HHS CPO Mechanical Ventilation

Ventilation

Movement of air into and out of the lungs during the respiratory cycle (mechanical)

• Does not involve gas exchange

Assessment → Auscultation, CXR, accessory muscle use, pt/ventilator synchrony, cardiovascular stability

Respiration

Movement of gases across a membrane (physiologic). Process of O2 and CO2 exchange in alveoli and in cells

Assessment → ABG, CBC, cardiovascular stability, LOC

Oxygenation-Hb Dissociation Curve

Relationship between blood oxygen levels and hemoglobin saturation

PaO₂ 60mmHg = SpO₂ 90-91%

Compliance

Relative ease in which the lungs inflate

High compliance → Easy to ventilate → Low ventilation pressures

• Increased compliance → emphysema (loss of elastic recoil)

• Decreased compliance → pulmonary fibrosis, pulmonary consoliation, ARDS

Resistance

Amount of resistent to the flow of air through the airways of the lungs during inspriation and expiration → determined by the diameter of airways

Low resistence → easy to ventilate → low ventilation pressures

• Airway resistance comprised of conducting airways, surrounding tissues

• Increased airway resistance → bronchospasm, mucosal edema, secretions, COPD/asthma

Goals of Mechanical Ventilation

• Improve ventilation

• Improve oxygenation

• Decrease WOB

• Provide prophylactic ventilation intra- and post-operatively

Mechanical Ventilation Indications

• Apnea

• Acute respiratory failure

• Impending respiratory failure

• Oxygenation failure

Mechanical Ventilation Contraindications

Advanced directives (i.e. AND)

Ventilator Complications

• Ventilator acquired pneumonia (VAP)

• Ventilator induced lung injury (VILI)

• Alveolar hypoventilation or hyperventilation

• Oxygen toxicity

• Hypotension

ETT Complications

• Vocal cord damage

• Tissue necrosis

• Plugging (secretions)

• Kinking

• Biting

Ventilator Acquired Pneumonia (VAP)

Pneumonia in pt with intermittent or continuous mech ventilation via ETT or tracheostomy tube

VAP Inclusion Criteria

Artificial airway must be in place for 48h prior to onset of infection and in place for at least two consecutive days, and:

• New/worsening/persistent infiltrates, consolidation, cavitation on CXR compatible with pneumonia

One of the following:

• WBC >12000 or <4000

• Temp >38 or <36

And both of the following:

• New onset of purulent sputum, change in sputum characteristics, inc in secretions or suctioning requirements

• Worsening gas exchange (ABGs)

And:

• Pt recieving abx specifically to treat VAP

Caring for VAP

• HOB 30-35

• Closed circuit/ETT/suction system

• Daily assessment of readiness to extubate

• Use oral tubes to access trachea or stomach

• Chlorahexadine oral care

• NIPPV if indicated/possible

• Provide optimal PEEP to prevent atelectasis

Inspiration

Active process, requires closed system

• P_vent > P_lung

• Gas flows along pressure gradient from vent → lungs (pos pressure)

• When pressures are equal, flow into lungs stops and inspiration ends

Expiration

Passive process, when inspiration ends ventilator opens to atmosphere with exhalation valve

• P_lung > P_atm

• Exhaled gas filtered before being released from ventilator

Mode

Method/type of respiratory support provided to patient

• Ventilator controlled breaths

• Patient initiated (triggered) breaths

• Spontaneous breaths

Fraction of Inspired Oxygen (FiO₂)

Percentage of oxygen delivered to pt

Tidal Volume (Vt)

Amount of gas inspired/expired during one respiratory cycle (one breath). Aim for Vt ~ 4-8 ml/kg of PBW

• Mandatory Vt → delivery of specific volume by vent

• Spontaneous Vt → pt determines vol of breath

Minute Volume (MV)

