Troubleshooting problems with mechanical ventilation starts with assessing how much control one has over specific variables, according to an expert at HM17.
“You want to be in charge of everything when you’re dealing with a ventilator, but you have to acknowledge that you only get to be in charge of some stuff,” said Peter Clardy, MD, an assistant professor of medicine at Harvard University in Cambridge, Mass., and its affiliate, Mount Auburn Hospital. He made his remarks during a rapid-fire science session at HM17.
Since successful algorithms for acute mechanical ventilation require control over many independent variables, knowing what is most stable and going from there can allow the physician to develop a workable plan of action, according to Dr. Clardy.
“It’s really good to be explicit about what is dependent and what is independent,” he said. Independent variables might be those specific to the ventilator, but will always include the positive end-expiratory pressure and the fraction of inspired oxygen. Other independent variables will depend on the mode of ventilation – either fully assisted, partially assisted, or noninvasive.
“If you’re in charge of volume, you have to worry about pressure,” he noted. “If you’re in charge of pressure you have to worry about volume.”
Dependent variables also can vary by mode of ventilation. Once the independent and dependent variables are mapped, it is easier to glean more information about the respiratory mechanics of the situation and the physiologic processes, such as the metabolic cost of breathing and whether it can be reduced, what can be done to prevent ventilator-induced lung injury, and how gas exchange can be supported.
Understanding the independent/dependent variable ratio can also help provide valuable clinical information, such as whether reversing hypoxemia and/or hypercarbia is necessary, or if there are signs of respiratory distress or dyspnea. Other clinical indications might include whether there is a need to prevent or reverse atelectasis, or reduce ventilatory muscle fatigue. Additionally, it will be easier to know whether sedation is possible, or if a neuromuscular blockade should be used. Such information can help determine whether to protect the airway.
“Respiratory distress in a patient who is already ventilated is quite common, so having a routinized way to assess these patients and their stability can help you think about what your moves are right there while you’re in the room,” Dr. Clardy explained. “All of that can be incredibly helpful.”
Dr. Clardy had no relevant financial disclosures.