Stomach surgery
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I now have rich, authoritative content from multiple surgical textbooks. Let me compile the comprehensive overview.
Stomach Surgery: Anatomy, Procedures & Surgical Technique
Gastric Anatomy Relevant to Surgery
The stomach is derived from the embryonic foregut and is one of the most well-vascularized organs in the body, protected by numerous extramural and intramural collateral vessels. It is divided into four anatomic regions:
| Region | Location |
|---|---|
| Cardia | Just distal to the gastroesophageal junction (GEJ) |
| Fundus | Above and to the left of the GEJ |
| Corpus (Body) | Between fundus and antrum |
| Antrum | Distal stomach, bounded by the pylorus |
The boundary between corpus and antrum is defined by a line from the incisura angularis (lesser curvature) to a point one-fourth the distance from the pylorus to the esophagus along the greater curvature.
Gastric Cell Types
| Cell Type | Location | Function |
|---|---|---|
| Parietal | Body | HCl secretion + intrinsic factor |
| Chief | Body | Pepsinogen |
| G cells | Antrum | Gastrin secretion |
| D cells | Antrum | Somatostatin |
| ECL cells | Body | Histamine |
| Surface epithelial | Diffuse | Mucus, bicarbonate, prostaglandins |
| Endocrine | Body | Ghrelin |
Vascular Anatomy
- Left gastric artery - arises from celiac trunk; supplies lesser curvature (ligated at its origin during gastrectomy)
- Right gastric artery - from hepatic artery; divides at hepatic artery origin during lymphadenectomy
- Short gastric arteries - from splenic artery; supply fundus (blood supply of proximal remnant after subtotal gastrectomy)
- Left gastroepiploic - from splenic artery
- Right gastroepiploic - from gastroduodenal artery
Major Gastric Surgical Procedures
1. Total Gastrectomy
Indication: Gastric cancer (especially proximal or diffuse), or tumors requiring >50% gastric removal.
Technique (Bailey & Love's, 28th Ed.):
- Long upper midline incision
- Stomach removed en bloc with entire greater and lesser omentum
- Duodenum divided with surgical stapler just distal to pylorus
- Hepatic, subpyloric, suprapyloric, left gastric, and splenic artery nodal chains dissected
- Esophagus divided with >5 cm clearance from tumor (frozen section of margins)
Reconstruction - Roux-en-Y esophagojejunostomy:
- Roux (alimentary) limb must be at least 50 cm to prevent bile reflux esophagitis
- Esophagojejunostomy performed with circular stapler (purse-string suture in esophageal stump, introduced through blind end of Roux loop)
- End-to-side jejunojejunostomy created distally
- Roux loop placed antecolic or retrocolic
Lymphadenectomy extent:
- D1: Perigastric nodes only
- D2: Clearance of major arterial trunks (standard in specialist centers); spleen and pancreas conserved where possible; station 10 nodes often spared
Bailey and Love's Short Practice of Surgery, 28th Ed.
2. Subtotal (Distal) Gastrectomy
Indication: Distal gastric tumors; peptic ulcer disease not responding to medical management.
Technique:
- Similar to total gastrectomy distally, but proximal stomach is preserved
- Blood supply to remnant derived from short gastric arteries
- Preferred reconstruction: Roux-en-Y gastrojejunostomy (reduces bile reflux vs. Billroth II/Polya)
- Billroth II is still used but associated with enterogastric reflux and bile reflux esophagitis
3. Proximal Gastrectomy
Indication: Smaller tumors near the GEJ; patients with less physiologic reserve; T1 tumors of upper stomach.
Key considerations (Current Surgical Therapy, 14th Ed.):
- Oncologic outcomes equivalent to total gastrectomy for appropriately selected cases
- Preferred only if >50% of stomach can be preserved; if <50% remains, total gastrectomy is preferred (bile reflux negates benefit)
- Diaphragm divided by electrocautery in midline, crura retracted laterally to mobilize distal esophagus
- Primary esophagogastrostomy end-to-side over a nasogastric tube, left overnight
- Anastomosis lies in the low mediastinum after diaphragm reapproximation
4. Pylorus-Preserving Gastrectomy
Indication: Early gastric cancer (T1N0M0) in the middle-third of the stomach, located at least 4 cm from the pylorus.
