Evaluation of Morbid Obese Patient

Preoperative Anesthetic Evaluation of Morbid Obese Patient

Goals:

1-Obtain data regarding the patient’s medical and surgical history.

2-Optimize current physiologic function.

3-Prepare an appropriate anesthetic plan.

1-Medications:

➧ The obese person must be assessed for the use of weight-reducing substances, herbal supplements, and anorexiant drugs.

➧ Chronic use of noradrenergic and serotonergic therapy can produce hypertension, tachycardia, anxiety, psychosis, and catecholamine depletion.

➧ Catecholamine depletion can lead to profound hypotension during induction and maintenance of anesthesia, which is refractory to indirect-acting vasopressors such as ephedrine.

➧ Phenylephrine hydrochloride (Neo-Synephrine) is usually effective in reversing low blood pressure.

➧ At least two weeks of abstinence from the drugs is recommended for adequate catecholamine levels to be recovered.

2-Laboratory Tests:

➧ Complete blood cell counts: may reveal Hct as high as 65%, which can result from contracted blood volume or polycythemia associated with cardiopulmonary disease.

- Leukocytosis (greater than 11,000) is a strong predictor of risk for acute myocardial infarction independent of tobacco smoking.

➧ Arterial blood gas analysis: that compares samples taken with the patient lying supine and sitting while breathing room provides baseline values and can distinguish simple obesity from Obesity Hypoventilation Syndrome.

➧ Renal function tests and Electrolytes: may reflect abnormal glucose and potassium levels, which are indicators of insulin resistance and potentiation of myocardial irritability.

- Diuretics and certain cardiac medications can worsen electrolyte disturbances.

- Blood urea nitrogen (BUN) and creatinine levels may be elevated in response to dehydration or renal dysfunction.

➧ Liver function tests: are typically elevated in obese patients, it is due to the infiltration of the hepatocytes with triglycerides (fatty liver, liver steatosis).

- The severity of fatty infiltration may alter the pharmacologic effects of many anesthetic drugs, thereby requiring dose reductions.

➧ Coagulation studies are necessary if regional anesthesia is planned or if coagulopathy exists.

- Patients taking anticoagulants for treatment of deep vein thrombosis or atrial fibrillation may exhibit elevated prothrombin and partial thromboplastin times.

- Nonsteroidal anti-inflammatory drugs may prolong bleeding times and affect surgical hemostasis.

➧ Pulmonary function tests: for obese patients undergoing abdominal or thoracic surgery to assist with the anesthetic planning.

➧ Chest radiography: is necessary to determine the presence of cardiomegaly, pulmonary infiltrates, and evidence of COPD.

3-Cardiac Assessment:

➧ History of prior MI, presence of HTN, angina, or PVD is crucial.

➧ Drug history gives clues about the patient's coexistent diseases.

➧ When possible cardiac medications should be continued up to the morning of surgery.

➧ Exercise tolerance: elicit valuable information about the myocardial function in morbidly obese patients.

- Limitations in exercise tolerance, history of orthopnea, and paroxysmal nocturnal dyspnea may indicate left ventricular dysfunction.

➧ ECG: is essential for the determination of resting rate, rhythm, and ventricular hypertrophy or strain. 

➧ Echocardiography: is useful for determining whether akinesis or wall motion abnormalities are present in the obese myocardium.

➧ Chest radiography: to identify pulmonary congestion, elevated diaphragm, and a tortuous aorta.

- The results of the radiographic study serve to guide preoperative pharmacologic and medical management (diuretics, beta-1 agonists, antibiotics).

4-Respiratory Evaluation:

➧ History of orthopnea, wheezing, sputum production, or smoking history.

➧ Recent upper respiratory infections, snoring, or sleep disturbances may indicate obstructive processes.

➧ Careful preoperative evaluation of the patient’s respiratory function identifies potential problems.

➧ A patient who becomes dyspneic and desaturates when recumbent experiences the same symptoms during induction of anesthesia in the supine position.

