## Management of Vomiting in Mechanical Gastric Outlet Obstruction ### Critical Distinction: Mechanical vs. Functional Obstruction **Key Point:** Prokinetic agents (metoclopramide, domperidone) are **contraindicated in mechanical obstruction** because they increase intraluminal pressure against a fixed anatomical blockade, worsening symptoms and risking perforation. ### Why Metoclopramide Is Harmful Here Metoclopramide works by: - Blocking dopamine receptors → enhancing acetylcholine effect - Increasing gastric contractions and antral peristalsis **In mechanical obstruction:** Increased gastric contractions against a fixed blockade (tumor, stricture, edema) leads to: 1. Increased intragastric pressure 2. Risk of gastric perforation 3. Worsening of vomiting and abdominal pain 4. Delayed definitive treatment **Warning:** Prokinetics are a **trap answer** in mechanical obstruction scenarios. They are appropriate only for functional/motility disorders (gastroparesis, GERD). ### Correct Management Algorithm ```mermaid flowchart TD A[Vomiting + Gastric Outlet Obstruction]:::outcome --> B{Mechanical or Functional?}:::decision B -->|Mechanical<br/>confirmed on imaging| C["STOP prokinetics<br/>immediately"]:::urgent C --> D["1. IV fluid resuscitation<br/>2. Nasogastric tube<br/>3. NPO status"]:::action D --> E{Etiology?}:::decision E -->|Malignancy| F["Endoscopic stenting<br/>or surgical bypass"]:::action E -->|Benign stricture| G["Endoscopic dilation<br/>or surgical reconstruction"]:::action E -->|Edema/inflammation| H["Medical management<br/>+ repeat imaging"]:::action B -->|Functional<br/>gastroparesis| I["Metoclopramide<br/>+ domperidone"]:::action ``` ### Symptomatic Management Without Prokinetics | Step | Rationale | |------|----------| | **IV fluid resuscitation** | Correct dehydration and electrolyte imbalance (hypochloremic hypokalemic metabolic alkalosis from vomiting) | | **Nasogastric tube** | Decompress stomach, relieve pressure, allow monitoring of output | | **Antiemetics** (ondansetron, metoclopramide STOPPED) | Control nausea/vomiting without worsening obstruction | | **NPO status** | Prevent further gastric distension | | **Definitive intervention** | Endoscopic stenting (malignancy), surgical bypass, or dilation (stricture) | **Clinical Pearl:** In gastric cancer with outlet obstruction, **endoscopic self-expanding metal stent (SEMS)** placement is now preferred over surgery in many cases, offering faster symptom relief and shorter hospital stay. However, the *immediate* next step is always decompression and fluid resuscitation. **High-Yield:** The mnemonic **"STOP-DECOMPRESS"** for mechanical obstruction: - **S**TOP prokinetics - **T**reat dehydration (IV fluids) - **O**ral NPO - **P**lace NG tube - **D**efine etiology (imaging) - **E**ndoscopy or surgery for definitive management - **C**ontinue antiemetics (5-HT₃ antagonists safe) - **O**bserve output and clinical response - **M**onitor electrolytes - **P**repare for intervention - **R**efer to gastroenterology/surgery - **E**valuate for complications - **S**upport nutrition (TPN if prolonged) - **S**ymptomatic relief [cite:Harrison 21e Ch 40; KD Tripathi 8e Ch 16]
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