New Device Monitors Oxygen Levels During Surgery

In the operating room, surgeons make crucial decisions based on the levels of blood flow and oxygen in a patient’s tissues. If a tissue has low oxygenation, the doctor tries to reestablish the blood flow. If surgeons are excising a tumor, they cut off the blood flow to it to prevent major blood loss. Now researchers have developed a noninvasive imaging system that can present real-time data on oxygenation levels at almost video frame rates (Anal. Chem., DOI: 10.1021/ac201467v).

Currently, surgeons monitor blood flow by injecting fluorescent dyes, by using Doppler monitors, or by visually inspecting the tissue’s color. They assess tissue oxygenation by inserting needle-like probes. But these approaches are invasive, not quantitative, and unable to collect information over large areas of tissue.

So Karel Zuzak of Digital Light Innovations, an Austin, Texas-based design firm, and his colleagues designed what they call a hyperspectral imaging system, which measures the level of oxygenated hemoglobin in tissue. Deoxygenated and oxygenated hemoglobin absorb different wavelengths of light. The researchers’ device uses an array of 768,432 independently controllable 16-μm mirrors—a technology used to drive 3-D televisions—to precisely tune light to these wavelengths and to direct it to an area of tissue. The reflected light, captured by a detector, indicates the tissue’s biochemistry. The system can calculate the level of oxygenated hemoglobin in each pixel of a 12.7-cm diameter region three times every second.

The team demonstrated the system on live pigs. After clamping an animal’s renal artery, they detected within milliseconds a decrease in kidney oxygenation. The decrease appeared on a computer screen as a shift from intense orange to greenish-blue. In another pig, when the team members clamped the renal artery, they noted that one kidney lobe still appeared oxygenated. The surgeons then found that this animal had a hidden, redundant artery. That surgery, Zuzak says, demonstrates the power of whole-field imaging over more localized methods: “Sampling oxygenation from one point is not enough,” doctors need an image of the whole organ, he says.

Urologic surgeon and team member Jeffrey Cadeddu of the University of Texas Southwestern Medical Center says the technique enabled him to quantify tissue oxygenation more precisely than with visual cues. This quantitative information allowed him to better control blood flow to the pigs’ kidneys, which resulted in less post-surgical tissue damage. He is collecting data to determine whether similar benefits might extend to people.

John Rectenwald, a vascular surgeon at the University of Michigan, Ann Arbor, who was not involved with the study, says he believes hyperspectral imaging could help surgeons make more-informed decisions when operating. For example, when amputating a diabetic patient’s leg, surgeons could better determine where to amputate and potentially avoid the need to operate again to remove tissue damaged by poor blood flow.

Wolfram Gauglitz, Digital Light Innovation’s vice president for business development, expects a device to be commercially available in 18 to 24 months.