Use of ultrahigh frequency ventilation in patients with ARDS. A preliminary report

Pneumothorax, an underappreciated complication with an airway exchange catheter

While airway exchange catheters (AEC) are designed to safely maintain a secure airway and sometimes allow for ventilation while exchanging an endotracheal tube or performing a trial tracheal extubation, their use is sometimes associated with devastating complications. Pneumothorax is an underappreciated complication with AECs that can occur even in the absence of high pressure ventilation with quick clinical deterioration. The development of a pneumothorax can be difficult to distinguish from other potential causes of clinical deterioration and the clinician should maintain a high level of suspicion for quick diagnosis and treatment. Here we report a case of tension pneumothorax leading to cardiovascular collapse that occurred very suddenly with the introduction of an AEC. This pneumothorax presented in an atypical manner by all monitors available except for blood pressure monitoring. Therefore this case highlights the need for strong clinical suspicion of pneumothorax with the use of AECs.

Feasibility of very high-frequency ventilation in adults with acute respiratory distress syndrome

OBJECTIVE

To assess the feasibility of using respiratory frequencies up to 15 Hz during high-frequency oscillatory ventilation (HFO) of adults with acute respiratory distress syndrome (ARDS).

DESIGN

Observational study.

SETTING

Medical intensive care unit at a tertiary care university hospital.

PATIENTS

Thirty adult patients receiving HFO at the discretion of their physicians for management of severe ARDS.

INTERVENTIONS

Clinical management algorithm for HFO that minimized delivered tidal volumes by encouraging the use of the highest frequency that allowed acceptable clearance of carbon dioxide. This contrasts with the typical use of HFO in adults, in which frequencies generally do not exceed 6 Hz.

MEASUREMENTS AND MAIN RESULTS

Patients were 42 +/- 15 yrs old, weighed 83 +/- 25 kg, and had failed conventional lung-protective ventilation due to refractory hypoxia or respiratory acidosis and high plateau airway pressures. During HFO, 25 of 30 patients maintained acceptable gas exchange at frequencies > 6 Hz; 12 reached maximal frequencies of > or = 10 Hz. Among patients whose maximal frequencies exceeded 6 Hz, mean maximal frequency was 9.9 +/- 2.1 Hz, at a mean oscillation pressure amplitude of 81 +/- 11 cm H2O. At those settings, blood gases were pH 7.31 +/- 0.06, PaCO2 was 58 +/- 21 mm Hg, and PaO2 was 82 +/- 33 mm Hg. Survival to hospital discharge among this severely ill cohort was 37%.

CONCLUSIONS

Most adults can maintain adequate gas exchange using HFO frequencies well above 5-6 Hz. Use of higher frequencies should minimize tidal volume and we speculate might thereby reduce ventilator-associated lung injury.

The feasibility of nitric oxide delivery with high frequency jet ventilation

A 27-year-old female with acute monocytic leukaemia (M5) developed acute respiratory distress syndrome (ARDS). Because of refractory hypoxaemia and severe barotrauma during conventional mechanical ventilation, the patient was switched to high frequency jet ventilation (HFJV) as a salvage therapy. Her refractory hypoxaemia improved temporarily but worsened again. Approval of the Institutional Review Board and the Food and Drug Administration was obtained to use nitric oxide (NO) with HFJV on a compassionate basis considering the grave situation. The NO delivery system was connected to the secondary flow circuit of the HFJV immediately after the humidifier. We measured the concentration of NO at least every hour by inserting a 7-Fr catheter connected to a McNeill analyzer into the endotracheal tube. Despite improvement of oxygenation, the patient's respiratory status deteriorated further and she died. In this case we were able to achieve reliable and constant levels of NO. The purpose of this report is to discuss the technical aspects and pitfalls of this method.

Centromere DNA, proteins and kinetochore assembly in vertebrate cells

The centromere is a specialized region of the chromosome that is essential for faithful chromosome segregation during mitosis and meiosis in eukaryotic cells. It is the site at which the kinetochore, the functional nucleoprotein complex responsible for microtubule binding and chromosome movement, is assembled through complex molecular mechanisms. Herein, I review recent advances in our understanding of centromeric DNAs as sites for kinetochore assembly and the mechanisms underlying kinetochore assembly in vertebrate cells.

Treatment of ARDS

Improved understanding of the pathogenesis of acute lung injury (ALI)/ARDS has led to important advances in the treatment of ALI/ARDS, particularly in the area of ventilator-associated lung injury. Standard supportive care for ALI/ARDS should now include a protective ventilatory strategy with low tidal volume ventilation by the protocol developed by the National Institutes of Health ARDS Network. Further refinements of the protocol for mechanical ventilation will occur as current and future clinical trials are completed. In addition, novel modes of mechanical ventilation are being studied and may augment standard therapy in the future. Although results of anti-inflammatory strategies have been disappointing in clinical trials, further trials are underway to test the efficacy of late corticosteroids and other approaches to modulation of inflammation in ALI/ARDS.