5-Airway Assessment:

➧ Most anesthetists use the evaluation of multiple patient physical characteristics to identify potential airway problems indicative of the unanticipated difficult airway.

➧ Patient physical characteristics that identify potential airway problems:

- Mallampati classification

- Interincisor distance

- Thyromental distance

- Head and neck extension

- Body weight and BMI

- History of difficult airway

- Length of upper incisors

- Visibility of the uvula

- Shape of the palate

- Compliance with the mandibular space and length

- Short, thick neck

- Pendulous breasts

- Hypertrophied tonsils and adenoids

- Beard

- Marginal room air pulse oximetry saturations

- Abnormal arterial blood gases

- Reduced tempormandibular and antlantooccipital joint movement

- Limited mouth opening, presence of neck or arm pain, or inability to place the head and neck into a sniffing position may indicate the need for awake fiberoptic intubation.

- Increasing neck circumference and Mallampati classification >3 have been identified as the two most important factors for morbidly obese patients.

6-Vascular Access:

➧ Venipuncture can be challenging in obese patients with excessive fat that obscures blood vessels from both visualization and palpation.

➧ Hemorrhage, hypothermia, and trauma also reduce the likelihood of accessing vessels.

➧ Ultrasound-guided central venous catheter placement may improve access and avoid iatrogenic pneumothorax.

7-Patient Education:

➧ Explanations of anticipated events during preoperative preparation: multiple venipunctures, central and arterial line insertions, awake intubation, postoperative ventilation, if needed, pain management, and protection of the patient’s privacy will relieve anxiety.

Read more ☛ Anesthetic Management of Morbid Obese Patient

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Anesthetic Management of Morbid Obese Patient

Anesthetic Management of Morbid Obese Patient

Preoperative:

A) Evaluation:

Read more ☛ Preoperative Anesthetic Evaluation

B) Preparation:

1-Equipments:

➧ New model operating room tables can accommodate up to 270 kg (600 pounds) of weight.

➧ Older model operating room tables could accommodate up to 135-160 kg (300 - 350 pounds) of weight.

➧ In cases of extreme morbid obesity, big-boy hydraulic beds are obtained and used in the operating room.

➧ Extra-large cuffs can be used on the upper/lower extremity. 

➧ Bed warming devices, fluid warmers, and warm airflow blankets should be employed to prevent hypothermia, which can occur rapidly when large areas of the body surface are exposed.

2-Monitoring:

➧ Selection of ECG leads when possible for detection of myocardial ischemia and pathology (leads II and V5).

➧ Placement of an arterial line for the monitoring hemodynamic status is advocated for all but minor procedures.

➧ Central venous and pulmonary artery catheters should be considered in patients undergoing lengthy operations or those with the serious cardio-pulmonary disease.

3-Aspiration prophylaxis:

➧ Obese patients have great volumes and more gastric fluid than people of normal weight.

➧ Gastro-esophageal reflux and hiatus hernia are more prevalent in the obese, predisposing them to esophagitis and pulmonary aspiration.

➧ Conditions that cause delayed gastric emptying, such as DM and traumatic injury, further increase the risk of aspiration.

➧ An obese patient is considered to have a “full stomach,” even if the fasting period is followed.

➧ Pre-induction administration of histamine-2 and dopamine receptor antagonist coupled with oral administration of non-particulate antacids decreases morbidity resulting from pulmonary aspiration and Mendelson’s syndrome.

➧ Head up the position of the patient, with the application of the Sellick's maneuver during rapid-sequence induction, limits the volume of vomitus that enters the trachea if regurgitation occurs.

➧ Nasogastric/Orogastric suctioning before emergence further reduces the amount of fluid available for aspiration.

4-Airway equipment:

➧ Appropriate laryngoscopy blades, handles, endotracheal tubes, masks, oral and nasopharyngeal airways, and stylets should be ready.

