Pre-hospital Pre-hospital CapnographyCapnography

Heidi Whitman, ICPwhitmaha@yahoo.com

Capnography Benefits Immediate breath-to-breath information

about patient respiratory status

Are they adequately ventilated?

Experiencing bronchospasm?

Are they breathing too quick or too slow?

Capnography Benefits

Insight to patient's cardiac output, and if they are perfusing well

Whether the patient has normal metabolic activity or if it's increased or decreased

Objective monitor of intubation status

Effectivenessof CPR

Anticipationof ROSC

Guide treatmentIn TBI and DKA

IndicationsAdvanced Airway verification

Cardiac arrest

Status 1 or 2 bronchospasm

Ventilation

Early detection of cellular hypoxia

Any Status 1 or Status 2 patient

Detect life-threatening conditions such as:

Tube Displacement

Respiratory Failure

Circulatory Failure

Capnography is:Capnogram Graphical waveform that measures, illustrates and documents patients exhaled carbon dioxide over time

Capnometry Quantitative numerical reading <average healthy range is 35-45 mmHg>

End-tidal CO2 Carbon dioxide level at the end of exhalation, when CO2 reaches its highest concentrations

The measurement of CO2 inEACH exhalation reflects:

The CO2 produced by metabolism

Transported by circulatory system <perfusion>

Exhaled by the respiratory system <ventilation>

Metabolism

Homeostatic body pH is about 7.35-7.45

Acidotic states are <7.35Alkalotic states are >7.45

Fatal pH range is outside of 6.9-8.0

Maintenance process by the body is called Acid-base balance

Metabolism

There are many acids in the body: Carbon dioxide, lactic acid (produced if tissues are starved of O2), ketoacids

Complex chemical interactions keep these acids in balance.

Such as..... the Grand Equation!H+HCO³̠ < >H²CO³ < >H²O+CO²

Hydrogen + bicarbonate <> carbonic acid <> water + carbon dioxide

Metabolism

These dangerous acids need to be removed.

BY BUFFERS!

Carbonic acid/bicarb buffering – buffers instantaneously

Protein buffering (hemoglobin binding to CO2 to be released thru respirations) – works in

minutesRenal buffering – takes several hours to days

Ventilation – Perfusion Balance

Oxygen >>> lungs > blood > tissue

Metabolism >>> O2 into energy + CO2

CO2 >>> eliminated from tissues > blood > lungs > exhalation

If the respiratory system and the circulatory system are in good working

order then the ETCO2 values will directly correlate to the CO2 levels in

the arterial blood gasses.

(The difference is about 2-4 mmHg.)

ETCO2 = ABG CO2

So.. Capnography can measure performance of:

MetabolismWhat's

happening at the

cellular level

PerfusionHow well

the circulation

is performing

VentilationHow well the lungs

are working

Bad Metabolism

Acids form. With a

severely shocked

patient they are very

acidic, very sick

Metabolic Acidosis

This may be tolerated if

circulation and oxygenation are

maintained. The acids >

converted to CO2 > blown off by

lungs.

Bad Perfusion

Failing circulation

cannot transport

acids to the lungs to be eliminated.

Metabolic Acidosis

Your only hope is to get the circulation

working more effectively.

Bad Ventilation

Hypoventilation. Carbon dioxide builds up in the

blood and is converted to

acid.

Respiratory Acidosis

Appropriate ventilations

Physiological Factors Affecting Capnography

Increase:

Decreased ventilationRespiratory insufficiencyIncreased muscular activity (such as shivering)Malignant hyperthermiaIncreased cardiac output (during resus)Effective drug treatment for bronchospasmTourniquet releasePain

Physiological Factors Affecting Capnography

Decrease:Increased ventilationsDecreased muscular activity (such as sedation

or muscle relaxants)HypothermiaDecreased cardiac output (cardiac arrest, AMI)Pulmonary embolismBronchospasm (initially decreased, then rises

as the patient tires out)Mucus pluggingSudden hypotension

Ventilation/Perfusion Mismatch

A ventilation/perfusion mismatch will occur if either of these are not functioning well..

(ventilating unperfused lung area; perfusing unventilated lung area)

A ventilation/perfusion mismatch will alter the correlation between ETCO2 and CO2 in the

arterial blood gasses.

