Efficiency of passive activated carbon anaesthetic gas capturing systems during simulated ventilation.

BACKGROUND: Interest in passive flow filter systems to remove sevoflurane from anaesthetic machine exhaust have increased recently to mitigate the environmental impact of volatile anaesthetics. These filter systems consist of chemically activated carbon, with limited evidence on their performance characteristics. We hypothesised that their efficiency depends on filter material. METHODS: Binding capacity was tested for three carbon filter materials (CONTRAfluran®, FlurAbsorb®, and Anaesthetic Agent Filter AAF633). Adsorption efficiency and resistive pressure were determined during simulated ventilation at different stages of filter saturation and fresh gas flow. In addition, sevoflurane concentration in filtered gas was measured at randomly selected anaesthesia workstations. RESULTS: Sevoflurane concentration in filtered gas exceeded 10 ppm when saturated with 184 ml sevoflurane each for CONTRAfluran and FlurAbsorb and 276 ml for AAF633. During simulated ventilation, sevoflurane concentration >10 ppm passed through CONTRAfluran and AAF633 at fresh gas flow 10 L min-1 only at maximum saturation, but through FlurAbsorb at all stages of saturation. The resistance pressure of all filters was negligible during simulated ventilation, but increased up to 5.2 (0.2) cm H2O during simulated coughing. At two of seven anaesthesia workstations, sevoflurane concentration in filtered exhaust gas was >10 ppm. CONCLUSIONS: Depending on the filter material and saturation, the likelihood of sevoflurane passing through passive flow carbon filters depends on the filter material and fresh gas flow. Combining the filter systems with anaesthetic gas scavenging systems could protect from pollution of ambient air with sevoflurane.

Understanding pediatric ventilation in the operative setting. Part II: Setting perioperative ventilation.

Approaches toward lung-protective ventilation have increasingly been investigated in recent years. Despite evidence being found in adults undergoing surgery, data in younger children are still scarce and controversial. From a physiological perspective, however, the continuously changing characteristics of the respiratory system from birth through adolescence require an approach based on the analysis of each individual patient. The modern anesthesia workstation provides such information, with the technical strengths and weaknesses being discussed in a review preceding the present work (see Part I). The present summary aims to provide ideas on how to translate the information displayed on the anesthesia workstation to patient-oriented clinical ventilation settings.

Understanding pediatric ventilation in the operative setting. Part I: Physical principles of monitoring in the modern anesthesia workstation.

The modern anesthesia workstation provides a wealth of information some of which is of particular interest when it comes to optimizing ventilation settings. This knowledge gains even more importance in the therapy of pediatric patients. In the absence of evidence-based recommendations on optimal ventilation settings in pediatric patients, the evaluation of individual factors becomes crucial and challenging at the same time. Even when equipped with the latest sensor technology, the user will always have to be in charge of interpreting the provided monitoring variables. The purpose of this review is to outline the clinical impact, technological background, and reliability of the most relevant information measured and calculated by a modern anesthesia workstation. It aims at translating the technical knowledge into a more competent and vigilant application in the clinical setting.

Incidence of gastric insufflation at high compared with low laryngeal mask cuff pressure: A randomised controlled cross-over trial.

