Page 695 - Clinical Application of Mechanical Ventilation

Case Studies 661

On examination, the patient was afibrile and had these vital signs: BP 110/
70 mm Hg, pulse 78/min, respirations 14/min (up to 40/min on occasion). His
facial muscles showed symmetry bilaterally. He had trouble sitting up due to exces-
sive pain in his lower extremities, especially on the left. Lung sounds revealed basi-
lar crackles on the right with decreased aeration on the left. A chest radiograph
showed left lower lobe atelectasis. The cranial nerves 2 to 12 appeared intact but
motor strength showed marked weakness. The patient was able to lift his right heel
2 to 3 inches with great difficulty but was unable to lift his left heel at all. His deep
tendon reflexes were completely absent.
Laboratory results revealed WBCs of 14,000 with 84% segs. The electrolytes
Restrictive lung disease and urinalysis were within normal limits. His FEV and FVC were 1.4 L and 1.7 L,
1
typically shows reduction in respectively. The FEV /FVC ratio was 82%. A CT scan of the brain revealed a
FEV 1 and FVC, resulting in a 1
normal FEV 1 /FVC%. completely normal study. A chest radiograph at the time showed bilateral consoli-
dation secondary to muscle weakness and left lower lobe atelectasis.

Indications

The patient had a 5-day history of progressive muscular weakness. For this reason, basic
spirometry was done Q4 hours through the night. His predicted forced vital capacity
(FVC) was 3.38 L and his initial vital capacity was 1.7 L (50% of the predicted value),
Mechanical ventilation is
indicated when the vital ca- which he maintained through the early evening. His predicted FEV was 3.12 L and
1
pacity falls below 1,000 mL or his initial measurement revealed 1.4 L (48% of predicted) for an 82% FEV /FVC ratio.
twice the patient’s predicted 1
tidal volume. By 3:30 a.m., the patient’s vital capacity had dropped to 1.2 L (35% of predicted) and
an arterial blood gas (ABG) at that time, on room air, revealed the following:
pH 7.37
PaCO 2 45 mm Hg
PaO 2 46 mm Hg
SaO 2 76%
-
HCO 24.9 mEq/L
3
f 24/min
F O 2 21%
I
Oxygen therapy was initiated at 2 L/min per nasal cannula. He rested well until
approximately 8:20 the next morning. The vital capacity at that time was slightly
over 1 L (30% of predicted) and the ABGs revealed:
pH 7.39
PaCO 2 43 mm Hg
PaO 2 52 mm Hg
SaO 2 86%
-
HCO 25.2 mEq/L
3
f 22/min
Every attempt was made to forestall clinical deterioration. The trends of bed-
side spirometry and serial blood gases showed that the patient was progressing

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