➧ Laryngeal mask airways (LMAs), fiberoptic and bronchoscopic devices, Eschman introducers, a jet ventilator (or Venturi apparatus), an emergency tracheotomy, and cricothyrotomy kits must be available if ventilation by mask or endotracheal tube is unsuccessful.

➧ A difficult airway cart with all available equipment should be placed in the operating room.

Intraoperative:

1-Effects of General Anesthesia on Respiration:

➧ General anesthesia depresses respiration in normal subjects so any preexisting pulmonary dysfunction is exaggerated by anesthesia.

➧ General anesthesia reduces FRC by 50% in obese patients, as compared with a 20% reduction in non-obese patients.

➧ FRC can be increased by ventilating with large tidal volumes (15-20 ml/kg), although this has been shown to improve arterial oxygen tension only minimally. Current ventilation recommendations include using tidal volumes of 10-12 ml/kg to avoid barotrauma.

➧ Positive end-expiratory pressure (PEEP) achieves an improvement in both FRC and arterial oxygen tension but at the expense of cardiac output and oxygen delivery.

➧ During laparoscopic surgeries, the respiratory rate should be 12-14 breaths/min.

➧ Prolonged (longer than 2-3 hours) and extensive procedures (involving the abdomen, thorax, and spine) negatively influence respiratory function.

➧ Sub-diaphragmatic packing, cephalad displacement of organs, and surgical retraction cause decreased alveolar ventilation, atelectasis, and pulmonary congestion.

➧ Recumbent/Trendelenburg positioning further reduces diaphragmatic excursion, which is already impaired by the weight of the panniculus, it also causes elevated filling pressures which then increase right ventricular preload.

➧ Myocardial oxygen consumption, cardiac output, pulmonary artery occluding pressures, peak inspiratory pressures, and venous admixtures are increased above upright-sitting values.

➧ In non-obese patients, cardiac output increases in response to supine posturing to maintain hemodynamic stability. By increasing left ventricular output the centrally located circulating volume is propelled forward, thereby minimizing pulmonary congestion and hypoxia.

➧ In morbidly obese patients, positive pressure, ventilation (which impedes venous return), and an inability to increase cardiac output may result in cardiopulmonary decompensation. This is exhibited intraoperatively by hypoxia, rales, ventricular ectopy, congestive heart failure, and hypotension. Bag ventilation by hand may be useful in reducing hypotension resulting from positive pressure.

➧ Adequate ventilator settings inflate the morbidly obese thorax to minimize hypoxia. Pressure or volume-controlled ventilators can be used to maintain adequate oxygenation and normocapnia.

➧ Avoidance of prolonged prone, Trendelenburg or supine positioning also decreases ventilation-perfusion mismatch.

➧ Optimization of oxygenation by using no less than 50% inspired oxygen is recommended.

➧ PEEP can reduce venous admixture and support adequate arterial oxygenation, but PEEP can impair arterial oxygenation in some patients when it is superimposed on large tidal volumes. Recommended PEEP should not exceed 15 cmH₂O.

➧ Intraoperative events, such as hemorrhage or hypotension, further impair ventilatory homeostasis and result in hypoxemia that extends into the postoperative period.

➧ A vertical abdominal incision, compared with a horizontal (transverse incision also prolongs postoperative hypoxia).

➧ Pain causes further reductions in diaphragmatic excursion and vital capacity, leading to atelectasis and ventilation-perfusion mismatch.

➧ 24 h. postoperative admission to a monitored bed is prudent for morbidly obese patients who exhibit higher morbidity and mortality apart from anesthesia and surgery.

2-Choice of Anesthetic Technique:

➧ The selection of the anesthetic technique is dependent on the patient, coexisting history, planned surgical procedure, anesthetist skills and preference, and patient preference.

➧ Anesthetic management of obese patients can include local or monitored anesthesia; general (narcotic, inhalation) anesthesia; regional blocks; or a combination of techniques.

➧ The use of a short-acting water-soluble anesthetic facilitates a smooth anesthetic induction, maintenance, and emergence.

