Obese Patients Flashcards
Adipose Tissue
Secretes numerous proteins
Considered an endocrine organ
Reservoir for convertible and usable energy
Maintain heat insulation
Central, Android, Abdominal Visceral Obesity
“Apple Shaped”
Waist circumference greater than 102 cm (40 inches) in MEN
Waist circumference greater than 88 cm (35 inches) in WOMEN
Obesity causes increased risk for ___
Ischemic Heart Disease
Diabetes
HTN
Dyslipidemia
Death
Peripheral Gynecoid or Gluteal Obesity AKA ___
Associated with ___.
“Pear Shaped”
Associated with:
Varicose Veins
non-insulin dependent DM
Medical risks are DECREASED in individuals with Gynecoid fat distribution compared to android pattern
Cardiovascular Conditions Associated with Obesity
CAD
HTN
Dyslipidemia
Cerebrovascular disease
Thromboembolic disease
Cardiomegaly
Congestive Heart Failure
Pulmonary Hypertension
Respiratory Conditions Associated with Obesity
Restrictive lung disease
Obesity Hypoventilation Syndrome
Obstructive Sleep Apnea
Endocrine Conditions Associated with Obesity
Type 2 Diabetes
Thyroid disorders
Gastrointestinal Conditions Associated with Obesity
- GERD
- Nonalcoholic fatty liver disease, steatosis, cirrhosis, hepatomegaly
- Hiatal or inguinal hernia
- Gallbladder disease
Miscellaneous Conditions Associated with Obesity
Gout, Low back pain, Osteoarthritis
Infertility & Obstetric complications
Wound Infections
Pancreatitis
Urinary Incontinence
Malignancy: Esophageal, gallbladder colon, breast, uterine, cervical, prostate, renal
Respiratory Physiology
Increased work of breathing
Increase O2 consumption
Increased CO2 production and disordered ventilation to perfusion matching
Respiratory rates are ______ while functional Residual capacity and expiratory reserve volume are ________
Respiratory rates are increased while functional residual and expiratory reserve volume are decreased
What do the changes to the respiratory physiology in the obese patient mean to us as anesthesia providers?
Decreased time to desaturation during apnea
increased O2 requirements
Hypoventilation with supine spontaneous ventilation
What is Obesity Hypoventilation Syndrome (Pickwickian)?
A complication of extreme obesity characterized by:
- hypercapnia
- OSA
- daytime hypersomnolence
- pulmonary HTN
- cyanosis-induced polycythemia
- arterial hypoxemia
- respiratory acidosis
- right-sided heart failure
* 8% of obese patients have OHS
With Obesity Hypoventilation Syndrome, patients develop ___.
Nocturnal episodes of central apnea (apnea without respiratory efforts)—> progressive desensitization of respiratory centers to hypercarbia
Obesity Hypoventilation Syndrome (Pickwickian) is defined as ________________.
Patients with BMI >30kg/m2, who experience daytime hypoventilation with awake PCO2 greater than 45 and sleep disordered breathing in absence of other causes of hypoventilation
Cardiovascular Physiology for obese pts
Increased circulating blood volume, although it is a lower proportion of total weight (50 mL/kg as compared with 75 mL/kg) compared with patients with normal body mass index (BMI).
SVR in obese patients is ___
Decreased
Cardiac output in obese patients is ___
Increased by 20-30mL per kg of excess body fat
Stroke index, cardiac index and heart rate in obese patients = _____
remains normal
*The increased cardiac output results occurs by means of expanded stroke volume
Left ventricular hypertrophy is related to ____.
The increase in cardiac output can lead to ____.
the duration of obesity
EITHER left ventricular failure (associated with HTN) or Right heart failure (associated with hypoxia and hypercapnia of OSA)
Metabolic Syndrome Defintion
Presence of three or more of the following:
- Elevated waist circumference- Men 40 inches (102cm) or greater, Women 35 inches (88cm) or greater
- Elevated triglycerides- 150mg/dL or greater
- Reduced HDL Cholesterol- Men less than 40 mg/dL. Women less than 50 mg/dL.
