Capnography for the Nonintubated Patient in the ED
Capnography for the Nonintubated Patient in the ED
CO2 measurement is the standard of care for confirmation of endotracheal tube placement in intubated patients. It is also effective for confirming effective ventilation with supraglottic airways. Monitoring capnographic waveforms provides rapid detection of loss of proper placement or function in all advanced airway devices. Some concern surrounds confirming intubation in the setting of recently ingested carbonated beverages. In one study, five dogs were administered carbonated beverages while esophageal and endotracheal CO2 monitoring was conducted. Although CO2 was detected transtracheally, it was rapidly diminishing and easily distinguishable from physiologic alveolar CO2 waveforms. This would appear to be more a theoretical concern than a clinical reality.
Cardiac chest compression effectiveness can be assessed as well as early detection of return of spontaneous circulation ( Figure 2). EtCO2 can also be utilized to assist in determining death. An EtCO2 of <10 mm Hg after 20 min of advanced life support resuscitation demonstrated 100% mortality. Salen et al. identified that EtCO2 levels > 16 mm Hg were significantly associated with survival from emergency department resuscitation. No patient survived with a level < 16 mm Hg. Head injury patients can have their ventilation rates optimized. By doing this, they avoid hyperventilation, which has been shown to increase mortality.
Plewa et al. reported noninvasive EtCO2 measured with forced expiration correlated with PaCO2 levels in nonintubated emergency department (ED) patients with respiratory distress in 1995.
Reported respiratory rates are inherently inaccurate and can affect emergent patient care. The rapid application and assessment by capnography can provide an accurate interpretation of patient's true respiratory rate within a few seconds, as opposed to a manual count for 30−60 s. This intrinsic value should not be underestimated. Plethymsography, which is currently utilized by many vital-sign monitors, relies on transthoracic impedance, which is highly susceptible to patient movements and therefore ineffective and often ignored by clinicians.
Many studies have reviewed EtCO2 monitoring in the setting of sedation and analgesia administration. Supplemental oxygen administration is a common practice and can delay the onset of hypoxia despite hypoventilation and hypercarbia. The American Academy of Pediatrics' guidelines recommend the use of EtCO2 during deep sedation. Increases of EtCO2 were measured from 0.16 to 22.3 mm Hg with a mean increase of 6.7 mm Hg for midazolam and ketamine with a mean increase of 8.8 mm Hg for combinations for midazolam and opiates. This particular study was conducted in children ages 1−16 years old for procedures such as fracture reduction, laceration repair, incision and drainage, and lumbar puncture. Additional studies demonstrate evidence of hypercarbia in the absence of hypoxia. In a prospective, randomized clinical trial of 126 pediatric patients who underwent sedation/analgesia procedures in an intensive care unit setting, 6% had hypercarbia (EtCO2 > 50 mm Hg) without any evidence of hypoxia (oxygen saturation < 90%). Propofol and benzodiazepine/opiate combinations produced a higher incidence of respiratory depression and higher levels of EtCO2. An adult study with 132 subjects underwent sedation with propofol in the ED. All patients received supplemental oxygen at 3 L/min. Capnography gave advanced warning for all hypoxic events (SpO2 < 93% for ≥ 15 s). A median time of 60 s and a range of 5 to 240 s demonstrated capnographic evidence of respiratory depression before hypoxia. A Spanish study during colonoscopy showed only 38% of hypoventilation episodes were detected by pulse oximetry. Numerous nonanesthesiologists utilize sedative hypnotics for sedation in outpatient settings. Capnographic monitoring appears to improve patient safety monitoring in these situations.
Patient-controlled analgesia (PCA) is on the rise in the ED and its use is widespread throughout the inpatient setting. The Veterans Health Administration integrated product team recommends PCA pumps with an integrated EtCO2 monitor as the pump of choice. Their analysis revealed integrated EtCO2 could have prevented > 60% of adverse events related to PCA pumps.
