Pre-Hospital Capnography Dr Nick Foster EMICS
Pre-Hospital Capnography
Dr Nick Foster EMICS
Early Warning: When do you want the patient’s parachute to open?
Capnography 4-10 minutes
Pulse Oximetry
Pulse Oximetry 30-60 seconds
ECG
ECG 10 seconds
No monitor = free fall!
Physiology
Carbon dioxide
A Capnograph will show you second by second where you are with the patient by showing you
The CO2 readingThe CO2 waveformThe Respiratory rateThe Oxygen saturationThe pulse rate
Metabolism/Perfusion/Ventilation
CapnographyCapnography
An EtCO2 value of e.g..38mm/Hg
with a trace
Time
5040302010
0
is as diagnostic as an ECG
► Application in clinical practice
Objectives
► How it works
► The physiology involved
►How it works
►CO2 monitoring technology
Capnometry: the measurement and numerical display of the CO2 level appearing in the airway
Capnograpahy: the measurement and graphical display of the CO2 level appearing in the airway
►CO2 monitoring technology
Compares the amount of infrared light absorbed by a sample of expired CO2 to a chamber with no CO2
Infrared spectroscopy
►CO2 monitoring technology Respiratory gases are continuously aspirated by a side port tube connection from the patients airwaySidestream sampling
Advantages
•Able to monitor intubated and non-intubated patients
•Uses thin tubing therefore less dead space
•Less likely to become contaminated with moisture because it is away from the airway
•Uses a zero reference to keep the monitoring calibration
►CO2 monitoring technology
Sidestream sampling
Disadvantages
•There is a lag time between sampling and measurement Advances: faster response time
•If the patient is breathing rapidly, there may be contamination of the inhaled and exhaled gases and give a falsely low CO2 reading. Advances: Lower sample rates now used
•The tubing can get obstructed by water and mucus
•Pre-hospital use is in its infancy
► The physiology involved
Physiology of RespirationPhysiology of Metabolism
Physiology of metabolism
An acidoisis makes the pH more acidic than usualAn alkalosis makes the pH more alkaline than usual
Metabolism
Homeostasis. The body tries to maintain a state of equilibrium despite everything we throw at it.
Body pH range 71.-7.8, homeostasis is about 7.3 -7.4
A body pH of 7.2 called acidaemiaA body pH of 7.5 called alkalaemia
Physiology of metabolism
There are a number of acids in the body• CO2• Lactic acid from cell activity if starved of oxygen.
Complex chemical interactions that keep these in balance.
These dangerous acids need to be removed
• Buffers: immediate• CO2 production: minutes• Renal excretion/Liver breakdown: days
Physiology of metabolism
A balance exists
ACID CO2Tissues Lungs
By looking at what goes into the body via the lungs (Oxygen) and what comes out (Carbon dioxide) you get a picture as to how damaged or ill the body is
Physiology of respiration
a natural waste product of cellular activity
Carbon dioxide
OxygenOxygen -> lungs -> alveoli -> blood
muscles + organs
OxygenOxygen
cells
OxygenOxygen
OxygOxygenen ++GlucoGlucosese
energy
COCO22
blood
lungs
COCO22
breath
COCO22
Physiology of respiration
Oxygen/Carbon dioxide interaction: Metabolism
CO2 produced by cellular metabolism diffuses across the cell membrane into the circulating blood.
5-10% carried in solution
20-30% bound to haemoglobin
60-70% carried as bicarbonate in the red blood cell
O2
CO2 O2
CO2
CO2
Physiology of respiration
Oxygen/Carbon dioxide interaction: Perfusion and Ventilation
Ventilation
Perfusion
• Oxygenation = oxygen → lungs→ alveoli→ blood
• Metabolism = oxygen is converted to energy + CO2
• CO2 elimination = CO2 → blood→ lungs→ exhalation
Physiology of respiration
Ventilation
Perfusion
METABOLISM PERFUSION VENTILATION
So CO2 levels provide evidence of three parameters going on the body
Physiology
What's happening at the cellular level How well the circulation is
performingHow well the lungs are working
METABOLISM PERFUSION VENTILATION
Physiology
If metabolism fails, acid forms (metabolic acid).
