ANAESTHESIA FOR MORBIDLY OBESE PATIENTS AND BARIATRIC SURGERY

DR.SANDEEP.G.B.NARAYANA MEDICAL COLLEGE

NELLORE

OVERVIEW

• DEFINITION

• EPIDEMIOLOGY

• SCALES

• PATHOPHYSIOLOGY

• OBESITY – ANAESTHESIA CHALLENGES

• BARIATRIC SURGERY & ITS COMPLICATIONS

DEFINITION

Body weight that exceeds the

expected or ideal weight by more than

10%, taking into account height, age,

body build and sex.

EPIDEMIOLOGY

• Incidence:

– Worldwide : 20 to 30% of adults

– India : 10-15% of adults

Aetiology

MEASURING SCALES

• BODY MASS INDEX (Quetelet's index) (Kg/m2)

• WAIST CIRCUMFERENCE

PATHOPHYSIOLOGY

• Resting blood flow to fat is 2 to 3 ml/100gm/min.

• With increasing obesity the percentage of perfusion to fat decreases {i,e not in direct proportion}

• 1 kg increase in fat above IBW needs 20 to 30 ml increase in C.O.

• For every 13.5 kg of fat added, app. 25 miles of neovascularisation is added to the body

CARDIOVASCULAR SYSTEM

CARDIOVASCULAR SYSTEM

OBESITY CARDIOMYOPATHY

• Various heart tissues are replaced by fat cells and become dysfunctional.

• Conduction defects, pressure induced atrophy of myocardial cells.

• Secrete adipokines which are deleterious to adjacent cells.

• ↑C.O and Blood Volume LV dilatation and hypertrophy diastolic dysfunction

• If wall thickening fails to keep in pace with chamber dilatation then systolic failure occurs.

• This leads to cardiomyopathy CCF and sudden cardiac arrest.

COAGULOPATHY

• Hypercoaguability :

– Obese individuals have higher levels of Fibrinogen, Factor VII, Factor VIII, Von Willebrand Factor, And Plasminogen Activator Inhibitor-1 (PAI-1).

– Hypofibrinolysis

RESPIRATORY SYSTEM

• Restrictive lung disease

• Obesity hypoventilation syndrome (OHS)

• Obstructive sleep apnea (OSA)

• Corpulmonale

Increased fatDecreased respiratory muscle function

Decreased chest wall complianceIncreased elastic resistance

Increased pulmonary blood flow

Decreased lung compliance

Decreased total respiratory compliance in supine position

↓FRC, ↓VC, ↓TLC

Shallow & rapid breathingIncreased work of breathing

Limited maximum ventilatory capacity

RESTRICTIVE LUNG DISEASE

FRC below CCSmall airway closure

V/Q mismatch & left to right shuntArterial hypoxemia

• Reduction in FRC is primarily a result of REDUCED ERV, but the relationship between FRC and closing capacity, the volume at which small airways begin to close, is adversely affected.

• Residual volume and closing capacity are unchanged

• Anesthesia worsens this situation such that up to a 50% reduction in FRC occurs in the obese anesthetized patient compared with 20% in the nonobese individual.

DEFINITIONS:

OBSTRUCTIVE SLEEP APNEA

1. Complete cessation of airflow.

2. Lasting 10 seconds or longer

3. 5 0r more times per hour of sleep

4. Decrease of atleast 4% in SaO2

OBSTRUCTIVE SLEEP HYPOPNEA

1. Partial reduction of airflow of greater than 50%.

2. Lasting atleast 10 seconds

3. 15 or more times per hour of sleep

4. Decrease of atleast 4% in SaO2

• Diagnosis is made by Polysomnography and is reported as the APNEA/HYPOPNEA INDEX (AHI).

• AHI is the Total number of episodes of apneaand hypopnea divided by the total sleep time.

Normal : 5 to 10 events per hour

Mild : 10 to 15 events per hour

Moderate: 15 to30 events per hour

Severe : > 30 events per hour

• TOTAL AROUSAL INDEX is the total number of arousals per hour.

• RESPIRATORY DISTURBANCE INDEX is the sum of total arousal index and apnea hypopneaindex.

• Patients diagnosed to have maoderate/ severe OSA have to undergo CPAP prior to elective surgery

Duration of CPAP

EFFECT

2 weeks Corrects abnormal ventilatory drive

3 weeks Increases LVEF in CHF

4 weeks Reduces B.P, HR, 35% increase in E.F

4-6 weeks Reduced tongue volume & increased pharyngeal space

8 weeks Reduction in CVS risk

3-6 months Reduction in PAH

OBESITY HYPOVENTILATION SYNDROME (OHS)/PICKWIKIAN SYNDROME

• Presence of obesity (BMI >30) and awake arterial hypercapnia (PaCO2 >45mm Hg) in the absence of known causes of hypoventilation.

