Warming, humidifying, and filtering inspired anaesthetic gases is done by heat and moisture exchangers (HME) and breathing system filters. They are made of glass fibres materials and are supported by a sturdy frame. Pleating increases the surface area to reduce resistance to air flow and boost efficiency.

Filters’ effectiveness is determined by the amount and size of particles they keep out of the patient’s airway. The efficiency of filters might be classified as 95, 99.95, or 99.97 percent. Pores with a diameter of 0.2 µm are common. The following are examples of typical particle sizes:
Red blood cell – 5 µm
Lymphocyte – 5-8 µm
Viruses – 0.02-0.3 µm
Bacteria – 0.5-1 µm
Depending on particle size, gas flow speed, and charge, particles are collected via a number of processes. Mechanical sieve, interception, diffusion, electrostatic filtration, and inertial impaction are some of the options:

Sieve:
The diameter of the particle the filter is supposed to collect is smaller than the apertures of the filter’s fibres.

Interception:
When a particle following a gas streamline approaches a fibre within one radius of itself, it becomes attached and captured.
Diffusion:

A particle’s random (Brownian) zig-zag path or motion causes it to collide with a fibre.
By attracting and capturing a particle from within the gas flow, it generates a lower-concentration patch within the gas flow into which another particle diffuses, only to be captured. At low gas velocities and with smaller particles (0.1µm diameter), this is more common.

Electrostatic:

These filters use large diameter fibre media and rely on electrostatic charges to improve fine particle removal effectiveness.

Impaction due to inertia:

When a particle is too large to respond fast to abrupt changes in streamline direction near a filter fibre, this happens. Because of its inertia, the particle will continue on its original course and collide with the filter fibre. When high gas velocities and dense fibre packing of the filter media are present, this sort of filtration mechanism is most prevalent.

Control of Substances Hazardous to Health (COSHH) was established by government under the Health and Safety at Work act in 1989. Their employers work on identification and management of those substances that are dangerous to health. The implications for anaesthetists include gas scavenging, equipment contamination and environmental safety. Adequate ventilation is required in areas where anaesthetic gases are present. The minimum air supply that is legally required in each specific area is: Operating theatres: 0.65 m3/second. Anaesthetic rooms: 0.15 m3/s. Preparation rooms: 0.1 m3/s. Recovery rooms need 15 air changes per hour

Mapleson classified breathing systems into A, B, C, D and E. Jackson-Rees subsequently modified the Mapleson E by adding a double-ended bag to the end of the reservoir tubing, creating the Mapleson F. A Mapleson E or T-piece does not have a reservoir bag.

A Mapleson A system is a very efficient system for use during spontaneous ventilation. However, it is not suitable for use with patients less than 25 kg, due to the increased dead space at the distal / patient end. This system can be modified into a Lack system or coaxial Mapleson A, where the fresh gas flows through an outer tube (30 mm) and exhaled gases flow through the inner tube (14 mm).

The adjustable pressure limiting valve (APL) or expiratory valve allows exhaled gas and excess fresh gas to leave the breathing system. It is a one-way, adjustable spring-loaded valve, and gases escape when the pressure in the system exceeds the valve opening pressure. During spontaneous ventilation a pressure of less than 1 cm of water (0.1 kPa) is needed when the valve is in the open position (not 2 cm of H2O).

The reservoir bag is highly compliant and when over inflated, the rubber bag can limit the pressure in the system to about 40 cm of H2O.

This is due to the law of Laplace, which states that the pressure will fall as the radius of the bag increases:

Pressure = 2 x tension/radius.

Electrocautery, also known as diathermy, is a technique for coagulation, tissue cutting, and fulguration that uses a high-frequency current to generate heat (cell destruction from dehydration).

The two electrodes in bipolar diathermy are the tips of forceps, and current passes between the tips rather than through the patient. Bipolar diathermy’s power output (40-140 W) is lower than unipolar diathermy’s typical output (400 W). There is no earthing in the bipolar circuit.

A cutting electrode and a indifferent electrode in the form of a metal plate are used in unipolar diathermy. The high-frequency current completes a circuit by passing through the patient from the active electrode to the metal plate. When used correctly, the current density at the indifferent electrode is low, and the patient is unlikely to be burned. Between the patient plate and the earth is placed an isolating capacitor. This has a low impedance to a high frequency current, such as diathermy current, and is used in modern diathermy machines. The capacitor has a high impedance to current at 50 Hz, which protects the patient from electrical shock.