➧ The objective for maintenance of anesthesia in the obese include:

-Strict maintenance of airway

-Optimum oxygenation

-Adequate skeletal muscle relaxation

-Avoidance of the residual effects of muscle relaxants

-Provision of appropriate intraoperative and postoperative tidal volume

-Effective postoperative analgesia

3-Airway Management:

➧ To facilitate airway management, an obese patient should be positioned with the head elevated (reverse Trendelenburg position) on the operating room table.

➧ This position promotes patient comfort, reduces gastric reflux, provides easier mask ventilation, improves respiratory mechanics, and helps maintain functional residual capacity (FRC).

➧ Reduced FRC in obese patients contributes to the rapid desaturation that occurs with induction of general anesthesia, to attenuate the desaturation and maximize oxygen content in the lungs, patients are pre-oxygenated with 100% oxygen for at least 3-5 min.

➧ The patient's head and neck should be carefully moved into the “sniffing position” by using pillows, doughnuts, or foam head supports.

➧ Without proper support and alignment of the oropharynx and trachea, ventilation may be obstructed and visualization of the laryngeal structures may be obscured.

➧ Some anesthetists make an “Awake Look” to visualize the difficulty of the airway. Careful administration of sedative drugs and application of topical anesthesia to the oropharyngeal structures, possibly including transtracheal and superior laryngeal nerve blocks. Nasal oxygen is used as a supplement during awake laryngoscopy.

➧ If the epiglottic and laryngeal anatomy is easily visible, successful asleep intubation can be done, if not, an intubating LMA or awake fiberoptic intubation should be used.

➧ The endotracheal tube must be safely secured to prevent movement during positioning and surgery.

➧ The anesthetist and another skilled anesthesia provider must also be in attendance during induction of anesthesia because muscle hypotonia in the floor of the mouth, followed by the rapid occurrence of soft tissue obstruction and hypoxia, requires one person to support the mask and airway while another person bag ventilates the patient.

➧ In the case of inability to Intubate/ventilate (CICV), the American Society of Anesthesiologists (ASA) difficult airway algorithm should be followed.

4-Volume Replacement:

➧ In obese patients, the estimated blood volume is actually diminished.

➧ Fat, which contains only 8-10% water, contributes less fluid to total body water than equivalent amounts of muscle.

➧ The percentage of total body water is 60-65% in non-obese adults while in morbid obese it is reduced to 40%; therefore calculation of estimated blood volume should be 45-55 ml/kg of actual body weight rather than 70 ml/kg in non-obese adults.

➧ Accurate volume replacement and avoidance of rapid rehydration lessen cardiopulmonary compromise.

➧ Fluid management is guided by blood pressure, heart rate, and urine output measurements. Dilutional coagulopathy, factor VIII inhibition, and decreased platelet aggregation can result from excessive administration.

➧ Volume expanders should not be administered at greater than 20ml/kg of Ideal Body Weight (IBW).

➧ Blood loss replacement of a 3:1 ratio (3 ml of crystalloid to 1 ml of blood loss) is applicable in morbidly obese patients.

➧ Blood products after careful identification should be replaced according to the patient’s laboratory values and hemodynamic or surgical needs.

5-Intraoperative Positioning:

➧ Surgical positioning of morbidly obese patients necessitates extra precautions for the prevention of nerve, integumentary, and cardiorespiratory compromise.

➧ Many peripheral nerves are subjected to possible ischemia or necrosis, the lunar, brachial plexus, radial, personal, and sphenoid nerves are the most vulnerable to injury in an anesthetized patient. In morbidly obese patients the incidence may be increased because of excessive weight on the anatomic structures.

➧ Care is necessary when one is positioning obese extremities in slings, draping them on Mayo stands, or securing them in lithotomy stirrups.

➧ Prolonged hyperextension, external rotation, or abduction can cause postoperative muscle pain, nerve palsies, or paralysis; therefore less flexion or abduction, and rotation of hips, legs, and arms may be necessary.

