Mechanical Ventilation.pptx By Azi Bulus Samuel BNSc, MSc- Pharm.

Mechanical Ventilation in critical and acute care

1. CRITICAL CARE NURSING (GNS 320) MECHANICAL VENTILATION

2. Objectives of the Presention By the end of this lectures student should be able to: define mechanical ventilation state the indications of mechanical ventilation discuss types of mechanical ventilation discuss the setting of mechanical ventilation outlines the modes of mechanilation management of patient on mechanical ventilation Withdrawal/ weaning the patient on mechanical ventilation enumerates the complications of mechanical ventilation

3. Outline of Presention Introduction/ Definition Indications of mechanical Ventilation Types of mechanical ventilation Negative Pressure Ventilation Positive Pressure Ventilation Volume Ventilation Settings of Mechanical Ventilation Modes of Mechanical ventilation Complications of mechanical ventilation

4. Introduction/ Definition Mechanical ventilation is the process by which the FIO 2 (21% [room air] or more) is moved in and out of the lungs by a mechanical ventilator. It is a means of supporting patients until they recover the ability to breath independently. It can also serve as a bridge to long term mechanical ventilation, or until a decision is made to withdraw ventilatory support.

5. Indications for mechanical ventilation apnea or impending inability to breath or protect the airway, acute respiratory failure, severe hypoxia, and respiratory muscle fatigue.

6. Types of Mechanical Ventilation The two major types of mechanical ventilation are negative pressure and positive pressure ventilation.

7. Negative Pressure Ventilation This involves the use of chambers that encase the chest or body and surround it with intermittent sub-atmospheric (or negative) pressure. The "iron lung" was the first form of negative pressure ventilation, developed during the polio epidemic. Intermittent negative pressure around the chest wall causes the chest to be pulled outward, reducing intrathoracic pressure. Air rushes in via the upper airway, which is outside the sealed chamber. Expiration is passive. The machine cycles off, allowing chest retraction.

8. Negative Pressure Ventilation This type of ventilation is similar to normal ventilation in that decreased intrathoracic pressures produce inspiration, and expiration is passive. Negative pressure ventilation is delivered by noninvasive ventilation and does not require an artificial airway. Several portable negative pressure ventilators are available for home use for patients with neuromuscular diseases, central nervous system disorders, diseases and injuries of the spinal cord, and severe COPD. Negative pressure ventilators are not routinely used for acutely ill patients.

9. Positive Pressure Ventilation (PPV) Primary method used with acutely ill patients. During inspiration the ventilator pushes air into the lungs under positive pressure. Unlike spontaneous ventilation, intrathoracic pressure is raised during lung inflation rather than lowered. Expiration occurs passively as in normal expiration. Modes of PPV are categorized into two groups: volume ventilation and pressure ventilation.

10. Volume Ventilation With volume ventilation a predetermined tidal volume (VT) is delivered with each inspiration, and the amount of pressure needed to deliver the breath varies based on compliance and resistance factors of the patient-ventilator system. Consequently, the VT is consistent from breath to breath, but airway pressures vary.

11. Pressure Ventilation With pressure ventilation, the peak inspiratory pressure is predetermined, and the VT delivered to the patient varies based on the selected pressure and compliance and resistance factors of the patient-ventilator system. With this understanding, careful attention must be given to the VT to prevent unplanned hyperventilation or hypoventilation. For example, when the patient breathes out of synchrony with the ventilator, the pressure limit may be reached quickly, and the volume of gas delivered may be small. Pressure ventilation is frequently used to treat critically ill patients.

12. Settings of Mechanical Ventilators Mechanical ventilator settings regulate rate, VT, O 2 concentration, and other characteristics of ventilation. Settings are based on the patient's status (e.g., ABGs, ideal body weight, current physiologic state, level of consciousness, respiratory muscle strength). Settings are evaluated and adjusted until oxygenation and ventilation targets have been reached. It is important that you check that all ventilator alarms are always on.

13. Settings of Mechanical Ventilators Cont... Alarms alert the staff to potentially dangerous situations such as mechanical malfunction, apnea, unplanned extubation, or patient asynchrony with the ventilator. On many ventilators the alarms can be temporarily suspended or silenced for up to 2 minutes for suctioning or testing while a staff member is in the room. After that time, the alarm system automatically turns back on.

14. Modes of Volume Ventilation The methods by which the patient and ventilator interact to deliver effective ventilation are called ventilator modes. The selected ventilator mode is based on how much working of breath (WOB) the patient should or can perform. WOB refers to inspiratory effort needed to overcome the elasticity and viscosity of the lungs along with the airway resistance. The mode is determined by the patient's ventilatory status, respiratory drive, and ABGs. Generally, ventilator modes are controlled or assisted. With controlled ventilatory support, the ventilator does all of the WOB. With assisted ventilatory support, the ventilator and patient share the WOB.

