These studies represent a cross section of clinical trails and journal articles published over the past 20 years. The origin of the principles that make the PosiTube possible can be traced back to Dr. Wee who first published his theories and studies of a device to distinguish oesophageal from tracheal intubations.

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In-Hospital Studies

Anaesthesia 1988 Jan;43(1):27-9
"The oesophageal detector device. Assessment of a new method to distinguish oesophageal from tracheal intubation."
Wee MY.
Department of Anaesthetics, Ninewells Teaching Hospital, Dundee.

A new method to distinguish oesophageal from tracheal intubation using the oesophageal detector device was evaluated. In 100 healthy adults, observers of differing experience reliably and rapidly detected 51 oesophageal and 49 tracheal intubations in a randomized, single-blind trial. In one case, blockage of the tracheal tube was detected swiftly and allowed corrective steps to be taken. This method can be used in patients with bronchospasm to detect correct tracheal placement when auscultation and decreased compliance of the chest may make clinical confirmation difficult. It can be concluded from this study that the oesophageal detector device is a reliable, rapid, inexpensive and easy to use method for the detection of oesophageal intubation and its very low cost should make it readily available in all situations where tracheal intubation is carried out.

 

Anaesth Intensive Care 1988 Aug;16(3):299-301
"A method of detecting oesophageal intubation or confirming tracheal intubation."
O'Leary JJ, Pollard BJ, Ryan MJ.
Department of Anaesthetics, Repatriation General Hospital, Concord, Sydney.

A method of testing the location of an endotracheal tube, in the trachea or oesophagus, was subjected to trial. The test involves drawing back on the plunger of a 50 ml syringe connected with airtight fittings to the endotracheal tube connector, with the endotracheal tube cuff deflated. The ability to withdraw 30 ml of air confirms tracheal intubation. When marked resistance to withdrawal of the plunger occurs and on release the plunger rebounds to its original position the oesophagus has been intubated. The method was 100% accurate in fifty intubations, 25 tracheal and 25 oesophageal. The technique has been in routine use by one author for several years without giving an incorrect answer and enthusiastic use by other authors is producing the same result.
 

Critical Care Med 1998 May;26(5):957-64
"Portable devices used to detect endotracheal intubation during emergency situations: a review."
Cardoso MM, Banner MJ, Melker RJ, Bjoraker DG.
Department of Anesthesiology, University of Florida College of Medicine, Gainesville, USA.
OBJECTIVES: To review the operational characteristics of commercial devices used to detect endotracheal intubation; and to identify an ideal device for detecting endotracheal intubation in emergency situations, especially in the prehospital setting during cardiac arrest. DATA SOURCES: Relevant articles from the medical literature are referenced. STUDY SELECTION: The authors identified the need for understanding the basic operation principles of portable devices used to detect endotracheal intubation and to correctly use them in unpredictable clinical situations. DATA EXTRACTION: Data from published literature. DATA SYNTHESIS: Recently, a number of new portable devices have been marketed for detecting endotracheal intubation, each having advantages and disadvantages, especially when used during emergency situations. The devices are classified based on their principle of operation. Some rely on CO2 detection (STATCAP, Easy Cap, and Pedi-Cap), others utilize the transmission of light (Trachlight, SURCH-LITE), one operates based on reflection of sound energy (SCOTI), and some depend on aspiration of air (TubeChek and TubeChek-B). A brief description of each device and its operational characteristics are reviewed. A comparative analysis among the devices is made based on size, portability, cost, ease of operation, need for calibration or regular maintenance, reliability for patients with and without cardiac arrest, and the possibility of use for adult and pediatric patients. False-negative and false-positive results for each device are also discussed. False-negative results mean that although the endotracheal tube is in the trachea, the device indicates it is not. False-positive results mean that although the endotracheal tube is in the esophagus, the device indicates it is in the trachea. CONCLUSIONS: Although no clinical comparative study of commercial devices to detect endotracheal intubation exists, the syringe device (TubeChek) has most of the characteristics necessary for a device to be considered ideal in emergency situations in the prehospital setting. It is simple, inexpensive, easy to handle and operate, disposable, does not require maintenance, gives reliable results for patients with and without cardiac arrest, and can be used for almost all age groups. The device may yield false-negative results, most commonly in the presence of copious secretions and in cases of accidental endobronchial intubation. Regardless of the device used, clinical judgment and direct visualization of the endotracheal tube in the trachea are required to unequivocally confirm proper endotracheal tube placement.

