Contents

3. Laryngoscopes.

Why do we intubate patients?

Particularly when the patient is on his / her side, face down or head down. Moreover if the patient is edentulous, obese or has a large tongue or beard, it may be difficult to maintain the airway even in the supine position. The laryngeal mask airway has loosened some of these reasons, and is often used now where an endotracheal tube (ett) would have been used in the past.

The ett prevents the aspiration of blood, mucus, gastric acid (which may regurgitate) or vomit. Materials such as these may cause pneumonitis or bronchial obstruction (leading to airway collapse).

The ett facilitates removal of mucus and other undesirable material from the airway.

Traditionally mechanical ventilation has been performed through an ett. The cuff on the ett provides a good seal and guarantees the selected tidal volume. However controlled ventilation can also be given by 1. Laryngeal mask airways, 2. Tracheostomies, 3. Non invasive face masks.

Endotracheal Tubes

• Uncuffed tubes: used in children under the age of 12. This is because the paediatric airway is narrowest in the sub glottic area, and it is essential that the fit is not too tight or else there will be necrosis of the mucosal lining. When intubating a child there must always be an audible leak.
• Reinforced Tubes

These are used under certain circumstances in theatre where there is concern that the ett withh be daamaged or kinked. The tube contains an internal metal ring that looks like a spring. The problem with these tubes is that they cannot be cut and tend to slide down one bronchus.

• Double Lumen Tubes

These are used in thoracic anaesthesia in order to preferentially ventilate one lung and allow the other lung to collapse. They are rarely used in ICU, the exception being in lung contusions, where it may be impossible to ventilate the sick lung without damaging the healthy one.

• Southfacing Tubes

These are used in ENT and dental surgery. They have no role in ICU as suction can only be performed through them with difficulty.

• Northfacing tubes.

These are used for nasal intubations in faciomaxillary surgery. Again they have no role in ICU. Nasal intubations in ICU are usually performed with standard etts.

Laryngoscopes

The process of intubation

1. Recent meal
2. Delayed gastric emptying: trauma, acute abdomen, morphine.
3. Incompetant lower oesophageal sphincter: obesity, hiatus hernia, pregnancy

• The patient goes asleep with the aid of an intravenous induction agent: thiopentone or propofol. These cause hypnosis and amnesia.
• To rapidly intubate the larynx, it is important to have a high degree of muscle relaxation very quickly. The drug used for this is suxamethonium. This acts by causing every muscle in the body to contract, and subsequently relax. The result of this is the sudden release of a lot of potassium into the bloodstream. Suxamethonium is contraindicated if there is hyperkalaemia, as it may cause cardiac arrest. Because it causes such widespread muscle contraction (rather like "cramping"), patients usually complain of muscle pains the next day.
• It is not conventional to premedicate patients undergoing rapid sequence induction or to administer sedatives such as midazolam or fentanyl prior to the administration of anaesthesia. The reason for this is that if you are unable to intubate the patient, then the anaesthetic agents will wear off and the patient will wake up within 5 mins, thus not putting the airway at risk.
• We avoid manually ventilating patients undergoing rapid sequence induction, as this inflates the stomach and encourages regurgitation.

The procedure of rapid sequence induction:

1. Preparation:

Drugs: thiopentone, suxamethonium, atropine, ephedrine.

Endotracheal tubes: a variety of sizes available and cut and checked (to make sure that the cuff is intact -–ie. Not punctures)

Laryngoscopes – 2 functioning laryngoscopes with a variety of blades.

Suction – on and under the pillow.

A Gum elastic bougie – to railroad the ETT is there is difficulty in placing the ett.

An intravenous cannula, with a free-flowing drip

2. Monitoring:

Blood pressure, ECG, pulse oximetery, end tidal CO2 (if available).

3. Assistant:

This person must be familiar with the RSI process and be able to apply cricoid pressure. The cricoid carthilage is the ring felt below the larynx. If this is displaced posteriorly, because it is circular shaped and solid, it compresses and closes the oesophagus (which lies behind it). This prevents passive regurgitation of gastric contents.

4. Induction:

The patient is preoxygenated for a full three minutes, to wash all of the nitrogen out of the lungs and create a resevoir of O2.

Thiopentone is administered, cricoid pressure is applied, followed by suxamethonium.

The patient is asleep when the eyelash reflex is lost, and relaxed when fasciculation stops.

The patient is intubated, the cuff inflated and the tube secured. Cricoid pressure is not released until the anaesthetist is happy that the tube is correctly placed. This is established by listening for bilateral breath sounds, observing uniform bilateral chest movement and an etCO2 trace (if available).

 

When the anaesthetist is happy that the airway is intact, he administers the remainder of the anaesthetic agents - fentanyl, nitrous oxide and the volatile agent which maintains anaesthesia (e.g. isoflurane). A non depolarising neuromuscular blocker may be added now to maintain muscle relaxation for the duration.

At the completion of surgery, the anaesthetic agent is turned off, 100% oxygen is administered, neuromuscular blockade is reversed and the patient is permitted to emerge from anaesthesia. The risk of aspiration of gastric contents is as high now as at the beginning. The airway is carefully cleaned with suction and the ett remains in situ until the patient is fully awake, lying on their side and is able to remove the tube themselves.