Induction in the Patient With a Full Stomach
Induction in the Patient With a Full Stomach
General anesthesia in patient with full stomach requires endotracheal intubation with a cuffed endotracheal tube. The cuff protects the lungs from soiling by gastric contents.
If Possible Reduce the Volume, Pressure and Acidity of the Stomach Contents
Patients with a stomach full of liquid, such as those with bowel obstruction or who are drunk should have a large nasogastric tube passed prior to general anesthesia. Often the patients will vomit during attempts at passing of a nasogastric tube. Remember that even after passing the tube the stomach is unlikely to be completely empty as nasogastric tubes are inefficient for removing liquids and useless for solids.
As discussed earlier certain elective patients, such as pregnant females in the third trimester, are at risk of acid aspiration despite being adequately fasted. This group of patients is best treated by decreasing the acidity and volume of gastric fluids by the use of ranitidine or cimetidine given 1 to 2 hours preoperatively. Unfortunately this is not adequate for emergencies that they should also be given 30mls of sodium citrate immediately before induction of anesthesia. Such techniques will raise the pH of the gastric fluid and make the consequences of aspiration less serious.
Consider the Best Form of Anesthesia
Due to the risks associated with general anesthesia the use of a spinal anaesthetic technique should be considered. This will avoid depressing the conscious level. Beware however of using deep sedation in combination with spinal anesthesia.
If general anesthesia is required in a patient at risk of having a full stomach the airway should be protected by a cuffed endotracheal tube. (Under the age of 10 an uncuffed endotracheal tube should be used.) The safest technique for introducing an endotracheal tube in this situation is called a rapid sequence induction (RSI or crash induction) using preoxygenation and cricoid pressure.
i) Preoxygenation: under normal circumstances the lungs contain a mixture of oxygen, nitrogen and carbon dioxide. At the end of expiration the volume of gas left in the lung (about 2 liters in adults) is called the Functional Residual Capacity (FRC). This contains the oxygen reserve on which the patient depends when they are not breathing. Most of the gas in the lung is nitrogen which can be replaced with oxygen thereby increasing the oxygen reserve. The technique of replacing the nitrogen contained in the FRC with oxygen is called preoxygenation or de-nitrogenation. After 3 minutes of breathing 100% oxygen most of the nitrogen has been replaced by oxygen.
ii) Cricoid pressure: the cricoid is a ring shaped cartilage situated between the first tracheal ring and the thyroid cartilage. When firm backward pressure is applied to it the esophagus is occluded preventing any regurgitated gastric fluid from entering the pharynx. It is completely reliable provided the pressure is put on the correct area.
Cricoid pressure (Sellick's maneuver) Pressure is exerted by the forefinger while the thumb and middle finger prevent lateral displacement of the cricoid ring (Figure 1.1).
Bimanual cricoid pressure: Counter pressure with a hand beneath the cervical vertebrae supporting the neck and minimizing distortions of the head position (Figure 1.2).
Technique of rapid sequence Induction
- Prepare your equipment and drugs - Check all the equipment carefully before starting and ensure that everything is at hand.
- Consider whether a nasogastric tube should be passed
- Assess how difficult endotracheal intubation is likely to be. If you expect difficulties think again whether local anaesthetic could be used or consider an awake intubation.
- Insert an intravenous cannula and demonstrate the position for cricoid pressure to your assistant.
Table 1.2 Equipment Required for a Crash Induction
- Tilting trolley or operating table
- Suction apparatus and tubing
- Anaesthetic machine, source of oxygen, anaesthetic circuit and facemask
- 2 appropriately sized laryngoscopes
- Correct size of cuffed endotracheal tube and one a size smaller
- Endotracheal tube introducer, syringe for cuff inflation and connections to circuit
- Range of oral airways (Anesthesia drugs - induction agent, atropine and suxamethonium)
- A trained assistant
- Preoxygenate the patient: Using an anesthetic breathing circuit, turn the oxygen to 6 to 8 litres/minute and apply the facemask to the patient. Ensure that there is a good seal between the mask and the patient's face. Ask them to breathe oxygen for three minutes. Do not allow the patient to breathe even a single breath of air during this phase or else the preoxygenation will have to be repeated. This is due to the volume of nitrogen that is contained in a single breath of air.
- Estimate the dose of induction agent which the patient will need (e.g., thiopentone 3- 5mg/kg) and give this intravenously, immediately followed by suxamethonium 1-2 mg/kg. As soon as consciousness is lost ask your assistant to apply cricoid pressure.
- Keep the facemask in place but do not ventilate the patient manually as some of the oxygen may enter the stomach increasing the intragastric pressure. As soon as the suxamethonium is effective intubate the patient, inflate the endotracheal tube cuff and check the position of the tube by listening to the lungs with a stethoscope. If intubation is delayed for any reason, or the patient's color deteriorates, manual inflation should be immediately carried out with cricoid pressure in place.
- When you are satisfied that the tube is placed correctly, fix it and then instruct your assistant to release the cricoid pressure.
- Proceed with the anaesthetic and surgery as planned. At the end of the surgery turn the patient on to their side and do not remove the endotracheal tube until the patient is fully awake and capable of protecting their own airway.