15. Modes of Volume Ventilation volume modes: controlled mandatory ventilation (CMV), assist-control ventilation (ACV), and synchronized intermittent mandatory ventilation (SIMV) pressure modes: pressure support ventilation (PSV), pressure-control ventilation (PCV), and inverse ratio ventilation (PC-IRV).

16. Assist-Control Ventilation (ACV) Here, the ventilator delivers a preset VT at a preset frequency. When the patient initiates a spontaneous breath, the ventilator senses a decrease in intrathoracic pressure and then delivers the preset VT· The patient can breathe faster than the preset rate but not slower. This mode allows the patient some control over ventilation while providing some assistance. ACV is used in patients with a variety of conditions, e.g., Guillain-Barre syndrome, pulmonary edema, and acute respiratory failure.

17. Assist-Control Ventilation (ACV) cont... In the ACV mode, the patient has the potential for hyperventilation. The spontaneously breathing patient can easily be overventilated, resulting in hyperventilation. Setting the volume or minimum rate too low and the patient is apneic or weak, the patient can be hypoventilated. Monitor ventilatory status (respiratory rate, ABGs, SpO 2 , and ScvO 2 or SvO 2 ). It is also important that the sensitivity or amount of negative pressure required to start a breath is appropriate to the patient's condition. For example, if it is too difficult for the patient to begin a breath, the WOB is increased and the patient may tire (i.e., the patient "rides" the ventilator) or develop ventilator asynchrony (i.e., the patient "fights" the ventilator).

18. Synchronized Intermittent Mandatory Ventilation With synchronized intermittent mandatory ventilation (SIMV), the ventilator delivers a preset VT at a preset frequency in synchrony with the patient's spontaneous breathing. Between ventilator delivered breaths, the patient is able to breathe spontaneously through the ventilator circuit. Thus, the patient receives the preset FlO 2 during the spontaneous breaths but self-regulates the rate and VT of those breaths.

19. Synchronized Intermittent Mandatory Ventilation This mode of ventilation differs from ACV, in which all breaths are of the same preset volume. It is used during continuous ventilation and during weaning from the ventilator. SIMV may also be combined with PSV (described later). Potential benefits of SIMV include improved patient-ventilator synchrony, lower mean airway pressure, and prevention of muscle atrophy as the patient takes on more of the WOB.

20. Synchronized Intermittent Mandatory Ventilation SIMV Disadvantages. With decrease spontaneous breathing decreases when the preset rate is low, ventilation may not be adequately supported. Patients with regular, spontaneous breathing should use low-rate SIMV. Weaning with SIMV demands close monitoring and may take longer because the rate of breathing is gradually reduced. Patients being weaned with SIMV may also have increased muscle fatigue associated with spontaneous breathing efforts.

21. Modes of Pressure Ventilation Pressure Support Ventilation (PSV). With PSV, positive pressure is applied to the airway only during inspiration and is used with the patient's spontaneous respirations. The patient must be able to initiate a breath in this modality. The level of positive airway pressure is preset so that the gas flow rate is greater than the patient's inspiratory flow rate.

22. Pressure Support Ventilation (PSV) As the patient starts a breath, the machine senses the spontaneous effort and supplies a rapid flow of gas at the initiation of the breath and variable flow throughout the breath. With PSV the patient determines inspiratory length, VT and respiratory rate. VT depends on the pressure level and airway compliance. PSV is used with continuous ventilation and during weaning.

23. Pressure Support Ventilation (PSV) PSV may also be used with SIMV during weaning. PSV is not often used as ventilatory support during acute respiratory failure because of the risk of hypoventilation and apnea. Advantages of PSV include increased patient comfort, decreased WOB (because inspiratory efforts are augmented), decreased O 2 consumption (because inspiratory work is reduced), and increased endurance conditioning (because the patient is exercising respiratory muscles).

24. Pressure-Control and Pressure-Control Inverse Ratio Ventilation. Pressure-control ventilation (PCV) provides a pressure-limited breath delivered at a set rate and may permit spontaneous breathing. The VT is not set, but determined by the pressure limit set. Pressure-control inverse ratio ventilation (PC-IRV) combines pressure-limited ventilation with an inverse ratio of inspiration (I) to expiration (E) The IIE ratio is the ratio of duration of inspiration to the duration of expiration. This ratio is normally 1:2 or 1:3. With IRV, the I/E ratio begins at 1:1 and may progress to 4:1. Prolonged positive pressure is applied, increasing inspiratory time.

