Mechanical Ventilation Flashcards
Respiratory Anatomy
what % of each?
Two Zones:
Conducting = trachea branching → bronchi, segmental bronchi → terminal bronchioles, (none of which contain any alveoli) only serves to deliver air to the respiratory zone
– 5% of lung volume
Respiratory = Bronchioles and alveolar ducts; responsible for gas exchange
– 95% of lung volume
Anatomical Dead Space
Conductive airway
-Does not participate in gas exchange
Lung Compliance
– Ability of the lungs to expand
– determined by elasticity or tendancy of form to return to its original state
C =ΔV ÷ ΔP
“Work of breathing”
Energy expended to created pressure gradient that allows airflow easily in and out of the lungs
– Air flows from high-pressure region (mouth/nouse) to low-pressure (lungs)
Tidal Volume
Tidal volume is the volume of air inspired and expired during one breath
– dead space volume and volume of fresh gass entering alveoli for gas exchange
6 to 8 ml/kg for Lung dz; 10-12 ml/kg for healthy lungs
Minute Volume
Minute volume is the volume of air inspired and expired during 1minute
Resistance
2 types
Resistance to breathing is a combination of frictional forces that must be overcome for negative intrathoracic pressure to be created and for air to enter the lungs
– Tissue resistance = need to move or displace the lungs, abdominal organs, ribcage, and diaphragm to create negative pressure
–Air resistance = air moving through the conductive airway dependent on the viscosity and density of the gas, and the length and diameter of the airway
* Ex; bronchospasm, increased secretions, mucosal edema, and physical narrowing or occlusion of endotracheal tubes
Hypoxemia criteria
– PaO2 less than 80 mmHg
– less than 60 mmHg (SpO2 > 90%) being severe hypoxemia
Causes for Hypoxemia
#5
- hypoventilation
- dysfunctional diffusion
- low inspired oxygen
- ventilation/perfusion mismatch caused by dead space ventilation or shunting
- Intrapulmonary shunt
Hypercapnia definition
what can cause it? #4
PaCO2 of more than 45 mmHg, with values over 60 mmHg being considered severe
–can be caused by hypoventilation, high inspired CO2, increased CO2 production, and dead space ventilation
What value is responsible for controlling CO2 levels?
Alveolar ventilation created by breathing
– Amount of fresh gas that moves in and out of the respiratory zone, which participates in gas exchange
–Alveolar ventilation inversely proportional to CO2 levels
(tidal volume - physiological dead space) x RR
Indications for Mechanical Ventilation
#4
- severe hypoxemia despite oxygen supplementation
- severe hypercapnia despite therapy
- excessive respiratory effort and risk of respiratory fatigue or arrest
- severe hemodynamic compromise to reduce oxygen consumption by removal of the work of breathing and change in metabolic rate from drug administration
Causes for hypoventilation that might indicate MV
#7
- Upper airway obstruction
- Respiratory depressant drugs
- Drug overdose
- Neuromuscular toxins
- Neurological disorders
- Pleural space disease
- Excessive dead space
MV needed if therapy not effective
Relation of PaCO2 and TBI
- Hypercapnia leads to vasodilation
- Hypocapnia to vasoconstriction
- affects ICP
MV for Post Arrest Care
Target PaCO2 for cats vs dogs
Effort to reduce tissue oxygen demand by removing the work of breathing, or as a part of respiratory optimization to provide ventilation due to apnea
– Control of PaCO2 to 32–43 mmHg in dogs and 26–36 mmHg in cats to prevent intracranial hypertension
Control Variables for MV
Pressure, Volume, Flow
“Dead Space” Definition
#3
Portion of the tidal volume that does not participate in gas exchange
Characterized as:
1. Apparatus = circuit from the Y-piece to the nose of the patient comprises apparatus dead space
2. Anatomic = conducting airways from the nose to the level of the alveoli
3. Alveolar = alveoli that are ventilated but not perfused in pulmonary capillaries
Physiological Dead Space
Anatomic + Alveolar dead space
–sum of portions that do not participate in gas exchange
–normally should be about the same as anatomic dead space however with V/Q inequality → PDS increases due to increase in alveolar dead space
Ventilator Breath Types: Mandatory
Trigger, Inspiration, Termination
Trigger: ventilator
Inspiratory Flow: ventilator
Termination cyce: ventilator
Ventilator Breath Types: Assisted
Trigger:
Inspiratory Flow:
Termination cycle:
Trigger: Patient
Inspiratory Flow: Ventilator
Termination cycle: Ventilator
Ventilator Breath Types: Spontaneous
Trigger: Patient
Inspiratory flow: Patient
Termination Cycle: Patient
Ventilator Breath Types: Supported
Trigger:
Inspiratory flow:
Termination cycle:
Trigger: Patient
Inspiratory flow: Ventilator
Termination cycle: Patient
Ventilator Mode Classifications
#3
- Continuous mandatory ventilation: All mandatory breaths are delivered
- Intermittent mandatory ventilation: Both mandatory and spontaneous breaths
- Continuous spontaneous ventilation: All spontaneous breaths
Pressure-controlled MV
what becomes the variable?
Pressure-controlled breath = the machine will maintain airway pressure as determined by the operator, and inspiration ends when a preset inspiratory time is reached
– TV and flow rate dependent on the magnitude of the preset airway pressure as well as the resistance and compliance of patient