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Background: Proportional assist ventilation (PAV) has been shown to maintain better patient-ventilator synchrony than pressure support ventilation (PSV); however, its clinical advantage regarding invasive ventilation of COPD patients has not been clarified. Objectives: To compare the effect of PAV and PSV on respiratory parameters of hypercapnic COPD patients with acute respiratory failure (ARF). Methods: Nine intubated hypercapnic COPD patients were placed on the PAV or PSV mode in random sequence. For each mode, four levels (L1–L4) of support were applied. At each level, blood gases, flow, tidal volume (VT), airway pressure (Paw), esophageal pressure (Pes) (n = 7), patient respiratory rate (fp), ventilator rate (fv), missing efforts (ME = fp – fv) were measured. Results: We found increases in ME with increasing levels of PSV but not with PAV. PO2 and VT increased whereas PCO2 decreased significantly with increasing levels of PSV (p < 0.05). With PAV, PCO2 decreased and VT increased significantly only at L4 whereas PO2 increased from L1 to L4. Runaways were observed at L3 and L4 of PAV. The pressure-time product (PTP) was determined for effective and missing breaths. The mean total PTP per minute (of effective plus missing breaths) was 160 ± 57 cm H2O/s·min in PSV and 194 ± 60 cm H2O/s·min in PAV. Conclusion: We conclude that in COPD patients with hypercapnic ARF, with increasing support, PSV causes the appearance of ME whereas PAV develops runaway phenomena, due to the different patient-ventilator interaction; however, these do not limit the improvement of blood gases with the application of both methods.Copyright © 2003 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Hypoxaemia due to right-to-left atrial shunt with normal pressures in the right heart cavities represents an underdiagnosed condition. A systematic approach to hypoxaemic respiratory failure based on pathophysiology can lead to an accurate diagnosis. https://bit.ly/4bTP8fJ., Competing Interests: Conflicts of interest: The authors have nothing to disclose., (Copyright ©ERS 2024.)

Hiccups-like contractions, including hiccups, respiratory myoclonus, and diaphragmatic tremor, refer to involuntary, spasmodic, and inspiratory muscle contractions. They have been repeatedly described in mechanically ventilated patients, especially those with central nervous damage. Nevertheless, their effects on patient-ventilator interaction are largely unknown, and even more overlooked is their contribution to lung and diaphragm injury. We describe, for the first time, how the management of hiccup-like contractions was individualized based on esophageal and transpulmonary pressure measurements in three mechanically ventilated patients. The necessity or not of intervention was determined by the effects of these contractions on arterial blood gases, patient-ventilator synchrony, and lung stress. In addition, esophageal pressure permitted the titration of ventilator settings in a patient with hypoxemia and atelectasis secondary to hiccups and in whom sedatives failed to eliminate the contractions and muscle relaxants were contraindicated. This report highlights the importance of esophageal pressure monitoring in the clinical decision making of hiccup-like contractions in mechanically ventilated patients.

Background: The driving pressure of the respiratory system is a valuable indicator of global lung stress during passive mechanical ventilation. Monitoring lung stress in assisted ventilation is indispensable, but achieving passive conditions in spontaneously breathing patients to measure driving pressure is challenging. The accuracy of the morphology of airway pressure (Paw) during end-inspiratory occlusion to assure passive conditions during pressure support ventilation has not been examined., Methods: Retrospective analysis of end-inspiratory occlusions obtained from critically ill patients during pressure support ventilation. Flow, airway, esophageal, gastric, and transdiaphragmatic pressures were analyzed. The rise of gastric pressure during occlusion with a constant/decreasing transdiaphragmatic pressure was used to identify and quantify the expiratory muscle activity. The Paw during occlusion was classified in three patterns, based on the differences at three pre-defined points after occlusion (0.3, 1, and 2 s): a "passive-like" decrease followed by plateau, a pattern with "clear plateau," and an "irregular rise" pattern, which included all cases of late or continuous increase, with or without plateau., Results: Data from 40 patients and 227 occlusions were analyzed. Expiratory muscle activity during occlusion was identified in 79% of occlusions, and at all levels of assist. After classifying occlusions according to Paw pattern, expiratory muscle activity was identified in 52%, 67%, and 100% of cases of Paw of passive-like, clear plateau, or irregular rise pattern, respectively. The driving pressure was evaluated in the 133 occlusions having a passive-like or clear plateau pattern in Paw. An increase in gastric pressure was present in 46%, 62%, and 64% of cases at 0.3, 1, and 2 s, respectively, and it was greater than 2 cmH 2 O, in 10%, 20%, and 15% of cases at 0.3, 1, and 2 s, respectively., Conclusions: The pattern of Paw during an end-inspiratory occlusion in pressure support cannot assure the absence of expiratory muscle activity and accurate measurement of driving pressure. Yet, because driving pressure can only be overestimated due to expiratory muscle contraction, in everyday practice, a low driving pressure indicates an absence of global lung over-stretch. A measurement of high driving pressure should prompt further diagnostic workup, such as a measurement of esophageal pressure.

