Table of Contents  

Prabaharan, Varma, and Al Taie: Anaesthetic challenges in a super-morbidly obese patient undergoing laparoscopic sleeve gastrectomy

Introduction

Obesity is a major health problem with mild to severe health implications, including an increased risk of coronary artery disease, hypertension, dyslipidaemia, diabetes mellitus, gall bladder disease, degenerative joint disease and sleep disorders. These health implications are often accompanied by socioeconomic and psychosocial impairment of the patient and such disorders threaten the health of people all over the world.1 The United Arab Emirates (UAE) ranks as the fifth fattest nation in the world, after the USA, Kuwait, Qatar and Bahrain, according to a recent study published by a BioMed Central Public Health journal.2

Decreased physical activity and excess consumption of foods with a high fat content are the main factors contributing to the obesity epidemic. Conservative interventions for the treatment of obesity include early education, a low-calorie diet, increased physical activity and, occasionally, medications. However, these treatments are not always effective and many obese people undergo bariatric surgical procedures.

Although there is no gold standard surgical procedure for the treatment of obesity, laparoscopic sleeve gastrectomy (LSG) is often the first choice, being more effective than a gastric band in the long term.3,4 LSG involves the surgical removal of the left side of the stomach, resulting in an organ which is approximately the size and shape of a banana and does not require rerouting of the intestine or implantation of an artificial device in the abdomen. Weight loss is achieved by the reduction in the stomach size and, therefore, capacity for food.4,5

Because of the simplicity of the procedure, reduced operative time and low complication rate, LSG is elected not only by patients with morbid obesity, but also in super-morbidly obese patients with a body mass index (BMI) > 50 kg/m2.

Case report

A 45-year-old man of height 181 cm, weight 252 kg and BMI 77 kg/m2 was scheduled for LSG. The ideal body weight (IBW) of this patient was 81 kg, calculated by his height (cm) minus 100. He suffered from hypertension, but this was well controlled with oral medications. This case investigates possibly the most overweight patient to undergo general anaesthesia in the UAE.

Preoperative investigations included haemography, a blood sugar test, serum electrolytes test, thyroid function test, liver function test, renal function test, urine examination, viral markers test, a lipid profile, coagulation profile, pulmonary function test, chest radiography, electrocardiography (ECG), echocardiography and obstructive sleep apnoea (OSA) screening (using the STOP-BANG questionnaire). Ultrasonography did not reveal any venous thrombus in the lower extremities. Informed consent was obtained from the patient before surgery by the surgical and anaesthetic teams.

A detailed airway examination was carried out and the Mallampati score was class 3, the neck circumference was 42 cm and the level of cervical extension was noted in order to predict the level intubation difficulty. The patient was premedicated with 10 mg metoclopramide and 150 mg ranitidine during the morning of the procedure. Enoxaparine, 0.5 mg/kg lean body weight (LBW), was given and elastic stockings provided for deep-vein thrombosis (DVT) prophylaxis. Preoperative antimicrobial prophylaxis was carried out in accordance with the hospital's protocol, with 2 g meropenam being given by injection 30 minutes before the intervention.

The patient was wheeled into the operating theatre on a specially designed trolley. Intravenous (i.v.) access was obtained with a 20 G i.v. cannula. During the operation, pulse oximetry, non-invasive blood pressure, ECG, end-tidal carbon dioxide concentration in the expired air (EtCO2), peripheral neuromuscular monitor and temperature were constantly monitored. In addition, a sequential pneumatic compressions device was applied to the patient's calves.

In addition to the conventional Macintosh laryngoscope, McCoy's blades, a bougie, laryngeal mask, video laryngoscope (GlideScope™) and an emergency tracheostomy kit were prepared. Oxygen (O2) saturation was recorded as 93% in the operating theatre.

Preoxygenation with 100% O2 was carried out with the patient in a ramped position by placing multiple folded blankets under the upper body, head and neck until the external auditory meatus and the sternal notch were horizontally aligned. An O2 mask was placed over the patients face to provide inhalation of 6 l/min of O2 with 10 cmH2O continuous positive airway pressure (CPAP), midazolam 0.05 mg/kg and fentanyl 1 μg/kg LBW. The anaesthetic induction was carried out with propofol 1.5 mg/kg LBW and succinylcholine 1 mg/kg total body weight (TBW).

