Axel Kleinsasser

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.

The Laryngeal Mask Airway ProSeal™ as a Temporary Ventilatory Device in Grossly and Morbidly Obese Patients Before Laryngoscope-Guided Tracheal Intubation

We determined the efficacy of the laryngeal mask airway ProSeal™ (PLMA) as a temporary ventilatory device in morbidly obese patients before laryngoscope-guided tracheal intubation. Sixty patients (body mass index 35–60 kg/m2) scheduled for elective surgery, who preferred airway management under general anesthesia, were studied. The induction of anesthesia was with midazolam/fentanyl/propofol and maintenance was with sevoflurane 1%–3% in oxygen 100%. The PLMA was inserted and an effective airway established. Rocuronium was given IV for paralysis. Oropharyngeal leak pressure, ease of gastric tube placement, residual gastric volume, fiberoptic position of the airway/drainage tube, and ease of ventilation at a tidal volume of 8 mL/kg was determined. The PLMA was then removed and laryngoscope-guided tracheal intubation attempted. The number of insertion/intubation attempts (maximum two each) and time taken to establish an effective airway with each device were recorded. An effective airway was obtained at the first insertion attempt in 90% of patients (54/60) and at the second attempt in 10% (6/60). The time taken to provide an effective airway was 15 ± 7 s (7–42 s). Oropharyngeal leak pressure was 32 ± 8 cm H2O (12–40 cm H2O). The residual gastric volume was 36 ± 46 mL (0–240 mL). Positive pressure ventilation without air leaks was possible in 95% of patients (57/60). The vocal cords were seen from the airway tube in 75% of patients (45/60), but the esophagus was not seen. The fiberoptic view from the drainage tube revealed mucosa in 93% of patients (56/60) and an open upper esophageal sphincter in 7% (4/60). Tracheal intubation was successful at the first attempt in 90% of patients (54/60), at the second attempt in 7% (4/60), and failed in 3% (2/60). In these latter two patients, the PLMA was reinserted and surgery performed uneventfully with the PLMA. The time taken to tracheally intubate the patient was 13 ± 10 s (8–51 s). There were no episodes of hypoxia (Spo2 <90%) or other adverse events. There were no differences in insertion success rate, or the time to successful insertion between the PLMA and laryngoscope-guided intubation. We conclude that the PLMA is an effective temporary ventilatory device in grossly or morbidly obese patients before laryngoscope-guided tracheal intubation.

Sevoflurane, but not Propofol, Significantly Prolongs the Q-T Interval

Prolongation of the Q-T interval may be associated with polymorphic ventricular tachycardia known as torsade de pointes, syncope and sudden death. Existing data show that isoflurane prolongs the Q-T interval, whereas halothane shortens it. The aim of this study was to determine whether sevoflurane or propofol affects the Q-T interval. Thirty female patients undergoing gynecologic surgery were randomly assigned to two groups, one receiving inhaled induction with sevoflurane and the other receiving total IV anesthesia with propofol. Before and 20 min after the induction, a six-lead electrocardiogram was recorded, and blood pressure was measured. The Q-T interval and heart rate adjusted Q-T interval (Q-Tc interval) were significantly prolonged during the administration of anesthesia with sevoflurane, while the Q-T interval was significantly shortened, and the Q-Tc interval was statistically unaffected during propofol anesthesia administration. We conclude that, in otherwise healthy female patients, sevoflurane prolongs the Q-Tc. Implications In this study, we evaluated the effect of sevoflurane induction and anesthesia versus propofol induction and anesthesia on the Q-T interval. Sevoflurane significantly prolonged the Q-T interval and the heart rate adjusted Q-T interval, whereas propofol shortened the Q-T interval but not the heart rate adjusted Q-T interval.