Background: The present study aimed to validate a recently proposed algorithm for assistance titration during proportional assist ventilation with load-adjustable gain factors, based on a noninvasive estimation of maximum inspiratory pressure (peak P mus ) and inspiratory effort (pressure-time product [PTP] peak P mus )., Methods: Retrospective analysis of the recordings obtained from 26 subjects ventilated on proportional assist ventilation with load-adjustable gain factors under different conditions, each considered as an experimental case. The estimated inspiratory output (peak P mus ) and effort (PTP-peak P mus ) were compared with the actual-determined by the measurement of transdiaphragmatic pressure- and the derived PTP. Validation of the algorithm was performed by assessing the accuracy of peak P mus in predicting the actual inspiratory muscle effort and indicating the appropriate level of assist., Results: In the 63 experimental cases analyzed, a limited agreement was observed between the estimated and the actual inspiratory muscle pressure (-11 to 10 cm H 2 O) and effort (-82 to 125 cm H 2 O × s/min). The sensitivity and specificity of peak P mus to predict the range of the actual inspiratory effort was 81.2% and 58.1%, respectively. In 49% of experimental cases, the level of assist indicated by the algorithm differed from that indicated by the transdiaphragmatic pressure and PTP., Conclusions: The proposed algorithm had limited accuracy in estimating inspiratory muscle effort and with indicating the appropriate level of assist., Competing Interests: Drs Amargiannitakis and Gialamas contributed equally to this work. Drs Kondili, Vaporidi, and Georgopoulos have received lecture fees (honoraria) from Covidien., (Copyright © 2020 by Daedalus Enterprises.)

Unlabelled: To compare, in a group of difficult to wean critically ill patients, the short-term effects of neurally adjusted ventilator assist (NAVA), proportional assist (PAV+) and pressure support (PSV) ventilation on patient-ventilator interaction., Methods: Seventeen patients were studied during NAVA, PAV+ and PSV with and without artificial increase in ventilator demands (dead space in 10 and chest load in 7 patients). Prior to challenge addition the level of assist in each of the three modes tested was adjusted to get the same level of patient's effort., Results: Compared to PSV, proportional modes favored tidal volume variability. Patient effort increase after dead space was comparable among the three modes. After chest load, patient effort increased significantly more with NAVA and PSV compared to PAV+. Triggering delay was significantly higher with PAV+. The linear correlation between tidal volume and inspiratory integral of transdiaphragmatic pressure (PTPdi) was weaker with NAVA than with PAV+ and PSV on account of a weaker inspiratory integral of the electrical activity of the diaphragm (∫EAdi)-PTPdi linear correlation during NAVA [median (interquartile range) of r(2), determination of coefficient, 16.2% (1.4-30.9%)]., Conclusion: Compared to PSV, proportional modes favored tidal volume variability. The weak ∫EAdi-PTPdi linear relationship during NAVA and poor triggering function during PAV+ may limit the effectiveness of these modes to proportionally assist the inspiratory effort., (Copyright © 2014 Elsevier B.V. All rights reserved.)

Purpose: To assess the impact of lung ultrasound (LU) on clinical decision making in mechanically ventilated critically ill patients., Methods: One hundred and eighty-nine patients took part in this prospective study. The patients were enrolled in the study when LU was requested by the primary physician for (1) unexplained deterioration of arterial blood gases and (2) a suspected pathologic entity [pneumothorax, significant pleural effusion (including parapneumonic effusion, empyema, or hemothorax), unilateral atelectasis (lobar or total), pneumonia and diffuse interstitial syndrome (pulmonary edema)]., Results: Two hundred and fifty-three LU examinations were performed; 108 studies (42.7%) were performed for unexplained deterioration of arterial blood gases, and 145 (57.3%) for a suspected pathologic entity (60 for pneumothorax, 34 for significant pleural effusion, 22 for diffuse interstitial syndrome, 15 for unilateral lobar or total lung atelectasis, and 14 for pneumonia). The net reclassification index was 85.6%, indicating that LU significantly influenced the decision-making process. The management was changed directly as a result of information provided by the LU in 119 out of 253 cases (47%). In 81 cases, the change in patient management involved invasive interventions (chest tube, bronchoscopy, diagnostic thoracentesis/fluid drainage, continuous venous-venous hemofiltration, abdominal decompression, tracheotomy), and in 38 cases, non-invasive (PEEP change/titration, recruitment maneuver, diuretics, physiotherapy, change in bed position, antibiotics initiation/change). In 53 out of 253 cases (21%), LU revealed findings which supported diagnoses not suspected by the primary physician (7 cases of pneumothorax, 9 of significant pleural effusion, 9 of pneumonia, 16 of unilateral atelectasis, and 12 of diffuse interstitial syndrome)., Conclusion: Our study shows that LU has a significant impact on decision making and therapeutic management.