Total amount volume the patient breaths over the course of a minute

• MV = RR x Vt

PEEP

Pressure left in alveoli at the end of exhalation

• Higher PEEP → more gas remaining in alveoli during exhalation

• Intrinsic PEEP of 5 cm H₂O lost with intubation → PEEP must be set

PEEP Indications

• Poor arterial oxygenation despite high FiO₂

• Pulmonary edema

• Pericardial bleeding

• Atelectasis

• Poor lung compliance

PEEP Advantages

• Inc pressure in lungs at end of expiration (increased surface area for gas exchange)

• Improves oxygenation by expanding collapsed alveoli

PEEP Hazards

• Decreased venous return

• ICP

• Increased risk of barotrauma

• Possibility of air trapping

Peak Inspiratory Pressure (PIP)

Highest amount of pressure developed in lungs during inspiration

Mean Airway Pressure (MAP)

Average pressure developed in lungs throughout entire respiratory cycle

• Reflection of lung compliance and resistance

• Both pressures measured in cmH₂O

Pressure Support (PS)

Positive pressure provided during inspiration, only available in modes with spontaneous breaths. Augments spontaneous inspiratory effort to increased Vt

• Reduces WOB

• Measured in cmH₂O, ranges 5-20

Assist/Control (A/C) Mode

Ventilator delivers either mandatory Vt (Volume) or mandatory pressure (Pressure)

• RR set is minimum RR pt will recieve

• Pt can initiate additional breaths, will be at pre-set vol or pressure

A/C Mode Indications

• Pt who may or may not have a drive to breathe

• Operative anesthesia

• Immediately following intubation

• Pt recieving sedation and/or paralytics

• Drug OD

• CNS injury

A/C Volume

Ventilator delivers constant Vt, PIP may vary from breath to breath

Indications → no respiratory complications (“healthy lungs”)

A/C Pressure

Ventilator delivers constant pressure control level (PIP remains constant). Vt may vary from breath to breath

Indications:

• Pt with lung compromise

• Acute lung injury

• High risk for barotrauma

• Lung protective strategy

• To prevent ventilator induced lung injury (VILI)

A/C Volume Advantages

• Volume is constant

• Easy to monitor PaCO₂

• Ability to measure resistance and compliance

A/C Volume Disadvantages

• Must carefully monitor PIP

• Does not satisfy air hunger

• Does not sustain inflation pressures to collapsed areas

A/C Pressures Advantages

• Constant pressure

• Better ability to improve oxygenation

• Initial high flow may satisfy air hunger

• Prevents VILI

A/C Pressures Disadvantages

• Must carefully monitor Vt

• Inspiratory time must be appropriately set

Synchronized Intermittent Mandatory Ventilation (SIMV)

Ventilator delivers either mandatory Vt (SIMV - volume control) or mandatory pressure (SIMV - pressure control). Includes mandatory RR and spontaneous RR.

• RR set is min RR pt will recieve, can add additional spontaneous breaths (vol controlled by pt)

• PS can be added to augment spontaneous Vt

SIMV Indications

• Pt waking from anesthesia/sedation, beginning to make spontaneous efforts

• May not make consistent spontaneous efforts, backup rate present

• Can be used as an intermediate step in ventilator weaning/discontinuance

SIMV Advantages

• Decreased risk of hyperventilation

• Decreased use of sedatives

• Facilitation of weaning process

• Mobilization of respiratory muscles

CPAP with PS (Pressure Support Ventilation)

Completely spontaneous mode of ventilation (pt controls RR, Vt)

• Pressure support added to augment pt’s spontaneous Vt

CPAP with PS Indications

• Final stage of ventilator weaning/discontinuance

• Sometimes used to maintain/support ventilation if pt is uncomfortable or asynchronous on A/C mode

CPAP with PS Advantages

• Allow pt to fully control breathing

• Mobilization of respiratory muscles

• Least effect on cardiac decompensation

Ventilator Weaning

Process of incrementally withdrawing mechanical ventilation support

Weaning Criteria

• Reason for initiating mech ventilation has resolved

• Pt has drive to breathe

• Appropriate ventilator setttings (FiO₂ <0.50, RR <35, PEEP <8cmH₂O)

