Alex Loeckinger

Does the ProSeal Laryngeal Mask Airway Prevent Aspiration of Regurgitated Fluid

In this randomized, cross-over cadaver study, we determined whether a new airway device, the ProSeal laryngeal mask airway (PLMA; Laryngeal Mask Company, Henley-on-Thames, UK), prevents aspiration of regurgitated fluid. We studied five male and five female cadavers (6–24 h postmortem). The infusion set of a pressure-controlled, continuous flow pump was inserted into the upper esophagus and ligated into place. Esophageal pressure (EP) was increased in 2-cm H2O increments. This was performed without an airway device (control) and over a range of cuff volumes (0–40 mL) for the classic laryngeal mask airway (LMA), the PLMA with the drainage tube clamped (PLMA clamped) and unclamped (PLMA unclamped). The EP at which fluid was first seen with a fiberoptic scope in the hypopharynx (control), above or below the cuff, or in the drainage tube, was noted. Mean EP at which fluid was seen without any airway device was 9 (range 8–10) cm H2O. EP at which fluid was seen was always higher for the PLMA clamped and LMA compared with the control (all, P < 0.0001). The mean EP at which fluid was seen for the PLMA unclamped was similar to the control at 10 (range 8–13) cm H2O. For the PLMA unclamped, fluid appeared from the drainage tube in all cadavers at 10–40 mL cuff volume and in 8 of 10 cadavers at zero cuff volume. Mean EP at which fluid was seen above the cuff was similar for the PLMA clamped and LMA at 0–30 mL cuff volume, but was higher for PLMA clamped at 40-mL cuff volume (81 vs 48 cm H2O, P = 0.006). Mean EP at which fluid was seen below the cuff was similar at 0–10 mL cuff volume, but was higher for the PLMA clamped at 20, 30, and 40 mL cuff volume (62, 68, 73 vs 46, 46, 46 cm H2O, respectively, P < 0.04). For the PLMA clamped and the LMA, fluid appeared simultaneously above and below the cuff at all cuff volumes. We concluded that in the cadaver model, the correctly placed PLMA allows fluid in the esophagus to bypass the pharynx and mouth when the drainage tube is open. Both the LMA, and PLMA with a closed drainage tube, attenuate liquid flow between the esophagus and pharynx. This may have implications for airway protection in unconscious patients. Implications The correctly placed ProSeal laryngeal mask airway allows fluid in the esophagus to bypass the oropharynx in the cadaver model. This may have implications for airway protection in unconscious patients.

Sustained Prolongation of the Qtc Interval after Anesthesia with Sevoflurane in Infants during the First 6 Months of Life

Background Sevoflurane, an inhalational anesthetic frequently administered to infants, prolongs the QT interval of the electrocardiogram in adults. A long QT interval resulting in fatal arrhythmia may also be responsible for some cases of sudden death in infants. As the QT interval increases during the second month of life and returns to the values recorded at birth by the sixth month, we evaluated the effect of sevoflurane on the QT interval during and after anesthesia in this particular population. Methods In this prospective two-group trial we examined pre-, peri-, and postoperative electrocardiograms of 36 infants aged 1 to 6 months scheduled for elective inguinal or umbilical hernia repair. Anesthesia was induced and maintained with either sevoflurane, or the well-established pediatric anesthetic halothane. Heart rate corrected (c) QTc and JTc interval (indicator of intraventricular conduction delays) were recorded from electrocardiograms before and during anesthesia, and at 60 min after emergence from anesthesia. Results Prolonged QTc was observed during sevoflurane anesthesia (mean [±SD], 473 ± 19 ms, P < 0.01). Sixty minutes after emergence from anesthesia, QTc was still prolonged (433 ± 15 ms) in infants treated with sevoflurane compared with those treated with halothane (407 ± 33 ms, P < 0.01). Analogous differences were found for the JTc interval. Conclusions Despite a shorter elimination time than better known inhalational anesthetics, sevoflurane induction and anesthesia results in sustained prolongations of QTc and JTc interval in infants in the first 6 months of life. Electrocardiogram monitoring until the QTc interval has returned to preanesthetic values may increase safety after sevoflurane anesthesia.