Capnogram

Normal Waveform

Capnogram

The initial upstroke indicates the beginning of exhalation.The top plateau indicates the end expiratory carbon dioxide levels as they reach their peak.The downstroke indicates inspiration as CO2 levels rapidly decrease.

Capnogram: Bronchospasm

For a patient with bronchospasm, are their wheezes generally on inspiration or exhalation?

So would you expect any capnography waveform changes to be on the upstroke or the downstroke?

Capnogram: Bronchospasm

“Sharkfin Waveform”

Capnography: Bronchospasm

Progression of waveforms as the bronchospasm is treated successfully

On Scene 10:35

After start of tx

Two nebs 11:12

Capnography: Bronchospasm

COPD vs CHF differentialsGauge effectiveness of asthma treatmentsEven in a noisy truck will still have an accurate assessment of lung status

Low capnometry numbers mean the patient is still compensating. High capnometry means the patient is tiring out and in respiratory failure.

Hypoventilation States

This ETCO2 is near 70 mmHg, while the respiratory rate is 8. Gauge severity of hypoventilation states: overdoses, sedation, stroke, seizure

Conversely...

Beware the patient with low respiratory rate and low

ETCO2....

They could be about to die on you

Overdoses

Capnography is also effective in assessing the depth and trend of responsiveness.

In one study of OD patients, a gradual rise in ETCO2 suggested a decreasing level of

consciousness despite the absence of a clear trend in GCS scores. The decision to perform

intubation appeared to be justified by their prolonged obtundation.

Capnography with Advanced Airways

“Equal breath sounds” can give you false positives. Capnography will never lie.

Studies find incidence of unrecognized tube displacement to be up to 20% without capnography.

With capnography: 0%

Immediate Alert to Emergencies

Apnea

Tube Dislodgement

Cardiac Arrest Applications

ROSC ROSC ROSC

This capnography trends graph shows the sudden rises in ETCO2 that correspond to moments before a return of pulses.

Time = 0 is ROSC. This chart shows a mean ETCO2 value of around 22, then it suddenly spikes to just

under 45 mmHg with ROSC and with the initial CO2 washout. Then it normalizes to around 35 mmHg.

30

15

45

ROSC

Mean ETCO2

Determine Cause of Arrest

Research has found that patients in respiratory induced cardiac arrest (asthma, hanging,

aspiration) had higher initial capnometry values than patients in primary cardiac arrest (VF/VT).

During the first minute of resuscitation, the respiratory arrest values came down and then

equalized with the VF/VT values.

These ETCO2 values then became predictors of ROSC, with higher values correlating to

eventual ROSC.Patients with initial ETCO2 <10 NEVER

achieved ROSC

Compression Effectiveness

One MinuteTwo Minutes

0

25

Rescuer Fatigue and Compressions during ResuscitationCardiac Output measured with Capnography

time

CO

2 (m

mH

g)

First Rescuer

Second Rescuer

Cardio-Cerebral Resuscitation (CCR) advocates changing the compressor every minute. This graph is from the Ochoa “Study of rescuer fatigue”.

Pacing and Cardiac Output

Capnography can also confirm mechanical capture with transcutaneous pacing.

Cardiac Output in Resuscitation

Cardiac Output ETCO2

2L 20

3L 28

4L 32

5L 36

Traumatic Brain Injury

Patients with TBI are CO2-sensitive and their ventilations should be carefully titrated.Aim for a ETCO2 of 35 mmHg.

Physiology: Low CO2 in the body causes vasoconstriction, which is beneficial in TBI's

with herniation. However excessive hyperventilation has shown to increase mortality up to 30% more. Excessive

vasoconstriction will actually cause more swelling on the brain and be counter-

productive.

Diabetic Ketoacidosis

Studies show that ETCO2 values of <29 mean the hyperglycemic patient is 100% in DKA.

Physiology: The metabolic acidosis of the hyperglycemic patient eventually causes

circulatory failure. This is why a low capnography value confirms DKA, whereas you

would expect a high value in an acidotic condition.

DKA

19 yom in DKA, RR-19, ETCO2-11 pH-7.01

What is a fatal pH?

Studies in Progress

Research is underway studying the efficacy of capnography as a guide during fluid

resuscitation in trauma patients with non-compressible bleeds.

The studies suggest that capnography can optimize the balance between permissive

hypotension and a low perfusion status in the patient.