Respiratory failure mechanical ventilation: Difference between revisions
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===Ventilator Modes=== | ===Ventilator Modes=== | ||
*'''Pressure support ventilation (PSV)''' | |||
** can be categorized as patient-initiated, pressure-targeted ventilation. With PSV, ventilatory assistance occurs only in response to the patient’s spontaneous inspiratory efforts. With each inspiratory effort, the ventilator raises airway pressure by a preset amount. When the inspiratory flow rate decays to a minimal level or to a percentage of initial inspiratory flow (eg, 25% of peak flow), inspiration is terminated. | |||
During PSV, patients are free to choose their own respiratory rate; inspiratory time, inspiratory flow rate, and tidal volume are determined, in part, by the patient’s respiratory efforts. This mode of ventilation should not be used in patients with unstable ventilatory drive, and care must be exercised when the patient’s respiratory mechanics are changing because of bronchospasm, secretions, or varying levels of auto–positive end-expiratory pressure (auto-PEEP). | |||
*'''Intermittent mandatory ventilation (IMV)''' | |||
** is a mode whereby mandatory breaths are delivered at a set frequency, tidal volume, and inspiratory flow rate. However, the patient can breathe spontaneously between the machine-delivered breaths. | |||
Most modern ventilators are capable of synchronized IMV (SIMV), whereby the ventilator attempts to deliver the mandatory breaths in synchrony with the patient’s own inspiratory efforts. In essence, the ventilator allows the patient an opportunity to breathe. If the patient makes an inspiratory effort during a window of time determined by the IMV rate, the ventilator delivers a mandatory breath in response to the patient’s inspiratory effort. However, if no inspiratory effort is detected by the ventilator, a time-triggered breath is delivered. | |||
Compared with standard IMV, SIMV may improve patient comfort and may limit dynamic hyperinflation, which may occur when a preset breath is delivered immediately after the patient’s spontaneous inspiratory effort (ie, before exhalation). | |||
*'''Assist-control ventilation''' | |||
**, patients receive a fixed tidal volume and inspiratory flow rate with each inspiratory effort, regardless of their respiratory rate. However, a backup rate is selected that guarantees that the patient receives a minimum number of breaths per minute. If the patient’s respiratory rate falls below the backup rate, the ventilator delivers the number of breaths necessary to reach that rate; such breaths are delivered independent of any inspiratory effort by the patient. | |||
*'''Volume-control mode''' | |||
**, respiratory rate, tidal volume, and inspiratory flow rate (or inspiratory time) are fixed. This mode is used most often in heavily sedated or paralyzed patients. | |||
*'''Pressure-control mode''' | |||
**, as contrasted with volume-control mode, airway pressure is raised by a set amount at a fixed number of times per minute. The physician or respiratory therapist also sets the inspiratory-to-expiratory (I:E) ratio or the inspiratory time. This mode is used most often in heavily sedated or paralyzed patients. | |||
*''Pressure-control inverse-ratio ventilation (PCIRV)'' | |||
** is a variation of simple pressure-control ventilation. In this mode, inspiration is set to be longer than expiration. The I:E ratio should rarely, if ever, exceed 3:1. | |||
===Positive-End Expiratory Pressure=== | ===Positive-End Expiratory Pressure=== | ||
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Overview
Mechanical ventilation
Mechanical ventilation aims to correct abnormalities in oxygenation of the blood and tissues, reduce the respiratory effort and prevent dynamic hyperinflation.
Principles of Mechanical Ventilation
- Mechanical ventilation is basically used to:[1]
- Increase PaO2
- Lower PaCO2
- Relieve respiratory effort
Indications
- Life threatening respiratory failure:[2][3][4][5]
- Severe respiratory failure with failure of non-invasive ventilation (NIV) in addition to rapid, shallow breathing, cardiopulmonary arrest, and severe hemodynamic compromise.
- Failure of noninvasive ventilation:
- Indications of failed NIV include:
- A lack of improvement in arterial carbon dioxide tension (PaCO2) and pH within 1.5 - 2 hours
- Encephalopathy
- Agitation
- Unclearable secretions
- Intolerable mask interface
- Decreased oxygen saturation
- Hemodynamic instability
- Indications of failed NIV include:
- Arterial blood gas abnormalities
- Incorrectable hypoxemia despite oxygen supplementation
- Severe respiratory acidosis unresponsive to therapy and/or NIV
Endotracheal intubation
- Endotracheal intubation acts as the connection between the ventilator and the patient.[6][4]
- Intubation can be performed endotracheally or through a tracheostomy.
