Field Diagnostics




INTRODUCTION



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Diagnostic evaluation of patients in the field continues to see new advancements. In addition to performance of a high-quality history and examination, EMS physicians should be able to perform a number of diagnostic procedures in the field. The procedures detailed below are core EMS physician skills; however, there are a number of equipment specific diagnostic maneuvers that are beyond the scope of this chapter due to variability in equipment manufactures. In addition to the diagnostics covered in this text EMS physicians should be familiar with use of the monitor functions of their agencies’ monitor/defibrillators, thermometers, and any point-of-care testing devices the agency cares: blood glucometers, lactate meters, and minianalyzers.




FIELD DIAGNOSTIC PROCEDURES



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Below is a list of field diagnostic techniques covered in this chapter.




  • Performing a prehospital 12-lead ECG



  • Waveform capnography



  • Prehospital ultrasound



  • Compartment pressure monitoring





12-LEAD ELECTROCARDIOGRAM



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    Indications

  • Chest pain



  • Back, neck, jaw, or arm pain without chest pain



  • Upper abdominal pain or reflux symptoms



  • Syncope (or near syncope)



  • Palpitations or unexplained tachycardia



  • Dyspnea of uncertain origin



  • Diaphoresis of uncertain origin



  • Anxiety (+/− sense of impending doom)



  • Suspected electrolyte abnormalities (DKA, CRF, adrenal insufficiency)



  • Found down for unknown period



  • Crush injuries and compartment syndrome



  • Environmental injury (hypothermia, hyperthermia, electrical injury, dysbarism, submersion/postdrowning)



  • Generalized weakness




    Essential Equipment

  • Monitor/defibrillator with 12-lead capability




    Technique

  • Proper placement of the leads is important to avoid incorrect diagnosis and negative changes on the ECG (Figure 63-1).



  • Place V1 electrode at the fourth intercostal space to the right of the sternum.



  • Place V2 electrode at the fourth intercostal space to the left of the sternum.



  • Place V3 electrode in the middle of V2 and V4.



  • Place V4 electrode at the fifth intercostal space at the midclavicular line.



  • Place V5 electrode at the anterior axillary line at the same level of V4.



  • Place V6 electrode at the midaxillary line at the same level as V4 and V5.



  • Place RL electrode below the torso but above the ankle.



  • Place LL electrode below the torso but above the ankle.



  • Place the RA electrode below the right shoulder and above the right elbow.



  • Place the LA electrode below the left shoulder and above the left elbow.





FIGURE 63-1.


12-Lead ECG lead placement.





    Interpretation

  • A thorough understanding of the electrophysiology of the heart is important for interpretation of the ECG. Recognition of basic and lethal rhythms is essential. Diagnosis directs therapy which in certain cases is lifesaving. The scope of this book does not lend itself to teach ECG readings and interpretation. EMS physicians must have a mastery of basic 12-lead interpretation inclusive of rhythms identification and evaluation of ischemia, MI, conduction delays, and signs of toxicological findings.





WAVEFORM CAPNOGRAPHY



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    Indications

  • Capnography is a measure of the partial pressure of carbon dioxide (CO2) in the respiratory gases. The role of waveform capnography in the prehospital medicine setting is to assist with diagnosis, provide guide to respiratory status of the patient, and to trouble shoot ventilator issues. Indications are as follows: Evaluation of proper endotracheal tube placement



  • Evaluation of patient’s breath-by-breath ventilation respiratory status



  • Ability to determine deterioration or maintenance of airway either pre- or postintubation




    Essential Equipment

  • Waveform capnograph or capable monitored defibrillator with module (Figure 63-2)





FIGURE 63-2.


Waveform capnography on the monitor with ECG and SpO2.





    Technique

  • Connect patient end of the tubing to endotracheal tube or nasal canula device.



  • Connect monitoring end of the cannula to the waveform capnographer or capnography module for the monitor defibrillator.




    Interpretation

  • Confirmation of placement of ETT and continued ventilator monitoring of an intubated patient.




    • A standard respiratory waveform should be noted. Continuous monitoring is indicated. Loss of waveform indicates loss of endotracheal tube placement of cardiac decompensation in most cases. The airway and cardiovascular status should be immediately evaluated (Table 63-1).




  • Evaluation of cardiopulmonary resuscitation.




    • If no waveform during CPR, rule out esophageal intubation.



    • Optimize chest compression for effective CPR so that ETCO2 values are between 10 and 20mm Hg. If it is 10mm Hg or less after initiation of ACLS, poor outcomes are expected.




  • After intubation, look for CO2 waveforms during chest compressions. A flat tracing should alert for a misplaced ET tube.





