The Pharmacodynamic Effects of Rocuronium When Dosed According to Real Body Weight or Ideal Body Weight in Morbidly Obese Patients

Weight-based dosing in medication use: what should we know?

BACKGROUND

Weight-based dosing strategy is still challenging due to poor awareness and adherence. It is necessary to let clinicians know of the latest developments in this respect and the correct circumstances in which weight-based dosing is of clinical relevance.

METHODS

A literature search was conducted using PubMed.

RESULTS

Clinical indications, physiological factors, and types of medication may determine the applicability of weight-based dosing. In some cases, the weight effect may be minimal or the proper dosage can only be determined when weight is combined with other factors. Medications within similar therapeutic or structural class (eg, anticoagulants, antitumor necrosis factor medications, P2Y12-receptor antagonists, and anti-epidermal growth factor receptor antibodies) may exhibit differences in requirements on weight-based dosing. In some cases, weight-based dosing is superior to currently recommended fixed-dose regimen in adult patients (eg, hydrocortisone, vancomycin, linezolid, and aprotinin). On the contrary, fixed dosing is noninferior to or even better than currently recommended weight-based regimen in adult patients in some cases (eg, cyclosporine microemulsion, recombinant activated Factor VII, and epoetin α). Ideal body-weight-based dosing may be superior to the currently recommended total body-weight-based regimen (eg, atracurium and rocuronium). For dosing in pediatrics, whether weight-based dosing is better than body surface-area-based dosing is dependent on the particular medication (eg, methotrexate, prednisone, prednisolone, zidovudine, didanosine, growth hormone, and 13-cis-retinoic acid). Age-based dosing strategy is better than weight-based dosing in some cases (eg, intravenous busulfan and dalteparin). Dosing guided by pharmacogenetic testing did not show pharmacoeconomic advantage over weight-adjusted dosing of 6-mercaptopurine. The common viewpoint (ie, pediatric patients should be dosed on the basis of body weight) is not always correct. Effective weight-based dosing interventions include standardization of weight estimation, documentation and dosing determination, dosing chart, dosing protocol, order set, pharmacist participation, technological information, and educational measures.

CONCLUSION

Although dosing methods are specified in prescribing information for each drug and there are no principal pros and cons to be elaborated, this review of weight-based dosing strategy will enrich the knowledge of medication administration from the perspectives of safety, efficacy, and pharmacoeconomics, and will also provide research opportunities in clinical practice. Clinicians should be familiar with dosage and administration of the medication to be prescribed as well as the latest developments.

Drug disposition in obesity: toward evidence-based dosing

Obesity and morbid obesity are associated with many physiological changes affecting pharmacokinetics, such as increased blood volume, cardiac output, splanchnic blood flow, and hepatic blood flow. In obesity, drug absorption appears unaltered, although recent evidence suggests that this conclusion may be premature. Volume of distribution may vary largely, but the magnitude and direction of changes seem difficult to predict, with extrapolation on the basis of total body weight being the best approach to date. Changes in clearance may be smaller than in distribution, whereas there is growing evidence that the influence of obesity on clearance can be predicted on the basis of reported changes in the metabolic or elimination pathways involved. For obese children, we propose two methods to distinguish between developmental and obesity-related changes. Future research should focus on the characterization of physiological concepts to predict the optimal dose for each drug in the obese population.

A Review of the Toxicologic Implications of Obesity

The increasing prevalence of obesity in developed nations has far-reaching implications for medical toxicology. The management of obese patients is complicated by comorbid illnesses, changes in cardiovascular and respiratory physiology, alterations in pharmacokinetics, and a lack of studies to identify appropriate dosing for current therapeutics and antidotes. In this review article, we examine obesity-associated physiologic and pharmacokinetic changes that may increase the vulnerability of obese patients to overdose. Further research is needed to characterize the relationship between drug toxicity and obesity.