With severe shock, the patient becomes very “acidic” and very ill
Metabolic acidosisThis may be tolerated if circulation and oxygenation are maintained. The acid is converted to CO2 and this is blown off by the lungs
METABOLISM PERFUSION VENTILATION
Physiology
If the circulation is failing, this “acid” cannot be transported to the lungs and the patient becomes iller
Metabolic acidosisCO2 cannot be removed from the lungs as it cannot get there. Your only hope is to get the circulation working more effectively
METABOLISM PERFUSION VENTILATION
Physiology
Carbon dioxide
If the breathing is inadequate, CO2 accumulates in the blood and is converted to acid
Respiratory acidosisBy ventilating the patient, we can get rid of the excessive CO2 and thereby reduce the damage the “acid” in the blood is doing to the tissues
Physiology
Metabolic acidosisAcid builds up (anaerobic metabolism)•Tissue hypoxia (anaemia, shock, severe infection, diabetic ketoacidosis)•Renal failure•Loss of body salts (severe diarrhoea)
Respiratory acidosisHypoventilation: CO2 builds up•Airway obstruction•Central neuro: brain injury, stroke, opiates•Periph neuro: spinal cord, MND•Chest wall disease (muscle, flail chest, trauma, pneumothorax•COPD•Pneumonia,
Respiratory alkalosisHyperventilation: CO2 blown off•Anxiety states•Asthma - low O2, low CO2•PE - low O2, low CO2BUT as exhaustion sets in -low O2 with rising CO2
Metabolic alkalosisAcid is lost•Severe vomiting (acid lost from stomach)
Capnography measurements
Normal waveform:
Capnography measurements
The waveform
I just want you to look at the display first for a minute and then I will break the wave down into its constituent parts
Capnography measurements
The waveform
The lungs are composed of tissue involved in gas exchange (alveoli) and tubes connecting them to the outside world (bronchi, trachea). These tubes ARE NOT involved in gas exchange and is called dead space.
Capnography measurements
The waveform
Phase IRepresents the CO2-free gas from the airways (anatomical and apparatus dead space).
Capnography measurements
The waveform
Phase IIConsists of a rapid upswing on the tracing (due to mixing of dead space gas with alveolar gas).
Capnography measurements
The waveform
Phase IIIConsists of an alveolar plateau representing CO2-rich gas from the alveoli. It almost always has a positive slope, indicating a rising PCO2
Capnography measurements
The waveform
Phase 0Is the inspiratory phase where normal air is breathed in. There is only 0.36mmHg of CO2 in the air compared to 40mmHg in expired air
Capnography measurements
The waveform
Normal waveform:
Capnography measurements
The waveform
Causes for a rise in end tidal CO2
Increased CO2 output
Increased Pulmonary perfusion
Reduced Alveolar Ventilation
Technical errors Machine faults
Fever Hypercatabolic states
Increased cardiac output Increased blood pressure
Hypoventilation by patientBronchial intubation (reduces the dead space)Rebreathing
Inadequate fresh gas flowsPoor ventilation by DrFaulty valves
Causes for a fall in end tidal CO2
Reduced CO2 output
Reduced Pulmonary perfusion
Increased Alveolar Ventilation
Technical errors Machine faults
HypothermiaHypocatabolic state (eg gross myxoedema)
Reduced cardiac output •Hypotension•Hypovolaemia•Pulmonary embolism•Cardiac arrest
Hyperventilation ApnoeaAirway blocked: obstruction, ET tube extubated
Circuit disconnection Sampling tube leak
Look for five characteristics of the waves, Height (normal = 38mmHg. Tall = high CO2,
small = low CO2) Rate Rhythm (regular, getting bigger (or smaller) Base line (how wide it is) Shape of the wave
Waveform analysis
Waveform analysis
Hyperventilation Baseline at zero, but height is reduced gradually
Hypoventilation Base line at zero, but height is increased gradually
Clinical applications
Intubated patients
Applications
ApplicationsIntubated patients
Intubation
Verification of tube placement and monitoring ET placement during transport AND its dynamic (cf to a CO2 disc)
5-20% of tubes are misplaced either at the time of intubation or during transfer.
