Introduction
Gastric dilatation and volvulus (GDV), commonly known as bloat, is an acute life-threatening condition, which is characterized by the malposition of the stomach when it rapidly fills with air and rotates. Gastric dilatation (the expanding of the stomach) and gastric volvulus (the twisting of the stomach without expansion) can occur separately, however, when they occur simultaneously the disease process to the body results in death if left untreated. Despite the first report of GDV in 1906, researchers have been unsuccessful in identifying a cause. Mortality rates range from 15–33%. While GDV can occur in many species (including cats and primates), deep chested and giant breed dogs are most commonly affected. Prompt recognition, rapid treatment, and surgery are required to increase the chance of survival.
Risk Factor
Approximately 22% of giant breed dogs and 24% of large breed dogs will develop GDV in their lifetime.
The Great Dane has the highest incidence (42.4%). The other most common breeds affected are the Weimaraner, Saint Bernard, Gordon Setter, Irish Setter, and the Standard Poodle. As these breeds get older, the risk of developing GDV also increases.
Some behaviour studies have suggested that fearful or anxious dogs may have an increased risk to developing GDV. It is speculated that the gastrointestinal tract may be adversely affected during times of stress, especially in the fearful dogs, which may lead to an increase risk to developing GDV.
Though there is no exact cause for GDV, many proposed risk factors could contribute. Exercise after a large meal, especially a meal of highly processed food or water, may be a risk factor. Dogs that were fed only one type of food appear to have an increase in risk, while dogs that were fed table scraps or canned food appear to have a lower risk. Despite the myriad of reports suggesting that it is food related, there has not been one definitive report showing a link between GDV and the types of food. Dogs that are male, geriatric, eating only one meal a day, eating too quickly or having a raised food dish may all increase the risk to developing GDV. One published report showed that large breed dogs that ate quickly out of a raised food dish had a 20% increase in risk and giant breeds had an increase of 50%.
Dogs that have developed GDV have been found to have increased gastrin concentrations. Gastrin is a hormone produced in the stomach that increases the release of gastric juice. In digestion, gastrin constricts the pyloric sphincter, causes oesophageal spasming and slows the rate of gastric emptying. This can lead to aerophagia and decreases the chance of vomiting with gastric dilation. Other risk factors include a decrease in oesophageal sphincter tone, myoelectric dysfunction and dogs that experience a delay in gastric emptying.
Pathophysiology
Most commonly the stomach rotates 90–270 degrees in a clockwise motion (viewed from behind). The fundus will generally shift to lie against the ventral abdominal wall while the pylorus will move along the ventral abdominal floor, eventually sitting dorsally and on the left side. This will cause the body of the stomach to shift right. Because the spleen is attached to the stomach by the gastrosplenic ligaments and vessels, the spleen will also follow the stomach and will become displaced, if not twisted as well.
Both air and fluid become entrapped within the stomach causing it to become enlarged. The gas may have become trapped because of aerophagia, but it may also be formed from bacterial formation. As the stomach fills with air, the caudal vena cava becomes compressed, leading to a decrease in venous return from the heart. A distended stomach can cause up to a 75% decrease in arterial flow to the gastric mucosa. Depending on the degree of rotation of the stomach, a partial or complete blockage of the portal vein may also occur. This may cause the liver or pancreas to become ischaemic to some degree. With the rotation of the spleen it too may become ischaemic.
As mentioned typically the patient presenting with a GDV will be a large breed, deep chested dog; however, it is important not to make this your only guideline. GDV has been documented in smaller deep chested breeds such as Dachshunds or dogs prone to over-eating such as Spaniels and Labradors. It has also been seen in puppies that have over-eaten. It can also occur in cats and other species though it is less common.
Pre-Surgical Treatment
Patients presenting with GDV usually have unmistakable signs. Signs include non-productive retching, abdominal distension, abdominal pain, anorexia, and restlessness. The stomach may be tympanic. Most patients will present in shock.
