All Über Capnography
All Über Capnography
Physiologically, carbon dioxide produced in the tissues and diffuse into the venous blood which reaches the right side of the heart and reaches the lungs via Pulmonal circulation. Here oxygen (O2) enters the blood and carbon dioxide (CO2) is given out which is eliminated during expiration.
The measurement of C02 in the expired air directly indicates changes in the elimination of C02 from the lungs. Indirectly, it indicates changes in the production of C02 at the tissue level and in the delivery of C02 to the lungs by the circulatory system. Therefore, capnography constitutes an important non-invasive technique that can Monitor C02 production, Pulmonal perfusion and alveolar ventilation as well as respiratory patterns.
Current terminology is summarized as follows.
A time capnogram can be divided into inspiratory (phase 0) and expiratory segments. The expiratory segment, similar to a single breath nitrogen curve or single breath CO2curve, is divided into phases I, II and III, and occasionally, phase IV, which represents the terminal rise in CO2 concentration. The angle between phase II and phase III is the alpha angle. The nearly 90 degree angle between phase III and the descending limb is the beta angle.
End-tidal carbon dioxide tension (PETCO2):
As explained in the physiology section, the CO2 concentration reaches a maximum at the end of exhalation. This maximum concentration is called end-tidal carbon dioxide concentration or tension depending on whether it is expressed in fractional concentration or mm Hg. End-tidal carbon dioxide reflects CO2 concentration of alveoli emptying last. The normal values of ETCO2 is around 5% or 35-37 mm Hg. The gradient between the blood CO2 (PaCO2) and exhaled CO2 (end tidal CO2 or PetCO2) is usually 5-6 mm Hg. PetCO2 can be used to estimate PaCO2 in patients with essentially normal lungs.
Measurement of exhaled carbon dioxide:
The exhaled CO2 (end-tidal CO2) is detected/ measured by various devices – Colorimetry, capnometry, capnography. When CO2 is absent as measured by these devices, it means either the endotracheal tube is in a wrong position (esophageal) or there is an absent/ decreased presentation of CO2 to the lungs as in a kardial arrest . When kardial output increases (e.g. After resuscitation), PetCO2 provides Informationen Über adequacy of ventilation and circulation (3).
Colorimetry:
As explained in the above section, the chemical device provides kontinuierlich, semiquantitative EtCO2 Überwachung. This device has 3 color ranges
A- Purple — EtCO2 < 0.5%
B- Tan — EtCO2 0.5-2%
C- Yellow – EtCO2 >2%
Normal EtCO2 is >4% hence the device should turn yellow when endotracheal tube is inserted in patients with intact circulation. Limitations of this device
1. It is a useful device to confirm endotracheal tube placement in patients not in kardial arrest. In patients with kardial arrest, a value of <0.5% EtCO2, the device is virtually of no use in confirming the endotracheal tube, because the tube could be in the esophagus or that the circulation is not bringing enough CO2 to the lungs. In non-arrest patients the device is 100% sensitive, while it is 69% in patients with kardial arrest (4).
2. The membrane can turn ‘yellow’ (implies EtCO2 > 2%) when the device is contaminated with acidic substances like gastric acid, Lidocaine-HCl, epinephrine HCl.
3. The device is unable to give a reading if it is clogged with secretions, or the device broken.
Capnography and Capnometry:
These devices provide both Wellenform (capnograph) and digital read out of end-tidal CO2. The digital read out of ETCO2 can be in mm Hg (partial pressure of CO2 in exhaled gas) or as % in exhaled gas. Most of the commonly used devices use ‘infra red absorption of CO2’ as principle of operation.
They can be main stream or side stream (as described in the physiology section).
Anwendungen of capnography out of Krankenhaus settings:
Endotracheal intubation:
When CO2 is absent as measured by above devices, it means either the endotracheal tube is in a wrong position (esophageal) or there is an absent/ decreased presentation of CO2 to the lungs as in a kardial arrest . When kardial output increases (e.g. After resuscitation), PetCO2 provides Informationen Über adequacy of ventilation and circulation (3).
Endo tracheal intubation is performed in various klinisch situations like respiratory failure, kardial arrest, coma etc. It is associated with complications, but none is more catastrophic than inadvertent esophageal intubation. Correct placement of the endotracheal tube is suggested by, but not confirmed by the following methods.
Bilateral, equal breath sounds.
Bilateral chest wall movements.
No breath sounds/ gurgling over the stomach/ epigastrium.
Fogging of the endotracheal tube.
Tube/ cuff palpation in the neck.
Disappearance of cyanosis or improvement of patients color.
None of the above methods can provide a ‘fool-proof’ confirmation of endotracheal tube placement. This is illustrated be the statement “ even a conscientious, careful anesthesiologist may be unable to differentiate tracheal from esophageal intubation by commonly employed methods (1). Stewart et al (2) attribute 1.8% complication rate for esophageal intubation in a study of intubation by paramedics.
A normal looking Wellenform and a ‘digital read out’ confirms that the endotracheal tube is in trachea. In low kardial output states like shock, kardial arrest or inadequate chest compressions, PetCO2 may not be detected. If a patient has had carbonated beverages (5) or if mouth to mouth ventilation has been attempted, CO2 may be detected after esophageal intubation (false positive). The EtCO2 should rapidly decrease to zero (within 3-6 breaths) in this situation and also the wave form will not be ‘Normal’ looking. Vukmir et al (6) reported a sensitivity and specificity of 100% for endotracheal tube localization by capnography.
