It is known that $$\int_ 0^{\infty}\frac {e^{-x - \frac {1} {x}}} {x}\, dx=2 K_0(2)$$, ,but now I want to got the closed form approximate result of $$\int_ 0^a\frac {e^{-x - \frac {1} {x}}} {x}\, dx$$, I have searched the classic Table of Integrals, Series, and Products, but there is no pattern match this situation. Is there some approaches to the problem?