What Is Mechanical Ventilation?

Mechanical ventilation, in the healthcare setting or home, helps patients breathe by assisting the inhalation of oxygen into the lungs and the exhalation of carbon dioxide. Depending on the patient’s condition, mechanical ventilation can help support or completely control breathing.

Essential information about ventilators:

Ventilator terms »
Rate, volume, sensitivity, flow, limits and measures of breathing
Settings »
The clinician determines appropriate ventilator settings according to the condition and needs of the patient
Modes »
Ventilators offer a variety of modes that determine how and when breath is delivered to the patient
Alarms »
Audible or visual alarms help monitor ventilator function and settings
Ventilation terms

Discussions about ventilation use the following terms:

Rate of breaths

Also referred to as respiratory rate, breathing rate, or frequency; can be a ventilator setting or respiratory status the ventilator tracks as the patient breathes

Volume of breaths

Usually expressed in milliliters (mL); frequently referred to as tidal volume or “VT”; can be a ventilator setting or respiratory status the ventilator tracks as the patient breathes

Sensitivity of breathing

Concerns how much inspiratory or “trigger” effort is required from the ventilator to recognize that the patient is trying to inhale; this can refer to a ventilator setting, but can also be used to describe the ventilator’s responsiveness to the patient’s breathing effort

Flow of breaths

Also referred to as peak flow or inspiratory flow; usually describes a ventilator setting but can be respiratory status the ventilator tracks as the patient breathes

Controls or limits on breathing volume, pressure or time

The ventilator can limit or control the inspiratory pressure, volume or time during breath delivery

Measured or mandatory breaths

Also referred to as mechanical breaths, describes breaths initiated by the ventilator delivered according to a consistent volume or pressure

Lung compliance and airway resistance

Lung compliance refers to the elasticity, stretch or ease with which the lung expands to receive volume

Airway resistance refers to the resistance encountered as oxygen enters the airway and to how easily the lung lets in air

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Ventilator settings

The clinician determines appropriate ventilator settings according to the condition and needs of the patient. The settings include:

FIO 2

The measure of oxygen the ventilator is delivering during inspiration.

Rate

The number of breaths delivered by the ventilator per minute.

Tidal volume

The volume of gas/air delivered with each breath.

Sensitivity

This alerts the ventilator when to recognize the start of a patient’s spontaneous breath (or breathing effort). When the ventilator recognizes the patient’s effort, it triggers a response, either to provide a mechanical breath or to support a spontaneous one.

Peak flow

The flow of gas/air (flow rate) used to deliver each mechanical breath to the patient.

Inspiratory and expiratory times

The total time required for one complete respiratory cycle. Typically, patients are comfortable with an expiratory time two to three times longer than the inspiratory time.

Cycling

The manner in which the ventilator ends the inspiratory phase of the breath and allows the patient to exhale. Ventilator breaths can be volume cycled, time cycled or flow cycled.

Limit

This setting restricts the volume, pressure or time air is delivered to the patient during the inspiratory phase.

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Ventilator modes


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Ventilator manufacturers offer combinations of modes and breath types that characterize how and when a breath is delivered to the patient.

Ventilator modes most commonly found on the home care ventilator include:

Assist/control (A/C)

All breaths delivered by the ventilator will control either volume or pressure. The ventilator delivers the same measured breath every time, whether the breath is patient initiated or ventilator initiated, based on the rate setting.

Continuous positive airway pressure ventilation (CPAP)

All breathing is initiated and sustained by the patient. The ventilator delivers no machine (mandatory) breaths. The ventilator controls the delivered oxygen concentration and delivers as much flow and volume as necessary to meet the patient’s inspiratory demands. The patient decides the tidal volume and number of spontaneous breaths.

This mode also allows the patient to breathe at a continuous, elevated airway pressure that can improve oxygenation (see PEEP/CPAP).

The ventilator can also apply positive pressure during spontaneous inspirations taken during CPAP mode to reduce the patient’s work to breathe.

