Thenar oxygen saturation (StO2) alterations during a spontaneous breathing trial predict extubation failure.

BACKGROUND: Weaning from mechanical ventilation (MV) is a cardiovascular stress test. Monitoring the regional oxygenation status has shown promising results in predicting the tolerance to spontaneously breathe in the process of weaning from MV. Our aim was to determine whether changes in skeletal muscle oxygen saturation (StO2) measured by near-infrared spectroscopy (NIRS) on the thenar eminence during a vascular occlusion test (VOT) can be used to predict extubation failure from mechanical ventilation. METHODS: We prospectively studied 206 adult patients with acute respiratory failure receiving MV for at least 48 h from a 30-bed mixed ICU, who were deemed ready to wean by their physicians. Patients underwent a 30-min spontaneous breathing trial (SBT), and were extubated according to the local protocol. Continuous StO2 was measured non-invasively on the thenar eminence. A VOT was performed prior to and at 30 min of the SBT (SBT30). The rate of StO2 deoxygenation (DeO2), StO2 reoxygenation (ReO2) rate and StO2 hyperemic response to ischemia (HAUC) were calculated. RESULTS: Thirty-six of the 206 patients (17%) failed their SBT. The remainder 170 patients (83%) were extubated. Twenty-three of these patients (13.5%) needed reinstitution of MV within 24 h. Reintubated patients displayed a lower HAUC at baseline, and higher relative changes in their StO2 deoxygenation rate between baseline and SBT30 (DeO2 Ratio). A logistic regression-derived StO2 score, combining baseline StO2, HAUC and DeO2 ratio, showed an AUC of 0.84 (95% CI 0.74-0.91) for prediction of extubation failure. CONCLUSIONS: Extubation failure was associated to baseline and dynamic StO2 alterations during the SBT. Monitoring StO2-derived parameters might be useful in predicting extubation outcome.

SARS-CoV-2 in Spanish Intensive Care Units: Early experience with 15-day survival in Vitoria.

PURPOSE: Community transmission of SARS-CoV-2 was detected in Spain in February 2020, with 216% intensive care unit (ICU) capacity expanded in Vitoria by March 18th, 2020. METHODS: We identified patients from the two public hospitals in Vitoria who were admitted to ICU with confirmed infection by SARS-CoV-2. Data reported here were available in April 6th, 2020. Mortality was assessed in those who completed 15-days of ICU stay. RESULTS: We identified 48 patients (27 males) with confirmed SARS-CoV-2. Median [interquartile range (IQR)] age of patients was 63 [51-75] years. Symptoms began a median of 7 [5-12] days before ICU admission. The most common comorbidities identified were obesity (48%), arterial hypertension (44%) and chronic lung disease (37%). All patients were admitted by hypoxemic respiratory failure and none received non-invasive mechanical ventilation. Forty-five (94%) underwent intubation, 3 (6%) high flow nasal therapy (HFNT), 1 (2%) extracorporeal membrane oxygenation (ECMO) and 22 (46%) required prone position. After 15 days, 14/45 (31%) intubated patients died (13% within one week), 10/45 (22%) were extubated, and 21/45 (47%) underwent mechanical ventilation. Six patients had documented super-infection. Procalcitonin plasma above 0.5µg/L was associated with 16% vs. 19% (p=0.78) risk of death after 7 days. CONCLUSION: This early experience with SARS-CoV-2 in Spain suggests that a strategy of right oxygenation avoiding non-invasive mechanical ventilation was life-saving. Seven-day mortality in SARS-CoV-2 requiring intubation was lower than 15%, with 80% of patients still requiring mechanical ventilation. After 15 days of ICU admission, half of patients remained intubated, whereas one third died.

Asynchronies during mechanical ventilation are associated with mortality.

