Extubation after breathing trials with automatic tube compensation,T-tube,or pressure support ventilation

BACKGROUND: Automatic tube compensation (ATC) is a new option to compensate for the pressure drop across the endotracheal or tracheostomy tube (ETT), especially during ventilator-assisted spontaneous breathing. While several benefits of this mode have so far been documented, ATC has not yet been used to predict whether the ETT could be safely removed at the end of weaning, from mechanical ventilation. METHODS: We undertook a systematic trial using a randomized block design. During a 2-year period, all eligible patients of a medical intensive care unit were treated with ATC, conventional pressure support ventilation (PSV, 5 cmH2O), or T-tube for 2-h. Tolerance of the breathing trial served as a basis for the decision to remove the endotracheal tube. Extubation failure was considered if reintubation was necessary or if the patient required non-invasive ventilatory assistance (both within 48 h). RESULTS AND CONCLUSIONS: After the inclusion of 90 patients (30 per group) we did not observe significant differences between the modes. Twelve patients failed the initial weaning trial. However, half of the patients who appeared to fail the spontaneous breathing trial on the T-tube, PSV, or both, were successfully extubated after a succeeding trial with ATC. Extubation was thus withheld from four and three of these patients while breathing with PSV or the T-tube, respectively, but to any patient breathing with ATC. It seems that ATC can be used as an alternative mode during the final phase of weaning from mechanical ventilation. Furthermore, this study may promote a larger multicenter trial on weaning with ATC compared with standard modes.     

生理呼吸功指导呼吸机脱机的临床意义

目的:评价生理呼吸功(WOBphy)对机械通气患者脱机的指导作用。方法:测定患者呼吸功(WOBt)和器械附加功(WOBimp)。并推算WOBphy。不符合常规脱机标准者,如WOBphy<0.70J/L,仍立即脱机拔管。结果:41例患者中28例符合常规脱机际准(常规组),WOBphy均<0.70J/L,拔管后1例再插管。13例患者不符合常规脱机标准(非常规组),WOBt高达1.37±0.50J/L,但 WOBphy均于0.70J/L,立即拔管后仪1例再插管。结论:以WOBphy<0.70J/L作为脱机标准,比常规脱机际准更准确。     

Relationship between respiratory pattern and work of breathing during halothane anesthesia with spontaneous ventilation

Journal of Anesthesia -     

Rebreathing, resistance and external work of breathing in three different coaxial Mapleson D systems

Using a lung model, rebreathing characteristics, resistance against gas flow and the external work of breathing were tested in three different coaxial Mapleson D systems: the Medicvent D system, the Bain original system and the Coax-II system. The rebreathing characteristics were found to be similar in all systems in both spontaneous and controlled ventilation. The Bain system was found to have the lowest resistance and work of breathing and the Coax-II system the highest. The differences were small and clinically insignificant. Both the resistance and the work of breathing increased with fresh gas flow. The resistance against expiration was found to be in the range 135-160 Pa at a total gas flow of 31 1.min-1, which is well within the acceptable level. The resulting end-expiratory pressure was never above 100 Pa (1 cmH2O) in any system. We concluded that there was no clinically significant difference among the three systems despite differences in design. The coaxial Mapleson D systems can also be used safely with high fresh gas flows with regard to resistance and end-expiratory pressures.     

Impairment of chest wall mechanics and increased chest wall work of breathing cause postoperative respiratory failure in patients who have undergone radical esophagectomy

Purpose. We verified the hypothesis that impairment of chest wall mechanics would be related to the cause of postoperative respiratory failure in patients undergoing radical esophagectomy. Methods. A total of 21 patients were studied. After management with mechanical ventilation to prevent respiratory failure for several days, trial weaning from the ventilator was performed. The patients were divided into a successful weaning group (S group) and an unsuccessful weaning group (US group), depending on the results of the weaning trial. We compared respiratory mechanics and the respiratory work of breathing during weaning from the ventilator between the two groups. Results. In the US group, lung and chest wall compliance was significantly lower and the development of intrinsic positive end-expiratory pressure (PEEPi) was observed. The work of breathing and the oxygen cost of breathing were significantly higher in the US group. The increased respiratory energy work was due to a moderate increase in lung work and a significant increase in chest wall work. Conclusion. Our results suggested that postoperative respiratory failure was related to increased respiratory energy expenditure, significantly deteriorated chest wall mechanics, and increased chest wall work, all of which are involved in the development of postoperative respiratory failure after radical esophagectomy. Received: September 11, 2000 / Accepted: January 22, 2001     

