Anesthesia for bariatric surgery: retrospective evaluation and literature review

Abstracts

BACKGROUND AND OBJECTIVES: Surgical treatment for morbid obesity is an effective way to maintain weight control in the long run. This study aimed at compiling complications, co-morbidities and major anesthetic aspects of patients submitted to bariatric procedures and at comparing results with data in the literature. METHODS: This study has reviewed the literature and retrospectively analyzed the records of patients submitted to bariatric surgery between September 2001 and December 2004. All patients were submitted to the laparotomy Capella technique performed by the same surgical team in the same hospital. RESULTS: Females were predominant, mean age was 39.6 years and mean body mass index (BMI) was 44.65 kg/m². Systemic arterial hypertension (SAH) was the most prevalente associate disease and complications observed were subclavian vein thrombosis, pulmonary infection, residual neuromuscular block, postoperative gastrointestinal bleeding, intestinal obstruction and anastomotic dehiscence. Mortality rate was 0.7%. CONCLUSIONS: Diseases such as SAH and osteoarthritis are highly prevalent in obese patients. There were major postoperative respiratory system complications. This stresses the importance of the anesthetic technique and of postoperative analgesia allowing for early ambulation and the ability to normally breathe and cough. It has been observed that several aspects of anesthesia for obese patients are already defined as beneficial or noxious; however, several subjects are still undefined and should be discussed and studied to constantly improve the anesthetic management of such patients.

ANESTHESIA, General; COMPLICATIONS; DISEASES; SURGERY, Abdominal

JUSTIFICATIVA E OBJETIVOS: O tratamento cirúrgico para a obesidade mórbida é forma eficaz de manutenção do controle ponderal por longo prazo. O objetivo deste trabalho foi realizar um levantamento das complicações, das comorbidades e dos principais aspectos do manuseio anestésico de pacientes submetidos à cirurgia da obesidade e comparar os resultados com os dados encontrados na literatura. MÉTODO: O trabalho foi realizado por meio de revisão bibliográfica e análise retrospectiva do prontuário dos pacientes submetidos à cirurgia bariátrica entre setembro de 2001 e dezembro de 2004. Todos foram submetidos ao mesmo procedimento, técnica de Capella, por laparotomia, realizada por uma única equipe cirúrgica e no mesmo hospital. RESULTADOS: Houve predomínio de pacientes do sexo feminino, a média de idade foi de 39,6 anos e o índice de massa corporal (IMC) médio foi de 44,65 kg/m². A hipertensão arterial sistêmica (HAS) foi a doença mais prevalente e as complicações encontradas foram trombose de veia subclávia, infecção pulmonar, bloqueio neuromuscular residual, sangramento gastrintestinal no pós-operatório, obstrução intestinal e deiscência anastomótica. O índice de mortalidade foi de 0,7%. CONCLUSÕES: As doenças como HAS e osteoartrose são muito prevalentes em pacientes obesos. Dentre as complicações do pós-operatório destacam-se as do sistema respiratório. Com isso percebe-se a importância do uso de técnica anestésica e de analgesia pós-operatória, que permita ao paciente a deambulação precoce, bem como a capacidade de respirar e tossir de forma adequada. Observou-se que muitos aspectos da anestesia do paciente obeso já estão definidos como benéficos ou prejudiciais; entretanto, vários assuntos ainda encontram-se indefinidos e cabe estudar e discutir para que se consiga melhorar cada vez mais o manuseio anestésico desses pacientes.

ANESTESIA, Geral; CIRURGIA, Abdominal; COMPLICAÇÕES; DOENÇAS

JUSTIFICATIVA Y OBJETIVOS: El tratamiento quirúrgico para la obesidad mórbida es una forma eficaz de mantener el control ponderal a largo plazo. El objetivo de este trabajo fue el de realizar una investigación de las complicaciones, de las comorbidades y de los principales aspectos del manejo anestésico de pacientes sometidos a la cirugía de la obesidad y comparar los resultados con los datos encontrados en la literatura. MÉTODO: El trabajo fue realizado a través de una revisión bibliográfica y de un análisis retrospectivo de la historia clínica de los pacientes sometidos a la cirugía bariátrica entre septiembre de 2001 y diciembre de 2004. Todos fueron sometidos al mismo procedimiento, técnica de Capella, por laparotomía, realizada por un solo equipo de cirugía y en el mismo hospital. RESULTADOS: Se registró un predominio de pacientes del sexo femenino. El promedio de edad fue de 39,6 años y el índice de masa corporal (IMC) promedio fue de 44,65 kg/m². La hipertensión arterial sistémica (HAS) fue la enfermedad más prevaleciente y las complicaciones encontradas fueron trombosis de la vena subclávica, infección pulmonar, bloqueo neuromuscular residual, sangramiento gastrointestinal en el postoperatório, obstrucción intestinal y dehiscencia anastomótica. El índice de mortalidad fue de un 0,7%. CONCLUSIONES: Las enfermedades como HAS y osteoartrosis son muy prevalecientes en pacientes obesos. Entre las complicaciones del postoperatório se destacan las del sistema respiratorio. Con eso notamos la importancia del uso de la técnica anestésica y de analgesia postoperatória que le permita al paciente la deambulación precoz, como también la capacidad de respirar y toser adecuadamente. Se observó que muchos aspectos de la anestesia del paciente obeso ya están definidos como benéficos o perjudiciales; sin embargo, varios asuntos todavía se encuentran indefinidos y cabe estudiarlos y discutir para lograr mejorar cada vez más el manejo anestésico de esos pacientes.