Treatment of the shock is the first priority. Because the patient is in shock and usually has severe abdominal pain, intravenous (IV) catheter placement, IV fluid therapy, and pain medication should be started before diagnostics. Two large-bore short peripheral catheters should be placed to maximize fluid resuscitation efforts. Short, large diameter catheters allow for higher fluid flow. Oxygen should be administered (generally given by flow-by) because many GDV patients are in respiratory distress due to the enlarged size of the stomach pressing on the diaphragm. All vitals and parameters should be monitored including pulse, respiration rate, blood pressure, mucous membrane colour, and ECG. Many GDV patients experience ventricular arrhythmias.
Fluid resuscitation is performed in stages to end-point parameters of improved perfusion, normal heart rate and normal blood pressure. Isotonic replacement crystalloids (e.g., Hartmann’s) are always administered with incremental doses.
The rapidly deteriorating hypovolaemic patient without significant haemorrhage can benefit from the infusion of hypertonic saline (4 ml/kg 7% solution) with synthetic colloid added in an effort to augment exogenous fluid infusion with interstitial fluid redistribution. As these patients are frequently large dogs, the use of hypertonic saline may enable rapid improvement of cardiovascular signs compared to isotonic crystalloids.
Analgesia should be administered immediately because it will, not only help alleviate the acute abdominal pain, but also it will help to reduce the stress for the patient.
Radiographs are not to be taken until fluids and temporary decompression has been initiated, unless euthanasia is an option over surgery. Radiographs should not delay surgical preparation. Abdominal x-rays are not performed routinely in our institution. Indication to go to surgery is given if orogastric decompression is not possible. However, if oral decompression is possible, a right lateral abdominal radiograph will show if a volvulus is present and will also indicate surgical treatment.
Laboratory Database
Obtaining pre-fluid blood samples for PCV/TS, electrolytes, venous gas, azostick and glucose, platelet count, activated clotting time, and saving samples for coagulation profile, serum chemistries, complete blood count, and urinalysis are recommended.
Pre-fluid values provide a baseline from which subsequent values are compared to and monitored. In addition, any significant abnormalities are addressed prior to surgical intervention.
Any clinical evidence of coagulation abnormalities in addition to laboratory abnormalities requires appropriate treatment prior to surgery; frozen plasma if DIC or coagulation factor defect is suspected.
Initial bloodwork should be obtained prior to starting IV fluids (obtain blood at the same time catheters are placed) to ensure that values are those of initial presentation. With any patient suspected of ischaemic disease, a blood lactate level should be obtained. Lactate acid build-up occurs when the body is unable to perform aerobic metabolism. During the anerobic process, lactate will start to build up indicating a worsening of illness. During GDV, blood supply to the stomach is decreased if not completely stopped (an ischaemic event). This causes the body to switch to an anerobic process, thus causing a build-up of lactate. Blood lactate values under 2 mmol/L are normal. In the case of gastric dilatation volvulus, levels greater than 6 mmol/L are associated with increased gastric necrosis. In 1999 one study of 102 dogs with GDV found that only 58% of dogs survived with a blood lactate greater than 6 mmol/L, while 99% of dogs survived with levels less than 6 mmol/L. However, a retrospective study showed this should not be a reason for euthanasia. The results of a second retrospective study in 2011 indicated that an initial presenting plasma lactate concentration >6.0 mmol/L is not predictive of macroscopic gastric wall necrosis or survival in dogs presenting with GDV. A decrease in plasma lactate concentrations >50% within 12 hours may be a good indicator for survival. Other bloodwork that should be run includes a complete blood count, packed cell volume, total protein, coagulation profile, serum chemistry profile, and electrolytes. Though it seems excessive, it is important to know whether any pre-existing disease exists and how decompensated the patient is. Since all GDV patients require surgery it is equally important to make sure that all electrolyte or other blood work abnormalities be rectified before the animal is placed under general anaesthesia. Since disseminated intravascular coagulopathy (DIC) can occur whenever there is major change in the vascular system, all GDV patients are considered at risk, which is why it is important to check a coagulation profile.