- Primarily performed in Japan and Korea
- Balance between quality-of-life preservation and adequate oncologic resection
- Ongoing trials to define ideal patient selection
5. Sleeve Gastrectomy (Bariatric)
Indication: Morbid obesity (BMI ≥40, or ≥35 with comorbidities).
Technique (Bailey & Love's, 28th Ed.):
- Lesser curve-based gastric tube created over a size 32-36 Fr bougie (some surgeons use larger to reduce leak risk)
- Linear stapling devices used to resect the fundus and lateral body
- Variations exist in stapler width and use of reinforcement strips
- Critical risk point: Staple line leak at the angle of His (high-pressure system due to intact pylorus; can take months to heal)
Mechanism of action:
- Initially thought purely restrictive; now known that gastric emptying is accelerated (not delayed) after sleeve
- Changes in satiety gut hormones (PYY, GLP-1) and bile salt metabolism play major roles
- Long-term: risk of symptomatic GERD and de novo Barrett's esophagus; weight regain may require revisional surgery
6. Roux-en-Y Gastric Bypass (RYGB)
Technique:
- Short vertical lesser curvature-based gastric pouch created
- Pouch-jejunostomy options: linear stapler with suture closure, circular stapler, or hand-sewn
- Leak test is routine
- Roux (alimentary) limb: 100-150 cm (antecolic or retrocolic)
- Biliopancreatic (afferent) limb: Kept short (50-100 cm) to reduce vitamin/mineral deficiencies
- Bowel continuity restored by Y-jejunojejunostomy (stapled or hand-sewn)
- Remnant stomach left in place but bypassed (not removed)
Mechanism: Complex - appetite reduction via changes in satiety hormones, altered energy expenditure, and changed food preferences. Roux-en-Y reconstruction prevents bile reflux compared to loop reconstruction.
7. One-Anastomosis Gastric Bypass (OAGB / "Mini-Gastric Bypass")
First described by Rutledge.
- Single anastomosis (antecolic loop gastrojejunostomy) - no Roux-en-Y configuration
- Longer gastric pouch than standard RYGB
- Technically less demanding with similar weight loss outcomes
- Concerns: Symptomatic biliary reflux causing gastritis/esophagitis, marginal ulcers, possible increased risk of Barrett's esophagus and gastric/esophageal cancer with long-term biliary reflux - outcomes still under investigation
8. Adjustable Gastric Banding (AGB)
- Band placed just below the GEJ via pars flaccida technique (through lesser omentum window)
- Creates a small "virtual" gastric pouch
- Sutured anteriorly with gastrogastric tunnelling sutures to prevent slippage
- Access port fixed to rectus sheath (upper abdomen) for band adjustments via Huber needle
- Declining in use due to long-term complications and inferior weight loss vs. RYGB and sleeve
9. Biliopancreatic Diversion / Duodenal Switch (BPD-DS)
Technique:
- Sleeve gastrectomy + division of duodenum distal to pylorus
- Duodenojejunostomy (maintains pylorus in alimentary stream)
- Distal Roux-en-Y jejunoileostomy with 100 cm common channel
- Greatest weight loss of all bariatric procedures
Limitations: Higher perioperative mortality (at least 2x vs. RYGB by meta-analysis), significant malabsorptive complications (2-20%), technically demanding duodenojejunal anastomosis. Currently comprises <2% of bariatric operations; often reserved as a revisional option after failed sleeve gastrectomy.
Advanced & Multivisceral Resection
For locally advanced gastric adenocarcinoma invading adjacent organs, en bloc multivisceral resection is required (may include distal pancreatectomy-splenectomy or pancreaticoduodenectomy). Despite higher morbidity, achieving an R0 resection provides significant survival benefit over palliative approaches.
In highly selected patients with low peritoneal disease (peritoneal cancer index ≤7), cytoreductive surgery (CRS) + HIPEC (hyperthermic intraperitoneal chemotherapy with mitomycin C) combined with gastrectomy and lymphadenectomy has shown a median overall survival of 2.1 years from diagnosis in phase II trials.
