Capnography

CAPNOGRAPHYCAPNOGRAPHY

• HistoryHistory• TerminologyTerminology• Why capnographyWhy capnography• PhysicsPhysics• TypesTypes• Basic physiologyBasic physiology• Components of capnography Components of capnography • Clinical applicationClinical application• Carry homeCarry home

• 1943- luft –CO2 absorbs infrared light1943- luft –CO2 absorbs infrared light• Ramwell – proved it beyond doubtRamwell – proved it beyond doubt• 1978- holland the first country to adopt1978- holland the first country to adopt• 1999 – ISA ‘desirable standard’ in 1999 – ISA ‘desirable standard’ in

anaesthesia monitoring standardsanaesthesia monitoring standards

terminologyterminology

• CapnometryCapnometry• CapnometerCapnometer• CapnographyCapnography• CapnogramCapnogram• CapnographCapnograph

OxygenationOxygenation

• Measured by pulse oximetry (SpOMeasured by pulse oximetry (SpO22) ) – Noninvasive measurementNoninvasive measurement– Percentage of oxygen in red blood cells Percentage of oxygen in red blood cells – Changes in ventilation take minutes Changes in ventilation take minutes

to be detected to be detected – Affected by motion artifact, poor perfusion Affected by motion artifact, poor perfusion

and some dysrhythmiasand some dysrhythmias

• Capnography provides information about Capnography provides information about COCO22 production, pulmonary perfusion, production, pulmonary perfusion,

alveolar ventilation, respiratory patterns, alveolar ventilation, respiratory patterns, and elimination of COand elimination of CO22 from the anesthesia from the anesthesia

circuit and ventilator. circuit and ventilator.

VentilationVentilation

• Measured by the end-tidal COMeasured by the end-tidal CO22

– Partial pressure (mmHg) or volume (% vol) of Partial pressure (mmHg) or volume (% vol) of COCO22 in the airway at the end of exhalation in the airway at the end of exhalation

– Breath-to-breath measurement, provides Breath-to-breath measurement, provides information within secondsinformation within seconds

– Not affected by motion artifact, poor perfusion Not affected by motion artifact, poor perfusion or dysrhythmiasor dysrhythmias

Oxygenation and VentilationOxygenation and Ventilation

• OxygenationOxygenation– Oxygen for Oxygen for

metabolismmetabolism

– SpOSpO22 measures measures

% of O% of O22 in RBC in RBC

– Reflects change in Reflects change in oxygenation within oxygenation within 5 minutes5 minutes

• VentilationVentilation– Carbon dioxide Carbon dioxide

from metabolismfrom metabolism

– EtCOEtCO22 measures measures

exhaled COexhaled CO22 at at

point of exitpoint of exit– Reflects change in Reflects change in

ventilation within ventilation within 10 seconds10 seconds

Why Capnography ?Why Capnography ?

• Capnography, an indirect monitor Capnography, an indirect monitor

helps in the differential diagnosis of hypoxia helps in the differential diagnosis of hypoxia to enable remedial measures to be taken before to enable remedial measures to be taken before hypoxia results in an irreversible brain damagehypoxia results in an irreversible brain damage

• Capnography has been shown to be effective in Capnography has been shown to be effective in the early detection of adverse respiratory eventsthe early detection of adverse respiratory events. .

• Capnography and pulse oximetry together Capnography and pulse oximetry together could have helped in the prevention of could have helped in the prevention of 93% of avoidable anesthesia mishaps 93% of avoidable anesthesia mishaps according to ASA closed claim study. according to ASA closed claim study.

• Capnography has also been shown to Capnography has also been shown to facilitates better detection of potentially facilitates better detection of potentially life-threatening problems than clinical life-threatening problems than clinical judgment alonejudgment alone

Case ScenarioCase Scenario

• 61 year old male61 year old male• C/O: “short-of-breath” and “exhausted”C/O: “short-of-breath” and “exhausted”• H/O: > 45 years of smoking 2 packs a day, H/O: > 45 years of smoking 2 packs a day,

3 heart attacks, high blood pressure3 heart attacks, high blood pressure• Meds: “too expensive to take every day ”Meds: “too expensive to take every day ”• Exam: HR 92, RR 18, 160/100, 2+ pitting Exam: HR 92, RR 18, 160/100, 2+ pitting

edema, wheezing, cracklesedema, wheezing, crackles

CHF?CHF? COPD?COPD?What other information would help in What other information would help in

making assessment of this pt.?making assessment of this pt.?

