DR SARITA BAJAJ,
MD DM (Endocrinology, AIIMS),
Associate Professor Medicine, MLN Medical College Allahabad
The morbidity and mortality rates during the perioperative period are greater in the diabetic compared with the nondiabetic of comparable age, for a number of reasons. Macrovascular disease is extremely common in both type 1 and type 2 patients. Cardiovascular complications are the major causes of surgical mortality in diabetics (30%). In addition a high percentage (especially in the over 50 age category) have impaired renal function and are prone to fluid and electrolyte imbalance, dehydration, and obtundation. During the postoperative period, the diabetic has a higher incidence of infection at the operative site as well as a greater potential for urinary tract infection, pneumonia, and other systemic infections. Wound healing may be impaired in the setting of persistent hyperglycemia (>240 mg/dL) as a result of modified fibroblast function. This defect, combined with infection, may result in incision dehiscence, which frequently leads to a difficult and protracted hospitalization and frequent readmissions. Consequently, the diabetic patient spends 30% to 50% more time in the hospital than the nondiabetic following surgery, even if the surgery proceeds without incident.
Safety and simplicity are the watchwords of the surgical management of diabetic patients. Safety should be ensured if the following protocols are observed. Simplicity is essential, as surgery is frequently required in diabetic patients and its bedside management is usually undertaken by junior doctors who may have little or no specialized knowledge of diabetes. Treatment regimens should not aim for near normoglycemia; it has been shown that this does not improve outcome, and the risks of hypoglycemia are considerably increased. Sensible and practical glycemic targets are discussed below. Hypoglycemia is a major hazard of surgery, which it is particularly important to avoid, as the surgical or postsurgical patient may be unaware of this or unable to communicate.
With the use of the modern management protocols, the major outcome measures of surgery (duration of hospital stay, morbidity and mortality) are now comparable in diabetic and non diabetic patients. It follows that the skill, care and motivation with which diabetic patients are managed - ideally supervised by a diabetic team (where available) are important to the success of surgery.
Management of the individual patient is determined by the severity and nature of surgical trauma and the duration of perioperative fasting.
Determinants of the management plan and pre-operative evaluation :
The preoperative evaluation should be done in the office before an elective operation or, less preferably, on the day of admission. History of previous glycemic control should be reviewed and control should be improved in symptomatic and asymptomatic patients with sustained hyperglycemia, reflected by a fasting blood glucose (FBG) level higher than 200 mg/dL, high HbA1c values (>10%), or both. Improved control during the perioperative period (blood glucose values between 120 mg/dL and 180 mg/dL) reduces the morbidity from fluid and electrolyte imbalance, decreases the risk of infection, and increases the wound-healing rate. Prior-day admission is still indicated for the poorly controlled diabetic (FBG >240mg/dL) and for those having major elective surgery such as coronary artery bypass graft (CABG) or renal transplant.
For patients posted for minor surgery, the OHA and insulin are stopped on the day of the surgery. Once the surgey is over and the patient permitted to resume oral feeds the OHA are started with half the dose which the patient was originally taking. On the second post operative day full dose of the OHA and/or insulin is started.
A small subset of type 2 patients with acceptable control (FBG < 140 mg/dL, other blood glucose values < 200 mg/dL and glycosylated hemoglobin [HbA1c] of 8% to 10%) on a special diet or OHA may not require insulin. Long acting sulfonylureas (eg chlorpropamide) should be stopped, substituting a shorter acting sulfonylurea, if necessary.
Glycemic control should be monitored carefully during the period before admission. These patients generally require only close observation. The operation should be scheduled for the morning, if possible. Breakfast and any morning dose of OHA are omitted. Throughout the perioperative period, frequent glycemic monitoring is required and glucose-containing infusion fluids must be avoided. Sulfonylurea drugs, if used, should be omitted until the first postoperative meal.
This approach is acceptable for a surgical procedure not invading a major body cavity and when the procedure is relatively simple and short (less than 2 hours). Type 2 patients undergoing major surgery that requires prolonged fasting are best managed using continuous glucose and insulin delivery as for type 1 patients. Poorly controlled type 2 subjects who do not achieve the above glycemic targets should also be treated in this way, after initial stabilization with insulin, either in hospital or at home.
All patients taking insulin, whether persons with type 1 or type 2 diabetes should receive insulin therapy during the surgical procedure (table 1). It is preferable to take diabetic patients for surgery in the morning as first case.
The kinetics of subcutaneous insulin absorption is unpredictable and hence not advocated. Normally the requirement of insulin is 0.3U to metabolize 1 gm of glucose.
Continuous insulin infusion (intravenous) is the most rational and physiologic method for perioperative management. This approach has been shown to be safe, effective, and flexible. Insulin infusion should be started the night before for early morning procedures and for patients needing improved glycemic control. Otherwise, the patient takes the usual evening dose of insulin or OHA.
In all patients requiring insulin, the insulin infusion must be started at least 2 to 3 hours before the operation in order to titrate to the desired level of control.
