Performance of noninvasive ventilation modes on ICU ventilators during pressure support: a bench model study

Objective Noninvasive ventilation (NIV) is often applied with ICU ventilators. However, leaks at the patient-ventilator interface interfere with several key ventilator functions. Many ICU ventilators feature an NIV-specific mode dedicated to preventing these problems. The present bench model study aimed to evaluate the performance of these modes. Design and setting Bench model study in an intensive care research laboratory of a university hospital. Methods Eight ICU ventilators, widely available in Europe and featuring an NIV mode, were connected by an NIV mask to a lung model featuring a plastic head to mimic NIV conditions, driven by an ICU ventilator imitating patient effort. Tests were conducted in the absence and presence of leaks, the latter condition with and without activation of the NIV mode. Trigger delay, trigger-associated inspiratory workload, and pressurization were tested in conditions of normal respiratory mechanics, and cycling was also assessed in obstructive and restrictive conditions. Results On most ventilators leaks led to an increase in trigger delay and workload, a decrease in pressurization, and delayed cycling. On most ventilators the NIV mode partly or totally corrected these problems, but with large variations between machines. Furthermore, on some ventilators the NIV mode worsened the leak-induced dysfunction. Conclusions The results of this bench-model NIV study confirm that leaks interfere with several key functions of ICU ventilators. Overall, NIV modes can correct part or all of this interference, but with wide variations between machines in terms of efficiency. Clinicians should be aware of these differences when applying NIV with an ICU ventilator. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Patient–ventilator synchrony and sleep quality with proportional assist and pressure support ventilation

Objective

To examine patient–ventilator asynchrony and sleep quality in non-sedated critically ill patients ventilated with proportional assist ventilation with load adjustable gain factors (PAV+) and pressure support (PSV).

Methods

This was a randomized crossover physiological study conducted in an adult ICU at a tertiary hospital. Patients who exhibited patient–ventilator asynchrony on PSV were selected. Polysomnography was performed in these patients over 24 h, during which respiratory variables were continuously recorded. During the study period, each patient was randomized to receive alternating 4-h periods of PSV and PAV+ equally distributed during the day and night. Sleep architecture was analyzed manually using predetermined criteria. Patient–ventilator asynchrony was evaluated breath by breath using the flow–time and airway pressure–time waveforms.

Results

Fourteen patients were studied. The majority (85.7 %) had either acute exacerbation of COPD as admission diagnosis or COPD as comorbidity. During sleep, compared to PSV, PAV+ significantly reduced the patient–ventilator asynchrony events per hour of sleep [5 (1–17) vs. 40 (4–443), p = 0.02, median (25–75th interquartile range)]. Compared to PSV, PAV+ was associated with slightly but significantly greater sleep fragmentation [18.8 (13.1–33.1) versus 18.1 (7.0–22.8) events/h, p = 0.01] and less REM sleep [0.0 % (0.0–8.4) vs. 5.8 % (0.0–21.9), p = 0.02).

Conclusions

PAV+ failed to improve sleep in mechanically ventilated patients despite the fact that this mode was associated with better synchrony between the patient and ventilator. These results do not support the hypothesis that patient–ventilator synchrony plays a central role in determining sleep quality in this group of patients.     

Influence of ventilator settings on patient–ventilator synchrony during pressure support ventilation with different interfaces

Objective

To evaluate patient–ventilator interaction during pressure support ventilation (PSV) delivered with three interfaces [endotracheal tube (ET), face mask (FM), and helmet (H)] at different pressurization times (Time_press), cycling-off flow thresholds (Tr_exp), and respiratory rates (RR) in a bench study, and with FM and H in a healthy volunteers study.

Design

Bench study using a mannequin connected to an active lung simulator, and human study including eight healthy volunteers.

Measurements

PSV was delivered through the three interfaces with three different RR in the bench study, and through FM and H at two different RR in the human study. The mechanical and the neural RR, Ti, Te, inspiratory trigger delay (Delay_trinsp), pressurization time, and expiratory trigger delay were randomly evaluated at various ventilator settings (Time_press/Tr_exp: 50%/25%, default setting; 20%/5%, slow setting; 80%/60%, fast setting).

