Wolfgang Heinrichs

Respiratory mechanics, gastric insufflation pressure, and air leakage of the laryngeal mask airway.

A potential risk of the laryngeal mask airway (LMA) is incomplete mask seal, which causes air leakage or insufflation of air into the stomach.The objective of the present study was to assess respiratory mechanics, quantify air leakage, and measure gastric air insufflation in patients ventilated via the LMA. Thirty patients were studied after induction of anesthesia but prior to any surgical manipulations. After the insertion of the LMA, patients were ventilated with increasing tidal volumes until one of the three following end points were reached: 1) gastric air insufflation, 2) airway pressure >40 cm H2 O, or 3) limitation of further increase in tidal volume by air leakage. The following variables were determined: inspired volume (V (I)), expired volume (VE), maximum inspiratory pressure (Pmax), airway pressure at gastric inflation (Pinfl), respiratory time constant (RC), compliance (C), resistance (R), and leakage fraction (FL). Respiratory mechanics were in the physiological range. Gastric insufflation occurred in 27% of the patients at inspiratory pressures between 19 and 33 cm H2 O. Air leakage of more than 10% was evident at inspiratory pressures between 25 and 34 cm H2 O. The end point of 40 cm H2 O airway pressure was reached in only three patients. We conclude that the LMA is not better in preventing airway pressure transmission to the esophagus than a conventional face mask. However, a high FL is associated with reduced gastric air insufflation. (Anesth Analg 1997;84:1025-8)

Assessment of pulmonary mechanics and gastric inflation pressure during mask ventilation.

INTRODUCTION Mask ventilation is a procedure routinely used in emergency medicine. Potential hazards are inadequate alveolar ventilation and inflation of the stomach with air, leading to subsequent regurgitation and aspiration. The aim of this study was to measure lung function and gastric inflation pressures during mask ventilation. METHODS For this purpose, 31 patients scheduled for routine urological procedures were studied during induction of anesthesia. Lung function was assessed by recording respiratory flow and pressure directly at the face mask. Gastric inflation was observed with a microphone taped to the epigastric area. RESULTS Gastric inflation occurred in 22 of the 31 patients. Mean gastric inflation pressure was 27.5 +/- 6.55 cm H2O, mean compliance was 67 +/- 24.1 ml/cm H2O, mean resistance was 17.4 +/- 6.41 cm H2O/L/sec, and the mean respiratory time constant was 1.1 +/- 0.26 seconds. CONCLUSIONS These data suggest that inspiratory pressure be limited to 20 cm H2O, and that an inspiratory time of at least four times the respiratory time constant be allowed. Monitoring airway pressure and gastric inflation is a simple technique that may improve the safe-ty of patients during mask ventilation.

Computed tomography-based tracheobronchial image reconstruction allows selection of the individually appropriate double-lumen tube size

OBJECTIVES To determine whether individualized selection of double-lumen tubes or alternatives based on three-dimensional reconstruction of the tracheobronchial image from routine preoperative computed tomography (CT) scans leads to clinically appropriate choices. DESIGN Prospective observational study; comparison to historic controls. SETTING Anesthesia and radiology facilities of a university medical center. PARTICIPANTS Forty-nine patients undergoing thoracic surgery requiring one-lung ventilation. INTERVENTIONS Three-dimensional image reconstruction of individual tracheobronchial anatomy was performed from routine preoperative spiral CT scans as well as from scans of five left-sided and four right-sided double-lumen tubes. Results of image-based tube size selection were compared with literature recommendations. Prospectively, individualized tube selection was performed by superimposition of printed transparencies of tubes over the tracheobronchial system and was validated using bronchoscopic and clinical criteria (n = 24). MEASUREMENTS AND MAIN RESULTS Three-dimensional reconstruction visualized individual anatomy with good accuracy and resolution. Correlations between patient morphology and tracheobronchial dimensions were weak (height versus mainstem bronchial diameters: r < 0.50). In 11 of 48 patients (23%). CT-fitted double-lumen tube sizes would have differed from a conventional height-based and gender-based selection. Individual, prospective, CT-based double-lumen tube selection was associated with (1) good fit and positioning confirmed by fiberoptic bronchoscopy, (2) adequate bronchial cuff seal volumes, (3) complete lung separation, and (4) oxygenation and ventilation parameters during one-lung ventilation similar to those with conventional size selection. In one patient, three-dimensional CT study allowed noninvasive evaluation of a tracheal stenosis precluding double-lumen tube placement. CONCLUSION Individualized selection of double-lumen tube size using CT-based reconstructions of tracheobronchial anatomy leads to clinically appropriate choices. Risks resulting from variations in tracheobronchial morphology are recognized in advance.

