Out-of-hospital tracheal intubation performed by skilled providers is widely accepted as the “gold standard” for advanced airway management in ill or injured patients (1). Tracheal intubation is associated with favorable patient outcome in a variety of clinical scenarios (2–5), although other studies have shown no difference or reduced survival rates with tracheal intubation in patients with traumatic brain injury or in children (6–8). Several studies have documented out-of-hospital tracheal intubation success rates as high as 98% in nontrauma or mixed patients groups (9–11). When providers do not frequently perform tracheal intubation, success rates as low as 50% have been noted (12). In a previous study, we (11) demonstrated a significantly increased incidence of difficult laryngoscopies in the out-of-hospital arena, even when tracheal intubation was performed by experienced anesthesiologists.
Unrecognized esophageal intubation is a clinical disaster. Some authors question the small, incremental benefit of tracheal intubation as compared with less skill-intensive techniques of airway management (1). Studies of nonphysician emergency responders in the United States have reported a wide range (6%–25%) of unrecognized misplaced intubations when evaluated by independent observers (13–16).
The aim of our study was to determine the incidence of misplaced tracheal tubes when tracheal intubation was performed out-of-hospital by a primary emergency physician(s), as evaluated by study emergency physicians at the scene of the medical emergency.
This study was approved by the Goettingen (Germany) institutional ethics committee which granted informed consent exemption. During a 5-yr period (September 1, 2000 to August 31, 2005) prospective, observational data were collected on consecutive patients who required transport by air from the scene of a medical emergency to our medical center and who underwent tracheal intubation prior to transport. The decision for air transport to our center was made by the primary emergency physicians. Indications for air transport included the need for expeditious treatment, clinical support from another emergency physician, or both.
Primary Emergency Physicians
Primary emergency physicians included surgeons, anesthesiologists, and internists from local primary hospitals within the operational area of the helicopter emergency medical service. Apart from their usual clinical responsibilities, these physicians participated in emergency medical services duties one or more days each month. Primary emergency physicians receive special clinical training in emergency care as recommended by the German Medical Association (17). In Germany, there are no requirements for emergency physicians to maintain airway management skills or to participate in continuing emergency medical education, and outcome data are not collected.
Study physicians were all members of the Department of Anesthesiology, Emergency and Intensive Care Medicine, Georg-August University, School of Medicine, Goettingen, Germany. Most of the study physicians were specialists in anesthesia, though some were in their last year of anesthesia training. All of the study physicians had at least 300 emergency calls or 3 yr of experience with a ground-based ambulance. Like the primary emergency physicians, all study physicians received special training in emergency care, but additionally received lectures and practical training on airway management, including simulated scenarios on the management of the difficult airway (18).
After tracheal intubation, primary emergency physicians confirmed correct tracheal tube placement based solely on physical examination (e.g., auscultation, chest movement, absence of epigastric sounds). When the study physician arrived, tracheal tube position was immediately reevaluated using a combination of direct visualization via laryngoscopy (tracheal tube passes through the vocal cords), continuous or colorimetric end-tidal carbon dioxide monitoring (etCO2), and physical examination. When cardiopulmonary resuscitation (CPR) was in progress and the study physician could not visualize the tracheal tube passing between the vocal cords, an esophageal detector device (EDD) was used. Easy aspiration of air into the syringe has been shown to be confirmatory of tracheal position of the tube (19,20).
Whenever unrecognized mainstem bronchial intubation was suspected by the study physician, the tracheal tube position was corrected using direct laryngoscopy and withdrawing the tracheal tube until the cuff was visible just distal to the vocal cords. The tracheal tube was then advanced 2 cm into the trachea and breath sounds were auscultated.
Whenever an esophageal intubation was detected by the study physician, tracheal intubation was reattempted by direct laryngoscopy or with the use of an alternative intubation device. A laryngeal mask airway, intubating laryngeal mask airway, and the Combitube™ were provided as alternative airway adjuncts. In these cases the laryngoscopic view (21), number of intubation attempts, and use of alternative adjuncts or surgical airway approaches were recorded. Patient data recorded for study purposes included age, gender, preliminary diagnosis, interval time between the primary emergency physician’s request for air transport and the time of the study physician’s first on-scene contact, interval time between the primary emergency physician’s intubation attempt and the study physician’s evaluation of the tracheal tube position, initial heart rhythm as obtained by the primary emergency physician, breathing status and heart rhythm as obtained by the study physician at the time tracheal tube position was evaluated, and airway maneuvers (intubation attempts, use of airway adjuncts including a surgical airway approach) used by the primary emergency physician or study physician. For the purposes of statistical analysis, all patients were allocated into three groups: patients with traumatic injuries (trauma), cardiopulmonary arrest (CPR), and other medical conditions.