SCIENTIFIC ARTICLE

Anesthesia for bariatric surgery. Retrospective evaluation and literature review

Anestesia para cirugía bariátrica. Evaluación retrospectiva y revisión de la literatura

Airton Bagatini, TSA^I; Rubens Devildos Trindade^II; Cláudio Roberto Gomes, TSA^III; Renésio Marcks^IV

^ICo-responsável pelo CET/SBA do SANE

^IIAnestesiologista do SANE

^IIIInstrutor do CET/SBA do SANE

^IVME₂ do CET/SBA do SANE

^{Correspondence to}

SUMMARY

BACKGROUND AND OBJECTIVES: Surgical treatment for morbid obesity is an effective way to maintain weight control in the long run. This study aimed at compiling complications, co-morbidities and major anesthetic aspects of patients submitted to bariatric procedures and at comparing results with data in the literature.

METHODS: This study has reviewed the literature and retrospectively analyzed the records of patients submitted to bariatric surgery between September 2001 and December 2004. All patients were submitted to the laparotomy Capella technique performed by the same surgical team in the same hospital.

RESULTS: Females were predominant, mean age was 39.6 years and mean body mass index (BMI) was 44.65 kg/m². Systemic arterial hypertension (SAH) was the most prevalente associate disease and complications observed were subclavian vein thrombosis, pulmonary infection, residual neuromuscular block, postoperative gastrointestinal bleeding, intestinal obstruction and anastomotic dehiscence. Mortality rate was 0.7%.

CONCLUSIONS: Diseases such as SAH and osteoarthritis are highly prevalent in obese patients. There were major postoperative respiratory system complications. This stresses the importance of the anesthetic technique and of postoperative analgesia allowing for early ambulation and the ability to normally breathe and cough. It has been observed that several aspects of anesthesia for obese patients are already defined as beneficial or noxious; however, several subjects are still undefined and should be discussed and studied to constantly improve the anesthetic management of such patients.

Key Words: ANESTHESIA, General; COMPLICATIONS: respiratory; DISEASES: morbid obesity; SURGERY, Abdominal: gastroplasty

RESUMEN

JUSTIFICATIVA Y OBJETIVOS: El tratamiento quirúrgico para la obesidad mórbida es una forma eficaz de mantener el control ponderal a largo plazo. El objetivo de este trabajo fue el de realizar una investigación de las complicaciones, de las comorbidades y de los principales aspectos del manejo anestésico de pacientes sometidos a la cirugía de la obesidad y comparar los resultados con los datos encontrados en la literatura.

MÉTODO: El trabajo fue realizado a través de una revisión bibliográfica y de un análisis retrospectivo de la historia clínica de los pacientes sometidos a la cirugía bariátrica entre septiembre de 2001 y diciembre de 2004. Todos fueron sometidos al mismo procedimiento, técnica de Capella, por laparotomía, realizada por un solo equipo de cirugía y en el mismo hospital.

RESULTADOS: Se registró un predominio de pacientes del sexo femenino. El promedio de edad fue de 39,6 años y el índice de masa corporal (IMC) promedio fue de 44,65 kg/m². La hipertensión arterial sistémica (HAS) fue la enfermedad más prevaleciente y las complicaciones encontradas fueron trombosis de la vena subclávica, infección pulmonar, bloqueo neuromuscular residual, sangramiento gastrointestinal en el postoperatório, obstrucción intestinal y dehiscencia anastomótica. El índice de mortalidad fue de un 0,7%.

CONCLUSIONES: Las enfermedades como HAS y osteoartrosis son muy prevalecientes en pacientes obesos. Entre las complicaciones del postoperatório se destacan las del sistema respiratorio. Con eso notamos la importancia del uso de la técnica anestésica y de analgesia postoperatória que le permita al paciente la deambulación precoz, como también la capacidad de respirar y toser adecuadamente. Se observó que muchos aspectos de la anestesia del paciente obeso ya están definidos como benéficos o perjudiciales; sin embargo, varios asuntos todavía se encuentran indefinidos y cabe estudiarlos y discutir para lograr mejorar cada vez más el manejo anestésico de esos pacientes.