High frequency currents (500 KHz – 1 MHz) are used in both unipolar and bipolar diathermy, which can cause tissue damage and interfere with pacemaker function (less so with bipolar diathermy).

The effect of diathermy is determined by the current density and waveform employed. The current is a pulsed square wave pattern in coagulation mode and a continuous square wave pattern in cutting mode.

Among the breathing circuits, the Lack circuit is the most efficient for spontaneous breathing.

An outer coaxial tube is present to deliver fresh air; exhaust air is routed to an inner tube, which is then delivered to a scavenging system. An expiratory valve is seen at the patient end, which is an advantage over other circuits. Moreover, the Lack circuit prevents rebreathing slightly greater than the alveolar minute ventilation at 4-5 litres per minute.

The Bain circuit prevents rebreathing at 160-200ml/kg per minute, and is a co-axial version of the Mapleson D circuit.

The Mapleson E circuit prevent rebreathing at a fresh gas flow (FGF) of approximately twice the patient’s normal minute volume. A modification of this, the Mapleson F, has a reservoir bag at the opposite end for the FGF. This circuit is appropriate for paediatric patients with a body weight less than 20 kg.

The nerve stimulators deliver a stimulus lasting for 1-2 milliseconds (not second) to perform nerve blockage.

There are just 2 leads (not 3); one for the skin and other for the needle.

Prior to the administration of the local anaesthesia, a current of 0.25 – 0.5 mA (not 1-2mA) at the frequency of 1-2 Hz is preferred.

If the needle tip is close to the nerve, muscular contraction could be possible at the lowest possible current.

Insulated needles have improved the block success rate, as the current is only conducting through needle tip.

Stimulus to the femoral nerve which is placed in the mid lingual line causes withdrawer of the quadriceps and knee extension, that’s the dancing patella ( not plantar flexion).

Mapleson breathing system (or circuit) analysed five different arrangements of components of the breathing system:
Mapleson A – It is the most efficient for spontaneous respiration. The flow of fresh gas required is 70-85 ml/kg/min, i.e., approximately 5-6 lit./min fresh gas flow for an average adult.
Mapleson B and C – inefficient for both SV and PPV; requires gas flow of two to three times minute volume (100 ml/kg/min). Not commonly used but category C may be used for emergency resuscitation.
Mapleson D – efficient for PPV at gas flow equivalent to patient’s minute volume; the Bain’s circuit is a coaxial version of the Mapleson D
Mapleson E and F – for paediatric use; requires gas flow at two to three times the patient’s minute volume. The Mapleson F consists of an open-ended reservoir bag (Jackson-Rees modification).

Dinamap continuously measures the systolic, diastolic and mean arterial pressure along with pulse rate, thereby providing a continuous monitoring of the blood pressure using the osscillitonometric principle of measurement.

The device loses accuracy towards the extremes of BP and is more accurate with systolic compared with diastolic pressure. In arrhythmias such as AF, the devices are also inaccurate due to the major fluctuations associated with the individual pulse pressure variations.

The manual BP device is still the gold standard for BP measurement and monitoring.

End-tidal carbon dioxide (ETCO2) monitoring has been an important factor in reducing anaesthesia-related mortality and morbidity. Hypercarbia, or hypercapnia, occurs when levels of CO2 in the blood become abnormally high (Paco2 >45 mm Hg). Hypercarbia is confirmed by arterial blood gas analysis. When using capnography to approximate Paco2, remember that the normal arterial–end-tidal carbon dioxide gradient is roughly 5 mm Hg. Hypercarbia, therefore, occurs when PETco2 is greater than 40 mm Hg.

The most likely explanation for the changes in capnograph is either exhaustion of the soda lime and a progressive rise in circuit dead space.

Inspect the soda lime canister for a change in colour of the granules. To overcome soda lime exhaustion, the first step is to increase the fresh gas flow (FGF) (Option A). Then, if need arises, replace the soda lime granules. Other strategies that can work are changing to another circuit or bypassing the soda lime canister, but remember that both these strategies are employed only after increasing FGF first. Exclude other causes of equipment deadspace too.

