Gastric dilation and volvulus (Proceedings)

Many patients present to general, emergency, and referral specialty veterinary facilities with conditions that require immediate surgical intervention. The success or failure of the subsequent surgical procedure starts when the patient is initially presented for treatment. These patients are often respiratory, metabolically, immunologically, and/or cardio-vascularly unstable. By inducing anesthesia in these patients without pre-operative evaluation and stabilization, we may be increasing their risk of adverse effects due to anesthesia. Effective pre-surgical stabilization of the emergent surgical patient is a complex process. It involves identifying what is sub-optimal in the patient. This process also involves providing the appropriate medications to improve their physical status, and carefully and thoroughly monitoring during the stabilization phase. In most instances, taking these steps will make the patient a better anesthetic candidate. A case-based discussion with focus on pre-surgical stabilization of a patient presenting with gastric dilatation-volvulus will be used to emphasize these points.

Gastric dilatation-volvulus (GDV) is a condition where the stomach becomes abnormally distended with air (dilatation) and then rotates upon its long axis (volvulus). This pathologic change in stomach conformation commonly results in a variety of life-threatening conditions. Common presenting complaints include non-productive retching, restlessness, increased salivation, abdominal distension, and weakness. Although most commonly seen in large breed dogs, GDV can occur in any breed.

Why Resuscitate Prior to Surgery

A patient that presents for gastric dilatation-volvulus is often in a state of disequilibrium. They can have changes in fluid balance, acid-base status, or electrolyte status. These alterations may manifest as abnormal blood pressure, electrical activity of the heart, or mentation. Patients that have these disturbances are at greater risk for the cardio-vascular and respiratory effects of most anesthetic agents. Anesthetics commonly decrease vascular tone, cardiac output, and/or respiratory drive in a dose-dependent manner. When this occurs, oxygen delivery to the tissues is decreased. This can lead to acid-base and electrolyte disturbance and subsequent cellular injury and death.

The physiologic response to pain can also alter a patient's equilibrium. Pain can lead to changes in blood pressure, heart rate, or respirations. Due to these effects, the patient can develop further abnormalities in acid-base status, electrolyte balance, and oxygen delivery.

The sum total of these alterations can be poor tissue perfusion and circulatory shock. The severe gastric distention causes significant increases in intra-abdominal pressure. This can lead to obstruction of the caudal vena cava and results in decreased venous return and cardiac output and decreased blood flow to the splanchnic and genitourinary viscera. The rotation of the stomach commonly leads to rupture of the short gastric and epiploic vessels, causing significant hemorrhage and further exacerbating hypovolemia.

Shock is a condition of abnormal perfusion of tissues which leads to a critical decrease in oxygen delivery (DO2) and/or an increase in tissue consumption of oxygen (VO2) and results in altered cell metabolism, cell death, and organ malfunction or failure. However, hypotension is not a sign of shock and is only observed in the later stages of shock. Shock has multiple stages. These stages are the compensatory stage, the early decompensatory stage, and the terminal decompensatory stage. In the compensatory stage, the body senses changes in blood flow and responds by vasoconstriction, increased heart rate and increased strength of heart contraction. Because of these compensatory mechanisms, blood pressure is maintained and it is possible to miss this stage. As low blood flow persists, there is reduced blood supply to the skin, skeletal muscle, gastrointestinal tract and kidneys and ischemic injury to these organs. With prolonged poor blood flow, leads to severe tissue hypoxia and multiple organ failure. This is the terminal decompensatory stage of shock and often ends in cardio-pulmonary arrest. Because the GI tract is the shock organ in the dog, bacterial and endotoxin translocation through the damaged gastrointestinal mucosal barrier into the bloodstream occurs and septicemia may ensue. This septicemia can further exacerbate the shock by inducing inflammatory cytokine release. By addressing the potential or documented shock, acid-base abnormalities, electrolyte abnormalities, and pain early in the stabilization process, damage to tissues far from the affected organ system can be minimized, presenting a patient that is less likely to have complications while receiving general anesthesia.

How to Effectively Resuscitate the GDV Patient for Emergency Surgery

When a patient first presents with suspected gastric dilatation-volvulus, the initial step in the stabilization process is identifying and correcting abnormalities in a patient's status. Identification is accomplished via primary survey examination, laboratory evaluation of venous blood gas and electrolytes, and monitoring of blood pressure/blood flow and cardiac conduction (ECG). Pre-fluid blood samples are collected for evaluation by patient-side rapid tests such as packed cell volume (PCV), total solids (TS), electrolyte, venous blood gas, lactate, and coagulation parameters. Pre-fluid blood samples are also collected for analysis of serum biochemical profile, complete blood count, and urinalysis to be performed once time permits. Pre-fluid laboratory values provide baseline data from which subsequent values are compared to and monitored. Therapy should be initiated simultaneously and directed at attempting to normalize these parameters prior to induction of anesthesia.