Summary Comparison
| Procedure | Primary Indication | Reconstruction | Key Technical Point |
|---|---|---|---|
| Total gastrectomy | Proximal/diffuse gastric Ca | Roux-en-Y esophagojejunostomy | ≥50 cm Roux limb; D2 lymphadenectomy |
| Subtotal gastrectomy | Distal gastric Ca / PUD | Roux-en-Y gastrojejunostomy | Preferred over Billroth II |
| Proximal gastrectomy | Small GEJ tumors | Esophagogastrostomy | Only if >50% stomach preserved |
| Sleeve gastrectomy | Obesity | None (no anastomosis) | 32-36 Fr bougie; leak at angle of His |
| RYGB | Obesity | Roux-en-Y gastrojejunostomy | Roux limb 100-150 cm |
| OAGB | Obesity | Loop gastrojejunostomy | Simpler but biliary reflux risk |
| BPD-DS | Severe obesity / revision | Duodenojejunostomy + Roux | Highest weight loss; highest morbidity |
| Gastric banding | Obesity | None | Declining use |
Sources: Bailey and Love's Short Practice of Surgery 28th Ed. | Current Surgical Therapy 14th Ed. | Mulholland and Greenfield's Surgery 7th Ed. | Sabiston Textbook of Surgery | Yamada's Textbook of Gastroenterology 7th Ed.
Abg
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I now have comprehensive, authoritative content from multiple textbooks. Here is the full guide:
Arterial Blood Gas (ABG) - Complete Guide
What is an ABG?
An arterial blood gas is a sample of blood drawn from an artery (usually the radial artery) that measures the body's acid-base status, ventilation, and oxygenation simultaneously. The pH of blood summarizes systemic acid-base balance and is the negative logarithm of hydrogen-ion concentration ([H+]).
The relationship between the key parameters is described by the Henderson-Hasselbalch equation:
pH = pK + log₁₀ ([HCO₃⁻] / [0.03 × PaCO₂])
The kidneys regulate plasma bicarbonate (HCO₃⁻), and the lungs regulate PaCO₂. Together they maintain a normal pH of 7.35-7.45.
Normal ABG Values
| Parameter | Normal Value | Normal Range |
|---|---|---|
| pH | 7.40 | 7.35 - 7.45 |
| PaCO₂ | 40 mmHg | 38 - 42 mmHg |
| PaO₂ | 100 mmHg | 75 - 100 mmHg |
| HCO₃⁻ | 24 mEq/L | 22 - 26 mEq/L |
| Base Excess | 0 | -4 to +4 |
| SaO₂ | >95% | - |
Key: Calculated HCO₃⁻ on the ABG and measured serum HCO₃⁻ (from electrolytes) should be within 2-3 mEq/L of each other. A larger discrepancy suggests a lab error or non-simultaneous sampling.
Step-by-Step ABG Interpretation
Step 1 - Assess pH
| pH | Interpretation |
|---|---|
| < 7.35 | Acidemia |
| 7.35 - 7.45 | Normal |
| > 7.45 | Alkalemia |
Step 2 - Identify the Primary Process
| pH | PaCO₂ | HCO₃⁻ | Disorder |
|---|---|---|---|
| ↓ | ↑ | Normal/↑ | Respiratory acidosis |
| ↓ | ↓ | ↓ | Metabolic acidosis |
| ↑ | ↓ | Normal/↓ | Respiratory alkalosis |
| ↑ | ↑ | ↑ | Metabolic alkalosis |
Rule: In respiratory disorders, PaCO₂ and pH move in opposite directions. In metabolic disorders, PaCO₂ moves in the same direction as pH (as compensation).
Step 3 - Check for Appropriate Compensation
Use the compensation formulas to decide if the secondary change is appropriate (simple disorder) or excessive/inadequate (mixed disorder):
| Primary Disorder | Expected Compensation Formula |
|---|---|
| Metabolic acidosis | PaCO₂ = 1.5 × [HCO₃⁻] + 8 ± 2 (Winter's Formula) |
| Metabolic alkalosis | PaCO₂ = 0.7 × [HCO₃⁻] + 20 ± 5 |
| Acute respiratory acidosis | ↑ HCO₃⁻ = ΔPaCO₂ / 10 |
| Chronic respiratory acidosis | ↑ HCO₃⁻ = 4 × (ΔPaCO₂ / 10) |
| Acute respiratory alkalosis | ↓ HCO₃⁻ = 2 × (ΔPaCO₂ / 10) |
| Chronic respiratory alkalosis | ↓ HCO₃⁻ = 5 × (ΔPaCO₂ / 10) |
If the measured value differs from the expected, a secondary (mixed) acid-base disorder is present.
