Contents

1. Clinical Scenarios*.
2. Endotracheal tubes
3. Laryngoscopes
4. The process of intubation
5. "Going asleep for intubation" – what anaesthetists do
6. Why critical care patients are different
7. The haemodynamic consequences of intubation / initiation of ventilation
8. The initiation of ventilation.
9. Criteria for initiation of mechanical ventilation.
10. Criteria for successful extubation
11. Key Points

*Solutions are not presented here at the moment. These scenarios are given to make you think, there are many ways of "skinning a cat", what is important is a safe and compelling arguement.

A 57 year old male presents with acute abdominal pain. His abdomen is distended, and on chest x-ray there is air under the diaphragm an effusion in his right base. His blood pressure is 70/40, pulse 130, resp rate 35. His blood gases are pH 7.1, PO2 6.5, PCO2 7.22, HCO- 18, BE –5.

The diagnosis is a perforated viscus, with septic shock. How would you go about intubating this patient?

A 74 year old female presents in severe respiratory failure as a result of COPD. Her PO2 is 5.5kPa (41mmHg) on FiO2 of 0.8 and CPAP of 7.5. Her CO2 is 12kPa (90mmHg). She is drowsy from CO2 narcosis. 

What criteria would you use to decide whether or not to mechanically ventilate this patient? 

A 16 year old male is rescued from a house fire. He has inhaled a lot of gas, and has a PO2 of 7kPa (52mmHg) and a carboxyhaemoglobin of 30%. His eyebrows are singed and there is soot on his tongue. 

Does this patient require mechanical ventilation and if so why?

Solutions:

These are three patients who will require ventilatory assistance. The first patient is hemodynamically unstable. The administration of even small amounts of hypnotic agent will cause a precipitous drop in this patient's blood pressure, which is currently being maintained by severe sympathetically mediated vasoconstriction (hypnotic agents reverse this). There is no conventional method for preparing this patient for intubation, but I would administer a small amount of local anesthetic spray to the tongue and pharynx, and intubate without muscle relaxants. When the airway is secured, manual ventilation should be gentle so as to avoid reducing preload.

There are three reasons for commencing mechanical ventilation: 1. Airway protection - eg. in unconscious patients following a head injury 
2. Ventilation failure - stroke, myasthenia gravis, Guillain Barre syndrome etc.
3. Oxygenation failure - which is caused by either increased dead space ventilation (pulmonary embolism/hypovolemia) or increased shunt (pneumonia, ARDS, pulmonary edema).

A number of criteria are conventionally given to help decide on whether or not to ventilate patients:
1. Respiratory rate >35 breaths/minute.
2. PaCO2 >55mmHg (acute retention, respiratory acidosis).
3. PaO2 <70mmHg on 100% oxygen or an AO2-aO2 gradient of >400mmHg.
4. Severe head injury - control of CO2
5. Airway protection / bronchopulmonary toilet.

The patient in case 2 requires ventilation on the basis of deteriorating blood gases (respiratory failure). The third patient requires intubation for airway protection, and for controlled ventilation with 100% O2 to reduce the carboxyhemoglobin load.

• There are a number of different types of endotracheal tubes.
• The commonest type is a plastic curved tube with a cuff which is fixed to the outer surface of the distal end. The cuff is inflated with air to provide a seal between the tube and the inner lining of the trachea. There is a amall indicator balloon which is attached by a small tube to the endotracheal tube. This serves to indicate that the cuff is inflated / deflated
• On the side of the tube the internal diameter is indicated: eg. 8.0 = 8cm internal diameter. This is the size of the tube. Smaller tubes are associated with increased resistance to gas flow. Larger tubes may damage the trachea. For most women a 7.5mm ETT will suffice, and a size 8.0 –8.5 for most men. The 7.5mm ETT will actually work well for most patients.
• These tubes are usually cut so that they don’t slip too far down and enter one of the main bronchi, thus ventilating only one lung.
• For most women the tube is sited at 19 – 20cm at lip level. For most men this is 21 – 23cm.

