THE OBESITY EPIDEMIC: ANESTHESIA IMPLICATIONS
From the 59th Postgraduate Assembly in Anesthesiology, presented by the New York State Society of
Anesthesiologists, Inc.
| PHYSIOLOGIC AND ANESTHETIC CONSIDERATIONS IN MORBIDLY OBESE PATIENTS —Jay B. Brodsky, MD,
Professor of Anesthesiology, Stanford University School of Medicine, Stanford, CA
|
| Preoperative evaluation: cardiovascular concerns—obese patients have increased tissue mass, increased blood volume,
increased left ventricular work, hypertension, and can develop cardiac hypertrophy, resulting in congestive heart failure
(CHF) if untreated; pulmonary concerns—adipose tissue metabolically active; obesity causes increase in O2
consumption and CO2 production, resulting in increased ventilation at rest; heavy chest leads to decreased compliance and
lung volume; patient can develop premature closure of airway, ventilation perfusion mismatch, and arterial hypoxemia;
functional residual capacity (FRC) decreases with increasing body mass index (BMI); FRC comprised of residual volume
(RV) and expiratory reserve volume (ERV); ERV reduced with obesity, RV remains the same; alveolar-arterial O2 difference
(measure of hypoxia) increases with increasing BMI; young morbidly obese patients hyperventilate at rest, CO2 level
remains stable; preoperative blood gas in young morbidly obese patient shows moderate reduction in arterial O2 tension, but
also see slight reduction in CO2 ; medications—determine which medications patient taking prior to surgery; some diet
medications affect anesthetics; sibutramine associated with hypertension and arrhythmias; orlistat associated with decreased
absorption of fat-soluble vitamins (if taken together, can exaggerate Coumadin [warfarin] effect)
|
| Preoperative testing: routine—obtain thyroid function tests, lipid profile, and liver function test; special tests—
required if considering other causes of obesity; consider echocardiography in older patients, especially those with CHF;
consider sleep studies to look for obstructive sleep apnea (OSA); check patient who had Roux-en-Y gastric bypass for vitamin
B12 , iron, and protein deficiencies
|
| Implications for anesthesia: prescription medications—avoid sedatives and respiratory depressants; continue antihypertensives,
but discontine angiotension-converting enzyme inhibitors (associated with marked hypotension after induction);
hold diabetic medications; consider H2 -receptor antagonist, proton pump inhibitor, or antacid prior to surgery if
concerned about aspiration
|
| Perioperative issues: need special beds for transport (before and after surgery) and special operative tables; avoid premedication;
bring patient to operating room, but have patient get off gurney and position themselves; positioning—
reverse Trendelenburg ideal position for surgery; supine position associated with marked increase in intra-abdominal
pressure, marked decrease in FRC, and potential for closed airway; elevate head and upper body using pillows or other
method; head-elevated laryngoscopy position (HELP) creates horizontal line between sternum and ear to improve view
and to relieve pressure on diaphragm; use padding to avoid pressure injuries resulting in neurologic injury or rhabdomyolysis;
monitoring—may need forearm blood pressure (BP) cuff; consider peripheral noninvasive BP monitoring during
bariatric surgery; problems associated with central line placement in morbidly obese patients (eg, catheter too short to enter
chest, potential for extravasation of fluid through proximal and medial lumens); drug dosage—routine practice to
base dosage on absolute body weight (not practical in morbidly obese patient); morbid obesity associated with increased
amount of adipose tissue, increased lean body weight (LBW) (ideal body weight [IBW] + 20%), increased extravascular
fluid, and decrease in proportion of fluid
|
| Anesthesia administration: induction agents—lipid soluble; because of cardiovascular effects, base dose on LBW;
succinylcholine for rapid sequence induction usually given based on TBW; to get predictable paralysis for rapid sequence
induction, give 1 mg/kg based on TBW; tidal volume ventilation—study showed 13 mL/kg IBW provides optimal oxygenation
without risk for barotrauma; choosing anesthetic agents—desflurane least lipid-soluble; sevoflurane, isoflurane,
and halothane have greater fat solubility; emergence and extubation faster with desflurane compared to sevoflurane,
and with sevoflurane compared to isoflurane; however, study found no difference in emergence and extubation rates in
morbidly obese patients when desflurane and sevoflurane titrated at same level; speaker recommends continuous infusion
of remifentanil with isoflurane as inhalation agent discontinued prior to end of operation; can use intravenous (IV) infusion
of remifentanil, alfentanil, or fentanyl; patients respond quicker once infusion discontinued; IV fluid
resuscitation—more rapid recovery seen in patients with 40 mL/kg based on IBW; nausea and vomiting—multimodal
