High-frequency percussive ventilation revisited

Non-invasive high-frequency ventilation in newborn infants with respiratory distress

BACKGROUND

Respiratory distress occurs in up to 7% of newborns, with respiratory support (RS) provided invasively via an endotracheal (ET) tube or non-invasively via a nasal interface. Invasive ventilation increases the risk of lung injury and chronic lung disease (CLD). Using non-invasive strategies, with or without minimally invasive surfactant, may reduce the need for mechanical ventilation and the risk of lung damage in newborn infants with respiratory distress.

OBJECTIVES

To evaluate the benefits and harms of nasal high-frequency ventilation (nHFV) compared to invasive ventilation via an ET tube or other non-invasive ventilation methods on morbidity and mortality in preterm and term infants with or at risk of respiratory distress.

SEARCH METHODS

We searched CENTRAL, MEDLINE, Embase, CINAHL and three trial registries in April 2023.

SELECTION CRITERIA

Randomised controlled trials (RCTs), cluster- or quasi-RCTs of nHFV in newborn infants with respiratory distress compared to invasive or non-invasive ventilation.

DATA COLLECTION AND ANALYSIS

Two authors independently selected the trials for inclusion, extracted data, assessed the risk of bias, and undertook GRADE assessment.

MAIN RESULTS

We identified 33 studies, mostly in low- to middle-income settings, that investigated this therapy in 5068 preterm and 46 term infants. nHFV compared to invasive respiratory therapy for initial RS We are very uncertain whether nHFV reduces mortality before hospital discharge (RR 0.67, 95% CI 0.20 to 2.18; 1 study, 80 infants) or the incidence of CLD (RR 0.38, 95% CI 0.09 to 1.59; 2 studies, 180 infants), both very low-certainty. ET intubation, death or CLD, severe intraventricular haemorrhage (IVH) and neurodevelopmental disability (ND) were not reported. nHFV vs nasal continuous positive airway pressure (nCPAP) used for initial RS We are very uncertain whether nHFV reduces mortality before hospital discharge (RR 1.00, 95% CI 0.41 to 2.41; 4 studies, 531 infants; very low-certainty). nHFV may reduce ET intubation (RR 0.52, 95% CI 0.33 to 0.82; 5 studies, 571 infants), but there may be little or no difference in CLD (RR 1.35, 95% CI 0.80 to 2.27; 4 studies, 481 infants); death or CLD (RR 2.50, 95% CI 0.52 to 12.01; 1 study, 68 participants); or severe IVH (RR 1.17, 95% CI 0.36 to 3.78; 4 studies, 531 infants), all low-certainty evidence. ND was not reported. nHFV vs nasal intermittent positive-pressure ventilation (nIPPV) used for initial RS nHFV may result in little to no difference in mortality before hospital discharge (RR 1.86, 95% CI 0.90 to 3.83; 2 studies, 84 infants; low-certainty). nHFV may have little or no effect in reducing ET intubation (RR 1.33, 95% CI 0.76 to 2.34; 5 studies, 228 infants; low-certainty). There may be a reduction in CLD (RR 0.63, 95% CI 0.42 to 0.95; 5 studies, 307 infants; low-certainty). A single study (36 infants) reported no events for severe IVH. Death or CLD and ND were not reported. nHFV vs high-flow nasal cannula (HFNC) used for initial RS We are very uncertain whether nHFV reduces ET intubation (RR 2.94, 95% CI 0.65 to 13.27; 1 study, 37 infants) or reduces CLD (RR 1.18, 95% CI 0.46 to 2.98; 1 study, 37 participants), both very low-certainty. There were no mortality events before hospital discharge or severe IVH. Other deaths, CLD and ND, were not reported. nHFV vs nCPAP used for RS following planned extubation nHFV probably results in little or no difference in mortality before hospital discharge (RR 0.92, 95% CI 0.52 to 1.64; 6 studies, 1472 infants; moderate-certainty). nHFV may result in a reduction in ET reintubation (RR 0.42, 95% CI 0.35 to 0.51; 11 studies, 1897 infants) and CLD (RR 0.78, 95% CI 0.67 to 0.91; 10 studies, 1829 infants), both low-certainty. nHFV probably has little or no effect on death or CLD (RR 0.90, 95% CI 0.77 to 1.06; 2 studies, 966 infants) and severe IVH (RR 0.80, 95% CI 0.57 to 1.13; 3 studies, 1117 infants), both moderate-certainty. We are very uncertain whether nHFV reduces ND (RR 0.92, 95% CI 0.37 to 2.29; 1 study, 74 infants; very low-certainty). nHFV versus nIPPV used for RS following planned extubation nHFV may have little or no effect on mortality before hospital discharge (RR 1.83, 95% CI 0.70 to 4.79; 2 studies, 984 infants; low-certainty). There is probably a reduction in ET reintubation (RR 0.69, 95% CI 0.54 to 0.89; 6 studies, 1364 infants), but little or no effect on CLD (RR 0.88, 95% CI 0.75 to 1.04; 4 studies, 1236 infants); death or CLD (RR 0.92, 95% CI 0.79 to 1.08; 3 studies, 1070 infants); or severe IVH (RR 0.78, 95% CI 0.55 to 1.10; 4 studies, 1162 infants), all moderate-certainty. One study reported there might be no difference in ND (RR 0.88, 95% CI 0.35 to 2.16; 1 study, 72 infants; low-certainty). nHFV versus nIPPV following initial non-invasive RS failure nHFV may have little or no effect on mortality before hospital discharge (RR 1.44, 95% CI 0.10 to 21.33); or ET intubation (RR 1.23, 95% CI 0.51 to 2.98); or CLD (RR 1.01, 95% CI 0.70 to 1.47); or severe IVH (RR 0.47, 95% CI 0.02 to 10.87); 1 study, 39 participants, all low- or very low-certainty. Other deaths or CLD and ND were not reported.