• Acceptable ABG

• PaO₂/FiO₂ ratio >200

• Rapid shallow breathing index (RSBI → RR/Vt) <105

• Acceptable bloodwork (CBC, lytes)

• Hemodynamic stability

• Adequate nutritional support

• Psycholocially prepared

Assess Weaning Tolerance

• Signs of increased WOB

• Diaphoresis

• Restlessness/agitation

• Central cyanosis

• Cardiopulmonary instability (change in HR by 20% for >5 min, fluctuationi in SBP >5 min, life threatening arrhythmia, angina)

• Decreased LOC

• Decreased drive to breathe

• Deteriorating ABGs and/or SpO₂

Spontaneous Breathing Trial (SBT)

Pt switched from A/C to CPAP/PS mode with minimal settings

• PEEP 5 cmH₂O and PS 5 cmH₂O

• Pt monitored for 30-120 min

• Assess for signs of intolerance

Gradual CPAP with PS wean

Pt switched from AC to CPAP/PS mode

• Initial PS set fairly high to achieve desired Vt (target set on A/C)

• PS gradually decreased based on pt tolerance

• Once PS less than 10 → suggest extubation

Intermittent Weaning Trials

Pt alternates between spontaneous breathing (CPAP/PS) and fully supported ventilation (A/C or CPAP with high PS)

• Weaned 3-4 times/day, time weaning will gradually increase

• Pt rested overnight on A/C or CPAP/high PS

Patient Alarm Causes

• Waking/fighting vent

• Coughing

• Accidental extubation

• Biting/kinked ETT

• Secretions

• Paralytic/sedation

• Compliance/resistance improvement/compromise

• ETT disconnect

• Cuff leak

• Bronchospasm

Circuit Alarm Causes

• Loose connecgtion

• Kinked tubing

• Water in tubing

• Hole in circuit

• Inline suction problems

• Blocked filter

Ventilator Alarm Causes

• Power failure

• Gas failure

• Accidental mode switch

• Inappropriate mode

High Inspiratory Pressure Alarm

Protects pt from barotrauma and informs of changes in lung compliance/resistance

• normally set at 40-45 cmH₂O

• if reached by PIP, vent allows exhalation to occur → pressure released immediately

• Vt may be compromised

High Inspiratory Pressure Alarm Causes

• Coughing

• Secretions

• Kinked ETT or circuit

• Biting ETT

• Asynchronous breathing

• Changes in lung characteristics (low compliance/high resistance)

• Blocked filter/HME

Low Inspiratory Pressure Alarm

Leak in ventilator system or improvement in pt compliance/resistance

• Normally set 10-15 cmH₂O below PIP

• Vt may be compromised

Low Inspiratory Pressure Alarm Causes

• Ventilator disconnect

• Leak in ventilator circuit

• ETT cuff leak

• Improvement in compliance or resistance

Low Exhaled Tidal Volume Alarm

Decrease in pt effort and/or leakage in system

• Usually set 100 ml below set Vt

Low Exhaled Tidal Volume Alarm Causes

• Decrease in spontaneous pt tidal volume (SIMV or CPAP/PS)

• Ventilator disconnect or leak

• Coughing

• ETT kinked or patient biting

• Secretion

Low Minute Volume Alarm

Decrease in Vt and/or RR

• Normally set 1L/min below estimated minute ventilation for pt

Low Minute Volume Alarm Causes

• Decrease in spontaneous Vt (CPAP/PS)

• Ventilator disconnect or leak

Apnea Alarm

Cessation of spontaneous respiratory efforts, normally set to time interval of 20 sec

• If pt doesn’t initiate a breath within 20 sec, ventilator goes to backup → A/C vol or press

Apnea Alarm Causes

• Change in neurological status

• Oversedation

• Lack of drive to breathe

• Pt holding breath