Elevated preoperative HA1C is associated with increased perioperative risk

The role of HA1C

HA1C provides insight into glucose control over the preceding 3–4 months. Elevated preoperative HA1C is associated with increased perioperative risk and holds promise as a preoperative screening modality.34,35 Gustafsson and colleagues,35 in a prospective study of 120 patients without known DM having major colorectal surgery, were able to show patients with preoperative HA1C > 6% were at significantly greater risk for pneumonia, urinary tract infection, pleural effusions, and postoperative ileus, and had significantly elevated postoperative glucose levels in this group of patients. Others retrospectively linked preoperative HA1C to postoperative complications. Dronge and colleagues36 showed that preoperative HA1C<7% is significantly associated with decreased infectious complications including pneumonia, wound infection, urinary tract infection, and sepsis. Hudson and colleagues37 demonstrated a preoperative HA1C > 6% in non-diabetics is independently associated with greater early mortality after elective cardiac surgery.

Elevated HA1C, as a marker of poor glycaemic control, correlates with increased perioperative risk in diabetic patients. Han and Kang38 demonstrated a significant increase in wound complications after total knee arthroplasty in diabetic patients with HA1C >8%. Diabetic patients with an HA1C >6.5% have an increased risk of pneumonia, urinary tract infection, and superficial wound infections after elective cardiac surgery when compared with diabetics with HA1C <6.5%.34 Currently, the ADA suggests that practitioners consider obtaining an HA1C on diabetic patients admitted to the hospital if the result of testing in the previous 2–3 months is not available. The ADA also suggests HA1C testing in patients with risk factors for undiagnosed DM who exhibit hyperglycaemia in the hospital.29

Although elevated HA1C is associated with adverse outcomes, there is a lack of data to show delaying elective surgery to correct HA1C is beneficial. Nonetheless, HA1C screening does allow identification of unrecognized DM and stratification of perioperative risk. Aggressive approaches to lowering HA1C in non-surgical patients have not been shown to decrease mortality.39 Future investigations will likely clarify the role of preoperative HA1C management on modifying surgical outcome.

Clinicians should be reminded that the accuracy of HA1C can vary by measurement technique. Erroneous results are possible in patients with haemoglobinopathies, chronic bleeding, iron deficiency, renal failure-induced anaemia, recent transfusions, or ongoing haemolysis.40

Preoperative Glycemic Management

Preoperative Glycemic Management

In patients using insulin, frequent glucose monitoring should be utilized to ensure that glucose values are within normal ranges. Patients should monitor blood glucose levels vigilantly including before and after meals as well as before sleeping. Additionally, finger stick glucose monitoring should be completed every 4 to 6 hours in any patient who is nil per os (NPO), with supplemental insulin used to correct hyperglycemia back to normal values [57]. When using supplemental-scale coverage, short-acting insulin (humulin, novolin) has a shorter duration of action than human insulin and may be given subcutaneously every 4 to 6 hours; however to prevent insulin stacking regular human insulin should not be given more than every 6 hours to correct hyperglycemia [57]. Traditionally, long-acting insulin (glargine, ultralente) is discontinued two to three days prior to surgery; glucose levels are instead stabilized by a combination of intermediate insulin (NPH) with short-acting insulin twice daily or regular insulin before meals and intermediate-acting insulin at bedtime [62]. However, if glycemic control is well managed in a patient being treated with glargine, it is acceptable to continue the same insulin regimen until the day of surgery [63]. Finally, it is important to confirm the form of diabetes present, as patients with type 1 diabetes must continue a basal rate insulin replacement preoperatively (0.2 to 0.3 U/kg/day of a long-acting insulin) [57].