Synchronized intermittent mandatory ventilation (SIMV)

The ventilator synchronizes machine breath delivery with the patient’s spontaneous breath efforts. This mode is a combination of set mandatory machine breaths synchronized with the patient’s own spontaneous breaths.

Pressure control ventilation (PCV or PC)

This is a type of mandatory breath that can be used in either A/C or SIMV modes and targets a specific pressure during inspiration. The delivered flow rate varies according to the patient’s demand and own lung characteristics, such as lung compliance and airway resistance. The delivered tidal volume also varies with changes in compliance and resistance. In PC mode, the clinician also sets a specific time for inspiration or inspiratory time.

Pressure support ventilation (PSV or PS)

This is a type of spontaneous breath that can be used in either CPAP or SIMV modes and targets a set inspiratory pressure, much like PC. But the PS inspiration ends as the lung gets full and the delivered flow decreases to a specific valve set by the clinician. The patient decides the respiratory rate and inspiratory time as well as the flow rate and tidal volume.

Positive end expiratory pressure (PEEP)

Mechanical positive pressure is applied at the end of exhalation to prevent the lungs from emptying completely and returning to a “zero” reading. The benefit of positive pressure at the end of exhalation is increased lung volume for improved oxygenation.

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Ventilator alarms


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Ventilators offer audible and visual alarms to alert the caregiver to changes in key patient and ventilator functions and settings. These alarms prompt a timely response, safeguarding the patient and proper functioning of the ventilator. Note: It is critical that whenever an alarm occurs, the caregiver evaluates the patient first before checking the ventilator.

High airway pressure alarms

These are also referred to as high inspiratory pressure (HIP) alarms. This alarm setting also provides a pressure limit function.

If the ventilator pressure reaches the set limit, an audible or visual alarm activates. The ventilator will temporarily stop the inspiration, allowing the patient to exhale immediately.

The alarm detects abnormally high inspiratory pressure and may activate in response to:

Kinks in the patient circuit or tracheostomy tube
Water in the ventilator circuit
Increased mucus or other secretions blocking the airway
Bronchospasm, or narrowing of the patient’s airway
Coughing, gagging or “fighting” the ventilator breath
Pneumonia or other changes in lung condition that affect airway resistance or lung compliance
After determining the condition that triggered the alarm, do whatever is needed to fix the situation, which could be suctioning the patient, repositioning the tube or adjusting the alarm settings. If the patient’s condition has worsened because of pneumonia or other illness, contact the physician promptly.

Low airway pressure alarms

These are also referred to as low inspiratory pressure (LIP) alarms.

These alarms are in response to:

Decrease in lung pressure due to a change in lung or patient condition
Increase in patient demand for oxygen because of agitation, pain or discomfort
Change in lung compliance or airway resistance
Low pressure alarms can also activate if there’s an air leak out of the breathing circuit caused by:

Patient-ventilator disconnection
Improper inflation of the tracheostomy tube cuff
Poorly fitting noninvasive nose masks or prongs
Loose circuit and tubing connections
Water condensate in the circuit
High and low rate alarms

A low or high rate alarm will trigger an audible and/or visual alert. An agitated or fatigued patient can have an increase in respiratory rate. Sedated patients or patients with impaired neuromuscular function can have a decreased respiratory rate.

High and low volume alarms

In addition to a high respiratory rate, high volume alarms may indicate increased patient demand for gas/air because of pain, anxiety or improper ventilator settings.

Low volume alarms are typically caused by air leaks. In pressure-based ventilation, these alarms may indicate worsening airway resistance or lung compliance.

What is Vital Signs Monitor ?

