I speak with Dr Dominic Cliff, a Consultant Anaesthetist with a special interst in acute pain. Dominic runs the acute pain service in Chester and has been instrumental in the adoption of rectus sheath catheters for post operative pain relief in major abdominal surgery.
Oooww!! You B!*^&$d!! Is my normal response should I hit my thumb with a hammer during DIY. Rarely would I stop and consider the different pathways and chemoreceptors activated by this unfortunate mishap. However, this is a fantastic example to illustrate the various pain pathways and where commonly used analgesics act. By understanding this in more depth, we can provide good quality, multi-modal analgesia targetting more than one area with our therapy.
The first reaction to the painful stimulus, in this case a hammer, is tissue damage and inflammation. Bradykinin, subsatance P and prostaglandins are released. This is the first part of the pain pathway we can target with Non-Steroidal Anti-Inflammatories (NSAIDs). Most commonly these would be (1):
Ibuprofen – PO 200-400mg PRN/TDS
Naproxen – PO 500mg initially, 250mg 6-8 hourly PRN thereafter
Diclofenac – PO 75-150mg per day in 2-3 divided doses, PR 75-150mg per day in 2 doses
Ketorolac – IV/IM 10mg initially, then 10-30mg 4-6 hourly PRN. Max 90mg per day.
A recent study published in Annals of Emergency Medicine investigated the analgesic ceiling of Ketorolac (2). It can be found here. There have been many discussions about this study by COREEM, REBEL EM and The Skeptics Guide to Emergency Medicine. The main result of the study found that ketorolac has a potential analgesic ceiling of 10mg. This means that by giving a dose above this, we risk increasing risk of potential side effects without any increase benefit of extra analgesic effect. Caution should be applied when considering the patients you may encounter. This study investigated emergency department patients and those you encounter on the ward with acute pain are a different population so it does not make this generalisable to that population. However, it is thought provoking.
Unfortunately, not all patients can take NSAIDs. Some cautions and contra-indications include:
- Elderly patients – not an absolute contra-idication, however they will be more susceptible to the undesirable effects of NSAIDs and should be used with caution
- Previous upper GI bleeds
- Renal dysfunction or at risk of
- Hypersensitivity to NSAIDs
- Asthma – also not a contraindication as some asthmatics will be able to tolerate NSAIDs. Often the patient will be able to tell you themselves.
- Ischaemic Heart Disease or other sclerotic arterial disease states due to increased thrombotic events associated with NSAIDs and cox-2 inhibitors.
- Heart failure
The BNF can give you a full list (1).
Following the chemical release in the tissues, nerve impulses are carried along two different types of nerve fibres; a-delta and c-fibres. The fast, immediate sensation is transmitted by a-delta fibres and the slower, more throbbing impulses is carried by c-fibres. Local anaesthetics act on these fibres by way of Na channel blockade. By far the two most commonly used and doseages (3) are:
Lidocaine 1% or 2% (max dose 3mg/kg or 7mg/kg with adrenaline)
Levobupivacaine 0.25% or 0.5% (max dose 2mg/kg, no adjustment with adrenaline)
Lidocaine can be used in patches, though these would often be prescribed by a pain specialist. Usually at the end of an operation, the surgeons will infiltrate the wound edges with levobupivocaine or another local anaesthetic. Especially in limb surgery, you may also find the patient has had a peripheral nerve block performed in order to provide analgesia both intra and post-operatively. The duration of action of these agents is very different. Lidocaine would have action for up to 60 minutes or 2.5 hours with adrenaline (4), whereas levobupivacaine may have an effect of 9 hours or longer depending on technique used (5).
Moving onward from the nociceptors we reach the spinal cord. Here we find opioid receptors. We use opioids of varying potency from mild (codeine) to strong (morphine). You may come across a drug class of opiates. These are synthetic opioids and include fentanyl, alfentanil and remifentanil. Most commonly, these would be used in anaesthetic practice.
Opioids act primarily via the μ receptor. According to RCEM guidelines (6), codeine can be initiated for moderate pain and morphine or other strong opioids reserved for those with severe pain. Realistically, these form the mainstay of treatment for severe pain. Below is a guide to dosing (7)
- Codeine – PO 30-60mg PRN max 240mg per day
- Morphine Sulphate Oral Solution (Oramorph) 10mg in 5ml – 5-10mg orally every 4 hours, dose adjusted to response
- Morphine Sulphate – IV – initially 5mg but dose can be increased if not sufficient, every 4 hours but frequency can be increased if needed. IM/SC – 10mg every 4 hours, adjusted according to response.
