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Mechanical Ventilation
Tariq Alzahrani M.D
Assistant Professor
College of Medicine
King Saud University
Anatomy
Lung has weight
-8
Ppl = -2
-5
Apex
Base
Chest Wall
Mechanical Ventilator
• Definition • Indication • Types • Classification• Modes • Goals • Monitor • Weaning• Complication
Indication
• Support of oxygenation–Oxygen responsive hypoxemias
• Pneumonia• Sepsis• Inhalation injury
–Oxygen refractory hypoxemias• Atelectasis• Aspiration / Drowning• Adult Respiratory Distress Syndrome (ARDS)
• Support of ventilation–Airway compromise–Muscle fatigue / weakness–Paralysis / spinal cord injury–Neuromuscular disease–Chest wall injury
Types
• Non invasive Ventilation
• Invasive Ventilation
ETT
tracheostomy
Classification • Volume controlled ventilation
• Pressure controlled ventilation
• Time controlled ventilation
CMVCMV
IPPVIPPV
SIMV
SIMV
MMVMMV
BIPAPBIPAP
CPAPCPAP
SPONT
SPONT
PCVPCV
VCVVCV
APRVAPRV
PLVPLV
PSPS
ASBASB
ILV
PRVCPRVC
VAPSVAPS
PAVPAV
Modes?
Auto ModeAuto Mode
AutoFlowAutoFlow
PPSPPS
VSVS
Modes • CMV
• AC
• PCV
• SIMV
• PSV
• Spo. V
Goals • Maintain patient comfort
• Allow a normal, spontaneous breathing pattern whenever possible
• Maintain a PaCO2 between 35-50 mmHg
• Maintain a PaO2 sufficient to meet cellular oxygen demands but avoid oxygen toxicity
• Avoid respiratory muscle fatigue and atrophy
PATIENT COMFORT SCALE
+ -
SpontaneousBreathing
ControlledMechanicalVentilation
AssistControl
Ventilation
SynchronizedIntermittentMechanicalVentilation
PressureSupport
Ventilation
PressureControl
Ventilation
SEDATIVES , ANALGESICS AND MUSCLE RELAXANTS
Monitor
Weaning • Factors to consider: • Awake, and off sedation (as much as possible).• Adequate nutrition, fluid status.• Free of infection.• Hemodynamically stable (preferably off pressors, angina controlled, no
active bleeding)• Normal acid-base status• Bronchospasm controlled• Normal electrolyte balance• Oxygenation (O2 requirements <0.5 and PEEP <5 cmH20)• Weaning Parameters:• Inspiratory negative pressure of -25 cmH2O• RR<30• Vt >6-8 ml/Kg• ABG status near normal
Causes of failure to wean:
1. Hypoxemia• Diffuse pulmonary disease• Focal pulmonary disease (Pneumonia)• Pulmonary edema (removal of positive pressure can increase
preload and lead to worsening heart failure)
2.Insufficient Ventilatory Drive:• response to metabolic alkalosis• Inadequate function of CNS drive (Ex: sedatives, malnutrition)
3. Excessive Ventilatory Drive:• Excessive CO2 production (sepsis, agitation, fever, high
carbohydrate intake)
4. Respiratory Muscle Weakness:• Neuromuscular disease• Malnutrition• Drugs (Neuromuscular blocking agents,
Corticosteroids,aminoglycosides)
5. Excessive Work of Breathing:• Airway obstruction• Bronchospasm• Secretions• Increased Raw (ETT)• ETT too small• Chest motion restriction (pain, bandages)
6. Acid base disorders 7. Phrenic nerve Injury
(especially with contralateral pulmonary disease)
Complication Ventilation-related complications: • Disconnection • Malfunction
Hemodynamic effects: decreased cardiac output due to impaired venous return to the right
heart and increased pulmonary venous resistance due to positive pressure alveolar distension
AutoPEEP • Barotrauma or Atelectasis • Oxygen toxicity • Respiratory alkalosis • Increased intracranial pressure
Suctioning-related complications: • Hypoxemia
a) patients should always be pre-oxygenated with 100% oxygen prior to suctioning
b) suction time should be limited • Arrhythmias • Nosocomial infections
Non-invasive ventilation
• Invasive vs. Non-invasive ventilation
Invasive Good control of airway Suitable for higher pressures
Non-invasive Avoidance of complications of intubation Avoidance of complic of invasive ventilation ( sinusitis…) If tolerated, more comfortable to awake pts. Breaks possible No sedation (or less sedation)
Indication
– Acute settings– Chronic disease
Goals
• Relieve symptoms
• Reduce work of breathing
• Improve gas exchange
• Minimize risk
• Avoid intubation
Exclusion criteria
1.Respiratory arrest2.Medically unstable3.Unconscious, unable to protect airways4.Excessive secretions5.Significant vomiting6.Agitated or uncooperative7.Facial trauma, burns, surgery or anatomic
abnormalities interfering with mask application
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