PURPOSE: This study aimed to assess the prevalence and time course of asynchronies during mechanical ventilation (MV). METHODS: Prospective, noninterventional observational study of 50 patients admitted to intensive care unit (ICU) beds equipped with Better Care™ software throughout MV. The software distinguished ventilatory modes and detected ineffective inspiratory efforts during expiration (IEE), double-triggering, aborted inspirations, and short and prolonged cycling to compute the asynchrony index (AI) for each hour. We analyzed 7,027 h of MV comprising 8,731,981 breaths. RESULTS: Asynchronies were detected in all patients and in all ventilator modes. The median AI was 3.41 % [IQR 1.95-5.77]; the most common asynchrony overall and in each mode was IEE [2.38 % (IQR 1.36-3.61)]. Asynchronies were less frequent from 12 pm to 6 am [1.69 % (IQR 0.47-4.78)]. In the hours where more than 90 % of breaths were machine-triggered, the median AI decreased, but asynchronies were still present. When we compared patients with AI > 10 vs AI ≤ 10 %, we found similar reintubation and tracheostomy rates but higher ICU and hospital mortality and a trend toward longer duration of MV in patients with an AI above the cutoff. CONCLUSIONS: Asynchronies are common throughout MV, occurring in all MV modes, and more frequently during the daytime. Further studies should determine whether asynchronies are a marker for or a cause of mortality.

Spermatogenesis in Leptodactylus chaquensis. Histological study.

The organization and the histological characteristics of Leptodactylus chaquensis testis throughout the reproductive cycle were analyzed in the presented study. Gonads of adult males, processed with routine techniques for optical microscopy, revealed that during the reproductive period the seminiferous tubules were characterized by presentation of a large number of cysts, germ cells at the same maturation stage supported by Sertoli cells. All the germ line cells were also present in the postreproductive period and maintained their morphological characteristics. Primary spermatogonia were large-sized cells found isolated or in small groups. The rest of the cells of the germ line formed cysts. Secondary spermatogonia showed morphological characteristics similar to their predecessors, although they were smaller. Primary and secondary spermatocytes showed images of the different stages of the first and second meiotic division respectively. One finding was the presence of intercytoplasmic bridges between the secondary spermatocytes. Primary spermatids were rounded cells with an acrosomal vesicle associated with the nucleus and had cysts that were characterized by large intercellular spaces. Secondary spermatids were elongated cells with a well defined acrosome, which in the spermatozoa had the shape of an arrowhead. Another peculiar characteristic of this species was the fusion of the walls of the seminiferous tubule with the efferent duct that formed a path for spermatozoa during spermiation. The presence in the seminiferous tubules of all stages of the spermatogenic line during the two periods of the cycle studied indicated that Leptodactylus chaquensis had a potentially continuous reproductive cycle.

Structural analysis of toad oviductal mucosa in relation to jelly components secretion throughout the reproductive cycle.

In amphibians, the components of the jelly coats that surround the oocytes at the time of fertilization and coordinate gamete interaction are secreted by the oviduct. We analysed the histological variations in the mucosa of the oviductal pars convoluta (PC) of Rhinella arenarum during the reproductive cycle and its relationship with secretion. During the preovulatory period, the mucosa reaches a high degree of morphological and functional development, with a large number of epithelial (ESC) and glandular secretory cells (GSC) loaded with contents that are secreted into the oviductal lumen. During the ovulatory period, the secretory cells (SC) of both layers present maximum secretory activity through apocrinia and merocrinia. While the ESC located at the tips of the folds release their content directly in contact with the oocytes, the GSC secrete material from the bottom of the epithelial folds that, by interaction with the secretion of the ESC in the lateral faces, form a product with a certain degree of organization. Secretion is a continuous process with formation of coats of increasing complexity from the intermediate proximal zone (IPZ) to the pars convoluta (pc) itself, and the passage of the oocyte is a requisite for the organization of the jelly coats around the gamete. During the early postovulatory period, although there is a marked decrease in the number and volume of the SC, the ESC still release material into the oviductal lumen. In the late postovulatory period the morphological characteristics of the PC begin to recovery although there is no evidence of secretion.

Thenar oxygen saturation during weaning from mechanical ventilation: an observational study.

