Father of ancient surgery, Acharya Sushruta has mentioned various menthod of Raktmokshana i.e Shringa, Jalauka and Alabu etc. Siravedha is one of them. Full description of Siravedha has been given by Acharya Sushruta in Sushruta Samhita Sharira Sthana chapter 8. All the Siras carries all doshas in the body. There is no Sira in the body which carries either the Vayu, the Pitta or the Kapha therefore Siras should be considered as Sarvavaha. According to ayurveda, disease is the result of prakupita doshas. Siravedha, letting out noxious blood from the body and it will cure the disease or therwise it will make a clear pathway towards further treatment modalities. Siravedha is the independent procedure or treatment to cure many diseases like gradhasi (sciatica), gout, vericose pain, skin diseases etc. Siravedha is the half treatment of Shalya Tantra.
शिराव्यधचिकित्साअर्ध शल्यतन्त्रे प्रकीर्त्तितः।। सु. शा. 8/23
According to Acharya Sushruat there are 700 Siras in our body but basic Siras are mainly 40. Origin of 40 Siras is nabhi and divided into, vatta, pitta, kapha and rakta. There are 98 Avedhya Siras in our body they should not be puncture, if punctured then it will cause the disability or even death.