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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.
To determine the effectiveness and safety of procedural sedation and analgesia (PSA) in a Canadian community emergency department (ED) staffed primarily by family physicians and to assess the role of capnometry monitoring in PSA.
Methods:
One hundred and sixty (160) consecutive procedural sedation cases were reviewed from the ED of a rural hospital in Huntsville, Ont. The ED is mainly staffed by family physicians who have received in-house training in PSA. Safety and effectiveness measures were extrapolated from a standardized PSA form by a blinded research assistant.
Results:
The mean age of the patient population was 33.6 years (standard deviation = 23.6). Fifty-four percent of the patients were male, and 33% of the cases were pediatric. PSA medications included propofol (84%), fentanyl (51%) and midazolam (15%), and the procedural success rate was 95.6%. The adverse event (AE) rate was 18% and included apnea (10%), inadequate sedation (3%), bradycardia (2%), desaturation (1%), hypotension (1%) and bag-valve-mask use (1%). In those aged ≥65 years there was a greater incidence of apnea. There were no episodes of emesis and there were no intubations. A modified jaw thrust manoeuvre was used in 23% of the cases. In the 64% of cases where capnometry was used, there was no association between its use and any AE measures.
Conclusion:
Procedural sedation was safe and effective in our environment. Capnometry recording did not appear to alter outcomes, although the data are incomplete.
To evaluate three prototype versions of semi-quantitative end-tidal CO2 monitors with different alarm features during prehospital or inter-facility use.
Methods:
Subjects were 43 adult, non-pregnant patients requiring intubation, or who already were intubated and required transport. Teams at one AirEvac and seven Advanced Life Support (ALS) paramedic stations were trained in the use of the monitors. Team members at each station evaluated each model for eight days. Participants completed questionnaires following each use.
Results:
The monitors performed properly in all cases, but in one case, vomit in the airway adapter tube prevented obtaining a readout. The monitors aided management in 40 of 43 cases (93%); in one, the monitor reading was reported as variable (between 20 and 30 mmHg) although the teams knew the monitors were semi-quantitative; in another, the monitor was not required, but performed properly; and the third was the one in which vomit in the tube prevented a reading. In 26 of 43 cases (60.4%), the monitor was used to confirm endotracheal tube placement (there were no instances of incorrect placement). In all cases, the devices were used to monitor respiration and oxygen saturation. Alarms were audible in the environment, but only preferred in the AirEvac situation. The “breath beep” feature was useful, particularly in patients in whom chest movements during respiration were difficult to observe.
Conclusions:
“Breath beeps” were clearly audible and were a useful feature in all prehospital and transport environments, while audible alarms were desired only in the AirEvac situation. Semi-quantitative CO2 detection is valuable in the ALS/AirEvac environment, even for teams with high intubation success rates.
The capnometric demonstration of end-tidal carbon dioxide (CO2) is a reliable method of differentiating between a correct endotracheal tube position and an accidental misplacement of the tube into the esophagus. Recently, several CO2 detectors have been introduced for monitoring end-tidal CO2 in the “out-of-hospital” setting, where quantitative capnometry with capnography is not yet available.
Hypothesis:
These devices are not influenced by carbon monoxide (CO) present in lethal concentration.
Methods:
A heated (37°C) 2.3 L reservoir bag filled one-third full with water (representing the stomach in esophageal misintubation) was machine ventilated (tidal volume: 450 ml; frequency: 16/min) with the following mixtures for three minutes each: 1) 95% O2, 5% CO; 2) 45% O2 5% CO, 50% N2O; and 3) 44% O2 5% CO, 50% N2O, 1% halothane. The presence of end-tidal CO2 was monitored with each of the following devices: 1) MiniCAP™ III CO2 Detector; 2) StatCAP™ CO2 Detector; 3) EasyCAP™ CO2 Detector; PediCAP™ CO2 Detector; and 5) Colibri™ CO2 Detector.
Results:
In none of the cases was the presence of CO2 signaled by the detector.
Conclusion:
The presence of 5% CO does not interfere with infrared spectrometry detection (MiniCAP™ and StatCAP™) or chemical detection (EasyCAP™, PediCAP™, and Colibri™) of CO2. The devices can be used safely in patients with CO poisoning for monitoring of endotracheal tube position.
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