Exam 1: Vent Support I Exam Summary

Spontaneous Ventilation

• Body's mechanism for conducting air in and out of the lungs.

External Respiration

• Exchange of oxygen (O2) and carbon dioxide (CO2) between alveoli and pulmonary capillaries.

Internal Respiration

• Movement of oxygen from systemic blood into cells at the cellular level.

Transpulmonary Pressure (PL)

• Pressure required to maintain alveolar inflation.

Transairway Pressure (PTA)

• Pressure gradient required to produce airflow in conducting tubes.

Transrespiratory Pressure (PTR)

• Pressure to inflate lungs and airways during positive-pressure ventilation.

Transthoracic Pressure (PTT)

• Pressure required to expand/contract lungs and chest wall.

Elastance

• Tendency of a structure to return to original shape after being stretched.

Compliance

• Ease with which a structure distends or stretches (opposite of elastance).

Viscous Resistance

• Opposition to movement offered by adjacent structures (e.g., lungs and organs).

Compliance Equation

• \Delta C = \frac{\Delta V}{\Delta P}, therefore \Delta P = \frac{\Delta V}{\Delta C}

Static Compliance (CS) Formula

• CS = \frac{VT}{(P_{plat} - EEP)}
  • Where:
    • VT = Tidal Volume
    • Pplat = Plateau Pressure
    • EEP = End-Expiratory Pressure

User Interface

• Control panel where ventilator settings are entered.

Control Logic

• Internal system that interprets settings and regulates output.

Input Power

• Ventilator's power source.

Drive Mechanism

• Mechanical device that produces gas flow.

Single-Circuit Ventilator

• Gas flows directly from power source to patient.

Double-Circuit Ventilator

• Primary power source compresses a mechanism (e.g., bellows), which then delivers gas to the patient.

Exhalation Valve

• Releases exhaled gas from expiratory line into room air.

Power Transmission and Conversion System

• Internal hardware that converts electrical/pneumatic energy into mechanical energy for breath delivery.

ICU Ventilators

• Regulate gas flow using flow-control valves like proportional solenoids or digital valves.

Ventilator Control

• Can control one variable at a time (pressure, volume, flow, time).

Volume-Controlled Ventilation

• Volume and flow remain constant; pressure varies with lung characteristics.
• Increase in resistance increases pressure.

Pressure-Targeted Ventilation

• Pressure is constant; volume varies with lung characteristics.
• Increase in resistance decreases volume.

Volume-Limited Mode

• Volume and flow are constant; pressure varies.
• Decrease in lung compliance increases peak pressure.

High-Frequency Oscillators

• Control both inspiratory and expiratory time.

Respiratory Rate Calculation

• 60 \frac{sec}{min} \div Breaths \frac{breaths}{min} = Seconds

Hypercapnic Respiratory Failure

• Inadequate ventilation leading to increased carbon dioxide levels.

Underlying Cause of Hypercapnic Respiratory Failure

• Alveolar hypoventilation.

Acute Hypercapnic Respiratory Failure

• May be caused by respiratory muscle fatigue.

Asthma Exacerbation

• Increases work of breathing due to bronchoconstriction and inflammation.

Impending Ventilatory Failure

• Deteriorating acid-base status and oxygenation, increased work of breathing; requires mechanical ventilation.

Goals of Mechanical Ventilation

• Support gas exchange, increase lung volume, reduce work of breathing.
• Reverse acute respiratory failure and distress.
• Prevent/reverse atelectasis.
• Permit sedation/paralysis.

Peak Expiratory Flow Rate (PEFR) Critical Value

• 75-100 L/min

Obstructive Sleep Apnea Treatment

• Continuous Positive Airway Pressure (CPAP).

Full Ventilatory Support

• Ventilator rate of 8 breaths/min or more.

Partial Ventilatory Support

• VC-IMV with rate < 8 breaths/min, MMV with patient participation.

Volume Control Ventilation

• Increased airway resistance increases peak airway pressure.

Continuous Positive Airway Pressure (CPAP) Indication

• Oxygenation problem indicated by PaO_2 < 60 mm Hg on non-rebreather.

Assisted Breath (PC-CMV)

• Patient triggered, pressure limited, time cycled.

Intermittent Mandatory Ventilation (IMV)

• Allows spontaneous breathing between mandatory breaths.

Incorrect Sensitivity Settings

• Can lead to ventilator asynchrony.

NIPPV Indications

• COPD with respiratory acidosis.

Mandatory Breath

• Triggered, limited, and cycled by the ventilator.

Tidal Volume Calculation

• Minute \,Ventilation = Respiratory\, Rate \times Tidal\, Volume
• Therefore: Tidal\, Volume = \frac{Minute \,Ventilation}{Respiratory\, Rate}

Inspiratory Time Calculation

• Inspiratory Time (TI) = Tidal Volume (VT) / Minute Ventilation (VE) (convert L/min to L/sec first).

I:E Ratio Calculation

• Total Cycle Time (TCT) = 60 sec / frequency
• Expiratory Time (TE) = TCT – Inspiratory Time (TI)
• I:E = 1:X

High Flow Rates

• Shorten inspiratory time and may increase peak pressures.

Slow Flow Rates

• May reduce peak pressures but can increase inspiratory time and lead to air trapping.

Constant Flow Pattern

• Provides the shortest inspiratory time.

Descending Waveform

• Occurs naturally in pressure ventilation.

Acceptable Arterial Oxygen Tension

• 60-100 mm Hg

Auto-PEEP

• Set extrinsic PEEP to 80% of auto-PEEP level.

Humidity Deficit Calculation

• Humidity \, Deficit = 44 \frac{mg}{L} - Absolute \, Humidity

Heated Humidifier

• Recommended if >4 HMEs are used in 24 hours.

Low Exhaled Tidal Volume Alarm

• Set 10-15% below set tidal volume.

Initial Response to Ventilator Alarm

• Ensure patient is being ventilated.

Minimizing Air Trapping

• Use PC-CMV with short inspiratory time, lower tidal volume, maintain clear airway, administer bronchodilators, and increase inspiratory flow.

Asthma Management

• Increased airway resistance from bronchospasm, secretions, and edema can cause uneven alveolar hyperexpansion, leading to barotrauma.