The current usage of hypothermia in British neurosurgery

Intraocular Temperature Distribution in Eyes Undergoing Different Types of Surgical Procedures during Vitreous Surgery

Vitreous temperature has been reported to vary during intraocular surgery. We measured the temperature at three intraocular sites, just posterior to the crystalline lens (BL), mid-vitreous (MV), and just anterior to the optic disc (OD), and investigated temperature changes before and after different types of surgical procedures in 78 eyes. The mean temperature at the beginning was 30.1 ± 1.70 °C in the anterior chamber, 32.4 ± 1.41 °C at the BL, 33.8 ± 0.95 °C at the MV, and 34.7 ± 0.95 °C at the OD. It was lowest at the BL, and highest at the OD. The mean temperature after cataract surgery was slightly lower especially at an anterior location. Thus, the temperature gradient became slightly flatter. The mean temperature after core vitrectomy was even lower at all sites and a gradient of the temperature was not present. The mean temperature after membrane peeling was significantly higher than that after core vitrectomy, and there was no gradient. The mean temperature after fluid/air exchange was lower at the BL and higher at the MV and at the OD. Thus, a gradient of higher temperatures at the OD appeared. The intraocular temperature distribution is different depending on the surgical procedure which can then change the temperature gradient. The temperature changes at the different intraocular sites and the gradients should be further investigated because they may affect the physiology of the retina and the recovery process.

Hypothermia Protects Cultured Human Retinal Pigment Epithelial Cells against Indocyanine Green Toxicity

PURPOSE

The aim of this study was to determine whether indocyanine green (ICG) is toxic to cultured human retinal pigment epithelial (ARPE-19) cells, and whether hypothermia can protect the ARPE-19 cells against the ICG toxicity.

METHODS

Cultured ARPE-19 cells were exposed to 0.25, 0.5, 1, 2.5, and 5 mg/mL of ICG dye at 37 and 4 degrees C for 30 min. The percentage of ARPE-19 cells that survived was determined by resazurin 1 day after the exposure.

RESULTS

Exposure of the RPE cells to a hypotonic saline solution with an osmolarity equal to 5 mg/mL of ICG did not induce a statistically significant decrease in the percentage of RPE cells that survived. Exposure of the ARPE-19 cells to ICG induced a significant decrease in the percentage of cell survival at all concentrations of ICG (P<0.05), except in 0.25 mg/mL at 37 degrees C. At 4 degrees C, on the other hand, ICG induced a statistically significant decrease in the percentage of RPE cell survival only at 5 mg/mL of ICG (P<0.05).

CONCLUSIONS

These results indicate that ICG is toxic to human RPE cells in culture, and that cell death cannot be attributed to the low osmolarity. Hypothermia of 4 degrees C has a protective effect against ICG toxicity.

Hypothermia protects cultured human retinal pigment epithelial cells against trypan blue toxicity

PURPOSE

To determine whether trypan blue (TB) is toxic to cultured human retinal pigment epithelial (ARPE-19) cells, and whether hypothermia can protect ARPE-19 cells against TB toxicity.

METHODS

ARPE-19 cells were cultured and exposed to balanced salt solution as a control, while other cells were exposed to 0.05, 0.2, and 0.5% TB dye at 37 and 4 degrees C for 5 and 30 min. The percentage of ARPE-19 cells that survived was determined by resazurin 1 day after the exposure.

RESULTS

A statistically significant decrease in the percentage of ARPE-19 cells surviving was found after exposure to 0.2 and 0.5% TB at any temperature or for any exposure duration (p < 0.01). The percentage of RPE cells surviving at 0.05% was not significantly different from that of controls except for a 30-min exposure at 37 degrees C. The percentage of cells surviving at 4 degrees C for a 5-min exposure to 0.5% TB and a 30-min exposure to 0.2 and 0.5% was significantly higher than that at 37 degrees C under each condition (p < 0.01 for all).

