The grades of evidence (I-III) and levels of recommendations (I-III) are defined at the end of the "Major Recommendations" field.
Level I
There are insufficient data to support a Level I recommendation for this topic.
Level II
Prophylactic hyperventilation (PaCO2 of 25 mm Hg or less) is not recommended.
Level III
Hyperventilation is recommended as a temporizing measure for the reduction of elevated intracranial pressure (ICP).
Hyperventilation should be avoided during the first 24 hours after injury when cerebral blood flow (CBF) is often critically reduced.
If hyperventilation is used, jugular venous oxygen saturation (SjO2) or brain tissue oxygen tension (PbrO2) measurements are recommended to monitor oxygen delivery.
Summary
In the absence of trials that evaluate the direct effect of hyperventilation on patient outcomes, the guideline developers have constructed a causal pathway to link hyperventilation with intermediate endpoints known to be associated with outcome. Independent of hyperventilation, CBF can drop dangerously low in the first hours following severe TBI. The introduction of hyperventilation could further decrease CBF, contributing to the likelihood of ischemia. The relationship between hyperventilation and metabolism, as well as cerebral oxygen extraction, is less clear. The one study that evaluated patient outcomes strongly suggests that hyperventilation be avoided for certain patient subgroups.
Definitions:
Grades of Evidence
Class I - Good quality randomized controlled trial (RCT)
Class II - Moderate quality RCT, good quality cohort, or good quality case-control
Class III - Poor quality RCT; moderate or poor quality cohort; moderate or poor case-control; or case series, databases, or registries
Levels of Recommendation
Levels of recommendation are Level I, II, and III, derived from Class I, II, and III evidence, respectively.
Level I - Recommendations are based on the strongest evidence for effectiveness, and represent principles of patient management that reflect a high degree of clinical certainty.
Level II - Recommendations reflect a moderate degree of clinical certainty.
Level III - Recommendations for which the degree of clinical certainty is not established.