High-frequency percussive ventilation and low tidal volume ventilation in burns: a randomized controlled trial. Crit Care Med. 2010;38:1970-1977. [PMID: 20639746 DOI: 10.1097/ccm.0b013e3181eb9d0b]

Inhalation Injury, Respiratory Failure, and Ventilator Support in Acute Burn Care

Sustaining an inhalation injury increases the risk of severe complications and mortality. Current evidential support to guide treatment of the injury or subsequent complications is lacking, as studies either exclude inhalation injury or design limit inferences that can be made. Conventional ventilator modes are most commonly used, but there is no consensus on optimal strategies. Settings should be customized to patient tolerance and response. Data for pharmacotherapy adjunctive treatments are limited.

Venovenous extracorporeal membrane oxygenation for respiratory failure refractory to high frequency percussive ventilation

BACKGROUND

High frequency percussive ventilation (HFPV) has demonstrated improvements in gas exchange, but not in clinical outcomes.

OBJECTIVES

We utilize HFPV in patients failing conventional ventilation (CV), with rescue venovenous extracorporeal membrane oxygenation (VV ECMO) reserved for failure of HFPV, and we describe our experience with such a strategy.

METHODS

All adult patients (age >18 years) placed on HFPV for failure of CV at a single institution over a 10-year period were included. Those maintained on HFPV were compared to those that failed HFPV and required VV ECMO. Survival was compared to expected survival after upfront VV ECMO as estimated by VV ECMO risk prediction models.

RESULTS

Sixty-four patients were placed on HFPV for failure of CV over a 10-year period. After HFPV initiation, the P/F ratio rose from 76mmHg to 153.3mmHg in the 69 % of patients successfully maintained on HFPV. The P/F ratio only rose from 60.3mmHg to 67mmHg in the other 31 % of patients, and they underwent rescue ECMO with the P/F ratio rising to 261.6mmHg. The P/F ratio continued to improve in HFPV patients, while it declined in ECMO patients, such that at 24 h, the P/F ratio was greater in HFPV patients. The strongest independent predictor of failure of HFPV requiring rescue VV ECMO was a lower pO2 (p = .055). Overall in-hospital survival (59.4 %) was similar to that expected with upfront ECMO (RESP score: 57 %).

CONCLUSIONS

HFPV demonstrated significant and sustained improvements in gas exchange and may obviate the need for ECMO and its associated complications.

Intravenous Autologous Bone Marrow-derived Mesenchymal Stromal Cells Delay Acute Respiratory Distress Syndrome in Swine

Rationale: Early post injury mitigation strategies in ARDS are in short supply. Treatments with allogeneic stromal cells are administered after ARDS develops, require specialized expertise and equipment, and to date have shown limited benefit. Objectives: Assess the efficacy of immediate post injury intravenous administration of autologous or allogeneic bone marrow-derived mesenchymal stromal cells (MSCs) for the treatment of acute respiratory distress syndrome (ARDS) due to smoke inhalation and burns. Methods: Yorkshire swine (n = 32, 44.3 ± 0.5 kg) underwent intravenous anesthesia, placement of lines, severe smoke inhalation, and 40% total body surface area flame burns, followed by 72 hours of around-the-clock ICU care. Mechanical ventilation, fluids, pressors, bronchoscopic cast removal, daily lung computed tomography scans, and arterial blood assays were performed. After injury and 24 and 48 hours later, animals were randomized to receive autologous concentrated bone marrow aspirate (n = 10; 3 × 106 white blood cells and a mean of 56.6 × 106 platelets per dose), allogeneic MSCs (n = 10; 6.1 × 106 MSCs per dose) harvested from healthy donor swine, or no treatment in injured control animals (n = 12). Measurements and Main Results: The intravenous administration of MSCs after injury and at 24 and 48 hours delayed the onset of ARDS in swine treated with autologous MSCs (48 ± 10 h) versus control animals (14 ± 2 h) (P = 0.004), reduced ARDS severity at 24 (P < 0.001) and 48 (P = 0.003) hours, and demonstrated visibly diminished consolidation on computed tomography (not significant). Mortality at 72 hours was 1 in 10 (10%) in the autologous group, 5 in 10 (50%) in the allogeneic group, and 6 in 12 (50%) in injured control animals (not significant). Both autologous and allogeneic MSCs suppressed systemic concentrations of TNF-α (tumor necrosis factor-α). Conclusions: The intravenous administration of three doses of freshly processed autologous bone marrow-derived MSCs delays ARDS development and reduces its severity in swine. Bedside retrieval and administration of autologous MSCs in swine is feasible and may be a viable injury mitigation strategy for ARDS.

An international RAND/UCLA expert panel to determine the optimal diagnosis and management of burn inhalation injury

BACKGROUND

Burn inhalation injury (BII) is a major cause of burn-related mortality and morbidity. Despite published practice guidelines, no consensus exists for the best strategies regarding diagnosis and management of BII. A modified DELPHI study using the RAND/UCLA (University of California, Los Angeles) Appropriateness Method (RAM) systematically analysed the opinions of an expert panel. Expert opinion was combined with available evidence to determine what constitutes appropriate and inappropriate judgement in the diagnosis and management of BII.

METHODS

A 15-person multidisciplinary panel comprised anaesthetists, intensivists and plastic surgeons involved in the clinical management of major burn patients adopted a modified Delphi approach using the RAM method. They rated the appropriateness of statements describing diagnostic and management options for BII on a Likert scale. A modified final survey comprising 140 statements was completed, subdivided into history and physical examination (20), investigations (39), airway management (5), systemic toxicity (23), invasive mechanical ventilation (29) and pharmacotherapy (24). Median appropriateness ratings and the disagreement index (DI) were calculated to classify statements as appropriate, uncertain, or inappropriate.

RESULTS

Of 140 statements, 74 were rated as appropriate, 40 as uncertain and 26 as inappropriate. Initial intubation with ≥ 8.0 mm endotracheal tubes, lung protective ventilatory strategies, initial bronchoscopic lavage, serial bronchoscopic lavage for severe BII, nebulised heparin and salbutamol administration for moderate-severe BII and N-acetylcysteine for moderate BII were rated appropriate. Non-protective ventilatory strategies, high-frequency oscillatory ventilation, high-frequency percussive ventilation, prophylactic systemic antibiotics and corticosteroids were rated inappropriate. Experts disagreed (DI ≥ 1) on six statements, classified uncertain: the use of flexible fiberoptic bronchoscopy to guide fluid requirements (DI = 1.52), intubation with endotracheal tubes of internal diameter < 8.0 mm (DI = 1.19), use of airway pressure release ventilation modality (DI = 1.19) and nebulised 5000IU heparin, N-acetylcysteine and salbutamol for mild BII (DI = 1.52, 1.70, 1.36, respectively).

CONCLUSIONS

Burns experts mostly agreed on appropriate and inappropriate diagnostic and management criteria of BII as in published guidance. Uncertainty exists as to the optimal diagnosis and management of differing grades of severity of BII. Future research should investigate the accuracy of bronchoscopic grading of BII, the value of bronchial lavage in differing severity groups and the effectiveness of nebulised therapies in different severities of BII.

Surviving Sepsis After Burn Campaign

INTRODUCTION

The Surviving Sepsis Campaign was developed to improve outcomes for all patients with sepsis. Despite sepsis being the primary cause of death after thermal injury, burns have always been excluded from the Surviving Sepsis efforts. To improve sepsis outcomes in burn patients, an international group of burn experts developed the Surviving Sepsis After Burn Campaign (SSABC) as a testable guideline to improve burn sepsis outcomes.

METHODS

The International Society for Burn Injuries (ISBI) reached out to regional or national burn organizations to recommend members to participate in the program. Two members of the ISBI developed specific "patient/population, intervention, comparison and outcome" (PICO) questions that paralleled the 2021 Surviving Sepsis Campaign [1]. SSABC participants were asked to search the current literature and rate its quality for each topic. At the Congress of the ISBI, in Guadalajara, Mexico, August 28, 2022, a majority of the participants met to create "statements" based on the literature. The "summary statements" were then sent to all members for comment with the hope of developing an 80% consensus. After four reviews, a consensus statement for each topic was created or "no consensus" was reported.

