Basic and properties Modes of ventilation.pdf
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The document provides a comprehensive overview of mechanical ventilation, including types of ventilators, key variables such as pressure and volume control, and different modes of ventilation such as controlled mechanical ventilation and synchronized intermittent mandatory ventilation. It discusses the significance of monitoring important parameters to avoid complications like barotrauma, and outlines methods for managing patients with various respiratory challenges. Additionally, it emphasizes the importance of understanding ventilatory support mechanisms to improve patient care in critical settings.
Basic and properties Modes of ventilation.pdf
- 1. Assist. Prof. Radhwan Hazem Alkhashab Consultant Anaesthesia & ICU 2025
- 2. Please download and install the Slido app on all computers you use What comes to your mind when you think of mechanical ventilation? ⓘ Start presenting to display the poll results on this slide.
- 3. Introduction Mechanical ventilation is an important tool in ICU for treatment of various ventilatory failure. To set the ventilator right you should know the ventilator language. In ventilator language we have variables and these form breaths and breaths form modes of ventilation.
- 4. Variables in ventilator Control variables: When providing ventilatory support, the mechanical ventilator can control four primary variables during inspiration. These four variables are Pressure. Volume. Flow. Time. Phase variables: A ventilator-supported breath may be divided into four distinct phases: (1) Trigger. (2) Limit (3) Cycling (4) Baseline.
- 5. 1.Pressurecontroller A ventilator is classified as a pressure controller if the ventilator controls the trans-respiratory system pressure (airway pressure minus body surface pressure). Further classification of a ventilator as a positive or negative pressure ventilator depends on whether the airway pressure rises above baseline (positive) or body surface pressure is lowered below baseline (negative).
- 6. A positive pressure ventilator applies pressure inside the chest to expand it. This type of ventilator requires the use of a tight- fitting mask, or more commonly, an artificial airway. A pressure greater than atmospheric pressure is applied to the lungs, causing them to expand. Once positive pressure is no longer applied, the patient is allowed to exhale passively to ambient pressure. Exhalation occurs because of the pressure differential between the lungs and the atmosphere and through the elastic recoil of the lungs and thorax. This is the type of ventilator most commonly used today.
- 7. Negative pressure ventilators apply subatmospheric pressure outside of the chest to inflate the lungs. The negative pressure causes the chest wall to expand, and the pressure difference between the lungs and the atmosphere causes air to flow into the lungs. Once negative pressure is no longer applied, the patient is allowed to exhale passively to ambient pressure. Regardless of whether a ventilator is classified as positive or negative pressure, the lungs expand as a result of the positive trans-respiratory system pressures generated. It is the trans-respiratory pressure gradient that largely determines the depth or volume of inspiration.
- 8. 2.Volumecontroller: To be classified as a volume controller, volume must be measured and used as a feedback signal to control the output (volume) delivered. A volume controller allows pressure to vary with changes in resistance and compliance while volume delivery remains constant.
- 9. ModesofVentilation • Fixed TV with each breath • Peak airway pressure can vary with each breath depending on: • Resistance to airflow during inspiration • Patient’s lung-chest wall compliance • Fixed peak airway pressure with each breath • TV can vary with each breath depending on: • Resistance to airflow during inspiration • Patient’s lung-chest wall compliance Volume Targeted Modes Pressure Targeted Modes
- 10. Phase variable: 1st Trigger This is the parameter that tells the ventilator to start inspiration. 1. Pressure trigger: Breath is delivered when ventilator senses patients spontaneous inspiratory effort. • sensitivity refers to the amount of negative pressure the patient must generate to receive a breath/gas flow. • If the sensitivity is set at 1 cm then the patient must generate 1 cm H2O of negative pressure for the machine to sense the patient's effort and deliver a breath. • Acceptable range -1 to -5 cm H2O below patient s baseline pressure. 2. Flow trigger: Ventilator senses a preset value of inspiratory flow due to patient effort. 3. Volume trigger: Ventilator can not sense volume but it calculate volume from dividing flow over time. 4. Time trigger: A preset interval of time passes then the ventilator starts inspiration this is usually in mandatory breath.
- 11. 2nd variable is limit This defines the extent of inspiratory flow (volume) or pressure that cannot be exceeded it is often the same as the target (control) but they are different variables. During a ventilator-supported breath, volume pressure and flow all rise above their respective baseline values. Inspiratory time is defined as the time interval between the start of inspiratory flow and the beginning of expiratory flow.. .
- 12. 3rd variable is cycle This is reverse of trigger that means it will tell the ventilator to end inspiration or in other words to switch from inspiration to expiration . Its either the ventilator senses a preset pressure , volume , flow or it will cycle by time usually in mandatory modes .
