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Accidental anaesthetic awareness

07 June 2019

A 41-year-old project manager, Mrs F, underwent breast uplift surgery, performed on a private basis.

Induction of anaesthesia was performed by Dr T using propofol and fentanyl, and a laryngeal mask airway was inserted. A muscle relaxant was also administered. Anaesthesia was maintained with a propofol infusion, and a remifentanil infusion was also used.

Shortly after Mrs F had been transferred from the anaesthetic room to theatre, it was noted her heart rate significantly increased, as did her blood pressure. Although this change was recorded on the anaesthetic monitoring printout, it was not recorded in the handwritten anaesthetic chart.

Dr T noted the changes and considered the increase in heart rate and blood pressure indicated the level of anaesthesia was light, and so the rate of infusion of both propofol and remifentanil were increased, and midazolam was also given.

Dr T did not record on the anaesthetic chart why these measures had been taken.

The surgery proceeded uneventfully, but on recovering from anaesthesia Mrs F stated to ward staff that she had “woken up” during the operation and could hear the surgeon talking and feel tugging and pushing. She tried to scream and move away, but could not. 

She later brought a claim against Dr T for intraoperative accidental awareness resulting in psychiatric injury.

Expert opinion

Dr T contacted Medical Protection, who instructed a consultant anaesthetist to provide an expert report.

The expert concluded that Dr T did not use a target controlled infusion pump (which would have used mathematical modelling to calculate and adjust the dose), and also failed to perform any calculation or refer to an infusion regime about the rate of propofol infusion that would be required to keep Mrs F adequately anaesthetised.

The expert calculated that the rate per hour at which the propofol was administered was around half of the rate that would be recommended for Mrs F, based on her weight. The infusion rate of remifentanil was also around half of what would be recommended.

The expert further considered that there was no surgical or anaesthetic requirement for muscle relaxation to be used in this particular case, and the use of a muscle relaxant contributed to the occurrence of awareness, as did the failure to monitor the depth of anaesthesia (although such monitoring would not be mandatory).

The expert held the view that it was appropriate for Dr T to have given midazolam and to increase the rate of infusion of propofol and remifentanil when Mrs F’s heart rate and blood pressure increased, and anaesthesia was suspected to be light. However, criticism was given with respect to the failure to clearly document this event on the anaesthetic chart.

Outcome

On the basis of the medical records and the expert report, it was considered the claim could not be defended and it was settled for a low sum.

Learning points

  • If a target-controlled infusion pump is not available to be used to administer total intravenous anaesthesia, then careful consideration and calculation of the rate to be infused must be performed. A number of infusion regimes have been described for use when manually adjusting infusion rates of propofol. Target-controlled infusion pumps are widely available and some consideration should be given to justifying the use of total intravenous anaesthesia without an appropriate infusion pump.
  • The risk of anaesthetic awareness is increased when a patient is paralysed, and thought should be given on whether use of a muscle relaxant is necessary for the particular procedure being performed.
  • Consider using a depth of anaesthesia monitor when administering total intravenous anaesthesia, especially when a muscle relaxant is also administered.
  • Contemporaneous record keeping should be accurate and reflect the events that have occurred.
  • If this case had been an HDC complaint in New Zealand, Dr T may have been vulnerable to criticism for not using an appropriate target-controlled infusion pump, especially if one was available. The lack of use of depth of anaesthesia monitoring when a muscle relaxant is administered, as well as not keeping contemporaneous records, may also lead to criticism.
  • The HDC may then have a number of recommendations if Dr T is found to be in breach of the Patient Code of Rights. These may include: referral of Dr T to the MCNZ for assessment of his competence in the practice of anaesthesia, apologising to the patient, and upskilling and reviewing his practice in the use of total intravenous anaesthesia and record keeping.
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