Capnography (ICP) Acknowledgement This training package was created by Leonie Wilton. Please direct any questions to your CSO or Team Leader. Offline Reading Download as PDF Welcome Introduction Basic Physiology & Waveforms Capnography in Cardiac Arrest Capnography in Post-ROSC Management Capnography Application
Appendix and FAQs CPG Links & References Summative Assessment Details Download PDF for of ine reading
Section 1 of 10 Welcome Welcome to the clinical development package which outlines the use of capnography in cardiac arrest (CA) management and post-rosc care. This package was originally prepared for paramedics. Some additional information has been added to make it more relevant to ICP practice, although it is anticipated much of this will be revision. Evidence-based research indicates capnography can provide clinicians with a sensitive indicator of compression effectiveness and ventilation performance; and this can be used as a tool to guide SAAS clinicians when delivering highperformance CPR. Integration of this monitoring into CA management aligns SAAS CPGs with SA Health Policy Guidelines and best practice models of care. References and hyperlinks are provided should you wish to expand your knowledge. Learning Objectives Review the basic principles of how carbon dioxide is measured, including physiology related to capnography Demonstrate an understanding of the structure of the waveform in capnography Review capnography utility in relation to cardiac arrest management Review capnography utility in relation to post-rosc management
Use capnography in accordance with the SAAS paramedic Cardiac Arrest and Post-ROSC Management CPGs (ICP) Overview The training will consist of: a review of the underlying physiology of capnography interpretation of basic waveforms and their clinical significance an outline of capnography utility in CPR and post-rosc management interpretation limitations and treatment implications a summative assessment Successful completion of the online package will require at least 80% correct responses to the 15 MCQ, and must occur prior to attending an OHCA conference. This package (including videos) will take approximately 1 hour to complete.
Section 2 of 10 Introduction The amount of carbon dioxide (CO 2 ) excreted by the lungs is determined by the amount of pulmonary blood flow and ventilation. Capnography is the monitoring of the concentration or partial pressure of CO 2 in respiratory gases. Traditionally, capnography has been used during anaesthesia and intensive care to confirm and monitor correct ETT placement, equipment circuits and adequacy of ventilation using mainstream or side-stream gas sampling. [10] Capnography provides instantaneous information about: ventilation (how effectively CO 2 is being eliminated by the lungs) perfusion (how effectively CO 2 is being transported through the vascular system) metabolism (how effectively CO 2 is being produced by cellular metabolism).[2] Recent evidence highlights the value of information provided by capnography to monitor the effectiveness of CPR; and hence is the main focus of this CDP. Interpretation of the waveforms outside of cardiac arrest requires a more detailed understanding of the relationship with various pathologies, implications for patient treatment, along with identification of normal variances and false values. The picture below demonstrates the breadth of potential application albeit with a ventilator circuit.
Correct interpretation of the capnographic curves can only be achieved by comparison with other parameters recorded simultaneously, such as HR, ECG, BP, body temperature and SpO 2 [19]. This device must be used as a prompt to check the patient and then the equipment to understand why a waveform trend may have changed. For your awareness, paramedics at this time are only authorised to use capnography in the setting of cardiac arrest and post-rosc management. Main advantages of capnography in CA and post ROSC care: Confirm effectiveness of compressions during CPR Predict and correlate ROSC with other clinical findings Detect decreasing/loss of cardiac output during post-rosc management Assist guiding ventilation to ensure a patient is not hyper or hypo-ventilated.