BACKGROUND: The success of ventilation with a laryngeal mask depends crucially on the seal between the mask and the periglottic tissue. Increasing the laryngeal mask's cuff volume is known to reduce oral air leakage but may lead to gastric insufflation. OBJECTIVE: We hypothesised that a lower cuff pressure would result in less gastric insufflation. We sought to compare gastric insufflation with laryngeal mask cuff pressures of 20 cmH2O (CP20) and 60 cmH2O (CP60) during increasing peak airway pressures in a randomised controlled double-blind cross-over study. We also evaluated the incidence of gastric insufflation at the recommended peak airway pressure of 20 cmH2O or less and during both intermittent positive airway pressure and continuous positive airway pressure. METHODS: After obtaining ethics approval and written informed consent, 184 patients ventilated via laryngeal mask received a stepwise increase in peak airway pressure from 15 to 30 cmH2O with CP20 and CP60 in turn. Gastric insufflation was determined via real-time ultrasound and measurement of the cross-sectional area of the gastric antrum. The primary endpoint was the incidence of gastric insufflation at the different laryngeal mask cuff pressures. RESULTS: Data from 164 patients were analysed. Gastric insufflation occurred less frequently at CP20 compared with CP60 (P < 0.0001). Gastric insufflation was detected in 35% of cases with CP20 and in 48% with CP60 at a peak airway pressure of 20 cmH2O or less. Gastric insufflation occurred more often during continuous than during intermittent positive airway pressures (P < 0.01). CONCLUSION: A laryngeal mask cuff pressure of 20 cmH2O may reduce the risk of gastric insufflation during mechanical ventilation. Surprisingly, peak airway pressure of 20 cmH2O or less may already induce significant gastric insufflation. Continuous positive airway pressure should be avoided due to an increased risk of gastric insufflation. CLINICAL TRIAL REGISTRATION: The study was registered in the German Clinical Trials Register (DRKS00010583) https://www.drks.de.

Low-pressure monopolar electroresection of the prostate for glands sized > 70 vs. < 70 cc performed with continuous irrigation and suprapubic suction: perioperative and long-term outcome.

PURPOSE: To evaluate long-term efficacy and safety of low-pressure transurethral resection of the prostate for prostates < 70 cc (group 1) vs. > 70 cc (group 2). PATIENTS AND METHODS: In this study patients operated with monopolar TURP between 2009 and 2012 were evaluated retrospectively. During surgery a specially designed trocar (18 Fr) was placed suprapubically and connected to a suction pump to maintain stable low-pressure conditions. After sample size calculations, long-term follow-up was completed for 70 invited patients in each group up to 9/2015. RESULTS: Follow-up period was 57 vs. 56 months for group 1 and 2, respectively (p = 0.56). At baseline there was no significant difference in age, IPSS, peak flow, and post void residual (PVR). Mean prostate volume was 47 cc (15-65) vs. 100 cc (70-163). Mean operating time was 55.4 vs. 82.6 min (p = 0.00). Blood transfusion was necessary in 0.0 vs. 2.9% (p = 0.16), and 0.0 vs. 1.4% developed TUR syndrome (p = 0.32). At follow-up mean relative improvement in IPSS was 63 vs. 57% (p = 0.29), QoL 64 vs. 64% (p = 0.93), peak flow 139 vs. 130% (p = 0.85), and PVR 58 vs. 63% (p = 0.80). Long-term complications included recurring adenoma in 1.4 vs. 4.3% (p = 0.31), and stricture in 7.2 vs. 5.8% (p = 0.73). 1 patient in each group reported worsening incontinence symptoms. CONCLUSIONS: In terms of safety and efficacy, the aforementioned modality of standardized monopolar TURP using suprapubic suction was non-inferior for prostates > 70 cc compared to the same procedure for prostates < 70 cc. This technique is a potential low-cost alternative for clinics that cannot afford modern laser approaches. STUDY REGISTER NUMBER: DRKS00006527.

Pressure-flow characteristics of breathing systems and their components for pediatric and adult patients.