INTRODUCTION

Obesity is today a severe health problem affecting virtually the whole world, especially developed and developing countries ^1,2. Obesity in the American population ranges from 20% to 25% and in Europe it ranges from 10% to 25% ¹. This phenomenon has increased in recent years and, in the USA, the prevalence of obesity between 18 and 29 years of age has increased from 12% in 1991 to 18.9% in 1993 ³. It is estimated that 1% to 6% of all health expenses in rich countries are related to obesity and public expenses are even higher due to losses in productivity and the payment of pensions ¹.

Surgical treatment for morbid obesity is an effective way to maintain weight control in the long run ^4-6. Sustained weight loss during 16 years is approximately 67% of excess weight ⁶. Obesity is the second risk of premature death which can be prevented in the United States, coming after smoking, and bariatric surgery may decrease in up to 89% the mortality risk of obese patients ⁶.

There are three surgical treatments for obesity: restrictive, disabortive and combined (restriction and disabortion) procedures, each one with their results and complication rates ⁷. It is known that the best results are achieved with combined and disabortive procedures as compared to purely restrictive techniques, although with higher complication and mortality rates ^8,9. Since the aim of the bariatric surgery is to reach the best results with minimum adverse effects, we have surveyed co-morbidities, complications and major aspects of the anesthetic management of patients submitted to the Capella technique ¹⁰ (restriction and disabortion). Results were then compared to data in the literature.

METHODS

This study has reviewed the literature and retrospectively analyzed the records of patients submitted to bariatric surgery between September 2001 and December 2004. All patients were submitted to the laparotomy Capella technique performed by the same surgical team in the same hospital. Total intravenous general anesthesia was used in all patients, always by the same anesthesiologists (two). All patients were submitted to routine lab tests, chest X-rays, ECG, abdominal EEG and high digestive endoscopy.

Pre-anesthetic evaluation was performed up to one week before surgery. Patients were premedicated with oral midazolam (7.5 mg) and clonidine (300 µg), 45 minutes before the procedure. Bolus dexmedetomidine (1 µg.kg^-1) was administered 10 minutes before anesthetic induction and intraoperative maintenance was achieved with 0.4 µg.kg^-1.h^-1. Anesthesia was induced and maintained with target-controlled propofol infusion with plasma concentration adjusted for 2.6 to 3 µg.mL^-1 associated to 0.3 to 0.6 µg.kg^-1.min^-1 remifentanil. Rapid sequence technique was used for tracheal intubation after succinylcholine administration (100 mg). Volume-controlled ventilation was applied with FiO₂ of 0.5 to 1 and PEEP of 5 cmH₂O.

Intraoperative neuromuscular block was achieved with atracurium and rocuronium with additional doses during anesthesia. Intravenous ketoprofen (100 mg) every 12 hours, tramadol (100 mg) and dipirone (2 g) every 6 hours were administered for postoperative analgesia, and morphine (5 mg) with minimum 2-hour intervals was administered as rescue analgesic, in addition to maintaining dexmedetomidine (0.4 µg.kg^-1.h^-1) in the first 24 postoperative hours. Nausea and vomiting were prevented with nasogastric tube, intravenous dexametasone (10 mg) at induction and intravenous ondansetron (8 mg) 30 minutes before surgery completion. Patients also received intravenous omeprazol (40 mg) every 12 hours as from anesthetic induction.

RESULTS

Participated in this study 150 patients with predominance of females (139 patients), mean age of 39.6 years and mean body mass index (BMI) of 44.65 kg.m^-2 – BMI = weight (in kg) height ^-2 (in meters). Demographics data and co-morbidities are shown in tables I and ^II, respectively.

There has been one death in the 40^th postoperative day by pulmonary embolism due to deep vein thrombosis, representing 0.7% mortality rate. There was also one case of subclavian vein thrombosis related to central venous catheter and two cases of postoperative pulmonary infection. One female patient needed re-intubation before being referred to the post-anesthetic recovery unit (PACU) due to residual neuromuscular block, and one male patient has developed postoperative gastrointestinal bleeding with no need for surgical reintervention. There were three cases of obstruction, one of anastomotic dehiscence, but no cardiovascular complication was observed. Abdominal wall complications were not included in this study. Complications are summarized in table III.

