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An introduction to dealing with common problems in mechanically
ventilated patients.
Click here
to download the accompanying Powerpoint tutorial (with English narration)
Assessment
The first priority in dealing with mechanical ventilation problems is to
assess the patient.
- How severe is the problem?
- Does the patient require immediate resuscitation?
Check:
- Is the chest moving and is it moving symmetrically?
- Is the patient cyanosed?
- What is the arterial saturation?
- Is the patient haemodynamically stable?
The next step is to diagnose the problem. Ventilator/circuit problems can be
distinguished from endotracheal tube/patient problems by taking the patient off
the ventilator and manually bagging the patient with a self-inflating
resuscitator.
High airway pressure
Why does it matter?
- High airway pressure may cause barotrauma
- It signifies a deterioration in the patient's clinical state
- It may result in hypoventilation of the patient
- many ventilators cycle from inspiration to expiration immediately if
the upper pressure alarm limit is reached. As a result inspiration is
terminated early and the tidal volume is reduced.
Causes
Ventilator problems
- inappropriate settings
- excessive tidal volume
- excessive flow or excessively short inspiratory time
- high airway pressure alarm limit too low
- ventilator malfunction - rare
Circuit problems
- fluid pooling in circuit
- fluid pooling in filter
- kinking of circuit
Endotracheal tube obstruction
eg due to sputum, kinking, biting
Increased airway resistance
eg bronchospasm
Decreased respiratory system compliance
- parenchymal disease
- pleural disease eg pneumothorax
- decreased chest wall compliance eg due to patient "fighting"
ventilator
- decreased ventilated lung volume
- sputum plugging
- lobar/lung collapse
- endobronchial intubation
Management
- assess patient
- disconnect patient from ventilator and manually ventilate using
self-inflating resuscitator. Assess the "feel" of the lungs. Is
the patient difficult to ventilate? If the patient is not difficult to
ventilate the problem is a problem with the ventilator or the circuit. If
the patient is difficult to ventilate it is a problem with the endotracheal
tube or the respiratory system.
- For ventilator and circuit problems check ventilator settings and
function, and check circuit for obstruction or kinking. For patient or ETT
problems examine the patient looking particularly for wheeze, asymmetrical
chest expansion and evidence of collapse. Pass a suction catheter through
the ETT to check its patency.
- CXR
- If the cause is still not clear measure inspiratory pause pressure
(approximates to alveolar pressure). If both airway and alveolar pressure
are high the problem is due to poor compliance. If only the airway pressure
is high the problem is one of high resistance.
Hypotension
The most important causes of hypotension occurring soon after the initiation
of mechanical ventilation are:
- relative hypovolaemia
- reduction in venous return exacerbated by positive intrathoracic
pressure
- drug induced vasodilation and myocardial depression
- all anaesthetic induction agents have some short lived vasodilatory ±
myocardial depressant effects
- gas trapping (dynamic
hyperinflation)
- tension pneumothorax
Hypotension due to relative hypovolaemia or anaesthetic induction agents
usually responds rapidly to fluid. Hypotension due to gas trapping can be
diagnosed and treated by disconnecting the patient from the ventilator. This
results in a rapid reversal of the hypotension.
Patient-ventilator dysynchrony
There are a large
number of causes of patient-ventilator dysynchrony which need to be considered.
It is important to identify and treat these causes and not simply to sedate the
patient more heavily. As well as all the possible causes of agitation there are
a number of ventilator parameters which must be considered. These include:
-
mode of
ventilation
-
I:E ratio
-
triggering
Desaturation
Causes
- endobronchial intubation
- accidental extubation
- pneumothorax
- pulmonary embolus
- any cause of increased intrapulmonary shunt
- any cause of hypoxic respiratory failure
- ventilator malfunction
Management
- increase FIO2 to 1.0
- check chest is moving
- briefly examine chest to determine cause of desaturation
- if cause is not obvious manually ventilate patient with 100% oxygen to
exclude ventilator malfunction as the cause
- treat underlying cause
- alter ventilator settings to
improve oxygenation
- CXR
Click here for more on mechanical
ventilation
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