|Year : 2019 | Volume
| Issue : 6 | Page : 64-69
OSCE : Equipment
Kundan Mittal1, Prashant Kumar2, HK Aggarwal3
1 Senior Professor and Incharge PICU and Respiratory Clinic, Pt B D Sharma, PGIMS Rohtak, Haryana, India
2 Professor Anaesthesia & Neurocritical Care, Pt B D Sharma, PGIMS Rohtak, Haryana, India
3 Senior Professor Medicine & Nephrology, Pt B D Sharma, PGIMS Rohtak, Haryana, India
|Date of Submission||25-Oct-2019|
|Date of Acceptance||23-Nov-2019|
|Date of Web Publication||20-Dec-2019|
Senior Professor Pediatrics, Pt B D Sharma, PGIMS, Rohtak Haryana
Source of Support: None, Conflict of Interest: None
Provision of respiratory support by positive pressure ventilation is one of important function of intensive care units. Mechanical ventilation is used to replace or supplement the work carried out by respiratory system. Mechanical ventilation is a supportive intervention rather therapeutic and is full of hazards.
Keywords: Mechanical Ventilator, Modes, High frequency ventilation
|How to cite this article:|
Mittal K, Kumar P, Aggarwal H K. OSCE : Equipment. J Pediatr Crit Care 2019;6:64-9
| Q. What is this equipment?|| |
Answer: This is the screen of mechanical ventilator; a mechanical device used to deliver positive pressure ventilation. A ventilator is simply a machine; a system of related elements designed to alter, transmit, and direct applied energy in a predetermined manner to perform useful work [augment or totally support cardio-respiratory function (ventilation and oxygenation) in a pre-determined manner for an indeterminate amount of time]. Ventilator is connected to pneumatic and/or electrical supply to deliver predetermined (on control panel using interface or graphic user interface) breath or gas flow to the patient.
The screen is showing various variables including graphics. Bottom of screen shows set or predetermined parameters and top displays measured/delivered parameters. Centre is showing two types of graphics (scalar and loops). Light indicates alarms. Left of corner is displaying mode of ventilation.
| Q. What are types of ventilator?|| |
Answer: Ventilator device can be non-invasive and invasive (negative and positive and conventional and high frequency ventilator). It is important to understand the concept and respiratory mechanics rather than machine. Do not run after fancy modes. If we know what we want to achieve and how it can be achieved than solution is there.
| Q. What are the purpose of invasive mechanical ventilator?|| |
Answer: Purpose of mechanical ventilator are;
- Maintenance of oxygenation
- Provision of adequate ventilation
- Preserve or return of respiratory mechanics to normal function
- Minimize the metabolic expenditure of respiratory system (work of breathing)
- Avoiding ventilator induced lung injury and complications
| Q. What are components of ventilator system?|| |
Answer: Ventilator system has six essential components;
- Compressed oxygen and air supplies
- Electrical/Battery power supply
- A ventilator
- A breathing circuit
- An artificial airway, and
- The patient’s pulmonary system
| Q. How ventilator works?|| |
Answer : Primarily ventilatory muscles cause the size of the thoracic cage to increase by overcoming the elastic forces of the lungs and thorax, resistance of the airways thus intrapleural pressure becomes negative and gas flows from atmosphere into lungs as a result of trans-airway pressure gradient. During expiration muscles of inspiration relax, elastic forces of the lungs and thorax cause the chest to decrease in volume resulting greater pressure at the alveolus than atmosphere thus exhalation occurs. All of the muscle activity used to breathe requires energy and work. Two pressures are needed to move gas into the lung; pressure needed to overcome the resistance to moving gas through airway (resistance load) and pressure needed to overcome the elastance of the lung in order to expand it (elastic load). The two pressures can be provided by either respiratory muscles (muscle pressure), by the mechanical ventilator (ventilator pressure) or both. Mechanical ventilator substitutes partially or completely ventilatory work done by the respiratory muscles. All mechanical ventilators have many things in common i.e. source of air and oxygen under pressure, blending of air and oxygen, and deliver the physician selected FiO2. On demand inspiratory valves open and pressurized and heated-humidified gas is delivered through inspiratory limb of ventilator circuit & endotracheal tube to the patient. Exhalation vale opens when inspiratory valve closes and exhaled gas is passed to atmosphere. In between various variables are measured and used during the process by user interface.
| Q. What do you understand by term mode?|| |
Answer: Refer to method of inspiratory support which is specific combination of breathing pattern and control variables during inspiration. Mode is specific combination of control, phase and conditional variables defined for both mandatory and spontaneous breaths.
