Perioperative management of morbidly obese patient for non bariatric surgeryDr vivek pushpDeptt. of anesthesiology & ccm BRD medical college gorakhpur

WHAT IS OBESITY?

OBESITY OBESITY A

metabolic disorder that is primarily induced and sustained by an over consumption or under utilization of caloric substrate.

Obesity is a complex multifactorial (genetic,enviormental,psychological)disease

“Across the globe Obesity become the most common Nutritional disorder and it is second only to smoking as a preventable cause of death. In anesthetic practice it present special challenges for both regional and general anaesthesia”.

INCIDENCEINCIDENCE Worldwide adult

population 7% In Affluent cultures, the poor

have the highest prevalence (27% US and 17% UK population)

In Developing world, affluent are at the highest risk.

Obese school children 60-85%

CAUSESGenetic

predisposition Sex/ Race/

Economic status

Psychological Environmental/ Emotional/ Cultural

 

Lean Body Mass FormulaLean Body Mass = Body Weight –

(Body Weight x Body Fat %) : Lean body mass is comprised of

everything in your body besides body fat.

Your lean body mass includes:◦organs◦blood◦bones◦muscle◦skin

Quantifying ObesityHeight/ Weight nomograms The Broca Index Body mass Index

The Broca`s IndexIdeal body weight(IBW) (kg)

◦For Female = Height (cm) – 105 ◦For Male = Height (cm) – 100

BMI=Body Weight (kg)/ Height2 (meters)BMI is defined as the patient's weight,

measured in kilograms, divided by the square of the patient's height, measured in meters, which yields a measurement bearing the unit kg/m2.

Overweight is defined as a BMI of >25 kg/m2

Obesity as a BMI >30Extreme obesity (old term "morbid

obesity") as a BMI of >40.

BMI (kgm-2) Definition

<18.5 Underweight

18.5-24.9 Ideal Weight

25-29.9 Overweight

30-39.9 Obese

40-49.9 Morbidly Obese

50-59.9 Super Obese

60-69.9 Super Super Obese

>70 Hyper Obese

Other method for quantifying obesity include- Skin fold thickness,Densiometry(under water weighing),DEXA,CT,MRI,Electrical Impedence.

EFFECTS OF OBESITY

Cardiovascular Changes

Increased blood volume and cardiac output leading to cardiomegaly, left ventricular hypertrophy and a potential for left ventricular failure.

Hypertension and ischaemic heart diseaseVenous access can sometimes be difficult.Thromboembolism risk is increased.The risk of pulmonary embolus and DVT is

doubledVenous return is reduced. 

Cardiomyopathies Cardiac failure Arrhythmias Sudden cardiac death Dyslipidaemias Venous insufficiency Cerebrovascular disease Peripheral vascular disease Atherosclerotic changes

Respiratory Changes Reduced compliance (both chest wall and lung),

in the airway resistance and reduced FRC will pre-dispose to atelectasis, increased shunt and hypoxia.

70% in work of breathing and a four fold in the Oxygen cost of breathing occur in case of morbid obese.

Pulmonary vasoconstriction, pulmonary hypertension and right ventricular hypertrophy.

These patients must be pre-oxygenated as they desaturate much quicker than non-obese (3–5 times).decrease in FRC impairs the ability of obese pts to tolerate periods of apnea ,such as during direct laryngoscopy for tracheal intubation.

Pulmonary mechanics: Inspiratory reserve volume(IRV), expiratory reserve volume(ERV), functional residual capacity(FRC), vital capacity(VC), total lung capacity(TLC) and minute ventilation(MV)( ) but tidal volume(TV) and residual volume(RV) (→).FRC may be below the closing capacity

resulting in the small airway closure→ V/P mismatch→ right to left shunting and hypoxemia

General anesthesia will accentuate these changes such that

a 50% decrease in FRC occurs in obese anaesthetised pts

compared with a 20% decrease in non obese individuals..

Worsened in: Improved by:◦ Supine Position PEEP

◦ Trendelenberg position Reverse Trendelenberg

Lu

ng

vo

lum

e

Normal

Obese, awake

Closing volume

Obese anaesthetized

Residual volume

Functional residual capacity

Oxygen consumption and carbon dioxide production are increased.

There is a higher incidence of difficult laryngoscopy and intubation.

The incidence of difficult intubation in morbid obesity is around 13%-

Altered anatomy:◦ Increase in soft tissue◦ Reduced head and neck mobility◦ Large tongue◦ Short neck◦ Large breasts◦ Anterior larynx◦ Restricted mouth opening

Obstructive sleep apnoea- 5%

Airflow cessation of >10 secs. and characterised by frequent episodes of apnea or hypopnea during sleep.

