Managing the acute abdomen (Part 3): postoperative management (Proceedings)

Postoperative management of acute abdomen patients includes general supportive measures and monitoring commonly performed with critically ill patients, analgesic medication, nutritional support, and specific interventions based on the underlying cause of the acute abdomen and/or the surgical manipulations employed to treat the condition. The general postoperative goals are to (1) optimize oxygen delivery and physical parameters, (2) ensure patient comfort and pain relief, (3) provide adequate nutrition until the patient is able to do so on its own, and (4) anticipate and react promptly to postoperative complications. Achieving these goals relies on appropriate vigilance and intervention, both of which may be hampered if the patient is not adequately instrumented. Hopefully, invasive instrumentations (such as central venous catheterization and feeding tube placement) were done prior to the termination of anesthesia in anticipation of postoperative need. If not, the advantages and disadvantages of employing invasive interventions in convalescing patients must be weighed on an individual basis.

Optimizing Oxygen Delivery and Physical Parameters

Oxygen delivery is optimized by ensuring adequate oxygen content of blood and establishing appropriate flow of blood to perfuse tissues. Practically speaking, that means maintaining adequate hemoglobin (Hgb) concentration and saturation and providing appropriate intravenous fluid therapy. Although there is no "standard" hemoglobin concentration to target, it is reasonable to attempt to maintain normal values [Hgb concentration = 15 g/dl; packed cell volume (PCV) = 45%]. When to use packed red blood cells or whole blood to ensure adequate PCV (and, therefore, Hgb) is based on the degree and rate of drop in PCV. As such, decisions are made on an individual basis. There is no specific target PCV or Hgb concentration, but it is usually best to keep the PCV greater than 20%. Polymerized bovine hemoglobin (Oxyglobin®, OPK Biotech, Cambridge, MA) is an alternative to blood in situations where intervention is necessary to increase Hgb concentration. In fact, there are anecdotal reports that recoveries of splenectomy patients are smoother and quicker when polymerized bovine hemoglobin is given than when it is not. Once the Hgb concentration is in an acceptable range (or even if it is not) an effort to make sure Hgb is maximally saturated with oxygen is warranted. If the patient's lungs are functioning normally Hgb should be 97 to 100% saturated while the animal is breathing room air. If not [as measured with pulse oximetry (SpO2) or arterial blood gas analysis (SaO2)], supplemental oxygen is indicated. It has been shown than many (22%) dogs experience postoperative pulmonary complications after celiotomy with approximately one fourth of these complications being transient hyopoxemia of undetermined cause; therefore, oxygen should be routinely supplemented during the first 24 hours after surgery for acute abdomen. Oxygen therapy is also indicated in patients with systemic inflammatory response syndrome (SIRS) regardless of the SpO2 or SaO2 because of increased oxygen demand. Nasal cannulation is the most efficient way to deliver oxygen in postoperative acute abdomen patients. In high risk patients the nasal tube is introduced and secured before recovery from anesthesia instead of waiting to see if oxygen is necessary, because removal of an unnecessary nasal tube poses less discomfort to a patient than introducing and securing the tube once the patient is awake.

