Culdocentesis

Culdocentesis is a procedure in which peritoneal fluid is obtained from the cul de sac of a female patient. It involves the introduction of a spinal needle through the vaginal wall into the peritoneal space of the pouch of Douglas. Prior to the wide availability of ultrasonography, it was considered particularly valuable in the diagnosis of ectopic pregnancy, at a time when 97% of ectopic pregnancies ruptured before diagnosis.

Recently, the frequency of tubal rupture has decreased. ^[1] Thus, the incidence of hemoperitoneum has declined, and the use of culdocentesis has decreased. In addition, ultrasonography, with its improved resolution and availability, has virtually replaced culdocenteses as the test of choice. The sensitivity and specificity of echogenic fluid found on ultrasound for establishing hemoperitoneum are both 100%, compared with 66% and 80%, respectively, for culdocentesis, and the negative predictive value of a nondiagnostic culdocentesis is 25% compared to 100% for echogenic fluid in the ectopic pregnancy subgroup of patients. Additional advantages of ultrasonography include its noninvasive nature and the provision of additional information about the pelvis. ^[2] For more information, see Medscape Reference article Ectopic Pregnancy Imaging.

Anatomy

The pouch of Douglas (recto-uterine pouch) is formed by reflection of the peritoneum between the rectum posteriorly and the posterior surface of the uterus anteriorly. The pouch often contains small intestine and a small amount of peritoneal fluid. It is the most dependent intraperitoneal space in both the upright and the supine position. Blood, pus, and other free fluids in the peritoneal cavity pool in the pouch because of its dependent location.

In the current practice with easy access to ultrasonography, culdocentesis is rarely performed for most of the indications below.

• To diagnose suspected leaking or ruptured ectopic pregnancy in the following clinical situations: ^{[1, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12]}

  • Hemodynamically unstable patients when ultrasonography is not immediately available

  • When ultrasonography or laparoscopy is not available

• In place of diagnostic peritoneal lavage to detect hemoperitoneum following blunt abdominal trauma, particularly in patients with previous abdominal surgery. ^{[13, 14, 15]}

• To diagnose ruptured ovarian cysts in patients with sudden onset of pelvic pain, sometimes following intercourse or a pelvic examination, or occurring midcycle.

• To obtain fluid for culture to aid in the diagnosis and treatment of pelvic inflammatory disease (PID).

• For diagnosis and treatment of ascites

In a set of guidelines developed to aid in the prevention and treatment of ovarian hyperstimulation syndrome (OHSS), ^[16] Corbett et al recommended that in patients with severe OHSS, outpatient culdocentesis be considered in the prevention of disease progression. ^[17]

See the list below:

• Pelvic mass, including ovarian tumors, tubo-ovarian abscesses, appendiceal abscesses, and pelvic kidney

• Fixed retroverted uterus: Mobile retroverted uterus may be manipulated out of the way by lifting on the cervix with a tenaculum.

• Coagulopathy

• Prepubescence: This limitation is suggested on the basis of anatomy, as the procedure would be difficult to perform through a small prepubertal vagina.

• Noncooperative patient

See the list below:

• Lidocaine (1-2%) with epinephrine is injected into the vaginal mucosa of the posterior fornix in the midline about 1 cm inferior to the point at which the posterior vaginal wall joins the cervix. ^[18]

See the list below:

• Bivalve vaginal speculum (Graves or Pederson)

• Tenaculum or Allis clamp

• Ring forceps

• Spinal needle, 18 gauge (ga)

• Sterile swabs or sponges

• Monsel solution (ferric subsulfate) for hemostasis

• Butterfly needle, 19 ga

• Needle, 25 ga, 1 inch

• Syringe, 20 mL

• Antiseptic (eg, povidone-iodine solution [Betadine])

• Lidocaine (1-2%) with epinephrine

• Sterile gloves

• Specimen container

• Light source

See the list below:

• Allow the patient to walk or sit up for a short time prior to the procedure to allow gravity to help bring the peritoneal fluid to the cul de sac.

• Place the patient in dorsal lithotomy position with the feet in stirrups. Elevating the head of the bed helps the intraperitoneal fluid gravitate to the retroperitoneal pouch for easier aspiration.

See the list below:

• Obtain informed consent prior to the procedure.

• Premedicate with narcotics or sedatives as needed.

• Radiographs, when indicated in stable patients, are taken prior to culdocentesis to avoid possible confusion if a pneumoperitoneum is detected following the procedure.

• Perform bimanual pelvic examination to rule out a fixed pelvic mass and to assess the position of the uterus prior to culdocentesis. ^[19] A bulging of the cul de sac into the posterior fornix suggests pooling of intraperitoneal fluid.

• Prepare the vagina with povidone-iodine solution.

• Place the patient in dorsal lithotomy position with the feet in stirrups. Elevate the head of the bed.

• Insert a bivalve vaginal speculum into the vagina and grasp the posterior lip of cervix with a tenaculum or ring forceps. In patients with retroverted uterus, anterior tenaculum placement is preferred, as it helps straighten the uterus. The patient should be forewarned that grasping the cervix with the tenaculum will be painful. Some practitioners inject the tenaculum site with local anesthetic.

