Eduardo Mireles-Cabodevila

A Rational Framework for Selecting Modes of Ventilation

Mechanical ventilation is a life-saving intervention for respiratory failure and thus has become the cornerstone of the practice of critical care medicine. A mechanical ventilation mode describes the predetermined pattern of patient-ventilator interaction. In recent years there has been a dizzying proliferation of mechanical ventilation modes, driven by technological advances and market pressures, rather than clinical data. The comparison of these modes is hampered by the sheer number of combinations that need to be tested against one another, as well as the lack of a coherent, logical nomenclature that accurately describes a mode. In this paper we propose a logical nomenclature for mechanical ventilation modes, akin to biological taxonomy. Accordingly, the control variable, breath sequence, and targeting schemes for the primary and secondary breaths represent the order, family, genus, and species, respectively, for the described mode. To distinguish unique operational algorithms, a fifth level of distinction, termed variety, is utilized. We posit that such coherent ordering would facilitate comparison and understanding of modes. Next we suggest that the clinical goals of mechanical ventilation may be simplified into 3 broad categories: provision of safe gas exchange; provision of comfort; and promotion of liberation from mechanical ventilation. Safety is achieved via optimization of ventilation-perfusion matching and pressure-volume relationship of the lungs. Comfort is provided by fostering patient-ventilator synchrony. Liberation is promoted by optimization of the weaning experience. Then we follow a paradigm that matches the technological capacity of a particular mode to achieving a specific clinical goal. Finally, we provide the reader with a comparison of existing modes based on these principles. The status quo in mechanical ventilation mode nomenclature impedes communication and comparison of existing mechanical ventilation modes. The proposed model, utilizing a systematic nomenclature, provides a useful framework to address this unmet need.

Amiodarone pulmonary toxicity after lung transplantation.

Atrial fibrillation occurs frequently after lung transplantation and is commonly treated with amiodarone. Pulmonary toxicity may result from amiodarone exposure and is characterized by non-specific respiratory manifestations. To our knowledge, there are no reports of this complication occurring after lung transplantation. We present a patient who developed radiologic evidence of amiodarone deposition in the lungs after bilateral lung transplantation.

Alternative modes of mechanical ventilation: A review for the hospitalist

Newer ventilators can be set to modes other than the pressure-control and volume-control modes of older machines. In this paper, the authors review several of these alternative modes (adaptive pressure control, adaptive support ventilation, proportional assist ventilation, airway pressure-release ventilation, biphasic positive airway pressure, and high-frequency oscillatory ventilation), explaining how they work and contrasting their theoretical benefits and the actual evidence of benefit. Newer ventilators can be set to modes other than the pressure-control and volume-control modes of older machines. We review how they work and contrast their theoretical benefits and actual evidence of benefit.

Sleep-Disordered Breathing in Neuromuscular Disease: Diagnostic and Therapeutic Challenges

&NA; Normal sleep‐related rapid eye movement sleep atonia, reduced lung volumes, reduced chemosensitivity, and impaired airway dilator activity become significant vulnerabilities in the setting of neuromuscular disease. In that context, the compounding effects of respiratory muscle weakness and disease‐specific features that promote upper airway collapse or cause dilated cardiomyopathy contribute to various sleep‐disordered breathing events. The reduction in lung volumes with neuromuscular disease is further compromised by sleep and the supine position, exaggerating the tendency for upper airway collapse and desaturation with sleep‐disordered breathing events. The most commonly identified events are diaphragmatic/pseudo‐central, due to a decrease in the rib cage contribution to the tidal volume during phasic rapid eye movement sleep. Obstructive and central sleep apneas are also common. Noninvasive ventilation can improve survival and quality of sleep but should be used with caution in the context of dilated cardiomyopathy or significant bulbar symptoms. Noninvasive ventilation can also trigger sleep‐disordered breathing events, including ineffective triggering, autotriggering, central sleep apnea, and glottic closure, which compromise the potential benefits of the intervention by increasing arousals, reducing adherence, and impairing sleep architecture. Polysomnography plays an important diagnostic and therapeutic role by correctly categorizing sleep‐disordered events, identifying sleep‐disordered breathing triggered by noninvasive ventilation, and improving noninvasive ventilation settings. Optimal management may require dedicated hypoventilation protocols and a technical staff well versed in the identification and troubleshooting of respiratory events.

