Note: refractive index sensing of turbid media by differentiation of the reflectance profile: does error-correction work?

A widely used method for determining refractive index postulates that the derivative of the angular profile for light reflected from the sample is maximum at the critical angle for total internal reflection (TIR). It is well-known that in turbid media this "differentiation method" yields errors in refractive index. Unexplained anomalies in previous error-calculations are eliminated if one uses a recent model of TIR which departs from traditional Fresnel theory. However we find that, in practical situations, the refractive index obtained by differentiation even after error-correction is significantly different from the best estimate for the refractive index obtained by curve-fitting the reflectance data. Thus the differentiation method lacks scientific validity in turbid media.

A comparative study of clonidine versus a combination of diazepam and atropine for premedication in orthopaedic patients.

Sixty patients in the age group of 18-60 years of A.S.A. Grade I/II risk, scheduled for elective orthopaedic surgeries under general anaesthesia were studied for pre-medication with either oral clonidine or with combination of effects of diazepam & atropine. Patients in Group A (clonidine group) received tablet clonidine 100 mcg (1 tablet) if less than 50 kg in weight and 200 mcg if weighing more than 50 kg two hours before surgery. Patients in Group B (Diazepam-atropine group) received one tablet of Diazepam (10 mg) orally two hours before surgery and injection atropine-sulphate 0.01 mg/kg half an hour preoperatively by intramuscular route. In our study, the sedative and anti-sialogogue effects of clonidine were comparable to those of diazepam-atropine combination, which are commonly used premedicants. The anti-anxiety effect of clonidine was found to be better than that of diazepam-atropine combination. Clonidine also proved to be a better agent for the attenuation of pressor response to laryngoscopy and intubation. Thus, oral clonidine is a better premedicant compared to atropine-diazepam combination. Also, it is a more acceptable agent because of its oral route of administration.

Comparative study of intrathecal pethidine versus lignocaine as an anaesthetic and a postoperative analgesic for perianal surgery.

100 patients with ASA risk I & II and undergoing perianal surgery were studied for anaesthetic effects and postoperative analgesia following either intrathecal pethidine or lignocaine. Saddle block was performed either with intrathecal pethidine 5% (50 mg/ml) 0.5 mg/kg or 1 ml of 5% lignocaine. Sensory and motor block postoperative analgesia, need for additional analgesia were studied. The onset of sensory and motor blockade with lignocaine was faster than pethidine. However the sensory and motor blockade lasted longer with pethidine. The duration of postoperative analgesia was 15.39 +/- 5.14 hours as against duration of postoperative analgesia with lignocaine which was 1.3 +/- 0.53 hours. Only 10% of patients in the pethidine group required intramuscular analgesic supplementation whereas 30% of patients in the lignocaine group required intramuscular analgesic supplementation.