capnografie nurse

Advanced Emergency Nursing JournalVol. 28, No. 4, pp. 301–313

c© 2006 Lippincott Williams & Wilkins, Inc.

Noninvasive Monitoring of End-TidalCarbon Dioxide in the EmergencyDepartment

Nicki Gilboy, RN, MS, CEN, FAEN;Michael R. Hawkins, CRNA, MS

AbstractNoninvasive monitoring of end-tidal carbon dioxide (ETCO2) is not new technology but its routineuse in the emergency department is a recent development. It is a better tool to evaluate ventilationwhen compared to oximetry because it provides the caregiver with breath-to-breath information.End-tidal carbon dioxide reflects the production, transportation, and elimination of CO2. This tech-nology has been used to evaluate endotracheal tube placement. Now with both side stream andmainstream monitoring available, emergency departments can use ETCO2 in a variety of situations.The emergency nurse needs to be able to evaluate the configuration of the waveform in additionto the numeric value. Key words: capnography, emergency department, end-tidal CO2, ETCO2,PetCO2

NONINVASIVE monitoring of end-tidalcarbon dioxide (ETCO2, EtCO2, orPetCO2), also known as capnogra-

phy, is not new technology but its routineuse in emergency care is a recent develop-ment. For many years emergency nurses haveused pulse oximetry to monitor oxygenation.Sometimes called the 5th vital sign, pulseoximetry has limitations because there is aslight time delay before oxygen saturationreflects hypoxia. ETCO2 is a better tool toevaluate ventilation because it provides thecaregiver with breath-to-breath information.Recent studies have advocated that capnog-raphy does in fact improve patient outcomesthrough the early recognition of hypoventila-tion, apnea, or airway obstruction, thus pre-venting hypoxic episodes (Corbo, Bijur, Lahn,

From the Emergency Department, Brigham & Women’sHospital, Boston, Mass (Ms Gilboy); and the Depart-ment of Anesthesia, Dartmouth-Hitchcock Medical Cen-ter, Lebanon, NH, and Dartmouth Medical School,Hanover, NH (Mr Hawkins).

& Gallagher, 2005; Hart, Berns, Houck, &Boenning, 1997; McQuillen & Steele, 2000;Miner, Heegaard, & Plummer, 2002; Soto, Fu,Vila, & Miguel, 2004; Tobias, 1999; Vargoet al., 2002).

Capnography is a continuous noninvasivetechnique that measures exhaled carbon diox-ide. Stated simply, it is the maximum car-bon dioxide level reached at the end of eachbreath. The technology was first developedby Luft in 1943 but the equipment was cum-bersome (Bhavani-Shankar, 2006; Tremper,1992). The technology has now advanced tothe point that it is easy to use and provides ac-curate information. Since 1986, the AmericanSociety of Anesthesiologists has consideredcapnography one of the “basic standards” formonitoring for all patients receiving anesthe-sia (American Society of Anesthesiologists,Committee on Standards of Care, 2005). Asthis technology has developed, its utiliza-tion by clinicians outside of the operatingroom/anesthesia realm has grown. For the

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emergency nurse, ETCO2 is another objectiveassessment tool that can be used with a vari-ety of patients.

Carbon dioxide is a byproduct of cellularmetabolism. It is transported from the tissuesin the venous blood to the lungs where itis exhaled into the environment. ETCO2 hasbeen referred to as the “ventilation vital sign”(Eichbrecht, 2001). Ventilation is the move-ment of air into the lungs and the displace-ment of carbon dioxide out of the lungs.There must be adequate circulation and ven-tilation to detect exhaled carbon dioxide.

Normal ETCO2 concentration in the patientwith healthy lungs and normal airway con-ditions is 30–43 mm Hg. ETCO2 values areabout equal to the amount of carbon dioxidein the alveoli and are 2–5 mm Hg less thanarterial PCO2 (Eichbrecht, 2001). Normal ar-terial PCO2 is 35–45 mm Hg.

ETCO2 monitoring should not be seen as areplacement for arterial blood gases (ABGs).ABGs, although invasive, provide more in-formation including oxygenation, ventilation,and acid base balance. ABGs provide informa-tion about only one moment in time versusETCO2, which displays continuous informa-tion about ventilation. Therefore, ETCO2 canbe used as an early warning system that allowsadditional time to intervene before the patientis compromised.