Laryngeal mask airway position and the risk of gastric insufflation

A potential risk of the laryngeal mask airway (LMA) is an incomplete mask seal causing gastric insufflation or oropharyngeal air leakage.The objective of the present study was to assess the incidence of LMA malpositions by fiberoptic laryngoscopy, and to determine their influence on gastric insufflation and oropharyngeal air leakage. One hundred eight patients were studied after the induction of anesthesia, before any surgical manipulations. After clinically satisfactory LMA placement, tidal volumes were increased stepwise until air entered the stomach, airway pressure exceeded 40 cm H2 O, or air leakage from the mask seal prevented further increases in tidal volume. LMA position in relation to the laryngeal entrance was verified using a flexible bronchoscope. The overall incidence of LMA malpositions was 40% (43 of 108). Gastric air insufflation occurred in 19% (21 of 108), and in 90% (19 of 21) of these patients, the LMA was malpositioned. Oropharyngeal air leakage occurred in 42%, and was independent of LMA position. We conclude that clinically unrecognized LMA malposition is a significant risk factor for gastric air insufflation. Implications: Routine placement of laryngeal mask airways does not require laryngoscopy. In our study, fiberoptic verification of mask position revealed suboptimal placement in 40% of cases. Such malpositioning considerably increased the risk of gastric air insufflation. (Anesth Analg 1998;86:867-71)

Adaptive Lung Ventilation (ALV) during Anesthesia for Pulmonary Surgery: Automatic Response to Transitions to and from One-Lung Ventilation

Adaptive lung ventilation is a novel closed-loop-controlled ventilation system. Based upon instantaneous breath-to-breath analyses, the ALV controller adjusts ventilation patterns automatically to momentary respiratory mechanics. Its goal is to provide a preset alveolar ventilation (V′ A) and, at the same time, minimize the work of breathing. Aims of our study were (1) to investigate changes in respiratory mechanics during transition to and from one-lung ventilation (OLV), (2) to describe the automated adaptation of the ventilatory pattern. Methods. With institutional approval and informed consent, 9 patients (33–72 y, 66–88 kg) underwent ALV during total intravenous anesthesia for pulmonary surgery. The ALV controller uses a pressure controlled ventilation mode. V′ A is preset by the anesthesiologist. Flow, pressure, and CO2 are continuously measured at the DLT connector. The signals were read into a IBM compatible PC and processed using a linear one-compartment model of the lung to calculate breath-by-breath resistance (R), compliance (C), respiratory time constant (TC), serial dead space (VdS) and V′ A. Based upon the results, the controller optimizes respiratory rate (RR) and tidal volume (VT) such as to achieve the preset V′ A with the minimum work of breathing. In addition to V′ A, only PEEP and FIO2 settings are at the anesthesiologists discretion. All patients were ventilated using FIO2 = 1,0 and PEEP = 3 cm H2O. Parameters of respiratory mechanics, ventilation, and ABG were recorded during three 5-min periods: 10 min prior to OLV (I), 20 min after onset of OLV (II), and after chest closure (III). Data analyses used nonparametric comparisons of paired samples (Wilcoxon, Friedman) with Bonferronis correction. Significance was assumed at p < 0.05. Values are given as medians (range). Results. 20 min after onset of OLV (II), resistance had approximately doubled compared with (I), compliance had decreased from 54 (36–81) to 50 (25–70) ml/cm H2O. TC remained stable at 1.4 (0.8–2.4) vs. 1.2 (0.9–1.6) s. Institution of OLV was followed by a reproducible response of the ALV controller. The sudden changes in respiratory mechanics caused a transient reduction in VT by 42 (8–59) %, with RR unaffected. In order to reestablish the preset V′ A, the controller increased inspiratory pressure in a stepwise fashion from 18 (14–23) to 27 (19–39) cm H2O, thereby increasing VT close to baseline (7.5 (6.6–9.0) ml/kg BW vs. 7.9 (5.4–11.7) ml/kg BW). The controller was, thus, effective in maintaining V′ A. The minimum PaO2 during phase II was 101 mmHg. After chest closure, respiratory mechanics had returned to baseline. Conclusions. Respiratory mechanics during transition to and from OLV are characterized by marked changes in R and C into opposite directions, leaving TC unaffected. The ALV controller manages these transitions successfully, and maintaines V′ A reliably without intervention by the anesthesiologist. VT during OLV was found to be consistently lower than recommended in the literature.

