Mechanical Ventilation.pptxFFFFFFFFFFFFFFFFFFFFFFFFF

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1. Mechanical Ventilation

2. Mechanical ventilation is a medical term for artificial ventilation where mechanical means is used to assist or replace spontaneous breathing. This may involve a machine called ventilator or breathing may be assisted by compressing a bag or set of bellows . Following an inspiratory trigger, a predetermined mixture of air (i.e., oxygen and other gases) is forced into the central airways and then flows into the alveoli. As the lungs inflate, the intra-alveolar pressure increases. A termination signal eventually causes the ventilator to stop forcing air into the central airways and the central airway pressure decreases. Expiration follows passively, with air flowing from the higher pressure alveoli to the lower pressure central airways.

3. Why are ventilators used ? To get oxygen into the lungs and body To help the lungs get rid of carbon dioxide To ease the work of breathing—Some people can breathe but it is very hard. They feel shortness of breath and uncomfortable. To breathe for a patient who is not breathing because of brain damage or injury (like a coma) or high spinal cord injury or very weak muscles. If a person has had a serious injury or illness that causes breathing effort to stop, a ventilator can be used to help the lungs breath until the person recovers.

4. Modes of mechanical ventilation The mode refers to the method of inspiratory support. Its selection is generally based on clinician familiarity and institutional preferences since there is a paucity of evidence indicating that the mode affects clinical outcome . Modern ventilators are classified by their method of cycling from inspiratory phase to the expiratory phase. T he signal to terminate the inspiratory activity of the machine is either a preset volume (for a volume-cycled ventilator), a preset pressure limit (for a pressure -cycled ventilator ), or a preset time factor (for a time -cycled ventilator ).

5. Volume-cycled ventilator requires the clinician to set the peak flow rate, flow pattern, tidal volume, respiratory rate, positive end-expiratory pressure (applied PEEP), and fraction of inspired oxygen ( FiO 2   ). Inspiration ends after delivery of the set tidal volume . The inspiratory time and inspiratory to expiratory (I:E) ratio are determined by the peak inspiratory flow rate. Increasing the peak inspiratory flow rate will decrease inspiratory time, increase expiratory time, and decrease the I:E ratio.

6. Volume-limited ventilation can be delivered via several modes, including; 1. C ontrolled mechanical ventilation  — During CMV, the minute ventilation is determined entirely by the set respiratory rate and tidal volume. The patient does not initiate additional minute ventilation above that set on the ventilator. 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. CMV does not require any patient work.

7. 2 . Assist control   — 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. Each patient-initiated breath receives the set tidal volume from the ventilator. Consider the following example. If the clinician sets the respiratory rate to 20 bpm and the tidal volume to 500 mL, the lowest possible minute ventilation is 10 L/min (20 bpm times 500 mL per breath). If the patient triggers an additional 5 breaths beyond the preset 20 breaths, the ventilator will deliver 500 mL for each additional breath and the minute ventilation will be 12.5 L/min (25 breaths per minute times 500 mL per breath).

8. 3. Intermittent mandatory ventilation    — In   IMV 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, it differs from AC in the way that the minute ventilation is increased. Specifically, patients increase the minute ventilation by spontaneous breathing, rather than patient-initiated ventilator breaths. Consider the following example. If the clinician sets the respiratory rate to 10 bpm and the tidal volume to 500 mL per breath, the lowest possible minute ventilation is 5 L/min (10 bpm times 500 mL per breath). If the patient initiates an additional 5 breaths beyond the preset 10 breaths, the tidal volume for each additional breath will be whatever size the patient is able to generate and the minute ventilation will be some amount greater than 5 L per minute. The precise minute ventilation depends on the size of the tidal volume for each spontaneous breath.

9. 4. synchronized intermittent mandatory ventilation   — SIMV is a variation of IMV, in which the ventilator breaths are synchronized with patient inspiratory effort. SIMV (or IMV) can be used to titrate the level of ventilatory support over a wide range. This is an advantage unique to these modes. Ventilatory support can range from full support (set respiratory rate is high enough that the patient does not overbreathe ) to no ventilatory support (set respiratory rate is zero).

10. Comparisons    — SIMV and AC are the most frequently used forms of volume-limited mechanical ventilation. Possible advantages of SIMV compared to AC include better patient-ventilator synchrony, better preservation of respiratory muscle function, lower mean airway pressures, and greater control over the level of support . In addition, auto-PEEP may be less likely with SIMV. In contrast, AC may be better suited for critically ill patients who require a constant tidal volume or full or near-maximal ventilatory support.

11. Pressure-cycled ventilation   requires the clinician to set the inspiratory pressure level, I:E ratio, respiratory rate, applied PEEP, and fraction of inspired oxygen(FiO 2 ). Inspiration ends after delivery of the set inspiratory pressure . The tidal volume is variable during pressure-limited ventilation. It is related to inspiratory pressure level, compliance, airway resistance, and tubing resistance. Specifically, tidal volumes will be larger when the set inspiratory pressure level is high or there is good compliance, little airway resistance, or little resistance from the ventilator tubing.