- The tube must be placed correctly, and this is confirmed through:
- Chest x-ray
- Chest auscultation
- Carbon dioxide detector
- Proper cuff pressure must be maintained and not exceed 25mmHg
- The airways should be suctioned to ensure patency of the airway:
- Suctioning may occur through an open or closed circuit suction catheter.
- Routine suctioning is not recommended as this may lead to complications such as:
- Desaturation
- Arrhythmias
- Bronchospasm
- Cough
- Entry of secretions into the lower respiratory tract
- The endotracheal tube insertion depth varies by gender and is measured from the lower incisors:
- In males: 23cm
- In females: 21cm
- The tube is affixed in place using tape to prevent accidental extubation or further downward movement toward the main bronchus.
Types of Mechanical Ventilation
Positive-pressure and Negative pressure ventilation
- There are two ways in which a pressure gradient may be created to allow air into the lungs:[7][8][3]
- Increase the air pressure in the bronchi (positive pressure)
- Decrease pressure in the alveoli (negative pressure)
Controlled and patient-initiated ventilation
- Ventilatory support may be controlled or patient-initiated:
- Controlled ventilation will deliver support independent of the patient's respiratory efforts
- Patient-controlled ventilation allows ventilation to be delivered in sync with the patient's own spontaneous breathing. In this type of ventilation, the patient's breathing is detected through pressure and airflow trigger mechanisms.
Pressure-targeted and volume-targeted ventilation
- With positive pressure ventilation, pressure or volume may be an independent variable:
- In volume-targeted ventilation, the tidal volume is set by the physician or respiratory assistant, the pressure in this case is a dependent variable.
- This means that airway pressure is the result of a set tidal volume and ispiratory volume, along with the patient's lung compliance, resistance and muscular activity.
- In pressure-targeted ventilation, airway pressure is set, and the volume is dependent.
- The tidal volume in this scenario is a result of inspiratory time, along with the patient's lung compliance, resistance and muscular activity.
- In volume-targeted ventilation, the tidal volume is set by the physician or respiratory assistant, the pressure in this case is a dependent variable.
Ventilator Modes
- Pressure support ventilation (PSV)
- can be categorized as patient-initiated, pressure-targeted ventilation. With PSV, ventilatory assistance occurs only in response to the patient’s spontaneous inspiratory efforts. With each inspiratory effort, the ventilator raises airway pressure by a preset amount. When the inspiratory flow rate decays to a minimal level or to a percentage of initial inspiratory flow (eg, 25% of peak flow), inspiration is terminated.
During PSV, patients are free to choose their own respiratory rate; inspiratory time, inspiratory flow rate, and tidal volume are determined, in part, by the patient’s respiratory efforts. This mode of ventilation should not be used in patients with unstable ventilatory drive, and care must be exercised when the patient’s respiratory mechanics are changing because of bronchospasm, secretions, or varying levels of auto–positive end-expiratory pressure (auto-PEEP).
- Intermittent mandatory ventilation (IMV)
- is a mode whereby mandatory breaths are delivered at a set frequency, tidal volume, and inspiratory flow rate. However, the patient can breathe spontaneously between the machine-delivered breaths.
Most modern ventilators are capable of synchronized IMV (SIMV), whereby the ventilator attempts to deliver the mandatory breaths in synchrony with the patient’s own inspiratory efforts. In essence, the ventilator allows the patient an opportunity to breathe. If the patient makes an inspiratory effort during a window of time determined by the IMV rate, the ventilator delivers a mandatory breath in response to the patient’s inspiratory effort. However, if no inspiratory effort is detected by the ventilator, a time-triggered breath is delivered.
Compared with standard IMV, SIMV may improve patient comfort and may limit dynamic hyperinflation, which may occur when a preset breath is delivered immediately after the patient’s spontaneous inspiratory effort (ie, before exhalation).
