Page 1540 - Hall et al (2015) Principles of Critical Care-McGraw-Hill

CHAPTER 111: Preoperative Assessment of the High-Risk Surgical Patient 1059

The aim of therapy is to avoid excess morbidity and mortality, which Recommendations for glucose infusion to prevent catabolism suggest
may be caused or exacerbated by extremes in blood glucose levels, between 5 and 10 g of glucose per hour, although the optimal dose of
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undue protein catabolism, and fluid and electrolyte disturbances. glucose necessary for prevention of fat and protein catabolism has not
been clearly determined. However, clinical experience suggests that
Risk Assessment: As discussed previously, diabetes is an important car- most surgical diabetics can be maintained within the normal blood glu-
diac risk indicator and it is accepted that diabetics encounter increased cose range with an insulin infusion set between 1 and 2 U/h.
perioperative morbidity and mortality. 66-68 Patients receiving total parenteral nutrition, which is generally up to
A perioperative myocardial infarction rate of 5.2% is reported in diabet- 25% dextrose, usually require an additional 2 to 3 units of insulin per
ics undergoing abdominal aortic reconstruction compared to 2.1% of non- hour. Apart from careful monitoring of blood glucose levels, the patient’s
diabetic patients. Inadequate control of blood glucose can lead to ketosis overall clinical status (particularly neurologic and hemodynamic)
and acidemia in type I patients and dehydration in types I and II diabetics. should be closely observed. Avoidance of hypoglycemic episodes while
Decreased wound healing occurs at glucose levels greater than 200 mg/dL. allowing mild hyperglycemia without ketosis is prudent in the diabetic
Glucose concentrations greater than 250 mg/dL have been shown to impair whose blood sugar is extremely difficult to control.
leukocyte function and exacerbate ischemic brain damage. In addition to What emerges from all the studies dealing with perioperative diabetes
the effects of abnormal blood glucose levels, diabetics are at particular management is that the most important factor in optimal perioperative
risk of atherosclerotic disease in cerebral, coronary, and renal vasculature. glycemic control is frequent measurement of blood sugar and appropri-
Peripheral vasculopathy is an important complication of diabetes. ate therapeutic interventions by trained staff. Perioperative metabolic
Preoperative clinical markers for increased perioperative complica- management should be planned and coordinated by surgeons, anes-
tions have been introduced previously. The important risk factors of cor- thetists, and diabetic care teams in conjunction with the patient when
onary artery disease, congestive heart failure, renal failure, and vascular possible. With the exception of type II diabetic patients presenting for
disease could all be considered simply sequelae of diabetes. Autonomic minor surgery, all diabetic patients should receive intravenous infusions
neuropathy is found in over 40% of patients presenting for surgery and of glucose with appropriate insulin to achieve normoglycemia until the
may alter hemodynamic responses to intubation and surgery. 69,70 preoperative regimen is resumed.
Apart from anesthesia for cataract extraction, choice of anesthetic
technique has not been associated with altered outcome. Thoracic ■ GLUCOCORTICOID SUPPLEMENTATION IN CHRONIC
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epidural and spinal anesthesia techniques are associated with reduced GLUCOCORTICOID USERS
intraoperative catecholamine release. However, to date, no study of
exclusively diabetic patients has compared outcome between regional Perioperative glucocorticoid supplementation for patients receiving
and general anesthesia techniques. steroid therapy is common. The rationale for its use is the avoidance of
hypoadrenalism, resulting in a variety of clinical signs including fever,
Risk Reduction: Preoperative evaluation should include thorough clinical nausea, dehydration, abdominal pain, hypotension, and shock. Other
assessment for cardiac, neurologic, and peripheral vascular abnormalities. evidence of hypoadrenalism includes low-voltage complexes on the
A careful history for the presence of ischemic heart disease or prior myo- ECG, hypoglycemia, and eosinophilia. Despite many patients presenting
cardial infarction should be supported by cardiac investigations where with chronic steroid use, the incidence of perioperative adrenal insuf-
appropriate. Glycosylated hemoglobin (HbA1c) levels less than 10% ficiency is low (0.01%-0.1%). 82
