It appears to me that the reproach made by user Laurent S. is relevant. Although it might not be evident before a spell of thinking what is not quite right, a quick reading leaves some impression of incoherence.

I      The word "facteur" is defined as follows.

(TLFi, B.) − Chacun des agents, des éléments qui concourent à un résultat.

The word "survenir", here, means this (I believe).

(TLFi, B. 1. b) Se produire brusquement, brutalement, de manière inopinée.

Things of which you can say that "elles se produisent" must be actions, and at that they must be of the type that can start in a rather unpredictable manner. (Of course the meaning can’t be that of "Cet artiste s’est produit dans notre ville plusieurs fois.", this must be clear.)

• L’accident s’est produit/est survenu au moment le plus terrible.
• Une altercation s’est produite/est survenue entre M. Arvel et son fils.
• La première attaque s’est produite/est survenue au milieu de la nuit.
• Sa naissance s’est produite/est survenue en l’un des derniers jours de l’automne.

Moreover, the word "facteur" is not the name of an action but that of an entity that does an action or to which correspond usual actions, since this word is defined primarily as "agent" ("agent" in English). On top of that, whether as an active part of a context or only as a potentially active one, the "facteur" is part of this context (agents qui concourent à un résultat) and therefore one is not often taken by surprise since there is an awareness of it and most often preparations aiming at counteracting the effect; this is generally true in the medical field (surgical complications for instance).

• La température de la pièce est un facteur dans le déroulement de cette expérience.
  (You can’t very well say "La température est survenue dans l’expérience" but you can say much more normally "une baisse/hausse de température est survenue…")

II     What can be said for the pair "facteur/survenir" is valid for "adaptation/survenir", there being however an additional error—that has been perceived by user Laurent S. (see same comment above)—: "adaptation des doses" being an action initiated by a human entity the random aspect rendered by "survenir" is incongruous.

III*       As a correct formulation I propose the following sentence.

• […] des facteurs perturbateurs du niveau d’anticoagulation qui ne sont pas liés au mois saint peuvent se manifester, ainsi (que le)/(qu’un) besoin d’une adaptation des doses pour les sujets en sous ou surdosage