BACKGROUND: Breathing circuits connect the ventilator to the patients' respiratory system. Breathing tubes, connectors, and sensors contribute to artificial airway resistance to a varying extent. We hypothesized that the flow-dependent resistance is higher in pediatric breathing systems and their components compared to respective types for adults. AIMS: We aimed to characterize the resistance of representative breathing systems and their components used in pediatric patients (including devices for adults) by their nonlinear pressure-flow relationship. METHODS: We used a physical model to measure the flow-dependent pressure gradient (∆P) across breathing tubes, breathing tube extensions, 90°- and Y-connectors, flow- and carbon dioxide sensors, water traps and reusable, disposable and coaxial breathing systems for pediatric and for adult patients. ∆P was analyzed for usual flow ranges and statistically compared at a representative flow rate of 300 mL∙s-1 (∆P300 ). RESULTS: ∆P across pediatric devices always exceeded ∆P across the corresponding devices for adult patients (all P < .001 [no 95% CI includes 0]). ∆P300 across breathing system components for adults was always below 0.2 cmH2 O but reached up to 4.6 cmH2 O in a flow sensor for pediatric patients. ∆P300 was considerably higher across the reusable compared to the disposable pediatric breathing systems (1.9 vs 0.3 cmH2 O, P < .001, [95% CI -1.59 to -1.56]). CONCLUSION: The resistances of pediatric breathing systems and their components result in pressure gradients exceeding those for adults several fold. Considering the resistance of individual components is crucial for composing a breathing system matching the patient's needs. Compensation of the additional resistance should be considered if a large composed resistance is unavoidable.

[Airway Management in Thoracic Anesthesia with Double-Lumen Tube]. / Atemwegsmanagement in der Thoraxanästhesie mit dem Doppellumentubus.

Lung separation and isolation with accomplished one-lung ventilation plays a key role in the airway management for thoracic surgery. Spectrum of indication contains thoracic surgery, procedure- and patient-dependent factors. Usually lung isolation is achieved with a double-lumen tube or a bronchial blocker. Knowledge in tracheobronchial anatomy is routinely requested for anesthesiologists just as the standard use of flexible fibreoptic bronchoscope. This review would give an overview and discussion about the airway management in patients during thoracic anesthesia with double-lumen tubes and recommendations for the clinical routine.

Pneumoperitoneum deteriorates intratidal respiratory system mechanics: an observational study in lung-healthy patients.

BACKGROUND: Pneumoperitoneum during laparoscopic surgery leads to atelectasis and impairment of oxygenation. Positive end-expiratory pressure (PEEP) is supposed to counteract atelectasis. We hypothesized that the derecruiting effects of pneumoperitoneum would deteriorate the intratidal compliance profile in patients undergoing laparoscopic surgery. METHODS: In 30 adult patients scheduled for surgery with pneumoperitoneum, respiratory variables were measured during mechanical ventilation. We calculated the dynamic compliance of the respiratory system (C RS) and the intratidal volume-dependent C RS curve using the gliding-SLICE method. The C RS curve was then classified in terms of indicating intratidal recruitment/derecruitment (increasing profile) and overdistension (decreasing profile). During the surgical interventions, the PEEP level was maintained nearly constant at 7 cm H2O. Data are expressed as mean [confidence interval]. RESULTS: Baseline C RS was 60 [54-67] mL cm H2O-1. Application of pneumoperitoneum decreased C RS to 40 [37-43] mL cm H2O-1 which partially recovered to 54 [50-59] mL cm H2O-1 (P < 0.001) after removal but remained below the value measured before pneumoperitoneum (P < 0.001). Baseline compliance profiles indicated intratidal recruitment/derecruitment in 48 % patients. After induction of pneumoperitoneum, intratidal recruitment/derecruitment was indicated in 93 % patients (P < 0.01), and after removal intratidal recruitment/derecruitment was indicated in 59 % patients. Compliance profiles showing overdistension were not observed. CONCLUSIONS: Analyses of the intratidal compliance profiles reveal that pneumoperitoneum during laparoscopic surgery causes intratidal recruitment/derecruitment which partly persists after its removal. The analysis of the intratidal volume-dependent C RS profiles could be used to guide intraoperative PEEP adjustments during elevated intraabdominal pressure.

Application of the Novel Ventilation Mode FLow-Controlled EXpiration (FLEX): A Crossover Proof-of-Principle Study in Lung-Healthy Patients.

