1. Prepare your equipment and drugs - where possible this should include all the apparatus listed in table 1. Check all the equipment carefully before starting and ensure that everything is to hand.

   Table 1 - Equipment required for a crash induction.

   (a) Tilting trolley or operating table (b) Suction apparatus and tubing (c) Anaesthetic machine, source of oxygen, anaesthetic circuit and facemask (d) 2 appropriately sized laryngoscopes (e) Correct size of endotracheal tube and one a size smaller (f) Endotracheal tube introducer, cuff syringe and connections to circuit (g) Range of oral airways (h) Anaesthesia drugs - induction agent, atropine and suxamethonium (i) A trained assistant

2. Consider whether a nasogastric tube should be passed.

3. 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.

4. Insert an intravenous cannula and demonstrate the position for cricoid pressure to your assistant.

5. Preoxygenate the patient. Using a Magill or other anaesthetic 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.

6. Estimate the dose of induction agent which the patient will need (eg thiopentone 5mg/kg) and give this intravenously, immediately followed by suxamethonium 1.5mg/kg. As soon as consciousness is lost ask your assistant to apply cricoid pressure.

7. 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.

   Note: if intubation is delayed for any reason, or the patient's colour deteriorates, manual inflation should be immediately carried out with cricoid pressure in place.

8. When you are satisfied that the tube is placed correctly, fix it and then instruct your assistant to release the cricoid pressure.

9. 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.

 
Difficulties with the Technique.

1. Intubation is unexpectedly difficult. Ensure that the cricoid pressure is not pushing the larynx to one side. If it is, move the larynx and cricoid cartilage by moving your assistant's hand to the correct position. Do not release cricoid pressure. If the suxamethonium needs to be repeated remember to give atropine before the second dose to avoid bradycardia, and ventilate the patient gently to prevent hypoxia. Maintain cricoid pressure at all times. If intubation proves impossible then carry on as described under failed intubation.

2. No oxygen. Obviously no preoxygenation can take place but it is still possible to use cricoid pressure as discussed above. In this situation the patient will need to be gently ventilated with air to prevent hypoxia after apnoea develops.

3. No suxamethonium. The best option here is to induce the patient in a head down position on the left side using a inhalation (gas) induction with halothane or ether in oxygen or oxygen enriched air. Once the patient is deeply anaesthetised they may be intubated whilst still in the lateral position. Cricoid pressure is not necessary in this situation as any regurgitated material will automatically run out of the mouth.

4. Failed intubation. If intubation proves impossible then it is best to accept the situation and adopt an alternative anaesthetic technique instead of wasting time with repeated intubation attempts. The possible options are to continue with a mask anaesthetic (provided the airway is easy to maintain while keeping an cricoid pressure) or to wake the patient up after turning them on their side and head down and attempt the procedure under local anaesthetic. Alternatively the patient may be allowed to wake up and an awake tracheostomy or intubation performed. The best course will depend on the condition of the patient and their degree of fasting, the operation planned, the facilities and level of expertise available.

5. The cricoid cartilage is difficult to identify. Using firm pressure with your index finger follow a line down the front of the neck from the front of the mandible. The first 'solid' structure you meet is the hyoid bone, followed by the thyroid cartilage (Adam's apple) which is much more prominent in males. Immediately below this you will feel a gap between the cricoid and thyroid cartilages (the cricothyroid ligament) and then the cricoid cartilage. Encourage your assistants to practice finding the cricoid cartilage on other colleagues until they are confident. Non-skilled assistants can provide cricoid pressure if they receive adequate instruction, and the position of the cricoid ring is marked on the skin in ink before starting.

6. The patient regurgitates despite the application of cricoid pressure. If there is only a small quantity of fluid suck it out of the pharynx and intubate the patient. Use a suction catheter to aspirate the trachea after intubation. If there is copious fluid then the patient should be turned on to the side and placed head down to protect the airway. Suction the pharynx and then intubate the patient.

   Note: When using small oxygen concentrators in association with drawover apparatus preoxygenation may be difficult as the machines can only provide 4 litres per minute of around 85 - 90% oxygen. When this mixture is used the patient will always entrain air into the drawover circuit making preoxygenation less efficient. One way round this is to fill a large plastic bag with 'oxygen' from the concentrator and use this as an oxygen reservoir during preoygenation. When used it should be attached to the inlet of the circuit. Remember to remove it before it empties completely.

 
Anticipated Difficult Intubation.

Awake intubation. This technique can be used to place an endotracheal tube before inducing anaesthesia. It is useful for patients in whom you expect intubation may be difficult and in whom maintaining an airway under anaesthesia may become a problem.

The best technique uses a fibreoptic bronchoscope but these are rarely available. A simpler technique is to give the patient a drying premedication with intramuscular atropine and then using some plain 2% lignocaine spray inside the mouth and then ask them to move the solution around the mouth. After a short time gently insert the laryngoscope as far as the patient will let you and spray some more lignocaine into the airway further down, then remove the scope. By repeating this manouvre you will soon see the epiglottis and cords and after spraying them well you be able to intubate the patient. Induce anaesthesia as soon as you have accomplished this. At all times be gentle and consider using sedation such as low dose diazepam and/or morphine to help you. Be careful however, not to depress respiration.

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