suggest satisfactory glycemic control. Evidence suggests that intensive Retrospective and prospective data suggest that routine steroid
insulin therapy to achieve strict control of blood sugar (80-110 mg/dL) supplementation for all glucocorticoid-treated patients may not be
improves outcome in nondiabetic surgical ICU patients and that general necessary. 83-85 Well-known adverse effects of exogenous glucocorticoids
practice (to maintain a blood sugar <200 mg/dL) may be inadequate include immunosuppression, exacerbation of osteoporosis, avascular
in the postoperative diabetic. Logically, an intensive regime adds necrosis of the femur, diabetes, peptic ulcer disease, diminished wound
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hypoglycemia risks and more recent studies of intensive insulin therapy healing, and neuropsychiatric disorders.
suggest that this risk exceeds any benefit. Daily endogenous cortisol release in normal adults approximates 25
Nondiabetic patients recovering from surgery commonly show transient to 30 mg per day at rest. Stressors such as major surgery or critical illness
hyperglycemia and diminished insulin secretion and end-organ responsive- increase endogenous production to 5 to 10 times that amount because of
ness in response to increased circulating catecholamines. However, these increased secretion of adrenocorticotropic hormone (ACTH) from the
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patients secrete sufficient insulin to suppress lipolysis and ketogenesis. anterior pituitary gland. Increased cortisol secretion returns to normal
Diabetics present with decreased or absent preoperative insulin secretion within 24 hours of skin incision in uncomplicated minor surgery. 86
and a preexisting insulin resistance, which serves to worsen the hypergly- The clinical rationale for steroid supplementation in the perioperative
cemic response to surgery. Decreased peripheral use of glucose results in period is based on the known protracted recovery of the hypothala-
lipolysis, ketogenesis, possible acidemia, glycosuria, and dehydration. A mus-pituitary-adrenal (HPA) axis following prolonged glucocorticoid
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variety of insulin regimens have been suggested for the routine periopera- administration. The stress response observed in typical perioperative
86
tive management of diabetics undergoing surgery. No single regimen has patients results in ACTH levels far in excess of that required for maximal
proved markedly superior. Currently, perioperative intravenous glucose adrenocortical stimulation. A number of studies 88-90 have suggested that
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infusions are recommended, and insulin may be administered via a variety patients on chronic steroid therapy undergoing elective major surgery
of dosages and routes. Subcutaneous administration of half the regular may not require perioperative steroid supplementation in addition to
daily dose before surgery, using a variable-rate glucose infusion to main- their regular steroid regimen. In a study of 40 renal transplant recipients
tain normoglycemia, has proved successful. Mixing insulin, potassium, on chronic prednisone therapy, none of the patients received more than
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and 5% or 10% glucose has also been suggested. 76,77 Most authors suggest baseline glucocorticoid therapy during admission for moderately stress-
a variable-rate insulin infusion using an automated syringe device with a ful surgery or critical illness. Despite biochemical evidence of decreased
simultaneous glucose infusion through an alternative intravenous access. 78,79 adrenal response to exogenous ACTH in 67% of the patients, none of the
Insulin requirements vary widely in the perioperative patient. The patients exhibited clinically overt hypoadrenalism, and 97% of all patients
normal state (approximately 0.25 unit of insulin per gram of glucose) is excreted normal or increased urinary cortisol concentrations during
influenced by many factors such as obesity, concomitant glucocorticoid their hospital stay. This suggested that cortisol concentrations were
administration, and the septic state, which may increase insulin require- sufficient to meet requirements during the time of stress. 85
ments to as high as 0.4 to 0.8 unit of insulin per gram of glucose. The Since endogenous cortisol secretion in normal individuals rarely
highest insulin requirements have been observed in patients undergoing exceeds 200 mg/day, exogenous steroid supplementation should be
CABG (0.8-1.2 U/g of glucose). 80 similar. To date, no data suggest that supplemental glucocorticoid

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