RESULTS

The committee developed sixty statements within fourteen topics that provide guidance for the early treatment of sepsis in burn patients. These statements should be used to improve the care of sepsis in burn patients. The statements should not be considered as "static" comments but should rather be used as guidelines for future testing of the best treatments for sepsis in burn patients. They should be updated on a regular basis.

CONCLUSION

Members of the burn community from the around the world have developed the Surviving Sepsis After Burn Campaign guidelines with the goal of improving the outcome of sepsis in burn patients.

Sample size estimation in clinical trials using ventilator-free days as the primary outcome: a systematic review

BACKGROUND

Ventilator-free days (VFDs) are a composite endpoint increasingly used as the primary outcome in critical care trials. However, because of the skewed distribution and competitive risk between components, sample size estimation remains challenging. This systematic review was conducted to systematically assess whether the sample size was congruent, as calculated to evaluate VFDs in trials, with VFDs' distribution and the impact of alternative methods on sample size estimation.

METHODS

A systematic literature search was conducted within the PubMed and Embase databases for randomized clinical trials in adults with VFDs as the primary outcome until December 2021. We focused on peer-reviewed journals with 2021 impact factors greater than five. After reviewing definitions of VFDs, we extracted the sample size and methods used for its estimation. The data were collected by two independent investigators and recorded in a standardized, pilot-tested forms tool. Sample sizes were calculated using alternative statistical approaches, and risks of bias were assessed with the Cochrane risk-of-bias tool.

RESULTS

Of the 26 clinical trials included, 19 (73%) raised "some concerns" when assessing risks of bias. Twenty-four (92%) trials were two-arm superiority trials, and 23 (89%) were conducted at multiple sites. Almost all the trials (96%) were unable to consider the unique distribution of VFDs and death as a competitive risk. Moreover, significant heterogeneity was found in the definitions of VFDs, especially regarding varying start time and type of respiratory support. Methods for sample size estimation were also heterogeneous, and simple models, such as the Mann-Whitney-Wilcoxon rank-sum test, were used in 14 (54%) trials. Finally, the sample sizes calculated varied by a factor of 1.6 to 17.4.

CONCLUSIONS

A standardized definition and methodology for VFDs, including the use of a core outcome set, seems to be required. Indeed, this could facilitate the interpretation of findings in clinical trials, as well as their construction, especially the sample size estimation which is a trade-off between cost, ethics, and statistical power. Systematic review registration PROSPERO ID: CRD42021282304. Registered 15 December 2021 ( https://www.crd.york.ac.uk/prospero/display_record.php?ID=CRD42021282304 ).

Critical Care of the Burn Patient

Care of the critically ill burned patient must integrate a multidisciplinary care team composed of burn care specialists. As resuscitative mortality decreases more patients are surviving to experience multisystem organ failure relating to complications of their injuries. Clinicians must be aware of physiologic changes following burn injury and the implicated impacts on management strategy. Promoting wound closure and rehabilitation should be the backdrop for which management decisions are made.

A review of the utility of high-frequency oscillatory ventilation in burn and trauma ICU patients

PURPOSE OF REVIEW

The purpose was to examine the utility of high-frequency oscillatory ventilation (HFOV) in trauma and burn ICU patients who require mechanical ventilation, and provide recommendations on its use.

RECENT FINDINGS

HFOV may be beneficial in burn patients with smoke inhalation injury with or without acute lung injury/acute respiratory distress syndrome (ARDS), as it improves oxygenation and minimizes ventilator-induced lung injury. It also may have a role in improving oxygenation in trauma patients with blast lung injury, pulmonary contusions, pneumothorax with massive air leak, and ARDS; however, the mortality benefit is unknown.

SUMMARY

Although some studies have shown promise and improved outcomes associated with HFOV, we recommend its use as a rescue modality for patients who have failed conventional ventilation.

Proceedings of the 2021 American Burn Association State and Future of Burn Science Meeting

Periodically, the American Burn Association (ABA) has convened a State of the Science meeting on various topics representing multiple disciplines within burn care and research. In 2021 at the request of the ABA President, meeting development was guided by the ABA's Burn Science Advisory Panel (BSAP) and a subgroup of meeting chairs. The goal of the meeting was to produce both an evaluation of the current literature and ongoing studies, and to produce a research agenda and/or define subject matter-relevant next steps to advance the field(s). Members of the BSAP defined the topics to be addressed and subsequently solicited for nominations of expert speakers and topic leaders from the ABA's Research Committee. Current background literature for each topic was compiled by the meeting chairs and the library then enhanced by the invited topic and breakout discussion leaders. The meeting was held in New Orleans, LA on November 2nd and 3rd and was formatted to allow for 12 different topics, each with two subtopics, to be addressed. Topic leaders provided a brief overview of each topic to approximately 100 attendees, followed by expert-lead breakout sessions for each topic that allowed for focused discussion among subject matter experts and interested participants. The breakout and topic group leaders worked with the participants to determine research needs and associated next steps including white papers, reviews and in some cases collaborative grant proposals. Here, summaries from each topic area will be presented to highlight the main foci of discussion and associated conclusions.

Expiratory high-frequency percussive ventilation: a novel concept for improving gas exchange

Background

Although high-frequency percussive ventilation (HFPV) improves gas exchange, concerns remain about tissue overdistension caused by the oscillations and consequent lung damage. We compared a modified percussive ventilation modality created by superimposing high-frequency oscillations to the conventional ventilation waveform during expiration only (eHFPV) with conventional mechanical ventilation (CMV) and standard HFPV.

Methods

Hypoxia and hypercapnia were induced by decreasing the frequency of CMV in New Zealand White rabbits (n = 10). Following steady-state CMV periods, percussive modalities with oscillations randomly introduced to the entire breathing cycle (HFPV) or to the expiratory phase alone (eHFPV) with varying amplitudes (2 or 4 cmH₂O) and frequencies were used (5 or 10 Hz). The arterial partial pressures of oxygen (PaO₂) and carbon dioxide (PaCO₂) were determined. Volumetric capnography was used to evaluate the ventilation dead space fraction, phase 2 slope, and minute elimination of CO₂. Respiratory mechanics were characterized by forced oscillations.

Results

The use of eHFPV with 5 Hz superimposed oscillation frequency and an amplitude of 4 cmH₂O enhanced gas exchange similar to those observed after HFPV. These improvements in PaO₂ (47.3 ± 5.5 vs. 58.6 ± 7.2 mmHg) and PaCO₂ (54.7 ± 2.3 vs. 50.1 ± 2.9 mmHg) were associated with lower ventilation dead space and capnogram phase 2 slope, as well as enhanced minute CO₂ elimination without altering respiratory mechanics.

Conclusions

These findings demonstrated improved gas exchange using eHFPV as a novel mechanical ventilation modality that combines the benefits of conventional and small-amplitude high-frequency oscillatory ventilation, owing to improved longitudinal gas transport rather than increased lung surface area available for gas exchange.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02215-2.

Impact of opioid free Anaesthesia versus opioid Anaesthesia on the immediate postoperative oxygenation after bariatric surgery: a prospective observational study

Introduction: Opioid induced respiratory depression (OIRD) is a preventable aetiology of postoperative respiratory depression with 85% of the episodes taking place in the first 24 postoperative hours. Due to altered respiratory functional metrics and frequently coexisting comorbidities, obese patients are at a particularly higher risk for such complications. The present study aimed to assess if an opioid-free anesthesia (OFA) was associated with a reduced immediate postoperative OIRD when compared to Opiod-based anesthesia (OA). Methods: Obese patients presenting for bariatric surgery were consecutively included in a non-randomized fashion. Lung protective ventilation strategies applied in both groups. In the OA group, Sufentanil was used for intraoperative analgesia in a liberal fashion. In the OFA group, patients received a pre-induction dexmedetomidine loading, followed by a lidocaine, ketamine and dexmedetomidine bolus immediately before induction, further maintained throughout the intraoperative period. Plethysmographic saturations were obtained before induction as well as after extubation and in the Post-anesthesia care unit (PACU). Opioid requirement and Postoperative Nausea and Vomiting incidence were similarly registered. Results: Thirty-four patients were included in the OFA group, and 30 in the OA group. No significant anthropometric and comorbidity differences were found between both groups. OFA patients had significantly lower pre-induction saturations after dexmedetomidine loading. No difference was found for post-extubation saturations as well as well as pre-PACU discharge. The need for supplemental oxygen at the PACU was higher in the OA group. Opioid requirement and cumulative consumption (MEDs) were significantly higher with OA. Conclusion: OFA was not associated with significant postoperative saturation changes but led to a lower need of postoperative supplemental oxygen therapy. OA led to higher opioid rescue need. No fatal respiratory complications were registered in both groups in the immediate postoperative period.

