Quote from Candyn
I have questions.
Why do we not want to hyperventilate a TBI patient?
And when you said "I've seen it done in our ED, but only when it appears that herniation is imminent and they're just trying to keep the brain together while transporting the patient to the OR." Does that mean it is ok to hyperventilate if they have imminent herniation? Why is that?
Hi there, most of the recent observational / clinical research shows that we shouldn't hyperventilate in cases of TBI for the reasons outlined by Esme12. The theoretical benefits described are the reason it used to be standard practise which is why some clinicians still do it. Hyperventilation compromises cerebral oxidative metabolism, can actually cause cerebral ishchaemia and worsen cerebral oedema, and most international guidelines advise against it. The move these days is toward aiming for a therapeutic PCO2 (in fact, normal to mild hypercapnoia), optimising cerebral blood flow and using other methods to lower ICP, such as definitive surgical management or IV administration of hypertonic solutions such as hypertonic saline or mannitol. "If ICP increases to equal MAP, CPP becomes zero, resulting in complete brain ishchaemia and brain death"(Merck). Anectodally, women tend to be on the receiving end of "over" ventilating for obvious reasons. To answer your question, if the patient is herniating, they are about to die, so I guess hyperventilating can be considered a "last ditch effort" because it may be felt that we can't really make it worse. So, if definitive management is an hour away, then it could be considered an option.
To give you an example, recently, we had a 60yr old lady who was hit by a cyclist, thrown backwards and sustained a large subdural. She had a prolonged loss of consciousness at scene and was GCS 14 when she arrived in ED. She remained GCS 14 for an hour or so and was about to be taken to theatre. She then (in the space of 10 minutes) dropped her GCS to 4, developed an ovoid pupil and was intubated. Neurosurg ordered mannitol and the senior ED physician hyperventilated her on the way to OT (keeping her brain together while transporting to OT). If there are focal signs of herniation such as ovoid pupils / pupillary changes, loss of reaction to light, bradycardia, decerebrate / decorticate posturing, hemiparesis, rapidly deteriorating GCS, most of our pre-hospital and ED physicians will just bag (but just at a normal rate) and may administer a dose of a hypertonic solution and rush to definitve management if possible.