ApplicationsIntubated patients
Cardiac arrest
CO2 is a a measure of cardiac output. Because CO2 tracks cardiac output, capnography can show you how effective CPR is.
It is the earliest sign of a returning circulation. It is even more effective than a pulse check
PEA – an ECG with no endtidal CO2.
ApplicationsIntubated patients
Cardiac arrest and CPR
Non-intubated patients
Applications
ApplicationsNon-intubated patients
Chest pain: MI or not an MI
Chest pain + tachyarrhythmia with normal capnogrpahy: Pt stable
Chest pain + tachyarrhytmia with CO2 at 10mmHg is about to have a cardiac arrest on you
Applications
3 patients who are short of breathWho has asthma, who has COPD
and who has CCF?
Applications3 patients short of breath
Waveform diagnostic of asthma/COPD. It indicates bronchospasm/airway obstruction
Asthma
NormalBronchospasm/Airway
Obstruction
The reason for the shark fin shape is due to the increased dead space present
Applications
AsthmaThe shape is a shark fin
Width of the shape gets smaller as the patient gets worse
Applications
Worsening asthma
This patient needs ventilatory assistance
Note the narrow base and tachypnoea and rising CO2
3 patients short of breathAsthma
Applications
Response to treatment with Terbutaline. Indices return to normal.This patient has asthma: Diagnosis.
3 patients short of breathAsthma
Applications COPD
Shark fin shaped waveform appearance showing airway obstruction.Wide base (cf asthma which was narrow)Elevated ETCO2 level 50mmHgPt has COPD
In contrast with asthma
3 patients short of breath
Applications CCF
•The low waveform height shows a low CO2 level. •It is not shark fin in shape so not COPD/asthma. •The low CO2 level indicates poor perfusion. •This is a poor circulation that could go with CCF. The heart is not pumping as well as it should
3 patients short of breath
Applications
Chest infection
Applications
Chest infectionFever causes the CO2 level to go up
and the pulse rate to go upThe pneumonia causes the SpO2
level to go down
Applications
Another patient with a chest infection
Endtidal CO2 27%SpO2 91RR 30Pulse 120
Seen by GP 5 days before and diagnosed flu. Fever for 6 days.Temp 104F, Left side chest sign, creps ++, increased breathsounds, Whisp pect, Diagnosis left pneumonia in fact Legionella developed empyema 4 days later.
Applications
Patient with pleuritic chest pain
Endtidal CO2 38SpO2 99 on airRR 14Pulse 80
Chest pain, pleuritic. 4 hours. ECG normal. Chest examination normal, normal percussion, normal breath sounds. Tender chest wall. Calves normal and no tenderness
ApplicationsRTA – M1 Car fire following RTA
Endtidal CO2 22SpO2 – on 99% oxygenRR 23Pulse 98
24 year old male, driver RTA car fire. Had to be pulled from the car by passers by. Airway open, no carbonaceous material around mouth, nares clear. Breathing spontaneous, good A/E. Cap refill <2 radial pulse 110/80 GCS 14/15. No focal neurology. No obvious fracture
Applications
The unconscious patient
ApplicationsThe unconscious patient
Look for hypoventilation i.e. a high endtidal CO2 readingAnd a low respiratory rate
ApplicationsThe unconscious patient
• Sedation:• Alcohol: a drunk with a normal CO2 is stable. A drunk who is hypoventilating is at risk• Drug ingestion:
Applications
Metabolic states
ApplicationsMetabolic states
With acidosis, the respiratory rate increases (e.g. diabetic ketoacidosis)
METABOLISM PERFUSION VENTILATION
Physiology reminder
If the circulation is failing, this “acid” cannot be transported to the lungs and the patient becomes iller
Metabolic acidosisCO2 cannot be removed from the lungs as it cannot get there. Your only hope is to get the circulation working more effectively
ApplicationsMetabolic states: a tale of two patient both with diabetic ketoacidosis
Who is the sickest of the two?