A Rationale for Safe Ventilation with Inhalation Injury: An Editorial Review

Lung injury from smoke inhalation manifests as airway and parenchymal damage, at times leading to the acute respiratory distress syndrome. From the beginning of this millennium, the approach to mechanical ventilation in the patient with ARDS was based on reduction of tidal volume to 6 milliliters/kilogram of ideal body weight, maintaining a ceiling of plateau pressure, and titration of driving pressure (plateau pressure minus PEEP). Beyond these broad constraints, there is little specification for the mechanics of ventilator settings, consideration of the metabolic impact of the disease process on the patient, or interaction of patient disease and ventilator settings. Various studies suggest that inhomogeneity of lung injury, which increases the risk of regional lung trauma from mechanical ventilation, may be found in the patient with smoke inhalation. We now appreciate that energy transfer principles may affect optimal ventilator management and come into play in damaged heterogenous lungs. Mechanical ventilation in the patient with inhalation injury should consider various factors. Self-injurious respiratory demand by the patient can be reduced using analgesia and sedation. Dynamic factors beginning with rate management can reduce the incidence of potentially damaging ventilation. Moreover, preclinical study is underway to examine the flow of gas based on the ventilator mode selected, which may also be a factor triggering regional lung injury.

Patient-centred outcomes are under-reported in the critical care burns literature: a systematic review

BACKGROUND

Developments in the care of critically ill patients with severe burns have led to improved hospital survival, but long-term recovery may be impaired. The extent to which patient-centred outcomes are assessed and reported in studies in this population is unclear.

METHODS

We conducted a systematic review to assess the outcomes reported in studies involving critically ill burns patients. Randomised controlled trials (RCTs) and cohort studies on the topics of fluid resuscitation, analgesia, haemodynamic monitoring, ventilation strategies, transfusion targets, enteral nutrition and timing of surgery were included. We assessed the outcomes reported and then classified these according to two suggested core outcome sets.

RESULTS

A comprehensive search returned 6154 studies; 98 papers met inclusion criteria. There were 66 RCTs, 19 clinical studies with concurrent controls and 13 interventional studies without concurrent controls. Outcome reporting was inconsistent across studies. Pain, reported using the visual analogue scale, fluid volume administered and mortality were the only outcomes measured in more than three studies. Sixty-six studies (67%) had surrogate primary outcomes. Follow-up was poor, with median longest follow-up across all studies 5 days (IQR 3-28). When compared to the suggested OMERACT core outcome set, 53% of papers reported on mortality, 28% reported on life impact, 30% reported resource/economic outcomes and 95% reported on pathophysiological manifestations. Burns-specific Falder outcome reporting was globally poor, with only 4.3% of outcomes being reported across the 98 papers.

CONCLUSION

There are deficiencies in the reporting of outcomes in the literature pertaining to the intensive care management of patients with severe burns, both with regard to the consistency of outcomes as well as a lack of focus on patient-centred outcomes. Long-term outcomes are infrequently reported. The development and validation of a core outcome dataset for severe burns would improve the quality of reporting.

Intermittent High-Frequency Percussive Ventilation Therapy in 3 Patients with Severe COVID-19 Pneumonia

BACKGROUND High-frequency percussive ventilation (HFPV) is a method that combines mechanical ventilation with high-frequency oscillatory ventilation. This report describes 3 cases of patients with severe COVID-19 pneumonia who received intermittent adjunctive treatment with HFPV at a single center without requiring admission to the Intensive Care Unit (ICU). CASE REPORT Case 1 was a 60-year-old woman admitted to the hospital 14 days after the onset of SARS-CoV-2 infection symptoms, and cases 2 and 3 were men aged 65 and 72 years who were admitted to the hospital 10 days after the onset of SARS-CoV-2 infection symptoms. All 3 patients presented with clinical deterioration accompanied by worsening lung lesions on computed tomography (CT) scans after 21 days from the onset of symptoms. SARS-CoV-2 infection was confirmed in all patients by real-time reverse transcription-polymerase chain reaction (RT-PCR) assay from nasal swabs. All 3 patients had impending respiratory failure when non-invasive intermittent HFPV therapy was initiated. After therapy, the patients had significant clinical improvement and visibly decreased lung lesions on followup CT scans performed 4-6 days later. CONCLUSIONS The 3 cases described in this report showed that the use of intermittent adjunctive treatment with HFPV in patients with severe pneumonia due to infection with SARS-CoV-2 improved lung function and may have prevented clinical deterioration. However, recommendations on the use of intermittent HFPV as an adjunctive treatment in COVID-19 pneumonia requires large-scale controlled clinical studies. In the pandemic context, with a shortage of ICU beds, avoiding ICU admission by using adjunctive therapies on the ward is a useful option.

High frequency percussive ventilation in pediatric acute respiratory failure

OBJECTIVE

High frequency percussive ventilation (HFPV) is used in acute respiratory failure, but is poorly described in pediatrics. We aimed to describe the clinical characteristics, ventilator settings, and outcomes of a large pediatric cohort, and to determine predictors of who would benefit from HFPV.

HYPOTHESIS

Gas exchange 2 h after HFPV initiation predicts success.

DESIGN

Single center retrospective cohort study testing association between gas exchange 2 h after HFPV initiation with success, defined a priori.

PATIENTS

Intubated children on HFPV for ≥2 h from 2012 to 2018.

METHODS

We described indications, ventilator settings, and gas exchange immediately before, 2 h after, and at termination of HFPV. Univariate and multivariate regression tested association of oxygenation and ventilation after HFPV initiation with success. Areas under the receiver operating characteristic (AUROC) curve and adjusted odds ratios (aORs) were computed.

RESULTS

We performed 237 courses of HFPV in 193 children (22% non-survivors), of which 162 (68%) were successful. In univariate analysis, pH (AUROC, 0.65) and PCO₂ (AUROC, 0.66) 2 h after HFPV predicted success. In multivariate analysis, pH (aOR: 1.67 per 1 SD; 95% confidence interval [CI]: 1.19-2.35), PCO₂ (aOR: 0.49 per 1 SD; 95% CI: 0.31-0.79), and oxygenation index (aOR: 0.66 per 1 SD; 95% CI: 0.44-0.97) 2 h after HFPV initiation were associated with success.

CONCLUSION

We describe the largest cohort of HFPV to date, with detailed description of indications and settings. Gas exchange after 2 h of HFPV was independently associated with success.

Ventilation practices in burn patients—an international prospective observational cohort study

Background

It is unknown whether lung-protective ventilation is applied in burn patients and whether they benefit from it. This study aimed to determine ventilation practices in burn intensive care units (ICUs) and investigate the association between lung-protective ventilation and the number of ventilator-free days and alive at day 28 (VFD-28).

Methods

This is an international prospective observational cohort study including adult burn patients requiring mechanical ventilation. Low tidal volume (VT) was defined as VT ≤ 8 mL/kg predicted body weight (PBW). Levels of positive end-expiratory pressure (PEEP) and maximum airway pressures were collected. The association between VT and VFD-28 was analyzed using a competing risk model. Ventilation settings were presented for all patients, focusing on the first day of ventilation. We also compared ventilation settings between patients with and without inhalation trauma.

Results

A total of 160 patients from 28 ICUs in 16 countries were included. Low VT was used in 74% of patients, median VT size was 7.3 [interquartile range (IQR) 6.2–8.3] mL/kg PBW and did not differ between patients with and without inhalation trauma (p = 0.58). Median VFD-28 was 17 (IQR 0–26), without a difference between ventilation with low or high VT (p = 0.98). All patients were ventilated with PEEP levels ≥5 cmH2O; 80% of patients had maximum airway pressures &lt;30 cmH2O.

Conclusion

In this international cohort study we found that lung-protective ventilation is used in the majority of burn patients, irrespective of the presence of inhalation trauma. Use of low VT was not associated with a reduction in VFD-28.