TERMINOLOGY

Capnography provides a numeric valuefor ETCO2 as well as a graphic display orwaveform of the concentration of exhaledcarbon dioxide in each breath. A capnogramis the plot of carbon dioxide concentrationin airway gas measured against time orvolume. This waveform depicts the CO2

concentration throughout each respiratorycycle (a plot of exhaled CO2 over time).ETCO2 values are expressed as either apercentage (%), partial pressure in millime-ters of mercury (mm Hg), or kilopascal(kPa) (Bhavani-Shankar, Kumar, Moseley, &Ahyee-Hallsworth, 1995; D’Mello & Butani,2002). The standard speed of the wave-

form going across the screen is 6.25 mm/sto allow the caregiver to see several breathson one screen. The speed can be increasedif necessary. Like an arterial line, the wave-form is graphed on a scale that can beadjusted so that the total waveform isvisible

EQUIPMENT

ETCO2 can be measured using a disposablecolormetric device or a capnometer. Stand-alone capnometers are available and mostbedside monitoring systems now have the ca-pability to continuously monitor ETCO2.

Emergency personnel have used colormet-ric ETCO2 detectors for years to assess endo-tracheal (ET) tube placement and for short-term monitoring of ventilatory status. Thisdisposable device provides a qualitative mea-sure of ETCO2 and is based on a chemicalreaction rather than on actual measurementof CO2 molecules. The user looks for a colorchange with each breath rather than an ac-tual number. The color change at the endof exhalation is then interpreted. The goal isto see a color change with each breath. De-pending on the device used, purple or blueindicates low or absent CO2 concentrationsand yellow is seen with high concentrationsof CO2. A colormetric ETCO2 detector doesnot change color with esophageal intubationor in the presence of inadequate systemicperfusion.

Capnometers can measure ETCO2 by twomethods, side stream or mainstream. Bothmethods are reliable and provide the care-giver with a continuous value and waveform.Either technology may be used for the intu-bated patient.

The mainstream method employs a sensoror an infrared measuring device placed di-rectly in-line between the ventilator breathingcircuit and the ET tube to continuously mea-sure ETCO2 (see Figure 1). The nurse caringfor this patient needs to ensure that the sensoris not pulling on the ET tube. Keep the sensorwindow clear of secretions or significant wa-ter vapor to prevent either false high readings

October–December 2006 � Vol. 28, No. 4 Noninvasive Monitoring of End-Tidal Carbon Dioxide 303

Figure 1. Mainstream cable and adaptors (Courtesy of Philips Medical Systems, Bothwell, WA).

or failure to detect a waveform (D’Mello &Butani, 2002).

Side stream monitoring can be used forboth the intubated and nonintubated pa-tients. In the intubated patient, a small adap-tor is placed between the ventilator circuitand the ET tube. For the nonintubated pa-tient, side stream monitoring uses a nasal sam-pling catheter similar to a nasal cannula (seeFigure 2). In both cases, a preset quantity ofexhaled gas is aspirated from the patient’s air-way and pumped to the monitor for analysis.CO2 is measured at the machine. This tech-

nique can be used for patients on room air orreceiving oxygen via facemask or nasal can-nula as a variety of sampling cannulas are avail-able. Because the sample is being pumped tothe monitor for measurement, there is a fewsecond delay between sampling and the in-formation appearing on the monitor screen(LaValle & Perry, 1995).

PHYSICS OF GAS MEASUREMENT

Historically, infra-red (IR) spectrography hasbeen the most widely used and cost-effective


Figure 2. Sidestream line (Courtesy of Philips Medical Systems, Bothwell, WA).

technology for measuring CO2 levels withportable capnometers or modules inserted ina larger monitoring system (LaValle & Perry,1995). IR spectrography is based on the prin-ciple that CO2 molecules absorb infra-red radi-ation at specific wavelengths. The capnome-ter contains special photodetectors tuned tothese wavelengths that enable the calculationof CO2 levels in the breath sample. CO2 se-lectively absorbs specific IR wavelengths of4.3 millimicrons. Because the amount of lightabsorbed is proportional to the concentra-tion of CO2, the concentration can be deter-mined by comparing that concentration witha known standard. In other words, the inten-sity of IR radiation projected through a gasmixture containing CO2 is diminished by ab-sorption; this allows the CO2 absorption bandof IR to be measured against the source IR,thus identifying a proportion of CO2 in thegas mixture (D’Mello & Butani, 2002; LaValle& Perry, 1995).

