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CRITICAL CARE AND TRAUMA

A Comparison of the Endotracheal Tube and the Laryngeal Mask Airway as a Route for Endobronchial Lidocaine Administration

Andreas W. Prengel, MD^*, Martin Rembecki, MD^*, Volker Wenzel, MD, and Gerald Steinbach, MD

*Department of Anesthesiology and Critical Care Medicine, Ruhr University, Bochum, Germany; Department of Anesthesiology and Critical Care Medicine, Leopold-Franzens-University, Innsbruck, Austria; and Department of Clinical Chemistry, University of Ulm, Ulm, Germany

Address correspondence and reprint requests to Andreas W. Prengel, MD, Department of Anesthesiology and Critical Care Medicine, Ruhr University, In der Schornau 23-25, 44892 Bochum, Germany. Address e-mail to Andreas.Prengel{at}ruhr-uni-bochum.de

	Abstract

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Drug administration via the endotracheal tube is recommended as a second-line approach in emergency settings such as cardiac arrest. It is unknown what amount of drugs are absorbed when they are given through the laryngeal mask airway as compared with the endotracheal tube. We administered lidocaine at a dose of 2 mg/kg diluted in 10 mL normal saline to 20 anesthetized patients undergoing routine surgical procedures. Ten patients received lidocaine into the endotracheal tube and 10 patients received lidocaine into the laryngeal mask airway. Blood samples were taken for measurement of lidocaine plasma concentrations, and the pharmacokinetics were calculated. Therapeutic plasma concentrations (>1.4 µg/mL) could be achieved in 10 of 10 patients after endotracheal tube instillation but in only 4 of 10 patients after laryngeal mask instillation (P < 0.05). Peak lidocaine concentrations (2.47 and 1.09 µg/mL) (P < 0.05) and the area under the time versus plasma concentration curve (117.7 and 91.2 µg · min · mL^-1) (P < 0.05) were higher after lidocaine administration into the endotracheal tube than into the laryngeal mask airway. In conclusion, the laryngeal mask airway is not a reliable route for the recommended dose of endobronchial lidocaine administration compared with the endotracheal tube.

Implications: Drug absorption after lidocaine administration into the laryngeal mask airway is not sufficient to achieve therapeutic lidocaine plasma concentrations. IV drug administration should be used whenever the laryngeal mask is used in the cardiac arrest setting.

	Introduction

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During cardiopulmonary resuscitation (CPR), endobronchial drug administration is a second-line approach for emergency drugs when attempts to gain IV access are unsuccessful or significantly delayed (1). In principle, epinephrine, lidocaine, atropine, and vasopressin may be administered endobronchially in this setting (2,3).

The laryngeal mask airway offers an accepted alternative for airway management during CPR (4) and may be especially helpful in the "cannot intubate, cannot ventilate" situation (5). Although lidocaine administration into the endotracheal tube is effective, it is unknown what amount of lidocaine will be absorbed and whether therapeutic plasma concentrations can be achieved when lidocaine is given through the laryngeal mask airway. If this approach would provide an alternative for drug administration in emergency situations such as CPR or shock, endobronchial drug administration would not be feasible with the endotracheal tube, but with a wider variety of airway devices.

The purpose of this study was therefore to compare lidocaine plasma concentrations after endobronchial lidocaine administration via the laryngeal mask airway as compared with the endotracheal tube.

	Methods

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This study was approved by our ethics committee, and written, informed consent was obtained from all subjects before enrollment into the study. Twenty patients undergoing elective surgical procedures volunteered and participated in the study. The following exclusion criteria were applied: anesthesia risk classification more than ASA II, special positioning required, anticipated blood loss of >200 mL, cardiac or pulmonary disease, arrhythmias, hypersensitivity to lidocaine or other local anesthetics, clinically relevant liver disease, or a positive Allen test.

Twenty patients were assigned to two groups receiving either an endotracheal tube (n = 10) or a laryngeal mask airway (n = 10). In the Laryngeal Mask Airway group, the airway sealing pressure was measured by closing the expiratory valve of the circle system at a fixed gas flow and documenting the airway pressure at which the aneroid manometer showed equilibrium. The position of the laryngeal mask in relation to the glottis was determined by advancing a fiberscope down to the mask aperture bars and using a classification of whether the vocal cords could be fully or only partially seen.

After the induction of anesthesia with 3–5 mg/kg of thiopental and 0.1 mg of fentanyl, subsequent paralysis with 0.1 mg/kg of cisatracurium, and insertion of either an endotracheal tube or a laryngeal mask airway, an arterial catheter was inserted into the radial artery. A baseline blood sample was obtained 15 min after initiation of mechanical ventilation. The ventilation rate was set at 12 breaths/min, the minute volume was set at 100 mL · kg^-1 · min^-1, and the fraction of inspired oxygen was 0.33. Anesthesia was maintained with isoflurane. A continuous infusion of lactated Ringer’s solution was given at a rate of 500 mL/h. Cardiac rhythm was monitored with a standard lead II electrocardiogram, and oxygen saturation was monitored with a pulse oximeter. Arterial blood pressure was monitored continuously with the radial artery catheter.