Results

Bench study: patient–ventilator synchrony was significantly better with ET, with lower Delay_trinsp and higher time of assistance (P < 0.001); the combination Time_press/Tr_exp 20%/5% at RR 30 produced the worst interaction, with higher rate of wasted efforts (WE) compared with Time_press/Tr_exp 80%/60% (20%, 40%, and 50% of WE versus 0%, 16%, and 26% of all spontaneous breaths, with ET, FM, and H, respectively; P < 0.01). In both studies, compared with H, FM resulted in better synchrony.

Conclusion

Patient–ventilator synchrony was significantly better with ET during the bench study; in the human study, FM outperformed H.     

Automatic adjustment of pressure support by a computer-driven knowledge-based system during noninvasive ventilation: a feasibility study

Objective

To evaluate the feasibility of using a knowledge-based system designed to automatically titrate pressure support (PS) to maintain the patient in a “respiratory comfort zone” during noninvasive ventilation (NIV) in patients with acute respiratory failure.

Design and setting

Prospective crossover interventional study in an intensive care unit of a university hospital.

Patients

Twenty patients.

Interventions

After initial NIV setting and startup in conventional PS by the chest physiotherapist NIV was continued for 45?min with the automated PS activated.

Measurements and results

During automated PS minute-volume was maintained constant while respiratory rate decreased significantly from its pre-NIV value (20?±?3 vs. 25?±?3?bpm). There was a trend towards a progressive lowering of dyspnea. In hypercapnic patients PaCO₂ decreased significantly from 61?±?9 to 51?±?2?mmHg, and pH increased significantly from 7.31?±?0.05 to 7.35?±?0.03. Automated PS was well tolerated. Two system malfunctions occurred prompting physiotherapist intervention.

Conclusions

The results of this feasibility study suggest that the system can be used during NIV in patients with acute respiratory failure. Further studies should now determine whether it can improve patient-ventilator interaction and reduce caregiver workload.

     

Neurally adjusted ventilatory assist (NAVA) improves patient–ventilator interaction during non-invasive ventilation delivered by face mask

Purpose

To determine if, compared to pressure support (PS), neurally adjusted ventilatory assist (NAVA) reduces patient–ventilator asynchrony in intensive care patients undergoing noninvasive ventilation with an oronasal face mask.

Methods

In this prospective interventional study we compared patient–ventilator synchrony between PS (with ventilator settings determined by the clinician) and NAVA (with the level set so as to obtain the same maximal airway pressure as in PS). Two 20-min recordings of airway pressure, flow and electrical activity of the diaphragm during PS and NAVA were acquired in a randomized order. Trigger delay (T _d), the patient’s neural inspiratory time (T _in), ventilator pressurization duration (T _iv), inspiratory time in excess (T _iex), number of asynchrony events per minute and asynchrony index (AI) were determined.

Results

The study included 13 patients, six with COPD, and two with mixed pulmonary disease. T _d was reduced with NAVA: median 35?ms (IQR 31–53?ms) versus 181?ms (122–208?ms); p?=?0.0002. NAVA reduced both premature and delayed cyclings in the majority of patients, but not the median T _iex value. The total number of asynchrony events tended to be reduced with NAVA: 1.0?events/min (0.5–3.1?events/min) versus 4.4?events/min (0.9–12.1?events/min); p?=?0.08. AI was lower with NAVA: 4.9 % (2.5–10.5 %) versus 15.8 % (5.5–49.6 %); p?=?0.03. During NAVA, there were no ineffective efforts, or late or premature cyclings. PaO₂ and PaCO₂ were not different between ventilatory modes.

Conclusion

Compared to PS, NAVA improved patient ventilator synchrony during noninvasive ventilation by reducing T _d and AI. Moreover, with NAVA, ineffective efforts, and late and premature cyclings were absent.     

Energy expenditure during weaning from mechanical ventilation: Is there any difference between pressure support and T-tube?

Background

The objectives of this study were to compare patients' energy expenditure (EE) during pressure support (PS) and T-tube (TT) weaning from mechanical ventilation (MV) through indirect calorimetry (IC) and to crosscheck these findings with the results calculated using Harris-Benedict (HB) equation.