Peri-operative management of the obese surgical patient 2015: Association of Anaesthetists of Great Britain and Ireland Society for Obesity and Bariatric Anaesthesia

Guidelines are presented for the organisational and clinical peri-operative management of anaesthesia and surgery for patients who are obese, along with a summary of the problems that obesity may cause peri-operatively. The advice presented is based on previously published advice, clinical studies and expert opinion.

Residual Curarization and Postoperative Respiratory Complications Following Laparoscopic Sleeve Gastrectomy. The Effect of Reversal Agents: Sugammadex vs. Neostigmine

BACKGROUND

Incomplete muscle relaxant reversal or re-curarization may be associated with postoperative respiratory complications. In this retrospective study we compared the incidence of postoperative residual curarization and respiratory complications in association with the type of muscle relaxant reversal agent, sugammadex or neostigmine, in patients undergoing laparoscopic sleeve gastrectomy.

MATERIAL AND METHODS

We reviewed the charts of all patients (179) undergoing laparoscopic sleeve gastrectomy from July 2012 to July 2013 at Wolfson Medical Center. Sugammadex 1.5-2 mg/kg (112 patients) or neostigmine 2.5 mg (67 patients) were used as reversal agents. Results were compared by the type of reversal agent employed. Compared parameters included demographic and anaesthetic data, residual curarization, oxyhemoglobin saturation (SpO2) in the recovery room (PACU), episodes of SpO2 lower than 90% in PACU, unexpected intensive care (ICU) admissions, incidence of atelectasis and pneumonia, re-intubation and duration of hospitalization.

RESULTS

Obstructive sleep apnea syndrome (OSAS) was more frequent in the sugammadex group (19% vs. 8%; p = 0.026). Total intravenous anesthesia (TIVA) was more frequently associated with sugammadex (33% vs. 16%; p = 0.007). There were no differences in postoperative residual curarization, SpO2 < 90% episodes, reintubation, ICU admissions, pulmonary complications and duration of hospitalization.

CONCLUSION

With the inherent limitations of a retrospective study, the use of sugammadex following laparoscopic sleeve gastrectomy showed no advantage over neostigmine in terms of residual curarization and respiratory complications.

Effective method of continuous rocuronium administration based on effect-site concentrations using a pharmacokinetic/pharmacodynamic model during propofol-remifentanil anesthesia

BACKGROUND

Rocuronium bromide (Rb) is a rapid onset, intermediate-acting neuromuscular blocking agent that is suitable for continuous administration. The appropriate rate of rocuronium administration is, however, difficult to determine due to large interindividual differences in sensitivity to rocuronium. The aim of this study was to clarify whether the simulated rocuronium concentration at the time of recovery to %T1 > 0 % after the initial administration of rocuronium is a good indicator of optimal effect-site concentrations during continuous rocuronium administration.

METHODS

Twenty-one patients were anesthetized with propofol. After induction, Rb 0.6 mg/kg was administered intravenously, and nerve stimulation using the single stimulation mode was conducted every 15 s. When %T1 recovered to >0 % after the initial administration of Rb, the effect-site concentration of rocuronium, calculated by pharmacokinetic simulation with Wierda's set of parameters, was recorded and defined as the recovery concentration (Rb r.c.). The administration rate of rocuronium was adjusted to maintain the Rb r.c. during surgery. Rb administration was discontinued just before the end of surgery, and the recovery time until %T1 > 25 % was recorded. Plasma Rb concentrations were measured at 1 and 3 h after the initiation of continuous Rb administration.

RESULT

The mean Rb r.c. was 1.56 ± 0.35 μg/ml, with minimum and maximum values of 1.09 and 2.08 μg/ml, respectively. The %T1 did not increase above 10 % in any of the patients during continuous administration of Rb, and the recovery period to %T1 > 25 % ranged from 9 to 29 min. The effect-site concentrations of Rb calculated with Wierda's parameters significantly correlated with plasma concentrations (P < 0.01) at both 1 and 3 h after the initial administration of Rb.

