Anesthetic techniques for subspecialty surgery

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Chapter 10 Anesthetic techniques for subspecialty surgery


Niraja Rajan, MBBS, Srikantha Rao, MD, MS, and Johan Raeder, MD, PhD



Common themes


This chapter deals with anesthesia for patients undergoing a few specific procedures. Unique surgical and anesthetic considerations associated with each type of procedure are discussed. A simple anesthetic plan for each category of procedure is provided. A few general principles are listed below.




Preoperative evaluation




Pay attention to common coexisting medical illnesses such as arterial hypertension and diabetes mellitus and ensure that these patients have taken their scheduled medication.




Premedication




While patients remain NPO for solid foods 6–8 hours prior to surgery, clear liquids up until 2 hours prior to surgery are acceptable.[1]



Patients anxious about the procedure may benefit from oral benzodiazepines such as 1–2 mg of lorazepam, either the night before or morning of surgery. The oral regimen can be supplemented with IV benzodiazepines, such as 1–2 mg of midazolam, prior to surgery when necessary, and especially in those with an anxiety trait.



Treat any preoperative pain using the patient’s established medication regimen.



Regional anesthesia and analgesia




The site for the block is marked and a “Patient Safety Time-out” is performed and documented before performing any blocks with due consideration to the patient’s anticoagulation status.





Induction




An IV catheter is placed in the appropriate limb, closest to the anesthesiologist in case the OR table is turned 90 or 180 degrees. The non-invasive blood pressure cuff, placed on the same or opposite limb has to be sized appropriately for large patients. Blood pressure should be measured in the sitting position and marked as “baseline” in patients undergoing shoulder surgery.




Maintenance




Anesthesia is maintained using oxygen with air or oxygen with nitrous oxide, along with an inhaled anesthetic agent or using a Total Intravenous Anesthetic (TIVA) technique or a combination of the two.



Analgesia is achieved using non-opioid drugs (i.e. acetaminophen, NSAIDs), local anesthetic infiltration (when feasible) and IV opioids, the latter carefully titrated.



Regional analgesia techniques are used if the block has not already been performed prior to surgery in the patient holding area.




Emergence




During emergence the patient needs to meet standard extubation criteria.



The removal of the laryngeal mask airway (LMA) or endotracheal tube can occur while the patient is still anesthetized (i.e., so-called “deep extubation”) or more awake, depending on the procedure and the desire to minimize coughing and bucking during emergence.




Discharge instructions




The patients are discharged to a familiar responsible caregiver with specific instruction to continue oral analgesics at regular intervals for at least 48 hours after discharge, given the slow onset to peak effect of oral analgesics.



They are instructed to be cognizant of postural hypotension and its consequences.





ENT procedures


Procedures on the ear, nose, or throat typically performed at ASCs include myringotomy and grommet tube insertion, tympanomastoidectomy, stapedectomy, sinus surgery, septoplasty, tonsillectomy, adenoidectomy, vocal cord injections, and polypectomy.



Preoperative


Patients should be screened for their suitability to be operated on at an ASC. Pediatric patients less than 3 years of age presenting for a tonsillectomy may have associated OSA (obstructive sleep apnea) and are not good candidates for outpatient surgery.[2,3] With adenoidectomy, the lower age limit for ambulatory care is usually 2 years.[4] Patients with severe asthma similarly may benefit from having their procedure done at an ambulatory unit or hospital with longer postoperative observation.


A clear method of communication, such as lip-reading or a sign language interpreter, may be necessary in hearing-impaired patients undergoing middle or inner ear procedures.


The patients who present for nasal surgery tend to suffer from chronic allergies and/or repeated upper respiratory tract infections. They may have associated gastroesophageal reflux and asthma. During the preoperative interview, it is important to remind these patients to breathe through their mouth upon emergence.



Premedication


Anxiolytics should be used with caution in patients with OSA. Tonsillectomy patients are cautioned about the use of NSAIDs in the preoperative period due to risk of bleeding, whereas COX-2 inhibitors are safe in this respect. Postoperatively, when hemostasis is established, there are no studies showing increased bleeding risk with traditional NSAIDs.[5] A review from the Cochrane Collaboration found that NSAIDs, excluding ketorolac, did not significantly alter postoperative bleeding compared with placebo.[4]



Intraoperative


The usual technique for most ENT procedures is general anesthesia (GA). Airway management is via (flexible) LMA or an endotracheal tube (i.e., oral RAE tube or other specialized tube) and is based on surgeon and anesthesiologist preference. Dexamethasone is given in higher doses in ENT surgery (10 mg) for both PONV and pain prophylaxis, and to reduce edema and perhaps pain. In middle ear surgery, nitrous oxide use should be avoided. Total intravenous anesthesia may help decrease PONV, because many ENT procedures are associated with increased PONV risk.


