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Troubleshooting

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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

  1. assess patient
  2. 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.
  3. 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.
  4. CXR
  5. 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

    • spontaneous modes are more comfortable than control modes

    • some evidence that BIPAP is more comfortable and improves synchrony.

  • I:E ratio

    • ratios that are similar to the 1:2 ratio of a normal breathing pattern more comfortable.

  • triggering

    • f

    • m

    • if the patient is having difficulty triggering the ventilator despite a sensitive setting consider the possibility that auto-PEEP due to dynamic hyperinflation is the problem.

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

 

©Charles Gomersall, April, 2014 unless otherwise stated. The author, editor and The Chinese University of Hong Kong take no responsibility for any adverse event resulting from the use of this webpage.
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