Decompression
Once GDV has been diagnosed and therapy for shock has been initiated, gastric decompression should be performed. Gastric decompression helps to improve cardiac output and blood pressure by alleviating pressure on the vena cava and portal vein. There are two methods that can be used to decompress the stomach: orogastric and gastrocentesis. Placement of an orogastric tube, which allows for the most decompression of the stomach. This method, however, generally causes more stress to the patient, and some patients may not tolerate it at all. A tube should be measured and marked from the point of the nose to the last rib. A roll of tape should be placed in the mouth just behind the incisors with someone shutting the animal’s mouth on the roll. The tube is then advanced with slightly firm pressure and a twisting motion. Be careful not to apply too much force on the tube because you could cause an oesophageal or gastric tear. Once you are in the stomach, contents should flow out of the tube into a bucket below the patient. If an orogastric tube cannot be placed, then a gastrocentesis should be performed, or gastrocentesis may be performed initially since it is often quicker, to remove some of the gas from the stomach. Since GDV patients are prone to DIC, it is important to check coagulation factors prior to starting this procedure. A gastrocentesis is done by inserting a 14 to 18-gauge needle or over-the-needle catheter into the stomach. The patient should be lying in left lateral recumbency to allow for the gastrocentesis to take place on the right side. The area should be clipped and prepped. Once the gastrocentesis has been performed and air has been removed, orogastric decompression can be attempted again to remove more of the air and contents.
Prior to surgery, broad-spectrum antibiotics are usually given because of the risk of gastric necrosis and perforation.
Lidocaine Treatment
Lidocaine is used in our institution for various effects in a GDV patient. Lidocaine is an effective pain-relieving substance, it is a viable option for treatment of ischaemic arrhythmias and it is potentially helpful in the prevention of reperfusion injuries.
Blood Pressure and ECG
Hypotension is usually present in the critical GDV patient. If significant haemorrhage and/or DIC are present, hypovolaemic resuscitation may be warranted until exploration. This entails careful endpoint resuscitation techniques using crystalloids and colloids/HBOC to a MAP of approximately 80 mm Hg (systolic around 100 mm Hg). The goal is to initiate some reperfusion without disturbing any clots that have formed until haemostasis is achieved surgically. A constant rate infusion (CRI) of hetastarch can be administered after resuscitation of the hypotensive animal at a rate of 0.8 ml/kg/h to help maintain blood pressure until cardiovascularly stable.
Normal to increased blood pressures is assessed with respect to intravascular volume status. Adequate or increased blood pressure may be the result of a compensatory response to hypovolaemia, and aggressive fluid resuscitation is still indicated.
Any auscultable or ECG arrhythmia should be treated with oxygen therapy. Any acid-base and electrolyte (potassium, calcium, and magnesium) abnormalities should be corrected. When improvement of perfusion does not occur, antiarrhythmics are administered. The most common arrhythmia treated is a ventricular tachycardia, and lidocaine is administered IV up to 4 mg/kg slow bolus. If this improves the rhythm, then a 50 mcg/kg/m CRI is started. Constant ECG is required.
If the blood pressure is not responsive to fluid resuscitation, dobutamine infusion (5–10 mcg/kg/m) may be required and underlying causes of nonresponsive shock investigated. Dopamine infusion (5–15 mcg/kg/m) may also be necessary. Clinical experience has shown, that animals in need of catecholamines to maintain blood pressure have decreased survival rates compared to animals that do not need catecholamines.
Oxygenation
As a result of circulatory compromise these patients may present hypoxic and also due to low blood pressure/poor perfusion have reduced tissue oxygen delivery, therefore, increasing the fraction of inspired oxygen (FiO2) will be beneficial.