12. In contrast, the peak airway pressure is constant during pressure-limited ventilation. It is equal to the sum of the set inspiratory pressure level and the applied PEEP. As an example, a patient with a set inspiratory pressure level of 20 cm H 2 O and an applied PEEP of 10 cm H 2 O will have a peak airway pressure of 30 cm H 2 O . Pressure-limited ventilation can be delivered using the same modes of ventilation that deliver volume-limited ventilation :

13. During pressure-limited CMV (also called pressure control ventilation), the minute ventilation is determined entirely by the set respiratory rate and inspiratory pressure level. The patient does not initiate additional minute ventilation above that set on the ventilator. During pressure-limited AC, the set respiratory rate and inspiratory pressure level determine the minimum minute ventilation. The patient is able to increase the minute ventilation by triggering additional ventilator-assisted, pressure-limited breaths. During pressure-limited IMV or SIMV, the set respiratory rate and inspiratory pressure level determine the minimum minute ventilation. The patient is able to increase the minute ventilation by initiating spontaneous breaths.

14. VOLUME-LIMITED VERSUS PRESSURE-LIMITED   — Pressure-limited ventilation was compared to volume-limited ventilation in a randomized trial and several observational studies : There were no statistically significant differences in mortality, oxygenation, or work of breathing. Favoring pressure-limited ventilation, it was associated with lower peak airway pressures, a more homogeneous gas distribution (less regional alveolar overdistension ), improved patient-ventilator synchrony, and earlier liberation from mechanical ventilation than volume-limited ventilation.

15. Favoring volume-limited ventilation, only it can guarantee a constant tidal volume, ensuring a minimum minute ventilation. Most studies comparing pressure-limited and volume-limited ventilation used a square wave (constant flow) pattern for both modes. When volume-limited mechanical ventilation with a ramp wave (decelerating flow) pattern was compared to pressure-limited ventilation, lower peak airway pressures were no longer an advantage of pressure-limited ventilation.

16. Invasive vs Non-invasive     Mechanical ventilation can be delivered invasively or non-invasively . Invasive positive pressure is sometimes referred to as conventional mechanical ventilation or traditional mechanical ventilation. It is delivered via an endotracheal tube or tracheostomy tube. The tracheostomy is able to stay in as long as needed and is more secure than an ET tube. At times a person can talk with a tracheostomy tube in place by using a special adapter called a speaking valve. In contrast, non-invasive positive pressure ventilation is delivered through an alternative interface, usually a face mask.

17. Indication MV is indicated when the patient’s spontaneous ventilation is inadequate to sustain life. In addition, it is indicated as a measure to control ventilation in critically ill patients and as prophylaxis for impending collapse of other physiological functions.

18. Common indications; Bradypnea or apnea with respiratory arrest Acute lung injury and ARDS Tachypnea (RR>30bpm) Vital capacity<15 ml/kg Minute ventilation>10L/min Clinical deterioration Respiratory muscle fatigue Obtundation or coma Hypotension Neuromuscular blockage…..

19. How are patients on ventilators monitored? Anyone on a ventilator in an ICU setting will be hooked up to a monitor that measures HR, RR, BP, and O 2 saturation. Other tests that may be done include CXR and blood drawn to measure O 2 and CO 2 .

20. How long is a ventilator used? A ventilator can be life saving, but its use also has risks. It also doesn’t fix the primary disease or injury; it just supports a patient until other treatments become effective . Doctors always try to help patients get off the ventilator at the earliest possible time . Some patients may be on a ventilator for only a few hours or days , while others may require the ventilator for longer. Some patients never improve enough to be taken off the ventilator completely.

21. Discontinuing mechanical ventilation is a two step process : 1. Readiness testing — refers to the evaluation of objective clinical criteria in order to decide whether a patient is ready to begin the process of discontinuing mechanical ventilation. Some clinicians also use physiological tests, known as weaning predictors, to predict whether a patient is ready because they are hesitant to begin weaning on the basis of clinical criteria alone. The rapid shallow breathing index (RSBI) is one of the best studied and most commonly used weaning predictors .

22. 2. Weaning — is the process of decreasing ventilator support and allowing patients to assume a greater proportion of their ventilation. It may involve either an immediate shift from full ventilatory support to a period of breathing without assistance from the ventilator ( i.e. a spontaneous breathing trial [SBT]) or a gradual reduction in the amount of ventilator support . An SBT refers to a patient breathing through the endotracheal tube either without any ventilator support (e.g. through a T-piece) or with minimal ventilator support ( e.g . a low level of pressure support, automatic tube compensation (ATC), or continuous positive airway pressure (CPAP)) Regardless of which approach is chosen, extubation is considered once the patient demonstrates the ability to breathe without the ventilator.

23. T-piece

24. Complication of MV Infections- ventilator associated pneumonia Pneumothorax- a part of the lung that is weak can become too full of air and start to leak. Lung damage-very high levels of O 2 may be harmful to the lungs. Maintenance of life- for pt. who are very sick, at times the ventilator only postpones death. Not every pt. improves just because they use a ventilator . Cxns that can occur during placement of ET include; - upper airway and nasal trauma, tooth avulsion, oropharyngeal and tracheal laceration, laceration or hematoma of the vocal cords, hypoxemia, intubation of esophagus and Aspiration.

25. References Up-to-date