Improve Patient-ventilator Synchrony Research Articles

SMART Trigger versus Flow and Pressure trigger performance during auto-PEEP

Background Intrinsic positive end-expiratory pressure (auto-PEEP) is a common problem in mechanically ventilated patients, which can lead to adverse effects on patients comfort, hemodynamics, lung mechanics and gas exchange. Triggering systems play a crucial role in the delivery of mechanical ventilation, and advancements in smart triggering technology aim to optimize patient-ventilator synchrony. This bench study aims to compare the performance of the novel SMART Trigger to traditional pressure and flow triggers in the context of auto-PEEP. Methods A lung model simulating severe obstructive pattern with high compliance (80 ml/cmH2O) and high resistance 30 cmH2O/L/s was connected to the Panther 5 ventilator (Origin Medical, California, USA). The mode was set at Volume Controlled with a tidal volume of 700 ml and mandatory breath per min (BPM) of 10/min and Inspiratory time of 2 seconds to intentionally create auto-PEEP. Simulated spontaneous breaths set at 20 BPM with increasing muscle pressure (Pmus) from -1 to maximum of -25 or till full trigger of all breaths. Three different triggering systems were evaluated: SMART Trigger (ST sensitivity 1 to 7), pressure trigger (-1 cmH2O), and flow trigger (1 l/min). The range of auto-PEEP levels induced increased incrementally with the increase in the respiratory rate ranging from 3 cmH2O for 10 BPM, 8 for 15 BPM, to 13 for 20 BPM. The following parameters were assessed for each triggering system: trigger sensitivity (defined as the number of breaths triggered above the mandatory breaths), and the trigger response time (time it takes from the beginning of muscle effort to the initiation of the breath. Results 100% of the breaths were triggered at Pmus (cmH2O) of -15 in the pressure trigger, -25 in flow trigger, -3 for ST1, -9 for ST2, -10 for ST3, -10 for ST4, -12 for ST5, -18 for ST 6, and -22 for ST 7. Trigger time (msec) for flow was 0.135 ± 0.02, for pressure 0.141 ± 0.04, for ST 1-4: 0.076 ± 0.03, for ST 5-7: 0.104 ± 0.04. Multivariate analysis of variance test showed significant difference between the time to trigger P <0.001. Conclusion This bench study highlights the potential advantages of SMART Trigger technology over conventional pressure and flow triggers during auto-PEEP. The SMART Trigger enhanced sensitivity and rapid response might contribute to improved patient-ventilator synchrony. Further research and clinical studies are warranted to validate these findings and explore the impact of smart trigger technology on patient outcomes in real-world scenarios. Keywords: SMART Trigger, Auto-PEEP, Trigger time

Neural control of pressure support ventilation improved patient-ventilator synchrony in patients with different respiratory system mechanical properties: a prospective, crossover trial.

BackgroundConventional pressure support ventilation (PSP) is triggered and cycled off by pneumatic signals such as flow. Patient-ventilator asynchrony is common during pressure support ventilation, thereby contributing to an increased inspiratory effort. Using diaphragm electrical activity, neurally controlled pressure support (PSN) could hypothetically eliminate the asynchrony and reduce inspiratory effort. The purpose of this study was to compare the differences between PSN and PSP in terms of patient-ventilator synchrony, inspiratory effort, and breathing pattern.MethodsEight post-operative patients without respiratory system comorbidity, eight patients with acute respiratory distress syndrome (ARDS) and obvious restrictive acute respiratory failure (ARF), and eight patients with chronic obstructive pulmonary disease (COPD) and mixed restrictive and obstructive ARF were enrolled. Patient-ventilator interactions were analyzed with macro asynchronies (ineffective, double, and auto triggering), micro asynchronies (inspiratory trigger delay, premature, and late cycling), and the total asynchrony index (AI). Inspiratory efforts for triggering and total inspiration were analyzed.ResultsTotal AI of PSN was consistently lower than that of PSP in COPD (3% vs. 93%, P = 0.012 for 100% support level; 8% vs. 104%, P = 0.012 for 150% support level), ARDS (8% vs. 29%, P = 0.012 for 100% support level; 16% vs. 41%, P = 0.017 for 150% support level), and post-operative patients (21% vs. 35%, P = 0.012 for 100% support level; 15% vs. 50%, P = 0.017 for 150% support level). Improved support levels from 100% to 150% statistically increased total AI during PSP but not during PSN in patients with COPD or ARDS. Patients’ inspiratory efforts for triggering and total inspiration were significantly lower during PSN than during PSP in patients with COPD or ARDS under both support levels (P < 0.05). There was no difference in breathing patterns between PSN and PSP.ConclusionsPSN improves patient-ventilator synchrony and generates a respiratory pattern similar to PSP independently of any level of support in patients with different respiratory system mechanical properties. PSN, which reduces the trigger and total patient's inspiratory effort in patients with COPD or ARDS, might be an alternative mode for PSP.Trial RegistrationClinicalTrials.gov, NCT01979627; https://clinicaltrials.gov/ct2/show/record/NCT01979627.

