Monday, May 14, 2012

Cold Space

The other morning, I awoke with my nose deciding it didn't want to function properly and allow me to breathe through both nostrils. The harbinger of a cold, one nostril was stubbornly blocked with the various accumulations of the night. Lovely image, I know. Personally, I blame the exertion and physical stress (particularly the dunking in cold water and subsequent extreme chills) of the zombie run for this state of affairs. I mean, trudging through wet, muddy trails with hundreds of other people in relatively close proximity, dunking in icy water and waiting (soaked) for the better part of an hour in the breezy cool of a spring afternoon can't be all that good for you. Couple that with staying up late and waking early and voilĂ . A cold.

I actually have a point for relating this. You see, as I commuted to work and noticed my breathing passages start to open, I mused upon what a cold must be like in space. We take for granted that gravity helps our sinuses and nasal cavities drain. But in space, where there is no (or only a weak) gravitational field, would someone with a stuffy nose find absolutely no relief from natural drainage? How would the lack of gravity affect blowing one's nose? Would it be easier or harder?

As I pondered these questions, my mind began to drift toward bigger issues. I might be stepping on Phil Plait's area a bit, but I hope he won't mind. What about more serious medical care in space?

Intravenous Delivery

Since gravity and flowing liquids figured foremost in my thoughts, I began to wonder how intravenous delivery systems would work. On Earth, once the needle is stuck into a patient's arm, a catheter runs from the needle to the IV bag, which is hung somewhere above the patient. Gravity and a manually adjusted valve dictate how quickly the fluid (saline, IV drug, etc.) flows from the bag to the patient. That flow rate is crucially important, especially when considering dosing of drugs. Too slow and the drug may not have the proper therapeutic effect. Too fast and you risk an overdose. Without any gravity to make the liquid flow from the bag to the patient, how would this system of delivery work in space?

Luckily, I'm not the first to consider this. Pretty early on, it became clear that dehydration was a significant risk. The extremely low humidity (about 20% on a shuttle, according to NASA) means that stuff tends to dry out a bit faster than normal. That includes people. The use of IV saline, then, had to be figured out to allow astronauts to quickly rehydrate. Toward the end of April 1993, the very first intravenous line in space was set up to do just that. The lack of gravity means that in order to get the fluid to flow, something needs to put pressure on it to force it down the line. A person could manage this manually, by squeezing the bag, but controlling the rate of flow would be a significant challenge. Because of this, a pump would need to be used. This could not only cause the saline, drug or nutritional liquid to flow in the right direction, but also ensure that the "drip" rate remains at a constant speed.

Another challenge regarding the use of IVs is how long a catheter can remain in place. Inevitably, bacteria grow in the catheter, necessitating the replacement of the tube. In space, some bacteria not only grow faster, but also become more virulent. These two factors combined mean that IV systems in space need to be replaced more frequently.

And then there is the problem of bubbles. Regardless of the environment, air bubbles in an IV line can be very dangerous, even fatal. On the ground, gravity again helps by allowing air to rise and the liquid to flow down. With no gravity, however, there is not real "up", and so air is not so easily eliminated from the tubing. Instead, a filter needs to be used to squeeze bubbles out of the solution.

A final dilemma facing astronauts using IVs is that water is heavy. With every pound being counted very carefully, and only limited space available, finding ways to minimize the amount of water taken to space is critical. One way is to cut back on the number of pre-filled IV bags, which would be a significant hindrance to prolonged space flight (e.g., a manned mission to another planet). To get around this limitation, the cargo could include dry ingredients that are reconstituted as needed. The only problem with this is ensuring that the water used to reconstitute the medicine is sterile. Enter a relatively new device: IntraVenous Fluid GENeration for Exploration Missions, or IVGEN. The idea behind IVGEN is to use normal cabin water, purifying it and mixing the medication (e.g., crystalline salt to make saline). Rather than using pre-filled bags, which may expire before they are needed, IVGEN could allow the production of IV solutions on an as-needed basis. As an aside, one cool aspect of this device is that its applications are not confined to space exploration; it could be extremely useful in third world countries, where pure water and proper storage conditions may be hard to find.

Something as relatively simple as an IV drip becomes considerably more complex once put in the context of a weightless environment. What about something that can be a challenge even on the ground?

Surgery

There are a host of issues that face surgeons in space (hmm...sounds like a new prime time TV show or something for The Muppets): bleeding, floating surgical tools, tangled suture threads, floating organs and so on. The behavior of blood in a weightless environment depends a great deal on the source of the bleed. Venous bleeding tends to adhere to or ooze over the wound area, the surface tension of the blood and blood-surface bonding being rather strong. Arterial bleeding, on the other hand, could form floating droplets, streamers or clouds of blood, depending on the strength of the bleeding. While sponges and suction should be sufficient to deal with most surgical bleeding, free-floating blood presents several hazards, such as contamination of spacecraft surfaces to obscuring the surgeon's vision.

Floating tools can also present a challenge for space-based surgeons. Imagine: the surgeon uses a scalpel to make an incision. She raises her hand and simply lets go of the scalpel. Assuming no other force acts on it, it should stay in place and not cause any problems. If it is bumped or nudged, though, it becomes a distinct hazard to the surgeon, patient and other medical assistants, not to mention the operating space itself. In the same way that the surgeon and patient need to be secured to prevent uncontrolled drifting about the cabin, tools must be properly secured so that they don't interfere with the procedure. Although surgery has yet to be required for any humans on space missions, animal studies have been done. The results show that while surgery can be performed successfully in space without any decrease in the surgeon's manual dexterity, procedures take longer due to the need to secure all of the tools and supplies needed for the surgery.

Given the concerns associated with things floating about, it should be no surprise that using minimally invasive procedures, such as laparoscopy, would be preferable to open surgery. Just as with my IV question above, others have naturally thought of this. Using NASA's KC-135 aircraft to simulate weightlessness, researchers have performed laparoscopic and thorascopic surgery on pigs as far back as 1993. Their experiences have shown that these minimally invasive procedures are feasible for use in space. Some advantages over open surgery not generally a concern on Earth are the reduced risk of debris entering the surgical field or the patient's body, as well as minimizing the contamination of the cabin from blood, pus or other fluids used during surgery.

There are other issues facing the practice of medicine in space (e.g., shorter shelf life of pharmaceuticals), many of which we may take for granted on the ground. There are a lot of interesting questions to ask, and when you let your mind ponder what may seem to be inconsequential questions, you may be surprised what you find for answers.

2 comments:

  1. I think the most surprising thing I discovered while researching this was that surgical outcomes (at least in non-human models) were about the same as on the ground. Oh, and though I didn't go into any detail, that a person's sense of force is altered, making advice like "apply pressure to the wound" a bit different.

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