Practical uses of end-tidal carbon dioxide monitoring in the emergency department

Evaluating a novel formula for noninvasive estimation of arterial carbon dioxide during post-resuscitation care

BACKGROUND

Controlling arterial carbon dioxide is paramount in mechanically ventilated patients, and an accurate and continuous noninvasive monitoring method would optimize management in dynamic situations. In this study, we validated and further refined formulas for estimating partial pressure of carbon dioxide with respiratory gas and pulse oximetry data in mechanically ventilated cardiac arrest patients.

METHODS

A total of 4741 data sets were collected retrospectively from 233 resuscitated patients undergoing therapeutic hypothermia. The original formula used to analyze the data is PaCO₂ -est1 = PETCO₂  + k[(PIO₂  - PETCO₂ ) - PaO₂ ]. To achieve better accuracy, we further modified the formula to PaCO₂ -est2 = k₁ *PETCO₂  + k₂ *(PIO₂  - PETCO₂ ) + k₃ *(100-SpO₂ ). The coefficients were determined by identifying the minimal difference between the measured and calculated arterial carbon dioxide values in a development set. The accuracy of these two methods was compared with the estimation of the partial pressure of carbon dioxide using end-tidal carbon dioxide.

RESULTS

With PaCO₂ -est1, the mean difference between the partial pressure of carbon dioxide, and the estimated carbon dioxide was 0.08 kPa (SE ±0.003); with PaCO₂ -est2 the difference was 0.036 kPa (SE ±0.009). The mean difference between the partial pressure of carbon dioxide and end-tidal carbon dioxide was 0.72 kPa (SE ±0.01). In a mixed linear model, there was a significant difference between the estimation using end-tidal carbon dioxide and PaCO₂ -est1 (P < .001) and PaCO₂ -est2 (P < .001) respectively.

CONCLUSIONS

This novel formula appears to provide an accurate, continuous, and noninvasive estimation of arterial carbon dioxide.

The sixth vital sign: prehospital end-tidal carbon dioxide predicts in-hospital mortality and metabolic disturbances

OBJECTIVE

To determine the ability of prehospital end-tidal carbon dioxide (ETCO₂) to predict in-hospital mortality compared to conventional vital signs.

METHODS

We conducted a retrospective cohort study among patients transported by emergency medical services during a 29-month period. Included patients had ETCO₂ recorded in addition to initial vital signs. The main outcome was death at any point during hospitalization. Secondary outcomes included laboratory results and admitting diagnosis.

RESULTS

Of 1328 records reviewed, hospital discharge data, ETCO₂, and all 6 prehospital vital signs were available in 1088 patients. Low ETCO₂ levels were the strongest predictor of mortality in the overall group (area under the receiver operating characteristic curve (AUC of 0.76, 95% confidence interval [CI] 0.66-0.85), as well as subgroup analysis excluding prehospital cardiac arrest (AUC of 0.77, 95% CI 0.67-0.87). The sensitivity of abnormal ETCO₂ for predicting mortality was 93% (95% CI 79%-98%), the specificity was 44% (95% CI 41%-48%), and the negative predictive value was 99% (95% CI 92%-100%). There were significant associations between ETCO₂ and serum bicarbonate levels (r = 0.429, P < .001), anion gap (r = -0.216, P < .001), and lactate (r = -0.376, P < .001).

CONCLUSION

Of all prehospital vital signs, ETCO₂ was the most predictive and consistent for mortality, which may be related to an association with metabolic acidosis.

Correlation of end-tidal carbon dioxide with arterial carbon dioxide in mechanically ventilated patients

Background:

Patients undergone mechanical ventilation need rapid and reliable evaluation of their respiratory status. Monitoring of End-tidal carbon dioxide (ETCO₂) as a surrogate, noninvasive measurement of arterial carbon dioxide (PaCO₂) is one of the methods used for this purpose in intubated patients.

Objectives:

The aim of the present trial was to study the relationship between end-tidal CO₂ tensions with PaCO₂ measurements in mechanically ventilated patients.