CONCLUSION

The results suggest that our method may be one of the most reliable protocols for the continuous administration of Rb described to date for maintaining suitable muscle relaxation during surgery without excessively prolonged effects.

Anesthetic drugs and bariatric surgery

The prevalence of obesity is increasing worldwide. For severely obese patients, bariatric surgery is the only effective option for sustained weight loss and associated health improvement. As a consequence, the number of bariatric surgical procedures being performed is growing exponentially. Systematic knowledge regarding the effect of obesity on the pharmacokinetics and pharmacodynamics of anesthetic agents is generally lacking, and data for morbidly obese (body mass index [BMI] 40-49 kg/m2)) and super-obese patients (BMI > 50 kg/m2) are almost completely non-existent. Most drug-dosing guidelines are based on results from relatively small studies in moderately obese patients. Future systematic pharmacological research is needed for improved and more rational peri-operative care of morbidly obese patients.

Highlights in muscle relaxants

The aim of this article is to provide an overview on neuromuscular blocking agents and a rational selection of the most appropriate agents, along with pharmacological and pharmacoeconomic considerations on neuromuscular blockers and their antagonists. Neuromuscular blocking agents are used during anesthesia to facilitate endotracheal intubation and provide surgically required paralysis. There is continuing development in the field of neuromuscular blocking agents, with new products appearing at regular intervals. All new agents come at increased costs. The proportion of anesthesia-related drug costs on a per-patient basis are small and vary from country to country, but account for no more than 12% of hospital drug budgets. However, given the large number of anesthetics performed over time, the total cost is significant. Moreover, such costs should be put into the perspective of the operating theater and patient admission costs. Appropriate selection of neuromuscular blocking agents can help not only to reduce biological costs secondary to complications, but also to make operating lists proceed smoothly and without incident. The paucity of outcome studies in relation to anesthetic drugs is not surprising given that anesthesia is used to facilitate the provision of therapy rather than being therapeutic in its own right. Accordingly, the assessment of anesthetic drugs has a different priority to therapeutic drugs. As anesthetic drugs are nontherapeutic, it is also difficult to determine the best choice of agent. However, new neuromuscular blocking agents are marketed on the basis of improvements in the frequency of side effects, safety, reliability, duration, reversibility and undesirable hemodynamic effects.

Sugammadex as a reversal agent for neuromuscular block: an evidence-based review

Sugammadex is the first clinical representative of a new class of drugs called selective relaxant binding agents. It has revolutionized the way anesthesiologists think about drug reversal. Sugammadex selectively binds rocuronium or vecuronium, thereby reversing their neuromuscular blocking action. Due to its 1:1 binding of rocuronium or vecuronium, it is able to reverse any depth of neuromuscular block. So far, it has been approved for use in adult patients and for pediatric patients over 2 years. Since its approval in Europe, Japan, and Australia, further insight on its use in special patient populations and specific diseases have become available. Due to its pharmacodynamic profile, sugammadex, in combination with rocuronium, may have the potential to displace succinylcholine as the "gold standard" muscle relaxant for rapid sequence induction. The use of rocuronium or vecuronium, with the potential of reverse of their action with sugammadex, seems to be safe in patients with impaired neuromuscular transmission, ie, neuromuscular diseases, including myasthenia gravis. Data from long-term use of sugammadex is not yet available. Evidence suggesting an economic advantage of using sugammadex and justifying its relatively high cost for an anesthesia-related drug, is missing.