DISCUSSION

The word obesity comes from the Latin word obesus, which means fattened by feeding ². To determine whether a person is obese one should start by defining normality patterns for the general population. It is known that the ratio of fatty tissue with regard to total body weight is 20% to 30% for females, 18% to 25% for males, 10% to 12% for a professional soccer player and 7% for a marathon runner ². Starting from these data and from weight evaluations related to height and gender, in which individuals would have the lowest general mortality rates, the ideal body weight (IBW) was determined and estimated as follows: IBW equals subtracting 100 for males and 105 for females from their respective height in centimeters ^2,11-14. Another criteria is lean body weight (LBW) which adds 30% to IBW due to increased muscular mass, which is concomitant to fatty tissue increase in obese people. There are currently several indices in the literature to evaluate obesity ^11,14, but the most popular is BMI. BMI is justified in an attempt to decrease the effect of weight on height and also helps subdividing excess weight in different categories ^2,11. Different criteria are found in the literature ^2,3,5,11-15 to define overweight, obesity and morbid obesity and most popular standards are shown in table IV.

BMI has some limitations, especially to anticipate health risks, since people with well-developed muscular mass may be classified as overweighed without really having excessive fatty tissue ².

Overweighed patients not eligible for surgical procedures should change their diet and lifestyle. For those with BMI > 30 or BMI > 27 with two or more co-morbidities, drugs should also be associated. Currently, safest and most popular drugs are sibutramine – 10 to 15 mg.day^-1 – serotonin and norepinephrine reuptake inhibitor; and orlistat – 120 mg during major meals – pancreatic lipase inhibitor decreasing intestinal fat absorption ^16,17.

Criteria for surgical obesity treatment according to the National American Health Institute are shown in table V.

Patients to be submitted to surgical obesity control should be pre-evaluated early to have enough time for needed consultancy or additional tests. Major physiological systems (cardiovascular, respiratory, endocrine, neurological, renal, urinary and digestive) should be reviewed during pre-anesthetic evaluation aiming at identifying risk factors which may interfere with the intraoperative period ¹⁸.

History of bleedings and/or allergies, previous anesthetic-surgical procedures and drugs being used with their respective doses and indications are also investigated. Special attention should be given to appetite-suppressing amphetamines which interact with anesthetic drugs, to sibutramine which may cause SAH, to orlistat, which may determine vitamin D deficiency, and to phenfluramine and phentermine, which may cause cardiac valvopathy and pulmonary hypertension ^3,5,16,17.

Whenever morbidly obese patients are evaluated special emphasis should be given to most prevalent co-morbidities in this unique group of patients, which are described in chart I ^{2,5,12,13,17,19}.

There are some studies ^20-26 on the prevalence of such co-morbidities, which are compared in table VI.

Among several clinical problems of obese patients ^2,17, the six most frequent co-morbidities of interest to anesthesiologists are SAH, osteoarthritis, obstructive sleep apnea syndrome (OSAS), gastroesophageal reflux (GER), diabetes mellitus (DM) and asthma in decreasing order of frequency ^12,20-26. These six disorders were also highly prevalent in our study, however OSAS was only the 5^th most common problem. This might have been due to diagnostics missed during preoperative evaluation. OSAS in general population varies from 4% to 10% ²⁷ and the result of 10% in our obese population is low, since obesity is a major risk factor for OSAS. Symptoms to be investigated in patients with suspicion of OSAS are snores, micro-emergences, sleep fragmentation, daily sleepiness, fatigue, lethargy, depression, morning headache, impotency and enuresis. These are most frequently found in patients with obesity, nasal obstruction, tonsils hypertrophy or adenoids, Pierre-Robin syndrome, Down syndrome, hypothyroidism, acromegaly, acondroplasia, renal failure and neurological disorders ^27,28. Final diagnosis is confirmed by polisonographic test with hypoapnea or apnea during 10 or more seconds, with a minimum of five episodes per hour (10 in the elderly) and decreased peripheral oxygen saturation (SpO₂) above 4% ²⁷. Long-duration OSAS patients may develop desensitization of respiratory centers to hypoxia and hypercapnia, resulting in the obesity hypoventilation syndrome, or Pickwick syndrome, characterized by obesity, sleepiness, hypoxia, hypercapnia, right ventricular failure and polycythemia ^2,12,13,27.

In addition to careful opioid, sedative or anxiolytic drugs administration to OSAS patients ^2,11, there is also fear of difficult intubation in obese patients with such syndrome. However Brodsky ² in his study has concluded that isolated OSAS in obese patients is not a risk factor for difficult intubation, but when followed by increased neck circumference, this risk increases. There is a special position to expose obese patients airways, which consists in elevating the dorsum in approximately 20º. This position favors the separation of breasts and the moving away of head and neck from the chest, and may be achieved with pads under shoulders and head, which may have their size progressively increased. With this, a mean increase of 20 cm in the sternomental distance is achieved ²⁹. Cangiani ³⁰ recommends the use of a trapezoid device (Simoni's trapeze) placed under patient's dorsum, producing the same effect in sternomental distance increase. It is worth reminding that OSAS patients are, per se, at higher risk for morbidity and mortality during anesthesia and surgery ²⁷.

