The quest for relief from pain is pursued in human medicine because its existence is known since the patient can verbalize their pain: what it feels like, where it is and the relief they feel when treatment is appropriate. As we all have experienced pain of various degree and duration, it is an excellent topic for comparison and understanding with our veterinary patients. As veterinary patients cannot tell us how painful they are, we as veterinarians and veterinary technicians/nurses have to understand what can cause pain and how pain manifests itself, which is discussed throughout this book, and how best to treat it.
Upon presentation immediate and appropriate treatment for the presenting problem should begin. Managing these problems frequently relieves some of the pain experienced (e.g. cooling a burn). The analgesic procedures are included in the scenarios; however, for definitive management of the presenting problem, the reader is referred elsewhere. Initial management is also based on inclusion/exclusion of preâexisting problems, medications and when the patient was last fed. An additional factor is the aggressive nature of the patient and how to deal with that (Chapter 22). Frequently, patients require diagnostic imaging and some may require surgical management. Specific analgesic/anesthetic protocols will be required for each circumstance. Preparation for intubation and assisted ventilation is essential. As cardiac arrhythmias may occur within 12â24 h (if not already present) following trauma, continuous ECG monitoring must be included in the ongoing patient assessment.
While management procedures contribute to a reduction in the pain experienced, analgesics are an essential component of case care in the urgent and emergent trauma, and for many critically ill, patients. Some degree of inflammation is present in these patients and is associated with great energy expenditure, the demands for which frequently cannot be met. The addition of pain, a great utilizer of energy, can contribute to associated morbidity, especially in the more seriously affected patients. In addition to the pain experienced by the primary problem, there is an additive effect of pain due to placement/presence of IV, urinary, thoracic, abdominal catheters and drains. Many undergo frequent manipulations and procedures that contribute to the overall pain experienced. Prior to analgesic and anesthetic selection, the pharmacologic aspects and contraindications for the various agents must be considered due to the fragile organ function of many of our ill or injured patients. Refer to the pharmacology and clinical application of sedatives (Chapter 9), opioids (Chapter 10), nonâsteroidal antiâinflammatory analgesics (Chapter 11), adjunct analgesia (Chapter 12) and anesthetics (Chapter 13). As pain is an individual experience associated with specific situations, general dosing of analgesics may not be appropriate. Refer to Chapter 8 for analgesic dosing suggestions for various levels of pain and the individual scenario chapters.
A common misconception is that analgesics mask physiological indicators of patient deterioration (e.g. tachycardia in response to hypotension) and are, therefore, withheld. Evidence to support that analgesics do not mask signs of patient deterioration is reported in both the human and veterinary literature [1]. In fact, improved outcomes of wellâmanaged pain in trauma patients is reported [2]. Our clinical observations show that when opioids are administered as a slow push or as a continuous rate infusion to treat pain an appropriate heart rate in response to hypotension, hypoxia, hypovolemia or hypercarbia still occurs. As tachycardia frequently occurs in the painful patient, treating the pain and eliminating this component as a cause for tachycardia, the persistence or recurrence of increased heart rate alerts the clinician to potential patient deterioration. If appropriate analgesia is not administered, tachycardia may be assumed to be pain and not patient deterioration. It is essential to obtain intravenous (IV) access, collect blood for laboratory evaluation and commence fluids while initiating opioid analgesia. Where hemorrhage or other hypovolemic states may exist, the severity of intravascular volume loss may be masked by the painâinduced âartificialâ blood pressure (BP) reading. With administration of an analgesic, the painâinduced sympathetic response is reduced, allowing the BP reading to reflect the true intravascular volume. Heart rate will still reflect volume loss. Studies confirm that opioids do not result in a deterioration in hemodynamics when administered to dogs with 30% blood loss. Should BP drop below normal during opioid administration, this reflects that hypovolemia and fluid administration should be increased to that required for the patient. Where blood loss is identified, continuous monitoring of BP and laboratory evaluation is essential to identify the patient requiring a blood transfusion. The biochemistry results will identify organ dysfunction and will assist with selection of an analgesic protocolâand an anesthetic protocol should this be required.
Another concern expressed by many veterinarians is the potential for adverse reactions associated with analgesic drug administration, especially so for cats. However, current evidence, based on many studies investigating the efficacy and tolerability of analgesics of several drug classes, indicates that adverse effects are minimal when used appropriately [3]. This applies to both cats and dogs [4]. Adverse effects, primarily those associated with opioid use, such as respiratory depression, are extrapolated from humans and are overâemphasized in dogs and cats. In thirty years of practice in the critical care setting, this author has witnessed only two such incidences, both associated with fentanyl patch application in very small dogs. With respect to ventilation, opioid administration after a traumatic incident frequently improves ventilation rather than impairs it. This has been confirmed by arterial blood gas assessment by the author. Based on the physiologic abnormalities present in the ill or injured cat and dog, selection, dosing and method of administration of analgesics require careful consideration to ensure efficacy without the potential for adverse effects. As an example, nonâsteroidal antiâinflammatory analgesics (NSAIAs) should never be administered to any ill or injured patient upon presentation (Chapter 11). The administration of NSAIAs in the emergent patient should be withheld until the volume, cardiovascular, liver and kidney status of the patient is determined to be within normal limits and there is no potential for deterioration, such as ongoing or occult hemorrhage. Human patients with severe or poorly controlled asthma, or other moderate to severe pulmonary disease, may deteriorate with cyclooxygenase 1 (COXâ1) selective NSAIA administration [5]. It is not known whether this may occur in cats and dogs; however, as bronchodilator physiology is similar across species, this may still be a concern. As asthmatic patients receive glucocorticoid therapy, NSAIA would be contraindicated. COXâ1 selective NSAIAs are not recommended for any patient scenario included in this book.
Concerns for opioid immunosuppressive effects, and subsequent infection, have been reported in the human literature. Based on the authorâs experience working with critically ill patients all receiving opioids, infections potentially associated with opioid use were not identified. However, as the immunosuppressive potential of some opioids, especially morphine, was raised [6], a twoâmonth prospective study was carried out at the authorâs institution, including all patients (ICU and surgical ward) with a variety of problems receiving opioids. Fentanyl, hydromorphone and buprenorphine were opioids used predominantly, in addition to NSAIAs, which demonstrated a 6/140 (4.3%) new infection rate. Survival rate was 98% with 2% euthanasia due to poor prognosis (e.g. neoplasia, severe head trauma). As with other reported studies, the tibial plateau levelling osteotomy (TPLO) procedure was the major orthopedic procedure represented in the infection rate (two of the six patients acquiring infections). Interestingly, critically ill patients rarely acquired infection, whereas the TPLO procedure is performed in healthy dogs. An earlier study investigating surgical site infections (SSIs) in dogs at the same institution receiving opioids during hospitalization included 846 dogs over a 45âweek period and i...
