Monitoring

Abstract

During a discussion I was having about near-infrared spectroscopy (NIRS )-derived tissue oximetry, an expert surgeon who has written a lot about NIRS asked, “If we could have the perfect patient monitor, what would it look like? It would be non-invasive. It would be continuous. It would be reliable. It would be inexpensive, so you could use it repeatedly on anyone and everyone. It would tell us information that we couldn’t figure out on our own. And it would not only tell us that something was wrong, it would tell us WHAT was wrong so we’d know what to do about it.” Until that perfect monitoring technology arrives, we must be intimately familiar with currently available monitoring technology and interpretation, including key pitfalls where monitor data can lead us astray in caring for severely injured trauma patients on or off the battlefield.

Civilian Translation of Military Experience and Lessons Learned

• Timothy A. Pritts 

Key Similarities

• No single laboratory value or device can replace the judgment of an experienced clinician.

• The diagnosis and treatment of partially compensated shock is a significant challenge.

• Standard monitors provide useful data, but it is the interpretation and actions taken that define the utility of ANY monitor.

• Technology will continue to make rapid advances, and the medical community must take advantage of this “golden age” in biotechnology.

Key Differences

• Weight and size of monitoring devices are of primary concern in the deployed setting but secondary concern in civilian hospital care.

• In addition, device function in extremes of weather, harsh conditions, and during ground or helicopter transport is a prime concern in the military setting.

• The military setting patient population skews more toward the younger and healthier cohorts, versus the increasing amount of elderly trauma victims in the civilian setting.

• Elderly patients may not mount an adequate cardiovascular response after hemorrhage and thus are inherently more challenging to monitor effectively.

In this chapter, Drs. Beekley and Johannigman discuss several aspects of monitoring the physiological status of trauma patients. If it existed, the ideal civilian and military patient monitor would be lightweight, noninvasive, and reliable and would provide continuous information in a way that would allow providers to determine if something was wrong as well as guidance as to how to correct physiological derangements. Unfortunately, the ideal patient monitoring system remains elusive in both the civilian and military settings.

The principal lesson from the chapter is that the best single monitoring device continues to be the brain of an experienced clinician. Several technological adjuncts are useful (and should be utilized in many settings), including pulse oximetry, electrocardiography, central venous pressure determination, central venous oxygen saturation, pulmonary artery catheterization, arterial lines, and intracranial pressure monitors (for patients with head injuries). Advanced monitoring systems, such as near-infrared spectroscopy, can provide more detailed data concerning a patient’s status through analysis of arterial pressure waveforms or tissue oxygenation status, but the data must still be integrated, interpreted, and acted upon by the clinician in order to improve patient care.

Determining volume status at the bedside remains a significant challenge. As the authors point out, in the early phases of resuscitation from hemorrhage shock, the solution is almost always to give more volume. In both civilian and military settings, it is useful to determine intravascular volume status as the resuscitation progresses. Measurement of central venous pressure , while commonly performed in the surgical intensive care unit, cannot be used to reliably determine preload or the potential hemodynamic response to further volume infusion. Pulmonary artery catheterization, while previously liberally used in the civilian setting to guide resuscitation, is less commonly used in civilian ICUs today. We feel that the best current method of determining volume status in our ICU is transthoracic echo. In the civilian setting, we have the luxury of 24 h access to this test as well as a physician skilled in its interpretation. While this is not practical in austere environments, both focused echocardiography and bedside ultrasound have been shown to be reliable and effective in assessing intravascular volume status in a method that is adaptable to austere environments. These techniques allow estimation of intravascular volume status in an efficient, reliable, and reproducible manner.

Determination of the patient’s shock status as well as monitoring resuscitation from shock is difficult in both the civilian and military settings. Traditional vital signs, including heart rate, blood pressure, and urine output, are valuable in identifying the patient with severe shock but may underestimate the physiological derangements of patients in compensated or partially compensated shock states. Identification of the physiologically “near-normal” patient is especially important with young trauma patients, who may maintain relatively normal vital signs until they reach the point of physiological collapse, as well as the elderly, who due to beta-blockade or cardiac disease may not become tachycardiac as shock progresses. As the authors discuss, determination of central venous oxygen saturation (with a central line) or mixed venous oxygen saturation (with a PA catheter), combined with arterial blood gas analysis, can provide useful data concerning the ratio of whole-body oxygen demand to oxygen delivery and help determine patients who are currently in shock. Additional helpful laboratory values include base deficit and serum lactate. Each of these is obtainable in virtually all care environments, and trends can be followed over time. When using lactate levels to guide a resuscitation, the provider must be aware that lactate clearance frequently lags the clinical picture by several hours and is also affected by hepatic function. Other strategies that have been employed in the clinical setting to guide resuscitation include gastric or rectal pH monitoring to determine the acid/base status of the viscera. Although they showed promise in clinical trials, these techniques have not become widely employed in either the civilian or military settings.

As Drs. Beekley and Johannigman point out, there is ample room for future improvement in monitoring of the trauma patient. One potentially exciting innovation is the use of arterial line-linked devices to continuously determine cardiac function parameters, including cardiac stroke volume, cardiac output, and estimates of intravascular volume status (Vigileo monitor, Edwards Lifesciences, Irvine, CA). These monitors are now in use in civilian ICUs but require a high-fidelity arterial line, which may potentially limit their utility in austere environments, especially during strategic or tactical critical care transport. Advanced versions of basic monitors, such as the Tempus Pro (RDT, Huntsville, AL), provide telemedicine capabilities and are entering into use in military and civilian settings.

The next generation of patient monitors will likely include decision support tools to offload busy clinicians. One such monitoring platform includes software to display and analyze patient data in real time and offers clinical decision support tools to maximize clinical use of available patient data (Decisio Health, Houston, TX). This platform is currently in use in a limited number of US civilian intensive care units but has the potential for widespread adaptation to austere environments as well. An additional step in patient care monitoring systems is to make them autonomous – that is, the device monitors the patient and then guides interventions based on the clinical data. Currently these systems include closed-loop control of oxygenation (currently in multicenter clinical trials) and decision support for burn resuscitation. These technological advances will have broad military and civilian applications and offer the opportunity to fine-tune aspects of resuscitation and trauma care.