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Kingdom of Saudi Arabia

king Fahd Hospital Jeddah

Intensive Care Unit

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Mechanical ventilation

Dr.Wail Bajhmoom

15.3.2005 A.D 5.2.1425A.H

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•Background.•Definitions.•Classifications. •Indications.

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•Physiologic aspects.

•Ventilator mode. •Complications. •Weaning.

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Background.•1929 was one of the first negative-pressure ventilators widely used for mechanical ventilation. This metal cylinder completely covered the patient up to the neck.

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•known as the iron lung, this device used negative pressure to cause a drop in the intrapulmonary pressure and to allow ambient airflow into the patient's lungs.

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•In the 1950s, the intensive use of mechanical ventilation started during the polio epidemic in Scandinavia and the United States. In Copenhagen, Denmark.

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•ventilating patients with polio and respiratory paralysis by manually forcing 50% oxygen through a tracheostomy reduced the mortality rate from 80% to 25%.

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Definition :

Ventilators are: specially designed pumps that can support the ventilator function of the respiratory system.

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They improve oxygenation through application of high oxygen content gas and positive pressure.

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Classifications.•Modern ventilators are classified by the method of cycling from the inspiratory phase to the expiratory phase.

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Classifications.•The signal to terminate the

machine's inspiratory activity can be:

•(volume-cycled ventilator),•(pressure-cycled ventilator),

•(time-cycled ventilator).

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volume-cycled ventilator

•a preset volume •is the most common form of ventilator cycling used in adult medicine

•because it provides a consistent breath-to-breath tidal volume.

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Indications:• Mechanical ventilation should

not be initiated without thoughtful consideration because intubation and positive-pressure ventilation could have potentially harmful effects.

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Indications:•Many factors are considered in the decision to institute mechanical ventilation.

•Respiratory failure is the primary indication

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Indications:•Apnea with respiratory arrest•Acute lung injury -R.R more than 30 BPM

-Minute ventilation>10 L/min

-PaO2, with supplemental (FIO2) less than 55 mm Hg

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• Chronic obstructive lung disease

- Blood gases - Persistent hypoxemia, PCO2 (acutely) greater than 50 mm Hg with pH less than 7.25

_ Clinical deterioration Respiratory

muscle fatigue, coma, hypotension, or tachypnea or bradypnea

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•Neuromuscular disease

• Clinical judgment should be used ;An increasing severity of the illness is

a sign that should alert the clinician to consider instituting mechanical ventilation.

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Physiologic aspects.• Most modern mechanical

ventilators function by providing warmed and humidified gas to the airway opening in conformance with various specific volume, pressure, and time patterns. The ventilator serves as the energy source for inspiration,

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• replacing the muscles of the diaphragm and chest wall. Expiration is passive, driven by the recoil of the lungs and chest wall

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Ventilator mode:

•This setting specifies the manner in which ventilator breaths are triggered, cycled, and limited .

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• Assist Control Mode Ventilation (ACMV) An inspiratory cycle is initiated

either by the patient's inspiratory effort or, if no patient effort is detected within a specified time window,

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• Every breath delivered consists of the operator-specified tidal volume.

• ACMV is the recommended mode for initiation of mechanical ventilation because it ensures a backup minute ventilation in the absence of an intact respiratory drive.

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•ACMV is not effective for weaning patients from mechanical ventilation because it provides full ventilator assistance on each patient-initiated breath.

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•Synchronized Intermittent Mandatory Ventilation

(SIMV) The major difference between

SIMV and ACMV is that in the former the patient is allowed to breathe spontaneously, i.e., without ventilator assist

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• If the patient fails to initiate a breath, the ventilator delivers a fixed-tidal-volume breath and resets the internal timer for the next inspiratory cycle.

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• SIMV is a useful mode of ventilation for both supporting and weaning intubated patients

• SIMV may be difficult to use in patients with tachypnea because they may attempt to exhale during the ventilator-programmed inspiratory cycle.

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• Continuous Positive Airway Pressure

(CPAP).This is not a true support-mode

of ventilation, since all ventilation occurs through the patient's spontaneous efforts.

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• CPAP is used to assess extubation potential in patients who have been effectively weaned and are requiring little ventilator support

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•Pressure-Control Ventilation (PCV) This form of ventilation is time

triggered, time cycled, and pressure limited. During the inspiratory phase, a given pressure is imposed at the airway opening, and the pressure remains at this user-specified level throughout inspiration

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•PCV is the preferred mode of ventilation for patients with documented barotrauma, since airway pressures can be limited,

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•Pressure-Support Ventilation (PSV) This form of ventilation is patient

triggered, flow cycled, and pressure limited; it is specifically designed for use in the weaning process.

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PSV is well tolerated by most patients who are being weaned: PSV parameters can be set in such a way as to provide full or nearly full ventilatory support and can be withdrawn slowly over a period of days in a systematic fashion to gradually load the respiratory muscles.

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COMPLICATIONS:• Endotracheal intubation and

positive-pressure mechanical ventilation have direct and indirect effects on several organ systems

• Including: -the lung and upper airways, the

cardiovascular system, and the gastrointestinal system.

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• barotrauma, nosocomial pneumonia, oxygen toxicity, tracheal stenosis, and deconditioning of respiratory muscles.

• emphysema, pneumomediastinum, subcutaneous emphysema, or pneumothorax.

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• Patients intubated for longer than 72 h are at high risk for nosocomial pneumonia as a result of aspiration from the upper airways via small leaks around the endotracheal tube cuff

• enteric gram-negative rods, Staphylococcus aureus, and anaerobic bacteria.

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• Oxygen toxicity is a potential complication when an FIO2 of 0.6 or greater is required for more than 72 h.

• Hypotension resulting from elevated intrathoracic pressures with decreased venous return

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• Gastrointestinal effects of positive-pressure ventilation include stress ulceration and mild to moderate cholestasis. It is common practice to provide prophylaxis with H2-receptor antagonists or sucralfate for stress-related ulcers.

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Weaning.• Many approaches to weaning

patients from ventilator support have been advocated.

• T-piece and CPAP weaning are best tolerated by patients who have undergone mechanical ventilation for brief periods

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Weaning.• SIMV and PSV are best for

patients who have been intubated for extended periods and require gradual respiratory-muscle reconditioning.

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ThANK YOU