Phase 4 also known as phase 0 (the yellow line): During this phase, CO2 values drop sharply as inspiration begins. The carbon dioxide concentration at the end of expiration is called the end-tidal carbon dioxide concentration (ETCO, normal range 35-40 mm Hg) which represents the alveolar carbon dioxide concentration. The phases I, II, and III represent expiration and phase IV, inspiration. Capnography Waveform Interpretation Normal end-tidal PCO2 is approximately: 38 mmHg or 5 the alpha angle is the transition from Phase II to Phase III the. However, the gradient in the acute phase of TBI is unknown. Normal capnography:- The normal capnogram has four different phases. This recommendation assumes a 0.5 kPa (3.8 mm Hg) ETCO 2 PaCO 2 gradient. The ETCO 2 is the numeric value on the monitor and is normally 4.5-6 kPa (35 – 45 mmHg). Current guidance recommends an end-tidal carbon dioxide (ETCO 2) of 4.04.5 kPa (30.033.8 mm Hg) to achieve a low-normal arterial partial pressure of CO 2 (PaCO 2 ), and reduce secondary brain injury. This is end-tidal CO2 (ETCO2) which is normally 35-45 mm Hg. The value at the end of the slope is called the End-Tidal CO 2 (ETCO 2), the maximal expired CO 2 concentration. The number is capnometry, which is the partial pressure of CO2 detected at the end of exhalation. The angle between phase 2 and phase 3 is called the Alpha Angle, the change from airway gas to alveolar gas. The P i CO 2 level, should be at or very close to Zero. The gently sloping plateau represents late expiration where alveolar gas which is rich in CO 2 is detected. Capnography is a non-invasive measurement during inspiration and expiration of the partial pressure of CO2 from the airway. The P E CO 2 level should be between 35 and 45 mmHg (these values are for the conscious, spontaneously breathing animal and not influenced by the use of anaesthetic and analgesic medications). Phase 3 (the red line): This phase is the alveolar plateau. The speed at which the CO 2 is exhaled determines the slope of this part of the curve. Patient stimulation, use of a BVM, or use of Naloxone may be appropriate based on the situation. EtCO 2 levels that rise from a normal baseline to or above 50 may indicate hypoventilation is occurring. CO 2 travels from the alveoli through the bronchi and trachea (the conducting airways) where gas is present but not able to be exchanged (anatomical dead space). Normal EtCO 2 levels range from 30s and 40s, but this may vary based on the patient’s underlying respiratory and metabolic status. Phase 2 (the pink line): At the beginning of expiration, exhaled CO 2 rapidly rises and so does the slope of the capnogram. Capnographs manufactured today display the ETCO2 as either a percentage (normal range: 5 to 6) or as mm Hg (normal range: 35 to 45 mm Hg). The lack of CO 2 detected in this phase results in a flat waveform. There is incredible utility in using EtCO2 in CPR.Phase 1 (the blue line): This is the inspiratory baseline and reflects the inspired gas (which has only a minuscule amount of CO 2). The trademark sign for hypoventilation is an elevated CO2 level above 45 mmHg in the presence of normal circulation and metabolism. The correlation between serum pCO2 and EtCO2 is also less understood animal studies do not show much correlation, and as you would expect with CPR, there will likely be some dead space and/or V/Q mismatch. The utility of EtCO2 in patients who are receiving bag mask ventilation (BVM) or have a laryngeal mask airway (LMA) is less understood and researched. The PQRST mnemonic should be applied to patients with an ETT. Approximately 20 minutes into a resuscitation, the likelihood of ROSC is significantly higher if EtCO2 >20 mm Hg and much less if EtCO2 <10 mm Hg. Termination (T)ĮtCO2 may provide an additional data point when deciding whether it is appropriate to terminate CPR. This can be seen in bronchospasm or a kinked or blocked ETT or circuit. This is an example of a waveform that looks like a “sharkfin,” which indicates expiratory obstruction.
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