There are also other causes for hypercarbia to develop intraoperatively:
1. Hypoventilation is the most common cause of hypercapnia. A. Inadequate ventilation can occur with spontaneous breathing due to drugs like anaesthetic agents, opioids, residual NMDs, chronic respiratory or neuromuscular disease, cerebrovascular accident.
B. In controlled ventilation, hypercapnia due to circuit leaks, disconnection or miscalculation of patient’s minute volume.
2. Rebreathing – Soda lime exhaustion with circle, inadequate fresh gas flow into Mapleson circuits and increased breathing system deadspace.
3. Endogenous source – Tourniquet release, hypermetabolic states (MH or thyroid storm) and release of vascular clamps.
4. Exogenous source – Absorption of CO2 from pneumoperitoneum.

Flowmeters measure the rate at which a specific gas, that the flowmeter has been calibrated for, passes through. This calibration is done at room temperature and standard atmospheric pressure with an accuracy of +/- 2%.

Reading the flowmeter is done from the top of a bobbin (the midpoint of a ball). Oxygen is the last gas to be added downstream to the mixture delivered to the back bar as a safety feature. This prevents delivery of a hypoxic mixture.

Inaccurate flow measurements occur when the bobbin sticks to the inside wall of the flowmeter. Stannic oxide has been used as a successful antistatic substance thus, reducing the aforementioned risk.

Carbon dioxide being easily delivered is found on some older machines, but those attached flowmeters are limited by a maximum flow of 500 ml /min. Thus avoiding the delivery of a hypercarbic mixture.

The operating theatre is an unusual place with several applications of electrical equipment to the human body. This can lead to potential dangers associated with it that need to be prevented. Electrical safety in the operation theatre is the understanding of how these potential dangers can occur and how they can be prevented.

Electricity can cause morbidity or mortality by one of the following ways:
(i) electrocution
(ii) burns
(iii) ignition of a flammable material, causing a fire or explosion.

Electrocution is dependant on factors like duration of contact with electric current, the current pathway and the frequency and size of current.

Option A: The higher the frequency, the less effects of electrocution on the body.

Option B & D: Equipment can be classified in classes and types.
The class designation describes the method used for protection against electrocution. Class I is basic protection, class II is double insulation and class III is safety extra low voltage.
The type designation describes the degree of protection based on the maximum permissible leakage currents under normal and fault conditions.
Type B:
can be class I, II or III but the maximum leakage current must not exceed 100 µA. It is therefore not suitable for direct connection to the heart.
Type BF
Similar to type B, but uses an isolated (or floating) circuit.
Type CF
Only type CF protect against microshock as they allow leakage currents of 0.05 mA per electrode for class I and 0.01 mA for class II. Microshock is a small leakage current that can cause harm because of direct connection to the heart via transvenous lines or wires, bypassing the impedance of the skin, leading to ventricular fibrillation. Microshock current of 100 ?A is sufficient to cause VF.

Option C: A 75mA electrocution can cause ventricular fibrillation. Use the following as a general guide to understand the effect of current size on the body.
1 mA – tingling pain
5 mA – pain
15 mA – tonic muscular contraction
50 mA – respiratory muscle paralysis
75 mA – ventricular fibrillation.

Option E: Wet skin reduces the resistance to current flow and therefore increases the effects of electrocution.

Increasing temperature increases the amount of water vapour contained in air; for example, at 20°C, air contains about 17 g/m3, and at 37°C, air contains about 44 g/m3. The wet and dry bulb hygrometer, like the hair hygrometer, measures relative humidity.

Under normal operating conditions, Heat and moisture exchangers (HMEs) allows relative humidity of up to 70% to be achieved. Mucus can impair their performance, and they should not be used for longer than 24 hours.

Hot water bath humidifiers might cause scalding, condensed water in the tubing can interfere with gas flow, and there is a danger of infection.

The ultrasonic humidifier operates at roughly 2 MHz and may attain relative humidity levels much above 100%.

There are different models of flowmeters determined by the applied pressure and its orifice. For instance, the watersight flowmeter functions through applying variable pressure, and it has a variable orifice. In contrast, the bubble flowmeter is operated using a constant pressure and orifice. Flowmeters such as rotameters, Heidbrink and Peak have a constant pressure but variable orifice. On the other hand, flowmeters including a simple pressure gauge, water depression, and pneumotachograph have a constant orifice but variable pressure.