Step 4 - Calculate the Anion Gap (AG)
AG = [Na⁺] - ([Cl⁻] + [HCO₃⁻]) Normal AG < 12-13 mEq/L
Always calculate the AG even if a metabolic acidosis is not obvious - it can unmask a hidden mixed disorder.
Albumin correction: Because albumin is a major unmeasured anion, the AG must be corrected when albumin is low:
Corrected AG = Observed AG + 2.5 × (4.0 - [measured albumin])
Step 5 - If Normal AG Acidosis, Check Urine Anion Gap
Urine AG = Urine [Na⁺] + [K⁺] - [Cl⁻]
- Negative urine AG → GI loss of bicarbonate (e.g., diarrhea)
- Positive urine AG → Renal loss (e.g., RTA)
Step 6 - If High AG Acidosis, Calculate Delta-Delta Ratio (Δ/Δ)
Δ/Δ = (AG - 12) / (24 - HCO₃⁻)
| Ratio | Interpretation |
|---|---|
| 1 - 2 | Pure high AG metabolic acidosis |
| < 1 | Concurrent non-AG metabolic acidosis |
| > 2 | Concurrent metabolic alkalosis OR compensated chronic respiratory acidosis |
Step 7 - Assess Oxygenation
Check PaO₂ and calculate the A-a gradient:
A-a gradient = PAO₂ - PaO₂ where PAO₂ = (FiO₂ × 713) - (PaCO₂ / 0.8)
Normal A-a gradient (on room air) ≈ Age/4 mmHg
| A-a Gradient | Implication |
|---|---|
| Normal | Hypoventilation is the cause of hypoxemia |
| Elevated | V/Q mismatch, diffusion impairment, or shunt |
Base Deficit/Excess
Base excess = amount of base needed to titrate 1 L of blood to pH 7.4 at 37°C.
- > +4 = metabolic alkalosis
- < -4 = metabolic acidosis (base deficit)
The Four Primary Disorders
1. Metabolic Acidosis
Definition: pH ↓, HCO₃⁻ ↓, PaCO₂ ↓ (compensation)
High Anion Gap Metabolic Acidosis - Mnemonic: MUDPILES
| Letter | Cause |
|---|---|
| M | Methanol |
| U | Uremia |
| D | Diabetic ketoacidosis (DKA) |
| P | Paraldehyde / Propylene glycol / Paracetamol (acetaminophen) |
| I | Iron / Isoniazid |
| L | Lactic acidosis (most common cause of high AG metabolic acidosis) |
| E | Ethylene glycol |
| S | Salicylates |
Normal Anion Gap Metabolic Acidosis - Mnemonic: HARDUP
| Letter | Cause |
|---|---|
| H | Hyperalimentation / Hospital-acquired saline |
| A | Acid infusion / Addison's disease / Acetazolamide |
| R | Renal tubular acidosis (RTA) |
| D | Diarrhea |
| U | Ureterosigmoidostomy |
| P | Pancreatic drainage / fistula |
Treatment: Target underlying cause. NaHCO₃ is given to raise pH >7.10 in severe acidosis, or >7.20 in severe metabolic acidosis with concurrent AKI.
2. Metabolic Alkalosis
Definition: pH ↑, HCO₃⁻ ↑, PaCO₂ ↑ (compensation)
Chloride-Responsive (urine Cl⁻ < 25 mmol/L - corrects with saline)
- Nasogastric suction
- Vomiting
- Chloride-wasting diarrhea
- Villous adenoma
- Diuretic use
Chloride-Unresponsive (urine Cl⁻ > 40 mmol/L - does NOT correct with saline)
- Primary hyperaldosteronism
- Secondary hyperaldosteronism (Bartter syndrome, Gitelman syndrome, CHF, liver failure)
- Cushing disease / exogenous steroids
- Severe hypercalcemia or hypomagnesemia
- Bicarbonate ingestion
- Licorice overdose (glycyrrhizic acid)
Treatment: Chloride-responsive: IV normal saline. Chloride-unresponsive: treat the underlying hormone/electrolyte disorder.