➧ Frequently repeated inspections of extremities for color and temperature can help diminish the incidence of positioning-related injuries.

➧ Lower back pain can be aggravated by both spinal and general anesthesia because of ligamentous relaxation that results in loss of lumbar curvature. Surgical towels placed under the lumbar spine before induction will enhance lordosis and reduce postoperative discomfort.

6-Integumentary Concerns:

➧ Decubitus, skin infection and wound dehiscence are exceedingly common in morbidly obese patients, therefore ensure all pressure points are padded and in a proper position.

7-Extubation:

➧ The risk of airway obstruction after extubation is increased in obese patients.

➧ A decision to extubate depends on the evaluation of the ease of mask ventilation and tracheal intubation, the length, and type of surgery, and the presence of preexisting medical conditions, including OSA.

➧ Criteria for extubation consist of:

-Awake state, tidal volume, and respiratory rate at preoperative levels

-Ability to sustain head lift or leg lift for at least 5 seconds

-Constant hand grip

-Effective cough

-Adequate vital capacity of at least 15 ml/kg and inspiratory force of at least -25 to -30 cm H₂0.

➧ Patients must be placed with their heads up or in a sitting position.

➧ If doubt exists regarding the ability of the patient to breathe adequately, the endotracheal tube is left in place.

➧ Extubation over an airway exchange catheter or a fiberoptic bronchoscope may be performed.

8-Regional Anesthesia:

➧ Regional anesthesia can be used as the primary anesthetic in selected cases or as an accompaniment to postoperative pain and mobility management.

➧ Difficulties are frequently encountered with morbidly obese patients as anatomical landmarks are not easily visualized or palpable.

➧ Brachial plexus anesthesia can be hampered by adipose tissue in the axillary region due to an inability to position the arm or undetectable pulses.

➧ Redundant roles of adipose tissue, unsatisfactory ventilation, and the inability of the patient to sustain optimal positioning make neuraxial anesthesia more challenging.

➧ For subarachnoid or epidural anesthesia it is recommended that the patient is sitting upright so that landmarks such as C7 or L3-L4 can be more easily identified and longer needles should be used.

➧ Generous infiltration with local anesthetic will provide greater patient comfort during needle insertion due to the repeated insertions and repositioning.

➧ Another consideration regarding subarachnoid or epidural anesthesia in morbid obese pregnant or surgical patients is the lack of predictability of the spread of local anesthetic. Undesirable cephalad spread of local anesthetic can be obviated by reducing the volume and increasing the patient’s upright sitting time.

Postoperative:

1-Pain Management:

➧ Postoperative pain management is facilitated by the use of oral analgesics, non-steroidal anti-inflammatory drugs, narcotics, patient-controlled analgesia, local infiltration of the surgical site, and epidural anesthesia

➧ Obese patients are more sensitive to the respiratory depressant effects of opioid analgesics; therefore caution and close monitoring are warranted. Supplemental oxygen and pulse oximetry monitoring are mandated.

2-Postoperative Complications:

➧ Morbidity and mortality rates are higher in obese patients than in non-obese patients.

➧ Ventilation abnormalities are exacerbated in obese patients with OSA and OHS and may last for several days.

➧ The maximum decrease in partial pressure of arterial oxygen occurs 2-3 days postoperatively.

➧ The risk of thromboembolism wound infections and atelectasis is amplified in patients with increased BMI.

➧ Thromboembolism is facilitated by immobility (Venous stasis, increased blood viscosity (polycythemia, hypovolemia) increased abdominal pressure, abnormalities in serum procoagulants, and anticoagulants.

➧ Antiembolic stockings and correctly fitting pneumatic compression boots can lessen the occurrence of deep vein thrombosis in the early postoperative period.

➧ Early ambulation and maintenance of vascular volume further reduce the likelihood of clots formation.

➧ Wound infections and pulmonary embolism are 50% higher in obese patients than in non-obese patients.

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