Anesthesia and Anesthesia and ObesityObesity

Lauren Hojdila, MSA, AA-CLauren Hojdila, MSA, AA-C

ObesityObesity

A condition of excessive body fatA condition of excessive body fat Associated health conditions Associated health conditions

include:include: HypertensionHypertension Coronary artery diseaseCoronary artery disease Diabetes mellitusDiabetes mellitus Obstructive sleep apneaObstructive sleep apnea HyperlipidemiaHyperlipidemia Gallbladder diseaseGallbladder disease

Obesity vs. OverweightObesity vs. Overweight

ObesityObesity

– An abnormally An abnormally high percentage high percentage of body weight as of body weight as fatfat

OverweightOverweight

– An increased An increased body weight body weight above a standard above a standard related to heightrelated to height

ObesityObesity

Android obesityAndroid obesity– Truncal distribution of adipose tissueTruncal distribution of adipose tissue– Associated with an increase in oxygen Associated with an increase in oxygen

consumption and an increased consumption and an increased incidence of cardiovascular diseaseincidence of cardiovascular disease

Gynecoid obesityGynecoid obesity– Adipose distribution in the hips, Adipose distribution in the hips,

buttocks, and thighsbuttocks, and thighs

*Intra-Abdominal fat is particularly associated with cardiovascular risk and left ventricular dysfunction*

BMI Classification

< 18.5 underweight

18.5–24.9 normal weight

25.0–29.9 overweight

30.0–34.9 class I obesity

35.0–39.9 class II obesity

≥ 40.0 class III obesity  

Obesity ClassificationsObesity Classifications

ObesityObesityEffects on Respiratory System Effects on Respiratory System

Decreased chest wall complianceDecreased chest wall compliance Decreased lung complianceDecreased lung compliance Decreased FRCDecreased FRC

Primarily a result of reduced expiratory Primarily a result of reduced expiratory reserve volumereserve volume

Reduced FRC can result in lung volumes Reduced FRC can result in lung volumes below closing capacity in the course of below closing capacity in the course of normal ventilationnormal ventilation

Obstructive Sleep Obstructive Sleep ApneaApnea Up to 5% of obese Up to 5% of obese

patients have patients have clinically significant clinically significant obstructive sleep obstructive sleep apneaapnea

Apnea is defined as 10 Apnea is defined as 10 seconds or more of seconds or more of total cessation of total cessation of airflow despite airflow despite continuous respiratory continuous respiratory effort against a closed effort against a closed glottisglottis

ObesityObesityEffects on Blood VolumeEffects on Blood Volume

Total blood volume is increased in Total blood volume is increased in the obese, but on a volume-to-the obese, but on a volume-to-weight basis, it is less than in weight basis, it is less than in nonobese individuals(50ml/kg nonobese individuals(50ml/kg compared to 70ml/kg)compared to 70ml/kg)

Most of this extra blood volume is Most of this extra blood volume is distributed to the fat organdistributed to the fat organ

ObesityObesityCardiovascular EffectsCardiovascular Effects

Cardiac output increases as much as Cardiac output increases as much as 20 – 30 ml/kg of excess body fat 20 – 30 ml/kg of excess body fat secondary to ventricular dilatation and secondary to ventricular dilatation and increasing stroke volumeincreasing stroke volume

The increased left ventricular wall The increased left ventricular wall stress leads to:stress leads to:

HypertrophyHypertrophy Reduced complianceReduced compliance Impaired left ventricular filling Impaired left ventricular filling Obesity cardiomyopathyObesity cardiomyopathy

ObesityObesityEffects on Gastrointestinal SystemEffects on Gastrointestinal System

Gastric volume and acidity are Gastric volume and acidity are increasedincreased

Most fasted morbidly obese patients presenting Most fasted morbidly obese patients presenting for elective surgery have gastric volumes in for elective surgery have gastric volumes in excess of 25 ml and gastric fluid pH less than excess of 25 ml and gastric fluid pH less than 2.5 ( the generally accepted volume and Ph 2.5 ( the generally accepted volume and Ph indicative of high risk for pneumonitis should indicative of high risk for pneumonitis should regurgitation and aspiration occur).regurgitation and aspiration occur).

Gastric emptying may actually be Gastric emptying may actually be faster in the obese, but because of faster in the obese, but because of their larger gastric volume (up to 75% their larger gastric volume (up to 75% larger), the residual volume is larger.larger), the residual volume is larger.

ObesityObesityObesity and DiabetesObesity and Diabetes

Impaired glucose tolerance in the Impaired glucose tolerance in the morbidly obese is reflected by a high morbidly obese is reflected by a high prevalence of type II diabetes mellitus prevalence of type II diabetes mellitus as a result of resistance of peripheral as a result of resistance of peripheral fatty tissues to insulinfatty tissues to insulin

Greater than 10% of obese patients Greater than 10% of obese patients have an abnormal glucose tolerance have an abnormal glucose tolerance test, which predisposes them to wound test, which predisposes them to wound infection and an increased risk of infection and an increased risk of myocardial infarction during periods of myocardial infarction during periods of myocardial ischemiamyocardial ischemia

ObesityObesityEffects on the AirwayEffects on the Airway

Anatomic changes that contribute to Anatomic changes that contribute to potential for difficult airway managementpotential for difficult airway management

Limitation of movement of the atlantoaxial joint and Limitation of movement of the atlantoaxial joint and cervical spine by upper thoracic and low cervical fat cervical spine by upper thoracic and low cervical fat padspads