The mainstay of stabilization therapy for gastric dilatation-volvulus involves the provision of fluid support. Fluid therapy increases vascular volume, thereby improving perfusion. This improved perfusion often improves many of the global perfusion abnormalities that are initially noted. Bolus fluid therapy is indicated in the severely volume depleted patient (absolute or relative). In the intravascular volume depleted patient, the volume of the fluid bolus and number of fluid boluses needed are determined based on resolution of clinical signs and normalization of measured parameters. This process is called goal-directed resuscitation, where therapy is directed to pre-determined end points. The patient should be re-assessed after each bolus to determine if the bolus has been effective in resolving the volume depleted state or if additional boluses are needed. Proper monitoring of the patient receiving fluid therapy is a hands-on endeavor. Much of the information we need is gained through serial examinations. No single parameter evaluated will necessarily provide all the information required to guide fluid therapy. Physical examination parameters that should be evaluated include a patient's weight, mentation, skin turgor, pulse rate and quality, respiratory rate and effort, serial lung auscultation for rales, mucus membrane color, and capillary refill time. If an indwelling urinary catheter is in place, serial evaluation of fluid input and urine output can provide significant information regarding whether too little or too much fluid therapy is being administered. Renal chemistry parameters (BUN, creatinine) in conjunction with urine specific gravity measurement provide additional information. Venous blood gas analysis and serum lactate measurement are other patient-side laboratory parameters that can provide information regarding tissue perfusion. Just as important, blood pressure/blood flow monitoring can provide valuable information to assess the patient's response to fluid therapy and whether sufficient fluid therapy has been administered to provide for tissue perfusion.

Crystalloid fluids are the most commonly administered therapy for resuscitation. Replacement crystalloid solutions contain dissolved solutes that approximate the solute concentration found in plasma water. These solutions are indicated for the rapid replacement of intravascular volume and electrolytes as seen with shock and hemorrhage. With replacement crystalloid fluids, only 20-25% of the infused volume of fluid remains within the intravascular space 1 hour after infusion. Therefore, large volumes of replacement crystalloids need to be administered to replace intravascular volume. The commonly available replacement solutions include normal saline (0.9% NaCl), Ringer's solution (lactate or acetate), Normosol R, and Plasmalyte A. Alone, repeated crystalloid boluses of 20-30ml/kg are administered until resuscitation goals are met. However, crystalloid fluids are often administered along with colloids to augment their vascular volume expanding effect.

Colloidal fluids are high molecular weight compounds that do not readily leave the intravascular space. They exert their effect of expanding intravascular volume by holding and potentially drawing water into the vasculature. Colloid fluid solutions are indicated for the treatment of hypovolemia and sepsis, among other conditions. Colloid solutions include plasma, human serum albumin (5% and 25%), canine specific albumin concentrates, and synthetic compounds such as hetastarch, dextrans, and Oxyglobin™. Synthetic colloids are administered in boluses of 5-10 ml/kg. When used in conjunction with colloids, smaller replacement crystalloid boluses of 15-20ml/kg are used. The maximum dose of hetastarch should not exceed 20ml/kg and of Oxyglobin™ should not exceed 30ml/kg.

ism has not been fully elucidated. Due to the sodium rapidly diffusing out of the vasculature, the effect of HYS is very transient (lasts up to 30 minutes). Hypertonic saline (7.2%) at doses of 3-5ml/kg is commonly used to rapidly increase intravascular volume. To prolong this effect, HYS is often combined with a colloidal fluid to help keep the fluid that has shifted from the extravascular space in the vascular space. Replacement crystalloid fluids should be administered after hypertonic saline infusion to replace the fluid that was translocated into the vasculature. Contra-indications for hypertonic saline include patients that are dehydrated (inadequate fluid to draw into intravascular space), hypokalemia, that may develop problems with hypervolemia (pre-existing heart or lung disease), or that have uncontrolled hemorrhage.