In Response.

We appreciate the interest of Drs Madhok and Mihm1 in our article2 and their suggestions on how to optimize sedation management in coronavirus disease 2019 (COVID-19) patients. The authors point out the interrelated problems of prolonged mechanical ventilation, choice of sedative drugs, and sedation depth1 that we would like to further address. A recently published analysis from 2 academic hospitals in Boston3—one of the most affected regions in the United States—revealed median duration of invasive mechanical ventilation of 16 days in COVID-19 patients who were successfully extubated. Given these prolonged periods of sedation and immobility, there clearly is a need to implement sedation approaches that would facilitate lung-protective ventilation but that would also limit the rates of oversedation, delirium, sedation-related encephalopathy, and subsequent functional disability in COVID-19 survivors. Older and frail patients are especially susceptible to these adverse outcomes. Propofol, ketamine, dexmedetomidine, and intravenous opioids have been the typical components of the multimodal regimen used across the 10 intensive care units (ICUs) dedicated to treatment of COVID-19 within our institution. This benzodiazepine-free approach has not been uniformly attainable in all patients with COVID-19. The addition of midazolam is typically seen in patients with rising triglyceride levels (due to propofol), rising creatine kinase levels (due to propofol), worsening QT interval prolongation (due to haloperidol, ketamine, azithromycin, and hydroxychloroquine), insufficient sedation depth during paralysis, and in patients with hemodynamic instability. Once introduced, we believe that benzodiazepines should be administered at lowest doses that are sufficient to achieve sedation targets and that allow regular neurologic assessments. Benzodiazepines should also be the first agents discontinued due to their deliriogenic effects and prolonged context-sensitive half time. As mentioned by Drs Madhok and Mihm,1 management of sedation that allows neurologic assessments in patients with COVID-19 is critical given the reports of acute neurologic complications such as cerebrovascular accidents.4 Escalation of the doses of benzodiazepines over the course of the ICU stay without appropriate neuromonitoring in place should be discouraged, and alternative solutions should be sought. It must be emphasized that further deepening the levels of sedation with propofol or benzodiazepines in already adequately sedated patients is unlikely to improve patient-ventilator synchrony, and a bolus dose of neuromuscular blockers might be more appropriate to achieve ventilator synchrony. The use of oral adjuncts (eg, quetiapine, propranolol, clonidine, gabapentin) has been proposed to reduce the doses and side effects of intravenous sedatives and to mitigate shortages of intravenous drugs. In our own experience, utility of these oral agents in critically ill COVID-19 patients has been limited due to high prevalence of ileus,5 intolerance of enteral feeding, and unreliable absorption. We propose that these oral agents might be useful during ventilator and intravenous sedation weaning in patients who manifest signs of withdrawal (hypertension, tachycardia, and delirium), are not on vasopressor support, and in whom bowel function has returned. We have frequently been introducing these enteral agents in patients with COVID-19 who require intermittent or prolonged mechanical ventilation after undergoing a tracheostomy. Finally, we propose that sedation management should be individualized based on respiratory variables. It has been established that COVID-19–induced acute respiratory distress syndrome (ARDS) is a heterogeneous entity.6 While deeper levels of sedation might be indicated in patients with severe hypoxemia and poor lung compliance (eg, during proning, paralysis, high levels of positive end-expiratory pressure [PEEP]), patients with well-preserved compliance might tolerate spontaneous modes of ventilation and lighter sedation levels (eg, dexmedetomidine alone). Bedside assessments of respiratory mechanics might be useful to identify patients with ARDS in whom high respiratory drive and larger tidal volumes are not injurious7 so that they are not exposed to deep sedation and prolonged controlled ventilation unnecessarily. A proactive practice of tailoring sedation and ventilator support might reduce the length of mechanical ventilation and improve long-term outcomes in patients with COVID-19. Dusan Hanidziar, MD, PhDEdward A. Bittner, MD, PhDDepartment of Anesthesia, Critical Care and Pain MedicineMassachusetts General HospitalBoston, Massachusetts[email protected]

