The effect of hyaluronidase on ultrasound-measured dispersal of local anaesthetic following sub-Tenon injection.

PURPOSE: To determine by B-scan ultrasonography if the addition of hyaluronidase affects the dispersal of anaesthetic fluid after sub-Tenon's injection. DESIGN: Single-centre prospective randomised double-blind study. MATERIALS AND METHODS: We performed a trial in 19 patients who were randomised to receive 5 ml of lidocaine 2% alone, or with hyaluronidase 15 IU/ml. A pre-anaesthetic B-scan ultrasound was performed followed by a standard infero-nasal sub-Tenon's injection. Further B-scan ultrasound studies were performed at 1, 3, and 5 min recording depth of local anaesthetic fluid. Data was analysed with Fisher's exact test and Student's t-test where appropriate. Results were considered significant when P<0.05. RESULTS: The maximum depth of local anaesthetic was significantly less in the hyaluronidase group than the control group at 3 and 5 min (0.79 vs1.65 mm, P-value 0.01 and 0.43 vs1.52 mm, P-value 0.002 respectively). There were no statistically significant differences in the akinesia, pain and surgical satisfaction scores between the two groups. CONCLUSIONS: The addition of hyaluronidase significantly augments the dispersal of local anaesthetic fluid, as measured by B-scan ultrasonography.

Hyaluronidase reduces local anaesthetic volumes for sub-Tenon's anaesthesia.

BACKGROUND: Volumes of local anaesthetics for sub-Tenon's anaesthesia vary. Lower volumes produce less akinesia, whereas higher volumes increase chemosis and intra-ocular pressures. Hyaluronidase is often added to local anaesthetics to improve akinesia without increasing the volume of the injection, but this is controversial. This randomized, sequential allocation study examines the addition of hyaluronidase on the minimum local anaesthetic volume (MLAV) required for a sub-Tenon's block. METHODS: Sixty-two patients having sub-Tenon's blocks for cataract surgery were randomized into two groups. The control group (n=31) received 2% w/v lidocaine and the study group (n=31) received 2% w/v lidocaine with hyaluronidase 15 IU ml(-1). Using parallel up-down sequential allocation from a 4 ml starting volume, the volumes in both groups were changed using a testing interval of 1 ml according to the quality of globe akinesia. The median effective local anaesthetic volume (MLAV) was calculated for both groups using probit regression. RESULTS: The groups were similar for age, sex, and ocular axial length. The MLAV in the hyaluronidase group was 2.6 ml [95% confidence interval (CI), 2.1-3.l] and 6.4 ml (95% CI, 5.1-8.1) in the control group (P<0.002). CONCLUSIONS: Hyaluronidase permits a significant 2.4-fold (95% CI, 1.8-3.4) reduction in MLAV for sub-Tenon's anaesthesia.

A comparison of lidocaine 2% with levobupivacaine 0.75% for sub-Tenon's block.

BACKGROUND AND OBJECTIVE: To compare the onset of action, and quality of block, of lidocaine 2% with levobupivacaine 0.75% for sub-Tenon's block in patients undergoing cataract surgery. METHODS: We performed a two-centre trial in 91 patients who were randomized to receive 4 mL of lidocaine 2% (n = 44) or levobupivacaine 0.75% (n = 47) for sub-Tenon's block, both with hyaluronidase 15 IUmL(-1). Onset of akinesia was assessed every 2 min for 10 min. Numbers of patients requiring supplementary injections to achieve clinically satisfactory akinesia or rescue analgesia were recorded. Data were analyzed with Fisher's exact test, U-test and t-test where appropriate. Results were considered significant when P < 0.05. RESULTS: The speed of onset was statistically significantly faster for lidocaine compared to levobupivacaine (3.02 vs. 5.06 min, P < 0.001). There was no statistical difference in number of patients requiring a supplementary injection of local anaesthetic (levobupivacaine 3 vs. lidocaine 0, P = 0.24), rescue analgesia with topical tetracaine (levobupivacaine 0 vs. lidocaine 2, P = 0.5), or ocular akinesia scores at the completion of surgery (lidocaine 1.4 vs. levobupivacaine 1.6, P = 0.12). Pain scores measured by a verbal analogue scale were not significantly different for injection, perioperatively or postoperatively. CONCLUSIONS: Both agents produce a rapid onset of anaesthesia when used for sub-Tenon's block. The difference between the two agents, although statistically significant, is not clinically important.

Review of local anaesthetic agents.

The currently available local anaesthetic agents are capable of providing high quality nerve blockade in a wide variety of clinical circumstances. Our understanding of the mechanisms and consequences of toxicity is increasing rapidly. Knowledge of the chemistry of local anaesthetics has enabled clinicians to exploit the increased safety of single isomer agents. However, the extent, if any, of this improvement in toxicity has yet to be proven. Established toxicity may be very difficult to treat and no specific reversing therapy is yet available. Until this occurs it is essential that practitioners of regional anaesthesia maintain their knowledge base and skill in techniques of administration of local anaesthetic, are able to recognise impending disaster, and constantly update their skills in resuscitation.

Post-splenectomy thrombocytopenia: implications for regional analgesia.