Sugammadex and ideal body weight in bariatric surgery

Background. The obese patients have differences in body composition, drug distribution, and metabolism. Sugammadex at T₂ recovery in a dose of 2 mg kg⁻¹ of real body weight (RBW) can completely reverse the NMB block; in our study we investigated the safety and efficacy of Sugammadex dose based on their ideal body weight (IBW). Methods. 40 patients of both sexes undergoing laparoscopic bariatric surgery were enrolled divided into 2 groups according to the dose of Sugammadex: the first received a dose of 2 mg kg⁻¹ of IBW and the second received a dose of 2 mg kg⁻¹ of RBW. Both were anesthetized with doses calculated according to the IBW: fentanyl 2 μg kg⁻¹, propofol 3 mg kg⁻¹, rocuronium 0,6 mg kg⁻¹, oxygen, air, and desflurane (6–8%). Maintenance doses of rocuronium were 1/4 of the intubation dose. Sugammadex was administrated at T₂ recovery. Results. The durations of intubation and maintenance doses of rocuronium were similar in both groups. In IBW group, the T₄/T₁ value of 0.9 was reached in 151 ± 44 seconds and in 121 ± 55 seconds in RBW group (P = 0.07). Discussion. Recovery times to T₄/T₁ of 0.9 are surprisingly similar in both groups without observing any postoperative residual curarization. Conclusion. Sugammadex doses calculated according to the IBW are certainly safe for a rapid recovery and absence of PORC.

Airway management in obese patients

The well-known difficulties in airway management in obese patients are caused by obesity-related airways and respiratory changes. Anesthesiologists confront a number of troubles, including rapid oxygen desaturation, difficulty with laryngoscopy/intubation and mask ventilation, and increased susceptibility to the respiratory depressant effects of anesthetic drugs. Preoperative assessment of the airways in the obese should include examination of specific predictors of difficult mask ventilation other than those for difficult intubation. Difficulties in airway management are decreased after providing optimal preoxygenation and positioning ("ramped"). Other strategies may include availability of alternative airway management devices, including new video laryngoscopes that significantly improve the visualization of the larynx and thereby facilitate intubation. If awake intubation is mandatory, it may be performed with fibrobronchoscope after providing an adequate topical anesthesia and sedation with short-acting drugs, such as remifentanil. Succinylcholine for rapid sequence induction might be replaced by rocuronium where sugammadex is available for reversal. A complete reversal of neuromuscular block, measured by train-of-four monitoring, should be obtained before extubation, which requires a fully awake patient in the same position with airway equipment used for intubation.

In non-obese patients, duration of action of rocuronium is directly correlated with body mass index

BACKGROUND

Administration of neuromuscular blocking agents using a dose calculated on actual body weight carries a risk of prolonged duration of action in obese patients whose body mass index (BMI) is > 30 kg · m(-2). In the present study, we hypothesized that there could be a correlation between BMI and the duration of action of rocuronium administered according to actual body weight in non-obese patients, in particular, overweight (BMI 25-30 kg · m(-2)) and underweight patients (BMI < 18.5 kg · m(-2)).

METHODS

Sixteen female patients (BMI 15-30 kg · m(-2), aged 45-60 yr) scheduled for elective surgery under total intravenous anesthesia were included in this study. Rocuronium 0.9 mg · kg(-1) was administered, and adductor pollicis train-of-four responses following ulnar nerve stimulation were monitored every minute with acceleromyography. The times from the injection of rocuronium until spontaneous recovery of first twitch to 5% (5% Duration) and 25% (25% Duration) of baseline were measured, and the correlation with BMI was analyzed.

RESULTS

A significant correlation between 5% Duration and BMI (r(2) = 0.56; P < 0.001) was found by linear regression analysis. A significant correlation was also found between 25% Duration and BMI (r(2) = 0.49; P = 0.003).

CONCLUSION

In adult female patients with a BMI in the range of 15-30 kg · m(-2), the duration of action of rocuronium increases with BMI when the drug is administered on the basis of mg per actual kg body weight.