Two bonded wires of dissimilar metals, iron/constantan or copper/constantan, make up a thermocouple (constantan is an alloy of copper and nickel). At the tip, a thermojunction voltage is generated that is proportional to temperature (Seebeck effect).

All of the other connections are non-linear.

For a single compartment model, the relationship between a decrease in plasma concentration of an intravenous bolus of a drug and time is a washout exponential.

A sine wave is the relationship between current and degrees or time from a mains power source.

A sigmoid curve represents the relationship between efficacy and log-dose of a pure agonist on mu receptors.

The pressure of a fixed mass of gas and its volume (Boyle’s law) at a fixed temperature are inversely proportional, resulting in a hyperbolic curve.

Adequate humidification is vital to maintain homeostasis of the airway. Heat and moisture exchangers conserve some of the exhaled water, heat and return them to inspired gases. Many heat and moisture exchangers also perform bacterial/viral filtration and prevent inhalation of small particles. Heat and moisture exchangers are also called condenser humidifier, artificial nose, etc. Most of them are disposable devices with exchanging medium enclosed in a plastic housing. For adult and paediatric age group different dead space types are available. Heat and moisture exchangers are helpful during anaesthesia and ventilatory breathing system. To reduce the damage of the upper respiratory tract through cooling and dehydration inspiratory air can be heated and humidified, thus preventing the serious complications. Moreover, they are the most appropriate humidification devices used for routine anaesthesia.

Gases can be bubbled through water to increase humidity. Passing gas through water at room temperature causes the gas to cool due to latent heat of vaporisation. The water bath can be heated. This improves the efficiency of the device and also reduces the incidence of bacterial colonisation.

Nebulisers use a venturi system which employs the Bernoulli effect. A gas at high flow passes through a constriction causing the gas to accelerate, reducing its potential energy allowing other gases or liquids to be entrained. This can include medications or in the case of humidification, water vapour. The size of the water droplet produced by nebulisation determines where in the airway it is deposited. Standard nebulisers produced droplets of 4 microns in diameter and these are deposited in the upper airway and trachea. Efficacy can be improved by passing the droplets over an anvil which further reduces particle size. The most efficient form of nebuliser is the ultrasonic nebuliser. Here a transducer immersed in water and vibrated at a frequency of 3MHz produces1-2micron droplets. These particles easily reach the bronchioles and provide excellent humidification.

Electromagnetic waves are categorized according to their frequency or equivalently according to their wavelength. Visible light makes up a small part of the full electromagnetic spectrum.

Electromagnetic waves with shorter wavelengths and higher frequencies include ultraviolet light, X-rays, and gamma rays. Electromagnetic waves with longer wavelengths and lower frequencies include infrared light, microwaves, and radio and televisions waves.

Different electromagnetic waves according to their wavelength from shorter to longer are X-rays, ultraviolet radiations, visible light, infrared radiation, radio waves. X-ray among electromagnetic waves has the shortest wavelength and higher frequency with wavelengths ranging from 10*-8 to 10* -12 and corresponding frequencies.

It’s a minute volume divider – True
The Manley MP3 ventilator is classed as a minute volume divider. The entire fresh gas flow or minute volume is delivered to the patient, having been divided into readily set tidal volumes.

Can efficiently ventilate patients with poor pulmonary compliance – False
Ventilating patients with poor pulmonary compliance is not easily achieved, which makes it an unsuitable ventilator for a modern ICU.

Can generate tidal volume up to 1500ml – False
It can generate tidal volumes up to 1000 ml (not 1500 ml), and the inflation pressure can be adjusted by sliding a weight along a rail.

Functions like a Mapleson A system during spontaneous ventilation – False
The ventilator functions like a Mapleson D breathing system (not Mapleson A) during spontaneous ventilation.

Has three sets of bellows – False
The fresh gas flow drives the ventilator which allows rapid detection of gas supply failure. It has two sets of bellows (not three) and three unidirectional valves.

A thermocouple, or a thermal junction, is temperature measuring device consisting of a pair of dissimilar metal (bimetallic) wires or strips joined together. Typically, copper and constantan (an alloy of 55% copper and 45% nickel) are used. When there is contact between these metals, a small voltage is generated in the order of millivolts. The magnitude of the thermojunction electromotive force (emf) is proportional to applied temperature (the Seebeck effect). This physical principle is applied in the measurement of temperature. The electromotive force at the measuring junction is proportional to temperature.