Materials and Methods:

End-tidal carbon dioxide levels were recorded at the time of arterial blood gas sampling. Patients who were undergoing one of the mechanical ventilation methods such as: synchronized mandatory mechanical ventilation (SIMV), continuous positive airway pressure (CPAP) and T-Tube were enrolled in this study. The difference between ETCO₂ and PaCO₂ was tested with a paired t-test. The correlation of end-tidal carbon dioxide to (ETCO₂) CO₂ was obtained in all patients.

Results:

A total of 219 arterial blood gases were obtained from 87 patients (mean age, 71.7 ± 15.1 years). Statistical analysis demonstrated a good correlation between the mean of ETCO₂ and PaCO₂ in each of the modes of SIMV, CPAP and T-Tube; SIMV (42.5 ± 17.3 and 45.8 ± 17.1; r = 0.893, P < 0.0001), CPAP (37 ± 9.7 and 39.4 ± 10.1; r = 0.841, P < 0.0001) and T-Tube (36.1 ± 9.9 and 39.4 ± 11; r = 0.923, P < 0.0001), respectively.

Conclusions:

End-tidal CO₂ measurement provides an accurate estimation of PaCO₂ in mechanically ventilated patients. Its use may reduce the need for invasive monitoring and/or repeated arterial blood gas analyses.

Correlation between capnography and arterial carbon dioxide before, during, and after severe chest injury in swine

The relationship between end-tidal carbon dioxide (EtCO(2)) and arterial carbon dioxide (PaCO(2))-if better defined-could facilitate the difficult task of ventilation in prehospital trauma patients. We aimed to study the PaCO(2)-EtCO(2) relationship before, during, and after chest trauma, hemorrhage, and resuscitation in swine. Twenty-four swine were intubated, anesthetized, and monitored in an animal intensive care unit during three phases: phase 1 (day 1, healthy animals); phase 2 (day 2, injury), which consisted of blunt chest trauma, hemorrhage, and resuscitation; and phase 3 (day 2, after injury). "Respiratory maneuvers" (changes in respiratory rate and tidal volume [TV], intended to vary the PaCO(2) over a range of 25 to 85 mmHg, were performed during phases 1 and 3. End-tidal CO(2) and PaCO(2) were recorded after each respiratory maneuver and analyzed using linear regression. During phase 1, PaCO(2) and EtCO(2) were strongly correlated (r(2) = 0.97, P < 0.01). During phase 2, animals developed decreased oxygenation (PaO(2):FiO(2) [fraction of inspired oxygen] ratio <200) and hypotension (mean arterial pressure, 20-50 mmHg); the PaCO(2)-EtCO(2) relationship deteriorated (r(2) = 0.25, P < 0.0001). During phase 3, oxygenation, hemodynamics, and the PaCO(2)-EtCO(2) relationship recovered (r(2) = 0.92, P < 0.01). End-tidal CO(2) closely correlates to PaCO(2) in healthy animals and after injury/resuscitation across a wide range of respiratory rates and tidal volumes. Once oxygenation and hemodynamics are restored, EtCO(2) can be used to predict PaCO(2) following chest trauma/hemorrhage and should be considered for patient monitoring. This work demonstrated that EtCO(2) alone can reliably be used to estimate PaCO(2) in uninjured subjects and in those subjects who have been resuscitated from severe injury. Immediately after blunt chest injury, the correlation between EtCO(2) and PaCO(2) is temporarily unstable. Under these circumstances (with abnormal oxygenation and/or hemodynamics), greater caution and other monitoring tools may be required.

New mainstream double-end carbon dioxide capnograph for human respiration

Most of the current respiratory devices for monitoring CO(2) concentration use the side-stream structure. In this work, we engage to design a new double-end mainstream device for monitoring CO(2) concentration of gas breathed out of the human body. The device can accurately monitor the cardiopulmonary status during anesthesia and mechanical ventilation in real time. Meanwhile, to decrease the negative influence of device noise and the low sample precision caused by temperature drift, wavelet packet denoising and temperature drift compensation are used. The new capnograph is proven by clinical trials to be helpful in improving the accuracy of capnography.