The operating table may be turned away from the anesthesiologist, by either 90 or 180 degrees, during surgery. IV lines, breathing circuits and monitoring cables must be routed appropriately.


To reduce bleeding after nasal surgery, arterial pressure is lowered using a deeper plane of anesthetic during surgery or administering labetalol 20 minutes before or small doses of esmolol just prior to extubation. The venous pressure is lowered by placing the head in the elevated position during surgery and extubating the patient in this position, and capillary bleeding is reduced by using topical vasoconstrictors. These may have side effects and the surgeon should be cognizant of the cardiovascular side effects of the vasoconstrictors used in the operative field.


During emergence and extubation, throat packs that may have been used by the surgeon in some of these procedures should be removed and their removal documented before extubation. Extubating the patient while still in a deep plane of anesthesia, to avoid the coughing and straining that often accompany ENT procedures, must be weighed against the potential risk of laryngospasm or pulmonary aspiration, and is based on the expertise and preference of the anesthesiologist. Using short-acting drugs such as esmolol, deliberate hypotension may be induced during emergence prior to extubation to minimize bleeding.



Postoperative


PONV is very common after these procedures and all ENT patients should receive at least two prophylactic anti-emetics, such as dexamethasone and ondansetron, in addition to risk reduction strategies. Post-tonsillectomy bleeding is a surgical complication. Patients are observed in the recovery room for two or more hours and are given instructions to seek immediate attention in case of bleeding after discharge. This may necessitate return to the OR, and patients are advised to remain within a 1–2 hour range of an appropriate hospital. Surgery to treat bleeding following a tonsillectomy is an emergency; patients are treated with full stomach considerations during induction of GA.



Laparoscopic surgery


Laparoscopic abdominal and pelvic surgery, while anatomically minimally invasive, is potentially physiologically disruptive. The carbon dioxide insufflated into the abdominal cavity must eventually be excreted, and poses problems once the body buffer capacity is exceeded (about 200 liters), especially in patients with poor lung function. The peak CO2 levels may occur up to 2 hours after surgery with the patient in the recovery room who may appear somnolent. Anesthesiologists need to work with the surgeons to reduce the hemodynamic effect of insufflated CO2, elevated intra-abdominal pressure, and reduced chest wall compliance, especially in obese patients[6,7] in lithotomy position (fluid overload) with steep head-down position (respiratory embarrassment, high airway pressures). It is also important to devise ventilation strategies to avoid barotrauma and volutrauma.



Preoperative


The patient should be warned about the occurrence of shoulder pain (referred pain) from diaphragmatic irritation by insufflated CO2. Many of the patients presenting for pelvic surgery have depression, anxiety, and chronic pain and may be on multiple anxiolytics and antidepressants, including serotonin-specific reuptake inhibitors. The anesthesiologist must be aware of the potential for drug interactions leading to serotonin syndrome when certain other medications such as meperidine, fentanyl, and promethazine are administered to these patients.[8]



Intraoperative


Attention must be paid to position the patient appropriately in order to avoid positional injuries. Pad all pressure points, especially when tucking the arms. In surgeries performed in the lithotomy position, be aware of positioning injuries in patients with back pain. Foot drop may occur from the lithotomy pole impinging upon the common peroneal nerve. The fingers on the hands tucked next to the hips are at risk of crush injury when the leg portion of the table is lowered or raised during surgery.


In general, during surgery on the external genitalia, GA is preferable to local or spinal anesthesia.



Postoperative


Visceral pain associated with pelvic endometriosis is compounded by pain caused by the surgical removal of these lesions from the peritoneal surfaces. In such patients, NSAIDs given IV soon after induction of anesthesia may be useful in reducing postoperative pain. There also may be a component of chronic pelvic pain that needs to be addressed in a few patients using multimodal analgesia with adjunct analgesics, such as gabapentin, magnesium, and ketamine.


These patients are at high risk for PONV and are managed with risk reduction strategies and two or more prophylactic agents such as dexamethasone and ondansetron. The use of NSAIDs may lower the requirement for IV opioids, reducing the likelihood of PONV.



Eye


A large number of ophthalmological procedures are performed on outpatients. Common procedures include cataract extraction, glaucoma procedures, procedures involving the cornea and conjunctiva such as corneal transplants, and strabismus correction. Patients range in age from the very young to the elderly. Patients for cataract and glaucoma surgery tend to be older and have multiple comorbidities. Patients for strabismus surgery tend to be pediatric and may have associated neurologic syndromes.


