In a recent review of the literature about pre-hospital intubation in traumatic brain injury (TBI) and the potential impact of hyperventilation, Gaither et al. explore the potential confounders for outcomes in previous studies.
The authors provide a nice overview about the “old school” rationale for hyperventilation in TBI and why it is unlikely a good idea!
Why hyperventilation thought to be beneficial in TBI: 1) decreases arterial PaCO2 with CNS vasoconstriction 2) decreased cerebral blood flow. Net result is improved cerebral perfusion pressure (CPP). However, hyperventilation after intubation may increase intrathoracic pressure, increase JVP and subsequently decrease CPP. Hypocarbia may also lead to free radical formation and cellular damage. So net result is PaCO2 of 25 isn’t a good idea! Probably best to target into something like 35.
The authors then outline the historical concerns about pre-hospital intubation (low success rates, long scene times and complications like hypoxia). However, they argue that perhaps its not the intubation itself that may confound these “worse” outcomes, but perhaps the greater potential for hyperventilation! And the detrimental effects may in fact occur post-intubation.
There’s some evidence that in pre-hospital settings where end-tidal CO2 is closely regulated (assuming high intubation success…which probably requires well-trained personnel) that patients do better if they’re intubated…just so long as we keep their ETCO2 under control! The following is a direct quote from the article:
“There is a strong possibility that the negative effects of intubation that have been identified in several clinical trials may be due to a paradox: intubation may protect the airway and prevent hypoxia, but it also makes it easier to inadvertently hyperventilate. Consequently, although intubation is intended to reduce secondary brain injury, it may enhance it if specific, intentional measures are not taken to ensure proper post intubation ventilation“
A nice conclusion is provide (which I fits well within the general tone of the article).
“When properly performed, intubation is effective for airway protection and ensures adequate oxygenation; it also makes hyperventilation (and associated negative outcomes) easier and more likely. Optimal outcomes require choosing the right patients, achieving the highest success rates through training, and avoiding hyperventilation after intubation in patients with traumatic brain injury”
This article makes a great case for well trained medical personnel who perform pre-hospital intubations and then provide the best post-intubation care possible.
Full text pdf is available here (secure area limited to ADHB staff only – ADHB has subscription access for staff to these journals through the Philson Library at the University of Auckland School Of Medicine)