The trachea was intubated with an endotracheal tube of 8.0 mm internal diameter. GlideScope™ was successfully used for intubation, and after intubation the orogastric tube was inserted to decompress the stomach and to further inject methylene blue. The neuromuscular agent atracurium, 0.5 mg/kg IBW, was administered and adjusted in order to obtain a unique response to the train-of-four (TOF) stimulus during the surgery. Fentanyl was readministered at 30-minute intervals in dosages of 1 μg/kg LBW.

Anaesthesia was maintained with O2, air, sevoflurane and intermittent positive-pressure ventilation. Pressure-controlled ventilation with tidal volumes of 8 ml/kg IBW and positive end-expiratory pressure (PEEP) of 10 cmH2O was instituted to maintain EtCO2 between 35 and 40 mmHg and oxygen saturation between 94 and 100%. The operation was executed in reverse Trendelenburg position, with the lower limbs abducted. Pneumoperitoneum was initiated to 15 mmHg intra-abdominal pressure. Blood gas analysis before the start of surgery showed pH 7.4, partial pressure of oxygen of 144 mmHg and partial pressure of CO2 of 51.2 mmHg. The corresponding values at the end of surgery were pH 7.34, 226 mmHg and 56.8 mmHg.

A total of 4000 ml i.v. crystalloids (10 ml/IBW/h) was infused during surgery. The patient's blood glucose level was in the range 90–150 mg/dl, blood loss was 100 ml, urine volume was 400 ml and the surgery lasted 100 minutes, with the anaesthesia lasting 155 minutes.

By the end of the procedure, the neuromuscular block had been reversed using neostigmine 0.04 mg/kg and atropine 0.01 mg/kg at 50% responsiveness to the TOF stimulus. The trachea was extubated in the same ramped position; however, the patient was awake and the TOF response was at 90% of control; therefore, CPAP was initiated.

Postoperative pain relief was provided with local anaesthetic wound infiltration of the port sites with 0.125% bupivacaine, i.v. paracetamol (2 g four times a day) and i.v. diclofenac (75 mg twice a day).

The patient started to walk 4 hours after surgery and was discharged from the surgical intensive care unit to the general ward the day after surgery. He was discharged from the hospital 5 days later without any complications.

Discussion

Management of anaesthesia in bariatric surgery is a challenge for an anaesthesiologist. There are certain elements that have to be taken into consideration during the perioperative period.

Concerns in the morbidly obese

Obesity is generally defined as a BMI > 30 kg/m2, morbid obesity as a BMI > 35 kg/m2 and super-morbid obesity as a BMI > 50 kg/m2. Morbidly obese patients often suffer from numerous chronic medical conditions (Table 1). The comorbidities associated with obesity and OSA should be optimized preoperatively.6

TABLE 1

The comorbidities associated with obesity

Region Comorbidities
Cardiac Systemic hypertension, coronary artery disease, dysrhythmias, cardiomyopathy, congestive heart failure
Respiratory Restrictive pulmonary disease, OSA, asthma, pulmonary hypertension
Neurological Stroke
Renal Renal dysfunction
Metabolic Metabolic syndrome, type 2 diabetes mellitus, hypothyroidism
Abdominal Hiatal hernia, gastro-oesophageal reflux, fatty liver infiltration
Others Airway abnormalities, DVT, primary open-angle glaucoma

Preoperative considerations

Preoperative assessment of the obese may be focused mainly on the cardiovascular, respiratory and endocrine systems as well as the airways. In addition to assessment of functional status, a history should be taken from the patient to determine if there are any symptoms of angina, paroxysmal nocturnal dyspnoea, orthopnoea or arrhythmias. Preoperative suspicion of OSA should lead to increased efforts to modify the anaesthetic techniques and improved monitoring in the postoperative period. A recent systematic review and meta-analysis of clinical screening tests for OSA reported that the STOP-BANG screening tool was user friendly and a good predictor of severe OSA (Table 2).7,8 A high risk of OSA is indicated by positive responses to three or more questions in Table 2. A low risk of OSA is indicated by fewer than three positive responses.

TABLE 2

The STOP-BANG scoring system

Areas that indicate OSA Question
S = snoring Do you snore loudly (louder than talking or loud enough to be heard through closed doors)?
T = tiredness Do you often feel tired, fatigued or sleepy during daytime?
O = observed Has anyone observed you stop breathing during your sleep?
P = pressure Do you have, or are you being treated for, high blood pressure?
B = BMI Do you have a BMI of > 35 kg/m2?
A = age Are you > 50 years old?
N = neck circumference Is the circumference of your neck > 40 cm?
G = gender Are you male?

