Email: anaesthesia.co.in@gmail.com CAPNOGRAPHY Dr. Radhika Dhanpal radhika.dhanpal@rediffmail.com Professor and Head Department of Anesthesiology and Critical Care, St. John’s Medical College Hospital Bangalore Email: anaesthesia.co.in@gmail.com www.anaesthesia.co.in

ASA House of delegates July 1, 2011 implementation of Oct 2010 decision “Standards for Basic Anesthesia Monitoring”During regional anesthesia (with no sedation ) or local anesthesia (with no sedation ), the adequacy of ventilation shall be evaluated by continual observation of qualitative clinical signs. During moderate or deep sedation, the adequacy of ventilation shall be evaluated by continual observation of qualitative clinical signs and monitoring for the presence of exhaled CO2 unless precluded or invalidated by the nature of the patient, procedure or equipment” ISA – Desirable standard 1999

Definition : Graphic display of instantaneous CO2 concentration Luft Collier Ramwell Holland in 1978 , was the first country to adopt it as a standard of monitoring during anaesthesia .

Terminology Capnometer The machine Capnography Wave form Capnometry Numerical Valve

Methods of measurement Infrared spectrography Raman spectrography Mass spectrography Photoacoustic spectrography Chemical colorimetric analysis

Raman spectrography Gas sample is aspirated into the analysing chamber where it is illuminated by a high intensity monochromatic argon laser beam. The light is absorbed by molecules which are then excited to unstable vibrational or rotational energy states, these Raman scattering signals are then measured.

Mass spectrography It separates gases and vapors of different molecular weight on the basis of their mass into a spectrum. By analyzing the spectrum, the composition and relative abundance of each gas in a sample can be determined .

Infrared method : Infrared waves at 4 Infrared method : Infrared waves at 4.3 mm are absorbed by certain gases producing absorption bands on the infrared electromagnetic spectrum.

Photoacoustic gas measurements The gas to be measured is irradiated by modulated light of a pre-selected wavelength . The light beam when chopped, generates an acoustic signal which is detected by two microphones.

Colorimetric method Chemically treated foam indicator attached to endotracheal tube.

Factors influencing the reading ; Atmospheric pressure : Changes in atmospheric pressure are usually of the order of 20 mm Hg . This results in a change in PaCO2 of less than 0.5 - 0.8 mm Hg PEEP . Water vapour : Can condense on the sensor cell and produce falsely high readings. This may be prevented by Heating sensor above body temperature sampling tube can be made of a semipermeable polymer that allows water vapour to pass outside. Absorbent filters.

TYPES - I Side stream capnography A pump aspirates gas samples from the patient’s airway through a 6 foot long capillary tube into the main unit at a rate of 50-200 ml/min Disadvantages Children Multiple sites for leaks and breakage Delay Scavenging needed Advantages Spontaneous breathing subjects Patients on O2 nasal cannula Easy to sterilise Use in unusual positions.

TYPES –II Main stream capnography Disadvantages : Heavy Hot Window to be kept clean Advantages : Faster No gas is removed No uncertainity by rate of gas sampling

Calibration : Periodically Gas of known CO2 concentration Calibration cells with mixtures of CO2 and N2 are available. Sampling tube should be the same type as the one used on the patient.

Type of capnogram Time capnogram Volume capnogram Fast 7mm/sec Slow 0.7 mm/sec

Time capnogram Inspiratory segment Expiratory segment Alpha angle Beta angle

Anatomical and apparatus dead space gas Phase II Rising CO2 No CO2 Anatomical and apparatus dead space gas Phase II Rising CO2 Mixing of dead space gas and alveolar gas. Phase III Static or rising CO2 Alveolar gas Phase IV Falling CO2 Beginning of inspiration α angle - 100-110º ; Airway Obstruction causes larger angle. β angle - 90º ; Rebreathing increases the angle.

Volume capnogram Advantage s Volume of CO2 per exhaled breath can be measured Significant changes in the morphology of the expired wave form can be detected Dead space can be partitioned Disadvantages Intubation mandatory Elaborate equipment Only monitors expiration

Interpretation of the waveform Height Frequency Rhythm Baseline Shape

PaCo2 – PEtCo2-1 Normal 2-5 mmHg Increased Decreases Age Large TV Pulmonary disorders Low Frequency Ventilation PE Pregnancy CO Infants Hypovolemia Anaesthesia

Metabolic PaCo2 – PEtCo2-2 Increase Decrease Hyperpyrexia Hypothermia Shivering Increased Muscle relaxation Convulsions Blood /NaHCO3 administration Release of an arterial clamp/tourniquet Dextrose containing fluids Parenteral hyperailmentation CO2 insufflation ( peritoneum , Pleura , joint )

PaCo2 – PEtCo2-3 Circulatory Increase Decrease Epinephrine injection CO CPR Surgical manipulations of the heart, great vessels, wedged PAC, PE Air Embolism

Uses Anaesthesia Verification of tracheal intubation Assist in blind oral or nasal intubation Needle cricothyroidotomy Jet stylet introducer Fiberoptic bronchoscopy Double lumen tube placement Monitoring of spontaneous ventilation Curare cleft HFJV Detection of circuit leaks Detection of malfunction of valves or faulty anaesthetic system.

Critical Care CPCR Determine the needs during mechanical ventilation Weaning Placement of NG tube Others PACU Patient transfer Post operative ward Procedural sedation Apnea test for brain death Emergency Department

REBREATHING WITH ELEVATED BASELINE

ESOPHAGEAL INTUBATION WITH CARBONATED BEVERAGES IN STOMACH

CO2 ABSORBENT EXHAUSTION

ESOPHAGEAL INTUBATION

ESOPHAGEAL INTUBATION FOLLOWING MASK VENTILATION.

EXPIRATORY VALVE MALFUNCTION

SPONTANEOUS BREATHING

NORMAL WAVEFORM

CURARE CLEFT

AIR LEAK

HYPERVENTILATION

CONTAMINATION OF CO2 SENSOR

SUCCESSFUL RESUSCITATION CARDIAC ARREST, SUCCESSFUL RESUSCITATION

HYPOVENTILATION

BRONCHOSPASM

IMV WITH INTERPOSED SPONTANEOUS RESPIRATION.

CARDIOGENIC OSCILLATIONS (RIPPLE EFFECT)

INSPIRATORY VALVE MALFUNCTION

POST SINGLE LUNG TRANSPLANTATION.

BAIN CIRCUIT/MAPELSON D (SIGNATURE CAPNOGRAM)

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