Thank you to Dr. Wolters for joining us today and to Tyler for presenting the case of a man w/ hx of SCC on pembrolizumab p/w 2 months of DOE & 1 wk of cough not responsive to levofloxacin. We discussed the role of ABGs > VBGs and the ddx for organizing PNA. The patient ended up having pneumonitis 2/2 to his PD-1 inhibitor which was discontinued and he was then started on steroids.
- There are several toxicities associated with PD-1 inhibitors. See here for prior pearls on these check point inhibitors!
- One needs to lose ~ 50% of their lung function to have SOB @ rest!!
- Try to obtain an ABG in a patient who is hypercarbic given the variability of a VBG and its estimation of pCO2. Per Dr. Wolter’s the pCO2 from a VBG can be wrong ~ 20% of the time.
- Reverse Halo Sign (RHS) on a CT Chest is a patch of normal lung surrounded by abnormal densities . There is a ddx and figure for RHS below!
ABG vs. VBG – Thank you Kenny for sharing!!
- Arterial: accurate O2 content; nl pH = 7.4 (7.35-7.45), CO2 = 40 (35-45)
- Venous: carries excess CO2 to be ventilated off in the long. ~3-5 mmHg higher than arterial blood
Evidence: Systemic review and meta analysis
- Arterial pH ~ 0.03 higher than venous
- Venous and arterial pCO2 do NOT correlate that well (off in ~ 20% of gases)
- Good negative predictive value of CO2 if low, but not as helpful if high
- If you want O2 status, you can use SpO2 as a surrogate marker, but ABG is more accurate
- If concerned for pH or CO2 status and ABG isn’t easy (ie painful and technically challenging); VBG as 1st pass -> understand limitations
- If the VBG doesn’t make sense or you want to be totally sure, get an ABG
Defined as the lung’s response and subsequent repair to any insult. Often associated with the reverse halo sign (RHS) characterized by a central clearing surrounded by denser air-space consolidation (often ground glass) in the shape of ring/crescent. This happens because in the following situations the lung heals from the center outwards. Was initially described in cryptogenic organizing PNA, however is now part of a wider DDX that includes the following:
- Autoimmune (Sarcoid, Wegener’s granulomatosis)
- Drug effect – PD-1 Inhibitors à 5% of patient’s will develop pneumonitis @ a mean of 7 months; 85% will respond to discontinuation & steroids.
- Infectious – endemic fungal infections, PCP PNA,
- Idiopathic – cryptogenic
Here is a great article and figure on the evaluation of Revere Halo Sign (RHS)