Our aim was to determine whether thenar tissue oxygen saturation (S(tO2)), measured by noninvasive near-infrared spectroscopy, and its changes derived from an ischaemic challenge are associated with weaning outcome. Our study comprised a prospective observational study in a 26-bed medical-surgical intensive care unit. Patients receiving mechanical ventilation for >48 h, and considered ready to wean by their physicians underwent a 30-min weaning trial. S(tO2) was measured continuously on the thenar eminence. A transient vascular occlusion test was performed prior to and at the end of the 30-min weaning trial, in order to obtain S(tO2) deoxygenation and reoxygenation rates, and estimated local oxygen consumption. 37 patients were studied. Patients were classified as weaning success (n=24) or weaning failure (n=13). No significant demographic, respiratory or haemodynamic differences were observed between the groups at inclusion. Patients who failed the overall weaning process showed a significant increase in deoxygenation and in local oxygen consumption from baseline to 30 min of weaning trial, whereas no significant changes were observed in the weaning success group. Failure to wean from mechanical ventilation was associated with higher relative increases in deoxygenation after 30 min of spontaneous ventilation.

Assessment of the inflammatory effect of low-dose oxygen in mechanically ventilated patients.

PURPOSE: Although low doses of oxygen (FiO2 <0.50) are considered nontoxic, recent studies have shown that even lower doses increase pulmonary inflammatory mediators. We aimed to evaluate the acute effects of reducing FiO2 on pulmonary inflammation in mechanically ventilated patients without respiratory failure. METHODS: This study was a prospective, single-center crossover study in a medical/surgical intensive care unit at a university hospital. Hemodynamically stable patients under mechanical ventilation for >24 h without severe respiratory failure (PaO2/FiO2 >250). A basal FiO2 of 0.40 was reduced to 0.21 provided SpO2 remained higher than 90 %. Patients who could not tolerate the reduction in FiO2 to 0.21 were excluded. RESULTS: We screened 40 patients, but only 28 (70 %) tolerated FiO2 0.21. We measured common clinical variables and inflammatory mediators in plasma and in exhaled breath condensate (EBC) at the end of three 4-h periods: (1) basal (FiO2 0.40), (2) after FiO2 reduction to 0.21, and (3) after returning FiO2 0.40. We used one-way ANOVA for repeated measurements with FiO2 as the grouping variable. Median values of inflammatory mediators in EBC showed nonsignificant changes among the three periods: NO2 + NO3 17.1, 14.1 and 11.0 µmol/L (p = 0.2), and 8-isoprostane 4.4, 8.2 and 5.3 pg/ml (p = 0.6) for the three periods, respectively. Plasma levels also showed nonsignificant changes during the period of the study: NO2 + NO3 12.6, 16.3 and 15.0 µmol/L (p = 0.9), TNFα 13.5, 18.0 and 14.5 pg/ml (p = 0.8), IL-4 12.9, 18.7 and 23.9 pg/ml (p = 0.1), IL-6 50.9, 35.1 and 28.3 pg/ml (p = 0.6), and IL-10 15.2, 22.2 and 22.2 pg/ml (p = 0.7) for the three periods, respectively. CONCLUSION: FiO2 0.40 in mechanically ventilated patients without severe respiratory failure did not increase systemic or pulmonary inflammation.

Histopathological and biological studies of the effect of cadmium on Rhinella arenarum gonads.

This study was to determine the lethal dose 50 (LD(50)) of CdCl(2) in adult Rhinella arenarum and analyzed the effect of two sublethal doses (0.5 and 5 mg/kg) of the xenobiotic in gonads. The 48 h LD(50) were 50.0 and 49.8 mg/kg for males and females respectively. Alterations in the ovary were evidenced by nuclear pleomorphism and cytoplasmic vacuolization of the oocytes at the early stages of development with the highest dose and an increase in the population of atretic oocytes. In the interstitial tissue we noticed congestion, edema and fibroblast proliferation. The nuclear maturation of the oocytes was affected by the xenobiotic in a dose- and time-dependent manner. In males, treatment with 5 mg/kg of cadmium (Cd) caused a decrease in the concentration, viability and straight progressive motility of sperm while there was an increase in immotile sperm. Testis histopathology revealed dilated seminiferous tubules, disappearance of cysts, tissue disorganization and leukocyte infiltration. Numerous germ cells showed hydropic tumefaction or signs of focal necrosis. The Cd content in animals intoxicated gonads with the highest sublethal dose was significantly higher than in the control. Results indicate that R. arenarum gonads are target for the xenobiotic, compromising the formation of gametes competent for fertilization, the effective CdCl(2) dose being 5 mg/kg.