To Block or Not: Updates in Neuromuscular Blockade in Acute Respiratory Distress Syndrome.

Objective: To review and evaluate neuromuscular blocking agents (NMBAs) in critically ill patients with acute respiratory distress syndrome (ARDS). Data Sources: A literature search utilizing PubMed was performed (January 1991 to January 2020) using the following search terms: (neuromuscular blocking agents OR neuromuscular blockade OR cisatracurium OR rocuronium OR vecuronium OR pancuronium OR atracurium) AND *acute respiratory distress syndrome OR acute lung injury). Publications in English were evaluated. Study Selection and Data Extraction: Relevant clinical studies in humans were considered. Data Synthesis: Although NMBAs have been used for decades in the setting of ARDS, questions regarding mortality benefit remain. Early NMBA, within 48 hours of lung injury, have been historically used in critically ill patients with ARDS to aid in increasing alveolar recruitment, improving patient-ventilator synchrony, and promoting oxygenation by the prevention of contraction of respiratory muscles. Until recently, the literature showed an improvement in 90-day adjusted mortality. However, recent literature has demonstrated the lack of a mortality benefit. The continued receipt of NMBAs, with no clear benefit, could potentially lead to increased costs, skin breakdown, corneal abrasions, venous thromboembolisms, intensive care unit acquired weakness, and awareness with inappropriate sedation. Relevance to Patient Care and Clinical Practice: This review aims at discussing the preferred NMBA based on mechanism of action and reviews specific clinical trial data for the use of NMBAs in ARDS, clinical implications of these trial data, complications for the use of NMBAs, and needed future directions. Conclusions: The mortality benefit of NMBAs in ARDS has contradicting evidence with potentially serious adverse effects and notable controversies.

Effect of Neurally Adjusted Ventilatory Assist on Patient-Ventilator Interaction in Mechanically Ventilated Adults: A Systematic Review and Meta-Analysis.

Patient-ventilator asynchrony is common among critically ill patients undergoing mechanical ventilation and has been associated with adverse outcomes. Neurally adjusted ventilatory assist is a ventilatory mode that may lead to improved patient-ventilator synchrony. We conducted a systematic review to determine the impact of neurally adjusted ventilatory assist on patient-ventilator asynchrony, other physiologic variables, and clinical outcomes in adult patients undergoing invasive mechanical ventilation in comparison with conventional pneumatically triggered ventilatory modes. We searched Medline, EMBASE, Cochrane Database of Systematic Reviews, Cochrane Central, CINAHL, Scopus, Web of Science, conference abstracts, and ClinicalTrials.gov until July 2018. Two authors independently screened titles and abstracts for randomized and nonrandomized controlled trials (including crossover design) comparing the occurrence of patient-ventilator asynchrony between neurally adjusted ventilatory assist and pressure support ventilation during mechanical ventilation in critically ill adults. The asynchrony index and severe asynchrony (i.e., asynchrony index > 10%) were the primary outcomes. Two authors independently extracted study characteristics and outcomes and assessed risk of bias of included studies. Of 11,139 unique citations, 26 studies (522 patients) met the inclusion criteria. Sixteen trials were included in the meta-analysis using random effects models through the generic inverse variance method. In several different clinical scenarios, the use of neurally adjusted ventilatory assist was associated with significantly reduced asynchrony index (mean difference, -8.12; 95% CI, -11.61 to -4.63; very low quality of evidence) and severe asynchrony (odds ratio, 0.42; 95% CI, 0.23-0.76; moderate quality of evidence) as compared with pressure support ventilation. Furthermore, other measurements of asynchrony were consistently improved during neurally adjusted ventilatory assist. Neurally adjusted ventilatory assist improves patient-ventilator synchrony; however, its effects on clinical outcomes remain uncertain. Randomized controlled trials are needed to determine whether the physiologic efficiency of neurally adjusted ventilatory assist affects patient-important outcomes in critically ill adults.