Elastic work of breathing during continuous positive airway pressure in intubated patients with chronic obstructive pulmonary disease (theoretical analysis and experimental validation)

Background: Continuous positive airway pressure (CPAP) is known to decrease inspiratory work of breathing in patients with chronic obstructive pulmonary disease (COPD). This effect is primarily attributed to a reduction in inspiratory elastic work of breathing (Wi,el) related to a decrease in intrinsic positive end-expiratory pressure (PEEP).
Methods: The aim of this study is to design a model for computation of Wi,el on the basis of respiratory mechanics in patients with COPD, at various intrinsic PEEP- and CPAP-levels. The model was used to estimate the optimal CPAP-level with respect to the intrinsic PEEP-level in terms of reduction of Wi,el. Calculations of the decrease in Wi,el due to CPAP obtained with the model were compared to changes in Wi,el and total work of breathing (Wi,tot) determined from respiratory measurements in patients with COPD.
Results: Model calculations revealed that Wi,el was minimal whenever a CPAP-level equal to the intrinsic PEEP-level was applied. When a CPAP-level exceeding the intrinsic PEEP-level was applied, the reduction in Wi,el was less. Comparing these results to the respiratory measurements, a similar pattern in reduction of Wi,el and Wi,tot was established, although absolute values of the differences were smaller in the experimental data.
Conclusion: This study indicates that in order to reduce Wi, el in patients with COPD, intrinsic PEEP should be measured and the CPAP-level adjusted to the intrinsic PEEP-level.     

Effect of expiratory resistance on gas-exchange and breathing pattern in chronic obstructive pulmonary disease (COPD) patients being weaned from the ventilator

BACKGROUND: The majority of patients with severe chronic obstructive pulmonary disease (COPD) have flow limitation, which has deleterious side effects. If these patients are mechanically ventilated, this often results in difficult weaning. Spontaneously breathing COPD patients experience a beneficial effect of pursed lip breathing. We investigated whether in intubated COPD patients application of an external resistance could produce the same beneficial effects on breathing pattern and gas-exchange as pursed lip breathing. METHODS: Ten COPD patients with flow limitation were studied during pressure support mechanical ventilation. Two types of expiratory resistances were applied: one fixed level of resistance and one with a resistive pressure decay. Each resistance was applied in 5 patients and the highest level was chosen that did not cause hyperinflation. Blood gas values and breathing pattern with and without resistance were compared. RESULTS: With resistance 1, gas-exchange and breathing pattern did not change significantly; average PCO2 changed from 8.0 to 8.1 kPa, PO2 from 10.2 to 10.3 kPa, tidal volume from 0.380 to 0.420 l, respiratory rate from 25 to 23 bpm and inspiratory:expiratory ratio from 1:1.9 to 1:2.0. With resistance 2, gas-exchange and breathing pattern did not change significantly; average PCO2 changed from 5.8 to 6.0 kPa, PO2 from 11.1 to 12.1 kPa, tidal volume from 0.733 to 0.695 l, respiratory rate from 16 to 18 bpm and inspiratory:expiratory ratio from 1:2.3 to 1:2.9. CONCLUSION: In intubated COPD patients being weaned from the ventilator, application of an external resistance did not have the same beneficial effects as pursed lip breathing.     