- 13. 4th variable is Base line Which can be zero or positive like in PEEP or ZEEP
- 14. Summary of modes & their variables
- 15. Definitions: Peak Inspiratory Pressure (PIP):The peak pressure is the maximum pressure obtainable during active gas delivery. This pressure a function of the compliance of the lung and thorax and the airway resistance including the contribution made by the tracheal tube and the ventilator circuit. Maintained at <45cm H2O to minimize barotrauma. Plateau Pressure: The plateau pressure is defined as the end inspiratory pressure during a period of no gas flow. The plateau pressure reflects lung and chest wall compliance.
- 16. Mean Airway Pressure- The mean airway pressure is an average of the system pressure over the entire ventilatory period. End Expiratory Pressure- End expiratory pressure is the airway pressure at the termination of the expiratory phase and is normally equal to atmospheric or the applied PEEP level.
- 17. o Apnea ventilation Apnea ventilation is a safety feature incorporated with the spontaneous breathing mode. In the event of apnea or an extremely slow respiratory rate, backup ventilation is invoked by the apnea ventilation feature and it delivers a predetermined tidal volume, respiratory rate, F,02, and other essential ventilator functions to the patient. Refractory Hypoxemia: Refractory hypoxemia is present when the PaO2 is ≤60 mm Hg at an FiO2 of ≥50%.
- 18. Please download and install the Slido app on all computers you use What challenges have you faced while using mechanical ventilation? ⓘ Start presenting to display the poll results on this slide.
- 19. Barotrauma Barotrauma is lung injury that results from the hyperinflation of alveoli past the rupture point. Although each patient is different, a PEEP greater than 10 cm H20 (or mean airway pressure >30 cm H,O, or a peak inspiratory pressure >50 cm H2O) are associated with an increased incidence of alveolar rupture or barotrauma.
- 20. Alveolar rupture can produce pneumothorax, tension pneumotho-rax, pneumomediastinum, pneumopericardium, and pneumoperitoneum. Subcutaneous emphysema or crepitus of unknown cause should always be interpreted as a sign that barotrauma has occurred. Since PEEP increases alveolar pressures and alveolar volumes, it has the potential to produce barotrauma especially when combined with volume-cycled ventilation. Therefore plateau pressures should be closely monitored in these patients as well as being vigilant for any signs of barotrauma
- 21. • Fluid Balance Positive pressure ventilation reduces cardiac output and thus renal perfusion. Urine output is decreased due to hypoperfusion of the kidneys. Mechanical ventilation also reduces urine output as a result of an increase in antidiuretic hormone (ADH) and reduction of atrial natriuretic factor (ANF). The end result of these changes is decreased fluid output and fluid retention.
- 22. Types of breath 1. Mandatory breath: this is triggered, limited and cycled by the ventilator and the patient has no role to do. We usually find this type in controlled modes where the breaths triggered and cycled by time. 2. Assisted mandatory or assisted controlled breath: this is mandatory but with modification that it can be triggered by the patient or by ventilator {time trigger} otherwise it is like mandatory breathe limited and cycled by ventilator. 3. Spontaneous breath: this is normal natural breath triggered, limited and cycled by the patient. 4. Supported spontaneous breath: this is simply a spontaneous breath supported by pressure to make it more effective .It is still triggered, limited and cycled by patient.
- 23. Mandatory breath This is triggered, limited and cycled by the ventilator and the patient has no role to do. We usually find this type in controlled modes where the breaths triggered and cycled by time.
- 24. Assisted Mandatory or Assisted Controlled Breath This is mandatory but with modification that it can be triggered by the patient or by ventilator {time trigger} otherwise it is like mandatory breathe limited and cycled by ventilator.
- 25. Spontaneous breath This is normal natural breath triggered, limited and cycled by the patient.
- 26. Supported spontaneous breaths This is simply a spontaneous breath supported by pressure to make it more effective .It is still triggered, limited and cycled by patient.
- 27. Modes classified according to control 1. Volume targeted modes (CMV,A/CMV and SIMV) 2. Pressure targeted modes (PCMV,PA/CMV,SIMV,PS-PEEP and CPAP)
- 28. Controlled mechanical ventilation {CMV} This is an old mode consists of mandatory breaths only leaving no role for the patient so it requires deep sedation with or without muscle relaxation. Hazards of this mode?
- 29. Assisted / controlled mechanical ventilation This mode differs from CMV by combining both mandatory and assisted mandatory breaths. Assisted breaths are triggered by the patient. If the patient does not trigger for any reason then the ventilator will trigger by time according to a preset backup respiratory rate.