Ophthalmological procedures are minimally invasive, do not cause hemodynamic instability, and are therefore considered low-risk procedures.



Preoperative


Preoperative testing is not required in patients undergoing cataract surgeries.[9] Children undergoing strabismus surgery may have underlying neurologic conditions and may be susceptible to MH. This should be determined during the preoperative screening process.



Premedication


An anxiolytic is given when indicated either orally or IV. Mannitol IV is given to reduce intraocular pressure in patients undergoing certain glaucoma and corneal procedures, at the discretion of the surgeon.



Intraoperative


Most superficial ophthalmological procedures can be successfully performed under mild sedation with topical local anesthetic. Procedures requiring retrobulbar blocks can be performed under moderate to deep sedation (alfentanil and/or propofol) for the establishment of the block, followed by anxiolysis as required for the rest of the procedure. Older patients with prolonged circulation times benefit from pretreatment with 5–10 mg ephedrine, flushing the IV line with 20 ml of flush and waiting a full 90 seconds before redosing propofol. General anesthesia is indicated for strabismus surgery, deeper ophthalmic procedures, uncooperative or claustrophobic patients, and when patients prefer to remain unconscious. If neuromuscular blocking drugs are needed, be aware of potential problems of raised intraocular pressure with succinylcholine. For the same reason, nitrous oxide should not be used during procedures in which intraocular gases have been used, such as surgery to correct retinal detachment.



Emergence


Attention must be paid to ensure a smooth emergence using techniques similar to those described in the ENT section. Short-acting opioids (alfentanil) before extubation prevent coughing (with its attendant increased intraocular pressure) and the benefits of deep extubation must be weighed against its risks.



Unique considerations


PONV


All patients undergoing eye surgery are at high risk of PONV and should receive multi-therapy with two or more agents for prophylaxis, accompanied by other risk reduction strategies.



Oculocardiac reflex


This reflex is elicited by pressure on the globe or manipulation of extraocular muscles. It manifests as bradycardia or may be accompanied by dysrhythmias ranging from junctional rhythm, ectopic atrial rhythm, AV block, or ventricular bigeminy or asystole. It may also be elicited by a retrobulbar block, ocular trauma, or by pressure on the ocular tissue in an empty orbit. The afferent limb is trigeminal and the efferent limb is vagal. Hypercarbia and hypoxemia and inadequate depth of anesthesia augment or exaggerate this reflex. Management strategies include maintenance of adequate anesthetic depth and ventilation. Close monitoring and asking the surgeon to cease stimulation usually suffice and the heart rate and rhythm return to baseline within 20 seconds. The reflex usually fatigues after repeated stimulation. Atropine is administered IV for persistent severe bradycardia or serious arrhythmias. The surgeon should cease ocular manipulation prior to the administration of atropine. Prophylactic atropine is not recommended because it may itself cause a variety of arrhythmias.



Complications of retrobulbar and peribulbar block


Retrobulbar and peribulbar blocks are well suited for most ophthalmologic procedures involving the anterior chamber. They provide both akinesia and anesthesia of the eyeball. They are usually performed by the surgeon. Common complications are retrobulbar hemorrhage and hematoma, systemic local anesthetic toxicity (when there is inadvertent intravascular injection), oculocardiac reflex, and possible spinal anesthesia. The anesthesiologist must be watchful to diagnose and treat any of these potential complications during the performance of the block.



Complications


Please see Table 10.1.



Table 10.1 Complications of retrobulbar block.






































Symptoms and signs Onset time Mechanism Treatment

Hypotension


Bradycardia


Nausea

2–30 minutes Oculocardiac reflex

Stop the stimulus


Increase fiO2


IV fluids


Atropine IV if persistent


Seizures


Apprehension


Perioral numbness


Tinnitus

Immediate Intravascular local anesthetic

Airway ventilatory support


Benzodiazepines IV, Propofol IV


Supportive as needed

Proptosis Immediate Retrobulbar hemorrhage

Gentle pressure to the eye for 20–30 minutes


Reschedule surgery

Shivering Few minutes Absorption of local anesthetic along optic nerve sheath into CNS Supportive

Apnea, bradycardia


Amaurosis


Loss of consciousness


Cardiac arrest

2–40 minutes Injection of local anesthetic into the brainstem

Airway and circulatory support


Usually resolves in 1–3 hours

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Jan 21, 2017 | Posted by in ANESTHESIA | Comments Off on Anesthetic techniques for subspecialty surgery
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