# Clinical Cases: Fluids and Electrolytes

## Case 1: Hypovolemia and Electrolyte Derangements in Bowel Obstruction

### Patient Demographics
- **Age:** 78 years
- **Sex:** Female
- **Occupation:** Retired teacher

### Chief Complaint
"I've been vomiting for 3 days and feel very weak."

### History of Present Illness
The patient presents with a 3-day history of progressive nausea, vomiting, abdominal distension, and crampy abdominal pain. She has been unable to keep down any food or liquids. Vomiting is bilious and occurs every few hours. She reports no bowel movement or passage of gas for the past 2 days. She feels dizzy when standing and has had minimal urine output. She has a history of multiple abdominal surgeries.

### Past Medical History
- Hysterectomy 30 years ago for fibroids
- Appendectomy in childhood
- Previous small bowel obstruction treated conservatively 5 years ago
- Hypertension

### Medications
- Lisinopril 10 mg daily
- Hydrochlorothiazide 25 mg daily (on diuretic!)

### Physical Examination
- **Vitals:** BP 88/52 mmHg (supine), HR 112 bpm, Temp 37.2C, RR 22/min
- **Orthostatics:** Unable to stand due to severe dizziness
- **General:** Cachectic elderly female, lethargic, dry mucous membranes
- **Skin:** Decreased turgor, tenting over sternum
- **Cardiovascular:** Tachycardic, regular, no murmurs, flat JVP
- **Abdomen:** Distended, tympanitic, diffuse tenderness, high-pitched bowel sounds
- **Extremities:** No edema, cool extremities with delayed capillary refill

### Initial Laboratory Results
- **Sodium:** 128 mEq/L (low)
- **Potassium:** 2.8 mEq/L (low)
- **Chloride:** 78 mEq/L (low)
- **Bicarbonate:** 38 mEq/L (high)
- **BUN:** 58 mg/dL (high)
- **Creatinine:** 2.4 mg/dL (baseline 0.9)
- **Glucose:** 98 mg/dL
- **pH:** 7.52 (alkalemic)
- **pCO2:** 48 mmHg (compensatory)
- **Lactate:** 3.2 mmol/L (elevated)
- **Urine sodium:** <10 mEq/L
- **Urine specific gravity:** 1.035

### Assessment of Volume Status

**Clinical Signs of Severe Hypovolemia:**
1. Hypotension (systolic <90 mmHg)
2. Tachycardia (HR >100)
3. Dry mucous membranes
4. Decreased skin turgor
5. Flat JVP
6. Altered mental status (lethargy)
7. Oliguria

**Laboratory Confirmation:**
1. BUN:Creatinine ratio >20:1 (58:2.4 = 24:1) - prerenal azotemia
2. Urine sodium <20 mEq/L - appropriate renal sodium conservation
3. Elevated urine specific gravity - concentrated urine
4. Elevated lactate - tissue hypoperfusion

**Estimated Volume Deficit:**
- Patient weight 55 kg
- Clinical assessment: ~15% body weight loss (severe)
- Estimated deficit: ~8 liters

### Acid-Base Analysis

**Primary Disorder:** Metabolic Alkalosis
- Elevated pH (7.52) with elevated bicarbonate (38 mEq/L)
- Cause: Loss of gastric acid (HCl) through vomiting

**Compensation:** Respiratory (hypoventilation)
- Expected pCO2 = 0.7 x (HCO3 - 24) + 40 = 0.7 x 14 + 40 = 49.8 mmHg
- Measured pCO2 = 48 mmHg (appropriate compensation)

**Classification:** Hypochloremic, hypokalemic metabolic alkalosis

### Electrolyte Abnormalities

**Hyponatremia (128 mEq/L):**
- Etiology: Hypovolemic hyponatremia
- Loss of sodium-containing GI fluids
- Volume depletion triggers ADH release, retaining water
- Treatment: Volume resuscitation with normal saline

**Hypokalemia (2.8 mEq/L):**
- Etiology: GI losses + renal losses
- Vomiting causes direct K+ loss
- Metabolic alkalosis drives K+ into cells
- Volume depletion activates RAAS, promoting renal K+ wasting
- Risk: Cardiac arrhythmias, muscle weakness, ileus

**Hypochloremia (78 mEq/L):**
- Etiology: Loss of HCl in gastric secretions
- Maintains metabolic alkalosis ("contraction alkalosis")
- Treatment: Chloride-containing fluids (normal saline)

### Fluid Resuscitation Plan

**Immediate Resuscitation (First 2 hours):**
1. Two large-bore IVs placed
2. Normal saline 2L bolus over 1 hour
3. Reassess vital signs and urine output
4. Second bolus 1L NS if still hypotensive

**Rationale for Normal Saline:**
- Chloride-rich solution corrects hypochloremic alkalosis
- Isotonic - provides volume expansion
- Potassium-free initially (will add once urine output established)

**Potassium Replacement:**
- After establishing urine output (>0.5 mL/kg/hr)
- Add KCl 40 mEq/L to maintenance fluids
- For K+ <3.0 with EKG changes: 10-20 mEq/hr via central line with cardiac monitoring
- Replace magnesium if low (hypomagnesemia impairs K+ repletion)

**Maintenance Fluids (after initial resuscitation):**
- D5 1/2 NS with 40 mEq KCl/L at 125 mL/hr
- Monitor electrolytes every 6 hours initially

### Additional Management
1. Nasogastric tube to suction (decompress bowel, quantify ongoing losses)
2. Replace NG output mL-for-mL with normal saline + 20 mEq KCl/L
3. NPO status
4. CT abdomen to evaluate obstruction
5. Hold diuretic and ACE inhibitor

### Response to Treatment (6 hours)

| Parameter | Admission | 6 Hours |
|-----------|-----------|---------|
| BP | 88/52 | 112/68 |
| HR | 112 | 88 |
| Urine output | Minimal | 60 mL/hr |
| Sodium | 128 | 132 |
| Potassium | 2.8 | 3.4 |
| Chloride | 78 | 92 |
| Bicarbonate | 38 | 32 |
| Creatinine | 2.4 | 1.6 |

### Clinical Image
![Electrolyte Transport Mechanisms](case_01_image.jpg)

**Image Description:** Schematic diagram illustrating potassium and sodium ion transport mechanisms across cell membranes, demonstrating the role of the Na+/K+ ATPase pump in maintaining electrolyte gradients.