Trial registration

Clinicaltrials.gov NCT02312869. Date of registration: 9 December 2014.

Advances in airway management and mechanical ventilation in inhalation injury

PURPOSE OF REVIEW

Airway management, mechanical ventilation, and treatment of systemic poisoning in burn patients with inhalation injury remains challenging. This review summarizes new concepts as well as open questions.

RECENT FINDINGS

Several life-threatening complications, such as airway patency impairment and respiratory insufficiency, can arise in burn patients and require adequate and timely airway management. However, unnecessary endotracheal intubation should be avoided. Direct visual inspection via nasolaryngoscopy can guide appropriate airway management decisions. In cases of lower airway injury, bronchoscopy is recommended to remove casts and estimate the extent of the injury in intubated patients. Several mechanical ventilation strategies have been studied. An interesting modality might be high-frequency percussive ventilation. However, to date, there is no sound evidence that patients with inhalation injury should be ventilated with modes other than those applied to non-burn patients. In all burn patients exposed to enclosed fire, carbon monoxide as well as cyanide poisoning should be suspected. Carbon monoxide poisoning should be treated with an inspiratory oxygen fraction of 100%, whereas cyanide poisoning should be treated with hydroxocobalamin.

SUMMARY

Burn patients need specialized care that requires specific knowledge about airway management, mechanical ventilation, and carbon monoxide and cyanide poisoning.

Weaning of Children With Burn Injury by Noninvasive Ventilation: A Clinical Experience

The aim of this study was to report the respiratory management of a cohort of infants admitted to a Pediatric Intensive Care Unit (PICU) over a 7-year period due to severe burn injury and the potential benefits of noninvasive ventilation (NIV). A retrospective review of all pediatric patients admitted to PICU between 2009 and 2016 was conducted. From 2009 to 2016, 118 infants and children with burn injury were admitted to our institution (median age 16 months [IQR = 12.2-20]); 51.7% of them had face burns, 37.3% underwent tracheal intubation, and 30.5% had a PICU stay greater than 7 days. Ventilated patients had a longer PICU stay (13 days [IQR = 8-26] vs 4.5 days [IQR = 2-13]). Both ventilation requirement and TBSA% correlated with PICU stay (r = .955, p < .0001 and r = .335, p = .002, respectively), while ventilation was best related in those >1 week (r = .964, p < .0001 for ventilation, and r = -.079, p = .680, for TBSA%). NIV was introduced in 10 patients, with the aim of shorten the invasive ventilation requirement. As evidenced in our work, mechanical ventilation is frequently needed in burned children admitted to PICU and it is one of the main factors influencing PICU length of stay. No difference was found in terms of PICU length of stay and invasive mechanical ventilation time between children who underwent NIV and children who did not, despite children who underwent NIV had a larger burn surface. NIV can possibly shorten the total invasive ventilation time and related complications.

Feasibility and impact of the implementation of a clinical scale-based sedation-analgesia protocol in severe burn patients undergoing mechanical ventilation. A before-after bi-center study

BACKGROUND

Severe burn patients undergo prolonged administration of sedatives and analgesics for burn care. There are currently no guidelines for the dose adaptation of sedation-analgesia in severe burn patients.

METHODS

We performed a before-after 2-center study to demonstrate the feasibility and efficacy of a sedation-analgesia scale-based protocol in severely burned patients receiving ≥24h of invasive mechanical ventilation. Before the intervention, continuous infusion of hypnotic and morphine derivatives was continued. During the Intervention phase, general anesthesia was relayed from day 1 by RASS/BPS-titrated continuous infusion of hypnotic and morphine derivatives and with short half-life drugs adminstered for daily burn dressings. The primary outcome was the duration of invasive mechanical ventilation in the ICU.

RESULTS

Eighty-seven (46.2%) patients were included in the Control phase and 101 (53.7%) in the Intervention phase. The median burned cutaneous surface was 20% [11%-38%] and median ABSI was 7 [5-9]. The durations of hypnotic and opioid infusions were not statistically different between the 2 phases (8 days [2-24] vs. 6 days [2-17] (P=0.3) and 17 days [4-32] vs. 8 days [3-23] (P=0.06), respectively). The duration of mechanical ventilation was 14 days [3-29] in the Control phase and 7 days [2-24] in the Intervention phase (P=0.7). When taking into account the competition between mortality and weaning from mechanical ventilation, we found no significant difference between the 2 phases (Gray test, P=0.4). The time-series analysis showed no difference for the duration of mechanical ventilation in the Intervention phase (P=0.6). Eighteen (20.7%) patients died in the Control phase, and 18 (18%) in the Intervention phase (P=0.6).

CONCLUSION

Scale-based lightening of continuous sedation-analgesia with repeated short general anesthesia for dressing is feasible in severe burn patients but failed to demonstrate a decrease in the duration of invasive mechanical ventilation.

Monitoring Lung Mechanics during Mechanical Ventilation using Machine Learning Algorithms

Evaluation of lung mechanics is the primary component for designing lung protective optimal ventilation strategies. This paper presents a machine learning approach for bedside assessment of respiratory resistance (R) and compliance (C). We develop machine learning algorithms to track flow rate and airway pressure and estimate R and C continuously and in real-time. An experimental study is conducted, by connecting a pressure control ventilator to a test lung that simulates various R and C values, to gather sensor data for validation of the devised algorithms. We develop supervised learning algorithms based on decision tree, decision table, and Support Vector Machine (SVM) techniques to predict R and C values. Our experimental results demonstrate that the proposed algorithms achieve 90.3%, 93.1%, and 63.9% accuracy in assessing respiratory R and C using decision table, decision tree, and SVM, respectively. These results along with our ability to estimate R and C with 99.4% accuracy using a linear regression model demonstrate the potential of the proposed approach for constructing a new generation of ventilation technologies that leverage novel computational models to control their underlying parameters for personalized healthcare and context-aware interventions.

Changes in ventilator settings and ventilation-induced lung injury in burn patients-A systematic review

OBJECTIVE

Ventilation strategies aiming at prevention of ventilator-induced lung injury (VILI), including low tidal volumes (V_T) and use of positive end-expiratory pressures (PEEP) are increasingly used in critically ill patients. It is uncertain whether ventilation practices changed in a similar way in burn patients. Our objective was to describe applied ventilator settings and their relation to development of VILI in burn patients.

DATA SOURCES

Systematic search of the literature in PubMed and EMBASE using MeSH, EMTREE terms and keywords referring to burn or inhalation injury and mechanical ventilation.

STUDY SELECTION

Studies reporting ventilator settings in adult or pediatric burn or inhalation injury patients receiving mechanical ventilation during the ICU stay.

DATA EXTRACTION

Two authors independently screened abstracts of identified studies for eligibility and performed data extraction.

DATA SYNTHESIS

The search identified 35 eligible studies. V_T declined from 14 ml/kg in studies performed before to around 8 ml/kg predicted body weight in studies performed after 2006. Low-PEEP levels (<10 cmH₂O) were reported in 70% of studies, with no changes over time. Peak inspiratory pressure (PIP) values above 35 cmH₂O were frequently reported. Nevertheless, 75% of the studies conducted in the last decade used limited maximum airway pressures (≤35 cmH₂O) compared to 45% of studies conducted prior to 2006. Occurrence of barotrauma, reported in 45% of the studies, ranged from 0 to 29%, and was more frequent in patients ventilated with higher compared to lower airway pressures.

CONCLUSION

This systematic review shows noticeable trends of ventilatory management in burn patients that mirrors those in critically ill non-burn patients. Variability in available ventilator data precluded us from drawing firm conclusions on the association between ventilator settings and the occurrence of VILI in burn patients.

Acute Respiratory Failure

Acute respiratory distress syndrome (ARDS) is a condition affecting critically ill patients, characterized by pulmonary inflammation and defects in oxygenation due to either direct or indirect injury to the lungs. These guidelines will define the diagnosis and management of ARDS, particularly among combat casualties and patients in the deployed environment. The cornerstone of management of ARDS involves maintaining adequate oxygenation while avoiding further pulmonary injury through lung-protective ventilation. Additional strategies for advanced respiratory failure, such as prone positioning, neuromuscular blockade, and extracorporeal membrane oxygenation will be reviewed here as well. Particularly important to the care of the patient with ARDS in the deployed environment is a familiarity with the challenges and indications for transport/aeromedical evacuation.

