driven
• Multifactorial
• Often dilutional + blood loss + marrow suppression

2️⃣ Definition

WHO Definition (general population):

• Hb <13 g/dL (men)
• Hb <12 g/dL (women)

⚠️ In ICU practice, transfusion decisions are NOT based on WHO definition but on:

• Hemodynamic stability
• Oxygen delivery-demand balance
• Ongoing bleeding
• Cardiac ischemia
• Lactate trend

3️⃣ Pathophysiology of ICU Anemia

A. 🔥 Inflammation-Mediated Anemia (Most Important)

Sepsis / trauma / surgery → cytokines (IL-6, TNF-α)

Effects:

1. ↑ Hepcidin → blocks ferroportin → iron trapped in macrophages
2. ↓ Erythropoietin production
3. Blunted marrow response
4. Reduced RBC lifespan (normally 120 days → ↓ to ~60–90 days)

This is similar to anemia of chronic disease, but more intense.

B. Iatrogenic Blood Loss

• Phlebotomy: 40–70 mL/day
• Arterial line sampling
• Dialysis circuits
• Procedures

In 7–10 days → clinically significant anemia.

C. Hemodilution

• Aggressive fluid resuscitation
• Septic shock
• Massive transfusion

Hb falls not because RBC lost, but plasma volume ↑.

D. Overt Blood Loss

• GI bleed
• Post-surgical
• Trauma
• DIC

E. Nutritional Deficiency

• Iron deficiency
• B12 deficiency
• Folate deficiency
• Protein-energy malnutrition

F. Hemolysis

• Sepsis-associated hemolysis
• ECMO
• CRRT
• Drug-induced
• Microangiopathy (TTP, DIC)

4️⃣ Types of Anemia Seen in ICU

5️⃣ Impact on Oxygen Delivery (DO₂)

DO2 =CO×(1.34×Hb×SaO2 +0.003×PaO2 )

👉 Hb is the major determinant of oxygen content.

But critical point:

ICU patients compensate by:

• ↑ Cardiac output
• ↑ Oxygen extraction
• ↓ SVR

Therefore mild-moderate anemia often tolerated.

6️⃣ Clinical Consequences in ICU

• ↑ Myocardial ischemia risk
• ↑ Ventilator dependence
• ↑ ICU length of stay
• ↑ Mortality (association, not always causation)

High-risk groups:

• Coronary artery disease
• Elderly
• Septic shock
• Severe hypoxemia
• Ongoing bleeding

7️⃣ Evaluation of Anemia in ICU (Structured Approach)

Step 1 – Confirm

• Hb trend
• Hematocrit
• Rule out lab error
• Dilution vs true drop

Step 2 – Acute vs Chronic?

Step 3 – Morphology (MCV)

Step 4 – Reticulocyte Count

• Low → marrow suppression
• High → bleeding / hemolysis

Step 5 – Special Tests

• Iron profile
• Ferritin (↑ in inflammation)
• LDH
• Haptoglobin
• Peripheral smear
• Coombs test
• B12/Folate
• Stool occult blood

8️⃣ Transfusion in ICU – Evidence-Based Practice

🔴 Landmark Trial: TRICC trial

Compared:

• Restrictive (Hb <7 g/dL)
• Liberal (Hb <10 g/dL)

👉 Restrictive strategy had:

• Similar or better survival
• Fewer complications

🔴 TRISS trial

In septic shock:

• 7 g/dL vs 9 g/dL
• No mortality difference

9️⃣ Current Guideline-Based Transfusion Thresholds

✔️ Hemodynamically Stable ICU Patients

Transfuse if Hb < 7 g/dL

✔️ Septic Shock

Threshold = 7 g/dL

✔️ Cardiac Surgery

7–8 g/dL

✔️ Acute Coronary Syndrome

Often 8–9 g/dL (individualized)

✔️ Active Bleeding

Clinical judgment + hemodynamics

🔟 Risks of Transfusion

• TRALI
• TACO
• Immunomodulation
• Infection risk
• Storage lesion
• Hyperkalemia
• Citrate toxicity

Transfusion is NOT benign.

11️⃣ Erythropoiesis Stimulating Agents (ESAs)

• Not routinely recommended
• Consider in:
• Chronic kidney disease
• Prolonged ICU stay
• Jehovah’s Witness patients

Risks:

• Thrombosis
• Hypertension

12️⃣ Iron Therapy in ICU

Oral:

• Poor absorption in inflammation

IV Iron:

• Consider if proven deficiency
• Avoid in active sepsis (controversial)

13️⃣ Blood Conservation Strategies 

✔️ Reduce Phlebotomy

• Pediatric tubes
• Closed blood sampling systems

✔️ Tolerate Lower Hb

• Use restrictive transfusion

✔️ Treat Underlying Cause

• Stop bleeding
• Control sepsis
• Correct deficiencies

✔️ Minimize Circuit Loss

• Optimize dialysis/ECMO protocols