Once the oxygen content of the blood is maximized, there must be adequate cardiac output. Although cardiac output is not frequently measured in clinical patients, indirect indicators of cardiac output such as arterial blood pressure, central venous pressure (CVP), and urine output can be monitored. Direct arterial blood pressure monitoring can be employed, particularly if an intraoperative arterial line is maintained in the postoperative period. Indirect methods (oscillometric, doppler) can be used concurrently with direct pressure measurements (to assess correlation for when the arterial line becomes dysfunctional) or in lieu of direct measurement. In most cases the target blood pressures are systolic = 120 mmHg, diastolic = 80 mmHg, and mean arterial pressure (MAP) = 90 mmHg. In patients with SIRS supranormal blood pressures are targeted. That is, an attempt is made to slightly overshoot what is normal (i.e., systolic = 140 mmHg, diastolic = 90 mmHg, and MAP = 100 mmHg). Therapeutic measures to optimize or supranormalize blood pressure include fluid therapy (often incorporating synthetic colloids), vasocontrictors (such as dopamine), and positive inotropes (such as dobutamine). Adjustments in fluid therapy are based on CVP monitoring. Because CVP is a trend monitor a baseline reading is taken and subsequent readings are performed to see if fluid rate adjustments are needed. For example, a drop in the CVP warrants an increase in fluid rate. Typically, a CVP in the "normal" range is desired. A CVP = 0 to 5 cm H2O is generally considered normal. Once again, with SIRS patients a supranormal reading (i.e., CVP = 8 to 10 cm H2O) is targeted. In the author's experience it is unusual to obtain CVP readings greater than 2 cm H2O in the early recovery period, possibly due to residual vasodilation from anesthetic agents. Low CVP may also be due to low colloid osmotic pressure (COP) necessitating synthetic colloids (hetastarch) to maintain intravascular volume. Colloid osmometry can be used to guide colloid therapy, targeting a normal COP (18 to 24 mmHg). If perfusion is adequate normal kidneys will produce urine (typically 1 to 2 ml/kg/hr). Urine output can be measured with an indwelling catheter attached to a sterile intravenous (IV) fluid bag with sterile IV tubing. Without puncturing the bag or otherwise risking contamination by disconnecting the tube, urine output can be measured by weighing the bag and subtracting the previous weight.

Ensuring Patient Comfort and Pain Relief

Patient comfort requires attentive nursing care. In the postoperative period attention to hygiene can be challenging because of the tethering effect of monitoring and feeding tube lines and the immobility of patient. Keeping the patient clean, dry, and free of soiling, and minimizing the frequency of interventions, particularly discomforting manipulations, will facilitate recovery and complement the use of analgesic medications.

Analgesic Medication

Analgesic therapy is important because abdominal pain is present at some point in each case of acute abdomen, and definitive therapy will not necessarily immediately resolve the pain. Most patients can be managed with either buprenorphine (dogs and cats) if the major source of pain is visceral (such as a distended organ), or morphine (dogs) if the major source of pain is musculoskeletal (such as abdominal wall trauma). Although morphine would likely be effective for visceral pain, potential side effects (nausea, emesis, urine retention, constipation, and greater chance of respiratory depression than buprenorphine) make morphine a less desirable analgesic for most acute abdomen cases. Currently, the most common postoperative analgesic protocol used by the author is buprenorphine given as a constant rate IV infusion (0.04 mg/kg/day) for the first 12 to 36 hours until a switch can be made to an oral opioid (or nonsteroidal anti-inflammatory drug if there are no gastrointestinal concerns). When used, morphine is most commonly given as a constant rate IV infusion (0.1 mg/kg/hr). As an adjunct to opioid analgesia, or to minimize the amount of opioids used, lidocaine (20 mcg/kg/min) may be used (dogs only) as a constant rate IV infusion for the first 12 to 24 hours. When given together for infusion, buprenorphine (or morphine) and lidocaine may be mixed in the same bag of fluids, typically normal saline or the maintenance crystalloid solution being used for fluid therapy.

Analgesics should be given as early in the course of treatment as possible, usually as soon as the physical examination is complete. Withholding analgesics for fear of masking important clinical signs should be the exception rather than the rule. Analgesics are not immediately given to animals in shock, but should be begun soon after the shock state is reversed using the same guidelines discussed above. The duration of analgesic administration may vary with the individual animal, but should be at least 24 hours in both postoperative and nonsurgical patients.

Nutritional Support

Despite the increased attention to the nutritional needs of hospitalized patients many patients with abdominal disorders fail to receive prompt nutritional support. There are many missed opportunities for jejunostomy tube placement during diagnostic and therapeutic celiotomies. Development of an "anticipation attitude" may be all that is necessary to implement prompt nutritional support for patients with abdominal conditions. Nearly all acute abdomen surgical patients should be instrumented with a jejunostomy tube because of common clinical signs seen in patients with abdominal disorders (anorexia, depression, vomiting, diarrhea, and pain) and the possibility that vomiting will occur (at least transiently) in the postoperative period. It is better to have an unneeded tube that can be removed than to need a tube after the opportunity to place it has passed.

