After arriving in theatre and before starting the anaesthetic your anaesthetist will carry out some routine tasks. The three most common tasks are setting up an intravenous access point, attaching monitors and pre-oxygenating.
Your anaesthetist will first set up intravenous access, what is known as “putting up a drip”. This involves inserting a thin plastic tube into a vein on your arm through which your anaesthetist can inject anaesthetic drugs and run intravenous fluids. This may be a little bit painful as it involves pricking the skin with a needle.
At the same time the anaesthetic nurse will attach several monitors to you. These are used to keep a continual check on your vital body activities, and will include:
- An ECG monitor. Three sticky electrodes are placed on your chest and leads are clipped onto these. The monitor then displays a continuous tracing of the electrical activity of your heart, each heartbeat being accompanied by an audible “beep” on the monitor. The ECG is an important guide to the anaesthetist that your heart rate is neither too fast nor too slow, that the normal rhythm is maintained, and that the heart muscle is getting enough oxygen.
- The blood pressure monitor. The nurse will place a cuff around your upper arm and this is attached to a machine that automatically inflates the cuff and measures your blood pressure at pre-set intervals during the anaesthetic.
- A pulse oximeter. This is a little probe that slips over the end of your finger and continually measures how much oxygen is in your blood.
All the measurements are displayed on a screen on the anaesthetic machine, and your anaesthetist will have these values continually available throughout the anaesthetic. If your condition changes your anaesthetist can then immediately correct this before the change becomes a threat to your wellbeing. Other monitors may be used, depending on how well equipped the theatre is, and these may include:
- A temperature probe which is used in conditions where your body temperature is likely to change. Most patients tend to drop their temperatures during the anaesthetic, and if this drop becomes excessive the anaesthetist will warm you with one of a number of devices available. Too low a temperature, or hypothermia as it is called, can have detrimental effects on your body, particularly your heart.
- A capnograph, which measures how much carbon dioxide you are breathing out. This monitor is very valuable for ensuring that your breathing is adequate, particularly if you have had to be paralysed and a ventilator is being used to breathe for you, but also gives information as to how well your heart is functioning.
- A nerve stimulator, which is used when muscle relaxants have been used and provides a measure of the adequacy of relaxation and also the satisfactory reversal of the paralysis at the end of the operation.
- A Central Venous Pressure (CVP) line. This is a catheter that is inserted into the internal jugular vein in the neck, and is advanced down the vein up to the point where it is just about to enter the heart. It is used to measure the venous pressure at that point, and this is extremely helpful in helping the anaesthetist decide whether more fluid needs to be infused in order for the heart to function optimally. It may also be used to inject drugs that will irritate and damage peripheral veins, and also drugs that have very powerful effects on the heart and blood vessels and have a very short duration of action. These drugs can be administered as a separate controlled infusion. The CVP line is usually inserted after you have gone to sleep, but if your medical condition poses a risk during the induction of anaesthesia it will be placed under local anaesthetic before the anaesthetic is started.
- An Arterial Line. A small cannula or catheter is sometimes placed into an artery at the wrist, and this is then connected to an electronic device that will measure the pressure in the artery and display the value on the monitor screen. This is necessary in operations where there are sudden and profound changes in blood pressure or when drugs are used which have a powerful effect on blood pressure. It is also very useful for taking a blood sample that can be analysed to provide information on the acidity of the blood and the oxygen and carbon dioxide in the blood. Like the CVP it is usually inserted after, and occasionally before, you go to sleep.
When everything is ready you will probably be given oxygen to breathe through a mask, the purpose of this being to replace the air in your lungs with oxygen, so that if your breathing is depressed there is a large reservoir of oxygen available to the blood passing through your lungs. This process is completed in about three minutes, and your anaesthetist can now put you to sleep.
How the lungs work
You and your oxygen unit