Malampatti test should be applied to evaluate airway. When there is suspicion of difficult airway, additional tests should be performed, such as mouth opening, cervical mobility and hyoid-mental distance ³². It is known that neck circumference is the best parameter to anticipate difficult intubation in obese patients. Patients with 40 cm neck circumference have 5% more probability of difficult intubation versus 35% for patients with 60 cm. The increase of 1 cm in neck circumference increases 1.13 times the possibility of difficult intubation ^3,33. Obesity not associated to increased neck circumference is not a predictive factor for difficult intubation ³³.

There has been 13% hiatal hernia in our study, confirmed by EDA and high prevalence of GER (22%), disorder which may partially explain the high incidence of asthma in obese patients ^20,24,26. Cholelithiasis was also found in 10% of patients, fatty liver disease in 20% (confirmed by abdominal ultrasound) and renal lithiasis in 5.3% (confirmed by abdominal ultrasound), which are common diseases in obese patients ^2,17. The high incidence of liver steatosis is to be highlighted since this condition may interfere with the metabolism of anesthetic drugs. Changes in liver enzymes are not an adequate method to track this disease because they are changed in just 1.04% of times ³¹. There were also observed 22% of dyslipidemia and 5.15% of hypothyroidism, which are values close to those found in the literature ^20,23,24.

Some authors indicate routine tests such as blood with platelet count, electrolytes, coagulation tests, urea and creatinine, fasting glycemia, chest X-rays, ECG, arterial blood gases analysis and pulmonary function tests ^3,12. Blood count detects anemia in just 16% of obese patients with documented iron and/or vitamin B12 defficiency ³¹. Hypokalemina may be present in patients under diuretics, however changes in blood potassium concentrations are uncommon in obese patients, remaining in approximately 1.6% ³¹. Changes in chest X-rays and ECG are approximately 4% and 15%, respectively, when routinely performed and most of the times these changes do not affect anesthetic-surgical planning ³¹. Preoperative chest X-rays may be used for postoperative comparison, since major complications are respiratory system complications ¹³.

Opioids are counterindicated as preanesthetic medication due to the possibility of respiratory depression and desaturation. Sedatives should be used in low doses due to the same problems. Muscular drugs should be avoided considering the unpredictable absorption due to the large amount of fatty tissue, which increases the possibility of inadvertent fatty tissue injection ³. OSAS patients should not receive sedatives and even less opioids as preanesthetic medication because they decrease pharyngeal muscle tone and also the response to hypoxemia and hypercabia, increasing the risk of airway obstruction ²⁷. In this study, OSAS patients were premedicated with clonidine only. Clonidine, a₂-agonist, may be used as preanesthetic medication to improve patients' hemodynamic status and decrease inhalational and intravenous anesthetics consumption ^34-37. In premedication doses (3 to 4 µg.kg^-1), clonidine has sedative, anxyolitic, analgesic and antisyalogogue effects, but may also induce arrhythmias and hypotension, which should be treated with atropine and an a₁-agonist, such as ephedrine, respectively ^36,37. Analgesia is another positive clonidine effect, synergic with opioids and decreasing their consumption ^36,37. It is also important that clonidine in therapeutic doses produces minor respiratory depression similar to that induced by physiological sleep and does not exacerbate respiratory depressing effects of opioids. It is, thus, a very useful drug for obese patients at risk for hypoxemia, especially those with simultaneous OSAS or obesity hypoventilation syndrome ³⁸.

Another significant premedication concern is the high incidence of GER in obese as compared to non-obese patients (16.67% versus 0.48%) ²⁶, being this just one of the factors increasing the possibility of regurgitation and pulmonary aspiration during anesthetic induction ^12,13. So, drugs to decrease gastric content and increase gastric pH, such as intravenous ranitidine (100 mg) 60 to 90 minutes before surgery, non-particulate antacids (questionable efficacy), such as magnesium citrate up to 30 mL before anesthetic induction, and metoclopramide, which speeds gastric emptying and increases lower esophageal sphincter tone are recommended ^12,13,15. According to Shenkman et al. ¹⁵ the most effective agent to increase gastric pH would be intravenous ranitidine (100 mg). This study has not routinely used these drugs and there was no regurgitation with pulmonary aspiration.

As a consequence of increased risk for thromboembolic events during bariatric surgery, preventive methods should be adopted ^12,13. In this study, subcutaneous 7500 UI non-fractionate heparin was administered during anesthetic induction and then every 12 hours until complete patient mobilization. This decreases the incidence of deep vein thrombosis ³.