Garcia et al. reported the successful noninvasive monitoring of EtCO2 in diabetic ketoacidosis (DKA) patients. This allowed continuous monitoring of EtCO2 as an accurate estimate of PCO2. One hundred and twenty-one patients were monitored for 6 h. Initial pH values were 7.08, respiratory rate was 35 breaths/min, EtCO2 18.6 torr, and venous PCO2 20 torr. At the conclusion of the observation period, the pH had improved to 7.29, respiratory rate to 22 breaths/min, EtCO2 to 35 torr, and the venous PCO2 to 36 torr. The correlation between EtCO2 and venous PCO2 was significant (r = 0.92, p = 0.0001). Limit of agreements between the two methods established an EtCO2 0.8 torr lower than venous PCO2 with 95% limits of agreement. This observation may allow the use of noninvasive EtCO2 monitoring in the clinical setting of DKA, decreasing blood draws and giving a continuous assessment for trending of clinical values.
EtCO2 provides a reliable assessment of a patient's ventilatory status in actively seizing and post-ictal patients. A pediatric ED enrolled 105 patients who were actively seizing and 61 post-ictal patients and monitored EtCO2, respiratory rates, O2 saturation, and heart rates. Capillary PCO2 was compared with EtCO2 and established 95% limit of agreement ± 4.2 torr. Seventy-nine patients had an oxygenation saturation of <93%. These patients had EtCO2 > 45 torr. Capnometry was able to reliably detect 5 patients with respiratory failure. EtCO2 rose to 70−99 torr despite maintaining O2 saturations > 97% on 2−4 L/min of oxygen. Each patient required assisted bag-valve mask ventilation and subsequent intubation. An additional 20 patients required brief periods of bag-valve mask ventilation support for significant respiratory compromise not requiring intubation and mean EtCO2 of 52 torr. The authors conclude noninvasive capnography was more sensitive than pulse oximetry in predicting a trend toward respiratory failure.
Characteristic waveform analysis and quantitative measurements can be utilized to monitor response to treatment in patients with asthma, COPD, and congestive heart failure. Bronchospasm and subsequent obstructive disease patterns can demonstrate the "shark-fin" appearance ( Figure 3B). During asthma exacerbations, a mild drop in the EtCO2 level might be noticed as the patient hyperventilates to compensate. When the exacerbation becomes severe, the CO2 levels will rise to abnormal levels as the patient tires and is unable to effectively ventilate. Effective treatment can be monitored not only by clinical parameters but also by objective findings of quantitative EtCO2 improvement and waveform analyses, such as the shark-fin appearance normalizing. Approximately 5% of patients with COPD will have a "hypoxic drive." Monitoring EtCO2 allows the provider to identify when EtCO2 starts to increase and therefore oxygen flow can be decreased.
Howe et al. provide preliminary data examining computer analysis of the waveform, specifically observing the slope of Phase II and Phase III and the α angle. Their pre-and post-treatment analysis found a significant difference in the slope of Phase II and the α angle as determined by the computer algorithm in nonintubated patients. This provides an effort independent process and also promotes continuous monitoring of respiratory status.
Although not able to reliably diagnose a pulmonary embolism (PE), the EtCO2 decreases secondary to increase in dead-space ventilation. Hemnes et al. reviewed 298 patients and attempted to define an EtCO2 level that would exclude pulmonary embolism. They measured EtCO2 within 24 h of contrast-enhanced helical computed tomography; lower extremity duplex, or ventilation perfusion scan. A PE was diagnosed in 13% of the enrolled patients. Mean EtCO2 levels in healthy volunteers were not different from patients without PE. End-tidal CO2 ≥ 36 mm Hg had an optimal sensitivity and specificity of 87.2% and 53%, respectively, for identifying patients without PE. A negative predicative value of 96.6% (95% confidence interval [CI] 92.3−98.5) demonstrates the value of this technique. They report this increased to 97.6% (99% CI 93.2−99.2) when combined with a Wells score ≤ 4. The authors determined a CT cost of $1739 and 120 of the studies could have been avoided for a potential cost savings of $208,680 in this small study.
A rare complication of anesthesia administration, and one occasionally associated with hyperadrenergic states, is a dramatic increase in EtCO2 that can be seen even before a change in temperature. This has been reported to be 3−4 times the patient's previous level. Monitoring a patient's baseline EtCO2 and recognizing this phenomenon of a rapid rise when succinylcholine or anesthetic agents are administered can be lifesaving.