After baseline blood samples were obtained, the ventilator was disconnected in both groups for 15 s to administer 2 mg/kg of 2% lidocaine hydrochloride diluted with normal saline to a total volume of 10 mL. Lidocaine was injected directly with a 10-mL syringe either into the outer aperture of the endotracheal tube or into the outer aperture of the laryngeal mask airway. In both groups, five forceful ventilations were performed within 5 s after lidocaine administration with a self-inflating bag. The endotracheal tube and the laryngeal mask airway were then reconnected to the ventilator. This point in time was taken to be zero for blood sample collection. Subsequently, at 30, 60, and 90 s and at 2, 3, 5, 10, 20, 60, and 120 min, blood samples were taken via the arterial cannula for measurement of lidocaine plasma concentrations and blood gases.

Blood gas analysis was performed immediately after withdrawal by using a blood gas analyzer. Blood samples for measurement of lidocaine plasma concentrations were stored at -70°C until analysis and were measured by an automated fluorescence polarization immunoassay (Abbot TDx analyzer; Abbot Laboratories, Chicago, IL). With this method, the lower level of detection was 0.1 µg/mL, and the coefficient of variation was 4.3%.

Pharmacokinetic values were determined from the lidocaine plasma concentration versus time curves. Peak concentrations of each group were calculated from the median of the largest individual patient levels. Time to peak was determined by the median of the individual time periods required to reach peak concentrations. The area under the lidocaine plasma concentration versus time curves from 0.5 to 120 min (AUC_0.5–120), a measure of relative bioavailability, was calculated by integration of the lidocaine plasma concentration versus time curves.

Values are expressed as median and 25th and 75th percentiles. After repeated analysis of variance was performed, differences between groups were evaluated by the Mann-Whitney U-test. Differences between PaO₂ levels before and after drug administration were evaluated by the Wilcoxon’s signed rank test. Fisher’s exact test was used to determine differences between groups regarding the occurrence of therapeutic blood levels. Probability values <0.05 were considered significant.

	Results

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Data are presented as mean (range). The average age of the patients was 40 yr (33–59 yr), and the average weight was 82 kg (72–90 kg). The individual maximal and minimal systolic arterial blood pressure values of all patients did not deviate >30% from the average baseline systolic arterial blood pressure of 120 mm Hg (120–138 mm Hg), which was measured before anesthesia induction. Age, weight, and baseline systolic blood pressure were not significantly different between groups.

In patients with endotracheal tube instillation, significantly larger lidocaine plasma levels were found at 0.5, 1, 2, 3, 5, 10, and 20 min after drug administration compared with patients with laryngeal mask instillation (Fig. 1). After drug administration into the endotracheal tube, all patients reached therapeutic lidocaine concentrations (>1.4 µg/mL), whereas after drug administration into the laryngeal mask airway, therapeutic lidocaine concentrations were reached in only 4 of 10 patients (P < 0.05). The highest individual plasma concentration of lidocaine was 4.95 µg/mL, and no patient had toxic blood levels (>6 µg/mL). In the Laryngeal Mask Airway group, laryngeal mask airways of size 4 (three patients) and size 5 (seven patients) were used. The median airway sealing pressure was 2.2 kPa (2.1–2.7 kPa) (22.5 cm H₂O [22.0–28.0 cm H₂O]). A multiphasic pattern of absorption with more than one peak concentration was seen in all patients in both groups. The largest lidocaine peak concentration was 2.47 µg/mL (2.05–3.29 µg/mL) in the Endotracheal Tube group and 1.09 µg/mL (0.79– 1.66 µg/mL) in the Laryngeal Mask Airway group (P < 0.05). The time to peak was 0.75 min (0.50–3.00 min) after lidocaine instillation into the endotracheal tube and 1.75 min (0.50–10.00 min) after lidocaine instillation into the laryngeal mask airway. The AUC_0.5–120 was 117.7 µg · min · mL^-1 (98.4–142.1 µg · min · mL^-1) in endotracheally intubated patients and 91.2 µg · min · mL^-1 (65.3–100.3 µg · min · mL^-1) in patients with a laryngeal mask airway (P < 0.05).

View larger version (25K): [in this window] [in a new window]   Figure 1. Lidocaine plasma concentrations within 2 h after 2.0 mg/kg of lidocaine administered by instillation into the endotracheal tube (n = 10, open boxes) or into the laryngeal mask airway (n = 10, hatched boxes). Each box plot represents median, 25th and 75th, and 10th and 90th percentiles. *P < 0.05 versus laryngeal mask airway.