BACKGROUND: Traditionally, mechanical ventilation is achieved via active lung inflation during inspiration and passive lung emptying during expiration. By contrast, the novel FLEX (FLow-controlled EXpiration) ventilator mode actively decreases the rate of lung emptying. We investigated whether FLEX can be used during intraoperative mechanical ventilation of lung-healthy patients. METHODS: In 30 adult patients scheduled for neurosurgical procedures, we studied respiratory system mechanics, regional ventilation, oxygenation, and hemodynamics during ventilation with and without FLEX at positive end-expiratory pressure (PEEP) of 5 and 7 cm H2O. The FLEX system was integrated into the expiratory limb and modified the expiratory flow profile by continuously changing expiratory resistance according to a computer-controlled algorithm. RESULTS: Mean airway pressure increased with PEEP by 1.9 cm H2O and with FLEX by 1 cm H2O (all P < .001). The expiratory peak flow was 42% lower with FLEX than without FLEX (P < .001). FLEX caused significant shifts in aeration from ventral to the dorsal lung regions. Respiratory mechanics, end-tidal carbon dioxide partial pressure, oxygenation, and hemodynamics were independent from FLEX and PEEP. We observed no critical incidents or FLEX malfunctions in any measurement that would have required an intervention or termination of the FLEX mode. CONCLUSIONS: FLEX can be used in lung-healthy patients who are mechanically ventilated during general anesthesia. FLEX improves the homogeneous distribution of ventilation in the lungs.

Characteristics of Double-Lumen Tubes Determine Bronchial Airway Pressure.

OBJECTIVES: To determine pressure-flow characteristics of double-lumen tubes (DLTs) with an outer diameter of 26 to 41 French and calculate bronchial pressure in a model setup and using data from patients who underwent one-lung ventilation with a DLT. DESIGN: Prospective experimental study and retrospective analysis of clinical measurements. SETTING: University medical center. PARTICIPANTS: Lung model and patients. INTERVENTIONS: Flow rates and pressure gradients across Robertshaw-type DLTs (∆P(DLT)) were measured in a physical model and the DLT-specific resistance coefficients were calculated from ∆P(DLT) according to Rohrer's approach. Bronchial pressure was calculated from airway pressure and ∆P(DLT) in a lung model and using data from 72 patients who underwent thoracic surgery and direct bronchial pressure measurements. MEASUREMENTS AND MAIN RESULTS: ∆P(DLT) increased with decreasing outer diameter of the DLT and more than doubled during one- compared with two-lung ventilation (p<0.001). ∆P(DLT) differed between inspiration and expiration (p<0.05) and was higher across the tracheal lumen compared with the bronchial lumen (p<0.001). Root mean square differences between calculated and measured bronchial pressures were less than 0.7 cmH2O in the lung model and less than 1.2 cmH2O in the clinical measurements. CONCLUSIONS: The DLTs' pressure-flow characteristics differed considerably depending on size, mode of ventilation (one or two lung), direction of flow, and lumen for ventilation. Rohrer's approach allowed for sufficient calculation of the bronchial airway pressure during both one- and two-lung ventilation.

The pressure drop across the endotracheal tube in mechanically ventilated pediatric patients.

BACKGROUND: During mechanical ventilation, the airway pressure (Paw) is usually monitored. However, Paw comprises the endotracheal tube (ETT)-related pressure drop (∆PETT ) and thus does not reflect the pressure in the patients' lungs. Therefore, monitoring of mechanical ventilation should be based on the tracheal pressure (Ptrach ). We systematically investigated potential factors influencing ∆PETT in pediatric ETTs. METHODS: In this study, the flow-dependent pressure drop across pediatric ETTs from four manufacturers [2.0-4.5 mm inner diameter (ID)] was estimated in a physical model of the upper airways. Additionally, ∆PETT was examined with the ETTs shortened to 75% of their original length and at different curvatures. In nine healthy mechanically ventilated children (aged between 9 days and 29 months), Ptrach was compared to Paw . RESULTS: ∆PETT was nonlinearly flow dependent. Low IDs corresponded to high ∆PETT . Differences between ETTs from different manufacturers were identified. Shortening of the ETTs' length by 25% reduced ∆PETT on average by 14% of the value at original length. Ventilation frequency and tube curvature did not influence ∆PETT to a relevant extent. In the pediatric patients, the root mean square deviation between Paw and Ptrach was 2.3 cm H2O. CONCLUSION: Paw and Ptrach differ considerably (by ∆PETT ) during mechanical ventilation of pediatric patients. The ETTs' ID, tube length, and manufacturer type are significant factors for ∆PETT and should be taken into account when Paw is valuated. For this purpose, Ptrach can be continuously calculated with good precision by means of the Rohrer approximation.