Preliminary evaluation of EtCO2 as a triage tool was presented in an abstract from the University of Florida Jacksonville. A small convenience sample of patients presenting to an urban academic ED demonstrated EtCO2 could be a sensitive (yet nonspecific) indicator of illness or injury. They showed 1 in 6 subjects presenting with normal vital signs and normal EtCO2 are admitted, and 1 in 2 subjects with normal vital signs and abnormal EtCO2 are admitted. In acute blunt-trauma patients with an EtCO2 < 26.25 mm Hg after 20 min, only 5% survived to discharge. This time delay of 20 min effectively eliminated those patients who had airway obstruction or the need for assisted ventilations, which might have accounted for an initial elevation in CO2. In mass-casualty incidents, it has been suggested that capnography can serve as an effective, rapid assessment and triage tool for victims of chemical exposure.
Kartal et al. evaluated the use of EtCO2 to exclude metabolic disturbances. They enrolled 240 patients and determined the EtCO2 values of ≥37 mm Hg essentially ruled out HCO3 levels of ≤21 mmol/L. This is another example demonstrating EtCO2 can give rapid predictive information for patients presenting to the emergency setting.
Many authors suggest using EtCO2 as a means of biofeedback for patients to utilize the waveform and quantitative measurements as visual feedback and coaching. The patient can be instructed to watch the monitor and visualize their breathing by watching the waveform. Patients can see their EtCO2 level rise and respiratory rate decrease. Additionally, their symptoms improve. This is a very effective technique for patients with hyperventilation primarily due to anxiety and panic attack.
Standard practice for intrahospital transport is to provide the same level of care, monitoring, and interventions that are available in the intensive care unit. EtCO2 monitoring assists in recognizing or preventing complications during transport of patients. Capnography is also recommended as an additional monitoring tool for minor trauma patients during interhospital transport to an emergency center.
Many associations and organizations, including Anesthesia Patient Safety Foundation and the American Society of Anesthesiologists, are incorporating into their guidelines the noninvasive monitoring of EtCO2 to assess a patient's ventilatory status. The 2012 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care stress the critical importance of continuous waveform capnography to confirm and monitor endotracheal intubation placement, assess the quality of cardiopulmonary resuscitation, and detect return of spontaneous circulation.
Discussion
Intubation and Capnography
CO2 measurement is the standard of care for confirmation of endotracheal tube placement in intubated patients. It is also effective for confirming effective ventilation with supraglottic airways. Monitoring capnographic waveforms provides rapid detection of loss of proper placement or function in all advanced airway devices. Some concern surrounds confirming intubation in the setting of recently ingested carbonated beverages. In one study, five dogs were administered carbonated beverages while esophageal and endotracheal CO2 monitoring was conducted. Although CO2 was detected transtracheally, it was rapidly diminishing and easily distinguishable from physiologic alveolar CO2 waveforms. This would appear to be more a theoretical concern than a clinical reality.
Cardiac chest compression effectiveness can be assessed as well as early detection of return of spontaneous circulation ( Figure 2). EtCO2 can also be utilized to assist in determining death. An EtCO2 of <10 mm Hg after 20 min of advanced life support resuscitation demonstrated 100% mortality. Salen et al. identified that EtCO2 levels > 16 mm Hg were significantly associated with survival from emergency department resuscitation. No patient survived with a level < 16 mm Hg. Head injury patients can have their ventilation rates optimized. By doing this, they avoid hyperventilation, which has been shown to increase mortality.
Nonintubated Roles
Plewa et al. reported noninvasive EtCO2 measured with forced expiration correlated with PaCO2 levels in nonintubated emergency department (ED) patients with respiratory distress in 1995.
Respiratory Rate
Reported respiratory rates are inherently inaccurate and can affect emergent patient care. The rapid application and assessment by capnography can provide an accurate interpretation of patient's true respiratory rate within a few seconds, as opposed to a manual count for 30−60 s. This intrinsic value should not be underestimated. Plethymsography, which is currently utilized by many vital-sign monitors, relies on transthoracic impedance, which is highly susceptible to patient movements and therefore ineffective and often ignored by clinicians.
