Airway pressure release ventilation in severe acute respiratory failure

Airway pressure release ventilation (APRV), a new ventilatory support technique, was compared with conventional intermittent positive-pressure ventilation plus PEEP (CPPV) in 18 patients with severe acute respiratory failure. Patients were initially stabilized on CPPV and then switched to APRV. The APRV provided effective ventilatory support in 17 of 18 patients; APRV achieved similar levels of alveolar ventilation as CPPV (for APRV, mean PaCO2 = 45.0 +/- 6.2 mm Hg; vs for CPPV, mean PaCO2 = 43.3 +/- 5.7 mm Hg), with significantly lower mean maximum airway pressures (38.9 +/- 10.1 cm H2O vs 64.6 +/- 15.4 cm H2O; p = 0.0001) and mean VT (0.79 +/- 0.11 L vs 1.05 +/- 0.15 L; p = 0.0002). No significant differences in mean airway pressure, end-expiratory pressure, FIO2, ventilator rate, arterial blood gas levels, and hemodynamic function were noted between APRV and CPPV.     

Airway management in critical illness

Airway management in the ICU can be complicated due to many factors including the limited physiologic reserve of the patient. As a consequence, the likelihood of difficult mask ventilation and intubation increases. The incidence of failed airways and of cardiac arrest related to airway instrumentation in the ICU is much higher than that of elective intubations performed in the operating room. A thorough working knowledge of the devices available for the management of the difficult airway and recommended rescue strategies is paramount in avoiding bad patient outcomes. In this review, we will provide a conceptual framework for airway assessment, with an emphasis on assessment of the patient with limited cervical spine movement or injury and of morbidly obese patients. Furthermore, we will review the devices that are available for airway management in the ICU, and discuss controversies surrounding interventions like cricoid pressure and the use of muscle relaxants in the critically ill patient. Finally, strategies for the safe extubation of patients with known difficult airways will be provided.     

Airway pressure release ventilation: a pediatric case series

Airway pressure release ventilation (APRV) is a relatively new mode of mechanical ventilation (MV) first described in animal studies in 1987 and in humans in 1988. It is a time-triggered, time-cycled, pressure-limited mode where a high level of continuous positive airway pressure (CPAP) is maintained with brief regular releases in pressure, and spontaneous breathing is allowed throughout the cycle. In theory, it is consistent with a lung protective approach while having some hypothetical advantages over HFOV. The use of this mode of ventilation in pediatrics has been limited. The authors describe their experience with this mode of ventilation in a series of pediatric patients.     

Airway strain during mechanical ventilation in an intact animal model

RATIONALE: Mechanical ventilation with large tidal volumes causes ventilator-induced lung injury in animal models. Little direct evidence exists regarding the deformation of airways in vivo during mechanical ventilation, or in the presence of positive end-expiratory pressure (PEEP). OBJECTIVES: To measure airway strain and to estimate airway wall tension during mechanical ventilation in an intact animal model. METHODS: Sprague-Dawley rats were anesthetized and mechanically ventilated with tidal volumes of 6, 12, and 25 cm(3)/kg with and without 10-cm H(2)O PEEP. Real-time tantalum bronchograms were obtained for each condition, using microfocal X-ray imaging. Images were used to calculate circumferential and longitudinal airway strains, and on the basis of a simplified mathematical model we estimated airway wall tensions. MEASUREMENTS AND MAIN RESULTS: Circumferential and longitudinal airway strains increased with increasing tidal volume. Levels of mechanical strain were heterogeneous throughout the bronchial tree. Circumferential strains were higher in smaller airways (less than 800 mum). Airway size did not influence longitudinal strain. When PEEP was applied, wall tensions increased more rapidly than did strain levels, suggesting that a "strain limit" had been reached. Airway collapse was not observed under any experimental condition. CONCLUSIONS: Mechanical ventilation results in significant airway mechanical strain that is heterogeneously distributed in the uninjured lung. The magnitude of circumferential but not axial strain varies with airway diameter. Airways exhibit a "strain limit" above which an abrupt dramatic rise in wall tension is observed.     

