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Seminar on basics of mechanical ventilation

The document discusses mechanical ventilation, outlining its purpose, types, indications, modes, and complications. It details the evolution of ventilatory systems from negative to positive pressure ventilation, alongside various modes such as controlled mechanical ventilation and pressure support. Monitoring, ventilator settings, and the importance of weaning are also highlighted to optimize patient outcomes during mechanical ventilation.

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MECHANICAL VENTILATION Dr Mohammed Hussein (R1) MICU, October 6 2023 4/19/2024 1
Outline • Introduction • Types of Mechanical Ventilation • Aims of Ventilatory Support • Indications • Modes of ventilation • Ventilator settings • Monitoring • Complications of mechanical ventilation • Weaning 4/19/2024 2
Introduction • Mechanical Ventilator: A device which assists or replaces spontaneous breathing ,Support ventilatory function and improve oxygenation. • Inspiratory trigger  predetermined air (O2 + other gases) forced into airways & alveoli  lungs inflate  ↑ intraalveolar pressure  termination signal – vent stops delivery  ↓airway pressure  expiration follows passively due to pressure gradiant. 4/19/2024 3
Several models evolving over time • Negative pressure ventilation – past • Positive pressure ventilation – present 4/19/2024 4
Negative pressure ventilators • Developed in 1929. • Used widely in 1940 polio epidemic. • The patient’s body was encased in an iron cylinder and negative pressure was generated Emerson JH, Loynes JA. The evolution of iron lungs: respirators of the body- encasing type. Cambridge:JH Emerson & Company; 1958. Google Scholar 4/19/2024 5
Positive-pressure ventilators A positive pressure is applied to the mouth or mask providing a positive pressure gradient from mouth to alveoli resulting in inspiration Invasive ventilation first used at Massachusetts General Hospital in 1955 This can be applied with a mask (non-invasive) or with a tracheal tube or tracheostomy (invasive). Current ICU ventilators are primarily positive pressure ventilators 4/19/2024 6
Noninvasive ventilation (NIV) • Provided with tight fitting face mask or nasal mask • Candidates for NIV trial: exacerbations of COPD and respiratory acidosis (pH <7.35) • Several RCTs – NIV is associated with low failure rate (15-20%) and good outcome (intubation rate, length of stay in ICU, mortality) in patients with ventilatory failure characterized by blood pH levels between 7.25 and 7.35 • For pH <7.25: As pH decreases, failure rate increases • For pH >7.35: NIV is not better than conventional therapy (oxygen therapy & pharmacotherapy like bronchodilator, steroid, antibiotics) 4/19/2024 7
Indication of NIPPV Pulmonary edema Asthma COPD Cardiogenic Pulmonary edema Chest trauma Assisting in early extubation 4/19/2024 8
4/19/2024 9
Conventional Mechanical Ventilation • Delivers conditioned gas (warmed, oxygenated, and humidified) via an endotracheal tube or tracheostomy tube at pressures above atmospheric pressure • Mechanical ventilators are comprised of four main elements: 1. A source of pressurised gas including a blender for air and O2. 2. An inspiratory valve, expiratory valve and ventilator circuit. 3. A control system, including control panel, monitoring and alarms. 4. A system to sense when the patient is trying to take breath. 4/19/2024 10
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Indications 1. Acute Respiratory Failure • Hypoxic/Hypercapnic 2. Air way protection • To prevent Aspiration in deeply sedated & unconscious pt • Maintain patency in obstruction (Asthma, Anaphylaxis, Tumor) 3. Pulmonary vascular disease:  PTE, Amniotic fluid embolism, tumor emboli 4. Hyperventilation Therapy - raised ICP 5. Hypoventilation: • Decreased central drive (General anesthesia, Drug overdose), PNS/respiratory muscle dysfunction 6. Increased ventilatory demand • E.g:- Severe sepsis, septic shock, severe metabolic acidosis 4/19/2024 12
Aims of Mechanical Ventilation • Achieve and maintain adequate pulmonary gas exchange (ventilation and oxygenation) • Reduce or eliminate excessive work of breathing • Optimize patient comfort • Minimize the risk of complications • Maintain and protect the airway and allow more effective clearance of secretions 4/19/2024 13
Modes Mode refers to the manner in which ventilator breaths are triggered, cycled, and limited The trigger, either an inspiratory effort or a time based signal, defines what the ventilator senses to initiate an assisted breath. The limiting factors -are operator-specified values, such as airway pressure Cycle refers to the factors that determine the end of inspiration. Other types of cycling include pressure cycling and time cycling. 4/19/2024 14
Modes of Ventilation 1. CMV 2. Assist control (AC) 3. Synchronized intermittent mandatory ventilation (SIMV) 4. Pressure support ventilation 5. CPAP 15 4/19/2024
Controlled mechanical ventilation (CMV) • During CMV, the minute ventilation is determined entirely by the set respiratory rate and tidal volume. • This may be due to pharmacologic paralysis, heavy sedation, coma, or lack of incentive to increase the minute ventilation because the set minute ventilation meets or exceeds physiologic need. 16 4/19/2024
VCV • Trigger – timed, limit – flow, termination – volume • Set: TV, flow rate, RR, FiO2, PEEP, inspiratory time • Monitor: Pplat, PIP, 4/19/2024 17
700 ml -70 70 l/min 50 cmH2O Volume control Pressure Flow Volume T 4/19/2024 18
PRESSURE-CONTROL VENTILATION (PCV) • Are ventilator-initiated breaths with a pressure limit. • Limits inflation pressure • Mandatory breath only • Set: PIP, I:E ratio, RR, PEEP, FiO2 • Inspiration ends at delivery of set PIP. • Tidal volume is variable, related to • PIP, compliance, airway resistance, tubing resistance • High VT: can be due to High PIP & low compliance 19 4/19/2024
…PCV 20 Time cycled(control)--inspiratory flow should return to normal 4/19/2024
PCV Advantage • Prevents excessive airway pressures • Avoid regional alveolar over distention • May lead to earlier liberation from MV Disadvantage • Very uncomfortable and requires deep sedation +/- paralysis • Unable to guarantee minimum VE 21 Indications= patients who are at particularly high risk from barotrauma and post thoracic surgery. 4/19/2024
Assist-Control Ventilation • ACMV is the most widely used mode of ventilation. • In this mode, an inspiratory cycle is initiated either by the patient’s inspiratory effort or, if none is detected within a specified time window, by a timer signal within the ventilator. • During AC, the clinician determines the minimal minute ventilation by setting the respiratory rate and tidal volume. • The patient can increase the minute ventilation by triggering additional breaths. 22 4/19/2024
Cont… • Each patient-initiated breath receives the set tidal volume from the ventilator. • Every breath delivered, whether patient- or timer-triggered, consists of the operator-specified tidal volume. • It is a mixed mode in which pts receive a mandatory breath with set tidal volume (if volume AC) or pressure (pressure AC). • In ACV, the mechanical breaths are limited by volume and/or flow and cycled by volume or time. 23 4/19/2024
