Non-Intrusive Evaluation of Trauma Patients

NON-INTRUSIVE EVALUATION OF TRAUMA PATIENTS

Anthony Sances, Jr" James J. Ackmann, San ford J. Larson, Joseph F. Cusick David C. Hemmy, Robert A. HoIst, Leonard Worman, Joseph H. Battocletti Victor Bernhard, Ronald Barr, Bernard Cohen, Sergio S. Cunha, Enrique Bravo-Fernandez The Medical College of Wisconsin Wood Veterans Administration Center Milwaukee, Wisconsin ABSTRACT

DESCRIPTION OF THE AUTOMATED SYSTEM

An automated, non-invasive computer assisted system for following trends in the electroencephalogram (EEG), somatosensory evoked potentials (SSEP), transcranial impedance (TCI), transthoracic impedance (TTI), and conventional variables has been developed for use in the trauma patient with head injury. The clinical evaluation is based on a percentage of normal. All physiologic data is stored in the computer system for graphical display on a video monitor. Preliminary findings show a correlation between EEG activity, SSEP, and severity of neurologic dysfunction. TCI is reduced in most patients with head trauma. TTI changes are observed secondary to fluid accumulation in the lungs.

The monitoring system (Figure 1) is computer based, using a LINC 8 computer with 8K of memory. The computer area equipment is shown (Figure 2). The bedside equipment (Figure 3) includes a constant current stimulator, two evoked potential amplifiers, EEG amplifiers, transcranial, transthoracic and peripheral impedance monitor, temperature monitor, pulse rate monitor, an arterial blood pressure transducer, an on-line ' PC0 2 monitor, and intracranial pressure monitor.

INTRODUCTION The physiologic evaluation of patients with trauma greatly depends upon clinical assessment and intrusive techniques. Technological advances in electronic instrumentation and system design are sufficiently advanced to permit a substantive evaluation of patients with trauma. A non-intrusive serial evaluation of the trauma patient can provide a safe and rapid physiologic evaluation. An automated system for measuring somatosensory evoked potentials (SSEP), electroencephalograms (EEG), transthoracic impedance (TTI), transcranial impedance (TCI) and the evaluation of the circulatory system using nuclear magnetic resonance blood flow measuring techniques has been evaluated in our laboratories. Arterial blood pressure, on-line PC0 2 , intracranial pressur~ pulse rate and body temperature are also used to follow patients with multiple trauma. A craniotomy checklist has been designed for the clinical evaluation of the patient for comparison with the physiologic data. Patients with clinical degeneration are graded on an absolute scale relative to 100 percent. The computerized system design was based on previous physiologic studies by others and those done in our laboratories. (1,2,3) Patients with multiple trauma including intracranial hematomas, penetrating wounds of the brain and closed head injuries of varying severity were among those studied in the special automated Intensive Care Unit located in the Milwaukee County General riospital. (4) Patients with stroke were studied at the Veterans Administration Center, Wood, Wisconsin.

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The computer and recording hardware are remotely located and connected to the bedside equipment through cables and conduits. Raw data can be recorded on magnetic tapes or displayed on a strip chart recorder. Evoked potentia Is and graphs of other variables versus time are generated on a digital plotter. Printed data summaries are obtained on a high speed printer and current data are displayed numerically at the nurses' station on a video tape monitor. A graphical display of the most current three hours of data can be called up on the video monitor. Transcranial, transthoracic and peripheral impedance is measured with a 4-electrode system. The system uses either disposable EKG or needle electrodes. For transcranial impedance, the electrodes are placed bilaterally on parasagittal planes approximately one centimeter medial to the mid orbital lines. The anterior pair of electrodes are positioned approximately two centimeters above the supraorbital ridges and the posterior electrodes are placed approximately two centimeters above the inion. A one kHz 25 microampere sinusoidal current is passed from the right anterior to the left posterior electrode. The resulting voltage drop is therefore proportional to the impedance. A similar technique is used for transthoracic impedance with electrodes placed on the mid axillary lines. Peripheral impedances are measured using the conventional 4 electrode method. EEG and evoked potentials are recorded from scalp electrodes placed bilaterally in parasagittal planes three cms lateral to the midline. Three electrodes are placed on either side at five cm intervals. Either collodion applied or needle electrodes are used for recording. The center electrode is indifferent and located midway between the orbital ridge and external occipital protru-

