Often the world of anaesthesia and the world of aviation are compared. There are many similarities and this section will describe a typical flight so you can appreciate some of the similarities. The flight we will take you through is from the United Kingdom to the holiday island of Sri Lanka.
Pre anaesthetic assessment
You wouldn't just walk into an operating room and anaesthetise a patient. Well in advance, you would talk to and examine your patient. You would pour over the investigations to anticipate problems and plan your anaesthetic. Pilots are no different. Way before they come anywhere near the aircraft, they plan the flight.
They study various factors and plan an appropriate route. The weather is an important determinant. If there is an expected patch of bad weather, they can plan to fly higher than it or around it. They also look for special notices such as certain military air spaces to avoid.
An huge component is the calculation of the required fuel for the journey. Unlike a car, if you run out of fuel in the air, you cannot simply stop at a nearby gas station for a unplanned fill up ! It is a bit like when you have to calculate the amount of oxygen you have to carry when transferring a patient by ambulance. You need to take the amount your patient needs and spare capacity for unexpected delays such as traffic or your ambulance needing a sudden tire change. Aircrafts have to carry enough fuel for the journey and enough for holding, going to an alternate airport etc. Aircrafts consume huge amounts of fuel. While taking too little fuel is dangerous, carrying too much can be very wasteful . On a long haul flight, if you carry one ton of extra fuel, half of it will be used up just to carry itself ! The fuel in an aircraft is stored mostly in the wings. The image below shows a fuelling truck fill up the wings of an aircraft. It takes fuel from a pipe in the ground and pumps it into the aircraft wing.
The pilots are also told of the expected takeoff weight. This will include the weight of the aircraft, fuel, passengers, and cargo. The aircraft we will fly today has a take off weight of up to 270,000 Kg.
The pilot doesn't do all the planning himself. In large airlines, there is a department for planning which prepares the material for the pilot to study. The prepared information is available on the internet for the pilots to study even before they reach the airport.
Some modern anaesthesia information systems also have this find of access where information is available in an electronic format from nearly anywhere.
In the operating room team
In the operating room you need more than the patient and anaesthetist for the surgery. You need , in addition to an anesthetist, surgeons, nurses, porters, sterilizers, and a host of hidden services such as those who provide sterile instruments etc. All have to work in harmony for the operation to take place efficiently and safely.
The world of aviation also heavily relies on team work for it to function safely and efficiently. A typical flight will need the support of pilots, cabin crew, engineers, fuellers, catering, baggage handlers, air traffic control, and in more relevant to modern times, security personnel.
Minimum Equipment
One of the important things the pilots will check is if the “Minimum Equipment List” is satisfied . Aircraft have a huge number of parts. Like any machine, some of these parts may malfunction. Before a flight begins, the engineering team will check the aircraft out. They will inform the pilots about any defects they have discovered. A check will be made against the Minimum Equipment List. This list mentions what items are absolutely necessary for the safe operation of the flight. If the defective item is in this list, then the aircraft is not allowed to fly till the item is repaired. If the defective part is not critical, then the flight can go ahead and the part repaired later.
In anaesthesia we operate minimum equipment lists as well. For an example, we would not start an anesthetic if the pulse oximeter is not working. However, if the case is a short carpel tunnel decompression, we may proceed if the temperature probe is faulty.
The picture below shows engineers checking one of the engines. It also shows how massive these machines are !
Jet engines work by sucking in air, compressing the sucked air, igniting it with fuel, and letting the hot gases exhaust from the rear end of the engine. The gas is exhausted from the rear at a very high speed, making the engine and the aircraft attached to it move forwards.
The suction generated by engines has to be treated with care, otherwise mishaps like the one below can happen. The baggage container was too near the engine. The powerful engine sucked it in!
Check List
In anaesthesia we are well used to checks and check lists. These are also very much part of a pilots life. They check and recheck everything. There are checklists for various stages of a flight such as pre start check list, take off checklist, climb check list , cruise check list and so on.
Ground engineers check an aircraft thoroughly before every flight. However, pilots also do a superficial check to make sure that they are happy with the condition of the aircraft. It is like in anaesthesia where even if the anesthetic machine has been checked by an assistant, the anaesthetist giving the anesthetic will do a final check.
The picture below shows one of the pilots doing an external check of his aircraft. Because it involves he or she going around the aircraft, it is called a "walk around".
The Glass Cockpit
In anaesthesia and aviation, the computer screen has dramatically modernised the presentation of information. In days gone by, anaesthetic displays were mostly separate. Blood pressure would be shown on the blood pressure machine, ECG would appear on the ECG machine, the pulse oximeter on its display and capnograph on its own display. Modern anaesthetic machines combine all this into one or two convenient screens.
In modern aircraft, the same has happened. In the past, things like altitude, airspeed,horizontal level, rate of climb and direction had their own dedicated displays as shown below:
Altitude
Airspeed
The "Artificial Horizon" :This instrument shows the aircrafts level with respect to land. The brown represents land and the blue represents sky.
This dial shows the speed that the aircraft is climbing or descending.
This shows the direction the aircraft is flying.
In a modern aircraft, all these separate instrument displays are combined into one convenient display.
Here is an old style cockpit with a crew of four (one seat is empty in the picture). It had many individual instrument displays.
