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Capnography and capnometry provide useful information that may help improve decision-making and reduce complications during transport. This chapter reviews specific clinical applications of capnography and capnometry: assuring proper endotracheal tube placement, monitoring airway circuit integrity, monitoring the consistency of mechanical ventilation, improving safety in procedural sedation, assessing cardiac output, and evaluating patients in cardiac arrest. Capnometry and capnography aid in the confirmation of correct endotracheal tube placement. End-tidal CO2 (ETCO2) measurement can accurately detect esophageal intubation because CO2 is exhaled through the trachea, and not the esophagus. Once an airway device is in place, continuous monitoring is important to assure ventilator circuit patency, including that of the endotracheal tube, and to assure consistent levels of ventilation. Capnography is the gold standard for monitoring patients on airway appliances and ventilator circuits, and there are useful roles for the technology during procedural sedation and evaluating patients in the time surrounding arrest states.
The usually more controlled circumstances of airway management in the operating room (OR) often provide better conditions, better monitoring, and more experienced personnel, particularly when a problem occurs, than is available in other critical care environments or the emergency department. While the detection of CO2 by capnography after completion of a difficult intubation procedure may suggest success, it may more precisely indicate only that the tube tip is somewhere in the respiratory path, although perhaps not exactly where the intubationist desires. A capnography pattern indicating declining CO2 in each subsequent breath over several breaths will help identify esophageal intubation. Unilateral pathophysiologic conditions that cause unilateral hypoventilation or high airway resistances would result in a biphasic waveform. Many techniques to facilitate blind nasal tracheal intubation use the detection of significant exhaled gas flow from a spontaneously breathing patient to indicate the proximity of the tube tip to the glottic opening.
The diagnosis of endotracheal tube (ETT)mal-position may be delayed in extremeenvironments. Several methods are utilized toconfirm proper ETT placement, but these methodscan be unreliable or unavailable in certainsettings. Thoracic sonography, previously utilizedto detect pneumothoraces, has not been tested toassess ETT placement.
Hypothesis:
Thoracic sonography could correlate withpulmonary ventilation, and thereby, help toconfirm proper ETT placement.
Methods:
Thirteen patients requiring elective intubationunder general anesthesia, and data from two traumapatients were evaluated. Using a portable,hand-held, ultrasound (PHHU) machine, sonographicrecordings of the chest wall visceral-parietalpleural interface (VPPI) were recorded bilaterallyin each patient during all phases of airwaymanagement: (1) preoxygenation; (2) induction; (3)paralysis; (4) intubation; and (5) ventilation.Results: The VPPI could be well-imaged for all ofthe patients. In the two trauma patients, rightmainstem intubations were noted in which specificpleural signals were not seen in the left chestwall VPPI after tube placement. These signsreturned after correct repositioning of the ETTtube. In all of the elective surgery patients,signs correlating with bilateral ventilation ineach patient were imaged and correlated withconfirmation of ETT placement byanesthesiology.
Conclusions:
This report raises the possibility that thoracicsonography may be another tool that could be usedto confirm proper ETT placement. This techniquemay have merit in extreme environments, such as inremote, prehospital settings or during aerospacemedical transports, in which auscultation isimpossible due to noise, or capnography is notavailable, and thus, requires further scientificevaluation.
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