By Jon-Emile S. Kenny [@heart_lung] When interpreting hemodynamic studies of drugs which – potentially – alter the resistance of the pulmonary vascular tree, we often turn to the calculated pulmonary vascular resistance [cPVR] as our guide. For instance, a vasopressor determined to increase the cPVR is wholly avoided in a patient with pulmonary arterial hypertension. We [… read more]
Jon-Emile S. Kenny [@heart_lung] “Doctrine once sown strikes deep its root, and respect for antiquity influences all men.” -William Harvey [1628] The use of hyperoncotic albumin to draw fluid from the interstitial space permeates dark corners of the critical care community. The ‘pull and push’ of 25% albumin followed by furosemide remains somewhat of a [… read more]
Jon-Emile S. Kenny [@heart_lung] While parts 1 and 2 of this trilogy considered the mechanical power applied to the lung skeleton and the effects of lung inhomogeneity [i.e. ‘stress raisers’], respectively; this final installment will draw the reader towards the pulmonary vasculature as a key mediator of ventilator induced lung injury [VILI]. That the pulmonary [… read more]
Jon-Emile S. Kenny [@heart_lung] Gattinoni and Quintel have, very recently, outlined their approach to managing the acute respiratory distress syndrome [ARDS] [1]. They argue that treatment of ARDS should minimize firstly, the mechanical power applied to the lungs – as described in part 1. Secondly, Gattinoni and Quintel note that, in the treatment of ARDS, [… read more]
Jon-Emile S. Kenny [@heart_lung] “Often, as new knowledge progresses, old knowledge is abandoned or forgotten.” -Luciano Gattinoni In a succinct and current treatise, Gattinoni and Quintel outline the modern management of the acute respiratory distress syndrome [ARDS] [1]. It is imperative, they reason, that treatment of ARDS minimizes firstly, the mechanical power applied to the [… read more]
Jon-Emile S. Kenny [@heart_lung] In part 2, I continue my commentary on this excellent review; part 1 may be found here. In this post I will consider patients with severe metabolic acidosis and those with right ventricular [RV] dysfunction and/or failure. Severe Metabolic Acidosis In patients with severe metabolic acidosis, alveolar ventilation tends to be maximal [… read more]
By Jon-Emile S. Kenny [@heart_lung] The problem with the lung in the acute respiratory distress syndrome [ARDS] is not that it is stiff, but rather, that it is small [1]. In the 1980s, CT scans of the lungs of patients with ARDS revealed that the functional lung was attenuated in size and that dependent densities [… read more]
ICU Physiology in 1,000 Words “The Hemodynamics of Prone” by Jon-Emile S. Kenny MD A physiological maelstrom has recently swirled about the hemodynamic effects of the prone position in severe ARDS [1-5]; but how exactly does this maneuver alter the cardiovascular system? A good approach to this problem is a Guytonian one whereby we consider [… read more]
Image: Rotoprone Acute respiratory distress syndrome (ARDS) injures the lungs in a heterogeneous pattern, and the damaged areas are particularly vulnerable to further ventilator-induced lung injury. This is why a lung-protective ventilator strategy using low tidal volumes reduces mortality from ARDS, experts believe. Tidal volumes of 6 mL/kg ideal body weight (calculated from height) using conventional [… read more]
Image: Dartmouth Nitric Oxide: No Benefit Even in Severe ARDS Giving inhaled nitric oxide to people with acute respiratory distress syndrome (ARDS) improves oxygenation, but has never been demonstrated to improve survival. Not many physicians seem to use nitric oxide for ARDS anymore, except possibly as salvage therapy in life-threatening refractory disease. Even that well-meaning [… read more]
Prevention and Management of Ventilator-Induced Lung Injury See also Part 1: Mechanisms of Ventilator-Induced Lung Injury The recognition that lifesaving mechanical ventilation can also be harmful, even lethal, has led to a sea change in the use of mechanical ventilation in critically ill patients — at least in theory. For people with acute respiratory distress [… read more]
Mechanisms of Ventilator-Induced Lung Injury (Part 1) See also Part 2: Prevention and Management of Ventilator-Induced Lung Injury Although invasive mechanical ventilation saves tens of thousands of lives each year, it can also be harmful, causing or worsening acute respiratory distress syndrome (ARDS) when misapplied. The repetitive stretching of lung tissue during positive pressure ventilation [… read more]
Mechanical Ventilation in ARDS Due to Sepsis See all PulmCCM reviews of: Surviving Sepsis Guidelines Sepsis is one of the main causes of acute respiratory distress syndrome (ARDS), in which the lungs are injured by circulating inflammatory mediators, resulting in severely impaired gas exchange usually requiring invasive mechanical ventilation. ARDS also results in poor lung [… read more]
Low Tidal Volume Ventilation Improves Outcomes in Elective Surgery Using low tidal volumes (6-8 mL/kg ideal body weight, or about 500 mL in the average man) during mechanical ventilation has been known for more than a decade to be lifesaving for people with acute respiratory distress syndrome (ARDS). Since reducing mortality by a relative 22% [… read more]
Prone Positioning Saves Lives in Severe ARDS Patients: NEJM It’s long been known that positioning patients with ARDS on mechanical ventilation face-down (prone) improves their oxygenation. (There are various theories why prone positioning helps, such as by reducing ARDS’s injurious heterogeneous alveolar overdistension.) The improved oxygen levels have never translated into improved outcomes in ARDS [… read more]
image: wikimedia Pulse Oximetry: The 30-Second Time Machine Why does it seem to take so long to re-oxygenate your crashing patient? Because your pulse oximeter is lying to you, no matter how good it is. Telescopes show us how a star looked millions or billions of years ago; pulse oximeters create a similar, though tiny [… read more]
In ARDS, Obesity May Protect Life (But Not Kidneys) by Blair Westerly, MD Obesity is an epidemic and common in intensive care units in the United States. Furthermore, while acute kidney injury (AKI) is also common in critically ill patients, obese patients carry additional risk for AKI because of increased baseline comorbidities. Both obesity and [… read more]
(image: Wikipedia) High-Frequency Oscillatory Ventilation (HFOV) for ARDS Two Randomized Trials: Early HFOV Doesn’t Help, May Harm High-frequency oscillatory ventilation (HFOV) has been proposed as a first-line therapy for acute respiratory distress syndrome (ARDS). By delivering 3-15 breaths per second of tiny tidal volumes (~70 mL), HFOV has appeal as the “ultimate” lung protective ventilator [… read more]
Low Tidal Volumes Improve Outcomes in Non-ARDS Patients Since the landmark ARDSnet trial of low tidal volume ventilation published in the NEJM in 2000, protecting the injured lung with low tidal volumes has been widely adopted. In case you missed it, that trial showed that low tidal volume ventilation (6 ml/kg IBW) improved mortality from [… read more]
In most areas of life, it helps to be tall, and needing treatment for ARDS further proves the rule. Tall people are less likely to get harmful lung-distending tidal volumes during mechanical ventilation, simply by virtue of having bigger lungs. It’s bad enough that we intensivists might discriminate against the under-six-feet crowd (of which I [… read more]
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