Background: The mechanical stress that the human diaphragm is exposed to during mechanical ventilation affects a variety of processes, including signal transduction, gene expression, and angiogenesis., Objectives: The study aim was to assess the change in the production of major angiogenic regulators [vascular endothelial growth factor (VEGF), fibroblast growth factor-2 (FGF2), and transforming growth factor beta 1 (TGFB1)] on the human diaphragm before and after contraction/relaxation cycles during mechanical ventilation., Methods: This observational study investigates the diaphragmatic mRNA expression of VEGF, FGF2, and TGFB1 in surgical patients receiving general anesthesia with controlled mechanical ventilation (CMV) with muscle relaxation (group A, n = 13), CMV without muscle relaxation (group B, n = 10), and pressure support of spontaneous breathing (group C, n = 9). Diaphragmatic samples were obtained from each patient at two time points: 30 min after the induction of anesthesia (t1) and 90 min after the first specimen collection (t2)., Results: No significant changes in the mRNA expression of VEGF, FGF2, and TGFB1 were documented in groups A and C between time points t1 and t2. In contrast, in group B, the mRNA levels of the above angiogenic factors were increased in time point t2 compared to t1, a finding which was statistically significant (pVEGF = 0.003, pFGF2 = 0.028, pTGFB1 = 0.001)., Conclusions: These findings suggest that the molecular response of the human diaphragm before and after application of diverse modes of mechanical ventilation is different. Angiogenesis via the expression of VEGF, FGF2, and TGFB1 was only promoted in CMV without muscle relaxation, and this may have important clinical implications., (Copyright © 2012 S. Karger AG, Basel.)

Background: In mechanically ventilated patients with COPD, the response of the expiratory resistance of the respiratory system (expiratory R(RS)) to bronchodilators is virtually unknown., Objective: To examine the effect of inhaled albuterol on expiratory R(RS), and the correlation of albuterol-induced changes in expiratory R(RS) with end-inspiratory resistance and the expiratory flow-volume relationship., Methods: We studied 10 mechanically ventilated patients with COPD exacerbation, before and 30 min after administration of albuterol. We obtained flow-volume curves during passive expiration, divided the expired volume into 5 equal volume slices, and then calculated the time constant and dynamic effective deflation compliance of the respiratory system (effective deflation C(RS)) of each slice via regression analysis of the volume-flow and post-occlusion volume-tracheal pressure relationships, respectively. For each slice we calculated expiratory R(RS) as the time constant divided by the effective deflation C(RS)., Results: Albuterol significantly decreased the expiratory R(RS) (mean expiratory R(RS) 42.68 ± 17.8 cm H(2)O/L/s vs 38.08 ± 16.1 cm H(2)O/L/s) and increased the rate of lung emptying toward the end of expiration (mean time constant 2.51 ± 1.2 s vs 2.21 ± 1.2 s). No correlation was found between the albuterol-induced changes in expiratory R(RS) and that of end-inspiratory resistance. Only at the end of expiration did albuterol-induced changes in the expiratory flow-volume relationship correlate with changes in expiratory R(RS) in all patients., Conclusions: In patients with COPD, albuterol significantly decreases expiratory resistance at the end of expiration. In mechanically ventilated patients, neither inspiratory resistance nor the whole expiratory flow-volume curve may be used to evaluate the bronchodilator response of expiratory resistance.

The aim of the paper is to identify the key physiological variables and ventilator settings involved in ventilation management, and required for an appropriate Clinical Decision Support System (CDSS). Based on the results of a questionnaire designed for the purpose of the research, 70 hours of physiological and ventilation data were recorded. Recorded data were classified by clinicians into three major lung pathologies and were further statistically analyzed for identifying strong relationships between monitored and controlled ventilator parameters. Correlation analysis was evaluated by Intensive Care Unit (ICU) clinicians. Based on the evaluators' majority voting the number and type of participating variables in a CDSS was drastically decreased. The number and type of monitored variables ranged from a single one to six, depending on the patient's lung pathology, and the controlled ventilator setting. Evaluation results were successfully applied to Neural Network models for providing suggestions on Tidal Volume and the Fraction of inspired Oxygen.

