Effects of MV

1

Mechanical Ventilation

Effects of MechanicalVentilation

2

Cardiovascular Effects

PPV ↓ QT ↑ HR↑ contractilityvasoconstriction

maintain BP

1. ↑ intrathoracic pressure2. card. tamponade effect3. loss of +/- press chg in

lungs w/spont breathing

normal

3

Blood Pressure DropDrops if:• normal compensatory mechanism lost

– Anesthesia, sedation– Polyneuritis– Anti-adrenergic drugs

• Catapres, Aldomet, Inderol, etc.

• hypovolemia

Effects of MV

2

4

Cardiovascular Effects

PPV ↓ QT ↑ HR↑ contractilityvasoconstriction

maintain BP

↓ BP

1. ↑ intrathoracic pressure2. card. tamponade effect3. loss of +/- press chg in

lungs w/spont breathing

normal

5

Fix Drop in BP• Patient positioning• IV fluids• digitalis• Dopamine• Dobutamine• Levophed• epinephrine

6

Cardiac Output Drop• will be greater:

– 1

– 2

– 3

Effects of MV

3

7

To lessen drop in QT

• 1-

• 2-

• 3-

8

Why Maintain BP?decreased QT & BP

⇓

9

Assessment of Cardiovascular Effects

• Blood pressure– normal =

• Cardiac output– normal =

Effects of MV

4

10

ICP and Cerebral Perfusion• Amount of blood flow to the brain

determined by:– 1-– 2-– 3- **– 4- **

11

Cerebral Perfusion Pressure

€

CPP = BP - ICP

€

BP = systolic + (2 X diastolic)3

normal CPP =

12

Decreased CPP

Decreased CPP → ↓ cerebral blood flow⇓

cerebral hypoxemiacerebral edema

Effects of MV

5

13

Causes of ↓ CPP• ↓ BP

– uncommon inhead injury

– seen morewith spinalinjuries andmultipletrauma

• ↓ QT– CMV– PEEP– CPAP– Hemorrhagic

shock– Heart failure

• Vasodilation

14

Causes of ↓ CPP• ↑ ICP

(pressure in CSF in subarachnoidspace, ventricles)

15

Intracranial Pressure• Skull is closed container• Contains brain, blood, CSF• Room for some expansion but not much• Any increase in volume of 1 content

without a decrease in volume of another→

Effects of MV

6

16

Intracranial Pressure• Normally: if blood or brain volume ↑,

same volume of CSF is displaced sothat ICP is maintained =

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Intracranial Pressure↑ ICP → compresses brain tissue

⇓

↓ cerebral blood flow ⇓↓ if sustained → irreversible brain

damage & death

18

Causes of ↑ ICP• Closed head injury• Tumors• Craniotomy• Cerebral hemorrhage• CVA (ABI)• Reyes Syndrome• Meningitis• Encephalitis• Near-drowning or any

severe anoxic episode

• CMV w/PEEP• Cough• Valsalva maneuver• Trend position• Elevated CVP• Hypoventilation (↑PaCO2)• Acidosis• Profound hypoxia• Vasodilating drugs

Effects of MV

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Prevent ↑ ICP• Maintain BP if patient is at risk for

increased ICP

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↓ Elevated ICP• head near mid-line, no pillow, HOB↑ 30-45°

• sedatives, muscle relaxants• low PEEP if possible• hyperventilation ** → ↑ pH → cerebral

vasoconstriction– PaCO2 25-30 mmHg X 24-48 hrs.

21

↓ Elevated ICP• hyperosmolar agents (osmotic diuretics)

– reduce brain water– reduce total body water– Mannitol

• loop diuretics– furosemide (Lasix)– acetazolamide (Diamox)

Effects of MV

8

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↓ Elevated ICP• barbiturate coma

• use of steroids is controversial• removal of CSF in some cases• hypothermia

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Assessment of ICP• 1-

• 2-

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Renal Effects

Positive pressure ventilation has 3 renaleffects………..

Effects of MV

9

25

Renal Effects1 decreased cardiac output

⇓↓ renal blood flow↓ glomerular rate

⇓⇓

26

Renal Effectsredistribution of blood inside kidney

⇓2

27

Renal Effects

↑ release of Antidiuretic Hormone (ADH)⇓

3

2 mechanisms:• receptors in LA sense ↓ blood volume → ↑ ADH

• receptors in carotid bodies, aortic arch sense chg inblood pressure, intrathoracic pressure → ↑ ADH

Effects of MV

10

28

Renal Effects• ABGs also affect renal function:

– ↓ PaO2 →

– ↑ PaCO2 →

29

Assessment of Renal Function• I & O

• BUN– 1-– 2-– Normal =– 4-

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Assessment of Renal Function• Creatinine

– Metabolic waste-product– Normal = < 2 mg/dl– Increased in renal failure– More sensitive than BUN

Effects of MV

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Assessment of Renal Function• Osmolarity

– Particles in solution– Renal failure → retain H2O → particles

diluted → ↓ osmolarity in blood, ↑ in urine

• Specific gravity– 1/∝ urine output– Normal =

32

Hepatic System• Liver

– 1-

– 2-• Dysfunction caused by:

– 1-

– 2-

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Assessment of Hepatic System• Bilirubin

– Produced by breakdown of RBC

Hgb → bilirubin + heme ↓ ↓ converted to H2O used to make soluble by liver new RBC

↓broken down by bacteria in intestines

– Normal =– If increased →

Effects of MV

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Assessment of Hepatic System• Total serum protein