therapy reduces nausea; dexamethasone (Decadron) frontline agent in treatment of postoperative nausea; atelectasis—
more common in obese patients before and after surgery; use head-up position for recovery and provide O2
|
| OSA AND AIRWAY MANAGEMENT —David A. Zvara, MD, Associate Professor, Department of Anesthesiology, Section
Head, Division of Cardiothoracic Anesthesiology, Wake Forest University School of Medicine, Winston-Salem, NC
|
| Background: perioperative outcome and risk—study of 500 patients with confirmed OSA found no difference in outcome
(eg, perioperative adverse event, unplanned hospital admission, death); regional anesthesia in obese patients—
may avoid airway complications; regional sedation may be required due to block failure risk (1.6 times more common in
ovese patients)
|
| Preoperative preparation: evaluate patient; counsel about awake intubation, sore throat, and tooth damage; consider
aspiration prophylaxis; recall medication alterations, eg, succinylcholine, based on real body weight; apnea and
preoxygenation—study looked at effect of obesity on safe duration of apnea in anesthetized patients; found shorter time
to drop in O2 levels in obese patients (even shorter in morbidly obese); preoxygenation important; 4 vital capacity breaths
within 30 sec of induction same as 3 min of 100% oxygenation; 25° head-up position better than supine position
|
| Positioning: head-up position improves FRC, longer time to desaturation; sniffing position in patients with OSA improves
airway patency; study in normal patients compared laryngoscopy in sniffing position vs mandibular advancement
vs burp maneuver vs combination of maneuvers; found combination of maneuvers allowed best possible view of airway
(likely same in obese patients); study in anesthetized obese patients found mandible advancement improved pharyngeal
patency; recommend mandibular advancement and burp maneuver in obese patients to improve patency; position patient
to create straight line from external auditory meatus to anterior sternum using support items or by manipulating bed
|
| Potential difficulties: difficult laryngoscopy—associated with increasing Mallampati scores, short sternomental distance,
short thyromental distance, large neck circumference, limited head and neck movement, receding mandible, and
prominent teeth; tracheal intubation—endotracheal tube difficulties associated with higher Mallampati scores and large
neck circumference (35% probability of difficult intubation at 60 cm); difficult intubation in patients with OSA—
occurred in one fifth of patients with OSA compared to 2% in controls; not associated with any one single factor; grade 4
views in some patients with OSA; Mallampati classification predictive of difficult intubation; conclusions—increased
BMI not predictive of difficult laryngoscopy, but airway characteristics are; sample odds ratios include pathologic temporomandibular
joint (21-fold increase), history of OSA (10-fold), higher Mallampati grade (4-fold increase), and male sex
(slight increase); masked ventilation—difficult in 7.8% of normal patients; Mallampati class 4 airway increased odds of
difficulty 10-fold; male sex increased odds 3-fold; history of snoring increased odds 2-fold; predicting difficult
intubation—meta-analysis of bedside screening tests found 5.8% incidence of difficult intubation; concluded individual
tests yielded poor sensitivity and moderate specificity; best combination of predictors is Mallampati score and thyromental
distance
|
| Other important considerations: laryngeal masked airways (LMA)—study in morbidly obese patients found tracheal
intubation success rate 93.3%; using LMA, successful ventilation in 100% and intubation in 96%; need device for
bail-out strategy; cannot intubate or ventilate—experienced by 50% of anesthesiologists in Canandian study; closed
claims analysis showed two thirds occurred on induction and 12% on extubation (combined, 4 in 5 occurrences)
|
| Difficult airway algorithm: decisions include: patient awake or asleep? noninvasive or invasive technique? preservation
or ablation of spontaneous ventilation? get help if unsuccessful at intubation while patient asleep; return to spontaneous
ventilation if possible; consider awakening patient; consider masked ventilation; use LMA or other device if unable
to mask ventilate; call for help; establish ventilation; make plans for emergency airway
|
| POSTOPERATIVE MANAGEMENT OF THE BARIATRIC PATIENT —Jon D. Samuels, MD, Assistant Professor of
Anesthesiology, Weill Medical College of Cornell University, New York, NY
|
| Overview of postanesthesia care unit (PACU) management: tracheal extubation—requires experienced
physician (possibly 2 physicians if emergent tracheal reintubation needed); criteria routine; have alternative airway devices
(noninvasive and invasive) immediately available; position patient optimally; formally address lung mechanics; determine
negative inspiratory force (NIF), do 10-sec head lift, and ensure mental status close to baseline
|
| Oxygenation and ventilation in high-risk patients: at risk for hypertension, cor pulmonale, OSA and hypopnea
