Page 667 - Clinical Application of Mechanical Ventilation

Case Studies 633

Clinical symptoms generally arise with carboxyhemoglobin levels above 16
to 20%. These symptoms include headaches, dizziness, inability to concentrate,
impaired judgment, lethargy, and confusion. Symptoms progressively increase
In spite of normal Hb between 20 and 60% HbCO, and exposures are fatal at 60 to 80% HbCO
and satisfactory SaO 2 , the
measured CaO 2 is low due to tissue asphyxiation. Lactic acidosis is a common sign that tissue oxy-
(12.7 vol %) because of the genation is impaired. Following a thorough assessment, the patient was then
high HbCO level (21.2 g %).
transported to the intensive care unit for further evaluation and treatment of his
injuries.

Indications

Physical examination revealed that the patient had received a moderate thermal
Elective intubation is burn to the airway as well as to his torso and extremities. He was electively intu-
done to maintain a patent air-
way in anticipation of airway bated to maintain an adequate airway and, as expected, he became edematous to
edema and obstruction. the point that his facial features were no longer recognizable.

Initial Settings

He was lightly sedated and placed on CPAP with pressure support of 15 cm H O,
2
and the spontaneous frequency was 16/min. He maintained a spontaneous V of
T
550 mL (approx. 7 mL/Kg) at an F O of 100% and PEEP of 6 cm H O. After
2
I
2
30 min, blood gases revealed:
pH 7.42
PaCO 2 36 mm Hg
PaO 2 255 mm Hg
-
The PaO 2 (255 mm Hg) HCO 22.8 mEq/L
should not be used to guide 3
oxygen therapy because dis- HbCO 19.2 g %
solved oxygen contributes a Hb 14.4 g %
very small fraction of arterial
oxygen content. CaO 2 14.7 vol %
SaO 2 94%
Mode CPAP
The measured CaO 2 PEEP 6 cm H O
showed improvement (from 2
12.7 to 14.7 vol %) after Pressure Support 15 cm H O
2
initiation of CPAP, PS, and f (spontaneous) 16/min
100% O 2 .
V (spontaneous) 550 mL
T
F O 2 100%
I
The patient was maintained on his present settings because he had a normal acid-
base balance and was breathing spontaneously. A high F O was maintained to re-
2
I
duce the half-life of HbCO. The half-life of HbCO is as follows:
F O 100% at 3 atmospheric pressure 15 to 23 min
I
2
F O of 100% and one atmospheric pressure 80 to 90 min
2
I
F O of 21% (air) and one atmospheric pressure 280 to 320 min
I
2
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