Building a Solid Building a Solid Understanding of Understanding of

Mechanical VentilationMechanical VentilationBy Chris Kallus, RRT, MEdBy Chris Kallus, RRT, MEd

Nursing2009,Nursing2009, June 2009 June 20092.5 ANCC contact hours2.5 ANCC contact hours

Online: www.nursingcenter.comOnline: www.nursingcenter.com

© 2009 by Lippincott Williams & Wilkins. All world rights reserved.© 2009 by Lippincott Williams & Wilkins. All world rights reserved.

Mechanical ventilationMechanical ventilation

More patients who are mechanically ventilated More patients who are mechanically ventilated are on general unitsare on general units

Follow facility’s procedures and protocolsFollow facility’s procedures and protocols

Assess Assess patient firstpatient first when problems arise when problems arise

Obtain physician orders as appropriateObtain physician orders as appropriate

Work with respiratory therapists when making Work with respiratory therapists when making ventilator changesventilator changes

Relationship between ventilator Relationship between ventilator settings and arterial blood gas settings and arterial blood gas

Step 1: Evaluate pH and PaCOStep 1: Evaluate pH and PaCO22

Step 2: Evaluate PaOStep 2: Evaluate PaO22 and FIO and FIO22

Step 3: Determine the solutionStep 3: Determine the solution

Step 1: Evaluate pH and PaCOStep 1: Evaluate pH and PaCO22

Hypoventilation causes patient’s pH to Hypoventilation causes patient’s pH to drop and PaCOdrop and PaCO22 to rise to rise

Hyperventilation, pH is >7.45; PaCOHyperventilation, pH is >7.45; PaCO22 is is <35 mmHg<35 mmHg

Changing “minute ventilation” setting will Changing “minute ventilation” setting will help get values back to normalhelp get values back to normal

Step 1: Evaluate pH and PaCOStep 1: Evaluate pH and PaCO22

““Minute ventilation” is determined by Minute ventilation” is determined by multiplying tidal volume by ventilator rate; multiplying tidal volume by ventilator rate; expressed as Veexpressed as Ve

Tidal volume is based on patient’s ideal Tidal volume is based on patient’s ideal body weight (IBW)body weight (IBW)

Normal tidal volume is between 10 and 12 Normal tidal volume is between 10 and 12 mL/kg of IBWmL/kg of IBW

Large tidal volumes can cause ventilator-Large tidal volumes can cause ventilator-induced lung injuryinduced lung injury

Calculating IBWCalculating IBW

Patients of different weights can have Patients of different weights can have same lung size; calculating IBW (in lbs) same lung size; calculating IBW (in lbs) helps choose right tidal volume helps choose right tidal volume

Men: 106 + 6(height in inches-60)Men: 106 + 6(height in inches-60)

Women: 105 + 5(height in inches-60)Women: 105 + 5(height in inches-60)

Lungs under pressureLungs under pressure Best indicator of alveolar overdistension

(too much pressure from mechanically delivered breaths) is peak alveolar pressure, which can be assessed by measuring plateau pressure, or pressure applied to small airways and alveoli during inspiration

Following delivery of tidal volume, you’ll see a number on ventilator called PIP, or amount of pressure it takes to deliver that volume. This number shouldn’t be used for trending or evaluation

Lungs under pressureLungs under pressure If you set ventilator to achieve a breath

hold following delivery of tidal volume, you should see pressure drop from peak to a holding pressure (the plateau pressure; should be 30 cm H2O or less)

If value is higher, overdistension is likely. Every time you perform ventilator check, assess plateau pressure. If value is trending upward or exceeds 30 cm H2O, talk to respiratory therapist about alternative, lung-protective strategies

Lungs under pressureLungs under pressure Alternative strategies include permissive

hypercapnia, airway pressure release ventilation, changing the mode to pressure control ventilation

If patient’s peak inspiratory pressure (PIP) is increasing but plateau stays the same, reason for pressure increase is in ventilator tubing or patient’s tracheobronchial tree

Lungs under pressureLungs under pressure If patient’s PIP is 35 cm H2O and plateau

pressure is 25 cm H2O and an hour later peak pressure is 65 cm H2O but plateau pressure is still 25 cm H2O, patient isn’t in danger of lung damage because reason for high PIP is an increase in airway resistance

Patient may be biting on ET tube or need an inline bronchodilator treatment or suctioning; this is why plateau pressure is more important ventilator pressure to monitor

Lungs under pressureLungs under pressure Transairway pressure is difference

between PIP and the plateau pressure; is typically <10 cm H2O. Investigate any pressure above this level

For example, a sudden increase means an ET tube may be occluded; a more gradual increase may mean patient is developing bronchoconstriction and may need an inline bronchodilator

Step 2: Evaluate PaOStep 2: Evaluate PaO2 2 and FIOand FIO22

Oxygenation status is evaluated by Oxygenation status is evaluated by calculating P/F ratiocalculating P/F ratio

P/F ratio = PaOP/F ratio = PaO22 divided by FIO divided by FIO22

>300 is considered normal>300 is considered normal

Lung injury and values <200 indicate Lung injury and values <200 indicate refractory hypoxemiarefractory hypoxemia

