Ventilator Management

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Ventilator Management:

Ventilator Management Ali Shahabbasi .MD BOARD CERTIFIED IN ANESTHESIOLOGY, CRITICAL CARE & PAIN MEDICINE

Ventilator Definition:

Ventilator Definition A ventilator is an automatic mechanical device designed to provide all or part of the work the body must produce to move gas into and out of the lungs. The act of moving air into and out of the lungs is called breathing, or, more formally, ventilation.

Modes of Mechanical Ventilation:

Modes of Mechanical Ventilation Volume-cycled mode Inhalation proceeds until a set tidal volume (TV) is delivered and is followed by passive exhalation. Because the volume-cycled mode ensures a constant minute ventilation, it is a common choice as an initial ventilatory mode A major disadvantage is that high airway pressures may be generated, potentially resulting in barotrauma .

Modes of Mechanical Ventilation:

Modes of Mechanical Ventilation Pressure-cycled mode A set peak inspiratory pressure (PIP) is applied, and the pressure difference between the ventilator and the lungs results in inflation until the peak pressure is attained and passive exhalation follows. The delivered volume with each respiration is dependent on the pulmonary and thoracic compliance. A major disadvantage is that dynamic changes in pulmonary mechanics may result in varying tidal volumes. This necessitates close monitoring of minute ventilation and limits the usefulness of this mode in many emergency department patients.

Modes of Mechanical Ventilation:

Modes of Mechanical Ventilation

Methods of Ventilatory Support:

Methods of Ventilatory Support Continuous Mandatory Ventilation (CMV) Breaths are delivered at preset intervals, regardless of patient effort. This mode is used most often in the paralyzed or apneic patient because it can increase the work of breathing if respiratory effort is present. Continuous mandatory ventilation (CMV) has given way to assist-control (A/C) mode

Methods of Ventilatory Support:

Methods of Ventilatory Support Assist-control ventilation (A/C or ACMV) The ventilator delivers preset breaths in coordination with the respiratory effort of the patient. With each inspiratory effort, the ventilator delivers a full assisted tidal volume. Spontaneous breathing independent of the ventilator between A/C breaths is not allowed. As might be expected, this mode is better tolerated than CMV in patients with intact respiratory effort.

Methods of Ventilatory Support:

Methods of Ventilatory Support Intermittent Mandatory Ventilation (IMV) With intermittent mandatory ventilation (IMV), breaths are delivered at a preset interval, and spontaneous breathing is allowed between ventilator-administered breaths. Spontaneous breathing occurs against the resistance of the airway tubing and ventilator valves, which may be formidable. This mode has given way to synchronous intermittent mandatory ventilation (SIMV).

Methods of Ventilatory Support:

Methods of Ventilatory Support Synchronous Intermittent Mandatory Ventilation (SIMV) The ventilator delivers preset breaths in coordination with the respiratory effort of the patient. Spontaneous breathing is allowed between breaths. Synchronization attempts to limit barotrauma that may occur with IMV when a preset breath is delivered to a patient who is already maximally inhaled (breath stacking) or is forcefully exhaling.

Methods of Ventilatory Support:

Methods of Ventilatory Support Pressure Support Ventilation (PSV) For the spontaneously breathing patient, pressure support ventilation (PSV) has been advocated to limit barotrauma and to decrease the work of breathing. Pressure support differs from A/C and IMV in that a level of support pressure is set (not TV) to assist every spontaneous effort. PSV is frequently the mode of choice in patients whose respiratory failure is not severe and who have an adequate respiratory drive.

Methods of Ventilatory Support:

Methods of Ventilatory Support Noninvasive ventilation (NIPPV) The application of mechanical ventilatory support through a mask in place of endotracheal intubation is becoming increasingly accepted and used in the emergency department. Considering this modality for patients with mild-to-moderate respiratory failure is appropriate. The patient must be mentally alert enough to follow commands. Clinical situations in which it has proven useful include acute exacerbation of chronic obstructive pulmonary disease (COPD) or asthma, decompensated congestive heart failure (CHF) with mild-to-moderate pulmonary edema, and pulmonary edema from hypervolemia . It is most commonly applied as continuous positive airway pressure (CPAP).

Indications For Mechanical Ventilation:

Indications For Mechanical Ventilation The principal indications for mechanical ventilation are airway protection and respiratory failure . ABG Criteria: PaO2 <55 mm Hg PaCO2 >50 mm Hg PH <7.32 Clinical criteria: • Apnea or hypopnea • Respiratory distress with altered mentation • Clinically apparent increasing work of breathing unrelieved by other interventions • Obtundation and need for airway protection Other criteria: • Controlled hyperventilation ( eg , in head injury). • Severe circulatory shock

Guidelines for Ventilator Settings:

Guidelines for Ventilator Settings Mode of ventilation The mode of ventilation should be tailored to the needs of the patient. In the emergent situation, the physician may need to order initial settings quickly. SIMV is versatile mode that can be used for initial settings. In patients with a good respiratory drive and mild-to-moderate respiratory failure, PSV is a good initial choice.

Guidelines for Ventilator Settings:

Guidelines for Ventilator Settings Tidal volume Observations of the adverse effects of barotrauma and volutrauma have led to recommendations of lower tidal volumes than in years past, when tidal volumes of 10-15 mL /kg were routinely used. An initial TV of 5-8 mL /kg of ideal body weight is generally indicated, with the lowest values recommended in the presence of obstructive airway disease and ARDS. The goal is to adjust the TV so that plateau pressures are less than 35 cm H2 O.

