It happens to the best of us. Whether you're an action-adventure lady-in-black slipping through dark alleys with criminals hard on your tail, or a fantasy princess in the front lines giving her life for her kingdom, sometimes we get stabbed in the chest.
As a writer, do you actually know what happens next? As a reader, are you taken in by pretty falsities or can you tell if she should have died or not? Let's go nitty-gritty.
So where you get stabbed matters.
First, let's say the knife goes in on the right side, anywhere along the body wall between the first and eighth intercostal spaces. Intercostal space means space between your ribs. Because your ninth rib (like all your ribs) curves downward, only the very top part of the eighth space, above the ninth rib, and towards the back, counts with the rest of the stab area we're talking about: we're talking an area roughly from your collarbone to about a hand's-width and a half below your breasts, on the right side. (If you want to be more exact, you can count ribs by remembering your collarbone is about above your second rib, and moving down from there) In this area, on the right side, your evil bad guy only needs to jab his knife between two ribs about 4 cm in to hit a lung. Then what?
As soon as you puncture your heroine's right lung, it will begin to shrivel up. Why? Two reasons. First, now there's a hole in her chest wall letting air in, and that air will push on her lung, crushing it. Your body works hard to maintain a perfect negative pressure to allow you to breathe, and that's totally thrown off when there's a puncture in the wall creating a positive air pressure. Second, you punctured her lung, so now it doesn't have the air in it to puff it up and help it push back against the air coming in through that hole. If you hadn't punctured her lung, at least when it was full of air it could push back a little. Every successive breath she'd be shrinking her lungs, letting more air in through that hole in her body wall to crush her lung--but at least she'd have a few successive breaths. But we're not talking about that. We're talking about your heroine with a punctured lung. Because there isn't really any space between your body wall and lung anyway—the space that exists is a “virtual space,” and it's just a little layer of mucous cells—it's highly unlikely that you'll puncture the thoracic wall and somehow manage to stop JUST ONE CELL LAYER SHORT of her lung. If she's super-lucky, or she's got a divine protection thing going on, that's something else, of course.
So your heroine's chest will fill with air—that's called pneumothorax. She'll feel a heavy, pressurized pain like there's a refrigerator crushing one side of her chest, or like something's sitting on her, or maybe like something's trying to get out of her chest every time she breathes. If she's got inner demons or a magical realism religious situation going on, you can incorporate that into this feeling. If your heroine's in the 20-21st century era or afterwards, the scifi wizard/spaceship's doctor will see her chest X-ray present with two uneven black hollows where lungs belong. In one side, the black hollow will look really large, and in the other it'll look pretty small, with the air tubes and the heart squished into each other like little white blobs.
What's the prognosis? (How likely is she to survive?) Well, if you don't get her medical help, she's breathing with only one lung, and she'll begin to feel dizzy. The pressure build up will eventually get so bad that you're crushing the non-punctured lung. Her heart will begin to work really, really hard, because it detects that her whole body isn't getting enough oxygen, and your heart always thinks not enough oxygen is its fault. The harder her heart's working, the more oxygen it needs. That sucks, because there isn't enough oxygen for it, so now you've got heart cells closest to the blood vessels eating up all the oxygen, and the heart cells downstream will suffocate and die. That's called ischemia, and it's how you get cardiac arrest. The harder her heart's working, the more her chances of survival plummet—the Annal of Thoracic Surgery found that survivors of lung lacerations tended to have a heart-rate of 107 bpm, which is still elevated, but not as high as the 130 bpm average for non-survivors. Bottom line, you can't breathe with only one lung. Eventually, her heart will die, she'll lose oxygen to her brain, and she will die. Because she can't breathe and her heart-rate's freaking out, she's likely feeling panicky, even if she's a super-calm person.
How will you save her?
Tune in next time to find out.
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All information from Grant's Atlas of Anatomy, Lippincott's Illustrated Q&A of Anatomy & Embryology, Moore's Essential Clinical Anatomy Third Edition, and the January 2010 article by Nishiumi N., et al, on pulmonary laceration in the Annal of Thoracic Surgery.