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Chapter: Essential Anesthesia From Science to Practice : Clinical cases

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Carpal tunnel release under Bier block

The following case will describe the use of intravenous regional anesthesia.

Carpal tunnel release under Bier block

The following case will describe the use of intravenous regional anesthesia.

Learning objectives:

·           pre-operative management of the asthmatic patient

·           intravenous regional anesthesia

·           local anesthetic toxicity

·           intra-operative bronchospasm.

A 50-year-old asthmatic woman comes for carpal tunnel release.

This minor procedure is usually performed as an outpatient. That is, the patient comes in the day of surgery, and returns home afterward.

History. She has frequent painful tingling of her right hand, consistent with carpal tunnel syndrome. Her past medical history is significant only for asthma since childhood. The asthma is controlled with albuterol metered dose inhaler (MDI) three times a day and more if necessary. She has never had surgery, and gives no family history of anesthetic complications. She takes only asthma medications and hormone replacement therapy. She has no allergies, but smokes two packs a day with a 50 pack-year smoking history. She drinks socially and takes no illegal drugs.

We will ask this patient additional questions regarding her lung disease, to deter-mine its severity, as well as whether her current medical therapy is optimal.

The patient describes chronic asthma without identified precipitating factors or seasonal variation. She has never been intubated for an asthmatic attack, but has been to the emer-gency room on several occasions. The last event was more than 2 years ago. She has not received steroids but has required extra doses of her MDI twice in the last week, which is about normal for her. She has not had a cold in the last 2 weeks. She has no recent pulmonary function tests (PFTs) or chest radiographs.

Pulmonary function tests are unlikely to alter our anesthetic management for this peripheral operation. Her medical therapy appears to be adequate.

Physical examination: Caucasian woman in no acute distress; weight 85 kg; height 5 4 (160 cm)

BP 135/80 mmHg; HR 90 beats/min; respiratory rate 16 breaths/min

Airway: Mallampati I, 4 fb mouth opening, 4 fb thyromental distance, full neck extension

 

CV: S1, S2 no murmur

Resp: Lungs with mild bilateral expiratory wheezes; mildly lengthened expiratory phase; no obvious use of accessory respiratory muscles.

While we require no pre-operative laboratory or other studies in this ASA II patient, bedside peak flow testing may be useful.

Asthmatic patients are at increased risk for intra-operative bronchospasm and post-operative pulmonary complications. Avoiding instrumentation of the airway reduces this risk, therefore we prefer local or regional anesthesia.

Anesthetic preparation: We discuss risks/benefits of local anesthesia/intravenous sedation vs. intravenous regional anesthesia (IVRA) vs. regional anesthesia vs. general anesthesia; the patient selects IVRA. We administer nebulized albuterol followed by an anxiolytic (Midazo-lam (Versed®) 2 mg i.v.)

We will perform an IVRA.

Establishment of regional anesthesia. Once in the operating room, we apply standard mon-itors (without using the right arm), including nasal cannula with a CO2 sensor. We place a second i.v. in her right hand, and then apply a double tourniquet to the upper arm. We squeeze out all blood currently in the arm by holding it up and tightly wrapping it in an elas-tic bandage. Then we inflate the tourniquet to about 100 mmHg above her systolic pressure. After injecting 50 mL of 0.5% plain lidocaine (in divided doses with a test aspiration every 10 mL) into the i.v. below the tourniquet (not the other i.v.!), we remove the catheter. Her arm will appear blanched and she will have a pins and needles sensation, then no sensation at all. We titrate sedation using propofol at 50–80 mcg/kg/min. This sedative is a particularly good choice in the asthmatic patient.

Everyone in the room should be aware the patient is awake.

Maintenance of anesthesia: We titrate the propofol infusion to effect, maintaining arous-ability to speech and an acceptable respiratory rate. Suddenly the patient complains of ringing in her ears and tingling around her mouth.

These are common early signs of local anesthetic toxicity. We check the tourniquet to insure the pressure is adequate, and perfusion of the arm has not returned. We ask the surgeons about bleeding at the surgical site and monitor the patient closely for sequelae of local anesthetic toxicity including seizures and cardiovascular collapse.

We immediately inflate the second tourniquet cuff and the symptoms subside. After 30 minutes the patient complains of pain at the site of the tourniquet. She is becoming restless and the surgeons still need at least another 30 minutes to complete the procedure.

Tourniquet pain is often the limiting factor in IVRA. It is difficult to manage, and with the remaining operative time, we need to use general anesthesia. Because instrumenting the airway is a major trigger for bronchospasm, the laryngeal mask airway (LMA) is probably a good choice in this setting.

We inform the patient she will be put to sleep for the remainder of the operation, to assure her comfort. We preoxygenate/denitrogenate with 100% oxygen by facemask, then induce with 200 mg propofol. We insert a #4 LMA with some difficulty. Within 2 minutes, spon-taneous ventilation resumes with an end-tidal CO2 of 45 mmHg. We continue propofol at 100 mcg/kg/min, with 50% N2O in oxygen. Ten minutes before the end of the operation we give 3 mg of morphine i.v. to minimize early post-operative pain. Three minutes later her respiratory rate has increased to 30 breaths per minute, and the end-tidal CO2 has fallen. Lung auscultation reveals bilateral wheezing.

Morphine can cause histamine release, inducing bronchospasm. We have sev-eral options for treatment. Volatile anesthetics are good bronchodilators, and can be used in the patient spontaneously breathing through an LMA. Halothane or sevoflurane are not pungent and work well as bronchodilators. However, halothane can sensitize the heart to the arrhythmogenic effects of sympatho-mimetic drugs. We use sevoflurane and do not hesitate to administer nebulized albuterol through the LMA, and, if all else fails, racemic epinephrine. A stetho-scope would have allowed early detection of wheezing and perhaps prevention of full-blown bronchospasm.

In retrospect, if the surgeons suspected this may not be a straightforward carpal tunnel release, requiring more than 30–40 minutes, then a regional anesthetic (brachial plexus block) would have afforded a longer duration of action and prob-ably avoided instrumentation of the airway. The mild local anesthetic toxicity could have been much worse with a complete failure of the tourniquet.

Emergence from anesthesia: During closure of the incision, we discontinue the anesthetic agents. When the bandage has been applied, we release the tourniquet and remove the LMA.

After an hour-long surgical procedure release of the tourniquet will not flood the system with local anesthetic and there is no longer risk of toxicity.

Post-anesthesia care: There should be little pain from this procedure. We leave the patient in the PACU with standing prn1orders of fentanyl for pain, rather than morphine, because of her bronchospastic reaction. We also write orders for an anti-emetic drug, should it be needed.

Discharge: When the patient is fully awake and tolerating oral intake, she can be discharged home with a caregiver, a prescription for an analgesic, and instructions not to drive for 24 hours.


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