MODES OF MECHANICAL VENTILATION

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ICU INVASIVE RESPIRATORY MANAGEMENT

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MODES OF MECHANICAL VENTILATION:

MODES OF MECHANICAL VENTILATION DR. RAFIA TABASSUM ANAESTHETIST, DEPT: ANAESTHESIA & SICU, PMCH NAWABSHAH,SIND-PAKISTAN

Case Presentation:

Case Presentation You are called from the intensive care unit ( ICU ) to assist with the initial management of a 28 - year - old man with no significant past medical history other than alcohol abuse who presented less than an hour ago with acute respiratory failure from community acquired pneumonia. On examination, the patient demonstrated marked dyspnea (respiratory rate of 40 bpm), febrile at 103.5 ° F and an altered mental status. His initial arterial blood gas on room air was pH = 7.12, PaCO 2 = 22 and PaO 2 = 45, which prompted the emergency room to intubate him and admit to the intensive care unit ( ICU ). His chest X - ray reveals dense left lower lobe consolidation and some otherwise patchy bilateral infiltrates, a well – positioned endotracheal tube and a normal cardiac silhouette. His vital signs are: sinus tachycardia at 140 bpm, BP = 100/60 mm Hg on 15 μ g/kg/min of norepinephrine. Laboratory studies are remarkable for a white blood cell count of 19.5/mm 3 with 20% bands and elevated blood urea nitrogen (42 mg/dl) and creatinine (3.4 mg/dl).

QUESTIONS?:

QUESTIONS? What mode and settings should you select now? Why? Will this be the mode you will use throughout the patient ’ s ICU course? Should you pick a mode that will permit you to start weaning the patient tomorrow morning? What modes would you consider if the patient ’ s condition did not respond well to your initial choice?

HISTORY OF MECHANICAL VENTILATION:

HISTORY OF MECHANICAL VENTILATION “But that life may be restored… an opening must be attempted in…the trachea, in which a tube or reed should be put; you will then blow into this, so that the lung may rise again…And as I do this, and take care that the lung is inflated in intervals, the motion of the heart and arteries does not stop…” Andreas Wesele Vesalius, 1543

Stephen Hales:

Stephen Hales Used a manual bellows to inflate the lungs (1743)  first mechanical ventilator Treatise on Ventilators (1751) Also identified Blood pressure Treatment for bladder stones Carbon dioxide

PowerPoint Presentation:

Non-invasive ventilation first used in Boston Children’s Hospital in 1928 Used extensively during polio outbreaks in 1940s – 1950s The iron lung created negative pressure in abdomen as well as the chest, decreasing cardiac output.

PowerPoint Presentation:

The 1947-1948 polio epidemic resulted in breakthroughs in the treatment of patients with respiratory paralysis Endotracheal intubation and mechanical ventilation was pioneered in Denmark Iron lung polio ward at Rancho Los Amigos Hospital in 1953.

MODERN VENTILATORS:

MODERN VENTILATORS Invasive ventilation first used at Massachusetts General Hospital in 1955 Mechanical ventilation evolved significantly in the 1970’s and 80’s with the introduction of microprocessors

MECHANICAL VENTILATION Goals::

MECHANICAL VENTILATION Goals: Maintain patient comfort Allow a normal, spontaneous breathing pattern whenever possible Maintain a PaCO2 between 35 - 45 mmHg Maintain a PaO2 sufficient to meet cellular oxygen demands but avoid oxygen toxicity Avoid respiratory muscle fatigue and atrophy

PowerPoint Presentation:

Ventilator mode can be defined as a set of operating characteristics that control how the ventilator functions.

