Age could be a factor, considering that two out of two cases described in the literature occurred in patients over 75; the volume of 40 ml of anesthetic solution may be another factor; patient body build, the distance between the infraclavicular fossa and the phrenic nerve; the interfascial infiltration distribution outside the perineural aponeurosis; and, of course, the individual anatomical variations.
Además, la contextura del paciente, la distancia desde la fosa infraclavicular hasta el nervio frénico, la infiltración interfascial fuera de la aponeurosis perineurovascular que puede difundirse y, por supuesto, las variaciones anatómicas interindividuales.