A new real-time and precision capnography for human respiration carbon dioxide concentration

This paper is a description of the designing of a new mainstream device to measure human respiration carbon dioxide concentration, based on non-dispersive infrared (NDIR) absorption technology. The device can be used to accurately monitor the cardiopulmonary status during anaesthesia and mechanical ventilation in real time. This new device can not only make up the error of real-time gas measurement of the side-stream device, but also make up the accuracy of the main-stream device. In the paper, four issues which can affect the measurement accuracy were considered: respiration gas flow, turbulence of the light source with all ranges of wavelength, temperature drift and signal noise. The experimental results showed that the device could produce a stable output signal and deviation of measurement accuracy could be achieved to within 4%.

Developing biologically-based assessment tools for physical therapy management of neck pain

SYNOPSIS

Neck pain is a common and episodic condition that is treated using a spectrum of interventions known to be moderately effective but is associated with a significant incidence of chronic pain. Recently, there has been increased focus on defining biological aspects of neck pain. Studies have indicated that neurophysiological, biomechanical, and motor control abnormalities are present and may be useful either in prognosis or classification. We review some of these findings in the context of our own work defining biological markers that may form the basis for clinical tests that can be used for prognosis, classification, or outcome evaluation in patients with neck pain. We have identified abnormalities in neurophysiology using quantitative sensory testing (vibration, touch, and current perception) and response to cold provocation that are related to neck disability. We have identified altered muscle biochemistry by measuring circulating muscle proteins in a lumbar surgery model and are now applying those methods to whiplash injury. We have incorporated capnography into treatment to address central physiological changes present in some patients by monitoring and training CO2 levels. We have developed an innovative new test, the Neck Walk Index, that captures abnormal control of head movement during slow gait as a means of differentiating patients with neck pain from either unaffected controls or individuals with other pathologies. We have used time-varying 3-dimensional joint orientation kinematics to assess deficits in motor control during an upper extremity reach task, the results showing that poor coordination and control of the shoulder girdle leads to shoulder guarding and inconsistencies in elbow joint movement. Despite some promising early results, future research is needed to determine how these measures help clinicians to diagnose, evaluate, and forecast future outcome for patients who present with neck pain.

LEVEL OF EVIDENCE

Diagnosis, level 5.

Evaluation of end-tidal carbon dioxide role in predicting elevated SOFA scores and lactic acidosis

The development of organ dysfunction is a key contributor to morbidity and mortality in sepsis. End-tidal carbon dioxide levels measured by non-invasive end-tidal capnography (ETCO2) may provide a rapid assessment of a patient's underlying metabolic status. The objective of this study was to explore the association between ETCO2 and (1) organ dysfunction [sequential organ failure assessment (SOFA) score], and (2) serum lactate levels in febrile emergency department (ED) patients. Prospective, observational cohort study of a convenience sample of 97 adult (age 18 years or older) patients presented to an academic urban ED with a fever and suspected infection. The outcomes were ED SOFA score and serum lactate level. Based on prior studies, we categorized an ETCO2 <35 mmHg, a priori, as abnormal for the exposure. We defined clinically significant organ failure as a SOFA score of >2, and an abnormal lactate as >4 mmol/L. The correlation of ETCO2 with SOFA and lactate level was analyzed using Pearson correlation coefficient. Operating characteristics were calculated with 95% confidence intervals, along with the area under the curve (AUC). Among 97 patients enrolled, 5 (5%) had an abnormal lactate and 34 (35%) had a SOFA score >2. A significant correlation was found between ETCO2 and SOFA score (r = -0.35, p < 0.01), and ETCO2 and lactate level (r = -0.35, p < 0.01). A receiver operator curve for ETCO2 and SOFA >2 had an AUC of 0.69. ETCO2 of <35 has a sensitivity of 0.73 (95% CI 0.56-0.85) and specificity 0.50 (0.38-0.62) in predicting SOFA scores >2. ETCO2 <35 has a sensitivity of 0.60 (0.22-0.88) and specificity 0.42 (0.32-0.52) in predicting lactate >4 with an AUC of 0.62. We found a small, but statistically significant correlation, between ETCO2 and SOFA scores; however, based on questionable operating characteristics, the test seems to have limited ability to meaningfully impact clinical decision making. Larger confirmatory studies are required before final assessment.