Nb: Paramedics will not be adjusting ventilation on a minute to minute basis according to CO 2 values; rather they will abide by the recommendations in the CPG relevant to that patient and use capnography to detect trends and confirm that ventilation rates are appropriate. For ICPs managing the post-rosc patient, it may be appropriate to cautiously adjust ventilations if CO 2 values are persistently high and the distance to hospital (and patient condition) warrants such intervention. This will be outlined in the ICP post-rosc management CPG. For more information, Capnography.com and capnoacademy.com have some useful information and simulation exercises. The terminology: EtCO 2 refers to maximum Partial pressure of CO 2 at the end of a breath ie end-tidal (about 36-40 mmhg in a healthy adult and the range for children is not significantly different). This is what we will be measuring. PaCO 2 refers to the Partial pressure of CO 2 in the arterial blood (it is generally 3-5 mmhg higher than EtCO 2 ) and normally in the range 35-45 mm Hg. Capnogram a plot of EtCO 2 versus time (there are also volume capnograms but time is common in clinical practice). Prediction of PaCO 2 from ETCO 2 is variable (the major limiting factors = blood flow to the lungs and mismatch between ventilation and perfusion); ETCO2 may be
misleadingly different in conditions with significant mismatch between ventilation and perfusion. Practice Question Capnography for SAAS paramedics and ICPs is most useful during CA management for: providing feedback about the quality of the seal of the i-gel primarily monitoring ventilation rates and tidal volumes indicating the effectiveness of compressions (including fatigue) during CPR; determining likely ROSC during CPR; and monitoring ventilation rates. diagnosing pulmonary obstructive conditions with 100% sensitivity providing an accurate measure of PaCO 2 to most appropriately direct resuscitative efforts SUBMIT
Section 3 of 10 Basic Physiology & Waveforms Physics/ the technology: The first modern capnograph is credited to Karl Fried rich Luft (1937) using infrared technology to measure CO 2 concentration; and is the technologic basis of CO 2 measurement used today. [1] Infrared light is absorbed by gases that have two or more different atoms. Since oxygen has two atoms which are not different it does not absorb infrared waves; whereas carbon dioxide gas has different atoms, it absorbs infrared waves. The more infrared waves that are absorbed the higher the level of CO 2. The amount of CO 2 detected is ultimately converted to a measurement and reflected in the shape and amplitude of the
capnogram seen on the monitor display. If you want to know more about the physics, refer to FAQ 7. There are 2 types of configurations available for CO2 measurement by infrared technology: Mainstream analysers contain their IR sensor in an adaptor that is connected in-line with the patient s ventilatory circuit (typically at the hub of the ETT, and it can only be used in intubated patients. Side-stream systems (used by SAAS and most capnographs) have the sensor remote from the patient, making it useful for both intubated and non -intubated patients. The Microstream sample line used by SAAS aspirates a continuous sample of air (about 50 ml/min) from the centre of the lumen of the airway adaptor in expired breath and delivers it to the sensor for analysis.
There are a number of factors that can influence the accuracy of readings: In a non-intubated patient, exhaled gases can mix with the ambient air or other gases, diluting the CO 2 concentration and falsely lowering the capnography reading [12]. The tendency for under-reading can occur with small sample volumes, increased dead space and small tidal volumes in paediatric patients Basic physiology and Phases: During capnometry, when a patient inhales air which contains negligible CO 2 (~0.04%) and exhales CO 2 (~4%), a waveform tracing is generated as per the diagrams below. To assist with recall some may consider the normal waveform to resemble the shape of an elephant under a blanket.
Phase 1 (dead space ventilation, A-B) represents the beginning of exhalation, where the dead space (area which does not participate in gas exchange and thus contains virtually no CO 2 ) is cleared from the upper airway. Phase II (ascending phase, B-C) represents the rapid rise in carbon dioxide (CO 2 ) concentration in the breath stream as the CO 2 from the alveoli reaches the upper airway (dead space gases mixed with alveolar gases).
Phase III (alveolar plateau, C-D) represents the CO 2 concentration reaching a uniform level in the entire breath stream from alveolus to nose. The height and slope of the alveolar plateau is dependent on CO 2 content in the alveoli, which in turn is related to ventilation, cardiac output and most importantly the V/Q relationship. Point D, occurring at the end of the alveolar plateau, represents the maximum CO 2 concentration at the end of the tidal breath and is appropriately named the end-tidal CO 2 (EtCO 2 ). This is the number that appears on the monitor display. (CO 2 evolving from alveoli) Phase IV or sometimes referred to as phase 0 (D-E) represents the inspiratory cycle Dead space: the total is a combination of anatomic (airways leading to the alveoli that do not participate in gas exchange); alveolar (ventilated area in the lung without blood flow) and mechanical (artificial airways including the BVM). Mechanical dead space: Reduction of dead space where possible is particularly relevant for paediatric patients. Extension tubes should never be placed on the patient side of the valve unless absolutely necessary, such as
when delivering inline nebulisation to the supine patient requiring assisted ventilation. Whilst previous teaching emphasised the importance of attaching the bacterial /HME filter between the patient and CO 2 sampling line to protect the MRX from aspirated contents via the capnography line, recent technical advice suggests that inbuilt filters (in the sampling line and monitor) may offer adequate protection. The bacterial/ HME (Pall) filter with a dead space of 35 ml should not be used on any patient under 40 kg. This recommendation has recently been endorsed by the clinical governance committee (CGC). Based upon expert advice, it will be at the clinician s discretion to include the HME filter in patients over 40 kg, as the filter within the sampling line along with the filter built into the monitor will afford sufficient protection from contamination. Should the sampling line become contaminated there will be a series of dashes and the line will need to be replaced. The necessity for protecting the BVM from contamination is mitigated by the introduction of disposable BVM units. Oxygen content and ventilation/perfusion (V/Q): Take the average 70 kg patient with a RR of 12 and tidal volume of 500 ml: Normal V (ventilation) is ~ 4 L of air per minute (nearly 2 L is lost to anatomical deadspace). Normal Q (perfusion) is ~ 5 L of blood per minute. So Normal V/Q ratio is ~ 4/5 or 0.8 CO 2 content is in turn dependent on the V/Q ratio of the alveoli.