TABLE 63-1

Conditions That Affect End-Tidal CO2 (ETCO2)






PREHOSPITAL ULTRASOUND



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Newer, more portable, ultrasound devices can be carried in helicopters and ambulances and may provide another noninvasive evaluation tool to providers and physicians in the field.



EFAST—EXTENDED FOCUSED ASSESSMENT WITH SONOGRAPHY FOR TRAUMA



    Indications

  • Ultrasound has become a standard of care in the diagnostic evaluation of the trauma patient. The eFAST examination is the point-of-care (POC) test used to evaluate seriously injured trauma patients. The most common indication is for thoracoabdominal trauma.




    • Identify free fluid in the abdominal cavity.



    • Identify a pneumothorax.



    • Identify a pericardial fluid/tamponade.





    Essential Equipment

  • Ultrasound machine



  • Low-frequency curvilinear probe for better penetration of tissues in the abdomen



  • High-frequency linear probe for better resolution in the thoracic cavity



  • Ultrasound gel




    Technique

  • Step 1: Lay the patient in the supine position.



  • Step 2: Use the low-frequency probe (exchange of probes delays obtaining diagnostic information).



  • Step 3: Perform the examination in a stepwise fashion, going in a clockwise or counterclockwise fashion is recommended.



  • Step 4: Scan the lung. Place the probe in the second or third intercostal space in the midclavicular line in the sagittal position. Gently slide the probe superiorly and inferiorly to look for lung sliding and comet tails (vertical artifacts from the pleural line). Then place the probe laterally at the sixth intercostal space. In M-mode, the lung sliding pattern is referred to as the seashore sign. On M-mode, the lung pulse (heartbeats pulsations of the expanded lung present when no lung sliding evident) is equivocal to lung sliding. Perform this on both sides of the lungs (Figure 63-3).



  • Step 5: Scan the hepatorenal space. Place the probe at the right lateral midaxillary line at the inferior portion of the ribs (Figure 63-4). Keep the probe pointed cephalad. Scan superiorly and inferiorly. In order for the most optimal visualization, direct the probe in an oblique direction. This visualizes the kidney in a normal anatomic position. First, look for free fluid between the kidney and the liver in the potential space known as Morrison pouch (Figure 63-5). Then, attempt to appreciate the integrity of the solid organ for possible solid organ laceration.



  • Step 6: Scan the bladder. Place the probe over the bladder in the longitudinal and transverse planes (Figure 63-6). Scan the bladder in all directions to evaluate for an intact bladder and evaluate for free fluid in the pelvis, seen posterior to the bladder in the rectovesicular space (Figure 63-7).



  • Step 7: Scan the splenorenal space. Place the probe in the left midaxillary line just beneath the thoracic ribs and slightly posterior (Figure 63-8). Direct the probe marker cephalad. Scan superiorly and inferiorly. The left kidney is slightly higher than the right kidney in comparison. In order for the most optimal visualization, direct the probe in an oblique direction. This visualizes the kidney in a normal anatomic position. First, look for free fluid between the kidney and the spleen (Figure 63-9). Then, attempt to appreciate the integrity of the solid organ for possible solid organ laceration.



  • Step 8: Scan the pericardial space. Place the probe in the subxiphoid space and rotate the probe approximately 30° to the right (Figure 63-10). Direct the probe slightly posteriorly. Look for a hypoechoic region (black stripe) between the pericardial sac and the myocardium (Figure 63-11).





FIGURE 63-3.


Lung slide. Imaging a pneumothorax. A: Rib shadowing is seen on both sides of the intercostal space. The echoic interface of the parietal and visceral pleura demonstrates the “sliding-lung” sign. B: The “sea-shore” sign. It is visible when the lung and chest wall are in contact with each other. Note the bright echogenic stripe of the pleural interface between the chest wall (“sea”) and the lung (“shore”). C: The “sea-shore” sign and the pleural interface are absent when a pneumothorax is present. (Reproduced with permission from Reichman EF, ed. Emergency Medicine Procedures. 2nd ed. New York, NY: McGraw-Hill; 2013.)






FIGURE 63-4.


Probe positioning for evaluating the hepatorenal space. Imaging of the hepatorenal recess. A: US probe placement with the corresponding US screen image. B: A view of the US beam (green) as it passes through the liver and kidney with the corresponding US image. (Reproduced with permission from Reichman EF, ed. Emergency Medicine Procedures. 2nd ed. New York, NY: McGraw-Hill; 2013.)


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Jan 22, 2019 | Posted by in EMERGENCY MEDICINE | Comments Off on Field Diagnostics
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