Vital signs (often shortened to just vitals) are a group of the 4 to 6 most important signs that indicate the status of the body’s vital (life-sustaining) functions. These measurements are taken to help assess the general physical health of a person, give clues to possible diseases, and show progress toward recovery.[1][2] The normal ranges for a person’s vital signs vary with age, weight, gender, and overall health.[3]

There are four primary vital signs: body temperature, blood pressure, pulse (heart rate), and breathing rate (respiratory rate), often notated as BT, BP, HR, and RR. However, depending on the clinical setting, the vital signs may include other measurements called the "fifth vital sign" or "sixth vital sign". Vital signs are recorded using the LOINC internationally-accepted standard coding system.[4][5]

Early warning scores have been proposed that combine the individual values of vital signs into a single score. This was done in recognition that deteriorating vital signs often precede cardiac arrest and/or admission to the intensive care unit. Used appropriately, a rapid response team can assess and treat a deteriorating patient and prevent adverse outcomes.[6][7][8]

Primary vital signs[edit]
There are four primary vital signs which are standard in most medical settings:

Body temperature
Heart Rate or Pulse
Respiratory rate
Blood pressure
The equipment needed is a thermometer, a sphygmomanometer, and a watch. Though a pulse can be taken by hand, a stethoscope may be required for a patient with a very weak pulse.

Temperature[edit]
Temperature recording gives an indication of core body temperature which is normally tightly controlled (thermoregulation) as it affects the rate of chemical reactions.

Temperature can be recorded in order to establish a baseline for the individual's normal body temperature for the site and measuring conditions. The main reason for checking body temperature is to solicit any signs of systemic infection or inflammation in the presence of a fever (temp > 38.5 °C/101.3 °F or sustained temp > 38 °C/100.4 °F), or elevated significantly above the individual's normal temperature. Other causes of elevated temperature include hyperthermia.

Temperature depression (hypothermia) also needs to be evaluated. It is also noteworthy to review the trend of the patient's temperature. A patient with a fever of 38 °C does not necessarily indicate an ominous sign if his previous temperature has been higher. Body temperature is maintained through a balance of the heat produced by the body and the heat lost from the body.

Temperature is commonly considered to be a vital sign most notably in a hospital setting. EMTs (Emergency Medical Technicians), in particular, are taught to measure the vital signs of: respiration, pulse, skin, pupils, and blood pressure as "the 5 vital signs" in a non-hospital setting.[9]

Pulse[edit]
Main article: Pulse
The pulse or heart rate is the rate at which the heart beats while pumping blood through the arteries. Its rate is usually measured either at the wrist or the ankle and is recorded as beats per minute. The pulse commonly taken is from the radial artery at the wrist. Sometimes the pulse cannot be taken at the wrist and is taken at the elbow (brachial artery), at the neck against the carotid artery (carotid pulse), behind the knee (popliteal artery), or in the foot dorsalis pedis or posterior tibial arteries. The pulse rate can also be measured by listening directly to the heartbeat using a stethoscope. The pulse varies with age. A newborn or infant can have a heart rate of about 130–150 beats per minute. A toddler's heart will beat about 100–120 times per minute, an older child's heartbeat is around 60–100 beats per minute, adolescents around 80–100 beats per minute, and adults' pulse rate is anywhere between 50 and 80 beats per minute.

Respiratory rate[edit]
Main article: Respiratory rate
Varies with age, but the normal reference range for an adult is 16–20 breaths/minute (RCP 2012). The value of respiratory rate as an indicator of potential respiratory dysfunction has been investigated but findings suggest it is of limited value. Respiratory rate is a clear indicator of acidotic states, as the main function of respiration is removal of CO2 leaving bicarbonate base in circulation.

Blood pressure[edit]
Main article: Blood pressure § Measurement
The blood pressure is recorded as two readings: a high systolic pressure, which occurs during the maximal contraction of the heart, and the lower diastolic or resting pressure. A normal blood pressure would be 120 being the systolic over 80, the diastolic. Usually the blood pressure is read from the left arm unless there is some damage to the arm. The difference between the systolic and diastolic pressure is called the pulse pressure. The measurement of these pressures is now usually done with an aneroid or electronic sphygmomanometer. The classic measurement device is a mercury sphygmomanometer, using a column of mercury measured off in millimeters. In the United States and UK, the common form is millimeters of mercury, whilst elsewhere SI units of pressure are used. There is no natural 'normal' value for blood pressure, but rather a range of values that on increasing are associated with increased risks. The guideline acceptable reading also takes into account other co-factors for disease. Therefore, elevated blood pressure (hypertension) is variously defined when the systolic number is persistently over 140–160 mmHg. Low blood pressure is hypotension. Blood pressures are also taken at other portions of the extremities. These pressures are called segmental blood pressures and are used to evaluate blockage or arterial occlusion in a limb (see Ankle brachial pressure index).

