Paracentesis and thoracentesis in the emergency department

Paracentesis and thoracentesis are the two percutaneous fluid taps the Fellowship candidate is expected to perform, teach and defend under examination. Both share the same logic: the percutaneous aspiration of a pathologic fluid collection for the diagnosis (the fluid analysis) or the relief of the symptoms (the therapeutic drainage), with the ultrasound guidance, the sterile technique, the local anaesthetic and the disciplined stepwise approach. The examiner will press three things on each: the indications and the differential that the fluid will resolve (the ascites for the portal hypertension and the spontaneous bacterial peritonitis; the pleural effusion for the transudate versus the exudate), the landmarks and the stepwise technique (the ASIS and the Z-track for paracentesis, the rib-space-below-the-fluid for thoracentesis), and the complications and their immediate rescue (the bowel perforation and the ascitic fluid leak for paracentesis, the pneumothorax and the re-expansion pulmonary oedema for thoracentesis).[3][4]

Definition and indications

Paracentesis is the percutaneous needle aspiration of ascitic fluid from the peritoneal cavity. It is performed for the diagnosis of the new or the worsening ascites, the suspected spontaneous bacterial peritonitis (SBP), or the malignant ascites; and for the therapy of the tense or the refractory ascites (the large-volume paracentesis, the drainage of several litres for the symptomatic relief). The AASLD recommends that every cirrhotic patient with the ascites admitted to the hospital undergoes a diagnostic paracentesis on the admission, and any patient with a new ascites, a worsening ascites, or the clinical features of the SBP (the fever, the abdominal pain, the hepatic encephalopathy, the renal impairment) has the tap without delay.[2]

Thoracentesis is the percutaneous needle aspiration of pleural fluid from the pleural space. It is performed for the diagnosis of the unexplained pleural effusion (the fluid analysis with the Light criteria for the transudate-versus-exudate distinction, the cell count, the culture, the cytology, the pH and the glucose), and for the therapy of the symptomatic large effusion (the dyspnoea relief) or the empyema (the drainage of the frank pus). The BTS pleural disease guideline recommends the diagnostic tap for every unexplained unilateral effusion of more than 10 mm depth on the ultrasound, and the therapeutic tap for the symptomatic effusion.[5]

Contraindications

The absolute contraindications are few. For the paracentesis, an overlying abdominal wall infection (the cellulitis, the abscess) at the intended puncture site, a massively distended bowel (the intestinal obstruction with the bowel loops lying against the abdominal wall), or a non-cooperative patient who cannot hold still are the absolute ones. A severe coagulopathy is a relative contraindication, not an absolute one: the contemporary evidence confirms that the diagnostic paracentesis is safe with an INR up to 2.0 and the platelets over 50 without the routine correction, because the puncture is small, the abdominal wall is compressible, and the major bleeding rate is under 1 per cent; the FFP or the platelet cover is reserved for the markedly abnormal coagulation or the very large-bore catheter.[2][3]

For the thoracentesis, the overlying chest wall infection, the suspected empyema with a loculated collection that needs a chest drain (rather than a needle tap), and the uncooperative patient with a cough that brings the pleura against the needle are the absolute contraindications. The coagulopathy carries a higher bleeding risk than for the paracentesis because the intercostal vessels are not compressible and the hemothorax can be significant; the BTS advises a careful risk-benefit balance for the INR above 1.5 or the platelets under 50, with the correction considered for the diagnostic tap and the mandatory correction for the therapeutic tap in the coagulopathic patient. A very small effusion (under 10 to 15 mm on the ultrasound, or the no-safe-fluid-window on the ultrasound) is a relative contraindication — the tap is unsafe, the chest drain or the watchful waiting is the alternative.[5]

Relevant anatomy and landmarks

The paracentesis site is the left or the right lower quadrant. The safe landmark is 2 cm superior and medial to the anterior superior iliac spine (ASIS), in the left lower quadrant (the left is preferred — the caecum on the right is fixed and gas-filled, the sigmoid on the left is mobile and empties with the patient's positioning). The alternative is the midline 2 cm below the umbilicus in the linea alba, used when the left lower quadrant is scarred or the ultrasound shows no safe window. The ultrasound confirms the depth of the fluid pocket, the absence of the bowel between the abdominal wall and the fluid, and the safe trajectory. The abdominal wall is thinnest at the linea alba and at the ASIS, and the inferior epigastric vessels run along the posterior rectus sheath — the lateral approach away from the midline and away from the rectus muscle avoids them. [1]