Preoperative testing

Commonly performed preanaesthesia tests include complete blood count, glucose, electrolytes and renal and hepatic function tests. However, preanaesthesia tests should be based on clinical indications and the invasiveness of the surgical procedure. Although obesity can influence pulmonary function [e.g. reduced expiratory reserve volume, forced expiratory volume and functional residual capacity (FRC)], pulmonary function tests (e.g. spirometry, chest radiographs and room air arterial blood gas analysis) are of no added benefit unless chronic obstructive pulmonary disease is suspected.9

The severity of OSA may be determined from a sleep study using the apnoea–hypopnoea index (AHI), which measures the frequency of apnoea (cessation of breathing for ≥ 10 seconds despite continuing ventilatory efforts) and hypopnoea (more than 50% diminished airflow for ≥ 10 seconds) events per hour. An AHI of 6–20 indicates mild OSA, an AHI 21–40 indicates moderate OSA and an AHI ≥ 40 indicates severe OSA.

Preoperative medications

Preoperative prophylaxis to prevent acid aspiration (e.g. H2-receptor antagonists and proton pump inhibitors) is commonly used. However, the value of their routine use is questionable as they may increase the risk of postoperative infections. Furthermore, risk of regurgitation of gastric contents for the morbidly obese and the non-obese appears to be similar.10 Administration of 1–2 mg i.v. midazolam has been used to provide anxiolysis and reduce the incidence of intraoperative awareness; however, it is prudent to avoid midazolam, if possible.

Femoral venous blood flow can be reduced by both pneumoperitoneum and Trendelenburg positioning, with an increased risk of lower extremity thrombosis. Low-molecular-weight heparin, sequential compression devices or placements of an inferior vena cava filter prior to surgery are considered to reduce the risk of DVT.6

Intraoperative considerations

Positioning

The operating table should sustain about 375 kg of weight and should be able to accommodate electrically controlled parallel extensions to facilitate adequate patient positioning during the operation. Special attention should be paid to the manoeuvres for protection of the compression zones (e.g. brachial plexus, ulnar and sciatic nerves) in order to avoid injury.6

Monitoring

A standardized anaesthesia monitoring protocol is required [ECG, non-invasive arterial blood pressure, pulse oximetry, anaesthetic gas, CO2 analyser and peripheral neuromuscular monitoring (TOF guard)]. Comparable and accurate blood pressure readings can be obtained from the wrist or ankle in situations if upper arm non-invasive blood pressure measurements are difficult. Arterial invasive monitoring has been carried out for those with associated cardiopulmonary disease and those with inadequate sphygmomanometer cuff readings only. Central venous catheterization can be implemented in patients with poor peripheral venous access.6

General anaesthesia

The optimal general anaesthetic technique would allow rapid and clear-headed recovery including early return of the patient's protective airway reflexes, which would allow maintenance of their airway. In addition, early recovery should reduce postoperative cardiac complications as a result of residual anaesthetic effects.

Preinduction considerations

Alterations in pulmonary function (e.g. reduced FRC and O2 reserves) in obese people may result in severe hypoxaemia, even after short periods of apnoea. Positioning of the patient in the head-elevated laryngoscopy position, which can be achieved by ‘stacking’ with blankets or a specially designed foam pillow, structurally improves maintenance of the passive pharyngeal airway and may be beneficial for mask ventilation as well as to improve the success of tracheal intubation. Other techniques used to avoid post-induction hypoxaemia include preoxygenation with 100% O2 until the end-tidal O2 is at least 90% and use of 10 cmH2O CPAP with the patient in a 25° head-up position.11 Preinduction techniques followed by 10 cmH2O PEEP during mask ventilation and after intubation have been shown to reduce post-intubation atelectasis and improve arterial oxygenation.12

Airway management

Predictors of difficult tracheal intubation include a high Mallampati score (class 3 or 4), neck circumference ≥ 40 cm, limited mandibular protrusion and severe OSA (AHI ≥ 40). GlideScope™ has a high success rate in the morbidly obese patients with a difficult airway13 and can be performed without excessive force being placed on the maxillary incisors.14

Because BMI alone is not a predictor of difficult intubation, tracheal intubation while the patient is awake may not always be possible.11,15 However, OSA has been reported to be a predictor of difficult airway;11 therefore, it is imperative that emergency airway equipment (e.g. video laryngoscopes, supralaryngeal devices and fibrescopes), as well as additional help, is immediately available during induction and emergence.