Airway pressure release ventilation (APRV). A human trial

After operative coronary revascularization, 14 consenting adults received conventional positive pressure ventilation (PPV). When they were hemodynamically stable, data were collected during PPV and then during airway pressure release ventilation (APRV). During APRV, airway pressure (Paw) was reduced periodically at the lowest frequency which produced normal PaCO2. As anesthesia resolved, the rate of APRV breaths was decreased until patients breathed only with CPAP. During PPV and APRV, pHa, PaO2/FIO2, and hemodynamic variables were similar. All patients were weaned from APRV without complication. Optimal ventilator design for patients with acute lung injury would provide CPAP as a primary intervention and secondarily would augment alveolar ventilation. The APRV supported oxygenation and ventilation in patients with mild acute lung injury, yet with much lower peak airway pressure than produced by PPV.     

Airway management in obesity hypoventilation syndrome

The role of tracheostomy is limited in the obesity hypoventilation syndrome unless severe upper airway obstruction exists. If it is performed, special techniques must be applied to overcome the problems associated with tracheostomy in the morbidly obese patient. If attention is paid to these details, however, tracheostomy provides clinically important benefits in this difficult clinical situation.     

Airway stenting: Applications and practice management considerations

BACKGROUND: Airway stenting is a procedure that is performed increasingly often, and the availability of metallic stents placed by flexible bronchoscopy may have contributed to the increased usage. These procedures have an impact on the required physician skill set and practice management. We review the indications for airway stenting, and how the requirement of combined therapies and technical aspects of central airway stenting pertain to practice management. PROCEDURE: We compared several reimbursement scenarios for managing stent placement using the Centers for Medicare and Medicaid Services relative value units (RVUs) and average reimbursement amounts. We also compared the reimbursement to other commonly performed activities performed by pulmonary and critical care physicians. An analysis of Medicare facility outpatient and inpatient payment for procedures using silicone and metallic stents was also conducted. RESULTS: Professional reimbursement is identical regardless of stent type, method of insertion, and anesthesia administered. The net facility reimbursement largely depends on stent costs. The RVUs alone are a poor comparator for the reimbursement of therapeutic bronchoscopy because of Correct Coding Initiatives edits. Considering the time necessary for performing advanced therapeutic bronchoscopy, the professional fees are not attractive. The net facility reimbursement largely depends on stent costs. CONCLUSION: The placement of airway stents is not reimbursed at competitive rates and may even lead to a net loss for the facility. The practice management benefits of central airway therapy are probably best obtained by a multidisciplinary airway team with an established cost center structure.     

Airway pressure release ventilation in a patient with acute pulmonary injury

Airway pressure release ventilation is a recently described method of ventilatory support. It allows spontaneous ventilation with CPAP but differs from conventional ventilatory modes because, with APRV, peak inflation pressure never exceeds the level of CPAP, and airway pressure decreases, rather than increases, when tidal volume is delivered. The risk of pulmonary barotrauma and adverse hemodynamic effects associated with conventional modes of positive-pressure mechanical ventilation may be decreased because of lower peak inflation and mean airway pressures. We describe a patient in whom several risk factors for these complications were present who was treated successfully with APRV.     

