Anaesthetic Emergencies

Rapid sequence induction

A rapid sequence induction is indicated when the stomach is not empty and therefore there is a high risk of vomiting or regurgitating on induction. This occurs in three groups of conditions. Firstly in emergency anaesthesia, when the condition precipitating the emergency is likely to also affect the emptying of the stomach; this also includes emergency as well as elective Caesarean sections. Secondly in primary gastrointestinal pathology necessitating surgery; this includes all forms of intestinal obstruction. Thirdly, many anaesthetists employ this technique in patients who have conditions known to be associated with significant delay in gastric emptying, such as hiatus hernia, reflux oesophagitis, auto-nomic neuropathy and severe uraemia.

After explanation and reassurance, the patient is preoxy-genated and monitoring commenced. Before loss of consciousness, pressure is applied by a trained assistant to the cricoid ring. The cricoid is the only tracheal ring which completely encircles the trachea. Firm cricoid pressure, known as Sellick's manoeuvre, does not collapse the ring or trachea, but instead seals the cephalad end of the oesophagus by apposing it against the vertebral column posteriorly. The chosen i.v. induction drug is administered.

After loss of consciousness, suxamethonium is administered. Maximal relaxation occurs after the fasciculations have ceased and this is when the trachea should be intub-ated. The cuff is sealed and then cricoid pressure is released. Ventilation proceeds as usual. The entire procedure should take between 30 and 90 s; with adequate preoxygenation this should not produce serious hypoxaemia.

This technique fundamentally involves administering muscle relaxants before the airway is controlled. This entails a calculated risk which should be balanced against the risk of vomiting and aspiration. Patients thought likely to vomit on induction are at a similar risk on awakening, and should be extubated in the left lateral position when awake.

Failure to intubate

The primary objective of intubation is to facilitate oxygenation. When intubation proves difficult, too time consuming, or impossible, oxygenation, more than ever, remains the primary objective. Failure to understand and apply this essential principle can have disastrous consequences.

A difficult intubation can be made 'easy' and an impossible one 'possible' by meticulous attention to the following: effective preoxygenation, correct positioning of the head and neck, readily available auxiliary equipment such as different laryngoscopes, bougies, etc.; also, it is important to allow time for full muscle paralysis to develop.

Intubation should be considered to have failed after three attempts, or before serious hypoxaemia develops. If this occurs, anaesthetists should apply the 'failed intubation drill'; the first step of this drill is to communicate with the theatre personnel and to ask for additional anaesthetic help. It is impossible to state too strongly that the patient must not be repalarysed in order 'to have one more try'. This drill is designed to protect the airway, oxygenate the patient, and allow rapid awakening.

Failure to intubate and ventilate

Certain manoeuvres may make it easier to ventilate patients. These include proper control of the airway by lifting the chin and thrusting the jaw forward, if necessary with both hands while the assistant squeezes the reservoir bag; an oro-pharyngeal airway may be of use; gentle continuous positive pressure to the airway may help. The patient should be moved to the left lateral position, if, as is likely, there is risk of regurgitation; this may help ventilation. If these fail there is a good case for removing or repositioning cricoid pressure, if it was being applied. A LMA has been used successfully to ventilate patients in this situation.

If all these attempts fail to enable ventilation the situation is very serious and a difficult decision arises.

Many anaesthetists would then perform a cryco-thyroid puncture with a large bore (14 G or 16 G) cannula, and connect it to the plunger of a 2 ml syringe. The plunger can then be connected to the catheter mount of a 6 mm tracheal tube, which in turn connects to a standard breathing system.

Some would perform a tracheostomy or a retrograde intubation with the aid of a guide wire; these techniques are time consuming, technically difficult, and are not free of risks.

Hypoxaemia may cause multiple arrhythmias, including bradycardia and cardiac arrest. Clearly, drugs given as part of resuscitation will not be effective until the hypoxaemia resolves.

Cardiorespiratory collapse during anaesthesia

Rarely cardiac arrest develops without warning in healthy patients. Much more often, however, a spiralling loop of complications in a compromised patient finally leads to cardiac arrest. There is no substitute for careful observation and a high index of suspicion. Monitor alarms must not be cancelled and should not be assumed to represent technical faults until the patient's condition has been assessed.

In principle the management is to remove the cause, commence usual cardiopulmonary resuscitation [23] and call for assistance.

Primary cardiac arrest

The most likely causes are anaphylaxis to anaesthetic agents, arrhythmias, profound hypovolaemia, myocardial ischaemia, and electrolyte imbalances. Specific management priorities include securing the airway, by intubation if possible, ventilation with 100% oxygen, and cardiac massage. In addition the following may be necessary:

1. Adrenaline (1 mg bolus): Maintains organ perfusion to heart and brain and has positive effects on heart rate and contractility.

3. Defibrillation: Electrolyte imbalances causing ventricular fibrillation may not respond to DC cardioversion until the cause has been corrected.

4. Fluids: Anaphylaxis causes intense vasodilatation, which may require enormous volumes of intravascular fluids. The type of fluid is probably less important than the amount.

Primary hypoxaemia

The most important causes are as follows:

1. Misplacement of the tracheal tube: Oesphageal intubation can go undetected for some time, even to an experienced anaesthetist. If in doubt, the position of the tube must be confirmed by these methods: layrngoscopy, adequate ventilation, end expired capnography and fibreoptic bron-choscopy. The latter two are the only certain methods. In addition, a correctly placed tube may have been displaced from the trachea, for example during patient transfer.

2. Upper airway obstruction: Often caused by laryngeal spasm or by a blocked or kinked tracheal tube.

3. Bronchoconstriction: Can be caused by asthma and/or anaphylaxis.

4. Pneumothorax: This can be very difficult to detect. A pneumothorax may rapidly deteriorate with positive pressure ventilation, especially if nitrous oxide is used.

5. Pulmonary or air embolism.

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