1. Capnogram Dr.C.N.Chandra Sekhar M.D

2. Definitions Capnometry: Measurement and numerical display of CO 2 level during resp.cycle Capnometer: Device that performs the measurement and displays the readings. Capnography: Graphic record with display on a screen or paper of carbondioxide concentration. Capnograph: the machine that generates the waveform Capnogram: the actual waveform.

3. CAPNOGRAPHIC DEVICES Infrared Absorption Photometry Colorimetric Devices Mass Spectrometry Raman Scattering

4. INFRARED First developed in 1859. Based on Beer-Lambert law: Pa = 1 - e -  DC Pa is fraction of light absorbed  is absorption coefficient D is distance light travels though the gas C is molar gas concentration The higher the CO 2 concentration, the higher the absorption. CO 2 absorption takes place at 4.28 µm N 2 O, H 2 O, and CO can also absorb at this wavelength Two types: side port and mainstream

5. ABSORPTION BANDS

6. SIDE PORT Gas is sampled through a small tube Analysis is performed in a separate chamber Very reliable Time delay of 1-60 seconds Less accurate at higher respiratory rates Prone to plugging by water and secretions Ambient air leaks

7. MAINSTREAM Sensor is located in the airway Response time as little as 40msec Very accurate Difficult to calibrate without disconnecting (makes it hard to detect rebreathing) More prone to the reading being affected by moisture Larger, can kink the tube. Adds dead space to the airway Bigger chance of being damaged by mishandling

8. COLORIMETRIC Contains a pH sensitive dye which undergoes a color change in the presence of CO 2 The dye is usually metacresol purple and it changes to yellow in the presence of CO 2 Portable and lightweight. Low false positive rate Higher false negative rate Acidic solutions, e.g., epi, atropine, lidocaine, will permanently change the color Dead space relatively high for neonates, so don’t use for long periods of time on those patients.

9. Physiology Just after inhalation, the lungs are rapidly filled with oxygen and other gases (negligable CO 2 ) CO 2 diffuses across capillaries and into the alveoli as O 2 moves from alveoli to capillaries As exhalation begins, CO 2 rich air is expelled from first the upper and then the lower airways The capnogram represents the movement of CO 2 over time All normal, healthy patients should ideally produce identical capnograms

10. Physiology (continued) Any deviation from a normal wave is due to an altered physiological state, a pathological state, or equipment malfunction Any factor that affects the production, diffusion, elimination or partial pressure of CO 2 will affect the capnogram The anesthetist must be able to distinguish between abnormal waveforms due to equipment failure/malfunction from those due to physiological conditions

11. Normal Capnogram

12. Phase I is the beginning of exhalation Phase I represents most of the anatomical dead space Phase II is where the alveolar gas begins to mix with the dead space gas and the CO 2 begins to rapidly rise The anatomic dead space can be calculated using Phase I and II Alveolar dead space can be calculated on the basis of : V D = V Danat + V Dalv Significant increase in the alveolar dead space signifies V/Q mismatch

13. Normal Capnogram Phase III corresponds to the elimination of CO 2 from the alveoli Phase III usually has a slight increase in the slope as “slow” alveoli empty The “slow” alveoli have a lower V/Q ratio and therefore have higher CO 2 concentrations In addition, diffusion of CO 2 into the alveoli is greater during expiration. More pronounced in infants ET CO 2 is measured at the maximal point of Phase III. Phase IV is the inspirational phase

14. PaCO 2 -PetCO 2 gradient Usually <6mm Hg PetCO 2 is usually less Difference depends on the number of underperfused alveoli Tend to mirror each other if the slope of Phase III is horizontal or has a minimal slope Decreased cardiac output will increase the gradient The gradient can be negative when healthy lungs are ventilated with high TV and low rate Decreased FRC also gives a negative gradient by increasing the number of slow alveoli

15. Uses Metabolic Assess energy expenditure Cardiovascular Monitor trend in cardiac output Can use as an indirect Fick method, but actual numbers are hard to quantify Measure of effectiveness in CPR Diagnosis of pulmonary embolism: measure gradient

16. PULMONARY USES Effectiveness of therapy in bronchospasm Monitor PaCO 2 -PetCO 2 gradient Worsening indicated by rising Phase III without plateau Find optimal PEEP by following the gradient. Should be lowest at optimal PEEP. Limited usefulness in weaning the vent when patient is unstable from cardiovascular or pulmonary standpoint Confirm ET tube placement

17. LIMITATIONS Critically ill patients often have rapidly changing dead space and V/Q mismatch Higher rates and smaller TV can increase the amount of dead space ventilation High mean airway pressures and PEEP restrict alveolar perfusion, leading to falsely decreased readings Low cardiac output will decrease the reading

18. ABNORMALITIES Increased Phase III slope Obstructive lung disease Phase III dip Spontaneous resp Horizontal Phase III with large ET-art CO 2 change Pulmonary embolism  cardiac output Hypovolemia Sudden  in ETCO 2 to 0 Dislodged tube Vent malfunction ET obstruction Sudden  in ETCO 2 Partial obstruction Air leak Exponential  Severe hyperventilation Cardiopulmonary event

19. ABNORMALITIES Gradual  Hyperventilation Decreasing temp Gradual  in volume Sudden increase in ETCO 2 Malignant Hyperthermia Increased Metabolic states Sodium bicarb administration Release of limb tourniquet Gradual increase Fever Hypoventilation Increased baseline Rebreathing Exhausted CO 2 absorber

20. Hyperventilation Progressively lower plateau (phase II) segment Baseline remains at zero Decreasing CO 2 levels

21. Hypoventilation Steady increase in height of Phase II Baseline remains constant

22. Spontaneous Ventilation Short Alveolar plateau Increased frequency of waveforms

23. Cardiogenic Oscillations Ripples during Phase III and Phase IV Due to changes in pulmonary blood volume and ultimately CO 2 pressure as a result of cardiac contractions

24. Curare Cleft Shallow dips in phase III plateau Can occur when patient is in a light plane of anesthesia Represent patient attempts to breathe independent of mechanical ventilation

25. Inspiratory Valve Malfunction Increasing elevation of baseline Increasing elevation of Phase II Smaller waveform represents rebreathing of CO 2

26. Bronchospasm Airway Obstruction COPD Sloping of inspiratory and expiratory segments Prolonged Phase II and Phase III

27. Rebreathing of Soda Lime Contamination with CO 2 Elevation of Phase II segment and baseline Elevation of baseline and Phase II, smaller inspiratory efforts Progressive elevation of Phase II and baseline

28. Bain System Smaller wave form represents rebreathing of CO 2

29. Slow ventilation Incompetent inspiratory valve Prolongation of Phase IV

30. Images reprinted from Capnography.com homepage Designed by Bhavani Shankar Kodali

31. Thank You