笹崎

Hemoptysis May Be Absent in DAH

“Silent DAH” → falling Hb + hypoxemia + diffuse opacities.

the absence of blood in the sputum does not rule out Diffuse Alveolar Hemorrhage (DAH). In fact, waiting for hemoptysis is a rookie mistake.

The "Smart" mental model is: "The Sponge vs. The Bucket."

• The Bucket (Stomach/Gut): If you bleed into your stomach, it fills up and you vomit (Hematemesis).

• The Sponge (Lung): The lungs have a massive surface area (\bm{50-100\ m^2}) designed to absorb fluid. The alveoli act like a giant sponge. They can soak up 1.5 to 2 Liters of blood—enough to cause hemorrhagic shock—before a single drop spills over into the central bronchi to trigger a cough reflex.

• The Reality: 33% of DAH patients present with "Silent DAH." They are dying of internal bleeding, but their handkerchief is clean.

Here is the consultant-level breakdown of the "Internal Hemorrhage," the "Carbon Monoxide Trap," and the "Lavage Verdict."

1. The Triad of Silent DAH

If the patient isn't coughing blood, how do you catch it? You look for the "Dissociation":

1. Falling Hemoglobin: The patient drops 2 g/dL of Hb in 24 hours with no obvious source (no GI bleed, no retroperitoneal hematoma).

2. Refractory Hypoxemia: The airspaces are filling with fluid (blood), creating a massive shunt.

3. New Diffuse Opacities: The CXR shows "Alveolar Filling" (Ground Glass or Consolidation) that spares the costophrenic angles (unlike edema) and the periphery (Butterfly distribution).

• The "Smart" Calculation: If the anemia is worsening while the X-ray is whitening, the blood is in the chest.

2. The Pathognomonic Sign: The DLCO Spike

• The Logic: In almost every lung disease (Pneumonia, Edema, Fibrosis), the diffusing capacity (DLCO) goes DOWN because the membrane is thickened or the surface area is lost.

• The Exception: DAH.
• The Mechanism: Carbon Monoxide (CO) binds to Hemoglobin avidly.
• In DAH, the alveoli are lined with free Hemoglobin (from the bleeding).
• The inhaled CO binds instantly to this extravascular Hb before it even crosses into the capillary.

• Result: The machine thinks the uptake is massive. You get a Super-Normal DLCO (> 100% predicted) or a spike of >30% from baseline.

• Rule: If a hypoxic patient has a high DLCO, it is DAH until proven otherwise.

3. The Verdict: Bronchoscopy with Sequential Aliquots

• The Question: Is it DAH or just "scope trauma"?
• The Test: Instill 60ml of saline, suction, and repeat 3 times in the same segment.

• Trauma/Bronchitis: The fluid gets clearer (bleeding washes away).

• DAH: The fluid stays bloody or gets Darker/Redder (Sequential Aliquots). This confirms the bleeding is coming from the deep alveolar reservoir.

Summary for the Bedside

this vasculitis patient is crashing. Hb is 7.0 (was 9.0 yesterday). CXR shows 'edema', but he has no hemoptysis.

1- The Pivot: 'Do not trust the sputum. The blood is trapped in the sponge.'

2- The Clue: 'Check his DLCO if possible. If he's too unstable, look at the urine for casts (Pulmonary-Renal Syndrome).'

3- The Action: 'Bronch him now. If the aliquots are bloody, start high-dose steroids and call for Plas#USIranStandoff $BTC ma Exchange. He is bleeding to death inside his own lungs.

Hemoptysis May Be Absent in DAH

“Silent DAH” → falling Hb + hypoxemia + diffuse opacities.

the absence of blood in the sputum does not rule out Diffuse Alveolar Hemorrhage (DAH). In fact, waiting for hemoptysis is a rookie mistake.

The "Smart" mental model is: "The Sponge vs. The Bucket."

• The Bucket (Stomach/Gut): If you bleed into your stomach, it fills up and you vomit (Hematemesis).

• The Sponge (Lung): The lungs have a massive surface area (\bm{50-100\ m^2}) designed to absorb fluid. The alveoli act like a giant sponge. They can soak up 1.5 to 2 Liters of blood—enough to cause hemorrhagic shock—before a single drop spills over into the central bronchi to trigger a cough reflex.

• The Reality: 33% of DAH patients present with "Silent DAH." They are dying of internal bleeding, but their handkerchief is clean.

Here is the consultant-level breakdown of the "Internal Hemorrhage," the "Carbon Monoxide Trap," and the "Lavage Verdict."

1. The Triad of Silent DAH

If the patient isn't coughing blood, how do you catch it? You look for the "Dissociation":

1. Falling Hemoglobin: The patient drops 2 g/dL of Hb in 24 hours with no obvious source (no GI bleed, no retroperitoneal hematoma).

2. Refractory Hypoxemia: The airspaces are filling with fluid (blood), creating a massive shunt.

3. New Diffuse Opacities: The CXR shows "Alveolar Filling" (Ground Glass or Consolidation) that spares the costophrenic angles (unlike edema) and the periphery (Butterfly distribution).

• The "Smart" Calculation: If the anemia is worsening while the X-ray is whitening, the blood is in the chest.

2. The Pathognomonic Sign: The DLCO Spike

• The Logic: In almost every lung disease (Pneumonia, Edema, Fibrosis), the diffusing capacity (DLCO) goes DOWN because the membrane is thickened or the surface area is lost.

• The Exception: DAH.
• The Mechanism: Carbon Monoxide (CO) binds to Hemoglobin avidly.
• In DAH, the alveoli are lined with free Hemoglobin (from the bleeding).
• The inhaled CO binds instantly to this extravascular Hb before it even crosses into the capillary.

• Result: The machine thinks the uptake is massive. You get a Super-Normal DLCO (> 100% predicted) or a spike of >30% from baseline.

• Rule: If a hypoxic patient has a high DLCO, it is DAH until proven otherwise.

3. The Verdict: Bronchoscopy with Sequential Aliquots

• The Question: Is it DAH or just "scope trauma"?
• The Test: Instill 60ml of saline, suction, and repeat 3 times in the same segment.

• Trauma/Bronchitis: The fluid gets clearer (bleeding washes away).

• DAH: The fluid stays bloody or gets Darker/Redder (Sequential Aliquots). This confirms the bleeding is coming from the deep alveolar reservoir.

Summary for the Bedside

this vasculitis patient is crashing. Hb is 7.0 (was 9.0 yesterday). CXR shows 'edema', but he has no hemoptysis.

1- The Pivot: 'Do not trust the sputum. The blood is trapped in the sponge.'

2- The Clue: 'Check his DLCO if possible. If he's too unstable, look at the urine for casts (Pulmonary-Renal Syndrome).'

3- The Action: 'Bronch him now. If the aliquots are bloody, start high-dose steroids and call for Plasma Exchange. He is bleeding to death inside his own lungs.