Picture this: prior to surgery you place a blood pressure cuff around the middle phalanx of your patient’s right middle finger, instead of a standard cuff on the upper arm, to measure blood pressure. Is this the future? After decades of watching intermittent readings from oscillometric (standard) blood pressure cuffs, will we be monitoring data from a continuous finger-cuff instead?
A study in the September 2023 issue of Anesthesiology showed that continuous finger-cuff arterial pressure monitoring helped anesthesia professionals a) reduce hypotension during the 15 minutes following induction of general anesthesia, and b) reduce hypotension during the duration of noncardiac surgery, compared to traditional intermittent oscillometric arterial pressure monitoring.
The study was done in a single medical center, the University Medical Center Hamburg–Eppendorf in Hamburg, Germany. A total of 242 patients aged 45 and older who were scheduled for noncardiac surgery were randomized to continuous finger-cuff arterial pressure monitoring or to intermittent traditional oscillometric arterial pressure monitoring. The continuous finger-cuff arterial pressure monitor used was the ClearSight system manufactured by Edwards Lifesciences, USA.
An appropriately sized finger-cuff (small, medium, or large) was positioned on the middle phalanx of the third or fourth finger of every patient, along with a standard intermittent oscillometric arterial pressure monitor on the opposite arm. Traditional oscillometric arterial pressures were measured at 2.5 minute intervals. The clinical monitoring for each patient was randomized to be either 1) unblinded continuous finger-cuff arterial pressure monitoring, or 2) intermittent standard oscillometric arterial pressure monitoring with the finger-cuff data blinded. The Hamburg medical center’s institutional routine was to maintain MAP (mean arterial pressure) above 65 mmHg, and intraoperative hypotension was treated with intravenous norepinephrine, which was given at the discretion of each attending anesthesiologist.
The Anesthesiology study had two primary endpoints. The first was the amount of hypotension during the 15 minutes following the induction of anesthesia, and the second was the time-weighted average MAP less than 65 mmHg during the entire surgery. Results showed that continuous finger-cuff arterial pressure monitoring helped anesthesia providers a) reduce hypotension within the first 15 minutes after starting induction of anesthesia, and b) reduce hypotension during the entire noncardiac surgery. Patients assigned to continuous finger-cuff monitoring received more than twice as much norepinephrine both within 15 minutes after starting induction of anesthesia and during the entire surgery, when compared with patients assigned to intermittent oscillometric monitoring. This presumably explains why there was significantly less hypotension in the continuous finger-cuff monitoring group.
Intraoperative hypotension carries risks of major postoperative complications, including acute kidney injury, myocardial injury, and death. Previous studies have validated that both the severity and the duration of intraoperative hypotension are associated with postoperative complications and mortality. Two previous trials validated the efficacy of continuous finger-cuff arterial pressure monitoring during surgery. In a study of 160 patients undergoing orthopedic surgery, continuous finger-cuff monitoring resulted in less than half the number of hypotensive events, defined as a MAP less than 60 mmHg (19 vs. 51 events). A second study of 316 patients undergoing noncardiac surgery showed that continuous finger-cuff arterial pressure monitoring nearly halved the amount of intraoperative hypotension, defined as the time-weighted average MAP less than 65 mmHg.
The Edwards Lifesciences website describes the ClearSight continuous finger-cuff monitoring system. In addition to continuous blood pressure monitoring, the ClearSight system records advanced hemodynamic parameters from the noninvasive finger cuff, including graphic trend displays on the Edwards Lifesciences HemoSphere monitor of:
• Cardiac output (CO)
• Stroke volume (SV)
• Stroke volume variation (SVV), and
• Systemic vascular resistance (SVR).
These parameters provide additional information which, if validated, can expand the information an anesthesia provider can monitor routinely. The parameters of continuous blood pressure (ART), continuous Mean Arterial Pressure (MAP), Cardiac output (CO) and Stroke volume (SV) are shown on the HemoSphere monitor below.
The technology behind the ClearSight continuous finger-cuff monitor involves a principle called the volume clamp method. Per the Edwards Lifesciences website, this “involves clamping the artery in the finger to a constant volume, by dynamically providing equal pressure on either side of the arterial wall. The volume is measured by a photo-plethysmograph built into the cuff. The counter pressure is applied by an inflatable bladder inside the cuff and is adjusted 1000 times per second to keep the arterial volume constant. Continuous recording of the cuff pressure results in real-time finger pressure waveform.”
Dr. Daniel Sessler, one of the world’s most respected and prolific anesthesia researchers, is a co-author of the recent Anesthesiology study. To me this validates the notion that continuous finger-cuff technology may eventually gain widespread adoption in operating room monitoring. (Note also that Dr. Sessler is a consultant for Edwards Lifesciences, and has received research funding from the company, as have some of the other authors of the Anesthesiology study.)
Unanswered questions regarding continuous finger-cuff blood pressure monitoring include:
- Would data show that more frequent utilization of oscillometric (standard) blood pressure readings, recordedwith our existing equipment every one minute instead of every 2.5 minutes, give as much information as a continuous finger-cuff?
- If a patient’s hand or fingers are jiggled or moved during monitoring, would the continuous finger-cuff give significant artifacts?
- Would clinicians use both traditional blood pressure cuff monitoring and continuous finger-cuff monitoring on the same patient, and make physiologic conclusions from both sources of input?
- Will other models of finger-cuff monitoring, different from the Edwards Lifesciences ClearSight model, vary in accuracy? Will clinicians trust new finger-cuff monitoring devices and their data?
- What will be the price of this technology?
The benefit/risk ratio of continuous finger-cuff monitoring appears to be high. The technology is noninvasive and unlikely to harm our patients in any way, as long as the data is accurate. The dollar cost of this new technology will influence its rate of adoption. Existing intermittent oscillometric (traditional) blood pressure monitoring devices are already present in every operating room as standard equipment on today’s budgets. If continuous finger-cuff blood pressure monitoring is both accurate and inexpensive, the new technology may be universally adopted. But because a majority of anesthetics are administered to reasonably healthy ASA 1 or ASA 2 patients, many of them in outpatient surgery centers, one could argue that measuring intermittent blood pressures every 2.5 to 3 minutes with oscillometric (traditional) blood pressure monitoring devices is an adequate monitoring interval for these patients. If the added cost of continuous finger-cuff monitoring is excessive, this technology may be limited to hospitals, where sicker patients are anesthetized for bigger and more invasive surgical procedures, and which present increased risk for patients with hypotension.
The Food and Drug Administration recently approved an additional monitoring system based on finger-cuff technology from Edwards Lifesciences, the Acumen Hypotension Prediction Index (HPI) software system. This system uses machine learning to alert clinicians of the likelihood a patient is trending toward hypotension, or low blood pressure.
Keep your eyes open for further studies on the ClearSight system, the Acumen system, and other continuous finger-cuff monitoring equipment. This technology may become part of our operating room life in the near future.