24 4/19/2024
Volume pre-set assist control • Advantages • Relatively simple to set • Guaranteed minimum minute ventilation • Rests muscles of respiration (if properly set) • Disadvantages • Not synchronized • Patient may “lead” ventilator • Inappropriate triggering may result in excessive minute ventilation •  lung compliance   alveolar pressure with risk of barotrauma • Often requires sedation to achieve synchrony. 4/19/2024 25
Intermittent Mandatory Ventilation • IMV allows the patient to breathe spontaneously between machine-cycled or mandatory breaths. • In the most frequently used synchronized mode (SIMV), mandatory breaths are delivered in synchrony with the patient’s inspiratory efforts at a frequency determined by the operator. • SIMV differs from ACMV in that only a preset number of breaths are ventilator-assisted. 26 4/19/2024
Cont… 27 4/19/2024
Cont… • IMV is similar to AC in two ways: • The clinician determines the minimal minute ventilation (by setting the respiratory rate and tidal volume) and • The patient is able to increase the minute ventilation. • However, IMV differs from AC in the way that the minute ventilation is increased. • SIMV allows patients with an intact respiratory drive to exercise inspiratory muscles between assisted breaths; thus it is useful for both supporting and weaning intubated patients. 28 4/19/2024
Pressure support (PSV) • The ventilator applies a pre-determined amount of positive pressure to the airways upon inspiration. • This form of ventilation is patient-triggered, flow-cycled, and pressure- limited. • The patient breathes spontaneously. • With PSV, patients receive ventilator assistance only when the ventilator detects an inspiratory effort. • PSV is well tolerated by most patients who are being weaned from MV. • Comfortable mode for awake and conscious patient • Can be combined with SIMV mode. 29 4/19/2024
Cont… 30 In flow cycled (supported) flow does not return to baseline 4/19/2024
Continuous positive airway pressure (CPAP) • Is the way of delivering PEEP but also maintains the set pressure through out the respiratory cycle. • Allows spontaneous breathing at elevated baseline pressure. • Set P = 5-15cmH2O • CPAP is most commonly used in the management of sleep related breathing disorders, cardiogenic pulmonary edema, and 31 4/19/2024
4/19/2024 32
Mechanical Ventilator Settings Trigger Tidal Volume Respiratory Rate PEEP Flow rate Fraction of Inspired oxygen(Fio2) Flow Pattern 4/19/2024 33
Trigger • Trigger sensitivity •  sensitivity preferable • Flow triggering generally more sensitive than pressure triggering •  flow or less negative pressure   sensitivity • Trigger types • pressure triggering or • A trigger sensitivity of -1 to -3 cmH2O is typically set. • flow triggering • initiated when the return flow is less than the delivered flow. 4/19/2024 34
Tidal volume • Optimal tidal volume for mechanically ventilated patients:- • without existing lung disease 6-8ml/kg of IBW. • For ARDS-4-6 ml/kg of IBW • Female PBW= 45.5 + 0.91 (Ht – 152.4) • Male PBW = 50 + 0.91 (Ht – 152.4) • As Tv inc., peak airway pressure also inc.(>45cmH20 barotrauma) 4/19/2024 35
Respiratory rate • Initial respiratory rate between 12 and 16 breaths per minute is reasonable. • RR adjustment- • Modification according to mode • Desired PH & paco2 • autoPEEP(if >5cmH20) • For ALI/ARDS-up to 35’ • MV= TV X RR 4/19/2024 36
PEEP • PEEP is used to mitigate end-expiratory alveolar collapse. • An initial PEEP is 5 cmH2O. • 20 cmH2O may be used in patients with ARDS. • Elevated levels of PEEP- • reduced preload(CO) • increases risk of barotrauma and • impaired cerebral venous outflow (increases ICP) 4/19/2024 37
Fraction of inspired oxygen(Fio2) • % of oxygen in each breath. • Titrated to meet patient needs. • Goal- • PaO2 above 60 mmHg and • SpO2 above 90 percent. 4/19/2024 38
Inspiratory time • Set as: • % of respiratory cycle • I:E ratio • Indirectly, by setting flow • Expiratory time not set • Remaining time after inspiration before next breath 4/19/2024 39
Inspiratory Time • Longer inspiratory time • Improved oxygenation • Higher mean airway pressure • Re-distribution • Lower peak airway pressure • More time available to deliver set tidal volume • Shorter inspiratory time • Less risk of gas trapping and PEEPi • Less effect on cardiovascular system 4/19/2024 40
Inspiratory to expiratory (I:E) ratio • Inspiratory time is equal to tidal volume divided by flow rate. • Normal I:E ratio: 1:2 to 1:3. • Can be reduced to 1:4 or 1:5 in COPD (longer expiratory time) • inverse I:E ratio may be necessary in states of low compliance, such as ARDS.
Flow rate • The peak flow rate is the maximum flow delivered by the ventilator during inspiration. • Peak flow rates of 60 L per minute may be sufficient, although higher rates are frequently necessary. • Increased peak flow rates – increase the peak airway pressure. decreased inspiratory time lowers the mean airway pressure, which can decrease oxygenation. 4/19/2024 42
Inspiratory flow Pattern • Different flow rates are associated with different airflow waveforms. 1. Square waveforms flow accelerates very quickly and then reaches a set rate, which is maintained throughout inspiration. Flow rate is constant This waveform allows for an adequate I:E ratio with a normal flow rate. Inspiratory arm
Inspiratory flow Pattern 2. Ramp waveforms flow rate rapidly accelerates but is followed by a gentle tapering. This waveform may require much higher flow rates to obtain an adequate I:E ratio. This waveform can be used if abnormally high PIP is encountered. Inspiratory arm Expiratory arm
Pressures • Peak inspiratory pressure- the pressure required to administer a set tidal volume • As the tidal volume increases, the pressure required to administer that volume also increases.. • Pawp above 45 cmH2O -the risk of barotrauma is increased. • plateau pressure - is the pressure after the delivery of the tidal volume but before the patient is allowed to exhale. • is maintained < 30 cmH2O. • Mean airway pressure- refers to the mean across the entire respiratory cycle, both inspiration and expiration 4/19/2024 45
Mean airway pressure Mean airway pressure Mean airway pressure Time Pressure Time Pressure  Tidal volume 4/19/2024 46
Mean airway pressure Mean airway pressure Mean airway pressure Time Pressure Time Pressure  Inspiratory time 4/19/2024 47
Dyssynchrony
4/19/2024 49
Waveform showing increased airways resistance Ppeak Pplat Pres ‘Square wave’ flow pattern
Recognizing secretion in the ETT 51 4/19/2024
Waveform showing decreased lung compliance Ppeak Pplat Pres ‘Square wave’ flow pattern
• Incomplete expiration leading to air trapping • Causes include • High minute ventilation • Expiratory flow limitation • Expiratory resistance Auto PEEP
Patient-ventilator dys-synchrony • State when the respiratory cycle of the patient does not match that of the ventilator. • It can happen during triggering process, flow delivery or breath cycling. • Clinical features: ↑HR, RR; ↓SO2; ↑expiratory mm activity, coughing, anxiety, visible inspiratory effort without triggering the ventilator; Ventilator waveforms • Consequences include: ↑Work Of Breath, prolongation of MV, perceived need for deeper sedation