AUTHORS' CONCLUSIONS

For initial RS, we are very uncertain if using nHFV compared to invasive respiratory therapy affects clinical outcomes. However, nHFV may reduce intubation when compared to nCPAP. For planned extubation, nHFV may reduce the risk of reintubation compared to nCPAP and nIPPV. nHFV may reduce the risk of CLD when compared to nCPAP. Following initial non-invasive respiratory support failure, nHFV when compared to nIPPV may result in little to no difference in intubation. Large trials, particularly in high-income settings, are needed to determine the role of nHFV in initial RS and following the failure of other non-invasive respiratory support. Also, the optimal settings of nHVF require further investigation.

The Effects of Massage Guns on Performance and Recovery: A Systematic Review

The use of massage guns has become increasingly popular in recent years. Although their use is more and more common, both in a clinical and sports context, there is still little information to guide the practitioners. This systematic review aimed to determine the effects of massage guns in healthy and unhealthy populations as pre- and post-activity or part of a treatment. Data sources used were PubMed, PEDro, Scopus, SPORTDiscus, Web of Science and Google Scholar, and the study eligibility criteria were based on "healthy and unhealthy individuals", "massage guns", "pre-activity, post-activity or part of a treatment" and "randomized and non-randomized studies" (P.I.C.O.S.). Initially, 281 records were screened, but only 11 could be included. Ten had a moderate risk of bias and one a high risk of bias. Massage guns could be effective in improving iliopsoas, hamstrings, triceps suralis and the posterior chain muscles' flexibility. In strength, balance, acceleration, agility and explosive activities, it either did not have improvements or it even showed a decrease in performance. In the recovery-related outcomes, massage guns were shown to be cost-effective instruments for stiffness reduction, range of motion and strength improvements after a fatigue protocol. No differences were found in contraction time, rating of perceived exertion or lactate concentration. Massage guns can help to improve short-term range of motion, flexibility and recovery-related outcomes, but their use in strength, balance, acceleration, agility and explosive activities is not recommended.

