Let the tangents at the points \( P \) and \( Q \) on the ellipse \( \dfrac{x^{2}}{2} + \dfrac{y^{2}}{4} = 1 \) meet at the point \( R(\sqrt{2},\, 2\sqrt{2} - 2) \). If \( S \) is the focus of the ellipse on its negative major axis, then \( SP^{2} + SQ^{2} \) is equal to __________________.