Hospital computerised records were reviewed to identify patients who had undergone splenectomy, then chart their platelet count before and for the 5 days after the operation. A pre-operative platelet count less than 100 x 10(9).l-1 occurred in 66% of leukaemia (n = 35), 56% of lymphoma (n = 41) and 5% of solid tumour (n = 39) patients. Platelet supplementation prior to epidural catheter insertion may reduce the risks of spinal bleeding. However, accidental catheter removal during a postoperative period of thrombocytopenia may lead to formation of an epidural haematoma. The lowest postoperative platelet count was less than 100 x 10(9).l-1 in 66% of leukaemia, 27% of lymphoma and 13% of solid tumour patients. Platelet counts varied considerably, so predicting an individual patient's postoperative nadir from the pre-operative count would be impossible. Consequently, placement of an epidural catheter in many of these patients could expose them to an increased risk of spinal bleeding if the catheter is removed accidentally.

The effect of facial hair and sex on the dispersal of bacteria below a masked subject.

Surgical face masks prevent the dispersal of bacteria from the upper airway to surfaces immediately in front of and below the face during talking. However, mask wiggling has been reported to increase dermabrasion and bacterial contamination of surfaces immediately below the face. Facial hair and recent shaving may alter the quantity of particles shed by dermabrasion when the mask is wiggled. We investigated the effect of mask wiggling in 10 bearded and 10 clean-shaven male subjects, and 10 female subjects. Wiggling the mask significantly increased the degree of bacterial shedding onto agar plates 15 cm below the lips in bearded males (p = 0.03) and females (p = 0.03), but not in clean-shaven males. At rest without mask wiggling the bearded subjects shed significantly more bacteria than clean-shaven males (p = 0.01) or females (p = 0.001). To reduce the risks of contamination of the sterile field when face masks are worn females and bearded males should avoid wiggling the face mask. Bearded males may also consider removing their beards.

A comparison of 1% ropivacaine with a mixture of 0.75% bupivacaine and 2% lignocaine for peribulbar anaesthesia.

In a single centre, randomised, double-blind study, 54 patients underwent intraocular surgery under peribulbar anaesthesia with either ropivacaine 1% or a mixture of bupivacaine 0.75% and lignocaine 2%, both with hyaluronidase 7.5 iu.ml-1. There were no significant differences in volume of anaesthetic required, time to onset of block, peri-operative pain scores or frequency of adverse events between the ropivacaine group and the lignocaine and bupivacaine group.

Surgical face masks and downward dispersal of bacteria.

The ability of face masks to prevent forward dispersal of bacteria is offset by the possibility that they may increase vertical shedding of bacteria from the face during facial movement. To investigate this, a blood agar plate was placed 30 cm directly below the lips of 20 volunteers who were encouraged to talk for 20 min while moving their heads from side to side, without a face mask for the first 5 min and then with a standard, soft pleated face mask for the subsequent 15 min. The agar plates were changed at 5-min intervals. Analysis of the number of bacterial colonies grown on each agar plate showed a statistically significant reduction in the median number of colonies cultured per plate when the mask was worn. Our results suggest that for procedures lasting less than 15 min, the operator should wear a face mask, particularly when the face is in close proximity to the operative field and the need for speaking is anticipated.

Failed intubation and emergency percutaneous tracheostomy.

Failed intubation associated with difficulty with ventilation is rare. Cricothyrotomy may provide a means of oxygenating the patient, but in practice it may be difficult to perform and does not establish a definitive airway. We report two patients in whom percutaneous tracheostomy was used as an emergency procedure. In both cases placement was extremely rapid and salvaged the situation, leaving a definitive airway.

Comparison of 0.75% levobupivacaine with 0.75% racemic bupivacaine for peribulbar anaesthesia.

In a single centre, randomised, double-blind study 50 patients scheduled for intra-ocular surgery received 0.75% levobupivacaine or 0.75% racemic bupivacaine for peribulbar anaesthesia. There were no significant differences in the mean (SD) volume of levobupivacaine (11 (2.7) ml) or racemic bupivacaine (10 (2.6) ml) required, time to satisfactory block (levobupivacaine-13 (5.6) min; racemic bupivacaine-11 (4.4) min), peri-operative pain scores or frequency of adverse events between levobupivacaine and racemic bupivacaine. The safer side-effect profile of levobupivacaine may offer significant advantages in the elderly population undergoing cataract extraction in whom intercurrent disease is common.

Endoluminal brushing for detection of central venous catheter colonization--a comparison of daily vs. single brushing on removal.

The fibrin assay system (FAS) has been designed to address the problem of in-situ diagnosis of central venous catheter (CVC) colonization. The FAS was evaluated in 12 critically ill patients with daily brushings, comparing results with culture of the catheter tip and blood. Data analysis of the FAS showed a sensitivity of 0 with a specificity of 1.0. The study was repeated in a further 12 high-risk patients with a single terminal brushing on catheter removal. This gave a sensitivity of 0.14 and a specificity of 0.8. Differences in sensitivity may be due to daily disruption of the endoluminal fibrin clot. Our results do not support the routine use of the FAS to detect CVC colonization in the intensive care unit.

A laboratory comparison of two techniques of emergency percutaneous tracheostomy.

This laboratory study was designed to compare the speed of placement of a percutaneous tracheostomy using two common methods and to evaluate any damage caused to the trachea. The same operator who was experienced with both techniques placed 10 percutaneous tracheostomies into a pig tracheal model, five using the Griggs tracheostomy forceps technique and five using the Ciaglia sequential dilatation technique. Placement of the tracheostomy was significantly faster using the Griggs technique (mean 89 s, range 69-105 s) than using the Ciaglia sequential dilator technique (mean 217 s, range 180-267 s). Damage to the posterior wall was noted in four of the tracheas. We concluded that the Griggs technique is rapid and in trained hands may be suitable for emergency airway access. In addition, the pig trachea model is easy to set up and provides a very useful training tool.