- Elevated blood pressure- 130/85 or greater
- Elevated fasting glucose- 100mg/dL or greater
Metabolic, Endocrine, GI Considerations
GI: Incidence of GERD, gallstones, pancreatitis, and non-alcoholic fatty liver increases with obesity
Obesity increases risk of cardiovascular disease and T2DM
Pharmacologic Considerations: Dosing is generally based on __________ for bolus doses and ______________ for infusions or repeat boluses
Dosing is generally based on volume of distribution for bolus doses and on clearance for infusions or repeat boluses.
Volume of Distribution
The volume of distribution is increased for lipophilic drugs
Less lipophilic drugs have little change
*Meaning, if you’re giving a lipophillic drug, you most likely would need to give MORE agent in the obese patient than the non-obese patient.
Lipophillic Drug Clearance is generally ____________ in obese patients
higher
*You may see increased needs for infusions or repeat boluses. For prolonged infusions of lipophyllic drugs, you may want to d/c the infusion earlier since it will hang around in the tissue for longer potentially.
Pharmacologic Considerations for obese patients
Prolonged infusions of highly lipophilic drugs= prolonged half-life
Consider discontinuing earlier rather than later
(For prolonged infusion of highly lipophilic drugs, the t1/2 and drug effect may be markedly prolonged after discontinuation of the infusion, due to increased Vd)
Pharmacokinetics Changes Associated with Obesity
- Increased fat mass
- Increased cardiac output
- Increased blood volume
- Increased lean body weight
- Changes in plasma protein binding
- Reduced total body water
- Increased renal clearance
- Increased volume of distribution of lipid-soluble drugs
- Decreased pulmonary function
Body Mass Index
Accepted measure of body habits that describes adiposity normalized for height
BMI Chart
Underweight = BMI less than 18.5
Normal = BMI 18.5-24.9
Overweight = BMI 25-29.9
Obesity Class I = 30-34.9
Obesity Class II = 35-39.9
Extreme Obesity Class III = greater than 40
Ideal Body Weight
Weight associated with maximum life expectancy. Calculated from patient’s HEIGHT
Men= Height (cm)-100 Women= Height (cm)- 105
Lean Body Weight
Difference between total body weight and fat mass
Sex-specific formula that includes height and weight
Accounts for weight increases= lean body mass increases as well
IBW x 1.3
reasonable to use LBW for most dosing except for lipophilic drugs- then use TBW
Meds to give vs. not to give obese patients
- Avoid long acting respiratory depressants like opioids and sedatives (due to the prevalence of sleep apnea in obese patients)
- use short acting and minimal fat soluble drugs
- Sevo and Des are great options (excellent recovery profile)
- Nitrous can be safely used in patients where requirement of O2 does not preclude it’s administration
- ALWAYS use a nerve stimulator**
- ABX prophylaxis- obese patients are more at risk for infection
Pharmacologic Considerations Propofol
Induction dose= LBW
Maintenance dose= TBW
Increased fat mass does NOT affect initial distribution/redistribution during induction
Cardiac depression at high doses is concerning
Pharmacologic Considerations Succinylcholine
Intubating Dose= TBW
Increased fluid compartment and pseudocholinesterase levels require higher doses to ensure adequate paralysis
Pharmacologic Considerations: Rocuronium, Vecuronium, Cisatricrium
All doses based on IBW
-Hydrophilic drugs given at IBW will ensure shorter duration and a more predictable recovery in respiratory challenged population
Pharmacologic Considerations: Fentanyl, Sufentanil
Loading dose use TBW
Maintenance dose use LBW and response
Increased distribution volume and elimination times correlate with degree of obesity
Pharmacologic Considerations Remifentanil
Infusion rates use=IBW
Distribution volumes and elimination rates are similar to normal-sized individuals: fast offset requires planning for postoperative analgesia
Pharmacologic Considerations Dexmedetomidine
Infusion rate 0.2mcg/kg/hr
Useful as an adjunct- lower than usual infusion rates are recommended to minimize adverse cardiac events
Pharmacologic Considerations Sugammadex
Use TBW
no change from usual dosing is required
Special Equipment Needs for Obese pts
-
Large and/or high weight capacity beds and operating tables
- Designated weight limits for operating tables may not remain valid if the patient is shifted on the table, the table is positioned other than level (eg, Trendelenburg, reverse Trendelenburg, lateral tilt), or the table is unlocked. Additional arm supports to widen the table may be necessary.
