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End-tidal carbon dioxide monitoring in pediatrics - clinical applications. MS BhendeDepartment of Paediatric Emergency Medicine, University of Pittsburgh School of Medicine, Children's Hospital of Pittsburgh, Pittsburgh, PA 15213, USA. , USA
Correspondence Address: Source of Support: None, Conflict of Interest: None PMID: 11832630
End-tidal CO2 monitoring is an exciting non-invasive technology that is more commonly used in the emergency department, intensive care unit and in the prehospital setting. Its main use has been in verifying endotracheal tube position, during mechanical ventilation and cardiopulmonary resuscitation, but it is being studied and used for other purposes as well. The new American Heart Association guidelines require secondary confirmation of proper tube placement in all patients by exhaled CO2 immediately after intubation and during transport. This article covers the clinical applications of end-tidal CO2 monitoring with special reference to the paediatric patient. Keywords: Capnography, methods,Carbon Dioxide, analysis,Cardiopulmonary Resuscitation, Child, Colorimetry, Human, Intubation, Intratracheal, adverse effects,Pediatrics, Pulmonary Gas Exchange, Tidal Volume,
End- tidal CO2 (ETCO2) monitoring is an exciting new technology that measures CO2 in the exhaled breath non-invasively. The principles of ETCO2 monitoring, instruments and capnograms are discussed in a companion article. This article focuses on the applications of ETCO2 monitoring to specific clinical situations with special reference to the paediatric patient. CO2 is produced during cellular metabolism, transported to the heart and exhaled via the lung and so ETCO2 reflects ventilation, metabolism and circulation.[1] If any two systems are kept constant then changes in the third system reflect changes in ETCO2. [1],[2],[3] This was first studied clinically by Smallhout and Kalenda in the 1970’s, and in the late 1980’s – 1990’s this methodology has been studied extensively in various clinical settings.[1],[2] The most common use of ETCO2 is to verify endotracheal tube (ETT) position. It is being increasingly studied and used during cardiopulmonary resuscitation (CPR) and other clinical settings.
Aetiologies of Hypocapnia and Hypercapnia Sudden loss of the capnograph i.e., decrease to zero should alert the clinician to a catastrophic event such as oesophageal intubation, total obstruction, or ventilator malfunction.[1],[2],[4] An exponential decrease of ETCO2 can be seen due to loss of pulmonary blood flow as in cardiac arrest or sudden hypotension, severe pulmonary embolism, or when patients are placed on cardiopulmonary bypass.[1],[2],[4] A gradual decrease in ETCO2 indicates decreased production such as in hypothermia. Rising ETCO2 can be seen either due to increased CO2 production, such as in sepsis, malignant hyperthermia, or due to decreased CO2 elimination when there is decreased alveolar ventilation.[1],[2],[4] An acute rise of ETCO2 is seen when a tourniquet is released, bicarbonate is administered and when there is return of spontaneous circulation (ROSC) during CPR.[1],[2],[4] Endotracheal Intubation Critically ill children need to have their airways controlled and ventilation managed optimally.[2] Endotracheal intubation is a commonly performed procedure in the operating rooms, intensive care units, emergency departments and in the prehospital settings.[2] Clinical evaluations such as breath sound auscultation, chest rise visualization, auscultating over the stomach, and clouding of the ETT tube have their limitations in evaluating tube placement.[5],[6],[7] Improperly placed tubes can result in serious complications such as hypoxia and cardiac arrest.[2] ETCO2 monitoring is a non-invasive method of evaluating ventilation and is helpful in assessing ETT placement.[1],[2],[4],[5],[6] CO2 is exhaled through the trachea and not usually from the oesophagus and so the measurement of CO2 in the expired air distinguishes tracheal from oesophageal intubation.[1],[2],[4],[5],[6] The gold standards for verifying ETT position are direct visualization of the ETT going through the vocal cords and CO2 in the exhaled air.[1],[2],[5] Incidence of oesophageal intubations has been reported to be 40% in the neonatal intensive care unit by Robert’s et al [8] and 18.5 % in the prehospital and ED setting in infants and children by Bhende et al.