Anesthetic Management of Common Emergencies in Small Animals

Chapter 39
Anesthetic Management of Common Emergencies in Small Animals

Or, who can think at 2 am?

Jane Quandt

College of Veterinary Medicine, University of Georgia, USA

Gastric Dilation-Volvulus

Q. What makes gastric dilation-volvulus (GDV) an emergency?

A. GDV leads to multiple systemic abnormalities with a high mortality rate. The distended stomach severely restricts ventilation by cranial displacement of the diaphragm and leads to hypoventilation. The hypoventilation can lead to hypercapnia and hypoxia, with decreased tissue oxygen availability and increased lactate, which can initiate cardiac arrhythmias. Pre-oxygenation prior to anesthesia, during the induction phase, is recommended. Acid-base abnormalities can vary. There can be metabolic alkalosis due to gastric sequestration of hydrogen ions, or metabolic acidosis can occur from decreased cardiac output and poor ventilation. Serum electrolytes, and acid-base status should be assessed prior to anesthesia and, if possible, corrected before anesthesia [1–3].

With GDV the abdominal distention can decrease cardiac output by up to 90% from normal. The severe gastric distention compresses the intra-abdominal veins, such as the caudal vena cava, portal vein, and the splanchnic vessels. This venous occlusion decreases the venous return which in turn decreases cardiac output and systemic blood pressure. There is also decreased hepatic and renal blood flow. Gastric decompression prior to surgery can improve ventilation and cardiac function [2]. Dogs with GDV commonly have cardiac arrhythmias that are mainly ventricular in origin. Arrhythmias are associated with increased mortality and can be present in up to 40% of patients with GDV [2] [3]. With gastric distension, the high intra-abdominal pressure significantly decreases blood flow to the GI tract which leads to intestinal ischemia and then to bacterial translocation, which can result in septic shock.

Q. Does measuring lactate levels provide any information?

A. The plasma lactate concentration at the time of hospital admission is a predictor of gastric necrosis and patient outcome [4]. Gastric necrosis appears to have a strong association with negative outcome and duration of hospital stay [4]. Plasma lactate concentration is normally 0.5–2.0 mmol/l. The plasma lactate concentration will increase with tissue hypoperfusion. A plasma lactate concentration of 7.4 mmol/l or higher is predictive of gastric necrosis and decreased chance of survival in dogs presenting with GDV [4].

Q. What fluids are used in resuscitation of the dog with GDV?

A. These dogs may present in both hypovolemic and septic shock. It is important to restore the circulating plasma volume using isotonic crystalloid fluids. After initial fluid volume resuscitation, a colloid such as hetastarch may be used to help in vascular fluid retention. The administration of large fluid volumes is best accomplished through the use of two large bore IV catheters in the cephalic or jugular veins [1,3]. Re-expansion of plasma volume will decrease the severity of cardiovascular depression prior to anesthetic induction. Crystalloids should be given at the rate of 20–40 ml/kg IV with a colloid such as hetastarch given at 10–20 ml/kg over 30 min [2].

Treatment with 7% hypertonic saline (4–5 ml/kg over 15 min) will help in the restoration of arterial blood pressure and perfusion. Hypertonic saline may provide additional benefits via modulation of systemic inflammation, increasing urine output, and intestinal motility [2,3]. It is imperative, however, that crystalloid fluids are given concurrently.

Q. Is it important to decompress the stomach in a GDV?

A. Gastric decompression should be done after fluid therapy has been initiated and the cardiovascular resuscitation has begun. Decompression will help to improve cardiovascular function but can result in hypotension due to the rapid release of endotoxins and ischemic by-products from reperfusion injury. Decompression is done via passage of an orogastric tube. Intubation of the airway may be desirable to protect the airway and prevent possible aspiration. The dog can be sedated and general anesthesia induced to facilitate endotracheal intubation and passage of the orogastric tube. If passage of the orogastric tube is not possible, trocarization of the area of greatest tympany can be done to relieve the gastric distention, but this runs the risk of inducing septic peritonitis [3].

Q. What is the evidence for the use of lidocaine constant rate infusion (CRI) in the GDV patient?

A. Severe complications resulting from GDV occur from the ischemia-reperfusion injury and systemic inflammatory response syndrome seen following repositioning of the compromised stomach. Associated complications can include hypotension, acute kidney injury, disseminated intravascular coagulation, and cardiac arrhythmias. Lidocaine has been shown to decrease the severity of reperfusion injury and the systemic inflammatory response [5]. A recent study has shown that lidocaine at 2 mg/kg IV given at the time of presentation and then followed by a CRI of 50 mcg/kg/min IV for 24 h during and after surgery decreased the occurrence of cardiac arrhythmias, acute kidney injury, and hospitalization time in dogs that underwent surgery for GDV. Lidocaine also provides analgesia which will decrease opioid requirements [5].

Q. What anesthetic drugs are commonly used for GDV?