This week we drop into some of the nitty gritty on PSA including preparation and patient assessment as well as discuss some common pitfalls.
Case: May 2017
83yF PMH HTN, HLD p/w fatigue and cyanosis. Reports that all day she has been feeling fatigued and was noted to have a blue color so her son called 911. On arrival she is cyanotic and hypoxic to 80-85% on NRB. Denies fevers, chills, chest pain, shortness of breath, cough, abdominal pain, nausea, vomiting, diarrhea, dysuria, hematuria. Patient denies any toxic ingestions or recent medication changes.
PMH / PSH
PMH: HTN, HLD
Medications: Celebrex, Meloxicam, Cyclosporine 0.05% 1 drop BID, Tolterodine, Pitvastatin, MVI, Omega 3
VS: 36.6, 90, 122/59, 25 80% on NRB
HEENT: NCAT, +periorbital and perioral cyanosis, OP clear, neck supple
Cardiovascular: RRR, no m/r/g
Pulmonary/Chest: Effort normal. No respiratory distress. No w/r/r
Abdominal: Soft, nt/nd, no r/g, normal BS
Extremities: Cyanosis to b/l hands and feet, warm to touch, no edema
Neurological: AAOx3, CN II-XII intact, strength and sensation intact
ABG: pH 7.484, PC02 32.8, P02 307, HC03 24.3 Lactate 1.8
WBC: 8.2, Neut 89%, Hgb 10.5, MCV 93.7, Hct 31.1, Plt 218
Na 141, K 4.7, Cl 103, BUN 35, Cr 1.0, Glucose 120, Ca 8.9, AG 12,
Bili Tot 0.4, Bili conj 0, Alk P 65, AST 18, ALT 22, Alb 3.4, Protein 6.1
CXR: No evidence for acute pulmonary pathology
What laboratory test will confirm your diagnosis?
A Co-Oximeter (Co-Ox) panel should be ordered which will report the percentages all the different types of hemoglobin currently present in the blood including MetHb (see More Info)
What is the treatment?
Methylene Blue given at 1-2mg/kg intravenously is the treatment for acquired MetHb (see More Info)
In this patient with acute onset cyanosis, hypoxemia on pulse oximeter without improvement on supplement oxygen, and a normal P02 on arterial blood gas analysis, suspicion for methemoglobinemia (MetHb) should immediately be raised. MetHb occurs when the iron in hemoglobin is oxidized from the ferrous (Fe2+) state into the ferric (Fe3+) state, thus making the heme molecule unable to bind new oxygen.