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