MECHANICAL VENTILATOR
Glossary
- Inspiratory capacity (CI): The amount of air a person can breathe, starting at the level of a normal expiration and distending their lungs to the maximum (3,500 ml approximately). CI = VC + VRI
- Total lung capacity (CPT): The volume of air in the respiratory system, after voluntary maximum inhalation. It corresponds to approximately 6 liters of air. It is the maximum volume at which the lungs can expand with the maximum possible effort (approximately 5,800 ml). CPT = VC + VRI + VRE + VR
- Vital capacity (CV): Is the amount of air that is possible to expel from the lungs after having inspired completely. They are around 4.6 liters. CV = VRI + VC + VRE
- Mechanical ventilation: or positive pressure ventilation is a procedure that supplements the patient's respiratory function or assists him or her to carry it out.
- Residual volume: the amount of air left in a person's lungs after exhaling completely.
- Respiratory frequency: is the number of breaths a person makes per minute. The frequency is usually measured when a person is at rest and simply consists of counting the number of breaths for one minute each time the chest is raised.
- Tidal volume (VT, or TV): is the amount of air that is displaced along normal inhalation and exhalation, in other words, the amount of air that is breathed throughout normal breathing. In a healthy young adult, the tidal volume is approximately 500 ml per inspiration or 7 ml / kg body mass.
VENTILATION AND RESPIRATORY MECHANICS: Pulmonary ventilation is the functional process by which gas is transported from the subject's surroundings to the pulmonary alveoli and vice versa. This process can be active or passive depending on whether the ventilatory mode is spontaneous, when it is performed by the activity of the respiratory muscles of the individual, or mechanical when the ventilation process is performed by the action of an external mechanism.
The level of ventilation is regulated from the respiratory center according to the metabolic needs, the gaseous state and the acid-base balance of the blood and the mechanical conditions of the lung-rib cage complex. The objective of the pulmonary ventilation is to transport oxygen to the alveolar space so that the exchange with the pulmonary capillary space occurs and evacuate the CO2 produced metabolic level.
Inspiratory Time and Relationship I: E: the inspiratory time is regulated taking into account how much time the patient requires to deliver the volume or pressure programmed. It should also be noted that it is not too short to generate discomfort in the patient, nor too long that hinders the time to exhale and generate a PEEP car by not being able to complete the delivery of the gas supplied in the inspiration.
The relationship between inspiration and expiration or I: E, is usually 1: 2, so if, for example, we program FR at 20 per minute, we will have the inspiration in 1 second and the expiration in 2 seconds, if we do changes in this I: E ratio we will also have to change the flow velocity, so that it can fulfill the inspiratory time as previously explained, without problems in the inspiration, in many fans we have a built-in program that makes the changes automatically.
Gas delivery method: there are basically two ways:
- To by volume: each respiratory cycle is delivered with the same level of flow and time, which determines a constant volume independent of the patient's effort and the pressure that is generated. The flow wave will generally be a square wave, since the delivery of the flow is constant, some equipment allows to change it to descending or sinusoidal, in order to decrease the inspiratory pressure. They can be controlled totally, partially or spontaneously.
- To by pressure: each respiratory cycle will be delivered in inspiration at a preselected pressure level, for a certain time. The volume and flow vary according to the impedance of the respiratory system and the strength of the inspiratory impulse. The most frequent form of flow delivery will be in descending ramp. In this modality, the changes in the compliance of the thoracic wall as well as the resistance of the system will influence the corresponding tidal volume. Thus, when there is greater resistance and less compliance, the volume will decrease and increase if compliance improves and resistance decreases. They can be controlled totally, partially or spontaneously.
- Volume controlled ventilation (CMV): All breaths are controlled by the ventilator and offers tidal volume (VT) and respiratory rate (FR) predetermined. It does not accept the initial stimulus of the patient so its use is reserved for patients who do not have spontaneous inspiratory effort or are paralyzed.
- Advantages of CMV: it provides total ventilatory support (tidal volume and constant respiratory frequency), then it controls the minute volume and determines the PaCO2 and the ventilatory pattern.
