AV shunt placement under peripheral nerve block

AV shunt placement under peripheral nerve block

The following case will emphasize peripheral nerve block anesthesia and risks associated with care of the diabetic patient.

Learning objectives:

·           anesthetic implications of chronic renal failure

·           anesthetic implications of diabetes

·           regional anesthesia of the upper extremity.

A 60-year-old man comes for placement of an AV (arterio-venous) fistula for dialysis.

An AV fistula is usually placed in the arm and takes less than 2 hours on average.

We expect no significant blood loss.

History: The patient with long-standing insulin-dependent diabetes has developed pro-gressive renal failure over the last several years, requiring peritoneal dialysis for the last 6 months (last dialysis was overnight).

A dialysis-dependent patient will have his electrolytes checked before the operation.

Review of systems: Chronic hypertension; diabetes, now with good control on insulin (HbA1c 6% last month); can walk 1 mile or climb a flight of stairs without chest pain; denies orthopnea or paroxysmal nocturnal dyspnea.

Diabetics are at risk of hypertension and chronic renal failure. Considering his risk for delayed gastric emptying, we insist that a diabetic patient remain npo after midnight. If not allowed to eat, his blood sugar may become dangerously low if he takes his morning insulin. Thus, we are very concerned with peri-operative control of his blood glucose, and therefore instruct him to take only half of his night-time dose of NPH, skip his morning insulin, and we schedule his operation early in the morning whenever possible. In the pre-operative holding area we check a “chem stick” (capillary blood glucose) before surgery and treat with insulin and/or glu-cose to maintain a level of 100 to 200 mg/dL (∼6.0–12.0 mmol/L). If a delay occurs in his surgery time, we might have the patient report to preoperative holding early for blood glucose management. While his cardiac status appears good, and the

Cardiac Guidelines (“Eagle criteria”) would not necessitate further evaluation, we might reasonably ask for a 12-lead ECG in the last 3 months, considering the risk of silent ischemia in hypertensive, diabetic patients.

Medications. Labetalol (for hypertension), insulin (NPH and regular), erythropoeitin (for anemia), Phoslo (to bind dietary phosphorus), calcitriol (to increase dietary calcium absorp-tion and replace vitamin D).

This is basically a standard “laundry list” of medications for the ESRD patient. Considering his risk of a cardiac event, more aggressive beta blockade, to lower heart rate below 70 beats/min, is indicated in this ASA IV patient.

Physical examination: Moderately obese white man in no distress; weight 100 kg; height 5 10 (175 cm);

BP 170/95 mmHg; HR 90 beats/min; respiratory rate 12 breaths/min

Airway: Mallampati II; 3fb mouth opening; 4fb thyromental distance; full neck extension

CV : S1, S2, no S3, S4 or murmur

Respiratory: lungs clear to auscultation

Neurologic: sensation intact in all extremities.

The risk of peripheral neuropathy in the long-standing diabetic looms large. Because we often use regional anesthesia for this operation and because regional anesthesia might be blamed for neurologic symptoms, we must obtain a baseline neurologic assessment and document any existing neurologic deficits. Had we heard ralesˆ during the pulmonary examination and suspected volume overload, a chest radiograph would have been in order.

Pre-operative studies: Hgb 12 g/dL; Hct 36%; Plt 300 000/µL; Na 145 mEq/L; K 3.6 mEq/L; glucose 110 mg/dL (6.1 mmol/L); Mg 1.7 mEq/L

ECG : NSR at 90 beats/min, normal intervals, ST segments at baseline.

Mild anemia commonly coexists with chronic renal failure.

Preparation for anesthesia. Following informed consent, we place an infraclavicular block pre-operatively in the “Block Room” under midazolam and fentanyl sedation. We use a stimulating needle to identify the nerve sheath, and inject 35 mL of 1.5% mepivacaine with 50 mcg clonidine without complications.

This anesthetic choice should provide surgical anesthesia of the forearm for 4–5 hours with continued analgesia. While we usually sedate patients for this procedure, the use of regional anesthesia will place less of a drug burden on the patient than general anesthesia would. Considering all the side effects of drugs, particularly when renal clearance is eliminated, a “minimalist” approach seems reasonable (though it should be noted that it has never been proven that regional anesthesia improves outcome over that of general anesthesia for these (or any) patients, except possibly for Cesarean delivery).

Confirmation of anesthesia. In the OR, we test the level of anesthesia by gently scratching the skin of descending dermatome levels.

Maintenance of anesthesia. With the help of a nasal cannula attached to a capnograph, we monitor respiratory rate, and administer oxygen to maintain a SpO₂> 95%. We titrate sedation to effect.

Intra-operative event – Hypertension: Approximately 45 minutes into the operation, the patient’s blood pressure has climbed to 195/110 mmHg with a heart rate of 95 beats/min. He is arousable and complains of a mild headache, but is not anxious or in pain from the operation.

Intra-operative hypertension has a long differential diagnosis. Leading the list in this patient, who denies surgical pain and anxiety, are iatrogenic fluid overload and exacerbation of underlying chronic hypertension, probably from missing a dose of anti-hypertensive medication. Because he cannot respond to diuretics, fluid restriction, beta blockade with the desired reduction of heart rate and, if necessary vasodilation are the best temporary measures until dialysis can be performed post-operatively.

Emergence from anesthesia. We attempt to time our sedation in anticipation of the end of surgery. We transfer the patient to the PACU for monitoring. At least partial recession of the block should be documented before discharge. We tell the patient not to touch anything hot with the affected hand because temperature perception will be impaired longer than motor or sensory functions.