Shares of Silk Road Medical Inc. soared in their public debut Thursday, enough to pace all gainers on the major U.S. exchanges. The first trade was at $33.15, or 66% above the $20 initial public offering price, at 11:36 a.m. Eastern. Since then, the stock has traded in a range of $32.73 to $37.30, and was recently 85% above its IPO price at $36.96. The medical device company sold 6 million shares in the IPO to raise $120 million, and could raise up to $138 million if the underwriters exercise all the options granted to buy additional shares. At the IPO price, the company was valued at $604.2 million. The IPO priced at the top of the expected range of $19 to $20, up from original expectations of $15 to $17, when the company said it has expected to offer 4.7 million shares for sale. The company went public at a time that the Renaissance IPO ETF has run up 32% year to date, while the S&P 500 has gained 15%.