A Comparison of Methohexital Versus Etomidate for Endotracheal Intubation of Critically Ill Patients

BACKGROUND Methohexital has been used for procedural sedation in the emergency department, but its use for endotracheal intubation in intensive care units has not been studied. OBJECTIVE To compare methohexital with etomidate with respect to their effectiveness and safety of use for endotracheal intubation in the intensive care unit. METHODS Retrospective, observational, single-center cohort study of consecutive patients admitted between December 2006 and August 2007 to a medical intensive care unit in a tertiary-care hospital. RESULTS Twenty-three patients who received methohexital and 23 who received etomidate for endotracheal intubation were included. The 2 groups differed in age (mean [SD], 55 [13] vs 64 [13] years, P = .03) but not in baseline demographics or illness severity scores. Mean (SD) doses given were 1 (0.2) mg/kg for methohexital and 0.2 (0.1) mg/kg for etomidate. Use of midazolam, fentanyl, and succinylcholine was similar between the groups. Rates of successful intubation after 1 attempt (78% vs 83%), time to successful intubation (mean, 5.9 vs 4 minutes), and number of intubation attempts (mean, 1.5 vs 1.2) also were similar. Change in hemodynamics (delta systolic blood pressure), vasopressor requirements, and amount of fluid resuscitation (normal saline) did not differ significantly between the groups. CONCLUSIONS Rates of successful intubation are similar with etomidate and methohexital. Methohexital provides adequate sedation and could be an alternative to etomidate, although both agents were often associated with development of hypotension. Prospective studies are needed to establish the safety of methohexital use in intensive care patients.

Should Airway Pressure Release Ventilation Be the Primary Mode in ARDS

Airway pressure release ventilation (APRV) was originally described as a mode to treat lung-injured patients with the goal to maintain a level of airway pressure that would not depress the cardiac function, deliver mechanical breaths without excessive airway pressure, and to allow unrestricted spontaneous ventilation. Indeed, based on its design, APRV has technological features that serve the goals of safety and comfort. Animal studies suggest that APRV leads to alveolar stability and recruitment which result in less lung injury. These features are sought in patients at risk for lung injury or with ARDS. APRV allows unrestricted spontaneous ventilation, which is welcome in the era of less sedation and increased patient mobility (the effects in terms of lung injury remain to be explored). However, we must highlight that the performance of APRV is dependent on the operator-selected settings and the ventilators performance. The clinician must select the appropriate settings in order to make effective the imputed benefits. This is a challenge when the ventilators performance is not uniform, and the outcomes depend on high precision settings (very short expiratory time), where small variations can lead to undesired outcomes (de-recruitment or large tidal volumes leading to lung injury). Finally, we do not have evidence that APRV (as originally described) improves relevant clinical outcomes of patients with ARDS. For APRV to become the primary mode of ventilation for ARDS, it will require development of sound protocols and technological enhancements to ensure its performance and safety. For now, APRV does have a greater potential for adversely affecting patient outcome than improving it; unless definitive data are forthcoming demonstrating outcome benefits from the use of APRV in ARDS, there is no reason to consider this approach to ventilatory support.