- Oxycodone – PO initial 5mg 4-6 hourly, dose adjusted according to response. IV – 1-10mg 4 hourly as needed. SC – initially 5 mg, as needed. Enteral vs parenteral equivolance is 2:1 (2mg orally = 1mg IV)
You must exercise caution when prescribing opioids for patients. A young patient without any comorbidities may well be able to tolerate a high dose of codeine, but an elderly patient with multiple underlying comorbidities may not be able to tolerate opioid medication (8). You really must consider the intended effect and individual patient before prescribing. It is not uncommon to find elderly patients with opiate toxicity following commencement of codeine at a dose too high for them. The same principal applies for stronger medication such as morphine. Just because you can given 10mg, does not mean you should. It may be better to prescribe a titrated amount in order to allow the nurse administering to give the amount needed, rather than just the maximum. Please remember, as morphine is excreted by the kidney, those with renal impairment need doses reducing and are at higher risk of toxicity (9). Oxycodone is sometimes used in place of morphine is renal failure and may be preferred. This is due to the more predictable metabolism of oxycodone and easier titration (10). However, it is still excreted by the kidneys and still warrants care.
What about just giving it a rub? As Dominic describes, the nerve impulses reaching the dorsal horn interact with an area called “the gate”. This involves a mechanoreceptor influencing the transmission of the pain signal to ascending spinal tracts. Rubbing the injured area (not suggested in all injuries or wounds, please apply common sense), modulates the ascending signal and reduces it, thereby reducing pain. A TENS machine is an example of this in clinical practice, but your mum intuitively understood this when she would rub your leg after you banged it.
As we ascend in the spino-thalamic tract eventually we reach the thalamus and signals are distributed to the relelvent somato-sensory area. It is at this point that descending pathways exert their action and Tramadol has it’s effect. Tramadol is often spoken of as an opiate, however, it has weaker opioid receptor action and also acts via serotonin and noradrenaline receptors (11). As Dominic mentions, someone with a tramadol overdose may not present with opiate toxicity signs, and may have a more serotoninergic appearance instead. This potentialy explains why some people cannot tolerate tramadol due the side effects of feeling dizzy or light headed. It also lowers seizure threshold in epileptic patients (12).
- Tramadol – IV/PO 50-100mg PRN/QDS
Finally, we have the limbic system. This is not a pharmaceutical therapy, but it is always worth talking to your patients. Pain is subjective experience and causes great anxiety for some patients, either actual pain or the threat of it. Pain creates emotional reactions and how you approach your patient will influence this.
In anaesthesia, we tell patients that operations hurt but they will have multiple treatments provided in order to manage their pain and discomfort is normal even if it occurs a few hours later. There are some people who I have encountered that have genuinely believed the operation would not result in pain. Regardless of the setting you work in, talk to your patients. Reassure them that you have treatments available to manage their pain, that your aim is to make them comfortable but you may not eliminate pain completely. The same applies if you are about to undertake a procedure, even a minor one such as venepuncture. Every patient feels the needle differently and they deserve to be told it might hurt.
I tell patients in the Emergency Department that I can see they are in pain and I can help their pain with some different drugs but I may not eliminate pain competely and we aim to reduce their pain to a manageable level for them. I have no evidence to back up what I say on this, but it appears effective from my experience. My reasoning is that this brief conversation reassures patients for a few reasons:
- You have acknowledged they are in pain
- You have told them you can help
- You have more than one things that will help
- There is an end point you are aiming for
- The endpoint is determined by them, not you, so they are empowered to request analgesia as they need it
I believe sets up realistic expectations for the patient. Total elimination of pain may be impossible for some and chasing this risks higher quantities of medications and increasing risks of undesirable effects. In telling a patient I want to get them to a point they can manage, it’s not because I have a sadistic streak, it’s because there will be a level of pain that is manageable for them and it is decided by them. A thumb hit with a hammer may hurt a lot and codeine may not eliminate pain but make it bearable, eliminating pain may require morphine, but if the patient can continue despite the pain then morphine isn’t justified.
Depending on the site these are placed at, these may be for a variety of different reasons, the main being analgesia. They will be placed by an anaesthetist pre-operatively. Below is a picture showing the anatomy of an epidural.
The catheter that is introduced through the needle sits within the epidural space and allows for a continuous infusion of either local anaethetic or local anaesthetic and low dose opiate together. Sometimes, the patient will have their own control button that will deliver a bolus if they need extra analgesia.
Epidurals can provide excellent analgesia when functioning well, however they do require some maintanence and attention. They also have some complications associated with them. In the podcast, Dominic runs through the more common problems and how to deal with them. If you are in any doubt about looking after an epidural, there will be an anaesthetist you can contact who can help.
Hypotension commonly occurs due to sympathetic blockade. Owing to the distribution of sympathetic nerve fibres, this may be above the level of the sensory block. Most post-op patient will have had a period of starvation prior to surgery and may be dehydrated and require IV fluids. One option of dealing with hypotension would be an IV fluid bolus (bolus, not faster background rate). The patient may need more than one. There will be patients who do not need fluids or who do not respond to them. These patients need discussing with an anaesthetist as they may need vasopressors in order to maintain their blood pressure. Do not turn off the epidural!
Inadequate analgesia occurs for a few reasons. The fluid infused via the epidural sits as a column within the epidural space. The height of that column determines the level of effect and is affected by gravity. It also undergoes absorption by the body which is why it needs to be a continuous infusion in order to replace what has been absorbed. The rate of absorption will vary. You can test the level of the block with a cold spray. First spray it over an area not covered by the epidural, such as the hand. Ask the patient if it was cold. Then, starting on the thigh or below, spray continuously and ask them to tell you when it feels the same as the area not covered by the epidural. This transition point is the height of the epidural.