25. Pressure-Control and Pressure-Control Inverse Ratio Ventilation. IRV gradually expands collapsed alveoli. The short expiratory time has a PEEP-like effect, preventing alveolar collapse. Because IRV imposes a non-physiologic breathing pattern, the patient needs sedation and often paralysis. PC-IRV is indicated for patients with acute respiratory distress syndrome (ARDS) who continue to have refractory hypoxemia despite high levels of PEEP. Not all patients with poor oxygenation respond to PC-IRV:

26. Airway Pressure Release Ventilation (APRV) Airway pressure release ventilation (APRV) permits spontaneous breathing at any point during the respiratory cycle with a preset continuous positive airway pressure (CPAP) with short timed pressure releases. The CPAP level (pressure high, pressure low) is adjusted to keep oxygenation goals while the timed releases (time high, time low) are increased or decreased to meet ventilation goals.

27. Airway Pressure Release Ventilation (APRV) VT is not a set variable and depends on the CPAP level, the patient's compliance and resistance, and spontaneous breathing effort. The mode is designed for patients who need high pressure levels for alveolar recruitment (open collapsed alveoli). One advantage of this mode is the ability to permit spontaneous respirations. This may reduce the need for deep sedation or paralytics.

28. Other Modes Advances in ventilator technology have led to the development of additional pressure modes. However, because of the nonstandardization of these options, the names and features are manufacturer specific. The superiority of these modes has not been established. Some examples include volum Meassured pressure ventilation and adaptive support ventilation.

29. Other Ventilatory Maneuvers Positive End-Expiratory Pressure (PEEP): is a ventilatory maneuver in which positive pressure is applied to the airway during exhalation. Normally during exhalation, airway pressure drops to near zero, and exhalation occurs passively. With PEEP, exhalation remains passive, but pressure falls to a preset level, often 3 to 20 cm H 2 O. Lung volume during expiration and between breaths is greater than normal with PEEP. This increases functional residual capacity (PRC) and often improves oxygenation with restoration of lung volume that normally remains at the end of passive exhalation.

30. Other Ventilatory Maneuvers (PEEP) cont... The mechanisms by which PEEP increases PRC and oxygenation include increased aeration of patent alveoli, aeration of previously collapsed alveoli, and prevention of alveolar collapse throughout the respiratory cycle. PEEP is titrated to the point that oxygenation improves without compromising hemodynarnics. This is termed optimal PEEP. Often 5 cm H 2 O PEEP (referred to as physiologic PEEP) is used prophylactically to replace the glottic mechanism, help maintain a normal PRC, and prevent alveolar collapse. PEEP of 5 cm H 2 0 is also used for patients with a history of alveolar collapse during weaning. PEEP improves gas exchange, vital capacity, and inspiratory force when used during weaning.

31. Other Ventilatory Maneuvers (PEEP) cont... In contrast, auto-PEEP is not purposely set on the ventilator but is a result of inadequate exhalation time. Auto-PEEP is additional PEEP over what is set by the HCP. This additional PEEP may result in increased WOB, barotrauma, and hemodynamic instability. Interventions to limit auto-PEEP include sedation and analgesia, large-diameter ET tube, bronchodilators, short inspiratory times, and decreased respiratory rates. Reducing water accumulation in the ventilator circuit by frequent emptying or use of heated circuits also limits auto-PEEP

32. Other Ventilatory Maneuvers (PEEP) cont... In patients with short exhalation times and early airway closure (e.g., asthma), setting PEEP above auto-PEEP can offset auto-PEEP effects by splinting the airway open during exhalation and preventing "air trapping:' In general, the major purpose of PEEP is to maintain or improve oxygenation while limiting risk of O 2 toxicity. FIO 2 can often be reduced when PEEP is used. PEEP is generally indicated in all patients who are mechanically ventilated. The classic indication for PEEP therapy is ARDS. PEEP is used with caution in patients with increased intracranial pressure, low cardiac output, and hypovolemia. In these cases, the adverse effects of PEEP may outweigh any benefits.

33. Other Ventilatory Maneuvers Continuous Positive Airway Pressure (CPAP) restores PRC and is similar to PEEP. However, the pressure in CPAP is delivered continuously during spontaneous breathing, thus preventing the patient's airway pressure from falling to zero. For example, if CPAP is 5 cm H 2 O, airway pressure during expiration is 5 cm H 2 O. During inspiration, 1 to 2 cm H 2 O of negative pressure is generated, thus, reducing airway pressure to 3 or 4 cm H 2 O. CPAP is commonly used in the treatment of obstructive sleep apnea. CPAP can be administered with a tight-fitting mask or an ET or tracheal tube. CPAP increases WOB because the patient must forcibly exhale against the CPAP. Therefore, it must be used with caution in patients with myocardial compromise.