When ventilation (V) exceeds perfusion : ie V/Q > 0.8 the alveoli contain relatively low PCO 2 there is deadspace in the lungs (eg ventilating unperfused lung area) eg pulmonary embolus (PE), hypovolaemia, tamponade, shocked patients, cardiac arrest When there is a V/Q mismatch caused by poor ventilation (v): the V/Q is < 0.8 the alveoli contain relatively high PCO 2 this is related to blood shunting (eg perfusing unventilated lung area) eg could be due to atelectasis, asthma or an ETT in the mainstream bronchus Ventilation perfusion mismatch can arise from shunting or physiological dead space. In patients who are critically unwell (where there is VQ mismatch), the correlation between EtCO 2 and PaCO 2 is particularly difficult to predict. Practice Question Which part of the capnography waveform represents exhalation?
Segments B-C and C-D Segments A-B and B-C Segments B-C; C-D and D-E Segments A-B (latter part) ; B-C and C-D Segments A-B and D-E SUBMIT
Section 4 of 10 Capnography in Cardiac Arrest End-tidal CO 2 monitoring during CPR can provide information about the effectiveness of resuscitative efforts that, up until this time, have been unavailable. Any trend changes should prompt the clinician to investigate why a change has occurred, whilst interpreting the information in conjunction with a thorough clinical assessment. It is non-invasive, easy to apply and the theory of its use during CPR is relatively straightforward. During cardiac arrest, when alveolar ventilation and metabolism are essentially constant, EtCO 2 reflects pulmonary blood flow. Therefore, EtCO 2 can be used as a non-invasive gauge of the effectiveness of cardiac compressions. As effective CPR leads to a higher cardiac output, EtCO 2 should rise, reflecting the increase in perfusion. Therefore, EtCO 2 can be used to judge the effectiveness of resuscitative attempts and thus lead to changes in technique that could improve the outcome [1]. Basic principle of directing uses of capnography during CPR [1]: During CPR EtCO 2 levels are low, reflecting the low cardiac output achieved by chest compression. End tidal CO 2 values are associated with compression depth and ventilation rate. Optimising the depth of compressions will increase the amount of CO 2 detected. Ideally, clinicians should see a slow increase in EtCO 2 as perfusion increases through effective chest compressions. Any changes should be promptly investigated and steps taken (where possible) to address the cause.
CO2 in relation to cardiac output: When activity of the heart is restored (ROSC), the dramatic increase in cardiac output (right image above) and resulting increase in perfusion, leads to a rapid increase in EtCO 2. The CO 2 that has accumulated during cardiac arrest is effectively transported to the lungs and exhaled. This process manifests as a sudden rise in EtCO 2 as shown in the representation below [2].
Significant correlation between partial pressure of end-tidal-co 2 (EtCO 2 ) and cardiac output that can indicate a return of spontaneous circulation (ROSC) demonstrated in animal and human models [5-9,13] ANZCOR [3] and AHA [21] guidelines for cardiac resuscitation emphasise the importance of continuing chest compressions without interruption until a perfusing rhythm is re-established. Experimental evidence indicates that interruptions in chest compressions are followed by sustained periods of reduced blood flow, which only gradually return to pre-interruption levels. According to an observational study of 145 patients with out of hospital cardiac arrest (OHCA), several seconds may be required after electrical conversion to a potentially perfusing rhythm before effective mechanical contractions and a subsequent rise in EtCO 2 occur [20].
