Adding the Third Dimension - Learning Windows 8 Game Development - page 264

If you are using an index buffer, you can use the following method:
m_d3dContext->DrawIndexed(
indexCount,
startingIndex,
baseVertex
);
This is pretty similar to the last one; however, here you can also define which vertex
in your buffer represents index 0. Sometimes, you may want to use this when you
have multiple meshes within a single vertex buffer and you have index buffers for
each mesh rather than the entire buffer. You can rebase the vertex buffer so that
you're referring to the correct vertices.