Excessive tissue folds in the mouth and pharynxExcessive tissue folds in the mouth and pharynx Short thick neckShort thick neck Suprasternal, presternal and posterior cervical fatSuprasternal, presternal and posterior cervical fat Very thick submental fat padVery thick submental fat pad

Obstructive sleep apneaObstructive sleep apnea Predisposes to airway difficulties during anesthesiaPredisposes to airway difficulties during anesthesia OSA patients have excess tissue deposited in their OSA patients have excess tissue deposited in their

lateral pharyngeal walls which may not be recognized lateral pharyngeal walls which may not be recognized during routine airway examinationduring routine airway examination

ObesityObesityEffects on Drug Distribution Effects on Drug Distribution

Volume of Distribution in Obese Volume of Distribution in Obese patients is affected by:patients is affected by:

Reduced total body waterReduced total body water Increased total body fatIncreased total body fat Increased lean body massIncreased lean body mass Altered protein bindingAltered protein binding Increased blood volumeIncreased blood volume Increased cardiac outputIncreased cardiac output

ObesityObesityEffects on Drug EliminationEffects on Drug Elimination

Hepatic clearance is not usually Hepatic clearance is not usually effectedeffected

Renal clearance of drugs is Renal clearance of drugs is increased in obesity because of increased in obesity because of increased renal blood flow and increased renal blood flow and glomerular filtration rateglomerular filtration rate

ObesityObesityHow does it effect drug dosing?How does it effect drug dosing?

Highly LipophilicHighly Lipophilic Barbiturates and benzodiazepines have an increased Barbiturates and benzodiazepines have an increased

volume of distributionvolume of distribution Less LipophilicLess Lipophilic

Little or no change in volume of distribution with Little or no change in volume of distribution with obesityobesity

Increased blood volume in the obese patient Increased blood volume in the obese patient decreases the plasma concentrations of decreases the plasma concentrations of rapidly injected intravenous drugs.rapidly injected intravenous drugs.

Fat has poor blood flow and doses calculated Fat has poor blood flow and doses calculated on actual body weight could lead to on actual body weight could lead to excessive plasma concentrations.excessive plasma concentrations.

* Review Barash et al table 47-5*

ObesityObesityPreoperative EvaluationPreoperative Evaluation

Previous anesthetic experiencesPrevious anesthetic experiences Attention should focus on the Attention should focus on the

cardiorespiratory system and airwaycardiorespiratory system and airway Signs of cardiac failureSigns of cardiac failure

Elevated jugular venous pressureElevated jugular venous pressure Pulmonary cracklesPulmonary crackles Peripheral edemaPeripheral edema

Signs of pulmonary hypertensionSigns of pulmonary hypertension Exertional dyspneaExertional dyspnea FatigueFatigue Syncope Syncope

ObesityObesityAirway EvaluationAirway Evaluation

Neck circumferenceNeck circumference The single biggest predictor of problematic The single biggest predictor of problematic

intubation in morbidly obese patientsintubation in morbidly obese patients 40 cm neck circumference = 5% probability of a 40 cm neck circumference = 5% probability of a

problematic intubationproblematic intubation 60 cm neck circumference = 35% probability of a 60 cm neck circumference = 35% probability of a

problematic intubationproblematic intubation

A larger neck circumference is A larger neck circumference is associated with the male sex, a higher associated with the male sex, a higher Mallampati score, grade 3 views at Mallampati score, grade 3 views at laryngoscopy, and obstructive sleep laryngoscopy, and obstructive sleep apneaapnea

ObesityObesityInduction of General AnesthesiaInduction of General Anesthesia

Adequate preoxygenation Adequate preoxygenation Rapid desaturation because of Rapid desaturation because of

increased oxygen consumption and increased oxygen consumption and decreased FRCdecreased FRC

Positive pressure ventilation during Positive pressure ventilation during preoxygenation decreases atelectasis preoxygenation decreases atelectasis formation and improves oxygenationformation and improves oxygenation

Patient positionPatient position The head-up (reverse tredelenburg) The head-up (reverse tredelenburg)

position provides the longest safe apnea position provides the longest safe apnea period during induction of anesthesiaperiod during induction of anesthesia

ObesityObesityPatient positioningPatient positioning

SupineSupine Causes ventilatory impairment and inferior vena Causes ventilatory impairment and inferior vena

cava and aortic compressioncava and aortic compression TrendelenburgTrendelenburg

Further worsens FRC and should be avoidedFurther worsens FRC and should be avoided Reverse tredelenburgReverse tredelenburg

Increased compliance results in lower airway Increased compliance results in lower airway pressurespressures

Prone Prone Detrimental effects on lung compliance, Detrimental effects on lung compliance,

ventilation and arterial oxygenationventilation and arterial oxygenation Increased intra-abdominal pressure worsens IVC Increased intra-abdominal pressure worsens IVC

and aortic compression and further decreases FRCand aortic compression and further decreases FRC

ObesityObesity Ventilating the obese patient Ventilating the obese patient

Tidal volumes greater than 13 ml/kg offer Tidal volumes greater than 13 ml/kg offer no added advantageno added advantage

Increasing tidal volume beyond 13 ml/kg increases Increasing tidal volume beyond 13 ml/kg increases PIP without improving arterial oxygen tensionPIP without improving arterial oxygen tension

Positive end-expiratory pressure (PEEP) is Positive end-expiratory pressure (PEEP) is the only ventilatory parameter that has the only ventilatory parameter that has consistently been shown to improve consistently been shown to improve respiratory function in obese patientsrespiratory function in obese patients

PEEP may reduce venous return and cardiac outputPEEP may reduce venous return and cardiac output

Dietary Consumption Dietary Consumption Available to PopulationAvailable to Population

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