Two wires with different coefficients of expansion, joined together, can be used as a switch for thermostatic control.

Semiconductors are NOT used in thermocouple. The resistance of the measuring junction of a thermocouple is irrelevant.

Laminar flow can be defined as the motion of a fluid where every particle in the fluid follows the same path of its previous particles. The following are properties of laminar flow of gas or fluids:

1. Smooth unobstructed flow of gas through a tube of relatively uniform diameter
2. Few directional changes
3. Slow, steady flow through straight smooth, rigid, large calibre, cylindrical tube
4. Outer layer flow slower than the centre due to friction, results in discrete cylindrical layers, or streamlines
5. Double flow by doubling pressure as long as the flow pattern remains laminar

Poiseuille’s Law relates the factors that determine laminar flow. It indicates the degree of resistance to fluid flow through a tube. The resistance to fluid flow through a tube is directly related to the length, flow and viscosity; and inversely related to the radius of the tube to the fourth power. This means that, when the radius is doubled, there is increase in flow by a factor of 16.

Tracheal tubes are made of either disposable plastic or reusable red rubber.

The tube size refers to the internal diameter (ID) in mm which is marked on the outside of the tube (some manufacturers mark the external diameter on the outside).

Plastic tubes have a radiopaque line spanning the entire length of the tube, which allows their position to be identified on x-rays. The bevel located at the end of the tube is left-facing and oval in shape, which improves the view of the vocal cords during intubation.

Oxford tubes are L-shaped and have a bevel that faces posteriorly. They have thick walls that increase the external diameter, making for a wider internal diameter.

RAE (Ring, Adair, and Elwyn) tubes are preformed and can either be north or south facing and cuffed or uncuffed. The cuffed RAE tubes have one Murphy eye, whereas the uncuffed has two Murphy eyes. Uncuffed tubes are primarily used in paediatric anaesthesia and the two Murphy eyes ensure adequate ventilation- should the tube be too long.

There are two types of defibrillators
AC defibrillator
DC defibrillator

AC defibrillator,
consists of a step-up transformer with primary and secondary winding and two switches. Since secondary coil consists of more turns of wire than the primary coil, it induces larger voltage. A voltage value ranging between 250V to 750V is applied for AC external defibrillator. And used to enable the charging of a capacitor.

DC defibrillator,
consists of auto transformer T1 that acts as primary of the high voltage transformer T2. Is an iron core that transfers energy between 2 circuits by electromagnetic induction. Transformers are used to isolate circuits, change impedance and alter voltage output. transformers do not convert AC to DC.

Diode rectifier composed of 4 diodes made of semiconductor material allows current to flow only in one direction. Alternating current (AC) passing through these diodes produces direct current (DC). Capacitor stores the charge in the form of an electrostatic field.

Capacitor is used to convert the rectified AC voltage to produce DC voltage but capacitors do not directly convert AC to DC.

Inductor induces a counter electromotive force(emf) that reduces the capacitor discharge value.

In step-down transformer primary coils has more turns of wire than secondary coil, so induced voltage is smaller in the secondary coil.

Medical gas cylinders are made up of molybdenum steel but not cast iron. They are checked and assessed at a regular interval.

At least one cylinder in each hundred are tested for tensile, pressure, smash, twist and straightening.

Nitrous Oxide cylinders contain a mixture of liquid and vapour at a pressure of approx. 4500 kPa or 45 Bar. Carbon dioxide cylinder contain gas at the pressure of 5000kPa.

The filling ratio is the ratio of mass of liquified gas in the cylinder to the mass of water required to fill the cylinder at the temperature of 15ºC. In the united kingdom, filling ratio of liquid nitrous oxide is 0.75. The cylinders are usually attached to the anaesthetic machine. As nitrous oxide is an N-methyl-d-aspartate receptor antagonist that may reduce the incidence of chronic post-surgical pain.

A Wrights Respirometer measures the volume of air exhaled over the course of one minute of normal breathing

It is unidirectional and measures tidal volume and minute volume of gas flow in one direction. It is placed at the expiratory side (lower pressure than inspiratory side therefore lower chances of gas leaks)

Slits are arranged such that incoming gas will rotate the vane at a rate of 150 revolutions per litre of flowing gas

The Wright respirometer tends to over-read at high flow rates and under-read at low flows because of mechanical causes like friction and inertia and the accumulation of water vapour

The ideal flow for accurate readings is 2 L/min for the respirometer. The respirometer reads the tidal volume and minute volume with a ±5–10% accuracy within the range of 4–24 L/min.

