Page 664 - Clinical Application of Mechanical Ventilation

630 Chapter 19

118/min, BP of 116/84 mm Hg, and pulmonary capillary wedge pressure (PCWP) of
11 mm Hg.

Patient Management

Carbon dioxide in the blood is a very potent vasodilator. Increased blood flow serves
Mild hyperventilation to promote swelling and edema following an acute injury to the brain. Blood flow to
is used to maintain a PaCO 2
between 34 and 35 mm Hg. the area, and the subsequent swelling, may be reduced during the first 24 hours by
maintaining the PaCO between 34 and 35 mm Hg (can be as low as 26 mm Hg,
2
see figure 15-3) while monitoring the ensuing edema with an ICP monitor.
Consequently, short-term, mild hyperventilation is used as a means to reduce
Cerebrospinal fluid may the PaCO level (hypocarbia) in the blood as well as to regulate the pressure result-
also be drained to minimize 2
the rise of intracranial ing from swelling of the brain after the injury. Following the insertion of the ICP
pressure from subsequent monitor, the level of hyperventilation can be assessed and titrated to maintain an
swelling of the brain.
ICP preferentially below 10 mm Hg to minimize further injury. Judicious use of
short-term hyperventilation should be monitored closely.
The PEEP level is usually maintained at or below 5 cm H O because the lungs
2
PEEP is contraindicated are generally not affected by head injury, and that additional pressure is transmit-
in head injuries unless severe
hypoxemia is present. ted to the head by the use of positive pressure to ventilate the patient. This level is
desirable unless the patient’s oxygen requirements exceed 60% F O , when higher
I
2
levels of PEEP may be indicated.
The ventilator settings were adjusted during the next several hours and the patient was
weaned to a frequency of 12/min resulting in a pH of 7.46 and PaCO of 34 mm Hg.
2
Key Medications

The patient remained sedated with Phenytoin®, Phenobarbital®, Diazepam®, and
Neurologic assessment Midazolam® during the acute phase of her hospitalization (i.e., 24 to 48 hours fol-
should be done after recovery
from drug-induced sedation. lowing the accident) to minimize the risk of further injury. After two days she was
weaned to awaken for neurologic assessment.
Since the lungs were relatively unaffected, she was not given bronchodilator ther-
apy. She was monitored for potential complications associated with artificial airway
and mechanical ventilation. She was suctioned as necessary and was given periodic
oral care to minimize the occurrence of infection.

Weaning

The patient was allowed to awaken fully and was changed to SIMV mode at 10/min
with a pressure support level at 15 cm H O in an attempt to begin the weaning pro-
2
cess. Blood gas analysis revealed the following:

pH 7.39
PaCO 2 40 mm Hg
PaO 2 83 mm Hg
-
HCO 23.3 mEq/L
3
Hb 13.8 g %

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