Effective volume of rebreathed air during breathing with facepieces increases with protection class and decreases with ambient airflow.

Wearing facepieces is discussed in the context of increasing the volume of rebreathed air. We hypothesized that rebreathed air volume increases with increasing filtering facepiece (FFP) class and that persons breathing via facepieces compensate for the additional dead-space. We have determined the effective amount of rebreathed air for a surgical masks and FFP2 and FFP3 respirators in a physical model and determined tidal volumes, breathing frequency, blood oxygen saturation, and transcutaneously measured blood carbon dioxide partial pressure (PCO2) in lung-healthy subjects breathing without and with facepieces at rest and during exercising on a recumbent ergometer. Rebreathed air volume increased with the facepieces' protection class and with increasing inspiration volume by 45 ± 2 ml to 247 ± 1 ml. Ambient airflow reduced rebreathed air volume by 17% up to 100% (all p < 0.001). When wearing facepieces, subjects increased tidal volume (p < 0.001) but not breathing frequency. Oxygen saturation was not influenced by facepieces. With FFP3 respirators PCO2 increased by up to 3.2 mmHg (p < 0.001) at rest but only up to 1.4 mmHg (p < 0.001) when exercising. Discomfort of breathing increased with increasing protection class of the facepiece but was consistently perceived as tolerable. We conclude that the amount of rebreathed air increases with increasing protection class of facepieces. Healthy adults were capable to compensate the facepieces' dead-space by adapting tidal volume at rest and during physical activity; thereby they tolerated moderate increases in PCO2. Ambient airflow may considerably reduce the amount of facepiece related rebreathed air.

Comparative usability of manual defibrillators - A human factors study.

Background: A manual defibrillator represents key equipment for resuscitation of cardiac arrest scenario. Improper or slow operation of a defibrillator may adversely affect acute care. A self-explanatory interface facilitates handling and decreases the risk of operating errors. Therefore, we evaluated the usability of four commercially available defibrillators. Methods: 31 medical students executed 15 consecutive tasks on each defibrillator (Physio-Control Lifepak 20e, Schiller Defigard Touch 7, Corpuls 3 and Zoll X-Series). The operators' gaze was measured via eye-tracking and frequencies of required assistances and task completion times were recorded. Additionally, subjective perception of usability was assessed by a standardized questionnaire. Results: Least assistances (16) were required when operating the Lifepak 20e and most (63) when operating the X-Series. Cumulative task completion times were shortest in the Lifepak 20e (124 ± 31 s), followed by the Corpuls 3 (220 ± 69 s), the Defigard Touch 7 (225 ± 81 s) and the X-Series (289 ± 85 s; p < 0.001). Completion times of specific tasks differed considerably between the devices. Eye-tracking revealed associated interface issues that impeded the operators' performance. Overall standardized usability was rated best for the Lifepak 20e (81 ± 15) and worst for the X-Series (44 ± 20). Conclusions: The usability of defibrillators differs considerably and task specifically between devices. Interface issues of tasks impaired the operators' efficiency specifically. The perceived usability and the perceived stress-level after operating the devices corresponded with objective measures of usability. Eliminating specific usability issues may improve the operator's performance and, as a consequence patient outcome.