RISK FACTORS:◦ Large collar size (over 16.5 inches)◦ Evening alcohol consumption◦ Pharyngeal abnormalities

PATHOPHYSIOLOGY:Passive collapse of the pharyngeal airway during deeper planes of sleep.

CLINICAL FEATURES: ◦ Snoring and intermittent airway obstruction◦ Resultant hypoxaemia and hypercapnia◦ Arousal and disruption of sleep◦ Daytime somnolence.

Pathophysiology of Sleep Apnea

Awake: Small airway + neuromuscular compensation

Loss of neuromuscular compensation

+Decreased pharyngeal

muscle activity

Sleep Onset

Hyperventilate: correct hypoxia & hypercapnia

Airway opens

Airway collapsesPharyngeal muscle

activity restored

Apnea Arousal from sleep

Hypoxia & Hypercapnia

Increased ventilatory effort

Clinical Consequences

Cardiovascular Complications

Morbidity

Mortality

Sleep FragmentationHypoxia/ Hypercapnia

Excessive Daytime Sleepiness

Sleep Apnea

Obstructive Sleep Apnea Hypopnea Syndrome(OSAHS) 5 or more apneic(complete cessation of air flow) events or

15 or more hypopneic(50% reduction of air flow) events per

hour of sleep despite of maintaining adequate ventilatory

capacity associated with a decrease in SpO2 ≥ 4%.

Regular hypopneic and apneic events → hypoxemia and

hypercarbia → rptd stimulation of resp centre → gradual

desensitisation of resp centre→ Alveolar

hypoventilation,Hypercapnia ( OHS)

Pickwickian Syndrome is OHS with cor pulmonale.

Obesity hypoventilation syndrome (pickwickian syndrome)Loss of the sensitivity to hypercarbia resulting

in a combination of hypoxia, Cor Pulmonale and Polycythaemia,respiratory acidosis,pulmonary hypertension,and right ventricular failure.

Diagnosis –Polysomnography (Apnea-Hypopnea index (AHI)), A score of 5-15 is ‘mild OSA’, 15-30 ‘moderate’, and ‘severe OSA’ is over 30

Treatment ◦ Removal of precipitants ◦ Surgical(uvulopalato pharyngoplasty)◦ Weight loss ◦ Nocturnal CPAP

Obesity

OSA or OHS

Hypoxia/hypercarbia

Pulmonary arterial hypertension

Pulmonary venous hypertension

Increased blood volume

Increased cardiac output

LV enlargement

LV Hypertrophy

RV enlargement and

hypertrophy

RV failure

LV failure Ischaemic heart disease

Hypertension

Adams jp murthy PG;obesity in anesthesia and intensive care.br j anaesth 2000;85;91-108

This presents the anaesthetist with a patient who may be difficult to bag-mask ventilate, difficult to intubate and will desaturate quickly

Anatomic changes affecting the Airway Deposit of adipose tissue in the lateral pharyngeal

walls

Deposit of adipose tissue external to the upper airway

Presence of hypopharyngeal adipose tissue

Presence of pretracheal adipose tissue

Alteration in the shape of the pharynx(long axis of

ellipse transverse to ellipse ant- post)

↓efficiency of the anterior pharyngeal dilator muscles

.

Gastrointestinal ChangesIncreased acidity and volume of gastric

contents. Hiatus hernia and gallstones(due to

hypercholestrolemia) are commonIncreased intra-abdominal pressure.There is a higher risk of regurgitation and

aspiration requiring rapid sequence induction if a difficult airway is not anticipated.

Fatty infiltration of liver (denoting the duration of obesity)

Tracheal extubation should be undertaken with the patient awake

Endocrine ChangesThere is an association with

glucose intolerance.HypercholesterolaemiaHypothyroidismCushing syndromeInsulinomatumor involving HypothalamusMetabolic Syndrome and PCOD.

“ Morbidly obese individuals have limited mobility and may therefore appear to be asymptomatic even in the presence of significant respiratory and cardiovascular impairment.”

Morphological Changes

PositioningTransferringMonitoring (arterial line may be

needed if NIBP is problematic) 

Surgical and Mechanical Issues

Reduced surgical accessDifficult visualisation of

underlying structuresExcess bleedingLonger operating timesHigher risk of infectionWound infection and wound

dehiscence

OTHERSGout Osteoarthritis of weight bearing

jointsBack pain Hepatic impairment/gallstones Abdominal herniae Breast and endometrial

malignancies

Preoperative evaluation

 

Detailed history Physical examination Suspect OSA ( h/o- Snoring). Examination of calf muscles for tenderness Examining signs of cardiac failure and diabetes.