Additional signs[edit]
In the U.S., in addition to the above four, it is required to record the patients Height, Weight, and Body Mass Index.[10]

Fifth vital signs[edit]
The "fifth vital sign" may refer to a few different parameters.

Pain is considered a standard fifth vital sign in some organizations such as the U.S. Veterans Affairs.[11] Pain is measured on a pain scale based on subjective patient reporting and may be unreliable.[12] Some studies show that recording pain routinely may not change management.[13][14][15] Other "fifth vital signs" include:
Menstrual cycle [16][17]
Glasgow Coma Scale [18]
Pulse Oximetry [19][20][21]
Blood Glucose level [22]
Sixth vital signs[edit]
There is no standard "sixth vital sign"; its use is more informal and discipline-dependent than the above.

End-tidal CO2.[23][18]
Functional status[24]
Shortness of breath[25]
Gait speed[26]

What is Anaesthetic Machine

The anaesthetic machine (UK English) or anesthesia machine (US English) or Boyle's machine is used by anaesthesiologists, nurse anaesthetists, and anaesthesiologist assistants to support the administration of anaesthesia. The most common type of anaesthetic machine in use in the developed world is the continuous-flow anaesthetic machine, which is designed to provide an accurate and continuous supply of medical gases (such as oxygen and nitrous oxide), mixed with an accurate concentration of anaesthetic vapour (such as isoflurane), and deliver this to the patient at a safe pressure and flow. Modern machines incorporate a ventilator, suction unit, and patient monitoring devices.

The original concept of Boyle's machine was invented by the British anaesthetist Henry Boyle (1875–1941) in 1917. Prior to this time, anaesthetists often carried all their equipment with them, but the development of heavy, bulky cylinder storage and increasingly elaborate airway equipment meant that this was no longer practical for most circumstances. The anaesthetic machine is usually mounted on anti-static wheels for convenient transportation.

Simpler anaesthetic apparatus may be used in special circumstances, such as the TriService Apparatus, a simplified anaesthesia delivery system invented for the British armed forces, which is light and portable and may be used effectively even when no medical gases are available. This device has unidirectional valves which suck in ambient air which can be enriched with oxygen from a cylinder, with the help of a set of bellows. A large number of draw-over type of anaesthesia devices are still in use in India for administering an air-ether mixture to the patient, which can be enriched with oxygen. But the advent of the cautery has sounded the death knell to this device, due to the explosion hazard.

Many of the early innovations in U.S. anaesthetic equipment, including the closed circuit carbon-dioxide absorber (aka: the Guedel-Foregger Midget) and diffusion of such equipment to anaesthetists within the United States can be attributed to Richard von Foregger and The Foregger Company.

In dentistry a simplified version of the anaesthetic machine, without a ventilator or anaesthetic vaporiser, is referred to as a relative analgesia machine. By using this machine, the dentist can administer a mild inhalation sedation with nitrous oxide and oxygen, in order to keep his patient in a conscious state while depressing the feeling of pain.