Ventilators for Noninvasive Ventilation in Adult Acute Care.

The use of noninvasive ventilation (NIV) is common in adult acute care. As evidence to support the use of NIV has developed, there has been a concurrent proliferation of NIV technology. Efforts have been made to improve patient-ventilator synchrony, monitoring capabilities, and portability of devices used to deliver NIV. The technological enhancements provide clinicians with myriad modes, settings, and capabilities designed to improve patient adherence with NIV. Although this technology is generally superior to that of the past, a great deal of variation exists between devices. Clinicians need to be accustomed to the devices available to them to maximize the potential for clinical improvement and patient tolerance. The purpose of this paper is to review current technology, current literature comparing devices, and various clinical considerations associated with NIV use in adult acute care.

Effect of sedation on respiratory function of patients undergoing mechanical ventilation

Sedation and analgesia for ventilated patients is an important treatment in intensive care unit (ICU). Patients receiving mechanical ventilation therapy comfortably and safely can improve patient-ventilator synchrony, reduce ventilation-related lung injury (VILI), improve compliance, decrease oxygen consumption and stress, prevent accidents, and reduce the incidence of complications and mortality in critical patients. Although sedation may protect lung function, it also has a greater impact on respiratory function. Therefore, based on domestic and overseas related researches about sedation therapy in ventilated patients, we expounded on the effects of sedation therapy, different sedatives and different sedative methods on respiratory function of ventilated patients. The effects of sedation improving patient-ventilator synchrony or protecting pulmonary function as well as problems about inhibition of spontaneous respiration or delayed extubation were discussed to provide references for sedation treatment in patients with mechanical ventilation.

Neurally Adjusted Ventilatory Assist Mode in Pediatric Intensive Care Unit and Pediatric Cardiac Care Unit

Neonatal, cardiac and pediatric intensive care units (ICUs) frequently use the neurally adjusted ventilatory assist (NAVA) mode of ventilation, which has been shown to improve patient-ventilator synchrony and decrease work of breathing as it uses neural impulse to guide patient and ventilator breaths. We reviewed uses of NAVA as the mode of ventilation and oxygenation in pediatric (P)ICU and cardiac (C)ICU patients. We found that NAVA mode improves patient-ventilator interaction by improving synchrony and thus decreasing work of breathing. This eventually improved all aspects of critical care, as demonstrated by decreased need for sedation, improvement in hemodynamics, improvement in patient comfort, decreased days on ventilator, decreased days in ICU and decreased hospital length of stay. Additional studies need to be done in order to help NAVA technology become a primary mode of ventilation in PICU and CICU. Further studies are also needed to evaluate the successful use of noninvasive-NAVA as a means of preventing endotracheal intubation or to allow early extubation in our population.

Early Paralysis for the Management of ARDS.

The use of neuromuscular blocking agents (NMBAs) early in the development of ARDS has been a strategy of interest for many years. The use of NMBAs with a concomitant deep sedation strategy can increase oxygenation and possibly decrease mortality when used in the early stages of ARDS. The mechanism by which this occurs is unclear but probably involves a combination of factors, such as improving patient-ventilator synchrony, decreasing oxygen consumption, and decreasing the systemic inflammatory response associated with ARDS. The use of NMBA and deep sedation for these patients is not without consequence. This discussion describes the rationale and evidence behind the use of NMBAs in the setting of ARDS.

Patient-Ventilator Interaction During Noninvasive Ventilation in Simulated COPD.