• Open the speculum as wide as the patient can tolerate to expose the posterior fornix and stretch the vaginal mucosa taut, making the procedure easier. A medium Graves speculum is suitable for most patients. In a patient with a small vagina or who has not had sexual intercourse, use a Pederson speculum instead. See image below.

  Culdocentesis procedure.

• With help of the tenaculum, apply forward traction on the cervix. This helps stretch the vaginal mucosa and pulls the mobile uterus out of retroversion in case of a retroverted uterus.

• Using a 25-ga needle, inject 2 mL of lidocaine with epinephrine into the vaginal mucosa of the posterior fornix in the midline about 1 cm inferior to the point at which the posterior vaginal wall joins the cervix. ^[18]

  • Randomized trials have not consistently demonstrated a significant reduction of pain with topical anesthetics. ^{[20, 21]}

  • Although local anesthesia is often unnecessary, it may be advantageous if multiple attempts at culdocentesis are needed. In addition, the epinephrine may reduce bleeding associated with the needle puncture by causing vasoconstriction.

  • Although culdocentesis is generally perceived as quite painful, some practitioners do not use local anesthetics for several reasons. First of all, vaginal mucosa is rather vascular in the posterior fornix. Needle puncture for anesthesia would cause confusing bleeding into the posterior cul de sac. Second, some of the local anesthetic agents might be aspirated as clear or blood-tinged fluid. Finally, it may be of limited effectiveness.

• Attach an 18-ga spinal needle to a 20-mL syringe with 2-3 mL normal saline and advance it about 2-2.5 cm using a rapid deliberate thrust while injecting 0.5-1 mL of saline through the point of lidocaine infiltration between the uterosacral ligaments in the posterior fornix. ^{[18, 22]}

  • If the puncture site is too high, the needle hits the substance of the cervix or uterus. If it is placed too low, the needle may enter the rectum or tunnel beneath the posterior peritoneum of the cul de sac.

  • The spinal needle is inserted parallel to the lower blade of the speculum.

  • Saline (rather than air) is preferred because if air is used, one must be careful in interpreting the presence of free peritoneal air on subsequent radiographs.

  • Free flow of saline confirms the correct placement of the needle in the cul de sac. It may otherwise be within the wall of the uterus or intestine. In that case, withdraw and redirect the tip of the needle until saline flows freely upon injection.

  • Some practitioners use a 19-ga butterfly needle held with ring forceps instead of a spinal needle for good control of the needle during the puncture and for a built-in guide for depth. ^[18]

  • The needles used for the local anesthetic and the puncture should be attached to a 20-mL syringe. A smaller syringe may not be long enough to allow adequate control of the needle, and the practitioner's hand may block the view of the puncture site if a smaller syringe is used.

• Apply negative pressure (pull back the syringe plunger) while slowly withdrawing the needle. Avoid aspirating any blood that has accumulated in the vagina from previous needle punctures or from cervical bleeding because this may give the false impression of a positive culdocentesis.

• If no fluid is withdrawn, withdraw the needle and reintroduce it, directing slightly to the left or right of the midline. Avoid directing the needle too far laterally, which can result in the puncture of a mesenteric or pelvic vessel.

• Observe any blood aspirated from the cul de sac for several minutes for clotting, which indicates a traumatic tap. A spray of bloody, frothy fluid is often seen as the needle emerges from the mucosa. This is blood from the rich venous plexus of the vaginal mucosa and should not be interpreted as a bloody tap. Blood-tinged or frankly bloody fluid can be spun for hematocrit and checked for clotting. Turbid or clear fluid should be examined microscopically after Gram stain and sent for aerobic and anaerobic culture. However, cultures obtained from culdocentesis fluid do not always accurately reflect the bacteriology of infection, as they are frequently contaminated by vaginal flora. Cytology can be run on this aspirate if malignancy is suspected.

• Apply pressure for any bleeding at the puncture or tenaculum site. Rarely, Monsel solution is used to cauterize the bleeder.

Assessment

See the list below:

• Normal culdocentesis result: A normal culdocentesis result in the absence of pathology should yield only 2-4 mL of clear to straw-colored peritoneal fluid.

• Nondiagnostic result

  • A dry tap (return of no fluid) has no diagnostic value; the needle may simply not have found the pool of fluid.

  • Nondiagnostic results are returned in 15% of culdocentesis procedures.

  • A dry tap should not be used to raise or lower the clinician’s suspicion of ectopic pregnancy, since 15% of patients with ectopic pregnancy may have a nondiagnostic culdocentesis.

  • When a dry tap occurs, the practitioner must resort to ultrasonography, laparoscopy, or other techniques, or rely completely on his or her clinical acumen to make the correct diagnosis.

  • Aspiration of less than 2 mL of clotted blood is nondiagnostic; this blood might have come from the vessel at the puncture site of the vaginal wall.

