Page 680 - Clinical Application of Mechanical Ventilation

646 Chapter 19

Over the next 24 hours, her condition quickly deteriorated, requiring 100% F O
I
2
and increasing levels of PEEP to maintain adequate oxygenation.
Patient Monitoring

The increasing pressure required to ventilate her lungs began to compromise her
Pressure Control-Inverse cardiac output and, as such, limit perfusion to her tissues. As a result, she was
Ratio Ventilation (PC-IRV) uses
a predetermined inspiratory deeply sedated and changed to pressure-controlled inverse ratio ventilation (PC-
pressure to minimize the oc-
2
currence of pressure-induced IRV) mode at a frequency of 12/min and an inspiratory pressure of 30 cm H O.
lung injury. Use of inverse I:E Her inspiratory time (T ) was adjusted accordingly to obtain an I:E ratio of 3:1.
ratio is intended to increase I
inspiratory time and lung Her PEEP and F O requirements were 8 cm H O and 100%, respectively. These
I
2
2
expansion, and to improve settings provided hyperexpansion of the chest in order to stabilize the thorax and
oxygenation.
limit movement of the rib fractures. She was monitored by an end-tidal CO moni-
2
tor. Frequent blood gases were done to evaluate her ventilatory and oxygenation
status. Blood gases drawn at this time revealed the following:
PC-IRV increases the pH 7.36
mean airway pressure, central PaCO 42 mm Hg
venous pressure, and pulmo- 2
nary artery pressure. PaO 2 62 mm Hg
SaO 2 90%
-
HCO 22.9 mEq/L
3
Hb 11.2 g %
Mode PC-IRV
T I 1.0 sec
I:E ratio 3:1
f 12/min
P INSP 30 cm H O
2
F O 2 100%
I
PEEP 8 cm H O
2
The patient appeared to tolerate these changes well. However, within 1 hour her
PC-IRV can cause hemo- hemodynamic values (including cardiac output) were reduced as a result of pressure
dynamic instability.
ventilation. The T was decreased to 0.82 sec (2:1 ratio) and frequency was increased
I
to 24/min. The PEEP was increased to 15 cm H O. Arterial and mixed venous
2
blood gases revealed the following:

Arterial
pH 7.38
PaCO 2 38 mm Hg
PaO 2 90 mm Hg
SaO 2 95%
-
HCO 21.8 mEq/L
3
B.E. 22.4 mEq/L
Hb 11.1 g %
CaO 2 14.9 vol %

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