CONCLUSIONS

These results indicate that TB is toxic to human RPE cells, and the toxicity is dose- and exposure duration-dependent. Exposing the cells at 4 degrees C had a protective effect against higher concentrations or longer exposure durations of TB compared to exposure at 37 degrees C.

Local hypothermia protects the retina from ischaemic injury in vitrectomy

AIMS

Hypothermic irrigating solutions were used during vitrectomy in pressure induced ischaemic eyes so that their effects on retinal function and histological changes could be investigated.

METHODS

After anaesthetised albino rabbits underwent closed vitrectomy, their vitreous cavities were continuously irrigated for 30 minutes at a perfusion pressure of 140 mm Hg. The rabbits were divided into three groups according to their intraocular perfusion temperatures--8 degrees C, 22 degrees C, and 38 degrees C. Electroretinograms were taken before and after irrigation. Glutamate levels in the vitreous were examined after irrigation. Eyes were enucleated on the seventh postoperative day and examined histologically.

RESULTS

On the seventh postoperative day, the recovery rate of a-wave amplitudes was significantly lower in the 38 degrees C group than in the 8 degrees C group, and that of b-wave amplitudes was significantly lower in the 38 degrees C group than in either the 8 degrees C or 22 degrees C group. Retinal damage in the 38 degrees C group revealed more severe histological impairment than in either the 8 degrees C or 22 degrees C group. Oedema of the inner retinal layer was significant in both the 22 degrees C and 38 degrees C groups. Glutamates reached peak values 30 minutes after the end of ischaemia in the 38 degrees C group. However, no significant glutamate increases were detected 15 to 60 minutes after ischaemia in either the 8 degrees C or 22 degrees C group.

CONCLUSION

Local hypothermia during vitrectomy in acute ischaemic eyes appears to decrease retinal damage.

Ocular hypothermia: anterior chamber perfusion

The anterior chambers of 27 rabbit eyes were perfused at constant pressure with room temperature (25 degrees C) or cooled (11 degrees C) balanced salt solution at constant flow rates of 4.8 ml/min or 8.5 ml/min. Intraocular temperature changes in the anterior chamber, anterior vitreous, mid vitreous, and posterior vitreous and on the retina surface were monitored with an intraocular thermocouple probe. Perfusion of the anterior chamber of the pigmented rabbit eye with cooled fluid significantly reduced the temperature of the anterior chamber and anterior vitreous and even that of the retina. Both an increase in the rate of perfusion and a lowering of the perfusion temperature enhanced the cooling effect. The observed decrease in temperatures returned to approximately normal 4 minutes following the cessation of perfusion.

Barbiturate therapy in cerebral ischaemia

Experimental and clinical studies of the protective effect of barbiturates in cerebral ischaemia are reviewed. Their action in protecting the brain from the effects of ischaemia is related to their action as anaesthetic agents and probably to the depression of neuronal function and metabolism but is incompletely understood. Their effect is dose related. Early administration is likely to be crucial to the success of barbiturate therapy as secondary events following an episode of cerebral ischaemia can lead to irreversible brain damage within 2--3 h. A potential collateral circulation appears to be essential for the protective effect of barbiturates. There may be a possibility of partly overcoming time delays in administration by giving larger doses of barbiturates.

Results of microsurgical management of intracranial aneurysms

This paper presents the results of a total of 468 aneurysm operations performed on a consecutive series of 463 patients in an 8-year period, using microsurgical techniques. About two-thirds of the patients were operated on within the first 2 weeks after hemorrhage. The postoperative mortality was 4.5%. A good result was obtained in 74.5% of cases, and a fair result in 11.8%, whereas 9.2% were permanently disabled. Hypothermia was used in 142 operations, and 326 were carried out under induced hypotension. Immediate and late results of surgery are discussed with reference to selection of patients, timing of surgery, and the anesthetic and operative procedures.