obesity Flashcards
Discuss the pathophysiology of obesity & list anaesthetic risks ass’d with it
Obesity is classified as a multisystem disease, a bio-psycho-social disorder linked with significant co-morbidities including cardiovascular disease, diabetes and higher risk of malignancy.
Increased adipokines–> pro-inflammatory cytokines–> insulin resistance & risk T2DM
Incr lipid production & free fatty acids
–> lipotoxicity–> NAFLD, cirrhosis
–> dyslipidaemia–> coronary artery disease
Incr SNS activity & RAAS activity
–> systemic & pulm HTN, coronary artery disease
Mechanical stress–> OSA (and manifestations including hypersomnolence, pulmonary hypertension), OHS, OA (inactivity), GORD
Final common pathways of T2DM, CAD & HTN= CCF, CVA, CKD
HIGHER RISK OF PERIOPERATIVE COMPLICATIONS:
-POCD RR 1.27
-more likely difficult airway (obesity isn’t an independent risk factor but high neck circumference & high MP score)
-upper airway obstruction, hypoxia with post-op desaturation, post-op resp failure or re-intubation (OSA, obesity hypoventilation syndrome)
-aspiration risk (more likely GORD, diabetes, previous weight loss surgery incr aspiration risk +++)
-restrictive lung disease- ventilation challenges esp in trendelengberg. Atelectasis, pneumonia. more likely to have asthma
-higher rates myocardial ischaemia (supply:demand mismatch as higher risk coronary artery disease, HTN, higher MRO2, cor pulmonale, cardiomegaly, PVD)
-thromboembolic events (stroke, DVT)
-blood loss
-DM & other endocrine issues (eg, hypothyroidism, dyslipidaemia)
-renal impairment
-wound infection
-difficult IV access & issues with manual handling in OT
-more likely postop ICU
what are some obstetric complications associated with obesity?
PIH, PET
instrumental delivery
LUSCS
fetal macrosomia
Pre-op assessment approach to obesity?
Consult:
Hx: associated conditions, degree of control, management & compliance- to risk stratify & optimise reversible risk factors in liaison w multi-D team incl allied health (dietetics). teachable moment & inform risk discussion:
-incr BMI independently ass’d w periop pulm complications, greater hospital LoS, longer OT times, SSI, higher EBL & renal failure; however the co-morbid conditions may be more important than BMI for periop risk. Also, other factors such as WHR or WC may more accurately predict metabolic health, comorbidity & periop risk.
Older pts + severe obesity ass’d w incr LoS, complications & early postop mortality; decr CV reserve & musculoskeletal fitness.
-Hx primary weight loss surgeries? (if sleeve gastrectomy aspiration risk +++, prolonged fast & RSI WITH ETT needed irrespective of symptoms. If have a roux-en-Y gastric bypass or other malabsorptive procedure, it may affect bioavailability of oral meds (shortening small bowel, smaller absorptive surface area) & pt has high risk aspiration- RSI with antacid premed routine as pts w adjustable band have SLOW +++ gastric emptying times. If adjustable band, avoid NGT unless acute abdominal or bowel obstruction (risk displacing band, perf prox stomach), shouldn’t deflate band unless considered essential & discussed with the bariatric surgeon as risk infection, band erosion into stomach or damage to band (also pt likely to gain wt in that time if deflated in advance of OT))
-Sleep-disordered breathing (OSA, OHS): screen for OSA using SNORING LOUDLY, EXCESSIVE DAYTIME SLEEPINESS, OBSERVED APNOEA/CHOKING/GASPING, HTN, BMI>35, >50, Neck >=16 inches, Male? (low risk 0-2, intermediate 3-4, high risk 5-8). Dyspnoea, SpO2 <95% on RA, STOP-BANG >=5. OHS= BMI >30, hypercapnia when awake (PaCO2 >45), raised bicarb (useful screening for OSA/OHS) & one of the sleep-related breathing disorders (OSA, sleep hypoventilation (PaCO2 incr by >10 when asleep & desaturate sans apnoeas/hypopnoeas), a combo), with exclusion of other causes of hypoventilation. Obesity, hypersomnolence, wakeful hypoventilation, erythrocytosis & when advanced, corpulmonale (pulm HTN, RHF). 50% of pts w BMI >50 have OHS. 15% of pts w OSA have OHS but 90% of pts w OHS have OSA.