Why Measure VentilationWhy Measure Ventilation——Non-Intubated PatientsNon-Intubated Patients

• Objectively assess acute Objectively assess acute respiratory disorders respiratory disorders – Asthma Asthma – COPDCOPD

• Possibly gauge response to treatmentPossibly gauge response to treatment

Why Measure Ventilation—Why Measure Ventilation—Non-intubated PatientsNon-intubated Patients

• Gauge severity of hypoventilation statesGauge severity of hypoventilation states– Drug intoxicationDrug intoxication– Congestive heart failureCongestive heart failure– Sedation and analgesiaSedation and analgesia– Stroke Stroke – Head injury Head injury

• Assess perfusion statusAssess perfusion status• Noninvasive monitoring of patients in DKANoninvasive monitoring of patients in DKA

• HistoryHistory• TerminologyTerminology• Why capnographyWhy capnography• Basic physiologyBasic physiology• PhysicsPhysics• TypesTypes• Components of capnography Components of capnography • Clinical applicationClinical application• Carry homeCarry home

CO2 transportCO2 transport

• 60% as bicarbonate ion60% as bicarbonate ion• 10-20% binds to amino group of proteins 10-20% binds to amino group of proteins

mostly hemoglobin mostly hemoglobin

HALDANE EFFECTHALDANE EFFECT• 5-10% directly dissolved in plasma 5-10% directly dissolved in plasma

End-tidal COEnd-tidal CO2 2 (EtCO(EtCO22))

r r Oxygen

O2

CO2O

2

VeinA te y


PerfusionPerfusion

Pulmonary Blood Flow

Right Ventricle

LeftAtrium

End-tidal COEnd-tidal CO22 (EtCO (EtCO22))

• Carbon dioxide can be measured Carbon dioxide can be measured

• Arterial blood gas is PaCOArterial blood gas is PaCO22 – Normal range: 35-45mmHgNormal range: 35-45mmHg

• Mixed venous blood gas PeCOMixed venous blood gas PeCO22

– Normal range: 46-48mmHgNormal range: 46-48mmHg

• Exhaled carbon dioxide is EtCOExhaled carbon dioxide is EtCO22 – Normal range: 35-45mmHgNormal range: 35-45mmHg


• Reflects changes inReflects changes in – VentilationVentilation - movement of air in and - movement of air in and

out of the lungsout of the lungs– DiffusionDiffusion - exchange of gases between - exchange of gases between

the air-filled alveoli and the pulmonary the air-filled alveoli and the pulmonary circulationcirculation

– Perfusion Perfusion - circulation of blood- circulation of blood


• Monitors changes in Monitors changes in – VentilationVentilation - asthma, COPD, airway - asthma, COPD, airway

edema, foreign body, strokeedema, foreign body, stroke– Diffusion Diffusion - pulmonary edema, - pulmonary edema,

alveolar damage, CO poisoning, alveolar damage, CO poisoning, smoke inhalationsmoke inhalation

– PerfusionPerfusion - shock, pulmonary - shock, pulmonary embolus, cardiac arrest, embolus, cardiac arrest, severe dysrhythmiassevere dysrhythmias

a-A Gradienta-A Gradient

r r Alveolus

PaCO2

VeinA te y


PerfusionPerfusion

Arterial to Alveolar Difference for CO2

Right Ventricle

LeftAtrium

EtCO2

End-tidal COEnd-tidal CO22 (EtCO (EtCO22))

• Normal a-A gradientNormal a-A gradient– 2-5mmHg difference between the EtCO2-5mmHg difference between the EtCO22

and PaCOand PaCO22 in a patient with healthy lungs in a patient with healthy lungs

– Wider differences found Wider differences found • In abnormal perfusion and ventilation In abnormal perfusion and ventilation • Incomplete alveolar emptyingIncomplete alveolar emptying• Poor samplingPoor sampling

Negative a-A gradientNegative a-A gradient

• PregnancyPregnancy• Infants and childrenInfants and children• During and after bypass During and after bypass • after coming of cardiac bypassafter coming of cardiac bypass• Low frequency high tidal volume Low frequency high tidal volume

ventilationventilation

Raman effectRaman effect

• Electromagnetic radiation and moleculeElectromagnetic radiation and molecule• The transfer of energy affects the vibration The transfer of energy affects the vibration

energy associated with bonds between the energy associated with bonds between the atoms in a moleculeatoms in a molecule

• Absorption of radiation at a particular Absorption of radiation at a particular wave length is associated with the specific wave length is associated with the specific type of bond between atoms in a type of bond between atoms in a molecule.molecule.