• Results from long term OSA

Main ventilatory impairment is :

•Alveolar hypoventilation irrespective of intrinsic lung disease•Day time hypersomnalence•Hypercapnia, hypoxemia and polycythemia•Pulmonary hypertension and right heart failure

Impaired ventilatory response to hypoxia + hypercapnia↓

Mechanical load of obesity + upper airway obstruction ↓

Prolonged hypoxia + Hypercapnia at night↓

Alteration in control of breathing↓

Progressive desensitization of respiratory centres to hypercapnia↓

Type II Resp. Failure

PARAMETER OHS OSA

Gender Males = females Males > females

Obesity (BMI ≥30 kg/m2) Yes May be

Ventilation pattern Hypoventilation Normal

PaCO2 (mm Hg) Increased (>45 mm Hg) Normal (increased during apnea)

Pao2 (mm Hg) Decreased; most severe during REM sleep

Normal (decreased during apnea)

Sao2 (%) Decreased Normal (decreased during apnea)

Nocturnal upper airway obstruction

No Yes

Pulmonary hypertension More common and severe Less common

Nocturnal monitoring Increased PaCO2 during sleep to >10 mm Hg from awake supine values. O2 desaturationduring sleep not explained by apnea or hypopnea

≥5 obstructive breathing events per hour of sleep

GASTROINTESTINAL SYSTEM

• Gastric volume and acidity are increased.

• Delayed gastric emptying

– because of increased abdominal mass that causes antral distention

– gastrin release

– a decrease in pH with parietal cell secretion.

– increased intragastric pressure,

– Increased frequency of transient LES relaxation

• An increased incidence of hiatal hernia and gastroesophageal reflux also increase aspiration risk.

• Gastric emptying is faster with high energy content intake such as fat emulsions, but because of larger gastric volume, the residual volume is increased.

• Fatty liver & Non alcoholic fatty liver disease

RENAL AND ENDOCRINE SYSTEMS

• Impaired glucose tolerance Type II D.M

• Subclinical hypothyroidism with electrolyte imbalance

• Glomerular hyperfiltration

• Excessive weight gain causes:-– increases renal tubular resorption

– impairs natriuresis through activation of the sympathetic and renin-angiotensin system as well as physical compression of the kidney.

– Loss of nephron function if prolonged obesity

METABOLIC SYNDROME

• FEATURES:-– Abdominal obesity

– Atherogenic dyslipidemia

– Hypertension

– Insulin resistance ± glucose tolerance

– Proinflammatory state

– Prothrombotic state

– Others: endocrine dysfn.,microalbuminuria, PCOS, hypoandrogenism, NAFLD, hyperuricemia

• DIAGNOSIS:- 3 of the following

PHARMACOLOGY

• Drug dosing should take into consideration the volume of distribution (VD) for administration of the loading dose, and on the clearance for the maintenance dose.

• Dosing should be calculated based on LBW/TBW.

• IBW (kg) = height (cm) – x

where x is 100 for adult males

105 for adult females.

• Lean body weight (LBW) is the total body weight (TBW) minus the adipose tissue

• In morbidly obese patients, increasing the IBW by 20 to 30% gives an estimate of LBW.

• The VD in obese patients is affected by

– reduced total body water,

– increased total body fat,

– increased lean body mass,

– Altered tissue protein binding,

– increased blood volume & cardiac output,

– increased blood concentrations of free fatty acids, cholesterol, and

– organomegaly.

• Plasma protein binding– Adsorption of lipophilic drugs to lipoproteins

(increases free fraction of drug)

– Plasma albumin unchanged

– Increased alpha 1 glycoprotein

• Drug clearance– Increased RBF

– Increased GFR

– Increased tubular secretion

– Decreased Hepatic blood flow in CCF

• Increased Vd prolongs drug elimination half-life even when clearance is unchanged or increased.

• Drugs that undergo phase I metabolism (oxidation, reduction, hydrolysis) are generally unaffected by changes induced by obesity, while phase II reactions (glucuronidation, sulfation) are enhanced

• Renal clearance of drugs is increased .