Vent triggers to start inspiration does not always correlate with the patient attempt to start inspiration Airflow what the patient is demanding does not match what the vent is providing Vent and patient went transitions from inspiration to expiration at different times
Principles of monitoring • Follow the patient clinical condition • Assess ventilation and oxygenation – ABGs • Follow vent parameters • Flow and pressure time curves • Pressure and volume alarms • Always evaluate for weaning readiness 57 4/19/2024
Alarms • Never ignore an alarm • Common causes of alarms • Dislodgement: check ETT length of insertion (av. 22) at incisor • Obstruction: secretion, blood clot, fighting patient biting the ETT • Suction, sedation • Pneumothorax: barotrauma • Equipment failure: air leak, disconnected corrugator tube, ↓ humidifier water, uninflated ETT cuff 58 4/19/2024
Complications of MV • During Act of intubation • Artificial air way related complication • Pulmonary complications • Non pulmonary complications 4/19/2024 59
During Act of intubation • Dental trauma • Aspiration – bag ventilation for preoxygenation can cause gastric distension + irritation during ETT insertion  vomiting • Laryngeal trauma – hoarseness, URTO • Laryngeal edema, ulceration, granuloma, vocal cord paralysis • Bronchospasm – mechanical irritation • Esophageal intubation • Right main bronchus intubation – it goes too far 4/19/2024 60
Artificial air way related complication • Failure of alarms or ventilator, Alarm “turned off” • Disconnection, circuit leaks • Obstruction by secretions • Inadequate nebulization or humidification • Overheated inspired air, resulting in hyperthermia • Dyssynchronous breathing pattern • Tube kinked, plugged • Cuff failure • Migration – ETT migrates with suctioning, coughing, movement • Tracheal stenosis – pressure necrosis  ulceration, scarring 4/19/2024 61
Pulmonary complications Ventilator Induced Lung Injury • Barotrauma, volutrauma • Alveolar overdistension  rupture  extra-alveolar air  Pneumothorax/emphysema, Pneumomediastinum, pneumopericardium, SC emphysema, air embolism • Atelectrauma (Cyclic atelectasis) – repeatitive opening and collapse of alveoli during ventilator cycle  shear stress injures them • Biotrauma – proinflammatory cytokines released from over distended lung  inflammatory injury • Risk factors: asthma, chronic lung disease, ARDS 4/19/2024 62
VILI – management • Protective lung ventilation principle • The plateau airway pressure be immediately lowered to ≤35 cm H 2 O • lowering the tidal volume, positive end-expiratory pressure, or inspiratory flow • increasing sedation, administering neuromuscular blockade, • advancing treatment of the underlying medical condition (eg, bronchodilators for asthma) 4/19/2024 63
Oxygen toxicity • Inappropriate O2 supplementation is deleterious • Hyperoxia  ↑reactive oxygen species (superoxide anion, hydroxyl radical, H2O2) [+depleted antioxidant system]  cellular injury • There is no single threshold of FiO2 defining a safe upper limit for prevention of oxygen toxicity. • Reducing FiO2 to lowest tolerable limit is a good principle for all patients 4/19/2024 64
Infectious Complications Risk factors • ETT bypasses the glottis closure protective mechanism allowing seepage of oropharyngeal content into airways. • ETT impairs cough reflex • Airway and parenchymal injury (primary illness + positive pressure ventilation) • ICU environment itself – heavy antibiotics use, sick patients in close proximity 4/19/2024 65
Non pulmonary complications • Hemodynamics  Decreased venous return  Reduced right ventricular output  Reduced left ventricular output • Gastrointestinal  Erosive esophagitis, stress ulceration, diarrhea, acalculous cholecystitis, and hypomotility • Renal – acute renal failure ( decrease CO, release of inflammatory Mediators), acid base disturbance. • MSS- bed sore, contracture • CNS: Critical illness polyneuropathy, myopathy, • ICU psychosis etc. 66 4/19/2024
Weaning from mechanical ventilation • The process of decreasing ventilator support & Discontinuation of mechanical ventilation or liberation from the mechanical ventilator • three step process that consists of Readiness Testing ,Weaning & extubation 67 4/19/2024
Readiness testing • Readiness Testing – 2 goals • Identify patients who are ready to wean • Protect against premature weaning • Objective clinical criteria and weaning predictors used 68 4/19/2024
Patients with uncertainty • For patients in whom uncertainty exists as to whether the readiness criteria will predict a successful weaning trial, we sometimes use a weaning predictor to identify potential candidates suitable for weaning or to confirm lack of readiness to wean (eg, patients with borderline readiness criteria or suspected respiratory muscle weakness). • Use of weaning predictors is most pertinent among patients in whom the risk associated with a failed spontaneous trial is significantly elevated (eg, patients with prolonged mechanical ventilation, patients with critical care neuromyopathy). • Among the predictors, the rapid shallow breathing index (RSBI) is our preferred weaning predictor because it is well studied, easy to measure, and no alternative predictor has been shown to be superior. • For patients who have an RSBI <105 breaths/minute/L (measured without ventilatory support), we initiate a weaning trial. • For patients who have an RSBI ≥105 breaths/minute/L (measured without ventilatory support), we maintain full ventilatory support. 4/19/2024 69
Choosing a weaning method • For patients who have been intubated for more than 24 hours and have been deemed as ready to wean ,we suggest a weaning trial. • Daily spontaneous breathing trials (SBTs) with inspiratory pressure support is our preferred method of weaning based upon randomized trials that have shown it is efficient, safe, and effective • Approximately 50 to 75 percent of patients pass the initial SBT and are able to be successfully extubated 4/19/2024 70
• Spontaneous breathing Trial • with minimal ventilator support a low level of pressure support(5-8mmH2O), or CPAP (5mmH2O) • Breathing through the ETT without any ventilator support (T-piece using 1–5 cmH2O • Duration of a weaning trial • 30 min to 120 min 71 4/19/2024
Extubation • Extubation refers to removal of the endotracheal tube. It is the final step in liberating a patient from mechanical ventilation. • Extubation should not be performed until it has been determined that the patient's medical condition is stable, a weaning trial has been successful, the airway is patent, and any potential difficulties in reintubation have been identified. Most patients are extubated during daytime hours • Prior to Extubation Evaluate for Airway protection and Airway patency 4/19/2024 72