	Discussion

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Although management of the airway and ventilation is the most difficult practical skill during CPR, the laryngeal mask airway provides a clear and secure airway without necessitating the skill required for laryngoscopy and tracheal intubation; further, compared with the endotracheal tube, ensuring and maintaining training with the laryngeal mask airway is relatively brief and simple (6,7). Insertion of a laryngeal mask airway is now accepted as an alternative method of airway management during CPR (4). However, endotracheal intubation remains the method of choice for securing and maintaining the airway during advanced life support, and, in addition, it provides an alternative route for drug administration (1).

Although epinephrine, vasopressin, atropine, and lidocaine may be administered endobronchially in the cardiac arrest setting, there is no consensus on the optimal dose (8), the site of drug delivery along the airway (9), or the type and volume of diluent (10,11). Although in anesthetized dogs distilled water as a diluent allowed better absorption of endobronchially administered epinephrine compared with normal saline, distilled water usually decreases PaO₂ more than normal saline (12).

An initial bolus of 1.0 to 1.5 mg of lidocaine IV is required to rapidly achieve therapeutic lidocaine levels and when administered endobronchially should be administered at 2 to 2.5 times the IV dose (13). Hence, 2 mg/kg of lidocaine is the smallest recommended dose for the endobronchial approach. As in previous studies (11,14), therapeutic lidocaine plasma concentrations were achieved when 2 mg/kg of lidocaine was given in 10 mL of 0.9% sodium chloride solution into the outer aperture of the endotracheal tube, and no detrimental side effects were observed.

In the Laryngeal Mask Airway group, airway sealing pressure as a measure of effective airway seal was within the normal range (15,16). To eliminate the possibility that incorrect placement and downfolding of the epiglottis would impede lidocaine absorption, the position of the laryngeal mask airway was controlled with a fiberscope in this study with regard to visualization of the vocal cords. In all patients, the vocal cords were either completely or partially visible, and the position of the laryngeal mask airway was considered correct. In contrast to the distal end of the endotracheal tube, the distal end of the laryngeal mask airway is not only in contact with the trachea, but also with the tissue surrounding the glottic opening. Hence, fluids instilled into the laryngeal mask airway will reach not only the tracheobronchial tree and the alveolar-capillary membrane (17), but also the epiglottic and periglottic mucosa. After providing laryngeal topical anesthesia with lidocaine in doses between 0.9 and 2.6 mg/kg (18), maximum plasma lidocaine concentrations were comparable to lidocaine levels after lidocaine administration into the laryngeal mask airway. These results suggest that most of the lidocaine after laryngeal mask instillation may have been absorbed by the epiglottic and periglottic tissue. A multiphasic pattern of absorption was observed in this and in previous studies (14). This phenomenon may be explained by varying rates of absorption from different absorption sites, i.e., the endobronchial mucosa, the alveolar-capillary membrane, and, in case of use of the laryngeal mask airway, the mucosa surrounding the larynx. Because of this multiphasic pattern of absorption, leading to the occurrence of up to three peak concentrations in individual patients, no absorption or elimination constants were calculated.

After lidocaine administration, a transient decrease in PaO₂ did occur in almost all patients and was not dependent on the use of the endotracheal tube or the laryngeal mask airway. However, the decrease in PaO₂ was transient and was not clinically important. Although using distilled water as diluent may have resulted in larger lidocaine plasma concentrations, decreases in PaO₂ are usually more, which therefore would decrease the safety margin toward hypoxia.

Our study has several limitations. Endobronchial drug administration during CPR is not as simple as in hemodynamically stable patients. Factors influencing drug absorption from the tracheobronchial mucosa and the alveolar-capillary membrane during CPR include cardiac output, vasoconstriction, lung permeability, and ventilation/perfusion ratio of the lung. If drug absorption is erratic with the laryngeal mask airway during normal cardiocirculatory conditions, drug absorption with the laryngeal mask airway during CPR, when the ventilation/perfusion ratio in the lung is severely abnormal, would probably be extremely poor. We did not perform preliminary dose adjustment studies in animals to find an optimal dose for lidocaine administration into the laryngeal mask airway. Hence, it cannot be ruled out that by using larger lidocaine doses, therapeutic plasma concentrations could have been achieved after lidocaine instillation into the laryngeal mask airway. In a laboratory study in swine, epinephrine applied via the esophageal lumen of the Combitube (Kendall-Sheridan, Mansfield, MA) in a 10-fold larger dosage than that used for endobronchial administration had similar effects on plasma epinephrine levels and hemodynamic variables, compared with endotracheal administration (19). An increase in drug dosage was successful in that study, but this does not address possible side effects of the administered drug. For example, a further increase in drug dosage in our study could have resulted in severe adverse effects, such as lidocaine-mediated hypotension.

In conclusion, this study shows that in comparison to the endotracheal tube, the laryngeal mask airway is not a reliable route for the recommended dose of endobronchial lidocaine administration. IV drug administration should be used whenever the laryngeal mask is used during cardiac arrest.

	Acknowledgments

 
This work was supported, in part, by institutional funding.

	References

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