Bi-level positive airway pressure ventilation maintains adequate ventilation in post-polio patients with respiratory failure

BACKGROUND: Patients suffering from post-polio syndrome still contribute significantly to the number of patients with chronic respiratory failure requiring home mechanical ventilation (HMV). Many of these patients are treated either with invasive (tracheostomy) or non-invasive (nasal mask) controlled mechanical ventilation i.e. volume-controlled ventilation (VCV). In this group of patients, we have previously shown that bi-level pressure support ventilation (bi-level PSV) decreases the oxygen cost of breathing. The aim of this study was to compare the effect of bi-level PSV, with special regard to the adequacy of ventilation and the oxygen cost of breathing, during the patients' ordinary VCV and spontaneous breathing. METHODS: Eight post-polio patients on nocturnal VCV were investigated. Five of them were tracheostomized and three of them used a nasal mask. Work of breathing was analysed by assessing differences in oxygen consumption (VO2) using indirect calorimetry. Blood gases were obtained regularly to assess adequacy of ventilation. RESULTS: Bi-level PSV decreases the oxygen cost of breathing in post-polio patients with respiratory failure without decreasing ventilation efficiency. Furthermore, PaCO2 decreased significantly using this mode of ventilation (P < 0.05). CONCLUSION: In this study, it was shown that bi-level PSV reduces the oxygen cost of breathing and gave a significant decrease in PaCO2 in PPS patients. These data suggest that bi-level PSV ventilation maintains adequate ventilation in patients who suffer from post-polio syndrome with respiratory failure.     

Work of breathing in anesthetized infants increases when a breathing system filter is used

BACKGROUND: There are concerns that the inclusion of a pediatric heat and moisture exchange filter (HMEF) is in a breathing system may cause an unacceptable increase in the work of breathing. This study is the first study to objectively measure the increase in work of breathing in the infant population when an HMEF is added to the pediatric breathing circuit. METHODS: Ten patients weighing 3-8 kg were studied in a randomized crossover trial. Work of breathing was analyzed using the integral of pressure-volume loops. RESULTS: The median increase in the work of breathing associated with the addition of an HMEF was 279 mJ x min(-1) (95% CI, 165-903 mJ x min(-1)). This equates with a percentage increase of 43% (95% CI, 25-138%). CONCLUSIONS: Because of the substantial increase in the work of breathing with an HMEF attached to the tracheal tube, consideration should be given to alternative means of humidification and filtration during periods of spontaneous ventilation in small infants.     

Performance of an oxygen delivery device for weaning potentially infectious critically ill patients

Oxygen delivery via a heat and moisture exchange filter with an attached T-shaped reservoir satisfies infection control requirements of high efficiency bacterial and viral filtration and low gas flows. In order to assess the performance of such a device in critically ill patients being weaned from mechanical ventilation, we simulated 16 patients using a human patient simulator, measuring fractional inspired oxygen and carbon dioxide concentrations and work of breathing at three oxygen flow rates. Oxygen concentration was dependent on peak inspiratory flow rate, tidal volume and oxygen flow rate. Rebreathing, as indicated by inspired carbon dioxide concentration, was greatest at high respiratory rates and low tidal volumes. Imposed inspiratory work of breathing was relatively high (mean 0.88 J.l(-1)[SD 0.30]). We conclude that this method of oxygen delivery is only suitable for patients in whom rapid extubation is anticipated.     

Bi-level positive airway pressure ventilation reduces the oxygen cost of breathing in long-standing post-polio patients on invasive home mechanical ventilation

BACKGROUND: Today, patients with chronic respiratory failure are commonly treated with non-invasive bi-level positive airway pressure ventilation, supporting spontaneous breathing. However, in conformity with previous clinical routine, many post-polio patients with chronic respiratory failure are still treated with invasive (i.e. via a tracheostomy) controlled mechanical ventilation (CMV). The aim of the study was to investigate the effect of invasive bi-level positive airway pressure ventilation on the work of breathing compared with that during the patients' ordinary CMV and spontaneous breathing without mechanical support. METHODS: Nine post-polio patients on invasive (tracheostomy) nocturnal CMV were investigated. Work of breathing was analysed by assessing differences in oxygen consumption (VO2) using indirect calorimetry. Hereby, the oxygen cost of breathing during the various ventilatory modes could be estimated and related to one another. Data on energy expenditure were also obtained. RESULTS: The oxygen cost of breathing decreased by approximately 15% during bi-level positive airway pressure ventilation compared with CMV and spontaneous breathing. There was no difference between predicted (Harris-Benedict equation) and measured energy expenditure. CONCLUSION: Invasive bi-level positive airway pressure ventilation reduces the oxygen cost of breathing in long-standing tracheostomized post-polio patients, compared with CMV. Furthermore, the Harris-Benedict equation provides a reasonable prediction of energy expenditure in this group of patients.     