The use of high-frequency percussive ventilation after cardiac surgery significantly improves gas exchange without impairment of hemodynamics

Objective

Respiratory failure represents a significant source of morbidity and mortality for surgical patients. High-frequency percussive ventilation (HFPV) is emerging as a potentially effective rescue therapy in patients failing conventional mechanical ventilation (CMV). Use of HFPV is often limited by concerns for potential effects on hemodynamics, which is particularly tenuous in patients immediately after cardiac surgery. In this manuscript we evaluated the effects of HFPV on gas exchange and cardiac hemodynamics in the immediate postoperative period after cardiac surgery, in comparison with CMV.

Methods

Twenty-four consecutive cardiac surgery patients were ventilated in immediate postoperative period with HFPV for two to four hours, then they switched to a CMV using the adaptive support ventilation mode for weaning. Arterial blood gases were performed during the first and second hour on HFPV, and at 45 minutes after initiation of CMV. Respiratory settings and invasive hemodynamic data (mixed venous oxygen saturation, central venous pressure, systemic and pulmonary blood pressure, cardiac output and index) were collected utilizing right heart pulmonary catheter and arterial lines during HFPV and CMV. Primary outcome was improvement in the ratio between partial pressure of oxygen to fraction of inspired oxygen (P/F ratio) and changes in hemodynamics.

Results

Analysis of data for 24 patients revealed a significantly better P/F ratio during the first and second hour on HFPV, compared with a P/F ratio on CMV (420.0 ± 158.8, 459.2 ± 138.5, and 260.2 ± 98.5 respectively, p < 0.05), suggesting much better gas exchange on HFPV than on CMV. Hemodynamics were not affected by the mode of the ventilation.

Conclusions

Improvement in gas exchange, reflected in a significantly improved P/F ratio, wasn't accompanied by worsening in hemodynamic parameters. The significant gains in the P/F ratio were lost when patients were switched to conventional ventilation. This data suggest that HFPV provides significantly better gas exchange compared with CMV and can be safely utilized in postoperative cardiac patients without any significant effect on hemodynamics.

Comparison of pressure, volume and gas washout characteristics between PCV and HFPV in healthy and formalin fixed ex vivo porcine lungs

OBJECTIVE

This study employs a recently developed experimental technique for comparison of the flow characteristics and the effectiveness of gas washout between pressure control ventilation (PCV) and high-frequency percussive ventilation (HFPV) in high-compliance and low-compliance ex vivo porcine respiratory tracts.

APPROACH

The ex vivo porcine lungs are filled with nitrogen prior to ventilating with atmospheric gas using either PCV or HFPV to investigate the flow characteristics and gas washout characteristics. The study considered freshly removed lungs from porcine carcasses that were humanely harvested for human consumption. Subsequently, the porcine lungs were exposed externally to formalin to simulate low-compliance conditions. The first order models of respiratory mechanics were employed to predict the lung compliance and resistance in normal and formalin exposed lungs. HFPV was operated in two different modes based upon the set pressures, namely HFPV-Low and HFPV-High. The peak pressures of HFPV and PCV were matched in HFPV-Low and the peak pressures are increased to about 20-30% in the HFPV-High mode.

MAIN RESULTS

Both HFPV-Low and HFPV-High mode deliver smaller tidal volume (V _T) as compared to PCV in high and compliance states (about 70% and 40% for healthy and formalin treated lungs, repsectively). Although the tidal volume delivered by HFPV-High and HFPV-Low are comparable, they reveal a substantial difference in washout time as well as total ventilation volumes. In a high compliant lung (healthy lung), HFPV-High washes out the nitrogen within the lung more rapidly, whereas HFPV-Low washes out the inert gas more slowly as compared to PCV. In a low-compliance lung, HFPV-Low delivers similar washout rates as PCV at a much smaller V _T and lower mean airway pressure.

SIGNIFICANCE

The ex vivo study supports the hypothesis that in low compliant lungs HFPV provides effective washout with a protective ventilation.

The abbreviated burn severity index as a predictor of acute respiratory distress syndrome in young individuals with severe flammable starch-based powder burn

Here, we investigated whether the abbreviated burn severity index (ABSI) scoring system predicts acute respiratory distress syndrome (ARDS) in a retrospective analysis of a severe flammable starch-based powder burn population. Demographics, total body surface area (TBSA) burn, the presence of mouth and nose burn, ABSI, inhalation injury, and clinical outcomes for each patient were analysed for association with inpatient ARDS based on the Berlin definition. We treated 53 patients (64% male, 36% female) and observed no fatalities. The median age, TBSA burn, and the ABSI were 22.2±3.6, 42.2±21, and 7.8±2.8, respectively. Inhalation injury was present in 56.6% of the cases, and mouth and nose burn was present in 30.2%. ARDS was prevalent at 30%. The mean abbreviated burn severity index (ABSI) was 10.6±1.5 in the ARDS group and 6.6±2.3 in the non-ARDS (P<0.001) group. The mean TBSA burn percentage for ARDS and the non-ARDS groups were 61.4±13.9% and 34±18%, respectively (P<0.001). The area under the curve of the receiver operating characteristic curves for an ABSI≥9 was 0.905. Our results show that the ABSI is effective for predicting ARDS in young individuals with severe starch-based powder burn.

High-Frequency Percussive Ventilation Rescue Therapy in Morbidly Obese Patients Failing Conventional Mechanical Ventilation

BACKGROUND

Morbidly obese patients with respiratory failure who do not improve on conventional mechanical ventilation (CMV) often undergo rescue therapy with extracorporeal membrane oxygenation (ECMO). We describe our experience with high-frequency percussive ventilation (HFPV) as a rescue modality.

METHODS

In a retrospective analysis from 2009 to 2016, 12 morbidly obese patients underwent HFPV after failing to wean from CMV. Data were collected regarding demographics, cause of respiratory failure, ventilation settings, and hospital course outcomes. Our end point data were pre- and post-HFPV partial pressure of arterial oxygen and PaO₂ to fraction of inspired oxygen (PF) ratios measured at initiation, 2, and 24 hours.

RESULTS

Twelve morbidly obese patients required HFPV for respiratory failure. Causes of respiratory failure overlapped and included cardiogenic pulmonary edema (n = 8), pneumonia (n = 5), septic shock (n = 5), and asthma (n = 1). After HFPV initiation, mean fraction of inspired oxygen FiO₂ was tapered from 98% to 82% and 66% at 2 and 24 hours, respectively. Mean PaO₂ increased from 60.9 mm Hg before HFPV to 175.1 mm Hg (P < .05) at initiation of HFPV, then sustained at 129.5 mm Hg (P < .05) and 88.1 mm Hg (P < .005) at 2 and 24 hours, respectively. Mean PF ratio improved from 66.1 before HFPV to 180.3 (P < .05), 181.0 (P < .05) and 148.9 (P < .0005) at initiation, 2, and 24 hours, respectively. The improvement in mean PaO₂ and PF ratios was durable at 24 hours whether or not the patient was returned to CMV (n = 10) or remained on HFPV (n = 2). Survival to discharge was 66.7%.

CONCLUSION

In our cohort of morbidly obese patients, HFPV was successfully utilized as a rescue therapy precluding the need for ECMO. Despite our small sample size, HFPV should be considered as a rescue therapy in morbidly obese patients failing CMV prior to the initiation of ECMO. Our retrospective analysis supports consideration for HFPV as another form of rescue therapy for obese patients with refractory hypoxemia and respiratory failure who are not improving with CMV.

Comparison of flow and gas washout characteristics between pressure control and high-frequency percussive ventilation using a test lung

OBJECTIVE

A comparison between flow and gas washout data for high-frequency percussive ventilation (HFPV) and pressure control ventilation (PCV) under similar conditions is currently not available. This bench study aims to compare and describe the flow and gas washout behavior of HFPV and PCV in a newly designed experimental setup and establish a framework for future clinical and animal studies.

APPROACH

We studied gas washout behavior using a newly designed experimental setup that is motivated by the multi-breath nitrogen washout measurements. In this procedure, a test lung was filled with nitrogen gas before it was connected to a ventilator. Pressure, volume, and oxygen concentrations were recorded under different compliance and resistance conditions. PCV was compared with two settings of HFPV, namely, HFPV-High and HFPV-Low, to simulate the different variations in its clinical application. In the HFPV-Low mode, the peak pressures and drive pressures of HFPV and PCV are matched, whereas in the HFPV-High mode, the mean airway pressures (MAP) are matched.