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.

Mechanical Ventilation in Pediatric and Neonatal Patients

Pediatric acute respiratory distress syndrome (PARDS) remains a significant cause of morbidity and mortality, with mortality rates as high as 50% in children with severe PARDS. Despite this, pediatric lung injury and mechanical ventilation has been poorly studied, with the majority of investigations being observational or retrospective and with only a few randomized controlled trials to guide intensivists. The most recent and universally accepted guidelines for pediatric lung injury are based on consensus opinion rather than objective data. Therefore, most neonatal and pediatric mechanical ventilation practices have been arbitrarily adapted from adult protocols, neglecting the differences in lung pathophysiology, response to injury, and co-morbidities among the three groups. Low tidal volume ventilation has been generally accepted for pediatric patients, even in the absence of supporting evidence. No target tidal volume range has consistently been associated with outcomes, and compliance with delivering specific tidal volume ranges has been poor. Similarly, optimal PEEP has not been well-studied, with a general acceptance of higher levels of F_iO₂ and less aggressive PEEP titration as compared with adults. Other modes of ventilation including airway pressure release ventilation and high frequency ventilation have not been studied in a systematic fashion and there is too little evidence to recommend supporting or refraining from their use. There have been no consistent outcomes among studies in determining optimal modes or methods of setting them. In this review, the studies performed to date on mechanical ventilation strategies in neonatal and pediatric populations will be analyzed. There may not be a single optimal mechanical ventilation approach, where the best method may simply be one that allows for a personalized approach with settings adapted to the individual patient and disease pathophysiology. The challenges and barriers to conducting well-powered and robust multi-institutional studies will also be addressed, as well as reconsidering outcome measures and study design.

Nasal High-Frequency Ventilation

Noninvasive high-frequency oscillatory (NHFOV) and percussive (NHFPV) ventilation represent 2 nonconventional techniques that may be useful in selected neonatal patients. We offer here a comprehensive review of physiology, mechanics, and biology for both techniques. As NHFOV is the technique with the wider experience, we also provided a meta-analysis of available clinical trials, suggested ventilatory parameters boundaries, and proposed a physiology-based clinical protocol to use NHFOV.

Haemophagocytic lymphohistiocytosis in pregnancy: a pertinent case during the COVID-19 pandemic

Haemophagocytic lymphohistiocytosis (HLH) is a rare, often fatal disease, and presents a diagnostic challenge in the pregnant patient. This challenge is particularly relevant during the current COVID-19 pandemic. We present a case of HLH in a pregnant woman presenting with fever predating the COVID-19 pandemic. A 33-year-old, gravida 2, para 1 at 27 weeks’ gestation presented with fever, transaminitis, thrombocytopenia and elevated ferritin. After treatment according to the HLH-94 protocol, caesarean delivery and weeks of intensive care, the patient recovered fully. With prompt diagnosis and a multispecialty team at our tertiary care facility, she and her baby overcame a dire prognosis. HLH should be considered in pregnant patients presenting with a febrile illness. Particularly in cases of severe COVID-19, secondary HLH must be considered as an associated diagnosis.

Acute respiratory failure and burn patient outcomes

PURPOSE OF REVIEW

Advances in the care of inhalational injuries have not kept pace with advances that have been seen in the treatment of cutaneous burns. There is not yet a standard of care for best outcomes for airway management of patients with known or suspected inhalational injuries. Clinicians must decide if to intubate the patient, and if so, whether to intubate early or late in their presentation. Unnecessary intubation affects morbidity and mortality. This review will summarize literature that highlights present practices in the treatment of patients with inhalation injuries.

RECENT FINDINGS

There have been promising investigations into biomarkers that can be used to quantify a patient's risk and better target therapies. Grading systems serve to better stratify the burn victim's prognosis and then direct their care. Special ventilator modes can assist in ventilating burn patients with inhalation injuries that experience difficulties in oxygenating.