[9] These were all detected oesophageal intubations and the ETT was later correctly placed in the trachea.[8],[9] ETCO2 for endotracheal intubation verification has been studied in animals[10],[11] and humans[12] in both the non-arrest[10],[12] and arrest settings.[11] ETCO2 has been shown to be superior to pulse oximetry in the early detection of oesophageal intubation especially if patients are preoxygenated with 100% O2.[6],[13],[14] This is because the absence of CO2 is detected in the very next breath after displacement of the ETT, while it takes a little while for O2 saturations to drop, and for physiological changes to take place.[6],[13],[14] False positive readings (readings indicating tracheal placement) that may occur after ingestion of carbonated beverages or bag-valve-mask ventilation, can be avoided by obtaining readings after 6 breaths. [15],[16] By the end of 6 breaths there is a CO2 wash out and true readings are obtained.[15],[16] Colorimetric detectors have been shown to be extremely accurate in animal studies, in children weighing >2 kg, and adults in the ICU, ED, OR, transport and prehospital settings.[16],[17],[18],[19],[20],[21] During CPR because of very limited pulmonary blood flow false negative readings may occur, i.e., the detector remains purple despite correct intratracheal placement.[9],[17],[20],[21] This may also occur in severely hypocarbic neonates.[19] The pedicap has been shown to be useful in identifying ETT position in neonates up to 1 kg.[22] The larger Easycap with the 38 cc dead space has been shown to accurately identify ETT placements in infants weighing > 2 kg.[2],[9],[16],[17],[19],[23] It should not be continuously used in small infants because of the danger of rebreathing expired air, but is fine to use in the controlled setting.[2],[23],[24] The capnoflo resuscitator has been shown to be useful in identifying airway mishaps in an animal model,[25] and for the initial verification of ETT position during transport of intubated children.[26] Its use was limited during transport after some time as it failed to show the reversible colour changes with inspiration and expiration.[26] Limitations of CO2 detectors are that they cannot detect hypo- or hypercarbia, right main stem bronchus intubation or oropharyngeal intubations in spontaneously breathing patients.[2],[9],[16],[21] If the detector is contaminated with acidic gastric contents or drugs such as epinephrine, there is fixed yellow discoloration and the detector is not reliable.[2],[23] Recently Gausche et al, [27] reported that the addition of out of hospital endotracheal intubation to a paramedic scope of practice that already includes bag-valve-mask ventilation did not improve survival or neurologic outcome of paediatric patients treated in an urban EMS system. They reported that endotracheal intubation in this setting caused prolonged scene times and fatal complications were frequent, and they questioned the practice of prehospital endotracheal intubation by paramedics.[27] Benefits of intubation by paramedics should be weighed against risks, and should take into account the experience of the paramedics, transport time, transport conditions, and the extent and nature of airway compromise. ETCO2 monitoring is the standard of care among anaesthesiologists, and has been strongly recommended in prehospital settings.[28] If experienced anaesthesiologists who perform intubations daily need to use ETCO2, the need is even more pressing for its use in the pre-hospital setting and the ED where intubations are performed less frequently and in less favourable settings.[2],[28] The new American Heart Association guidelines for Advanced Cardiac Life Support and Paediatric Advanced Life Support require secondary confirmation of proper tube placement in all patients with a perfusing rhythm by capnography or exhaled CO2 detection immediately after intubation and during transport.[29] If the patient is pulseless they recommend the use of a CO2 device, but if the device shows no colour change because of extremely low pulmonary blood flow, they then recommend the use of some other means of checking tube placement such as direct visualization.[29] This is a crucial step in preventing the tragedy of unrecognised oesophageal intubations.