Lonny Ashworth

Are Inhaled Drugs Delivered to the Bronchial Smooth Muscles Through the Bronchial Circulation

Bronchial smooth muscles (BSM) contract in response to a number of endogenous and exogenous stimuli resulting in bronchoconstriction, which causes an increase in airway resistance. Medications used to reverse this bronchoconstriction are commonly given by inhalation. In addition, bronchoprovocation testing is often performed to detect and quantify nonspecific bronchial hyperresponsiveness in patients suspected to have bronchial asthma. One of the most common bronchoprovocation agents used for this test, methacholine, is also given by inhalation (Crape et al., 1999). It has been assumed that, after inhalation, drug molecules get deposited on the surface of the bronchial mucosa, traverse across the airway wall, enter into the BSM and then exert their effect on BSM. However, we reasoned that because BSM are situated deep in the airway wall, it is unlikely that methacholine exerts its effect on BSM by this mechanism. Bronchial circulation supplies blood and nutrients to the airways. We have previously shown that there is a dense bronchial vascular plexus in the airway wall (Charan et al., 1984). Therefore, we hypothesized that drugs and chemicals that are administered by inhalation get absorbed into the bronchial vascular plexus first, and then are transported to the BSM by the bronchial blood flow. To test this hypothesis, we infused methacholine directly into the bronchial circulation and compared its bronchoconstricting effects with intratracheal administration of methacholine. We reasoned that if our hypothesis was correct, we would observe a greater degree of bronchoconstriction with small dosages of methacholine administered into the bronchial artery versus intratracheal administration of the drug.

Limiting volume with modern ventilators

Background: The acute respiratory distress syndrome (ARDS) network low tidal-volume study comparing tidal volumes of 12 ml/kg versus 6 ml/kg was published in 2000. The study was stopped early as data revealed a 22% relative reduction in mortality rate when using 6 ml/kg tidal volume. The current generation of critical care ventilators allows the tidal volume to be set during volume-targeted, assist/control (volume A/C); however, some ventilators include options that may prevent the tidal volume from being controlled. The purpose of this bench study was to evaluate the delivered tidal volume, when these options are active, in a spontaneously breathing lung model using an electronic breathing simulator. Methods: Four ventilators were evaluated: CareFusion AVEA (AVEA), Dräger Evita® XL (Evita XL), Covidien Puritan Bennett® 840TM (PB 840), and Maquet SERVO-i (SERVO-i). Each ventilator was connected to the Hans Rudolph Electronic Breathing Simulator at an amplitude of 0 cm H2O and then 10 cm H2O. All four ventilators were set to deliver volume A/C, tidal volume 400 ml, respiratory rate 20 bpm, positive end-expiratory pressure 5 cm H2O, peak flowrate 60 L/min. The displayed tidal volume was recorded for each ventilator at the above settings with additional options OFF and then ON. Results: The AVEA has two options in volume A/C: demand breaths and V-sync. When activated, these options allow the patient to exceed the set tidal volume. When using the Evita XL, the option AutoFlow can be turned ON or OFF, and when this option is ON, the tidal volume may vary. The PB 840 does not have any additional options that affect volume delivery, and it maintains the set tidal volume regardless of patient effort. The SERVO-i’s demand valve allows additional flow if the patient’s inspiratory flowrate exceeds the set flowrate, increasing the delivered tidal volume; this option can be turned OFF with the latest software upgrade. Conclusions: Modern ventilators have an increasing number of optional settings. These settings may increase the delivered tidal volume and disrupt a low tidal-volume strategy. Recognizing how each setting within a mode affects the type of breath delivered is critical when caring for ventilator-dependent patients.

Implementation of Do Not Attempt Resuscitate Orders in a Japanese Nursing Home

Objective: To investigate whether do not attempt resuscitation (DNAR) orders can be implemented in a standard nursing home in Japan, where routine DNAR orders are not yet common in many facilities including hospitals. Method: Ninety-eight residents in a 100-bed nursing home were evaluated. All of the eligible residents and/or their family members were asked whether they wanted to receive resuscitation, including mechanical ventilation. Result: The residents were 54 to 101 years of age (mean 83.3), with 27 males and 71 females. After administering the questionnaire, 92 (94%) patients did not want resuscitation and mechanical ventilation. Conclusion: In a nursing home, it was possible to obtain advance directives by which most residents/families rejected resuscitation and mechanical ventilation. This could avoid unnecessary and undesirable resuscitation procedures.

Clinical Management of Pressure Control Ventilation: An Algorithmic Method of Patient Ventilatory Management to Address “Forgotten but Important Variables”

Pressure controlled ventilation is a common mode of ventilation used to manage both adult and pediatric populations. However, there is very little evidence that distinguishes the efficacy of pressure controlled ventilation over that of volume controlled ventilation in the adult population. This gap in the literature may be due to the absence of a consistent and systematic algorithm for managing pressure controlled ventilation. This article provides a brief overview of the applications of both pressure controlled ventilation and volume controlled ventilation and proposes an algorithmic approach to the management of patients receiving pressure controlled ventilation. This algorithmic approach highlights the need for clinicians to have a comprehensive conceptual understanding of mechanical ventilation, pulmonary physiology, and interpretation of ventilator graphics in order to best care for patients receiving pressure controlled ventilation. The objective of identifying a systematic approach to managing pressure controlled ventilation is to provide a more generalizable and equitable approach to management of the ICU patient. Ideally, a consistent approach to managing pressure controlled ventilation in the adult population will glean more reliable information regarding actual patient outcomes, as well as the efficacy of pressure controlled ventilation when compared to volume controlled ventilation.

Cardiopulmonary Implications of Neuromuscular Blockade

Neuromuscular blocking agents (NMBAs) are used to facilitate mechanical ventilation in critically ill patients. Individual NMBAs differ in their metabolism and elimination, side effects, and duration of action. These differences help designate which NMBA has the greatest efficacy, given different scenarios. A common theme with all NMBAs is their ability to ablate spontaneous breathing; hence, vigilant cardiopulmonary monitoring is warranted when NMBAs are used.