Anesthesia Pharmacology Chapter 21:  Gastrointestinal Pharmacology 

• Gastrokinetic agents: useful in reducing gastric fluid volume.

  • Rationale: Reduction of gastric fluid volume: important to decrease risk of aspiration pneumonitis

    •  High-risk patients:

      • acute pain; "full stomach" -- emergency surgery

      • patient with hiatus hernia

      • patient with esophageal reflux

  •  Aspiration gastric contents may lead to chemical pneumonitis

  • Pulmonary aspiration of gastric content: rare in elective surgery

  • Drinking clear fluid -- up to three hours before surgery: no measurable gastric volume or pH effect in healthy children (age group: 2-12 years){note: healthy patients; clear liquids only}

  •  in adults: possibly, relatively high-risk of pulmonary complications if aspiration volume:

    1. > 25 ml and

    2. pH < 2.5

• Metoclopramide (Reglan)

  • Classification: dopamine agonist

  • Gastrokinetic activity:

    •  stimulates upper gastrointestinal motility

    •  increases gastroesophageal sphincter tone

    •  relaxes the pylorus

    •  relaxes the duodenum

  • Clinical Uses:

    • Reduction of preoperative gastric fluid volume

    • Anti-emesis

      • 0.15 mg/kg IV metoclopramide (Reglan) reduces vomiting incidents in children after tonsillectomy {administered on arrival in post-anesthesia care unit}

    • Symptomatic relief of gastroesophageal reflux

    • Treatment of gastroparesis

    • Metoclopramide (Reglan) (10-20 mg IV)-- speeds gastric emptying; useful:

      • before anesthesia induction

      • facilitation of small-bowel intubation

      • enhanced radiographic small intestine examination

    • Anesthesia induction-cases in which metoclopramide (Reglan)-mediated gastric-emptying may be beneficial:

      • patients who have recently eaten

      • trauma patients

      • patients with diabetes mellitus and symptoms of gastroparesis

        • oral, 10-20 mg dosage

      • parturients (particularly those with a history of esophagitis {"heartburn", indicating lower esophageal sphincter dysfunction and gastric hypomotility}

      • obese patients

  • Mechanism of Action:

    • selective cholinergic stimulation of the GI tract (gastrokinetic effect)

      • affects smooth muscle of the proximal GI tract;requires some basal cholinergic tone

  • Increases of the rate of gastric emptying

    • no known effect on gastric acid secretion or gastric fluid pH

  • Routes of Administration:

    •  Oral: 10 mg -- onset within 30-60 minutes

    •   Parenteral: 5-20 milligrams -- 15-30 minutes before induction

      • IV administration over 3-5 minutes-- prevents abdominal cramping (occurs with more rapid infusion)

  •  No guarantee of gastric emptying with metoclopramide

    • significant gastric fluid could still remain

    •  prior administration of other drugs (e.g. opioids) or concurrent atropine administration may offset metoclopramide's effect on the upper gastrointestinal tract.

      • However, gastric stasis due to morphine may be reversed by metoclopramide (Reglan); opioid-mediated nausea/vomiting may be reduced by metoclopramide (Reglan)

      • In parturients undergoing elective cesarean section with epidural anesthesia,metoclopramide (Reglan) {0.15 mg/kg IV} reduces early, postoperative nausea & vomiting

    • Gastric volume will not be reduced further (elective surgery) in the presence of already small gastric volumes

  • May not be effective: following sodium citrate administration

  • Particularly effective in reducing aspiration pneumonia's risk when metoclopramide is combined with a H₂ receptor antagonist (e.g. Ranitidine) before elective surgery

  •  Side effects

    • may include extrapyramidal reactions and stimulation of prolactin secretion due to dopamine receptor antagonist properties

      • Extrapyramidal reactions:-- frequency = < 1% with chronic metoclopramide (Reglan) administration

        • Dystonic:

          • oculogyric crisis

          • opisthotonus

          • trismus

          • torticollis

        • Akathisia {restlessness, lower extremity}

    • abdominal cramps following rapid IV administration (less than three minutes)

    • cardiac arrhythmias: in patients receiving ondansetron (Zofran) + metoclopramide (Reglan) IV

• Cisapride (Propulsid)--REMOVED FROM US MARKET (Cardiac arrhythmias including ventricular tachycardia, ventricular
  fibrillation, torsades de pointes, and QT prolongation have been reported in patients taking cisapride)

• Use of gastrokinetic drugs does not diminish the need for correct, diligent anesthetic techniques to protect the airway during anesthesia:

  •  induction

  •  maintenance

  •  emergence

1. Moyers, J.R., Preoperative Medication, Chapter 21, In: Clinical Anesthesia 3rd edition, (Barash, P.G., Cullen, B.F. and Stoelting, R.K., eds) Lippincott-Ravin, Philadelphia, New York, 1997, pp. 519-529

2. Stoelting, R.K., "Antacids in Gastrointestinal Prokinetics", in Pharmacology and Physiology in Anesthetic Practice, Lippincott-Raven Publishers, 1999, pp 444-451.