Post Operative pain Management

 

Post Operative Pain Management

Pain is defined as unpleasant sensory and emotional experience associated with potential tissue injury as given by International Association for Study of Pain (IASP).

Pain is experienced as central hypothalamoneuroendocrinal response or peripheral limbic/cortical response.

Taylor (2000) stated that prolonged severe pain by surgery will lead to

Increased metabolic rate

Increased lactic acid production

G.I ileus or paralysis

Increased protein metabolism

Decreased food intake

Delayed wound healing

Decreased removal of airway secretions

Self mutilation

Debilitating CNS functions

 

Depending on duration pain can be classified as

1.Acute

2.Chronic

 

The types of pain are

1. Somatic –Pain from skin, muscle or bone.
2. Viseral from thoracic and abdominal.
3. Neuropathic from nervous system.
    
   Veterinarians have to
   a)Recognise the pain
   b)Assess the pain
   c)Prevent the pain
   d)Treat the pain
    
   a)Recognise the pain by Clinical signs like
    
   1.Increased heart rate

            2.Increased blood pressure

            3.Increased peripheral vasoconstriction leading to pale mucous membranes

4.Sweating

5.Hyperventilation

6.Vocalisation

7.Change in the sleep pattern

8.Change in the temperament, anxiety and fear

9.Change in breathing pattern

10.Slow locomotion or lameness

11.Restlessness,trying to escape pain

12.Exagerated response to touch of surgical site.

 

b) Assessment of the degree of pain suffered by

 

1.Anthropomorphism- Prediction of severity of pain by surgery caused to tissues and anatomy of surgical injury. Extrapolation by human experience.

2. By the severity of the clinical signs and symptoms

 

            c) Prevent the pain by

            1. Preemptive analgesia- Analgesia should be given before animal comes out of

anaesthesia. Analgesia should be continued till pain is manageble or tolerable.    After major surgery,potent narcotic analgesic should be given for 48-72 hrs after that NSAIDs for maintenance.

General strategies for prevention or control of pain

Aim different points in pain transmission pathway.

1. Limit nociceptor stimulation:
    
   a)By gentle handling and minimise trauma
   b)Preoperative administration of NSAIDs like Ketoprofen/Carprofen, which will decrease cyclooxygenase for decrease production of prostaglandins, there by decreaseing the sensitivity of nociceptors.

                  II.        Interruption of peripheral neural transmission

                        a)By local anaesthetic infiltration

                        b)By nerve blocks

                        c)By I/V regional anaesthesia

                       

1. Inhibition of pain transmission at the spinal cord
   a)By systemic/epidural administration of oipiods or
   b)By alpha 2 adrenergic agonists or
   c)By local anaesthetics
     
2.   Modulation of brain pathways
   Systemic administration of opioids/alpha 2 agonists/NSAIDs

 

 

 

 

 

1. Balanced/ Multimodal analgesia
   Simultaneous use of number of strategies like
   a)Infiltration of surgical site + Systemic NSAIDs
   b)Epidural anaesthesia + NSAIDs
               
               

Treatment of pain is by selection and different techniques of administration of    analgesic drugs----Local/Regional/Systemic

1. Local Analgesia: Bupivacaine is four times more powerful analgesic compared to Lignocaine but is having slow onset, used for nerve blocks.
2. Local I/V Regional: After application of esmarchs bandage/tourniquet lignocaine is given I/V for regional anaesthesia.
3. Epidural Local anaesthesia (Regional)
4. Systemically opioid analgesics are used.
   Selection of  analgesic will depend on
   a)Expected intensity of pain
   b)Duration of action required
   c)Desired speed of onset of action
    

1. Expected intensity of pain:
   1.Intense analgesia by pure agonist drugs like morphine /methadone /pethidine /fentanyl.
   2.Less intense analgesia by partial agonist drugs like butorphanol /burenorphine /pentazocine.

       b)   Duration of action required:

             1.Longest duration of action by Buprenorphine 6-8hrs.

             2.Moderate duration of action by Morphine/Methadone 4hrs.

             3.Short acting by Pethidine/Butorphenol 1hr.

             4.Ultra short acting by Fentanyl 20mints.

 

1. Desired speed of onset of action
   I/V is desirable for faster rate of onset of analgesia, with intense peak effect compared to i/m or s/c.
    
   Side effects of opioids
   Decrease the heart rate , treated by atropine
   Decreased respiratory rate
   Increased GI motility
   Vomiting  in dogs

1. Epidural morphine:
   Excellent analgesia of pelvis/hind limbs upto 23 hrs by combining with pethidine as best combination.(Pethidine 1mg/kg+Morphine 0.1mg/kg)
2. Intra articular oipiods:
   In inflammation, opioid receptors increase and pharmokinetics of opioids are similar to that in epidural space. Morphine is used along with bupivacaine  for intraarticular use.
3. Transdermal fentanyl  patches with 100microgm/hr capacity, which steady state plasma concentration reaching in 24 hrs. It is recommended 12 hrs before surgery for cats and 24 hrs before surgery for  dogs , lasting analgesic effect for 3 days.
4. Sustained release morphine tablets (MS-Contin)
   For severe long term pain in osteosarcoma, tablets to be given every 12hrs.
5. Tramadol (Tramal SR)
   Weak opioid receptor agonist, oral 2-4mg/kg BID in dogs/cats, side effects are sedation and vomiting.
6.  NSAIDs- for chronic musculo skeletal pain
   Eg: Meloxicam/Carprofen/Ketoprofen are COX2 inhibitors with less gastric and renal damage at 0.1mg/kg in dogs and cats.
7. Tranquilizer in pain control
   Tranquilizer with opioid analgesic is having potentiating effect like with Benzodiazepine(1mg/kg) + Acepromazine(0.01mg/kg)  by I/V.