It's sometimes not worth following every rule. Use this and you are fine.
p Lorem ipsum, <b>volutpat</b>. Ut wisi enim ad minim veniam.
You can also use Markdown directly in Slim if a lot of bolds and italics appear in your text, for example:
p Normal slim syntax.
markdown:
Lorem Markdownum, **volutpat**. Ut wisi *enim* ad minim `veniam`.