Obesity and Anesthesia Part 2

Obesity and Anesthesia Part 2 By Heidi Calhoun-Nudd Outline  Room/ Equipment preparation  Pre operative evaluation  Induction  Maintenance   General anesthesia Regional anesthesia  Post op complications  Pharmacology Your Assignment Tomorrow is…..  Room 16 0750 Roux en y 44 Fe 1400 Lap Gastric Band 36 M 2100 Lap Gastric band 29 Fe How will you prepare?????? Room Preparation       Ensure OR table capable of weight load Ventilator capable of pressure control ventilation Appropriate range of BP cuffs Padding Possible ultrasound for line placement Gather additional airway equipment- LMA’s, bougie, fiberoptic, difficult airway cart, shortie laryngoscope handle, etc.  Bed ramping  A-line  Central line equip Heading out to pre op….. Developing a pre anesthetic plan for obese pt  History -Cardiopulmonary -Daily activity/ tolerance level -Sleep patterns -Tobacco use -Gastrointestinal symptoms -NPO status, prep -Anesthetic history- old records Pre anesthetic labs/testing  Electrolytes with liver function tests  Glucose  CBC  CXR  EKG  Echo to investigate ventricular function  Pulmonary function tests  Baseline ABG’s Possible PFT changes  FEV1/ FVC ratio normal  Restrictive vs. obstructive  Premature closure/atelectasis of small airways  VQ abnormalities   right to left shunt perfusion of non ventilated alveoli Evaluating for sleep apnea  Hints for undiagnosed sleep apnea      Excessive somnolence Daytime somnolence Snoring Awaken from sleep choking Morning headaches Anesthetic plan ETT vs Mask General  Because of risk of aspiration obese pts are usually intubated for all but the shortest of general anesthetics.  Controlled ventilation with large tidal volumes allows for better oxygenation. Airway assessment  Neck flexion  may be limited by multiple fat pads, chest and breasts  Mouth opening  may be limited r/t large tongue, fleshy cheeks, and abundance of adipose tissue  Larynx  may be “ high and anterior”  Airway obstruction  occurs frequently Difficult Airway Defined Clinical situation in which a conventionally trained anesthesiologist experiences problems with mask ventilation, with tracheal intubation, or with both. Morbid Obesity and Tracheal Intubation  Study by Brodsky, Lemmens, Brock-Utne,Vierra, and Saidman studied 100 morbidly obese pts (BMI>40kg/m2) to identify which factors complicate direct laryngoscopy and tracheal intubation.  Preoperative measurements (height, weight, neck circumference, width of mouth opening, sternomental distance, and thyromental distance) and Mallampati score were recorded.  View during direct laryngoscopy was graded, and the number of attempts at tracheal intubation was recorded.  Neither absolute obesity nor body mass index was associated with intubation difficulties.  Large neck circumference and high Mallampati score were the only predictors of potential intubation problems.  They concluded that obesity alone is not predictive of tracheal intubation difficulties. Neck circumference in difficult intubation  Neck circumference  odds of a problematic intubation in a particular patient with a neck circumference 1 cm larger than that of another patient are 1.13 X the odds for a difficult intubation Neck circumference in difficult intubation  According to Barish  Problematic intubation in morbidly obese patients is approximately  5% with a 40-cm neck vs  35% likelihood with a 60 cm neck. Other Predictors of difficult airway  Mallampati  greater than or = to 3 at increased risk  H/O sleep apnea  BMI  Thyromental distance  Neck ROM Difficult Airway  Incidence of difficult laryngoscopy and tracheal intubation is unknown, but it may be 7.5% in the “normal” surgical population.  