三通喉罩通气在成人肺部止血的应用

目的探讨三通喉罩通气在成人支气管镜肺部止血的临床应用。方法实施肺部止血的成人患者9例,年龄21～62岁,在快速诱导麻醉下实施三通喉罩插入。插入成功后,三通喉罩的标准端口连接呼吸机（或麻醉机）进行机械或人工控制通气,从三通喉罩另一带有密封胶帽端口置入纤维支气管镜,经声门进入气管、支气管,实施肺部止血术。记录麻醉前5min时（T0）,插入喉罩后即刻（T1）,通气1min时（T2）,通气3min时（T3）,通气10min时（T4）,通气20min时（T5）,通气30min时（T6）,手术结束时（T7）的收缩压（SBP）、舒张压（DBP）、心率（HR）、脉搏氧饱和度（SpO2）;记录患者通气T1、T2、T3、T4、T5、T6、T7的潮气量（VT）、气道峰压（Ppeak）及呼气末二氧化碳分压（PETCO2）;记录麻醉和手术的效果和过程。结果全部9例手术顺利完成,SpO2在麻醉诱导开始后有明显改善,术中无明显下降;术中全部病例气道压力小幅升高,仍属于正常压力范围,血压、心率无明显变化;术后恢复良好,无明显并发症。结论三通喉罩用于支气管镜肺部止血具有安全、可靠、效果满意、并发症少等优点,在机器控制呼吸下实施手术,取得了呼吸的控制权,保证了良好的通气和氧供,方便了手术操作,提高了麻醉安全性。     

Airway mechanics and ventilation in response to resistive loading during sleep: influence of gender

The male predominance in obstructive sleep apnea (OSA) is currently poorly understood although differences in pharyngeal airway anatomy and physiology have been proposed. As the response to inspiratory resistive loading (IRL) provides important information on both airway collapsibility (mechanics) and ventilatory control, we compared this respiratory response in eight normal women and eight age and body mass index (BMI)-matched men, during stable nonrapid eye movement (NREM) sleep. Upper airway mechanics, ventilation, plus activation of two dilator muscles (genioglossus [GG] and tensor palatini [TP]) were monitored during basal breathing (BL), followed by four sequentially applied loads (5, 10, 15, 25 cm H(2)O/L/s) for three breaths each. Men developed more severe hypopnea in response to identical applied external loads than did women. At a resistance of 25 cm H(2)O/L/s, VT decreased by 26 +/- 1% in women compared with 44 +/- 1% in men (differences between sexes p < 0.05). Pharyngeal resistance (Rpha) in response to IRL increased significantly more in men than women (37.3 +/- 11.2 cm H(2)O/L/s in men at maximal load, compared with an increase of 6.6 +/- 3.9 cm H(2)O/L/s in women, p < 0.05). Men and women had near identical minute ventilation responses to total load (applied extrinsic plus measured intrinsic), implying no differences in central drive or load response. There were no significant increases in GG or TP activation in response to IRL in either sex. We conclude that normal men are more vulnerable to load-induced hypoventilation than women, due to increased upper airway collapse, which could not be explained by differences in dilator muscle activation. This implies a fundamental difference in the upper airway anatomy and/or tissue characteristics between the two sexes.     

Airway pressure release ventilation: A neonatal case series and review of current pediatric practice

BACKGROUND:

The use of airway pressure release ventilation (APRV) in very low birth weight infants is limited.

OBJECTIVE:

To report the authors’ institutional experience and to review the current literature regarding the use of APRV in pediatric populations.

METHODS:

Neonates <1500 g ventilated using APRV from 2005 to 2006 at McMaster Children’s Hospital (Hamilton, Ontario) were retrospectively reviewed. Publications describing APRV in children from 1987 to 2011 were reviewed.

RESULTS:

Five infants, 24 to 28 weeks’ gestational age, were ventilated using APRV. Indications for APRV were refractory hypoxemia (n=3), ventilatory dyssynchrony (n=1) and minimizing sedatives (n=1). All infants appeared to tolerate APRV well with no recorded adverse events. Current pediatric evidence regarding APRV is primarily observational. Published experience reveals that APRV settings in pediatrics often approximate those used in adults, thus deviating from the original guidelines recommended in children. Clinical outcomes, such as oxygenation, ventilation and sedation requirements, are inconsistent.

CONCLUSIONS:

APRV is primarily used as a rescue ventilation mode in children. Neonatal evidence is limited; however, the present study indicates that APRV is feasible in very low birth weight infants. There are unique considerations when applying this mode in small infants. Further research is necessary to confirm whether APRV is a safe and effective ventilation strategy in this population.     