MAIN RESULTS

HFPV-Low mode delivers smaller tidal volume (V T) as compared to PCV under all lung conditions, whereas HFPV-High delivers a larger V T. HFPV-High provides rapid washout as compared to PCV under all lung conditions. HFPV-Low takes a longer time to wash out nitrogen except at a low compliance, where it expedites washout at a smaller V T and MAP compared to PCV washout.

SIGNIFICANCE

Various flow parameters for HFPV and PCV are mathematically defined. A shorter washout time at a small V T in low compliant test lungs for HFPV could be regarded as a hypothesis for lung protective ventilation for animal or human lungs.

Acute Respiratory Distress Syndrome in Burn Patients: A Comparison of the Berlin and American-European Definitions

The purpose of this study was to compare the Berlin definition to the American-European Consensus Conference (AECC) definition in determining the prevalence of acute respiratory distress syndrome (ARDS) and associated mortality in the critically ill burn population. Consecutive patients admitted to our institution with burn injury that required mechanical ventilation for more than 24 hours were included for analysis. Included patients (N = 891) were classified by both definitions. The median age, % TBSA burn, and injury severity score (interquartile ranges) were 35 (24-51), 25 (11-45), and 18 (9-26), respectively. Inhalation injury was present in 35.5%. The prevalence of ARDS was 34% using the Berlin definition and 30.5% using the AECC definition (combined acute lung injury and ARDS), with associated mortality rates of 40.9 and 42.9%, respectively. Under the Berlin definition, mortality rose with increased ARDS severity (14.6% no ARDS; 16.7% mild; 44% moderate; and 59.7% severe, P < 0.001). By contrast, under the AECC definition increased mortality was seen only for ARDS category (14.7% no ARDS; 15.1% acute lung injury; and 46.0% ARDS, P < 0.001). The mortality of the 22 subjects meeting the AECC, but not the Berlin definition was not different from patients without ARDS (P = .91). The Berlin definition better stratifies ARDS in terms of severity and correctly excludes those with minimal disease previously captured by the AECC.

Inhalation Injury in the Burned Patient

Inhalation injury causes a heterogeneous cascade of insults that increase morbidity and mortality among the burn population. Despite major advancements in burn care for the past several decades, there remains a significant burden of disease attributable to inhalation injury. For this reason, effort has been devoted to finding new therapeutic approaches to improve outcomes for patients who sustain inhalation injuries.The three major injury classes are the following: supraglottic, subglottic, and systemic. Treatment options for these three subtypes differ based on the pathophysiologic changes that each one elicits.Currently, no consensus exists for diagnosis or grading of the injury, and there are large variations in treatment worldwide, ranging from observation and conservative management to advanced therapies with nebulization of different pharmacologic agents.The main pathophysiologic change after a subglottic inhalation injury is an increase in the bronchial blood flow. An induced mucosal hyperemia leads to edema, increases mucus secretion and plasma transudation into the airways, disables the mucociliary escalator, and inactivates hypoxic vasocontriction. Collectively, these insults potentiate airway obstruction with casts formed from epithelial debris, fibrin clots, and inspissated mucus, resulting in impaired ventilation. Prompt bronchoscopic diagnosis and multimodal treatment improve outcomes. Despite the lack of globally accepted standard treatments, data exist to support the use of bronchoscopy and suctioning to remove debris, nebulized heparin for fibrin casts, nebulized N-acetylcysteine for mucus casts, and bronchodilators.Systemic effects of inhalation injury occur both indirectly from hypoxia or hypercapnia resulting from loss of pulmonary function and systemic effects of proinflammatory cytokines, as well as directly from metabolic poisons such as carbon monoxide and cyanide. Both present with nonspecific clinical symptoms including cardiovascular collapse. Carbon monoxide intoxication should be treated with oxygen and cyanide with hydroxocobalamin.Inhalation injury remains a great challenge for clinicians and an area of opportunity for scientists. Management of this concomitant injury lags behind other aspects of burn care. More clinical research is required to improve the outcome of inhalation injury.The goal of this review is to comprehensively summarize the diagnoses, treatment options, and current research.

A bench study of inhaled nitric oxide delivery during high frequency percussive ventilation

BACKGROUND

Safe and effective delivery of inhaled nitric oxide (INO) requires the appropriate interface of ventilator and INO delivery device.

METHODS

We compared INO delivery using four configurations with the Transport Sinusoidal Bronchotron® and INOmax DSIR Plus^® in a lung model. Ventilator settings and lung model values were held constant. Delivered NO, NO₂ , and inspired oxygen (FIO₂ ) were measured. The mean difference between set and measured NO was calculated and compared using ANOVA.

RESULTS

Placement of the injector module in line with the sliding venturi resulted in a ventilator failure. With both continuous flow techniques there was no appreciable NO₂ generated and the mean difference between set NO and measured NO at 20 and 40 ppm was -16.5 ppm and -33.2 ppm at flows of 5 and 10 L/min. Placement of the injector module between the sliding venturi and lung model resulted in an increase of NO2 to a peak of 2.4 ppm (mean 2.3 + 0.1) and a mean difference between set and measured NO of + 11.3 ppm and +30 ppm at 20 and 40 ppm, 300 cycles per minute (cpm), and 22.1 ppm and 37.6 ppm, at 20 and 40 ppm, 600 cpm. None of the test configurations delivered INO within 30% of set concentrations. No alarms or interruption of INO delivery occurred.

CONCLUSION

The dual gas delivery system of the Bronchotron prevents accurate delivery of INO. The combination of these two devices should be accomplished with caution and vigilance.

High frequency percussive ventilation increases alveolar recruitment in early acute respiratory distress syndrome: an experimental, physiological and CT scan study

Background

High frequency percussive ventilation (HFPV) combines diffusive (high frequency mini-bursts) and convective ventilation patterns. Benefits include enhanced oxygenation and hemodynamics, and alveolar recruitment, while providing hypothetic lung-protective ventilation. No study has investigated HFPV-induced changes in lung aeration in patients with early acute respiratory distress syndrome (ARDS).

Methods

Eight patients with early non-focal ARDS were enrolled and five swine with early non-focal ARDS were studied in prospective computed tomography (CT) scan and animal studies, in a university-hospital tertiary ICU and an animal laboratory. Patients were optimized under conventional “open-lung” ventilation. Lung CT was performed using an end-expiratory hold (Conv) to assess lung morphology. HFPV was applied for 1 hour to all patients before new CT scans were performed with end-expiratory (HFPV EE) and end-inspiratory (HFPV EI) holds. Lung volumes were determined after software analysis. At specified time points, blood gases and hemodynamic data were collected. Recruitment was defined as a change in non-aerated lung volumes between Conv, HFPV EE and HFPV EI. The main objective was to verify whether HFPV increases alveolar recruitment without lung hyperinflation. Correlation between pleural, upper airways and HFPV-derived pressures was assessed in an ARDS swine-based model.

Results

One-hour HFPV significantly improved oxygenation and hemodynamics. Lung recruitment significantly rose by 12.0% (8.5–18.0%), P = 0.05 (Conv-HFPV EE) and 12.5% (9.3–16.8%), P = 0.003 (Conv-HFPV EI). Hyperinflation tended to increase by 2.0% (0.5–2.5%), P = 0.89 (Conv-HFPV EE) and 3.0% (2.5–4.0%), P = 0.27 (Conv-HFPV EI). HFPV hyperinflation correlated with hyperinflated and normally-aerated lung volumes at baseline: r = 0.79, P = 0.05 and r = 0.79, P = 0.05, respectively (Conv-HFPV EE); and only hyperinflated lung volumes at baseline: r = 0.88, P = 0.01 (Conv-HFPV EI). HFPV CT-determined tidal volumes reached 5.7 (1.1–8.1) mL.kg^-1 of ideal body weight (IBW). Correlations between pleural and HFPV-monitored pressures were acceptable and end-inspiratory pleural pressures remained below 25cmH₂0.

Conclusions

HFPV improves alveolar recruitment, gas exchanges and hemodynamics of patients with early non-focal ARDS without relevant hyperinflation. HFPV-derived pressures correlate with corresponding pleural or upper airways pressures.