There are two basic regimens for administering insulin and glucose. The preferred method uses a separate infusion of insulin and glucose to allow for independent adjustments of each infusion rate. In the 'separate-line' system one infusion line is used to deliver 10% glucose solution at 100ml/h, preferably using an electronic drip-counter, while a syringe-driver pump administers insulin through the other, usually at 2-4U/h. The insulin infusion can either be given into a separate vein, or 'piggy-backed' into the glucose line. This approach provides flexibility and can be rapidly adjusted depending on the hourly variation in blood glucose values.
The alternate method is to combine insulin and glucose as a mixture at a preestimated individualized concentration. Potassium chloride is added to the glucose ('glucose-potassium-insulin', or 'GKI' infusion), to counteract the risk of hypokalemia. Table 2 provides a simple protocol for managing diabetic patients (type 1 or type 2) undergoing surgery.
The GKI regimen has gained widespread acceptance because of its simplicity and effectiveness. To a 500-ml bag of 10% dextrose are added 10 mmol potassium chloride and 15U soluble insulin. This mixture is infused over 5h. This regimen delivers similar amounts of glucose and insulin to the separate-line system, but is considerably simpler and, because insulin and glucose are given in balanced proportions, the infusion rate is not so critical; an electronic pump is therefore not essential. It also avoids one of the main problems of giving insulin and glucose separately, namely one of the infusions running out or being interrupted by pump malfunction or the intravenous cannula becoming blocked or dislodged; if the other infusion continues, dangerous hypo-or hyperglycemia may result.
When adding insulin and potassium solutions to the bag, it is important to use a needle that is long enough to clear the self-sealing bung, to mix the bag well and to label it clearly with the dosages of the additives, During a GKI infusion, blood glucose should be monitored at least hourly until insulin requirements have been determined, according to the schedule shown in table 2. The insulin delivery rate is altered by substituting a new bag containing a different dosage, and the potassium content is varied according to regular plasma electrolyte measurements. Dilutional hyponatremia may occur when GKI infusion is prolonged. This should be treated by additional saline infusion, and if necessary by slowing the GKI infusion rate. In patients at risk of volume overload, more concentrated dextrose infusions (eg 20%) can be given in smaller volumes, with appropriate adjustments of insulin and potassium content.
The GKI infusion is versatile and can also be used in type 1 patients undergoing radiological or endoscopic investigations that require fasting, or when patients are unable to eat because of anorexia or vomiting. This method, however lacks the flexibility frequently needed for a complicated operation, such as a kidney transplant and coronary artery bypass graft, or control in a patient with type 1 diabetes during major surgery. It is an acceptable method for many elective procedures, when infusion pumps are not available and when frequent variations in insulin needs are not anticipated.
To successfully monitor and regulate an insulin infusion regimen, a system for the accurate measurement of blood glucose levels at the bedside must be in place. In the absence of rapid and accurate bedside blood glucose monitoring with a meter, it is not safe to implement a regimen of continuous regular insulin infusion. Furthermore, the anesthesiologist must do blood glucose analyses every hour during the operation and adjust the insulin infusion accordingly.
The infusion is continued until the patient is tolerating oral feeding. Excellent glycemic control can be achieved and maintained even with a prolonged surgical or recovery process.
During the reintroduction of foods such as clear liquids, it is preferable to continue a low maintenance dose infusion supplemented with small boluses of regular insulin (subcutaneous) preprandially. The size of the bolus depends on the amount of allocated carbohydrate (1U of insulin per 10g of carbohydrate). This is a very safe system because the insulin dose remains adequate.
Once food tolerance is established, the infusion is stopped and the insulin-treated diabetic may be returned to the former dosage or may need a number of days of frequent (premeal) doses of regular insulin. The transition regimen is developed according to the guidelines discussed in table 3. The previous day's total insulin dose is used to determine the most appropriate form of therapy. By calculating a basic dose, with adjustments made depending on premeal blood glucose values and anticipated carbohydrate content, safe control can be achieved. A small dose (10 to 15 U) of intermediate-acting insulin (NPH or Lente) is added at bedtime to provide coverage until the following morning.
Patients are continued on the above treatment plan until postoperative complications have stabilized and glycemic control is satisfactory. As soon as the patient is able to eat normally again, the usual treatment regimen can be restarted. Frequent glycemic monitoring is essential because of the variable effects of surgical trauma and other factors such as inactivity, postoperative infection and changes in medication.
A vital aspect of care is adequate blood glucose monitoring. This is generally done by nursing staff at the bedside, using glucose-oxidase reagent strips, read either visually or by meter. During intra-operative period the blood glucose should be monitored every hour and less frequently as necessary thereafter. The accuracy of these monitoring methods may be poor, and validation with occasional laboratory measurements may be advisable. All hospitals that use reagent strips for diabetic monitoring should have some form of quality-control system to ensure reasonable accuracy, and all staff involved should be carefully trained in their use. The other alternative is to estimate the blood sugar in the laboratory by conventional methods. A word of caution is that the blood should not be drawn from the arm that is connected to the infusion line which may show a falsely high value.