Methods

This study is a randomized crossover controlled trial. Patients with clinical criteria for weaning from MV were randomized to PS-TT or TT-PS, with EE measurement for 20 minutes in PS and TT through IC. Energy expenditure was estimated through HB equation with and without activity factor. Statistical analysis used the Student t test for paired samples and Pearson correlation coefficient, as well as Bland-Altman method.

Results

Forty patients were included. The mean age and Acute Physiology and Chronic Health Evaluation II score were 56 ± 16 years and 23 ± 8, respectively, with predominance of male patients (70%). Mean EE of patients in TT (1782 ± 375 kcal/d) was 14.4% higher than in PS (1558 ± 304 kcal/d; P < .001). In relation to the EE obtained with the HB equation, the mean (SD) value calculated was 1455 (210) kcal/d, and when considering the activity factor, it was 1609 (236) kcal/d, all of them presenting correlation with the values from IC in PS (r = 0.647) and TT (r = 0.539). However, the limits of agreement between the measured EE and the estimated EE suggest that the HB equation tends to underestimate the EE.

Conclusion

Comparison of EE in PS and in TT through IC demonstrated that there is increased EE in the TT mode. The results suggest that the HB equation underestimates the EE of patients in weaning from MV.     

Heliox and noninvasive positive-pressure ventilation: a role for heliox in exacerbations of chronic obstructive pulmonary disease?

Evidence-based respiratory therapy for exacerbations of chronic obstructive pulmonary disease (COPD) includes oxygen, inhaled bronchodilators, and noninvasive positive-pressure ventilation. Examining the physics of gas flow, a case can be made either for or against the use of helium-oxygen mixture (heliox) in the care of patients with COPD. The evidence for the use of heliox in patients with COPD exacerbation is not strong at present. Most of the peer-reviewed literature consists of case reports, case series, and physiologic studies in small samples of carefully selected patients. Some patients with COPD exacerbation have a favorable physiologic response to heliox therapy, but predicting who will be a responder is difficult. Moreover, the use of heliox is hampered by the lack of widespread availability of an approved heliox delivery system. Appropriately designed randomized controlled trials with patient-important outcomes, such as avoidance of intubation, decreased intensive-care-unit and hospital days, and decreased cost of therapy, are sorely needed to establish the role of heliox in patients with COPD exacerbation, including those receiving noninvasive positive-pressure ventilation. Lacking such evidence, the use of heliox in patients with COPD exacerbation cannot be considered standard therapy.     

NASCAR pit-stop model improves delivery room and admission efficiency and outcomes for infants <27 weeks’ gestation

AimTo evaluate a new process based on teamwork in a manner similar to the race car pit stop on organization and efficiency during the “Golden Hours” for extremely preterm infants.MethodsA team designed an improved process focused on checklists, preparation, assigning roles, and best practices, for the care of infants <27 weeks’ gestation in the delivery room (DR) through admission to the neonatal intensive care unit (NICU). Clinical outcomes 2 years before and after implementation were analyzed. A survey was administered to NICU staff prior to and 14 months after implementation. The survey assessed organization and efficiency in the DR and during the admission process of the target population.ResultsThere were 62 inborn infants prior to and 90 infants after implementation with overall survival of 90.3% and 86.6%, respectively (p = 0.61). Infants were more stable on admission with a mean arterial blood pressure equal to or greater than their gestational age in the post intervention group compared to the pre-cohort (76% vs 57%, p = 0.02) and discharged home at a lower mean postmenstrual age (39.0 ± 2.2 vs 40.1 ± 3.5 weeks, p = 0.04) The survey demonstrated improvement in assessment of roles being clearly defined in the DR and in the organization and the efficiency both in the DR and during the NICU admission (p < 0.05).ConclusionsA systematic approach to the care of the <27 weeks’ gestation neonate increased staff perception of improved organization and efficiency in the DR through admission processes and improved outcomes.     

Recently published papers: delivery, volume and outcome--what is best for our patient?

Many studies have demonstrated that prompt appropriate treatment for the critically ill patient improves outcome. Moving patients to the best place for instituting care, however, is not always associated with improved outcome. Recent studies on delivering patients to the best place for treatment as well as further work on the effects of volume are discussed. Finally, a large retrospective cohort study comparing outcomes of patients treated with continuous venovenous haemofiltration or intermittent haemodialysis is outlined.     