(Waist-to-hip ratio >1 in women & >0.8 in men increases the risk for IHD, Stroke, Diabetes & Death)

Prior anesthetic records should be obtained.◦ History of previous surgeries◦ Anesthetic challenges (i.e. ease or difficulty in securing

the airway, intravenous access)◦ Need for ICU admission, Surgical outcomes◦ Weight of the patient at that time.

The Upper Airway Assessment

Atlanto-occipital joint extension Mallampati classificationTemporomandibular joint (TMJ)

assessment with interincisor distance Mentohyoid distance Dentition Pretracheal adipose thickness Neck circumference Hypertrophic tonsils and adenoids.

Special attention should be paid to Circulatory, Pulmonary, and Hepatic function

Circulatory evaluationSigns and symptoms of left or right

ventricular failure Classic physical signs of cardiac failure (e.g.

sacral edema) may be difficult to identify. History of Hypertension and Diabetes Blood pressures must be taken with the

appropriate size cuff. Intravenous and intraarterial access sites

should be checked in anticipation of technical difficulties

Electrocardiographic abnormalities Echocardiogram

Respiratory evaluationSmoking historyHistory of hypoventilation and somnolencePulmonary function tests with spirometry

baselinearterial blood gases Chest x-rayPatients with a history of heavy snoring should

have a formal sleep study or Polysomnogram (PSG).

Severity of obstructive sleep apnea and hypopnea syndrome (OSAHS), apnea-hypopnea index (AHI)

Home Oxygen therapy with continuous positive airway pressure (CPAP) ,response and compliance should be noted.

Hepatic function testsSerum albumin and globulin Serum aspartate

aminotransferase Serum alanine aminotransferase Direct and total bilirubin Alkaline phosphatase Prothrombin time, and Cholesterol levels.

Recommended Preoperative Laboratory Evaluations

Routine investigations

ECG is mandatory

2D-Echo

CXR

X-ray neck

Baseline ABG(will help evaluate carbon dioxide

retention and provide guidelines for perioperative

oxygen administration and possible institution of and

weaning from postoperative ventilation)

Screening for diabetes

LFT

Lipid Profile

PFT (if needed)

Polysomnogram (if history of heavy snoring)

Preparation-

Challenges for the Anesthesiologist

Airway management: Awake fibreoptic intubation Positioning, Monitoring Choice of anesthetic technique and anesthetic

agents Pain control Fluid management Consider asking for Assistance. A typical operating table will support 150 kg, but

the tilting/tipping may not function. The sphygmomanometer cuff width should be

20% greater than the diameter of the arm Invasive blood pressure monitoring may be

required

DvtHeparin, 5000 IU subcutaneously,

administered before surgery and repeated every 12 h until the patient will be fully mobile, or low molecular weight heparins (LMWH) injected subcutaneously 40 mg every 12 h resulted in a decreased incidence of postoperative DVT complications

Stockings, Early mobilization.

NPO status, and a large bore intravenous access inserted.

An experienced Assistant The full complement of alternate

airway, noninvasive and invasive (e.g. cricothyriodotomy set and surgical tracheotomy set) airway devices should be available.

ECG NIBP

◦ Cuffs with bladders that encircle ideally of 75% or minimum of 50% of the upper arm circumference should be used

Invasive BP Pulse oxymetry

EtCO2

Temperature Neuromuscular monitoring Central Venous pressure monitoring Hourly urine output is evaluated to assess

fluid balance

Monitors

Premedication

Preoperative medications Avoid CNS and respiratory depressants.(sedatives or

narcotics).

Antibiotic prophylaxis; increased risk of postoperative

wound infection

Anticholinergics(Glyco) if awake intubation is planned.

Aspiration prophylaxis(H2-receptor antagonists and

proton pump inhibitors).

Continue antihypertensive medications.

If required O2 supplementation and monitoring.

Premedication should not be given IM as it may be

inadvertently administered into adipose tissue leading to

unpredictable absorption.

Positioning

Strapping to the operating table in combination

with a malleable bean bag

Padding of pressure areas

Special tables for extra load (two tables)

The head up reverse trendelenburg position

provides the longest safe apnea period during

induction

Lateral tilt to avoid compression of vena cava

“Stacking” using towels or folded blankets

under the shoulders and the head to

compensate for the exaggerated flexed position

of posterior cervical fat .

The object is to position the patient so that the

tip of the chin is at the higher level than the

chest to facilitate laryngoscopy and intubation.