Trial registration

ClinicalTrials.gov, NCT02510105. Registered on 1 June 2015. The trial was retrospectively registered.

Electronic supplementary material

The online version of this article (doi:10.1186/s13054-017-1924-6) contains supplementary material, which is available to authorized users.

Optimal Strategies for Severe Acute Respiratory Distress Syndrome

Acute respiratory distress syndrome (ARDS) occurs in more than 10% of intensive care unit admissions and in nearly 25% of ventilated patients. Mortality remains high at 40%, and, for patients who survive, recovery continues for months or even years. Early recognition and minimizing further lung injury remain essential to successful management of severe ARDS. Advanced treatment strategies, which complement lung protective ventilation, include short-term neuromuscular blockade, prone positioning, and extracorporeal membrane oxygenation. Alternative ventilator strategies include high-frequency ventilation and airway pressure release ventilation. This article reviews these options in patients with severe ARDS.

Effects of intrapulmonary percussive ventilation on airway mucus clearance: A bench model

AIM

To determine the ability of intrapulmonary percussive ventilation (IPV) to promote airway clearance in spontaneously breathing patients and those on mechanical ventilation.

METHODS

An artificial lung was used to simulate a spontaneously breathing patient (Group 1), and was then connected to a mechanical ventilator to simulate a patient on mechanical ventilation (Group 2). An 8.5 mm endotracheal tube (ETT) connected to the test lung, simulated the patient airway. Artificial mucus was instilled into the mid-portion of the ETT. A filter was attached at both ends of the ETT to collect the mucus displaced proximally (mouth-piece filter) and distally (lung filter). The IPV machine was attached to the proximal end of the ETT and was applied for 10-min each to Group 1 and 2. After each experiment, the weight of the various circuit components were determined and compared to their dry weights to calculate the weight of the displaced mucus.

RESULTS

In Group 1 (spontaneously breathing model), 26.8% ± 3.1% of the simulated mucus was displaced proximally, compared to 0% in Group 2 (the mechanically ventilated model) with a P-value of < 0.01. In fact, 17% ± 1.5% of the mucus in Group 2 remained in the mid-portion of the ETT where it was initially instilled and 80% ± 4.2% was displaced distally back towards the lung (P < 0.01). There was an overall statistically significant amount of mucus movement proximally towards the mouth-piece in the spontaneously breathing (SB) patient. There was also an overall statistically significant amount of mucus movement distally back towards the lung in the mechanically ventilated (MV) model. In the mechanically ventilated model, no mucus was observed to move towards the proximal/mouth piece section of the ETT.

CONCLUSION

This bench model suggests that IPV is associated with displacement of mucus towards the proximal mouthpiece in the SB patient, and distally in the MV model.

Update in Management of Severe Hypoxemic Respiratory Failure

Mortality related to severe-moderate and severe ARDS remains high. We searched the literature to update this topic. We defined severe hypoxemic respiratory failure as Pao₂/Fio₂ < 150 mm Hg (ie, severe-moderate and severe ARDS). For these patients, we support setting the ventilator to a tidal volume of 4 to 8 mL/kg predicted body weight (PBW), with plateau pressure (Pplat) ≤ 30 cm H₂O, and initial positive end-expiratory pressure (PEEP) of 10 to 12 cm H₂O. To promote alveolar recruitment, we propose increasing PEEP in increments of 2 to 3 cm provided that Pplat remains ≤ 30 cm H₂O and driving pressure does not increase. A fluid-restricted strategy is recommended, and nonrespiratory causes of hypoxemia should be considered. For patients who remain hypoxemic after PEEP optimization, neuromuscular blockade and prone positioning should be considered. Profound refractory hypoxemia (Pao₂/Fio₂ < 80 mm Hg) after PEEP titration is an indication to consider extracorporeal life support. This may necessitate early transfer to a center with expertise in these techniques. Inhaled vasodilators and nontraditional ventilator modes may improve oxygenation, but evidence for improved outcomes is weak.

Reciprocal Risk of Acute Kidney Injury and Acute Respiratory Distress Syndrome in Critically Ill Burn Patients

OBJECTIVE

To evaluate the association between acute respiratory distress syndrome and acute kidney injury with respect to their contributions to mortality in critically ill patients.

DESIGN

Retrospective analysis of consecutive adult burn patients requiring mechanical ventilation.

SETTING

A 16-bed burn ICU at tertiary military teaching hospital.

PATIENTS

Adult patients more than 18 years old requiring mechanical ventilation during their initial admission to our burn ICU from January 1, 2003, to December 31, 2011.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A total 830 patients were included, of whom 48.2% had acute kidney injury (n = 400). These patients had a 73% increased risk of developing acute respiratory distress syndrome after controlling for age, gender, total body surface area burned, and inhalation injury (hazard ratio, 1.73; 95% CI, 1.18-2.54; p = 0.005). In a reciprocal multivariate analysis, acute respiratory distress syndrome (n = 299; 36%) demonstrated a strong trend toward developing acute kidney injury (hazard ratio, 1.39; 95% CI, 0.99-1.95; p = 0.05). There was a 24% overall in-hospital mortality (n = 198). After adjusting for the aforementioned confounders, both acute kidney injury (hazard ratio, 3.73; 95% CI, 2.39-5.82; p < 0.001) and acute respiratory distress syndrome (hazard ratio, 2.16; 95% CI, 1.58-2.94; p < 0.001) significantly contributed to mortality. Age, total body surface area burned, and inhalation injury were also significantly associated with increased mortality.

CONCLUSIONS

Acute kidney injury increases the risk of acute respiratory distress syndrome in mechanically ventilated burn patients, whereas acute respiratory distress syndrome similarly demonstrates a strong trend toward the development of acute kidney injury. Acute kidney injury and acute respiratory distress syndrome are both independent risks for subsequent death. Future research should look at this interplay for possible early interventions.

Inhalation Injury: Pathophysiology, Diagnosis, and Treatment

The classic determinants of mortality from severe burn injury are age, size of injury, delays of resuscitation, and the presence of inhalation injury. Of the major determinants of mortality, inhalation injury remains one of the most challenging injuries for burn care providers. Patients with inhalation injury are at increased risk for pneumonia (the leading cause of death) and multisystem organ failure. There is no consensus among leading burn care centers in the management of inhalation injury. This article outlines the current treatment algorithms and the evidence of their efficacy.

Transferring patients with refractory hypoxemia to a regional extracorporeal membrane oxygenation center: key considerations for clinicians

Because of technological advancements and encouraging experiences during the 2009 influenza A (H1N1) epidemic, many critical care clinicians consider extracorporeal membrane oxygenation (ECMO) a reasonable strategy for managing patients with refractory hypoxemia when standardized therapies have failed. Although the literature remains unclear as to whether it should be considered a routine or a rescue strategy in the management of patients with severe acute respiratory distress syndrome, experts agree that ECMO therapy is most likely to result in positive outcomes and fewer complications when provided at regional ECMO centers. Some institutions have developed the expertise and resources required to provide this sophisticated therapy, but significantly more facilities may choose to send their patients to a tertiary ECMO center when they do not respond to usual care. This article provides information essential for health care teams who refer their patients to such centers. The clinical indications for, and the use of, ECMO therapy in the management of refractory hypoxemia is briefly reviewed, followed by a description of how ECMO works to provide gas exchange and tissue perfusion. The primary considerations for circuit management, hemodynamic support, and pulmonary care are described, and significant complications of the therapy are identified. The remainder of the article focuses on the patient care and preparatory activities that occur before and during ECMO initiation, so that health care teams, patients, and their families can be confident of an efficient, safe, and highly skilled transfer of care between institutions.

Ventilation strategies in paediatric inhalation injury

Inhalation injury increases morbidity and mortality in burns victims. While the diagnosis remains largely clinical, bronchoscopy is also helpful to diagnose and grade the severity of any injury. Inhalation injury results from direct thermal injury or chemical irritation of the respiratory tract, systemic toxicity from inhaled substances, or a combination of these factors. While endotracheal intubation is essential in cases where upper airway obstruction may occur, it has its own risks and should not be performed prophylactically in all cases of inhalation injury. The evidence-base informing the selection of optimal ventilation strategy in inhalation injury is sparse, and most recommendations are based on extrapolation from (largely adult) studies in acute respiratory distress syndrome (ARDS). Conventional ventilation using a lung-protective approach (i.e. low tidal volume, limited plateau pressure, and permissive hypercarbia) is recommended as the initial approach if invasive ventilation is required; various rescue strategies may become necessary if there is a poor response. The efficacy of many widely used pharmacologic adjuncts in inhalation injury remains uncertain. Further research is urgently required to address these gaps in our knowledge.