Patient AEndtidal CO2 30mmHgSpO2 100RR 30Pulse 120
Patient BEndtidal CO2 30mmHgSpO2 99RR 10Pulse 120
ApplicationsMetabolic states
A diabetic with a normal ETCO2 is not sickA diabetic with a low ETCO2 is a sick person. An ETCO2 of 6mmHg is bordering on a cardiac arrest
ApplicationsMetabolic states
55 year old male collapsed at home
Endtidal CO2 24SpO2 92RR 10Pulse 80
Alcoholic, Myxoedema ( had not taken thyroxine for two years) very pale (Hb 2.4) BP 80/-, hepatic encephalopathy, jaundice, hypotensive. He died 3 days later
This patient is very ill.
Applications
The head injured patient
Applications
The head injured patient
Midazolam light anaesthesiacapnography and assisted ventilation to maintain homeostasis
Why is Pre-Hospital Capnography important
Why is Pre-Hospital Capnography important
We cannot do anything about those who are going to die whatever we do. (Triage)
However we should be able to recognise and prevent those who would otherwise die needlessly
Why is Pre-Hospital Capnography important
Preventable needless deaths occur • Immediately at the time of injury
Hypoxia and Airway obstruction
• Later following their injuryHypercarbia (too much CO2 )
AcidaemiaCerebral vasodilation
Hypoxia (not enough O2 )Hypoxic encephalopathyCardiac arrest
Why is Pre-Hospital Capnography important
Time is important. For every minute of “no pre-hospital resuscitation”, the risk of dying increases by 4.3%
Why is Pre-Hospital Capnography important
Airway
Breathing
Circulation
Scene Management
The only thing about ABC is that it occurs at the beginning of the alphabet but it ain’t very practical and doesn't really help
ApplicationsReal life incidents
Ilkeston 2330hrs head on RTA – four casualties three unconscious, one conscious but with a fractured L3 spine
female• GCS 7• SpO2 100 • Pulse 120
•RR 10•End tidal CO2 72mmHg
The ABC had been followed
But as I arrived, she had her first fit
capnography
Why is Pre-Hospital Capnography important
Airway
Breathing
Circulation
Scene Management
Just because they are BREATHING, does NOT mean they are oxygenating and ventilating properly
Why is Pre-Hospital Capnography important
Airway
Breathing
Circulation
Scene Management
and just because they have a CIRCULATION doesn’t mean the blood’s going to the right places or may even be going in the wrong direction.
Why is Pre-Hospital Capnography important
Airway
Breathing
Circulation
Scene Management
So having caused you all to have sleepless nights, I would like to suggest an alternative concept
Why is Pre-Hospital Capnography important
Airway
Breathing
Circulation
Scene Management
Ventilation
Perfusion
Capnography
Why is Pre-Hospital Capnography important
Airway
Ventilation
Haemorrhage control
Assisting the circulation
Procedural sedationTo facilitate extrication
To facilitate manipulation
Pre-hospital anaesthesia
Severe trauma management is not ABC
Perfusion
Ventilation
Airway
Beware………………..The patient with the low
CO2 and the low respiratory rate
They could be about to die on you
Take home tip
When do you want the parachute to open?
Capnography 4-10 minutes
Pulse Oximetry
Pulse Oximetry 30-60 seconds
ECG
ECG 10 seconds
No monitor = free fall!