34. Other Ventilatory Maneuvers Automatic Tuba Compensation (ATC): is an adjunct designed to overcome WOB through an artificial airway. It is currently available on many ventilators. ATC is increased during inspiration and decreased during expiration. It is set by entering the internal diameter of the patient's airway along with the desired percentage of compensation. ATC may become less effective in patients with excessive secretions and who require longer-term ventilation.

35. Other Ventilatory Maneuvers Bilevel Positive Airway Pressure (BiPAP). In addition to O 2 , BiPAP provides two levels of positive pressure support: higher inspiratory positive airway pressure and lower expiratory positive airway pressure. It is a noninvasive modality and is delivered through a tight-fitting face mask, nasal mask, or nasal pillows. The patient must be able to spontaneously breathe and cooperate with this treatment. BiPAP is used for COPD patients with heart failure and acute respiratory failure and for patients with sleep apnea. BiPAP may also be used after extubation to prevent reintubation. Patients with shock, altered mental status, or increased airway secretions are not candidates for BiPAP because of the risk of aspiration and the inability to remove the mask.

36. Other Ventilatory Maneuvers High-Frequency Oscillatory Ventilation (HFOV): High-frequency oscillatory ventilation involves delivery of a small VT (usually 1to5 mL/kg of bodyweight) at rapid respiratory rates (100 to 300 breaths/minute) in an effort to recruit and maintain lung volume and reduce intrapulmonary shunting. While HFOV may be a useful mode for patients with life-threatening hypoxia, it has not improved survival or provided lung protection in patients with ARDS. Patients receiving HFOV must be sedated and may be paralyzed to suppress spontaneous respiration.

37. Other Ventilatory Maneuvers Nitric Oxide (NO): is a gaseous molecule that is made intravascularly and participates in the regulation of pulmonary vascular tone. Inhibition of NO production results in puhnonary vasoconstriction, and administration of continuous inhaled NO results in puhnonary vasodilation. NO may be administered via an ET tube, a tracheostomy, or a face mask. Currently, NO is used as a diagnostic screening tool for pulmonary hypertension and to improve oxygenation during mechanical ventilation in this patient population. Although the use of NO does not reduce mortality in patients with ARDS, it may be used in patients with life-threatening hypoxia.

38. Other Ventilatory Maneuvers Prone Positioning: is the repositioning of a patient from a supine or lateral position to a prone (on the stomach, face down) position. This repositioning improves lung recruitment (i.e., alveolar expansion) through various mechanisms. Gravity reverses the effects of fluid in the dependent parts of the lungs as the patient is moved from supine to prone. The heart rests on the sternum, away from the lungs, contributing to an overall uniformity of pleural pressures. The prone position is a relatively safe (although nurse-intensive), supportive therapy used in critically ill patients with severe ARDS to improve oxygenation.

39. Other Ventilatory Maneuvers Extracorporeal Membrane Oxygenation (ECMO): is an alternative form of pulmonary support for the patient with severe respiratory failure. It is used more frequently in the pediatric and neonatal populations but is increasingly being used in adults. ECMO is a modification of cardiac bypass and involves partially removing blood from a patient with large-bore catheters, infusing O 2 , removing CO 2 , and returning the blood to the patient. This intensive therapy requires systemic anticoagulation and is a time-limited intervention. A skilled team of specialists, including a perfusionist, is required continuously at the bedside.

40. Complications of Positive Pressure Ventilation Cardiovascular System. PPV can affect circulation because of the transmission of increased mean airway pressure to various structures in the thorax. With increased intrathoracic pressure, thoracic vessels are compressed. The compression causes decreased venous return to the heart, left ventricular end-diastolic volume (preload), and CO, and results in hypotension. Mean airway pressure is further increased if PEEP is being titrated (greater than 5 cm H 2 0) to improve oxygenation.

41. Complications of Positive Pressure Ventilation If the lungs are noncompliant (e.g., ARDS), airway pressures are not as easily transmitted to the heart and blood vessels. Thus, effects of PPV on CO are reduced. Conversely, with compliant lungs (e.g., COPD), there is increased danger of transmission of high airway pressures and negative effects on hemodynamics. Compromised venous return by PPV is worsened by hypovolemia (e.g., hemorrhage) and decreased venous tone (e.g., sepsis, spinal shock). Restoration and maintenance of the circulating blood volume are important in minimizing cardiovascular complications.

42. END COMMENTS OBSERVATION & QUESTIONS