Burns management in ICU: Quality of the evidence: A systematic review

BACKGROUND

The objective of this study was to assess the quality of readily available evidence regarding critical care aspects of the management of patients with severe burn injuries.

METHOD

PUBMED, EMBASE, Cochrane Databases and bibliographies of included studies and burns review articles were searched from inception of databases to end of February 2015. We included systematic reviews, randomised controlled trials (RCTs) and cohort studies with concurrent controls on the topics of (a) fluid resuscitation (b) analgesia (c) haemodynamic monitoring and targets (d) ventilation (e) blood transfusion. The quality of the studies was assessed using validated tools.

RESULTS

Fifty six studies fulfilled the inclusion criteria. Twenty three on fluid resuscitation, 22 on analgesia, nine on haemodynamic monitoring and two on ventilation. No studies were found on blood transfusion practice. There were ten systematic reviews, 38 RCTs and eight cohort studies with concurrent controls. The majority of studies were single centre trials with small numbers of patients, surrogate outcomes and high risk of bias.

CONCLUSIONS

There is very little high quality evidence to guide clinical practice in early management of the severely burnt patient. Eleven of 56 studies found in our search of critical care topics were of good methodological quality with low risk of bias.

Mechanical Ventilation as a Therapeutic Tool to Reduce ARDS Incidence

Trauma, hemorrhagic shock, or sepsis can incite systemic inflammatory response syndrome, which can result in early acute lung injury (EALI). As EALI advances, improperly set mechanical ventilation (MV) can amplify early injury into a secondary ventilator-induced lung injury that invariably develops into overt ARDS. Once established, ARDS is refractory to most therapeutic strategies, which have not been able to lower ARDS mortality below the current unacceptably high 40%. Low tidal volume ventilation is one of the few treatments shown to have a moderate positive impact on ARDS survival, presumably by reducing ventilator-induced lung injury. Thus, there is a compelling case to be made that the focus of ARDS management should switch from treatment once this syndrome has become established to the application of preventative measures while patients are still in the EALI stage. Indeed, studies have shown that ARDS incidence is markedly reduced when conventional MV is applied preemptively using a combination of low tidal volume and positive end-expiratory pressure in both patients in the ICU and in surgical patients at high risk for developing ARDS. Furthermore, there is evidence from animal models and high-risk trauma patients that superior prevention of ARDS can be achieved using preemptive airway pressure release ventilation with a very brief duration of pressure release. Preventing rather than treating ARDS may be the way forward in dealing with this recalcitrant condition and would represent a paradigm shift in the way that MV is currently practiced.

Multifrequency Oscillatory Ventilation in the Premature Lung: Effects on Gas Exchange, Mechanics, and Ventilation Distribution

BACKGROUND

Despite the theoretical benefits of high-frequency oscillatory ventilation (HFOV) in preterm infants, systematic reviews of randomized clinical trials do not confirm improved outcomes. The authors hypothesized that oscillating a premature lung with multiple frequencies simultaneously would improve gas exchange compared with traditional single-frequency oscillatory ventilation (SFOV). The goal of this study was to develop a novel method for HFOV, termed "multifrequency oscillatory ventilation" (MFOV), which relies on a broadband flow waveform more suitable for the heterogeneous mechanics of the immature lung.

METHODS

Thirteen intubated preterm lambs were randomly assigned to either SFOV or MFOV for 1 h, followed by crossover to the alternative regimen for 1 h. The SFOV waveform consisted of a pure sinusoidal flow at 5 Hz, whereas the customized MFOV waveform consisted of a 5-Hz fundamental with additional energy at 10 and 15 Hz. Per standardized protocol, mean pressure at airway opening ((Equation is included in full-text article.)) and inspired oxygen fraction were adjusted as needed, and root mean square of the delivered oscillatory volume waveform (Vrms) was adjusted at 15-min intervals. A ventilatory cost function for SFOV and MFOV was defined as (Equation is included in full-text article.), where Wt denotes body weight.

RESULTS

Averaged over all time points, MFOV resulted in significantly lower VC (246.9 ± 6.0 vs. 363.5 ± 15.9 ml mmHg kg) and (Equation is included in full-text article.)(12.8 ± 0.3 vs. 14.1 ± 0.5 cm H2O) compared with SFOV, suggesting more efficient gas exchange and enhanced lung recruitment at lower mean airway pressures.

CONCLUSION

Oscillation with simultaneous multiple frequencies may be a more efficient ventilator modality in premature lungs compared with traditional single-frequency HFOV.

Incidence of ventilator associated pneumonia in burn patients with inhalation injury treated with high frequency percussive ventilation versus volume control ventilation: A systematic review

BACKGROUND

Pneumonia increases mortality in burn patients with inhalation injuries. We evaluated whether the use of High Frequency Percussive Ventilation (HFPV) in burn patients with inhalation injuries can decrease rates of Ventilator Associated Pneumonia (VAP) compared to Volume Control Ventilation (VCV).

METHODS

Data were gathered from PubMed, EMBASE, Web of Science, reference lists, and hand search. For unpublished data we searched ClinicalTrials.gov and RePORTER. We included observational and Randomized Controlled Trials (RCTs) that compared rates of VAP with the use of HFPV and VCV in adult burn patients with inhalation injury. Two reviewers independently extracted data from the retrieved studies and assessed them for eligibility, methodology, and quality.

RESULTS

281 abstracts were reviewed, of which 4 studies (540 patients) were included. Two were observational and two were RCTs. All studies had moderate risk of bias. One study had low external validity while others had moderate external validity. The two observational studies found non-concordant results. One study found a 24% statistically significant reduction in the rates of VAP while the other found no difference. The two RCTs had small sample sizes. There was no significant difference in VAP rates between HFPV and VCV. The VCV arms of the four studies were heterogeneous. Only one study used low tidal volumes, whereas the rest used high tidal volumes in the VCV arm.

CONCLUSION

Evidence about decreased incidence of VAP in burn patients with inhalation injuries who are on HFPV compared to those on VCV is inconclusive. Although enhanced airway clearance by HFPV was thought to play a role in decreasing VAP in this population, high tidal volume in the VCV arms could be a confounding factor that should be eliminated in future studies before a firm conclusion can be reached. More RCTs comparing HFPV to low tidal volume VCV are needed.

A Survey of Mechanical Ventilator Practices Across Burn Centers in North America

Burn injury introduces unique clinical challenges that make it difficult to extrapolate mechanical ventilator (MV) practices designed for the management of general critical care patients to the burn population. We hypothesize that no consensus exists among North American burn centers with regard to optimal ventilator practices. The purpose of this study is to examine various MV practice patterns in the burn population and to identify potential opportunities for future research. A researcher designed, 24-item survey was sent electronically to 129 burn centers. The χ, Fisher's exact, and Cochran-Mantel-Haenszel tests were used to determine if there were significant differences in practice patterns. We analyzed 46 questionnaires for a 36% response rate. More than 95% of the burn centers reported greater than 100 annual admissions. Pressure support and volume assist control were the most common initial MV modes used with or without inhalation injury. In the setting of Berlin defined mild acute respiratory distress syndrome (ARDS), ARDSNet protocol and optimal positive end-expiratory pressure were the top ventilator choices, along with fluid restriction/diuresis as a nonventilator adjunct. For severe ARDS, airway pressure release ventilation and neuromuscular blockade were the most popular. The most frequently reported time frame for mechanical ventilation before tracheostomy was 2 weeks (25 of 45, 55%); however, all respondents reported in the affirmative that there are certain clinical situations where early tracheostomy is warranted. Wide variations in clinical practice exist among North American burn centers. No single ventilator mode or adjunct prevails in the management of burn patients regardless of pulmonary insult. Movement toward American Burn Association-supported, multicenter studies to determine best practices and guidelines for ventilator management in burn patients is prudent in light of these findings.