The NHL CBA sets out the factors to consider when looking to suspend a player (or impose supplementary discipline). It's found at Exhibit 8 of the CBA and is entitled Procedures Relating To Commissioner Discipline.
Here is what Brendan Shanahan needs to consider when deciding whether to impose a suspension:
6. Factors In Determining Supplementary Discipline
In deciding on supplementary discipline, the following factors will be taken into account:
(a) The type of conduct involved: conduct outside of NHL rules; excessive force in contact otherwise permitted by NHL rules; and careless or accidental conduct. Players are responsible for the consequences of their actions.
(b) Injury to the opposing Player(s) involved in the incident.
(c) The status of the offender, and specifically whether he is a "first" or "repeat" offender. Players who repeatedly violate NHL rules will be more severely punished for each new violation.
(d) The situation of the game in which the incident occurred: late in the game, lopsided score, prior events in the game.
(e) Such other factors as may be appropriate in the circumstances.
This is why you often hear things like whether the player is a "repeat offender" (6c) and whether the hit was intentional (6a).
The section also provides that "Players are responsible for the consequences of their actions". This seems to apply when a player intentionally goes after another. However, "actions" would not include a case where two players inadvertently collide (as per column below on Wolski/Alfredsson), as the term "actions" seems to mean an act delivered with intent.
Generally speaking, intent can be very difficult to determine with certainty. For the most part, a player won't say he intended to hurt another player. Reference can be had to the surrounding circumstances in seeking to determine intent, and in some cases, it may be clear whether intent played a role. Still, short of being able to crawl into a player's head, determining intent can be tough. As well, things become a bit murkier where a decision maker tries to determine what part of a hit was intended - the general body contact or the specific contact to the head.
These decisions are tough to make and a lot of scrutiny will ultimately fall on Shanahan since the NHL has identified him as the person responsible for making the decisions. Perhaps to slow Shanahan's aging process, the NHL may want to consider a committee arrangement whereby a consensus is reached by a group of people and then that decision is delivered by the NHL or a designated executive.