– Normal =– Albumin =– ↓ albumin →– ↓ total protein →

• Skin color• Mental status

35

Gastric, Splanchnic EffectsPPV →↑ resistance to blood flow

↓

may contribute to gastric mucosal edema ↓ ↓

GI bleeding altered GI function & bowelabsorption properties

↓

malnutritionprotein depletionaltered healing

metabolic acidosis ← diarrheafluid depletion

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Assessment• 1-

• 2-

• 3-

• 4-

• 5-

Effects of MV

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Neurological Effects• Neuro system affected by

– Hypoxia– Decreased QT– Changes in acid-base status– Build-up of metabolic waste products– Decreased glucose levels

38

Neurological Effects• PPV can → ↑ ICP if:

venous pressure ↑ QT ↓

⇓

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Assessment• Observe ventilatory pattern• Airway reflexes• Response to pain• Purposeful movement• Anxiety level, restlessness• Level of consciousness (Glascow Coma

Scale)

Effects of MV

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Glascow Coma Scale

54321

Oriented and conversesDisoriented and conversesInappropriate wordsIncomprehensible soundsNo response

Bestverbalresponse

654321

Obeys verbal commandLocalizes painful stimuliFlexion/withdrawal to painDecorticate response to painDecerebrate response to painNo response to pain

Bestmotorresponse

4321

Open spontaneouslyOpen to verbal commandOpen to painNo response

Eyes

RATINGRESPONSETEST

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Pulmonary Effects• Ventilation• Pulmonary Perfusion

To theBlackboard!

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Pulmonary Effects

• V/Q mismatch → ↑ VD

• ↑ shunt

Effects of MV

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Pulmonary Effects - PVR

• ↑ airway pressure thinning & → compression

↑ alveolar pressure of capillaries ↓

44

However -• If TE long enough & no PEEP or exp

resistance, the drop in pulmonaryperfusion is offset by normal flow duringexp == no net effect on PVR

45

Remember!Severe hypoxia ⇒ ↑ PVR by

vasoconstriction causing pulmonary hypertension

⇓if PPV improves oxygenation

⇓reverses vasoconstriction

Effects of MV

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46

Using PEEP When FRC ↓

• Alveoli open improving V/Q

• If too high: CL ↓ & PVR ↑

47

Effect on Ventilatory Status• Goal of eucapneic ventilation is not

achieved if ventilator is mismanagedinducing abnormalities– Hypoventilation– Hyperventilation

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Effect on Ventilatory StatusHypoventilation ◊ ↓ PaO2

® 〈↑ PaCO2 〈 ® right shift oxyHgb curve↓ pHcellular damagecoma↑ plasma K+ ◊ cardiac dysfunctioncerebral vasodilation ◊ ↑ ICP

Effects of MV

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Rx Hypoventilation

• 1-

• 2-

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Effect on Ventilatory StatusHyperventilation

®↓ PaCO2

® left shift oxyHgb curve↑ pH↓ plasma K+ ◊ cardiac arrhythmiascerebral vasoconstriction ◊ ↓ ICPif sustained ◊ tetany↓ drive to breathe = “alkalotic apnea”

51

Rx Hyperventilation

• 1-

• 2-

Effects of MV

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Body Position

• Change position frequently to avoidatelectasis

• If unilateral lung disease - place patienthow?

53

Hazards of O2 Therapy• O2-induced bradypnea

– Hypoxic drive (COPD)– Problem if inadequate ventilation not

provided

54

Hazards of O2 Therapy• Absorption atelectasis

– Esp. if FIO2 > 0.70– Leads to shunt

Effects of MV

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Hazards of O2 Therapy• Oxygen toxicity

– Adults: FIO2 > 0.60 > 6 hrs ⇒ damage topulmonary tissue

– Infants: PaO2 > 80 mmHg ⇒ ROP– Best to use least FIO2 necessary– Use PEEP if FIO2 > 0.60

56

Barotrauma• Normal lungs can withstand 80-

140 cmH2O• Increased risk of barotrauma with:

– High MAP, high PIP, large VT with PEEP• Monitor CL• Pneumothorax, pneumomediastinum,

pneumopericardium,pneumoperitoneum, subcutaneousemphysema

57

Metabolic Acid-BaseImbalance• Happens when PaCO2 is near patient’s

normal but pH is not -

pH 7.20PaCO2 40 mmHgHCO3

- 15 mEq/l

Effects of MV

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Metabolic Acidosis• May require administration of bicarb -

€

mEq req = base deficit x BWK4

•Give 1/2, then repeat ABG•Treat cause

59

Metabolic AlkalosispH 7.58PaCO2 40 mmHgHCO3

- 32 mEq/l

• 1-• 2-

60

Mechanical Failure• Good monitoring• Alarms on & functioning

Effects of MV

21

61

Psychological Complications• Patients in ICU are very ill

– High noise level– Patient-staff interaction– 24 hrs of “day”– Isolation from family

• Leads to– Acute sleep deprivation– Increasing confusion– Lethargy– Less responsiveness

62

Psychological Complications• Now add ventilator, lose control over:

– Breathing– Mobility– Privacy– Speech– Eating

63

Psychological Complications• Plus, inadequate knowledge of

– Machines– Tubes– Monitors– Alarms

• Decreased confidence in staff

Effects of MV

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64

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To Help• EXPLAIN• Talk to• Calendars, clocks• Windows• Quiet periods• Coordinated care• Communication boards

66

Nutritional Complications• Critical illness need ↑ nutrition• If malnourished -

– Altered healing of wounds, infections– Weakened respiratory muscles– Decreased surfactant production– Decreased albumin levels

• Overfeed → ↑ VO2, ↑VCO2

• Feed emulsified fats