• Highly lipophilic substances such as barbiturates and benzodiazepines show significant increases in VD for obese individuals

• Exceptions to this rule include the highly lipophilic drugs Digoxin, Procainamide, And Remifentanil

• IBW- Propofol, Vec, Rocuronium, Remifentanyl

• TBW- Thio, Midaz, Sch, Atra, Cis-atra, Fentanyl, Sufentanil

• Maintainence- Propofol- TBW

Sufentanil- IBW

INVESTIGATIONS

• CBC, FBS,RFT,SCREENING,LFT• ECG

– Low voltage complexes– LVH/Strain– Prolonged QT/QTc– Inferolateral T wave abnormalities– RAD/RBBB– P- Pulmonale

• CXR, X –ray neck• ECHO• Polysomnography• Lipid profile

TREATMENT

• Medical treatment

– Behavioural modifications

– Dietary & herbal medications

– Phamacological: Sibutramine/ Orlistat

– Implantable electrical stimulators

• Surgical treatment- BARIATRIC SURGERY

BARIATRIC SURGERY

• Malabsoptive- jejenoilealbypass / RYGB/ biliopancreatic diversion

• Restrictive- Gastroplasty / adjustable gastric banding

PREOPERATIVE CONSIDERATIONS

• PAC:-– Look for HTN/DM/CCF/OHS

• OHS -AHI >30- rapid and severe desaturation on induction

-CPAP>10 – difficult face mask ventilation

– Previous h/o surgeries/ anesthetic administration/ airway problems/ICU admissions

• STOP BANG:– Snoring, Tiredness, Observed apnea, blood

Pressure, BMI, Age, Neck circumference, Gender

• For repeat bariatric surgery

– Screen for metabolic and nutritional abnormalities.

– Acute postgastric reduction surgery neuropathy.

– Electrolyte and coagulation indices

• Evidence of OSA and OHS should be sought

– associated with difficult laryngoscopy

– a neck circumference >40 cm correlates with an increased probability of OSA.

– patients on CPAP at home should be instructed to bring it with them as it may be needed postoperatively

• Lab investigations- lipid profile / FBS/ LFT/ CBC/ ECG/2D ECHO/RFT/ VIT-B12/ THYROTROPIN/PFT

• Arterial blood gas measurements

• NBM for 12 hrs

• Avoid pre operative sedatives & hypnotics

• Multimodal antiemetic therapy

• Continue routine medications

CONCURRENT, PREOPERATIVE, AND PROPHYLACTIC MEDICATIONS

• Usual medications should be continued except insulin and OHA.

• Antibiotic prophylaxis

• Prophylaxis against Aspiration Pneumonitis and DVT.

• Dexmedetomidine, because of its minimal respiratory depressant effects, may be considered for anxiolysis

• DVT prophylaxis:

– Risk factors: venous stasis, BMI ≥60, truncalobesity, and OHS/OSA

– Subcutaneous heparin 5,000 IU administered before surgery and repeated every 8 to 12 hours until the patient is fully mobile

Or

Enoxaparin, 40 mg, injected subcutaneously every 12 hours

AIRWAY

• Limitation of movement of the atlantoaxial joint & cervical spine by upper thoracic and low cervical fat pads; excessive tissue folds inthe mouth and pharynx;

• Short, thick neck• Suprasternal, presternal, and posterior cervical fat;• A very thick submental fat pad.

• OSA

• Excess pharyngeal tissue deposited in the lateral pharyngeal walls may not be noticed during routine airway examination

• Neck circumference has been identified as the single biggest predictor -5% with a 40-cm & 35% probability at 60-cm

INTRAOPERATIVE CONSIDERATIONS

• POSITIONING

– Specially designed tables or two regular operating tables

– operating tables capable of holding up to 455 kg, with a little extra width to accommodate the extra girth

– Strapping obese patients to the operating table in combination with a malleable bean bag helps keep them from falling off the operating table.

– protecting pressure areas - pressure sores, neural injuries, and rhabdomyolysis (carpal tunnel syndrome).

• SUPINE POSITIONING

– Ventilatory impairment

– Inferior vena cava and aortic compression

– FRC and oxygenation are decreased

– Head-down positioning further worsens FRC

– Significant increase in oxygen consumption and

cardiac output.

• Head-up position & Intraoperative PEEP can

– decrease alveolar-arterial oxygen tension difference

– increase total respiratory compliance

– Decreases peak and plateau airway pressures

• Lateral decubitus position allows for better diaphragmatic excursion and should be favoured over prone positioning

MONITORING

• Std monitoring

• Invasive arterial pressure monitoring may be indicated for the super morbidly obese.

• BIS and entropy monitoring to titrate depth of anaesthesia

• Monitoring of neuromuscular junction

• Central venous catheterization may also be required for intravenous access

INDUCTION, INTUBATION, AND MAINTENANCE

• Adequate preoxygenation is vital & performed with 10 L/min of oxygen to avoid rapid desaturation.

• Application of PPV during preoxygenation decreases atelectasis formation and improves oxygenation.

• 4 vital capacity breaths with 100% O2 within 30 seconds have been suggested as superior to the usually recommended 3 minutes of 100% preoxygenation in

obese patients.

• Larger doses of induction agents may be required

• Increased dose of Sch is necessary because of an increase in activity of pseudocholinesterase.

