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