A new capnograph based on an electro acoustic sensor

End tidal carbon dioxide measurements with an electro acoustic capnograph prototype have been demonstrated. The aim of this study was to verify that it is possible to obtain an adequate capnogram using the prototype and to investigate the influence of ambient temperature and humidity variations. By simultaneous measurements with a reference capnograph, on subjects performing exercise, hypo- and hyperventilation, P(ET)CO(2) readings from the reference were compared with the output signal from the prototype. The capnogram from the prototype correlated well with the reference in terms of breath time. The first parts of the expiration and inspiration phases were steeper for the reference than the prototype. The output signal from the prototype correlated well with the reference P(ET)CO(2) readings with a correlation coefficient of 0.93 at varied temperature and relative humidity.

End tidal carbon dioxide monitoring in prehospital and retrieval medicine: a review

End tidal carbon dioxide (ETCO2) monitoring is the non-invasive measurement of exhaled CO2. The Intensive Care Society guidelines include (ETCO2) monitoring as one of the objective standards required for monitoring patients in transport, and the American Heart Association recommends that all intubations must be confirmed by some form of ETCO2 measurement. The physiological principles and technology underlying ETCO2 measurement and the clinical indication for its use in the prehospital environment are reviewed. ETCO2 monitoring has been widely established in the prehospital environment and is of particular use for verification of endotracheal tube placement. It is non-invasive and easy to apply to breathing circuits. The units now available are compact and rugged, with extended battery operating times, which are ideally suited for prehospital use and should be considered as an essential item for advanced airway management.

End tidal carbon dioxide measurement using an electro acoustic sensor

End tidal carbon dioxide measurement with an electro-acoustic sensor is demonstrated. The sensor consists of an acoustic resonator coupled to a low cost electro-acoustic element. By simultaneous measurements with a reference sensor, the new device was tested on subjects performing exercise, hypo- and hyperventilation whereby the CO<inf>2</inf>concentration ranged from 2.1 to 7.0 kPa. The output from the experimental device correlated well with the reference CO<inf>2</inf>readings with a correlation coefficient of 0.976. Response time for expiration less than 0.8 seconds was noted. The new device could be useful in situations where selectivity to other gases is not important.

The Utility of Supplemental Oxygen During Emergency Department Procedural Sedation and Analgesia With Midazolam and Fentanyl: A Randomized, Controlled Trial

STUDY OBJECTIVE

To determine whether supplemental oxygen reduces the incidence of hypoxia by 20% in study patients receiving midazolam and fentanyl for emergency department procedural sedation and analgesia.

METHODS

Patients were randomized to receive either supplemental oxygen or compressed air by nasal cannula at 2 L per minute. Physicians were blinded to the gas used and end-tidal carbon dioxide (ETCO2) data. Respiratory depression was defined a priori as oxygen saturation less than 90%, ETCO2 level greater than 50 mm Hg, an absolute change from baseline of 10 mm Hg, or loss of the ETCO2 waveform.

RESULTS

Of the 80 patients analyzed, 44 received supplemental oxygen and 36 received compressed air. Twenty supplemental oxygen patients and 19 compressed air patients met at least 1 criterion for respiratory depression. Six supplemental oxygen patients and 5 compressed air patients experienced hypoxia (P=.97; effect size 0%; 95% confidence interval -15% to +15%). Fourteen patients in each group met ETCO2 criteria for respiratory depression but were not hypoxic. Physicians identified respiratory depression in 8 of 11 patients who became hypoxic and 0 of 28 patients who met ETCO2 criteria for respiratory depression but who did not become hypoxic. There were no adverse events.

CONCLUSION

Supplemental oxygen did not reduce (or trend toward reducing) the incidence of hypoxia in patients moderately sedated with midazolam and fentanyl. However, our lower-than-expected rate of hypoxia limits the power of this comparison. Blinded capnography frequently identified respiratory depression undetected by the treating physicians.

Breath Analysis: Potential for Clinical Diagnosis and Exposure Assessment

Breath tests are among the least invasive methods available for clinical diagnosis, disease state monitoring, and environmental exposure assessment. In recent years, interest in breath analysis for clinical purposes has increased. This review is intended to describe the potential applications of breath tests, including clinical diagnosis of diseases and monitoring of environmental pollutant exposure, with emphasis on oxidative stress, lung diseases, metabolic disorder, gastroenteric diseases, and some other applications. The application of breath tests in assessment of exposure to volatile organic compounds is also addressed. Finally, both the advantages and limitations of breath analysis are summarized and discussed.