Along with careful insulin regulation, there are a number of oral glycemic control drugs that should be discontinued before surgery. Biguanides (metformin) sensitize specific tissues to insulin, mediating efficient uptake of glucose in muscle and fat while preventing hepatic glucose formation. Metformin usage is discontinued before surgery in the United States and Europe due to renal function complications that may arise intraoperatively (such as hemodynamic instability or decreased renal perfusion), increasing the risk of lactic acidosis [64, 65]. Alpha glucosidase inhibitors (acarbose, miglitol) weaken the effect of oligosaccharidases and disaccharidases in the intestinal brush border, effectively lowering the absorption of glucose after meals. However, in preoperative fasting states, this drug has no effect and thus should be discontinued until the patient resumes eating [66]. Thiazolidinediones (pioglitazone, rosiglitazone) mechanism of action is similar to that of metformin and however is not associated with lactic acidosis. Nevertheless, these drugs are generally discontinued as they are not insulin secretagogues and may also cause fluid retention in the postoperative phase [57, 67]. Sulfonylureas (glibenclamide, glimepiride, and glipizide) trigger insulin production and may induce hypoglycemia in a fasting preoperative patient. If a patient has mistakenly taken a sulfonylurea on the day of surgery, the operation may still be completed; however, careful glucose monitoring is imperative and IV dextrose may be required [65, 68]. Glucagon-like peptide-1 (GLP-1) agonists (exenatide, liraglutide) are held the day of surgery as they slow gastric motility and may delay restoration of proper gastrointestinal function during recovery. Finally, because dipeptidyl peptidase-4 (DPP-4) inhibitors (sitagliptin, linagliptin) work by a glucose dependent mechanism (reducing the risk of hypoglycemia even in fasting patients) they may be continued if necessary; however, these medications primarily reduce glycemic levels after meals and their effects will be greatly marginalized in preoperative NPO patients [57].

There currently exists no evidence-based guideline dictating when to cancel surgery due to hyperglycemia. As a rule, elective surgery should not be performed on patients in a compromised metabolic state (DKA, HHS, etc.). Although no strict standard for surgical cancellation has been determined, the Yale New-Haven Hospital recommends postponing surgery if glucose is greater than 400 mg/dL. Similarly, at Boston Medical Center, it is recommended to postpone nonurgent surgical procedures if glucose is >500 mg/dL. In the event surgical cancellation is required, physicians should first manage any metabolic pathologies if present. After resolution of any underlying metabolic abnormalities, clinicians may then aim to restore blood glucose back to target range using combination insulin therapy as described above [69].

Oxygen consumption (VO2) is measured in a 70-kg subject on a treadmill at 2500 Ml per minute. This corresponds to:

A. 1 metabolic equivalent (MET)

B. 5 METs

C. 10 METs

D. 15 METs

E. 20 METs

One MET is equal to the amount of energy expended during 1 minute at rest, which is roughly 3.5 mL of oxygen per kg of bodyweight per minute (3.5 mL/kg/min).

For a 70-kg (150 lb.) person one MET would equal 250 mL O2 per minute.

So 2500 mL would correspond to 10 METs.

Recall that 4 METs are the equivalent of climbing two flights of stairs at a reasonable rate without stopping, or walking on level ground at 4 mph; and 10 METs are equivalent to participating in strenuous activity such as swimming, skiing, playing basketball or jogging at about 6 mph

 A 67-year-old man is to undergo a radical retropubic prostatectomy. He has aortic stenosis with a gradient of 37 mm Hg at rest. He has an allergy to penicillin. Which of the following is the best regimen for subacute bacterial endocarditis (SBE) prophylaxis in this patient?

A. Ampicillin and gentamicin

B. Vancomycin and gentamicin

C. Clindamycin and gentamicin

D. Clindamycin alone

E. None of the above

(E)

·       In 2007, the American Heart Association revised the guidelines for prevention of infective endocarditis (IE).

·       Presently, only patients with underlying cardiac conditions with the highest risk for an adverse outcome from IE should receive antibiotic prophylaxis for selected dental procedures.

·       Prophylaxis is not recommended for patients undergoing elective genitourinary (GU) or gastrointestinal (GI) procedures.

·       The cardiac conditions with the highest risk include: prosthetic cardiac valves, previous IE, several types of congenital heart disease (CHD), and cardiac transplantation recipients who develop cardiac valvulopathy.

·       Any of the antibiotics listed in the question or cephalexin 2 g orally (or other first or second generation oral cephalosporin in equivalent dosage) or clindamycin 600 mg orally, IM or IV should be administered 30 to 60 minutes before the procedure.

This patient has aortic stenosis and does not need any prophylaxis