Airway protection • Is the ability to guard against aspiration during spontaneous breathing It requires sufficient cough strength and an adequate level of consciousness • Universally accepted threshold levels of cough strength, level of consciousness, and suctioning frequency that prohibit extubation have not been established. For many patients, it is reasonable to delay extubation if the cough strength is weak, the GCS is <8 , or suctioning is required more frequently than every two to three hours. 1. Cough strength (peak expiratory flow rate (PEF) >60 L/min) 2. Secretions (< 2.5 ml/hr) no more suctioning than once 2-3 hrs 3. Level of consciousness (able to obey command) 73 4/19/2024
Airway patency • Cuff leak test: (assessing the presence of air movement around a deflated endotracheal tube cuff) • To identify pts at risk to develop post extubation laryngeal edema. • A "cuff leak" refers to normal airflow around the ETT after the cuff of the ETT is deflated. Its absence suggests there is reduced space between the ETT and the larynx. • The cuff leak predicts post-extubation stridor with a sensitivity of 15 to 85 % and a specificity of 70 to 99 %. 74 4/19/2024
Cont’d  The cuff leak can be detected qualitatively or quantitatively: • Qualitative assessment by deflating the cuff and then listening for air movement around the ETT using a stethoscope. • Quantitatively is by deflating the ETT cuff and measuring the difference between the inspired and expired TV of ventilator-delivered breaths during volume-cycled MV (<110 ml or 12-24% of the delivered tidal volume) = diminished patency 75 4/19/2024
How do we prevent post-extubation complications? • Post extubation complications Post-extubation laryngeal edema Hypoxia and re-intubation • Short course of glucocorticoid therapy before extubation. Methylprednisolone (20 mg) administered every four hours for a total of four doses. Alternatively, a single dose of methylprednisolone 40 mg four hours prior to extubation may be used 76 4/19/2024
Extubation procedure • The patient is placed into an upright position and both the oral cavity and the endotracheal tube (ETT) are suctioned. • Instructions are given for the patient to take a deep breath and then exhale. • During exhalation, the cuff is deflated and the ETT is removed in a single, smooth motion. Orogastric tubes are typically removed simultaneously. 77 4/19/2024
References • Up-to-date, online • Hand book of Mechanical Ventilation, User’s guide • Practical Guide for Mechanical Ventilation,4th edition • Harrison’s 21st edition 4/19/2024 78

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Seminar on basics of mechanical ventilation

  • 1.
  • 2.
    Outline • Introduction • Typesof Mechanical Ventilation • Aims of Ventilatory Support • Indications • Modes of ventilation • Ventilator settings • Monitoring • Complications of mechanical ventilation • Weaning 4/19/2024 2
  • 3.
    Introduction • Mechanical Ventilator:A device which assists or replaces spontaneous breathing ,Support ventilatory function and improve oxygenation. • Inspiratory trigger  predetermined air (O2 + other gases) forced into airways & alveoli  lungs inflate  ↑ intraalveolar pressure  termination signal – vent stops delivery  ↓airway pressure  expiration follows passively due to pressure gradiant. 4/19/2024 3
  • 4.
    Several models evolvingover time • Negative pressure ventilation – past • Positive pressure ventilation – present 4/19/2024 4
  • 5.
    Negative pressure ventilators •Developed in 1929. • Used widely in 1940 polio epidemic. • The patient’s body was encased in an iron cylinder and negative pressure was generated Emerson JH, Loynes JA. The evolution of iron lungs: respirators of the body- encasing type. Cambridge:JH Emerson & Company; 1958. Google Scholar 4/19/2024 5
  • 6.
    Positive-pressure ventilators A positive pressureis applied to the mouth or mask providing a positive pressure gradient from mouth to alveoli resulting in inspiration Invasive ventilation first used at Massachusetts General Hospital in 1955 This can be applied with a mask (non-invasive) or with a tracheal tube or tracheostomy (invasive). Current ICU ventilators are primarily positive pressure ventilators 4/19/2024 6
  • 7.
    Noninvasive ventilation (NIV) •Provided with tight fitting face mask or nasal mask • Candidates for NIV trial: exacerbations of COPD and respiratory acidosis (pH <7.35) • Several RCTs – NIV is associated with low failure rate (15-20%) and good outcome (intubation rate, length of stay in ICU, mortality) in patients with ventilatory failure characterized by blood pH levels between 7.25 and 7.35 • For pH <7.25: As pH decreases, failure rate increases • For pH >7.35: NIV is not better than conventional therapy (oxygen therapy & pharmacotherapy like bronchodilator, steroid, antibiotics) 4/19/2024 7
  • 8.
    Indication of NIPPV Pulmonaryedema Asthma COPD Cardiogenic Pulmonary edema Chest trauma Assisting in early extubation 4/19/2024 8
  • 9.
  • 10.
    Conventional Mechanical Ventilation •Delivers conditioned gas (warmed, oxygenated, and humidified) via an endotracheal tube or tracheostomy tube at pressures above atmospheric pressure • Mechanical ventilators are comprised of four main elements: 1. A source of pressurised gas including a blender for air and O2. 2. An inspiratory valve, expiratory valve and ventilator circuit. 3. A control system, including control panel, monitoring and alarms. 4. A system to sense when the patient is trying to take breath. 4/19/2024 10
  • 11.
  • 12.
    Indications 1. Acute RespiratoryFailure • Hypoxic/Hypercapnic 2. Air way protection • To prevent Aspiration in deeply sedated & unconscious pt • Maintain patency in obstruction (Asthma, Anaphylaxis, Tumor) 3. Pulmonary vascular disease:  PTE, Amniotic fluid embolism, tumor emboli 4. Hyperventilation Therapy - raised ICP 5. Hypoventilation: • Decreased central drive (General anesthesia, Drug overdose), PNS/respiratory muscle dysfunction 6. Increased ventilatory demand • E.g:- Severe sepsis, septic shock, severe metabolic acidosis 4/19/2024 12
  • 13.
    Aims of MechanicalVentilation • Achieve and maintain adequate pulmonary gas exchange (ventilation and oxygenation) • Reduce or eliminate excessive work of breathing • Optimize patient comfort • Minimize the risk of complications • Maintain and protect the airway and allow more effective clearance of secretions 4/19/2024 13
  • 14.
    Modes Mode refers tothe manner in which ventilator breaths are triggered, cycled, and limited The trigger, either an inspiratory effort or a time based signal, defines what the ventilator senses to initiate an assisted breath. The limiting factors -are operator-specified values, such as airway pressure Cycle refers to the factors that determine the end of inspiration. Other types of cycling include pressure cycling and time cycling. 4/19/2024 14
  • 15.
    Modes of Ventilation 1.CMV 2. Assist control (AC) 3. Synchronized intermittent mandatory ventilation (SIMV) 4. Pressure support ventilation 5. CPAP 15 4/19/2024
  • 16.
    Controlled mechanical ventilation(CMV) • During CMV, the minute ventilation is determined entirely by the set respiratory rate and tidal volume. • This may be due to pharmacologic paralysis, heavy sedation, coma, or lack of incentive to increase the minute ventilation because the set minute ventilation meets or exceeds physiologic need. 16 4/19/2024
  • 17.