The Use of Quantitative End-Tidal Capnometry to Avoid Inadvertent Severe Hyperventilation in Patients With Head Injury After Paramedic Rapid Sequence Intubation

BACKGROUND

This study aimed to determine whether field end-tidal carbon dioxide CO2 (ETCO2) monitoring decreases inadvertent severe hyperventilation after paramedic rapid sequence intubation.

METHODS

Data were collected prospectively as part of the San Diego Paramedic Rapid Sequence Intubation Trial, which enrolled adults with severe head injuries (Glasgow Coma Score, 3-8) that could not be intubated without neuromuscular blockade. After preoxygenation, the patients underwent rapid sequence intubation using midazolam and succinylcholine. A maximum of three intubation attempts were allowed before Combitube insertion was mandated. Tube confirmation was accomplished by physical examination, qualitative capnometry, pulse oximetry, and syringe aspiration. Standard ventilation parameters (tidal volume, 800 mL; 12 breaths/minute) were taught. One agency used portable ETCO2 monitors, with ventilation modified to target ETCO2 values of 30 to 35 mm Hg. Trial patients transported by aeromedical crews also underwent ETCO2 monitoring. The primary outcome measure was the incidence of inadvertent severe hyperventilation, defined as arterial blood gas partial pressure of CO2 (pCO2) of less than 25 mm Hg at arrival, for patients with and those without ETCO2 monitoring. These groups also were compared in terms of age, gender, clinical presentation, Abbreviated Injury Score, Injury Severity Score, arrival arterial blood gas data, and survival.

RESULTS

The study enrolled 426 patients and administered neuromuscular blocking agents to 418 patients. Endotracheal intubation was successful for 355 of these patients (85.2%). Another 58 patients (13.6%) underwent Combitube insertion. For 291 successfully intubated patients, arrival pCO2 values were documented, with continuous ETCO2 monitoring performed for 144 of these patients (49.4%). Patients with ETCO2 monitoring had a lower incidence of inadvertent severe hyperventilation than those without ETCO2 monitoring (5.6% vs. 13.4%; odds ratio, 2.64; 95% confidence interval, 1.12-6.20; p = 0.035). There were no significant differences in terms of age, gender, clinical presentation, Abbreviated Injury Score, Injury Severity Score, arrival partial pressure of oxygen (PO2) and pH, or survival. The patients in both groups with severe hyperventilation had a significantly higher mortality rate than the patients without hyperventilation (56 vs. 30%; odds ratio, 2.9; 95% confidence interval, 1.3-6.6; p = 0.016), which could not be explained solely on the basis of their injuries.

CONCLUSIONS

The use of ETCO2 monitoring is associated with a decrease in inadvertent severe hyperventilation.

Critical review of non-invasive respiratory monitoring in medical care

Respiratory failure can be difficult to predict. It can develop into a life-threatening condition in just a few minutes, or it can build up more slowly. Thus continuous monitoring of respiratory activity should be mandatory in clinical, high-risk situations, and appropriate monitoring equipment could be life-saving. The review considers non-invasive methods and devices claimed to provide information about respiratory rate or depth, or gas exchange. Methods are categorised into those responding to movement, volume and tissue composition detection; air flow; and blood gas concentration. The merits and limitations of the methods and devices are analysed, considering information content and their ability to minimise the rate of false alarms and false non-alarms. It is concluded that the field of non-invasive respiratory monitoring is still in an exploratory phase, with numerous reports on specific device solutions but less work on evaluation and adaptation to clinical requirements. Convincing evidence of the clinical usefulness of respiratory monitors is still lacking. Devices responding only to respiratory rate, and lacking information about actual gas exchange, will have limited clinical value. Furthermore, enhancement in specificity and sensitivity to avoid false alarms and non-alarms will be necessary to meet clinical requirements. Miniature CO2 sensors are identified as one route towards substantial improvement.

Tight control of prehospital ventilation by capnography in major trauma victims

BACKGROUND

Tracheal intubation combined with controlled ventilation of the lungs is an important part of the prehospital management of major trauma victims, but gauging the adequacy of ventilation remains a major problem.