Anaesthesia drugs and obesity

Obesity causes physiological changes that can affect the pharmacokinetics and pharmacodynamics of anaesthetic agents. An overview of these changes is given below:

  • increased fat mass

  • increased cardiac output

  • increased blood volume

  • increased LBW

  • changes in plasma protein binding

  • reduced total body water

  • increased renal clearance

  • increased volume of distribution of lipid-soluble drugs.

The common approach to anaesthetic drug administration is to give water-soluble drugs according to IBW and lipid-soluble drugs according to TBW. Lean body mass increases by approximately 20–40% in those suffering from obesity, so adding 30% to the IBW is a convenient dose adjustment. Weight calculations commonly used for the dosing of medications are shown below.

BMI = TBW(kg)/height(m2)LBW = IBW×1.3IBW(kg) = height(cm)100 (formen)or105(forwomen)

or

IBW = 0.8×TBW(formen)or0.75×TBW(forwomen)

Specific dosing recommendations for some common anaesthetic agents in obesity are listed in Table 3.

TABLE 3

Weight-based dosing of common i.v. anaesthetic drugs. Adapted from Ogunnaike BO, Jones SB, Jones DB, Provost, D, Whitten CW. Anesthetic considerations for bariatric surgery. Anesth Analg 2002; 95:1793–18056

Drug Dosinga Comments
Propofol LBW
Maintenance: TBW
Increased fat mass does not affect initial distribution/redistribution during induction. Cardiac depression at high doses is a concern
Thiopental TBW Increased volume of distribution, blood volume and cardiac output suggest a higher dose requirement
Midazolam TBW
Maintenance: IBW
Central volume of distribution increases in line with body weight. Increased absolute dose. Prolonged sedation because larger initial doses are needed to achieve adequate serum concentrations
Succinylcholine TBW Plasma cholinesterase activity increases in proportion to body weight, necessitating an increased absolute dose
Vecuronium IBW Recovery may be delayed if given according to TBW because of increased volume of distribution and impaired hepatic clearance
Rocuronium IBW Recovery may be delayed if given according to TBW because of increased volume of distribution and impaired hepatic clearance
Atacurium TBW Absolute clearance, volume of distribution and half-life do not change. Unchanged dose per unit body weight without prolonged recovery because of organ independent elimination
Fentanyl TBW Increased volume of distribution and half-life, which correlates positively with the severity of obesity

a The dosing parameter is the bolus loading dose unless indicated otherwise.

Induction of general anaesthesia

Rapid-sequence induction of general anaesthesia with propofol (dosed according to LBW), succinylcholine (1–1.5 mg/kg IBW) and cricoid pressure is considered the standard of care in the morbidly obese. However, the need for rapid-sequence induction in those who are obese with no other risk factors (e.g. diabetes mellitus) is controversial.17 Controlled induction of anaesthesia should allow appropriate titration of i.v. anaesthetic and prevent haemodynamic instability that may occur from a predetermined dose as well as allow adequate ventilation and avoid hypoxia between induction and tracheal intubation.

Maintenance of general anaesthesia

Because of its amnestic and analgesic properties, nitrous oxide (N2O) reduces anaesthetic and analgesic requirements and facilitates recovery. Nevertheless, the use of N2O has been questioned because of an increased number of cases of postoperative nausea and vomiting and pressure effects through expansion of closed spaces. However, a systematic review in 2008 concluded that there is no convincing reason to avoid N2O.18

Mechanical ventilation

Obesity is associated with changes in pulmonary function (e.g. reduction in lung volumes, increase in peak inspiratory pressures and decrease in pulmonary compliance). Lung-protective ventilation strategies in the obese would include the use of pressure-controlled ventilation with low tidal volumes (6–8 ml/kg IBW) and PEEP of 10–15 cmH2O.19,20 Recruitment manoeuvres are beneficial in obese patients and should be applied, particularly before and after laparoscopic surgery.21 Unfortunately, the effects of recruitment manoeuvres are short-lasting and often limited by haemodynamic instability. It is important to avoid hyperventilation (and hypocapnia) as this may result in metabolic alkalosis and lead to postoperative hypoventilation. Mild hypercapnia (i.e. ETCO2 of 40 mmHg) can improve tissue oxygenation through improved tissue perfusion resulting from increased cardiac output and vasodilatation as well as increased O2 offloading from the shift of the oxyhaemoglobin dissociation curve to the right.