Guidelines for Ventilator Settings:

Guidelines for Ventilator Settings Respiratory rate A respiratory rate (RR) of 8-12 breaths per minute is recommended for patients not requiring hyperventilation for the treatment of toxic or metabolic acidosis, or intracranial injury. High rates allow less time for exhalation, increase mean airway pressure, and cause air trapping in patients with obstructive airway disease. The initial rate may be as low as 5-6 breaths per minute in asthmatic patients when using a permissive hypercapnic technique.

Guidelines for Ventilator Settings:

Guidelines for Ventilator Settings Supplemental oxygen therapy The lowest FiO2 that produces an arterial oxygen saturation (SaO2) greater than 90% and a PaO2 greater than 60 mm Hg is recommended. No data indicate that prolonged use of an FiO2 less than 0.4 damages parenchymal cells.

Guidelines for Ventilator Settings:

Guidelines for Ventilator Settings Inspiration/expiration ratio The normal inspiration/expiration (I/E) ratio to start is 1:2. This is reduced to 1:4 or 1:5 in the presence of obstructive airway disease in order to avoid air-trapping (breath stacking).

Guidelines for Ventilator Settings:

Guidelines for Ventilator Settings Inspiratory flow rates Inspiratory flow rates are a function of the TV, I/E ratio, and RR and may be controlled internally by the ventilator via these other settings. If flow rates are set explicitly, 60 L/min is typically used. This may be increased to 100 L/min to deliver TVs quickly and allow for prolonged expiration in the presence of obstructive airway disease.

Guidelines for Ventilator Settings:

Guidelines for Ventilator Settings Positive end-expiratory pressure (PEEP) PEEP has several beneficial effects and may be clinically underutilized. PEEP has been found to reduce the risk of atelectasis trauma and increase the number of "open" alveoli participating in ventilation. One obvious beneficial effect of PEEP is to shift lung water from the alveoli to the perivascular interstitial space. This is of clear benefit in cases of cardiogenic as well as noncardiogenic pulmonary edema. An additional benefit of PEEP in cases of CHF is to decrease venous return to the right side of the heart by increasing intrathoracic pressure.

Guidelines for Ventilator Settings:

Guidelines for Ventilator Settings Positive end-expiratory pressure (PEEP) An additional benefit of PEEP in cases of CHF is to decrease venous return to the right side of the heart by increasing intrathoracic pressure. Applying physiologic PEEP of 3-5 cm H2 O is common to prevent decreases in functional residual capacity in those with normal lungs. The reasoning for increasing levels of PEEP in critically ill patients is to provide acceptable oxygenation and to reduce the FiO2 to nontoxic levels (FiO2 <0.5). The level of PEEP must be balanced such that excessive intrathoracic pressure (with a resultant decrease in venous return and risk of barotrauma ) does not occur.

Guidelines for Ventilator Settings:

Guidelines for Ventilator Settings Sensitivity / Triggering Triggering refers to the mechanism through which the ventilator senses inspiratory effort and delivers gas flow. In modern ventilators the demand valve is triggered by either a fall in pressure (pressure triggered) or a change in flow (flow triggered). With pressure triggered a preset pressure that typically is set at -1 to -2 cm H2 O to be achieved before the ventilator delivers fresh gas into the inspiratory circuit. With flow triggered a preset flow sensitivity (usually 2 lit/min) is employed as the trigger. Newer ventilators offer the ability to sense by inspiratory flow instead of negative force.

Ventilator Troubleshooting Managing Complications in the ED:

Ventilator Troubleshooting Managing Complications in the ED The complications most commonly encountered in the emergency department include: hypoxia Hypotension high pressure alarms low exhaled volume alarms.

Ventilator Troubleshooting Managing Complications in the ED:

Ventilator Troubleshooting Managing Complications in the ED High pressure alarms are triggered when resistance to ventilation is high. This may occur secondary to reduced lung elasticity or airway obstruction, or extrinsic compression. Thus, patients should be evaluated for pneumothorax , bronchospasm , elevated abdominal pressure, mainstem intubation, tube plugs or kinks, tube biting, dynamic hyperinflation/air trapping, psychomotor agitation, and worsening pulmonary compliance secondary to progressive pulmonary disease. Tube suctioning and adequate patient sedation are recommended after other causes of obstruction are ruled out.

Ventilator Troubleshooting Managing Complications in the ED:

Ventilator Troubleshooting Managing Complications in the ED Low exhaled volume alarms are triggered by air leaks. These are most frequently secondary to ventilatory tubing disconnect from the patient's tracheal tube but will also occur in the event of balloon deflation or tracheal tube dislodgement. Tube placement, balloon inflation, and connection to the ventilator should be carefully verified.

Ventilator Troubleshooting Managing Complications in the ED:

Ventilator Troubleshooting Managing Complications in the ED Hypoxia after intubation may occur secondary to hypoventilation, worsening cardiac shunting, inadequate FiO2, mainstem intubation, aspiration, tube dislodgement, or pulmonary edema. The causes of high airway pressures and low exhaled volumes described above can result in hypoxia if they cause hypoventilation. Despite the use of numerous safety precautions, cases are occasionally documented of ventilators being connected to compressed air or nitrous oxide rather than oxygen Increasing FiO2 and adjusting ventilatory settings to increase PEEP or respiratory rate are useful first steps after excluding equipment failure and mechanical causes of hypoxia.

Ventilator Troubleshooting Managing Complications in the ED:

Ventilator Troubleshooting Managing Complications in the ED Hypotension after intubation is usually attributable to diminished central venous blood return to the heart secondary to elevated intrathoracic pressures. This can be treated with fluid infusions and/or adjustment of ventilatory settings to lower intrathoracic pressure (reducing PEEP, tidal volume, and, if air trapping is suspected, respiratory rate). Hypotension may also be secondary to vasovagal reaction to intubation, rapid sequence induction, sedation, and tension pneumothorax .

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