CAPNOGRAPHY

CAPNOGRAPHY

1. CAPNOGRAPHY DR.MAHESWARI JAIKUMAR [email protected]

2. DEFINITION The term capnography refers to the non invasive measurement of the partial pressure of carbon dioxide (CO 2 ) in exhaled breath expressed as the CO 2  concentration over time. The relationship of CO 2  concentration to time is graphically represented by the CO 2  waveform, or capnogram  

3. Capnography  is the monitoring of the concentration or  partial pressure  of  carbon dioxide  (CO 2 ) in the respiratory gases. It is mainly used as a monitoring tool for use during  anesthesia  and  intensive care .

4. It is usually presented as a graph of expiratory CO 2  (measured in millimeters of mercury, "mmHg") plotted against time, or, less commonly, but more usefully, expired volume. When the measurement is taken at the end of a breath (exhaling), it is called "end tidal" CO 2  (ETCO 2 ).

5. During anesthesia , there is interplay between two components: the patient and the anesthesia administration device (which is usually a breathing circuit and a  ventilator ) The critical connection between the two components is either an  endotracheal tube  or a mask, and CO 2  is typically monitored at this junction.

6. Capnography directly reflects the elimination of CO 2  by the  lungs  to the anesthesia device. Indirectly, it reflects the production of CO 2  by tissues and the circulatory transport of CO 2  to the lungs.

7. NORMAL CAPNOGRAPH

8. ABNORMAL CAPNOGRAPH

9. INDICATIONS

10. CLINICAL APPLICATIONS

11. DIAGNOSTIC USAGE Capnography provides information about CO 2  production,  pulmonary   perfusion,  alveolar  ventilation,  respiratory patterns , and elimination of CO 2  from the anesthesia breathing circuit and ventilator.

12. The shape of the curve is affected by some forms of lung disease; in general there are obstructive conditions such as  bronchitis ,  emphysema  and  asthma , in which the mixing of gases within the lung is affected.

13. Conditions such as  pulmonary embolism  and congenital heart disease, which affect perfusion of the lung, do not, in themselves, affect the shape of the curve, but greatly affect the relationship between expired CO 2  and arterial blood CO 2

14. Capnography can also be used to measure carbon dioxide production, a measure of  metabolism . Increased CO 2  production is seen during fever and shivering. Reduced production is seen during anesthesia and  hypothermia .

15. ADVANTAGES This technique allows insight into the alveolar ventilation, perfusion and metabolism of breathing The appropriate tracing/mark on a pulse oximeter guarantees that the recorded oxygen saturation provided is valid.

16. Secondly, the evaluation of the provided waveform gives key information about latent, underlying physiologic conditions and the ongoing processes of diseases.

17. Capnometry is a non-invasive monitoring technique. It allows quick and reliable insight into aspects like: ventilation, circulation, and metabolism. In diagnosis, monitoring, and prediction of outcome capnometry is an important tool, especially in the pre-hospital setting

18. Conditions such as pulmonary embolisms (PE's) and congenital heart disease, affecting perfusion of the lung do not affect the shape of the curve, but have an affect on the relationship between expired CO2 and arterial blood CO2.

19. Capnography can also be used to measure carbon dioxide production. Increased CO2 production is seen during fever and shivering. Reduced production is seen during anesthesia and hypothermia.

20. WORKING MECHANISM Capnographs usually work on the principle that CO 2  absorbs  infrared radiation . A beam of infrared light is passed across the gas sample to fall on a sensor. The presence of CO 2  in the gas leads to a reduction in the amount of light falling on the sensor, which changes the voltage in a circuit.

21. The analysis is rapid and accurate, but the presence of  nitrous oxide  in the gas mix changes the infrared absorption via the phenomenon of collision broadening. This must be corrected for measuring the CO 2  in human breath by measuring its infrared absorptive power.

22. CAPNOGRAM MODEL The capnogram waveform provides information about various respiratory and cardiac parameters. The capnogram   double-exponential  model attempts to quantitatively explain the relationship between respiratory parameters and the  exhalatory  segment of a capnogram waveform

23. CAPNOGRAM

24. This model explains the rounded "shark-fin" shape of the capnogram observed in patients with  obstructive lung disease .

