The Endocrine System:
Patients with diabetes mellitus are prone to a number of vascular complications associated with elevated levels of blood glucose.26 In particular, chronic hyperglycemia increases the risk of developing coronary artery disease (CAD), myocardial ischemia and infarction (MI), hypertension, neuropathy, and chronic renal failure.
Throughout the perioperative period, the stress of surgery and preoperative fasting can result in marked swings in blood glucose, volume depletion, thrombogenesis, arrhythmias, and silent MIs. Perioperative hyperglycemia also impairs wound healing, and increases the risk of infection. It is important to ask patients about their glucose control, and inquire about their usual blood glucose level and compliance with therapy (diet/oral hypoglycemic agents/insulin/combination therapy). The presence of co-morbidities should be verified, including cardiac ischemia, neuropathy, and nephropathy. If patients are on insulin, it is important to ensure they have followed the preoperative fasting instructions and insulin orders. Typically, patients are instructed to take half of their morning dose of insulin and omit any oral hypoglycemic agents on the day of surgery. At the time of admission to hospital, a glucometer measurement is obtained and an intravenous infusion containing glucose (e.g., 5% dextrose in water [D5W] at 100 mL∙hr-1) is initiated. Continued management is typically achieved using a “sliding scale” basing additional insulin administration on the results of glucometer measurements repeated at regular intervals. Alternatively, tighter control of blood glucose levels may be desired in the perioperative period. This is generally achieved using a glucose - insulin intravenous infusion protocol.
Patients with thyroid disease may experience difficulties under anesthesia.27 Profound hypothyroidism is associated with myocardial depression and exaggerated responses to sedative medications. Hyperthyroid patients are at risk for perioperative thyroid storm. Thyroid goiters may either directly compress the airway or involve the recurrent laryngeal nerve, leading to vocal cord palsy and placing the patient at risk for airway obstruction.
Patients with pheochromocytoma can be particularly challenging for the anesthesiologist, surgeon, and internist involved in their care. These patients are at risk for extreme swings in blood pressure and heart rate throughout the perioperative period. They also require intensive preoperative therapy with adrenergic blocking drugs prior to surgery.28
Adrenal corticosteroid production increases postoperatively in response to the stress of surgery. Chronic intake of oral steroids may suppress production of adrenal corticosteroids. Patients who are on corticosteroid therapy are at risk of developing postoperative adrenal insufficiency due to their inability to increase endogenous corticosteroid production to match the imposed stress of surgery. The incidence of adrenal suppression is not predictable and depends on the potency and frequency of steroid use as well as the length of steroid therapy.29 Patients who have received a dose of prednisone > 20 mg per day for more than 5 days in the past 12 months may be at an increased risk of developing postoperative adrenal insufficiency. Supplementation with parenteral corticosteroids may be required to prevent adrenal insufficiency in the perioperative period.
The Renal System:
Disorders of fluid and electrolytes are common and may require correction in the perioperative period. Generally, all fluid and electrolyte disorders should be corrected prior to elective surgery.
Patients with acute and chronic renal failure have abnormal fluid, electrolyte, and drug excretion and may require perioperative dialysis management.31 Patients should be asked about the relative progression (or stability) of their disease, and particular attention must be paid to fluid and hemodynamic management in order to avoid further renal insult. Patients on hemodialysis (HD) should also be asked about their schedule so arrangements can be made to perform HD within the 24-hr period prior to surgery. Potassium levels do not reach a steady state between the intra and extracellular compartments for several hours after HD; hence, measurement of electrolytes (including potassium) immediately following HD is generally not helpful, and it may be misleading, as potassium flux has not reached a steady state.
The Hematologic System:
Anemia (of various etiologies) is common in surgical patients. The presence of anemia increases the likelihood of a patient receiving blood products in the perioperative period. Perioperative transfusion is associated with an increase in morbidity and mortality.32 When time permits, therapeutic interventions should be considered to treat and correct the anemia prior to surgery.
There is no defined “transfusion trigger” for patients having surgery, rather, a “patient-specific” decision whether or not to transfuse perioperatively is encouraged. Factors to consider include the chronicity of the anemia, the risk of perioperative blood loss, and the presence of other coexisting diseases. A preoperative blood “type and screen” should be considered, and if transfusion is a possibility, this should be discussed with the patient, and the patient’s consent should be obtained for blood product administration prior to commencing surgery. The surgeon should be advised to optimize hemostasis and minimize blood loss. Blood conservation strategies should also be discussed with the patient and operating room (OR) team (see Chapter 21).
Careful management is required for patients with bleeding disorders secondary to clotting factor deficiencies, platelet abnormalities, or medication therapy. Neuraxial anesthesia is generally contraindicated in patients who have a bleeding disorder. Patients with a history of deep vein thrombosis (DVT), pulmonary embolism (PE), cerebral vascular accident (CVA), or atrial fibrillation may be receiving long-term anti-coagulant therapy. These patients require special attention to minimize the risk of bleeding vs the risk of thrombotic complications (DVT, PE, CVA) in the perioperative period.
Depending on the nature of the proposed surgery, anticoagulation therapy (such as acetylsalicylic acid [ASA], coumadin, antiXa inhibitors, and clopidogrel) may need to be stopped. These patients may require “bridging therapy” with low-molecular-weight heparin to “bridge” them in the immediate preoperative period. A preoperative consult (general medicine, hematology, or thrombosis) may be needed for patients requiring bridging therapy.
For further information on management of anticoagulation both before and after surgery, consult the ACCP Guidelines.16,17
Special Populations:
Pediatrics:
Children are not simply “small adults”, they are influenced by a variety of developmental, pharmacological, and physiological changes that influence the delivery of anesthesia (see Chapter 26: Pediatric Anesthesia). In addition to a regular history, ask about the pregnancy and birth history, premature delivery and its complications, and the presence of any known syndromes or organ dysfunction in the child. The preoperative visit is especially important for children as it provides an opportunity to familiarize the child with procedures that will take place in the OR. Consider that the child may benefit