2.6: Rapid sequence Induction

Ideally all patients should be fasted before anaesthesia. If the stomach is not empty when consciousness is lost, the patient may regurgitate gastric material that may be aspirated into the lungs causing a chemical and infective pneumonitis as well as airway obstruction(Mendelson’s syndrome). Based on animal studies, as little as 25 ml of gastric fluid with a pH less than 2.5 can cause severe pneumonitis.

Aspiration Pneumonitis

The more acidic the gastric fluid, the greater the lung damage. The acid causes a loss of surfactant. Pneumonitis develops within hours. The patient will become dyspnoeic,tachypnoeic, tachycardic, hypoxic and may develop bronchospasm. X-ray changes occur within 8 to 24 hours. Treatment includes oxygen, bronchodilators and physiotherapy.Bronchoscopy can help remove large particles. If secondary bacterial infection occurs the patient will require antibiotics. In non-hospital patients, anaerobic organisms predominate and penicillin may be the appropriate choice of antibiotic. In hospitalised patients both anaerobic and aerobic organisms are commonly found and these patients may require penicillin plus gentamicin plus metronidazole. Corticosteroids are not of  proven benefit in any aspiration syndrome.

Predisposing Patient Factors

Factors predisposing to aspiration include a full stomach, hiatus hernia, reflux oesophagitis, gastrointestinal obstruction, gastrointestinal bleeding, oesophage alachalasia, oesophageal strictures, nasogastric tube, ineffective laryngeal reflexes, ileus,intra-abdominal infection, trauma, anxiety, pain, pregnancy, obesity and some drugs(e.g. opioids).The anesthetist must identify the patients at risk of aspiration of gastric contents and undertake action to reduce the risk of aspiration.

Recommendations

1. If possible, delay anaesthesia/surgery until the patient has had adequate fasting time. However the patient must not be put at risk by delaying urgent surgery.Some patients will not empty their stomach even after 6 hours of fasting and must be treated as non-fasted.2.

 

2. Attempt to reduce the volume and acidity of the stomach contents. Empty the stomach with a nasogastric tube. Remember that a nasogastric tube is unlikely tocompletely empty the stomach. The nasogastric tube should be removed immediately before anaesthesia. H-2 antagonists (ranitidine, cimetidine) 2 hours preoperatively and non-particulate antacids (sodium citrate 30 ml) 30 minutes preoperatively will reduce acidity. Metoclopramide can increase the lower oesophageal sphincter tone and increase stomach emptying.3.

 

3. Consider the best type of anaesthesia. Local anaesthetic techniques without sedation will maintain laryngeal reflexes and will protect against aspiration. If general anaesthesia is required, the lungs must be protected by a cuffed endotracheal tube (before the age of puberty an uncuffed endotracheal should be used). The best method for intubation is a “rapid sequence induction” (RSI) using pre oxygenation and cricoid pressure.

 Rapid Sequence Induction

Rapid sequence induction requires careful preparation and good assistance. The anesthetist must assess the patient’s airway. It may be wise to choose a different anaesthetic technique if the anesthetist believes that intubation may be difficult.

Recommended technique of Rapid Sequence Induction

1. Prepare all equipment and drugs. Oxygen, suction, anaesthetic machine, anaesthetic circuit, masks,endotracheal tubes, laryngoscopes, tilting operating table, induction agent,suxamethonium.Ensure you have an assistant.

2.  

   Insert an intravenous cannula.

3. Demonstrate the position for cricoid pressure to the assistant. The cricoid pressure must not be released until the anesthetist is certain that the endotracheal tube is correctly placed within the trachea and that the cuff is inflated. There must be no air leak.

4. Pre oxygenate the patient. The lungs contain approximately 79% nitrogen and 21%oxygen. At the end of a normal expiration there is a volume of air remaining in the lungs called the functional residual capacity (FRC). The FRC has several physiological functions including acting as an oxygen reserve on which the patient depends when they are not breathing. The normal FRC is 30 ml/kg in the adult. If the patient breaths 100% oxygen for 3 minutes most of the nitrogen in the FRC will be replaced with oxygen. Ideally this allows the patient up to 7 minutes of apnoea before becoming hypoxic.

5. Administer the induction agent and as soon as consciousness is lost ask the assistant to apply cricoid pressure (Sellick’s manoeuvre). The assistant must not release the cricoid pressure until instructed by the anesthetists. The cricoid is the only complete ring of cartilage in the larynx and trachea. When firm backward pressure is applied to the cricoid, it will compress the oesophagus between the cricoid and a vertebral body preventing any regurgitated gastric fluid from entering the pharynx. Cricoid pressure requires 2 to 4 kg of pressure. If the cricoid pressure is incorrectly applied it may hinder intubation. If intubation is unexpectedly difficult the anesthetist must check that the cricoid pressure is not pushing the larynx to one side. The anesthetist should move the assistant’s hand to the correct position but the cricoid pressure must not be released. If intubation is impossible, the cricoid pressure must be maintained.

6. Administer suxamethonium (1.5 mg/kg) (scoline, succinylcholine).Suxamethonium is the only muscle relaxant that should be used for a rapid sequence induction. It has an ultra short duration of action (3 to 5 minutes). Pre oxygenation may provide up to 7 minutes reserve of oxygen. If intubation is impossible the patient should have return of spontaneous respiration before they become hypoxic. If the patient does become hypoxic before the return of spontaneous respiration the an esthetist must give gentle mask ventilation. The cricoid pressure must not be released.

   If suxamethonium is not available or contraindicated then the anesthetist may need to use a local anaesthetic technique or consider using an inhalation induction with the patient in a head down position on the left side. Once the patient is deeply anesthestized they are intubated whilst still in the lateral position. Any regurgitated material should drain away from the airway.

7. Prepare to intubate. Once the suxamethonium has been given, the anesthetist should keep the facemask in place but must not attempt to ventilate the patient manually, unless the patient becomes hypoxic, as some of the oxygen may be forced into the stomach, increasing intragastric pressure and increasing the risk of aspiration. As soon as the suxamethonium is effective the anesthetist must intubate the patient, inflate the endotracheal tube cuff, check the position and check that there is no air leak.

8. Release cricoid pressure only when the patient is intubated.

9. Extubate the patient when fully awake and on their side. The patient is at risk of aspiration when recovering from the anaesthesia. They should be turned onto their side to allow any stomach contents that are regurgitated to drain away from their airway. The anesthetist should remove any regurgitated gastric contents with gentle suction. The patient must be fully awake and capable of protecting their own airway before the endotracheal cuff is deflated and the tube removed.