25. EMERGENCY MEDICAL SERVICES Capnography is increasingly being used by  EMS  personnel to aid in their assessment and treatment of patients in the pre hospital environment.

26. These uses include verifying and monitoring the position of an  endotracheal tube  or a  blind insertion airway device . A properly positioned tube in the  trachea  guards the patient's airway and enables the  paramedic  to breathe for the patient. A misplaced tube in the  esophagus  will lead to the patient's death if it goes undetected.

27. Capnography provides a rapid and reliable method to detect life-threatening conditions ( malposition of  tracheal tubes , unsuspected ventilatory failure, circulatory failure and defective breathing circuits) and to circumvent potentially irreversible patient injury.

28. During procedures done under sedation, capnography provides more useful information, e.g. on the frequency and regularity of ventilation, than  pulse oximetry .

29. When expired CO 2  is related to expired volume rather than time, the area beneath the curve represents the volume of CO 2  in the breath, and thus over the course of a minute, this method can yield the CO 2  per minute elimination, an important measure of metabolism.

30. Sudden changes in CO 2  elimination during lung or heart surgery usually imply important changes in cardio respiratory function.

31. Changes in the shape of the capnogram are diagnostic of disease conditions, while changes in end-tidal CO 2  (EtCO 2 ), the maximum CO 2  concentration at the end of each tidal breath, can be used to assess disease severity and response to treatment.

32. Capnography is also the most reliable indicator that an endotracheal tube is placed in the trachea after intubation.

33. Capnography provides instantaneous information about ventilation (how effectively CO 2  is being eliminated by the pulmonary system), perfusion (how effectively CO 2  is being transported through the vascular system), and metabolism (how effectively CO 2  is being produced by cellular metabolism).

34. PRINCIPLES OF OPERATION Carbon dioxide (CO 2 ) monitors measure gas concentration, or partial pressure, using one of two configurations: mainstream or sidestream .

35. Mainstream devices measure respiratory gas (in this case CO 2 ) directly from the airway, with the sensor located on the airway adapter at the hub of the endotracheal tube (ETT).

36. Sidestream devices measure respiratory gas via nasal or nasal-oral cannula by aspirating a small sample from the exhaled breath through the cannula tubing to a sensor located inside the monitor 

37. DIFFERENCE BETWEEN CAPNOGRAPHY & PULSE OXIMETRY

38. REFERENCES Friesen RH, Alswang M. End-tidal PCO2 monitoring via nasal cannulae in pediatric patients: accuracy and sources of error. J Clin Monit 1996; 12:155. Gravenstein N. Capnometry in infants should not be done at lower sampling flow rates. J Clin Monit 1989; 5:63. Sasse FJ. Can we trust end-tidal carbon dioxide measurements in infants? J Clin Monit 1985; 1:147. Yamanaka MK, Sue DY. Comparison of arterial-end-tidal PCO2 difference and dead space/tidal volume ratio in respiratory failure. Chest 1987; 92:832. Hardman JG, Aitkenhead AR. Estimating alveolar dead space from the arterial to end-tidal CO(2) gradient: a modeling analysis. Anesth Analg 2003; 97:1846. Stewart RD, Paris PM, Winter PM, et al. Field endotracheal intubation by paramedical personnel. Success rates and complications. Chest 1984; 85:341. Shea SR, MacDonald JR, Gruzinski G. Prehospital endotracheal tube airway or esophageal gastric tube airway: a critical comparison. Ann Emerg Med 1985; 14:102. Pointer JE. Clinical characteristics of paramedics' performance of endotracheal intubation. J Emerg Med 1988; 6:505. Jenkins WA, Verdile VP, Paris PM. The syringe aspiration technique to verify endotracheal tube position. Am J Emerg Med 1994; 12:413. Bozeman WP, Hexter D, Liang HK, Kelen GD. Esophageal detector device versus detection of end-tidal carbon dioxide level in emergency intubation. Ann Emerg Med 1996; 27:595.

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