There was one case of late death (more than 30 postoperative days) due to pulmonary embolism. The international bariatric surgery record ⁵ has published in 2002 a survey on complications of obesity procedures with a total of 17,676 patients and has found 0.25% mortality, with pulmonary embolism as the major cause (15 cases). Low molecular weight heparin seems to be more effective to prevent thromboembolic events, but further studies are still needed for this confirmation. Scholten et al. ³⁹ have concluded that 40 mg subcutaneous enoxaparin every 12 hours decrease the incidence of deep vein thrombosis as compared to 30 mg, without increasing bleeding rates. This same author has shown that subcutaneous 5000 UI non-fractionate heparin every 8 hours is equivalent to enoxaparin once a day to prevent thromboembolic events. Another method to prevent thromboembolism is to use pneumatic devices on lower limbs. When these devices are used throughout the lower limb there is 240% increase in femoral vein flow speed. Compressions should produce 35 mmHg pressure on ankles, 30 mmHg on knees and 20 mmHg on thighs. When used on ankles only, they increase 180% femoral vein flow speed. Ankle pressure of 35 mmHg shall be maintained for 12 seconds ⁴⁰. No pneumatic device was used in our study. A survey by the American Society of Bariatric Surgery, showed that 50% of its members use subcutaneous 5000 UI non-fractionated heparin every 8 to 12 hours, 33% use pneumatic devices, 13% use low molecular weight heparin and 4% use other methods³.

Obese patients may be monitored with ECG, pulse oximetry, vesical catheter, capnography and peripheral nerve stimulator ¹⁵. We have not used peripheral nerve stimulator and clinical parameters were used to evaluate the level of neuromuscular block. There has been one case of residual neuromuscular block with the need for re-intubation before referral to the PACU.

Routine invasive blood pressure monitoring may be a very practical method with low complication rates. While Lins et al. ^3,12 recommend invasive blood pressure monitoring, Ogunnaike et al. recommend it only in special situations, such as inadequate cuff size, conic arm impairing cuff positioning, superobese patients (BMI > 50 kg/m²) and patients with severe cardiopulmonary co-morbidity. If the option is non invasive blood pressure, a cuff covering 75% to 100% of the arm should be used; cuff may be placed on wrist or ankle for better adaptation ^3,12,13. One should not forget that even with extra-large cuffs, blood pressure values may be overestimated in 20% to 30% as compared to invasive blood pressure monitoring ^14,15. In this study, invasive blood pressure monitoring was routinely used.

A controversial area in the management of bariatric surgery patients is how to reach venous access: peripheral vein or central vein catheterization? This study has routinely used central venous access due to major peripheral access difficulties and best postoperative comfort. There has been one subclavian vein thrombosis. Ogunnaike et al. recommend central venous access only in the presence of peripheral access difficulties, while Shenkman et al. ¹⁵ routinely use central venous access.

Special operating room tables or the coupling of two normal ones may be needed to assure safety during bariatric procedures ^3,12,15. Traditional tables support approximately 205 kg, while special tables may support up to 455 kg ³. One should also pay attention to the adequate positioning of the patient on the table, because obese patients tend to slide when their position is changed ³. Special attention should be given to areas of higher pressure and peripheral nerve pathways, because those patients have a higher incidence of ischemic injuries and nervous compressions, especially those superobese ³⁹. Warner et al. ⁴¹, in a retrospective study, have found BMI > 38 kg/m² in 29% of patients with ulnar neuropathy.

Another important factor to be reminded is that morbidly obese patients present with restrictive pneumopathy with decreased functional residual capacity (FRC) and should remain with head, shoulders and chest elevated during preparation and anesthetic induction to improve functional residual capacity / closing volume ratio, helping the distribution of blood gases ^{12,13,15,29,42,43}. In the supine position, and especially with the head down, there is major worsening of ventilatory mechanics. Prone position may also be poorly tolerated by obese patients due to increased intra-abdominal pressure ^12,13,15.

According to Shenkman et al. ¹⁵, anesthesia should be induced by two anesthesiologists. Pre-oxygenation with 100% oxygen should be adopted for all patients ¹². There is no arterial oxygen content difference in obese patients oxygenated for three minutes with 100% oxygen under mask, as compared to only four vital capacity inspirations with 100% oxygen under mask ¹⁵. In our study, previous oxygenation for one minute with spontaneous ventilation under mask was used for all patients. Intubation in rapid sequence is also recommended with 1 mg.kg^-1 LBW succinylcholine; its fast onset decreases the possibility of tracheal intubation failure ¹². Tracheal intubation difficulties may be anticipated and awaken intubation under topic anesthesia, with our without the aid of fibrobronchoscope, should be performed in patients with clear signs of difficult airways ^12,15.