Obese patients are believed to be more difficult to intubate than those of normalweight patients. Identified difficult airway considerations  Once difficult airway is identified preparation of a variety of supplies and equipment is needed:          Consider awake fiberoptic Maximize position ie ramping, rev trendelenberg Prepare variety of tubes, blades, ex MAC 4 LMA’s, intubating LMA’s Bougie Shortie laryngoscope handle Glidescope, fiberoptic Difficult airway cart- jet ventilate Have surgeon available for tracheostomy Heading Back to Room 16 Premedication  Very light to no sedative premedication, if given monitor closely  H2 blocker, reglan, sodium citrate  Anticholinergic if anticipated difficult airway/ fiberoptic  Heparin sq Morbid obesity is a major independent risk factor for sudden death from post op PE, heparin 5,000 IU should be administered prior to surgery and q 8-12 hrs till mobility restored Remember with any IM ordered meds-~~~~~~Avoid IM absorption r/t unpredictable absorption~~~~~~ Positioning  Regular OR tables have a maximum wt limit of 205 kg, but some available to hold up to 455kg.  Particular care should be taken to protect pressure areas as obese are at increased risk for pressure sores and neural injury.  Brachial plexus and lower extremity nerve injury are frequent. Positioning con.  Changing pt position sitting to supine can:  Increase O2 consumption  Increase cardiac output  Increase pulmonary pressures  Supine position    Inferior vena cava and aortic compression Ventilatory impairment Further decreased FRC Decreased oxygenation Positioning con  Trendelenberg often required for bariatric surgery further  worsens FRC and should be avoided if possible  Reverse trendelenberg provides longest safe apnea period during induction of anesthesia Figure 1. In the operatingroom, patients in Group 1 were placed supine and had a 7-cm headrest placed underneath their occiput. Figure 2. Patients in Group 2 had folded blankets placed under their upper body, head and neck until horizontal alignment between the sternal notch space and the external auditory meatus was achieved. Induction Induction  Adequate preoxygenation is vital in this pt population!!  Rapid desaturation with LOC  FRC O2 consumption Rapid desaturation Preoxygenation  Four vital capacity breaths with 100% oxygen within 30 seconds has been shown to be superior to the usually recommended 3 minutes of preoxygenation in obese pts.  Application of positive pressure during preoxygenation helps prevent atelectasis. Induction of General anesthesia  Difficult to mask  tight mask fit  mask straps  2 hands  Preoxygenate well d/t decreased FRC  Proper positioning ie.  Ramping vs sniffing  Elevate HOB 25 degrees  Difficult airway algorithm Induction -General anesthesia Induction: RSI or awake fiberoptic Breath sounds may be difficult to appreciate requiring ETCO2 for confirmation of placement Two anesthesia providers General Anesthesia and Mechanical Ventilation  Mechanical ventilation= -higher airway pressures Decrease chest wall compliance Decrease lung compliance -start FIO2 of 100% Increase in O2 consumption Increase CO2 production -avoid hypercarbia -consider PEEP -Tidal volumes of 10-12 ml/kg Maintenance General anesthesia  Avoid spontaneous respirations under general anesthesia  controlled ventilations with large tidal volumes allow for improved oxygenation vs. shallow spontaneous respirations  Decreased PaO2 and Increased A-a gradient is exaggerated with induction of anesthesia  PEEP  decreases alveolar atelectasis  improves PaO2 at the expense of cardiac output and O2 delivery  Addition of PEEP can worsen pulmonary hypertension in pts with extreme obesity Obesity and Volatile Anesthetics  Volatiles-metabolized more extensively in obese pts  Especially important with respect to deflourination of halothane  Increased metabolism and predisposition to hypoxia may explain increased risk for halothane hepatitis in obese pts. Fluid Balance and Blood Loss  Increased difficulty assessing fluid status  Excess adipose tissue may mask peripheral perfusion complicating fluid balance assessment.  Blood loss is usually > in obese  R/T increased difficulty of assessing surgical site, causing need for larger incisions.  Early administration of colloids and blood may be necessary  obese are less able to compensate for small volume loss.  However, caution with rapid infusions of excessive amounts R/T preexisting cardiac failure. Regional Anesthesia  Useful alternative to avoid difficult airway.  May be technically difficult to assess landmarks.  May need longer needles.  Sitting position facilitates identification landmarks.  