Enhanced recovery after surgery (ERAS) has been on the agenda of our medical colleagues since the 1980s when Kehlet et al. first determined that the more pronounced the stress response is in the perioperative period, the longer the recovery from surgery. Recent guidelines typically list 15 to 20 perioperative factors to be considered for enhanced recovery programmes and this article highlights those relevant to veterinary practice.
The stress response is a homeostatic mechanism comprised of hormonal and metabolic changes, which occur in response to anaesthesia and surgery (and anaesthesia without surgery). It is described as an ebb and flow, whereby catabolism occurs to provide substrates for the subsequent recovery; however, this evolutionary survival mechanism is most likely deleterious in a modern surgical context (Desborough et al., 2000).
Minimising the stress response
As an example from human medicine, an optimal ERAS programme for major abdominal surgery (and specific to this surgery) includes minimally invasive surgery (ideally a laparoscopic approach), avoidance of mechanical bowel preparation, avoidance of overloading with fluids before administration of epidural analgesia (or preferably avoidance of epidural analgesia), goal directed fluid therapy, aggressive post-operative nausea, vomiting and pain prophylaxis, limitation of intraoperative and post-operative opioids by using non-opioid analgesics and avoidance of unnecessary drains and catheters (Joshi and Kehlet, 2016). Such elements have been shown to reduce post-operative complications such as ileus, nausea and vomiting, and to encourage early feeding. Early mobilisation is essential.
The questions posed by Kehlet (2017) that we should consider with our patients are:
- Why is the patient in the hospital today?
- What are the reasons for developing a complication?
Encouraging early discharge is a key area of ERAS. Failure to mobilise following surgery in people is a huge risk factor for thrombotic events and, while we don’t tend to see this in our canine and feline patients, there are risks such as hospital-acquired infections to avoid. Of course, we would all rather see our patients returned to the care of their owners as soon as possible.
One of our aims for reducing initiation of the stress response has to be a smooth anaesthetic, where depth of anaesthesia and use of analgesics prevent nociception while at the same time avoiding excessive depth. It is known in humans that even short periods of deep anaesthesia correlate with a greater incidence of post-operative delirium, which is linked to a decline in cognitive function. The alpha-2 agonists fit the bill perfectly here, providing dose-dependent sedation and analgesia, working synergistically with opioids (Grimm et al., 2000). Preliminary studies in dogs indicate a reduction in measured stress hormones with medetomidine premedication compared to acepromazine (Vaisanen, 2002) and clinical experience shows a smoother anaesthetic with either medetomidine or dexmedetomidine premedication.
Using locoregional techniques
The opioid crisis in the USA is driving a change to opioidfree regimens in human post-operative pain management, with increasing evidence that other analgesics are more effective in the immediate post-operative period. Opioids have their place in daily surgical and anaesthetic practice but come with adverse effects. With multimodal techniques, notably preventive local anaesthesia, we can improve patient comfort and reduce our post-operative opioid use.
Bini et al. (2018) compared the effects of methadone 0.3mg/kg either every four hours or according to pain score (prn) in dogs undergoing TPLO surgery, in which a locoregional technique was used. Dogs in the prn group showed improved food intake, less vomiting and less vocalisation compared to the “by the clock” approach to administration.
Further evidence in support of the huge role of locoregional techniques comes from a study in which dogs undergoing stifle surgery received a femoral and sciatic nerve block (Figure 1), spinal anaesthesia or a fentanyl infusion. Outcome measures included plasma glucose and cortisol measurements to document the stress response and pain scores to guide interventional analgesic requirement (methadone 0.1mg/kg). Analgesia with a peripheral nerve block or spinal anaesthesia prevented the glycaemic and cortisol responses to surgery, promoted better recovery quality and decreased post-operative pain scores compared with fentanyl (Romano et al., 2015).
What must be considered with these two examples is that analgesia must be specific to the procedure. With this knowledge, anaesthetists are beginning to determine optimal analgesic options for common veterinary procedures. It is recognised that nerve blocks for cats undergoing dental extractions result in reduced anaesthetic requirements and improved comfort post-operatively (Aguiar et al., 2014). Further work also recommends long-term analgesia for cats with severe dental disease following extractions (Watanabe et al., 2018), with the aim of enhancing recovery.
Clearly, pain scoring plays a pivotal role in determining patient comfort. Studies in people show that post-operative assessment must include a procedure-specific functional outcome in addition to patient-reported pain scores. The example for the dog undergoing stifle surgery would be the ability to undergo physiotherapy in the 24 hours following surgery with minimal pain. This also highlights the need to move the pet from the kennel to perform the pain scoring.
With optimal perioperative management we can enhance recovery from the stress of anaesthesia and surgery. Focusing on suitable outcome measures for each surgery is necessary to determine the success of our interventions.