Out of sci-fi and into the OR
At first glance it would be easy to mistake Children's Hospital
Boston cardiac surgeon Pedro del Nido, MD, for a racecar enthusiast
working the controls of an arcade game. A binocular display immerses
him in the scene before him and his hands disappear into the maw
of the huge console at which he sits. But no thumping arcade music
or flashing lights threaten to distract him. The sounds of the
operating room are hushed, broken only by occasional subdued question
or command, as del Nido concentrates on closing an errant artery
in 6-year-old Tessa Greenhalgh's tiny heart—from across
the room.
Sitting at the console of the da Vinci robotic surgical system,
del Nido views a three-dimensional, magnified display of Tessa's
heart. It appears just as clear and present as if he had opened
her chest and were standing at her side, but the image is produced
by two lenses at the end of a finger-thick wand inserted into
Tessa's chest through a small incision. The two controls in his
deft grasp operate instruments at the ends of two other wands.
Between del Nido and his young patient, 20 feet of cables, half
a ton of robot, and a mountain of computer processing power translate
his hand and finger movements into the movements of surgical forceps,
scalpels and clips inside Tessa's chest. The translation provides
an opportunity to scale down the surgeon's movement, if needed,
and to filter out the slightest tremor, making the robot even
more precise than a surgeon operating directly.
The absolute calm and confidence that del Nido displays in the
operating room and with patients is what brought Tessa's parents
to Children's. In October 2003, when their nurse practitioner
heard a mechanical-sounding murmur in Tessa's neck, she sent them
to their local hospital for an evaluation. The cardiologist there
diagnosed her with a congenital heart defect called patent ductus
arteriosus. An artery that bypasses the undeveloped lungs in fetuses
should have closed when she was born, but never did. Her heart
was working too hard to recycle blood that should have been on
its way to the rest of her body. The doctor recommended a surgery
that would have left Tessa with a 10-inch scar and kept her out
of school for weeks, so a family friend who is a physician recommended
they try Children's for a second opinion. The family left their
first visit with del Nido "feeling no doubt" about what
the surgeon was capable of, says Tessa's mother Tina Craig. "He
was able to put our minds at rest."
That feeling of support followed them through the whole procedure.
When Tessa checked in on Monday for her Tuesday morning surgery,
nurses brought picture books and took the time to answer every
question she had, including the big one, "will I have to
get any shots?"
Reach in and touch
In the late 1980s, minimally invasive surgery became commonplace
for many straightforward procedures. The video-endoscope lets surgeons
see into the chest or abdomen through a small incision, and similarly
inserted long-handled instruments can be used to cut or reposition
tissue. Patients are often back at work (or play) in days rather
than the weeks it takes to recover from conventional abdominal or
chest surgery. But the straight handles and fixed instruments provide
little dexterity for the complex work of cardiac reconstruction.
Because the instruments pivot where they enter the chest or abdominal
wall, moving an instrument to the right requires moving the handle
to the left. It takes a little time to adjust to the backwards movements,
like learning to steer a boat with a rudder.
The da Vinci system has changed all that. The system's instruments
flex in a wrist-like movement near the surgical site, precisely
emulating the hand and finger movements of the surgeon at the
console, so surgeons can function in the same way they always
have, rather than learning to reverse years of training. With
more flexibility inside the patient, the tools also let them work
in tighter spaces and put less strain on the tissues around the
openings.
The next generation
Seeing the system's potential for use with children, del Nido
began working with the company and with engineers at Harvard and
Boston University to develop the next generation of robotic tools.
"We wanted to start with the technology, figure out the problems,
then convert it for pediatric use," he says. Del Nido's efforts
have already paid off. The instruments originally designed by
da Vinci's creator, Intuitive Surgical, are eight millimeters
in diameter, which is fine for adults, but often too big for children.
So del Nido worked with Intuitive to develop a new set of five-millimeter
tools that are much more appropriate for younger patients, and
in early 2004 became the first surgeon in the world to use the
instruments on a pediatric patient.
Now that some of the technical hurdles have been cleared, del
Nido says the smaller instruments are sure to become popular with
surgeons who operate on adults. "If the idea is to be minimally
invasive," says del Nido, "then the smaller the better."
He's also a lead investigator on a $5 million partnership grant
from the National Institutes of Health to develop three-dimensional
ultrasound technology that will allow surgeons to see inside a
beating heart in real time.
Luckily, Tessa's heart could be repaired from the outside, where
there is enough space to see and move instruments. Surgery on
the valves and muscles inside the heart still requires bypass,
in which a machine takes over the work of the heart and lungs
while a surgeon works on the still and empty heart. Shutting down
the heart and lungs, even for a short time, poses certain risks,
including greater chance of clotting and stroke, as well as further
injury to the heart itself.
If we can operate inside the chest without opening it up, what's
keeping us from working inside a beating heart, wondered del Nido.
A lot, it turns out, but that hasn't daunted him or his colleagues
on the partnership grant, Pierre Dupont at Boston University and
Robert Howe at Harvard's Biorobotics Laboratory. One of the first
problems is seeing through the continuous rush of blood in the
heart. Three-dimensional ultrasound has been used to image heart
valves and other soft tissues for several years, but never in
real time. Working with Philips Medical Systems, they were able
to speed image processing enough to get a three-dimensional view
of a working heart valve at 30 frames per second.
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Challenges to spare
Sound waves reflect very differently from metal surfaces than from
soft tissue, so del Nido and his colleagues soon found that when
they introduced instruments into the ultrasound field, they either
distorted the whole image or the instruments just disappeared. Dupont
describes the effect like looking at a bright light reflected in
a mirror. If you look straight at it, you're blinded, but if it
reflects in another direction, you can't see it at all. Dupont's
group of graduate students is exploring several approaches to this
problem, including using non-metallic instruments or coatings and
equipping the instruments with electromagnetic beacons, providing
a sort of "you are here" sign in the ultrasound image.
Other challenges include keeping the surgeon oriented within
the less-familiar ultrasound view, finding the safest locations
to enter the heart and the quickest, simplest ways to close the
holes behind them. For fine work, as is needed to repair a mitral
valve, surgeons can't work on a constantly moving surface. It's
like trying to thread a needle on the heaving deck of a boat.
For such situations, the team is devising a way to synchronize
heart, image and instruments so the image will appear still, even
as the heart beats on.
The new prototypes won't be available next year, or even the
year after, but ultimately the efforts will pay off in surgical
tools and methods that are truly appropriate for children and
even for fetal surgery. Meanwhile even with today's instruments,
Tessa was back in school a week to the day after her surgery,
far sooner than she would have been just a few years ago.