Mechanical ventilation in acute lung injury and acute respiratory distress syndrome

Mechanical ventilation provides life-sustaining support for most patients with acute lung injury and acute respiratory distress syndrome; however, traditional approaches to mechanical ventilation may cause ventilator-associated lung injury, which could exacerbate or perpetuate respiratory failure caused initially by conditions such as pneumonia, sepsis, and trauma. This article reviews the theory, laboratory data, and results of recent clinical trials that suggest that modified ventilator strategies can reduce ventilator-associated lung injury and improve clinical outcomes.

High-frequency ventilation for acute lung injury and ARDS

In patients with acute lung injury (ALI) and ARDS, conventional mechanical ventilation (CV) may cause additional lung injury from overdistention of the lung during inspiration, repeated opening and closing of small bronchioles and alveoli, or from excessive stress at the margins between aerated and atelectatic lung regions. Increasing evidence suggests that smaller tidal volumes (VTs) and higher end-expiratory lung volumes (EELVs) may be protective from these forms of ventilator-associated lung injury and may improve outcomes from ALI/ARDS. High-frequency ventilation (HFV)-based ventilatory strategies offer two potential advantages over CV for patients with ALI/ARDS. First, HFV uses very small VTs, allowing higher EELVs with less overdistention than is possible with CV. Second, despite the small VTs, high respiratory rates during HFV allow the maintenance of normal or near-normal PaCO2 levels. In this review, the use of HFV as a lung protective strategy for patients with ALI/ARDS is discussed.

High-frequency percussive ventilation improves oxygenation in patients with ARDS

STUDY OBJECTIVES

To evaluate changes in respiratory and hemodynamic function of patients with ARDS and requiring high-frequency percussive ventilation (HFPV) after failure of conventional ventilation (CV).

DESIGN

Retrospective case series.

SETTING

Surgical ICU (SICU) and medical ICU (MICU) of an academic county facility.

MEASUREMENTS AND RESULTS

Thirty-two consecutive patients with ARDS (20 from SICU, 12 from MICU) who were unresponsive to at least 48 h of CV and were switched to HFPV were studied. Data on respiratory and hemodynamic parameters were collected during the 48 h preceding and the 48 h after institution of HFPV and compared. Between the period of CV and the period of HFPV, the ratio of PaO2 to the fraction of inspired oxygen (F(IO2)) increased ([mean+/-SE] 130+/-8 vs. 172+/-17; p = 0.027), peak inspiratory pressure (PIP) decreased (39.5+/-1.7 vs. 32.5+/-1.9 mm Hg; p = 0.002), and mean airway pressure(MAP) increased (19.2+/-1.2 vs. 27.5+/-1.4 mm Hg; p<0.001). The rate of change of PaO2/F(IO2) per hour was also significantly improved between the two periods. The same changes in PaO2/F(IO2), PIP, and MAP were observed when the last value recorded while the patients were on CV was compared with the first value recorded after 1 h of HFPV. This improvement was sustained but not amplified during the hours of HFPV. The patterns of improvement in these three parameters were similar in SICU and MICU patients as well as in volume-control and pressure-control patients. There were no changes in hemodynamic parameters.

CONCLUSION

The HFPV improves oxygenation by increasing MAP and decreasing PIP. This improvement is achieved soon after institution of HFPV and is maintained without affecting hemodynamics.

Ventilation in the trauma and surgical patient

Changes in the understanding of the pathophysiology of ARDS and effects of mechanical ventilation with high pressures have led to treatment strategies that resulted in improved survival rates. The central principle in these strategies is to avoid ventilation induced lung injury by allowing the lungs to rest. A number of promising new treatments emphasizing this principle are under investigation. Physicians caring for patients who develop ARDS should make every effort to avoid alveolar overdistention by ventilating patients in the compliant portion of pressure-flow loop and avoid peak inspiratory pressures in excess of 40 cm H2O.

The American-European Consensus Conference on ARDS, part 2: Ventilatory, pharmacologic, supportive therapy, study design strategies, and issues related to recovery and remodeling. Acute respiratory distress syndrome

The acute respiratory distress syndrome (ARDS) continues as a contributor to the morbidity and mortality of patients in intensive care units throughout the world, imparting tremendous human and financial costs. During the last 10 years there has been a decline in ARDS mortality without a clear explanation. The American-European Consensus Committee on ARDS was formed to re-evaluate the standards for the ICU care of patients with acute lung injury (ALI), with regard to ventilatory strategies, the more promising pharmacologic agents, and the definition and quantification of pathologic features of ALI that require resolution. It was felt that the definition of strategies for the clinical design and coordination of studies between centers and continents was becoming increasingly important to facilitate the study of various new therapies for ARDS.