3. Respiratory Acidosis
Definition: pH ↓, PaCO₂ ↑ (>40 mmHg), HCO₃⁻ ↑ (compensation)
Mechanism: Inadequate CO₂ clearance or CO₂ overproduction.
Causes:
- Lung/airway disease: Airway obstruction, COPD, pneumothorax, pleural effusion, pulmonary edema, pneumonia
- Chest wall disease: Flail chest, obesity hypoventilation syndrome
- Respiratory muscle weakness: Myopathies, Guillain-Barré, hypokalemia, hypophosphatemia
- Decreased respiratory drive: Intracranial mass/hemorrhage, sedatives, narcotics, anesthesia
Treatment:
- Increase minute ventilation (↑ tidal volume × respiratory rate on ventilator)
- Noninvasive ventilation (BiPAP) for COPD exacerbation or heart failure
- If no improvement in 2 hours: proceed to invasive ventilation
- Severe cases: VV-ECMO as salvage modality
- Caution: Do not overcorrect a patient with chronically elevated baseline PaCO₂ - can cause cerebral ischemia and ventilator weaning difficulty
4. Respiratory Alkalosis
Definition: pH ↑, PaCO₂ ↓ (<40 mmHg), HCO₃⁻ ↓ (compensation)
Mechanism: Rate of CO₂ elimination exceeds production (hyperventilation).
Causes:
- Anxiety / pain / agitation
- Fever, sepsis
- Salicylate toxicity (classically causes respiratory alkalosis FIRST, then anion gap metabolic acidosis)
- Pulmonary embolism, pneumothorax, pneumonia
- Brain tumor / intracranial lesion
- Pregnancy, liver failure, heart failure
- High altitude
- Drugs: salicylates, catecholamines, progesterone
Symptoms of acute respiratory alkalosis (from hypocalcemia due to increased Ca²⁺-albumin binding):
- Lip and extremity paresthesias
- Carpal-pedal spasm
- Muscle cramps, syncope
Treatment: Treat the underlying cause. On a ventilator, inducing mild respiratory alkalosis can be used temporarily as an adjunct for refractory acidosis or traumatic brain injury.
Mixed Acid-Base Disorders
Mixed disorders occur when two or more primary disorders are present simultaneously. Clues:
- pH is normal but AG is elevated
- Compensation is greater or lesser than expected by the formulas
- Clinical context (e.g., patient on diuretics with poor perfusion = metabolic alkalosis + metabolic acidosis from lactic acidosis)
Oxygenation Assessment from ABG
| Condition | PaO₂ | A-a Gradient | Cause |
|---|---|---|---|
| Normal | 75-100 | Normal | - |
| Hypoventilation | ↓ | Normal | Neuromuscular, CNS, sedation |
| V/Q mismatch | ↓ | Elevated | COPD, PE, interstitial lung disease |
| Diffusion impairment | ↓ | Elevated | Pulmonary edema, ILD |
| Shunt | ↓ | Elevated | Does NOT correct with O₂ |
V/Q mismatch responds to supplemental O₂. True shunt (intracardiac, consolidated lung) does not correct with oxygen.
Quick Reference Summary
pH < 7.35 → Acidemia
PaCO₂ ↑ → Respiratory acidosis
HCO₃⁻ ↓ → Metabolic acidosis → Check AG
AG ↑ → MUDPILES
AG normal → HARDUP → Check urine AG
pH > 7.45 → Alkalemia
PaCO₂ ↓ → Respiratory alkalosis
HCO₃⁻ ↑ → Metabolic alkalosis → Check urine Cl⁻
Cl⁻ < 25 → Chloride-responsive (give saline)
Cl⁻ > 40 → Chloride-unresponsive (treat cause)
Always check compensation with formulas - mismatch = mixed disorder
Always calculate AG - even with normal pH
Sources: Current Surgical Therapy 14th Ed. | Barash Clinical Anesthesia 9th Ed. | Rosen's Emergency Medicine | Mulholland & Greenfield's Surgery 7th Ed. | Washington Manual of Medical Therapeutics
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