assissted ventilation in surgical patients Basics of mechanical ventilation for non anesthetists , surgeons needs basic information

1. ASSISTED VENTILATION
IN
SURGICAL PATIENTS
Radhwan Hazem Alkhashab
Consultant anaesthesia & ICU
2021
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2. Mechanical ventilation is a useful modality for
patient who are unable to sustain the level of
ventilation necessary to maintain the gas
exchange function (oxygen & carbon dioxide
elimination).
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3. Is an important tool in intensive care unit. It is
often used to support ventilation and to less
extent to improve oxygenation.
A ventilator is a machine that has no intrinsic
intelligence .
This means your setting what makes the
difference between the two extremes
{improving or killing the patient}.

4. ICU ventilator

5. Use of mechanical ventilation varies greatly
from short term to long term & from acute
care in the hospital to extended care at home.
One of the most frequent uses of mechanical
ventilation is for the management of
postoperative patients recovering from
anesthesia & medications.
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6. Postoperative procedures accounted for 35%
of all patients who were placed on
mechanical ventilation for more than 24h.
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7. Indication for mechanical ventilation
1.Ventilatory failure :Inability of pulmonary system
to maintain proper removal of CO2.
This result in (hypercapnia ) a high blood PCO2 when
CO2 production exceed its removal ,respiratory
acidosis results.
Causes :
-Drugs (sedative, general anesthesia , muscle relaxants
,drug overdoses).
-Neuromuscular disorder .
-Chest wall deformity.
-Airway diseases (COPD) , asthma.
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8. 2.Hypoxemic respiratory failure :
when oxygen therapy fail to oxygenate blood , such
patient are able to ventilate well ( PCO2 are low).
Causes :
pneumonia , aspiration , mild-moderate acute
respiratory distress syndrome , pulmonary emboli.
Parameter : PO2< 50mmHg.
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9. Patient with acute ventilatory failure require intubation
& ventilation if they hypoventilate to a PCO2 >
50mmHg with a pH < 7.3.
Patients with acute ventilatory failure superimposed
on chronic ventilatory failure may have higher
PCO2up to 80mmHg before requiring intubation ,
since they develop a compensatory metabolic
alkalosis.

10. Parameters
for
mechanical ventilation

11. 1.Clinical parameters:
 CNS: agitation , restlessness , loss of upper airway
reflexes ,deterioration in level of consciousness ,
coma.
 Respiratory system : apnea , tachypnea , muscle
fatigue .
 CVS : sever hypotension , arrhythmia .

12. 2.Mechanical parameters :
1. R.R. > 35 B.P.M.
2. VT < 5 ml/kg. (tidal volume: each normal
breath cycle 6-10ml/kg).
3. Vital capacity < 15 ml /kg.
( vital capacity : maximum volume of gas
that can be exhaled after maximal
inspiration 60 – 70ml/kg).
4. RSBI: RR/Vt (in liter) > 100.
5. VD/Vt > 0.6

13. 3. Blood gas tension :
1. PaO2 < 60 mmHg , when F.I.O2= 0.5
2. PaCO2 >50 mmHg ,with low PH.
3. PaCO2 < 25 mmHg.

15. Ventilator settings
Aim :
Improve both oxygen exchange & acid – base status .
1. Fraction of inspired oxygen (FIO2) :
Start with 100% then decrease the concentration
according to PaO2 ( 60-80mmHg) , the best safe
concentration is between 40-50% to avoid oxygen
toxicity.

16. (Ventilator settings) cont.
2. Tidal volume : 6-8 ml/kg , in acute lung injury ,
low tidal volume ( 6ml/kg ) is chosen to decrease
the possibility of more lung injury by high tidal
volume , the accurate assessment for appropriate
tidal volume is depend on peak airway pressure
which reflect the lung state to variant tidal volume,
the Peak airway pressure should be below 35-40
cm/H2O.

17. 3. Respiratory rate (frequency):
Is set to achieve adequate ventilation & should be
between 10 – 20 BPM, other than this range may lead
to ventilation disturbances & then to metabolic
derangement.

18. 4. Positive end expiratory pressure.(PEEP)
Is application of positive pressure to the expiration
circuit , to increase the FRC of the lung, preventing
collapse of some alveoli while overdistending
others. This lead to improve ventilation-perfusion
matching in the pulmonary circulation.

19. Indication of PEEP
1. In severely hypoxemic patients to improve arterial
oxygenation.
2. To decrease the fraction of inspired oxygen to avoid
pulmonary oxygen toxicity.
Benefits of PEEP:
Two universal pulmonary effects of PEEP are
redistribution of extravascular water and increased
functional residual capacity (FRC). The
redistribution of interstitial water improves
oxygenation, lung compliance and V/Q matching.