**Attribution:** Image from Wikimedia Commons, licensed under CC BY-SA 4.0. Source: https://commons.wikimedia.org/wiki/File:Schematic_of_potassium_and_sodium_ion_transport_mechanisms.svg

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## Case 2: Hyperkalemia in Surgical Patient

### Patient Demographics
- **Age:** 68 years
- **Sex:** Male
- **Occupation:** Retired electrician

### Chief Complaint
"Routine lab check before hernia surgery."

### History of Present Illness
The patient is scheduled for elective inguinal hernia repair tomorrow. He presents for preoperative laboratory evaluation. He feels well with no acute complaints. His only symptom is the reducible right groin bulge he has had for 6 months.

### Past Medical History
- Chronic kidney disease stage 4 (baseline creatinine 3.8 mg/dL, GFR 18)
- Type 2 diabetes mellitus
- Hypertension
- Peripheral vascular disease

### Medications
- Lisinopril 40 mg daily
- Spironolactone 25 mg daily
- Insulin glargine 20 units at bedtime
- Metoprolol 50 mg twice daily

### Physical Examination
- **Vitals:** BP 138/82 mmHg, HR 64 bpm, regular
- **General:** Well-appearing male in no distress
- **Cardiovascular:** Regular rate and rhythm, no murmurs
- **Abdomen:** Soft, non-tender, right inguinal hernia reduces easily
- **Extremities:** No edema, diminished dorsalis pedis pulses bilaterally

### Laboratory Results
- **Potassium:** 6.8 mEq/L (CRITICAL VALUE)
- **Sodium:** 136 mEq/L
- **Chloride:** 108 mEq/L
- **Bicarbonate:** 18 mEq/L
- **BUN:** 62 mg/dL
- **Creatinine:** 4.2 mg/dL (slightly above baseline)
- **Glucose:** 142 mg/dL

### EKG Findings
- Heart rate 62 bpm
- Peaked T waves (most prominent in V2-V4)
- Widened QRS complex (120 ms)
- Flattened P waves
- No sine wave pattern

### Risk Factors for Hyperkalemia
1. Chronic kidney disease (decreased excretion)
2. ACE inhibitor (lisinopril) - reduces aldosterone
3. Potassium-sparing diuretic (spironolactone)
4. Diabetes (insulin deficiency impairs K+ shift into cells)
5. Possible tissue injury/hemolysis (verify not pseudohyperkalemia)

### Emergency Management

**Immediate Actions:**
1. Cardiac monitor placed
2. Repeat potassium drawn (verify not hemolyzed) - confirmed 6.7 mEq/L
3. Surgery cancelled

**Treatment Protocol for Severe Hyperkalemia (K+ >6.5 with EKG changes):**

**Step 1: Cardiac Membrane Stabilization (immediate)**
- Calcium gluconate 10% 1 ampule (10 mL) IV over 2-3 minutes
- Onset: 1-3 minutes
- Duration: 30-60 minutes
- Repeat if EKG abnormalities persist
- Does NOT lower potassium

**Step 2: Shift Potassium Intracellularly (minutes)**
- Regular insulin 10 units IV + D50W 25g IV
- Onset: 15-30 minutes
- Duration: 4-6 hours
- Expected K+ decrease: 0.5-1.0 mEq/L
- Monitor glucose hourly

**Step 3: Additional Shift Therapy**
- Albuterol 10-20 mg nebulized
- Onset: 15-30 minutes
- Duration: 2-4 hours
- Additive effect with insulin

**Step 4: Potassium Elimination**
- Loop diuretic (furosemide 40 mg IV) - limited effect with CKD stage 4
- Sodium polystyrene sulfonate 30g PO (onset 2-6 hours)
- Patiromer or sodium zirconium cyclosilicate (newer agents)
- **Hemodialysis** - definitive treatment for refractory hyperkalemia

### Response to Treatment

| Time | Potassium | EKG |
|------|-----------|-----|
| 0 min | 6.8 | Peaked T, wide QRS |
| 15 min (post-calcium) | 6.8 | Improved QRS |
| 60 min (post-insulin) | 5.9 | Near-normal |
| 4 hours | 5.2 | Normal |

### Disposition
- Admitted for observation and ongoing potassium management
- Nephrology consultation obtained
- Medications adjusted:
  - Lisinopril reduced to 10 mg
  - Spironolactone discontinued
  - Low-potassium diet education
- Surgery rescheduled in 1 week after potassium optimized
- Repeat labs showed K+ 4.8 mEq/L on adjusted medications

### Teaching Points
1. Always verify hyperkalemia is not pseudohyperkalemia (hemolysis)
2. EKG changes indicate cardiac toxicity requiring emergent treatment
3. Calcium stabilizes membranes but does not lower potassium
4. Insulin + glucose provides rapid shift into cells
5. Definitive treatment requires potassium elimination
6. Review all medications that contribute to hyperkalemia
7. CKD patients on ACE-I and K+-sparing diuretics at high risk