Calculating intrinsic positive end-expiratory pressure from end-expiratory flow in mechanically ventilated children-A study in physical models of the pediatric respiratory system.

RATIONALE: The high resistance of pediatric endotracheal tubes (ETTs) exposes mechanically ventilated children to a particular risk of developing intrinsic positive end-expiratory pressure (iPEEP). To date, determining iPEEP at the bedside requires the execution of special maneuvers, interruption of ventilation, or additional invasive measurements. Outside such interventions, iPEEP may be unrecognized. OBJECTIVE: To develop a new approach for continuous calculation of iPEEP based on routinely measured end-expiratory flow and ETT resistance. METHODS: First, the resistance of pediatric ETTs with inner diameter from 2.0 to 4.5 mm were empirically determined. Second, during simulated ventilation, iPEEP was either calculated from the measured end-expiratory flow and ETT's resistance (iPEEPcalc ) or determined with a hold-maneuver available at the ventilator (iPEEPhold ). Both estimates were compared with the end-expiratory pressure measured at the ETT's tip (iPEEPdirect ) by means of absolute deviations. RESULTS: End-expiratory flow and iPEEP increased with decreasing ETT inner diameter and with higher respiratory rates. iPEEPcalc and iPEEPhold were comparable and indicated good correspondence with iPEEPdirect . The largest absolute mean deviation was 1.0 cm H2 O for iPEEPcalc and 1.1 cm H2 O for iPEEPhold . CONCLUSION: We conclude that iPEEP can be determined from routinely measured variables and predetermined ETT resistance, which has to be confirmed in the clinical settings. As long as this algorithm is not available in pediatric ICU ventilators, nomograms are provided for estimating the prevailing iPEEP from end-expiratory flow.

Comparison of Force Distribution during Laryngoscopy with the C-MAC D-BLADE and Macintosh-Style Blades: A Randomised Controlled Clinical Trial.

Background: The geometry of a laryngoscope's blade determines the forces acting on the pharyngeal structures to a relevant degree. Knowledge about the force distribution along the blade may prospectively allow for the development of less traumatic blades. Therefore, we examined the forces along the blades experienced during laryngoscopy with the C-MAC D-BLADE and blades of the Macintosh style. We hypothesised that lower peak forces are applied to the patient's pharyngeal tissue during videolaryngoscopy with a C-MAC D-BLADE compared to videolaryngoscopy with a C-MAC Macintosh-style blade and direct laryngoscopy with a Macintosh-style blade. Beyond that, we assumed that the distribution of forces along the blade differs depending on the respective blade's geometry. Methods: After ethical approval, videolaryngoscopy with the D-BLADE or the Macintosh blade, or direct laryngoscopy with the Macintosh blade (all KARL STORZ, Tuttlingen, Germany), was performed on 164 randomly assigned patients. Forces were measured at six positions along each blade and compared with regard to mean force, peak force and spatial distribution. Furthermore, the duration of the laryngoscopy was measured. Results: Mean forces (all p < 0.011) and peak forces at each sensor position (all p < 0.019) were the lowest with the D-BLADE, whereas there were no differences between videolaryngoscopy and direct laryngoscopy with the Macintosh blades (all p > 0.128). With the D-BLADE, the forces were highest at the blade's tip. In contrast, the forces were more evenly distributed along the Macintosh blades. Videolaryngoscopy took the longest with the D-BLADE (p = 0.007). Conclusions: Laryngoscopy with the D-BLADE resulted in significantly lower forces acting on pharyngeal and laryngeal tissue compared to Macintosh-style blades. Interestingly, with the Macintosh blades, we found no advantage for videolaryngoscopy in terms of force application.

Establishment and validation of intravenous anesthesia with dexmedetomidine for pigs under assisted spontaneous breathing: A preclinical model of intensive care conditions.

