\documentclass{standalone}
\usepackage{tikz}
\begin{document}
\begin{tikzpicture}[>=latex, inner sep=0pt, node distance=2.8cm,
rec/.style={rectangle, draw=black, fill=blue!20, minimum height=1cm,
text width=5cm, align=center},
side ways/.style={rectangle, rotate=90},
dummy/.style={}
]
\node (d1) [dummy] at (0,0) {};
\node (r1l) [rec, left of=d1] {\# of records identified through database searches};
\node (r1r) [rec, right of=d1]{\# of additional records identified through other sources};
\node (r2) [rec, text width=8cm, below of=d1]{\# of records after duplicates removed};
\node (r3l) [rec, text width=3cm, below of=r2]{\# of records screened};
\node (r3r) [rec, text width=3cm, right of=r3l, xshift=1cm]{\# of records excluded};
\node (r4l) [rec, text width=3cm, below of=r3l]{\# of full-text articles assessed for eligibility};
\node (r4r) [rec, text width=3cm, below of=r3r]{\# of full-text articles excluded, with reasons};
\node (r5) [rec, text width=4cm, below of=r4l]{\# of studies included in qualitative synthesis};
\node (r6) [rec, text width=4cm, below of=r5]{\# of studies included in quantitative synthesis (meta-analysis)};
\node (t1) [side ways, above of=r1l]{Identification};
\node (t2) [side ways, left of=t1, xshift=-1.4cm]{Screening};% shifted by half the node distance
\node (t3) [side ways, left of=t2, xshift=-1.4cm]{Eligibility};
\node (t4) [side ways, left of=t3]{Included};
\draw[->] (r1l) -- (r2);
\draw[->] (r1r) -- (r2);
\draw[->] (r2) -- (r3l);
\draw[->] (r3l) -- (r3r);
\draw[->] (r3l) -- (r4l);
\draw[->] (r4l) -- (r4r);
\draw[->] (r4l) -- (r5);
\draw[->] (r5) -- (r6);
\end{tikzpicture}
\end{document}