Chapter 4: Mechanical Ventilation Part 2

What are the Positive Pressure Basic Ventilation Modes?

• Control Modes

• Mixed Modes

• Spontaneous Modes

• Other

What are the Control Modes?

• Controlled Mode/Mandatory Ventilation (CMV)

• Assist-Controlled Mode Ventilation (A/C)

• Assist Mode (A)

What are Mixed Modes?

• Intermittent Mandatory Ventilation (IMV)

• Synchronized Intermittent Mandatory Ventilation (SIMV)

What are Spontaneous Modes?

• Pressure Support Ventilation (PSV)

What are the other types?

• Positive End Expiratory Pressure (PEEP)

What are the types of Positive Pressure Ventilation Cycling Mechanisms?

• Volume Cycled

• Pressure Cycled

• Flow Cycled

• Time Cycled

Volume Cycled:

• Inspiration terminated after delivery of a pre-set tidal volume

Pressure Cycled:

• Inspiration terminated when a pre-set maximum pressure is reached

• Volume delivered varies from breath to breath

Flow Cycled:

• Inspiration terminated when a particular flow rate is reached

Time Cycled:

• Inspiration terminated following a pre-set inspiratory time

(Mode Characteristics) What are the Parameters?

• What initiates the breath? (Machine, Patient, Both)

• What terminates the breath? (volume, pressure, flow, time)

• What are the flow characteristics?

• What are the pressure characteristics?

• What is the tidal volume, V_T?

Assist Control (A/C):

• (Variation of CMV – now used predominantly)

• Full ventilatory support

• Patient controls respiratory rate (RR); but, can’t inspire sufficiently to reach or maintain Vmin

• Uses either Pre-Set Volume OR Pre-Set Pressure parameters

• AND–has a pre-set minimum RR

• Triggers:

  • when patient initates a breath, the machine continues until the pre-set volume/pressure is achieved

  • if patient does not spontaneously inhale when the machine expects an inhalation based on RR

• Does not allow for independent patient breathing at whatever effort (volume/pressure) the patient produces

• Can be used indefinitely

What are the advantages of Assist Control?

• Reduced work of breathing

• Allows patient to increase Vmin

What are the disadvantages of Assist Control?

• Potential for inappropriate hyperventilation (too much volume too often can result in this)

  • Leads to possibility of respiratory alkalosis (higher ph)

• Airway pressures vary w/ changes in lung compliance (lung elasticity) → varying of pressures may be too much for patient to handle

What is Synchronized IMV (SIMV)?

• Modified/Improved IMV

• Partial ventilatory support

• 3 breath types are used:

  • Mandatory breath: a minimum number of fully assisted breaths per minute. Machine breaths can be patient- or time triggered, are flow limited, & volume-cycled

  • Synchronized breaths: Patient’s spontaneous inspiration + the machine breath (at or near the time of the mandatory breath)

    • If the patient’s breath is a bit quicker than anticipated, the machine senses the patient’s breath, synchronizes w/ it, & waits until exhalation has completed to deliver it’s next breath

  • Patient’s spontaneous breath w/o machine assist (in-between mandatory breaths)

What are the advantages of SIMV?

• Decreases “air-stacking” issue of IMV

• Helps preserve respiratory muscle strength

• Decreases risk of barotrauma (too much pressure can cause lungs to burst

• Facilitates weaning

What are the disadvantages of SIMV?

• May be longer weaning times when compared to trach patients w/ t-pieces

• NOTE: SIMV = A/C for the patient w/ weak respiratory drive

What is Pressure Support Ventilation (PSV, PS)?

• Flow-cycled

• Supplements/Aids spontaneous breathing by supplying preset positive pressure during the full INSPIRATION to overcome airway resistance / dead space

  • Higher pressure → large tidal volume delivered

• Can be used w/ OR w/o other ventilator modes

  • Often see AC + PS, & SIMV + PS

• If used, might be set higher than PEEP setting

What are the advantages of PSV, PS?

• Reduced WOB

• When used w/ intubated patients can help compensate for small lumen of ET tube

What are the advantages of PSV, PS?

• Barotrauma (too much pressure)

• Can deeter weaning bc patient cannot work as hard

(Internal Ventilator Monitoring) Machine Alarms:

• Low pressure in the system (disconnection)

• High pressure → increased airway resistance

  • May happen w/ use of Passy Muir Valve

• Power failure

• Exhaled tidal volume issue

• Apnea

External Ventilator Monitoring:

• Clinical Judgement!

  • Chest Movement

  • Auscultaion

    • Diminished or absent breath sounds?

    • Unusual breath sounds like wheezing, or crackles?

  • Pulse Oximetry = Oxygen saturation of Hemoglobin

  • Capnography (PetCO2) = level of CO2 exhaled (that passes across the sensor in the vent tubing!)

    • should, but doesn’t always correlate w/ PaCO2 in the blood

  • Transcutaneous Oxygen/CO2 monitoring

Arterial Blood Gases:

• Blood drawn & send to lab for analysis

  • PaO2 & PaCO2

• Measures only that point in time when blood was drawn

Ventilator Weaning:

• Some facilities have protocols; some don’t

• Some facilities have “Weaning Teams”

  • Typically includes an SLP

• Generally:

  • Intubated patient? Spontaneous Breathing Trial; if ok, then, off the vent

  • Trached patient?

    • Progression from AC → SIMV → CPAP or Weaning Trials

      • Weaning trials = time off the ventilator (some facilities call “sprinting”)

    • If initially tolerated, then, time off is slowly increased over the course of days/weeks

    • Alternate the amount of time off/time on

    • May progress to off all day, on at night only, then, off completely

Trach Weaning:

• “Decannulation” - removing trach

  • some facilities have protocols; others don’t

• Progressive reduction in trach size (ex: 8 to 6 to 4)

• Cuffed or cuffless

  • Or, cuffed to fenestrated trach (if that’s what ur facility uses) (TRY TO DISCOURAGE FENESTRATED)

• Speaking Valve Trials

• Capping Trials

What are Capping Trials?

• Progressively increase the time patient can tolerate being capped

• Some facilities have a 3-day protocol:

  • Speaking valve x 48 hours

  • Cap x 24 hours

  • Decannulate

Weaning Issues:

• Nutrition

• Aspiration PNA

• Anxiety

Nutrition:

• High caloric demands

• Must be able to maintain adequate nutrition orally or need DHT or PEG

  • swallowing is affected by Trach & Vent

  • how much swallowing is affected depends on the person

Aspiration PNA:

• Colonization of bacteria on the ET tube or trach

• Reflux

• Oral diet

Anxiety:

• Sense of dependency on the machine; fear of going off it

• Fear of decannulation –not having access for “pulmonary toilet,” i.e., pulmonary hygiene via suctioning

Psychosocial Considerations:

• Loss of control of the most basic function

• Fear of not being able to breathe

• Inability to communicate

• Body Image from Trach

• Isolation

  • Patient & Caregiver