Ideal Mode of Ventilation:

Ideal Mode of Ventilation Synchronizes with the patient’s spontaneous respiratory effort Maintains adequate and consistent tidal volume and minute ventilation at low airway pressures Responds to rapid changes in pulmonary mechanics or patient demand Provides the lowest possible WOB

Ventilatory mode is defined by the method by which the ventilator cycles from expiration to inspiration as well as whether the patient is able to breathe spontaneously:

Ventilatory mode is defined by the method by which the ventilator cycles from expiration to inspiration as well as whether the patient is able to breathe spontaneously

Conventional Modes:

Conventional Modes

Pressure cycled and volume cycled ventilation:

Pressure cycled and volume cycled ventilation Pressure-cycled modes deliver a fixed pressure at variable volume Volume-cycled modes deliver a fixed volume at variable pressure Volume-cycled modes Control Assist Assist/Control Intermittent Mandatory Ventilation (IMV) Synchronous Intermittent Mandatory Ventilation (SIMV) Pressure-cycled modes Pressure Support Ventilation (PSV) Pressure Control Ventilation (PCV) PEEP CPAP BiPAP

PowerPoint Presentation:

Spontaneous Positive end expiratory pressure (PEEP) Continuous positive airway pressure (CPAP) Bilevel positive airway pressure (BiPAP) Controlled mandatory ventilation (CMV) Assist control (AC) Intermittent mandatory ventilation (IMV) Synchronized intermittent mandatory ventilation (SIMV) Mandatory minute ventilation (MMV)

PowerPoint Presentation:

Adaptive support ventilation (ASV) Proportional assist ventilation (PAV) Volume assured pressure support (VAPS) Pressure regulated volume control (PRVC) Pressure control ventilation (PCV) Airway pressure release ventilation (APRV) Inverse ratio ventilation (IRV) Pressure support ventilation (PSV)

Spontaneous ventilation:

Spontaneous ventilation Is not an actual mode on the ventilator since the rate and tidal volume are determined by the patient It provides inspiratory flow to the patient in a timely manner Used with adjunctive modes like PEEP

Positive End Expiratory Pressure (PEEP):

Positive End Expiratory Pressure (PEEP) Increases the end expiratory or baseline airway pressure to a value greater than atmospheric(0cmH2O) on ventilator manometer Not a stand alone mode rather applied in conjunction with other modes Indications Intrapulmonary shunt and refractory hypoxemia Decreased FRC and lung compliance Useful in maintaining pulmonary function in non-Cardiogenic pulmonary edema, especially ARDS

Physiology of PEEP:

Physiology of PEEP Re inflates collapsed alveoli and maintains alveolar inflation during exhalation PEEP Decreases alveolar distending pressure Increases FRC by alveolar recruitment Improves ventilation Increases V/Q, improves oxygenation, decreases work of breathing

DISADVANTAGES:

DISADVANTAGES High intrathoracic pressures can cause decreased venous return and decreased cardiac output May produce pulmonary barotrauma May worsen air-trapping in obstructive pulmonary disease Increases intracranial pressure Alterations of renal functions and water metabolism

Continuous Positive Airway Pressure (CPAP):

Continuous Positive Airway Pressure (CPAP) PEEP without preset ventilator rate or volume Physiologically similar to PEEP May be applied with or without use of a ventilator or artificial airway Requires patient to be breathing spontaneously CPAP may be given via a facial mask , nasal mask or ET tube

Advantages and disadvantages of the CPAP mode.:

Advantages and disadvantages of the CPAP mode.

BiPAP:

BiPAP An airway pressure strategy that applies independent positive airway pressure to both inspiration and expiration It helps in preventing intubation of endstage COPD patients and in supporting patients with chronic ventilator failure Initial settings of IPAP and EPAP are 8cm and 4cm of H2O respectively Can be used as a CPAP device by setting IPAP and EPAP at the same level IPAP may be increased in increments of 2cmH 2 O to enhance pressure boost to improve alveolar ventilation, normalize PaCO2 and reduce the work of breathing EPAP should be increased by 2 cm H 2 O to increase functional residual capacity and oxygenation in patients with intrapulmonary shunting

CONTROLLED MANDATORY VENTILATION (CMV):

CONTROLLED MANDATORY VENTILATION (CMV) Delivers the preset tidal volume at a time triggered respiratory rate. Ventilator controls both the tidal volume and respiratory rate of the patient. Should only be used with a combination of sedatives, respiratory depressants and neuromuscular blockers.

