anaesthesia for morbidly obese patients and bariatric surgery
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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
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