Acad Emerg Med 1995 Jun;2(6):503-7Evaluation of a prototype esophageal detection device.
Marley CD Jr, Eitel DR, Anderson TE, Murn AJ, Patterson GA.
Hanover General Hospital, PA 17331, USA.

OBJECTIVE: To determine the ability of a prototype esophageal detection device (EDD) to identify esophageal misplacement of an endotracheal (ET) tube. METHODS: A prospective, randomized, blinded study of detection of esophageal intubation was conducted using 51 elective surgical patients who met inclusion criteria. A squeeze-bulb aspirator that creates a negative pressure of -80 to -90 torr was used for detection of esophageal intubation. The bulb should reinflate rapidly if the tube is in the non-collapsible trachea, but should not reinflate if the tube is in the collapsible esophagus. Each patient was prepared for surgery in the usual manner. The anesthesiologist placed an ET tube into the trachea. An identical tube was advanced the same distance into the esophagus. The tubes were labeled "A" or "B" according to a computer-generated random number list. An evaluator, who was blinded to the placement of the tubes, assessed one tube with the EDD. For most patients, a second evaluator, who was blinded to both tube placement and the results of the first evaluator, assessed the other tube. During evaluation, the tube cuffs were deflated. After data collection, the esophageal tube was removed and surgery was completed. RESULTS: All 45 esophageal tube placements were correctly identified. Thirty-five of the 40 ET tubes were correctly identified. Of the five ET tubes mislabeled, three were found in a mainstem bronchus. All had delayed bulb re-expansion. CONCLUSION: This prototype EDD is a useful method of identifying esophageal misplacement of an ET tube in anesthetized adult surgical patients.

Annals of Emergency Medicine 1992 Sep;21(9):1073-6                                                                     "The esophageal detector device: a rapid and accurate method for assessing tracheal versus esophageal intubation in a porcine model."
Foutch RG, Magelssen MD, MacMillan JG.
Department of Emergency Medicine, Madigan Army Medical Center, Tacoma, Washington.

STUDY OBJECTIVES: To assess time and accuracy of the esophageal detector device (EDD), disposable end-tidal CO2 monitor (ETCO2), and standard clinical methods for detection of endotracheal tube placement. DESIGN: Prospective, randomized, single-blinded, controlled laboratory investigation. METHODS: Thirty airway managers (physicians, nurse anesthetists, and paramedics) used one pig (Sus scrofa) as the intubated, respiratory depressed/arrest model. INTERVENTIONS: Part 1: A standard 7.5-mm endotracheal tube was placed in either the esophagus or the trachea of the anesthetized swine. Anatomic location was verified by bronchoscopy. Airway managers blinded to the endotracheal tube location were assigned randomly to identify tube position by one of three methods (EDD, ETCO2, or clinical methods). Speed and accuracy of the assessment were recorded. Part 2: A second identical tube was placed, so that both the esophagus and the trachea were intubated; then, the esophageal tube was bag-ventilated for one minute. Each blinded airway manager, using only the EDD, determined placement site of both tubes. RESULTS: Part 1: Mean time to determine tube placement for group A (EDD) was 13.8 seconds; group B (ETCO2), 31.5 seconds; and group C (clinical methods), 39 seconds. Comparison by analysis of variance yielded a value of P less than .001. Both groups A and B were 100% accurate, whereas 30% of the subjects from group C mistakenly assessed an esophageal tube as in the trachea. Part 2: The EDD remained 100% sensitive and specific despite prior ventilation of the esophageal tube. CONCLUSION: In this porcine model, the EDD and ETCO2 were more accurate than clinical methods in determining endotracheal tube placement. The EDD demonstrated a significant time advantage over both ETCO2 and clinical methods. Prior ventilation of the esophageal tube does not interfere with the accuracy of the EDD.

Anaesthesist 1995 Sep;44(9):613-23
"Preclinical control of intubation and artificial respiration. Animal experiment and literature review"
[Article in German]
Petroianu G, Maleck W, Bergler WF, Ellinger K, Osswald PM, Rufer R.
Fakultat fur klinische Medizin Mannheim, Universitat Heidelberg.

