Module 1: Analgesia

Sections:

1. Guiding Principles
2. Pain Assessment
3. Medications
4. Weaning Analgesics
5. Preprinted Orders
6. Link to Drug Monographs
7. Go to Next Module
8. Return to Main Menu
9. Take the Test

1. Guiding Principles

• It is assumed that all patients in critical care will experience some pain or discomfort, and that pain control is frequently inadequate.
• Pain may be related to monitoring devices, routine nursing care, immobilization, trauma, surgery, procedures and pre-existing disease.
• Pain that is not adequately controlled can lead to agitation, interfere with sleep and contribute to the stress response, causing tachycardia, increased oxygen consumption, immunosuppression, hypercoagulability and persistent catabolism.
• Unresolved pain can contribute to pulmonary dysfunction through muscle rigidity and guarding.
• The first intervention upon identification of pain should be to perform a pain assessment.
• Analgesics are the appropriate medication if pain is the cause of the discomfort.
• Non-pharmaceutical interventions should also be considered as they may reduce or relieve requirements.
• Examples of non-pharmaceutical interventions include: back rubs, repositioning, mouth care, music therapy, noise and lighting reduction, family visits and facilitation of rest and sleep.
• It is easier to prevent pain than to treat established pain.
• The ideal analgesic has a rapid onset of action, is easy to titrate, lacks accumulation and is inexpensive.
• Analgesic dosing often needs to be adjusted in the elderly and in patients with renal insufficiency.
• Patients often require larger doses of analgesia upon initiation of analgesia therapy until comfort is achieved.
• Post-operative patients should have a progressive decrease in analgesic requirements the further they are from their surgical day.
• Due to changing requirements, analgesic doses must be reassessed on a daily basis and reduced as pain decreases.

2. Pain Assessment

• The most reliable indicator of pain is the patient's reporting of pain.
• It is important to ask the patient about their pain and to evaluate the location, characteristics and aggravating or alleviating factors.
• Reasons for pain should be explored if pain is severe and unrelenting. For example, a hallmark of compartment syndrome is the presence of pain that is disproportionate to the type of injury and is caused by tissue ischemia or necrosis.
• Pain assessment has been divided into two methods:
  1. Assessment of the patient who is able to communicate
  2. Assessment of the patient who is unable to communicate.
• Perform a pain assessment and document at the start of each shift, q4h (between 0700 and 2200 hrs) and prn with each intermittent bolus or change in analgesia.

Critical Care Pain Assessment
A: Patient Unable to Communicate	B: Patient Able to Communicate
Assess for Autonomic Responses: changes in HR, RR, BP diaphoresis Assess for Non-Verbal Signs: grimacing frowning facial expressions Assess for Physical Signs: rigidity guarding resisting	Assess using PQRST mnemonic: P (provokes, precipitates) location of pain aggravating and alleviating factors Q (quality) dull, sharp, stabbing, pins and needles R (radiation, referral) area of radiation associated symptoms (nausea, vomiting, shortness of breath) S (severity) ask patient to rate their perception of the pain's severity on a scale from 1-10 have patient point to the score that represents their level of pain, using a visual analogue scale that depicts "no pain" as "0" and "worst possible pain" as "10". T (time) onset (e.g. at rest, with activity, during coughing) duration of pain constant versus intermittent

3. Medications

Drug Dosing and Effect

• Intravenous infusions of analgesics start to act immediately, however, they will not provide significant analgesia until the infusion reaches "steady state".
• The time to reach steady state is related to the duration of effect of the drug itself.
• The duration of effect is measured in time described as half-lives.
• A half-life is the time it takes for the drug effect to reduced by one half.
• It generally takes 3 half lives to approach steady state and 5 half-lives to achieve steady state.
• The longer the half-life of a drug, the longer it takes to reach steady state.
• At the initiation of an infusion and when the infusion rate is increased, loading doses must be administered in order to provide immediate analgesia.
• Loading doses are prn intermittent doses that are given repeatedly to achieve and maintain the desired analgesia until the infusion reaches steady state.

