Page 538 - Clinical Application of Mechanical Ventilation

504 Chapter 15

Advanced cardiac life support is the primary method to manage cardiac arrest. Ther-
apeutic hypothermia (32 to 34ºC) has been used to lower the oxygen utilization and
to improve the neurologic outcomes in cardiac arrest victims (Madl et al., 2004).
Treatments of severe hypotension should be aimed at the underlying causes.
For cardiac arrest, restoration of the heart function is the primary goal. Use
of ACLS, oxygen, antiarrhythmics, beta agonists, fluid, and vasopressors are
essential procedures to manage severe hypotension due to cardiac arrest.

Decrease in CPP Due to Shock

Hypotension as a result of shock is usually due to lack of circulating volume. This
The CPP may become deficiency may be due to severe blood loss (absolute hypovolemia) or vasodilatation
inadequate when the MAP is
too low. (relative hypovolemia, as in septic shock). As in cardiac arrest, hypotension causes
abnormally low systolic, diastolic, and mean arterial pressures (MAP). Since CPP
is the difference between the MAP and ICP, a drop in MAP will lower the CPP
(TCPP 5 TMAP 2 ICP).
Severe hypotension
can impair neurological Based on the relationship of MAP and ICP, a higher CPP may be maintained
functions. A drop in MAP will by raising the MAP or by lowering the ICP. In clinical practice, ICP control is
lower the CPP (TCPP 5
TMAP 2 ICP). typically not necessary because ICP tends to stay below its clinical threshold (i.e.,
,20 mm Hg) under normal conditions. In conditions of severe hypotension,
CPP may become suboptimal. The CPP can be maintained above the critical
threshold by raising the MAP (Changaris et al., 1987; Rosner & Daughton,
1990).
ICP control is typically
not necessary because ICP In the absence of hemorrhage, the MAP should be managed initially by maintain-
tends to stay below its clinical
threshold (i.e., , 20 mm Hg). ing an adequate fluid balance. It may then be followed by using a vasopressor such
as norepinephrine or dopamine. Systemic hypotension (SBP ,90 mm Hg) should
be avoided and controlled as soon as possible because early hypotension is associ-
ated with increased morbidity and mortality following severe brain injury (Chesnut
The CPP can be et al., 1993; Marmarou et al., 1991).
maintained above the critical
threshold by raising the MAP.
Decrease in CPP Due to Brain Injury

Traumatic brain injury raises the ICP due to swelling of the brain within a confined
An increase in ICP (e.g., fixed space (skull). The increase in ICP reduces the CPP and blood supply to the
traumatic brain injury) can
reduce the CPP and blood brain (TCPP 5 MAP 2 cICP). The end result is energy depletion and develop-
supply to the brain (TCPP 5 ment of HIE.
MAP 2 cICP).

Evaluation and Treatment of HIE

The severity of anatomic and physiologic changes in the brain and spinal cord may
be evaluated by examining the structure and function of the brain. The tests may
include CT or MRI scan, EEG, ultrasound, and evoked potential test (analysis of
brain wave). These tests may also be used to evaluate the effectiveness of treatments
for HIE (Kohnle, 2011).

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