As shown below, modern automation and displays have made the cockpit much more elegant. The computers have got rid of two of the crew members. Today , even the biggest jets need only two pilots (and many computers !) to fly.
Taxi
"Taxi" in aviation means that the aircraft is moving on the airport. In this case, our aircraft is taxing towards the runway for take off.
Aircrafts are very heavy objects. Just as heavy patients can develop sores in areas of high pressure contact , heavy aircraft can cause damage to airport surfaces if they exert too much weight over a small area. For this reason, large aircraft have many tires to increase the surface area of contact, as shown below.
When moving patients across onto operating tables, we all know how important it is to make sure that the patients bed has its brakes on. Inadequate brakes may make the bed move and seriously harm the patient, just like what happened to the aircraft below.
A certain airline company was accepting a newly manufactured aircraft. The normal procedure is for the purchasing company to participate in the checking of the aircraft prior to accepting it. One of the tests involved running the engines on full power while applying maximum braking power to prevent the aircraft lurching forwards.
The testing team (purchasing company and manufacturer personnel) powered up the engines to maximum. Unfortunately, due to improper use of the brakes, the aircraft accelerated forwards and within a few seconds, ended up like this:
Fortunately , though there were serious injuries, no one died.
However, our aircraft below is using its brakes properly and is heading towards the runway for take off.
Take Off
The aircraft lines up on the runway and readies itself for takeoff.
Take off is the equivalent of anaesthetic induction. Many things happen and it is a time of maximum concentration.
Prior to induction, anaesthetist calculate the likely required doses of our drugs. Pilots also do something similar. In the planning stage of the flight, based on the weight of the aircraft, weather, and other factors, they pre-calculate the required engine power and speed needed to get the aircraft airborne.
Having lined up on the runway , they move the thrust leavers forward ( red arrows below). These are the equivalent of an accelerator pedal of a car. The aircraft engines roar to life.
As the aircraft accelerates down the runway, one of the pilots keeps an eye on the speed. At the pre-calculated speed is reached, he will say “ROTATE”. Hearing this command, the other pilot makes the aircraft rotate upwards.
Cruise
Cruise is the equivalent of the maintenance phase of anaesthesia. Large changes in altitude don't occur and things get quieter and more stable. The cabin crew serve drinks and meals. The pilots settle down to a calmer routine. Just like anaesthetists having long and short cases, pilots can have very short flights or may have those that last many long hours . The flight time to Sri Lanka is 12 hours and the view outside is magnificent.
Autopilot
The autopilot system is a very sophisticated system that is somewhat similar to a target controlled infusion syringe pump used in total intravenous anaesthesia. Just like you would dial the required propofol concentration, the pilot dials the altitude. In the cockpit below, the pilot has dialled an altitude of 36,000 feet (see red arrow).
The computer works out the best way to achieve this. Like the computer that controls the motor in a syringe pump, the autopilot makes adjustments to the engines and flight control surfaces to achieve the desired altitude.
The autopilot system can do much more than simply change altitude. It can completely fly the aircraft to the programmed destination, with the pilots simply monitoring its performance.
Breathing System
The aircraft is a breathing system! However, unlike the breathing systems we use in anaesthesia, the patients actually sit inside the tubing !
Like any breathing system, you need fresh gas flow. This is taken from the engines. A little bit of the air sucked in by the engines is diverted into the cabin where the passengers sit.
Just like a circle breathing system used in anaesthesia, to save "fresh gas flow", some of the air in the cabin is recirculated. This recirculation of air helps reduce fuel consumption since the engines have to work less hard.
Also like a circle system, the recirculation of air helps preserve heat and moisture. Carbon dioxide absorbers are not required because the fresh gas flow is quite high and this washes out carbon dioxide from the circuit.
Air from the aircraft is exhausted via an out flow valve. In the picture below (pink arrow) the out flow valve is shown fully open.
Anesthesia systems have safety valves to prevent rupture of tubing in case the outflow valve is jammed. In the aircraft, there is a similar protection. The valve shown by the blue arrow is an over pressure valve. If, due to a fault, the pressure inside the aircraft builds up to a dangerous degree, this valve opens up to relieve the excess pressure, preventing the aircraft from rupturing like a balloon.
Due to the high altitude in which aircrafts fly, the cabin needs to be pressurised. This is achieved by the outflow valve being carefully adjusted to build up the pressure inside the cabin. It is similar to how we screw down a breathing system valve to provide CPAP.
Back Up Systems
Just like in anaesthesia, aircrafts have a lot of back up systems to cope with failure. In the aircraft, one of the most interesting back up devices is what is called a "ram air turbine". If all electrical power fails in the aircraft, this device automatically gets deployed. It is basically a windmill. The airflow (shown with blue arrows) spins the turbine which in turn is connected to a small generator. This then powers essential equipment on the aircraft, something crucial in today's computerised systems.
Landing
After cruising for many hours, the aircraft is made to gradually descend.
Soon it is time to prepare for the landing. The landing is similar to us waking up a patient from an anaesthetic. Timing is important. Just like you don't want a patient to wake up before or too much after the end of surgery, for the pilot, the important thing is to get the aircraft on the runway, not before or after it!