THE ETCO2 WAVEFORM

As the patient breathes, a characteristic wave-form is created (see Figure 3). In the past, ref-

erence sources have used different methodsof labeling the components of the time capno-gram waveform. For example, terms such as“PQRS,”“ABCDE,”“EFGHIJ,”and “phases I–IV”have been used. This has resulted in muchconfusion with teaching and a lack of stan-dardization. Recently, there has been an effortto standardize the nomenclature for the sakeof communication, teaching, and research.The following is a description of terminologycurrently being utilized (Bhavani-Shankar &Philip, 2000; Lumb, 2000; Morgan, Mikhail,Murray, & Larson, 2002).

A time capnogram can be divided into twosegments (see Figure 3a), inspiration and ex-piration. Inspiration has one phase (0). Expi-ration has three phases (I, II, and III) and ithas two angles, alpha (α) and beta (β). Duringexpiration, Phase I represents the CO2-freegas from the breathing circuit apparatus andanatomical dead space. Phase II representsthe rapidly increasing S-shaped curve that is amixture of dead space and alveolar gas. PhaseIII, also referred to as the alveolar plateau,represents CO2-rich gas from the end of ex-piration. The alveolar plateau almost alwayshas a positive slope, indicating a rising PCO2.


Figure 3. (a) Normal ETCO2 waveform. (b) Dashed line shows ETCO2 waveform abnormalities that may

occur separately or together. (A) Varying alveolar time constraints such as asthma; (B) Phase VI terminal

upswing seen in pregnancy or obesity; (C) rebreathing of expired gases. Courtesy John Forrestall, Designer,

Warrenstreet Architects, Inc, Concord, NH.

This is due to several factors: the alveolar gasthat is sampled later in expiration is in factricher in CO2, the pulmonary capillaries ex-crete CO2 at a constant rate during expiration,and as expiration occurs, the lung volumes de-crease thereby increasing the concentrationof CO2 and resulting in a rise in the slopeof the alveolar plateau. The angle betweenPhases II and III is referred to as the alpha (α)angle. It is normally between 100◦ and 110◦.An alpha (α) angle above 110◦ and a steepslope of Phase III can represent lung pathol-

ogy, specifically obstructive lung disease suchas asthma or chronic obstructive pulmonarydisease. The angle in the capnogram betweenthe end of Phase III and the beginning of in-spiration (Phase 0) is referred to as the beta(β) angle. It is generally about 90◦ and doesnot change unless there is rebreathing of CO2.Rebreathing CO2 may be due to excessive ap-paratus dead space or from a malfunction ofthe breathing circuit (Lumb, 2002).

In addition to the phases listed above,occasionally, Phase IV is described as an


Figure 4. Spontaneous breathing with blunted ETCO2 waveform (Courtesy of Respironics, Pittsburgh,

PA).

abnormality in the normal capnogram. Anacute increase of the slope at the end of PhaseIII is called phase IV (Figure 3b). The cause ofthis is uncertain but may relate to a rapid in-crease in measured CO2 due to a small func-tional residual capacity such as in pregnancyor severe obesity.

The Phase III slope and alpha (α) and beta(β) angles of the capnogram waveform allowthe provider to identify abnormalities in venti-lation. When reviewing “abnormalities”in thewaveform of a time capnogram, it is importantto remember that technical problems such asthe response time of the analyzer, excessivelengths of sampling tubing, inadequate sam-pling rates may be the cause of the abnor-mality that will result in a “blunting” of thewaveform (see Fig 4). Measuring CO2 with asidestream system via a facemask or nasal can-ula of a spontaneous breathing patient alsoproduces waveforms that are blunted or lessdefined than that previously described. Thecapnogram provides valuable information ona breath-to-breath basis. It can assist theemergency nurse in determining respiratoryrate, correct placement of ET tube, approxi-mate arterial CO2, metabolic rate, and cardiacoutput.

