Scuba Diving is an incredible experience. It is serenely beautiful but also terrifyingly exigent. You instantly feel like James Bond.... up until you resurface in the community pool next to the water aerobics class. A scuba diver has to be very careful about the percentage of oxygen in their scuba tank. It is more complicated than simply filling a tank with "air." As a 5th grader, I was astonished to learn that air contains nitrogen, oxygen, and other trace gases. If a scuba tank had pure oxygen, the diver would die from oxygen toxicity. Divers mix oxygen with other gases like nitrogen, and even helium. A fetus getting oxygen like a scuba diver is more than just a silly metaphor. The placenta functions much like a scuba tank. While getting air from the placenta, amniotic fluid is swallowed and fills the developing lungs. Pulmonary surfactant coats alveoli in the lungs and increases surface area, allowing a fully matured fetus to breathe air upon delivery. It can take 8 months for surfactant to reach adequate levels. This means that surfactant and oxygen delivery are the bread and butter of neonatologists caring for preemies. Much like a scuba diver calculating the oxygen levels and pressures of their dive, medical professionals must understand how to optimize the oxygen delivery to the fetus/neonate without compromising maternal well-being. Unfortunately, our understanding of this subject is frustratingly limited (Rooyen, 2015). We more or less know how fetal O2 processes work, but we don't entirely know what the optimal ranges are, and they often aren't even measured during medical procedures that can impact them.
Did you know that in Denver the oxygen percentage (20%) is the same as L.A.? But how? The O2% is the same, but partial pressure isn't. You may find "boost oxygen" canned air for sale in gift shops in Colorado but it's a complete scam. Unless you are using medical grade oxygen then a few puffs of slightly concentrated oxygen are going to do very little for the change in partial pressure at altitude. Our professors have hinted at partial pressure being a topic of discussion in the near future. Let's use scuba as an example to introduce partial pressure. The deeper you go in water, the higher partial pressure gets. The weight of the water above compresses you, squeezing air in your body, increasing partial pressure. To compensate for this, deep-sea divers' scuba tanks are prepared with O2 levels as low as 8%. The pressure is so great that even the typical 20% OX (scuba divers record oxygen as "ox" colloquially) could cause toxicity. And at super-duper depths nitrogen becomes a narcotic so helium must be used as the "filler" gas. Scuba diving can have other dramatic effects on the body that you may have heard of such as "the bends." This is caused by resurfacing too quickly, leading to a rapid decrease in the partial pressure of the gases in the body. In fact, there is a well-known scuba diving rule that you should never get on an airplane within 24 hours of diving. Although, given that airplane cabins are pressurized I suspect this rule (that is actually taught in scuba diving classes) may have been started by someone trying to sneak in an extra day of vacation in the Bahamas.
So, what ought we to do? Send our wife to the Himalayas for 6 months before pregnancy? Not quite, in a healthy pregnancy, avoiding sudden changes in oxygen or partial pressure from environmental changes, or medications should allow the body to adapt on its own and inherently maintain the O2 and PO2 "sweet spot" to minimize defects and complications. Due to HbF's higher affinity for oxygen it is more resistant to the negative effects of hyperoxia so a good rule of thumb is to favor conditions that may induce too much OX rather than too little. Pregnant women are sometimes given 100% pure supplemental oxygen, under certain circumstances, and the increased affinity of fetal hemoglobin means that healthcare providers would be wise to make the mothers oxygen levels a priority should hers be low. However, giving the mother 100% oxygen does affect the partial pressure of fetal O2, causing jarring equilibrium shifts to the delicate oxygen delivery network. It should be common knowledge that a medical intervention of that manner, although seemingly trivial, should not be performed willy nilly, but only if it is medically necessary as it does present some risk, although quite minimally, to the fetus. If too much oxygen is present for too long the fetus may suffer damage similar to a scuba diver with too much OX in their tank.
Childbirth is a messy ordeal. The transition from placental oxygen to using the lungs is sudden and violent. The newborn may experience fetal acidosis from hypoxia, the mother may be experiencing blood loss, among a host of other complications. Medical professionals need to understand how the fetus is receiving oxygen and how their actions impact that. Complications may arise that affect both the mother and fetus, and complex decisions have to be made in a moment's notice. Anesthesia can cause a pregnant woman to become hypoxic, for example. In most cases the fetal oxygen delivery isn't even being measured or monitored. Even a short absence of oxygen can be teratogenic. Medical professionals need to consider how even minor medical interventions may affect the oxygen saturation and partial pressure of fetal O2 in much the same way that a scuba diver must carefully plan their dive.
手工 By Ryan Sabin B618 BLOG
Works Cited
Office of the District Attorney, County of Santa Barbara. (2024, July 19). Boost Oxygen ordered to pay $413,000 for false advertising relating to recreational oxygen. The Santa Barbara Independent. https://www.independent.com/2024/07/19/boost-oxygen-ordered-to-pay-413000-for-false-advertising-relating-to-recreational-oxygen/
Van Rooyen, I. F. (2015, July 2). Effects of high maternal oxygen concentrations on the fetus. Clinical Gate. https://clinicalgate.com/effects-of-high-maternal-oxygen-concentrations-on-the-fetus/
This was a very interesting post and was very fun to read. You mentioned it takes about 8 months for surfactant to develop in the fetus. What exactly does surfactant do in the lungs, and why is it an issue for premature babies?
ReplyDeleteSurfactant increases the surface area. I'm not entirely sure how it does that though. It's a concept that comes up in organic chemistry though. Dish soap and things like that can act as "surfactants" because they are amphiphilic (have nonpolar and polar components).
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