- 30. AC ( Assist control ventilation) mode Indications: 1. Myasthenia gravis. 2. GBS. 3. Post cardiac / resp arrest. 4. ARDS. 5. Pulmonary oedema. Advantages: Minimal work of breathing and patient controls RR which helps normalize PaCO2.
- 31. Synchronized Intermittent Mandatory Ventilation This mode was invented aiming to give more comfortability to patient by giving him chance to breath spontaneously yet giving him a preset number of mandatory breaths to guarantee minute ventilation. This mode can be used as a starting ventilatory mode because it guarantee a fixed minute ventilation and as a weaning mode by gradual decrease in number of mandatory breaths.
- 32. Synchronized Intermittent Mandatory Ventilation This mode combines both spontaneous and mandatory breaths . In the past the mandatory breaths of this mode were not synchronized with spontaneous breaths and the mode was called intermittent mandatory ventilation. This asynchronization created a problem called stacking which means that mandatory tidal volume will buildup over spontaneous tidal volume . Stacking lead to patient discomfort and may lead in severe cases to volutrauma and/or barotrauma.
- 33. Differences between IMV & SIMV IMV mode may cause breath stacking since the mandatory breaths are delivered at a set time interval with no regard to the patient's breathing frequency. SIMV mode does not cause breath stacking since the mandatory breaths are delivered slightly sooner or later than the preset time interval but within a time window.
- 35. SIMV This problem was solved by synchronizing the inspiration of the mandatory breath with inspiration of the patient or with an interval of absence of respiratory effort. Note: synchronization is not triggering and the patient does not trigger the mandatory breaths in this mode.
- 36. (IMV) Mandatory Breath Triggering Mechanism The SIMV mandatory breaths may be either time triggered or patient triggered. The triggering mechanism is determined by whether or not the patient makes a spontaneous inspiratory effort just prior to the delivery of a time-triggered breath.
- 37. Advantages of SIMV Mode Since SIMV promotes spontaneous breathing and use of respiratory muscles, SIMV (1) Maintains respiratory muscle strength/avoids muscle atrophy, (2) Reduces ventilation to perfusion mismatch, (3) Decreases mean airway pressure: which enhances the patient`s cardiovascular function. (4) Facilitates weaning.
- 38. SIMV This mode has two disadvantages: 1. Hyperventilation because the patient spontaneous minute ventilation will be added to mandatory minute ventilation. 2. Hypoventilation during weaning.
- 39. Pressure Targeted Modes Here the constant parameter or variable is the pressure. These include (PCMV, PA/CMV, P/SIMV, PS and CPAP).
- 40. Pressure targeted modes advantages In addition to lung protection pressure targeted modes have other advantages which are compensation for limited leak and variable flow rate during inspiration which offers better distribution of ventilation and more patient comfortability.
- 41. PCMV Pressure controlled (mandatory) mechanical ventilation (PCMV): This mode has the advantages of pressure targeted modes but still needs deep sedation with or without muscle relaxation.
- 42. P /SIMV Pressure - synchronized intermittent mandatory ventilation (P/SIMV): Pressure are used to support patient`s effort during SIMV , this help to augment the tidal volume.
- 43. Pressure support (PS) Supports spontaneous breathing of the patients. • Each inspiratory effort is augmented by ventilator at a preset level of inspiratory pressure. • Patient triggered, flow cycled and pressure controlled mode. • Applies pressure plateau to patient airway during spontaneous breathing. • Commonly applied to SIMV mode during spontaneous ventilation to facilitate weaning PSV (Pressure Support Ventilation) mode
- 44. Pressure support (PS) Cycling primarily done by flow cycling by reaching either a percentage of peak inspiratory flow rate or a preset absolute value of flow. This type of cycling is most comfortable for the patient because it usually matches normal cycling. If this cycling mechanism fail (due to leak for example) then 2ndary mechanism works by time will cycle.
- 45. Pressure support (PS) This is the best mode for patients who have mild to moderate lung injury at the same time have good respiratory efforts because it guarantees maximum patient-ventilator synchrony and at the same time if the PS is set right then it will provide good ventilation.
- 46. Indications for the PSV mode Pressure support is commonly applied in the SIMV mode when the patient takes spontaneous breaths. Pressure support is not active during the mandatory breaths. Pressure support is typically used in the SIMV mode to facilitate weaning in a difficult to wean patient. In this application, pressure support (1) Increases the patient's spontaneous tidal volume, (2) Decreases the patient's spontaneous respiratory rate. (3) Decreases the work of breathing.
- 47. Disadvantage of PS This mode does not guarantee fixed minute ventilation because : • It does not guarantee fixed VT because it depends on patient efforts. • It does not guarantee fixed RR because it depends on patient rate. The problem of rate solved in some types of ventilator by setting a backup rate and in other ventilators by combining P/SIMV with PS.