    VCV • Trigger –timed, limit – flow, termination – volume • Set: TV, flow rate, RR, FiO2, PEEP, inspiratory time • Monitor: Pplat, PIP, 4/19/2024 17
  • 18.
    700 ml -70 70 l/min 50cmH2O Volume control Pressure Flow Volume T 4/19/2024 18
  • 19.
    PRESSURE-CONTROL VENTILATION (PCV) •Are ventilator-initiated breaths with a pressure limit. • Limits inflation pressure • Mandatory breath only • Set: PIP, I:E ratio, RR, PEEP, FiO2 • Inspiration ends at delivery of set PIP. • Tidal volume is variable, related to • PIP, compliance, airway resistance, tubing resistance • High VT: can be due to High PIP & low compliance 19 4/19/2024
  • 20.
    …PCV 20 Time cycled(control)--inspiratory flowshould return to normal 4/19/2024
  • 21.
    PCV Advantage • Prevents excessiveairway pressures • Avoid regional alveolar over distention • May lead to earlier liberation from MV Disadvantage • Very uncomfortable and requires deep sedation +/- paralysis • Unable to guarantee minimum VE 21 Indications= patients who are at particularly high risk from barotrauma and post thoracic surgery. 4/19/2024
  • 22.
    Assist-Control Ventilation • ACMVis the most widely used mode of ventilation. • In this mode, an inspiratory cycle is initiated either by the patient’s inspiratory effort or, if none is detected within a specified time window, by a timer signal within the ventilator. • During AC, the clinician determines the minimal minute ventilation by setting the respiratory rate and tidal volume. • The patient can increase the minute ventilation by triggering additional breaths. 22 4/19/2024
  • 23.
    Cont… • Each patient-initiatedbreath receives the set tidal volume from the ventilator. • Every breath delivered, whether patient- or timer-triggered, consists of the operator-specified tidal volume. • It is a mixed mode in which pts receive a mandatory breath with set tidal volume (if volume AC) or pressure (pressure AC). • In ACV, the mechanical breaths are limited by volume and/or flow and cycled by volume or time. 23 4/19/2024
  • 24.
  • 25.
    Volume pre-set assistcontrol • Advantages • Relatively simple to set • Guaranteed minimum minute ventilation • Rests muscles of respiration (if properly set) • Disadvantages • Not synchronized • Patient may “lead” ventilator • Inappropriate triggering may result in excessive minute ventilation •  lung compliance   alveolar pressure with risk of barotrauma • Often requires sedation to achieve synchrony. 4/19/2024 25
  • 26.
    Intermittent Mandatory Ventilation • IMVallows the patient to breathe spontaneously between machine-cycled or mandatory breaths. • In the most frequently used synchronized mode (SIMV), mandatory breaths are delivered in synchrony with the patient’s inspiratory efforts at a frequency determined by the operator. • SIMV differs from ACMV in that only a preset number of breaths are ventilator-assisted. 26 4/19/2024
  • 27.
  • 28.
    Cont… • IMV issimilar to AC in two ways: • The clinician determines the minimal minute ventilation (by setting the respiratory rate and tidal volume) and • The patient is able to increase the minute ventilation. • However, IMV differs from AC in the way that the minute ventilation is increased. • SIMV allows patients with an intact respiratory drive to exercise inspiratory muscles between assisted breaths; thus it is useful for both supporting and weaning intubated patients. 28 4/19/2024
  • 29.
    Pressure support (PSV) •The ventilator applies a pre-determined amount of positive pressure to the airways upon inspiration. • This form of ventilation is patient-triggered, flow-cycled, and pressure- limited. • The patient breathes spontaneously. • With PSV, patients receive ventilator assistance only when the ventilator detects an inspiratory effort. • PSV is well tolerated by most patients who are being weaned from MV. • Comfortable mode for awake and conscious patient • Can be combined with SIMV mode. 29 4/19/2024
  • 30.
    Cont… 30 In flow cycled(supported) flow does not return to baseline 4/19/2024
  • 31.
    Continuous positive airwaypressure (CPAP) • Is the way of delivering PEEP but also maintains the set pressure through out the respiratory cycle. • Allows spontaneous breathing at elevated baseline pressure. • Set P = 5-15cmH2O • CPAP is most commonly used in the management of sleep related breathing disorders, cardiogenic pulmonary edema, and 31 4/19/2024
  • 32.
  • 33.
    Mechanical Ventilator Settings Trigger TidalVolume Respiratory Rate PEEP Flow rate Fraction of Inspired oxygen(Fio2) Flow Pattern 4/19/2024 33
  • 34.
    Trigger • Trigger sensitivity • sensitivity preferable • Flow triggering generally more sensitive than pressure triggering •  flow or less negative pressure   sensitivity • Trigger types • pressure triggering or • A trigger sensitivity of -1 to -3 cmH2O is typically set. • flow triggering • initiated when the return flow is less than the delivered flow. 4/19/2024 34
  • 35.
    Tidal volume • Optimaltidal volume for mechanically ventilated patients:- • without existing lung disease 6-8ml/kg of IBW. • For ARDS-4-6 ml/kg of IBW • Female PBW= 45.5 + 0.91 (Ht – 152.4) • Male PBW = 50 + 0.91 (Ht – 152.4) • As Tv inc., peak airway pressure also inc.(>45cmH20 barotrauma) 4/19/2024 35
  • 36.
    Respiratory rate • Initialrespiratory rate between 12 and 16 breaths per minute is reasonable. • RR adjustment- • Modification according to mode • Desired PH & paco2 • autoPEEP(if >5cmH20) • For ALI/ARDS-up to 35’ • MV= TV X RR 4/19/2024 36
  • 37.
    PEEP • PEEP isused to mitigate end-expiratory alveolar collapse. • An initial PEEP is 5 cmH2O. • 20 cmH2O may be used in patients with ARDS. • Elevated levels of PEEP- • reduced preload(CO) • increases risk of barotrauma and • impaired cerebral venous outflow (increases ICP) 4/19/2024 37
  • 38.
    Fraction of inspiredoxygen(Fio2) • % of oxygen in each breath. • Titrated to meet patient needs. • Goal- • PaO2 above 60 mmHg and • SpO2 above 90 percent. 4/19/2024 38
  • 39.
    Inspiratory time • Setas: • % of respiratory cycle • I:E ratio • Indirectly, by setting flow • Expiratory time not set • Remaining time after inspiration before next breath 4/19/2024 39
  • 40.
    Inspiratory Time • Longerinspiratory time • Improved oxygenation • Higher mean airway pressure • Re-distribution • Lower peak airway pressure • More time available to deliver set tidal volume • Shorter inspiratory time • Less risk of gas trapping and PEEPi • Less effect on cardiovascular system 4/19/2024 40
  • 41.