| Q. What are various type of modes available?|| |
Answer: Commonly available modes are;
- Positive end-expiratory pressure (PEEP)
- Continuous positive airway pressure (CPAP)
- Controlled mandatory ventilation (CMV)
- Assist/control (AC- CMV- Pressure or Volume)
- Intermittent mandatory ventilation (IMV)
- Synchronized intermittent mandatory ventilation (SIMV)
- Pressure support ventilation (PSV)
- Mandatory minute ventilation (MMV)
- Bilevel positive airway pressure (BiPAP)
- Adaptive support ventilation (ASV)
- Proportional assist ventilation (PAV)
- Volume-assured pressure support (VAPS)
- Pressure-regulated volume control (PRVC)
- Adaptive pressure control (APC)
- Volume ventilation plus
- Pressure-controlled ventilation (PCV)
- Airway pressure release ventilation (APRV)
- Biphasic positive airway pressure (Biphasic PAP)
- Inverse ratio ventilation (IRV)
- Automatic tube compensation (ATC)
- Neurally adjusted ventilator assist (NAVA)
- High-frequency oscillatory Ventilation (HFOV)
| Q. What do you understand by term dual mode?|| |
Answer: Dual control modes are able to control either pressure or volume based on measured input variable. Mode changes from pressure to volume on measured input. Dual control can be either within a breath or breath to breath.
Dual Control within a breath: (DCWB) Defined as when two variables become control variable during inspiration in the same breath. It can switch from one mode to another within breath. It measures flow input to switch pressure targeting to flow targeting in the middle of breath. Pressure targeted breath and flow is controlled.
Volume assured pressure support (VAPS)
Pressure augmentation (PA)
Dual Control breath to breath (DCBB): Physician set the volume target breath and pressure-controlled breath the delivered to achieve desired target volume. DCBB measures volume input to manipulate the pressure support level of subsequent pressure targeted breath.
Pressure limited, time cycled
Pressure regulated volume control
Adaptive pressure ventilation
Volume targeted pressure control
Adaptive support ventilation
| Q. Classify modes of high frequency ventilation (HFV).|| |
Answer: High frequency uses mandatory rate higher (usually >100/min) than normal and tidal volume lower than normal.
- High frequency jet ventilation: HFJV
- High frequency oscillatory ventilation: HFOV
- High frequency positive pressure ventilation: HFPPV
- High frequency percussive ventilation: HFPV
- High flow frequency interruption: HFFI
| Q. What do understand about following terms: elastance, compliance, time constant, resistance, mean airway pressure?|| |
- Elastance is defined as the change in pressure (ΔP) divided by the change in volume (ΔV)— refers to the property of a substance to oppose deformation. It is opposite of compliance ΔV ÷ ΔP), the property of a substance to allow distension or lengthening when subjected to pressure. Compliance is of two types; static and dynamic.
Static Compliance = Tidal volume/Pplat-PEEP or autoPEEP
Dynamic compliance = Tidal volume/PIP-PEEP or autoPEEP
- Resistance (R) refers to the opposition to generation of flow. It is measured as the amount of pressure needed to generate a unit of flow (Δ P ÷ Δ Flow). It is dynamic component (PIP-Pplat/ Flow L/sec)
- Time Constant (TC) is the time required for ventilator pressure to equilibrate with alveolar pressure when air flow ceases (both during inspiration and expiration) C x R
- Mean airway pressure is the average pressure applied to the airway during the ventilatory cycle. It is related to both the amount and duration of pressure applied during the inspiratory phase.
| Five different ways to increase mean airway pressure:|| |
- Increase the respiratory flow rate, producing a square wave inspiratory pattern
- Increase the peak inspiratory pressure
- Reverse the inspiratory-expiratory ratio or prolong the inspiratory time without changing the rate
- Increase positive end-expiratory pressure; and
- Increase the ventilatory rate by reducing the expiratory time without changing the inspiratory time
|Figure 1: Criteria to determine trigger during a breath on mechanical ventilator|
Click here to view
| Q. How will you classify ventilatory breath?|| |
Answer: Ventilatory breath can be classified as under;
| Q. What is four phase breath and phase variables?|| |
Answer: The phase variable is a variable that is measured and used by the ventilator to initiate some phase of the breath cycle. A condition variable is used by a ventilator’s control circuitto make decisions. A simple conditional formula takes the form of a “if-then” statement. That is, if the value of a conditional variable reaches some present level, then some actions occur to change the ventilatory pattern.
To understand a breath cycle, you must know how the ventilator starts, sustains, and stops inspiration. Respiratory cycle may be divided into four distinct phases;
| Breath Phase|| |
- End of expiration and beginning of inspiration
- Delivery of inspiration
- End of inspiration and beginning of expiration
- Expiratory phase
| Phase Variables|| |
- Trigger variable: Begins inspiration. Triger can be time, pressure, flow and volume triggered. Pressure and flow are commonly used variables for patient triggering.
- Limit variable: Limits the magnitude of any control variable (pressure, flow, volume, time) during inspiration. It does not end the inspiration.
- Cycle variable: Ends of inspiratory gas flow. It can be flow, pressure, volume or time triggered.
- Baseline variable: Determines what happens during expiration. Pressure and flows can be controlled during exhalation.
| Q. Describe common modes used in PICU.|| |
Answer: Common modes used are PCV, VCV, Assist control, PSV and SIMV
Volume control mode (VCV): This mode delivers preset tidal volume at a time triggered respiratory rate and constant inspiratory flow [waveforms (sine, constant, decelerating)] set by physician). It can be classified as assist control mode with volume ventilation. Back up rate is set in assist mode so that if patient does not breathe, ventilator will deliver the adequate minute ventilation.