During noninvasive ventilation (NIV) of COPD patients, delayed off-cycling of pressure support can cause patient ventilator mismatch and NIV failure. This systematic experimental study analyzes the effects of varying cycling criteria on patient-ventilator interaction. A lung simulator with COPD settings was connected to an ICU ventilator via helmet or face mask. Cycling was varied between 10 and 70% of peak inspiratory flow at different breathing frequencies (15 and 30 breaths/min) and pressure support levels (5 and 15 cm H2O) using the ventilator's invasive and NIV mode with and without an applied leakage. Low cycling criteria led to severe expiratory cycle latency. Augmenting off-cycling reduced expiratory cycle latency (P < .001), decreased intrinsic PEEP, and avoided non-supported breaths. Setting cycling to 50% of peak inspiratory flow achieved best synchronization. Overall, using the helmet interface increased expiratory cycle latency in almost all settings (P < .001). Augmenting cycling from 10 to 40% progressively decreased expiratory pressure load (P < .001). NIV mode decreased expiratory cycle latency compared with the invasive mode (P < .001). Augmenting the cycling criterion above the default setting (20-30% peak inspiratory flow) improved patient ventilator synchrony in a simulated COPD model. This suggests that an individual approach to cycling should be considered, since interface, level of pressure support, breathing frequency, and leakage influence patient-ventilator interaction and thus need to be considered.

Non-invasive neurally adjusted ventilatory assist in preterm infants: a randomised phase II crossover trial

ObjectiveTo compare non-invasive ventilation neurally adjusted ventilatory assist (NIV-NAVA) and non-invasive pressure support (NIV-PS) in preterm infants on patient–ventilator synchrony.DesignA randomised phase II crossover trial.SettingNeonatal intensive care units of two...

Neurally adjusted ventilatory assist.

Purpose of reviewCompared with the conventional forms of partial support, neurally adjusted ventilatory assist was repeatedly shown to improve patient–ventilator synchrony and reduce the risk of overassistance, while guaranteeing adequate inspiratory effort and gas exchange. A few animal studies also suggested the potential of neurally adjusted ventilatory assist in averting the risk of ventilator-induced lung injury. Recent work adds new information on the physiological effects of neurally adjusted ventilatory assist.Recent findingsCompared with pressure support, neurally adjusted ventilatory assist has been shown to improve patient–ventilator interaction and synchrony in patients with the most challenging respiratory system mechanics, such as very low compliance consequent to severe acute respiratory distress syndrome and high resistance and air trapping due to chronic airflow obstruction; enhance redistribution of the ventilation in the dependent lung regions; avert the risk of patient–ventilator asynchrony due to sedation; avoid central apneas; limit the risk of high (injurious) tidal volumes in patients with acute respiratory distress syndrome of varied severity; and improve patient–ventilator interaction and synchrony during noninvasive ventilation, irrespective of the interface utilized.SummarySeveral studies nowadays prove the physiological benefits of neurally adjusted ventilatory assist, as opposed to the conventional modes of partial support. Whether these advantages translate into improvement of clinical outcomes remains to be determined.

Neurally adjusted non-invasive ventilation in patients with chronic obstructive pulmonary disease: does patient-ventilator synchrony matter?

Patient–ventilator interaction represents an important clinical challenge during non-invasive ventilation (NIV). Doorduin and colleagues’ study shows that non-invasive neurally adjusted ventilatory assist (NAVA) improves patient–ventilator interaction compared with pressure support ventilation in patients with chronic obstructive pulmonary disease. There is no doubt nowadays that NAVA is the most effective mode of improving the synchrony between patient and machine, but the key question for the clinicians is whether or not this will make a difference to the patient’s outcome. The results of the study still do not clarify this issue because of the very low clinically important dyssynchrony, like wasted efforts, in the population studied. Air leaks play an important role in determining patient–ventilator interaction and therefore NIV success or failure. Apart from the use of a dedicated NIV ventilator or specific modes of ventilation like NAVA, the clinicians should be aware that the choice of interface, the humidification system and the appropriate sedation are key factors in improving patient–ventilator synchrony.