Large animal models are frequently used to investigate new medical approaches. In most cases, animals are kept under general anesthesia and mandatory mechanical ventilation during the experiments. However, in some situations assisted spontaneous breathing is essential, e.g. when simulating conditions in a modern intensive care unit. Therefore, we established an anesthesia regime with dexmedetomidine and midazolam/ketamine in porcine models of assisted spontaneous breathing. The total intravenous anesthesia was used in lung healthy pigs, in pigs with oleic acid induced acute respiratory distress syndrome and in pigs with methacholine induced bronchopulmonary obstruction. We were able to maintain stable conditions of assisted spontaneous breathing without impairment of hemodynamic, respiratory or blood gas variables in lung healthy pigs and pigs with induced acute respiratory distress syndrome for a period of five hours and in pigs with induced bronchopulmonary obstruction for three hours. Total intravenous anesthesia containing dexmedetomidine enables stable conditions of assisted spontaneous breathing in healthy pigs, in pigs with induced acute respiratory distress syndrome and in pigs induced bronchopulmonary obstruction as models of intensive care unit conditions.

Comprehensive evaluation of manikin-based airway training with second generation supraglottic airway devices.

BACKGROUND: Supraglottic airway devices (SADs) are an essential second line tool during difficult airway management after failed tracheal intubation. Particularly for such challenging situations the handling of an SAD requires sufficient training. We hypothesized that the feasibility of manikin-based airway management with second generation SADs depends on the type of manikin. METHODS: Two airway manikins (TruCorp AirSim® and Laerdal Resusci Anne® Airway Trainer™) were evaluated by 80 experienced anesthesia providers using 5 different second generation SADs (LMA® Supreme™ [LMA], Ambu® AuraGain™, i-gel®, KOO™-SGA and LTS-D™). The primary outcome of the study was feasibility of ventilation measured by assessment of the manikins' lung distention. As secondary outcome measures, oropharyngeal leakage pressure (OLP), ease of gastric tube insertion the insertion time, position and subjective assessments were evaluated. RESULTS: Ventilation was feasible with all combinations of SAD and manikin. By contrast, an OLP exceeding 10 cm H2O could be reached with most of the SADs in the TruCorp but with the LTS-D only in the Laerdal manikin. Gastric tube insertion was successful in above 90% in the Laerdal vs 87% in the TruCorp manikin (P<0.009). Insertion times differed significantly between manikins. The SAD positions were better in the Laerdal manikin for LMA, Ambu, i-gel and LTS-D. Participant's assessments were superior in the Laerdal manikin for LMA, Ambu, i-gel and KOO-SGA. CONCLUSIONS: Ventilation is possible with all combinations. However, manikins are variable in their ability to adequately represent additional functions of second generation SADs. In order to achieve the best performance during training, the airway manikin should be chosen depending on the SAD in question.

Coaxial Tubing Systems Increase Artificial Airway Resistance and Work of Breathing.

BACKGROUND: Tubing systems are an essential component of the ventilation circuit, connecting the ventilator to the patient's airways. Coaxial tubing systems incorporate the inspiratory tube within the lumen of the expiratory one. We hypothesized that by design, these tubing systems increase resistance to air flow compared with conventional ones. METHODS: We investigated the flow-dependent pressure gradient across coaxial, conventional disposable, and conventional reusable tubing systems from 3 different manufacturers. Additionally, the additional work of breathing and perception of resistance during breathing through the different devices were determined in 18 healthy volunteers. RESULTS: The pressure gradient across coaxial tubing systems was up to 6 times higher compared with conventional ones (1.90 ± 0.03 cm H2O vs 0.34 ± 0.01 cm H2O, P < .001) and was higher during expiration compared with inspiration (P < .001). Additional work of breathing and perceived breathing resistance were highest in coaxial tubing systems, accordingly. CONCLUSIONS: Our findings suggest that the use of coaxial tubing systems should be carefully considered with respect to their increased resistance.