Lower airway humidification in spontaneously breathing tracheostomized patients: comparative study of trachea spray versus heated humidifier

BACKGROUND: Our aim was to compare inhalation with molecular water (vaporizing humidifier) and particulate water (trachea spray) in spontaneously breathing tracheostomized patients. METHODS: We performed a randomized, 2-way crossover study and a prospective, comparative, nonblinded study. Tracheal humidity and temperature were measured before and after use of a humidifier and spray for 1 week. RESULTS: After both inhalation and spray, the tracheal temperature and total water content increased significantly (study 1). The temperature gradient between ambient and tracheal air was significantly higher after spray, but not after inhalation (study 2). The water gradient increased nonsignificantly after spray and inhalation. The water gradient after inhalation or spray did not differ significantly. CONCLUSIONS: Molecular water is not superior to particulate water because of temperature and humidity increase after both forms of water delivery. Because of its easy use, portability, and moisturizing effect, a trachea spray may offer additional options in postoperative tracheostomy care.     

Breathing pattern associated with respiratory comfort during automatic tube compensation and pressure support ventilation in normal subjects

BACKGROUND: Automatic tube compensation (ATC) is a new option to support spontaneously breathing tracheally intubated patients. We have previously demonstrated an increased respiratory comfort compared to pressure support ventilation (PSV) in volunteers. Here we characterized the breathing pattern during ATC associated with respiratory comfort in comparison to PSV. Furthermore, we studied whether ATC can be substituted by a simple modification of PSV. METHODS: We exposed 10 volunteers breathing through a 7.5 mm endotracheal tube via mouthpiece to PSV with 1) immediate and 2) delayed pressure rise and to 3) ATC. Immediate changes of the respiratory pattern after mode shifts were analyzed in detail. Furthermore, the volunteers were instructed to indicate changes in comfort after transitions between these modes as increased, unchanged, or decreased. RESULTS: Decreased comfort was associated with a substantial increase of tidal volume, minute ventilation, gas flow, and pressure. No differences in respiratory comfort were perceived between immediate and delayed pressure rise during PSV. Conclusion: PSV resulted in excessive tidal volumes and airflow, which was perceived as discomfort. This cannot be avoided by a delayed pressure rise but can be by the more comfortable ATC. ATC seems to adapt better to the ventilatory demand than PSV.     

Quality of life following surgery for sleep disordered breathing: subtotal reduction adenotonsillectomy versus adenotonsillectomy in Australian children

Background: Adenotonsillectomy (AT) is indicated for children with obstructive sleep disordered breathing; however it has associated well‐documented morbidity. A subtotal reduction AT has made a resurgence overseas, given a significantly reduced morbidity. This study hypothesized that full AT would provide a greater improvement in quality of life (QOL) when compared with a subtotal reduction AT (SRAT) in children with obstructive sleep disordered breathing. Methods: This cohort study used a single surgeon consecutive series of 181 children from the database of the senior author (ASC) following full AT (n= 118) or SRAT (n= 63). QOL was measured by the Glasgow Children's Benefit Inventory (GCBI), which was mailed to parents 3 months to 2 years post‐operatively. Results: Ninety‐one of the 155 (59%) questionnaires were returned. There was an increase in QOL for children following AT (GCBI Total =+41.5) and SRAT (GCBI Total =+49.5). A significant increase in QOL was noted for all four domains of the GCBI. The GCBI total and four domains had no statistically significant difference in the improvement of scores by the two surgical groups. Conclusion: In this study, an SRAT provides identical post‐operative QOL outcomes to full AT when performed for sleep disordered breathing in children. This adds to the evidence that in the absence of infective episodes, SRAT can be considered as a lower risk alternative to full AT.     