On arrival in the hospital emergency department, tracheal tube position was confirmed by the attending trauma team with the use of continuous CO2 monitoring and chest radiograph.
The primary outcome measure was misplaced tracheal tube position as determined by the study physician. Misplaced position included mainstem bronchial and esophageal intubations. Misplacement rates between patient type and gender were analyzed using a χ2 test. A probability value (P) of <0.05 was considered significant. Statistical analysis was performed using Stastistica version 6.1 (StatSoft, Tulsa, OK).
During the study period, tracheal intubation was attempted by primary emergency physicians in 153 patients. In four patients, the primary emergency physicians abandoned attempts at tracheal intubation and secured the patient’s airway with a Combitube™ (Tyco Healthcare Group LP, Mansfield, MA) (two patients) or percutaneous surgical airway (Portex Mini-Trach II™-Seldinger Kit, Portex Limited, Hythe, Kent, England) (two patients). One patient with a Combitube was later converted to tracheal intubation by a study physician. The tracheal tube position was evaluated by the study physician in the remaining 149 patients.
The 149 patients included 21 (14.1%) patients who required CPR, 84 (56.4%) trauma patients, and 44 (29.5%) patients with other medical conditions. The mean patient age was 57.0 (±22.7) years. Ninety-nine (66.4%) patients were men. The mean time from the emergency dispatcher call to the first study physician-patient contact was 17.5 (±9.9) min.
Study physicians determined that 10 (6.7%) tracheal tubes were misplaced in the esophagus and that 16 (10.7%) were placed in the right mainstem bronchus. No tracheal tube was found in the left mainstem bronchus. Esophageal intubation occurred in 1 (4.8%) patient undergoing primary CPR, 6 (7.1%) trauma patients, and 3 (6.8%) medical patients. Right mainstem bronchial intubation was seen in 1 (4.8%) patient during CPR, 11 (13.1%) patients with trauma, and 2 (8.3%) patients with other conditions (Table 1). All tracheal tube positions were evaluated by a combination of physical examination, direct laryngoscopy, and etCO2 monitoring, except for two patients in cardiac arrest, where the tracheal tubes could not be seen between the vocal cords or in the esophagus on laryngoscopy. In these two patients an EDD was used and indicated correct tracheal tube placement.
The study physicians were able to tracheally intubate all patients evaluated to have esophageal tracheal tube placement in one (9) or two (1) attempts. During laryngoscopy, Cormack–Lehane laryngeal views of grade I (5) grade II (3), or grade III (2) were recorded. No alternative tracheal intubation adjuncts were used. No unrecognized bronchial or esophageal intubations were detected when patients arrived in the emergency department.
Seven of 10 patients with unrecognized esophageal intubations died within the first 24 h of treatment. One patient died within the course of clinical treatment. Two patients survived and eventually recovered without neurological sequelae. Table 2 shows characteristics of patients with unrecognized esophageal intubations. Fourteen of 139 (10.1%) patients with correct tracheal tube position died on scene or within the first 24 h of treatment.
Unrecognized mainstem bronchial and esophageal intubation are the most serious complications of attempted tracheal intubation (1). The novel aspect in our study was the verification of tracheal tube position at the scene of the emergency. Previous studies (Table 3) have examined the placement of tracheal tubes by nonphysicians, after patient transport to an emergency department (13–16).
Detection of mainstem bronchial intubation is made by clinical examination, including observation of unilateral chest expansion, unequal breath sounds on auscultation, and depth of tracheal tube placement (1). According to Brunel et al. (22) 60% of mainstem intubations occurred despite the presence of equal breath sounds on examination. Additionally, massive unilateral aspiration can lead to diminished lung sounds, which may be misinterpreted as bronchial intubation. None of the secondary confirmation techniques (etCO2 or EDD) will differentiate between a tube placed in a main bronchus and one placed correctly in the trachea (1).