Anesthetic Pharmacology and the Morbidly Obese Patient

Anesthesiologists are increasingly being faced with treating obese patients. Physiologic and anthropometric associated with obesity-most notably increases in cardiac output, changes in tissue perfusion and increases in total body weight (TBW), lean body weight (LBW), and fat mass affect the pharmacokinetics (PK) of anesthetic agents. In addition, redundancy of airway tissue, obstructive and central sleep apnea and CO2 retention affect the pharmacodynamics (PD) of anesthetics and narrow the therapeutic window of numerous anesthetic drugs. Safe and effective pharmacologic management of the obese patient requires a thorough understanding of how obesity affects the PK and PD of anesthetics.

Anesthesia for bariatric surgery

BACKGROUND

Bariatric surgery has a lot of problems in anesthesia. We retrospectively compared anesthesia for bariatric surgery in yellow race with that in normal weight patients.

METHODS

Twenty patients who received bariatric surgery and 20 normal body weight patients who received abdominal surgery in Japan were enrolled. Induction condition, depth of epidural space, dose of anesthetics, duration of the effects of muscle relaxants, ventilation, and fluid management in bariatric surgery were analyzed and compared with those in normal body weight patients.

RESULTS

An epidural catheterization was successful under ultrasound guide in the bariatric group. The depth epidural space was significantly larger in the bariatric group. Cormack and Lehane classification and the number of intubation attempt were not different between the two groups, while one bariatric case was once awakened to intubate blindly. Pressure-controlled ventilation was used in the bariatric group. Four bariatric patients were continuously ventilated after surgery. The doses of anesthetics and fluid infusion rate were not different between the two groups when calculated by ideal body weight in the bariatric group. The duration of the effects of rocuronium and pancuronium were shorter in the bariatric group.

CONCLUSIONS

For anesthesia of yellow race patients undergoing bariatric surgery, intravenous anesthetics and acetate Ringer's solution with 1% glucose could be administered per ideal body weight, the effects of muscle relaxants lasted shorter, pressure-controlled ventilation could keep oxygenation with adequate carbon dioxide, and ultrasound assist was useful in epidural catheterization in the bariatric patients.

Perioperative management of the morbidly obese adolescent with heart failure undergoing bariatric surgery

The incidence and prevalence of adolescent obesity and adolescent heart failure are increasing, and anesthesiologists increasingly will encounter patients with both conditions. A greater understanding of the physiologic challenges of adolescent heart failure as they relate to the perioperative stressors of anesthesia and bariatric surgery is necessary to successfully manage the perioperative risks faced by this growing subpopulation. Here, we present a representative case of a morbidly obese adolescent with heart failure who underwent a laparoscopic bariatric operation and review the limited available literature on perioperative management in this age group. Specifically, we review evidence and offer recommendations related to preoperative evaluation, venous thromboembolism prophylaxis, positioning, induction, airway management, monitoring, anesthetic maintenance, ventilator management, and adverse effects of the pneumoperitoneum, rhabdomyolysis, and postoperative care.

[Anesthesia and bariatric surgery]

Today obesity is accepted as an independent disease. The WHO describes obesity as an epidemic disease occurring worldwide and associated comorbidities affect all organ systems. Bariatric operations lead to an improvement or even complete remission of obesity-correlated comorbidities. Bariatric operations are conducted as restrictive, malabsorptive, or mixed procedures. The preoperative anesthetic evaluation of comorbidities is carried out with a special focus on preexisting impairments of cardiac and lung function (e.g. cardiomyopathy, obstructive respiratory dysfunctions). Extremely obese patients are at risk of aspiration. Airway management at anesthesia induction includes normal intubation or, if additional risk factors are present, either fiber optic awake intubation or rapid sequence induction. The pharmacokinetics of all applicable drugs are altered in extremely obese patients and they are at risk for developing postoperative thromboembolic complications with a high mortality rate. Therefore early and sufficient thrombotic prophylaxis is important.