Troop Head Elevation Pillow

Anaesthetic management

Intubation techniqueAnticipate for difficult airway and prepare in

same line Awake intubation in morbid obese patient

LA DL Glottis visualized GA intubate

Not visualized Awake

intubation

or

Awake fiberoptic

We should be ready for emergency tracheostomy

Drug handling in obesityUnpredictable Volumes of

distribution Binding Elimination of drugs Reduction in total body waterHigher fat massHigher lean mass Higher GFRIncreased renal clearance

PHARMACOKINETICS OF DRUGS

Drugs are dosed in the morbidly obese on the basis

of their lipophilicity.

Highly Lipophilic drugs have increased volume of

distribution so drug doses are calculated on the

basis of the patients Total Body Weight (TBW).

Examples are: Thiopentone Propofol Benzodiazepines Fentanyl Sufentanyl Succinylcholine Atracurium Cisatracurium

Weakly lipophilic or lipophobic drugs have unchanged

volume of distribution so drug doses are calculated on the

basis of the patients lean body weight (LBW). Examples are:

Alfentanil

Ketamine

Vecuronium

Rocuronium

Morphine sulphate

Certain Lipophilic drugs are adminstered according to LBW

are Digoxin,Procainamide,Remifentanyl((Vd) remain same).

Calculating initial doses based on LBW with subsequent

doses determined by pharmacologic response to the initial

dose is a reasonable approach.

Anaesthetic drugs Insoluble anesthetic gases resistant to

metabolic degradation and without lipid depot compartmentalization, combined with rapid return of reflexes are preferred.

For intubation muscle relaxants with rapid sequence induction should be used. Succinylcholine and Rocuronium are the available choices.

For maintenance of anesthesia-Desflurane/sevoflurane+ Cisatracurium +intravenous infusion of Remifentanyl is prefered.N2O should be avoided particularly in Pt with Pulm HTN.

Desflurane and Remifentanil infusion are used for maintenance anesthetic because of rapid onset, consistent profile, and rapid offset

Extubation Criteria

Intact neurologic status, fully awake and alert, with head lift greater than 5 seconds

Hemodynamic stability Normothermia. The core temperature

>36°C.Train-of-four (TOF) reversal documented by

peripheral nerve stimulator (T4/T1 >0.9). Full reversal of neuromuscular blocking

agents. Respiratory rate (>10 and < 30

breaths/minute)

Baseline Peripheral Oxygenation, as judged by pulse Oximeter (SPO2 >95% on FIO2 of 0.4).

If an arterial line is present, an arterial blood gas may be checked.

Acceptable blood-gas results (FIO2 of 0.4: pH, 7.35 to 7.45; PaO2, >80 mm Hg; PaCO2, < 50 mm Hg).

Acceptable Respiratory Mechanics: negative inspiratory force (NIF) (>25 to 30 cm H2O; vital capacity (VC) >10 mL/kg IBW; tidal volume (VT) >5 mL/kg ideal body weight [IBW]).

Acceptable Pain Control No demonstrated or suspected Laboratory

abnormalities

Post-operative Considerations

Extubate awake, sitting up. ICU care, may need CPAP. Oxygen and oximetry. Obstructive sleep apnoea is most

common some days after surgery. Adequate analgesia to allow deep

breathing/coughing.Physiotherapy DVT prophylaxis

Postoperative analgesia There is no clear data proving the superiorty of

one technique over other for post op analgesia.It depends on type ,site , duration, severity of surgery.

Multi Modal Perioperative Analgesia(MMPA) I,e preemptive infiltration local anesthetic at the incision site +NSAIDS+ PCEA(patient controlled epidural analgesia)/PCIA(patient controlled intrathecal analgesia) is a new and advanced method to deal with post op pain.

In certain situation where sedation is to be avoided Dexmedetomidine,Ketorolac,Clonidine,Magnesium sulphate are better alternative of Opoids.

Postoperative complicationsPostanesthetic hypoxemia Respiratory depression Early ventilatory failure with need for

reintubation Positional ventilatory collapse Hemodynamic instability Postoperative nausea and vomiting

(PONV)Venous thromboembolism Anastomotic leak Wound infection.

Regional anesthesiaMay be impossible

with standard equipment and techniques due to; ◦Obscured

landmarks ◦Difficult positioning ◦Extensive layers of

adipose tissue◦ 

Regional AnaesthesiaEngorged extradural

veins and extra fat constricting the potential space, less local anaesthetic 75-80% of the normal dose is needed for epidurals

Leave extra catheter in the space as it may be subject to drag as the flexed patient relaxes.

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