Absorption of radiation depends on Absorption of radiation depends on the wavelength of radiationthe wavelength of radiation

• Energy of radiation is proportional to the Energy of radiation is proportional to the frequency of radiation frequency of radiation

• the transfer of energy between the the transfer of energy between the radiation and molecule results in a change radiation and molecule results in a change in the wavelength of radiationin the wavelength of radiation

Raman spectrographyRaman spectrography

• Raman Spectrography uses the principle of "Raman Raman Spectrography uses the principle of "Raman Scattering" for COScattering" for CO22 measurement. measurement.

• The gas sample is aspirated into an analyzing chamber, The gas sample is aspirated into an analyzing chamber, where the sample is illuminated by a high intensity where the sample is illuminated by a high intensity monochromatic argon laser beam.monochromatic argon laser beam.

• The light is absorbed by molecules which are then excited The light is absorbed by molecules which are then excited to unstable vibrational or rotational energy states (Raman to unstable vibrational or rotational energy states (Raman scattering). scattering).

• The Raman scattering signals (Raman light) are of low The Raman scattering signals (Raman light) are of low intensity and are measured at right angles to the laser beam. intensity and are measured at right angles to the laser beam.

• The spectrum of Raman scattering lines can be used to The spectrum of Raman scattering lines can be used to identify all types of molecules in the gas phaseidentify all types of molecules in the gas phase

Mass spectrograpyMass spectrograpy

Chemical method of COChemical method of CO22 measurement - measurement -

pH sensitive chemical indicatorpH sensitive chemical indicator

Effect of atmospheric pressureEffect of atmospheric pressure

• FEtCO2=partial pressure(atmospheric FEtCO2=partial pressure(atmospheric pressure-water vapour pressure)*100pressure-water vapour pressure)*100

• At atm pressure of 760mmHg, At atm pressure of 760mmHg,

FEtCO2=38(760-47)*100 =5%FEtCO2=38(760-47)*100 =5%

at atm pressure of 500mmHgat atm pressure of 500mmHg

FEtCO2=38(500-47)*100 =8%FEtCO2=38(500-47)*100 =8%

Influence of water vapourInfluence of water vapour

1.1. Effect of condensed water:Effect of condensed water:

Water vapor may condense on the Water vapor may condense on the window of the sensor cell and absorb IR window of the sensor cell and absorb IR light, thereby produce falsely high C02 light, thereby produce falsely high C02 readingsreadings

2. Effect of water vapor. 2. Effect of water vapor.

The temperature of the sampling gases The temperature of the sampling gases may decrease during the passage from the may decrease during the passage from the patient to the unit, resulting in a decrease in patient to the unit, resulting in a decrease in the partial pressure of water vapor. This can the partial pressure of water vapor. This can cause an apparent increase in C02 cause an apparent increase in C02 concentration of about 1.5-2%concentration of about 1.5-2%

FEtCO2=partial pressure(atmospheric pressure-water vapour pressure)*100

Volume capnographyVolume capnography Time capnographyTime capnography

Time capnographyTime capnography

AdvantagesAdvantages• Simple and convenientSimple and convenient• Monitor non-intubated patientsMonitor non-intubated patients• Monitor dynamics of inspiration and Monitor dynamics of inspiration and

expirationexpiration

DisadvantagesDisadvantages• Poor estimation of V/Q status of lungsPoor estimation of V/Q status of lungs• Physiologic space dead spacePhysiologic space dead space

SidestreamSidestream

Side-stream CapnographsSide-stream Capnographs

advantagesadvantages

Easy to connectEasy to connect

No problems with sterilizationNo problems with sterilization

Can be used in awake patientsCan be used in awake patients

Easy to use when patient is in Easy to use when patient is in unusual positions such as in prone unusual positions such as in prone positionposition