- Disadvantages of CMV: ventilation support does not change in response to increased needs, can generate discordance (asynchrony) with the ventilator, so for better coordination may require sedation and paralysis; As a consequence, a variable peak pressure (PIP) can appear and there is also a high risk of cardiovascular compromise.
- Controlled assisted ventilation (AC): The breaths are delivered as programmed in tidal volume, peak flow and waveform, as well as the base respiratory frequency. The respirations initiated by the machine or the patient are delivered with these parameters, the sensitivity can be adjusted so that the patient can generate a higher respiratory frequency than the programmed one
- Advantages of AC: we will have a Minimal Ventilation (VM) minimum assured, also the volume will be guaranteed with each breath. A better chance of synchronization with the patient's breathing will be given, which then can send its frequency.
- Disadvantages of AC: if the spontaneous frequency is high, respiratory alkalosis can occur, high pressure can also be generated in the upper airways and have associated complications. Excessive patient work if the flow or sensitivity are not programmed correctly. There may be poor tolerance in awake patients, or without sedation. It can cause or worsen the PEEP car. Possible respiratory muscle atrophy if this form of support is prolonged for a long time.
Constant values
- Running volume: 500 ml
- Inspiratory reserve volume: 3,000 ml (with inspiratory effort)
- Expiratory reserve volume: 1,100 ml (with expiratory effort)
- Residual volume: 1,200 ml Vital capacity: inspiratory reserve volume (3,000 ml) + expiratory reserve volume (1,000 ml) + circulating volume (500 ml) = 4,500 ml
- Inspiratory capacity: circulating volume (500 ml) + inspiratory reserve volume (3,000 ml) = 3,500 ml
- Expiratory capacity: circulating volume (500 ml) + expiratory reserve volume (1,000 ml) = 1,500 ml
- Total lung capacity: vital capacity (4,500 ml) + residual volume (1,200 ml) = 5,700 ml
A person at rest performs 12 breaths per minute; if 500 ml is mobilized at each air inlet and outlet, 6000 ml will be mobilized in one minute.
Programming Code
Call libraries to LCD and matricidal
keyboard
Code of the keyboard, we declared a pair of
constants rows and columns of the keyboard, and ones arrays for indicate to the
library what pines of arduino correspondence to rows and columns of the keypad.
We defined what symbols correspondence to
each position of the keys too.
First, we pass the characters to numerical value, after
we crate a void to save in a matrix the numerical values and with this is with
the that we can able to work.
If the key is the number one, the machine
will start the test, which will trigger the alarm, the compressor and the
pressure on the sensor that is appropriate.
We prove the compressor sending a pulse to
the pin of compressor and reading this pulse in the pin 22, if pin 22 is high,
the compressor be working.
We prove the alarm sending a pulse to the
pin of the led and buzzer, this buzzer will sound and led will turn on, also we
ask if the person listen the buzzer for
continue to the test.
We prove the pressure sending a pulse to
the compressor and to the two-electro valve, thus insufflating the pump and we
will check the pressure reading the analog voltage of pressure sensor in the
pin A0 of us arduino, if the pressure is the indicated to the input, the
pressure will be ok.
After the pressure was ok, the mechanical
ventilator will be able to work. If
some parameter of the test its incorrect the test will repeat.
If the key is the letter “B” the person ingress
to the adult ventilation.
If the key is the letter “C” the person
ingress to the pediatric ventilation
If the key is the letter “D” the person
ingress to the newborn ventilation
After this, the person put the weight
according to the patient; this weight will serve us for the mode of ventilation
by volume due to the current volume it is gave by 7ml/Kg, so the weight will
multiply for seven and we will get the correct volume for work, but if the mode is of the pressure,
the person should put the pressure in mmHg according to the patient
Getting physiology graphs.
In this
case, we can see pressure and volume graphs and their values depends of each
patient. In this mechanical ventilator we used a MPX-5100 pressure sensor,
giving us a change of voltage when the pressure change in the airways. To
Characterize the voltage vs Pressure, we divide it in three cases depending the
patient.
Newborn Patient.