New modes of assisted mechanical ventilation

Recent major advances in mechanical ventilation have resulted in new exciting modes of assisted ventilation. Compared to traditional ventilation modes such as assisted-controlled ventilation or pressure support ventilation, these new modes offer a number of physiological advantages derived from the improved patient control over the ventilator. By implementing advanced closed-loop control systems and using information on lung mechanics, respiratory muscle function and respiratory drive, these modes are specifically designed to improve patient–ventilator synchrony and reduce the work of breathing. Depending on their specific operational characteristics, these modes can assist spontaneous breathing efforts synchronically in time and magnitude, adapt to changing patient demands, implement automated weaning protocols, and introduce a more physiological variability in the breathing pattern. Clinicians have now the possibility to individualize and optimize ventilatory assistance during the complex transition from fully controlled to spontaneous assisted ventilation. The growing evidence of the physiological and clinical benefits of these new modes is favoring their progressive introduction into clinical practice. Future clinical trials should improve our understanding of these modes and help determine whether the claimed benefits result in better outcomes.

Therapeutic Range of Spontaneous Breathing during Mechanical Ventilation

In the 4th century before the common era, the Greek philosopher and physician Hippocrates expressed his wisdom on the value of activity to the sick and the healthy by stating that: “The sick will of course profit to a great extent from gymnastics with regard to the restoration of their health and the healthy will profit with regard to its maintenance” (On Regimen in Acute Diseases, 3, 400 BCE). In contemporary critical care medicine, driven by the goal of protecting our patients from self-inflicted injury, pain, and anxiety – and in contrast to Hippoctrates’ suggestions – we have built a culture of immobilizing our patients: we prescribe high doses of opioids, sedatives, anxiolytics, and anti-pychotics, and with the best intentions, place bed-rest and restraints orders. In patients with severe respiratory failure, we frequently use immobilizing ventilator settings such as volume control ventilation. Recent data have been increasingly challenging this tenet in relation to the fields of neuropsychiatry, rehabilitation, and respiratory medicine1–5. In this issue of Anesthesiology, two papers bring new information on why the concept of muscle activity is also relevant to lung biochemistry and regional function. Guldner et al.6 and Bruells et al.7 provide important experimental data on the relationship between the dose of diaphragmatic activity (spontaneous contribution to breathing during mechanical ventilation) and the resulting response in terms of lung mechanical stress, gas exchange, and markers of muscle deconditioning. As the main respiratory muscle, the diaphragm contributes 72% for tidal breathing8 and its role in respiratory mechanics and gas exchange goes well beyond this global number. One of the reasons is its curvature during spontaneous breathing in the supine position, which facilitates expansion of dependent lung regions9, optimizes the regional distribution of lung ventilation, and prevents loss of dependent lung aeration and increase in shunt observed when muscle paralysis is produced10. Accordingly, modes of ventilation proposed since the 1970s tried to explore those advantages in patients with acute respiratory failure. The beneficial effects of maintaining continuous spontaneous breathing during mechanical ventilation of patients with acute respiratory failure have been described by Putensen and coworkers in two well-designed studies11,12. However, in patients with severe respiratory failure, barriers to spontaneous breathing during mechanical ventilation including patient-ventilator asynchrony, high oxygen consumption of the respiratory pump muscles, and the risk of barotrauma, have hindered a clear determination of the value of spontaneous breathing during mechanical ventilation.

Noninvasive Ventilation and Breathing-Swallowing Interplay in Chronic Obstructive Pulmonary Disease*

To investigate breathing-swallowing interactions in patients with chronic obstructive pulmonary disease requiring noninvasive mechanical ventilation and, if needed, to develop a technical modification of the ventilator designed to eliminate ventilator insufflations during swallowing. We conducted a prospective, open-label, interventional study. Fifteen consecutive chronic obstructive pulmonary disease patients with exacerbations requiring ICU admission and NIV. Swallowing performance and breathing-swallowing interactions were investigated noninvasively by chin electromyography, cervical piezoelectric sensor, and inductive respiratory plethysmography. Two water-bolus sizes (5 and 10 mL) were tested in random order. Swallowing was tested with and without noninvasive mechanical ventilation, in random order. First, a standard mechanical ventilator capable of delivering noninvasive mechanical ventilation was used. Second, a marketed device was equipped with an off-switch for use during swallowing. Swallowing performance and breathing-swallowing interactions were investigated noninvasively by chin electromyography, cervical piezoelectric sensor, and inductive respiratory plethysmography. Two water bolus sizes (5 and 10 mL) were tested in random order. Swallowing was tested with and without noninvasive mechanical ventilation in random order. First, a standard mechanical ventilator capable of delivering noninvasive mechanical ventilation was used. Swallowing efficiency, breathing-swallowing synchronization, and Borg Scale dyspnea scores improved significantly with noninvasive mechanical ventilation. However, swallowing induced ventilator triggering followed by autotriggering. To improve patient-ventilator synchrony, a marketed device was equipped with an off-switch for use during swallowing. This device completely eliminated swallowing-induced ventilator triggering and postswallow autotriggering. Patients with chronic obstructive pulmonary disease admitted to the ICU for acute exacerbations had abnormal breathing-swallowing interactions and dyspnea, which improved with noninvasive mechanical ventilation. Furthermore, a ventilator device with a simple switch-off pushbutton to eliminate insufflations during swallows prevented swallowing-induced ventilator triggering and postswallow autotriggering.

