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Pharmacotherapy for Mechanical Ventilation 443

TABLE 13-15 Adverse Patient Outcomes Associated with Pain

Reaction Induced by Pain Adverse Outcomes

Tissue initiated stress hormone response Breakdown of body tissue
Increased blood clotting
Increased metabolic rate
Increased water retention
Decreased immune function
Activation of autonomic functions Increased blood pressure
Increased heart rate
Muscle splinting Decreased tidal volume
Decreased respiratory rate
Decreased minute ventilation
Immobility Formation of deep vein thrombosis and
pulmonary embolism
Diminished gastrointestinal function Delay of bowel and gastric function

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to assess because of their inability to speak. Hemodynamic and respiratory instability,
and immediate life-threatening concerns also overshadow the presence of pain. Subse-
quently, pain control for these patients is often inadequate (Wheeler, 1993).
Pain can cause anxiety, discomfort, and delirium in patients on mechanical ven-
tilation. Interference with sleep also compounds the level of anxiety, thus further
elevating the perception of pain. Pain is also associated with many adverse outcomes
in the intensive care unit (Table 13-15). Opioid analgesics are commonly used to
opioid analgesics: Drugs that
are used to control pain via the control pain to allow earlier patient mobilization and to decrease hospital stay.
central nervous system. Examples
are morphine, codeine, and Mechanism of Action. Opioid analgesics produce analgesia by binding to opioid re-
meperidine (Demerol, a synthetic
compound). ceptors in and outside the central nervous system. Several subtypes of opiate recep-
tors have been identified. The mu, kappa, and sigma receptors are known to have
important nociceptive (neural receptors for painful stimulus) properties in humans.
Binding and activating these receptors also help explain the adverse pharmacologic
profile of these drugs (Table 13-16) (Teeple, 1990).
Opiates may be further classified depending on whether they are agonists,
agonist-antagonists, or pure antagonists at these receptors (Table 13-17). Full ago-
nists produce a maximal response within cells to which they bind; agonist-antagonists
Full agonists produce a
maximal response within cells activate one type of opiate receptor while blocking another; and antagonists only
to which they bind. block opiate receptors (Teeple, 1990).
Table 13-17 contains only representative samples from each class. It is not a com-
plete listing of all opioids.
Agonist-antagonists Most agonist-antagonist drugs are agonists at the sigma receptor. As the dose of
activate one type of opiate these drugs is increased for deeper analgesia, the more likely they may cause signifi-
receptor while blocking
another. cant psychological effects such as delirium. This class of drugs is not routinely used
in ventilator patients and will not be discussed further.

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