Flat capnogram seen with all except aEUR'
Bronchospasm Flat capnograph is seen in :? Equipment failure Disconnection Total occlusion Accidental extubation Inadequate mechanical ventilation increased (ETCO2) Bronchospasm paial - steep platen not flat capnogram (Flat capnograph is seen in severe bronchospasm). Capnography Capnography is the monitoring of the concentration or paial pressure of CO2 in the expired gases. Its main development has been as a monitoring tool for use during anaesthesia and intensive care. Capnographs usually work on the principle that CO2 absorbs infrared radiation. A beam of infrared radiation is passed across the gas sample to fall on to a sensor. The presence of CO, in the gas leads to a reduction in the amount of light falling on the sensor which changes the voltage in the circuit. A capnogram plots CO2 concentration over time and consists of four phases : The X axis measures time and the Y-axis shows the concentration of CO2. The phase I The phase I stas with exhalation. The first gases that pass over the capnography sensor usually do not contain carbon-di-oxide because they are the gases that fill the physiological dead spaces in the "conducting airway" (Lungs, bronchic, trachea, mouth and nose). This phase is the baseline of the capnograph. Phase II Phase II is known as the expiratory upstroke and trace steep rise in CO2 level. This phase measures a mixture of dead space (No CO2) and alveolar (CO2). Phase III This phase represents the expiratory platen which represents mostly alveolar gas exhalation. The plateu is indicative of the homeostasis of the patient. The gases released at the end of expiratory plateu have the highest concentration of CO2. This is also known as the end tidal point and is what is measured with calorimetry, capnometry or capnography. Phase IV This phase reflects the inhalational phase, which brings oxygenated gases into the lung, returning the gas levels and the capnograph waveform to the beginning of a new cycle and the baseline. Clinical applications Use of ETCO2 monitoring with intubated patients: ETCO2 monitoring is useful in gauging the severity of hypoventilation states such as drug and ethanol intoxication, diabetic ketoacidosis, congestive hea failure, stroke, head injury and/ sedation. Monitoring allows ongoing assessment of the perfusion's status, changes in ventilation status and changes in air movement as measured by ETCO2, can diagnose problems with asthma, COPD, airway edema, stroke or foreign body obstruction. Verification of Endotracheal tube placement There are several ways to evaluate the placement of an endotracheal tube which are :- auscultation of lungs for bit, breath sounds and absence of sounds in the belly, visual assessment of chest movement and clouding of endotracheal tube from the exhaled air. Displacement of the endotracheal tube Displacement of an endotracheal tube is most likely to occur when moving a patient, especially when moving the patient in or out of an ambulance or when dealing with an awake or agitated patient postoperatively. Continuous capnographic monitoring rapidly identifies the problem. The typical waveform for a displaced endotracheal tubes has the normal square like fonns that would gradually, reduce and tail off to the baseline (flat capnogratn). Adequacy of cardiopulmonary resuscitation ETCO37measurement during CPR can both assess effectiveness of the CPR and predict survivability as well. Levels of ETCO2 have predictive correlation to cardiac output. As pulmonary blood flow decreases during cardiac arrest, CO2 levels in the bloodstream are decreased which can be evaluated using a capnograph waveform. Studies have shown that without a return to ETCO2 levels of 10 mmHg or more after 20 minutes of CPR there is 100% moalio. rate. Return of spontaneous circulation ETCO2 monitoring is sensitive enough to register a rapid rise in CO2 production (indicates metabolism) well before either pulse or blood pressure is detectable. Evaluation during Asthma treatment A patient suffering bronchospasm or an asthma attack will have a characteristic "shark fin" waveform. This is because the bronchospasm alters the ascending phase and the platen phase with a slower rise in CO2. The effectiveness of treatment can be quickly evaluated by observation of the waveform as it returns to a more nonnal square or step shape. Severe asthma causes flat capnograph. Head injury patient Hyperventilation can increase blood pressure and with head injury patients increased blood pressure can exacerbate cerebral edema. Monitoring of ETCO2 can assist the clinician in maintaining stable CO2 levels thus avoiding secondary injury from accidental increased cerebral edema. Acute and critical care uses In addition to confirming correct Eli placements and predicting moality following cardiac arrest, capnography can play an impoant role in the critical care setting. Capnography offers a rapid alarm for ventilator disconnection, identified by a flat line on capnogram. It also assists with early identification of a dislodged tube in an awake or agitated patients.
Accidental extubation
Bronchospasm
Dissociation of anesthetic tube
Mechanical ventilation fading