> For the complete documentation index, see [llms.txt](https://docs.snomed.org/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.snomed.org/snomed-ct-specifications/snomed-ct-editorial-guide/readme/authoring/domain-specific-modeling/procedure/index-2/index/centesis.md).

# Centesis

*Centesis* may be defined as the act of puncturing a body cavity or space with a hollow needle and drawing out fluid. Each centesis procedure involves both a puncture action and a needle aspiration action. It is correct to have two relationship groups for centesis procedures.

One group has a Method (attribute) of Puncture - action (qualifier value) and a Procedure site - Direct (attribute) of the structure being punctured.

A second group has a Method (attribute) of Aspiration - action (qualifier value) and a Procedure site - Indirect (attribute) of the space being aspirated.

* For example,
  * 91602002 |Thoracentesis (procedure)| has:
    * Role group 1:
      * Method = Puncture - action
      * Procedure site - Direct (attribute) = Pleural membrane structure (body structure)
      * Using device = Needle, device
    * Role group 2:
      * Method = Aspiration - action
      * Procedure site - Indirect (attribute) = Pleural cavity structure (body structure)
      * Using device = Needle, device

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