While this is a common and benign condition, its presentation, ETCO2, and capnography waveform is similar to more serious conditions.
Shortness of breath from anxiety-induced hyperventilation is caused by an excess of CO2 exhalation. Diabetic ketoacidosis (DKA) may present with difficulty breathing, rapid respiratory rate, and low ETCO2 as the body attempts to compensate for acidosis. With pulmonary embolism, a blocked pulmonary artery causes less CO2-rich blood to return to the lungs, and less CO2 is released with each breath. Other respiratory conditions can cause a low ETCO2 reading or hypocapnea. Think perfusion, metabolic or psychological problem when ETCO2 is low High ETCO2 helps predict respiratory arrest before a change in mentation and decompensation occur, and time to prepare airway equipment.
Respiratory failure from fatigue may occur even when patients inhale enough oxygen, thus having a normal pulse-ox reading. Increased work of breathing and CO2 retention may eventually lead to respiratory arrest and assisted ventilation is needed. This causes CO2 to accumulate in the lungs and more of it to be excreted with each breath (hypercapnea), which would cause the ETCO2 level to rise. In severe cases of respiratory distress, increased effort to breathe does not effectively eliminate CO2. The height of the capnography waveform accompanies this number on the monitor, as well as the respiratory rate. The amount of CO2 at the end of exhalation, or end-tidal CO2 (ETCO2) is normally 35-45 mm HG. CO2 is a byproduct of cellular metabolism, which gets transported in the blood to the lungs for elimination. Think respiratory failure when ETCO2 is highĬapnography adds objective data to physical exam findings, which helps determine the severity of respiratory distress. A rectangular capnography waveform means that there is no bronchoconstriction, and that no bronchodilator is needed. A nebulized bronchodilator would not help, and may harm, respiratory conditions not caused by bronchoconstriction. While both compromise air exchange and increase the effort needed to breathe, air still leaves the alveoli consistently and generates a rectangular capnography waveform. These causes include fluid in the alveoli, such as from CHF, and excessive mucus secretion in the lower airways, such from pneumonia or bronchitis. A nebulized bronchodilator, such as albuterol, is indicated when patients have a shark-fin waveform and bronchoconstriction to open lower airways and increase air movement.Ī rectangular-shaped waveform means that there is no constriction of the lower airways, and that there must be another cause of the patient’s respiratory distress. The more pronounced the shark fin and the longer the exhalation phase, the more constricted the lower airways are. īronchoconstriction may also cause a longer expiratory phase, seen as a longer waveform. This causes the normally rectangular-shaped capnography waveform to have a “shark-fin” appearance. With bronchoconstriction, caused by asthma, COPD, and sometimes pneumonia, air is released inconsistently from the constricted lower airways. A normal waveform is rectangular shaped, with a slight elevation during the plateau. The waveform then slopes downward at the beginning of inhalation and returns to baseline. A spike is seen when CO2-filled air released from the alveoli first passes the nose and lips, and then plateaus when all air is exhaled from the alveoli. The waveform begins at baseline when exhaled air from the dead space in the upper airway reaches the sensor, which contains no measurable CO2.
Capnography is measured with an adapter between the bag-valve device and the mask, or with nasal prongs that sample exhaled air from the mouth and nose.
The shape of the capnography waveform represents air movement through the lungs, similar to how an ECG tracing represents electrical activity in the heart.
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