Can be used in collaboration with Can be used in collaboration with simultaneous oxygen simultaneous oxygen administration via a nasal prongadministration via a nasal prong

disadvantagesdisadvantages Delay in recording due to movement Delay in recording due to movement

of gases from the ET to the unitof gases from the ET to the unit

Sampling tube obstructionSampling tube obstruction

Water vapor pressure changes Water vapor pressure changes affect COaffect CO22 concentrations concentrations

Pressure drop along the sampling Pressure drop along the sampling tube affects COtube affects CO22 measurements measurements

Sampling of CO2 from nasal cannulaeSampling of CO2 from nasal cannulae

Adequacy of spontaneous respirationAdequacy of spontaneous respiration

Sampling of CO2 from oxygen mask

mainstreammainstream

MainstreamMainstream

• AdvantagesAdvantages No sampling tubeNo sampling tube

No obstructionNo obstruction

No affect due to pressure dropNo affect due to pressure drop

No affect due to changes in water vapor No affect due to changes in water vapor pressurepressure

No pollutionNo pollution

No deformity of capnograms due to non No deformity of capnograms due to non dispersion of gasesdispersion of gases

No delay in recordingNo delay in recordingSuitable for neonates and childrenSuitable for neonates and children

• Disadvantages Disadvantages weight of the sensor, (the newer weight of the sensor, (the newer sensors are light weight minimizing sensors are light weight minimizing traction on the endotracheal tube)traction on the endotracheal tube)

Long electrical cord, but it is Long electrical cord, but it is lightweight.lightweight.

Sensor windows may clog with Sensor windows may clog with secretions( they can be replaced secretions( they can be replaced easily as they are disposable)easily as they are disposable)

Difficult to use in unusual patient Difficult to use in unusual patient positioning such as in prone positioning such as in prone positions.positions.

Capnographic WaveformCapnographic Waveform

• Normal waveform of one respiratory cycleNormal waveform of one respiratory cycle• Similar to ECGSimilar to ECG

– Height shows amount of COHeight shows amount of CO22

– Length depicts timeLength depicts time


• Waveforms on screen and printout Waveforms on screen and printout may differ in durationmay differ in duration– On-screen capnography waveform is On-screen capnography waveform is

condensed to provide adequate information condensed to provide adequate information the in 4-second viewthe in 4-second view

– Printouts are in real-timePrintouts are in real-time– Observe RR on deviceObserve RR on device


• Capnograph detects only COCapnograph detects only CO22 from ventilationfrom ventilation

• No CONo CO22 present during inspiration present during inspiration– Baseline is normally zeroBaseline is normally zero

A B

C D

E

BaselineBaseline

Phase I Dead space ventillation Phase I Dead space ventillation

Beginning of exhalationBeginning of exhalation

A B

IBaselineBaseline

Phase II Phase II Ascending PhaseAscending Phase

Alveoli

COCO22 present and increasing in exhaled air present and increasing in exhaled air

IIA

B

C

Ascending PhaseAscending PhaseEarly ExhalationEarly Exhalation

Phase III AlPhase III Alveolar Plateauveolar Plateau

COCO22 exhalation wave plateaus exhalation wave plateaus

A B

C D

III

Alveolar PlateauAlveolar Plateau

Capnogram Phase IIICapnogram Phase IIIEnd-TidalEnd-Tidal

End of the the wave of exhalation contains the End of the the wave of exhalation contains the highest concentration of COhighest concentration of CO2 -2 - number seen on number seen on monitormonitor

A B

C D End-tidal

Capnogram Phase IVCapnogram Phase IVDescending PhaseDescending Phase

• Inhalation beginsInhalation begins• Oxygen fills airwayOxygen fills airway

• COCO22 level quickly level quickly

drops to zerodrops to zero

Alveoli

Capnogram Phase IVCapnogram Phase IVDescending PhaseDescending Phase

Inspiratory downstroke returns to baselineInspiratory downstroke returns to baseline

A B

C D

EIV

Descending Phase Descending Phase InhalationInhalation

Inspiratory segmentInspiratory segment

• Phase 0: Phase 0: InspirationInspiration

• Beta Angle - Angle Beta Angle - Angle between phase III between phase III and descending and descending limb of inspiratory limb of inspiratory segmentsegment

Expiratory segmentExpiratory segment

• Phase I - Anatomical Phase I - Anatomical dead spacedead space

• Phase II - Mixture of Phase II - Mixture of anatomical and anatomical and alveolar dead spacealveolar dead space

