Carefully adjusting mechanical ventilator settings in the intensive care unit to pump smaller breaths into very sick lungs can reduce the chances of dying by as much as 8%, according to a Johns Hopkins study appearing in the British Medical Journal.
"Adjusting the ventilator to keep the breath size and lung pressures lower can have a dramatic effect on whether or not a patient dies from their lung injury, even long after they leave the ICU," says Dale Needham, MD, PhD, lead study investigator and critical care specialist. "People with acute lung injury are very sick and often in the hospital for weeks, not days."
The researchers evaluated the ventilator settings and subsequent survival or death of 485 men and women, most over 50 years of age, who had spent at least a week or more in intensive care at four Baltimore-area hospitals. All study participants had life-threatening acute lung injury. The study participants were evaluated for 2 years following their injury.
The researchers found that over the entire ICU stay, on average, for every one unit increase in the ventilator setting, or tidal volume, calculated in milliliters per kilogram of predicted body weight of the patient, there was a commensurate 18% jump in the risk of mortality over 2 years, a finding which Needham says, "represents a huge difference" and reinforces the message to critical care specialists to keep tidal volumes and lung pressures adherent to known lung-protective ventilator settings.
Previous research had shown that using lung-protective ventilator settings reduced inflammation and decreased the amount of time that other vital organs, such as the heart and kidneys, were not functioning normally. Short-term survival rates also improved.
Needham says that in people with acute lung injury, including acute respiratory distress syndrome, larger breath sizes put more stress on the lungs because only a small portion of healthy tissue is available to service the body’s oxygen needs.
"Using a smaller breath size simply places less stress on the lungs," he adds.
Among the researchers’ other key findings were that only 41% of the 6,240 ventilator settings reviewed in the study were adherent with lung-protective ventilation, using smaller breaths and reduced pressure.
"Our study shows there is still a lot of room for improvement in how we treat acute lung injury in the ICU," says Needham, who points out that one of the biggest barriers to fixing the problem is a lack of understanding of the best methods for having ICU staff quickly recognize acute lung injury and change their traditional practice to adopt lung-protective ventilation.
Another barrier is miscalculating the correct tidal volume setting, as the formula is based on predicted body weight instead of actual body weight. Estimates show that as many as two-thirds of ICU patients are overweight, which has no bearing on physical lung size. People who are the same height and gender will have similarly sized lungs, even if one weighs significantly more than the other.
"Such details can have lasting effects," says Needham. "Critical care practitioners have to refocus our efforts on not simply getting patients out of the ICU alive, but on changing traditional medical care in the ICU to improve patients’ recovery over the longer term."
Source: Johns Hopkins Medical Institutions