The pressure limit of a newborn patient in
this mechanical ventilator is 60mmHg, where the voltage at this value is
0.44volts. Making a linear regression, we have the next Equation:
Replacing in the
equation m =230.77, for that reason the linear regression is:
Respect to
the volume graphs, we make it depend the pressure value, we can have a volume
value with a specific pressure value, in this case, for a newborn patient the
pressure limit is 60mmHg and the maximum
volume value is given by the maximum weight in the system (5Kg-35mL), for that
reason in this case the linear regression is made between pressure and volume
with the following equation:
Replacing
the values, we get y=0.5833x where y is the volume to know and x is the
pressure value given by the sensor.
Pediatric Patient
The
pressure limit of a pediatric patient in this mechanical ventilator is 80mmHg,
where the voltage at this value is 0.54volts. Making a linear regression, we
have the next Equation:
Replacing in the
equation m =222.22, for that reason the linear regression is:
Respect to
the volume graphs, we make it depend the pressure value, we can have a volume
value with a specific pressure value, in this case, for an adult patient the
pressure limit is 80mmHg and the maximum
volume value is given by the maximum weight in the system (65Kg-455mL), for
that reason in this case the linear regression is made between pressure and
volume with the following equation:
Replacing
the values, we get y=5.6875x where y is the volume to know and x is the
pressure value given by the sensor.
Adult patient
The
pressure limit of an adult patient in this mechanical ventilator is 100mmHg,
where the voltage at this value is 0.62volts. Making a linear regression, we
have the next Equation:
Replacing in the
equation m =227.27, for that reason the linear regression is:
Respect to
the volume graphs, we make it depend the pressure value, we can have a volume
value with a specific pressure value, in this case, for an adult patient the
pressure limit is 100mmHg and the
maximum volume value is given by the maximum weight in the system (220Kg-1.540L),
for that reason in this case the linear regression is made between pressure and
volume with the following equation:
Replacing
the values, we get y=10.26x where y is the volume to know and x is the pressure
value given by the sensor.
Power Stage
The power
stage is designed like in the picture, the first part is composed by an
optocoupler 4n25, it receives the Arduino’s pulse to turn on the compressor ,
the optocoupler has the function to isolate the ground system of the Arduino
from the voltage source, them with a tip122 and a 2n2222a transistor, the
current increases and go to a relay, the relay activate the compressor and the
electro valves with a different Arduino
pin. When the compressor is on, one
electro valve is on, that is the inspiration process and them, after 1 or 2
seconds, depending the I:E relationship the compressor and the electro valves
turn off and the second electro valve turns on completing the expiration.
MAINTENANCE MANUAL MECHANICAL VENTILATOR
To perform the respective maintenance of the equipment it is necessary to take into account the following recommendations:
- . It is necessary to disconnect the equipment.
- Uncover the equipment carefully without disconnecting any of the cables.
- Aspirate the equipment to remove dust, speck etc. (Use masks)
- Perform a visual inspection (damaged capacitors, loose resistors, loose cables etc).
- Download the equipment streams.
- Check the type of power supply of the equipment, if enough voltage and current is arriving: Compressor: 110-120 V Sensor and relay supply: 12 V
- Check the hoses are well connected
- Turn on the equipment
- Check that there are no loose wires in the arduino.
- Check if the arduino is connected to a power supply (USB port or charger)
- Connect the patient simulator ballon
- Perform the test to check the state of the equipment
- Check for oxygen leaks
- Check in the flow sensor is working correctly
- Test all keyboard keys.
MECHANICAL VENTILATOR USER'S MANUAL
The mehanical ventilator has an LCD where it will indicate the keys that each procedure represents, as can be seen in the following image.
Where A is used to enter the process.
It is necessary to connect the compressor to the 120 V socket and the sensor, electrovalves to 12 V (protoboard elements) Wait for the team to pledge Perform the test recommended by the equipment before performing its respective operation, as you can see in the following video
After the equipment confirms that it is in optimal conditions to start ventilation, the user can choose the following patient options:
B: Adult patient, where the weight range that can be entered is 66-220 kg
C: Pediatric patient, where the weight range is from 6 - 65 kg
D: Neonatal Patient, where the weight range is 1-5 Kg
After entering the type of patient to be ventilated and the weight it is necessary to choose what type of ventilation you want:
* Pressure
# Volume
