Table 1. The information of these 7 included studies.

Author and year of publication	Location of study	Sample size	Primary outcomes	Inclusion criteria (exclusion criteria)
Dean et al. 2014 [11]	Spain	63	Surgical time; surgical blood loss; drain time; drainage fluid volume of first 3 days.	Patients with squamous cell carcinoma (SCC) of the oral cavity without any treatment before surgery.
Ferri et al. 2013 [8]	Italy	61	Operative time; intraoperative blood loss; drainage fluid volume of first 2 days; postoperative pain; hospital stay; shoulder syndrome.	Inclusion criteria: age >18 years old; acceptance to participate in the study; scheduled neck dissection (ND) with Primary head and neck SCC. Exclusion criteria: preoperative medication or irradiation; coagulation disorders; pregnancy; case in which the ND specimen could not be separated from the primary tumor.
Koh et al. 2008 [12]	Republic of Korea	65	Operating time; grade of intraoperative bleeding; drain time; duration of hospital stay.	Patients with thyroid papillary carcinoma; and excluding patients who required lateral compartment ND or mediastinal dissection for preexisting lymph node metastasis or had clinical or laboratory indicators of coagulation disorders.
Miccoli et al. 2009 [15]	Italy	37	Operative time; drainage volume of 24hours and 48hours.	Patients with the diagnosis of papillary thyroid carcinoma and lymph node metastases in the lateral compartment.
Salami et al. 2008 [16]	Italy	20	Duration of operation; intraoperative blood loss of first 3 days	Patients with laryngeal carcinomas, extended up to the base of the tongue; cervical metastatic lymph nodes at levels II, III, and IV; and a negative evaluation for metastatic disease.
Shin et al. 2013 [7]	Republic of Korea	59	Operative time; intraoperative blood loss; suction drainage amount; drainage duration.	Inclusion criteria: age >18 years old; the preoperative diagnosis of all the patients was HNSCC; only tumors originating from the oral cavity, oropharynx, hypopharynx, and larynx. Exclusion criteria: the ND specimen could not be separated from the primary tumor.
Walen et al. 2011 [14]	Canada	34	Operative time; intraoperative blood loss; vascular complications; neurologic complications; drainage fluid volume of first 48 hours and 1 week; hospital stay.	Inclusion criteria: age >18 years old; HNSCC need a levels I–IV ND. Exclusion criteria: if there was any prior treatment for head and neck cancer or if they were unwilling or unable to give informed consent.