Introduction
In emergency medicine we anticipate treating patients with a wide variety of disease processes. In many cases patients will require sedation or anesthesia for evaluation and to provide appropriate treatment. In this article we will briefly review best practices of sedation and anesthesia to optimize patient outcomes, identify alfaxalone’s attributes as the ideal anesthetic drug and finally, we will focus on walking through some common emergency room cases utilizing Alfaxan Multidose.
Figure 1. A critically ill post-operative patient in recovery
Anesthesia best practices
Initial patient evaluation and planning in the emergency room is often quickly performed with attention focused on the presenting complaint and the cardiovascular and respiratory systems. Appropriate drug selection including those that provide analgesia, sedation, or general anesthesia, along with vigilant monitoring will help to optimize patient outcome.
It is imperative to select drugs that are short acting and reversible. There’s no denying that opioids and benzodiazepines fit this requirement. Fentanyl is an opioid that provides potent analgesia, is short-acting and can be administered as an IV bolus followed with a constant rate infusion if necessary. If fentanyl is not available other full mu-agonist opioids that can be used include hydromorphone, methadone or morphine. Butorphanol offers mild to moderate analgesia along with some sedation. The cardiovascular and respiratory effects of opioid administration are dose dependent and reversible with naloxone.
Opioids act synergistically with sedatives including benzodiazepines and alpha-2 adrenergic agonist drugs. Benzodiazepines can produce sedation in debilitated patients, have minimal cardiovascular and respiratory depressant effects and are reversable with flumazenil. However, it is important to remember that sedation with a benzodiazepine is inconsistent in excitable or aggressive patients. In these patients, dexmedetomidine is a more dependable option. Dexmedetomidine provides sedation with additive analgesia; however, it should be avoided in patients that have compromised cardiovascular function. Often, a low dose of dexmedetomidine administered with an opioid can provide both ideal sedation and sufficient analgesia for many emergency room procedures. Dexmedetomidine is reversible with atipamezole.
Alfaxalone’s attributes in the emergency room
Figure 2: Oxygen support provided to brachycephalic animal with respiratory distress
The ideal anesthetic induction drug provides a calm, pain and anxiety free anesthetic induction, as well as a rapid, reliable, and repeatable transition to unconsciousness with general muscle relaxation allowing for easy intubation. The anesthetic agent should limit disruption to the cardiopulmonary system and be eliminated from the body quickly with a smooth and uneventful recovery. Additionally, the ideal anesthetic drug should possess a large margin of safety with no known contraindications for use with other drugs or in special patient populations. Finally, it’s important that the anesthetic is labeled in the target species providing the end user reassurance that the product has been properly tested and registered by the Center for Veterinary Medicine, FDA.
Evaluation of the effect of alfaxalone on blood pressure, an important indicator of anesthetic safety especially in critically ill patients, has been evaluated in the good clinical practice (GCP) field studies of alfaxalone in client owned dogs and cats (ASA 1 and 2). Results showed that in premedicated dogs and cats induced and maintained with alfaxalone, there was little effect on arterial blood pressure. For premedicated dogs and cats transitioned to maintenance with isoflurane, there was a greater decrease in systolic blood pressure. The data shows that alfaxalone is less hypotensive at equipotent doses than isoflurane and that on its own maintains clinically acceptable blood pressure and subsequently, tissue perfusion.
Common emergency room cases
Figure 3: Urinary catheter and closed collection system in an anesthetized cat
Urinary obstruction
Nearly 1.5% of all cats that present to 24-hour specialty care facilities and universities in the past 20 years have urethral obstruction. Most cats that present with urethral obstruction are overweight, middleaged, neutered-male cats but female cats and dogs can also be affected. Common presenting complaints observed by the pet owner include abnormal urination at home or frequent trips to the litterbox. A diagnosis of urethral obstruction can be confirmed with abdominal palpation and ultrasound showing a distended bladder, with or without uroliths, and possibly free fluid in the abdomen if the bladder has ruptured or leaked.
The focus of treatment for a cat with urethral obstruction is managing the most life-threatening side effects while removing the urethral obstruction to the bladder if not yet ruptured. Intravenous catheterization is followed by administration of a balanced crystalloid fluid solution. Often heavy sedation or anesthesia is required to relieve urethral obstruction. Alfaxalone in combination with an opioid provides analgesia and minimal disruption to the cardiovascular system for this patient population. There are several publications available describing the administration of alfaxalone in combination with an opioid to produce rapid, deep, short-lasting sedation in cats.