    Inspiratory to expiratory(I:E) ratio • Inspiratory time is equal to tidal volume divided by flow rate. • Normal I:E ratio: 1:2 to 1:3. • Can be reduced to 1:4 or 1:5 in COPD (longer expiratory time) • inverse I:E ratio may be necessary in states of low compliance, such as ARDS.
  • 42.
    Flow rate • Thepeak flow rate is the maximum flow delivered by the ventilator during inspiration. • Peak flow rates of 60 L per minute may be sufficient, although higher rates are frequently necessary. • Increased peak flow rates – increase the peak airway pressure. decreased inspiratory time lowers the mean airway pressure, which can decrease oxygenation. 4/19/2024 42
  • 43.
    Inspiratory flow Pattern •Different flow rates are associated with different airflow waveforms. 1. Square waveforms flow accelerates very quickly and then reaches a set rate, which is maintained throughout inspiration. Flow rate is constant This waveform allows for an adequate I:E ratio with a normal flow rate. Inspiratory arm
  • 44.
    Inspiratory flow Pattern 2.Ramp waveforms flow rate rapidly accelerates but is followed by a gentle tapering. This waveform may require much higher flow rates to obtain an adequate I:E ratio. This waveform can be used if abnormally high PIP is encountered. Inspiratory arm Expiratory arm
  • 45.
    Pressures • Peak inspiratorypressure- the pressure required to administer a set tidal volume • As the tidal volume increases, the pressure required to administer that volume also increases.. • Pawp above 45 cmH2O -the risk of barotrauma is increased. • plateau pressure - is the pressure after the delivery of the tidal volume but before the patient is allowed to exhale. • is maintained < 30 cmH2O. • Mean airway pressure- refers to the mean across the entire respiratory cycle, both inspiration and expiration 4/19/2024 45
  • 46.
    Mean airway pressure Meanairway pressure Mean airway pressure Time Pressure Time Pressure  Tidal volume 4/19/2024 46
  • 47.
    Mean airway pressure Meanairway pressure Mean airway pressure Time Pressure Time Pressure  Inspiratory time 4/19/2024 47
  • 48.
  • 49.
  • 50.
    Waveform showing increasedairways resistance Ppeak Pplat Pres ‘Square wave’ flow pattern
  • 51.
    Recognizing secretion inthe ETT 51 4/19/2024
  • 52.
    Waveform showing decreasedlung compliance Ppeak Pplat Pres ‘Square wave’ flow pattern
  • 53.
    • Incomplete expirationleading to air trapping • Causes include • High minute ventilation • Expiratory flow limitation • Expiratory resistance Auto PEEP
  • 55.
    Patient-ventilator dys-synchrony • Statewhen the respiratory cycle of the patient does not match that of the ventilator. • It can happen during triggering process, flow delivery or breath cycling. • Clinical features: ↑HR, RR; ↓SO2; ↑expiratory mm activity, coughing, anxiety, visible inspiratory effort without triggering the ventilator; Ventilator waveforms • Consequences include: ↑Work Of Breath, prolongation of MV, perceived need for deeper sedation
  • 56.
    Vent triggers tostart inspiration does not always correlate with the patient attempt to start inspiration Airflow what the patient is demanding does not match what the vent is providing Vent and patient went transitions from inspiration to expiration at different times
  • 57.
    Principles of monitoring •Follow the patient clinical condition • Assess ventilation and oxygenation – ABGs • Follow vent parameters • Flow and pressure time curves • Pressure and volume alarms • Always evaluate for weaning readiness 57 4/19/2024
  • 58.
    Alarms • Never ignorean alarm • Common causes of alarms • Dislodgement: check ETT length of insertion (av. 22) at incisor • Obstruction: secretion, blood clot, fighting patient biting the ETT • Suction, sedation • Pneumothorax: barotrauma • Equipment failure: air leak, disconnected corrugator tube, ↓ humidifier water, uninflated ETT cuff 58 4/19/2024
  • 59.
    Complications of MV •During Act of intubation • Artificial air way related complication • Pulmonary complications • Non pulmonary complications 4/19/2024 59
  • 60.
    During Act ofintubation • Dental trauma • Aspiration – bag ventilation for preoxygenation can cause gastric distension + irritation during ETT insertion  vomiting • Laryngeal trauma – hoarseness, URTO • Laryngeal edema, ulceration, granuloma, vocal cord paralysis • Bronchospasm – mechanical irritation • Esophageal intubation • Right main bronchus intubation – it goes too far 4/19/2024 60
  • 61.
    Artificial air wayrelated complication • Failure of alarms or ventilator, Alarm “turned off” • Disconnection, circuit leaks • Obstruction by secretions • Inadequate nebulization or humidification • Overheated inspired air, resulting in hyperthermia • Dyssynchronous breathing pattern • Tube kinked, plugged • Cuff failure • Migration – ETT migrates with suctioning, coughing, movement • Tracheal stenosis – pressure necrosis  ulceration, scarring 4/19/2024 61
  • 62.
    Pulmonary complications Ventilator InducedLung Injury • Barotrauma, volutrauma • Alveolar overdistension  rupture  extra-alveolar air  Pneumothorax/emphysema, Pneumomediastinum, pneumopericardium, SC emphysema, air embolism • Atelectrauma (Cyclic atelectasis) – repeatitive opening and collapse of alveoli during ventilator cycle  shear stress injures them • Biotrauma – proinflammatory cytokines released from over distended lung  inflammatory injury • Risk factors: asthma, chronic lung disease, ARDS 4/19/2024 62
  • 63.
    VILI – management •Protective lung ventilation principle • The plateau airway pressure be immediately lowered to ≤35 cm H 2 O • lowering the tidal volume, positive end-expiratory pressure, or inspiratory flow • increasing sedation, administering neuromuscular blockade, • advancing treatment of the underlying medical condition (eg, bronchodilators for asthma) 4/19/2024 63
  • 64.
    Oxygen toxicity • InappropriateO2 supplementation is deleterious • Hyperoxia  ↑reactive oxygen species (superoxide anion, hydroxyl radical, H2O2) [+depleted antioxidant system]  cellular injury • There is no single threshold of FiO2 defining a safe upper limit for prevention of oxygen toxicity. • Reducing FiO2 to lowest tolerable limit is a good principle for all patients 4/19/2024 64
  • 65.
    Infectious Complications Risk factors •ETT bypasses the glottis closure protective mechanism allowing seepage of oropharyngeal content into airways. • ETT impairs cough reflex • Airway and parenchymal injury (primary illness + positive pressure ventilation) • ICU environment itself – heavy antibiotics use, sick patients in close proximity 4/19/2024 65
  • 66.
    Non pulmonary complications •Hemodynamics  Decreased venous return  Reduced right ventricular output  Reduced left ventricular output • Gastrointestinal  Erosive esophagitis, stress ulceration, diarrhea, acalculous cholecystitis, and hypomotility • Renal – acute renal failure ( decrease CO, release of inflammatory Mediators), acid base disturbance. • MSS- bed sore, contracture • CNS: Critical illness polyneuropathy, myopathy, • ICU psychosis etc. 66 4/19/2024
  • 67.
