John D Davies

Prolonged postoperative respiratory support after proximal thoracic aortic surgery: Is deep hypothermic circulatory arrest a risk factor?

PURPOSE In addition to the pulmonary risks associated with cardiopulmonary bypass, thoracic aortic surgery using deep hypothermic circulatory arrest (DHCA) may subject the lungs to further injury. However, this topic has received little investigation to date. MATERIALS AND METHODS A prospective cohort review was performed on all patients undergoing proximal thoracic aortic surgery with (n = 478) and without (n = 135) DHCA between July 2005 and February 2013 at a single institution. The primary outcome was prolonged postoperative respiratory support (PPRS), defined as any of the following: >1 day of mechanical ventilation at either fraction of inspired oxygen >0.4 and/or positive end-expiratory pressure >5 mm Hg, >2 days of supplemental O2 requirement of at least 2.5 L/min, or discharge with new O2 requirement. Independent risk factors for PPRS were identified using multivariable logistic regression. RESULTS Postoperative respiratory support was required in 100 patients (20.9%) with and 30 patients (22.2%) without DHCA (P = .74). Independent predictors of PPRS after proximal aortic surgery included the following: age, diabetes, history of stroke, preoperative creatinine, American Society of Anesthesiologists class 4, redo-sternotomy, total arch replacement, and transfusion requirement. Use of DHCA was not an independent risk factor for PPRS in the entire cohort. Subanalysis of only DHCA patients revealed that longer DHCA times were independently associated with PPRS. CONCLUSIONS Prolonged postoperative respiratory support is common after proximal aortic surgery. The use of DHCA was not associated with this complication in the overall cohort, although longer DHCA times were predictive when only the subset of patients undergoing DHCA was analyzed. Knowledge of the risk factors for PPRS after proximal aortic surgery should improve preoperative risk stratification and postoperative management of these patients.

Clinical Management Strategies for Airway Pressure Release Ventilation: A Survey of Clinical Practice

BACKGROUND: Airway pressure release ventilation (APRV) is a commonly used mode of ventilation designed to increase mean airway pressure and thus oxygenation. Different strategies for clinical management have been described in the literature but are largely based on physiologic concepts, animal data, and small clinical trials. The purpose of this study was to determine how APRV is currently managed by surveying practicing respiratory therapists with experience using APRV. METHODS: A 15-item survey was developed by the authors and posted on the AARConnect online media platform in January 2016 after being declared exempt by our institutions institutional review board. Survey questions were derived from a literature review of recommended APRV settings. Responses were limited to one per institution. RESULTS: The survey was completed by 60 respondents who used APRV. Of the 4 key initial APRV settings (P high, P low, T high, and T low), there was good agreement among survey responders and published guidelines for setting initial T high (4–6 s) and initial P low (0 cm H2O). There was some disagreement regarding initial P high, with 48% of responders matching P high to conventional ventilation plateau pressures but another 31% using conventional ventilation mean airway pressure plus 2–5 cm H2O. The most disagreement was with the T low setting, with only 47% of survey responders agreeing with published guidelines about using the expiratory flow signal to set T low. There was good agreement among survey responders and published guidelines for what changes to make when gas exchange was outside of the targeted range. A substantial number of respondents accepted P high and APRV release volumes that may exceed lung-protective limits. CONCLUSIONS: There is only limited consensus among practitioners for initial APRV settings, probably reflecting the paucity of good clinical outcome data and confusion surrounding the physiology of this mode.

Approaches to Manual Ventilation

Manual ventilation is a basic skill that involves airway assessment, maneuvers to open the airway, and application of simple and complex airway support devices and effective positive-pressure ventilation using a bag and mask. An important part of manual ventilation is recognizing its success and when it is difficult or impossible and a higher level of support is necessary to sustain life. Careful airway assessment will help clinicians identify what and when the next step needs to be taken. Often simple airway maneuvers such as the head tilt/chin lift and jaw thrust can achieve a patent airway. Appropriate use of airway adjuncts can further aid the clinician in situations in which airway maneuvers may not be sufficient. Bag-mask ventilation (BMV) plays a vital role in effective manual ventilation, improving both oxygenation and ventilation as well as buying time while preparations are made for endotracheal intubation. There are, however, situations in which BMV may be difficult or impossible. Anticipation and early recognition of these situations allows clinicians to quickly make adjustments to the method of BMV or to employ a more advanced intervention to avoid delays in establishing adequate oxygenation and ventilation.

Should a Portable Ventilator Be Used in All In-Hospital Transports?

Movement of the mechanically ventilated patient may be for a routine procedure or medical emergency. The risks of transport seem manageable, but the memory of a respiratory-related catastrophe still gives many practitioners pause. The risk/benefit ratio of transport must be assessed before movement. During transport of the ventilated patients, should we always use a transport ventilator? What is the risk of using manual ventilation? How are PEEP and FIO2 altered? Is there an impact on the ability to trigger during manual ventilation? Is hyperventilation and hypoventilation a common problem? Does hyperventilation or hypoventilation result in complications? Are portable ventilators worth the cost? What about the function of portable ventilators? Can these devices faithfully reproduce ICU ventilator function? The following pro and con discussion will attempt to address many of these issues by reviewing the current evidence on transport ventilation.

Airway Pressure Release Ventilation Letter—Reply

We thank Dr Light for his insights on airway pressure release ventilation (APRV)[1][1] and will address his comments one by one below. However, we first re-emphasize that the purpose of our study[2][2] was not to address the clinical value of APRV—that can only be accomplished with randomized

The Ongoing Question of Where Clinicians Should Place the Nebulizer in the Ventilator Circuit: This Time With Epoprostenol

In this issue of Respiratory Care, Anderson and colleagues[1][1] determined the differences in epoprostenol deposition based on nebulizer position in the ventilator circuit in an adult lung model using vibrating mesh technology. The study involved placing the nebulizer at 4 different positions in

Orthopnea in Obese Adult Patients: Can It Be Quantified From Lung Function Testing?

Obesity is an overwhelming public threat. It has been estimated that more than one third of the adult population is obese despite the fact that the prevalence has remained stable since 2004.[1][1] The good news is that the prevalence of obesity has leveled off; the bad news is that the number

Should A Tidal Volume of 6 mL/kg Be Used in All Patients?

It has been shown that mechanical ventilation by itself can cause lung injury and affect outcomes. Ventilator-induced lung injury is associated with high tidal volumes in lungs afflicted with ARDS. However, the question is: Do high tidal volumes have this same effect in normal lungs or lungs that have respiratory compromise stemming from something other than ARDS? Many clinicians believe that a tidal volume strategy of 6 mL/kg predicted body weight should be standard practice in all patients receiving mechanical ventilation. There is a growing body of evidence related to this issue, and this is the debate that will be tackled in this paper from both pro and con perspectives.