CLINICAL APPLICATIONS OF ETCO2

MONITORING

Verification of ET Tube Placement

ETCO2 monitoring is used to verify ET tubeplacement in the trachea. As the patient isventilated, the exhaled carbon dioxide canbe measured with a colormetric device or

a capnometer (see Figure 5). The AmericanHeart Association Guidelines for AdvancedCardiac Life Support (ACLS) and Pediatric Ad-vanced Life Support (PALS) call for the use ofan ETCO2 device to confirm ET tube place-ment for all patients with a perfusing rhythm(Cummins, 2003). For the patient with nopulse, the American Heart Association recom-mends ETCO2 monitoring but, if no CO2 is de-tected, another method of tube confirmationshould be used. Alternatives include direct vi-sualization of the tube through the cords or anesophageal detector device (Cummins, 2003).

It is recommended that ETCO2 be moni-tored on all intubated patients during inter-facility transport to immediately identify ETtube dislodgement or obstruction (Figure 6).ETCO2 should also be continuously moni-tored in the intubated pediatric patient asa higher, more anterior glottic opening anda shorter trachea makes accidental dislodge-ment of the tube more likely.

In addition, many emergency nurses are in-volved in the transport of intubated, mechan-ically ventilated patients to radiology or otherin-hospital locations. If the patient is venti-lated with a bag-valve device during transport,capnography can ensure that the patient isnot hypo- or hyperventilated because of vari-ations in the provider’s tidal volume or deliv-ered rate.

Cardiopulmonary Resuscitation

Research supports the value of ETCO2 mon-itoring during cardiac arrest. When a patientarrests, ETCO2 levels fall abruptly because ofthe absence of cardiac output and pulmonaryblood flow. With the initiation of effective


Figure 5. Intubation. (A) Esophageal intubation. (B) Correct endotracheal tube placement (Courtesy of

Respironics, Pittsburgh, PA).

cardiac compressions, there will be an in-crease in ETCO2. As the person performingcardiac compressions becomes fatigued and isno longer compressing effectively, ETCO2 val-ues will fall. With the return of an adequatelyperfusing rhythm, the ETCO2 value will re-turn to normal levels.

Several studies have looked at ETCO2

values during cardiac arrest to determinewhether they can be used to predict outcome.Levine, Wayne, and Miller (1997) concludedthat an ETCO2 level of 10 mm Hg or less20 min after the initiation of ACLS in patientswith electrical activity but no pulse can be apredictor of death. Of the 150 cardiac arrestvictims included in this study, 35 patients sur-vived to hospital admission. They had an av-erage ETCO2 level of 32.8 ± 7.4 mm Hg after20 min of ACLS whereas the nonsurvivors had

Figure 6. Unplanned extubation. (Courtesy of Respironics, Pittsburgh, PA).

an average ETCO2 level of 4.4 ± 2.9 mm Hg(Levine et al., 1997).

Procedural Sedation

In the emergency department (ED), procedu-ral sedation is used for patients of all agesfor a variety of reasons. Medications are ad-ministered to raise the pain threshold, de-crease anxiety, and provide some amnesia forthe event while minimally depressing the pa-tient’s level of consciousness. At the sametime, the patients maintain their ability toprotect their own airway and are able torespond appropriately to verbal commands.The medications used for procedural sedationare often respiratory depressants. In the past,monitoring parameters included vital signs,oxygen saturation, pain rating, and level of


sedation. With the focus on patient safety,optimal monitoring may come to includeside stream capnography. Measuring ETCO2

during procedural sedation provides breath-to-breath information and will detect prob-lems such as apnea, respiratory depression,and hypoperfusion. These changes will beseen almost immediately where it may takeminutes for oxygen saturation to decrease(Eisenbacher & Heard, 2005). Side steam tech-nology allows the patient to receive oxygenby nasal cannula and at the same time ETCO2

is measured. The nasal cannula used formonitoring ETCO2 delivers oxygen throughone prong and pulls an exhaled gas samplethrough the other prong.