Balanced or total venous techniques for anesthetic maintenance may be used separately or associated to neuraxial block ¹². Target-controlled propofol infusion is already a very popular technique and seems to be a good option for bariatric surgery. Shenkman et al. ¹⁵ prefer general inhalational anesthesia associated to local epidural anesthetics, due to drugs optimization, supply of high oxygen concentrations, good muscle relaxation and especially decreased inhalational anesthetics consumption. Another method to decrease intraoperative anesthetic consumption and decrease the possibility of emergence during anesthesia is bispectral index (BIS) to monitor brain function ^28,35.

During anesthetic maintenance of morbidly obese patients, desflurane has promoted the fastest emergence, higher mobility and lower incidence of desaturation up to 2 postoperative hours as compared to target-controlled propofol infusion or isoflurane administration, in addition to fastest emergence as compared to sevoflurane ⁴⁴. It is worth reminding that the metabolism of halogenated agents is increased in obese patients, so halothane should be avoided ^12,13. Propofol seems to promote faster anesthetic emergence as compared to isoflurane, the same being true for sevoflurane as compared to isoflurane in morbidly obese patients ^45,46. For intraoperative muscle relaxation, 50 mg atracurium or rocuronium may be administered after rapid sequence intubation with additional doses preferably based on the results of peripheral nerve stimulator. Remifentanil continuous infusion is an interesting choice due to its short life and good hemodynamic stability ⁴⁷. Its pharmacokinetics does not seem to change in obese patients and to prevent excessive doses they should be calculated taking into consideration the ideal body weight or the lean weight ⁴⁸. This study has used lean body weight remifentanil (0.3 to 0.6 µg.kg^-1.min^-1). Morphine, although less lipophilic than other opioids, should be avoided for intraoperative anesthesia of obese patients due to its long action time ¹⁵.

Dexmedetomidine, an a₂-agonist, was used in this study for decreasing inhalational or intravenous anesthetic consumption during anesthetic maintenance ^36,49. It should be started at least 10 minutes before induction to obtain adequate serum levels at induction and to attenuate cardiac tracheal intubation reflexes ^36,49. Initial bolus dose is approximately 1 µg.kg^-1 lean body weight for 10 minutes and maintenance dose is 0.2 to 0.7 µg.kg^-1.h^-1 lean body weight. With these doses it is possible to observe 20% decrease in blood pressure and up to 44% decrease in heart rate, however these effects are responsive to vasopressors, a₁-agonists and parasympatholytics ^36,49. Dexmedetomidine continuous infusion may be maintained for the first 24 postoperative hours for analgesia and sedation, with the advantage of promoting hemodynamic stability with minor respiratory depression ^36,49. Its postoperative administration does not prolong PACU stay ⁴⁹.

Mechanical ventilation may be adjusted for a tidal volume of 11 mL.kg^-1 PCI with FiO₂ varying from 0.5 to 1 and associated PEEP of 5 to 10 cmH₂O. These respiratory parameters should be adjusted according to expired or transcutaneous CO₂, pulse oxymetry and pressure / volume curves to prevent barotraumas ^50,51. Auler Jr. et al. ¹¹ recommend PEEP associated to tidal volume not higher than 11 mL.kg^-1 PCI to prevent hypoxemia according to most recent publications on respiratory mechanics. However this is still an area of several controversies in the literature ^12,52.

Patients submitted to bariatric surgery have two fixed risks of postoperative nausea and vomiting (PONV), which are the intraperitoneal procedure itself and the need for general anesthesia. Other risk factors may vary according to patient (age, gender, previous history, gastroparesis), surgical procedure (duration, postoperative pain, more prolonged fast) and anesthesia (preanesthetic medication with opioids, inhalational agents) ⁵³. At least two drugs are indicated to prevent PONV due to the presence of at least two risk factors in patients submitted to bariatric procedures. Continuous intravenous propofol (used in this study) may be considered preventive measure against PONV ⁵³. We have also used dexametasone and ondansetron to prevent PONV. It was believed that obesity was a risk factor for PONV ⁵³, possibly due to the storage of inhalational anesthetics in fatty tissue with increased exposure to its emetic effects, to decreased gastric emptying and to difficult ventilation under mask with air distension of the stomach ^53,54. However, recent studies have shown that gastric emptying before surgery completion does not decrease PONV ⁵⁵ and that ventilation under mask before intubation does not increase its incidence ⁵⁶. A systematic review by Kranke et al. ⁵⁴ in 2001 has provided enough data to confirm that increased BMI is not a risk factor for PONV.

Postoperative analgesia is based on two models which are not exclusive; the former uses intravenous NSAIDS and a₂-agonists (technique adopted in our study) and the latter uses epidural opioids or local anesthetics. Intravenous agents technique may be very carefully used with regard to opioids considering that this group of patients is prone to desaturation¹². Postoperative epidural analgesia with catheter using local anesthetics or opioids in continuous infusion or intermittent doses is preferred by some authors for the possible advantage of allowing earlier ambulation with less pulmonary and thromboembolic complications ^12,13,15. Field infiltration with local anesthetics, as well as patient-controlled analgesia with opioids, are effective and doses should be calculated based on ideal body weight ¹².

