General Surgery · Year 3 · from General Surgery

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)

Clinical Image

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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