Supplying supplemental oxygen therapy to the pre-surgical GDV patient is recommended. Many of these patients do not have diseases to the lungs but supplemental oxygen therapy can still be benficial. Many of these patients have increased tissue oxygen demand and decreased oxygen flow to vital tissues. Incremental increases in oxygen supply provided by supplemental oxygen therapy can have benefit to tissues that are receiving marginal blood perfusion. There is very little downside to providing supplemental oxygen to the patient as this form of therapy is not toxic in the short-term. Supplemental oxygen therapy can be provided in a variety of ways. The most common ways initial oxygen support is provided is by flow-by or a mask with or without a diaphragm. Both of these methods have the potential to be effective (FiO2 30-50%); however, high flow rates are needed. Nasal prongs, nasal cannulas, and oxygen hoods are easy devices to place and can provide up to 70% oxygen enriched environment with smaller oxygen flow rates.

Hands-on monitoring of the patient receiving supplemental oxygen includes evaluating the patient's rate and effort of breathing, mucus membrane color, and auscultation of the thorax. The advantage of hands-on monitoring is the ability to make a rapid assessment and thus respond quickly. However, in some instances, a patient may not be ventilating adequately but only subtle clinical signs are present. For example, a patient may have pink mucus membranes, a slightly increased respiratory rate and effort, and slightly increased broncho-vesicular lung sounds. These changes may be attributed to pain but also may be subtle signs of a ventilation problem. Serial arterial blood gas analysis, pulse oximetry and capnography may assist in making these determinations.

Pain is an unpleasant sensory and emotional experience associated with actual or potential tissue damage. Pain is now becoming the fifth vital sign in patient evaluations. The assessment of animal pain is more complex than the assessment of non-neonatal human pain. It involves both behavioral and physiological responses. The outward signs of pain in animals often involve changes from normal. This is further complicated by what is the normal baseline response in a patient we are not always familiar with when they were normal. Changes in behavior, neurologic status, cardio-vascular status, respirations, gastro-intestinal function, or musculo-skeletal function can all be signs of pain. There are many different scales that allow individuals to subjectively and objectively assess pain. Still, good judgment should be used for the patient's benefit and we encourage the administration of multimodal analgesia for the pre-surgical GDV patient's benefit.

Finally, emergent pre-surgical GDV patients should receive antibiotics prior to anesthesia and surgery. These patients may be immune-compromised due to the disease process and/or shock they are experiencing. Also, the gastro-intestinal tract may have experienced ischemic injury secondary to the volvulus and hypoperfusion, leading to the possibility of bacterial translocation. Additionally, hypothermia is often a consequence of general anesthesia. Hypothermia can decrease the effectiveness of an immune response. A broad-spectrum antibiotic is usually all that is warranted unless indicated via culture.

Complete gastric emptying via oro-gastric intubation prior to surgery is an area of controversy. By performing gastric decompression prior to surgery, intra-abdominal pressure may be relieved earlier in the disease course, which will improve ventilation and perfusion parameters. However, by delaying gastric decompression until the stomach can be visually evaluated will make iatrogenic trauma to a compromised gastric wall less likely. Percutaneous trocarization of the stomach to provide some decompression during initial resuscitation may be performed, providing some immediate pain relief with less anxiety. The lateral abdominal wall is percussed and the most tympanic/resonant area is trocharized. Risks associated with trocarization include puncture of intra-abdominal organs, including the spleen.

By paying close attention to the pre-surgical patient's fluid balance, perfusion, acid-base status, electrolyte status, immune status, and managing the patient's pain, we can improve their readiness for anesthesia and surgery. This, in turn, will reduce anesthetic and post-anesthetic complications and improve outcomes.

How to Prepare the GDV Patient for Emergency Surgery

To minimize the time under anesthesia, patient preparation for surgery is performed prior to the induction of anesthesia. Rapid intravenous anesthetic induction is performed to immediately control the airway. Induction agents with rapid onset of anesthesia and minimal cardio-respiratory depressing effects are preferred. Because the amount of pressure placed on the diaphragm by the dilated stomach will hinder effective chest expansion, assisted ventilation is recommended regardless of spontaneous ventilatory efforts.

Appropriate intra-operative monitoring includes both hands-on and machine monitoring. Hands-on monitoring includes checking anesthetic depth, heart rate via esophageal stethoscope, and palpation of pulses. Machine monitoring includes continuous ECG for dysrhythmias; blood pressure monitoring, especially when the stomach is decompressed completely and the pressure on the central vein is released, as this can lead to a sudden decrease in preload and subsequent acute hypotension; capnography to assess ventilation; and pulse oximetry to look for trends of change in hemoglobin oxygen saturation.

