Snorkel makes surgery calmer for kids

If you think designing for adults is difficult, try making a medical device for three- to nine-year olds. Philadelphia anesthesiologist Geoffrey A. Hart saw how terrified kids became when wrapped in a cocoon or papoose to be sedated for operations. So he envisioned a friendlier solution. His pediatric sedation device has been almost ten years in the making and has undergone numerous design revisions.

PediSedate(TM) resembles a simple headset for listening to a Sony Walkman. But the translucent blue device has not one sharp edge. It looks as smooth and friendly as the candy gummy bears it's patterned after. In addition, it hooks up to a child's Nintendo Game Boy or CD player so that a young patient can play with something familiar while breathing anesthesia through a disposable, plastic nosepiece. That's crucial since nitrous oxide sedation takes about four minutes-an eternity for a squirming child in a stressful situation.

Conventional sedation methods reminded Hart of a torture chamber. "Children are restrained against their will on this long table while someone injects anesthesia with a long needle," he says. "When I first saw this, I said, 'This is the new millennium. Why do we still need to do this? Isn't there a better way?"

It's all about control. Hart is not an engineer, so he hired Design Continuum (West Newton, MA) to create a product to match his vision. The company does engineering research, design, and development for clients in consumer products, technology, and medicine. They've amassed 280 patents through contract jobs for Andersen Windows, BMW, Johnson Controls, Master Lock, Moen, Polaroid, Procter and Gamble, Reebok, Samsung, and Zeiss.

Hart had stringent requirements:

Continuum began with scores of interviews with child psychologists, anesthesiologists, and of course, with children themselves.

"Originally we thought children wanted a device that would shut the world out, because there was all this trauma going on around them," says Allan Cameron, BFA, principal industrial designer at Design Continuum. But after talking with child experts, the project group discovered that, just like adults, children need control. "They want to close off when they want to, but when something is going on, they want to know and understand what it is all about," Cameron says.

That is why they designed for a large open area around the ear pads. "When something is going on, the child can turn the volume down and hear what is being said," Cameron continues. "Then when a child is ready, he or she can turn up the volume and shut it out. Even at four years old, they will still have control."

Breathe through the snorkel. Perhaps the hardest design challenge for the team was the snorkel-the gas delivery and vacuum tube portion of the headset, says David Chastain, project leader and principal engineer at Design Continuum.

The nose mask has two hoses, for both inhaling and exhaling. But engineers didn't want to build a frame across the child's face because that could add more stress. So they included both tubes inside a single strut. The first carries nitrous oxide and oxygen to the nosepiece, so the patient can inhale. Then as the patient exhales, an umbrella valve opens and the second tube sucks away CO₂ and any excess gas.

Putting both connections on the same side was difficult. "In the original design, the snorkel was smaller than it is now," Chastain says. But it could not accommodate the disposable nose mask that fits inside the nose shroud. In addition, gas had to arrive at the child's nose in adequate supply so he wouldn't feel starved as he was inhaling. The snorkel also had to be soft and flexible to adjust to the child's head, yet be self-supporting.

Where engineering meets design. Enter the gooseneck. Putting a slender, flexible element within the snorkel gave it support without adding too much size and weight. It's flexible but holds its shape, like a desk lamp or microphone stand.

But the gooseneck only extended so far. Designers still had to build a support for the nose shroud and disposable nose mask. They wanted one long continuous piece. But engineering felt that wasn't strong enough; they demanded an outer shell at the shroud.

"Here is where engineering meets design," says Chastain. "We pushed the soft part of the snorkel through and snapped it into the rigid part." This provided a minimal visual transition while keeping it as compact, smooth, and trim as possible.

That creative tension is the way Continuum works; lines are blurred between ME and ID. "I need to do ME functions," says Kevin Young, principal industrial designer, "and John MacNeill, a mechanical engineer, has to have ID abilities."

They needed all their cooperation to solve the nose mask design. "We solved this as a group," Chastain says. "We said, 'We are the guys. And we will stay here until we figure it out.' We worked out approaches together, then John [MacNeill] went away to design it in CAD."

Listen to the earpiece. Like the snorkel, the earpiece underwent many transformations.