Nuevos modos de ventilación asistida

Recent major advances in mechanical ventilation have resulted in new exciting modes of assisted ventilation. Compared to traditional ventilation modes such as assisted-controlled ventilation or pressure support ventilation, these new modes offer a number of physiological advantages derived from the improved patient control over the ventilator. By implementing advanced closed-loop control systems and using information on lung mechanics, respiratory muscle function and respiratory drive, these modes are specifically designed to improve patient-ventilator synchrony and reduce the work of breathing. Depending on their specific operational characteristics, these modes can assist spontaneous breathing efforts synchronically in time and magnitude, adapt to changing patient demands, implement automated weaning protocols, and introduce a more physiological variability in the breathing pattern. Clinicians have now the possibility to individualize and optimize ventilatory assistance during the complex transition from fully controlled to spontaneous assisted ventilation. The growing evidence of the physiological and clinical benefits of these new modes is favoring their progressive introduction into clinical practice. Future clinical trials should improve our understanding of these modes and help determine whether the claimed benefits result in better outcomes.

Neurally adjusted ventilatory assist (NAVA) in pediatric intensive care—A randomized controlled trial

Neurally adjusted ventilatory assist (NAVA) has been shown to improve patient-ventilator synchrony during invasive ventilation. The aim of this trial was to study NAVA as a primary ventilation mode in pediatric intensive care and to compare it with current standard ventilation modes. One hundred seventy pediatric intensive care patients were randomized to conventional ventilation or NAVA. The primary endpoints were time on the ventilator and the amount of sedation needed. To enable comparison between sedative agents, a "sedative unit" was defined for each drug. The median time on the ventilator was 3.3 hr in the NAVA group and 6.6 hr in the control group (P = 0.17), and the length of stay in the PICU 49.5 hr in the NAVA group and 72.8 hr in the control group (P = 0.10, per protocol P = 0.03). The amount of sedation needed in the total patient population did not differ between the groups (P = 0.20), but when postoperative patients were excluded (19 vs. 20 patients), the amount was significantly lower in the NAVA group (0.80 vs. 2.23 units/hr, P = 0.03). Lower peak inspiratory pressure and a lower inspired oxygen fraction were found in the NAVA group (P = 0.001 for both). Arterial blood CO2 tensions were slightly higher in the NAVA group up to 32 hr of treatment (P = 0.008). There were no significant differences in the other ventilatory or vital parameters, arterial blood gas values or complications. We found NAVA to be a safe and feasible primary ventilation mode for use with children. It outscored standard ventilation in some aspects, as it was able to enhance oxygenation even at lower airway pressures and led to reduced use of sedatives during longer periods of treatment.

Dexmedetomidine to wean patient of severe kyphoscoliosis with cerebral palsy in intensive care unit