- 48. (CPAP) This is the same as PEEP but CPAP is more technically accurate term because the pressure is keep positive during the whole respiratory cycle not only at the end of expiration. It was known for long time that artificial ventilation affects oxygenation badly this is because it increases both ventilation/perfusion mismatch and basal collapse. So doctors used high FIO2 to manage this problem but this is injurious and the maximum FIO2 can be given with least harm is 50%. So doctors looked for another solution and that is CPAP or PEEP.
- 49. Advantages for CPAP or PEEP 1. Improve oxygenation by: Opening collapsed alveoli during inspiration: so increasing number of ventilated alveoli and decreasing percentage of shunt. This is occurring especially in basal areas and diseased areas. Actually before the use of CPAP doctors used high VTs (10-15 ml/kg Bwt) to open basal collapses. But this turns to be harmful to lung and the use of high VTs was abundant. Prevent collapse during expiration: by increase FRC above closing capacity. Ventilate alveoli filled with edema fluid: by shifting fluid out of them.
- 50. Advantages for CPAP or PEEP 2. Improve compliance of the lung by: Opening collapsed alveoli (recruitment) Shifting edema fluid out of alveoli and interstitial space. 3. Prevent lung injury.
- 51. Disadvantages of peep 1. Decrease venous return. 2. Barotrauma. 3. Increase intracranial pressure. 4. Decrease renal blood flow.
- 52. Indication for BIPAP 1. BIPAP appears to be of value in preventing intubation of the end-stage COPD patient. 2. In supporting patients with chronic ventilatory failure. 3. Patients with restrictive chest wall disease. 4. Neuromuscular disease. 5. Nocturnal hypoventilation.
- 53. BIPAP Initial settings The BiPAP system may be used in one of three modes: 1. Spontaneous. 2. Spontaneous/ timed. 3. Timed. Mode selection depends on a patient's needs and ability to breath spontaneously. In general, if the patient is breathing spontaneously, the IPAP and EPAP may be set at 8 cm H20 and 4 cm H20, respectively.
- 54. The spontaneous/ timed mode is used as a backup mechanism and the breaths per minute (BPM) is set two to five breaths below the patient's spontaneous rate. In the timed mode, set IPAP and EPAP as above and the BPM slightly higher than the patient's spontaneous rate. NOTE : BIPAP appears to be of value in preventing intubation of the end stage COPD patient and in supporting patients with chronic ventilatory failure.
- 55. Inverse Ratio Ventilation I:E ratio The ratio of inspiratory time (I time) to expiratory time (E time) is known as the I:E ratio. In conventional mechanical ventilation, the I time is traditionally lower than the E time so that the I:E ratio ranges from about 1:1.5 to 1:3. This resembles the normal I:E ratio during spontaneous breathing, and it is considered physiologically beneficial to normal cardiopulmonary function. Since the mid-1980s, investigators have been extending the inspiratory time during mechanical ventilation to promote oxygenation in patients with ARDS. The inverse I:E ratio in use is between 2:1 and 4:1 and often it is used in conjunction with pressure control ventilation
- 56. Physiology of IRV Inverse ratio ventilation (IRV) improves oxygenation by (1) reduction of intrapulmonary shunting, (2) improvement of V/Q matching, and (3) decrease of dead space ventilation. Adverse Effect During IRV, the increase in mPaw and the presence of auto-PEEP both contribute to the increase of mean alveolar pressure and volume, the incidence of barotrauma may be as high as that obtained by conventional ventilation with high levels of PEEP
- 57. Barotrauma (volutrauma) Barotrauma or volutrauma is the term used to describe lung tissue injury or rupture that results from alveolar over distention. General agreement is that in most cases, peak inspiratory pressures greater than 50 cm H2O, plateau pressures greater than 35 cm H20, mean airway pressures greater than 30 cm H20, and PEEP greater than 10 cm H20 may induce the development of barotrauma. The risk of barotrauma also increases with the duration of positive pressure ventilation.
- 58. Barotrauma can occur at mean airway pressures lower than 30 cmH,0 either due to patient susceptibility or to an uneven distribution of ventilation. COPD patients are more susceptible to barotrauma presumably due to air trapping and weakened parenchymal areas (e.g., lung blebs and bullae). Other lung injuries that may occur as a result of positive pressure ventilation include pulmonary interstitial emphysema, pneumomedi-astinum, pneumoperitoneum, pneumothorax, tension pneumothorax, and subcutaneous emphysema.
- 60. Please download and install the Slido app on all computers you use What do you believe is the most critical factor to monitor when using mechanical ventilators? ⓘ Start presenting to display the poll results on this slide.