Oesophageal malposition of an endotracheal tube is among the leading causes of anaesthesia incidents. While clinical manoeuvres for detection of tube malposition are unreliable, monitoring (i.e. capnography) can prevent such incidents. The problem is particularly important in prehospital care, where capnography is not (yet) widely available. We tested three devices used for differentiating oesophageal from endotracheal intubation: 1. Non-CO2-dependent Oesophageal Detector Device (ODD) as described by Pollard and Wee, 2. Semi-quantitative chemical disposable capnometer EasyCAP (Nellcor), 3. Non-quantitative infrared miniaturized capnometer MiniCAP (MSA). METHODS. 50 anaesthetized minipigs were intubated with a Magill tube. An identical additional tube was placed in the oesophagus. The cuffs of both tubes were inflated. Unexperienced personnel (students, laboratory technicians) were asked to determine the position of one of the tubes by using one of the devices according to the randomization plan. The decision had to be taken within 30 s. Using the ODD, the proband first injected 100 ml air into the lung (or stomach) and then tried to aspirate the same volume. EasyCAP and MiniCAP were used according to manuals. RESULTS. Each device was used 25 times with a tracheal tube and 25 times with an oesophageal tube. All tube position identifications were correct. When ventilating the oesophagus/stomach for capnometric control, regurgitation into the tube occurred six times (five times with the EasyCAP and once with the MiniCAP). In these cases, the decision was based on this occurrence and not on the display of the device. While using the ODD no regurgitation occurred. CONCLUSION. These devices are useful for preclinical practice. According to the literature and our experience, the ODD is superior for the initial control of tube position, especially in cardiac arrest. Capnometry is needed, however, for continuous control of ventilation.
 

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Prehospital Disaster Med 1997 Jan-Mar;12(1):57-63
"Comparison of a colorimetric end-tidal CO2 detector and an esophageal aspiration device for verifying endotracheal tube placement in the prehospital setting: a six-month experience."
Schaller RJ, Huff JS, Zahn A.
Department of Emergency Medicine, Eastern Virginia Medical School, Norfolk, USA.

INTRODUCTION: Hand held, colorimetric, end-tidal CO2 detector devices are being used to verify correct endotracheal tube (ETT) placement. The accuracy of these devices has been questioned in situations of cardiac arrest. The use of the esophageal detector device (EDD) is an easy alternative for detection of ETT placement, and may be more accurate in situations of cardiac arrest. HYPOTHESIS: The use of the esophageal aspiration device in comparison with a colorimetric end-tidal CO2 detector is more accurate in detecting proper ETT placement and easier to use in the prehospital setting than is the colorimetric end-tidal CO2 detection device. METHODS: This was prospective alternating weeks, 6-month study in a prehospital setting. Participants included all patients older than 18 years who were intubated by the Portsmouth, Virginia Emergency Medical Services (EMS) personnel from 01 July 1993 through 31 December 1993. The aspiration device used, also known as an esophageal detector device (EDD), was a 60 ml, luer-lock syringe attached to a 15 mm ETT adapter. Its efficacy was compared with an already accepted method of ETT position detection, the colorimetric end-tidal CO2 detector. Each device was used on alternating weeks, and correct ETT placement was determined by the receiving emergency department physician using standard techniques. Chi-square analysis and Fisher's Exact test were used to compare parameters, time of device use, and ease of use. Sensitivity and specificity were calculated, and provider preference was assessed using a survey instrument administered following completion of the study. RESULTS: There were 49 patients who met the inclusion criteria, but six were excluded because of situational circumstances rendering use of the device a possible compromise of patient care. Twenty-five patients were in the EDD group, and 18 were in the end-tidal CO2 detector group. There was no statistically significant difference detected between groups for the gender ratio, underlying condition, CPR in progress, perceived difficulty of intubation, or percentage of nasotracheal intubation. The EDD was significantly easier to use (p < 0.005). There was no statistically significant difference in time required for use of end-tidal CO2 detector device versus the EDD. The sensitivity and specificity for correct tracheal placement using the EDD was 100%, and the sensitivity for correct tracheal placement using the end-tidal CO2 detector device was 78%. Use of the EDD was preferred over use of the end-tidal CO2 detector device by 75% of participating EMS providers. One case of nasotracheal intubation with an ETT placement above the cords raised the question of accuracy of this device in situations where direct visualization is not utilized. CONCLUSION: The EDD was accurate in all cases of orotracheal intubation, and was easier to use than was end-tidal CO2 detector device. It was preferred by 75% of participating EMS providers. In cases in which the ETT may be above the vocal cords, caution must be used with interpreting the results obtained by use of the EDD.
 