Indications:

Indications “Fighting” or “bucking” the ventilator means the patient is severely distressed and vigorously struggling to breathe. Patients rapid spontaneous efforts become asynchronous with the ventilators ability to provide an adequate inspiratory flow resulting in high pressure limit cycling, thus decreases ventilator delivered tidal volume Tetanus or seizure activities Complete rest for the patient for 24 hours Crushed chest injury patients in whom paradoxical chest wall movement produced due to spontaneous inspiratory efforts

COMPLICATIONS:

COMPLICATIONS Disconnection or Ventilator fails to operate is a primary hazard- in a sedated or apneic patient is the potential for apnea and hypoxia.

Assist/Control Mode:

Assist/Control Mode Ventilator delivers a fixed volume Assist Mode Pt initiates all breaths, but ventilator cycles in at initiation to give a preset tidal volume Pt controls rate but always receives a full machine breath Assist/Control Mode .Mandatory mechanical breath either triggered by patient spontaneous inspiratory efforts (assist) Time triggered by a preset respiratory rate – (control) POTENTIAL HAZARD-alveolar hyperventilation-higher pH and low PaCO2-respiratory alkalosis

Intermittent mandatory ventilation (IMV):

Intermittent mandatory ventilation (IMV) Pt receives a set number of ventilator breaths Different from Control: pt can initiate own (spontaneous) breaths Different from Assist: spontaneous breaths are not supported by machine with fixed TV Ventilator always delivers breath, even if pt exhaling Breath stacking is the complication.

SYNCHRONIZED INTERMITTENT MANDATORY VENTILATION(SIMV):

SYNCHRONIZED INTERMITTENT MANDATORY VENTILATION(SIMV) Ventilator delivers control breath (mandatory) to the patient at or near the time of spontaneous breath- TIME TRIGGERED Mandatory breaths are synchronised with the patients spontaneous breathing effort to avoid breath stacking- PATIENT TRIGGERED If the patient is breathing spontaneously between the mandatory breaths and if patient begins to inspire just prior to ventilator time trigger, ventilator delivers mandatory breath as an assisted patient triggered breath.

ADVANTAGES OF SIMV:

ADVANTAGES OF SIMV Maintains respiratory muscle strength/avoids muscle atrophy Reduces ventilation and perfusion mismatch Decreases mean airway pressure Facilitates weaning

Pressure Support Ventilation (PSV):

Pressure Support Ventilation (PSV) Patient determines RR, VE, inspiratory time – a purely spontaneous mode Parameters Triggered by pt’s own breath Limited by pressure Affects inspiration only Uses Complement volume-cycled modes (i.e., SIMV) Does not augment TV but overcomes resistance created by ventilator tubing PSV alone Used alone for recovering intubated pts who are not quite ready for extubation Augments inflation volumes during spontaneous breaths BiPAP (CPAP plus PS)

PowerPoint Presentation:

Advantages The patient can control the depth, the length and the flow of each breath Allows flexibility in ventilatory support Disadvantages Excessive levels of support can result in: Respiratory alkalosis Hyperinflation Ineffective triggering Apneic spells

Airway Pressure Release Ventilation (APRV):

Airway Pressure Release Ventilation (APRV) APRV involves the periodic release of pressure while breathing in the CPAP mode. CPAP breaths are given at two levels of pressure – P high and P low Mandatory breaths begin with the timed closure of a release valve, and the pressure rises from P low to P high . At this elevated level of CPAP ( P high ), the patient is allowed to breathe spontaneously.

