Acute Pain Management
(1)
Introduction
Because most patients
in acute pain can be adequately treated with narcotics, the occurrence
of inadequate pain relief usually relates to inappropriate
administration. Several factors contribute to this problem.
(2)
Administration
considerations
Often dosage duration
and strength are miscalculated. Clinicians also tend to unduly
emphasize the risks of narcotic therapy; respiratory depression
(discussed later) and addiction. Addiction represents a syndrome of
psychological dependence on a drug and aberrant drug related
behaviors, leading to an overwhelming involvement with the drug. In
contrast, physical dependence is a pharmacological property of
narcotics characterized by the development of an abstinence syndrome
upon abrupt discontinuation of the narcotic. This is not addiction,
and is not itself a substantial risk in clinical practice, because any
adverse effects can be prevented by tapering the drug before
discontinuation. Surveys of postoperative or burn patients indicate
that less than 0.5 percent of patients with no prior history of
substance abuse will develop problems after therapeutic use.
Therefore, the risk of addiction should not be used to justify limited
administration of the narcotic in the treatment of acute pain.
(3)
Patient variability
The minimum effective
analgesic concentration (MEAC) is the lowest blood concentration of
narcotic agonist consistent with the patient's report of complete
analgesia. The MEAC varies at least five-fold among patients. The
physician relies upon the patient's report on the quality of the
pain. Pain is always subjective.
(4)
Treatment options
The mainstay of pain
management is as needed (PRN) dosing. However, there are two reasons
why PRN dosing regimens for acute pain may fail. First, patients
usually expect pain relief
to be delivered immediately upon request. PRN dosing can
frequently contribute to a failure in this process. This occurs
because either the patient waits too long to request more pain
medication or, the staff cannot immediately administer the drug.
Second, blood concentrations fluctuate between 4 hour dosing intervals
(e.g., meperidine 50-75 mg IM q 4 hours PRN pain) such that the MEAC
is maintained only 35 percent of the time, or patients are in pain 65
percent of the time. Drugs used in the treatment of acute pain must
be viewed as agents that need to be titrated on a frequent basis
rather than being administered on a set dosing regimen determined by
the average patient.
(5) Stepcare Approach
Like the approach to the treatment of hypertension, acute pain
management uses a stepcare system of drug administration.
-
Step 1 - In patients
tolerating oral (PO) medications, nonsteroidal anti-inflammatory
drugs (NSAIDs) are the first line of therapy.
-
Step 2 - In patients not
controlled by NSAIDs or in whom they are contraindicated, add or
initiate a weak narcotic analgesic.
-
Step 3 - In patients not
controlled by step 1 or 2, reassess the cause of pain and then
replace the weak narcotic with a potent narcotic.
-
Step 4 - If the patient is
still not controlled or is not a candidate for oral treatment,
initiate IM or IV therapy.
Remember
intramuscular (IM) narcotic therapy results in large swings in
concentrations, is uncomfortable for the patient, and provides
analgesia for less than 50 percent of the every 4-hour dosing
regimen. However in some cases, IM narcotic therapy may be the best
available option (e.g. for a patient being transported without direct
physician supervision). For intravenous therapy, initiate treatment
with small aliquots of narcotic (e. g. morphine sulfate 2 to 4 mg
every 5-10 minutes). Adjust the dose depending on the patient’s age
and physical condition. After 2 to 3 hours, an average hourly
requirement can be determined.
(5)
Complications
It is imperative to
anticipate the adverse effects of narcotic use. Constipation,
sedation, nausea, and vomiting are expected adverse effects.
Providing stool softeners, careful monitoring, and antiemetics
prophylactically will prevent many of these problems.
(6)
Respiratory depression
Respiratory
depression is probably the best example of a serious adverse
pharmacological effect that is only rarely encountered clinically but
generates concern sufficient to cause undertreatment. The occurrence
of respiratory depression is extremely uncommon in patients who
undergo gradually escalating doses. Narcotic induced respiratory
depression, if not caused by a massive overdose, is always heralded by
the gradual onset of obtundation and slowed respiratory rate: signs
that signal an impending problem that needs to be managed
appropriately. Monitoring drug effects by assessing the level of
consciousness and respiratory rate can greatly diminish the risk of
serious respiratory depression.
Revised by
CAPT C.G. Bush, MC, USN, Anesthesia Department, Naval Hospital,
Groton, CT. (1999).
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Preface
· Administrative Section
· Clinical Section
The
General Medical Officer Manual , NAVMEDPUB 5134, January 1, 2000
Bureau
of Medicine and Surgery, Department of the Navy, 2300 E Street NW, Washington, D.C.,
20372-5300
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