The aim of the study was to investigate Propofol's effect on breathing stability in brain damage patients, as quantified by the Loop Gain (LG) of the respiratory system (breathing stability increases with decreasing LG). In 11 stable brain damage patients full polysomnography was performed before, during and after propofol sedation, titrated to achieve stage 2 or slow wave sleep. During each period, patients were ventilated with proportional assist ventilation and the % assist was increased in steps, until either periodic breathing (PB) occurred or the highest assist (95%) was achieved. The tidal volume amplification factor (VT(AF)) at the highest assist level reached just before PB occurred was used to calculate LG (LG=1/VT(AF)). In all but one patient, PB was observed. With propofol, the assist level at which PB occurred (73 + or - 19%) was significantly higher, than that before (43 + or - 35%) and after propofol sedation (49 + or - 29%). As a result, with propofol LG (0.49 + or - 0.2) was significantly lower than that before (0.74 + or - 0.2) and after propofol sedation (0.69 + or - 0.2) (p<0.05). We conclude that Propofol decreases LG. Therefore it exerts an overall stabilizing effect on control of breathing., (Copyright 2010 Elsevier B.V. All rights reserved.)

Aim: This article is a report of a study conducted to determine if a nursing-implemented protocol of daily interruption of sedative infusions vs. sedation as directed by the intensive care unit team would decrease duration of mechanical ventilation., Background: Continuous rather than intermittent infusion of sedative and analgesic agents leads to greater stability in sedation level, but has been correlated with prolongation of mechanical ventilation and hospitalization of critical care patients. Daily interruption of sedative infusions in mechanically ventilated patients has reduced the duration of mechanical ventilation and length of stay in intensive care., Method: A randomized controlled trial was carried out from November 2004 to March 2006 with 97 patients receiving mechanical ventilation and continuous infusion of sedative drugs in an intensive care unit in Greece. The primary outcome measure was the duration of mechanical ventilation. Secondary outcomes were length of intensive care unit stay, length of hospital stay, overall mortality, total doses of sedative and analgesic medicines and Ramsay scores and duration of cessation of sedative infusions per day., Results: The median duration of mechanical ventilation was 8.7 days vs. 7.7 days (P = 0.7). Length of intensive care unit stay (median: 14 vs. 12, P = 0.5) and in the hospital (median: 31 vs. 21, P = 0.1) was similar between the intervention and control groups. The absence of statistically significant differences in these variables remained when patients with brain injury were examined separately., Conclusion: The nursing-implemented protocol of daily interruption of sedative infusions was neither beneficial nor harmful compared with usual practice, which has as its primary target the earliest possible awakening of patients.

Introduction: Physiological determinants of weaning success and failure are usually studied in ventilator-supported patients, comparing those who failed a trial of spontaneous breathing with those who tolerated such a trial and were successfully extubated. A major limitation of these studies was that the two groups may be not comparable concerning the severity of the underlying disease and the presence of comorbidities. In this physiological study, we assessed the determinants of weaning success in patients acting as their own control, once they are eventually liberated from the ventilator., Methods: In 30 stable tracheotomised ventilator-dependent patients admitted to a weaning center inside a respiratory intensive care unit, we recorded the breathing pattern, respiratory mechanics, inspiratory muscle function, and tension-time index of diaphragm (TTdi = Pdisw/Pdimax [that is, tidal transdiaphragmatic pressure over maximum transdiaphragmatic pressure] x Ti/Ttot [that is, the inspiratory time over the total breath duration]) at the time of weaning failure (T0). The measurements were repeated in all the patients (T1) either during a successful weaning trial (successful weaning [SW] group, n = 16) or 5 weeks later, in the case of repeated weaning failure (failed weaning [FW] group, n = 14)., Results: Compared to T0, in the FW group at T1, significant differences were observed only for a reduction in spontaneous breathing frequency and in TTdi (0.21 +/- 0.122 versus 0.14 +/- 0.054, P = 0.008). SW patients showed a significant increase in Pdimax (34.9 +/- 18.9 cm H2O versus 43.0 +/- 20.0, P = 0.02) and decrease in Pdisw/Pdimax (36.0% +/- 15.8% versus 23.1% +/- 7.9%, P = 0.004)., Conclusions: The recovery of an inadequate inspiratory muscle force could be the major determinant of 'late' weaning success, since this allows the patients to breathe far below the diaphragm fatigue threshold.

