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![Page 1: Chapter 15 PAIN MANAGEMENT Eileen Mann. Introduction This presentation focuses on the healthcare of patients experiencing pain. It adds to the knowledge.](https://reader035.fdocuments.us/reader035/viewer/2022062318/5519bbb15503465b578b49c1/html5/thumbnails/1.jpg)
Chapter 15 PAIN MANAGEMENT
Eileen Mann
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Introduction
This presentation focuses on the healthcare of patients experiencing pain. It adds to the knowledge you will already have gained by reading the book chapter.
Part 1 – Epidural AnalgesiaPart 2 – Postoperative Nausea and
VomitingPart 3 – The Multidimensional Nature of
PainPart 4 - Entonox
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PART 1: Epidural Analgesia
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Epidural Analgesia
Involves the infusion of a local anaesthetic and commonly an opioid into the epidural space surrounding the spinal cord.
The epidural space extends from the foramen magnum to the sacral canal.
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Why Use Epidurals?
• High quality analgesia• Reduced complications/bedstay• Needs much less opioid, resulting in
reduced side effects such as PONV, delayed nutrition, sedation
• Reduced respiratory infections• Increases mobility leading to less
muscle wasting and deep vein thrombosis
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Locating the Epidural Space
Spinal
cordSpinal column
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Spinal Nerves
Cervical - 8 pairs interconnect to form the cervical plexus and the brachial plexus. These innervate the back of the head, neck, shoulders, arms, hands and diaphragm
Thoracic - directly connected to the muscles between the ribs, deep back muscles, abdomen and thorax
Lumbar - supplies the muscles of the lower limbs and trunk, external genitalia, groin and lower limbs
Sacral - forms the sacral and coccygeal plexus, innervating the thighs, buttocks, legs, feet and the anal/genital area
Coccyx - one pair of nerves supplies the skin in the region of the coccyx
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Who may benefit from an epidural?
• Patients recently undergone abdominal incisions
• Serious pelvic & leg fractures
• Major pelvic and leg surgery
• Particularly useful following chest trauma
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Epidural is performed with the patient sitting or lying down with their back
curved outwards
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Contraindications
• Patient refusal• Coagulopathy• Local infection• Inadequate
facilities, equipment, training, staffing levels
• Anatomical abnormality
•Hypovolaemia•Sepsis/fever•Back problems•Neurological condition
•Allergy
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Caudal Analgesia
This involves placing local anaesthetic into a continuation of the epidural space that is located at the lower end of the spine.
It produces a block of the sacral and lumbar nerve roots which is ideal for perineal surgery.
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Local Anaesthetics
• Blocks the initiation and spread of action potentials within the nerves
• Blocks conduction in small diameter nerve fibres (A delta & C fibres) more readily than large fibres (A beta)
• Therefore pain sensation is blocked more easily than other sensory modalities (touch etc.)
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Opioids
• Thought to bind to opioid receptors in the substansia gelatinosa of the spinal cord interfering with the pain impulse
• Provides analgesia which lasts longer than systemic opioids
• Does not cause motor or sensory blockade, or hypotension
• Fentanyl 50 - 200 mcg will last around 3 - 6 hours
• Diamorphine 0.5 - 5 mg will last 6 - 12 hours
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Opioid Side Effects
• Effects receptors in the medullary respiratory centre leading to potential respiratory depression
• Sedation
• Itching
• Nausea
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Local Anaesthetic Side Effects
Local anaesthetics block conduction in all types of nerves:
• Sympathetic block - hypotension, urinary retention
• Sensory block - pressure sores
• Motor block - weakness, immobility, falls.
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Complications of Combined Local Anaesthetic/Opioid Epidurals
Early: • Hypotension• High sensory and
motor block • Respiratory
depression• Sedation• Cardiovascular
complications• Head/neck/backache• Anaphylaxis
Late:• Haematoma• Epidural
abscess• Infection and
sepsis• Unresolved
motor and sensory loss
• Itching• Leaking
epidural
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The Ideal Outcome
A sensory pain block with no motorblock and minimal side effects. An
alertpatient capable of early
mobilisation and able to participate inactive physiotherapy.
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Monitoring
• Consciousness level
• Colour
• Heart rate
• Blood Pressure
• Respirations
• Oxygen saturation
• Temperature
• Wound
• Urine output
• Motor/sensory levels
• PAIN
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PART 2: Postoperative Nausea and Vomiting (PONV)
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Why Treat Nausea and Vomiting?
• Humanitarian reasons• Increase in autonomic activity• Increase in closed compartment
pressure• Delayed hydration and nutrition• Delayed discharge from hospital• Delayed return to work and normal
functioning
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P.O.N.V.
A vastly underrated problem.
