My character suffers the following injuries. I want the injuries to be severe enough that they require immediate surgery, but also that he recovers after about a month in the hospital and a stay in rehab.
1. Character is standing in the road, tries to run but is hit by the car front on. Body smashes into the windscreen, sending him up into the air.
2. Hits his head on the pavement on landing and suffers broken bones as a result.
3. He blacks out from the impact and wakes up several hours later. In this instance, would he be able to survive for several hours with the kinds of injuries he could have?
4. Possible injuries I thought he could have included: bleeding on the brain, broken leg/s and/or arms, fractured ribs which could cause a puncture to one of his lungs.
5. As a result he suffers from retrograde amnesia when he wakes up at the scene because of the injuries to his brain. Cannot remember his name/where he is or other events in his memory. Again here I am not sure what kind of specific head trauma could cause this.
6. After surgery to the brain, he is put into an induced coma to monitor the swelling. He will eventually wake up from this about a month later.
The accident you describe would include some very serious injuries— perhaps not even survivable. It’s not just the injuries the character suffers getting thrown from the impact onto the pavement, but also the injuries he suffers from getting hit by the car. An impact that is so violent that it throws someone into the air would also likely shatter the windshield indicating to EMS responders that there was a lot of violent energy associated with this collision— which means bad things for the patient.
My first opinion is if you want this character to wake up in a few hours would be that he doesn’t fall directly on his head after he’s thrown into the air from the first impact. Overall, for your scenario, you might want to lessen the violence of this crash if you want him up in a few hours. It wouldn’t be surprising for this patient to require surgery to fix broken bones and/or internal bleeding.
A pedestrian surviving this crash is not impossible but it is more on the improbable side. This patient will have a lengthy hospital stay. May not wake up for days or months— not just hours. What you outline is a high speed impact to a pedestrian.
To answer some of your medical questions— surgery may be required for the bleeding on the brain depending on its location. All patients who have a brain bleed do not necessarily go to surgery. A punctured lung will require a chest tube to be placed which further complicates your patient’s medical picture. This patient would be placed on a breathing machine for sure to stabilize him until all these injuries could be sorted out.
Could a patient with a significant brain bleed be conscious at the scene after the accident? Yes. There is a specific type of brain bleed that fits this scenario called an epidural bleed. It does have a characteristic lucid period before the patient becomes unconscious again. It does require surgery to correct. If no surgical intervention is done then the patient will likely die. Honestly, as a writer, you have a lot of leeway in regards to what to do with amnesia. Any type of traumatic brain injury (and this certainly qualifies) could cause amnesia.
Medically induced comas are used frequently in medicine as a way to help control brain swelling. However, the medicines are not used forever. Peak brain swelling usually occurs 48-72 hours after the injury. After this time has passed, the medical team will evaluate when to decrease the medications keeping the patient in the coma. Keep in mind, even after these medications are discontinued, the patient may never wake up. Further studies would need to be done to determine the extent of the damage to his brain. These changes will evolve over time becoming more stable the more time that goes on.
My recommendation would be to lessen the severity of the crash. The car hits him, he hit the windshield, breaks it and then falls to the ground. This alone could cause a femur fracture and brain injury for which he could suffer amnesia and require surgery. If it’s an epidural bleed then he gets surgery, perhaps with some swelling and therefore the medically induced coma, but wakes up in a month. The leg is set in surgery with pinning or a rod. I think just having these two things is enough for your scenario.
All the rest might prove too complicating.