The application discloses a set of surgical instruments that may be used to access a human or animal body cavity for medical purposes without causing damage to internal tissues or organs therein, and methods of using the same. The instruments include a safety needle and flexible sheath that may be coupled together and used to establish a minimally invasive method to access a targeted body cavity while preventing or reducing damage to organs or tissues within the targeted cavity. Additional instruments are included within the invention that may be used to establish an access port in the wall of the targeted cavity. That port may be used to introduce catheters or other instruments into the body cavity. It may also be used as a drainage tube for draining or injecting gases and/or fluids from or into the targeted cavity.