Nurses' detection of ineffective inspiratory efforts during mechanical ventilation.

UNLABELLED: BACKGROUND PATIENT: ventilator dyssynchrony is common and may influence patients' outcomes. Detection of such dyssynchronies relies on careful observation of patients and airway flow and pressure measurements. Given the shortage of specialists, critical care nurses could be trained to identify dyssynchronies. OBJECTIVE: To evaluate the accuracy of specifically trained critical care nurses in detecting ineffective inspiratory efforts during expiration. METHODS: We compared 2 nurses' evaluations of measurements from 1007 breaths in 8 patients with the evaluations of experienced critical care physicians. Sensitivity, specificity, positive predictive value, negative predictive value, and the Cohen κ for interobserver agreement were calculated. RESULTS: For the first nurse, sensitivity was 92.5%, specificity was 98.3%, positive predictive value was 95.4%, negative predictive value was 97.1%, and κ was 0.92 (95% CI, 0.89-0.94). For the second nurse, sensitivity was 98.5%, specificity was 84.7%, positive predictive value was 70.7%, negative predictive value was 99.3%, and κ was 0.74 (95% CI, 0.70-0.78). CONCLUSION: Specifically trained nurses can reliably detect ineffective inspiratory efforts during expiration.

Validation of the Better Care® system to detect ineffective efforts during expiration in mechanically ventilated patients: a pilot study.

PURPOSE: Ineffective respiratory efforts during expiration (IEE) are a problem during mechanical ventilation (MV). The goal of this study is to validate mathematical algorithms that automatically detect IEE in a computerized (Better Care®) system that obtains and processes data from intensive care unit (ICU) ventilators in real time. METHODS: The Better Care® system, integrated with ICU health information systems, synchronizes and processes data from bedside technology. Algorithms were developed to analyze airflow waveforms during expiration to determine IEE. Data from 2,608,800 breaths from eight patients were recorded. From these breaths 1,024 were randomly selected. Five experts independently analyzed the selected breaths and classified them as IEE or not IEE. Better Care® evaluated the same 1,024 breaths and assigned a score to each one. The IEE score cutoff point was determined based on the experts' analysis. The IEE algorithm was subsequently validated using the electrical activity of the diaphragm (EAdi) signal to analyze 9,600 breaths in eight additional patients. RESULTS: Optimal sensitivity and specificity were achieved by setting the cutoff point for IEE by Better Care® at 42%. A score >42% was classified as an IEE with 91.5% sensitivity, 91.7% specificity, 80.3% positive predictive value (PPV), 96.7% negative predictive value (NPV), and 79.7% Kappa index [confidence interval (CI) (95%) = (75.6%; 83.8%)]. Compared with the EAdi, the IEE algorithm had 65.2% sensitivity, 99.3% specificity, 90.8% PPV, 96.5% NPV, and 73.9% Kappa index [CI (95%) = (71.3%; 76.3%)]. CONCLUSIONS: In this pilot, Better Care® classified breaths as IEE in close agreement with experts and the EAdi signal.

Effects of vascular flow and PEEP in a multiple hit model of lung injury in isolated perfused rabbit lungs.

BACKGROUND: High vascular flow aggravates lung damage in animal models of ventilator-induced lung injury. Positive end-expiratory pressure (PEEP) can attenuate ventilator-induced lung injury, but its continued effectiveness in the setting of antecedent lung injury is unclear. The objective of the present study was to evaluate whether the application of PEEP diminishes lung injury induced by concurrent high vascular flow and high alveolar pressures in normal lungs and in a preinjury lung model. METHODS: Two series of experiments were performed. Fifteen sets of isolated rabbit lungs were randomized into three groups (n = 5): low vascular flow/low PEEP; high vascular flow/low PEEP, and high vascular flow/high PEEP. Subsequently, the same protocol was applied in an additional 15 sets of isolated rabbit lungs in which oleic acid was added to the vascular perfusate to produce mild to moderate lung injury. All lungs were ventilated with peak airway pressure of 30 cm H2O for 30 minutes. Outcome measures included frequency of gross structural failure, pulmonary hemorrhage, edema formation, changes in static compliance, pulmonary vascular resistance, and pulmonary ultrafiltration coefficient. RESULTS: In the context of high vascular flow, application of a moderate level of PEEP reduced pulmonary rupture, edema formation, and lung hemorrhage. The protective effects of PEEP were not observed in lungs concurrently injured with oleic acid. CONCLUSIONS: Under these experimental conditions, PEEP attenuates lung injury in the setting of high vascular flow. The protective effect of PEEP is lost in a two-hit model of lung injury.