syndrome, and difficult masked ventilation; study showed 1.13 increase in odds ratio for each 1 cm increase in neck circumference;
high-risk patients associated with difficult tracheal intubation, shorter time to desaturation, increased respiratory
suppression with sedatives, hypnotics, and anesthetics; continuous positive airway pressure (CPAP) or bilevel positive airway
pressure (BiPAP) improves postoperative cardiorespiratory function in patients with OSA independent of improvement
in oxygenation
|
| Patient positioning: position patient so reintubation possible (eg, semi-Fowler position); can use ramp or commercially
available device; recommend prophylaxis against additional injuries; place patient in position to avoid positional airway
collapse
|
| Postoperative nausea and vomiting: mechanical nausea and vomiting usually more severe; can occur with peritonitis,
and usually caused by stomal stenosis or anastomotic leak; nonmechanical responsive nausea—responds to multimodal
therapy beginning with 5-HT3 -receptor antagonist; look for mechanical etiology in resistant type; alert bariatric
surgeon if nausea resists therapy (may indicate possible anastomotic leak); considerations in obese or morbidly obese
patients—studies show nausea and vomiting not more common in these patients (BMI not risk factor); morbidly obese
patients have increased intragastric volume and decreased pH, increased intra-abdominal pressure because of pneumoperitoneum,
prolonged gastric emptying time, impaired gastroesophageal junction antireflux mechanisms, and higher incidence
of difficult masked ventilation and gastric aspiration on induction and emergent sequence, and postoperative
hypoventilation; management approaches—pro-emetogenic drugs include etomidate, ketamine, emetogenic inhalation
anesthetics, opioids, and nitrous oxide; use minimal amount of narcotic agent; metoclopramide contraindicated in patients
with psychiatric history or taking other medications that interact; dexamethasone useful for prophylaxis; ondansetron
front-line agent; use of O2 as antiemetic requires fraction of inspired O2 (FIO2 ) of 80%; most patients
extubated and on nasal cannula; patients with OSA given CPAP; if patient not high risk and further prophylaxis needed
for nausea, give face mask and FIO2 80%; adult surgical procedures associated with 25% to 30% incidence of nausea and
vomiting (postdischarge, 35%); currently looking at long-acting 5-HT3 -receptor antagonist (eg, palonosetron)
|
| Prophylaxis of venous thrombolic disease: up to 25% of untreated patients develop deep vein thrombosis with associated
mortality rate 17%; risk factors for thromboembolic disease include age >55 yr, prior history, inadequate lower
extremity venous circulation, and poor ability to ambulate or to comply with instructions; despite recommendations for
prophylaxis, implementation rates inadequate in bariatric surgical population; extrinsic system most recommended, eg,
low molecular weight heparin and unfractionated heparin effective; antiplatelet agents do not work (intrinsic; use of warfarin
questioned); also consider nonpharmacologic devices, eg, inferior vena cava filters, graded elastic compression
stockings, intermittent pneumatic compression, and foot pumps
|
| Patients with OSA: evaluate patient carefully; mild cases termed obstructive sleep hypopnea and more severe cases
termed OSA, obesity hypoventilation syndrome, or Pickwickian syndrome; increased risks—patients with obesity hypoventilation
syndrome and Pickwickian syndrome at higher risk for hypercapnia unrelated to pulmonary disease and
OSA with cor pulmonale; patients at increased risk for morbidity and mortality during surgery, difficult masked ventilations,
higher incidence of difficult intubation, precipitous O2 desaturation, and apnea after routine settings of patient-controlled
anesthesia; identifying OSA—defined as cessation of airflow for >10 sec despite continued ventilatory effort,
with drop in saturation of >4% accompanied by snoring; OSA associated with >50% drop in airflow; measure apnea/hypopnea
index; when determining if patient has OSA, look for upper body or central obesity, relative micrognathia, poor
Mallampati scores, increased neck circumference, hypertension, and history of difficult intubation
|
| Safe care in PACU: assess and record pain scores systematically; involve patient in administration of opioid or analgesic;
measure pain scores at rest and during cough and movement; acute pain service (physician and nurse) improves patient satisfaction;
recommend ongoing quality assurance and improvement audit
|
Educational Objectives
| The goal of this activity is to provide a greater understanding of anesthetic considerations in morbidly obese patients, airway
management in obese patients and those with obstructive sleep apnea (OSA), and postoperative management of the
bariatric patient. After hearing and assimilating this program, the clinician will be better able to:
|
 | 1. List the medical comorbidities related to obesity.