Currently, it is thought that ill animals may not necessarily require more caloric intake than healthy animals; however, ill animals require at least the resting energy requirement (RER). Research suggests that the most accurate formula for calculating RER in dogs and cats weighing between 2 and 45 kg is: [30 × kg body weight] + 70. The formula for calculating RER in patients outside this weight range is: 70 × kg¾ . It is unusual to be able to totally meet the energy requirements of an animal that is not eating. A reasonable goal is to supply half of the RER during the first 24 hours of nutritional support and attempt to reach the full RER thereafter. Septic animals likely require something above RER. Until more definitive data is available this author recommends attempting to reach 1.5 × RER by the third day of nutritional support in septic patients. Meeting the absolute energy needs of any patient is an ideal goal that is seldom achieved. However, some nutrition is better than no nutrition and may be enough to hasten recovery to the point of oral intake, at which time the animal should be able to meet its energy needs (via oral intake plus nutritional support).

Jejunostomy tubes require liquid diets because of the small tube diameter (5 to 10 french). Jejunostomy feedings are administered via continuous infusion instead of boluses because the small intestine is not designed for acute distention. Polymeric diets are diets that require some digestion to monomeric nutrients. Monomeric diets contain nutrients that are readily absorbed with little or no digestion. Peptamen® (Baxter Health Care, Deerfield, IL) is an example of a monomeric diet. Polymeric diets are used more commonly because they are more economical than monomeric diets. CliniCare® Canine/Feline Liquid Diet (Abbott Laboratories--Animal Health, North Chicago, IL) is a polymeric liquid veterinary diet formulated for dogs and cats. CliniCare® RF Feline Liquid Diet (Abbott Laboratories--Animal Health, North Chicago, IL) is a liquid diet formulated for cats that have renal disease, but can be used in both dogs and cats with critical illnesses. The caloric density for each of the CliniCare® products is 1.0 kcal/ml. Human liquid diets can be used for short-term nutritional support in veterinary patients. Common human polymeric diets include Ensure Plus® (Ross Products Division, Abbott Laboratories, Columbus, OH), Pulmocare® (Ross Products Division, Abbott Laboratories, Columbus, OH) and Jevity® (Ross Products Division, Abbott Laboratories, Columbus, OH). Energy density is higher for Ensure Plus® (1.5 kcal/ml) and Pulmocare® (1.5 kcal/ml) than for Jevity® (1.1 kcal/ml). Pulmocare® contains lower carbohydrate than Ensure Plus® and Jevity® which is advantageous for patients with pulmonary disease because carbon dioxide production will be minimized. The advantage of Jevity® is that it is isotonic and contains fiber; therefore, it will cause less osmotic diarrhea than hyperosmolar products like Ensure Plus® and Pulmocare®.

Vigilance for Postoperative Complications

Postoperative complications can be consequences of the underlying disease and/or the surgical manipulations. Dogs are prone to ventricular arrhythmias after splenectomies and gastric dilatation-volvulus correction necessitating continuous electrocardiographic monitoring for the first 48 hours. Rarely do these arrhythmias require specific antiarrhythmic medication, but monitoring is warranted in case a life-threatening arrhythmia develops, at which time antiarrhythmic drugs become necessary. Also, electrocardiographic monitoring assists in differentiating tachyarrhythmias from sinus tachycardia, the latter of which may indicate that pain management is inadequate. After intestinal resection and anastomosis animals are monitored for dehiscence. Physical parameters such as body temperature, attitude, and abdominal tenderness are monitored to give first indication of a leaky anastomosis. Generally, it is accepted that the strength of the anastomosis should be sufficient by the fifth postoperative day alleviating the concern for dehiscence as long as the animal appears clinically normal. Diagnostic peritoneal lavage may be required to confirm or refute the presence of intestinal leakage in animals with questionable clinical status. Animals treated surgically for peritonitis sometimes have their abdominal incisions left partially open (open peritoneal drainage). These patients are prone to hypoalbuminemia and also must be observed for saturation of abdominal bandaging which may require a prompt bandage change.

The above examples are just a few of the complications related to specific abdominal conditions or surgeries. In general, meticulous attention to surgical wounds, routine monitoring of tubes and cleansing of tube exit sites, and adherence to sound nursing hygiene will afford prompt recognition of surgical complications and the opportunity for expedient intervention.