Mechanical Ventilation: The Basics and Beyond

Presented By:

Diana Gedamke, BSN, RN, CCRN

Marion College - Fond du Lac

Mechanical Ventilation

“…an opening must be attempted in the trunk of the trachea, into which a tube of reed or cane should be put; you will then blow into this, so that the lung may rise again…and the heart becomes strong…”

Andreas Vesalius (1555)

Mechanical Ventilation

• First described in 1555

• First used in patient care during the polio epidemic of 1955

• Medical students became human ventilators

• First positive pressure ventilator was used at Massachusetts General Hospital

Indications for MV

• Acute Respiratory Failure (66%)

• Coma (15%)

• Acute Exacerbation of COPD (13%)

• Neuromuscular Disorders (5%)

Esteban et al. How is mechanical ventilation employed in the intensive care unit? An international utilization review. Am J Respir Crit Care Med 2000;161: 1450 - 8.

Indications for MV

• Acute Respiratory Failure– ARDS– Heart Failure– Pneumonia– Sepsis– Complications of Surgery– Trauma

Objectives of MV

• Decrease WOB

• Reverse life-threatening hypoxemia or acute progressive respiratory acidosis

• Protect against ventilator-induced lung injury

• Wean and extubate as soon as possible

Caring for the Mechanically Ventilated Patient

• Endotracheal tube • Position

• Stability

• Cuff inflation

• Patency

• Oral cavity• Trauma to lip and palate

• Secretions

Caring for the Mechanically Ventilated Patient

• Patient Position• Patient-Ventilator Synchrony• Physical Assessment

– VS, General assessment, breath sounds

• Ventilator Mode• Alarms• Reason for intubation

– MV in disease states

• Does patient still need to be intubated and mechanically ventilated?

Endotracheal Tube

• Nasal or oral• Size (6 – 8.5 cm)• Position

– 21 cm from the teeth in women & 23 cm in men

– Confirm position by CXR (even when breath sounds are bilateral)

– 3 - 5 cm above carina

• Affects of head position

Endotracheal Tube

• Position– End Tidal CO2 to confirm ETT placement

Normal Airway

Endotracheal Tube Positioning

Complications of Intubation and Mechanical Ventilation

• Sinusitis - occurs in > 25% of patients ventilated > 5days; nasal > oral; subtle findings (unexplained fever & leukocytosis), polymicrobial

• Laryngeal damage - ulceration, granulomas, vocal cord paresis, laryngeal edema

• Aspiration/Ventilator-associated pneumonia - occurs despite cuffed tube

• Tracheal necrosis - tracheal stenosis, tracheomalacia

• Death – ventilator malfunction/inadvertent

disconnection/endotracheal tube dysfunction/VAP

Preventing Infection

• Sterile suctioning – assess as routine part of assessment; only

suction when patient needs it

• Elevate HOB to 45 degrees

Positive Pressure Ventilation

• Volume-cycled ventilation

• Pressure-preset ventilation

PB 7200

Volume-cycled Ventilation

• Delivers a preset volume of gas with each machine breath—airway pressures increase in response to the delivered breath

• Airway pressures are higher in patients with low compliance or high resistance—high pressures indicate risk of ventilator-induced lung injury

Spontaneous Breathing vs. Positive Pressure Ventilation

Volume-cycled Ventilation

• Assist Control (AC)

• Synchronized Intermittent Mandatory Ventilation (SIMV)

Assist-control (AC)

• Most widely used mode of MV

• Delivers a minimum number of fixed-volume breaths

• Patients can initiate extra assisted breaths (will get full set volume with each effort)

Pressure-time TracingsAssist Control Mode

Synchronized Intermittent Mandatory Ventilation (SIMV)

• Delivers preset number of fixed-volume breaths

• Patient can breathe spontaneously between breaths (rate and depth determined by patient)

• Patients often have trouble adapting to intermittent nature of ventilatory assistance

Pressure-time TracingsSIMV Mode

Pressure-preset Ventilation

• Delivers a predefined target pressure to the airway during inspiration

• Resulting tidal volume (VT) and inspiratory flow profile vary with the impedance of the respiratory system and the strength of the patient’s inspiratory efforts

• Includes pressure-control (PC) and Pressure support (PS)

Pressure-control (PC) Ventilation

• Delivers a preset gas pressure to the airway for a set time and at a guaranteed minimum rate

• Patient can breathe in excess of set rate

• Tidal volume achieved depends on pressure level, lung mechanics, and patient effort

