1 Guildford, UK 2 Dublin, Ireland
EditorThe paper by McCaul and colleagues1 is misleading. The terms residual curarization and postoperative residual curarization (PORC) were described in 1979,2 and this and the vast majority of subsequent studies carried out focus on residual curarization in the recovery room. To state that 70% of patients had PORC at the point of antagonism of neuromuscular block is hardly postoperative. A similar case can be made for assessing the incidence of PORC at tracheal extubation.
Residual curarization in the recovery room is a different matter altogether. In this environment an anaesthetist is not usually present, and certainly not on a one-to-one ratio with patients. It is here that the problems of PORC are greatest because there may be a delay in diagnosis and treatment. The potential problems of hypoventilation and poor airway protection are thus much greater than they are in the operating theatre. The authors do not state what the incidence of PORC is in the recovery room. My colleagues and I demonstrated a PORC rate of 14% after atracurium by bolus dosing and 36% after atracurium infusions.3 The title of McCauls paper implies PORC is a new phenomenon with atracuriumit is not.
In essence, these authors have redefined PORC at a much earlier time than other authors, explaining the very high incidence reported. As a result, it is not possible to compare their findings with those of other workers.
W. J. Fawcett
Guildford, UK
EditorThank you for the opportunity to reply to Dr Fawcetts letter concerning our paper1 on residual curarization after the use of atracurium. While we did not measure the train-of-four (TOF) in the recovery room, we did report on the incidence of clinical problems attributable to PORC. Nineteen patients (47.5%) had clinical evidence of impaired neuromuscular function in the recovery room as evidenced by 40 clinical events. Of those patients, 18/19 had had a TOF ratio <0.7 at extubation.
As stated, many previous studies focused on PORC in the recovery room. What is unclear in these studies is pertinent: information about the temporal correlations between neuromuscular blocking drug usage and pharmacological antagonism, and the TOF ratios at the time of antagonism and at extubation, is required. By focusing on such information, it is our contention that PORC in the recovery room will be decreased. Stating incidences of PORC in the recovery room is not very useful as many variables are not controlled (e.g. time to transfer from operating room to recovery, interval since last dose of neuromuscular blocking drug/antagonist, etc.). The core of the problem and the way to reduce it lies in what happens in the operating room.
A. J. McShane
Dublin, Ireland
References
1 McCaul C, Tobin E, Boylan JF, McShane AJ. Atracurium is associated with postoperative residual curarization. Br J Anaesth 2002; 89: 7669
2 Viby-Mogensen J, Jorgensen BC, Ording H. Residual curarization in the recovery room. Anesthesiology 1979; 50: 53941[ISI][Medline]
3 Fawcett WJ, Dash A, Francis GA, Liban JB, Cashman JN. Recovery from neuromuscular blockade: residual curarisation following atracurium or vecuronium by bolus dosing or infusions. Acta Anaesthesiol Scand 1995; 39: 28893[ISI][Medline]