MCQ 20

A 35 year old man is brought to the casualty after being rescued from a house fire. 100% oxygen is administered by nonrebreather mask, and his oxygen saturation is 99% by pulse oximetry. Pulse rate is 115/min, respiration rate is 30/min, and blood pressure is 120/70 mm Hg. There is no stridor, no use of the accessory muscles of respiration, and GCS is 15. There are facial burns as well as singed nasal hairs and soot in the posterior oropharynx. Lungs are clear with good air entry bilaterally.
Which one of the following is most correct about this patient’s condition?
A. The pressure of facial burns reliably predicts the presence of airway injury.
B. Direct laryngoscopy or bronchoscopy should be performed for airway injury.
C. This patient is at low risk for delayed 2 days postinhalation injury to the lower airways.
D. Dexamethasone should be empirically administered.
Answer : B (Direct laryngoscopy or bronchoscopy should be performed for airway injury)

MCQ 11:

All the following drugs are dialysable except:

a – Salicylate

b – Sertaline

c - Ethylene Glycol

d - Methanol

(This question appeared both in 2008 and 2009 FNB Entrance)

Ans: b – Sertaline

Click here to read more about toxins removed by hemodialysis

Toxicology:

Toxins removable by Hemodialysis:
- Salicylates
- Lithium
- Methanol
- Ethylene Glycol
- Isopropanol

Toxins removable by Hemoperfusion
- Barbiturates
- Carbamazepine
- Theophylline
- Valproic Acid

MCQ 4:

Decrease in spO2 is seen in all except:

a – Meth-hemoglobinemia

b- Carboxy-hemoglobinemia

c – Sulfhemoglobinemia

d – Fetal hemoglobin

 

Ans: Carboxy-hemoglobinemia

 

The effect of HbCO may be discerned by examining its absorption spectrum. At 920 nm, HbCO has an extremely low absorbance and therefore does not contribute to total absorbance. At 660 nm,
however, HbCO has an absorbance very similar to that of HbO2 , and SpO2 will therefore be falsely high. (ref: Miller)

COHb is typically read by a two-diode oximeter as 90% oxyhemoglobin and 10% reduced hemoglobin, resulting in false elevations of SpO₂. In the emergency department setting or shortly after ICU admission, a gap between pulse oximetry and Po₂ or cooximetrically measured oxygen saturation may suggest elevated COHb levels, particularly in patients with smoke inhalation or potential carbon monoxide poisoning. (Ref: Irwin and Rippe)

MCQ 3:

A patient has a pulse oximeter saturation (spO2) of 85%, where as his saturation on ABG (saO2) is 93%, what is the likely cause???

Possible diagnosis:

a – Carboxyhemoglobin

b – Methhemoglobin

c – Fetal hemoglobin

d – sulfhemoglobin

Ans: b – Methhemoglobinemia.

Because methemoglobin absorbs more light at 660 nm than at 990 nm, it affects pulse oximetry readings when methemoglobin levels exceed 6%. Moreover, higher levels of methemoglobin tend to bias the reading toward 85% to 90%. (Ref: Irwin and Rippe.)

In the presence of high HbMet concentrations, the measured SpO2 approaches 85%, independently of the actual arterial oxygenation. (Ref: Miller)