|
| 2. Describe the preoperative evaluation and concerns related to the obese or morbidly obese patient.
|
| 3. Discuss the perioperative risk factors associated with OSA and obesity.
|
| 4. Evaluate the practice guidelines for the difficult airway.
|
| 5. Discuss the postanesthesia care unit (PACU) issues in the bariatric surgical patient.
|
Discussed on This Program
Desflurane [Suprane]
Dexamethasone [Decadron, several others]
Etomidate [Amidate]
Fentanyl citrate [Sublimaze]
Halothane [Fluothane]
Isoflurane [Forane]
Ketamine HCl [Ketalar]
Metoclopramide [several trade names]
Ondansetron HCl [Zofran, Zofran ODT]
Orlistat [Xenical]
Palonosetron HCl [Aloxi]
Remifentanil HCl [Ultiva]
Sevoflurane [Ultane]
Sibutramine HCl [Meridia]
Succinylcholine chloride [Anectine, Anectine Flo-Pack, Quelicin]
Warfarin sodium [Coumadin]
Suggested Reading
Brodsky JB et al:Obesity, surgery, and inhalation anesthetics—is there a "drug of choice"? Obes Surg 16:734, 2006;
Brodsky JB et al: Nitrous oxide and laparoscopic bariatric surgery. Obes Surg 15:494, 2005; Brodsky JB et al: Is
the super-obese patient different? Obes Surg 14:1428, 2004; Brodsky JB et al: Anesthetic considerations for bariatric
surgery: proper positioning is important for laryngoscopy. Anesth Analg 96:1841, 2003; Brodsky JB et al: Morbid obesity
and tracheal intubation. Anesth Analg 94:732, 2002; Chand B et al: Perioperative management of the bariatric surgery
patient: focus on cardiac and anesthesia considerations. Cleve Clin J Med 73:S51, 2006; Collins JS et al:
Laryngoscopy and morbid obesity: a comparison of the "sniff" and "ramped" positions. Obes Surg 14:1171, 2004; Dhonneur
G et al: Tracheal intubation of morbidly obese patients: LMA CTrach vs direct laryngoscopy. Br J Anaesth
97:742, 2006; Feld JM et al: Fentanyl or dexmedetomidine combined with desflurane for bariatric surgery. J Clin
Anesth 18:24, 2006; Lemmens HJ et al: Anesthetic drugs and bariatric surgery. Expert Rev Neurother 6:1107, 2006;
Lemmens HJ et al: Estimating blood volume in obese and morbidly obese patients. Obes Surg 16:773, 2006; Lemmens
HJ et al: The dose of succinylcholine in morbid obesity. Anesth Analg 102:438, 2006; Lemmens HJ et al: Estimating
ideal body weight--a new formula. Obes Surg 15:1082, 2005; Lemmens HJ et al: General anesthesia, bariatric
surgery, and the BIS monitor. Obes Surg 15:63, 2005; Passannante AN et al: Anesthetic management of patients with
obesity and sleep apnea. Anesthesiol Clin North America 23:479, 2005; Perilli V et al: Comparison of positive end-expiratory
pressure with reverse Trendelenburg position in morbidly obese patients undergoing bariatric surgery: effects on
hemodynamics and pulmonary gas exchange. Obes Surg 13:605, 2003; Zvara DA et al: Positioning for intubation in
morbidly obese patients. Anesth Analg 102:1592, 2006.
Faculty Disclosure
In adherence to ACCME guidelines, the Audio-Digest Foundation requests all lecturers to disclose any significant financial
relationship with the manufacturer or provider of any commercial product or service discussed. For this issue, the faculty
reported nothing to disclose.
Drs. Brodsky, Zvara, and Samuels were recorded December 9-13, 2005, in New York, NY at the 59th Postgraduate
Assembly in Anesthesiology, presented by the New York State Society of Anesthesiologists, Inc. The Audio-Digest
Foundation thanks the speakers and the sponsor for their cooperation in the production of this program.
|