Many patients fear nausea and vomiting more than postoperative pain.
30% elect to forgo opioids and tolerate pain if this stops the nausea.
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Patients at Risk from PONV
• History of PONV and/or motion sickness
• Females > males (pre menopause)
• Young > old
• Type of procedure performed
• Use of opioids
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Chemical Receptors in the Vomiting Centre in the Brain
Acetylcholine: • cyclizine, hyoscine
Dopamine antagonist: • droperidol, metoclopramide,
phenothiazines
5 Hydroxytryptamine (serotonin):• ondansetron
Histamine
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Antiemetics
All give 30-45% reduction of symptoms at best
May reduce vomiting more than nauseaPharmacodynamics/kinetics poorly
understood for older drugsMultimodal antiemetic therapy?Cyclizine, prochlorperazine and
ondansetron all have more or less equal efficacy.
Metoclopramide has no antiemetic action in the postoperative setting.
The role of steroids?
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Antiemetics
Ondansetron available as i.v.+ melts• Cyclizine i.v.i ( side effect
problems)• Prochlorperazine P.O
Buccastem (i.m., p.r.)
Best evidence :• Ondansetron 8mg i.v. PLUSPLUS• Dexamethasone 8mg i.v.
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Summary
• Carry out a risk assessment• Prophylaxis• Avoid emetogenic drugs if possible• Combination therapies • Complementary therapies• Educate patients and staff
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PART 3: The Multidimensional Nature of Pain
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Definition of Pain
“An unpleasant sensory and emotional experience associated with actual or
potential tissue damage, or described in terms of such damage”
IASP 1986
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‘Pain of recent onset and probably limited duration. It usually has an identifiable temporal and causal
relationship to injury and disease’.IASP 1986
Acute pain will always respond to analgesia
Definition of Acute Pain
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‘Pain lasting for long periods of time. It usually persists beyond the
time of healing of an injury and frequently there may not be any
clearly identifiable cause’.
IASP 1986
Chronic pain may or may not be opioid responsive and other
analgesic regimes may also be ineffective
Definition of Chronic Pain
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The Acute/Chronic Debate
Q. Where does acute pain end and chronic pain begin? Do changes happen much earlier than previously thought?
Q. What is the biological mechanism that is driving pain?
Q, What are the impact of psychosocial factors?
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Acute AND Chronic Pain
• Acute – nociceptive (biologically active)• Chronic – nociceptive/neuropathic,
mixed• Acute on Chronic episodic/background• Visceral• Idiopathic
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Acute TO Chronic Pain
Pain is usually event related and starts as an acute episode with a high level of biological activity. The pain is initially reversible.
Changes tend to become fixed depending upon: the nature and duration of the original cause of pain, age of the patient, psychosocial influences such as pain memory, culture, pain affect and possibly genetic susceptibility.
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Types of Pain Syndromes (IASP 1986)
• Chronic pain
• Cancer related pain
• Somatic pain (superficial & deep)
• Visceral pain
• Neuropathic pain
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Theories of Pain
• Specificity theory • Pattern theory
• Neuromatrix
• Gate Control Theory
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The Gate Control Theory
• Modulating ‘gating’ mechanism
• Large diameter fibres (touch) ‘closed’ the gate
• Small diameter fibres (nociceptors) ‘opened’ the gate
• Affective/cognitive descending ‘modulation’
• Pain is multidimensional
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Nociceptors
Two types of afferent fibres:
A DELTA: Mylenated, fast (>30m/s) “fast” painBright, sharpSomatic
C FIBRES: Unmyelenated, slow (.5-2 m/s)
“slow” painDull diffuse, continuous, deep
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Cross Section of the Spinal Cord
A Beta
A Delta
C FibresSubstantia Gelatinosa
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“GATING” MECHANISMS
Located within the dorsal horn of the spinal cord, but also found within the brain stem, hypothalamus and thalamus
Somatosensory cortex
ThalamusHypothalamus
Brainstem
Substantia gelatinosa
Sensory input from the periphery
Ascending mechanism
Descending mechanism
Autonomic response
Limbic system
1
2
3
4
5
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Physiology (Sensory)
1. Nociceptors A-delta, B-delta, C fibres2. Chemicals – histamine, bradykinin3. Neurochemical mediators 4. Ascending transmission5. Descending transmission6. Pain systems dynamic and “plastic” 7. Pain perception can be modulated by
both pharmacological and non pharmacological strategies at all levels of the nervous system.
8. Changes may become fixed - remapping
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Primary Hyperalgesia
• Reduction in the pain threshold in the area of damage. e.g. skin burn, pharyngitis, sprained ankle
• Locally released chemical inflammatory mediators: potassium, histamine, bradykinin, leukotrienes, serotonin, histamine, substance P, arachadonic acid metabolites (prostaglandins etc)
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Secondary Hyperalgesia
• Non-nociceptors acquire capacity to evoke pain
• Central pain pathways adjust and change – pain memory?