A patient with a vertical incision may have pain at the top of their incision, indicating the height of the fluid column is too low. These patients either need a bolus to increase the column height or an increase in the rate or both. Speak to an anaesthetist first as providing a neuraxial anaesthetic bolus should be undertaken by those trained and often there is an unlock code to operate the epidural pump itself.
A block may be present on a single side of the body if the patient has been lying on one side for a long time. You can simply ask the patient to lie on their back or the nurses to reposition them in bed. This would redistribute the fluid in the epidural space and restore a bilateral block.
If the block level is much higher than the patient requires, the rate needs to be turned down or the patient sat up more.
Rectus Sheath Catheters
Rectus sheath catheters (RSC) are different from epidurals. These are used for abdominal surgery. In Chester, we use these at the end of laparotomies for post-op analgesia. Two catheters are inserted into the rectus sheath by the surgeon prior to closure of the incision and a bolus of local anaesthetic through each catheter to open the space. The catheters are then connected to a single pump infusing local anaesthetic continuously. They provide anaesthesia to the surgical incision alone and not to the visceral organs. We pair them with a morphine patient controlled analgesia pump (PCA) to manage aditional pain.
The advantage is with no epidural, there are no complications associated with epidurals and do not require the same level of maintenance. The disadvantage is the fact that an opiate PCA has to accompany them which introduces the complications of such drugs instead.
Certainly in our practice, we have found RSC provide good pain relief for patients and allow them to mobilise sooner. At present, no RCT data exists for RSC, however the TERSC trial (13) has completed recruitment with publication of results awaited for comparison of thoracic epidurals to RSC for major abdominal surgery. What evidence that does exist mirrors the experiences we have had at Chester. Pain relief can potentially be equivalent with epidurals, incidences of hypotension are reduced and patients may mobilise sooner (14). However, the evidence is observational, single centre and small numbers.
Depending on the practices where you work, RSC may be an intervention that could introduce benefit to patients. If you frequently experience poor functioning epidurals or find a large number of complications from them then this could be worth discussing with your senior’s across surgery and anaesthesia. Bear in mind, we use them inserted before closure by the surgeon and when the TERSC study is published their protocol has been for ultrasound guided placement by the anaesthetist prior to the incision (13).
Acute pain has multiple targets for therapies and little of many different treatments is better than one big slug of morphine.
Talk to your patients and work hard to reassure them when they are in pain.
The answer to problems with epidurals is not to turn them off, consider the problem and if needed speak to an anaesthetist for help to deal with it.
Rectus Sheath Catheters are an alternative to epidurals, however the evidence at present is not of high enough quality to make sweeping changes to practice but observational data suggested association with favourable results.
As ever, please take a look at some of the evidence for yourself and discuss with those around you if considering a change to your practice rather than taking our word for it.
Please get in touch with any comments, corrections or suggestions for future topics.
- BNF April 2017, Section 10.1.1: Non-steroidal Anti-inflammatory Drugs, accessed via www.medicinescomplete.com, May 2017
- Motov S et al, Comparison of Intravenous Ketorolac at Three Single-Dose Regimens for Treating Acute Pain in the Emergency Department: A Randomized Controlled Trial. Ann Emerg Med. 2016; Articles in Press
- BNF April 2017, Section 15.2: Local Anaesthesia, accessed via www.medicinescomplete.com, May 2017
- www.drugs.com/monograph/lidocaine-hydrochloride-local-anesthetic.html accessed 07/05/17 18:45
- Foster RH and Markham A, Levobupivacaine: a review of its pharmacology and use as a local anaesthetic. Drugs. 2000 Mar;59(3):551-79
- France J et al, Royal College of Emergency Medicine Best Practice Guideline, Management of Acute Pain in Adults, last revised December 2014, accessed May 2017
- BNF April 2017, Section 4.7.2: Opioid Analgesic, accessed via www.medicinescomplete.com, May 2017
- Pergolizzi J et al, Opioids and the management of chronic severe pain in the elderly: consensus statement of an International Expert Panel with focus on the six clinic… Pain Pract. 2008 Jul-Aug;8(4):287-313
- Conway BR et al. Opiate toxicity in patients with renal failure. BMJ 2006;332: 345-6
- Ordóñez Gallego A, Oxycodone: a pharmacological and clinical review. Clin Transl Oncol. 2007 May;9(5):298-307
- Grond S, Clinical pharmacology of tramadol. Clin Pharmacokinet. 2004;43(13):879-923
- BNF April 2017, Section 4.7: Analgesics, accessed via www.medicinescomplete.com, May 2017
- Wilkinson K, Thoracic Epidural analgesia versus Rectus Sheath Catheters for open midline incisions in major abdominal surgery within an enhanced recovery programme (TERSC): study protocol for a randomised controlled trial Trials. 2014 Oct 21;15:400