• 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 llooks like a spring. The problem with these tubes in the ICU is that they cannot be cut.

• 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 are the instruments used for performing intubations. A laryngoscope consists of a blade, of varying sizes (1 to 4), which includes a fibreoptic light source, and a handle, which contains the power source for the light.
• For most laryngoscopes the blade is curved. For small babies, on uses a straight blade. This is because the technique for intubating infants is different.

• When anaesthetising patients for emergency surgery, anaesthetists use a process called a "rapid sequence induction". The objective is to secure the airway rapidly and prevent soiling of the lungs with gastric contents.
• The patient goes asleep with the aid of an intravenous induction agent: thiopentone or propofol. These cause hypnosis and amnesia. They have a common problem in that they cause peripheral vasodilatation (propofol>thio), and cause a drop in the blood pressure.
• 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. Sux is contraindicated if there is hyperkalaemia, as it may cause cardiac arrest.

1. Preparation:

Drugs: thio, sux, 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.

 

• Hypoxaemia
• Acidosis – respiratory or metabloic.
• Hypotension ® hypovolaemia: absolute due to haemorrhage or third space fluid loss, relative due to compensation, which may be exposed when there is a loss of vascular tone.
• The rapid sequence induction is not always appropriate in critical care patients.
• They are often drowsy, acidotic, hypotensive and dehydrated. Even a small amount of peripheral vasodilatation (with propofol) may expose intravascular dehydration and send the blood pressure spiralling downwards.
• The method used for administering amnesic agents to these patients depends directly on their clinical condition. On occasion one can perform a RSI, and the patient will not be aware of intubation. Sometimes it may only be possible to give a small amount of sedation. Often it is necessary to intubate the patient awake.

1. Awake intubation +/- local anaesthesia applied topically.
2. Sedation with midazolam +/- local.
3. Midazolam + suxamethonium.
4. Ketamine + suxamethonium (small babies).
5. Thio + sux

It is essential that all resuscitative agents are available following intubation.

• The inevitable outcome of intubation in the ICU is hypotension, by a variety of means. It is important to always have vasoactive agents at hand when intubating patients: Ephedrine, phenylephrine or metaraminol (all vasoconstrictors) along with adrenaline. The latter, while very effective in gradually reversing hypotension over minutes by infusion, given in bolus form often causes rebound hyper-hypertension!
• The initiation of manual or mechanical ventilation is also associated with hypotension due to an increase in interthoracic pressure and a reduction in preload.
• Inotropes are frequently required following intubation, and should always be available in this event.

• Although the trend in ventilatory strategies is to permit the patient to initiate his/her own breaths and control ventilation using pressure support and PEEP, this is not appropriate immediately following intubation.
• It is essential to reverse the metabolic abnormalities and acidosis, correct the blood gases, treat the precipitating factor, and paln out the subsequent ICU management. I would suggest mandatory ventilation in the early stages, with pressure support for the patient’s own breaths. A SIMV rate of 10, Tidal Volume of 5-10ml/kg, PEEP 5, pressure support of 20. The pressure support is titrated against the tidal volumes taken, the FiO2 as appropriate, and the IMV rate is weaned at the patient begins to "breath up".

1. Intubation involves the placement of a plastic tube into the larynx.
2. Cuffed curved tubes are used in the ICU.
3. The tube is inserted using a laryngoscope, occasionally facilitated with a bougie.
4. Anaesthesia for intubation may be general, local or sedation. Powerful vasodilatory agents are avoided as severe hypotension may follow intubation.
5. Although the framework of the rapid sequence induction is essential for intubating patients in ICU, the execution is different as the anaesthetic agents are varied as appropriate.
6. Hypotension following intubation is treated with fluids, vasoconstrictors and inotropes.
7. Intubation and ventilation are merely one process in the ICU management of patients; they facilitate airway protection and ventilation.