Ax with bicarb +/- ABG, spirometry. BMI > 45 get a VBG in clinic looking @ bicarb (or on U&E; if normal, unlikely OHS. Pathophys of OHS= reduced lung volumes, altered vent control, leptin resistance impacts vent drive all–> hypoventilation, hypox, hypercarbia. OHS VERY high risk resp & heart failure, ICU admission. CPAP helps OHS pts but a lot need BiPAP w added oxygen in 10% (w CPAP only, only about 75% get eucapnia, 60% normoxia). Peak improvements within 1 month (ie. stabilise OHS pts on CPAP for 1/12 prior to elective surgery). The BiPAP is set to a level to resolve aph-noeas/hypopnoease, the IPAP set to a level to correct hypoxaemia by improved alveolar ventilation. Pts w OHS need postop NIV & CPAP stabilisation pre-op.
PLAN: for likely difficult airway (4x incr risk difficult intubation & mask ventilation. consider further Ix/optimisation pre-op if time eg. commence CPAP & use post-op. sometimes require BiPAP (esp if OHS). postop HDU/ICU if not improved in time for surgery.
-asthma: dyspnoea/wheezing- asthmatic symptoms common in obesity, not always reversible w B2 agonists (may be chronic pro-inflammatory state from excess adipose–> small airway collapse. symptoms will improve w weight loss)
-HTN & heart disease (eg. LVH (related to duration of obesity), LV failure, conduction abnormalities, cardiomyopathy): if poorly controlled HTN, incr periop risk (labile BP during anaesthesia, incr cardiac, neurol & renal complications; improve control if SBP >170mmHg & DBP >110mmHg). If clinical signs of heart failure, pre-op ECG & echo if structural heart disease suspected. consider referral to cardiologist & medical optimisation before surgery
*they have incr circulating blood vol but it’s a lower proportion TBW (50mL/kg vs 75mL/kg w normal BMI). Decr SVR, incr CO 20-30mL/kg excess fat. cardiac index & HR are normal, the incr CO is due to incr SV.
-DM? check HbA1c; elevated ass’d w periop morbidity, delay surgery if A1C >=9% (elevated HbA1c ass’d w adverse infection & cardiovascular outcomes) but no evidence that improving preop glucose control improves postop outcomes. micro/macrovascular complications & ANS neuropathy, optimise control in liaison w endocrine
-functional capacity difficult to assess in obese pts- 4 METs indicates lower risk. Pts with obesity & @ least 1 risk factor for CHD (DM, smoking, HTN, hyperlipidaemia) or poor ET should have 12-lead ecg & CXR prior to surgery.
-pulmonary HTN may occur secondary to sleep-disordered breathing (cor pulmonale)
-may have polycythaemia from chronic hypoxaemia
-GORD: obesity ass’d with hiatus hernia, DM/ANS neuropathy, high IAP which all risk GORD. routine RSI not required if fasted & no additional risk factors such as intra-abdo pathology (obesity not incr aspiration risk, it’s the ass’d comorbidities)
-liver disease- NASH/NAFLD: cirrhosis/deranged LFTs. liver-shrinking diet of <1000 calories/day may help reverse disease process
-renal impairment; CKD risk incr in pts w BMI >=35 cf normal BMI
-VTE risk factors & risk minimisation plan
-particularly screen for features of metabolic syndrome (3 of: HTN, central adiposity, impaired glucose tolerance/DM, incr TGs, reduced HDL)
/examination
expect incr RR, reduced FRC & ERV; may have V/Q mismatch & R)–> L) shunt which worsen w GA esp supine, OSA
Assess fat distribution (peripheral or central)
peripheral O2 saturation <95% on RA?
