Normal Capnography Overview

A time-based capnogram displays four phases: Inspiration (Phase I), Dead Space/Alveolar Gas Mixture(Phase II), Alveolar Plateau (Phase III), and Exhalation/Fresh Gas (Phase IV).

The plateau in the capnogram representing a constant $CO_2$ level during the exhale, indicating the mixing of alveolar gases.

The partial pressure of $CO_2$ in the exhaled gas at the end of the exhalation.

The angle between phases II and III of the capnogram. It's indicative of lung's time constants, which correlates with V/Q (ventilation/perfusion) ratio.

The angle between phases III and IV relating to the presence or extent of rebreathing.

A method of plotting $CO_2$ concentration against time. The plot is a graph of exhaled $CO_2$ over time.

A method of plotting $CO_2$ against the exhaled volume.

The baseline of the capnogram should ideally reflect no $CO_2$ concentration. Usually 0 mm Hg.

A non-invasive technique used to monitor exhaled carbon dioxide ($CO_2$) levels, providing insights into ventilation, perfusion, and metabolic activity.

It is a surrogate for arterial carbon dioxide ($PaCO_2$) and provides valuable information about the adequacy of ventilation and perfusion.

Capnography can confirm proper placement of an artificial airway (trachea) during intubation, differentiating it from esophageal intubation.

Capnography helps assess the ventilation-perfusion ratio (V/Q), identifying imbalances in oxygen and carbon dioxide exchange.

Capnography provides continuous monitoring of respiratory status, including ventilation, perfusion, and metabolic rate.

Misinterpreting data, increased mechanical dead space with mainstream analyzers, potential airway traction, and auto-triggering of mechanical ventilators with sidestream analyzers.

Capnography readings can be inaccurate, requiring arterial blood gas analysis for confirmation. Low cardiac output can falsely mimic disconnect or esophageal intubation.

A capnogram with two peaks, indicating that gas flow is coming from the right and left lungs at different rates. This usually occurs during endobronchial intubation.

During cardiac arrest, the PETCO2 (partial pressure of end-tidal CO2) is significantly low, indicating a decrease in cardiac output and pulmonary perfusion.

The successful restoration of blood flow after cardiac arrest, indicated by a significant increase in PETCO2 on the capnogram.

A method that plots the partial pressure of carbon dioxide (PCO2) against the volume of exhaled air.

Increasing PEEP (Positive End-Expiratory Pressure) shifts the volumetric capnogram curve to the right, indicating an increase in dead space volume.

A progressive rise in PETCO2 (end-tidal CO2) can indicate either inadequate ventilation or a heightened metabolic rate.

A steady rise in end-tidal CO2 could signal problems like hypoventilation or a hypermetabolic state.

A capnogram with a steadily decreasing plateau, often observed in hyperventilation or decreased metabolic rate. The exhaled CO2 levels steadily decline due to increased ventilation or a decrease in the body's metabolic processes.

A capnogram with a distinctive sawtooth or shark fin shape, characteristic of airway obstruction (like in asthma). It signifies incomplete emptying of dead space during each breath, leading to irregular CO2 concentrations.

Airway obstruction, particularly in conditions like asthma, results in a sawtooth capnogram due to incomplete emptying of dead space during each breath. The trapped air leads to a characteristic irregular CO2 pattern.

A steadily decreasing plateau on the capnogram signifies hyperventilation, where the body is expelling excessive CO2 due to increased ventilation. This leads to lower CO2 levels in the exhaled breath.

Hypothermia causes a decrease in metabolic rate, leading to a reduction in CO2 production. This results in a steadily decreasing plateau on the capnogram as exhaled CO2 levels decline.

The waveform shows a characteristic downslope in phase 3, indicating air trapping and reduced alveolar gas exchange.

The waveform shows an elevated baseline and plateau, indicating incomplete exhalation and rebreathing of exhaled CO2.

The successful restoration of blood flow after cardiac arrest (ROSC) is indicated by a significant increase in PETCO2.

These are waveform fluctuations seen during the late alveolar plateau (Phase III) and descending limb (Phase IV) of a capnogram, indicating heart activity influencing CO2 levels.

Cardiogenic oscillations on a capnogram suggest a strong relationship between heart function and CO2 levels, often seen in patients with heart conditions.

Cardiogenic oscillations occur during these phases because the alveoli are at their largest volume, making them more sensitive to pressure changes from the heart.

A patient with a strong heartbeat might have notable oscillations on their capnogram, reflecting the heart's influence on CO2 levels.

Patients with heart failure might exhibit more prominent cardiogenic oscillations, as their weakened hearts have a larger impact on CO2 levels.

Cardiogenic oscillations occur because the heart's pumping action affects pressure within the lungs, which, in turn, influences the CO2 levels at the end of exhalation.

Cardiogenic oscillations are more noticeable in patients with heart problems, such as heart failure, where the heart's weakened function has a greater impact on CO2 levels.

Cardiogenic oscillations appear on the capnogram during the late plateau phase (Phase III) and the descending limb (Phase IV) of exhalation, as these are the periods when alveolar gas exchange is most sensitive to pressure changes from the heart.

Cardiogenic oscillations on a capnogram suggest a strong connection between heart function and CO2 levels, signifying potential cardiovascular issues.

The partial pressure of carbon dioxide in the exhaled gas at the end of exhalation. It is often used as a surrogate for arterial carbon dioxide levels ($PaCO_2$).

The volume of air in the respiratory system that does not participate in gas exchange. This is commonly used in relation to volume-based capnography.

Time-based capnography plots CO2 concentration against time, while volume-based capnography plots CO2 concentration against exhaled volume.