  • As a general rule, hematocrit level below 12-15% of the patient’s usual level indicates either a minor amount of bleeding or a hemorrhagic tap. ^[3] About 15% of ectopic pregnancies have negative or nondiagnostic culdocentesis results. ^[5]

• Positive result

  • A positive tap is one in which more than 2 mL of nonclotting blood is obtained. Absolute volume may be related to the needle position or the rate of bleeding, so larger amounts of blood have no particular significance. Approximately 82-95% of ectopic pregnancies display nonclotting blood on culdocentesis. ^[3]

  • Romero et al reported that an ectopic pregnancy was found in 99% of cases when a positive pregnancy test and a positive culdocentesis result were present. ^[7] However, the bleeding in a ruptured ectopic pregnancy is occasionally so brisk that the blood does not have time to become defibrinated and, thus, clots. The hematocrit level of this blood specimen, if from a ruptured ectopic pregnancy, is more than 12-15% in 97% of cases. ^{[3, 4]}

  • A positive culdocentesis result in the presence of ectopic pregnancy does not necessary indicate tubal rupture, as 45-60% of ectopic pregnancies with peritoneal blood may be unruptured.

  • Intraperitoneal blood from a source other than ectopic pregnancy (eg, ovarian cyst, ruptured spleen) may remain unclotted after aspiration for days in the syringe as a result of the defibrination activity of the peritoneum. Thus, a positive culdocentesis in the presence of a positive pregnancy test does not always prove an ectopic pregnancy. ^[23] The false positive rate of this test is around 2-9%. A ruptured corpus luteum cyst in the presence of an intrauterine pregnancy is probably the most common cause of a false-positive test result.

  • Hemoperitoneum has been noted to occur in 45-62% of cases of unruptured ectopic pregnancy proved at surgery. ^{[5, 7, 23]}

  • A positive culdocentesis result can also occur in nonpregnant women (eg, retrograde menstruation).

• Negative result

  • A culdocentesis is considered negative when the aspirated fluid is pus, cystic, or straw-colored.

  • Aspiration of clear fluid is generally reassuring, but more than 10 mL of clear fluid most likely indicates a ruptured ovarian cyst, aspiration of an intact corpus luteum cyst, ascites, or, possibly, carcinoma. It does not automatically rule out ectopic pregnancy, since ectopic pregnancy may coexist with other pathology. ^[24]

  • Aspirated dark brown, chocolate-like material represents old blood. A ruptured endometrioma is the most likely the cause, but any cysts that contain old blood, including cyst of a chronic ectopic pregnancy, can contain chocolate-like fluid.

  • Purulent fluid indicates infection. Pelvic inflammatory disease is the most common gynecological cause, but nongynecological causes such as diverticulitis and appendicitis should also be considered in the differential diagnosis.

  • Rarely, greasy or fatty fluid is obtained during culdocentesis. Such fluid is from a ruptured teratoma.

  • A false-negative result is produced in 15% of ectopic pregnancies; these pregnancies are generally unruptured.

  • A negative result excludes hemoperitoneum and tubal rupture.

• For more information on interpretation of culdocentesis fluid, see the table below.

Table. Interpretation of Culdocentesis Fluid (Open Table in a new window)

Complications are rare with culdocentesis. However, the following complications can occur:

• A deceptive result: This could provide unwarranted reassurance or lead to unnecessary treatment.

• Rupture of an unsuspected tubo-ovarian abscess (most serious), ^[19] ovarian teratoma, or endometrioma: This could result in pelvic peritonitis.

• Puncture of the bowel or pelvic kidney: Puncture of the bowel occurs relatively frequently, but this occurrence does not generally result in serious morbidity. Occasionally, air or fecal matter can be aspirated, confirming inadvertent puncture of the rectum. Although this may be disconcerting, it is seldom of serious clinical concern and requires no immediate change in therapy.

• Bleeding from the puncture site: Very rarely, the source could be large pelvic vessels.

• Puncture of a malignant ovarian cyst: This could disseminate malignant cells throughout the peritoneal cavity.

• Rupture of tubal pregnancy

• Needle injury to intrauterine pregnancy in a retroverted uterus

In the emergency setting, culdocentesis can be a critical diagnostic procedure. In an unstable patient with a strong clinical suspicion for a ruptured ectopic pregnancy, the procedure may facilitate lifesaving surgery by confirming the diagnosis without the need for time-consuming ultrasonographic examinations. Because culdocentesis is a safe and simple procedure, every practitioner who deals with the emergency evaluation of women, particularly women of childbearing age, should know how to perform this procedure. This is particularly true for physicians practicing in areas with no immediate availability of ultrasonography. More recent studies from developing countries have shown that this procedure helped make the diagnosis of tubal pregnancy in more than 70-80% of patients. ^{[25, 26]}

By no means should culdocentesis be used for definite diagnosis of tubal pregnancy in a stable patient when ultrasonography is available, since a tubal pregnancy may not have ruptured or leaked into the peritoneal cavity. In addition, blood aspirated during culdocentesis does not provide information concerning whether the blood is from an ectopic pregnancy or from some other cause of intraabdominal bleeding. Thus, using the procedure on a widespread basis, rather than in unstable emergent situations, could be misleading. ^[27]