Waveform Capnography Monitoring

ISBN-13: 9781616690106 43
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CONTINUOUS WAVEFORM CAPNOGRAPHY MONITORING What Is Capnography? Capnography is the sensing of exhaled CO2. Carbon dioxide is produced in the body as a by-product of metabolism and is eliminated by exhaling. By measuring exhaled CO2, many types of pulmonary assessments can be made. Continuous Waveform Capnograpy is written as PETCO2 which stands for patient end-tidal carbon dioxide. Normal PETCO2 Values: 35-40 mm Hg PETCO2 less than 10 indicates ineffective chest compressions. Potential Applications of Capnography • Detecting esophageal placement of endotracheal tubes during intubation • Detecting disconnection of the patient from mechanical ventilation • Providing sedation protection • Avoiding ABG analysis in selected clinical situations • Detecting changes in cardiac output to identify heart failure and hypovolemia • Detecting changes in dead space (e.g., pulmonary emboli) • Recognizing alveolar emptying (e.g., effectiveness of bronchodilator therapy) • Predicting survival in cardiopulmonary resuscitation Whether you are managing a critically ill patient, or stabilizing a post arrest patient, you must pay careful attention to the patient's ventilation and perfusion to ensure that adequate blood and oxygen are flowing to vital organs. A great tool to manage both, is waveform capnography, because it provides direct and indirect information to assist you in patient care. Waveform capnography directly measures the elimination of carbon dioxide from the lungs. It indirectly measures the production of carbon dioxide by the body and delivery of carbon dioxide to the lungs by the circulatory system. So it gives you direct information about the patient's ventilation status and indirect information about the patient's perfusion status. Waveform capnography devices which display both a waveform and a number will give you the most comprehensive information. Connect the monitor between the advanced airway and the bag or ventilator. Use of Capnography During Intubation Carbon dioxide is eliminated from the lungs but not from the stomach or esophagus (unless a carbonated beverage has been consumed). It is easy to determine when a tube, such as an endotracheal or nasogastric tube, has been placed in the trachea. When tracheal placement occurs, a capnogram shows exhaled CO2. If esophageal placement occurs, a flat line occurs or no CO2 is detected. Detecting Disconnection from Mechanical Ventilation Capnography is one of the fastest ways to determine if a patient has become disconnected from the ventilator. Capnography, unlike ventilator alarms,monitors the patient. Immediately upon disconnection from the ventilator, the waveform on the capnogram disappears and goes flat. Waveform capnography provides a graphic demonstration of the carbon dioxide exhaled with every breath. Humans with healthy lungs have a characteristic waveform that is divided into inspiration and expiration. Capnography is also the most reliable indicator that an endotracheal tube is placed in the trachea after intubation. Oxygenation and ventilation are distinct physiologic functions that must be assessed in both intubated and spontaneously breathing patients. The waveform is typically divided into 4 phases: PHASE 1: When the patient first begins to inhale, the curve falls sharply to zero. As the patient continues to inhale, the reading on the monitor should remain at zero because the patient should not be inhaling Carbon dioxide. PHASE 2: When the patient first exhales, the initial portion of the breath consists of the air that is in the "dead space" from the breathing tube and the trachea. As air from the alveoli begins to empty into the circuit, carbon dioxide starts to pour out. This is shown as an upward deflection at the beginning of the exhaled carbon dioxide curve. PHASE 3: As exhalation continues, carbon dioxide continues to pour out of the lungs until the next breath is initiated. Phase 4: The downward slope after the curve has peaked. The highest value in the curve is called the end-tidal CO2. For patients with normal perfusion, an end tidal CO2 reading less than 35mm Hg indicates hyperventilation. A reading of more than 45 suggests hypoventilation. In the patients with adequate circulation, the key uses for waveform capnography include the placement and monitoring of an advanced airway and the management of ventilation. In the cardiac arrest patient, waveform capnography primarily monitors the effectiveness of chest compressions during CPR and signals the return of spontaneous circulation or (ROSC). The higher the end-tidal CO2 levels are, the higher the cardiac output is during resuscitation. A reading of less than 10 mm Hg indicates the cardiac output is insufficient to achieve ROSC. If the tube is in the correct location, then the quality of CPR must be increased by minimizing interruption in compressions, achieving a speed of at least 100 compressions per minute, achieving a depth of at least 2 inches, allowing complete chest recoil, switching providers about every two minutes to avoid fatigue and avoiding excessive ventilations. Sudden changes in the waveform should trigger immediate reassessment of the patient. When the waveform jumps up during resuscitation, this may indicate ROSC. However a sudden drop in a waveform of 2- points or more could indicate a sudden, severe decrease in cardiac output that might be caused by a pulmonary embolus, acute blood loss, or a life-threatening arrhythmia. A decrease to zero indicates no gas exchange or no carbon dioxide delivery such as a displaced endotracheal tube, or the sudden stopping of blood flow such as ventricular fibrillation. Let's look at some examples that show how waveform can indicate what's happening in the patient's ventilation and perfusion status. Progressive upward trends in the waveform over time can show that the patient is being hypoventilated or hyperventilated. Hyperventilation causes cerebral vasoconstriction. A fast ventilation rate also increases mean airway pressure, which may decrease venous return to the heart and reduce cardiac output. A waveform that looks like a shark's fin shows a delay in the carbon dioxide getting to the sampler. This can be caused by a partial obstruction such as bronchospasm, upper airway obstruction or endotracheal tube kinking. A rising baseline suggests that carbon dioxide is reentering the side stream sampler during the inspiratory phase of ventilation. This reading might indicate that the patient is rebreathing carbon dioxide. This waveform has a prolonged phase 4 or inhalation section. This suggests there's air entering the trachea beyond the entryway that's being monitored. This happens if the cuff on the tube is deflated or if the tube is too small for the patient. In both the arrest patient and the post-cardiac arrest patient, ventilation and perfusion must be optimized to prevent lung injury, cerebral ischemia, and cardiogenic shock. Providing Sedation Protection The main reason a PETCO2 value increases is reduced alveolar ventilation. Obtaining a blood gas can confirm this possibility. During sedation, weaning from ventilation or managing reactive airway patients, the PETCO2 is the first indication of danger. • If the PETCO2 increases by 10mm Hg, airway protection should be implemented. • If sedation or analgesia is being administered, stop the infusion until the PETCO2 returns to near baseline or increase ventilation, if possible. • Monitor the patient simultaneously for comfort and awareness. Avoiding Unnecessary Arterial Blood Gas Testing When the PaCO2 – PETCO2 gradient is normal, the PaCO2 can be estimated from the PETCO2. It is important to note the gradient when results of ABG analysis are obtained. When using PETCO2 to estimate PaCO2, it is helpful to simultaneously measure expired ventilation (V·E). If the V·E and PETCO2 remain constant, then the PaCO2 – PETCO2 gradient is unlikely to have changed. Detecting Changes in Pulmonary Dead Space Normally, the PETCO2 level correlates closely with PaCO2. The PETCO2 is usually 1-5mm Hg lower than the PaCO2. The difference between the PaCO2 and PETCO2 is called the PaCO2 – PETCO2 gradient. Predicting Survival in Cardiopulmonary Resuscitation Exhaled CO2, specifically PETCO2, is a noninvasive indicator of cardiac output. The lower the cardiac output, the lower the PETCO2. If PETCO2 is less than 10mm Hg after 20 minutes of cardiopulmonary resuscitation, the code is almost always unsuccessful. The use of waveform capnography can dramatically enhance your ability to manage the cardiopulmonary patient.