SAB are not as tech difficult as epidural but ht of block in obese can be unpredictable may spread upward within short time. Emergence  Prompt extubation reduces chance of long term ventilator dependence.  Ideally extubated semi recumbent  Early initiation of CPAP or BiPAP to prevent atelectasis  Adequate analgesia to promote deep breathing.  Encourage early ambulation.  Monitor blood gases and O2 sat closely Post op pain control  By decreasing amt of opiods, can decrease amt of respiratory depression.  Modalities to decrease amount of opioids:  Epidural analgesia decrease DVT incidence, improved analgesia, early GI motility recovery   Incisional local anesthetic infiltration. Non-opioid analgesics intraop ketolorac, clonidine, ketamine, lidocaine, methylprednisone, produce analgesia with less sedation  Consider closer monitoring post op  You do not want to have respiratory failure in obese pt with difficult airway. Increased risk for Deep Vein thrombosis/ PE  Deep vein thrombosis  twice as common in obese patients .  Most common complication of bariatric surgery  due to prolonged immobilization, polycythemia, and increased abdominal pressure with increased pressure on deep vein. GI disturbances  Increased incidence of gastro-esophageal reflux.     Increase in intra abdominal pressure High volume and low pH of gastric contents Delayed gastric emptying Gastric volume is 75% higher than the normal individuals  High risk for aspiration of gastric contents/ pneumonia. Propofol Induction:**IBW** Maintenance:TBW Systemic clearance and Vd at steady state correlates well with TBW. High affinity for excess fat and other well-perfused organs. High hepatic extraction and conjugation relates to TBW Thiopental Midazolam TBW Increased Vd. Increased blood volume, CO, amd muscle mass. Increased absolute dose. Prolonged duration of action. Central Vd increases in line w/ body wt. Increased absolute dose. Prolonged sedation because higher loading doses needed to achieve adeq serum concentrations Plasma cholinesterase activity increases in proportion to body wt. Increased absolute dose Recovery may be delayed if given according to TBW because of increased volume of distribution and impaired hepatic clearance TBW Succinylcholine Vecuronium TBW **IBW** Rocuronium Atracurium Cistatricurium Fentanyl Sufentanil **IBW** Faster onset and longer duration of action. Pharmacokinetics and pharmacodynamics not altered in obese pts Absolute clearance, Vd, and elimination half-life do not change. Unchanged dose per unit body wt w/ out prolongation of recovery because of organ independent elimination Increased Vd and elimination half-time which correlates positively w/ the degree of obesity. Distributes as extensively in excess body mass as in lean tissues. Dose should account for total body mass. Fentanyl dosing based on a derived pharmacokinetic mass correlates better w/ clearance TBW TBW Induction TBW, Maintenance **IBW** Case Study  Female 44 years presents for lap banding.         Weight 159 kg PMH: DM II, smoker, HTN, GERD PSH: T+A, tubal ligation, + h/o PONV Meds: Metformin, Lisinopril, Protonix Presents BS 210, SOB with exert, lung sounds clear CBC, BMP values WNL EKG- NSR CXR clear  Pre op   IV access Additional labs/ tests     Induction plan: Maintenance: Emergence: Questions????  1. All of the following are true regarding the obese patient and regional anesthesia except:     A. B. C. D. Sitting position helps in identification of landmarks for SAB placement Is a useful anesthetic alternative to avoid difficult airway Block level can be unpredictable May require shorter spinal needle  2. PEEP should always be used in the obese patient undergoing general anesthesia to improve oxygenation   A. True B. False A. Decrease FRC B. Inferior vena cava compression C. Aortic compression D. Improved oxygenation A. Excessive somnolence B. Daytime somnolence C. Snoring D. Awaken from sleep choking E. Excessive salivation A. True B. False  3. Effects of the supine position on the obese patient include all of the following except:      4. Possible signs of undiagnosed sleep apnea include all of the following except:       5. Because of the excess adipose tissue in the obese patient, blood loss is usually less.  