The thoracentesis site is the posterior chest, where the dependent fluid collects in the seated patient. The landmark is the upper border of the rib below the fluid level, one to two intercostal spaces below the top of the effusion — never at the top of the effusion (the lung comes down as the fluid drains, and a tap at the top risks the pneumothorax). The needle is advanced over the upper border of the lower rib, avoiding the neurovascular bundle that runs along the lower border of each rib (the V-A-N — vein, artery, nerve — in the costal groove). The ultrasound, performed in the same seated position the tap will be done, marks the level of the fluid, the depth, and the safe interspace; the BTS standard is the real-time ultrasound-guided thoracentesis.[4][5][8]

Equipment

The paracentesis tray contains a ring clamp or a haemostat to stabilise the catheter at the abdominal wall (the catheter can kink or dislodge with the bowel movement), a multiple-hole catheter-over-needle (typically 18 to 20 gauge, 8 to 10 cm long) for the therapeutic drainage, a 20 to 22 gauge spinal needle for the diagnostic tap, lidocaine 1 per cent with a 25G needle for the skin wheal and a longer needle for the deeper infiltration, the syringes (5 mL for the local anaesthetic, 30 to 60 mL for the diagnostic collection), the sterile collection tubes (the aerobic and anaerobic blood culture bottles inoculated at the bedside, the EDTA tube for the cell count, the plain tube for the protein and the albumin and the amylase, the cytology container), the drainage bag for the large-volume paracentesis, the sterile gloves, gown, drape, the chlorhexidine or povidone-iodine, the gauze and the dressing, and the sharps container.[3]

The thoracentesis tray contains a catheter-over-needle (typically 16 to 18 gauge, 6 to 8 cm long) or the needle-catheter assembly for the therapeutic drainage, a 20 to 22 gauge needle for the diagnostic tap, lidocaine 1 per cent, the three-way stopcock and the collection bag or the vacuum bottle, the self-sealing valve to keep the system closed (the air entry prevention), the collection tubes (the heparinised syringe for the pH and the gas analysis, the plain tube for the protein and the LDH and the glucose, the EDTA for the cell count, the culture bottles, the cytology container), the sterile gloves, gown, drape, the chlorhexidine, the gauze and the dressing, and the sharps container. The post-thoracentesis chest X-ray is not routinely required after the ultrasound-guided uncomplicated tap, but is performed for the symptomatic patient, the air aspiration, or the difficult procedure.[4][5]

Patient preparation and consent

The consent is the discussion of the indication, the alternatives (the watchful waiting, the chest drain for the empyema, the diuretic for the heart-failure transudate), the common complications (the pain, the bleeding, the infection, the bowel injury for the paracentesis; the pneumothorax, the bleeding, the re-expansion pulmonary oedema for the thoracentesis), and the post-procedure care. The consent is documented; in the emergency or the encephalopathic patient, the procedure is performed under the emergency exception and the consent is documented after. [1]

The positioning is critical for both procedures. For the paracentesis the patient is placed supine with the head elevated 20 to 30 degrees, the bladder emptied (the catheterisation if the patient is unable to void, to avoid the bladder injury). The ultrasound is performed in the same position the tap will be done, marking the deepest pocket of the fluid (the dependent lower quadrant), the distance from the skin to the fluid, and the absence of the bowel in the trajectory. For the thoracentesis the patient is placed seated upright, leaning forward over a bedside table with the arms resting on the pillows — the position that opens the intercostal spaces and brings the dependent fluid posteriorly. The ultrasound confirms the level of the fluid (the top of the effusion, marked on the skin), the depth, and the safe interspace. The patient who cannot sit is tapped in the lateral decubitus position with the effusion side down, under the ultrasound.[3][4]

The coagulation is checked (the INR, the platelets), the anticoagulant and the antiplatelet therapy are noted — the prophylactic low-molecular-weight heparin is held for one dose where feasible, the therapeutic anticoagulant is managed by the site choice and the post-procedure observation rather than the routine reversal (the bleeding rate is low). The skin is prepped with the chlorhexidine, the full sterile barrier is used (the cap, the mask, the sterile gown, the sterile gloves, the sterile drape), and the time-out is performed before the puncture. [1]

Stepwise technique — the paracentesis

The paracentesis is run to a sequence so that no element is missed. [1]

The two structural errors are to omit the Z-track (the persistent ascitic fluid leak that soaks the dressing and the bed) and to omit the albumin replacement for the large-volume drainage (the paracentesis-induced circulatory dysfunction that precipitates the hepatorenal syndrome in the cirrhotic).[2][7]

Stepwise technique — the thoracentesis

The thoracentesis follows a parallel sequence, with the chest-specific safeguards. [1]