BP
CV examination esp signs RHF
AIRWAY ASSESSMENT VITAL:
Predictors for diff BMV:
(male
older adult, obese
short TMD, snoring/OSA
edentulous
facial hair/beard
retrognathia/inability to protrude mandible
thick/abnormal neck
MP3-4)
Predictors difficult DL:
prior diff intubation
lack of submental compliance
NC >40cm
IID<4cm
TMD<6cm
SMD <12cm
head/neck E <30deg from neutral
MPIII or IV
-ve ULBT
Difficult SGA:
male
obesity
poor dentition/large incisors
reduced MO
tonsillar hypertrophy
glottic/hypopharyngeal/supraglottic pathology
reduced C-spine ROM
prev neck radiation
Functional capacity difficult to assess- may c/o limitation due to joint symptoms; as per ACC/AHA, does the pt have risk for periop MACE combined pt/surg risk (RCRI), if low risk (<1%), no further testing. If elevated risk, exercise capacity >=4METs no further testing. if poor or unknown, pharmacologic stress test if will impact decision-making or periop care.
/investigations (none routine however given the complexity of obesity, FBE, renal function, HbA1c, ecg likely to be useful, ?venous bicarb surrogate of resp failure related to OSA. If suspect malnourishment (eg. mal-positioned gastric band- LFTs, coags, Alb)
ecg & echo if signs RHF
Obesity class III with risk factor for CHD (DM, smoking, HTN, dyslipidaemia) or poor ET, 12-lead ecg & CXR
low threshold for echo & preop sleep studies in severely obese pts aged >=50yo
Optimise:
Planning:
appropriate facility for their surgery (facilities generally have BMI criteria (eg. <=35kg/m2, depending on factors such as maximal equipment ratings). All facilities require a BMI above which the pt is referred for early consult w an anaesthetist. medically stable ASA 3 or 4 may be appropriate for day case, if OSA carefully screen & only discharge if minimal opioid & discharge analgesia no include post-op opioid.
pts w OSA continue CPAP
Explain/consent: teachable moment
Disposition:
what’s the preferred form of stress echo for obese pts?
transoesophageal dobutamine stress echo (accuracy of thallium-201 for myocardial perfusion scanning significantly diminished if pt has BMI >30)
Intraop planning for obesity & postop considerations:
(Monitoring: low threshold art line (can be difficult to get good BP readings) or forearm (may overestimate)- also consider that IVCs & epidurals may have some migration with soft tissue movement & dislodge so have “buffer length”)
depth of anaesthesia for both TIVA & VA to assist titrating & limiting slow wake-up
Assistant: skilled, consider “extra set of hands”
(Drugs: ABx prophylaxis (these pts have higher wound infection complication rate)
analgesia- multimodal incl regional & opioid sparing, consider alpha agonists)
Equipment: long IVC (I use ultrasound all regional techniques in all pts & for my IV/art access in morbidly obese), consider secure CVC, US for access & neuraxial.
higher risk awareness identified in obese pts in NAP5 shortly after induction; depth-of anaesthesia monitoring mandatory (clinical & pEEG), esp as Pk models used for propofol TCI aren’t validated in obese pts. use volatiles with low B:G partition coefficient)
Ask assistant to have guedel, npa, HFNO, consider difficult airway trolley
consider weight rating of the bed & how this is impacted if bed moved
patient transfer (hovermatt >100kg, weight ratings may not be valid if pt shifted or table not level. consider additional arm supports to widen the table or 2 tables).