Simple schematic of an anaesthesia machine
A modern anaesthesia machine includes the following components:

Connections to piped hospital oxygen, medical air, and nitrous oxide.
Reserve gas cylinders of oxygen, air, and nitrous oxide attached via a specific yoke with a Bodok seal.
A high-flow oxygen flush which provides pure oxygen at 30-75 litres/minute
Pressure gauges, regulators and 'pop-off' valves, to protect the machine components and patient from high-pressure gases
Flow meters (rotameters) for oxygen, air, and nitrous oxide, low Flow meters oxygen nitrous oxide
Updated vaporizers to provide accurate dosage control when using volatile anaesthetics such as isoflurane and sevoflurane
An integrated ventilator to properly ventilate the patient during administration of anaesthesia
A manual ventilation bag in combination with an Adjustable Pressure Limiting (APL) valve
Systems for monitoring the gases being administered to, and exhaled by the patient
Systems for monitoring the patient's heart rate, ECG, blood pressure and oxygen saturation, in some cases with additional options for monitoring end-tidal carbon dioxide and temperature
breathing circuits, circle attachment, or a Bain's breathing system
Safety features of modern machines[edit]
Based on experience gained from analysis of mishaps, the modern anaesthetic machine incorporates several safety devices, including:

an oxygen failure alarm (aka 'Oxygen Failure Warning Device' or OFWD). In older machines this was a pneumatic device called a Ritchie whistle which sounds when oxygen pressure is 38 psi descending. Newer machines have an electronic sensor.
Nitrous cut-off or oxygen failure protection device, OFPD: the flow of medical nitrous-oxide is dependent on oxygen pressure. This is done at the regulator level. In essence, the nitrous-oxide regulator is a 'slave' of the oxygen regulator. i.e., if oxygen pressure is lost then the other gases can not flow past their regulators.
hypoxic-mixture alarms (hypoxy guards or ratio controllers) to prevent gas mixtures which contain less than 21-25% oxygen being delivered to the patient. In modern machines it is impossible to deliver 100% nitrous oxide (or any hypoxic mixture) to the patient to breathe. Oxygen is automatically added to the fresh gas flow even if the anaesthetist should attempt to deliver 100% nitrous oxide. Ratio controllers usually operate on the pneumatic principle or are chain linked (link 25 system). Both are located on the rotameter assembly, unless electronically controlled.
ventilator alarms, which warn of low or high airway pressures.
interlocks between the vaporizers preventing inadvertent administration of more than one volatile agent concurrently
alarms on all the above physiological monitors
the Pin Index Safety System prevents cylinders being accidentally connected to the wrong yoke
the NIST (Non-Interchangeable Screw Thread) or Diameter Index Safety System, DISS system for pipeline gases, which prevents piped gases from the wall being accidentally connected to the wrong inlet on the machine
pipeline gas hoses have non-interchangeable Schrader valve connectors, which prevents hoses being accidentally plugged into the wrong wall socket
The functions of the machine should be checked at the beginning of every operating list in a "cockpit-drill". Machines and associated equipment must be maintained and serviced regularly.

Older machines may lack some of the safety features and refinements present on newer machines. However, they were designed to be operated without mains electricity, using compressed gas power for the ventilator and suction apparatus. Modern machines often have battery backup, but may fail when this becomes depleted.

The modern anaesthetic machine still retains all the key working principles of the Boyle's machine (a British Oxygen Company trade name) in honour of the British anaesthetist Henry Boyle. In India, however, the trade name 'Boyle' is registered with Boyle HealthCare Pvt. Ltd., Indore MP.

A two-person pre-use check (consisting of an anaesthetist and an operating department practitioner) of the anaesthetic machine is recommended before every single case and has been shown to decrease the risk of 24-hour severe postoperative morbidity and mortality.[1] Various regulatory and professional bodies have formulated checklists for different countries.[2] A free transparent reality simulation of the checklist recommended by the United States Food & Drug Administration is available from the Virtual Anesthesia Machine web site ( see below) after registration which is also free. Machines should be cleaned between cases as they are at considerable risk of contamination with pathogens.[3]

An anaesthetic machine
The Anesthesia machine contains mechanical respiratory support (ventilator) and O2 support as well as being a means for administering anesthetic gases which may be used for sedation as well as total anesthesia. An anesthesia cart holds extra IV push meds for anesthesia, sedation and reversal, extra equipment that the person giving anesthesia/sedation might need, and the hardware for respiratory support and resuscitation.