Drug Context or Distribution:

• A number of sedative and analgesic agents distribute throughout the body in a complex way.
• Biologically active drug is the component of the dose that is dissolved in the blood.
• Dissolved drug is able to cross the blood brain barrier, where it acts on receptors in the brain to produce analgesia or sedation.
• Most sedatives and analgesics accumulate predominantly in tissues, or become bound to proteins.
• This movement of drug into tissues or onto protein has the following consequences:
  • More drug may be needed when initiating therapy, until tissue and protein stores become saturated.
  • Prolonged drug effect may continue after the drug is stopped, as the drug redistributes and moves back into the bloodstream.

Drug Clearance:

• Drugs that are hepatically cleared must be given in higher doses when given enterally, as compared to intravenously.
• This is because drugs that have hepatic clearance are absorbed from the gut and are first transferred to the liver where a portion of the drug is metabolized before the remaining drug is released into the bloodstream.
• Intravenous administration bypasses the liver.
• Morphine and fentanyl are both metabolized by the liver.
• One of morphine's metabolites is active (the metabolite has a morphine-like effect, producing analgesia and sedation).
• This active morphine metabolite is renally excreted; prolonged analgesia and sedation will occur in renal failure.
• None of fentanyl's metabolites are active analgesics or sedatives; prolonged drug effect does not occur in renal failure.

Morphine:

• Morphine is the gold standard to which all other analgesics are compared, and is the narcotic of choice in critical care.
• It is used for moderate to severe acute pain and severe chronic pain.
• It is given on a prn basis to most patients, with doses adjusted according to the severity of the pain and the patient's response.
• An intravenous infusion of morphine with prn doses for breakthrough pain should be started for severe pain, or when frequent dosing is required.
• Dose reductions are needed in renal failure and in the elderly.
• It can produce histamine release, causing vasodilation and hypotension.

Fentanyl:

• Fentanyl is one hundred times more potent than morphine.
• It has a faster onset of action than morphine, and does not produce histamine release.
• It has a shorter duration of action than morphine when used on a prn basis or when infused for a short duration.
• It is the analgesic of choice in patients with renal dysfunction, morphine allergy or ongoing hemodynamic instability.
• An intravenous infusion of fentanyl with prn doses for breakthrough pain should be started for severe pain or when frequent dosing is required.

4. Weaning Analgesics

• There is evidence that daily interruption of continuous infusions of IV analgesics and sedatives result in a reduction in the number of days on a ventilator and ICU length of stay.
• When IV infusion rates are repeatedly increased versus administration of intermittent boluses as a means of responding to acute pain, the risk for excessive analgesia dosing exists.
• Post-op pain should decrease over time, therefore, maintenance doses may lessen as the patient's stay continues.
• To decrease the potential for excessive analgesic administration, daily weaning of analgesics should be automatically attempted, when the patient meets the following criteria:
  • pain control is adequate
  • patient is not receiving neuromuscular blocking agents
  • patient is hemodynamically stable
  • patient is stable on the ventilator

  Weaning Protocol:

For continuous morphine infusion:

• if morphine dose is <4 mg/hr, reduce infusion by 50% and reassess for further weaning in 6 hours
• if morphine >4 mg/hr, reduce infusion by 25% and reassess for further weaning in 6 hours
• discontinue infusion if rate <1 mg/hr
• if pain control becomes inadequate or patient becomes agitated during analgesia weaning, administer a morphine bolus and return to the previous infusion rate

For continuous fentanyl infusion:

• if fentanyl dose is <50 mcg/hr, reduce infusion by 50% and reassess for further weaning in 6 hours
• if fentanyl dose is >50 mcg/hr, reduce infusion by 25% and reassess for further weaning in 6 hours
• discontinue infusion if rate <10 mcg/hr
• if pain control becomes inadequate or patient becomes agitated during analgesia weaning, administer a fentanyl bolus and return to the previous infusion rate

5. Preprinted Orders (pdf format)

6. Links to Drug Monographs:

Fentanyl Monograph

Morphine Monograph

Naloxone Monograph

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Last Updated: May 23, 2005
Brenda Morgan, Clinical Educator, CCTC