Prognostic value of different dead space indices in mechanically ventilated patients with acute lung injury and ARDS.

STUDY OBJECTIVE: The aim of this prospective observational study was to evaluate the utility of derived dead space indexes to predict survival in mechanically ventilated patients with acute lung injury (ALI) and ARDS. STUDY POPULATION: Thirty-six patients with ALI (Murray score, > or =1; Pao(2)/fraction of inspired oxygen [Fio(2)] ratio, < 300) in critical care departments at two separate hospitals entered the study. MEASUREMENTS: At ICU admission, 24 h, and 48 h, we measured the following: simplified acute physiologic score II; Pao(2)/Fio(2) ratio; respiratory system compliance; and capnographic indexes (Bohr dead space) and physiologic dead space (Enghoff dead space [Vdphys/Vt]), expired normalized CO(2) slope, carbon dioxide output, and the alveolar ejection volume (Vae)/tidal volume fraction (Vt) ratio. RESULTS: The best predictor was the Vae/Vt ratio at ICU admission (Vae/Vt-adm) and after 48 h (Vae/Vt-48 h) [p = 0.013], with a sensitivity of 82% and a specificity of 64%. The difference between Vae/Vt-48 h and Vae/Vt-adm show a sensitivity of 73% and a specificity of 93% with a likelihood ratio (LR) of 10.2 and an area under the receiver operating characteristic (ROC) curve of 0.83. The interaction between the Pao(2)/Fio(2) ratio and Vae/Vt-adm predict survival (p = 0.003) with an area under the ROC curve of 0.84, an LR of 2.3, a sensitivity of 100%, and a specificity of 57%. The Vdphys/Vt after 48 h predicted survival (p = 0.02) with an area under the ROC curve of 0.75, an LR of 8.8, a sensitivity of 63%, and a specificity of 93%. Indexes recorded 24 h after ICU admission were not useful in explaining outcome. CONCLUSIONS: Noninvasive measures of Vae/Vt at ICU admission and after 48 h of mechanical ventilation, associated with Pao(2)/Fio(2) ratio provided useful information on outcome in critically ill patients with ALI.

Bedside evaluation of pressure-volume curves in patients with acute respiratory distress syndrome.

PURPOSE OF REVIEW: To describe the physiologic and diagnostic utility of static pressure-volume curves of the respiratory system at the bedside in patients with acute lung injury or acute respiratory distress syndrome. RECENT FINDINGS: The pressure-volume curve of the respiratory system is a useful tool for the measurement of respiratory system mechanics in patients with acute lung injury or acute respiratory distress syndrome. The pressure-volume curve has a sigmoid shape, with lower and upper points on the inspiratory limb and a point of maximum curvature on the expiratory limb. Visual and mathematical pressure-volume curve analysis may be useful for understanding individual lung mechanics and for selecting ventilator settings. Among the different techniques for acquiring pressure-volume curves at the bedside, the constant slow flow method is the simplest to perform, the most clinically reliable and has the fewest limitations. SUMMARY: Measurement of pressure-volume curves at the bedside in critically ill patients with acute lung injury or acute respiratory distress syndrome should be considered a useful respiratory monitoring tool to assess physiologic lung status and to adjust ventilator settings, when appropriate, to minimize superimposed lung injury associated with mechanical ventilators.

Contributions of vascular flow and pulmonary capillary pressure to ventilator-induced lung injury.