The two structural errors are to tap at the top of the effusion (the lung comes down as the fluid drains, and the needle enters the lung — the pneumothorax) and to drain too much, too fast (the re-expansion pulmonary oedema — the rare but lethal complication).[4][6]

Drug doses — the local anaesthetic

The local anaesthetic infiltration is the only drug in the standard paracentesis or the thoracentesis. Lidocaine 1 per cent is the agent, with a maximum dose of 3 mg per kilogram plain (about 20 mL in the 70 kg adult) or 7 mg per kilogram with adrenaline (about 50 mL in the 70 kg adult). The infiltration is performed with a 25G needle for the skin wheal and a longer needle for the deeper track, aspirating before each aliquot to avoid the intravascular injection. For the thoracentesis, the deeper infiltration walks the needle over the upper border of the lower rib, anaesthetising the periosteum and the parietal pleura — the anaesthetic track IS the needle track, and the first aspiration of the pleural fluid confirms the depth. [1]

The albumin replacement is the second drug of the large-volume paracentesis. The AASLD and the consensus recommend 8 to 10 g of the 25 per cent albumin per litre of the ascitic fluid drained above 5 litres (the 6 to 8 g per litre if the drained volume is 5 litres or less and the patient is low-risk). The rationale is the prevention of the paracentesis-induced circulatory dysfunction — the effective hypovolaemia, the activation of the renin-angiotensin-aldosterone system, and the precipitation of the hepatorenal syndrome — the complication that the Sort NEJM trial established the albumin prevents in the SBP, and that the albumin prevents in the large-volume paracentesis by the same mechanism.[2][7]

The antibiotics for the SBP are the third drug of the diagnostic paracentesis, started at once on the diagnosis of the ascitic neutrophil count of 250 per mm cubed or more. The first-line empirical regimen is the third-generation cephalosporin — the cefotaxime 2 g intravenously every 8 hours or the ceftriaxone 2 g intravenously daily for 5 to 7 days, with the albumin 1.5 g per kilogram at the diagnosis and 1 g per kilogram on day 3 to prevent the hepatorenal syndrome and reduce the mortality (the Sort NEJM trial).[7]

Differential diagnosis — the fluid analysis: SAAG and Light's criteria

The fluid analysis is the single most examinable block of the topic, and it answers the differential that brought the patient to the procedure. For the ascites, the serum-ascites albumin gradient (SAAG) — the serum albumin minus the ascitic albumin — separates the portal-hypertensive (high-gradient, at 1.1 g per dL or more) from the non-portal (low-gradient, under 1.1 g per dL) ascites. Runyon's 1992 paper established the SAAG as superior to the old transudate-exudate concept, with the 97 per cent accuracy for the portal hypertension. For the pleural effusion, the Light criteria — the pleural-to-serum protein ratio over 0.5, OR the pleural-to-serum LDH ratio over 0.6, OR the pleural LDH over two-thirds the upper limit of normal — separate the transudate from the exudate.[1][5]

The discriminating tests the examiner rewards are: the SAAG over 1.1 for the portal hypertension (the cirrhosis, the heart failure, the Budd-Chiari); the SAAG under 1.1 for the non-portal (the peritoneal carcinomatosis, the TB, the pancreatic); the Light criteria for the pleural transudate-versus-exudate; the pleural pH and the glucose for the complicated parapneumonic effusion (under 7.2 or under 3.3 mmol per litre = drain); and the cytology for the malignancy. The ascitic absolute neutrophil count of 250 per mm cubed or more defines the SBP — irrespective of the symptoms or the culture — and the empirical antibiotics and the albumin start at once.[1][2][5]

Complications — procedure-related and disease-related

The complications of the paracentesis divide into the local, the infectious, and the rare-but-serious. The local complications are the pain, the minor bleeding at the site, and the persistent ascitic fluid leak — the leak is the consequence of the omitted Z-track and is managed with the single suture at the puncture site, the ostomy bag if the leak is large, and the surgical review for the leak beyond 48 hours or the peritonitis. The infectious complications are the cellulitis at the site and the iatrogenic SBP — prevented by the sterile technique and the full barrier. The rare-but-serious complications are the major bleeding (the abdominal wall haematoma, the inferior epigastric artery laceration, the haemoperitoneum in the coagulopathic — under 1 per cent), the bowel perforation (the distended or the adherent bowel, presenting with the peritonitis over hours — managed with the IV antibiotics, the imaging, and the surgical review if the peritonitis develops), and the post-paracentesis circulatory dysfunction (the hypovolaemia, the renal impairment, the hepatorenal syndrome after the large-volume drainage — prevented by the albumin).[2][3]