SUMMARY

Inhalational injuries are a significant source of morbidity and mortality in thermally injured patients. Treatment modalities, such as modified ventilator settings, alteration in fluid resuscitation, and a standardized grading system may improve morbidity and mortality.

A Critical Update of the Assessment and Acute Management of Patients with Severe Burns

Significance: Burns are debilitating, life threatening, and difficult to assess and manage. Recent advances in assessment and management have occurred since a comprehensive review of the care of patients with severe burns was last published, which may influence research and clinical practice. Recent Advances: Recent advances have occurred in the understanding of burn pathophysiology, which has led to the identification of potential biomarkers of burn severity, such as protein C. There is new evidence about the potential superiority of natural colloids over crystalloids during fluid resuscitation, and new evidence about components of initial and perioperative management, including an improved understanding of pain following burns. Critical Issues: The limitations of the clinical examination highlight the need for imaging and biomarkers to assist in estimations of burn severity. Fluid resuscitation reduces mortality, although there is conjecture over the ideal method. The subsequent perioperative period is associated with significant morbidity and the evidence for preventing and treating pain, infection, and fluid overload while maximizing wound healing potential is described. Future Directions: Promising developments are ongoing in imaging technology, histopathology, biomarkers, and wound healing adjuncts such as hyperbaric oxygen therapy, topical negative pressure therapy, stem cell treatments, and skin substitutes. The greatest benefit from further research on management of patients with burns would most likely be derived from the elucidation of optimal fluid resuscitation protocols, pain management protocols, and surgical techniques from randomized controlled trials.

Strain, strain rate, and mechanical power: An optimization comparison for oscillatory ventilation

The purpose of this study was to assess the potential for optimization of mechanical ventilator waveforms using multiple frequencies of oscillatory flow delivered simultaneously to minimize the risk of ventilator-induced lung injury (VILI) associated with regional strain, strain rate, and mechanical power. Optimization was performed using simulations of distributed oscillatory flow and gas transport in a computational model of anatomically derived branching airway segments and viscoelastic terminal acini under healthy and injured conditions. Objective functions defined by regional strain or strain rate were minimized by single-frequency ventilation waveforms using the highest or lowest frequencies available, respectively. However, a mechanical power objective function was minimized by a combination of multiple frequencies delivered simultaneously. This simulation study thus demonstrates the potential for multifrequency oscillatory ventilation to reduce regional mechanical power in comparison to single-frequency ventilation, and thereby reduce the risk of VILI.

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.

Management of Pulmonary Failure after Burn Injury: From VDR to ECMO

This article highlights the challenges in managing pulmonary failure after burn injury. The authors review several different ventilator techniques, provide weaning parameters, and discuss complications.

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.

Parenchymal strain heterogeneity during oscillatory ventilation: why two frequencies are better than one

High-frequency oscillatory ventilation (HFOV) relies on low tidal volumes cycled at supraphysiological rates, producing fundamentally different mechanisms for gas transport and exchange compared with conventional mechanical ventilation. Despite the appeal of using low tidal volumes to mitigate the risks of ventilator-induced lung injury, HFOV has not improved mortality for most clinical indications. This may be due to nonuniform and frequency-dependent distribution of flow throughout the lung. The goal of this study was to compare parenchymal strain heterogeneity during eucapnic HFOV when using oscillatory waveforms that consisted of either a single discrete frequency or two simultaneous frequencies. We utilized a three-dimensional, anatomically structured canine lung model for simulating frequency-dependent ventilation distribution. Gas transport was simulated via direct alveolar ventilation, advective mixing at bifurcations, turbulent and oscillatory dispersion, and molecular diffusion. Volume amplitudes at each oscillatory frequency were iteratively optimized to attain eucapnia. Ventilation using single-frequency HFOV demonstrated increasing heterogeneity of acinar flow and CO₂ elimination with frequency for frequencies greater than the resonant frequency. For certain pairs of frequencies, a linear combination of the two corresponding ventilation distributions yielded reduced acinar strain heterogeneity compared with either frequency alone. Our model demonstrates that superposition of two simultaneous oscillatory frequencies can achieve more uniform ventilation distribution, and therefore lessen the potential for ventilator-induced lung injury, compared with traditional single-frequency HFOV. NEW & NOTEWORTHY In this study, we simulated oscillatory ventilation with multiple simultaneous frequencies using a computational lung model that includes distributed flow and gas transport. A mechanism of benefit was identified by which ventilation with two simultaneous frequencies results in reduced acinar strain heterogeneity compared with either frequency alone. This finding suggests the possibility of tuning the spectral content of ventilator waveforms according to patient-specific mechanical heterogeneity.