Vargo et al. (2002) demonstrated the use-fulness of capnography in adults during pro-cedural sedation. Forty-nine adult patientsreceiving sedation for an upper endoscopywere monitored using side stream capnogra-phy, pulse oximetry, and other standard meth-ods including observation. Endoscopy per-sonnel were blinded to the capnography data.Capnography detected 54 episodes of apneaor “disordered respirations” in 28 patients.Only 50% of these episodes were identifiedby pulse oximetry. None were identified byvisual inspection.

Miner et al. (2002) found that monitor-ing ETCO2 during procedural sedation coulddetect respiratory depression. Nearly half(44.6%) of the 74 adults undergoing proce-dural sedation in an ED experienced respira-tory depression. All episodes were identifiedby capnography (Miner et al., 2002).

The value of ETCO2 monitoring duringprocedural sedation has been clearly demon-strated; in fact enrollment of patients in oneED study was stopped because of the number

Figure 7. Hypoventilation (Courtesy of Respironics, Pittsburgh, PA).

of abnormal ETCO2 findings (Burton, Harrah,Germann, & Dillon, 2006). In this study of 60procedural sedation cases, both adult and pe-diatric, 36 patients had abnormal ETCO2 find-ings. In addition, 20 acute respiratory eventswere documented. In 17 of these 20 acuteevents (85%), ETCO2 monitoring indicatedhypoventilation or apnea. For 70% of theseacute events, ETCO2 monitoring identifiedthe change prior to changes in oxygen satu-ration or observed changes in respiratory rate(Burton et al., 2006).

Prior to sedation, a baseline ETCO2 valueshould be obtained in addition to observingthe waveform. The nurse needs to take intoaccount the effect of pain and anxiety on res-piratory rate and depth. During the proce-dure, look for changes in shape and size ofthe waveform in addition to significant vari-ation in values and reassess airway, breathing,and circulation status if changes occur. Duringprocedural sedation the respiratory depres-sant effect of the medications will be seen asa decreased ETCO2 value and a smaller wave-form, which drops to 0 during episodes of ap-nea. When hypoventilation is recognized andthe patient is stimulated to breathe, there willbe an increase in the amplitude of the wave-form and the ETCO2 value (see Figure 7).

Gastric Tube Placement

A relatively new use for ETCO2 monitoringis confirmation that a gastric tube is not inthe respiratory tract. Research has repeatedlydemonstrated that auscultation is an inaccu-rate and potentially dangerous way to verifygastric or feeding tube placement (Metheny& Titler, 2001). Radiographic confirmation ofcorrect tube placement is the only reliable


method of confirming tube placement (Amer-ican Association of Critical Care Nurses,2005). ETCO2 has value in verifying that thetube is not in the respiratory tract but it doesnot verify tube location within the gastroin-testinal (GI) tract. Hence, ETCO2 is an adjunctmethod but does not replace other methodsof verification (Metheny & Titler, 2001).

Burns, Carpenter, and Truwit (2001) stud-ied 20 adult ventilated patients in a medi-cal intensive care unit during placement of asalem sump tube (13) or a small-bore feedingtube (7). The ETCO2 monitor was attached tothe tube during placement. The absence of aCO2 waveform during placement was consis-tent with GI placement. Four of the 13 salemsump tubes were initially inserted into theairway, and a CO2 waveform was observed.The tube was removed and reinserted with noCO2 waveform observed (Burns et al., 2001).

Araujo-Preza, Melhado, Gutierrez, Maniatis,and Castellano (2002) studied the effective-ness of ETCO2 monitoring, using a colormet-ric device to verify feeding tube placementin 53 intubated and mechanically ventilatedadults. The tube was inserted to a distanceof 30 cm, the disposable ETCO2 detector wasattached for 1 min and observed for a colorchange. The feeding tube was then advancedto the appropriate point and second chest X-ray taken. Fifty-two of the 53 feeding tubeswere placed in the GI tract, and no colorchange was observed indicating that no CO2

was detected. The one tube placed in the tra-chea demonstrated a color change indicatingthe presence of carbon dioxide. To verify thesensitivity of this technique, 20 feeding tubeswere placed in the trachea through an ETtube. Carbon dioxide was detected in all 20patients (Araujo-Preza et al., 2002).