The complications of the thoracentesis are the pneumothorax (1 to 6 per cent, lower with the ultrasound guidance; the iatrogenic from the lung puncture, or the trapped lung preventing the re-expansion), the bleeding (the chest wall haematoma, the intercostal artery laceration in the elderly with the tortuous intercostal vessels, the haemothorax in the coagulopathic), the infection (the cellulitis, the empyema from the contamination), the vasovagal (the cough, the bradycardia, the hypotension on the pleural puncture — managed with the supine positioning and the fluids), and the re-expansion pulmonary oedema — the rare (under 1 per cent) but potentially lethal complication of the rapid re-expansion of the collapsed lung, presenting with the cough, the dyspnoea, the hypoxia, the frothy sputum within 24 hours of the large-volume drainage. The Feller-Kopman series established the risk factors — the large volume drained (over 1.5 litres), the rapid drainage, the chronicity of the collapse, and the negative pleural pressure — and the BTS recommends the cessation at the first symptom, the 1.5-litre limit, and the pleural manometry for the larger drainage.[5][6]

Pitfalls and practical tips

The pitfalls invert the discipline. Tapping without the ultrasound when the ultrasound is available — the avoidable bowel injury and the failed tap. Omitting the Z-track in the paracentesis — the persistent ascitic fluid leak that soaks the dressing and the bed. Tapping at the top of the effusion in the thoracentesis — the lung puncture and the pneumothorax as the lung re-expands. Draining more than 1.5 litres of the pleural fluid — the avoidable re-expansion pulmonary oedema. Forgetting the albumin in the large-volume paracentesis — the paracentesis-induced circulatory dysfunction and the hepatorenal syndrome. Sending the ascitic culture on the swab instead of the inoculated blood culture bottle — the halved culture yield and the missed SBP. Not sending the cytology in the suspected malignancy — the missed diagnosis that demands the 50 to 100 mL for the highest yield. Reversing the coagulopathy routinely before the paracentesis — the unnecessary blood-product exposure for the procedure with the under-1-per-cent bleeding rate.[2][5]

The practical tips are the mirror. The ultrasound for every paracentesis and every thoracentesis, marking the fluid pocket, the depth, and the absence of the bowel or the lung in the trajectory. The Z-track for every paracentesis. The 2-cm-superior-and-medial-to-the-ASIS site for the paracentesis, the one-to-two-spaces-below-the-fluid site for the thoracentesis. The lidocaine 1 per cent (3 mg per kilogram plain), aspirating before each aliquot. The inoculated blood culture bottles for the ascitic and the pleural culture. The albumin for the large-volume paracentesis. The 1.5-litre limit for the thoracentesis, with the cessation at the first symptom. The cytology in the 50 to 100 mL container for the suspected malignancy. The conservative management of the bowel perforation unless the peritonitis develops. The post-thoracentesis chest X-ray only if the air was aspirated or the patient is symptomatic.[3][4][8]

Post-procedure care and disposition

After the paracentesis the patient is observed briefly, the vital signs and the puncture site checked, and the dressing inspected for the leak. The diagnostic tap is a same-day procedure — the patient is discharged with the safety-net advice to return for the fever, the abdominal pain, the bleeding or the leak beyond 24 hours. The large-volume paracentesis is observed for the orthostatic hypotension and the renal function — the albumin is given as outlined, the urine output monitored, and the patient discharged when the haemodynamically stable. The underlying condition determines the disposition — the cirrhotic with the first SBP to the medical ward for the antibiotics and the consideration of the secondary prophylaxis (the norfloxacin 400 mg daily), the malignant ascites to the oncology or the palliative pathway. [1]

After the thoracentesis the patient is observed briefly, the vital signs and the oxygenation checked, and the breath sounds compared with the pre-procedure baseline. The post-procedure chest X-ray is performed only if the air was aspirated, the patient is symptomatic, or the procedure was difficult. The diagnostic tap is a same-day procedure. The therapeutic tap is observed for the re-expansion symptoms (the cough, the dyspnoea, the hypoxia) for the first few hours — the patient is discharged when the oxygenation is stable, the breath sounds are improved, and the symptoms have not developed. The underlying condition determines the disposition — the parapneumonic effusion to the medical team for the antibiotics and the drainage of the complicated effusion (the pH under 7.2, the chest drain), the malignant effusion to the oncology or the respiratory pathway for the pleurodesis.[5]

