We used dynamic CT to identify two different time constants of lung aeration and their individual contribution to the total increase in cross-sectional lung area in healthy and experimentally damaged lungs. In five healthy pigs, inflation and deflation between 0 and 50 cm H2O was imposed during dynamic (250 ms/image) CT acquisition, and repeated after experimental lung injury by saline lavage. The fractional areas of density ranges, which represent aerated lung parenchyma, were determined planimetrically, and their time for expansion during the manoeuvre was fitted using a bi-exponential model. Thus, two compartments, their sizes, i.e. their relative contributions to lung area aerated by the manoeuvre, and their specific time constants (tau) were sought. Healthy lungs were characterized best by a one-compartmental behaviour with one tau only, both during inflation (median tau=0.5 s; range 0.4-0.6 s) and deflation (1.2 s; 1.1-1.3 s). In damaged lungs two compartments were found both during inspiration and expiration, with 86% (78-87%) of the recruitable lung area following a short tau of 0.5 s (0.5-0.6), and 14% (13-22%) following a longer tau of 9.1 s (8-16.8 s) during inflation. During expiration, damaged lungs had a short tau of 0.8 s (0.5-1.0 s) for 94% (84-100%) of deflated lung area, and a longer tau of 26.5 s (7.1-34.3 s) for 6% (0-16%). We conclude that dynamic CT indicates the relative size and temporal behaviour of functional compartments in normal and abnormal lungs. Our findings suggest that after lung damage, cyclic ventilation with inspiratory periods of <10 s duration will not achieve maximum recruitment for a chosen inspiratory pressure. In ARDS, the short expiratory tau predisposes to atelectasis formation if expiratory times are >1 s.
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 H2O, or 3) limitation of further increase in tidal volume by air leakage. The following variables were determined:inspired volume (VI), 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 H2O. Air leakage of more than 10% was evident at inspiratory pressures between 25 and 34 cm H2O. The end point of 40 cm H2O 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.
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.
This is the first study assessing severe incidents and complications from a national outcome-tracking database. Annual identification and review of cases, perhaps with standardized database queries in the respective departments, might provide more detailed information about the cascades that lead to unfortunate outcomes.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.