R.P. Mahajan

5th National Audit Project (NAP5) on accidental awareness during general anaesthesia: summary of main findings and risk factors

We present the main findings of the 5th National Audit Project (NAP5) on accidental awareness during general anaesthesia (AAGA). Incidences were estimated using reports of accidental awareness as the numerator, and a parallel national anaesthetic activity survey to provide denominator data. The incidence of certain/probable and possible accidental awareness cases was ~1:19,600 anaesthetics (95% confidence interval 1:16,700-23,450). However, there was considerable variation across subtypes of techniques or subspecialities. The incidence with neuromuscular block (NMB) was ~1:8200 (1:7030-9700), and without, it was ~1:135,900 (1:78,600-299,000). The cases of AAGA reported to NAP5 were overwhelmingly cases of unintended awareness during NMB. The incidence of accidental awareness during Caesarean section was ~1:670 (1:380-1300). Two-thirds (82, 66%) of cases of accidental awareness experiences arose in the dynamic phases of anaesthesia, namely induction of and emergence from anaesthesia. During induction of anaesthesia, contributory factors included: use of thiopental, rapid sequence induction, obesity, difficult airway management, NMB, and interruptions of anaesthetic delivery during movement from anaesthetic room to theatre. During emergence from anaesthesia, residual paralysis was perceived by patients as accidental awareness, and commonly related to a failure to ensure full return of motor capacity. One-third (43, 33%) of accidental awareness events arose during the maintenance phase of anaesthesia, mostly due to problems at induction or towards the end of anaesthesia. Factors increasing the risk of accidental awareness included: female sex, age (younger adults, but not children), obesity, anaesthetist seniority (junior trainees), previous awareness, out-of-hours operating, emergencies, type of surgery (obstetric, cardiac, thoracic), and use of NMB. The following factors were not risk factors for accidental awareness: ASA physical status, race, and use or omission of nitrous oxide. We recommend that an anaesthetic checklist, to be an integral part of the World Health Organization Safer Surgery checklist, is introduced as an aid to preventing accidental awareness. This paper is a shortened version describing the main findings from NAP5--the full report can be found at http://www.nationalauditprojects.org.uk/NAP5_home.

Preliminary findings in the neurophysiological assessment of intercostal nerve injury during thoracotomy

OBJECTIVE Previous work has suggested that intercostal nerve injury is a major factor in the aetiology of chronic post-thoracotomy pain. The aim of this study was to establish if there was identifiable intercostal nerve injury during thoracotomy. METHODS Intercostal nerves were stimulated and motor evoked potentials were recorded from intercostal muscles in 13 patients undergoing thoracotomy. Measurements were taken before and after entering the pleural space, after removal of the rib retractor and after intercostal space closure. RESULTS Intercostal nerves functioned normally before and after entering the pleural space. After the rib retractor was removed, there was a total conduction block in the nerve immediately above the incision in every patient. In the nerves above this, six had a total block, one a partial block and three had normal conduction. There was a total conduction block in the nerve immediately below the incision in all but one patient. Of the nerves below this, four had a total block, two a partial block and three had normal conduction. In the cases of total conduction block, there was either a discrete block at the level of the distal end of the rib retractor or impairment throughout the whole nerve. Intercostal space closure did not injure any previously uninjured nerve. In a solitary patient where rib retraction was not employed, there was no impairment of the intercostal nerves throughout the operation. CONCLUSIONS This study demonstrates for the first time that intercostal nerve injury occurs routinely due to rib retraction during thoracotomy. We believe that it may be an important step toward understanding the cause of post-thoracotomy neuralgia.

The intensity of postoperative shivering is unrelated to axillary temperature

The relationship between axillary temperature and postoperative shivering was examined in 302 patients who entered one recovery room in the Derbyshire Royal Infirmary over a one‐month period. No relationship was found between temperature and the occurrence of shivering, or between conscious level and the occurrence of shivering.

Evaluation of intubating conditions with rocuronium and either propofol or etomidate for rapid sequence induction

We have assessed the effect of two induction agents on tracheal intubating conditions after rocuronium 0.6 mgkg−1 in unpremedicated patients undergoing simulated rapid sequence induction. Following pre‐oxygenation, anaesthesia was induced with propofol up to 2.5 mgkg−1 (n = 35) or etomidate 0.3 mgkg−1 (n = 36), and further increments as required. After loss of verbal contact, cricoid pressure was applied and rocuronium was injected. Laryngoscopy was performed at 45 s and intubation attempted at 60 s after rocuronium had been given. Ninety‐four per cent of patients in the propofol group had clinically acceptable (good or excellent) intubating conditions compared to only 75% in the etomidate group (p = 0.025). Owing to coughing, one patient in the etomidate group could not be intubated on the first attempt. A greater pressor response also followed intubation after induction with etomidate. We conclude that etomidate and rocuronium alone cannot be recommended for intubation at 60 s under rapid sequence induction conditions.