VTE prophylaxis (TEDs (should be full-length so not tourniquet), SCUDs, IVT & periop hydration, pharmacologic, early mobilisation)
(Transfer:
*Positioning:
Pt to mobilise their self wherever possible, care w manual handling (hover mat)
Ramp, tragus in line with upper sternum, chin 5-10cm above sternum allows OA, PA & LA to all be in line. consider also reverse trendelenburg
consider intra-op positioning-implications for ventilation (eg. trendelenberg or lithotomy), risks of sliding, risks of pressure areas
if procedure under spinal, still position pt for airway rescue
*Pre-oxygenation meticulously with FiO2 100% & great seal to EtO2 of 90% and flows to prevent rebreathing (10-12L/min), consider NHF or PSV-pro (decr time to desat, incr O2 requirements); the high FiO2 may cause resorption atelectasis but this can be reversed by recruitment maneouver & PEEP after intubation.
limited pre-meds (low-dose incremental sedative)
(Resus:
Induction plan:
A:
low threshold for RSI, cuffed ETT (obesity without other risk factors doesn’t incr the risk of pulmonary asp’n & RSI may be suboptimal; base decision re: pharmacologic aspiration prophylaxis & RSI on standard risk factors (however still use rapid acting NMBA for intubation to shorten the duration for mask ventilation). If do RSI, may need to use gentle BMV +/- HFNO to incr apnoea time. Ensure fasted 2hrs clear, 6hrs solid (8hrs high protein or fatty food))
plan A very likely videolaryngoscope, could consider iLMA
Drug dosing scalar for some drugs is debated (complex Pk & Pd of obesity; therapeutic window narrowed or side effects exagg by some drugs)
propofol induction lean BW (IBW underdosing as incr VD in obese, total BW overdose as peripheral compartments receive relatively less blood flow & contribute less to initial VD- lean BW correlates closely w CO & Cl) & maintenance TBW (OR Adj40BW as per SOBA)
consider low solubility volatile for maintenance & timing
NDMR relaxant lean BW (sux total)
local anaesthetic & tracheal tube size ideal BW (SOBA LAs lean BW, as is paracetamol)
opioids LBW & adjust doses down as they’ll be more sensitive to opioids (OIVI); avoid long-acting
highly lipophilic (eg. midaz) TBW
antibiotics TBW (gent LBW)
reversal agents Adj40BW
Analgesia multimodal, opioid-sparing (eg. alpha-2 agonists), benefit of regional in pts w OSA negated if pt requires mod-deep sedation; also consider pts ability to lie flat etc if opting for neuraxial/regional. consider that if sedating, it’d be light which may not be appropriate for anxious pts. hypercapnia inappropriate esp if pulm HTN.
Neuraxial meds incrementally (titrated epidural or CSE) vs single shot, since LA can spread higher due to high intraspinal pressure, high block may lead to resp difficulty.
higher number of attempts common, use US.
B:
more likely to require intubation as SGA may not maintain appropriate seal @ the higher Paw needed in obesity. ETT with CV more appropriate if BMI >45kg/m2, primarily abdo obesity, surgery >2hrs, lithotomy or head down, for ALL pts who’ve had weight loss procedures.
If use SGA, use a 2nd generation with higher seal pressures.
lung-protective vent since obesity= independent risk for postop pulm complications. (6-8mL/kg IBW, Pplat<30cmH2O, titrate PEEP (higher for obese, 8-10cmH2O as absence of high-quality studies showing optimal level) & rate based on compliance, CO2 (AVOID hypercapnia if PHTN or RHF) & co-morbidities + judicious use of recruitment manoeuvres; FiO2 minimal to maintain SpO2 >93%)
* PEEP of 15cmH2O may be appropriate for obese pts having laparoscopy. or inverse I:E ratio (1.5:1 or 2:1) may improve intra-op oxygenation & resp mechanics.
