Page 480 - Clinical Application of Mechanical Ventilation

446 Chapter 13

Although opioids may produce a dose-dependent clinical spectrum ranging from
pain relief to sedation, deep coma, and anesthesia, low-dose opiates are often com-
bined with low-dose sedatives (benzodiazepines) to minimize the adverse effects of
these two agents.

Gastrointestinal Effects. The gastrointestinal effects of opioids include delayed
gastric emptying, constipation, and nausea (Levine, 1994). Since tolerance to
constipation does not occur, or occurs very slowly during opiate administra-
tion, cathartic agents should be given on a regular basis to activate bowel
cathartic agents: Active movements.
purgatives used to produce bowel
movements. Nausea and vomiting during opiate administration may be due to three different
mechanisms. First, opiates may reduce gastric motility that results in nausea after
eating. Second, opioids seem to cause nausea that is due to sensitization of the ves-
Delayed gastric empty- tibular apparatus. This type of nausea is brought on by changes in position or head
ing, constipation, and nausea
are the primary adverse movement. Third, these drugs may directly stimulate the medullary chemoreceptor
effects of narcotic analgesics trigger zone. Nausea from this mechanism is usually present continuously (Jacox
on the GI system.
et al., 1994).
Other adverse effects related to opioid use include miosis (contraction of pupils),
altered levels of stress hormones, and uncommon allergic reactions.

Clinical Considerations. Opioid tolerance, physical dependence, and psychological
de pendence are important concepts to understand when considering analgesic ther-
apy. Misuse of these terms has led to ineffective practices in prescribing, administer-
ing, and treatment of patients in pain.

Tolerance. Tolerance is defined as the need to increase dosage requirements to maintain
effective pain relief. In addition, tolerance may occur to some adverse opioid effects
such as respiratory depression, miosis, sedation, and nausea (Foley, 1993).

Physical Dependence. Physical dependence is defined as the precipitation of a with-
drawal syndrome upon abrupt termination of the drug or after administration of
a narcotic antagonist (naloxone). Clinically, the withdrawal symptoms include ir-
ritability, joint pain, chills and hot flashes, anxiety, nausea, vomiting, lacrimation,
rhinorrhea, diaphoresis, abdominal cramps, and diarrhea. Withdrawal symptoms
may be avoided in physically dependent patients by gradual dosage reduction of the
opiate (Hammack et al., 1994).

Psychological Dependence. Psychological dependence is an addictive behavior char-
Since ventilator patients acterized by drug seeking, preoccupation with obtaining and using the drug, and
cannot communicate effec-
tively, these clinical signs may drug use for other than analgesic purposes (euphoria).
be used to reflect inadequate
pain control. Assessment of Adequate Pain Control. Pain assessment is important in ensuring ad-
equate pain relief and enhancing patient recovery. Cooperative, awake, and alert
patients may be assessed with pain intensity and pain distress scales. Unfortunately,
ventilator patients are frequently unable to participate in their pain management
plan. In this case, clinical signs such as tachycardia, blood pressure changes, dilated
pupils, diaphoresis, grimacing, restlessness, and guarding may be signs that indicate
inadequate analgesia (Table 13-19).

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