Perioperative management of morbid obesity

Data from the NHS Information Centre reveals that more than one in three adults (36.9%) is overweight. In addition, almost a quarter of adults (24% of men and 25% of women aged 16 or over) are obese, with their need for treatment placing a growing burden on the NHS (The NHS Information Centre 2010). Given these proportions, and that an increasing number of morbidly obese patients are undergoing weight loss surgery and procedures related to obesity, it is an opportune time to review the perioperative care of morbidly obese patients.

Anaesthesia for bariatric surgery

Although many smaller studies have addressed anaesthetic care for bariatric surgical patients, comprehensive systematic literature reviews have yet to be compiled, and much evidence includes expert panel opinion. This review summarises study results in bariatric surgical patients regarding pre-anaesthesia evaluation, the perioperative impact of sleep-disordered breathing, airway management at anaesthetic induction and emergence, maintenance of anaesthesia, postoperative pain management, utility of clinical-care pathways and feasibility of outpatient bariatric surgery. The 'ramped' upper-body, reversed Trendelenburg position at anaesthetic induction and manual application of positive end-expiratory pressure (PEEP) is recommended. Intra-operative hypoxaemia can be treated with the combination of PEEP and recruitment manoeuvres, and attention to airway management at emergence is critical. Local anaesthetic wound infiltration and non-steroidal anti-inflammatory drugs should be part of multimodal opioid-sparing postoperative analgesia. Implementation of bariatric clinical-care pathways seems beneficial. Considering the prevalence of sleep apnoea in these patients, outpatient bariatric surgery remains controversial, but is probably safe for certain procedures, provided there is strict adherence to preoperative eligibility and home-care protocols.

Anesthesia for a 228-kg patient (body mass index, 90.6) undergoing laparoscopic sleeve gastrectomy

We undertook anesthesia of a 40-year-old woman with body weight of 228 kg and body mass index (BMI) of 90.6 kg/m(2) who was undergoing laparoscopic sleeve gastrectomy. This case may be the largest known patient undergoing general anesthesia in our country. Anesthesia was induced in a 30° head-up position with midazolam, fentanyl, droperidol, and inhalation of sevoflurane and nitrous oxide without muscle relaxants, and maintained with propofol, remifentanil, and pancuronium under pressure-controlled ventilation. The Airway Scope could not be inserted into her mouth, but her trachea was successfully intubated with a Macintosh laryngoscope. Dosages of anesthetics and fluid infusion rate were calculated first per ideal body weight. Then, infusion of propofol and remifentanil and administration of muscle relaxant were controlled by bispectral index, hemodynamics, and train-of-four response, respectively. Postoperative 12-h pressure-controlled ventilation and pain management by subcutaneous infusion of fentanyl and droperidol were successful. Subcutaneous heparin 5,000 units twice per day postoperatively did not induce thromboembolism.

Difficulties in managing the surgical patient who is morbidly obese

Managing patients who are morbidly obese in the intensive care unit is associated with a variety of problems uncommonly experienced with the those who are not morbidly obese. Clinicians experience a myriad of unique problems and circumstances, from the need for special beds and lifts to unusual and unknown volumes of distribution resulting in unclear drug dosing. This review examines several issues including sedation, invasive monitoring, venous thromboembolism prophylaxis, surgical infections, nutritional support, and other complications that may be of particular importance to the critically ill patient who is morbidly obese. In many cases, care is altered based on the complicating issues surrounding morbid obesity. In other cases, the presence of obesity suggests no alterations in our routine critical care delivery. A comprehensive review of the literature is undertaken, data are critically considered, and overall opinion is rendered based on the available peer-reviewed literature. In many cases, data are not available that address the specific patient population in question, so related papers (like gastric bypass data) are considered. Many issues do not have definitive answers based on randomized controlled trials, and much is left to treating clinician opinion and local practice patterns. Where good data exist, however, one should consider carefully and individually deviation from the evidence-based approach.