INTUBATION

• If a difficult intubation is anticipated, awake intubation is a prudent approach.

• Sedative-hypnotic in minimal doses.

• Sedation with Dexmedetomidine provides adequate anxiolysis and analgesia without respiratory depression.

• Hypoxia and aspiration of gastric contents should be prevented at all costs.

STACKING

• RAMPING ADVANTAGES:– Improves laryngoscopic view

– The gradient for passive regurgitation is reduced

– The safe apnea period is increased.

• 25-30 degrees reverse trendelenburg position with manual PEEP/NIPPV improves oxygenation

• For HELP placement, the preformed Troop Elevation Pillow may be used in place of folded towels or blankets .

MAINTAINENCE

• Continuous infusion of a short-acting intravenous agent, such as Propofol, or any of the inhalation agents, or a combination, may be used.

• Inhalatinal agents that are minimally metabolized are useful agents, with Desflurane possibly providing better hemodynamic stability and faster washout.

• Rapid elimination and analgesic properties make N2O an attractive choice, but high oxygen demand limits its use.

• Short-acting opioids, combined with a low-solubility inhalation agents, facilitate a more rapid emergence without increasing opioid-related side effects.

• Cis-atracurium possesses an organ-independent elimination profile and is a favorable NDMR for use during maintenance.

INTRAOPERATIVE OXYGENATION

• No effect on increasing TV (Pressure controlled ventilation with low tidal volumes 6-8ml/kg )

• VC and recruitment maneuvers – Increased oxygenation

– Decrease atelectasis

– Shortens PACU stay

– Less respiratory complications.

• The recruitment maneuver consists of providing escalating levels of PEEP in 5 cm increments upto a maximum airway pressure of 40-42cm H2O, continue for 10 breaths and reduce PEEP back to basal levels.

FLUID MANAGEMENT:

• Although the total circulating blood volume is increased, it is less than normal on a weight basis, since fat contains little water.

• Adequate preoperative hydration and higher intraoperative fluid administration (20-40 ml/kg) reduce postoperative complications

• Blood loss is usually greater.

• Excess adipose tissue may mask peripheral perfusion, making fluid balance difficult to assess.

• Early infusion of colloids and blood products may be necessary because they are less able to compensate for small volumes lost, – but rapid infusion of excessive amounts should be

avoided because pre-existing CCF is common

INTRAGASTRIC CALIBRATION TUBE

• Intragastric calibration tube is used instead of a Ryle’s tube.

• It is a bilumen tube with one port for suction and another port in which 15-20ml of saline is injected to inflate the intragastric balloon.

• This balloon enables the surgeon to place the gastric band just below the esophagogastricjunction which is then tightened and helps in deciding the size of the gastric pouch.

EMERGENCE

• Prompt extubation reduces the likelihood of ventilator-dependence.

• Patient should be fully awake, follow oral commands, have adequate muscle strength, Adequate tidal volume and brisk airway reflexes.

• Reverse residual neuromuscular blockade.

• Extubated in the same position as for intubation

• Supplemental oxygen should be administrated after extubation.

LIFTING AND TRANSFERING

• There is an increased incidence of atelectasis.

• Initiation of CPAP or BiPAP may improve oxygenation but does not facilitate CO2 elimination.

• Adequate analgesia, use of a properly fitted elastic binder for abdominal support, early ambulation, deep breathing exercises, and incentive spirometryare all useful adjuncts.

• Pulseoximetry and ABG should be monitored appropriately.

REGIONAL ANESTHESIA

• Help avoid potential intubation difficulties

• Difficult because of inability to identify usual bony landmarks

• Central neuraxial block is easier in the lumbar region because the midline in this area has a thinner layer of fat than other areas of the spinal column.

• Longer needles and the sitting position are other useful tools that facilitate central neuraxialanesthesia.

• Epidural vascular engorgement and fatty infiltration reduce the volume of the space, making dose requirements of L.A 20 to 25% less in obese patients

• The height of a SAB can be unpredictable because of considerable upward spread within a short time, causing cardiorespiratorycompromise.

• A continuous catheter SAB therefore seems an attractive choice that allows careful titration of the L.A to desired effect and level.

• Spirometric parameters such as PEFR and maximum mid expiratory flow are reduced in obese patients receiving subarachnoid block

• Combined epidural and general anesthesia

CONCLUSION

ComorbiditiesPositive pressure ventilationDrug dosingAirway & intubation problemsRapid desaturationPositioning Post operative hypoxiaTechnical difficulties in regional techniques.Higher level of blockade

REFERENCES

• Miller’s Anesthesia

• Barasch clinical anesthesia

• Stoeltings coexisting diseases

• Internet

Thank you