Intraoperative fluid management

Adequate preoperative hydration (i.e. encourage patients to consume water until 2 hours preoperatively) and higher intraoperative fluid administration (20–40 ml/kg) have been reported to reduce postural hypotension, postoperative dizziness, drowsiness, nausea and fatigue.22 In addition, because the morbidly obese are at a high risk of rhabdomyolysis,23 administration of higher fluid volumes may reduce the potential for myoglobinuric acute renal failure associated with rhabdomyolysis.

Emergence from anaesthesia

In contrast to traditional practice, the primary aim at the end of the surgery should be to wash out the inhaled anaesthetic rather than increase the CO2 levels. Adequate ventilation (probably with the use of pressure support ventilation) during recovery from anaesthesia and muscle relaxants should allow washout of inhaled anaesthetics and facilitate emergence as well as reduce postoperative pulmonary atelectasis and hypoxaemia.

One of the major concerns in obese patients, particularly those with OSA, is the risk of airway obstruction after tracheal extubation. Thus, prior to tracheal extubation, the patient must be fully awake, alert and follow verbal commands (i.e. deep extubation is not advisable). Importantly, coughing and reflex movements of the hand towards the tracheal tube should not be confused with purposeful movements. Extubation should be performed in a semi-upright (25–30° head-up) position, when possible. The authors of a study from 2010 reported that CPAP introduced immediately after tracheal extubation is superior to CPAP initiated later in the recovery room for maintaining lung function at 24 hours after laparoscopic bariatric surgery.24

Postoperative considerations

Patients who receive CPAP preoperatively should also receive CPAP postoperatively. Although supplemental O2 is beneficial for most patients, it should be administered with caution as it may reduce hypoxic respiratory drive and increase the incidence and duration of apnoeic episodes. Because obese patients may have unrecognized OSA, recurrent hypoxaemia may be better treated with CPAP or bilevel positive airway pressure along with O2 rather than O2 alone.

Obesity causes changes in the pharmacology of the anaesthetic drugs. Highly lipophilic drugs, such as barbiturates, benzodiazepines and opioids have a large distribution volume; therefore, calculation of the dosage is made according to the actual weight. In the case of moderately lipophilic drugs, the dosage is calculated according to the LBW, which varies by 20–40%. It is currently considered that adding 20% to IBW correctly estimates LBW. Succinylcholine doses for intubation are given according to TBW to ensure excellent intubating conditions, whereas the non-depolarizing muscle relaxants used for operative maintenance are given according to IBW. Although the distribution volume for the lipophilic anaesthetic drugs is large, the pharmacokinetics may vary as a result of protein binding and hepatic and renal clearance.25,26

For muscle paralysis, atracurium is preferred as it provides consistent recovery time because elimination is non-organ dependent. Regarding the choice of the volatile agent, two randomized studies27,28 showed the superiority of sevoflurane over isoflurane during bariatric surgery, as a result of its haemodynamic stability and because recovery time is quick and nausea and vomiting are infrequent.

Multimodal approaches to postoperative pain management include i.v. opioid administration based on IBW, local anaesthetics injected into the wound or port site, neuraxial anaesthesia and the use of non-steroidal anti-inflammatory agents.29 Acetaminophen is used in standard dosages because the distribution volume is small but the clearance is high in obese patients; therefore, frequent increase of the dosage is necessary. Intravenous opioids may lead to postoperative respiratory depression if given in continuous infusion, but if administered judiciously with the help of PCA pump, the risk is minimized.30

All obese patients must be encouraged to undergo early ambulation to prevent thromboembolic complications.

Conclusion

Anaesthetic management of super-morbidly obese patients undergoing bariatric surgery is a huge challenge for an anaesthetist. However, increased understanding of the physiology in the morbidly obese, progress in the surgical techniques and introduction of easily titratable anaesthetic drugs has substantially improved the safety for this unique group of patients when undergoing surgery.

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