Emergency department management of the airway in obese adults

Airway management in obese adults can be challenging, and much of the literature on this subject focuses on elective surgical cases, rather than acutely ill patients. In this article, we review the emergency department evaluation of the airway in obesity, discussing anatomy, physiology, and pharmacology. In addition, we describe techniques and devices used to improve intubating conditions in the obese patient. After our review of the relevant literature, we conclude that research in this particular area of acute care remains in its infancy.

Effect of obesity on the pharmacokinetics of drugs in humans

The prevalence of obesity has dramatically increased in recent years and now includes a significant proportion of the world's children, adolescents and adults. Obesity is linked to a number of co-morbidities, the most prominent being type 2 diabetes mellitus. While many agents are available to treat these conditions, the current knowledge regarding their disposition in the obese remains limited. Over the years, both direct and indirect methodologies have been utilized to assess body composition. Commonly used direct measures include underwater weighing, skinfold measurement, bioelectrical impedance analysis and dual-energy x-ray absorptiometry. Unfortunately, these methods are not readily available to the majority of clinicians. As a result, a number of indirect measures to assess body composition have been developed. Indirect measures rely on patient attributes such as height, bodyweight and sex. These size metrics are often utilized clinically and include body mass index (BMI), body surface area (BSA), ideal bodyweight (IBW), percent IBW, adjusted bodyweight, lean bodyweight (LBW) and predicted normal weight (PNWT). An understanding of how the volume of distribution (V(d)) of a drug changes in the obese is critical, as this parameter determines loading-dose selection. The V(d) of a drug is dependent upon its physiochemical properties, the degree of plasma protein binding and tissue blood flow. Obesity does not appear to have an impact on drug binding to albumin; however, data regarding alpha(1)-acid glycoprotein binding have been contradictory. A reduction in tissue blood flow and alterations in cardiac structure and function have been noted in obese individuals. At the present time, a universal size descriptor to describe the V(d) of all drugs in obese and lean individuals does not exist. Drug clearance (CL) is the primary determinant to consider when designing a maintenance dose regimen. CL is largely controlled by hepatic and renal physiology. In the obese, increases in cytochrome P450 2E1 activity and phase II conjugation activity have been observed. The effects of obesity on renal tubular secretion, tubular reabsorption, and glomerular filtration have not been fully elucidated. As with the V(d), a single, well validated size metric to characterize drug CL in the obese does not currently exist. Therefore, clinicians should apply a weight-normalized maintenance dose, using a size descriptor that corrects for differences in absolute CL between obese and non-obese individuals. The elimination half-life (t((1/2))) of a drug depends on both the V(d) and CL. Since the V(d) and CL are biologically independent entities, changes in the t((1/2)) of a drug in obese individuals can reflect changes in the V(d), the CL, or both. This review also examines recent publications that investigated the disposition of several classes of drugs in the obese--antibacterials, anticoagulants, antidiabetics, anticancer agents and neuromuscular blockers. In conclusion, pharmacokinetic data in obese patients do not exist for the majority of drugs. In situations where such information is available, clinicians should design treatment regimens that account for any significant differences in the CL and V(d) in the obese.

Should dosing of rocuronium in obese patients be based on ideal or corrected body weight?

BACKGROUND

Pharmacokinetic studies in obese patients suggest that dosing of rocuronium should be based on ideal body weight (IBW). This may, however, result in a prolonged onset time or compromised conditions for tracheal intubation. In this study, we compared onset time, conditions for tracheal intubation, and duration of action in obese patients when the intubation dose of rocuronium was based on three different weight corrections.

METHODS

Fifty-one obese patients, with a median (range) body mass index of 44 (34-72) kg/m2, scheduled for laparoscopic gastric banding or gastric bypass under propofol-remifentanil anesthesia were randomized into three groups. The patients received rocuronium (0.6 mg/kg) based on IBW (IBW group, n = 17), IBW plus 20% of excess weight (corrected body weight [CBW]20% group, n = 17), or IBW plus 40% of excess weight (CBW40% group, n = 17). Propofol was administered as a bolus of 200 mg and an infusion at 5 mg x kg(-1) x h(-1) and remifentanil was administered at 1.0 microg x kg(-1) x min(-1), both according to CBW40%. Neuromuscular function was monitored with train-of-four nerve stimulation and acceleromyography. The primary end point was duration of action, defined as time to reappearance of the fourth twitch in train-of-four.

