Monitoring of trauma patients during emergency surgery can be especially challenging for the anesthesiologist. Attempts to maintain an adequate depth of anesthesia to prevent awareness and pain can often be compromised by the unfavorable hemodynamic effects of anesthetics in patients experiencing hemorrhagic shock with ongoing bleeding. The functioning of even basic monitors may be problematic in settings of significant hypotension. Once surgical hemostasis is accomplished, resuscitative endpoints may not be clearly established and will vary depending on patient-specific factors and trauma etiology. Excessive fluid resuscitation can lead to adverse consequences that can impact patient morbidity and survival such as pulmonary edema, congestive heart failure, bowel edema, abdominal compartment syndrome, unplanned postoperative open abdomen, and airway edema. The monitoring strategy in trauma patients, as with all surgical patients, follows the American Society of Anesthesiologists (ASA) Standards for basic monitoring – that oxygenation, ventilation, circulation, and temperature should be continually evaluated. This can usually be accomplished using routine non-invasive monitors early in the surgery. However, additional (mostly invasive) monitors are often indicated and implemented in trauma patients. Ultimately, the decision to use a monitor should be based on a number of factors including: • Accuracy of the generated data • Potential complications related to generating the data • Clinical relevance of the data • Impact of the data on clinical outcome Generally, a single data point or measurement is less informative than a dataset trend, and trend monitoring can be very useful in assessing therapeutic efficacy and changes in patient status. The strategy used to guide resuscitation may affect patient outcome, and fluid therapy is an important component of this strategy. A relevant question often asked is: will the patient's cardiac output (stroke volume) be increased with a fluid bolus? Available monitors differ in their ability to predict “recruitable” cardiac output. The purpose of this chapter is to discuss the commonly available and practical monitors stratified in terms of basic assumptions and limitations that can affect data interpretation, patient risk, and, when applicable, their role in defining resuscitative endpoints.
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