Pulmonary gas exchange after cardiopulmonary resuscitation with either vasopressin or epinephrine

Objective It is well established that epinephrine administered during cardiopulmonary resuscitation results in pulmonary gas exchange disturbances. It is uncertain how vasopressin affects gas exchange after cardiopulmonary resuscitation. Design Prospective, randomized experimental study. Setting Animal research laboratory. Subjects Twenty domestic pigs. Interventions Animals were subjected to ventricular fibrillation and cardiopulmonary resuscitation by using either vasopressin or epinephrine. Hemodynamic and pulmonary gas exchange (multiple inert gas elimination technique) variables were recorded before cardiopulmonary resuscitation and 10, 30, 60, and 120 mins after return of spontaneous circulation when either epinephrine (control) or vasopressin was used. Measurements and Main Results At 10 mins after return of spontaneous circulation, blood flow to low VA/Q lung units was increased in animals treated with epinephrine (17.8 ± 6 vs. 2.6 ± 3%, mean ± sd, p < .01). Resulting carbon dioxide elimination was impaired in animals treated with epinephrine but not in animals treated with vasopressin (Paco2, 55 ± 2 vs. 46 ± 4 torr, p < .05). Thirty minutes after return of spontaneous circulation, blood flow to lung units with a normal VA/Q ratio was reduced in animals treated with epinephrine (79 ± 1 vs. 84 ± 12%, p < .05), resulting in a depressed Pao2 (147 ± 4 vs. 127 ± 10 torr, p < .05). Conclusion Vasopressin compared with epinephrine for cardiopulmonary resuscitation resulted in better gas exchange variables in the early postresuscitation phase.

Airway management during spaceflight : A comparison of Four airway devices in simulated microgravity

Background The authors compared airway management in normogravity and simulated microgravity with and without restraints for laryngoscope-guided tracheal intubation, the cuffed oropharyngeal airway, the standard laryngeal mask airway, and the intubating laryngeal mask airway. Methods Four trained anesthesiologist–divers participated in the study. Simulated microgravity during spaceflight was obtained using a submerged, full-scale model of the International Space Station Life Support Module and neutrally buoyant equipment and personnel. Customized, full-torso manikins were used for performing airway management. Each anesthesiologist–diver attempted airway management on 10 occasions with each device in three experimental conditions: (1) with the manikin at the poolside (poolside); (2) with the submerged manikin floating free (free-floating); and (3) with the submerged manikin fixed to the floor using a restraint (restrained). Airway management failure was defined as failed insertion after three attempts or inadequate device placement after insertion. Results For the laryngoscope-guided tracheal intubation, airway management failure occurred more frequently in the free-floating (85%) condition than the restrained (8%) and poolside (0%) conditions (both, P < 0.001). Airway management failure was similar among conditions for the cuffed oropharyngeal airway (poolside, 10%; free-floating, 15%; restrained, 15%), laryngeal mask airway (poolside, 0%; free-floating, 3%; restrained, 0%), and intubating laryngeal mask airway (poolside, 5%; free-floating, 5%; restrained, 10%). Airway management failure for the laryngoscope-guided tracheal intubation was usually caused by failed insertion (> 90%), and for the cuffed oropharyngeal airway, laryngeal mask airway, and intubating laryngeal mask airway, it was always a result of inadequate placement. Conclusion The emphasis placed on the use of restraints for conventional tracheal intubation in microgravity is appropriate. Extratracheal airway devices may be useful when restraints cannot be applied or intubation is difficult.

Large cuff volumes impede posterior pharyngeal mucosal perfusion with the laryngeal tube airway

