End Tidal CO2 and Capnography in EMS Bonner County EMS
Definitions • END Tidal CO2 – patient’s exhaled carbon dioxide. Normal values range between 35 and 45 mmHg • Capnography – refers to the graphic waveform displayed showing the levels of CO2 during the various phases of respiration. • pH – measurement of the acidity or alkalinity (base) in blood. Based on a scale of 14, a pH of 7.0 is neutral. A pH below 7.0 is an acid; the lower the number, the stronger the acid. A pH above 7.0 is a base; the higher the number, the stronger the base. Blood pH is slightly alkaline (base). Normal range is 7.36-7.44.
Definitions • Respiratory acidosis – a pH less than 7.36 caused by an impairment of the gas exchange process (oxygen for carbon dioxide) in the lungs. Impaired ventilation is a common cause • Metabolic acidosis – a pH less than 7.36 caused by bodily process other than respiratory impairment. • Respiratory Alkalosis – a pH greater than 7.45 caused by a respiratory rate and/or function that exceeds the bodily need for removal of CO2. Most common cause is hyperventilation. • Metabolic Alkalosis - a pH greater than 7.45 caused by vomiting, the use of steroids or diuretic drugs, or the overuse of antacids or laxatives.
To monitor respiratory status • Problems in oxygenation will show almost instantly as a high ETCO2 reading while Pulse Oximetry will be delayed. • Anything but a square waveform indicates some type of problem. • Normal or high ETCO2 during hyperventilation suggests a pathology versus low ETCO2 which is suggestive of anxiety. • It can be used as a bio-feedback device to help patients slow respirations
Seizure patients • In seizing patients a low ETCO2 indicates inadequate respirations and they should be managed aggressively. • Normal waveform in normal ETCO2 range calls for less aggressive interventions.
COPD, CHF and Asthma • If the waveform is not shark fin, then bronchodilators may do more harm than good. • If the shark fin does appear, then bronhcospasm is present and treatment with bronchodilators is indicated.
Intubation • An ETCO2 waveform corresponding to administered ventilations is considered to be a definitive sign of proper placement. It should be combined with positive breath sounds and absent gastric sounds. • A dramatic drop during intubated ventilations may signal a kinked tube or a tube impaired by secretions. • If a RSI patient restarts their respiratory efforts the waveform will reflect this signaling a need for additional medications.
CPR and ROSC • During CPR a steady decrease in ETCO2 and waveform size may be the result of CPR responder fatigue. • Maintaining and monitoring high levels of ETCO2 during CPR is a great real-time feedback mechanism for providers doing compressions. • A sudden dramatic increase in ETCO2 is a strong indicator that pulses have been regained. • ETCO2 less than 20 mmHg throughout the duration of a code signals a poor outcome.
Metabolic Conditions • Low ETCO2 (less than 29 mmHg) in the absence of respiratory abnormalities is a sign of metabolic acidosis. • A 2002 study showed that 95% of diabetic children entering the ER with an ETCO2 reading less than 29 mmHg were in ketoacidosis. • Hypothermia can result in a decreased production of CO2 resulting in low reading. • Hyperthermia can result in increased oxygen consumption and resulting hypercarbia – increased ETCO2.
Cardiac Output • A low level of ETCO2 may indicate low cardiac output. • A sudden decrease in ETCO2 may signal a drop in blood pressure before blood pressure measurement catches it.
Head Injuries & Other Trauma • It is likely that EtCO2 readings in trauma victims, especially multi-system victims, are more accurate measures of perfusion than of ventilation status. • The EtCO2 readings in patients with chest injury may be reflecting a ventilation-perfusion mismatch. • Ventilation–Perfusion mismatch occurs when the volume of blood delivered to the lungs the volume of air in and out of the lungs are not proportional. Chest wounds can cause this, as well as a pulmonary embolism. • In head injuries use capnography to avoid hyperventilation and hypoventilation by maintaining ETCO2 between 32-35 mmHg.
Ventilation-Perfusion Mismatch • The measure is a ratio of air delivered to the lung versus blood delivered to the lung. • A “high” ratio is where air is delivered to an area of the lung where gas exchange is not occurring or is impaired due to reduced blood flow. A pulmonary embolism is a classic example of this. This will contribute to low ETCO2 readings and low oxygen readings. • A “low” ratio is where there is an impediment to airflow in the alveoli. Blood is available to facilitate gas exchange, but not enough air is present. This may contribute to high ETCO2 readings and low oxygen readings. This is common with Asthma, COPD and CHF with pulmonary edema.
BCEMS ETCO2 • There are three types of ETCO2 attachments available. • Nasal w/oxygen tubing. • Nasal w/o oxygen tubing for use under a nonrebreather. • In-line for intubated patients. • Do not be concerned with the cost of these items. We want you to use ETCO2 regularly.