• Inspiratory flow rate variable

Pressure Support (PS)

• Delivers preset airway pressure for each breath

• Variable parameters: Inspiratory and expiratory times (respiratory rate), flow rate, and tidal volume (VT)

SIMV + PS

• Spontaneous breaths allowed in SIMV are assisted by PS

New Modes of MV

• New modes often introduced

• Involves nothing more than a modification of the manner in which positive pressure is delivered to the airway and of the interplay b/n mechanical assistance and patient’s resp effort

• Goals: enhance respiratory muscle rest, prevent deconditioning, improve gas exchange, prevent lung damage, improve synchrony, foster lung healing

Ventilator Settings

• Respiratory rate• Tidal volume

• FiO2

• Inspiratory:Expiratory (I:E) ratio• Pressure limit• Flow rate • Sensitivity/trigger• Flow waveform

Inspiratory Flow (V) Waveform

Square waveform Decelerating Waveform

(constant flow) (decelerating flow)

Inspiratory Flow (V) Waveform

• Square waveform: volume of gas is evenly distributed across inspiratory time. Has highest peak pressure and lowest mean airway pressure. Ideal for those at risk for autopeeping due to short inspiration time

Inspiratory Flow (V) Waveform

• Decelerating waveform: Volume of gas flow is high at the beginning of inspiration then tapers off toward the end of the breath. Has lowest peak pressure and highest mean airway pressure. Increased inspiratory time; useful in ARDS.

Patient-Ventilator Synchrony

• Check for: – Symmetric chest inflation– Regular breathing pattern– Respiratory rate < 30 bpm– Synchrony between patient effort and machine

breath– Paradoxical breathing

Patient-Ventilator Synchrony

• Inspiratory effort expended by patients with acute respiratory failure is 4 - 6 x normal

• Don’t eliminate respiratory effort: causes deconditioning and atrophy

Patient-Ventilator Asynchrony

• Possible causes:– Anxiety or pain– Ventilator settings may not be appropriate:

check ABG and alert individual responsible for ventilator orders

– Auto-PEEP– Pneumothorax

Ventilator Alarms and Common Causes

High Pressure Low Pressure Low Exhaled Volume

Kink in tubing

Patient biting ETT

Ventilator disconnected from ETT

Pressures exceeding high pressure limit

Secretions Cuff leak Cuff leak

Coughing Extubation Ventilator disconnected

Bronchospasm

Foreign body

Definitions

• PEEP – positive-end-expiratory pressure applied during mechanical ventilation

• CPAP - continuous positive airway pressure applied during spontaneous breathing

PEEP

• Improves oxygenation - increases functional residual capacity (FRC) above closing volume to prevent alveolar collapse

– permits reduction in FIO2

• Reduces work of breathing

• Increases intrathoracic pressure - decreases venous return to right heart - decreases CO

• Titrate to least amt. necessary to achieve O2 sat > 90% or PO2 > 60 mm Hg with FiO2 < 0.6

Auto-PEEP

• Auto-PEEP/intrinsic PEEP (PEEPi)/inadvertent PEEP/occult PEEP - positive end expiratory alveolar pressure occurring in the absence of set PEEP. Occurs when expiratory time is inadequate.

Assessing Flow Waveform for Presence of Auto-PEEP

Resistance and Compliance

Definitions

• Peak Airway Pressure (Ppk)– An increase in Ppk indicates either an increase in

airway resistance or a decrease in compliance (or both).

• Plateau Pressure (Ppl) - end-inspiratory alveolar pressure

Airway Pressure Analysis

Ventilator-Induced Lung Injury

• High volumes and pressures can injure the lung, causing increased permeability pulmonary edema in the uninjured lung and enhanced edema in the injured lung

• Alveolar overdistention + repeated collapse and re-opening of alveoli

Mechanical Ventilation in Obstructive Lung Disease

• resistance to expired flow

• results in air trapping/hyperinflation

• hyperinflation may result in cardiopulmonary compromise

• Goal: meet minimal requirements for gas exchange while minimizing hyperinflation

• Allow increased time for expiratory flow

Increasing Time for Exhalation

• Decrease inspiratory time– Increase flow rate– Square waveform

• Decrease minute ventilation (VE)– RR x TV

Monitoring Patients with Obstructive Lung Disease Requiring Mechanical

Ventilation

• Monitor plateau pressure: in general, Pplat < 30 cm H20 to decrease risk of hyperinflation and alveolar overdistension