PurposeThe laryngeal tube airway (LTA) is a new extraglottic airway device with a large proximal cuff that inflates in the laryngopharynx and a distal conical cuff that inflates in the hypopharynx. We determine the influence of the cuff volume and anatomic location on pharyngeal mucosal pressures for the LTA.MethodsFifteen fresh cadavers were studied. Microchip sensors were attached to the (anatomic location) anterior, lateral and posterior surface of the distal cuff (hypopharynx) and proximal cuff (laryngopharynx) of the size 4 LTA. Oropharyngeal leak pressure (OLP) and mucosal pressures were measured at 0–140 mL cuff volume in 20-mL increments. In addition, mucosal pressures for the proximal cuff were measured in three awake, topicalized volunteers.ResultsOLP and mucosal pressure at all locations increased with cuff volume (all:P < 0.01). Mucosal pressures were highest posteriorly. Mucosal pressures only exceeded 35 cm H2O (pharyngeal mucosal perfusion pressure) in the anterior and posterior laryngopharynx and when the cuff volume was > 80–100 mL. Mucosal pressures were similar for cadavers and awake volunteers.ConclusionMucosal pressures for the LTA increase with cuff volume, are highest posteriorly and potentially exceed mucosal perfusion pressure when cuff volume exceeds 80–100 mL.ZusammenfassungObjectifLe tube d’intubation laryngé (TIL) est un nouvel appareil d’intubation extraglottique muni d’un grand ballonnet proximal qui se gonfle dans le laryngopharynx et d’un ballonnet conique distal qui se gonfle dans l’hypopharynx. Nous avons déterminé l’influence du volume du ballonnet et du site anatomique sur les pressions de la muqueuse pharyngienne avec l’utilisation du TIL.MéthodeNous avons étudié 15 cadavres récemment décédés. Des micropuces ont été fixées à la surface antérieure (site anatomique), latérale et postérieure du ballonnet distal (hypopharynx) et proximal (laryngopharynx) du TIL de taille 4. La pression de fuite oropharyngienne (PFO) et les pressions de la muqueuse ont été mesurées pour un volume de ballonnet de 0–140 mL en paliers de 20 mL. De plus, les pressions de la muqueuse pour le ballonnet proximal ont été mesurées à l’état d’éveil chez trois volontaires sous anesthésie topique.RésultatsPour tous les sites anatomiques, la PFO et la pression de la muqueuse ont augmenté avec le volume du ballonnet (tous : P < 0,01). Les pressions de la muqueuse ont été plus élevées sur la face postérieure et elles ont dépassé 35 cm H2O (pression de perfusion de la muqueuse pharyngienne) seulement dans le laryngopharynx antérieur et postérieur et avec un volume de ballonnet > 80–100 mL. Les pressions de la muqueuse ont été similaires chez les cadavres et les volontaires éveillés.ConclusionAvec le TIL, les pressions de la muqueuse augmentent avec le volume du ballonnet, sont plus élevées dans la partie postérieure et dépassent potentiellement la pression de perfusion de la muqueuse quand le volume du ballonnet est audessus de 80–100 mL

A pig model of high altitude pulmonary edema.

High altitude pulmonary edema (HAPE) affects unacclimatized individuals ascending rapidly to high altitude. The pathogenesis of HAPE is not fully elucidated, and many investigative techniques that could provide valuable information are not suitable for use in humans; thus, an animal model is desirable. Rabbits, sheep, dogs, and ferrets have been shown not to consistently develop HAPE, and studies in rats are limited by the animals small size and inconsistent response. Pigs develop a marked pulmonary vasoconstrictive response to hypoxia, and preliminary studies of HAPE in pigs have been promising. To determine the suitability of pigs as an animal model of HAPE, we exposed six subadult (20 to 25 kg) pigs to normobaric hypoxia (10% oxygen) for 48 hr. One week before, and immediately after exposure to hypoxia, under anesthesia, arterial blood gases were obtained and bronchoalveolar lavage (BAL) and chest x-ray were performed. Hypoxia increased alveolar-arterial pressure difference for oxygen from 22 +/- 9 to 38 +/- 5 torr, p < 0.01) and red cell (from 12.3 +/- 5.9 to 27.4 +/- 5.3 cells x 10(5)/mL(-1), p < 0.001) and white cell (from 1.59 +/- 0.90 to 7.88 +/- 3.36 cells x 10(5)/mL(-1), p < 0.05) concentrations in BAL in all animals. Total BAL protein concentration increased by 64% and fractional albumin by 38% (both p < 0.05) posthypoxia. One animal had evidence of pulmonary edema on X ray. Some pigs develop findings consistent with early HAPE when exposed to normobaric hypoxia. Increasing the duration of hypoxic exposure or exercising the animals in hypoxia may better model the disease process observed in humans with clinically significant HAPE.

Brief Report: Pressure Support Ventilation during an Ascent and on the Summit of Mt. Everest? A Theoretical Approach

At extreme altitude, air has an almost identical composition compared to air at sea level, while its pressure is altitude-dependently lower. When supplementary oxygen is used to achieve an acceptable inspiratory pressure of oxygen (PI(O2)) during climbing, the barometric pressure difference to lower altitudes is not compensated for. In this report, we tried theoretically to apply pressure support ventilation (PSV) to partially compensate for low barometric pressures. PSV is widely used for respiratory home care and is applicable via a nasal mask. Since there are light-weight units with long battery lives on the market, we speculated that these units may to some extent replace bottled oxygen. PSV was in theory applied at barometric pressures of 400 torr (Everest Base Camp), 284 torr (South Col), and 253 torr (summit of Mt. Everest). We found that during PSV at a mean airway pressure of 16.5 torr on the summit of Mt. Everest, a fraction of inspired oxygen (FI(O2)) of 0.34 sufficed to achieve an alveolar partial pressure (PA(O2)) of 67 torr. PSV increases PI(O2) by 3.5 torr, which in theory elevates the maximum oxygen consumption (V(O2max)) by 218 mL.min(-1) in an acclimatized climber in this setting. An additional benefit of PSV at extreme altitude may come from the unloading of the respiratory muscles.