Esophageal intubation
Role in CPR:
The relationship between kardial output and EtCO2 is logarithmic (3). Decreased presentation of CO2 to the lungs is the major rate limiting determinant of the EtCO2 during low flow. White R.D. et al (7) used EtCO2 measurement in out-of Krankenhaus kardial arrest. They concluded that capnography can detect the presence of Pulmonal blood flow even in the absence of major pulses (pseudo-electromechanical dissociation- EMD) and also can rapidly indicate changes in Pulmonal blood flow (kardial output) caused be alterations in kardial rhythm.
Data suggests that PetCO2 also correlated with coronary perfusion pressure (CPP) (8). It is also known to correlate with cerebral perfusion pressure and blood flow during CPR (9), but not with neurologic outcome. This correlation between perfusion pressure and ETCO2 is likely to be secondary to the relationship of PETCO2 and kardial output.
Callaham M et al (10) used initial PetCO2 readings to predict return of spontaneous pulse during CPR. Patients who developed a pulse had a mean PetCO2 of 19 +/- 14 Torr at the start of resuscitation and those who did not had a mean PetCO2 of 5 +/- 4 Torr. Using an initial PetCO2 value of 15 torr identified 71% of the patients who were subsequently resuscitated with a specificity of 98%. PetCO2 value is not a sufficient criterion by itself for terminating resuscitation efforts.
Studies in animals and humans demonstrated that PetCO2 decreases when a large dose of epinephrine was used during CPR (11). Callaham M et al (12) in their study, report that epinephrine administration may decrease EtCO2 tensions in kardial arrest, it does so unpredictably in individual patients and it does not eliminate the predictive value of this measurement. EtCO2 decreases an average 0.3 Torr after epinephrine administration. This decrease in EtCO2 has been attributed to increase in shunt fraction and also due to drop in kardial output secondary to increased afterload by epinephrine (11). The duration of decrease in EtCO2 has not been quantified, but clinically can be useful for timing subsequent epinephrine dosing (13).
EtCO2 can be used as a feedback to optimize chest compressions during CPR (14). Überwachung PetCO2 during kardial arrest may detect unrecognized CPR provider fatigue.
Other Anwendungen:
EtCO2 Wellenform analysis can give Informationen of leaks in breathing circuit, airway obstruction (asthma, COPD). Refer to capno-magic Bildschirm.
Diagnosis of Pulmonal embolism
Estimation of PaCO2 in mechanically ventilated patients: End-tidal PCO2 can be used to estimate arterial PaCO2 in patients with healthy lungs.
By: Venkatesh Srinivasa MD & Bhavani Shankar Kodali MD
References:
1. Solazzi R W, Ward R J : The spectrum of medical liability cases. Int. Anesthesiol Clin 1984, 22:43.
2. Stewart R D, Paris P M, Winter P M :Field endotracheal intubation by paramedic personnel. Chest 1984, 85:341-345.
3. Ornato J P, Garnett A R, Glauser F L, Virginia R: Relationship between kardial output and the end-tidal carbondioxide tension. Ann Emerg med 1990, 19: 1104-1106.
4. Ornato J P et al: Multicenter study of a tragbar, hand-size, colorimetric end-tidal carbondioxide detection device. Ann Emerg Med, May 1992; 21: 518-523.
5. Garnett A R, Germin C A, Germin A S: Capnographic wavefoms in esophageal intubations: effect of carbonated beverages. Ann Emerg Med 1989; 18:387-90.
6. Vukmir R B, Heller M B, Stein K L: Confirmation of endotracheal tube placement: A miniaturized Infrarot qualitative carbondioxide detector. Ann Emerg Med July 1991; 20:726-729.
7. White R D, Asplin B R: Out of Krankenhaus quantitative Überwachung of end-tidal carbondioxide pressure during CPR. Ann Emerg Med January 1994; 23;25-30.
8. Sanders A B, Atlas M, Ewy G A et al: Expired PCO2 as an index of coronary perfusion pressure. Am J Emerg Med 1985; 3: 147-149.
9. Lewis L M, Sthothert J, Standeven J et al : Correlation of end-tidal carbondioxide to cerebral perfusion during CPR. Ann Emerg Med 1992; 21:1131-4.
10. Callaham M, Barton C: Prediction of outcome of CPR from end-tidal carbondioxide concentration. Crit Versorgung Med 1990; 18:358-362.
11. Chase P B, Kern k B, Sanders A B et al: Effects of graded doses of epinephrine on both non invasive and invasive measures of myocardial perfusion and blood flow during cardio-Pulmonal resuscitation. Crit Versorgung Med 1993; 21:413-9.
12. Callaham M, Barton C, Mathay M: Effect of epinephrine on the ability of end-tidal carbondioxide readings to predict initial resuscitation from kardial arrest. Crit Versorgung Med 1992; 20:337-343.
13. Ward k R, Yealy D M: End-tidal carbondioxide Überwachung in Notfall medicine, part2: klinisch Anwendungen. Academic Notfall Med 1998; 5: 637-646.
14. Kalenda Z: Capnogram as a guide to the efficacy of kardial massage. Resuscitation 1978; 6:259-63.
Meditech EtCO2 Produkte
Mainstream EtCO2 Sensor 
Internal Side stream EtCo2 module 
External Side Stream ETCO2 module 
MD 90E capnography 
MD90E with Big Bildschirm LCD, clearly zeigt an the EtCO2/CO2,Respiration rate,SpO2 and Pulse,Side stream mode, keeping work under the heavy humid envir