What is the best support surface in prevention and treatment,as of 2012, for a patient at risk and/or suffering from pressure ulcer sore? Developing French guidelines for clinical practice

IntroductionThe use of support surfaces in the prevention and treatment of pressure ulcers prevention is an important part of care for a patient at risk and/or suffering from sore(s).ObjectivesDefine which support surfaces to use in prevention and treatment of at-risk and/or pressure sore patients.MethodologyA systematic review of the literature querying the several Pascal Biomed, PubMed and Cochrane Library databases from 2000 through 2010.Results (Grade A)In prevention, a structured foam mattress is more efficient than a standard hospital mattress. An alternating pressure mattress is more effective than a visco-elastic mattress limiting the occurrence heel pressure ulcers, but those that do occur are more serious. A low-air-loss bed is more efficient than a mixed pulsating air mattress in prevention of heel pressure ulcers. Some types of sheepskin can reduce sacral pressure ulcer incidence in orthopedic patients. Use of an overlay on an operating table limits the occurrence of peroperative and postoperative pressure ulcers. An air-fluidized bed improves pressure ulcer healing.DiscussionThe data in the literature are not always relevant and do not suffice to dictate a clinician's choices. We are compelled to recognize the methodological limitations of many studies, the lack of corporate interest in conducting such studies and the relatively small number of available trials. However, the effectiveness of some support surfaces reaches a sufficient level of evidence, especially when they are associated with postural, hydration and nutritional measures.ConclusionSupport surfaces are recommended in prevention and treatment of patients at risk and/or already suffering from pressure ulcer, and their use should constitute part of an overall preventive or curative strategy.     

Pressure support and pressure assist/control: are there differences? An evaluation of the newest intensive care unit ventilators

BACKGROUND: Pressure support (PS) has been widely studied in both patients and lung models, but there is little data available evaluating pressure assist/control (P A/C, frequently referred to as PCV) and no data comparing the operational capabilities of these two modes on the newest generation of ICU ventilators. We used a spontaneously breathing lung model to evaluate the response of the following new generation ventilators to varying inspiratory demand in both PS and P A/C: Bear 1000, Dr?ger Evita 4, Hamilton Galileo, Nellcor Puritan-Bennett 840 and 740, Siemens Servo 300A, TBird AVS. METHODS: A bellows-in-a-box lung model was set at a respiratory rate of 12 breaths/min, inspiratory time of 1.0 second, and peak inspiratory flows (modified square wave) of 40, 60, and 80 L/min. Each ventilator was set at three levels of PS and P A/C: 10, 15, and 20 cm H(2)O. On all ventilators, flow-triggering was set as sensitive as possible without causing self-triggering. RESULTS: Trigger pressure, trigger pressure-time product, inspiratory trigger time delay, ventilator-delivered peak flow, inspiratory area as a percent of the ideal inspiratory area, expiratory time delay, supraplateau expiratory pressure change, and expiratory area all varied among ventilators and at different lung model peak flows (p < 0.01 and >/= 10% difference). However, PS and P A/C on a given ventilator only differed with regard to expiratory variables (p < 0. 01 and >/= 10% difference). CONCLUSION: In a given ventilator little difference exists in gas delivery and response variables between PS and P A/C, but performance differences do exist among the ventilators evaluated. Ventilator performance is diminished at high lung model peak flows and low pressure settings. (I)), whereas PS gives control over ending inspiration to the patient. What has not been clearly defined is the gas delivery and ventilator response differences, if any, between these two (PS and P A/C) pressure targeted assist modes. Most new generation intensive care unit (ICU) ventilators provide both pressure support (PS) and pressure assist/control (P A/C) ventilation.19,20 The specific operational difference between these two modes is the mechanism that transitions inspiration to expiration. With pressure support the primary mechanism is a decrease in peak inspiratory flow to a predetermined level, whereas with P A/C mechanical T(I) is preset.19,20 We compared the operation of seven of the newest generation ICU ventilators in a spontaneously breathing lung model in both PS and P A/C. We hypothesized that there would be no difference in variables assessed between PS and P A/C except for the transition to expiration and that there would be no difference in response among ventilators evaluated.