The American-European Consensus Conference on ARDS, part 2. Ventilatory, pharmacologic, supportive therapy, study design strategies and issues related to recovery and remodeling

The acute respiratory distress syndrome (ARDS) continues as a contributor to the morbidity and mortality of patients in intensive care units throughout the world, imparting tremendous human and financial costs. During the last ten years there has been a decline in ARDS mortality without a clear explanation. The American-European Consensus Committee on ARDS was formed to re-evaluate the standards for the ICU care of patients with acute lung injury (ALI), with regard to ventilatory strategies, the more promising pharmacologic agents, and the definition and quantification of pathological features of ALI that require resolution. It was felt that the definition of strategies for the clinical design and coordination of studies between centers and continents was becoming increasingly important to facilitate the study of various new therapies for ARDS.

High-frequency oscillatory ventilation for adult respiratory distress syndrome--a pilot study

OBJECTIVE

To evaluate the safety and effectiveness of high-frequency oscillatory ventilation using a protocol designed to recruit and maintain optimal lung volume in patients with severe adult respiratory distress syndrome (ARDS).

SETTING

Surgical and medical intensive care units in a tertiary care, military teaching hospital.

DESIGN

A prospective, clinical study.

PATIENTS

Seventeen patients, 17 yrs to 83 yrs of age, with severe ARDS (Lung Injury Score of 3.81 +/- 0.23) failing inverse ratio mechanical conventional ventilation (PaO2/FiO2 ratio of 68.6 +/- 21.6, peak inspiratory pressure of 54.3 +/- 12.7 cm H2O, positive end-expiratory pressure of 18.2 +/- 6.9 cm H2O).

INTERVENTIONS

High-frequency oscillatory ventilation was instituted after varying periods of conventional ventilation (5.12 +/- 4.3 days). We employed lung volume recruitment strategy that consisted of incremental increases in mean airway pressure to achieve a PaO2 of > or = 60 torr (> or = 8.0 kPa), with an FiO2 of < or = 0.6.

MEASUREMENTS AND MAIN RESULTS

High-frequency oscillator ventilator settings (FiO2, mean airway pressure, pressure amplitude of oscillation [delta P] frequency) and hemodynamic parameters (cardiac output, oxygen delivery [DO2]), mean systemic and pulmonary arterial pressures, and the oxygenation index (oxygenation index = [FiO2 x mean airway pressure x 100]/PaO2) were monitored during the transition to high-frequency oscillatory ventilation and throughout the course of the high-frequency protocol. Thirteen patients demonstrated improved gas exchange and an overall improvement in PaO2/FiO2 ratio (p < .02). Reductions in the oxygenation index (p < .01) and FiO2 (p < .02) at 12, 24, and 48 hrs after starting high-frequency oscillatory ventilation were observed. No significant compromise in cardiac output or DO2 was observed, despite a significant increase in mean airway pressure (31.2 +/- 10.3 to 34.0 +/- 6.7 cm H2O, p < .05) on high-frequency oscillatory ventilation. The overall survival rate at 30 days was 47%. A greater number of pretreatment days on conventional ventilation (p < .009) and an entry oxygenation index of > 47 (sensitivity 100%, specificity 100%) were associated with mortality.

CONCLUSIONS

High-frequency oscillatory ventilation is both safe and effective in adult patients with severe ARDS failing conventional ventilation. A lung volume recruitment strategy during high-frequency oscillatory ventilation produced improved gas exchange without a compromise in DO2. These results are encouraging and support the need for a prospective, randomized trial of algorithm-controlled conventional ventilation vs. high-frequency oscillatory ventilation for adults with severe ARDS.

Evolving concepts in the ventilatory management of acute respiratory distress syndrome

With few modifications, a high tidal volume, normoxic, normocapnic ventilation paradigm developed as the standard approach to supporting most critically ill patients. Large tidal volumes, high end-tidal (plateau) alveolar pressures, and low levels of positive end-expiratory pressure are still common in many ICUs during ventilation of acute respiratory distress syndrome (ARDS). A body of scientific literature now suggests that this traditional approach may retard healing of the injured lung. A relatively small but growing number of practitioners are shifting their first priority from optimizing oxygen exchange, oxygen delivery, or respiratory system compliance to ensuring adequate lung protection. This article reviews the basis for concern about traditional ventilatory support in ARDS and develops an approach based on current evidence and newer options for management.

New modes of mechanical ventilation

Many new approaches to mechanical ventilation have been developed. This article discusses these new strategies and modes. These include lung protection conventional ventilation strategies, long inspiratory time strategies, pressure-targeted breath enhancements, airway pressure-related release ventilation, and proportional-assist ventilation.