20. Complication of PEEP
1. Barotraumas :
2. A diminish in cardiac output with PEEP therapy is
attributable to two mechanism,
1st is due to decrease venous return to the right
heart.
which is resulting from increased intrathoracic
pressure. The increase in mean airway pressure
associated with PEEP increases the pleural and
pericardial pressure, decreasing the cardiac
transmural pressure, which may significantly
decrease the end-diastolic volume and stroke
volume of both ventricles. This reduced stroke
volume can be restored by preload augmentation.

21. Complication of PEEP / cont.
A 2nd mechanism is right ventricular dysfunction. PEEP
increases right ventricular afterload because of
increased pulmonary vascular resistance.
In patient with cardiogenic pulmonary edema, the
lowering of venous return to the heart during
mechanical ventilation may lesson edema & actually
improve oxygenation

22. 3.Affects renal function by reducing urine volume,
GFR , sodium excretion, and free water clearance.
The direct effects on renal function appear to be due
to a decrease in renal perfusion.
4. Increase in ICP due to high intrathoracic pressure.

23. Clinical monitoring of patient on MV
1.Clinical state of patient ( LOC , vital sings ,
Synchrony of chest & abdominal movement, absence of
cyanosis, & symmetry of chest movement.
2. ABG :
drawn 20-30 minutes after initiation of ventilation or
after ventilator setting changed. Aims:(PaO2 60-80
mmHg, PaCO2=30-45mmHg,pH=7.33-7.49).
3.Peak airway pressure: (is the highest pressures
measured in the airway during end inspiration,

24. Modes of Ventilation are classified
according to control (target)
 Fixed TV with each
breath
 Peak airway pressure
can vary with each
breath depending on:
◦ Resistance to airflow
during inspiration
◦ Patient’s lung-chest
wall compliance
 Fixed peak airway pressure
with each breath
 TV can vary with each breath
depending on:
◦ Resistance to airflow
during inspiration
◦ Patient’s lung-chest
wall compliance
Volume-Controlled or
Targeted Modes
Pressure-Controlled or
Targeted Modes

25. Mandatory breath
Mandatory breath: this is triggered,and cycled by
the ventilator and the patient has no role to do. We
usually find this type in controlled modes.

26. Modes classified according to control or
target variable to:
 Volume targeted modes (CMV,A/CMV and
SIMV)
 Pressure targeted modes (PCMV ,PS-PEEP
and CPAP)

27. Controlled mechanical {mandatory}
ventilation {CMV}
 This is an old mode consists of mandatory breaths
only leaving no role for the patient so it requires
deep sedation with or without muscle relaxation.
 This mode was abandoned when it was found that
respiratory muscles contraction if stopped for any
reason then they become atrophied quickly leading
to a worse outcome.

28. Synchronized intermittent mandatory
ventilation {SIMV}
This mode was invented aiming to make patient
comfort by giving him chance to breath
spontaneously yet giving him a preset number of
mandatory breaths to guarantee minute
ventilation.
This mode can be used as a starting ventilatory
mode because it guarantee a fixed minute
ventilation and as a weaning mode by gradual
decrease in number of mandatory breaths.

29. Synchronized intermittent mandatory ventilation
{SIMV}

30. Conclusion
SIMV is the best of volume targeted modes
because it serves both aims of good
ventilation and patient-ventilator
synchrony.

31. Pressure support ventilation (PS)
This mode used as primary ventilatory support mode &
as weaning mode , it depend on presetting pressure
instead of preset tidal volume (i.e. airflow is limited by
pressure rather than preset volume ).
Advantages :
1.Decrease work of breathing.
2.Improve patient ventilator synchrony.
3.Patient comfort.
4.Useful mode for asthmatic attack patient to avoid high
peak airway pressure.

32. Complication of mechanical ventilation
1. Barotrauma :
High airway pressure may damage airway epithelium
leading to ventilator –induced lung injury (VILI), also
high airway pressure may induce rupture of the
alveolar wall at its weakest point, leading to egress of
air into bronchovascular sheath & air may tracks to
mediastinum & pleura, leading to
pneumomediastinum, pneumothorax,
pneumoperitonium, & subcutaneous emphysema.

33. 2.volumetrauma.
3.Increase intracranial pressure.
4.fluid retention.
5.renal failure.
6.hyponatremia.
MV complication (cont.)

34. MV complication (cont.).
7.local trauma to nares & mouth.
8.tracheal necrosis & hemorrhage from high
ETT cuff pressures
9.Nosocomial infection such as sinusitis &
pneumonia.
10.Oxygen toxicity.