The AVL-mode: a safe closed loop algorithm for ventilation during total intravenous anesthesia.

The Adaptive Lung Ventilation Controller (ALV-Controller) represents a new approach to closed loop control of ventilation. It is based on a pressure controlled ventilation mode. Adaptive lung ventilation signifies automatic breath by breath adaptation of breathing patterns to the lung mechanics of an individual patient. The specific goals are to minimize work of breathing, to maintain a preset alveolar ventilation to prevent the occurrence of intrinsic PEEP.We ventilated 5 patients undergoing major abdominal procedures using ALV. ALV was tolerated well in all patients. Alveolar ventilation was preset between 5500 and 6500 ml/min. Serial dead space (Vds) and respiratory time constant (resistence* compliance) of the patients ranged from 104 to 164 ml and 0.74 to 1.5 s, respectively. The resulting respiratory rates ranged from 8 to 15 breaths/min, the tidal volumes from 542 to 829 ml, and the applied maximum inspiratory pressures from 15.5 to 18.9 mbar. Expiratory time was sufficient in all cases to allow complete expiration and to avoid intrinsic PEEP. I: E-relations ranged from 0.36 to 0.76. After a step change in alveolar ventrilation rise times of the breathing patterns were recorded at values from 7 to 67 s. Overshoot did not reach statisic significance compared to the variations in breathing patterns which occurred during stable measuring periods. Accuracy of the controller was high (27.8 ml difference between preset and applied alveolar ventilation in the mean) and stability was sufficient for clinical purposes.The results of this preliminary study show that the breathing patterns selected by the controller were well adapted to the lung mechanics of the patients. Respiratory rates, inspiratory pressures and tidal volumes were within the clinically acceptable range in all patients.

Successful treatment of a patient with ARDS after pneumonectomy using high-frequency oscillatory ventilation.

Abstract High frequency oscillatory ventilation (HFOV) was used in a patient who developed the acute respiratory distress syndrome 5 days following a right pneumonectomy for bronchogenic carcinoma. When conventional pressure-controlled ventilation failed to maintain adequate oxygenation, HFOV dramatically improved oxygenation within the first few hours of therapy. Pulmonary function and gas exchange recovered during a 10-day period of HFOV. No negative side effects were observed. Early use of HFOV may be a beneficial ventilation strategy for adults with acute pulmonary failure, even in the postoperative period after lung resection.

Adaptive Lung Ventilation (ALV) : Evaluierung eines neuen closed loop-gesteuerten Beatmungsalgorithmus bei Eingriffen in überstreckter Seitenlage

