boermedicals
https://www.boermedicals.com/resources/blog/working-principle-and-clinical-application-of-pneumoperitoneum-needle.html
The working principle of the veress pneumoperitoneum needle
The pneumoperitoneum needle has a spring protection device inside. When puncturing the abdominal wall, the needle core retracts into the needle sheath due to resistance, and the pointed end of the needle sheath can pierce the abdominal wall. When the needle sheath punctures the peritoneum and enters the abdominal cavity, the resistance disappears and the needle core pops out of the needle sheath under the action of the spring, making the front end of the pneumoperitoneum needle blunt to avoid damaging the organs in the abdominal cavity. However, it should be noted that the pneumoperitoneum needle will lose its protective function when there are adhesions in the peritoneal cavity.