• Brief stimulation of nociceptors can cause major changes in the receptive fields in the spinal cord.
• Repetitive peripheral stimulation causes response to progressively increase.
• Possibly due to loss of central inhibition.
• Acute gene expression altering receptors.
• Remapping at cord and brain level.
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“Pain Windup”
Pain continuing or worsening when the cause is stable or
improving.
FEATURES: • Reduced threshold• Augmented response• Ongoing activity• Pain adjacent to but beyond the
limits of tissue injury.
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Pain Management
ACUTE PAIN
Relatively easy to treat but needs effective early therapy to reduce the risk of wind up/cortical remapping. A narrow therapeutic window. **
**At one year following hernia surgery 29% of patients reported pain in the area of the hernia, 11% reported that it impaired their work or leisure activity but only 4.5% had sought medical advice (Bay Nielsen et al 2001)
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CHRONIC PAIN
Once established often relatively difficult to treat.
Can be resistant to ordinary analgesia. Psychosocial interventions needed, central changes, autoimmune components.
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Recent Developments
• Better understanding of the mechanisms
• Improved use of assessment tools • Advances in imaging – CAT, PET and
fMRI• Evidence based health care –
improved guidelines and algorithms• New drugs for pain management • New modes of delivery & more
appropriate use• The role of non pharmacological
therapy - cognitive and behavioural strategies
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Summary
• Pain is multidimensional
• The assessment and management of pain should reflect the sensory, affective and cognitive components
• Sociocultural components are important
• Future developments are likely to focus on genetic variability
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PART 4: Entonox
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Identification
Presented in cylinders that are painted blue with a white and blue shoulder.
The gas is pressurised and is self administered by the patient via a pressure regulator and demand valve.
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Mechanism of Action
True mechanism of analgesia is not known.
The effects of Entonox take place within the pain centres of the brain and spinal cord.
The gas forms an essential ingredient in general anaesthesia.
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Pharmacokinetics
Entonox is an analgesic agent that is composed of 50% nitrous oxide and 50% oxygen.
It offers rapid onset of potent analgesia with speedy reversal of effects.
It is inhaled, absorbed through the lungs into the blood within which it is carried to the brain where analgesia occurs.
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The effects of Entonox are felt within three to four breaths and maximised after 2 minutes.
The effects rapidly disappear once Entonox inhalation is discontinued.
Residual effects are hard to display after 30-40 minutes. Despite this patients are usually advised not to drive for 12 hours.
Pharmacodynamics
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Metabolism and Excretion
Entonox is rapidly excreted from the body.
It is excreted, largely unchanged, by the lungs into the surrounding air.
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Toxicity
Prolonged use of Entonox in an enclosed space may subject staff to undue exposure.
Prolonged use (exceeding 6-8 hours) may have an adverse effect on vitamin synthesis.
Use over 6 hours may also interfere with folate metabolism and DNA synthesis which can impair bone marrow function.
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Use of Entonox
Ideal for situations where pain is of short duration.
Can be used in combination with other analgesics such as paracetamol, NSAIDs and opioids.
A mouthpiece/face-mask and bacterial filter is required for individual patient use.
The gas is safe for any age group as long as they are able to comprehend and physically operate the system.
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• Changing dressings, packs and removing drains
• Suturing and removing sutures• Redressing burns• Invasive procedures : catheterisation,
cannulation, sigmoidoscopy• Changing and removing clothing• Applying traction; removing skeletal
pins• Physiotherapy• Renal colic; constipation• Lifting and moving patient
Clinical Uses of Entonox
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Precautions
Patient refusal or known allergy
Entonox will cause an enclosed air pocket in the body to expand rapidly in volume as the gas mixture is absorbed from the blood into the space. Therefore Entonox is contra-indicated in all cases where there is air trapped within a body space.
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Contraindications • Artificial, spontaneous or traumatic
pneumothorax• Intestinal obstruction• Air embolism, following a recent
underwater dive/ decompression sickness• Myringoplasty• Intoxication• Severe bullous emphysema• Head injuries with impaired consciousness.• Maxillofacial injuries with a risk of inhaling
blood• Patient non-compliance
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Drug Interactions
There are no major incompatibilities with other drugs and Entonox, when used with other analgesics, can form
part of an effective multimodal approach to pain control.
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Side Effects
• May cause drowsiness
• Allergic and sensitivity reactions are rare
• Minor effects on the heart and cardiovascular system
• Minimal effects on respiration
• Can cause nausea