High performance CPR indicates that pulse checks need only occur once a non-shockable, organised rhythm appears on the ECG in the charge and check period (2 minutely analysis). A notable rise in waveform capnography suggestive of ROSC may appear at any time during CPR. In this situation, compressions should continue but cardiac drugs which are due should be withheld until after the next charge and check cycle (2 minutely), as these would be detrimental in a patient who has potentially regained a life sustaining rhythm. Resuscitation council recommendations Current ANZCOR (2016), ILCOR, AHA (2010), ERC and Advanced Paediatric Life Support (2016) guidelines advise the usefulness of capnography in adults and children during cardiac arrest resuscitation efforts to indicate the effectiveness of CPR [3,21,22]. EtCO 2 can be used as one marker of cardiac output since a spike in waveform will be detected when the patient goes into ROSC during cycles of CPR. Nevertheless it needs clinical correlation. During a cardiac arrest, the EtCO 2 value (ie in mmhg) should not be used as a guide for ventilation, and clinicians should be wary about using it to guide ventilation in the immediate post resuscitation phase. [ANZCOR 11.8.14] Low CO 2 in expired breath from a patient under CPR may imply: inadequate cardiac compression or excessive ventilation or both a treatable condition (eg pneumothorax, hypovolaemia, cardiac tamponade, severe aortic stenosis or PE (note it may not be clear what underlying causes are contributing or to what extent); this in conjunction with other information may assist in the clinicians decision making about the appropriateness of mobiling under CPR. [ANZCOR Guideline 12.1.6]
Utility of Capnography in CPR: CO 2 trend waveform during CPR and indication of fatigue [23] During CPR, decreasing amplitude of the capnogram and lower EtCO 2 values may indicate fatigue, characterised by ineffective compressions. Leaning on the chest (providing poor recoil) can compromise venous return; and this may also lead to a decrease in amplitude of the waveform. Reevaluation of the clinician s compression technique must occur and if unable to be rectified may prompt an early change of roles if necessary to ensure there is minimal time off chest. An example of re-establishing effective compressions can be seen in the example below with increasing EtCO 2 upon change of operator.
Capnography is an adjunctive tool; and should never replace a thorough patient assessment and correlation of clinical findings. Success story: 96 minute of CPR with capnography Effective CPR can facilitate adequate cerebral and pulmonary circulation. The pulmonary circulation can be indirectly monitored by capnographic waveform and end tidal carbon dioxide values. The following video illustrates the values of capnography during CPR. YOUTUBE Capnography in Cardiac Arrest
Capnography in Cardiac Arrest VIEW ON YOUTUBE Practice question During resuscitative efforts a 55 year old witnessed cardiac arrest with good bystander CPR has been under CPR for 15 minutes and has capnography as outlined following several shocks and adrenaline (the top line is an EtCO 2 level of 45 mm Hg). This low amplitude waveform could best be explained by: Airflow obstruction ie mucous plugging/ bronchospasm
Inadequate depth of compressions, excessive ventilations or both Contamination of the sampling line ROSC The patient has just had a can of coke prior to arresting SUBMIT
Section 5 of 10 Capnography in Post-ROSC Management Whilst a peak in EtCO 2 level may be one of the earliest signs of ROSC and may occur before return of a palpable pulse or blood pressure, it is one marker and needs to be correlated with clinical findings. Values are higher after an initial asphyxia arrest and with bystander CPR, and these decline over time after cardiac arrest. Whilst studies have shown some correlation between EtCO 2 values during CPR, ROSC rates and mortality, EtCO 2 values should be considered only as part of a multi-modal approach to decision making for prognostication during CPR. [13] Post-ROSC management The cardiac arrest leader can monitor ventilation by primarily observing the waveform trend and correlating this with the numerical respiratory rate displayed in the parameter block (AwRR = airway respiratory rate). ANZCOR [3] advise against focussing on the specific EtCO 2 value in the early post ROSC patient and recommend the clinician: avoid hyperventilation (notable declining height in CO 2 waveform and lowering EtCO 2 ; also evident by increased frequency of capnograms) avoid hypoventilation (significant increasing height in CO 2 waveform and high EtCO 2 ; also evident by reduced frequency of capnograms)
Basic rules for interpretation (just like an algorithm for ECG interpretation): The CO 2 waveform is analysed for five characteristics: Height which depends on the end-tidal CO 2 value Frequency which depends on the respiratory rate Rhythm which depends on the state of the respiratory centre or on the function of the person ventilating (in hospital this would be the ventilator) Baseline which should be zero (unless there is breath stacking or incomplete exhalation) Shape there is only one normal shape The waveforms you will observe on the screen will generally have a 10 second lag (due to sampling time) and the printout will look more elongated since the print out is real time (25mm/second) and the monitor is compressed time. MRX trace with RR 12 and EtCO 2 38 mm Hg; SpO 2 99%; HR 65 bpm.