OBJECTIVE: To evaluate the influence of vascular flow on ventilator-induced lung injury independent of vascular pressures. DESIGN: Laboratory study. SETTING: Hospital laboratory. SUBJECTS: Thirty-two New Zealand White rabbits. INTERVENTIONS: Thirty-two isolated perfused rabbit lungs were allocated into four groups: low flow/low pulmonary capillary pressure; high flow/high pulmonary capillary pressure; low flow/high pulmonary capillary pressure, and high flow/low pulmonary capillary pressure. All lungs were ventilated with peak airway pressure 30 cm H2O and positive end-expiratory pressure 5 cm H2O for 30 mins. MEASUREMENTS AND MAIN RESULTS: Outcome measures included frequency of gross structural failure (pulmonary rupture), pulmonary hemorrhage, edema formation, changes in lung compliance, pulmonary vascular resistance, and pulmonary ultrafiltration coefficient. Lungs exposed to high pulmonary vascular flow ruptured more frequently, displayed more hemorrhage, developed more edema, suffered larger decreases in compliance, and had larger increases in vascular resistance than lungs exposed to low vascular flows (p < .05 for each pairwise comparison between groups). CONCLUSIONS: These findings suggest that high pulmonary vascular flows might exacerbate ventilator-induced lung injury independent of their effects on pulmonary vascular pressures.

Massive brain injury enhances lung damage in an isolated lung model of ventilator-induced lung injury.

OBJECTIVE: To assess the influence of massive brain injury on pulmonary susceptibility to injury attending subsequent mechanical or ischemia/reperfusion stress. DESIGN: Prospective experimental study. SETTING: Animal research laboratory. SUBJECTS: Twenty-four anesthetized New Zealand White rabbits randomized to control (n = 12) or induced brain injury (n = 12) group. INTERVENTIONS: After randomization, brain injury was induced by inflation of an intracranial balloon-tipped catheter, and animals were ventilated with a tidal volume of 10 mL/kg and zero end-expiratory pressure for 120 mins. Following heart-lung block extraction, isolated and perfused lungs were subjected to injurious ventilation with peak airway pressure 30 cm H2O and positive end-expiratory pressure 5 cm H2O for 30 mins. MEASUREMENTS AND MAIN RESULTS: No difference was observed between groups in gas exchange, lung mechanics, or hemodynamics during the 2-hr in vivo period following induction of brain injury. However, after 30 mins of ex vivo injurious mechanical ventilation, lungs from the brain injury group showed greater change in ultrafiltration coefficient, weight gain, and alveolar hemorrhage (all p < .05). CONCLUSIONS: Massive brain injury might increase lung vulnerability to subsequent injurious mechanical or ischemia-reperfusion insults, thereby increasing the risk of clinical posttransplant graft failure.

Patterns of colonization by Pseudomonas aeruginosa in intubated patients: a 3-year prospective study of 1,607 isolates using pulsed-field gel electrophoresis with implications for prevention of ventilator-associated pneumonia.

OBJECTIVE: To identify routes and patterns of colonization with Pseudomonas aeruginosa in intubated patients to design strategies of prevention for respiratory infection. DESIGN AND SETTING: Prospective and observational study in the 16-bed intensive care unit of a teaching hospital. PATIENTS AND PARTICIPANTS: Ninety-eight intubated patients were investigated over a 3-year period. Those ventilated less than 72 h were excluded. MEASUREMENTS AND RESULTS: Samples from the tap water from each patient's room, stomach, oropharynx, subglottic secretions, trachea, and rectum were collected when the patient was intubated, and then three times per week. Pulsed-field gel electrophoresis was performed to type the strains. We identified 1,607 isolates pertaining to 35 different pulsotypes. Overall 54.2% of patients presented colonization, and tracheal colonization was present in 30.5%. Ten patients had colonization at intubation, and four of these developed ventilator-associated pneumonia (VAP) after a mean of 4+/-2 days. ICU-acquired colonization occurred in 31 patients, and 4 of these developed VAP after a median of 10+/-5 days. P. aeruginosa was isolated from the room's tap water in 62.4% of samples. More than 90% of tap water samples had pulsotypes 1 and 2, which were frequently isolated in the stomach (59%) but were only rarely associated with VAP. CONCLUSIONS: Although colonization/infection with P. aeruginosa in intubated patients tends to be endogenous, exogenous sources should not be ruled out. A combination of early identification (and eradication) of airways colonization by P. aeruginosa plus infection control measures targeted to reduce cross-contamination should be the basis to prevent pulmonary infection.

Clinical review: the implications of experimental and clinical studies of recruitment maneuvers in acute lung injury.