Intra-operative laboratory evaluations augment the hands-on and machine monitoring. Arterial blood gas analysis confirms that the instruments are working adequately and allow an assessment of the pH status. PCV/TS are essential in assessing the need for red blood cell and/or plasma transfusions, especially in the actively hemorrhaging patient. Lactate levels that are not decreasing following adequate fluid resuscitation suggest continued maldistribution of blood flow and may portend a poorer prognosis.

Emergency Surgery in the GDV Patient

A ventral midline abdominal incision from xiphoid to pubis is made. This approach allows adequate exposure for complete evaluation of the abdominal viscera. Oro-gastric intubation is attempted by gently guiding the tube into the stomach after palpation of the gastric antrum and cardia. Most patients with gastric dilatation-volvulus have their stomach rotated with the pylorus traveling ventrally and to the left, so one hand is used to press the right side of the dilated stomach down and the pyloric region is grasped with the other hand and gently pulled up ventrally and to the right. If oro-gastric intubation is not possible and the stomach is not able to be placed back into a normal anatomical position, a large bore needle can be attached directly to a suction apparatus for gas and fluid removal. If there is a large amount of ingesta or foreign material within the gastric lumen, a gastrotomy is performed and the ingesta removed.

Hemorrhage is controlled with packing and/or ligation. Any area of stomach wall with questionable viability is noted, and the rest of the abdomen is evaluated. Gastrectomy may not be required once blood flow is re-established, but it may take several minutes for perfusion to return. The spleen is often congested. Evaluation for thromboses is made by palpation of the splenic arteries and inspection of the color of the parenchyma. Lack of palpable splenic arterial pulse or dark-purple color means the tissues have lost their blood supply and a partial or complete splenectomy may be warranted. The liver, pancreas, intestines, and genitourinary organs are evaluated for pathology.

Once abdominal viscera evaluation is completed, the stomach is inspected again. Most commonly trauma to the gastric wall occurs along the fundus and cardia. If there are any black or dark purple regions, these should be resected. Any area that does not bleed bright red blood is suspect and should be removed. Large invaginations of ischemic tissues are not recommended because of potential life-threatening hemorrhage that can occur when the tissues slough. In contrast to the serosa, when the mucosa is black resection is not always necessary. The mucosa will regenerate if there is a healthy submucosa. Postoperative monitoring for intra-gastric hemorrhage is important. The spleen is again inspected and either partially or completely removed if areas of infarction are present.

The type of gastropexy performed is dependent on the surgeon's preference and the time involved. If there has been any removal of gastric tissue, a tube gastrostomy/gastropexy, or combination tube gastrostomy and incisional gastropexy should be performed to permit continuous decompression and microenteral nutrition administration. Most catastrophic GDV patients will require adequate postoperative decompression, making gastrostomy tube placement necessary. If the stomach is left intact, any gastropexy is acceptable. The incisional gastropexy is a rapid procedure and provides reliable adhesion formation. It is not recommended to suture the gastric wall to the linea alba, even in the critical GDV patient. Any future abdominal surgeries will be severely compromised by the adhesions formed.

Maintaining gastric decompression post operatively 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. Naso-gastric tubes are appropriate when gastric resection is not required. Naso-gastric tubes are preferably placed intra-operatively with proper placement assured by palpation. Small volume infusion of glucose containing electrolyte solutions feed the gastric mucosal cells, which rely on intra-luminal contents for nutrition.

Copious saline lavage and suction of the abdomen is necessary prior to abdominal closure. A routine 3-layer closure is performed. Any evidence of peritonitis warrants culture and sensitivity of the peritoneum and abdominal drainage.

Post-operative Care of the GDV Patient

Due to loss into the GI tract, the post-operative GDV patient may continue to require large volumes of fluid replacement. Continuing colloidal infusion at a maintenance rate promotes intravascular fluid retention during the healing process. Monitoring the volume of fluid removed via gastric decompression assists in more accurately determining volumes lost. When suction volumes decrease, this may indicate when oral alimentation may be initiated. Infusion a balanced electrolyte/carbohydrate solution promotes gastric mucosal healing and feeding.

Continuous or intermittent monitoring of the vital signs, as well as continuous ECG and blood pressure monitoring will assist in detecting hypotension and/or dysrhythmias, especially if splenectomy is performed, that may require immediate therapy. Monitoring PCV/TS, glucose, BUN, albumin, electrolytes, acid/base status, and lactate levels may uncover organ decompensation.

Intravenous analgesia 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 their use.