Special populations

The coagulopathic patient (the INR up to 2.5, the platelets over 50) has the paracentesis without the routine correction — the under-1-per-cent bleeding rate justifies the procedure; the FFP or the platelets are reserved for the markedly abnormal coagulation, the renal failure with the uraemic platelet dysfunction, or the very large-bore catheter. The thoracentesis in the coagulopathic patient is approached more cautiously — the intercostal vessels are not compressible, the hemothorax can be significant, and the abnormal coagulation is weighed with the urgency of the diagnostic question. The cirrhotic patient with the first SBP receives the antibiotics and the albumin, the secondary prophylaxis with the norfloxacin, and the work-up for the liver transplant. The malignant-ascites patient benefits from the therapeutic paracentesis for the symptomatic relief, with the cytology sent on the first tap; the long-term management is the indwelling peritoneal catheter (the PleurX) and the palliative oncology. The obese patient needs the ultrasound for the deeper fluid pocket and the longer needle or catheter. The pregnant patient is positioned in the left lateral tilt, the bladder emptied, and the puncture performed by the experienced operator with the ultrasound — the paracentesis is safe in the pregnancy when the indication warrants. The patient on the antiplatelet or the anticoagulant therapy: the aspirin is continued, the clopidogrel is held for 5 to 7 days if feasible for the therapeutic tap, the prophylactic low-molecular-weight heparin is held for one dose, and the therapeutic anticoagulant is managed by the site choice and the observation.[2][5]

Evidence and regional guidelines

The contemporary framework is built on three pillars. The AASLD Practice Guideline for the management of the adult patient with the ascites due to the cirrhosis (Runyon 2013) codified the SAAG, the diagnostic paracentesis on every cirrhotic admission, the large-volume paracentesis with the albumin replacement, and the SBP diagnosis and treatment — the global standard.[2] The British Thoracic Society Guideline for the Pleural Disease (Roberts 2023) is the contemporary standard for the thoracentesis — the ultrasound guidance for the diagnostic and the therapeutic tap, the 1.5-litre limit for the single drainage, the pleural manometry for the larger drainage, the post-tap chest X-ray only for the symptomatic or the air-aspirated, and the fluid-analysis panel with the Light criteria, the pH and the glucose, the cytology and the culture.[5] The Runyon 1992 paper established the SAAG as superior to the transudate-exudate concept for the ascites, with the 97 per cent accuracy for the portal hypertension — the foundational evidence the examiner rewards.[1] The Sort 1999 NEJM trial established the albumin in the SBP to reduce the renal impairment and the mortality, the evidence that extends to the albumin in the large-volume paracentesis by the same mechanism.[7] The Thomsen 2006 NEJM videos codified the stepwise technique for both procedures.[3][4] The Feller-Kopman 2007 series characterised the re-expansion pulmonary oedema and its risk factors.[6] The Sperandeo 2022 series confirmed the safety of the real-time ultrasound-guided thoracentesis.[8]

Exam pearls

• The SAAG over 1.1 g per dL = portal hypertension (the cirrhosis, the heart failure, the Budd-Chiari); under 1.1 = the peritoneal cause (the carcinomatosis, the TB, the pancreatic). The Runyon 1992 evidence, 97 per cent accurate.
• The SBP = the ascitic neutrophil count of 250 per mm cubed or more — the cefotaxime 2 g intravenously every 8 hours and the albumin 1.5 g per kilogram at the diagnosis, 1 g per kilogram on day 3. The Sort 1999 evidence.
• The paracentesis site: 2 cm superior and medial to the ASIS (left preferred) or 2 cm below the umbilicus in the midline — ultrasound for the fluid pocket and the absence of the bowel. The Z-track is mandatory.
• The thoracentesis site: the posterior chest, seated, one to two spaces below the top of the effusion, advanced over the upper border of the lower rib. Never at the top of the effusion.
• The Light criteria: the protein ratio over 0.5, OR the LDH ratio over 0.6, OR the pleural LDH over 2/3 ULN (any one) = exudate. None = transudate.
• The pleural pH under 7.2 or the glucose under 3.3 mmol per litre = drain (the complicated parapneumonic, the empyema, the malignancy).
• The re-expansion pulmonary oedema: drain no more than 1.5 litres at one sitting, stop at the first chest tightness, the cough or the new pain. The Feller-Kopman evidence.
• The albumin 8 to 10 g per litre above 5 litres drained in the large-volume paracentesis — prevents the paracentesis-induced circulatory dysfunction and the hepatorenal syndrome.
• The coagulopathy is a relative, not an absolute, contraindication — the paracentesis is safe with the INR up to 2.0 and the platelets over 50 without the routine correction.
• The ascitic culture: inoculate the blood culture bottles at the bedside — the yield is doubled over the agar swab. [1]

Short answer questions

Red flags