ZusammenfassungALV stellt ein neues automatisches Beatmungsverfahren dar. Wir verglichen an 20 Patienten in Nephrektomielagerung ALV mit der konventionellen CMV-Beatmung. Ziele der Studie waren 1) Auswirkungen der Lagerung auf Atmungsmechanik und Gasaustausch festzustellen, 2) die vom ALV-Regler gewählten Beatmungsparameter mit den traditionell unter CMV eingestellten zu vergleichen und 3) die individuelle Anpassung der Beatmungsparameter unter ALV zu beurteilen. Zunächst wurden Atmungsmechanik- und Gasaustauschwerte in Rückenlage und 20 min nach Umlagerung verglichen. Danach wurden die Patienten nach einem randomisierten Crossover-Design sowohl ALV als auch CMV beatmet. Unter CMV wurde ein Atemzugvolumen von 10 ml/kg KG, eine Atmungsfrequenz von 10 AZ/min, ein I:E-Verhältnis von 1:1,5 und eine endinspiratorische Pause von 30% der Inspirationszeit eingestellt. Unter ALV wurde eine gewünschte alveoläre Ventilation von 70 ml/kg Körpergewicht und Minute vorgegeben. Nach Umlagerung nahm die Compliance von 61,6 auf 47,9 ml/cm H2O ab, die respiratorische Zeitkonstante verkürzte sich von 1,2 auf 1,08 s und der physiologische Totraum nahm von 158,9 auf 207,5 ml zu. Der ALV-Regler beatmete die Patienten mit Beatmungsparametern, die zwar im Mittel weitgehend identisch mit den unter CMV vorgegebenen waren, die aber eine individuelle Anpassung an die unterschiedliche Atmungsmechanik beobachten ließen.AbstractThe lateral decubitus position is the standard position for nephrectomies. There is a lack of data about the effects of this extreme position upon respiratory mechanics and gas exchange. In 20 patients undergoing surgery in the nephrectomy position, we compared a new closed-loop-controlled ventilation algorithm, adaptive lung ventilation (ALV), which adapts the breathing pattern automatically, to the respiratory mechanics with conventionally controlled mandatory ventilation (CMV). The aims of our study were (1) to describe positioning effects on respiratory mechanics and gas exchange, (2) to compary ventilatory parameters selected by the ALV controller with traditional settings of CMV, and (3) to assess the individual adaptation of the ventilatory parameters by the ALV controller. The respirator used was a modified Amadeus ventilator, which is controlled by an external computer and possesses an integrated lung function analyzer. In a first set of measurements, we compared parameters of respiratory mechanics and gas exchange in the horizontal supine position and 20 min after changing to the nephrectomy position. In a second set of measurements, patients were ventilated with ALV and CMV using a randomized crossover design. The CMV settings were a tidal volume of 10 ml/kg body weight, a respiratory rate of 10 breaths/min, an I:E ratio of 1:1.5, and an end-inspiratory pause of 30% of inspiratory time. With both ventilation modes FiO2 was set to 0.5 and PEEP to 3 cm H2O. During ALV a desired alveolar ventilation of 70 ml/kg KG·min was preset. All other ventilatory parameters were determined by the ALV controller according to the instantaneously measured respiratory parameters. Positioning induced a reduction of compliance from 61.6 to 47.9 ml/cm H2O; the respiratory time constant shortened from 1.2 to 1.08 s, whereas physiological dead space increased from 158.9 to 207.5 ml. On average, the ventilatory parameters selected by the ALV controller resembled very closely those used with CMV. However, an adaptation to individual respiratory mechanics was clearly evident with ALV. In conclusion, we found that the effects of positioning for nephrectomy are minor and may give rise to problems only in patients with restrictive lung disease. The novel ALV controller automatically selects ventilatory parameters that are clinically sound and are better adapted to the respiratory mechanics of ventilated patients than the standardized settings of CMV are.

Staff Education for Simulation: Train-the-Trainer Concepts

The need for training the trainers in the world of clinical simulation should lead to the goal of developing a universal standard for simulation center staff qualifications. This will help clinical simulation to become a universally utilized educational tool with comparable levels of training standards. The idea of specifying the minimal requirements of capabilities of staff for certain positions within a simulation center will eventually lead to degrees and internationally accepted “simulation facilitators.” The topics described in this chapter just point out the basic simulation-specific skills, and they can easily be widened and deepened into each of the branches of interest and the specific training needs. Despite the trend of clinical simulation to become more and more interdisciplinary between the different branches of clinical practitioners, the presented Train-the-Trainer concept does not yet take other simulation equipment, such as partial-task trainers or surgical trainers, into account. A stronger focus on Human Factor aspects including role-plays and active reviews or including techniques for course and participant evaluation would be desirable to add to the program. Currently, no examination of the success of a class or a formal recertification process has been established, and an implementation of a second level of Train-the-Trainer training for repeating and intensifying the introduced topics is missing.