    Weaning from mechanicalventilation • The process of decreasing ventilator support & Discontinuation of mechanical ventilation or liberation from the mechanical ventilator • three step process that consists of Readiness Testing ,Weaning & extubation 67 4/19/2024
  • 68.
    Readiness testing • ReadinessTesting – 2 goals • Identify patients who are ready to wean • Protect against premature weaning • Objective clinical criteria and weaning predictors used 68 4/19/2024
  • 69.
    Patients with uncertainty •For patients in whom uncertainty exists as to whether the readiness criteria will predict a successful weaning trial, we sometimes use a weaning predictor to identify potential candidates suitable for weaning or to confirm lack of readiness to wean (eg, patients with borderline readiness criteria or suspected respiratory muscle weakness). • Use of weaning predictors is most pertinent among patients in whom the risk associated with a failed spontaneous trial is significantly elevated (eg, patients with prolonged mechanical ventilation, patients with critical care neuromyopathy). • Among the predictors, the rapid shallow breathing index (RSBI) is our preferred weaning predictor because it is well studied, easy to measure, and no alternative predictor has been shown to be superior. • For patients who have an RSBI <105 breaths/minute/L (measured without ventilatory support), we initiate a weaning trial. • For patients who have an RSBI ≥105 breaths/minute/L (measured without ventilatory support), we maintain full ventilatory support. 4/19/2024 69
  • 70.
    Choosing a weaningmethod • For patients who have been intubated for more than 24 hours and have been deemed as ready to wean ,we suggest a weaning trial. • Daily spontaneous breathing trials (SBTs) with inspiratory pressure support is our preferred method of weaning based upon randomized trials that have shown it is efficient, safe, and effective • Approximately 50 to 75 percent of patients pass the initial SBT and are able to be successfully extubated 4/19/2024 70
  • 71.
    • Spontaneous breathingTrial • with minimal ventilator support a low level of pressure support(5-8mmH2O), or CPAP (5mmH2O) • Breathing through the ETT without any ventilator support (T-piece using 1–5 cmH2O • Duration of a weaning trial • 30 min to 120 min 71 4/19/2024
  • 72.
    Extubation • Extubation refersto removal of the endotracheal tube. It is the final step in liberating a patient from mechanical ventilation. • Extubation should not be performed until it has been determined that the patient's medical condition is stable, a weaning trial has been successful, the airway is patent, and any potential difficulties in reintubation have been identified. Most patients are extubated during daytime hours • Prior to Extubation Evaluate for Airway protection and Airway patency 4/19/2024 72
  • 73.
    Airway protection • Isthe ability to guard against aspiration during spontaneous breathing It requires sufficient cough strength and an adequate level of consciousness • Universally accepted threshold levels of cough strength, level of consciousness, and suctioning frequency that prohibit extubation have not been established. For many patients, it is reasonable to delay extubation if the cough strength is weak, the GCS is <8 , or suctioning is required more frequently than every two to three hours. 1. Cough strength (peak expiratory flow rate (PEF) >60 L/min) 2. Secretions (< 2.5 ml/hr) no more suctioning than once 2-3 hrs 3. Level of consciousness (able to obey command) 73 4/19/2024
  • 74.
    Airway patency • Cuffleak test: (assessing the presence of air movement around a deflated endotracheal tube cuff) • To identify pts at risk to develop post extubation laryngeal edema. • A "cuff leak" refers to normal airflow around the ETT after the cuff of the ETT is deflated. Its absence suggests there is reduced space between the ETT and the larynx. • The cuff leak predicts post-extubation stridor with a sensitivity of 15 to 85 % and a specificity of 70 to 99 %. 74 4/19/2024
  • 75.
    Cont’d  The cuffleak can be detected qualitatively or quantitatively: • Qualitative assessment by deflating the cuff and then listening for air movement around the ETT using a stethoscope. • Quantitatively is by deflating the ETT cuff and measuring the difference between the inspired and expired TV of ventilator-delivered breaths during volume-cycled MV (<110 ml or 12-24% of the delivered tidal volume) = diminished patency 75 4/19/2024
  • 76.
    How do weprevent post-extubation complications? • Post extubation complications Post-extubation laryngeal edema Hypoxia and re-intubation • Short course of glucocorticoid therapy before extubation. Methylprednisolone (20 mg) administered every four hours for a total of four doses. Alternatively, a single dose of methylprednisolone 40 mg four hours prior to extubation may be used 76 4/19/2024
  • 77.
    Extubation procedure • Thepatient is placed into an upright position and both the oral cavity and the endotracheal tube (ETT) are suctioned. • Instructions are given for the patient to take a deep breath and then exhale. • During exhalation, the cuff is deflated and the ETT is removed in a single, smooth motion. Orogastric tubes are typically removed simultaneously. 77 4/19/2024
  • 78.
    References • Up-to-date, online •Hand book of Mechanical Ventilation, User’s guide • Practical Guide for Mechanical Ventilation,4th edition • Harrison’s 21st edition 4/19/2024 78

Editor's Notes

  • #4 The principal benefits of MV during respiratory failure are improved gas exchange (by improving ventilation-perfusion (V/Q) matching) and decreased work of breathing.
  • #7 Invasive ventilation first used at Massachusetts General Hospital in 1955 Candidates for NIV trial: exacerbations of COPD and respiratory acidosis (pH <7.35) Several RCTs – NIV is associated with low failure rate (15-20%) and good outcome (intubation rate, length of stay in ICU, mortality) in patients with ventilatory failure characterized by blood pH levels between 7.25 and 7.35 For pH <7.25: As pH decreases, failure rate increases For pH >7.35: NIV is not better than conventional therapy (oxygen therapy & pharmacotherapy like bronchodilator, steroid, antibiotics)
  • #13 Hyperventilation — Use of mechanical ventilation to lower PaCO2 to 26 to 30 mmHg has been shown to rapidly reduce ICP through vasoconstriction and a decrease in the volume of intracranial blood; a 1 mmHg change in PaCO2 is associated with a 3 percent change in CBF. Hyperventilation also results in respiratory alkalosis, which may buffer post-injury acidosis. The effect of hyperventilation on ICP is short-lived (1 to 24 hours). Following therapeutic hyperventilation, the patient's respiratory rate should be tapered back to normal over several hours to avoid a rebound effect. The most common reasons for instituting MV are acute respiratory failure with hypoxemia which accounts for ~65% of all ventilated cases, and hypercarbic ventilatory failure—e.g., due to coma (15%), exacerbations of chronic obstructive pulmonary disease (COPD; 13%), and neuromuscular diseases (5%).
  • #15 Time cycling – lasts for a fixed period of time Volume cycline – lasts until a preset volume is delivered before switching to expiratory phase Pressure cycle – lasts until a preset pressure is reached Flow cycle – inspiratory phasts occurs till when the gas flow falls below acertain level
  • #17 The patient does not initiate additional minute ventilation above that set on the ventilator. CMV does not require any patient work.