- Assist-control ventilation
- , patients receive a fixed tidal volume and inspiratory flow rate with each inspiratory effort, regardless of their respiratory rate. However, a backup rate is selected that guarantees that the patient receives a minimum number of breaths per minute. If the patient’s respiratory rate falls below the backup rate, the ventilator delivers the number of breaths necessary to reach that rate; such breaths are delivered independent of any inspiratory effort by the patient.
- Volume-control mode
- , respiratory rate, tidal volume, and inspiratory flow rate (or inspiratory time) are fixed. This mode is used most often in heavily sedated or paralyzed patients.
- Pressure-control mode
- , as contrasted with volume-control mode, airway pressure is raised by a set amount at a fixed number of times per minute. The physician or respiratory therapist also sets the inspiratory-to-expiratory (I:E) ratio or the inspiratory time. This mode is used most often in heavily sedated or paralyzed patients.
- Pressure-control inverse-ratio ventilation (PCIRV)
- is a variation of simple pressure-control ventilation. In this mode, inspiration is set to be longer than expiration. The I:E ratio should rarely, if ever, exceed 3:1.
Positive-End Expiratory Pressure
Inspiratory Flow
Ventilator Induced Lung Injury
References
- ↑ Frat JP, Thille AW, Mercat A, Girault C, Ragot S, Perbet S, Prat G, Boulain T, Morawiec E, Cottereau A, Devaquet J, Nseir S, Razazi K, Mira JP, Argaud L, Chakarian JC, Ricard JD, Wittebole X, Chevalier S, Herbland A, Fartoukh M, Constantin JM, Tonnelier JM, Pierrot M, Mathonnet A, Béduneau G, Delétage-Métreau C, Richard JC, Brochard L, Robert R (June 2015). "High-flow oxygen through nasal cannula in acute hypoxemic respiratory failure". N. Engl. J. Med. 372 (23): 2185–96. doi:10.1056/NEJMoa1503326. PMID 25981908.
- ↑ Davidson AC, Banham S, Elliott M, Kennedy D, Gelder C, Glossop A, Church AC, Creagh-Brown B, Dodd JW, Felton T, Foëx B, Mansfield L, McDonnell L, Parker R, Patterson CM, Sovani M, Thomas L (April 2016). "BTS/ICS guideline for the ventilatory management of acute hypercapnic respiratory failure in adults". Thorax. 71 Suppl 2: ii1–35. doi:10.1136/thoraxjnl-2015-208209. PMID 26976648.
- ↑ 3.0 3.1 Confalonieri M, Garuti G, Cattaruzza MS, Osborn JF, Antonelli M, Conti G, Kodric M, Resta O, Marchese S, Gregoretti C, Rossi A (February 2005). "A chart of failure risk for noninvasive ventilation in patients with COPD exacerbation". Eur. Respir. J. 25 (2): 348–55. doi:10.1183/09031936.05.00085304. PMID 15684302.
- ↑ 4.0 4.1 Phua J, Kong K, Lee KH, Shen L, Lim TK (April 2005). "Noninvasive ventilation in hypercapnic acute respiratory failure due to chronic obstructive pulmonary disease vs. other conditions: effectiveness and predictors of failure". Intensive Care Med. 31 (4): 533–9. doi:10.1007/s00134-005-2582-8. PMID 15742175.
- ↑ Slutsky AS (December 1993). "Mechanical ventilation. American College of Chest Physicians' Consensus Conference". Chest. 104 (6): 1833–59. PMID 8252973.
- ↑ Tobin MJ, Perez W, Guenther SM, Lodato RF, Dantzker DR (August 1987). "Does rib cage-abdominal paradox signify respiratory muscle fatigue?". J. Appl. Physiol. 63 (2): 851–60. doi:10.1152/jappl.1987.63.2.851. PMID 3654445.
- ↑ Shorr AF, Sun X, Johannes RS, Yaitanes A, Tabak YP (November 2011). "Validation of a novel risk score for severity of illness in acute exacerbations of COPD". Chest. 140 (5): 1177–1183. doi:10.1378/chest.10-3035. PMID 21527510.
- ↑ Tabak YP, Sun X, Johannes RS, Gupta V, Shorr AF (September 2009). "Mortality and need for mechanical ventilation in acute exacerbations of chronic obstructive pulmonary disease: development and validation of a simple risk score". Arch. Intern. Med. 169 (17): 1595–602. doi:10.1001/archinternmed.2009.270. PMID 19786679.