Ventilation: Perfusion Assessment

Alveolar dead space is that area of the lungthat has no perfusion. Physiologic dead spaceis the sum of both anatomical dead space andalveolar dead space. In the healthy individ-ual, most physiologic dead space is anatom-ical. Any significant reduction in lung perfu-sion (i.e., air embolism, upright position, de-

creased cardiac output, or hypotension) willincrease physiologic dead space (especiallyalveolar dead space). Normally ventilation (V)is about 4 L/min, and perfusion (Q) is about5 L/min. Thus they are “nearly balanced”witheach other for a V/Q ratio of 0.8. If a mis-match develops, it affects the ETCO2 value.Exhaled CO2 levels decrease, and the am-plitude of the waveform will be decreased.Usually the difference between ETCO2 andPaCO2 is 2–5 mm Hg. With an increase inphysiologic deadspace, a V/Q mismatch de-velops and the difference between ETCO2

and PaCO2 widens. The larger the rise in phys-iologic deadspace, the bigger the difference invalues. For example, with a pulmonary embo-lus there is a decrease in blood flow to an areaof the lung but no change in alveolar ventila-tion. The ETCO2 value decreases and there isa widening of the difference between PaCO2

and ETCO2 (Ahrens & Sona, 2003).

Asthma and Obstructive Lung Diseases

ETCO2 can be used to assess the severity ofan asthma exacerbation and the effectivenessof interventions. ETCO2 values vary with theseverity of the episode. Initially, with a mildexacerbation, the patient may hyperventilateand ETCO2 will decrease. With a severe exac-erbation, there will be an increase in the alphaangle and a steep sloping ascending limb inthe Phase III slope (Figure 8). It has been sug-gested that this occurs from sequential emp-tying of “fast”and then “slow”alveoli.1 The an-gle of the Phase III slope will depend on thedifference between the amount of “fast” ver-sus “slow”alveoli. Typically, bronchospasm ofasthmatic origin is proportional to the angleof this slope. The concentration of CO2 in the“slow” alveoli is much higher. Patients withobstructive lung disease empty the fast alveolifirst and then the slow alveoli. With advanceddisease, more slow alveoli exist; hence, theslope of Phase III is steeper.

1“Fast” aveoli are noncompliant (stiff) with low resis-

tance. “Slow” alveoli are overcompliant (more compliant

than normal alveoli) with high resistance and higher CO2

concentration.


Figure 8. Asthma and airway obstruction. Note increase in the alpha angle and therefore a change in the

Phase III slope. A steep sloping ascending limb is also present. (Courtesy of Respironics, Pittsburgh, PA).

The National Asthma Education and Pre-vention Program Expert Panel 2 report sug-gests obtaining ABGs to evaluate PaCO2 “inpatients with suspected hypoventilation, se-vere distress, or with an FEV1 or peak flowless than or equal to 30% of predicted aftertreatment” (National Asthma Education andPrevention Program Second Expert Panel onthe Management of Asthma, 1997, p. 28). Astudy of 39 nonintubated adults experiencinga severe asthma attack found that the agree-ment between ETCO2 obtained by capnog-raphy and PaCO2 obtained from an arterialblood gas was high (Corbo et al., 2005). ABGsare invasive and costly and provide the health-care team information about one moment intime. The early initiation of ETCO2 monitor-ing will allow the care team to continuouslyassess the patient and monitor the effect ofinterventions.

Low Flow States

The carbon dioxide produced by cellularmetabolism is transported in the blood tothe lungs for elimination. If for some reasonblood flow is inadequate, CO2 builds up inthe underperfused tissues. At the same time,because of the low perfusion of the lungs,less CO2 is eliminated and the ETCO2 valuefalls. When blood carbon dioxide levels rise,the patients increase their respiratory rate anddepth as a compensatory mechanism in an at-tempt to eliminate the excess CO2.

CURRENT RESEARCH

Is capnography a useful noninvasive tool thatcan be used to rapidly identify the patient

with metabolic acidosis? Traditionally, this isdetermined by ABGs. Sidestream capnogra-phy could be initiated upon patient presenta-tion and the waveform and value evaluated aspart of the initial assessment. With metabolicacidosis the initial physiologic response is tocompensate by increasing minute ventilation(respiratory rate per minute times tidal vol-ume). Therefore, a low-ETCO2 value wouldbe obtained. Limited studies have evaluatedthe use of capnography to identify metabolicacidosis. More evidence is needed before wechange practice.