Novel events in the molecular regulation of muscle mass in critically ill patients

Non‐technical summary A clinical trait of critically ill patients following trauma, surgical complications and/or sepsis is the presence of a marked skeletal muscle wasting, which severely compromises muscle function, especially the respiratory muscles, and clinical outcomes such as morbis, mortality and the length of hospitalization. However, the molecular mechanisms responsible for this are largely unresolved. In this paper we provide novel and interesting translational data that show how the muscle mass is regulated during critical illness. The present observations also show that the muscle signalling pathways are not only important for the size of muscle mass, but could also play a significant role in the whole body glucose control. This is extremely important and relevant to the clinical setting as uncontrolled blood glucose concentrations in critically ill patients impact on clinical outcome. From a clinical perspective, the present data suggest therapeutic strategies to preserve muscle mass and metabolic function in critical illness.

The minimum effective doses of pethidine and doxapram in the treatment of post‐anaesthetic shivering

This study was designed to find the minimum effective doses of doxapram and pethidine to stop post‐anaesthetic shivering. Two hundred and twenty healthy patients who shivered following routine surgery were allocated randomly to receive one of 10 doses of doxapram (0.18, 0.23, 0.29, 0.35, 0.41, 0.47, 0.7, 0.93, 1.17 and 1.4 mg.kg−1), one of five doses of pethidine (0.12, 0.18, 0.23, 0.29 and 0.35 mg.kg−1) or saline. Probit analysis demonstrated that the number of patients who stopped shivering with doxapram was independent of the amount of drug given in this dose range. The lowest dose of doxapram (0.18 mg.kg−1) was significantly more effective than placebo (p < 0.01). For pethidine there was a dose‐dependent effect on shivering to a maximum of 95% of patients successfully treated with 0.35 mg.kg−1. We conclude that 0.35 mg.kg−1 of pethidine is the minimum dose required to treat post‐anaesthetic shivering effectively. We also conclude that 0.18 mg.kg−1of doxapram is as effective as 1.4 mg.kg−1 in the treatment of post‐anaesthetic shivering. Further study is required to find the minimum effective dose of doxapram.

National critical incident reporting: improving patient safety

One of the key features of the patient safety ‘movement’ is the belief that safety can be improved by learning from incidents and near misses, rather than pretending they have not happened. Critical incident investigation was first used in the 1940s as a technique to improve safety and performance among military pilots. This focus on critical indents enabled the researchers to investigate the differences between behaviours that led to success and those that led to failure, and to derive conclusions about how people should be encouraged to act, especially by redesigning their work environments to produce more desirable outcomes. In 1978, Cooper and colleagues used what they described as a ‘modified critical incident technique’ to interview anaesthetists and obtain descriptions of preventable incidents. It is now commonplace for individual departments of anaesthesia to record and discuss adverse incidents and near misses with a view to learning from the problems encountered and preventing their re-occurrence. However, the knowledge of, and learning from, these incidents tends to be shared only at a local level, and any subsequent improvement in patient safety thus remains local. In order to share and expand learning more widely at a national level, a number of critical incident reporting systems have been set up in different countries. In Australia, the Australian Incident Monitoring Study began in the late 1980s as an anaesthesia-specific venture. Later, the Australian Patient Safety Foundation extended incident reporting beyond anaesthesia. An anaesthesia-specific, on-line reporting system has been operating in Switzerland since the mid-1990s and, more recently, the German Society of Anaesthesiology and Intensive Care has set up its own Patient Safety Optimisation System. Both these sites offer the opportunity to report incidents and read those posted by others. Denmark also has a nationally conceived Patient Safety Database to which reports can be uploaded, although this is not specific to anaesthesia. So far, some important improvements, locally and nationally, can be attributed to the lessons learned from incident reporting. Individual anaesthetists will be able to cite many instances where they have learned something which changed their practice for the better. On the departmental level, it has been possible to use incident reporting to purchase new monitoring equipment and to withdraw stocks of drugs given in error. Others have found that latent errors can be addressed, and feel that incident reporting provides a means of continuous quality improvement to which all members of the department can contribute. A further benefit is the effect on non-technical factors affecting anaesthetic practice, such as teamwork, communications, and organizational culture. National systems have also resulted in some publications, 11 including an Australian manual for the management of critical situations in anaesthesia. The enduring value of critical incident reporting within the Australian system has been reinforced by a comparative analysis of the most recent 1000 incidents (reported between 2002 and 2006) and the initial 2000 incidents, which revealed many similarities but also some new concerns—for instance, misuse of the laryngeal mask airway beyond its recommended indications. On a more conceptual level, a link between intraoperative incidents and postoperative problems has also been established, underlining the importance of attending to factors that predispose to problems. Despite these very useful publications, we believe that the full potential of critical incident reporting still remains unexplored. In particular, a comprehensive approach to learning from incidents, wider dissemination, and significant impact on standards, quality, research, and patient outcome are yet to be realized. In the UK, the Royal College of Anaesthetists (RCoA) has consistently encouraged incident reporting in