Objective: During pressure support ventilation (PS), an abrupt increase in ventilator pressure above the pre-set level is considered to signify expiratory muscle activity. However, relaxation of inspiratory muscles may also cause the same phenomenon, and this hypothesis has not been explored. The aim of this study is to examine the cause of this increase in ventilator pressure, during PS, in critically ill patients., Design: Retrospective study., Setting: In a university intensive care unit., Methods: Fifteen patients instrumented with esophageal and gastric balloons, and in whom airway pressure (P (aw)) during PS exhibited an acute increase above the pre-set level towards the end of mechanical inspiration were retrospectively analyzed. For each breath, the time of the rapid increase in P (aw) was identified (t (Paw)) and, using the transdiaphragmatic (P (di)) and gastric (P (ga)) pressure waveforms, related to: (1) the end of neural inspiration (peak P (di)) and (2) the time at which P (ga) started to increase rapidly after the end of neural inspiration indicating expiratory muscle recruitment., Results: The t (Paw) was observed 32+/-34ms after the end of neural inspiration, well before (323+/-182ms) expiratory muscle recruitment (identified in eight patients). There was a significant linear relationship between the rate of rise of P (aw) after t (Paw) and the rates of decline of P (di) and inspiratory flow., Conclusion: We conclude that, during PS ventilation, the relaxation of inspiratory muscles accounts for the acute increase in P (aw) above the pre-set level, in addition to the contribution made by the occurrence of expiratory muscle activity.

Introduction: Near the end of a maximal voluntary breath-hold, re-inhalation of the expired gas allows an additional period of breath-holding, indicating that the breaking point does not depend solely on chemical drive. We hypothesized that afferents from respiratory muscle and/or chest wall are significant in breath-holding., Methods: Nineteen normal adults breathed room air through a mouthpiece connected to a pneumotachograph and were instructed to breath-hold with and without voluntary regular respiratory efforts against an occluded airway., Results: Fifty one trials with and 53 without respiratory efforts were analyzed. The mean number of efforts per minute was 19+/-2.3 and the mean lowest airway pressure (P(aw)) -16.6+/-5.4 cmH(2)O. Breath-holding time (BHT) did not differ without (33.0+/-18.2 s) and with (29.3+/-12.3 s) efforts. In five patients arterial blood gasses were measured before and at the end of breath-holding and they did not differ between trials without and with efforts, indicating similar chemical drive. Our results suggest that afferents from respiratory muscle and/or chest wall are not the major determinants of BHT.

Background: Proportional-assist ventilation with load-adjustable gain factors (PAV+) automatically adjusts the flow and volume assist to represent constant fractions of resistance and elastance of the respiratory system, respectively. Resistance and elastance are calculated at random intervals of 4-10 breaths, by applying a 300 ms pause maneuver at the end of selected inspirations., Objectives: To determine whether the large number of end-inspiratory occlusions during PAV+ operation influences sleep quality in critically ill patients who exhibited good patient-ventilator synchrony during pressure support (PS, baseline)., Methods: One and two nights' polysomnography was performed in sedated (protocol A, n=11) and non-sedated (protocol B, n=9) patients, respectively, while respiratory variables were continuously recorded. In each protocol the patients were ventilated with PAV+ and PS at two levels of assist (baseline and high)., Results: In both protocols sleep quality did not differ between the modes of support or the assist levels. In sedated patients sleep efficiency was slightly but significantly higher with PAV+ than with high PS, while it did not differ between modes in non-sedated patients. The two modes of support had comparable effects on respiratory variables. Independent of the mode of support and particularly at high assist, a significant proportion of patients developed periodic breathing during sleep (27% in protocol A and 44% in protocol B)., Conclusion: In patients exhibiting good patient-ventilator synchrony during PS, the large number of short-term end-inspiratory occlusions with PAV+ operation did not adversely influence sleep quality. With both modes high assist may cause unstable breathing during sleep.

Background: Several in vitro studies have shown that at similar tidal volume (VT), bronchodilator delivery to target sites is significantly lower during controlled mechanical ventilation (CMV) than that during simulated spontaneous breathing. However, the influence of active respiratory efforts on the magnitude of b2-agonist induced bronchodilation in mechanically ventilated patients has not been examined., Objective: To examine the influence of controlled and assisted modes of ventilatory support on the bronchodilative effect induced by b2-agonists administered with a metered dose inhaler (MDI) and a spacer device in a homogeneous group of mechanically ventilated patients with acute exacerbation of chronic obstructive pulmonary disease (COPD)., Methods: Prospective clinical study. Ten mechanically ventilated patients with acute exacerbation of COPD were prospectively randomized to receive 4 puffs of salbutamol (S, 100 micro g/puff) either with volume-controlled (VC) or pressure-support (PS) ventilation. On PS the pressure level was such that VT was comparable between ventilatory modes. After a 6-h washout period, patients were crossed-over to receive the drug by the alternative mode of ventilation. Static and dynamic airway pressures, minimum (R(int)) and maximum (R(rs)) inspiratory resistance, the difference between R(rs) and R(int) (DeltaR), end-inspiratory static compliance of the respiratory system (C(rs)), intrinsic positive end-expiratory pressure (PEEP(i)) and heart rate (HR) were measured before and at 15, 30, 60, 120, 180 and 240 min after S administration., Results: S caused a significant decrease in dynamic and static airway pressures, PEEP(i), R(int) and R(rs). These changes were not influenced by the ventilatory mode and were evident at 15, 30, 60 and 120 min after S. HR, C(rs) and DeltaR did not change after S administration., Conclusions: Considering the use of propofol with its presumed bronchodilative properties as a shortcoming of our study, it is concluded that the magnitude of bronchodilation induced by salbutamol delivered by an MDI and a spacer device in mechanically ventilated COPD patients is not affected by the presence or absence of active respiratory efforts.

