Uncertainty in the amount of power delivered by CO2 medical lasers.

Carbon dioxide medical lasers are being used for various clinical applications with considerable success. Despite the bulk of the generating equipment, the use of light, articulated arms to deliver the power beam to either hand-held or microscope-mounted aiming heads allows accurate power placement. In addition, the beam can be focussed to a small spot size, minimizing damage to adjacent tissue provided that the output power and the precise duration of application are known, and the shielding of deeper tissue has been adequate. In an attempt to assess the reliability of the laser beam as a significant surgical tool (particularly suitable for fine cutting functions in microsurgical procedures), we tested the power output of some of the CO2 surgical lasers now available in Australia. An alarming discrepancy was found between the actual power delivered and the higher power value displayed as being delivered. As these medical lasers were tested and passed as fully functioning by their local agents, it is suggested that purchasers of CO2 lasers should be aware of these possible power inadequacies and subject their equipment to frequent power checks. Otherwise much longer applications of the laser beam will be needed to accomplish the cutting action required, with the consequent infliction of more damage to the surrounding tissues.

Programming of insulin delivery with meals during subcutaneous insulin infusion.

The serum insulin elevation after subcutaneous (s.c.) infusion of 10 U of neutral regular insulin given over 5 or 30 min has been examined in normal subjects to find a delivery profile that would simulate the normal serum insulin response to a meal. Endogenous insulin release, assessed by measurement of C-peptide, was suppressed by an i.v. infusion of 1 U/h neutral regular insulin, beginning 60 min before the s.c. administration and continuing throughout the study. The increment in serum insulin levels after the 5-min s.c. infusion reached a peak of 62 +/- 9.5 mU/L at 45 min, and the rate of elevation of insulin levels closely approximated the normal insulin response to a 50-g, 500 kcal mixed meal. The increment in serum insulin levels with the 30-min s.c. infusion reached a peak of 41 +/- 1.4 mU/L at 75 min. The incremental insulin response up to 180 min (area under the curve) after the 5-min s.c. infusion was 30% greater than the response to the 30-min infusion. On the basis of these studies, we conclude that insulin delivery for meals during s.c. insulin infusion need not be initiated before the meal, but should be given over a period of approximately 5 min or less. Further study is required to delineate the effects of concentration, local degradation, and rate of delivery on entry of s.c. insulin to the vascular system.