Sedation and Analgesia Utilization
Many studies have reviewed EtCO2 monitoring in the setting of sedation and analgesia administration. Supplemental oxygen administration is a common practice and can delay the onset of hypoxia despite hypoventilation and hypercarbia. The American Academy of Pediatrics' guidelines recommend the use of EtCO2 during deep sedation. Increases of EtCO2 were measured from 0.16 to 22.3 mm Hg with a mean increase of 6.7 mm Hg for midazolam and ketamine with a mean increase of 8.8 mm Hg for combinations for midazolam and opiates. This particular study was conducted in children ages 1−16 years old for procedures such as fracture reduction, laceration repair, incision and drainage, and lumbar puncture. Additional studies demonstrate evidence of hypercarbia in the absence of hypoxia. In a prospective, randomized clinical trial of 126 pediatric patients who underwent sedation/analgesia procedures in an intensive care unit setting, 6% had hypercarbia (EtCO2 > 50 mm Hg) without any evidence of hypoxia (oxygen saturation < 90%). Propofol and benzodiazepine/opiate combinations produced a higher incidence of respiratory depression and higher levels of EtCO2. An adult study with 132 subjects underwent sedation with propofol in the ED. All patients received supplemental oxygen at 3 L/min. Capnography gave advanced warning for all hypoxic events (SpO2 < 93% for ≥ 15 s). A median time of 60 s and a range of 5 to 240 s demonstrated capnographic evidence of respiratory depression before hypoxia. A Spanish study during colonoscopy showed only 38% of hypoventilation episodes were detected by pulse oximetry. Numerous nonanesthesiologists utilize sedative hypnotics for sedation in outpatient settings. Capnographic monitoring appears to improve patient safety monitoring in these situations.
Patient-controlled analgesia (PCA) is on the rise in the ED and its use is widespread throughout the inpatient setting. The Veterans Health Administration integrated product team recommends PCA pumps with an integrated EtCO2 monitor as the pump of choice. Their analysis revealed integrated EtCO2 could have prevented > 60% of adverse events related to PCA pumps.
Diabetic Ketoacidosis
Garcia et al. reported the successful noninvasive monitoring of EtCO2 in diabetic ketoacidosis (DKA) patients. This allowed continuous monitoring of EtCO2 as an accurate estimate of PCO2. One hundred and twenty-one patients were monitored for 6 h. Initial pH values were 7.08, respiratory rate was 35 breaths/min, EtCO2 18.6 torr, and venous PCO2 20 torr. At the conclusion of the observation period, the pH had improved to 7.29, respiratory rate to 22 breaths/min, EtCO2 to 35 torr, and the venous PCO2 to 36 torr. The correlation between EtCO2 and venous PCO2 was significant (r = 0.92, p = 0.0001). Limit of agreements between the two methods established an EtCO2 0.8 torr lower than venous PCO2 with 95% limits of agreement. This observation may allow the use of noninvasive EtCO2 monitoring in the clinical setting of DKA, decreasing blood draws and giving a continuous assessment for trending of clinical values.
Seizure Patients
EtCO2 provides a reliable assessment of a patient's ventilatory status in actively seizing and post-ictal patients. A pediatric ED enrolled 105 patients who were actively seizing and 61 post-ictal patients and monitored EtCO2, respiratory rates, O2 saturation, and heart rates. Capillary PCO2 was compared with EtCO2 and established 95% limit of agreement ± 4.2 torr. Seventy-nine patients had an oxygenation saturation of <93%. These patients had EtCO2 > 45 torr. Capnometry was able to reliably detect 5 patients with respiratory failure. EtCO2 rose to 70−99 torr despite maintaining O2 saturations > 97% on 2−4 L/min of oxygen. Each patient required assisted bag-valve mask ventilation and subsequent intubation. An additional 20 patients required brief periods of bag-valve mask ventilation support for significant respiratory compromise not requiring intubation and mean EtCO2 of 52 torr. The authors conclude noninvasive capnography was more sensitive than pulse oximetry in predicting a trend toward respiratory failure.
Trending and Objective Assessment in Respiratory Distress
Characteristic waveform analysis and quantitative measurements can be utilized to monitor response to treatment in patients with asthma, COPD, and congestive heart failure. Bronchospasm and subsequent obstructive disease patterns can demonstrate the "shark-fin" appearance ( Figure 3B). During asthma exacerbations, a mild drop in the EtCO2 level might be noticed as the patient hyperventilates to compensate. When the exacerbation becomes severe, the CO2 levels will rise to abnormal levels as the patient tires and is unable to effectively ventilate. Effective treatment can be monitored not only by clinical parameters but also by objective findings of quantitative EtCO2 improvement and waveform analyses, such as the shark-fin appearance normalizing. Approximately 5% of patients with COPD will have a "hypoxic drive." Monitoring EtCO2 allows the provider to identify when EtCO2 starts to increase and therefore oxygen flow can be decreased.