After the obstructive cause has been removed continue to pay attention to patient comfort and provide appropriate analgesic drugs, such as buprenorphine. Prior to discharge it is important for the patient to be capable of urinating on their own with no effort following removal of the urinary catheter. Monitor for re-obstruction before discharge.
Gastric Dilatation and Volvulus
Figure 4. Pathognomonic radiographic image of a patient with GDV (i.e. the “smurf hat”)
Another common case presentation to the veterinary emergency room is gastric dilatation and volvulus or GDV. This is a life-threatening emergency that requires stabilization and immediate surgery to resolve. Gastric dilatation and volvulus is most commonly seen in large, deep chested breeds such as German Shepherds, Great Danes, Labrador and Golden Retrievers. Generally, dogs with gastric dilatation and volvulus present with unproductive vomiting or retching, excessive salivation, and discomfort with a hard abdomen. These dogs can also present completely obtunded or collapsed. Gastric dilation and volvulus causes a pyloric outflow obstruction which leads to an accumulation of air and fluid in the stomach. As the stomach expands, this causes hemodynamic disturbances involving compression of major vessels and decreased venous return, as well as exaggerated pressure on the diaphragm impeding ventilation, leading to respiratory distress. As the duration of GDV increases, patients experience hypovolemic shock with hypotension, venous stasis, resulting in metabolic acidosis, and eventually cardiovascular collapse. As a result, these patients present with tachycardia, often with ventricular arrythmias such as ventricular premature contractions and ventricular tachycardia.
Following a physical examination, a diagnosis of GDV is confirmed by obtaining a right lateral abdominal radiograph and potentially observing the characteristic “smurf hat” appearing stomach. These patients are painful and analgesia with a full mu-agonist opioid is recommended. Gastric decompression by either orogastric tube decompression or trocarisation of the left, lateral cranial abdomen will help with hemodynamic stabilization before surgery. Following initial treatment of restoring vascular volume and gastric decompression, anesthesia with a product that provides minimal cardiorespiratory depression such as alfaxalone is instituted and surgical correction of the volvulus is completed to return the stomach to its normal position. A gastropexy can also be performed after correction of the volvulus to prevent risk of re-occurrence.
In a clinical study, Psatha, et al. concluded that induction with alfaxalone following methadone premedication in these critical patients, several of which presented as GDVs, provided similar results to the neuroleptic combination with propofol. Additionally, the alfaxalone group had less excitation during induction when compared to the neuroleptic combination.
Summary
There is no substitute for good anesthetic practices including vigilant monitoring, utilizing the lowest possible dose of medications and choosing medications that are reversible and have limited side effects. In the emergency room, decisions must be made quickly and confidently to avoid secondary trauma to already critically ill patients. Short acting and potent medications such as opioids, benzodiazepines and alfaxalone containing products can help achieve repeatable and reliable outcomes in our critical patients.
References
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- Norgate D, Ter Haar G, Kulendra N, Veres-Nyeki KO. A comparison of the effect of propofol and alfaxalone on laryngeal motion in non-brachycephalic and brachycephalic dogs. VAA 2018 doi: 10.1016/j.vaa.2018.06.013
- Psatha E, Alibhai HI, Jimenez-Lozano A, Armitage-Chan E, Brodbelt DC. Clinical efficacy and cardiorespiratory effects of alfaxalone, or diazepam/fentanyl for induction of anaesthesia in dogs that are a poor anaesthetic risk. Vet Anaesth Analg. 2011 Jan;38(1):24-36.
- Ribas T, Bublot I, Junot S, Beaufrere H, Rannou B, Gagniere P, Cadore JL, Pariaut R. Effects of intramuscular sedation with alfaxalone and butorphanol on echocardiographic measurements in healthy cats. Journal of Feline Medicine and Surgery. Sept 2014 online P 1-7.
This content is sponsored by Alfaxan and Think Anesthesia, an educational platform providing veterinary professionals with both on-demand and live training material, primarily focused on anesthesia and analgesia.