Postoperative pain
Relief of management
surgical pain with minimal side effect is a primary goal in PACU care
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In addition to improve patient comfort, relief of pain reduces sympathetic NS (SNS)
response & helps control postop hypertension & tachycardia
Carefully assessed prior to giving analgesics .
Eliminating pain can also precipitate hypoventilation & hypoxemia by accentuating
the depressant effects of previously administered opioids.
Methods of providing postoperative pain relief
Drug treatment
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Opioid
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Non-steriodal ant-inflammatory drugs
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Paracetamol & combinations
Regional anesthetic techniques :
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Central neuraxial blocks (spinal & epidural)
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Peripheral nerve blocks
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Local infiltration .
Psycological methods
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Relaxation
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Hypnosis
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Psychoprophylaxis .
The Intensive Care Unit (ICU)
The intensive care unit is the hospital facility within which the highest levels of continuous
patient care & treatment are provided.
Who should be admitted :
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The cost of providing ICU services is very high & the resources are finite
ICU care must be directed toward patients who are most likely to benefit
It is equally important to identify patient who are not ill enough & those who will die
despite ICU treatment .
Indication of ICU admission
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Patient requiring or likely to requiring advanced respiratory support.
Patient requiring support of two or more organ systems.
Patient with co-morbidity who require support for an acute reversible failure of another
organ system.
Advanced Respiratory Support
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Mechanical ventilatory or non – invasive ventilation
The possibility of sudden deterioration in respiratory function requiring immediate
tracheal intubation & mechanical ventilation
Basic respiratory support
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The need for an inspired oxygen concentration of more than 40% .
The possibility of progressive deterioration to the point of needing advanced
respiratory support .
The need for physiotherapy to clear secretions at least 2 hourly .
Patient in whom the tracheal tube has been removed recently after a prolong period
of intubation & mechanical ventilation .
The need for mask CPAP or non – invasive ventilation .
Patient whose trachea intubated to protect the airway but do not need mechanical
ventilation.
Circulatory support
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The need for vasoactive drugs .
Support for circulatory instability caused by hypovolaemia for any cause unresponsive
to modest volume replacement .
Patient resuscitated after cardiac arrest where ICU or HDU care is considered
clinically appropriate .
Indications for mechanical ventilation
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The main indication for mechanical ventilation is :
Respiratory failure .
Other clinical indications include :
a prolonged postoperative recovery .
Altered conscious level ,
Inability to protect the air way .
Exhausion when the patient is likely to proceed to respiratory failure .
Control of intracranial pressure in head injury .
Airway protection following drug overdose .
Following cardiac arrest .
For recovery after prolonged major surgery or trauma .
The aim of mechanical / artificial ventilation is :
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Is to improve gas exchange .
To reduce the work of breathing .
To avoid complications while maintaining optimal conditions for recovery .
Respiratory failure
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This is primary indication for respiratory support .
Pulmonary gas exchange is sufficiently impaired to cause hypoxaemia with
or without hypercarbia .
The causes of respiratory failure :
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Inadequate gas exchange
Pneumonia
Pulmonary oedema
Acute respiratory distress syndrom (ARDS)
Inadequate breathing
Chest wall problems eg fractured ribs , flial chest
Pleural wall problems eg pneumothorax ,haemothorax
Respiratory muscle failure eg myasthenia gravis, poliomyelitis, tetanus
CNS depression eg drugs, brain stem compression
Obstructed breathing
Upper airway obstruction eg epiglottitis, croup, oedema, tumor .
Lower airway obstruction eg bronchospasim .
Types of mechanical ventilation
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The most commonly used type of artificial ventilation is intermittent
positive pressure ventilation (IPPV).
The lungs are intermittently inflated by positive pressure generated by a
ventilator.
& gas flow is delivered through an endotracheal or tracheostomy or mask ?
Tracheal intubation is usually achieved by the oral route although nasal
intubation may be better tolerated by the patient during prolonged
ventilation .
Tracheal intubation :
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Allows institution of IPPV .
Reduces dead space
Facilitates airway suctioning .
It is also possible to deliver positive pressure ventilation to cooperate patient
in non-invasive manner through a tight – fitting face or nasal mask (NIPPV).
Two main types of ventilators commonly in use in ICU
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Those that deliver a preset tidal volume .
And those that deliver a preset inspiratory pressure during each inspiration .
Modern ventilators allow different modes of ventilation & the clinician must select the
safest & most appropriate mode of ventilation for the patient .
Types of ventilation
volume- cycled ventilation
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Occurs when the ventilator delivers a preset tidal volume regardless of the pressure
generated
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The lung compliance (stiffness) of the lungs determines the airway pressure generated
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So this pressure may be high if the lungs are stiff, with the resultant risk of barotrauma
(rupture of alveoli resulting in pneumothorax & mediastinal emphysema).
