Outline
perioperative management alternatives for the diabetic patient.
The goals of perioperative management are to
avoid hyperglycemia and hypoglycemia. Severe hyperglycemia pre-disposes
patients to osmotic diuresis as well as ketosis or nonketotic hyperosmolar
states. Hypoglycemia risks CNS damage. Recent studies from the ICU and cardiac
surgery indicate that serum glucose concentrations above 120 mg/dL may
significantly increase mortality and morbidity. Traditionally, the
perioperative target for serum glucose was 120–200 mg/dL, to minimize the
potential for hypo-glycemia. This is probably still a reasonable goal for minor
or moderately invasive procedures in noncritically ill patients. Patients who
are critically ill or are having major procedures should have tighter glycemic
control, in the range of 80–110 mg/dL. Protocols for tight glycemic control are
still evolving, and several have been published (see Suggested Readings). This
tighter control is more labor- and resource-intensive, and is currently not
practical for all diabetic patients.
Oral hypoglycemic agents should be discontinued
while patients are fasting. Residual hypoglycemic effects are opposed by
administering 5% dextrose, if needed. The frequency of blood glucose
measurements to monitor for hyperglycemia and hypoglycemia depends on the
desired degree of control.
Because patients refrain from eating and
drinking before surgery and anesthesia, insulin doses may be with-held or
reduced, depending on the underlying physiology. Type I diabetics need insulin
to avoid DKA. Type II diabet-ics with elevated fasting glucose concentrations
also bene-fit from insulin therapy while fasting. Frequently, one half of the
usual subcutaneous insulin dose is administered. Blood glucose concentrations
determine the need for 5% dextrose infusion, typically started at 100 mL/hr.
Insulin and dextrose infusions are adjusted based on blood glucose
determinations at 1-hour intervals for major procedures or critically ill
patients, and up to 4-hour intervals for minor procedures. Intravenous
administration is far more reliable than subcutaneous dosing during periods of
hemody-namic instability, vasoconstrictor administration, and/or hypothermia.
Bolus intravenous insulin dosing results in
rapid decline of glucose levels for short periods of time. In contrast,
con-tinuous intravenous administration of 0.01–0.02 U/kg/hr provides the
optimal and easiest means of controlling serum glucose concentrations. The most
reliable control is obtained with separate infusions of 5% dextrose and insulin
mixed with half-normal saline to a concentration of 0.1 U/cc. Flushing the
intravenous tubing with the insulin solution prevents significant loss of
insulin to the plastic tubing. During periods of rapid glucose fluxes, blood
glucose determinations are performed every hour. Measurements can be made every
4 hours after a steady state has been reached.
Autonomic dysfunction and/or severe cardiac
disease may indicate invasive monitoring. Autonomic neuropathy predisposes
patients to hypotension accompanying regional anesthesia and increases the risk
of aspiration pneumonitis from gastroparesis. Aspiration prophylaxis and rapid
sequence induction may be indicated. Peripheral neuropathies require particular
care during positioning and moving to avoid traumatic injury. Hyperglycemia-induced
osmotic diuresis indicates urinary bladder drainage.
Postoperatively, rapid resolution of sepsis and
decreased levels of circulating catecholamines contribute to acute
hypoglycemia.
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