Mechanical ventilation can cause and perpetuate lung injury if alveolar overdistension, cyclic collapse, and reopening of alveolar units occur. The use of low tidal volume and limited airway pressure has improved survival in patients with acute lung injury or acute respiratory distress syndrome. The use of recruitment maneuvers has been proposed as an adjunct to mechanical ventilation to re-expand collapsed lung tissue. Many investigators have studied the benefits of recruitment maneuvers in healthy anesthetized patients and in patients ventilated with low positive end-expiratory pressure. However, it is unclear whether recruitment maneuvers are useful when patients with acute lung injury or acute respiratory distress syndrome are ventilated with high positive end-expiratory pressure, and in the presence of lung fibrosis or a stiff chest wall. Moreover, it is unclear whether the use of high airway pressures during recruitment maneuvers can cause bacterial translocation. This article reviews the intrinsic mechanisms of mechanical stress, the controversy regarding clinical use of recruitment maneuvers, and the interactions between lung infection and application of high intrathoracic pressures.

Extubation failure: diagnostic value of occlusion pressure (P0.1) and P0.1-derived parameters.

OBJECTIVE: To evaluate the ability of the new, built-in occlusion pressure (P0.1) measurement to predict extubation failure. DESIGN AND SETTING: Prospective observational multicentre study in the ICU of five general hospitals. PATIENTS: Hundred thirty patients on mechanical ventilation longer than 48 h when considered ready for weaning. MEASUREMENTS AND RESULTS: Patients underwent a 30-min spontaneous breathing trial with simultaneous monitoring of occlusion pressure (P0.1) and breathing pattern (f/Vt). Sixteen patients (12%) failed the weaning trial and full ventilatory support was resumed, while 114 tolerated the trial and were extubated. Twenty-one (18%) required reintubation within 48 h. The area under the ROC curve for diagnosing extubation failure was 0.53 for f/Vt, 0.59 for P0.1 and 0.61 for P0.1*f/Vt (p=NS). Accordingly, P0.1*f/Vt more than 100 detected extubation failure with a sensitivity of 0.89, specificity of 0.35, positive predictive value of 0.21 and negative predictive value of 0.94. CONCLUSION: During a first trial of spontaneous breathing on pressure support ventilation (PSV), bedside P0.1 and P0.1*f/Vt are of little help, if any, for predicting extubation failure.

Application of continuous positive airway pressure to trace static pressure-volume curves of the respiratory system.

OBJECTIVE: To evaluate a new technique for pressure-volume curve tracing. DESIGN: Prospective experimental study. SETTING: Animal research laboratory. SUBJECTS: Six anesthetized rats. INTERVENTIONS: Two pressure-volume curves were obtained by means of the super-syringe method (gold standard) and the continuous positive airway pressure (CPAP) method. For the CPAP method, the ventilator was switched to CPAP and the pressure level was raised from 0 to 50 cm H2O in 5 cm H2O steps and then decreased, while we measured lung volume using respiratory inductive plethysmography. Thereafter, lung injury was induced using very high-volume ventilation. Following injury, two further pressure-volume curves were traced. Pressure-volume pairs were fitted to a mathematical model. MEASUREMENTS AND MAIN RESULTS: Pressure-volume curves were equivalent for each method, with intraclass correlation coefficients being higher than.75 for each pressure level measured. Bias and precision for volume values were 0.46 +/- 0.875 mL in basal measurements and 0.31 +/- 0.67 mL in postinjury conditions. Lower and upper inflection points on the inspiratory limb and maximum curvature point on the deflation limb obtained using both methods and measured by regression analysis also were correlated, with intraclass correlation coefficients (95% confidence interval) being.97 (.58,.99),.85 (.55,.95), and.94 (.81,.98) (p <.001 for each one). When inflection points were estimated by observers, the correlation coefficient between methods was.90 (.67,.98) for lower inflection points (p <.001). However, estimations for upper inflection points and maximum curvature point were significantly different. CONCLUSIONS: The CPAP method for tracing pressure-volume curves is equivalent to the super-syringe method. It is easily applicable at the bedside, avoids disconnection from the ventilator, and can be used to obtain both the inspiratory and the deflation limbs of the pressure-volume curve. Use of regression techniques improves determination of inflection points.