Page 685 - Clinical Application of Mechanical Ventilation

Case Studies 651

and a nasal cannula at 6 L/min simply to maintain oxygen saturation of 86% to
92% without activity. Every effort was made to forestall clinical deterioration within
the treatment parameters that family members permitted. Practitioners were able to
convince the family to utilize free-standing CPAP at 12 cm H O and F O of 50% to
2
I
2
improve oxygenation, but the patient became fatigued to the extent that she was only
able to tolerate the procedure 20 minutes every 2–3 hours, if at all. At that time she
had a vital capacity of 0.9 L and MIP of 275 cm H O. This treatment continued for
2
CPAP requires adequate
spontaneous breathing. 2 days as she became refractory to oxygen therapy and was finally unable to maintain
Development of respiratory adequate oxygen saturation. Her chest radiograph revealed patterns of homogenous
muscle fatigue is the primary
concern for prolonged CPAP densities (i.e. uniform reticulogranular patterns or ground glass appearance) in both
usage in critically ill patients. lung fields. This sign is indicative of the development of acute respiratory distress
syndrome (ARDS).

Initial Settings

Every attempt was made to avoid ventilatory failure and prevent intubation, but the
patient’s condition continued to deteriorate, and she became progressively fatigued.
Her age and previous health were positive factors in postponing ventilatory failure,
but she eventually became overwhelmed by fatigue. She was moderately sedated,
intubated with a size 7.5 endotracheal tube, and placed on volume-controlled ven-
tilation on assist/control at a frequency of 25/min, V of 600 mL (approx. 11 mL/
T
Kg), F O of 100%, and PEEP of 8 cm H O. Arterial and mixed venous blood
I
2
2
gases on these settings revealed the following:
Arterial
pH 7.57
PaCO 2 33 mm Hg
PaO 2 58 mm Hg
SaO 2 88%
-
HCO 29.5 mEq/L
3
Hb 10.1 g %
Mixed Venous
pH 7.38
PvO 2 33 mm Hg
SvO 2 58%
C(a-v)O 2 4.6 vol %
Qs/QT 37%

The ventilator frequency Ventilator Settings
was decreased because of the Mode A/C
low PaCO 2 (33 mm Hg).
f 25/min
V T 600 mL
F O 2 100%
I
The PEEP was increased PEEP 8 cm H O
because of the low PaO 2 (58 mm 2
Hg) in spite of 100% F I O 2 . Her ventilator frequency was reduced to 14/min, and her PEEP was increased to
10 cm H O.
2

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