Urine glucose monitoring during surgery is not safe particularly when the patient is on intravenous glucose. The results of urine glucose may be strongly positive when the blood glucose may not be high. A large dose of insulin given based on the strongly positive urine test for glucose may produce deleterious hypoglycemia.
Emergency surgery is as likely if not more likely in the diabetic than in the nondiabetic subject. Management will depend to a large extent on the metabolic condition of the patient. Surgical emergencies, particularly if there is underlying infection, can cause rapid metabolic decompensation with dehydration, hyperglycemia, and ketoacidosis. Uncontrolled diabetes may also be precipitated in patients not previously known to have diabetes. The problem necessitating surgery may have led to metabolic decompensation; this should first be corrected if possible, unless the operation cannot be delayed.
One trap for the unsuspecting is that patients with diabetic ketoacidosis can present with symptoms indistinguishable from an acute abdomen. In these patients the signs and symptoms resolve on metabolic correction. A useful rule of thumb is that if such patients are less than 25 years old, the problem is likely to be metabolic, whereas if they are older, a genuine surgical emergency should be suspected. The sensible approach in such patients is to manage conservatively in the early stages with the emphasis on correction of the metabolic derangement. If the problem is metabolic rather than surgical, then it will resolve in the next 3 to 4 hours. In the presence of ketoacidosis, the operation should be delayed for 4 to 6 hours when possible while the patient is given standard therapy.
Diabetic patients require close attention when admitted for an emergency operation. The first priority is to assess glucose control, level of hydration, and acid-base status. Preoperative management will require an aggressive approach to correct fluid and electrolyte imbalances, reverse acid-base disorders, and optimize blood glucose levels. Separate insulin and fluid infusion systems are excellent for such intercurrent management. The insulin dose (rate per hour) and fluid needs should be tailored to each patient according to the severity of the metabolic decompensation and the patient response. The management of ketoacidosis involves higher insulin infusion rate (0.1 U per kilogram of body weight per hour). The infusion is generally preceded by an intravenous injection of regular insulin (10 U). Adjustments are then made according to hourly blood glucose levels. Once blood glucose values return to 240 mg/dL, 5% dextrose should be included in the rehydration fluids. Adequate potassium replacement is critical, as is close monitoring of fluid balance, acid-base status, electrolytes, and renal function. Once the patient's condition is stable for 4 to 6 hours, the operation can generally be performed safely. It is important to note that following reversal of the acute stressful condition lower insulin infusion rates will be required for a given blood glucose level.
Laparoscopic surgical procedures are rapidly coming into widespread use, although so far there are few reports of outcome in diabetic patients. Although the degree of surgical trauma is generally assumed to be less than for conventional open surgery, the degree of metabolic disturbance and the severity of insulin resistance induced appear to be comparable.
Our aim is to make patients safe for surgery. For this we need an understanding team work between the surgeon, anesthetist, and the diabetologist. When the patient is under anesthesia, "The ideal is to have diabetic therapy supervised by a diabetic team where available" (KGMM Alberti).
Table 1: Indications for Insulin Therapy during major Surgery
|All insulin-taking diabetes (type 1 and type 2)||Type 2 diabetes treated with diet or oral hypoglycemic agents and in acceptable control|
|Type 2 diabetics on diet and/or oral hypoglycemic agents but with chronic hyperglycemia (ie FBG>180 mg/dl and HbA1c>10%)||Average FBG
* HbA1c = 10%
* Surgery duration < 2 hours
*Body cavity not invaded
* Food intake anticipated after operation
Table 2:A Simple protocol for managing patients with TYPE 1 or TYPE 2 diabetes undergoing surgery. These guidelines are suitable for use by junior hospital staff with limited specialist experience of diabetes.
Table 3: Postoperative management of patients with diabetes
* Continue perioperative insulin infusion until food is tolerated, then plan new regimen
* Overlap (30 minutes) the initial subcutaneous dose of regular insulin before stopping infusion
* Type 2 diabetics previously treated with diet and/or OHA: prescribe usual medication if BG <180 mg/dL. Higher BG may require transient regular insulin every 6 hours (premeals) as per blood glucose (bedside monitoring) sliding scale
* Insulin-treated diabetics: Prescribe usual regimen or use prior 24 to 48 hour insulin dosage to develop a new basic dose regimen. The dose selected should be 80% to 100% of the previouse day's total dose. Needs may be higher during persistent stress, infection, pain, steroids or high food intake (total parenteral nutrition).
The selected basic dose may be given premeal (breakfast [25%], lunch [25%], dinner[25%]), as regular insulin and NPH given at bedtime (25%). Aim to keep BG in safe range (120-200 mg/dL).
|Premeal BG (mg/dL)||Basic dose (soluble insulin)|
|<80||4 U less|
|81 - 120||3 U less|
|121 - 180||Basic dose (no adjustment)|
|181 - 240||2 U more|
|241 - 300||3 U more|
|>300||4 U more|
* Modify the basic dose regularly (every 1 to 2 days) according to the sliding -scale needs. Additional doses of regular insulin may be needed at other times (eg 10 pm to 2 am)
* Establish the most suitable insulin regimen or the patient's previous regimen before patient discharge