Airway management in patients with unstable cervical spine fractures

We conducted a retrospective study of traumatic, unstable cervical spine fractures requiring operative repair to determine the airway management technique and whether any neurologic complication resulted from the intubation. One hundred thirty-three patients with 140 fractures were reviewed relative to fracture site, oral versus nasal route of intubation, and location of intubation (surgery versus emergency department or field). Fracture site incidence was determined as follows: C-1, ten (7.1%); odontoid/C-2, 17 (12.1%); C-3, eight (5.7%); C-4, 21 (15.0%); C-5, 41 (29.2%); C-6, 38 (27.1%); and C-7, five (3.5%). Ten of the injuries resulted from blows to the neck or head, 25 from falls, seven from diving, and six from sports-related injuries. The remaining eighty-five patients were in motor vehicle accidents. Nine patients were nasally intubated in the ED, and one patient was orally intubated in the field. Ninety-four of the patients intubated in surgery were intubated nasally: 29 were intubated orally while in-line stabilization was maintained. No neurologic complications occurred in any patient. These data suggest that, under controlled circumstances, patients with unstable cervical spine fractures can be safely intubated with standard, nonsurgical approaches.     

Airway management of the critically ill patient: rapid-sequence intubation

Advances in emergency airway management have allowed intensivists to use intubation techniques that were once the province of anesthesiology and were confined to the operating room. Appropriate rapid-sequence intubation (RSI) with the use of neuromuscular blocking agents, induction drugs, and adjunctive medications in a standardized approach improves clinical outcomes for select patients who require intubation. However, many physicians who work in the ICU have insufficient experience with these techniques to adopt them for routine use. The purpose of this article is to review airway management in the critically ill adult with an emphasis on airway assessment, algorithmic approaches, and RSI.     

机械通气过程中人-机不同步的原因判断与处理

机械通气是救治各种类型重症呼吸衰竭的主要手段.在众多机械通气相关并发症中,人-机不同步或人-机对抗是发生频率高但又容易被临床医生忽视的问题之一.人-机协调是指患者的呼吸泵(由呼吸驱动、神经肌肉系统、肺和胸廓的机械力学特征决定)与呼吸机(机械泵,由呼吸机模式和参数的设置决定)之间的配合.     

Non-invasive ventilation in the management of respiratory failure

Abstract Non-invasive positive pressure ventilation (NIPPV) has been used increasingly to treat various forms of respiratory failure, with benefits in terms of gas exchange improvement, avoidance of endotracheal intubation and a decreased mortality. This review will focus on the recent developments and recommendations in the use of NIPPV in the treatment of acute and chronic respiratory failure, the methodology in the application of NIPPY, and briefly on its proposed mechanism of action.     

Airway size and structure in the normal fetal and infant lung and the effect of premature delivery and artificial ventilation

Light microscopic morphometric techniques were used to study the inflated airways of 17 normal infants from 22 wk of gestation to 8 months postnatal age, plus three young adults. In addition, the lungs of four premature and seven mechanically ventilated infants were studied. A computer-assisted digitizer was used to measure airway diameter and to determine the area of cartilage, gland, and muscle in each type of airway. Epithelial height was also measured, and goblet cell number was counted. Using histochemical stains, types of glycoprotein were identified in goblet cells and submucosal glands. Between 22 wk of gestation and 8 months of age, the normal infant showed a linear increase with age in airway diameter. With age the area of muscle and submucosal gland increased in total amount and showed a significant linear increase when related to the size of the airways, except the submucosal gland in hilar airways. By contrast, the increase in cartilage was only commensurate with the increase in size of intrapulmonary airways, but showed a linear size-related increase in the main bronchus. Epithelial height and goblet cell number increased with age in the bronchi, but not more peripherally. Premature infants had for their postconceptional age normal-sized airways with an increase in amount of bronchial smooth muscle and an increase in number of goblet cells. Ventilated infants had a greater increase in smooth muscle (p less than 0.05 to p less than 0.002) and goblet cells (p less than 0.05) and an increase in submucosal gland area (p less than 0.04) whether or not the infant had had hyaline membrane disease.