Continuous Positive Airway Pressure at 10 cm H2O During Cardiopulmonary Bypass Improves Postoperative Gas Exchange

Postbypass pulmonary dysfunction including atelectasis and increased shunting is a common problem in the intensive care unit. Negative net fluid balance and continuous positive airway pressure (CPAP) have been used to reduce the adverse effects of cardiopulmonary bypass (CPB) on the lung. To determi

Does gender affect human pulmonary gas exchange during exercise

Women may experience greater pulmonary gas exchange impairment during exercise than men. To test this we used the multiple inert gas elimination technique to study eight women and seven men matched for age, height and V̇O2 max (∼48 ml kg−1 min−1) during normoxic and hypoxic (inspired PO2= 95 Torr) cycle exercise. Resting lung function was similar between the sexes, except for a lower carbon monoxide diffusing capacity (DLCO) in women (P < 0.05). Arterial PO2,PCO2 and alveolar–arterial O2 difference (A−aDO2) were not significantly different in men and women. Despite a lower diffusing capacity for O2 (DLO2) in women, the ratio DLO2/βQ̇ (which estimates pulmonary end‐capillary diffusion equilibrium) was similar between men and women and estimates of diffusion limitation during hypoxic exercise were not different between the sexes. Ventilation–perfusion inequality (described by the second moment of the perfusion distribution, logSD) increased during both normoxic and hypoxic exercise. Surprisingly, logSD values were slightly lower for women under all conditions (P < 0.05), but this did not significantly affect gas exchange. These data indicate that these active women, despite a lower DLCO and DLO2, do not experience greater exercise‐induced abnormalities in gas exchange than men matched for age, height, aerobic capacity and lung size. Possibly fitness level and lung size are more important in determining whether or not pulmonary gas exchange impairment occurs during exercise than sex per se.

Pressure support ventilation versus continuous positive airway pressure ventilation with the ProSeal laryngeal mask airway: A randomized crossover study of anesthetized pediatric patients

Continuous positive airway pressure (CPAP) and pressure support ventilation (PSV) improve gas exchange in adults, but there are little published data regarding children. We compared the efficacy of PSV with CPAP in anesthetized children managed with the ProSeal™ laryngeal mask airway. Patients were randomized into two equal-sized crossover groups and data were collected before surgery. In Group 1, patients underwent CPAP, PSV, and CPAP in sequence. In Group 2, patients underwent PSV, CPAP, and PSV in sequence. PSV comprised positive end-expiratory pressure set at 3 cm H2O and inspiratory pressure support set at 10 cm H2O above positive end-expiratory pressure. CPAP was set at 3 cm H2O. Each ventilatory mode was maintained for 5 min. The following data were recorded at each ventilatory mode: ETco2, Spo2, expired tidal volume, peak airway pressure, work of breathing patient (WOB), &dgr; esophageal pressure, pressure time product, respiratory drive, inspiratory time fraction, respiratory rate, noninvasive mean arterial blood pressure, and heart rate. In Group 1, measurements for CPAP were similar before and after PSV. In Group 2, measurements for PSV were similar before and after CPAP. When compared with CPAP, PSV had lower ETco2 (46 ± 6 versus 52 ± 7 mm Hg; P < 0.001), slower respiratory rate (24 ± 6 versus 30 ± 6 min−1; P < 0.001), lower WOB (0.54 ± 0.54 versus 0.95 ± 0.72 JL−1; P < 0.05), lower pressure time product (94 ± 88 versus 150 ± 90 cm H2O s−1min−1; P < 0.001), lower &dgr; esophageal pressure (10.6 ± 7.4 versus 14.1 ± 8.9 cm H2O; P < 0.05), lower inspiratory time fraction (29% ± 3% versus 34% ± 5%; P < 0.001), and higher expired tidal volume (179 ± 50 versus 129 ± 44 mL; P < 0.001). There were no differences in Spo2, respiratory drive, mean arterial blood pressure, and heart rate. We conclude that PSV improves gas exchange and reduces WOB during ProSeal™ laryngeal mask airway anesthesia compared with CPAP in ASA physical status I children aged 1–7 yr.