Fearon and Steele (2002) evaluated the util-ity of ETCO2 as a predictor of the presenceand severity of acidosis in a convenience sam-ple of 42 children being evaluated for dia-betic ketoacidosis. They found a significant re-lationship between serum HCO3 and ETCO2.In addition, the ETCO2 value in children diag-nosed with DKA was significantly lower thanthat in the rest of the sample.

The most common electrolyte abnormalityin children brought to the ED with vomitingand diarrhea is a low-serum HCO3 level. Na-gler, Wright, and Krauss (2006) reported astrong correlation between ETCO2 and serumHCO3 levels in 130 children with gastroen-teritis. They concluded that capnography “of-fers an objective noninvasive measure of theseverity of acidosis in patients with gastroen-teritis” (Nagler et al., 2006).

PRACTICAL APPLICATION

A change in the ETCO2 value or waveform is asignal for the nurse to reassess the ABCs. Doesthe ETCO2 correlate with the patient’s other


vital signs and assessment findings? Does thevalue and waveform make sense? Check thepatient and the equipment. Is the patient ap-neic? Is the sample line kinked? Is the ventila-tor disconnected? Is the ET tube plugged? Isthe patient extubated?

INTRODUCING CAPNOGRAPHY TO THE ED: THE

BRIGHAM EXPERIENCE

The installation of a new central monitoringsystem in the ED at Brigham & Women’s Hos-pital brought with it new capabilities. Onewas the ability to monitor ETCO2. The goalsfor orientation to this technology were sim-ple: we wanted the nurse caring for the pa-tient with ETCO2 monitoring to be able toset up the equipment, interpret the ETCO2

value and waveform, and apply the informa-tion to the patient situation. New technologyoften raises staff anxiety so it was impor-tant that the department have a well-thought-out educational initiative. To facilitate theincorporation capnography into nursing prac-tice, a three-part educational program wasdeveloped.

1. A self-learning packet and post test.A detailed self-learning packet reviewedthe physiology behind ETCO2, the ba-sic principles, and key concepts suchas normal and abnormal waveforms. Aquestion-and-answer format was used.Multiple waveforms were included withexplanations of what each showed andwhy. Continuing education credit wasawarded. A self-learning packet was cho-sen because this teaching method was

Table 1. Clinical conditions and effect on capnography values

Clinical condition Effect on ETCO2 Reason

Hypothermia Gradual decrease Decreased production

Hypermetabolic states (sepsis, malignant Increase Increased production

hyperthermia)

Hyperventilation Decrease Increased elimination

Hypotension Decrease Decreased transport

highly rated in a recent staff needsassessment.

2. Demonstration of the technical skillsof setting up, calibrating, and trou-ble shooting the capnography equip-ment. The monitoring company held atrain-the-trainer program for the educa-tors and permanent charge nurses. Thehands-on component was conducted bythe educators on the unit in multi-ple small group sessions. Both main-stream and side stream capnography wasdemonstrated, and then each nurse hadthe opportunity to practice setting itup. Sessions varied in length, depend-ing on the participants and the num-ber of questions. The permanent chargenurses are designated “super users” andare able to answer questions and trou-bleshoot issues. They provided invalu-able advice about the implementationprocess.

3. Return demonstration. For Part 3,the educators have developed severalETCO2 monitoring clinical scenarios.Each nurse will set up both sidestream and mainstream monitoring, an-swer questions about the patient sce-narios including interpreting the valueand waveform, and identify appropri-ate nursing interventions. The educatorsfound that using the concepts of CO2

production, transportation and elimina-tion were helpful to nurses in under-standing why ETCO2 values change withdifferent conditions. See Table 1 for asummary of this information.


SUMMARY

Capnography use in the ED will continueto grow as emergency nurses become morecomfortable with the technology and inter-pretation of waveforms and values. The objec-tive information obtained will assist with pa-tient care decisions and promote safer patientcare.

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