prehospital capnography
DESCRIPTION
Developed for the Wairarapa Ambulance Service, NZTRANSCRIPT
Pre-hospital Pre-hospital CapnographyCapnography
Heidi Whitman, [email protected]
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.