  • #19 Or by the patient
  • #20 Time triggered time cycled pressure limited Good for VILI
  • #22 Very uncomfortable and requires deep sadation +/- paralysis Unable to guarantee minimum VE
  • #23 In ACV, mechanical breaths can be triggered by the ventilator or the patient. With the former, triggering occurs when a certain time has elapsed after the previous inspiration if the patient fails to make a new inspiratory muscle effort
  • #24 The inspiratory flow-shape delivery is usually a square (constant) during ACV, although some ventilators also permit sinusoidal and/or ramp (ascending or descending) gas flows.
  • #26 The advantages are its relative simplicity, the tidal volume and minimum ventilatory rate are setting, thus guaranteeing a minimum minute ventilation and, if properly set, it rests the muscles of respiration. The disadvantages: Not synchronized with patient’s breathing - ventilator initiated breath may come on top of a patient initiated breath. Patient may “lead” ventilator (ie try to suck gas out of the ventilator) if inspiratory flow not high enough Inappropriate triggering (eg as a result of hiccoughs) may result in excessive minute ventilation Fall in lung compliance results in high alveolar pressure with risk of barotrauma Often requires sedation to achieve synchrony.
  • #27 With this mode, the operator sets the number of mandatory breaths of fixed volume to be delivered by the ventilator; between those breaths, the patient can breathe spontaneously. If the patient fails to initiate a breath, the ventilator delivers a fixed-tidal-volume breath and resets the internal timer for the next inspiratory cycle
  • #29 Specifically, patients increase the minute ventilation by spontaneous breathing, rather than patient-initiated ventilator breaths.
  • #30 High insp presure-large tidal volume-decreased RR Combined with SIMV Indicated for patients with small spontaneous tidal volume and difficult to wean patients. It is a mode used primarily for weaning from mechanical ventilation.
  • #31 The purpose of adding PSV for pt initiated breath is to overcome the resistance of ET tube and Vent circuit Flow cycle threshold
  • #32 Refers to the delivery of a continuous level of positive airway pressure. Patient controls rate and tidal volume No breath delivered by machine
  • #35 The trigger sensitivity determines how easy it is for the patient to trigger the ventilator to deliver a breath. In general increased sensitivity is preferable in order to improve patient-ventilator synchrony (ie to stop the patient "fighting" the ventilator) but excessively high sensitivity may result in false or auto-triggering (ie ventilator detects what it "thinks" is an attempt by the patient to breath although the patient is apnoeic). Triggering may be flow-triggered or pressure triggered. Flow triggering is generally more sensitive. The smaller the flow or the smaller the negative pressure the more sensitive the trigger
  • #36 During volume-limited ventilation, the tidal volume is set by the clinician and remains constant. During pressure-limited ventilation, the tidal volume is variable. It is directly related to the inspiratory pressure level and compliance, but indirectly related to the resistance of the ventilator tubing. The clinician typically changes the tidal volume by adjusting the inspiratory pressure level. Although normalization of pH through elimination of CO2 is desirable, the risk of lung damage associated with the large volume and high pressures needed to achieve this goal has led to the acceptance of permissive hypercapnia. Protective ventilatory strategy
  • #37 For patients receiving AC-the RR is typically set four breaths per minute below the patient's native rate For patients receiving SIMV the rate is set to ensure that at least 80 percent of the patient's total minute ventilation is delivered by the ventilator.
  • #38 maintain FRC, treat shunt, dec. work of breathing A typical initial applied PEEP is 5 cmH2O. However, up to 20 cmH2O may be used in patients with ARDS. Recruitment maneuvers
  • #40 It can be set as a percentage of the respiratory cycle or as a ratio of inspiration to expiration, the so called I:E ratio. Note that on most ventilators the expiratory time is not set directly but is merely the remaining time after inspiration before the next breath
  • #41 Longer inspiratory times result in improved oxygenation due to a higher mean airway pressure and the longer time available for re-distribution of gas from more to less compliant alveoli. At the same time peak airway pressures are reduced because more time is available to deliver the set tidal volume. On the other hand shorter inspiratory times reduce the risk of gas trapping and intrinsic PEEP by leaving more time for expiration. The cardiovascular effects of mechanical ventilation may also be lessened by the lower mean intrathoracic pressure.
  • #43 COPD
  • #46 Plateau pressure Static pressure in the alveoli at the end of inspiration Should be <30 cmH2O to prevent volutrauma
  • #47 Airway pressure can be increased in a number of ways. It is easier to understand why these methods increase mean pressure if one remembers that the mean airway pressure refers to the mean across the entire respiratory cycle, both inspiration and expiration. The most obvious method of increasing the pressure is to increase the tidal volume but this will also increase the peak and plateau airway pressures and therefore increase the chance of ventilator induced lung injury.
  • #48 Prolonging the inspiratory time increases the mean pressure without increasing the peak pressure
  • #52 Waveform oscillations indicate secretions in the larger air ways, ET Tube or ventilator circuit Large oscillations throughout the breath phase are more likely in proximal airways and fine oscillationsrepresent more distal airway
  • #54 High minute ventilation can be high RR or Vt, giving less time for expiration Expiratory flow limitation – airway collapse, bronchospasm, inflammation Expiratory resistance – narrow or kinked tube, inspissated secretions, asynchrony Auto PEEP is worse when pressure triggering is used Auto PEEP = End expiratory alveolar pressure-applied PEEP , EEAP measured by end expiratory breath hold
  • #55 Rx – Correct underlying cause Adjust I:E ratio Applied PEEP – can improve expiratory limitation, 50-80 % of measured Auto-PEEP
  • #57 Ideally, the patient’s and the ventilator respiratory cycle should be synchronous (there is less than 200 millisecond dyssynchrony as there is delay of the machine recognizing the patients inspiratory effort)
  • #58 • Alarms must never be ignored or disarmed
  • #59 Auscultate/chest x-ray or U/S Correct accordingly Communicate biomedical engineer Change machine if possible
  • #65 Oxidant injury to airways and lung paranchyma. The safe oxygen concentration or duration of exposure remains unclear.
  • #68 Monitoring how well weaning is going well? V/S, ABG, work of breathing
  • #69 Objective clinical criteria : OPTIONAL Hgb > 8-10 Core T˚ < 38-38.5 ˚C Mentation: awake and alert or easily arousable
  • #72 Pressure support to overcome ETT resistance
  • #75 This may be due to laryngeal edema, another laryngeal injury, secretions, or a large ETT within a relatively small larynx. Pts without a cuff leak are at increased risk for post-extubation stridor.
  • #77 Despite all precautions, ~10–15% of extubated patients require reintubation.
  • #78 Following extubation, the oral cavity is again suctioned and supplemental oxygen is administered by facemask. The oxyhemoglobin saturation, HR, RR, and BP are monitored throughout the extubation process. Patients with increased secretions may require more frequent or nasotracheal suctioning.