Post-bariatric surgery complications are still a problem for surgeons and anesthesiologists. Courcoulas et al. ²², in a retrospective study with 4674 bariatric surgeries between 1999 and 2001 have found 813 adverse results (17.4%) and 28 deaths (0.6%). These same authors have studied and concluded that adverse events – complications and deaths – are directly related to the number of surgical procedures performed by the surgeon per year: surgeons with less than 10 procedures per year had 28% adverse results and 5% death risk as compared to 14% and 0.3%, respectively, for surgeons with higher number of procedures (more than 100 per year).

Some studies ^20-25,57 have evaluated complication rates in bariatric surgeries and are shown in table VII.

A serious problem is that studies are very different in terms of surgical and anesthetic techniques, group of patients and postoperative complications classification, thus impairing a comparison among their results. Respiratory complications, however, are the most common. This is due to the association of obesity and upper abdominal manipulation, both related to decreased FRC, tidal volume and forced vital capacity, increasing the incidence of atelectasis, pulmonary infection and hypoxemia ^51,58,59. Our study has reported three pulmonary complications: two infections and one re-intubation before referral to PACU.

There has been just one late death due to pulmonary embolism among the 150 patients included in this study, representing 0.7% mortality rate. Mortality rates in the literature ^8,58 vary from 0.1% to 1.1% depending on the surgical technique, and purely restrictive procedures have the lowest death rates. According to a publication of 2002, of the International Bariatric Surgery Record, a review of 17,676 patients submitted to bariatric surgery between 1986 and 2002 has shown early mortality rate of 0.25% (n = 47). Major cause of death was pulmonary embolism (n = 15) followed by cardiac complications (n = 11) ⁵. It is known that the number of deaths among obese patients submitted to abdominal procedures is higher as compared to non-obese ¹³.

It is believed that surgical morbid obesity treatment is economically feasible for decreasing the number of diseses of obese patients ⁶⁰. However, there is still no consensus in the literature on the subject. Agren et al. ¹, in a retrospective and controlled study carried out in Sweden with 962 patients distributed in a surgical group (n = 481) and a control group under conservative treatment (n = 481) and lasting 6 years to evaluate expenses with healthcare between both groups, have observed that the surgical group had annual expenses US$ 1,200 higher as compared to the control group due to the increased number of other surgical procedures (especially cosmetic surgeries) and a much higher number of hospital days per year. Authors have then concluded that in spite of the decrease in co-morbidities achieved by bariatric procedures, there was no parallel decrease in hospital care during the 6 years of follow-up. Mean intraoperative expenses were US$ 4,333 ± 2,068.

Conversely, Christou et al. ⁶, in a prospective controlled study lasting five years to investigate decrease in morbidity, mortality and health expenses in two groups of patients, one for surgical treatment (n = 1035) and the other for non-surgical treatment (n = 5746) have found 45% decrease in expenses (admissions and medical calls) in the group of surgical patients, however they have not specified whether intraoperative expenses were included.

CONCLUSION

This study has observed that morbidly obese patients have several diseases associated to excessive fatty tissue. We have concluded that diseases such as SAH and GER are very common in obese patients. SAH, osteoarthritis, OSAS, GER, DM and asthma are common diseases of interest to the anesthesiologist and which should be always investigated during preoperative evaluation.

Among postoperative complications, respiratory system problems are to be highlighted. In our study they were the most prevalent together with thromboembolic complications (1.3%). These observations highlight the importance of an anesthetic technique and postoperative analgesia allowing patients to early ambulate and adequately breathe and cough.

Anesthesia for bariatric surgery is a challenge for the anesthesiologist. Patients have their own characteristics which should be observed from the preanesthetic evaluation to the postoperative period. It is known that even with recent advances in the understanding of obesity pathophysiology, these patients still have higher morbidity/mortality rates as compared to non-obese patients and the anesthesiologist must know their uniquenesses to offer them the best possible treatment. Several aspects of anesthesia for obese patients are already defined as beneficial or noxious; however, several subjects are still undefined and should be discussed and studied to constantly improve the anesthetic management of such individuals.

REFERENCES

Submitted for publication 18 de agosto de 2005

Accepted for publication 31 de janeiro de 2006

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*

Received from Centro de Ensino e Treinamento do SANE. Porto Alegre, RS

Publication Dates

• Publication in this collection
  29 May 2006
• Date of issue
  June 2006

History

• Accepted
  31 Jan 2006
• Received
  18 Aug 2005