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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
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16
Intracranial Pressure• Normally: if blood or brain volume ↑,
same volume of CSF is displaced sothat ICP is maintained =
17
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
22
↓ Elevated ICP• barbiturate coma
• use of steroids is controversial• removal of CSF in some cases• hypothermia
23
Assessment of ICP• 1-
• 2-
24
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-
30
Assessment of Renal Function• Creatinine
– Metabolic waste-product– Normal = < 2 mg/dl– Increased in renal failure– More sensitive than BUN
Effects of MV
11
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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-
33
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
12
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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
36
Assessment• 1-
• 2-
• 3-
• 4-
• 5-
Effects of MV
13
37
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 ↓
⇓
39
Assessment• Observe ventilatory pattern• Airway reflexes• Response to pain• Purposeful movement• Anxiety level, restlessness• Level of consciousness (Glascow Coma
Scale)
Effects of MV
14
40
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
41
Pulmonary Effects• Ventilation• Pulmonary Perfusion
To theBlackboard!
42
Pulmonary Effects
• V/Q mismatch → ↑ VD
• ↑ shunt
Effects of MV
15
43
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
16
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
48
Effect on Ventilatory StatusHypoventilation ◊ ↓ PaO2
® 〈↑ PaCO2 〈 ® right shift oxyHgb curve↓ pHcellular damagecoma↑ plasma K+ ◊ cardiac dysfunctioncerebral vasodilation ◊ ↑ ICP
Effects of MV
17
49
Rx Hypoventilation
• 1-
• 2-
50
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
18
52
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
19
55
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
20
58
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
22
64
65
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