Respiratory Support in Patients With Amyotrophic Lateral Sclerosis

Despite advances in the medical therapy of amyotrophic lateral sclerosis (ALS), the management of ALS remains predominantly supportive, with a primary focus on the respiratory system, including support of ventilation and clearance of secretions. Two papers in this issue of Respiratory Care address

Contemporary Reviews in Sleep MedicineSleep-Disordered Breathing in Neuromuscular Disease: Diagnostic and Therapeutic Challenges

&NA; Normal sleep‐related rapid eye movement sleep atonia, reduced lung volumes, reduced chemosensitivity, and impaired airway dilator activity become significant vulnerabilities in the setting of neuromuscular disease. In that context, the compounding effects of respiratory muscle weakness and disease‐specific features that promote upper airway collapse or cause dilated cardiomyopathy contribute to various sleep‐disordered breathing events. The reduction in lung volumes with neuromuscular disease is further compromised by sleep and the supine position, exaggerating the tendency for upper airway collapse and desaturation with sleep‐disordered breathing events. The most commonly identified events are diaphragmatic/pseudo‐central, due to a decrease in the rib cage contribution to the tidal volume during phasic rapid eye movement sleep. Obstructive and central sleep apneas are also common. Noninvasive ventilation can improve survival and quality of sleep but should be used with caution in the context of dilated cardiomyopathy or significant bulbar symptoms. Noninvasive ventilation can also trigger sleep‐disordered breathing events, including ineffective triggering, autotriggering, central sleep apnea, and glottic closure, which compromise the potential benefits of the intervention by increasing arousals, reducing adherence, and impairing sleep architecture. Polysomnography plays an important diagnostic and therapeutic role by correctly categorizing sleep‐disordered events, identifying sleep‐disordered breathing triggered by noninvasive ventilation, and improving noninvasive ventilation settings. Optimal management may require dedicated hypoventilation protocols and a technical staff well versed in the identification and troubleshooting of respiratory events.

Application of mid-frequency ventilation in an animal model of lung injury: a pilot study.

BACKGROUND: Mid-frequency ventilation (MFV) is a mode of pressure control ventilation based on an optimal targeting scheme that maximizes alveolar ventilation and minimizes tidal volume (VT). This study was designed to compare the effects of conventional mechanical ventilation using a lung-protective strategy with MFV in a porcine model of lung injury. Our hypothesis was that MFV can maximize ventilation at higher frequencies without adverse consequences. We compared ventilation and hemodynamic outcomes between conventional ventilation and MFV. METHODS: This was a prospective study of 6 live Yorkshire pigs (10 ± 0.5 kg). The animals were subjected to lung injury induced by saline lavage and injurious conventional mechanical ventilation. Baseline conventional pressure control continuous mandatory ventilation was applied with VT = 6 mL/kg and PEEP determined using a decremental PEEP trial. A manual decision support algorithm was used to implement MFV using the same conventional ventilator. We measured PaCO2, PaO2, end-tidal carbon dioxide, cardiac output, arterial and venous blood oxygen saturation, pulmonary and systemic vascular pressures, and lactic acid. RESULTS: The MFV algorithm produced the same minute ventilation as conventional ventilation but with lower VT (−1 ± 0.7 mL/kg) and higher frequency (32.1 ± 6.8 vs 55.7 ± 15.8 breaths/min, P < .002). There were no differences between conventional ventilation and MFV for mean airway pressures (16.1 ± 1.3 vs 16.4 ± 2 cm H2O, P = .75) even when auto-PEEP was higher (0.6 ± 0.9 vs 2.4 ± 1.1 cm H2O, P = .02). There were no significant differences in any hemodynamic measurements, although heart rate was higher during MFV. CONCLUSIONS: In this pilot study, we demonstrate that MFV allows the use of higher breathing frequencies and lower VT than conventional ventilation to maximize alveolar ventilation. We describe the ventilatory or hemodynamic effects of MFV. We also demonstrate that the application of a decision support algorithm to manage MFV is feasible.

Pilot Balloon Malfunction Caused by Endotracheal Tube Bite Blocker

A patients bite is a frequent cause of endotracheal tube (ETT) obstruction, which affects the volume and pressure delivered by the ventilator. Bite-related ETT obstruction is a frequent cause of ventilator alarm activation, and can cause respiratory failure, negative-pressure pulmonary edema, and