Annals of Emergency Medicine 1996 May;27(5):595-9
"Esophageal detector device versus detection of end-tidal carbon dioxide level in emergency intubation."
Bozeman WP, Hexter D, Liang HK, Kelen GD.
Department of Emergency Medicine, Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.

STUDY OBJECTIVES: To confirm the ability of the esophageal detector device (EDD) to indicate positioning of endotracheal tubes (ETTs) in patients intubated under emergency conditions and to compare the performance of the EDD with that of end-tidal carbon dioxide (ETCO2). METHODS: This single-subject study comprising a prospective case series was conducted in the emergency department of an urban university hospital. All adult patients were intubated either in the ED or by paramedics in the field. ETT position was initially evaluated by means of auscultation, then EDD, and, finally, spectrographic qualitative ETCO2 monitoring in each patient. Discrepancies between the EDD and ETCO2 results were resolved by means of direct laryngoscopy. RESULTS: In 100 intubated patients, both the EDD and ETCO2 monitoring detected the single esophageal intubation that occurred. Of the remaining 99 tracheal intubations, the EDD correctly indicated tracheal placement in 98 (sensitivity, 99%) and was indeterminate in 1 case because of blockage of the ETT by secretions resulting from pulmonary edema. By comparison, ETCO2 monitoring correctly indicated tracheal placement in 86 cases (sensitivity, 87%) and was incorrect in 13 cases (P < .01). ETCO2 monitoring failed in 2 patients with pulmonary edema and in 11 patients with cardiac arrest. Among the 37 patients in the cardiac arrest group, the EDD correctly indicated ETT placement in 37 patients (sensitivity, 100%). In contrast, ETCO2 monitoring correctly indicated ETT placement in 26 patients (sensitivity, 70%; P < .01). CONCLUSION: The EDD reliably confirms tracheal intubation in the emergency patient population. The EDD is more accurate than ETCO2 monitoring in the overall emergency patient population because of its greater accuracy in cardiac arrest patients. [Bozeman WP, Hexter D, Liang HK, Kelen GD: Esophageal detector device versus detection of end-tidal carbon dioxide level in emergency intubation.
 

Prehospital Disaster Med 1996 Jan-Mar;11(1):60-2
"The esophageal detector device: accuracy and reliability in difficult airway settings."
Kapsner CE, Seaberg DC, Stengel C, Ilkhanipour K, Menegazzi J.
University of Pittsburgh Affiliated Residency in Emergency Medicine, Pittsburgh, Pennsylvania, 15219, USA.

INTRODUCTION: The esophageal detector device (EDD) recently has been found to assess endotracheal (ET) tube placement accurately. This study describes the reliability of the EDD in determining the position of the ET tube in clinical airway situations that are difficult. METHODS: This was a prospective, randomized, single-blinded, controlled laboratory investigation. Two airway managers (an emergency-medicine attending physician and a resident) determined ET-tube placement using the EDD in five swine in respiratory arrest. The ET tube was place in the following clinical airway situations: 1) esophagus; 2) esophagus with 1 liter of air instilled; 3) trachea; 4) trachea with 5 ml/kg water instilled; and 5) right mainstem bronchus. Anatomic location of the tube was verified by thoracotomy of the left side of the chest. RESULTS: There was 100% correlation between the resident and attending physician's use of the EDD. The EDD was 100% accurate in the determining tube placement in the esophagus, in the esophagus with 1 liter of air instilled, in the trachea, and in the right mainstem bronchus. The airway managers were only 80% accurate in detecting tracheal intubations when fluid was present. CONCLUSIONS: The EDD is an accurate and reliable device for detecting ET-tube placement in most clinical situations. Tube placement in fluid-filled trachea, lungs, or both, which occurs in pulmonary edema and drowning, may not be detected using this device.