berance. Recordings are bipolar with the anterior electrode positive. The EEG is recorded with the previously described scalp electrodes. One-minute epochs of EEG from either side are separated into several frequency bands by means of a peak amplitude detection system. Percentage of activity in the canonical frequency bands of 0.5 to 4 Hz (delta), 4 to 8 Hz (theta), 8 to 13 Hz (alpha), and 13 to 20 Hz (beta), are determined for a one-minute epoch. In addition, the mean frequency and average amplitude are computed and displayed. Zero crossing analysis was used for the serial evaluation of the stroke patients. One centimeter diameter, stainless steel disc electrodes are used for stimulation of peripheral nerves for the evoked potential studies. One electrode is placed over the median nerve at the flexion crease of each wrist, while the other is five centimeters proximal to it. A rectangular current of approximately 4 Hz of 0.4 msec duration is used. The amplitude is increased until a motor response is obtained. This usually occurs at 5 to 10 mA peak current levels. A synchronizing pulse is delivered to the computer with each stimulus pulse. Typically, 200 responses from the contralateral scalp are averaged using an analysis interval of 100 msec. The program is sufficiently flexible so that 1/4 second and 1/2 second analysis times can be done. Both mean amplitude and variance are calculated permitting the statistical comparison of different responses. The system can accommodate photic and auditory stimuli. In some patients, off-line evoked potential studies were done with a CTC-2000 averaging computer (Figure 4).* An intra-arterial catheter is used for simultaneous measurement of PC0 and arterial blood pres2 sure.** Intracranial pressure is monitored with a subarachnoid screw and a conventienal pressure transducer. Monitoring proceeds automatically. Any combination of variables can be selected at the computer console. The sampling epoch is 10 minutes; however, this can be easily modified. The first three minutes of each epoch are used to evaluate all variables except the EEG and evoked potential. Average values of these variables for the three minutes are calculated and considered representative of the entire 10-minute epoch. One minute epochs of EEG from both sides are then analyzed. The numerical data are displayed at the nurses' station and this cycle is repeated every ten minutes. During every third or sixth

*The CTC-2000 averaging computer is manufactured by the Clinical Technology Corporation, Kansas City, Missouri. **Developed by the Medical Systems Division of General Electric, Milwaukee, Wisconsin

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epoch (30 or 60 minutes) evoked potentials are recorded from each side of the head in response to stimulation of the contralateral median nerve. Evoked potentials are graphed by the digital plotter. A program is being developed to numerically display the amplitude, latency, and type of waveform for evaluation of the trends in the evoked potential. The following sections present a brief review of the findings of evoked potentials, EEG, impedance, and nuclear magnetic resonance studies done in our laboratories with some reference to the works of others. Since PC0 , arterial blood pressure, 2 pulse rate and temperature are standard measurement variables, they will not be discussed. EVOKED POTENTIAL FINDINGS Somatosensory evoked potentials recorded serially in patients with head injury and those following elective surgery showed the following: 1. In patients with volume occupying lesions such as brain tumors and intracranial hematomas, evoked potential waveforms were essentially monophasic with attendant periodic fluctuations of the general evoked potential configuration. (4) 2. In patients secondary to cerebral ischemia, evoked potentials were markedly reduced in amplitude, but without significant modification in latency of the primary component. (5,6) 3. Evoked potentials frequently showed marked changes in configuration prior to observable clinical changes. 4. Furthermore, the evoked potential observations were useful for the medical management of patients and often precipitated additional medical or neurosurgical procedures. Evoked potential studies in more than thirty patients with head injury have shown that this method is valuable in evaluating early changes in neurologic function. More than 2,000 evoked potential studies have been done in patients in our laboratories. (7) A system for pattern recognition of evoked potentials useful for rapid evaluation of neurologic dysfunction is being designed. ELECTROENCEPHALOGRAPHIC STUDIES The EEG studies in patients with head injury have shown an increased amount of low frequency activity in the delta range with an attendant decrease of high frequency activity. (4) The increase of low frequency activity often accompanied the changes in evoked potentials previously discussed. Furthermore, these changes were frequently observed prior to obvious clinical changes. Similarly, in studies done on 25 normal subjects and 30 patients with stroke, we found a two to three times increase in percentage activity in the delta range of those patients with stroke in contrast to the normal subjects. An increase in low frequency activity was observed in those patients whose clinical condition worsened while a decrease

in low frequency activity was seen in patients during recovery . (8) While the studies in stroke patients were not done continuously, nevertheless, the changes observed in EEG were similar to those in on-line studies of patients with head injury. TRANSCRANIAL IMPEDANCE STUDIES In a study of transcranial impedance in 310 volunteers, we found an average impedance of approximately 87 ohms with range of impedance of 55 to 112 at a standard deviation of 11 ohms. In patients with head injury, the transcranial impedance varied from 25 to 65 with an average value of 40 ohms. Some patients with brain tumor had abnormally low transcranial impedances. A transcranial impedance increase of 10 to 20% was observed in monkeys given Urea or Manitol. Three patients who had been given Manitol showed an increased impedance of 10 to 20% . While transcranial impedance following surgery has been complicated by scalp edema, recent studies suggest that it should be possible to establish a baseline impedance for a normal individual using various electrode regional impedance measuring techniques to determine the effect of cerebral edema upon the measured values of impedance. TRANSTHORACIC IMPEDANCE STUDIES In dog studies in our laboratories, impedance changes up to 30% were observed prior to abnormal elevation of pulmonary wedge pressure secondary to IV infusion of 3% saline or normal saline with 25 grams of albumin per liter. Changes in thoracic impedance could be observed in the canine secondary to approximately 25 mls. of intravascular fluid infusion. Studies done by others have shown that measurement of transthoracic impedance in patients has been helpful in determination of interthoracic fluid volume. (9,10,11) Therefore, this system is being studied to determine its utility in following transthoracic changes in the patient with multiple trauma. PERIPHERAL IMPEDANCE STUDIES Research in our laboratories and that of others has demonstrated the feasibility of detecting peripheral vascular disturbances using impedance techniques. (9,12,13,14,15) Studies in our laboratories in approximately 200 patients shows that this method holds promise for early detection of deep vein thrombophlebitis and other peripheral vascular problems. NUCLEAR MAGNETIC RESONANCE FLOWMETER STUDIES Studies in our laboratories have been conducted to measure blood flow in the radial artery in humans and those from the region of jugular bulb subsequent to magnetic depolarization of blood at the confluence of the sinuses. These studies have demonstrated that blood flow can be obtained from the human subject using nuclear magnetic resonance techniques and that this method holds promise for monitoring patients with multiple trauma. Systems

