Pain management (Proceedings)

Pain Management Techniques

There are a wide variety of pain management techniques. I hope to cover a few here. Some of the different areas we will cover are injectable analgesia, epidurals, wound soaker catheters, local blocks, NSAIDs, and alternative methods. Each group will be expanded upon, with specific examples.

Injectable analgesia

This section covers many different drugs administered through a variety of routes (IV, IM, SQ). Typically, injectable analgesia is referring to opioids. NSAIDs, alpha-2 agonists, and dissociatives, however, can also be included in this section. The procedure and the patient's analgesic requirements will affect the drug given, the dose given, the frequency at which the drug is given, and also the route of administration.When drugs are not given at a continuous rate, there may be periods of low to no analgesia as the drug is cleared off and then periods with higher analgesia soon after administration. This is known as peaks and valleys. When giving intermittent injections it is important to assess patients often for pain. Examples of procedures where intermittent injections would be appropriate pain management are post-operatively for an ovariohysterectomy, or a simple mass removal.

Some injectable analgesic drugs can also be administered at a continuous rate to achieve optimum analgesia. Most commonly we are referring to opioid agonists such as fentanyl, hydromorphone, or morphine. Other drugs common given as constant rate infusions (CRIs) to help treat pain are lidocaine, ketamine, and alpha-2 agonists. A CRI will provide a consistent level of analgesia. Lower doses of drugs are needed because of the consistent rate. Titration of drugs administered as a CRI is usually possible. Critical patients often benefit from CRIs both under anesthesia and post-operatively. Intra-operative CRIs, of certain drugs, decrease the minimum alveolar concentration, allowing for a decrease in inhalant anesthetic. This is important with critical patients that often do not have good blood pressure.

CRIs can be maintained through a syringe pump or using a fluid bag and drip set. The combination of morphine, lidocaine, and ketamine is often added to a bag of fluids and set to a certain rate for that patient. This bag of fluids can be administered through a fluid pump, or in situations without one, the dial on the drip set can be used to control the rate of the fluid. The later is a bit riskier, if the patient's catheter was a little positional and he was to stretch his leg out, the fluids might speed up and the patient may receive more drug than initially intended. The opposite could be true as well, the line could stop flowing and the patient would not be receiving any medication. A pump will typically alert someone when an occlusion is present. Fentanyl can be administered as a CRI directly through a syringe pump attached to the patient's IV catheter, or diluted within a bag of fluids and administered at a faster rate.

The cost of administering a CRI is typically more than with intermittent injections (depending on the drug). This is because of the additional equipment necessary. The following is an example of a fentanyl CRI dosing chart. When saved as an excel spreadsheet, the patient weight could be added to one box and the program can calculate the rest for you. Using straight fentanyl, a syringe pump would be set for mL/hr.

Epidurals

Opiate epidurals typically have less systemic effects than IV or IM opioids and provide excellent analgesia. This procedure does require some special skills to perform properly. Drugs administered epidurally are typically preservative-free morphine (duramorph), and or local anesthetics, and or alpha-2 agonists. A decreased MAC makes epidurals a very useful technique for intra-operative and post-operative pain management. Expense is a little more than with constant rate infusions due to the supplies needed and the special skills required. Other drawbacks are that sometimes, the effectiveness varies (obese patients are difficult), the hair at the epidural site does not regrow, and patient's may have bladder retention following epidural administration.

To perform an epidural, it is recommended that the patient is under general anesthesia or very heavily sedated to be sure that they do not move. This should be a sterile procedure requiring sterile gloves, a clip and sterile prep of the area. Spinal needles should be used because there is a stylet inside to prevent it from becoming occluded with tissues before entering the epidural space. Also, spinal needles are slightly blunter intentionally so that a person can feel each layer of tissue as the needle is advanced into the appropriate space.

In order to avoid the spinal cord, epidurals should be administered between L7 and S1. Palpation is easier with lean patients than the obese. The veterbral body of L6 is often more prominent than L7. There should be a gap, albeit tiny in smaller patients, between L7 and S1. This is where the needle should be inserted. The spinal cord usually ends around L6 and the subarachnoid space usually ends at L7 in dogs. The cat's anatomy is slightly different in that the spinal cord runs to the sacrum and the subarachnoid space usually ends slightly caudal to L7. If the subarachnoid space is entered, CSF fluid is obtained (fluid will come up and out of the needle); when this is the case, administration of half of the intended amount of drug is appropriate. It is much more common to enter the subarachnoid space on a cat due to their anatomy.

Epidurals are great for orthopedic procedures, hind limb amputations, and some abdominal surgeries like splenectomies.

