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Matthew Ho, MD PhD 🇸🇬

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Feb 25 • 6 tweets • 2 min read

Differentials for hypoxemia based on Aa gradient

ABG vs VBG:
- pH: VBG
- pCO2: VBG (not accurate in shock or hypercapnia); ABG for severe shock or if precise pCO2 needed in hypercapnia
- PO2: ABG (but SpO2 generally good enough)
- CO or methemoglobin: co-ox

Rough correlation between PaO2 and SpO2.

Causes of dissociation between SpO2 and PaO2
- shift in oxyHb curve
- dyshb: CO, methemoHb, sulHb
- Equipment failure
- Venous blood sample
- Localized hypoxemia (e.g., ischemic limb)
- Excessive oxygen consumption after sample collection (e.g., leukocytosis, thrombocytosis)

Saturation gaps: > 5% difference between SaO2 (ABG) and SpO2 (pulse ox)
- SaO2 (or PaO2) > SpO2: methemoglobin, sulfhemoglobin
- SpO2 > SaO2 (or PaO2): CO, cytosis, venous sample

journal.chestnet.org/article/S0012-…

litfl.com/dissociated-ox…

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Matthew Ho, MD PhD 🇸🇬

@MatthewHoMD

Feb 26

Summary of oxygen delivery devices taught to me by Mayo RT

Source of oxygen
- Wall taps by bedside: 0–15L/min
- Home concentrator: 0–10L/min

Oxygen delivered at 100%, put through different devices at different rates to adjust the oxygen concentration that the patient inspires

TLDR
- Low oxygen (<35%): nasal prongs
- Moderate oxygen (35-60%): venturi (high flow but mix with room air)
- High oxygen (>60%): non rebreather or HFNC
- PEEP needed (e.g., ADCHF, OSA): CPAP
- Hypercapnic: BiPAP
- Failure, unable to protect airway: mechanical ventilation

0. Inogen (pulse-dose oxygen therapy); not used in hospital
- Delivers only during inspiration; not expiration
- Up to 4L but intermittent; much less oxygen as unlike continuous oxygen therapy which fills the oral cavity, naso/oropharyngeal with reservoir of oxygen, this does not

Read 12 tweets

Matthew Ho, MD PhD 🇸🇬

@MatthewHoMD

Feb 25

Quantifying proteinuria has confused me for the longest time so I wanted to revisit some definitions. A thread.

1. Proteinuria =/= albuminuria
- Glomerular prot: mostly albumin
- Tubular prot: LMW proteins (e.g., B2M)
- Overflow prot: light chains, myoglobin, hb
- Postrenal prot: inflammation, bleed, malignancy

2. What is proteinuria?
- Normal protein excretion: < 150 mg/24h or spot PCR < 50 mg/g; < 300 mg/24h (pregnancy)
- Moderate prot: 150-500
- Severe prot: 500-3500
- Nephrotic-range: > 3500 mg/24h
- Proteinuria without albuminuria suggests nonglomerular causes

Read 6 tweets

Matthew Ho, MD PhD 🇸🇬

@MatthewHoMD

Feb 25

@n_gangat

Summary tweet on my approach to anemias. credit to @n_gangat, @RichGodby, @zhuoerxie, Dr Ron Go, @VincentRK for teaching. Comments/critiques welcome!

1. Approach to anemia

2. Approach to iron deficiency anemia

3. Iron deficiency in chronic inflammatory states (ashpublications.org/hematology/art…)

Read 9 tweets

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