Howe et al. provide preliminary data examining computer analysis of the waveform, specifically observing the slope of Phase II and Phase III and the α angle. Their pre-and post-treatment analysis found a significant difference in the slope of Phase II and the α angle as determined by the computer algorithm in nonintubated patients. This provides an effort independent process and also promotes continuous monitoring of respiratory status.
Pulmonary Embolism
Although not able to reliably diagnose a pulmonary embolism (PE), the EtCO2 decreases secondary to increase in dead-space ventilation. Hemnes et al. reviewed 298 patients and attempted to define an EtCO2 level that would exclude pulmonary embolism. They measured EtCO2 within 24 h of contrast-enhanced helical computed tomography; lower extremity duplex, or ventilation perfusion scan. A PE was diagnosed in 13% of the enrolled patients. Mean EtCO2 levels in healthy volunteers were not different from patients without PE. End-tidal CO2 ≥ 36 mm Hg had an optimal sensitivity and specificity of 87.2% and 53%, respectively, for identifying patients without PE. A negative predicative value of 96.6% (95% confidence interval [CI] 92.3−98.5) demonstrates the value of this technique. They report this increased to 97.6% (99% CI 93.2−99.2) when combined with a Wells score ≤ 4. The authors determined a CT cost of $1739 and 120 of the studies could have been avoided for a potential cost savings of $208,680 in this small study.
Malignant Hyperthermia
A rare complication of anesthesia administration, and one occasionally associated with hyperadrenergic states, is a dramatic increase in EtCO2 that can be seen even before a change in temperature. This has been reported to be 3−4 times the patient's previous level. Monitoring a patient's baseline EtCO2 and recognizing this phenomenon of a rapid rise when succinylcholine or anesthetic agents are administered can be lifesaving.
Triage
Preliminary evaluation of EtCO2 as a triage tool was presented in an abstract from the University of Florida Jacksonville. A small convenience sample of patients presenting to an urban academic ED demonstrated EtCO2 could be a sensitive (yet nonspecific) indicator of illness or injury. They showed 1 in 6 subjects presenting with normal vital signs and normal EtCO2 are admitted, and 1 in 2 subjects with normal vital signs and abnormal EtCO2 are admitted. In acute blunt-trauma patients with an EtCO2 < 26.25 mm Hg after 20 min, only 5% survived to discharge. This time delay of 20 min effectively eliminated those patients who had airway obstruction or the need for assisted ventilations, which might have accounted for an initial elevation in CO2. In mass-casualty incidents, it has been suggested that capnography can serve as an effective, rapid assessment and triage tool for victims of chemical exposure.
Kartal et al. evaluated the use of EtCO2 to exclude metabolic disturbances. They enrolled 240 patients and determined the EtCO2 values of ≥37 mm Hg essentially ruled out HCO3 levels of ≤21 mmol/L. This is another example demonstrating EtCO2 can give rapid predictive information for patients presenting to the emergency setting.
Anxiety/Hyperventilation
Many authors suggest using EtCO2 as a means of biofeedback for patients to utilize the waveform and quantitative measurements as visual feedback and coaching. The patient can be instructed to watch the monitor and visualize their breathing by watching the waveform. Patients can see their EtCO2 level rise and respiratory rate decrease. Additionally, their symptoms improve. This is a very effective technique for patients with hyperventilation primarily due to anxiety and panic attack.
Intrahospital and Interhospital Transport
Standard practice for intrahospital transport is to provide the same level of care, monitoring, and interventions that are available in the intensive care unit. EtCO2 monitoring assists in recognizing or preventing complications during transport of patients. Capnography is also recommended as an additional monitoring tool for minor trauma patients during interhospital transport to an emergency center.
Patient Safety
Many associations and organizations, including Anesthesia Patient Safety Foundation and the American Society of Anesthesiologists, are incorporating into their guidelines the noninvasive monitoring of EtCO2 to assess a patient's ventilatory status. The 2012 American Heart Association Guidelines for Cardiopulmonary Resuscitation and Emergency Cardiovascular Care stress the critical importance of continuous waveform capnography to confirm and monitor endotracheal intubation placement, assess the quality of cardiopulmonary resuscitation, and detect return of spontaneous circulation.
