Page 700 - Clinical Application of Mechanical Ventilation

666 Chapter 19

pH 7.48
PaCO 2 47 mm Hg
PaO 2 114 mm Hg
SaO 2 97%
-
HCO 34 mEq/L
3
Mode A/C
f 18/min
V T 670 mL
F O 2 40%
I
PEEP 10 cm H O
2
These parameters were maintained until the 24th ventilator day, when the patient
appeared to improve clinically and began to breathe significantly on his own. The
patient became increasingly uneasy about his breathlessness. As a result, the settings
were changed to SIMV mode, frequency of 18/min, tidal volume of 700 mL (ap-
prox. 14 mL/Kg), and F O of 40%. PEEP was reduced to 5 cm H O and pressure
I
2
2
support was initiated to augment his spontaneous volume. Blood gases taken after
these changes indicated marked improvement in oxygenation and acid-base balance:
pH 7.47
PaCO 2 38 mm Hg
PaO 2 117 mm Hg
SaO 2 94%
-
HCO 27 mEq/L
3
Mode SIMV
f 18/min
V T 700 mL
F O 2 40%
I
PEEP 5 cm H O
2
PS 15 cm H O
2
At this point, the F O was reduced to 35% and remained relatively stable for
2
I
the next 19 days. A bronchoscopy was performed on ventilator day 32 to clear an
obstructed left lower lobe bronchus. This was achieved without difficulty and, by
ventilator day 39, the frequency was decreased from 18 to 12/min. The following
day, the frequency was decreased to 10/min. His spontaneous frequency ranged
between 29 and 32/min.

Weaning

On ventilator day 40, the patient continued to show evidence of improved alveolar
The pressure support lev- ventilation. Brief T-piece (Briggs “T” adaptor) trials off the ventilator, sometimes
el is titrated and subsequently
adjusted until spontaneous as little as 10 to 15 minutes every 2 to 4 hours, were initiated to encourage the use
tidal volume 5 10 to 15 mL/ of respiratory muscles. Gradually, by the 54th ventilator day, he was able to toler-
kg or spontaneous frequency
,25/min. ate short periods off the ventilator, from 30 minutes to an hour twice a day, and
on CPAP with minimal pressure support (10 to 15 cm H O) the remainder of the
2

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