Sir, Patients with severe kyphoscoliosis with cerebral palsy may present with an acute respiratory failure (ARF) precipitated by an acute respiratory infections, requiring invasive mechanical ventilation.[1] Weaning from ventilator support may be challenging due to agitation and lack of patient co-operation. A 27-year-old male patient suffering from cerebral palsy and congenital kyphoscoliosis (scoliotic angle>1000) was admitted to the intensive care unit with dyspnoea, cough and fever. Patient was drowsy with tachycardia, tachypnoea, blood pressure (BP) 90/66 mm Hg and saturation (SpO2) 86%. On auscultation bibasilar inspiratory crackles were heard. There were no signs of congestive cardiac failure. Arterial blood gas (ABG) showed pH of 7.32, pCO2 45 mm Hg, pO2 50 mm Hg and haematocrit 40%. Chest X-ray showed severe chest deformity and haziness [Figure 1]. Patient was intubated and mechanically ventilated without much difficulty. Initial ventilator settings were volume control ventilation, tidal volume 400 ml, FiO2 1.0, positive-end expiratory pressure 8 mm Hg and frequency 20/min. ABG sample taken after an hour showed pO2 250 mm Hg, pCO2 40 mm Hg, SpO2 100% and FiO2 was hence subsequently reduced to 0.5 while maintaining adequate saturation. On 2nd day ventilation was changed to the synchronized intermittent mandatory ventilation mode with pressure support of 12 cm H2O, but he became visibly agitated, developed tachypnoea and his heart rate rose to 160/min. On auscultation bilateral crackles were still present with lot of secretions. Infusion of midazolam 2 mg/h was started to sedate the patient. Injection paracetamol 1 g 8 hourly was started for analgesia. Fluids were given to increase central venous pressure from 2 to 6 cm H2O, which settled his HR to 130/min and BP 106/70 mm Hg. On day 3, secretions reduced, but reducing the midazolam infusion lead to tachypnoea and HR of 164/min. We then started patient on injection dexmedetomidine (DEX). A loading dose 1 mcg/kg for 10 min was given followed by 0.2 mcg/kg/h maintenance infusion. Injection midazolam was stopped and no haemodynamic compromise was observed.Figure 1: Chest X-ray anteroposterior viewAfter 18 h of starting DEX, patient was successfully breathing on continuous positive airway pressure and subsequently T-piece. Injection DEX was stopped. ABG after half an hour was good, vitals were stable and patient was no longer agitated and hence he was extubated. The primary goal in patients presenting with ARF in severe kyphoscoliosis is correction of arterial hypoxemia. Our patient was intubated considering his mental condition[2] and he developed agitation requiring sedation to decrease excessive central respiratory drive and improve patient-ventilator synchrony. The recent revised guidelines for pain, agitation and delirium in the critically-ill suggest the use of propofol or DEX instead of benzodiazepines (BZP) for agitation, but also summarised that the current literature supports only modest differences in outcomes with BZP-based versus non-BZP-based sedation (3). BZP remain important for managing agitation in intensive care unit (ICU) patients, especially for treating anxiety, seizures and alcohol or BZP withdrawal.[3] Thus injection midazolam was started as it is easily available in our setup but could not be tapered successfully and so we used DEX next. DEX is a highly selective alpha-2 agonist. A major advantage is that it is associated with minimal respiratory depression[4] thus, allowing continuous sedation during the entire weaning process until extubation. DEX also inhibited the haemodynamic stress response during weaning from mechanical ventilation in our patient. It also helps eliminate emergence agitation when sedation is being tapered. Lack of addictive properties, cumulative effects or clinical signs of withdrawal, make DEX an attractive potential alternative to current ICU sedation regimens.[5] We did not observe any bradycardia or hypotension with DEX. It could be because of minimum infusion dose that was used for maintenance and normovolemia. The sedative and analgesic property of DEX helped us wean the patient successfully. Thus, we were able to use DEX safely and effectively in a condition where patient cooperation was just not possible and respiratory depression at the time of extubation could be dangerous due to severe restrictive lung disorder.

Newer nonconventional modes of mechanical ventilation

The conventional modes of ventilation suffer many limitations. Although they are popularly used and are well-understood, often they fail to match the patient-based requirements. Over the years, many small modifications in ventilators have been incorporated to improve patient outcome. The ventilators of newer generation respond to patient's demands by additional feedback systems. In this review, we discuss the popular newer modes of ventilation that have been accepted in to clinical practice. Various intensive care units over the world have found these modes to improve patient ventilator synchrony, decrease ventilator days and improve patient safety. The various modes discusses in this review are: Dual control modes (volume assured pressure support, volume support), Adaptive support ventilation, proportional assist ventilation, mandatory minute ventilation, Bi-level airway pressure release ventilation, (BiPAP), neurally adjusted ventilatory assist and NeoGanesh. Their working principles with their advantages and clinical limitations are discussed in brief.