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for on-line measurement of flow in peripheral limbs and cerebral structures are under construction. (16) SUMMARY The automated system for measuring somatosensory evoked potentials, transcranial impedance, transthoracic impedance, peripheral impedance, and electroencephalographic potentials have been helpful in following clinical changes in patients. Furthermore, many of these physiologic changes have occurred prior to clinical observations and have been helpful in the management of the patient with multiple trauma. ACKNOWLEDGEMENT This research was supported in part by National Institutes of Health Grant No. GM19680 and Contract No. HL70-2216 and by United States Army Medical Research and Development Command Contract No. DADA17-71C-1093. REFERENCES (1) Sances, A. , Jr., Llaurado, J.G., Larson, S.J.: Instrumentation and methods in clinical and research medicine: A collaborative program Marquette University/Medical College of Wisconsin, Medical Progress Through Technology 2:157~170, 1974. (2) Sances, A., Jr., Llaurado, J.G., and Larson, S.J.: Clinical research as a guide to curriculum. Chapter in The Practice of Clinical Engineering - Its Sources, Status and Implementation, James C. Aller, ed., Academic Press (In Press). (3) Ackmann, J.J., Larson, S.J., Sances, A., Jr., Reigel, D.H., Battocletti, J.H., Jarzembski, W.B., Dallmann, D.E., Bowman, R.L., Kudravcev, V.: Computerized non-invasive monitoring of the trauma patient, Proc 25th Ann Conf Eng Med Biol 14.6, October, 1972 . (4) Larson, S.J., Sances, A., Jr., Ackmann, J.J., Reigel, D.H.: Non-invasive evaluation of head trauma patients, Surgery 74:34-40, 1973. (5) Larson, S.J., Sances, A. , Jr., and Baker, J.B.: Evoked cortical potentials in patients with stroke, Circulation 23(Suppl. 11) :15-19, May 1966. (6) Larson, S.J., Sances, A., Jr., Christenson, P.C.: Evoked somatosensory potentials in man, Arch Neurol 15:88-93, July 1966. (7) Sances, A. , Jr., and Remond, A.: Quantitative neurologic evaluation - Workshop report in Automated Multiphasic Health Testing, C. Berkley, ed., Engineering Foundation, New York, 1971, pp. 101-108.

(8) Cohen, B.A., Bravo-Fernandez, E.J., Sances, A. Jr., Makowski, G.G., Saltzberg, B.: Computer analysis of electroencephalograms on stroke patients, Proc 27th Ann Conf Eng Med Biol, Philadelphia, Pa., 16:18.3, Oct. 6-10, 1974 . (9) Farman, J.V. et al: Impedance spirometry ir. clinical monitoring, Brit Med J 4:27-29, 1967. (10) VanDeWater , J.M., et al: Bioelectric impedance: New developments and clinical application, Arch Surg 102:541-547, 1971. (11) Pomerantz, M., et al: Clinical eva luation of transthoracic electrical impedance as a guide to intrathoracic fluid volumes, Ann Surg 171:686-691, 1970. (12) Couch, N.P., et al: Non-invasive measurement of peripheral arterial flow in the clinical setting, Arch Surg 102:435-439, May 1971.

figure 2.

Computer equlp1llent .

(13) Allison, R.D.: Clinical applications of impedance plethysmography, Clin Med 74:33-41, 1967. (14) Wheeler, H.B., et al: Diagnosis of occult deep vein thrombosis by a non-invasive bedside technique, Surgery 170 :20-28, 1971. (15) Derblom, H., et al: Electrical impedance plethysmography as a method of evaluating the peripheral circulation, Acta Chir Scand 136 :579-586, 1970. (16) Battocletti, J.H., Sances, A., Jr., Larson, S.J., Evans, S.M., Bowman, R.L., Kudravcev, V., and Ackrnann, J.J.: Clinical applications and theoretical analysis of NMR blood flowmeter, Biomedical Engineering 10:12-20, Jan. 1975 .

Figure J.

Bedside equiptnent.

Video display (nurses station)

Flgure 4,

Figure 1.

Block diagram of monitoring system.

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Clinical Technoloqy Corporat.lon Model .2000 averaging computer used for off-ll.ne studies.