[29] It is important not only to correctly intubate a patient but also to make certain that the ETT stays in place. ETT dislodgement can take place during prehospital transport because of rough road conditions, and during interhospital transport because of patient movement or unsecured ETT.[19],[30] This can happen especially in children where the distance between the vocal cords and the carina is small.[19] So it is important not only to check initial placement but to use ongoing monitoring of the ETT position.[19],[30] Detectors and portable infrared capnometers are useful during transport and in the prehospital setting.[2],[19],[30] Cardiopulmonary Resuscitation ETCO2 monitoring is a valuable tool during CPR. During cardiac arrest, ETCO2 levels falls to low levels abruptly at the onset of cardiac arrest, increases after the onset of effective CPR and returns to normal levels at return of spontaneous circulation (ROSC).[31],[32] During effective CPR, end-tidal CO2 has been shown to correlate with cardiac output,[33] coronary perfusion pressure,[34] efficacy of cardiac compression, ROSC, and even survival.[35] The colorimetric detectors which were shown to correlate with infrared capnometry in a paediatric canine arrest model,[36] have been shown to have prognostic value in both adult [37],[38] and paediatric CPR.[9] The higher the initial value of ETCO2 the greater was the short term survival.[9],[37] In most adult and animal studies of CPR ventricular fibrillation is the mode of arrest. It shows a characteristic pattern of a sudden drop in CO2 which increases with effective CPR.[31],[32] The most common cause of paediatric cardiac arrests is due to respiratory arrest.[36] The initial ETCO2 has been shown in a paediatric asphyxial arrest canine model to be markedly elevated and then decrease to low levels during CPR finally increasing at ROSC.[39] This is due to accumulation of CO2 in the lungs after respiratory arrest and prior to cardiac arrest.[39] ETCO2 of at least 10 mm Hg during first 20 minutes was shown to be associated with ROSC.[40] Levine et al., found ETCO2 of 10 mm or less at 20 minutes predicted death and concluded that CPR could be reasonably terminated in those patients.[41] So ETCO2 has been found to be a useful tool during CPR, and could be potentially useful in determining when to terminate CPR. Respiratory Problems ETCO2 has been used to monitor mechanically ventilated patients, to detect hypercapnic episodes and to help wean the patient off the ventilator when there is minimal pulmonary disease.[2] Yaron et al., studied the capnograms during asthma and found them to correlate with spirometry.[42] If this is found to be true in children it would be an extremely useful tool to monitor the severity of asthma, as ETCO2 is non-invasive and effort independent. Nasal capnometry has been shown to correlate well with PCO2 in children with seizures, which could help the clinician decide when to provide ventilatory support to the patient. [43] So far, ETCO2 monitoring has not been shown to be helpful in monitoring hyperventilation of head injury patients.[44] It has been successfully used to monitor sleep apnoea patients and has been recommended by the American Thoracic Society.[45] Miscellaneous Capnography has been shown to be extremely useful during transport of critically ill patients in not only continuously assessing ETT position, but also to optimally ventilate patients.[19],[46],[47],[48] Studies have shown that significant alterations in ventilation status (pH, PETCO2, PaCO2,) can occur during transport.[47],[48] Having the ability to monitor ETCO2 during transport would allow pre-hospital care providers to be more cognitive of the ventilation status of the patient.[2],[30] ETCO2 monitoring may be useful to identify hypoventilation during procedural sedation, especially when the patient’s ventilatory efforts cannot be visualised.[49]
End-tidal CO2 is a relatively new technology and is becoming a very useful tool in the paediatric emergency department, intensive care unit and in the pre-hospital setting. Besides being useful in verifying endotracheal tube position, it can have a very powerful role during CPR, shock, respiratory distress, seizures, asthma and procedural sedation. Clinical studies need to define its exact role in different clinical settings. The AHA mandate of checking all intubations with ETCO2 has the potential to avoid catastrophic oesophageal intubation.
The author thanks Margaret Jasko for secretarial support.
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