Capnogram Waveforms: The waveforms illustrated below are semi-schematic diagrams depicting their ideal shape. Nonintubated capnography has merit for use in the continuous assessment of patients with poor perfusion or ventilation; however the wave forms may not be quite as precise as intubated capnography due to mixing of gases/ poor seal. Normal This is a normal capnogram (in real time) seen commonly during controlled ventilation or spontaneous ventilation.
There is only one normal shape with the following features: A rapid increase (phase II) Nearly horizontal plateau with slight upward sloping phase III Rapid decrease to zero following the peak (inspiration phase IV) Rounded corners Slope of the plateau depends on the condition of the airways and lung tissue End-tidal value is only equivalent to the alveolar CO 2 when a nearly horizontal plateau is seen Disconnection/ Technical fault/ Apnoea: A sudden drop to zero or to a low level almost always indicates a technical disturbance/defect. In the patient under CPR who had a previously detected waveform check for total disconnection, any issue with ventilation equipment (if the patient were intubated this could be a kinked or blocked ET-tube) or the CO 2 sampling line may be defective and need replacing. In spontaneously breathing patients a sudden drop could not only indicate technical fault but the patient has become apnoeic, so it is important in this circumstance to CHECK PATIENT FIRST and then CHECK EQUIPMENT.
No waveform flatline Typically due to a misplaced ETT but could also reveal no metabolic activity; no CPR in cardiac arrest; exsanguination or profound shock; equipment failure; airway obstruction. Inability to detect CO 2 in expired breath from a patient receiving adequate chest compression may be due to lack of ventilation. Hypoventilation (bradypnoeic): Trending escalation in CO 2 : There is a progressively increasing end-tidal EtCO 2 values with waves growing taller with each breath/expiration. Base line remains at zero. The shape of the waveform remains normal.
There are 4 components responsible for increased EtCO 2 : Increased CO 2 production Increased pulmonary perfusion ie Cardiac output, BP Decreased alveolar ventilation hypoventilation, partial airway obstruction Equipment malfunction i.e. inadequate fresh gas flow A high CO 2 in expired breath implies inadequate ventilation [3]. Whilst treating to EtCO 2 numbers is not advocated due to limited correlation in actual PaCO 2 and EtCO 2 values in the cardiovascularly deranged patient, it is worth considering that hypoventilation is not the cause and should be a prompt to check your ventilation rate and volume. Consider ventilation strategy in the post-rosc patient For ICPs, if the EtCO 2 is persistently high (ie > 45 mmhg) post ROSC and there is a reasonable transport time, cautiously increasing the ventilation rate to reduce the EtCO 2 by 1 mmhg per minute should be considered (as per post-rosc CPG). As a general guide, vary the ventilation rate by no more than 10% to gradually reduce the EtCO 2 towards the upper range of normal.
Hypoventilation (hypopnoeic) Note the top waveform is bradypnoeic hypoventilation whereas the bottom reflects hypopnoeic hypoventilation (google images). Hyperventilation: During hyperventilation, the height of the capnogram decreases gradually whilst the baseline remains at zero. Progressive depression of cardiac output or metabolism can also decrease the height of the capnogram.
A gradual lowering of the EtCO 2 (normal shape but height of plateau falls) can also be seen in ventilated patients due to: Gradual hyperventilation Lowering body temperature Decreasing perfusion An exponential decrease in CO 2 generally indicates either: Sudden disturbance in lung function Circulatory arrest Sudden decrease in BP Sudden severe hyperventilation This trend should prompt an immediate check of the patient s output (and commence compressions without delay if required). If the output is adequate check the effectiveness of ventilation. In the spontaneously ventilating patient with a persistently low EtCO 2, causes may include hyperventilation secondary to compensation for hypoxia, metabolic acidosis, pain or profound
shock. Expiratory problems In general, any airway obstruction limiting expiration can result in an increase in the phase III as well. Depending on the severity of airway obstruction, phase II can also be prolonged. This waveform resembles a shark fin which loses the alveolar plateau. The waveform changes below may be caused by a kinked or blocked airway device; a foreign body; bronchospasm; emphysema and bronchial asthma.