This patient is morbidly obese and has a high risk of developing hypoxia. This will be exacerbated by the patient’s supine position, as a result of:

Functional residual capacity has been reduced (FRC)
Increased closing capacity (CC)
Reduced tidal volume due to increased airway resistance, decreased thoracic cage compliance, and decreased respiratory muscle strength and endurance
Following induction of general anaesthesia, there is a tendency for atelectasis and increased O2 consumption due to the increased workload of respiratory muscles and the overall increase in metabolism.

Pre-oxygenation with 100 percent oxygen via a tight-fitting mask can be done using either tidal volume breaths for three to five minutes or four vital capacity breaths in normal circumstances. In the head-up position, this patient is much more likely to be adequately pre-oxygenated, maximising the FRC and minimising the CC. In spontaneously breathing patients, the Mapleson A and circle systems are both effective, but the Mapleson D requires 160-200 ml/kg/minute to prevent rebreathing.

Pulse oximeters combine the principles of oximetry and plethysmography to noninvasively measure oxygen saturation in arterial blood. A sensor containing two or three light emitting diodes and a photodiode is placed across a perfused body part, commonly a finger, to be transilluminated. Oximetry depends on oxyhaemoglobin and deoxyhaemoglobin, and their ability to absorb the beams of light produced by the light emitting diodes: red light at 660 nm and infrared light at 960 nm.

The isosbestic point is the point wherein two different substances absorb light to the same extent. For oxyhaemoglobin and deoxyhaemoglobin, the points are at 590 nm and 805 nm. These are considered reference points where light absorption is independent of the degree of saturation.

Non-constant absorption of light is often due to the presence of an arterial pulsation, whilst constant absorption of light is seen in non-pulsatile tissues.

Most pulse oximeters are inaccurate at low SpO2, but is accurate at +/- 2% within the range of 70% to 100% SpO2. All pulse oximeters demonstrate a delay in between changes in SaO2 and SpO2, and display average readings every 10 to 20 seconds, hence they are unable to detect acute desaturation episodes.

Breathing system is an assembly of components which connects patient’s airway to anaesthesia machine through which controlled composition of gas mixture is dispensed. It delivers gas to the patient, removes expired gas and controls the temperature and humidity of the inspired mixture. It allows spontaneous, controlled, or assisted respiration. It may also provide ports for gas sampling, airway pressure, flow and volume monitoring.

Breathing systems have been classified by Conway and Mapleson.
Conway suggested a functional classification:
– Circuits requiring a CO2 absorber
– Circuits not requiring a CO2 absorber

William Mapleson designated varying arrangements of breathing system components (masks, breathing tubes, fresh gas flow inlets, adjustable pressure-limiting valves, and reservoir bags) as Mapleson A-E circuits.
Mapleson A: Arranged as FGF inlet, reservoir bag, APL valve, mask.
In this circuit, because the reservoir bag is between the FGF inlet valve and the APL valve, expired gas from the patient may re-enter the system and fill the reservoir bag during controlled ventilation. This is the most efficient system for spontaneous breathing as the FGF must only be equal to a patient’s minute ventilation to prevent rebreathing.

Mapleson B: Arranged as reservoir bag, FGF inlet, APL valve, mask.
In this circuit, the FGF inlet is closer to the APL valve, which helps prevent the rebreathing concern in the Mapleson A circuit as above during controlled ventilation.

Mapleson C: Arranged as reservoir bag, FGF inlet, APL valve, mask.
In this circuit, the arrangement is the same as the Mapleson B circuit. However, this circuit is shorter as it does not contain elongated corrugated tubing. This circuit also has the FGF inlet close to the APL valve to aid in preventing rebreathing.

Mapleson D: Arranged as reservoir bag, APL valve, FGF inlet, and mask.
In this circuit, the arrangement interchanges the FGF inlet and APL valve of the Mapleson A circuit. This system prevents rebreathing by directing FGF towards the APL valve rather than towards the patient during exhalation.

Mapleson E: Arranged as corrugated tubing, FGF inlet, and mask.
In this circuit, there is no reservoir bag and no APL valve. Given the inability to alter the pressure of the circuit, this is ideal for spontaneously ventilating neonates or paediatric patients where low-pressure ventilation is desired. The system prevents rebreathing, similar to the Mapleson D circuit.

