Gastrointestinal System Changes During Pregnancy

Gastrointestinal System Changes in Pregnancy

• Mechanical and hormonal alterations lead to changes in the gastrointestinal system during pregnancy.
• The enlarging uterus puts pressure on the stomach, causing an incompetent lower esophageal sphincter.
• Progesterone reduces the competence of the lower esophageal sphincter.
• Placental gastrin increases gastric acid secretion.
• These changes cause reflux of gastric acid into the esophagus and delayed gastric emptying.
• Pregnant patients are at risk for aspiration during anesthesia.

Anesthetic Considerations for Gastrointestinal Changes in Pregnancy

• Pregnant patients should be considered to have "full stomachs" regardless of fasting.
• Administer medications to reduce gastric acidity and volume before anesthesia.
• Use a non-particulate antacid, such as sodium citrate, and Metoclopramide (Plasil) 10mg IV to stimulate gastric emptying and increase lower esophageal sphincter tone.
• Position the patient with a roll under the right hip and a slight reverse Trendelenburg position to prevent passive reflux.
• Apply cricoid pressure until the patient is intubated.
• Avoid routine administration of positive pressure ventilation before intubation.

Pre-operative and Intra-operative Management

• Position patients at a 45° angle before induction to reduce the fall in FRC.
• Pre-oxygenate to maximize oxygen content in the FRC.
• Administer antimuscarinic drugs, such as atropine or glycopyrrolate, before induction to reduce saliva in the airway.
• Use mechanical ventilation, especially for obese patients, to reduce airway collapse and atelectasis.
• Apply positive end-expiratory pressure (PEEP) to maintain alveolar patency and prevent hypoxia.
• Use recruitment maneuvers to open collapsed portions of the lung.

Post-operative Management

• Continue oxygen into the postoperative period for patients at risk of hypoxia.
• Use a head-up tilt to increase FRC and prevent atelectasis.
• Extubate obese patients onto a CPAP mask to prevent airway collapse and atelectasis.
• Ensure good postoperative analgesia and encourage patients to take deep breaths and cough.

Inhalational Anesthetics

• Definition: Inhalational anesthetics are chemical compounds that can be delivered via inhalation and possess general anesthetic properties.
• Administration: Inhalational anesthetics are administered through a face mask, laryngeal mask airway, or tracheal tube connected to an anesthetic vaporizer and delivery system.
• Main use: Inhalational anesthetics are used to maintain anesthesia, and some can be used for induction.

Minimum Alveolar Concentration (MAC)

• Definition: MAC is the alveolar concentration of an inhaled anesthetic that prevents movement in 50% of patients in response to a standardized stimulus.
• Examples: Halothane MAC 0.75%, Isoflurane MAC 1.2%, Desflurane MAC 6.0%, Sevoflurane MAC 2.0%

Factors Affecting MAC

• Factors increasing MAC:
  • Hyperthermia
  • Hypernatraemia
  • Sympatho-adrenal stimulation
  • Chronic alcohol abuse
  • Chronic opioid abuse
  • Increases in ambient pressure
  • Hypercapnia
  • Decreasing age
  • Thyrotoxicosis
• Factors decreasing MAC:
  • Nitrous oxide
  • Hypothyroid/myxedema
  • Hypocapnia
  • Hypothermia
  • Hyponatraemia
  • Increasing age
  • Hypoxaemia
  • Hypotension
  • Anemia
  • Pregnancy
  • CNS depressant drugs
  • Other drugs: lithium, lidocaine, magnesium, acute alcohol abuse

Ideal Inhalational Anesthetic Characteristics

• Non-flammable, non-explosive at room temperature
• Stable in light
• Does not cause airway irritation
• Has minimal respiratory and cardiovascular effects
• Does not cause uterine relaxation or skeletal muscle relaxation
• Does not potentiate non-depolarizing neuromuscular blockade

This quiz covers the mechanical and hormonal changes that occur in the gastrointestinal system during pregnancy, including effects on the stomach and esophageal sphincter.