• Permissive hypercapnia

Respiratory Failure Due to Asthma

• Watch for overventilation post intubation • High Ppk common• May require sedation to establish synchronous

breathing with ventilator• Avoid paralytics• Ventilate as stated above (Increase exhalation time

by decreasing RR and TV, increasing inspiratory flow rate, and using square waveform)

• May want to use SIMV

Respiratory Failure Due to COPD

• Ppk typically not as elevated as in asthma; when it is, think other pathologic processes

• Many patients with COPD have chronic hypercapnia; ventilatory support titrated to normalize pH and not PCO2

• Small levels of set PEEP may decrease WOB• May try NIPPV

Noninvasive Positive Pressure Ventilation (NIPPV)• Cooperative patient• Functionally intact upper airway• Minimal amount of secretions• Done by full face or nasal mask• Watch for gastric distension; may increase risk of

aspiration• May use standard ventilators• Monitor patients closely for decompensation and

need for intubation

Non-recruitable

Recruitable

Normal

ARDS: A Three Lung Unit Model

Respiratory Failure Due to ARDS

• Refractory hypoxemia

• Avoid ventilator induced lung injury– pressure-limited approach

• keep Pplat < 30 cm H20

• small tidal volumes (6 ml/kg)

– permissive hypercapnia

• Avoid O2 toxicity; apply moderate levels of PEEP

ARDS

• May need to increase inspiratory time

• Inverse ratio ventilation (IRV)– I:E > 1:1– May require sedation/paralysis– Use as second-line strategy if PEEP fails to

improve oxygenation

Mechanical Ventilation in Patients with Neuromuscular

Weakness• Present with acute or subacute respiratory failure, usually

with hypercapnia

• progressive neurologic dysfunction (amyotrophic lateral sclerosis, muscular dystrophies, Guillain-Barre, CNS dysfunction due to head injury or drug ingestion)– usually ventilated without difficulty unless RF is complicated by

secondary conditions (atelectasis or pneumonia)

– lung compliance and gas exchange remain relatively normal

Does My Patient Still Need to Be Intubated and Mechanically Ventilated?• Evaluate daily when patient is

hemodynamically stable and improving

• Use “weaning checklist”

Discontinuation of MV

• Most (80 - 90%) are able to have MV discontinued after reversal of physiologic process requiring support

• No single approach to weaning has been shown to be better than any other

• A particular approach, when improperly applied, can prolong process

• General rules: work, rest, feed, allow to sleep

Weaning “Checklist”

1. Patient status• Reversal of physiologic derangements requiring ventilatory

support • Globally improving patient

2. Mental status• Alert, cooperative, able to follow commands

3. Secretions/airway protection• Absence of copious, thick, secretions• Patient ability to handle secretions/protect airway/intact gag

reflex

Weaning “Checklist”

4. Oxygenation• In general, need Pa02 > 60 torr (SaO2 >90%) on

FiO2 < = 0.4 and PEEP < = 5.0 cm H2O

5. Ventilation • Baseline PCO2 achieved with Ve < 12 L/min• Rapid shallow breathing index, f/VT < 100 during

spontaneous breathing (VT is in liters, e.g. 25/.4 = 62.5 with Ve = 10 L/min is predictive of success)

Weaning “Checklist”• If criteria 1 – 5 are met, decrease ventilatory support by,

decreasing pressure support, or a trial of CPAP or t-piece. If tolerating after 2 hours, extubate.

• If any of the above criteria are not met, continue ventilatory support and correct physiologic derangements (see below).

• With regard to #5 (ventilation), if f/VT > 100, there is inadequate strength (assessed by NIF) or excessive ventilatory load (assessed by compliance) or both. (The patient must be strong enough for any given load to maintain spontaneous respirations.)

Weaning “Checklist”

• NIF must be more negative than –25 cm H2O• If not, increase strength (check TFTs, nutrition,

Ca, Mg, PO4, K, avoid fatigue, avoid lung hyperinflation,? paralytics, ? aminoglycosides, ? critical illness polyneuropathy)

• Increased ventilatory load – what is causing decreased compliance? (ARDS, pulmonary edema, pneumonia, atelectasis)

Weaning Methods

1. Trials of spontaneous breathing alternating with full ventilatory support

2. SIMV (longer than spontaneous breathing and PS)

3. PS

Weaning• Monitor clinical parameters: HR, RR, subjective

distress, pulse oximetry, cardiac rhythm• If patient deteriorates either clinically or

physiologically, terminate weaning trial• In general, initiate only one weaning trial in a 24-

hour period

Extubation• Reliable indices are not available• LOC• Gag• Cough• Secretions• Head lift• Do early in day• Suction and re-intubation equipment • Laryngeal edema, laryngeal spasm

Re-intubation

• 10 - 20% of patients require re-intubation

• Mortality in these patients is > 6x as high as mortality among patients who can tolerate extubation

Case Study• You are the ICU nurse picking up Mr.