Pathophysiology, research challenges, and clinical management of smoke inhalation injury

Smoke inhalation injury is a serious medical problem that increases morbidity and mortality after severe burns. However, relatively little attention has been paid to this devastating condition, and the bulk of research is limited to preclinical basic science studies. Moreover, no worldwide consensus criteria exist for its diagnosis, severity grading, and prognosis. Therapeutic approaches are highly variable depending on the country and burn centre or hospital. In this Series paper, we discuss understanding of the pathophysiology of smoke inhalation injury, the best evidence-based treatments, and challenges and future directions in diagnostics and management.

Management of blunt pulmonary injury

Thoracic injuries account for 25% of all civilian deaths. Blunt force injuries are a subset of thoracic injuries and include injuries of the tracheobronchial tree, pleural space, and lung parenchyma. Early identification of these injuries during initial assessment and resuscitation is essential to reduce associated morbidity and mortality rates. Management of airway injuries includes definitive airway control with identification and repair of tracheobronchial injuries. Management of pneumothorax and hemothorax includes pleural space drainage and control of ongoing hemorrhage, along with monitoring for complications such as empyema and chylothorax. Injuries of the lung parenchyma, such as pulmonary contusion, may require support of oxygenation and ventilation through both conventional and nonconventional mechanical ventilation strategies. General strategies to improve pulmonary function and gas exchange include balanced fluid resuscitation to targeted volume-based resuscitation end points, positioning therapy, and pain management.

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.

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.

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.

Reduction of Respiratory Motion During PET/CT by Pulsatile-Flow Ventilation: A First Clinical Evaluation

Respiratory motion negatively affects PET/CT image quality and quantitation. A novel Pulsatile-Flow Ventilation (PFV) system reducing respiratory motion was applied in spontaneously breathing patients to induce sustained apnea during PET/CT.

METHODS

Four patients (aged 65 ± 14 y) underwent PET/CT for pulmonary nodule staging (mean, 11 ± 7 mm; range, 5-18 mm) at 63 ± 3 min after (18)F-FDG injection and then at 47 ± 7 min afterward, during PFV-induced apnea (with imaging lasting ≥8.5 min). Anterior-posterior thoracic amplitude, SUVmax, and SUVpeak (SUVmean in a 1-cm-diameter sphere) were compared.

RESULTS

PFV PET/CT reduced thoracic amplitude (80%), increased mean lesion SUVmax (29%) and SUVpeak (11%), decreased lung background SUVpeak (25%), improved lesion detectability, and increased SUVpeak lesion-to-background ratio (54%). On linear regressions, SUVmax and SUVpeak significantly improved (by 35% and 23%, respectively; P ≤ 0.02).

CONCLUSION

PFV-induced apnea reduces thoracic organ motion and increases lesion SUV, detectability, and delineation, thus potentially affecting patient management by improving diagnosis, prognostication, monitoring, and external-radiation therapy planning.

