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.