Rationale: The helmet is a new interface with the potential of increasing the success rate of non-invasive ventilation by improving tolerance., Objectives: To perform a physiological comparison between the helmet and the conventional facial mask in delivering non-invasive ventilation in hypercapnic patients with chronic obstructive pulmonary disease., Methods: Prospective, controlled, randomized study with cross-over design. In 10 patients we evaluated gas exchange, inspiratory effort, patient-ventilator synchrony and patient tolerance after 30 min of non-invasive ventilation delivered either by helmet or facial mask; both trials were preceded by periods of spontaneous unassisted breathing., Measurements: Arterial blood gases, inspiratory effort, duration of diaphragm contraction and ventilator assistance, effort-to-support delays (at the beginning and at the end of inspiration), number of ineffective efforts, and patient comfort., Main Results: Non-invasive ventilation improved gas exchange (p<0.05) and inspiratory effort (p<0.01) with both interfaces. The helmet, however, was less efficient than the mask in reducing inspiratory effort (p<0.05) and worsened the patient-ventilator synchrony, as indicated by the longer delays to trigger on (p<0.05) and cycle off (p<0.05) the mechanical assistance and by the number of ineffective efforts (p<0.005). Patient comfort was no different with the two interfaces., Conclusions: Helmet and facial mask were equally tolerated and both were effective in ameliorating gas exchange and decreasing inspiratory effort. The helmet, however, was less efficient in decreasing inspiratory effort and worsened the patient-ventilator interaction.

Rationale: T-piece trials and spontaneous breathing trials through the tracheostomy tube are often used as weaning techniques. They are usually performed with the cuff inflated, which may increase the inspiratory load and/or influence the tidal volume generated by the patient. We assessed diaphragmatic effort during T-piece trials with or without cuff inflation., Settings: Respiratory intensive care unit, Methods: We measured breathing pattern, transdiaphragmatic pressure (Pdi), the pressure-time product of the diaphragm, per minute (PTPdi/min) and per breath (PTPdi/b), and lung mechanics (lung compliance and resistance) in 13 tracheotomized patients ready for a weaning trial. V(T) was recorded with respiratory inductive plethysmography (RIP-V(T)) or pneumotachography PT-V(T)). Patients completed two T-piece trials of 30[Symbol: see text]min each with or without the cuff inflated., Results: RIP-V(T) and PT-V(T) values were similar with the cuff inflated, but PT-V(T) significantly underestimated RIP-V(T) when the cuff was deflated, and therefore the RIP-V(T) was chosen as the reference method. The RIP-V(T) was significantly greater and the Pdi and PTPdi/min significantly lower when the cuff was deflated than when it was inflated. The efficiency of the diaphragm, calculated by the ratio of PTPdi/b over RIP-V(T), was also improved, while no changes were observed in lung mechanics., Conclusions: Diaphragmatic effort is significantly lower during a T-piece trial with a deflated cuff than when the cuff is inflated, while RIP-V(T) is higher, so that the diaphragm's efficiency in generating tidal volume is also improved.

Background: Airway resistance depends not only on an airway's geometry but also on flow rate, and gas density and viscosity. A recent study showed that at clinically relevant concentrations, the mixtures of volatile agents with air and oxygen and oxygen-nitrogen affected the density of the mixture. The goal of the current study was to investigate the effect of different minimum alveolar concentrations (MACs) of three commonly used volatile agents, isoflurane, sevoflurane, and desflurane, on the measurements of airway resistance., Methods: A two-chamber fixed-resistance test lung was connected to an anesthesia machine using the volume control mode of ventilation. Pulmonary resistance was calculated at baseline (25% oxygen in air); at 1.0, 1.5, and 2.0 MAC; and also at the same concentrations, 1.2% and 4%, of isoflurane, sevoflurane, and desflurane mixtures with 25% oxygen in air. The analysis of variance test for repeated measures and probabilities for post hoc Tukey and least significant difference tests were used., Results: Isoflurane affected pulmonary resistance only at 2 MAC. Sevoflurane caused a significant increase of pulmonary resistance at 1.5 and 2 MAC, whereas desflurane caused the greatest increase in pulmonary resistance at all MAC values used. At 1.2% concentration, no difference from the baseline resistance was observed, whereas at 4%, the three agents produced similar increases of pulmonary resistance., Conclusion: High concentrations of volatile agents in 25% oxygen in air increased the density of the gas mixture and the calculated resistance of a test lung model with fixed resistance.