- Mechanical transfer mechanisms (ex. inflatable lateral transfer mattress)
- Additional Personnel
- Extra-long needles
- Ultrasound
Preanesthetic Evaluation Cardiac
-
Need an ECG- for determination of resting rate, rhythm, and ventricular hypertrophy or strain.
- Axis deviation and atrial tachyarrhythmias are relatively common
- Investigation of prior myocardial infarction and the presence of hypertension, angina, or peripheral vascular disease is crucial.
- Limitations in exercise tolerance, history of orthopnea, and paroxysmal nocturnal dyspnea may indicate left ventricular dysfunction.
- Exercise testing may elicit valuable information, but might not be feasible
Pre-anesthetic Evaluation: respiratory
OSA, orthopnea, wheezing, sputum production, or smoking history.
Airway evaluation (assesses for potential for difficult mask ventilation)
- Redundant tissue around the neck (restricting neck motion) and fat in the airway (decreasing glottic opening) together increase the difficulty of successfully intubating the trachea.
- A neck circumference of 40 cm was associated with 5% likelihood difficult intubation and that increases to 35% for circumference 60cm or greater.
- Awake intubation and the need for postoperative ventilation.
Anesthetic Management: Monitoring
BP Cuffs that encircle a minimum of 75% of the upper arm should be used
Forearm measurements OVERESTIMATE both systolic and diastolic bp
Consider and A-line
Airway Equipment Needed
Obese patients are more likely to require intubation:
Patients with BMI >40 kg/m2
Patients with primarily abdominal obesity
Major abdominal or thoracic surgery
Most surgery lasting >2 hours
Head down positioning
Confirm availability and access to difficult mask and intubation equipment
Airway Management
- head elevated laryngoscopy position (HELP)
- towels under the patient’s shoulders and head, and putting the patient in the reverse Trendelenburg position to increase the patient’s FRC.
- This creates a horizontal line connecting the patient’s sternal notch with the external auditory meatus.
The HELP position creates a horizontal line connecting the patient’s ____________with the _____________.
-The HELP Position creates a horizontal line connecting the patient’s sternal notch with the external auditory meatus.
Intubation PEARLs for obese pts
- The airway should be secured expeditiously as patients with obesity desaturate quickly (r/t decrease FRC and increase oxygen requirements)
- maximize O2 content in the lungs, patients are preoxygenated with a 100% mask O2 for at least 3 to 5 minutes with continuous positive airway pressure (CPAP)
- Afterward preoxygenation, nasal O2 may be used for apneic diffusion oxygenation during intubation
- In the setting of cannot intubate and cannot ventilate, a difficult algorithm should be used
Rapid Sequence Induction
A rapid-sequence induction should be reserved for patients with a known aspiration risk
Ultrasonography of the stomach has been proposed as a tool for clinicians to identify obese patients at risk for aspiration.
If cricoid pressure is used: 20 Newtons (N), and that the force can be increased to 30 N as loss of consciousness occurs.
Ventilation and Oxygenation Management
- GA causes a 50% reduction in FRC in the obese anesthetized patient (only 20% in nonobese patients)
- The addition of PEEP of 10 achieves an improvement in both FRC and arterial O2 tension, but only at the expense of cardiac output and O2 delivery.
- Ventilation recommendations include using tidal volumes of 6–10 mL/kg of IBW to avoid barotrauma.
- Pressure- or volume-controlled ventilators can be used to maintain adequate oxygenation and normocapnia.
- The intermittent manual application of large volume “sighs” can also augment the FRC.