The Effects of Sevoflurane and Nitrous Oxide on Middle Cerebral Artery Blood Flow Velocity and Transient Hyperemic Response

UNLABELLED We studied the effects of sevoflurane, with and without nitrous oxide, on the indices of cerebral autoregulation (transient hyperemic response ratio and the strength of autoregulation) derived from the transient hyperemic response (THR) test. Twelve patients (ASA physical status I or II) aged 18-40 yr presenting for routine non-neurosurgical procedures were recruited. The middle cerebral artery blood flow velocity was continuously recorded using transcranial Doppler ultrasonography. Preinduction THR tests were performed before the patients were anesthetized with alfentanil, propofol, and vecuronium. End-tidal carbon dioxide concentration and mean arterial pressure (to within 10% with a phenylephrine infusion) were maintained at their preinduction values. THR tests were performed sequentially at the following end-tidal sevoflurane concentrations: 2.2% in oxygen, 3.4% in oxygen, 3.4% with 50% nitrous oxide in oxygen, and 2.2% with 50% nitrous oxide in oxygen. Neither 2.2% nor 3.4% sevoflurane significantly affected cerebral autoregulation. The addition of 50% nitrous oxide to the 2.2%, but not the 3.4%, concentration of sevoflurane increased middle cerebral artery blood flow velocity and decreased autoregulatory indices significantly. IMPLICATIONS Transient hyperemic response is preserved during sevoflurane anesthesia but is significantly impaired when nitrous oxide is added to the lower concentration of sevoflurane (2.2%). These findings have implications for neurosurgical patients undergoing general anesthesia.

Effects of norepinephrine and glyceryl trinitrate on cerebral haemodynamics: transcranial Doppler study in healthy volunteers

BACKGROUND The effects of vasoactive substances on cerebral haemodynamics are not fully known. We studied the effects of norepinephrine and glyceryl trinitrate (GTN) on cerebral haemodynamics in healthy volunteers. METHODS The effects of norepinephrine (n=10) and GTN (n=10) on the middle cerebral artery flow velocity (MCAFV), cerebral autoregulation, reactivity to carbon dioxide, and estimated cerebral perfusion pressure (eCPP) were studied using transcranial Doppler ultrasound. Established methods were used for calculating zero flow pressure (ZFP). Measurements were made at baseline, and after i.v. infusion of the study drug to the endpoints of 25% increase in mean arterial pressure (MAP) for norepinephrine (0.02-0.1 microg kg(-1) min(-1)), or 15% decrease in MAP for GTN (0.5-2.5 microg kg(-1) min(-1)). RESULTS The MCAFV remained unchanged with norepinephrine, but decreased slightly with GTN {from [median (inter-quartile range)] 53 (38, 62) to 48 (33, 52) cm s(-1)}. Cerebrovascular reactivity did not change significantly with either drug. The eCPP did not change significantly with norepinephrine, but increased significantly with GTN [from 49 (32, 54) to 62 (47, 79) mm Hg]. ZFP increased with norepinephrine [from 39 (28, 48) to 56 (46, 62) mm Hg] and decreased with GTN [from 35 (30, 49) to 12 (-7, 20) mm Hg]. CONCLUSIONS Norepinephrine, despite increasing arterial pressure, did not increase the eCPP. The eCPP increased significantly with GTN, despite decreased MAP. Cerebral vascular tone is an important determinant of CPP during pharmacologically induced changes in arterial pressure.

Gastro-oesophageal reflux during day case gynaecological laparoscopy under positive pressure ventilation: laryngeal mask vs. tracheal intubation

This study aimed to evaluate whether or not the use of intermittent positive pressure ventilation via the laryngeal mask airway is associated with a higher risk of gastro‐oesophageal reflux when compared with intermittent positive pressure ventilation via a tracheal tube in patients undergoing day case gynaecological laparoscopy in the head down position. Sixty healthy women were randomly allocated to receive either the laryngeal mask or cuffed tracheal tube for intra‐operative airway maintenance. Using continuous oesophageal pH monitoring, four patients in the tracheal tube group and none in the laryngeal mask group had evidence of gastro‐oesophageal reflux (as indicated by a decrease in oesophageal pH to below 4). The difference in the incidence of reflux did not achieve statistical significance (p = 0.11). In conclusion, we found no evidence to suggest that the use of intermittent positive pressure ventilation via the laryngeal mask increases the risk of gastro‐oesophageal reflux in patients undergoing elective day case gynaecological laparoscopy.