Quality Anaesthetic monitoring Merlin Training for Vets and Nurses • To familiarise users with the controls of Merlin • To familiarise users with the pneumatic connections of Merlin • To ensure that users understand the behaviour of Merlin in terms of gas flow, both during normal use and with the machine OFF/Power • To train users to set up Merlin for Volume Cycling in a range of patients and to understand the implications and effects of changing different • To train users to respond to patients 'fighting the ventilator' and to establish breathing control using IPPV • To train users to set up Merlin for Pressure Cycling and to understand the benefits of Pressure Cycling over Volume Cycling • To train users how to run a Leak test as part of their daily routine Registered Office: 12 Henley's Business Park, Manor Road, Abbotskerswell, Newton Abbot, Devon TQ12 5NF * w^*"*' *" CRN:4694235; VAT No 585 6341 12. Managing Director: Keith Simpson BVSc MRCVS MIET(Electronics)

Registered Office: 12 Henley’s Business Park, Manor Road, Abbotskerswell, Newton Abbot, Devon TQ12 5NF CRN:4694235; VAT No 585 6341 12. Managing Director: Keith Simpson BVSc MRCVS MIET(Electronics)

Merlin Controls Despite its appearance Merlin only has 5 control knobs and three switches to control all forms of ventilation. The control functions will be covered first. Their role in the full control of assisted ventilation will be covered more fully later. The control knobs will be discussed first, left to right. Flow Rate / Volume The first knob has dual functionality depending on which cycling mode is selected. All volumes are in whole mls and all Flow values are in decimal values e.g. 2.5, so it is easy to tell which mode is selected. If the number is a whole number then the knob is in...

Maximum Airway Pressure This control knob has dual functionality. It always represents a maximum permissible airway pressure but depending on the operating mode of the ventilator this will be interpreted in one of two different ways. In volume cycling mode the Maximum Airway Pressure is the 'Safety Valve' pressure that the airway is allowed to reach before inspiration is halted. As such in normal use it rarely has any effect on the operation of the machine. The Maximum Airway Pressure should be set to approximately 10 cm above the normal Peak Inspiratory Pressure (PIP). For example the normal...

Flow Rate / Volume Switch This switch changes the control function from a Volume Control (in mls) to a Flow Control (in L/min). This does NOT set the ventilator into a pressure cycling mode but simply provides another way of determining how to deliver a volume breath. When the switch is down the value shown by the control is in mls and the Tidal Volume is exactly the same as shown on the top line of the main display. When the switch is up the value shown is a flow value and that combined with the inspiratory time will determine the delivered volume. Again the actual volume, calculated by the...

Quality Anaesthetic monitoring This shows the ratio between the inspiratory time and expiratory time. It is usual when using prolonged mechanical ventilation to maintain this ratio at greater than 1:2, so that expiration is always at least twice as long as inspiration. This reduces the effect of mechanical IPPV on the cardiovascular In volume cycling mode this value is continuously updated as changes are In pressure cycling mode this value is updated at the end of each inspiratory This value measures the dynamic compliance of the patient and the patient circuit. Usually the patient compliance...

Quality Anaesthetic monitoring Pneumatic connections Merlin does not need a pressurised gas supply to drive the piston or cylinder so the only gas connections are those to and from the anaesthetic machine The connections to and from the patient are simple. A port labelled To Patient delivers gas down to the patient and a port labelled From Patient receives exhaled gas from the patient. Use a normal Y-piece with connecting tubes to connect Merlin to the patient. All incoming gas to the machine enters via the Gas In port and all gas leaving the machine exits via the Gas Out port. Because of this...

Quality Anaesthetic monitoring For a non-rebreathing circuit, Fresh Gas Flow (FGF) is delivered from the common gas outlet of the anaesthetic machine. Because the inlet valves inside Merlin cut off this gas flow during certain phases of the breathing cycle it is important that a reservoir bag be placed in the path of the incoming gas so that the fresh gas can continue to flow and fill this bag when the inlet valves are closed. Because this reservoir bag may become full it is necessary to fit an APL valve to this reservoir bag. In summary, to set the machine up for non-rebreathing, a reservoir...

Quality Anaesthetic monitoring Gas Flow through the Merlin ventilator As described above there is a continual flow of gas through Merlin and the patient. The only difference in a rebreathing circuit is that the waste gas is MERLIN VALVES Inspiratory Valve From Patient" Expiratory Valve FGF enters Merlin by the Gas-In port and fills up the cylinder. When inspiration starts, the inspiratory valve cuts off the FGF inlet and the expiratory valve cuts off the Gas-out port so gas is driven into the patient. At the end of inspiration both of these valves open and the patient exhales passively. Because...

Quality Anaesthetic monitoring Setting up for Volume Cycling Volume cycling is the simplest form of ventilation to use. It is conceptually easier because a dog of a certain size can be reasonably equated to a tidal volume. The set up for a typical 30kg Labrador will be described. Tidal Volume First, it is important to know the weight of your patient in kg. Secondly, using the Merlin Volume Chart or using the value of 10mls tidal volume per kg bodyweight the tidal volume is calculated. Set the Tidal Volume control to 300. Note: If the control only shows values between 0.1 and 25.0 then make sure...