To keep kids from feeling "closed-in," Continuum designers originally suggested that the earpiece have a spider web-like design. But this had two flaws. First, it had more potential breaking points than a solid form. And second, it was too hard to clean.

So they designed two different parts-One earpiece is a complete oval, and the other an open circle. The open area allows engineers to clip a pulse-oximeter to a child's ear lobe, and monitor the percentage of oxygenated hemoglobin in her blood. A capnometer in the vacuum line measures exhaled CO₂. Between the two, the anesthesiologist has second-to-second knowledge of the patient's respiratory function.

Pick your materials carefully. "The first cast urethane resin we tried was too rigid and the parts weren't compliant enough once we got everything glued together," says Chastain. "So we tried a softer resin and found that to be too flexible." In the end, engineers used the more rigid material for the outer headband shell and the softer material for the inner shell. "It was Goldilocks and the Three Bears syndrome," laughs Cameron; juuuuuust right.

And by casting the urethane, engineers had a robust, easy to clean material, through which they could run speaker cables, and capture the adjustable earpiece assemblies, keeping everything enclosed.

Another materials challenge was color, since the final design comes in translucent blue or cranberry (preferred by boys and girls). They used urethane plastics, not silicone rubber, and not every plastic could be colored accurately.

One size fits all. One of the chief design challenges was the variety of head sizes between three and nine year olds.

That's where hands-on models are indispensable. "Our approach is to model early and model often," says Chastain. This is evident by the scores of foam, mechanical, and Z-Corp. samples of potential devices that cover the engineers' desks. Continuum's in-house, Z-Corp. prototyping machines read CAD drawings then "print" solid models of the parts by spraying layers of super glue over a fine white powder.

Continuum engineers and designers made the models adult-scale so they could try them on. "We even brought in our children to get an idea of what mechanical degrees of freedom we needed in the piece," says Chastain. He adds that the children "were very opinionated about which models they liked best."

Even CAD-guru MacNeill valued the physical models. "I was brought in for the last three or four months of the project, to do a lot of mechanical breadboarding, making crude mockups," he says. "We'd buy a pair of Radio Shack headphones, rip them apart, and put tubes in them. So my task was to interpret the industrial design into something functional that would perform sucessfully."

Challenging an expert. MacNeill admits he was challenged by the design, despite being one of only 32 Pro/ENGINEER users worldwide certified by PTC as an Engineering Provider, Mechanical Design Level 2. "The surface complexity was difficult," he says. "Especially where the flexible snorkel attaches to the hard urethane part. You have to be pretty smart about how you approach your model."

"So the first thing I had to do was take my engineering hat off and ask, 'What is the most effective way of creating this form?'" MacNeill says. "Here is where I will lean on an industrial designer and say, 'How would you define this form from the top view? What shapes are important to you? How do these parts relate?'"

To avoid the technical restrictions of CAD, MacNeill doesn't even touch a keyboard until he sketches out his approach on paper. "Then I talk to the designer again and tell him what I'm thinking," he says. MacNeill defines what shapes he plans to draw in the projected view, in the top view, and in the side view. "Then we talk about where will the parting line go, how do we break apart the parts, how big should the parts be."

"Then I start doing the dirty work in CAD and spend a couple of weeks getting the surfaces right, which was challenging due to the fact there were no sharp edges in the design," MacNeill says. "I initially create a master surface model which carries all the surfaces of the assembly, then break out the individual parts."

As he builds surfaces, he also analyzes the more practical aspects, such as the parting lines, structural ribs, and moldability. Pro/E lets him design parts flexibly, and explore different options. Above all, it's a collaborative process. MacNeill often makes suggestions to the designer, "But I have to defer to the designers as to what is the necessary form," he says.

"This is that transition between science and art where one starts thinking, 'Okay, how are we going to make this?' and you become the engineer again and get into the reality of how this works," says MacNeill.

Although the design is still in clinical trials, it has a high acceptance rate among children, says Hart. "We set out to take away or allay the fear of the child, minimize pain, and provide comfort and familiarity to make the patient feel more like they are at home rather than in this strange environment. This system accomplishes 95% of that," he says.