fully reverse- neostigmine 50mcg/kg with glyco 10mcg/kg
C:
BP <=3-minutely, forearm may be more appropriate than upper arm (conical)
Maintenance:
ABCDE (pressure area care ++ (risk nerve injury, rhabdo) care with repositioning & traction injuries, glycemic control, temp, euvolaemia)
Emergence plan
Time of high risk- ensure emergency equipment available to manage potential difficulties
POSITION THE PT AS I DID FOR INTUBATION
Only extubate when fully reversed to TOFR >0.9 & airway reflexes returned
Pts w OHS more likely to have difficulty weaning from mech vent
Postop:
Recovery- pt 30 degrees head up
Obese pts are @ higher risk of hypoxia post-op due to physiologic changes; administer supplemental oxygen titrated to keep SpO2 >90%
consider oro- or nasopharyngeal airway or NIV (discuss with surgeons appropriateness)
give incentive spirometry
must be able to maintain adequate oxygenation when left unstimulated to be able to cease O2 monitoring, otherwise need continuous O2/OSA monitoring on the ward & consideration of HDU
May require prolonged PACU stay
Consider differentials for hypoventilation; opioid or BZD
Analgesia- aiming to facilitate mobilisation
Ward/HDU (if significant co-morbidities)
consider OSA monitoring if not controlled; postop CPAP essential if OSA, consider if undiagnosed
Follow-up
when are most of the airway complications in obesity?
extubation (*care w pt position on extubation)
how may obesity affect pk? what are general principles of drug dosing?
incr lean mass & fat mass but greater fat & relatively less lean mass & water
incr TG, chol & FFA may reduce PB but there are incr acute phase proteins
renal & hepatic changes influence elimination
CV & resp changes (circulation, pH)
lean body weight best for most drug doses, except emergency meds (NAdr/Adr) ideal BW, sux total body weight, atropine lean BW.
what’s the “obesity paradox”?
DEFINED BY BMI
underweight pts (BMI<18.5kg/m2) tend to have highest mortality rates
overweight & obese class 1 & pts have lower incidence complications & mortality than pts with normal weight UNTIL class 3 obesity which is ass’d w incr periop M&M
what’s BMI? why is the clinical utility of BMI questioned? what’s a better measure of obesity risk in perioperative setting?
wt (kg) / (height in m)^2
it doesn’t accurately reflect visceral fat accumulation, the likely culprit for most of the metabolic & clinical consequences of obesity
Doesn’t describe composition & distribution of body tissue (muscle/adipose) or metabolic state.
waist circumference- >88cm women, >102cm men, it’s strongly associated with cardiac events, metabolic syndrome, difficult airway & ventilation, overall periop risk. regional fat distribution may be critical in determining the CV risk associated with obesity (central obesity ass’d w adipose tissue accumulating around visceral organs)
why anaes a problem for OSA?
reduced pharyngeal tone (UAO out of proportion to sedation- even 0.5mcg/kg fentanyl can increase apnoeas by 50%!)
reduced vent drive
reduced CO2 responsiveness
in the 2019 JAMA PCRT investigating pts with PSG-diagnosed sleep apnoea undergoing standard perioperative care, what were the findings for primary outcome (composite of cardiac death, myocardial injury, CCF, thromboembolism, new AF & CVA)?
adj HR: 2.23x highr risk (sig) of primary outcome in those with severe OSA
BMI & neck circumference & age cutoffs for STOPBANG?
35, 40, 50
is there a genetic link with OSA?
if 1st degree relative, 1.5-2x risk OSA
what’s underweight according to BMI? ASA grade?
what’s class 1 obesity according to BMI? ASA grade?
what’s class 2 obesity according to BMI? ASA grade?
what’s class 3 obesity according to BMI? ASA grade?
<18.5
>25 overweight
>=30-34.9kg/(m2), ASA1
>=35-39.9, ASA2
>=40, ASA3
what’s the metabolic syndrome?
3 or more of a cluster of features are required for diagnosis, metabolic syndrome are ass’d with increased risk CVD, T2DM, obesity + met syndrome ass’d w postop mortality, cardiac complications, pulmonary complications, AKI, stroke, sepsis.
features are:
central obesity
HTN
impaired glucose tolerance or DM
incr triglycerides
decr HDL cholesterol