Rationale: In mechanically ventilated patients respiratory system impedance may vary from time to time, resulting, with pressure modalities of ventilator support, in changes in the level of assistance. Recently, implementation of a closed-loop adjustment to continuously adapt the level of assistance to changes in respiratory mechanics has been designed to operate with proportional assist ventilation (PAV+)., Objectives: The aim of this study was to assess, in critically ill patients, the short-term steady-state response of respiratory motor output to added mechanical respiratory load during PAV+ and during pressure support (PS)., Patients and Interventions: In 10 patients respiratory workload was increased and the pattern of respiratory load compensation was examined during both modes of support., Measurements and Results: Airway and transdiaphragmatic pressures, volume and flow were measured breath by breath. Without load, both modes provided an equal support as indicated by a similar pressure-time product of the diaphragm per breath, per minute and per litre of ventilation. With load, these values were significantly lower (p<0.05) with PAV+ than those with PS (5.1+/-3.7 vs 6.1+/-3.4 cmH2O.s, 120.9+/-77.6 vs 165.6+/-77.5 cmH2O.s/min, and 18.7+/-15.1 vs 24.4+/-16.4 cmH2O.s/l, respectively). Contrary to PS, with PAV+ the ratio of tidal volume (VT) to pressure-time product of the diaphragm per breath (an index of neuroventilatory coupling) remained relatively independent of load. With PAV+ the magnitude of load-induced VT reduction and breathing frequency increase was significantly smaller than that during PS., Conclusion: In critically ill patients the short-term respiratory load compensation is more efficient during proportional assist ventilation with adjustable gain factors than during pressure support.

Objective: During assisted modes of ventilatory support the ventilatory output is the final expression of the interaction between the ventilator and the patient's controller of breathing. This interaction may lead to patient-ventilator asynchrony, preventing the ventilator from achieving its goals, and may cause patient harm. Flow, volume, and airway pressure signals are significantly affected by patient-ventilator interaction and may serve as a tool to guide the physician to take the appropriate action to improve the synchrony between patient and ventilator. This review discusses the basic waveforms during assisted mechanical ventilation and how their interpretation may influence the management of ventilated patients. The discussion is limited on waveform eye interpretation of the signals without using any intervention which may interrupt the process of mechanical ventilation., Discussion: Flow, volume, and airway pressure may be used to (a) identify the mode of ventilator assistance, triggering delay, ineffective efforts, and autotriggering, (b) estimate qualitatively patient's respiratory efforts, and (c) recognize delayed and premature opening of exhalation valve. These signals may also serve as a tool for gross estimation of respiratory system mechanics and monitor the effects of disease progression and various therapeutic interventions., Conclusions: Flow, volume, and airway pressure waveforms are valuable real-time tools in identifying various aspects of patient-ventilator interaction.

During assisted mechanical ventilation, the total pressure applied to respiratory system is the sum of ventilator and muscle pressure. As a result, the respiratory system is under the influence of two pumps, the ventilator pump (ie, Paw), which is controlled by the physician's brain and the capabilities of the ventilator, and the patient's own respiratory muscle pump (Pmus), which is controlled by the patient's brain. The patient-ventilator interaction is mainly an expression of the function of these two brains, which should be in harmony to promote patient-ventilator synchrony. The achievement of this harmony depends exclusively on the physician, who should be aware that during assisted mechanical ventilation the respiratory system is not a passive structure but reacts to pressure delivered by the ventilator via various feedback systems and, depending on several factors both to the ventilator and patient, may modify the function of the ventilator. Finally, the physician should know that the ventilator imposes significant constraints to the respiratory system, the magnitude of which depends heavily on the triggering variable, the variable that controls the gas delivery and the cycling off criterion.