METHODS

Ninety-seven major trauma victims who underwent tracheal intubation in the field and controlled ventilation of the lungs during prehospital treatment by a Helicopter Emergency Medical Service were assigned randomly to one of two groups: (1) monitor group (n=57) and (2) monitor-blind group (n=40), according to whether the anaesthetist could or could not see an attached capnograph screen. In the monitor-blind group ventilation was set by using a tidal-volume of 10 ml kg(-1) estimated body weight and an age-appropriate ventilatory frequency. In the monitor group, ventilation was adjusted to achieve target end-tidal carbon dioxide values determined by the 'physiological state' of the trauma victim. Arterial blood gases were measured upon hospital admission while maintaining the ventilation initiated in the field and the Pa(CO(2)) value obtained was used as the determinant of the adequacy of prehospital ventilation.

RESULTS

The incidence of 'normoventilation' was significantly higher (63.2 vs 20%; P<0.0001) and the incidence of 'hypoventilation' upon hospital admission was significantly lower (5.3 vs 37.5%; P<0.0001) in the monitor group; patients with severe head and chest trauma and haemodynamically unstable patients and those with a high injury severity score were significantly more likely to be 'normoventilated' upon hospital admission in the monitor group than in the monitor-blind group.

CONCLUSIONS

The data support the routine use of prehospital capnographic monitoring using target end-tidal carbon dioxide values adapted to the physiological state of the patient in major trauma victims requiring tracheal intubation in the field.

Hyperventilation in traumatic brain injury patients: inconsistency between consensus guidelines and clinical practice

BACKGROUND

This study assessed patients with traumatic brain injury (TBI) to determine whether prehospital and community hospital providers employed hyperventilation therapy inconsistent with consensus recommendation against its routine use.

METHODS

This prospective analysis of 37 intubated TBI patients without herniation, undergoing helicopter transport to an urban Level I center, entailed flight crews' noting of assisted ventilation rate (AVR) and end-tidal carbon dioxide (ETCO2) upon their arrival at trauma scenes or community hospitals. A priori-set levels of AVR and ETCO2 were used to assess frequency of guideline-inconsistent hyperventilation, and Fisher's exact and Kruskal-Wallis tests assessed association between guideline-inconsistent hyperventilation and manual vs. mechanical ventilation mode.

RESULTS

Inappropriately high AVR and low ETCO2 were seen in 60% and 70% of patients, respectively. Manual ventilation was associated with guideline-inconsistent hyperventilation assessed by AVR (p = 0.038) and ETCO2 (p = 0.022).

CONCLUSION

Prehospital and community hospital hyperventilation practices are not consistent with consensus recommendations for limitation of hyperventilation therapy.

A risk management audit: are we complying with the national guidelines for sedation by non-anaesthetists?

OBJECTIVES

To assess the effect of a preprinted form in ensuring an improved and sustained quality of documentation of clinical data in compliance with the national guidelines for sedation by non-anaesthetists.

DESIGN

The process of retrospective case note audit was used to identify areas of poor performance, reiterate national guidelines, introduce a post-sedation advice sheet, and demonstrate improvement.

SETTING

Emergency Department, Musgrove Park Hospital, Taunton.

SUBJECTS

Forty seven patients requiring sedation for relocation of a dislocated shoulder or manipulation of a Colles' fracture between July and October 1996 and July and October 1997.

MAIN OUTCOME MEASURES

Evidence that the following items had been documented: consent for procedure, risk assessment, monitored observations, prophylactic use of supplementary oxygen, and discharging patients with printed advice. Case note review was performed before (n = 23) and after (n = 24) the introduction of a sedation audit form. Notes were analysed for the above outcome measures. The monitored observations analysed included: pulse oximetry, respiratory rate, pulse rate, blood pressure, electrocardiography, and conscious level.

RESULTS

Use of the form significantly improved documentation of most parameters measured.

CONCLUSIONS

Introduction of the form, together with staff education, resulted in enhanced documentation of data and improved conformity with national guidelines. A risk management approach to preempting critical incidents following sedation, can be adopted in this area of emergency medicine.