The slope of the phase III is increased, and phase II is prolonged. With response to treatment, there is normalisation of the capnogram. Low end tidal CO 2 Note a normal respiratory rate and plateau but a lower than normal EtCO2 can be observed in ventilated pts who: Are in shock (ie have a PE) With a normal RR and TV but with a low body temperature Having effective CPR performed during cardiac arrest
Sudden change in baseline A gradual up-shift in baseline (ie elevated from zero) can result from an increasing dead space, resulting in rebreathing. It could also indicate incomplete exhalation, a calibration error, or the CO 2 absorber is contaminated. Where possible reduce any unnecessary connections which could contribute to increased dead space or check filter for contamination. Summarising basic rules: http://www.capnography.com/clips A useful link is included if you d like to hear about pitfalls.
Capnography versus Pulse Oximetrythe measurement of ventilation vs oxygenation: Certainly the oximeter is an excellent method for detecting hypoxia, however it doesn t necessarily aid in the identification of the aetiology. Capnography on the other hand can reveal situations that may lead to hypoxia (ie more rapidly detects airway obstruction and hypoxaemia before the oximeter may reveal desaturation). Note the strip below. The patient has become apnoeic and this is detected well before the changes in oximetry levels are evident. Practice Question Observing a waveform alone only tells you part of the picture, and it is important to correlate this with other findings. Consider the capnogram below with the decreasing amplitude in EtCO 2 observed over a few minutes. Which answer best explains this waveform in a spontaneously breathing patient who is post-rosc:
A slight leak in the seal of the i-gel, with dilution of gases leading to decreased EtCO 2 even if no significant evidence of leak pull out the i-gel just in case. Likely impending circulatory arrest if the waveform continues to decline in amplitude correlate clinically (check quality of pulse) & be prepared to start compressions This waveform reflects the different shape seen in a patient monitored with nasal capnography - it is of no concern Sudden hypoventilation of unknown aetiology - continue to observe closely Normal waveform expected as EtCO 2 levels normalise from accumulated levels post cardiac arrest ignore the change in trend SUBMIT
Section 6 of 10 Capnography Application Attachment: If the clinician deems the HME bacterial filter is required in grossly soiled airways, it is placed between the SGA (i-gel) and the EtCO 2 sampling line. This configuration will offer additional protection of the sampling line, MRX and BVM from contamination, but is not recommended in patients under 40 kg due to the extra dead space (as discussed in section 2). The EtCO 2 port is located on the left side of the MRX under the pocket flap and can be exposed by pulling down the protective cover; to ensure a firm connection insert and twist clockwise by 90
degrees (figure 2). If there are issues with EtCO 2 reading, this is a good place to start to ensure the connection is firm. An EtCO 2 waveform should appear on the MRX (figure 3)
Checklist: Back to the basics airway; breathing; circulation (has anything changed and why has it changed?); thoroughly evaluate patient respiratory and cardiovascular status; take appropriate action. Troubleshoot the technology identify kinked or cut tubing; poor attachment with monitor obstruction of capnography detector; disconnection of BVM ventilation; dislodgement or malposition of the advanced airway device (especially true of ETT but can also apply to a SGA & poor seal) Trust the technology it plays a large part in decision making; do not discard the technology simply because it does not match your expectations; never ignore information that does not make sense as it may be the key to the problem; but use it wisely to correlate with other clinical findings
Take action gather accurate information to drive clinical decision making and communicate effectively with colleagues. Troubleshooting This entails looking at how the 3 main components (monitor, sampling line and patient) interact. https://www.capnoacademy.com/2017/10/25/troubleshooting-capnography-philips/ Practice Question You are the cardiac arrest leader and advise the clinician at the airway to connect capnography. What answer does not account for the following waveform: In a patient under CPR no waveform could be due to complete airway obstruction The post-rosc patient who was breathing re-arrested; no CPR in progress
In the patient under CPR there is no detectable EtCO2 possibly a result of exsanguination, profound shock or a long down time Even a slight leak in the i-gel will result in an undetectable EtCO2 waveform In a patient receiving adequate CPR this could be due to equipment failure SUBMIT
