# Clinical Cases: Advanced Procedures and Skills

## Case 1: Lumbar Puncture with CSF Interpretation

### Clinical Image
![Lumbar puncture procedure positioning and technique](case_01_image.jpg)
*Source: [Wikimedia Commons - Lumbar Puncture](https://commons.wikimedia.org/wiki/Category:Lumbar_puncture) - CC BY-SA 4.0*

### Case Presentation
A 28-year-old previously healthy man presents with 2 days of severe headache, fever to 39.2 degrees Celsius, and photophobia. He is alert but appears uncomfortable, holding his neck stiffly. Physical examination reveals positive Kernig and Brudzinski signs. CT head without contrast shows no mass effect or midline shift. The sub-intern is asked to perform the lumbar puncture. After obtaining informed consent and explaining the risks (headache, bleeding, infection, nerve injury), she positions the patient in lateral decubitus with knees drawn to chest. She identifies the L4-L5 interspace at the level of the iliac crests, performs sterile preparation with chlorhexidine, and infiltrates local anesthesia from skin to periosteum. The spinal needle is inserted with stylet in place, bevel oriented laterally. A "pop" is felt as the needle passes through the dura. Opening pressure is measured at 28 cm H2O (elevated). CSF is cloudy. Four tubes are collected, each 2 mL. CSF analysis reveals: WBC 2,400/microL with 95% neutrophils, protein 185 mg/dL, glucose 28 mg/dL (serum glucose 110 mg/dL, ratio 25%). Gram stain shows gram-positive diplococci. The patient is immediately started on ceftriaxone 2g IV, vancomycin 1g IV, and dexamethasone 0.15 mg/kg for suspected pneumococcal meningitis. Blood and CSF cultures later confirm Streptococcus pneumoniae.

### Key Learning Points
- Lumbar puncture contraindications: mass effect on imaging, coagulopathy (platelets less than 50,000 or INR greater than 1.5), skin infection at puncture site, hemodynamic instability
- Normal CSF: WBC less than 5, protein less than 45 mg/dL, glucose greater than 60% of serum; bacterial meningitis shows WBC greater than 1000 (neutrophil predominant), very low glucose, elevated protein
- Opening pressure is measured with legs extended in lateral decubitus; normal is less than 20 cm H2O
- Do not delay antibiotics for lumbar puncture if the procedure will be delayed; blood cultures should be obtained but treatment should not wait

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## Case 2: Paracentesis for Spontaneous Bacterial Peritonitis

### Clinical Image
![Ultrasound-guided paracentesis technique](case_02_image.jpg)
*Source: [Wikimedia Commons - Ultrasound](https://commons.wikimedia.org/wiki/Category:Ultrasonography) - CC BY-SA 3.0*

### Case Presentation
A 62-year-old man with alcoholic cirrhosis (Child-Pugh C) presents with increasing abdominal distension, diffuse abdominal tenderness, and confusion. He is afebrile but appears ill. His abdomen is tense with shifting dullness. Per protocol, diagnostic paracentesis is performed on all cirrhotic patients admitted to the hospital. The sub-intern performs the procedure using ultrasound guidance. The patient is positioned supine with slight leftward tilt. Ultrasound identifies a large pocket of ascites in the left lower quadrant, lateral to the rectus muscle to avoid the inferior epigastric vessels. Using sterile technique, the sub-intern infiltrates local anesthesia to the peritoneum and uses Z-track technique (offsetting skin and deep entry points) to reduce post-procedure leak. A needle is inserted perpendicular to the skin, aspirating as it advances. Straw-colored fluid is obtained. She collects 60 mL: inoculating blood culture bottles at bedside (10 mL each, aerobic and anaerobic), sending cell count with differential, albumin, and total protein. Results return showing ascitic fluid WBC 850/microL with 420 polymorphonuclear cells (PMN greater than 250), ascitic albumin 0.8 g/dL (serum albumin 2.4 g/dL, SAAG = 1.6). The diagnosis is spontaneous bacterial peritonitis (SBP). Ceftriaxone 2g IV daily is initiated, along with albumin 1.5 g/kg on day 1 and 1 g/kg on day 3 (for hepatorenal syndrome prophylaxis). Cultures later grow E. coli.

### Key Learning Points
- All patients with cirrhosis admitted to the hospital should have diagnostic paracentesis to evaluate for SBP, regardless of symptoms
- SBP is diagnosed when ascitic fluid PMN count is greater than 250/microL; cultures are positive in only about 50% of cases
- SAAG (serum-ascites albumin gradient) greater than 1.1 g/dL indicates portal hypertension; less than 1.1 suggests non-portal hypertension causes (malignancy, infection, pancreatitis)
- Z-track technique and lateral insertion (avoiding the rectus sheath) minimize complications of bleeding and persistent leak

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## Case 3: Thoracentesis with Light's Criteria Application

### Clinical Image
![Pleural effusion on chest X-ray requiring thoracentesis](case_03_image.jpg)
*Source: [Wikimedia Commons - Pleural Effusion](https://commons.wikimedia.org/wiki/Category:Pleural_effusion) - CC BY-SA 4.0*

### Case Presentation
A 55-year-old woman with history of breast cancer (in remission for 5 years) presents with progressive dyspnea over 2 weeks. Chest X-ray reveals a large left pleural effusion. She has no fever, cough, or chest pain. She has no known heart failure, liver disease, or kidney disease. Given the unclear etiology and cancer history, diagnostic and therapeutic thoracentesis is planned. Using ultrasound, the sub-intern identifies the effusion, confirms depth of approximately 3 cm from skin to fluid, and marks the optimal entry site. The patient sits upright leaning forward over a bedside table. Using sterile technique, local anesthesia is infiltrated, and the needle is inserted just above the rib (to avoid the neurovascular bundle along the lower rib margin). Approximately 1.2 liters of serosanguineous fluid is removed (stopping before 1.5 L to avoid re-expansion pulmonary edema). She reports immediate improvement in breathing. Fluid analysis: protein 5.2 g/dL (serum 7.0 g/dL, ratio 0.74), LDH 420 U/L (serum 180 U/L, ratio 2.3), glucose 45 mg/dL. Light's criteria indicate an exudative effusion (meets 2 of 3 criteria: protein ratio greater than 0.5 and LDH ratio greater than 0.6). Cytology returns positive for adenocarcinoma consistent with breast primary. She is diagnosed with malignant pleural effusion from recurrent breast cancer.

### Key Learning Points
- Light's criteria distinguish exudate from transudate: exudate if ANY of the following are met: pleural/serum protein greater than 0.5, pleural/serum LDH greater than 0.6, or pleural LDH greater than 2/3 upper limit of normal for serum
- Transudates result from hydrostatic/oncotic imbalances (heart failure, cirrhosis, nephrotic syndrome); exudates result from pleural inflammation or impaired lymphatic drainage (infection, malignancy, PE)
- Limit therapeutic thoracentesis to 1.5 L to prevent re-expansion pulmonary edema
- Enter above the rib to avoid the intercostal neurovascular bundle; use ultrasound to confirm fluid location and depth, reducing pneumothorax risk