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What is pain?

An unpleasant sensory and emotional experience associated with actual or potential tissue damage


What are the general problems with pain

  1. It's often under-treated
  2. Uncontrolled pain produces detrimental SE that we don't want
  3. The treatment of pain carry risks and/or side effects
  4. Many patients and providers have misconceptions about the treatment of pain
    • fear of addiction
    • fear of side effects (ex: constipation)
  5. Pain increases the patient's stay in PACU, ICU, and the hospital in general


What is acute pain?

  • Pain caused by a noxious stimulus d/t injury, trauma, acute disease process, or abnormal function of muscle or viscera
  • almost always nociceptive pain
  • results in neuroendocrine response
    • ​stress response with HPA and SNS activation


Endocrine and CV response to pain


  1. Increased catecholamines
  2. Increased cortisol
  3. Increased aldosterone and ADH, renin, and angiotensin II
  4. Immune system suppression


  1. Increased HR, BP, SVR, CO, contractility
  2. Enhanced myocardial irritability
  3. Vasoconstriction, including coronary artery constriction
  4. Increased myocardial O2 consumption with decreased myocardial O2 supply (think ischemia)
  5. Increased plasma viscosity
  6. Increased water retention
  7. Vasoconstriction and fluid retention increase the workload of the heart


Pulmonary Effects of Pain

  • Decreased lung volumes (VC, TV,FRC)
  • Phrenic nerve dysfunction
  • Inadequate cough (don't want to agitate the pain)
  • Inadequate ventilation
    • (will decrease TV, VC, and FRC --> FRC may approach closing volume and cause atelectasis and VQ mismatch)
  • May have limited movement of respiratory muscles due to spasm of muscles
  • Decreased ability to clear airway secretions
  • Susceptible to pneumonias
  • Increased total body O2 consumption which increases respiratory workload Increased CO2 production


Heme Effects of Pain

  1. Hypercoagulability
    • Natural anticoagulants decrease
    • natural procoagulants increase
    • Inhibition of fibrinolysis 
    • Increased platelet reactivity/adhesiveness 
    • Increased plasma viscosity 
    • Increased risk of DVTs and vascular grafting failure, poor wound healing, MI risk
  2.  Immunosuppression→ Potentiates postoperative immunosuppression (poor wound healing)
    • Depressed lymphocyte response 
    • Decreased cell mediated immunity 
    • Alterations in balance of T-helper cells 
    • Increased interleukins and cytokines


GI/GU Effects of Pain


  1. Hypersecretion of gastric acid
  2. Slowed GI motility
  3. (risk of aspiration and paralytic ileus)


  1. Urinary retention


Neurendocrine Response to Pain

Basically reacting as if the body is in stress:

  1. Increased catecholamines
  2. Increased catabolic hormones
    • increased cortisol
    • increased glucagon → mobilize glucose stores
  3. Decreased anabolic hormones
    • Decreased insulin
  4. Increased ADH, Aldosterone, renin, and angiotensin II
    • Sodium and water retention
  5. Increased
    • Blood glucose
    • Free fatty acids
    • Ketone bodies
    • Lactate


What is chronic pain?

  • Pain that serves no purpose
  • Pain that persists beyond the usual coarse of an acute disease after a reasonable amount of time for healing to occur
  • Poorly controlled acute pain can transition to chronic pain
    • Intensity of acute pain is significant predictor of chronic pain


Chronic Pain may occur after these procedures

  1. Limb amputations (30-83%)
  2. Thoracotomy (22-67%)
  3. Sternotomy (28%)
  4. Breast surgery
  5. Gallbladder surgery


Chronic pain is associated with an imbalance in _____

Neuromodulation controls

  • Attenuated neuroendocrine response (unlike acute pain) →
  • Exhausted supplies of endorphins and serotonin →
  •  Predominance of C-fiber stimulation


Chronic pain is associated with ____ in the periphery

chronic inflammation

  1. Continuous release of inflammatory mediators in the periphery sensitizes functional nociceptors and activates dormant nociceptors
    • There is sensitization of nociceptors and hyper-excitability
  2. Functional changes occur in the dorsal horn of the spinal cord (neuroplasicity)
  3. Dormant nociceptors are activated
  4. Recruitment of additional nerve fibers and pathway tracts
  5. Pain is perceived as more painful
  6. Reflexes can create excessive muscle tension, with actual disruption of microcirculation


Cancer pain

Pain caused by:

  1. tumor invasion of the bone
  2. tumor compression of peripheral nerves
  3. Treatments of cancer (chemo and radiation)
    • mostly d/t tissue destruction


Physical and psych components of cancer pain


  • worse due to loss of sleep, appetite, nausea & vomiting


  • heightened anxiety
  • feelings of loss
  • low self-esteem
  • changes in life goals
  • disfigurement


What is allodynia?

Pain in response to a stimulus that shouldn't normally cause pain


Pain Preop Evaluation

  1. Evaluate pain
    • Pain history
    • Physical exam
    • Self report measurement scales
    • Medications for pain
    • Document
  2. Preparation
    • Adjustments and/or continuation of meds
  3. Develop plan


Benefits of adequate post-op pain control

  1. Reduction of the stress response
  2. Shorter times to extubation
  3. shorter ICU stay
  4. early discharge
  5. Improved respiratory function
  6. Earlier return of bowel function
  7. Earlier enteral nutritional intake
  8. Early mobilization
  9. decreased risk DVTs
  10. Reduction in:
    • sensitization
    • neuroplasticity
    • wind-up phenomenon and
    • transition to chronic pain
  11. Increased patient satisfaction


When does post-op pain control begin?


Goal is to prevent pain before it happens.


Who requires that we do a pain assessment of our patients?



Respiratory and routes of opioid administration

Incidence of respiratory depression does not vary across routes. You get depression despite whatever route you choose.


Preferred routes of opioid administration


Then sublingual or rectal (avoid first pass effect)


Opioids exert their effects via these receptors

Mu and Kappa


Is there an analgesic ceiling with opioids?


The dose is only usually limited by tolerance or SE.


Most common drugs for PCA use

Morphine and hydromorphone


NSAIDs work by inhibiting ____



By using NSAIDs with opioids, the pain response is attenuated in both these locations

The spinal cord (opioids) and in the periphery (NSAIDs)


Using NSAIDs can decrease opioid requirement by ___%




  1. Decreased hemostasis
    • Platelet dysfunction
    • Inhibition of thyromboxane A2
  2. Renal dysfunction
  3. GI hemorrhage
  4. Liver dysfunction
  5. Effects on bone healing/ osteogenesis


Ketamine as an adjuvant drug

Small doses to act as adjunct to LAs and opioids. Enhances the analgesic effect and reduces SE.


These drugs may be used as adjuvants

  1. Ketamine
  2. Tramadol (Ultram)
  3. Nalbuphine (Nubain)
  4. Methadone
  5. Acetaminophen