Step 2: Evaluate PaOStep 2: Evaluate PaO2 2 and FIOand FIO22

FIOFIO22 is always expressed as a decimal (ex., is always expressed as a decimal (ex., FIOFIO22 of 1.0 = 100% oxygen) of 1.0 = 100% oxygen)

Only reason to keep FIOOnly reason to keep FIO22 above 100% is in above 100% is in treating carbon monoxide poisoningtreating carbon monoxide poisoning

As delivered, FIOAs delivered, FIO22 increases, PaO increases, PaO22 should should increase; if not, patient has refractory increase; if not, patient has refractory hypoxemiahypoxemia

Step 2: Evaluate PaOStep 2: Evaluate PaO2 2 and FIOand FIO22

P/F ratio is good indicator of how much P/F ratio is good indicator of how much oxygen patient is breathing (FIOoxygen patient is breathing (FIO22) and how ) and how much is moving into circulation (PaOmuch is moving into circulation (PaO22))

In critically ill patients, 3 common causes In critically ill patients, 3 common causes of refractory hypoxemia:of refractory hypoxemia:

- pneumothorax- pneumothorax - atelectasis- atelectasis - pulmonary edema- pulmonary edema

3 Common causes of refractory 3 Common causes of refractory hypoxemiahypoxemia

Pneumothorax - rapid deterioration in Pneumothorax - rapid deterioration in patient condition, absent breath sounds, patient condition, absent breath sounds, high pressure ventilator alarmhigh pressure ventilator alarm

Atelectasis – gradual, usually identified on Atelectasis – gradual, usually identified on chest X-raychest X-ray

Pulmonary edema - may occur in patients Pulmonary edema - may occur in patients with history of heart failure, decreasing with history of heart failure, decreasing SpOSpO22 accompanied by fine crackles in lung accompanied by fine crackles in lung basesbases

3 Common causes of refractory 3 Common causes of refractory hypoxemiahypoxemia

HCP will rule out pneumothorax first as HCP will rule out pneumothorax first as increasing ventilator volume will worsen increasing ventilator volume will worsen pneumothoraxpneumothorax

If atelectasis or pulmonary edema, PEEP If atelectasis or pulmonary edema, PEEP will be addedwill be added

PEEPPEEP

Restores or maintains lung volumeRestores or maintains lung volume

Using PEEP also lets you use lower FIOUsing PEEP also lets you use lower FIO22 to to reach a target PaOreach a target PaO22

Generally, to reduce the risk of oxygen Generally, to reduce the risk of oxygen toxicity, FIOtoxicity, FIO22 should be below 0.5 provided should be below 0.5 provided PaOPaO22 is OK and SpO is OK and SpO22 is 92% or higher is 92% or higher

Step 3: Determine the solutionStep 3: Determine the solution

Goal is PaOGoal is PaO22 60 to 100 mmHg 60 to 100 mmHg

Pulse oximetry values are best used for Pulse oximetry values are best used for trending rather than spot-checking trending rather than spot-checking oxygenationoxygenation

Follow facility protocol and work with Follow facility protocol and work with respiratory therapist to make ventilator respiratory therapist to make ventilator changeschanges

Ventilator modesVentilator modes

Assist/control - tidal volume delivered in Assist/control - tidal volume delivered in response to every patient effort; can be response to every patient effort; can be used in most patients except those with used in most patients except those with COPD due to risk of hyperinflation of lungsCOPD due to risk of hyperinflation of lungs

SIMV - delivers tidal volume only at a set SIMV - delivers tidal volume only at a set time interval; patient can breathe in time interval; patient can breathe in between, suitable for all patients, including between, suitable for all patients, including COPDCOPD

Ventilator modesVentilator modes

Continuous positive airway pressure Continuous positive airway pressure (CPAP) - can be used for ventilator (CPAP) - can be used for ventilator weaning, and patients with sleep apnea; weaning, and patients with sleep apnea; basically, PEEP with 10 breaths per minutebasically, PEEP with 10 breaths per minute

Ventilator strategies to deliverVentilator strategies to deliver tidal volume tidal volume

Volume control ventilation - sets tidal Volume control ventilation - sets tidal volume so patient receives same tidal volume so patient receives same tidal volume with each mechanical breath; also volume with each mechanical breath; also called volume target, volume cycled, called volume target, volume cycled, volume limitedvolume limited

ABGs remain constant with this strategyABGs remain constant with this strategy

Ventilator strategies to deliverVentilator strategies to deliver tidal volume tidal volume

Pressure support ventilation (PSV) - sets Pressure support ventilation (PSV) - sets PIP; monitor patient for risk of PIP; monitor patient for risk of hypo/hyperventilationhypo/hyperventilation

Pressure support ventilation (PSV) - add-on Pressure support ventilation (PSV) - add-on strategy for patients with low tidal volume strategy for patients with low tidal volume and mild respiratory distress; adds and mild respiratory distress; adds pressure boost on inspiration, decreases pressure boost on inspiration, decreases work of breathingwork of breathing