The consequences of bronchial intubation include collapse of the contralateral lung and hyperinflation of the intubated lung. This may result in hypoxia and pneumothorax, respectively, and has been associated with a significant increase in morbidity (23,24). Other preclinical studies have found incidences of unrecognized bronchial intubation between 0% and 7.8% but these data were self-reported and thus subject to reporting bias (12,25,26). The frequent incidence of bronchial intubation in our study (10.7%) may be more objective, because the evaluation was made by independent observers.
While the potential benefits of successful prehospital tracheal intubation remain controversial, the harm caused by unrecognized esophageal intubation is indisputable. Silvestri et al. (16) reported that unrecognized esophageal intubation in 14 patients resulted in mortality in nine patients and neurological impairment in two patients. These data are similar to our findings where seven of 10 patients with unrecognized esophageal tracheal tube placements died within the first 24 h and one within the course of clinical treatment. All fatal outcomes cannot be attributed to esophageal tracheal tubes alone, since an unknown number of patients may have succumbed due to the severity of their critical illness. However, only 10.1% of patients with correct tracheal tube position died within the same time frame.
Two studies on prehospital intubation by paramedics reported unrecognized esophageal intubation rates of 0.4% (27,28). Both of these studies were retrospective reviews. Nolan (29) suggests it is likely that they under-estimate the true incidence of unrecognized esophageal intubation. Conversely, other studies of out-of-hospital tracheal intubation by paramedics have demonstrated unrecognized esophageal intubation rates between 6% and 25% (Table 2), when tracheal tube position was verified by independent observers.
The incidence of misplaced tracheal tubes in the current study may be artificially low by virtue of the regulations governing study physician’s response. If the primary emergency physician determines that a patient’s death occurs before the arrival of the study physician, the contact between the study physician and the patient may not occur. Therefore some patients, who died after an esophageal intubation by the primary emergency physicians, may not have been entered into the study, introducing a reporting bias. Another limitation of our study is the lack of reporting of confounding variables: primary emergency physicians recognizing and correcting misplaced tracheal tubes, factors hindering attempts at tracheal intubation, specialty, training, and competency of primary emergency physicians, and patient condition (e.g., level of consciousness).
The training required by primary emergency physicians is designed to give them the ability to clinically identify misplaced tracheal tubes. However, our results confirm the findings by others that etCO2 monitoring can significantly improve detection. Silvestri et al. (16) reported a decrease in unrecognized esophageal intubations by paramedics from 25% to 9% with the implementation of a new airway management protocol that required continuous etCO2 monitoring of all intubated patients. They observed no esophageal intubations when there was 100% compliance with the protocol.
In the current study, successful tracheal intubation was performed by the study physicians in all patients in whom esophageal tracheal tube placement by the primary emergency physicians was detected. All study physicians had undergone advanced airway management training, including simulated difficult airway management scenarios. Several studies have shown that advanced clinical experience and simulator training have improved airway management skills for both physicians and paramedics (18,30).
This continued training is of particular importance for those clinicians whose duties include prehospital airway management and who do not perform airway management techniques on a regular basis. Gries et al. (31) have shown that German emergency medical service physicians performed tracheal intubation only once every 0.5–1.5 mo. All providers of prehospital emergency medical care need to be particularly proficient not only in tracheal intubation, but also in the use of alternative instruments (11). Recently, Hohlrieder et al. (32) demonstrated that gum elastic bougie-guided insertion of the ProSeal™ laryngeal mask airway is superior to conventional laryngoscope-guided tracheal intubation for airway management by novices. Bag-mask ventilation as a rescue strategy after failed tracheal intubation should be considered, with low inspiratory pressure and flow, and a high inspiratory fraction of oxygen (33), as Scott (34) stated in 1986: “Patients do not die from failure to intubate—they die from failure to stop trying to intubate or from undiagnosed esophageal intubation.”
In summary, the incidence of unrecognized out-of-hospital esophageal intubation is frequent when etCO2 monitoring and EDD are not used for tube placement confirmation by emergency medical service physicians with basic training. Unrecognized esophageal intubation is associated with a high mortality rate. This study suggests that if emergency physicians are experienced in airway management and additional confirmatory adjuncts are used, esophageal intubation can be detected and tube position can be corrected more frequently. Consequently, clinicians whose duties include prehospital airway management should regularly attend courses on airway management and receive continuing training. Furthermore they should be provided with etCO2 monitoring and EDDs to aid in their determination of tracheal tube position.
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