Management of Blunt Pulmonary Injury

Thoracic injuries account for 25% of all civilian deaths. Blunt force injuries are a subset of thoracic injuries and include injuries of the tracheobronchial tree, pleural space, and lung parenchyma. Early identification of these injuries during initial assessment and resuscitation is essential to reduce associated morbidity and mortality rates. Management of airway injuries includes definitive airway control with identification and repair of tracheobronchial injuries. Management of pneumothorax and hemothorax includes pleural space drainage and control of ongoing hemorrhage, along with monitoring for complications such as empyema and chylothorax. Injuries of the lung parenchyma, such as pulmonary contusion, may require support of oxygenation and ventilation through both conventional and nonconventional mechanical ventilation strategies. General strategies to improve pulmonary function and gas exchange include balanced fluid resuscitation to targeted volume-based resuscitation end points, positioning therapy, and pain management.

Inhalation injury: epidemiology, pathology, treatment strategies

Lung injury resulting from inhalation of smoke or chemical products of combustion continues to be associated with significant morbidity and mortality. Combined with cutaneous burns, inhalation injury increases fluid resuscitation requirements, incidence of pulmonary complications and overall mortality of thermal injury. While many products and techniques have been developed to manage cutaneous thermal trauma, relatively few diagnosis-specific therapeutic options have been identified for patients with inhalation injury. Several factors explain slower progress for improvement in management of patients with inhalation injury. Inhalation injury is a more complex clinical problem. Burned cutaneous tissue may be excised and replaced with skin grafts. Injured pulmonary tissue must be protected from secondary injury due to resuscitation, mechanical ventilation and infection while host repair mechanisms receive appropriate support. Many of the consequences of smoke inhalation result from an inflammatory response involving mediators whose number and role remain incompletely understood despite improved tools for processing of clinical material. Improvements in mortality from inhalation injury are mostly due to widespread improvements in critical care rather than focused interventions for smoke inhalation.

Morbidity associated with inhalation injury is produced by heat exposure and inhaled toxins. Management of toxin exposure in smoke inhalation remains controversial, particularly as related to carbon monoxide and cyanide. Hyperbaric oxygen treatment has been evaluated in multiple trials to manage neurologic sequelae of carbon monoxide exposure. Unfortunately, data to date do not support application of hyperbaric oxygen in this population outside the context of clinical trials. Cyanide is another toxin produced by combustion of natural or synthetic materials. A number of antidote strategies have been evaluated to address tissue hypoxia associated with cyanide exposure. Data from European centers supports application of specific antidotes for cyanide toxicity. Consistent international support for this therapy is lacking. Even diagnostic criteria are not consistently applied though bronchoscopy is one diagnostic and therapeutic tool. Medical strategies under investigation for specific treatment of smoke inhalation include beta-agonists, pulmonary blood flow modifiers, anticoagulants and antiinflammatory strategies. Until the value of these and other approaches is confirmed, however, the clinical approach to inhalation injury is supportive.

Nontraditional modes of mechanical ventilation: progress or distraction?

As technology continues to develop, a wide range of novel and nontraditional modes of mechanical ventilation have become available for the management of critically ill patients. Proportional assist ventilation, neurally adjusted ventilatory assist and adaptive support ventilation are three novel modes of ventilation, which attempt to optimize patient-ventilator synchrony. Improved interactions between patient and ventilator may be important in improving clinical outcomes. Another important priority for mechanically ventilated patients is lung protection, and nontraditional modes of ventilation that may be implemented to minimize ventilator-associated lung injury include airway pressure release ventilation and high-frequency ventilation. Novel and nontraditional modes of ventilation may represent important tools in the critical care environment; however, continued investigation is needed to determine the overall impact of these various approaches on outcomes for mechanically ventilated patients.

Long-range critical care evacuation and reoperative surgery

Long-range critical care aeromedical evacuation has significantly contributed to the unprecedented survival during recent military operations. With advances in critical care, patients with increased injury severity and overall complexity are routinely evacuated while resuscitation is ongoing. Additional specialty teams now provide advanced pulmonary rescue therapies for the most critically ill patients. As part of the continuum of trauma care, an overseas fixed facility provides follow-on emergency surgical critical care to optimize patient outcomes before final evacuation to the continental United States.