Section 7 of 10 Appendix and FAQs Appendix
FAQs / interest only 1. Some facts about compression depth and ventilation rate: The measurement of EtCO 2 varies directly with the cardiac output produced by chest compression and has been described in both prehospital [13] and ICU patients [8]. Two prospective, observational studies (EMS and ICU) found an EtCO 2 level <3 mmhg immediately after cardiac arrest, with a higher level generated during cardiac compressions and a mean peak >7.5 mmhg just before return of spontaneous circulation (ROSC) [13]. Another observational study of data collected during human CPR found a positive correlation between the depth of chest compressions and EtCO 2 (10 mm increase in compression depth increased EtCO 2 by 1.4 mmhg), as well as ventilation rate and EtCO 2 (increase of 10 breaths/minute decreased ETCO 2 by 3 mmhg), and confirmed that higher EtCO 2 values during CPR correlate with increased ROSC and survival [2] 2. Can capnography be used as a prognostic indicator some words of caution? ANZCOR has put a higher value on not relying on a single variable (ETCO 2 ) and cut-off value when their usefulness in actual clinical practice, and variability according to the underlying cause of cardiac arrest, has not been established. The aetiology (e.g. asphyxia, PE) of cardiac arrest could affect ETCO 2 values, and there is concern about the accuracy of ETCO 2 values during CPR. ANZCOR recommends against using ETCO 2 cut-off values alone as a mortality predictor, or for the decision to stop a resuscitation attempt (CoSTR 2015, strong recommendation, low-quality evidence). ANZCOR suggests that an ETCO 2 10 mm Hg or greater measured after tracheal intubation or after 20 min of resuscitation, may be a predictor of ROSC (CoSTR 2015, weak recommendation, low-quality evidence). 3. Will SAAS introduce capnography for paramedics outside CA?
We are starting with the basics. More training will be required to ensure interpretation and clinical practice is safe and translates to better patient outcomes. 4. Can we use capnography to make decisions about termination? Currently ANZCOR (2016) states it is not presently possible to specify a EtCO 2 which predicts survival or quality of survival and more research is warranted. 5. Recording of capnography on the PCR Documenting in the presenting complaint section would include that capnography was recorded and a positive waveform noted (record value i.e. EtCO 2 25 mmhg stating observation and trends, however interpretation of the value is not required as it may be confounded by a number of variables). Attach the code summary to PCR. 6. How is SAAS measuring the effectiveness of CA management? Cardiac arrest performance meetings are regularly held by CPAPs and any important information derived from these will be conveyed as appropriate in a Quality and Safety Matters newsletter or clinical communications. Collecting data is important to drive future performance and implement positive evidence-based changes. What is the physics behind waveform capnography?
Currently, the most common capnography technology used by clinicians is infrared absorption spectroscopy. The basic principle is based on the Beer Lambert Law. Amount of infrared rays absorbed is proportional to the concentration of the infrared absorbing substance. Infrared is absorbed by gases that have two or more different atoms. Oxygen therefore does not absorb infrared waves, whereas CO 2 does
CO 2 absorbs infrared light at a specific wave length (4.26 μm).
The concentration of CO 2 in a sample of mixed gases can be calculated by infrared absorption spectroscopy, whereby a beam of infra red radiation from a light source can be conducted through a sample of air to a photodetector. The greater the concentration of CO 2 in the sample, the more light is absorbed by the gas, decreasing the intensity of the light that reaches the detector.
The difference between the intensity of infrared light absorbed and that which passes through the sample yields a calcu lation of CO 2 concentration. In essence the higher the concentration of CO 2 then the greater the amplitude of the capnograms.
Section 8 of 10 CPG Links & References Links to CPGs on SAASNet CPG-029-ICP Cardiac Arrest (Adult) - ICP Draft CPG - Post-ROSC Management Download References REFERENCES.pdf 46.4 KB
Section 9 of 10 Summative Assessment Details Successful completion of the online package will require at least 80% correct responses to the 15 MCQs. You are allowed three attempts for the quiz. Please speak to your team leader if you have used up all three attempts. Once you have passed the quiz, you can obtain your certificate of completion by returning to your portal. Go to quiz
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