The state of anaesthesia

One of the first changes seen with the induction of anaesthesia is the loss of upper airway reflexes, when this occurs, the effort of breathing in will cause the throat to partially collapse. This is similar to the changes that cause snoring during sleep. This partial obstruction is so well known that anaesthetists automatically correct for this to maintain a satisfactory airway. However, patients with either severe snoring, or who are having surgery to their throat or palate may be at greater risk than normal of developing severe problems in maintaining their airway after the operation. They are closely monitored in the recovery ward in theatre, until all the anaesthetic drugs have worn off, which with the modern anaesthetic agents is rarely more than a few hours.

Patients with Obstructive Sleep Apnoea (OSA) are potentially at much more risk. The failure to maintain a normal airway during sleep indicates that the airway will also be completely lost during anaesthesia. However, there are also other serious problems with OSA. The repetitive falls in oxygen during the obstructions lead to damage to the heart, and to changes in the normal control of breathing.

Some patients are grossly overweight and they are often very sleepy. All these cause problems in the administration of a safe anaesthetic (the causes of increased airway collapse will often also affect the ability of the anaesthetist to maintain a patent airway as well). The heart failure and changes in the control of breathing make the patient very vulnerable to sedative drugs including the powerful pain-killers such as morphine, most anaesthetic drugs, and the benzodiazepines, diazepam for instance.

Obesity leads to greatly increased risks, by itself, from difficulty in laying flat, from breathing against the weight of the fat on the chest and abdomen, and from an increased need for oxygen. Obesity also leads to an increased risk of stomach acid leaking up the oesophagus with the possible fatal result of inhaling gastric acid.

Many patients who have OSA are effectively treated by nasal CPAP. It is important to bring the machine into hospital with you, and to show the nurses how it works. They, and many of the doctors, may not have seen one before and may need to help set it up for you after the operation.

While all operations are stressful, and the idea of a sedative drug as a premedication before surgery appears attractive, these drugs should be avoided because, even with CPAP, patients with OSA are at risk from a dangerous depression of their breathing.

The CPAP system should be taken to the theatre. It will be used as soon as the operation is over, and the anaesthetic is being reversed in the recovery ward within the theatre. This is a particularly important time because many of the protective reflexes present when awake are only slowly returning. One of the last to return is the maintenance of a patent airway.

After most operations pain is likely, and the powerful opiate drugs usually used, commonly morphine-like drugs, are likely to cause severe depression of breathing. They can usually be avoided, or at least their use limited, using other methods of pain control such as local anaesthetic infusions, epidural infusions, or in combination with other types of less potent pain-killers.

Pain after operation is only one of the side effects, sleep itself is dramatically altered by surgery and it may take many nights for sleep to return to normal. The sleep on the first night after surgery is very light and fragmented, with almost no deep sleep (NREM Stage 3 & 4).

Over the next two to three nights there is a rebound recovery of these sleep stages. They may increase to over 60% of the entire night’s sleep instead of the normal 20%; and because these are the stages where obstructive apnoea is most likely, these nights are very hazardous unless CPAP is being effectively provided.

Further problems may also occur if the surgery has been on the upper airway itself, e.g., uvulo-palatopharyngo- plasty (UPPP) in adults or tonsillectomy in children. These operations can cause swelling of the lining of the throat for about 24-48 hours, and so initially may cause more obstruction than was originally present prior to surgery. It is because of this that very careful assessment before discharge home is the routine, and some people will be supervised in a high dependency or even an intensive care unit if they are severely affected by their OSA.