Pressure – preset ventilation
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The ventilator delivers a preset target pressure to the airway during inspiration
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The resulting tidal volume delivered is therefore determined by the lung compliance & the
airway resistance
Modes of ventilation
Controlled Mechanical Ventilation (CMV)
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Ventilation with CMV is determined entirely by machine settings including the
airway pressure , tidal volume, resoiratory rate , & I : E ratio
This mode of ventilation is not often used in ICU as it does not allow any
synchronisation with the patients own breathing
As a consequence CMV is not well tolerated
Patient require heavy sedation or NM – blockade to stop them (fighting) the
ventilator, thereby resulting in inefficient gas exchnge
CMV is normally used in theatre when the patient is receiving a full general
anesthetic to optimise surgical condition
Assisted Mechanical ventilation (AMV)
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There are several different modes of ventilation designed to work with the patients
own respiratory effort
The patients inspiratory effort is detected & triggers the ventilator to boost the
inspiratory breath
These modes have two impotant advantages:
They are better tolerated by the patient
They allow the patient to perform muscular work throughout the breath, therby
reducing the likelihood of developing respiratory muscular atrophy
The ventilator – assisted breaths can be supported either by a preset inspiratory
pressure or by a preset tidal volume
There are several variations of assisted ventilation
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Intermittent Mandatory ventilation (IMV)
is a combination of spontaneous & mandatory ventilation.
Between the mandatory controlled breaths , the patient can breath spontaneously &
unassisted.
IMV ensures a minimum minute ventilation, but there will be variations in tidal volume
between the mandatory breaths & the unassisted breaths
Synchronised Intermittent Mandatory ventilation (SIMV)
With SIMV , the mandatory breaths are synochronised with the patients own
inspiratoy effort which is more comfortable for the patient
Pressure- support ventilation (PSV) or assisted spontaneous breaths (ASB)
A preset pressure – assisted breath is triggered by the patient own inspiratory effort
This is one of the most comfortable forms of ventilation
The preset pressure level determines the level of respiratory support & can be
reduced during weaning
There are no mandatory breaths delivered , & the ventilation relies on the patient
making some respiratory effort.
No back up ventilation, should the patient become apnoeic, unless this mode is
combined with SIMV
Positive End Expiratory pressure (PEEP)
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Is used with all forms of IPPV
A positive pressure is maintained during expiration expanding underventilated lung, &
preventing collapse of the distal airways.
This results in improved arterial oxygenation.
However , PEEP causes a rise in intrathoracic pressure & can reduce venous return &
so precipitate hypotension , particularly in hypovolaemic patients.
With low levels of PEEP (5-10 cmH2O), these effects are usually correctable by IV
volume loading.
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Continuous Positive Airway Pressure (CPAP)
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Is effectively the same as PEEP, but in spontaneously breathing patients.
Criteria for starting mechanical ventilation
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Resoiratory rate >35 or < 5 breaths/min .
Exhaustion , with laboured pattern of breathing ,
Hypoxia ,central cyanosis , SaO2<90% on oxygen or PaO2<8 kpa.
Hypercarbia – PaCO2> 8 kpa.
Decreasing conscious level .
Significant chest trauma .
Tidal volume < 5ml/kg or vital capacity < 15 ml/kg
Initiation Mechanical ventilation
Optimizing oxygenation
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When settling a patient on the ventilator, it is good practice to initially set FiO2 at 1.0
& then wean rapidly to a FiO2 adequate to maintain SaO2 of >93%.
FiO2 of greater than 0.6 for long peroids should be avoided if possible because the risk
of oxygen – induced lung damage .
Strategies to improve oxygenation (other than to increase FiO2) include:
Increasing the mean airway pressure by either raising the PEEP to 10 cmH2O
Or ,by increasing the peak inspiratory pressure .
Avoiding very high inflating pressure (above 35cmH2O) as this may cause barotrauma
to the lung .
More complex strategies to improve oxygenation may be required in severely hypoxic
patient eg. ARDS or acute lung injury from a variety of causes.
In sever hypoxia , it may be possible to improve oxygenation by increasing the PEEP
further to 15 cmH2O(or above) & using small (6-8ml/kg) tidal volume more frequently
Another strategy is to prolong the inspiratory time . Normal inspiratory to expiratory
ratio 1:2 but oxygenation may be improved if this ratio is changed to 1:1 or even 2:1
In sevsre ARDS the patient can be repositioned & ventilated in prone position
Re-expanding collapsed alveoli & improving the distribution of blood perfusion in the
lung relative to ventilation .
Weaning from mechanical ventilation
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Weaning is the process by which the patients dependence on
mechanical ventilation is gradually reduced to the point where
spontaneous breathing sufficient to meet metabolic needs may be
sustained.
Because of the adverse effect of mechanical ventilation, weaning
should be undertaken at the earliest opportunity.
Criteria for weaning
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Clear consciousness with adequate gag & cough reflex .
Cardiovascular stability.
Stable metabolic state
Adequate pulmonary function .
Tidal volume > 5 ml/kg .
Vital capacity > 10 ml/kg.
SaO2 > 90% on oxygen 40% or PaO2 > 10 kpa
PaO2 < 6 kpa