NEW ORLEANS—Five decades ago, the thought of continuously monitoring patients with pulse oximetry was a revolutionary one. Now, this practice in critical care and procedural settings is the standard of care around the world. There is some evidence suggesting that continuous multiparameter hemodynamic and oxygenation monitoring in the acute care setting of hospital wards should one day become equally commonplace.
With two prospective trials, Ashish K. Khanna, MD, revealed that this type of monitoring resulted in significant decreases in patients’ chances of exceeding critical thresholds in mean arterial pressure (MAP), heart rate and blood oxygenation (SpO2). Whether these improvements equate to decreases in hard outcomes such as myocardial injury was unclear, however.
“Traditionally, we monitor patients on the general hospital floor once every shift or with four to six spot-checks,” said Khanna, an associate professor of anesthesiology and the vice chair of research at the Wake Forest University School of Medicine, in Winston-Salem, N.C. “However, over the past 10 years or so, we have accumulated observational and retrospective data showing that vital sign changes on the general hospital floor are common and not picked up by intermittent monitoring.
“In the meantime, there’s a period of approximately six to 12 hours before a critical event where there are gradual and subtle changes in patients’ vital signs,” Khanna added. “This is the golden period where early intervention can prevent a disastrous event. But if we don’t have continuous monitoring, then we’re not going to pick up those changes. We’re only going to discover them when patients are actually on the verge of cardiac arrest or have already arrested.”
As part of this interventional randomized trial, the researchers modeled the risk for a composite outcome of hypotension (MAP =65 mm Hg), tachycardia (heart rate =110 beats per minute) and/or hypoxemia (SpO2 =90%), comparing continuous and intermittent ward monitoring in a cohort of relatively high-risk adult noncardiac surgical patients. The study’s exploratory outcome was the association between the two monitoring modalities and myocardial injury after noncardiac surgery, measured as a high-sensitivity troponin I value more than 40 pg/mL.
Khanna and his colleagues included 879 patients (average age, 70.7 years) in the study, 448 of whom underwent continuous monitoring and 431 intermittent monitoring. The participants were more than 65 years of age or more than 45 years with at least one cardiovascular risk factor. Of the final cohort, 70.1% (n=616) were ASA physical status III and 18.1% (n=159) were ASA IV. Importantly, a median of 80 hours of continuous monitoring data were obtained from the patients.
“We used an innovative trial design we call the ‘alternating interventions model,’ where every four weeks we switched from continuous monitoring with alarms open and available to caregivers to continuous monitoring that was blinded and silenced with alarms not available to caregivers,” Khanna said. “In the latter case, nurses had to resort to traditional intermittent spot-check monitoring. We did this for one complete year.”
Presenting the results at the 2022 annual meeting of the American Society of Anesthesiologists, it was found that patients who underwent intermittent monitoring were at much greater risk for exceeding the study’s predetermined critical thresholds. These patients were 81% more likely to have a MAP less than 65 mm Hg (P<0.001), 14% more likely to have a heart rate of more than 110 beats per minute (P<0.001), and 39% more likely to have SpO2 of 90% or lower (P<0.001). The composite outcome of any event occurring was 28% more likely to happen in intermittently monitored patients (P<0.001).
Monitoring for Serious Outcomes Indecisive
“Obviously, the really important question is whether or not continuous monitoring will change hard outcomes,” Khanna added. The study found that patients who underwent intermittent monitoring were at 5% greater risk for myocardial injury than their counterparts who were continuously monitored, but this was not significant (P=0.801).
“I have some hypotheses on why we did not see a significant difference in myocardial injury,” Khanna said. “Most importantly, the overall incidence of hypotension—defined as a MAP of 65 mm Hg—was low in both study arms, and when hypotension occurred, it did not persist for prolonged periods of time. Persistent hypotension is the biggest driver of myocardial injury.”
In fact, the biggest difference observed between groups was hypoxemia, which the researchers said is not as significant a driver of myocardial injury as is tachycardia or hypotension. Nevertheless, Khanna was still encouraged by the results of the trial, and ultimately believes it will act as a springboard for more research in the field.
Specter of Alarm Fatigue
The researchers also recognized the potential drawbacks inherent in continuous ward monitoring, the most significant of which may be the fear of converting a general hospital floor into a high-dependency unit. More intensive monitoring also raises the specter of increased alarms and concomitant practitioner alarm fatigue. Finally, as Khanna noted, not every patient who crosses one of the study’s critical thresholds will necessarily need care.
“Tachycardia is probably not going to harm a 20-year-old, but the same tachycardia might harm a 65-year-old with coronary artery disease,” he said.
Khanna maintained that the risk for missing critical events is far greater than any potential operational drawbacks. “One loss of life or one extra ICU readmission has an incredibly strong impact on healthcare resource utilization, caregiver morale, family morale and patients’ lives,” he said. “So I hope we ultimately get there. Maybe three to five years from now, some kind of continuous monitoring will be a necessary part of our practice for all our inpatients.”
By Michael Vlessides
Khanna’s work at Wake Forest University’s Department of Anesthesiology is funded by the Department of Defense, Edwards Lifesciences, Masimo, Medtronic, National Institutes of Health/National Heart, Lung, and Blood Institute, and Trevena Pharmaceuticals.