Subjective visual perceptions during vitreoretinal surgery under local anaesthesia.

PURPOSE: To evaluate the visual experiences of patients during vitreoretinal surgery under local anaesthesia (LA). METHODS: Prospective questionnaire survey of 80 patients within 30 min of completion of vitreoretinal surgery under LA. Preoperative visual acuity, surgical procedure and its duration, efficacy of the local block, as well as intraoperative perceptions of flashes, colours, movements, and seeing instruments were documented. RESULTS: A sub-Tenon's block was performed in 62/80 (77.5%) and a peribulbar block in the remainder. Overall, 72 (90%) of patients perceived light at some stage during their surgery. Of these, 51 (70.83%) observed movements, 45 (62.5%) saw colours, 38 (52.77%) saw instruments, and 24 (33.33%) saw flashes. The commonest observations were colourful swirls, black pipes, and the colour red. Most patients found these experiences pleasant or bearable; two found them frightening, and four would like to have been warned preoperatively about them. Preoperative visual acuity, diagnosis, gender of the patient, degree of akinesia, and the duration of surgery did not associate with visual perceptions. Logistic regression analysis showed that younger people were more likely to experience flashing lights (P=0.03) and to see instruments (P=0.04), patients having a sub-Tenon's block to perceive light (P=0.005), and those who did not receive awake sedation were more likely to see instruments (P=0.04). CONCLUSIONS: Visual experiences are common during vitreoretinal surgery undertaken under LA. Where appropriate, patients should be forewarned about these experiences and reassured that they are not normally frightening.

Effect of wrist position on power grip and key pinch strength following carpal tunnel decompression.

Power grip and thumb key pinch strength were measured pre- and immediately postoperatively in 30 patients with carpal tunnel syndrome while the wrist was in flexion and extension. The carpal tunnel decompression was performed under local infiltration with 1% lignocaine. Grip strength decreased more in wrist flexion than in wrist extension. No difference was found in thumb pinch strength. The authors conclude that some of the immediate postoperative loss of grip strength in wrist flexion can be attributed to prolapse of flexor tendons out of the carpal tunnel in this position.

Altered globe dimensions of axial myopia as risk factors for penetrating ocular injury during peribulbar anaesthesia.

We measured the range of equatorial horizontal widths (EHW) in axially myopic eyes and identified the sites of staphyloma using B scan echography. One hundred eyes in 50 patients were studied. The axial lengths (ALs) were sorted into five groups of increasing severity of myopia. The group mean AL, group mean EHW and the ratio of EHW/AL was calculated for each range. The results suggest that the increase in the AL in an axially myopic eye is associated with an increase in the EHW. However, this increase in the group mean EHW is relatively small (2.3 mm) compared with the increase mean AL (8.2 mm) across the entire range. The ratio of EHW/AL decreased with an increase in the group mean AL. Therefore, the increase in EHW in an axially myopic eye is unlikely to be a significant risk factor for inadvertent ocular injury for peribulbar injections if a careful single medial canthal approach is used. There was high incidence of staphylomas in eyes with AL > 29 mm, most were inferior to the posterior pole of the globe, and there were none at the equator.

Practical limitations of the Deltatrac indirect calorimeter.

Indirect calorimetry is used to assess energy requirements. The Deltatrac Metabolic Monitor is a relatively inexpensive indirect calorimeter which uses a 'fixed' flow of ambient air to collect expired air. Only oxygen and carbon dioxide concentrations are measured and the 'fixed flow' is assumed in the calculation of oxygen consumption ((.)VO(2)) and carbon dioxide production ((.)VCO(2)). Using inert gas dilution we have studied the effect on (.)VO(2), and on the variability in (.)VO(2), of changing and lengthening the 1.77 m length of 35 mm tubing supplied with the instrument to collect expired air, and of using a mask to collect expired air instead of the manufacturer's hood. One would anticipate that changing the tubing could cause a change in resistance to gas flow and thus affect the true flow rate. This would alter the gas concentrations seen by the analysers, but the 'fixed flow' would still be assumed so the results would be in error. Adding extra lengths of manufacturers tubing caused an apparent rise in (.)VO(2) of 0.36%/m of tubing added, and using 22 mm tubing instead of the manufacturer's 35 mm tubing increased (.)VO(2) by 0.42% for each 10 cm of tubing added. Using the mask to collect expired air instead of the canopy (.)VO(2) was higher, possibly due to the energy cost of holding the mask, and was more variable, probably because of poorer mixing of the expired air. To measure (.)VO(2) using a mask with the same precision as a 10 min measurement made with the hood would entail measuring (.)VO(2) for 14.5 min. The methods used to collect expired air (mask or canopy, length and type of tubing) when measuring metabolic rate with the Deltatrac do affect the results obtained but these effects are small and predictable.

Convulsions after enflurane in a schizophrenic patient receiving neuroleptics.

A schizophrenic patient suffered from an episode of unexpected grand mal seizure following an enflurane unaesthetic for biopsy of an orbital lesion. The seizure was brief and subsided spontaneously. An assessment of the anaesthetic technique and a thorough neurological examination which included a CT scan and an EEG, failed to demonstrate any obvious cause for the convulsion. The patient was not an epileptic and was receiving neuroleptic drugs preoperatively for the treatment of schizophrenia. A synergistic role of enflurane and neuroleptic drugs is producing seizure activity in this patients is a distinct possibility. Caution is therefore recommended when administering enflurane to patients on neuroleptic drugs.