Recombinant angiotensin-converting enzyme 2 improves pulmonary blood flow and oxygenation in lipopolysaccharide-induced lung injury in piglets.

Objective: To study angiotensin-converting enzyme 2 in a piglet model with acute respiratory distress syndrome and to evaluate the therapeutic potential of this substance in a preclinical setting, as this model allows the assessment of the same parameters required for monitoring the disease in human intensive care medicine. The acute respiratory distress syndrome is the most severe form of acute lung injury with a high mortality rate. As yet, there is no specific therapy for improving the clinical outcome. Recently, angiotensin-converting enzyme 2, which inactivates angiotensin II, has been shown to ameliorate acute lung injury in mice. Design: Prospective, randomized, double-blinded animal study. Setting: Animal research laboratory. Subjects: Fifteen anesthetized and mechanically ventilated piglets. Interventions: Acute respiratory distress syndrome was induced by lipopolysaccharide infusion. Thereafter, six animals were assigned randomly into angiotensin-converting enzyme 2 group, whereas another six animals served as control. Three animals received angiotensin-converting enzyme 2 without lipopolysaccharide pretreatment. Measurements and Main Results: Systemic and pulmonary hemodynamics, blood gas exchange parameters, tumor necrosis factor-&agr;, and angiotensin II levels were examined before acute respiratory distress syndrome induction and at various time points after administering angiotensin-converting enzyme 2 or saline. In addition, ventilation-perfusion distribution of the lung tissue was assessed by the multiple inert gas elimination technique. Animals treated with angiotensin-converting enzyme 2 maintained significantly higher Pao2 than the control group, and pulmonary hypertension was less pronounced. Furthermore, angiotensin II and tumor necrosis factor-&agr; levels, both of which were substantially increased, returned to basal values. Multiple inert gas elimination technique revealed a more homogeneous pulmonary blood flow after treatment with angiotensin-converting enzyme 2. In intergroup comparisons, there were no differences in pulmonary blood flow to lung units with subnormal ventilation/perfusion ratios. Conclusions: Angiotensin-converting enzyme 2 attenuates arterial hypoxemia, pulmonary hypertension, and redistribution of pulmonary blood flow in a piglet model of acute respiratory distress syndrome, and may be a promising substance for clinical use.

Inert gas exchange during pneumoperitoneum at incremental values of positive end-expiratory pressure

UNLABELLED Laparoscopy is a surgical technique for a growing variety of abdominal operations. In patients undergoing this procedure, arterial blood oxygenation and hemodynamics are frequently depressed. This study evaluated the effect of different levels of positive end-expiratory pressure (PEEP) during intraperitoneal CO(2) insufflation on the lungs ventilation-perfusion distribution in a porcine model. We studied 13 anesthetized pigs with an intraperitoneal pressure of 15 cm H(2)O applied at either incremental values of PEEP (5-20 cm H(2)O, increments of 5 cm H(2)O) or a constant PEEP of 5 cm H(2)O. The effects of CO(2) pneumoperitoneum on inert gas exchange and hemodynamics were examined with the multiple inert gas elimination technique. During pneumoperitoneum, gas exchange was most augmented by 15 and 20 cm H(2)O of PEEP. Although the differences in hemodynamics between the individual settings were insignificant, 10 cm H(2)O of PEEP provided the smallest impairment of hemodynamics. We conclude that PEEP of 15 H(2)O during pneumoperitoneum resulted in a modest hemodynamic depression but significant gas exchange augmentation in our experiment. IMPLICATIONS Anesthetized pigs, with a pneumoperitoneum of 15 cm H(2)O, were treated either with incremental values of positive end-expiratory pressure (5-20 cm H(2)O, increments of 5 cm H(2)O) or with a constant positive end-expiratory pressure of 5 cm H(2)O. Fifteen and 20 cm H(2)O resulted in significantly improved pulmonary gas exchange compared with 5 cm H(2)O.

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.