Flow-by techniques are often used during the initial stages but this, particularly for larger patients, is usually only a short-term option. A useful technique is the placement of nasal oxygen catheters, which can be utilised both pre- and post-surgery. Humidification of the oxygen is important if using nasal oxygen catheters for a period of longer than 3–4 hours since this technique will bypass a portion of the patient’s upper airway. GDV patients will frequently have compromised ventilation due to the over-distension of the stomach. Sternal recumbency offers the best opportunity for a patient to ventilate itself properly but these patients are normally extremely uncomfortable and should be allowed to assume the position most comfortable for them.
Intraoperative/Anaesthesia Considerations
Pre-anaesthetic protocols vary and the individual patient should be assessed to determine what is appropriate. Phenothiazine tranquilizers (acepromazine) usually avoided as they can cause vasodilation and hypotension. Ideally, a benzodiazepine (diazepam) should be included in the pre-anaesthetic protocol because it serves as a muscle relaxant and can help reduce anxiety by slowing down the central nervous system. Other pre-anaesthetic drugs include: fentanyl and alfaxan or propofol. Propofol can cause vasodilation and respiratory distress and should be limited to those animals that have been stabilized. Once intubated, the patient should be monitored very closely, which should include ECG, blood pressure, pulse oximetry, and capnography. Mechanical ventilation may be required in order to maintain adequate oxygenation.
It is imperative that intraoperative blood pressure be maintained at a mean arterial pressure of 80 mm Hg. ‘Surgical rate’ fluids generally include using a crystalloid at 5–10 ml/kg/h. Using a CRI of analgesics may allow for a decrease in inhalant anaesthesia and help increase blood pressure. However, because some medications can cause respiratory depression it is important to have mechanical or assisted ventilation ready if needed. If the patient is hypovolaemic despite efforts (be sure that the patient is on an appropriate plane of anaesthesia), vasoactive medications should be started. Commonly dobutamine (5–20 mcg/kg/m) and/or dopamine (5–10 mcg/kg/m) are administered as a CRI to help improve cardiac contractility. If inotropic support alone does not improve blood pressure, then a pressor agent such as noradrenaline (at 0.05–0.4 mcg/kg/m) can be used.
Postoperative Considerations
Continuous or intermittent monitoring of the vital signs will detect development of hypotension and/or dysrhythmias that may require immediate therapy. Monitoring PCV/TS, glucose, BUN, albumin, electrolytes, acid/base status, and lactate levels may uncover organ decompensation. Intravenous analgesia and antibiotic administration is continued until oral feedings and medications are tolerated. The use of promotility agents such as metoclopramide and cisapride may improve gastric emptying more rapidly than without. Supplemental oxygen therapy is also recommended in the postoperative period.
Maintaining gastric decompression postoperatively is recommended in the critical GDV patient. Gastrostomy tube placement allows large volume decompression and removal of large clots that can occur with large resections. Nasogastric tubes are appropriate when gastric resection is not required. Nasogastric tubes are preferably placed intraoperatively with proper placement assured by palpation. Small volume infusion of electrolyte/glucose/glycine containing fluids feeds the gastric mucosal cells, which rely on intraluminal contents for nutrition. Placed appropriately, intestinal feeding tubes provide immediate intestinal feeding postoperatively. It allows home care if gastric feeding is not possible once the animal is ready to be discharged. It also reduces the cost of parenteral nutrition because caloric requirements can usually be supplied within a few days.
Monitoring nasogastric tube suction volumes assists in more accurately determining volumes lost. When suction volumes decrease, this may indicate when refeeding may be initiated. Infusion of a balanced electrolyte/carbohydrate solution promotes gastric mucosal healing and feeding. Regular assessment of the patient’s abdomen size is also recommended to assess for rebloating.
GDV patients can be particularly challenging and require intensive nursing care but it is these aspects of their care which make a successful outcome so rewarding.
The GDV patient is one of the most challenging but perhaps the most rewarding patient to nurse. By close observation and monitoring, good communication with the veterinary surgeon and taking the time to give TLC, all of the things that make us veterinary nurses we can have a really positive impact on the outcome of these cases.
References
References are available upon request.