U.S. stock index futures pointed to a higher open on Wednesday after a highly-volatile session for China's Shanghai Composite, with investors left largely unimpressed by the stimulus measures from the People's Bank of China.

Investors are finding it difficult to know which direction to turn, with global indices flipping wildly between gains and losses after brutal selling seen at the start of the week. China's benchmark Shanghai Composite finished down 1.3 percent after fluctuating throughout the day.