Introduction: The cuff-leak test has been proposed as a simple method to predict the occurrence of post-extubation stridor. The test is performed by cuff deflation and measuring the expired tidal volume a few breaths later (VT). The leak is calculated as the difference between VT with and without a deflated cuff. However, because the cuff remains deflated throughout the respiratory cycle a volume of gas may also leak during inspiration and therefore this method (conventional) measures the total leak consisting of an inspiratory and expiratory component. The aims of this physiological study were, first, to examine the effects of various variables on total leak and, second, to compare the total leak with that obtained when the inspiratory component was eliminated, leaving only the expiratory leak., Methods: In 15 critically ill patients mechanically ventilated on volume control mode, the cuff-leak volume was measured randomly either by the conventional method (Leakconv) or by deflating the cuff at the end of inspiration and measuring the VT of the following expiration (Leakpause). To investigate the effects of respiratory system mechanics and inspiratory flow, cuff-leak volume was studied by using a lung model, varying the cross-sectional area around the endotracheal tube and model mechanics., Results: In patients Leakconv was significantly higher than Leakpause, averaging 188 +/- 159 ml (mean +/- SD) and 61 +/- 75 ml, respectively. In the model study Leakconv increased significantly with decreasing inspiratory flow and model compliance. Leakpause and Leakconv increased slightly with increasing model resistance, the difference being significant only for Leakpause. The difference between Leakconv and Leakpause increased significantly with decreasing inspiratory flow (V'I) and model compliance and increasing cross-sectional area around the tube., Conclusion: We conclude that the cross-sectional area around the endotracheal tube is not the only determinant of the cuff-leak test. System compliance and inspiratory flow significantly affect the test, mainly through an effect on the inspiratory component of the total leak. The expiratory component is slightly influenced by respiratory system resistance.

Objectives: To study the pattern of lung emptying and expiratory resistance in mechanically ventilated patients with chronic obstructive pulmonary disease (COPD)., Design: A prospective physiological study., Setting: A 12-bed Intensive Care Unit., Patients: Ten patients with acute exacerbation of COPD., Interventions: At three levels of positive end-expiratory pressure (PEEP, 0, 5 and 10 cm H(2)O) tracheal (Ptr) and airway pressures, flow (V') and volume (V) were continuously recorded during volume control ventilation and airway occlusions at different time of expiration., Measurements and Results: V-V' curves during passive expiration were obtained, expired volume was divided into five equal volume slices and the time constant (tau) and dynamic deflation compliance (Crs(dyn)) of each slice was calculated by regression analysis of V-V' and post-occlusion V-Ptr relationships, respectively. In each volume slice the existence or not of flow limitation was examined by comparing V-V' curves with and without decreasing Ptr. For a given slice total expiratory resistance was calculated as tau/Crs(dyn), whereas expiratory resistance (Rrs) and time constant (tau(rs)) of the respiratory system were subsequently estimated taken into consideration the presence of flow limitation. At zero PEEP, tau(rs) increased significantly toward the end of expiration due to an increase in Rrs. PEEP significantly decreased Rrs at the end of expiration and resulted in a faster and relatively constant rate of lung emptying., Conclusions: Patients with COPD exhibit a decrease in the rate of lung emptying toward the end of expiration due to an increase in Rrs. PEEP decreases Rrs, resulting in a faster and uniform rate of lung emptying.

The aim of the study was to assess the effects of varying the pressurisation rate during noninvasive pressure support ventilation on patients' breathing pattern, inspiratory effort, arterial blood gases, tolerance to ventilation and amount of air leakage. A total of 15 chronic obstructive pulmonary disease patients recovering from an acute episode of hypercapnic acute respiratory failure were studied during four randomised trials with different levels of pressurisation rate. No significant changes were observed in breathing pattern and arterial blood gases between the different runs. The pressure time product of the diaphragm, an estimate of its metabolic consumption, was significantly lower with all pressurisation rates than with spontaneous breathing, but was significantly lowest with the fastest rate. However, air leak, assessed by the ratio between expired and inspired tidal volumes, increased and the patients' tolerance of ventilation, measured using a standardised scale, was significantly poorer with the fastest pressurisation rate. In chronic obstructive pulmonary disease patients recovering from an episode of acute hypercapnic respiratory failure and ventilated with noninvasive pressure support ventilation, different pressurisation rates resulted in different reductions in the pressure time product of the diaphragm; this reduction was greater with the fastest rate, but was accompanied by significant air leaks and poor tolerance.

Although liver metastases are commonly found in cancer patients, fulminant hepatic failure (FHF) secondary to diffuse liver infiltration is rare. Furthermore, clinical presentation and laboratory findings are obscure and far from being pathognomonic for the disease. We report a case of a patient who died in the intensive care unit of our hospital from multiple organ failure syndrome secondary to FHF, as a result of liver infiltration from poorly differentiated small cell lung carcinoma. We also present the current knowledge about the clinical picture, laboratory findings and physical history of neoplastic liver-metastasis-induced FHF.