James, who was admitted and intubated yesterday for pneumonia. You enter the room and notice that he is tachypneic and restless. His ventilator settings are: AC, rate 14, VT 700, FiO2 60%. He is currently breathing at a rate of 24. His O2 sat is 100%.

Case Study

• What lab test would you check to assess his ventilatory status?

• ABG

• What are possible causes of his increased respiratory rate?

• Secretions, anxiety, pain, vent settings may not be appropriate

Case Study

• ABG results: pH 7.48, PCO2 28, pO2 120

• Based on the ABG, his vent settings are changed to SIMV, rate 10, PS +10, VT 700, FiO2 40%. How will these settings help Mr. James?

Case Study

• You are the ICU nurse caring for a patient that was intubated for an exacerbation of COPD. When you enter the room, you notice that the patient is breathing out of synchrony with the ventilator and appears agitated and restless. The high pressure alarm is sounding. What could be the possible causes?

Case Study

• Secretions, wrong vent settings (possible hyperinflation), anxiety

Case Study

• You start your shift at 7:00 am and are picking up a patient that has been intubated for over a week for ARDS. You are told that he is doing well and may be able to be weaned today. When you complete your assessment, what will you specifically look at to report on rounds?

Case Study

• Patient status

• Mental status

• Secretions/airway protection

• Oxygenation

• Ventilation

Case Study

Patient status• Reversal of physiologic derangements requiring ventilatory

support • Globally improving patient

2. Mental status• Alert, cooperative, able to follow commands

3. Secretions/airway protection• Absence of copious, thick, secretions• Patient ability to handle secretions/protect airway/intact gag

reflex

Case Study

Oxygenation• In general, need Pa02 > 60 torr (SaO2 >90%) on FiO2

< = 0.4 and PEEP < = 5.0 cm H2O

5.Ventilation • Baseline PCO2 achieved with Ve < 12 L/min

• Rapid shallow breathing index, f/VT < 100 during spontaneous breathing (VT is in liters, e.g. 25/.4 = 62.5 with Ve = 10 L/min is predictive of success)

Case Study

• Increase strength: check TFTs, nutrition, Ca, Mg, PO4, K, avoid fatigue, avoid lung hyperinflation,? paralytics, ? aminoglycosides, ? critical illness polyneuropathy

• Decrease load: ARDS, pulmonary edema, pneumonia, atelectasis

Case Study

– Your patient with ARDS remains hypoxemic despite a high FIO2. What are other strategies to improve oxygenation?

– Increase PEEP, check HBG, prone positioning, change vent settings to increase inspiratory time

Case Study Question

• In caring for a ventilated patient, what strategies should you use to decrease the risk of VAP?

• Closed suctioning only when needed

• Frequent oral care

• Upright patient

Case Study Question

• Your intubated patient is requiring moderate amounts of PEEP to improve oxygenation. Discuss strategies to decrease the risk of complications from increased PEEP.

• Increase volume, vasopressors, positive inotropic therapy, may need to decrease PEEP

Case Study

• You are caring for a patient that was intubated for hypoxemic respiratory failure due to ARDS. Initial vent settings are AC, RR 18, TV 10 cc/kg, PEEP 7.5 cm H2O. On these settings, her Ppk is 45 cm H2O and Pplat is 38 cm H2O. There is no auto-PEEP. ABG is PO2 70 mm Hg, PCO2 46 mm Hg, and pH 7.32. Which of the following ventilator changes would you make first?

Case Study

A) decrease FiO2

B) decrease TV

C) increase PEEP

D) decrease inspiratory flow rate

E) change to pressure control

ReferencesTobin MJ. Advances in mechanical ventilation. N Engl J

Med, Vol. 344, No. 26, June 28, 2001.

Hall et al. Principles of Critical Care (2nd ed). 1999. (MV chapter)

Campbell RS et al. Pressure-controlled versus volume-controlled ventilation: does it matter? Resp Care 2002 (47;4)416 - 426.