Mortality,functional and return to work outcomes of major trauma patients injured from deliberate self-harm

BackgroundSelf-harm and intentional injuries represent a significant public health concern. People who survive serious injury from self-harm can experience poor outcomes that negatively impact on their daily life. The aim of this study was to investigate a cohort of major trauma patients hospitalised for self-harm in Victoria, and to identify risk factors for longer term mortality, functional recovery and return to work.Method482 adult major trauma patients who were injured due to self-harm and survived to hospital discharge, and were captured by the population-based Victorian State Trauma Registry (VSTR), were included. For those with a date of injury from January 1, 2007 to December 31, 2013, demographics and injury event data, Glasgow Outcome Scale Extended (GOS-E) and return to work (RTW) outcomes at 6, 12 and 24 months post-injury were extracted from the registry. Post-discharge mortality was identified through the Victorian Registry of Births, Deaths and Marriages (BDM). Multivariable logistic regression was used to determine predictors of the GOS-E and RTW and survival analysis was used to identify predictors of mortality.ResultsA total of 37 (7.7%) deaths occurred post-discharge. There were no clear predictors of all-cause mortality. Overall, 36% of patients reported making a good recovery at 24 months. Older age (p = 0.01), transport-related methods of self-harm (p = 0.02), higher Injury Severity Score (p < 0.001) and having a Charlson Comorbidity Index weighting of one or more (p = 0.02) were predictive of poorer functional recovery. Of patients who were working or studying prior to injury, 54% reported returning to work by 24 months post-injury. Higher Injury Severity Score was an important predictor of not returning to work (p = 0.002).ConclusionThe vast majority of major trauma patients who self-harmed and survived to hospital discharge were alive at two years post-injury, yet only half of this cohort returned to work and just over a third of patients experienced a good recovery.     

Effect of continuous positive airway pressure (CPAP) in patients with chronic obstructive pulmonary chsease (COPD) depending on intrinsic PEEP levels

The application of continuous positive airway pressure (CPAP) is known to reduce inspiratory work of breathing in intubated patients with chronic obstructive pulmonary disease (COPD). This effect is caused by a decrease in elastic work related to a reduction in intrinsic PEEP. The aim of this study was to relate the decrease in inspiratory work due to CPAP to the intrinsic PEEP levels obtained during spontaneous breathing without positive pressure. Ten intubated patients with COPD who had been ventilated for acute respiratory failure were studied. Intrinsic PEEP was determined during tracheal occlusions performed at end-expiration when the patient was breathing without positive airway pressure. Inspiratory work was computed during breathing through a circuit with a CPAP of 0.5 kPa and the same circuit without positive pressure. Intrinsic PEEP-levels ranged from 0.26 to 1.31 kPa. Compared to spontaneous breathing without positive pressure, CPAP reduced the total inspiratory work per liter of ventilation (Wltot) from 1.42±0.48 to 1.24±0.50 J·1^-1 (means±SD P <0.01). This decrease was found to be related to the intrinsic PEEP-levels: the largest reductions were found in the patients with an intrinsic PEEP-level close to the CPAP-level applied. In intubated patients with COPD, the decrease in Wltot due to a CPAP of 0.5 kPa was found to be related to the intrinsic PEEP-levels present when no positive airway pressure was applied. The intrinsic PEEP measured during tracheal occlusions could be used to estimate the effect of CPAP in these patients.     

Effort–reward imbalance at work: the effects of work stress on anger and cardiovascular disease symptoms in a community sample

Two studies of the Effort–Reward Imbalance (ERI) model of work stress with different end points were undertaken in community samples from the Adelaide (Australia) metropolitan area. Study 1 examined the relationship between ERI at work and state anger. Study 2 extended the first and examined the relationship between ERI, anger and cardiovascular disease (CVD) symptoms. Hierarchical multiple regression confirmed a significant relationship between ERI and state anger in Study 1 even after controlling for extraneous variables. Study 2 showed that ERI increases CVD symptoms via the mediating variable of anger (an indirect effect). Furthermore, Study 2 revealed that people of lower income were more likely to experience higher anger. The results of both studies have far ranging consequences for the emotional and physical health of individuals who are experiencing an imbalance between their efforts and perceived rewards at work and those with lower incomes may be more vulnerable. The wider public health implications of the relationship between work stress, and emotional and physical well being in the community are discussed. Copyright © 2005 John Wiley & Sons, Ltd.