Jackson Rees later modified the Mapleson E by adding an open ended bag, which has since become known as the Mapleson F.
Mapleson F: Arranged as APL valve directly connected to reservoir bag, corrugated tubing, FGF inlet, and mask.
The system prevents rebreathing similarly to Mapleson D by directing FGF towards the APL valve.

Eye damage is the most common potential hazard associated with laser energy. Everyone in the laser treatment room has the risk of eye exposure when working with a Class 3b or Class 4 healthcare laser system, and damage to various structures in the eye depending on wavelength of the laser if they are unprotected.

Red and near-infrared light (400-1400 nm) has very high penetration power. The light causes painless burns on the retina after it is absorbed by melanin in the pigment epithelium just behind the photoreceptors.

Infrared radiation (IR), or infrared light (>1060 nm), is a type of radiant energy that’s invisible to human eyes and hence won’t elicit the protective blink.

Ultraviolet light (<400 nm) is also a form of electromagnetic radiation which is can penetrate the cornea and be absorbed by the iris or the pupil and cause burn injuries or cataract occur due to irreversible photochemical retinal damage. Safety eyewear is the best method of providing eye protection and are designed to absorb light specific to the laser being used. Laser protective eyewear (LPE) includes glasses or goggles of proper optical density (OD). The lenses should not be glass or plastic. The LPE should withstand direct and diffuse scattered laser beams. The laser protection supervisor (LPS) or LSO is an individual who is responsible for any clinical area in which lasers are used. They are expected to have a certain level of equipment and determine what control measures are appropriate, for each individual system, but their presence does not guarantee the chances of having an eye injury. Class 1 lasers are generally safe under every conceivable condition and is not likely to cause any eye damage. Class 3b or Class 4 medical laser systems are utilized in healthcare which have their own safety precautions. Polarized spectacles can make your eyes more comfortable by eliminated glare, however, they will not be able to offer any protection against wavelengths at which laser act.
Using short bursts to reduce energy is also not correct as it would still be harmful to eye.

Exposure to anaesthetic hazards is one among the occupational exposures in manipulating toxic agents or inhaling toxic gases during anaesthetic practices.

Toxic gases mainly nitrous oxide, is one of the most gaseous anaesthetic agents that constitutes an important source of pollution. One of the safe and effective technics used in anaesthesia and reducing the amount of pollution is the Total Intravenous Anaesthesia (TIVA) which consists of using opioids in analgesia and propofol for the induction and the maintenance of anaesthesia. It refers to the administration intravenously of an anaesthetic, sedative, and/or tranquilizer. A less polluting but not the best way to get rid of the toxic aesthetic agents is the scavenger system that collects and expels the gas outside the medical environment. Yet, this technique still represents a hazard for the environment and still increase the risk of exposure for the health workers and clinical staff.

Fume cupboards are also not recommended to use because of their high pollution potency, mainly of the air resulting in a great harm for medical workers.

Supraglottic airways as well as the Air Changes per Hour technics could be harmful for both patients and health workers, increasing the risks of transmitted diseases, namely nosocomial infections.

Therefore, the Total Intravenous Anaesthesia technique (TIVA) is most likely to be safe and recommended to use.

Professor Mapleson classified non-rebreathing circuits based on the position of the APL valve, which controls fresh gas flow.

The Mapleson A (Magill) circuit is most effective in spontaneous breathing, requiring only 70-100 ml/kg (the patient’s minute volume) of fresh gas flow. The patient inhales fresh gas from the reservoir bag and tubing during inspiration. During expiration, the patient adds dead space gas (gas that hasn’t been exchanged) to the tubing and reservoir bag in addition to the fresh gas flow. At the patient’s end, alveolar gas is vented through the APL valve. During the expiratory pause, the fresh gas flow causes more gas to be released.

The Mapleson A is inefficient during controlled ventilation. Venting occurs during inspiration rather than during the expiratory phase, as it does during spontaneous ventilation. As a result, unless a high fresh gas flow of >20 L/minute is used, alveolar gas is rebreathed.

During spontaneous ventilation, the Mapleson D circuit is inefficient.

The oxygen concentration in a Hudson mask is insufficient to allow for adequate pre-oxygenation.