Pressure control mode (PCV): It delivers positive pressure up to a preset limit above PEEP for a preset inspiratory time. Flow depends on airway pressure and respiratory compliance achieving high level initially and decelerating towards zero at the end of inspiration. Since pressure is limited and change in respiratory mechanics will alter the tidal volume and minute ventilation. The risk of barotrauma is less in this mode and decelerating flow is advantageous. This mode is primarily used in paediatrics patient having decreased compliance and relatively high resistance or alveolar space disease.
Assist-Control Ventilation (CMV with assist): Patient receives all breaths set by physician. In between patient can trigger the breath and delivered all set values.Breath types are both mandatory and assisted.
Assisted Ventilation (AMV): No set frequency, all breaths are patient triggered and delivered at the ventilator’s set tidal volume or pressure. All breaths are assisted breaths.
Pressure Support Ventilation: Patient triggered (flow or pressure), pressure limited and flow cycled breath. Constant pressure during inspiration produces decelerating ramp flow pattern.
Synchronized Intermittent Mandatory Ventilation (SIMV): It is modified version of IMV mode having characteristics of CMV, assist-CMV and spontaneous breath in which ventilator creates a time window (SIMV period and spontaneous period) around scheduled delivery of mandatory breath and attempt to deliver the breath in concern with the patient inspiratory effort. It synchronizes patient breath and if detects patient efforts then machine breath is not delivered.
| Types of SIMV Mode|| |
SIMV (volume control) + Pressure support
SIMV (pressure control) + Pressure support
SIMV (PRVC) + Pressure support
| Q. What are clinical uses of graphics?|| |
- Identify lung injury during mechanical ventilation
- Monitor disease status
- Oxygenation and ventilation
- Air leaks
- Air trapping
- Patient response
- Trouble shooting
| Q. How will you set ventilatory settings?|| |
Many ventilators ask for patient weight, age, leak and tubal compensation, sigh breath, inspiratory limbs etc. Most of the today ventilator will blink light for setting parameters once the mode of ventilation is selected.
- Mode: In pediatric population pressure-controlled ventilation is the most common mode of ventilation. Initially children are put on A/CMV or SIMV mode. In this mode we have to set the Ti time. Flow is automatically adjusted. In some situation we may set PRVC/VTPC mode, a dual control mode, where set tidal volume is delivered by adjusting pressure within limits.
- Respiratory frequency: It is the respiratory rate/ min. The rate is adjusted in physiological range keeping in mind the I:E ratio (kept 1:2 to 1;3) and the desired minute ventilation. The estimated minute ventilation is usually 4 times of RR x TV or BSA.
- Inspiratory time: In pressure mode Ti is set usually 0.35 sec for newborn, 0.5- 0.6 sec infants, 0.6-0.8 for children and 1.0 sec for adolescents. In volume ventilation Ti can be adjusted by flow, RR, and volume.
▪Ti = Tidal volume/ flow rate
- Tidal volume: Tidal volume 6-8 ml/kg is set in volume ventilation and not in pressure ventilation.
▪Tidal volume = Ti x flow rate
- Peak inspiratory pressure (PIP): Set PIP in pressure ventilation 15-20 cm/H2O to achieve adequate tidal volume but should not exceed beyond 35. There is no need to set PIP in volume ventilation. In pressure support mode pressure support is also set around 10.
- PEEP: Peak end expiratory pressure is usually set 3-5 cm/H2O. In children with ARDS, higher PEEP is required.
- FiO2: Set FiO2 of 1.0 initially. It should be adjusted targeting PaO2>80mmHg or looking at SpO2>96%. Gradually it should be brought down to below 60.
- Trigger sensitivity: Trigger sensitivity is set in assistmodes. Flow is preferred over pressure sensitivity in pediatric patients.
- Set humidifier chamber on.
| Q. What are side effects of positive pressure ventilation?|| |
Answer: Common side effects are;
- Increased physiological dead space ventilation
- Volutrauma: Alveolar-capillary membrane injury
- Barotrauma: Alveolar membrane disruption
- Interstitial emphysema
- Gas embolism
- Decreased systemic venous return
- Decreased cerebral perfusion
- Decreased renal, intestinal, hepatic blood flow
Source of Funding: Nil
Conflict of Interest: Nil
| References|| |
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Chang DW. Clinical Application of Mechanical Ventilation. 4th
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Pilbeam SP. Mechanical Ventilation: Physiological and Clinical Application. 6th
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Hess DR. Essentials of Mechanical Ventilation. 3rd
ed. McGraw-Hill education; New York: 2014
Rimensberger PC. Pediatric and Neonatal Mechanical Ventilation. Springer; Switzerland:2015
Rajiv PK, Vidyasagar D, Lakhminrusimha S. Essentials of Neonatal Ventilation. Elsevier; India:2020