• Phase III - Alveolar Phase III - Alveolar plateauplateau

• Alfa angle - Angle Alfa angle - Angle between phase II and between phase II and phase III (V/Q status of phase III (V/Q status of lunglung

Capnography WaveformCapnography Waveform

Normal range is 35-45mm Hg (5% vol)Normal range is 35-45mm Hg (5% vol)

Normal WaveformNormal Waveform

45

0

Capnography Waveform PatternsCapnography Waveform Patterns

0

45

HypoventilationHypoventilation RR : EtCO2

45

0

Hyperventilation Hyperventilation RR : EtCO2

45

0

NormalNormal

Capnography-3 sources of informationCapnography-3 sources of information

• No. – PEtCO2 valuesNo. – PEtCO2 values• Shapes of capnogramShapes of capnogram• (a-ET)PCO2 differences(a-ET)PCO2 differences

(a-ET)PCO2 differences(a-ET)PCO2 differences

• (a-ET)PCO2 difference is a gradient of (a-ET)PCO2 difference is a gradient of alveolar dead space.alveolar dead space.

increase decrease

AgeEmphysemaLow cardiac output statesHypovolemiaPulmonary embolism

Pregnancy and Children

Five characteristics of capnogram Five characteristics of capnogram should be evaluatedshould be evaluated

The shape of a capnogram is identical in all humans with The shape of a capnogram is identical in all humans with healthy lungs. healthy lungs.

Any deviations in shape must be investigated to Any deviations in shape must be investigated to determine a physiological or a pathological cause of determine a physiological or a pathological cause of the abnormalitythe abnormality

• FrequencyFrequency• RhythmRhythm• HeightHeight• BaselineBaseline• Shape Shape

Resuscitation- trendResuscitation- trend

• A terminal upswing A terminal upswing at the end of phase at the end of phase 3, known as phase 3, known as phase 4, can occur in 4, can occur in pregnant subjects, pregnant subjects, obese subjects obese subjects and low and low compliance statescompliance states

The slope the expiratory plateau is increased as a The slope the expiratory plateau is increased as a normal physiological variation in pregnancynormal physiological variation in pregnancy

Prolonged inspiratory descending limbProlonged inspiratory descending limb

• due to dispersion due to dispersion gases in the sampling gases in the sampling line or as well as line or as well as prolonged response prolonged response time of the analyzer. time of the analyzer. Seen in children who Seen in children who have faster have faster respiratory ratesrespiratory rates

Base line elevated inBase line elevated in

• Inadequate fresh gas flowInadequate fresh gas flow• Accidental administration of CO2Accidental administration of CO2• RebreathingRebreathing• Insp / exp valve malfunctionInsp / exp valve malfunction• Exhausted CO2 absorberExhausted CO2 absorber

Elevation of base lineElevation of base line

Contamination of CO2 monitorContamination of CO2 monitor

• sudden elevation sudden elevation of base line and of base line and top linetop line

Expiratory valve malfunctionExpiratory valve malfunction

• Expiratory valve Expiratory valve malfunction can malfunction can result in prolonged result in prolonged abnormal phase 2 abnormal phase 2 and phase 0and phase 0

Inspiratory valve malfunction Inspiratory valve malfunction

• Elevation of the Elevation of the base line, base line, prolongation of prolongation of down stroke, down stroke, prolongation of prolongation of phase IIIphase III

Bain circuitBain circuit

• Inspiratory base Inspiratory base line and phase I line and phase I are elevated above are elevated above the zero due to the zero due to rebreathing. Note rebreathing. Note the rebreathing the rebreathing wave during wave during inspiration. inspiration.

HypoventilationHypoventilation

• Gradual elevation Gradual elevation of the height of the of the height of the capnogram, base capnogram, base line remaining at line remaining at zerozero

hyperventillationhyperventillation

• Gradual decrease Gradual decrease in the height of the in the height of the capnogram, base capnogram, base line remaining at line remaining at zerozero

Oesophageal intubationOesophageal intubation

Cardiogenic oscillations.Cardiogenic oscillations.

• Ripple effect, Ripple effect, superimposed on superimposed on the plateau and the the plateau and the descending limb, descending limb, resulting from small resulting from small gas movements gas movements produced by produced by pulsations of the pulsations of the aorta and heart.aorta and heart.