Ventilation Management: Goals and Recommendations to Prevent Hypoxemia
HOB Elevated 30 degrees (reverse trend back-up Fowler)
Use CPAP during induction
Preoxygenate with 100% O2
If O2 Sat is < or equal to 95% performa. blood gas
Ventilation Management: Goals and Recommendations to Prevent/Reverse Atelectasis
Restrict the use of FIO2 to less than 0.8 during maintenance
Recruitment maneuvers after intubation by using sustained 8-10 sec pressure of 40 cm H2O or greater- monitor for side effects- hypotension and bradycardia
Uses of high FIO2= accelerates atelectasis
Ventilation Management: Goals and Recommendations to Maintain Lung recruitment
Use PEEP (10-12)
monitor for hypotension and decreasing arterial O2
Ventilation Management: Goals and Recommendations to Prevent reoccurrence of Atelectasis
Intermittent intraoperative re-recruitment
Monitor higher oxygenation and respiratory system compliance achieved after recruitment
Ventilation Management: Goals and Recommendations to Avoid Lung Overdistention
Use tidal volume of 6-10 mL/kg of IDEAL BODY WEIGHT
Keep end-inspiratory pressure below 30cm H2O
Consider mild permissive hypercapnia if necessary
-Increase the ventilation rate to control excessive hypercapnia instead of using larger tidal volumes or high ventilatory pressures
Ventilation Management: Goals and Recommendations to Maintain Postoperative Lung Expansion
- Use CPAP or BiPAP immediately after extubation
- Administer supplemental O2
- Keep upper body elevated
- Maintain good pain control
- Use incentive spirometer
- Encourage early ambulation
Volume Replacement
- The normal adult percentage of total body water is 60%. In the severely obese, it is reduced to 40%.
- Therefore, calculation of estimated blood volume should be 50 mL/kg of actual body weight rather than the 70 mL/kg apportioned in nonobese adults.
Intraoperative Positioning
- Positioning of obese requires extra precautions for the prevention of nerve, integumentary, and cardiorespiratory compromise.
- Risk for nerve injury is INCREASED in the patient with obesity
- Patients with obesity often have decreased ROM, assess preoperatively
- Extra-long straps and wide adhesive tape can secure the panniculus and reduce shifting when the operating table is changed.
The risk of airway obstruction after extubation is ___________ in obese patients.
Increased
Extubation
Confirm appropriate reversal of NMBA
Extubate sitting up or head of bed up
Leave ETT in place if patient is not breathing adequately- extubate over an airway exchange or via fiberoptic bronchoscope may be performed
Pain Management
Use non-opioids when possible: NSAIDs, patient-controlled analgesia, local infiltration of the surgical site, and epidural anesthesia.
Obese patients are more sensitive to the respiratory-depressant effects of opioid analgesics
Consider applying patient’s CPAP machine in the early post–general anesthetic period.
Postoperative opioids must be used judiciously
How should SRNAs guide their management of drugs in obese patients?
- no clear way exactly, limited literature
- When possible and appropriate, anesthetic medications should be titrated to effect with incremental doses or incrementally adjusted infusions.
- Modified drug dosing may be required because of obesity-related increases in lean body weight (LBW), cardiac output, and blood volume.
What medications should you ask about in the obese pt population?
- Weight reducing substances, herbal supplements, and anorexiant drugs
- Insulin and oral hypoglycemic dosing may be held or decreased on the day of surgery
- Most cardiac medications (except ACEI and ARBs) should be continued up to and including the morning of surgery.
What labs should be drawn for obese pts?
•Should focus on comorbid disease states such as renal, hepatic, cardiovascular, and endocrine states related to obesity.
OR Beds for obese pts
- Newer-model operating room tables - 600 lb.
- Older-model standard operating room tables - 300 lb
For Succinylcholine, use ____.
For Nondepolarizing NMBAs, used for maintenance use ___.
For Succinylcholine, use TBW
For Nondepolarizing NMBAs, used for maintenance use IBW
STOP BANG
- Snoring: do you snore loudly?
- Tired: do you often feel tired
- Observed: has anyone observed you stop breathing during sleep?
- Blood Pressure: do you have or being treated for HTN?
- BMI > 35?
- Age >50?
- Neck circumference >40cm2
- Gender, male?
High risk = yes to 3 or +
Low risk = yes to fewer than 3
The STOP-Bang screening tool has a senitivity of ___.
up to 93% for OSA