Automated anesthesia record systems

ZusammenfassungDie Einführung automatischer Anästhesieprotokollsysteme wurde bereits 1979 versucht, wobei ein effizienter Einsatz erst in den letzten Jahren zur Realität wurde. Vorteile. Die Vorteile eines elektronischen Protokollsystems sind die kontinuierliche Dokumentation mit hoher Qualität, die Vergleichbarkeit der Daten aufgrund der Verfügbarkeit in einer Datenbank, die Verminderung des Arbeitsaufwandes f¨r den Anästhesisten und die Verfügbarkeit zusätzlicher Informationen. Nachteile. Durch das handschriftiliche Führen eines Anästhesieprotokolls findet eine Bewußtmachung des anästhesieologischen Verlaufs statt. Werden die Daten jedoch automatisch registriert, könnte die mentale Verarbeitung der Daten durch den Anästhesisten verloren gehen. Neue Publikationen zeigten jedoch, daß durch die Verwendung von “intelligenten” Alarmsystemen und Verbesserungen der grafischen Datenpräsentation die manuelle Datenaufzeichnung im Hinblick auf die Aufmerksamkeit des Anästhesisten nicht erforderlich ist. Technische Anforderungen. Das technische Design automatischer Anästhesieprotokollsysteme hängt von der Netzwerktechnologie des jeweiligen Krankenhauses ab. Unter Einhaltung entsprechender Sicherheitsmaßnahmen ist eine Verbindung zum Internet sinnvoll. Die Datenverwaltung sollte nach dem sog. Client Server Prinzip erfolgen. Standard in Bezug auf die Programmiersprache ist die sog. SQL (structured query language). In der nahen Zukunft werden aber auch “objektorientierte” Datenbanken mit noch größerer Flexibilität vorhanden sein. Ausblick. Derzeit kann der Kauf von keinem der kommerziell verfügbaren Systeme ohne Einschränkungen empfohlen werden. Es fehlen allgemeningültige Standards für den späteren Datentransfer und die Kosten-Nutzen Frage ist noch nicht gelöst. Die Vorteile der Dokumentation mit hoher Datenqualität und die bessere Information über den Zeit- und Resourcenverbrauch werden jedoch in den nächsten Jahren zu einer Einführung automatischer Anästhesieprotokollsysteme führen.AbstractThe introduction of electronic anaesthesia documentation systems was attempted as early as in 1979, although their efficient application has become reality only in the past few years. The advantages of the electronic protocol are apparent:· Continuous high quality documentation,· comparability of data due to the availability of a data bank,· reduction in the workload of the anaesthesist and· availability of additional data.Disadvantages of the electronic protocol have also been discussed in the literature. By going through the process of entering data on the course of the anaesthetic procedure on the protocol sheet, the information is mentally absorbed and evaluated by the anaesthesist. This information may, however, be lost when the data are recorded fully automatically – without active involvement on the part od the anaesthesist. Recent publications state that by using intelligent alarms and/or integrated displays manual record keeping is no longer necessary for anaesthesia vigilance.The technical design of automated anaesthesia records depends on an integration of network technology into the hospital. It will be appropriate to connect the systems to the Internet, but safety requirements have to be followed strictly. Concerning the database, client server architecture as well as language standards like SQL should be used. Object oriented databases will be available in the near future.Another future goal of automated anaesthesia record systems will be using knowledge based technologies within these systems. Drug interactions, disease related anaesthetic techniques and other information sources can be integrated.At this time, almost none of the commercially available systems has matured to a point where their purchase can be recommended without reservation. There is still a lack of standards for the subsequent exchange of data and a solution to a number of ergonomic problems still remains to be found. Nevertheless, electronic anaesthesia protocols will be required in the near future. The advantages of accurate documentation and quality control in the presence of careful planning outweigh cost considerations by far.