Airway obstruction (eg., bronchospasm). Phase II and phase III Airway obstruction (eg., bronchospasm). Phase II and phase III are prolonged and alpha angle (angle between phase II and are prolonged and alpha angle (angle between phase II and

phase III) is increasedphase III) is increased

bronchospasmbronchospasm

duringduring After reliefAfter relief

Curare effectCurare effect

Malignant hyperpyrexiaMalignant hyperpyrexia

hypothermiahypothermia

• A gradual decrease in A gradual decrease in end tidal carbon end tidal carbon dioxide dioxide

hypothermia,hypothermia,

reduced metabolism, reduced metabolism, hyperventilation, hyperventilation, leaks in the sampling leaks in the sampling systemsystem

KyphoscoliosisKyphoscoliosis

• The COThe CO22 waveform waveform

has two humps. has two humps. resulted in a resulted in a compression of the compression of the right lungright lung

• Capnogram during Capnogram during spontaneous spontaneous ventilation in ventilation in adultsadults

• Sampling Sampling problems such air problems such air or oxygen dilution or oxygen dilution during nasal or during nasal or mask sampling of mask sampling of carbon dioxide in carbon dioxide in spontaneously spontaneously breathing patients. breathing patients.

Detection of pulmonary air embolismDetection of pulmonary air embolism

• A rapid decrease of PETCO2 A rapid decrease of PETCO2 in the absence of changes in in the absence of changes in blood pressure, central blood pressure, central venous pressure and heart venous pressure and heart rate indicates an air embolism rate indicates an air embolism without systemic without systemic hemodynamic consequences.hemodynamic consequences.

• as the size of air embolism as the size of air embolism increases, a reduction in increases, a reduction in cardiac output occurs which cardiac output occurs which further decreases PETCO2 further decreases PETCO2 measurement. A reduced measurement. A reduced cardiac output by itself can cardiac output by itself can decrease PETCO2decrease PETCO2. .

Effective circulating blood volume can Effective circulating blood volume can reduce the height of capnogramsreduce the height of capnograms

Phases of the CapnogramPhases of the Capnogram

Phase I

Expiration

Represents anatomical dead space

Phase II

Expiration

Mixture of anatomical and alveolar dead space

Phase III

Expiration

Plateau of alveolar expiration

Phase 0

Inspiration

Rapid fall

in CO2 concentration

Phase IV

Exhalation

Compromised thoracic compliance

HyperventilationHyperventilation

Progressively lower plateau (phase II) segment

Baseline remains at zero

Decreasing CO2 levels

HypoventilationHypoventilation

Steady increase in height of Phase IISteady increase in height of Phase IIBaseline remains constantBaseline remains constant

Spontaneous VentilationSpontaneous Ventilation

Short Alveolar plateauShort Alveolar plateau

Increased frequency of waveformsIncreased frequency of waveforms

Cardiogenic OscillationsCardiogenic Oscillations

Ripples during Phase II and Phase III Ripples during Phase II and Phase III

Due to changes in pulmonary blood volume and ultimately Due to changes in pulmonary blood volume and ultimately COCO2 2 pressure as a result of cardiac contractionspressure as a result of cardiac contractions

Curare CleftCurare CleftShallow dips in phase II plateauShallow dips in phase II plateauCan occur when patient is in a light plane of anesthesiaCan occur when patient is in a light plane of anesthesia

Represent patient attempts to breathe independent of mechanical ventilation

BronchospasmBronchospasmAirway ObstructionAirway ObstructionCOPDCOPD Sloping of inspiratory and expiratory segments

Prolonged Phase II and Phase III

Rebreathing of Soda LimeRebreathing of Soda LimeContamination with COContamination with CO22

Elevation of Phase II segment and baseline

Elevation of baseline and Phase II, smaller inspiratory efforts

Progressive elevation of Phase II and baseline

Bain SystemBain System

Smaller wave form represents rebreathing of CO2

Slow ventilationSlow ventilationIncompetent inspiratory valveIncompetent inspiratory valve

Prolongation of Phase 0Prolongation of Phase 0

• Capnography provides Capnography provides another objective data another objective data point in making a point in making a difficult decisiondifficult decision

Capnography

Education

Transcript of Capnography