PowerPoint Presentation:

The opening of the release valve drops the pressure back to P low for a brief period of time – usually 1–2 s – during which interval again the patient is allowed to breathe spontaneously. The drop in airway pressure from P high to P low allows greater washout of CO2 to occur. In paralyzed patients, the mode becomes identical to the PC-IRV mode. The indications for APRV are similar to those for pressure controlled ventilation (PCV) – i.e., ALI and ARDS

Adaptive Support Ventilation (ASV):

Adaptive Support Ventilation (ASV) During adaptive support ventilation (Hamilton ®), the ventilator continuously monitors and adjusts the pressure, rate and flow to achieve a minimum or desired minute ventilation In the absence of spontaneous triggering, the ventilator delivers machine-triggered time-cycled mandatory breaths. When inspiratory effort is present, patient-triggered flow-cycled breaths are delivered

MANDATORY MINUTE VENTILATION (MMV):

MANDATORY MINUTE VENTILATION (MMV) The patient is able to breathe spontaneously and receives mechanical breaths also, while the machine monitors the exhaled minute ventilation. In this mode, the machine then continuously adjusts the number of mechanical breaths so that the sum of spontaneous plus mechanical breaths multiplied by the VT equals the desired set minute ventilation.

Alternative Modes:

Alternative Modes I:E inverse ratio ventilation (IRV) ARDS and severe hypoxemia Prolonged inspiratory time (3:1) leads to better gas distribution with lower PIP Elevated pressure improves alveolar recruitment No statistical advantage over PEEP, and does not prevent repetitive collapse and reinflation Prone positioning Addresses dependent atelectasis Improved recruitment and FRC, relief of diaphragmatic pressure from abdominal viscera, improved drainage of secretions Logistically difficult No mortality benefit demonstrated ECMO Airway Pressure Release (APR) High-Frequency Oscillatory Ventilation (HFOV) High-frequency, low amplitude ventilation superimposed over elevated Paw Avoids repetitive alveolar open and closing that occur with low airway pressures Avoids overdistension that occurs at high airway pressures Well tolerated, consistent improvements in oxygenation, but unclear mortality benefits R/rate of 60–120 breaths/min, frequency of 120–600 times/min (2–10 Hz), to-and-fro gas movement at rates of 180–3000 times/min (3–50 Hz). Disadvantages Potential hemodynamic compromise Pneumothorax Neuromuscular blocking agents

QUESTIONS?:

QUESTIONS? What mode and settings should you select now? Why? Will this be the mode you will use throughout the patient ’ s ICU course? Should you pick a mode that will permit you to start weaning the patient tomorrow morning? What modes would you consider if the patient ’ s condition did not respond well to your initial choice?

Case presentation revisited:

Case presentation revisited Shortly after arrival to the ICU, the patient had a repeat chest X - ray, which revealed progressive bilateral infiltrates consistent with the acute respiratory distress syndrome. He was placed on volume - cycled assist control mode with a tidal volume of 6 mg/kg of predicted body weight, respiratory rate = 20 bpm, FiO 2 of 0.80, PEEP = 12 cm H 2 O and inspiratory flow rate to achieve an I : E ratio of approximately 1 : 1. On those settings, the patient demonstrated a total respiratory rate of 30 – 32 bpm, SaO 2 = 94 – 97% and peak inspiratory pressures of 25 – 30 cm H 2 O. An ABG obtained on those settings revealed pH = 7.24, PaCO 2 = 20 mm Hg and PaO 2 = 76 mm Hg.

PowerPoint Presentation:

Assist control mode was chosen in this setting due to its ability to: Provide a guaranteed VT of a size that is known to reduce ventilator induced lung injury and Permit the patient to take as many machine supported breaths as needed to achieve the desired minute ventilation Although weaning and liberation from mechanical ventilation can be achieved directly from AC mode once a patient has passed an SBT, it is likely this patient would be transitioned to a weaning mode, most likely PSV, once his oxygenation requirements and demand for VE had reduced sufficiently.

PowerPoint Presentation:

Choosing a weaning mode from the onset would not be appropriate, as it would be unlikely to reduce length of time on the ventilator and significantly increase the risk of inadequate ventilation and oxygenation during the early ICU course. Should the patient not improve or deteriorate on AC mode, common options that could be considered as alternate strategies would be either PCV or APRV.

PowerPoint Presentation:

Thank you