Wound Soakers

Wound soaker catheters are diffusion catheters (with holes on the patient side) that are placed into the wound bed during surgery. They infuse local anesthetics to the tissues and nerves to provide analgesia. Commercially available diffusion catheters can be obtained from ReCathCo and MILA. Red rubber urinary catheters can be made into wound soakers by practices trying to save money.

Administration through the wound soaker can either be done as a CRI or as intermittent boluses. A CRI can be set up with a pump or balloon device. The balloon is available from ReCathCo (Surefuser Elastomeric Infusion System) and is an option for veterinarians that want to send patients home with a CRI. The wound soaker is attached to the balloon that is attached to the dog. If a patient in the hospital has a wound soaker that is attached to a pump, the fluid line should be clearly marked as "No IV Access". Hyperactive patients that continue to tangle their fluid lines may not be a good candidate for the pump. These patients could benefit more from either the balloon, or intermittent doses of bupivicaine. Cats should only be dosed with bupivicaine on an interval basis; this is due to their low tolerance of local anesthetics.

Based on human literature, when wound soakers are placed inta-operatively and used post-operatively to treat pain, a significant decrease in systemic opioid requirements occurs. Some knowledge of the equipment is necessary for proper placement of the wound soaker. If the wound soaker is not placed properly, the appropriate nerves will not get blocked. While wound soakers have never been reported as a source of contamination, it is possible so aseptic techniques should be utilized.

Some procedures for which wound soakers are indicated are a limb amputation, a median sternotomy, and some of the much larger mass removals. Wound soakers are not ideal in cases where there is a drain in the area (open or closed suction).

Local Blocks

Minimally invasive, local blocks can provide excellent additional analgesia. They tend to be relatively inexpensive due to the limited supplies needed, and the low cost of local anesthetics.

The person performing the local blocks must have a basic knowledge of anatomy, and understand the importance of avoiding blood vessels. Local anesthetics given intravenously have a greater risk of causing toxicity. The appropriate dose of lidocaine is 2 mg/kg for dogs or cats. Bupivicaine dosing is 1.5 mg/kg for dogs or cats. Much lower doses are recommended because they can still provide excellent analgesia. Local signs of toxicity could include skeletal muscle changes (especially when given IM). Seizures, decreased heart function and decreased BP are all systemic signs of toxicity. Sometimes local anesthetics can cause vasodilation resulting in hypotension.

There are many different local blocks that could aid in pain management. Pre-operatively brachial plexus blocks (distal humeral fracture), dental blocks, and ring blocks (declaw) are helpful. During surgery a surgeon could perform an intra-articular block (orthopedic surgery), intra-pleural (thoracotomy), or incisional block (C-Section).

NSAIDs

Nonsteroidal anti-inflammatory drugs work by inhibiting prostaglandin formation. Prostaglandins are a necessary part of the inflammation process. They also can be found in gastrointestinal mucosa, facilitate platelet aggregation, and regulate renal blood flow.

NSAIDs have negative and potentially life threatening side effects. These negative side effects do not come from the act of stopping the inflammatory process, but instead from the other functions prostaglandins serve on the body. By administering an NSAID and inhibiting prostaglandin formation, the GI tract is susceptible to ulcerations, the platelets may not function appropriately, and the kidneys are at a greater risk. Knowing this, we should not give NSAIDs to a patient with GI ulcers, decreased platelet function, or compromised kidney function. Patient selection is a very important part of NSAID administration, a patient with a history of reaction to an NSAID should not receive one.

When sending patients home with an NSAID, client communication is very important. The client should be aware to discontinue the medication if the animal is not eating, the patient is having diarrhea, or bloody stool. NSAIDs should never be mixed or switched without a period of time between the two drugs.

Alternative Methods

There are lots of additional pain management strategies that I have grouped into alternative methods. Some of these methods are very common place, others are not as much. Sedatives and tranquillizers are useful in the hospital to calm anxious patients in order to allow their pain management work. Opioids in combination with a sedative such as acepromazine, or dexmedetomidine have more profound analgesic effects than when given alone. In recent years, there has been a big demand from small animal owners for alternative practices such as chiropractic, acupuncture, Reiki, and laser therapy.

Ice packs wrapped up and placed on an incision decrease inflammation. Alternately, warm packs wrapped up and placed on an area help to bring new blood supply to that area. Patients in hospital can benefit from fentanyl injectable administered as a CRI. Patients discharged from the hospital (or hospitals without fentanyl injectable) can benefit from fentanyl patches. A patch can take up to 12 hours to take effect but may last for up to three days.