RESULTS

The median (range) duration of action was 32 (18-49), 38 (25-66), and 42 (24-66) min in the IBW, CBW20%, and CBW40% groups, respectively (P = 0.001 for comparison of the IBW and CBW40% group). There were no significant differences in onset time (85 vs 84 vs 80 s) or in intubation conditions 90 s after administration of rocuronium.

CONCLUSIONS

In obese patients undergoing gastric banding or gastric bypass, rocuronium dosed according to IBW provided a shorter duration of action without a significantly prolonged onset time or compromised conditions for tracheal intubation.

Update on best practice recommendations for anesthetic perioperative care and pain management in weight loss surgery, 2004-2007

To reevaluate and update evidence-based best practice recommendations published in 2004 for anesthetic perioperative care and pain management in weight loss surgery (WLS), we performed a systematic search of English-language literature on anesthetic perioperative care and pain management in WLS published between April 2004 and May 2007 in MEDLINE and the Cochrane Library. We identified relevant abstracts by using key words, retrieved full text articles, and stratified the resulting evidence according to systems used in established evidence-based models. We updated prior evidence-based best practice recommendations based upon interim literature. In instances of controversial or inadequate scientific evidence, the task force reached consensus recommendations following evaluation of the best available information and expert opinion. The search yielded 1,788 abstracts, with 162 potentially relevant titles; 45 were reviewed in detail. Despite more information on perioperative management of patients with obstructive sleep apnea (OSA), evidence to support preoperative testing and treatment or to guide perioperative monitoring is scarce. New evidence on appropriate intraoperative dosing of muscle relaxants allows for greater precision in their use during WLS. A novel application of alpha-2 agonists for perioperative anesthetic care is emerging. Key elements that may enhance patient safety include integration of the latest evidence on WLS, obesity, and collaborative multidisciplinary care into clinical care. However, large gaps remain in the evidence base.

[Evaluation of tracheal intubation conditions in morbidly obese patients: a comparison of succinylcholine and rocuronium]

OBJECTIVE

To compare tracheal intubation conditions in morbidly obese patients 60 seconds after administration of succinylcholine or rocuronium doses based on real weight or ideal weight.

METHOD

We evaluated patients with a body mass index (BMI) of 40 kg x m(-2) or more but no other indications of difficult-intubation risk. Induction was performed under fentanyl and propofol at doses calculated based on real weight. Patients were assigned to 1 of 4 groups for tracheal intubation. Group 1 received 1 mg of succinylcholine per kilogram of ideal weight, group 2 received 1 mg of succinylcholine per kilogram of real weight, group 3 received 0.6 mg of rocuronium per kilogram of ideal weight, and group 4 received 0.6 mg of rocuronium per kilogram of real weight. Tracheal intubation was performed 60 seconds later and intubation conditions were recorded using a clinical scoring system.

RESULTS

Eighty patients with a mean BMI of 47.5 kg x m(-2) were enrolled. The difficult intubation rate was 3.75%. All patients were intubated. Laryngoscopy conditions and position and movement of vocal cords were similar in all 4 groups. Reaction to cuff inflation revealed intergroup differences; group 3 presented slight limb movements, diaphragm movement, and sustained cough for more than 10 seconds.

CONCLUSION

These results suggest that administration of succinylcholine calculated based on real weight or ideal weight and rocuronium based on real weight can provide clinically acceptable conditions for tracheal intubation in morbidly obese patients with no other difficult-intubation criteria.

Obesity in critical care

PURPOSE OF REVIEW

To review literature germane to the care of critically ill obese patients with emphasis upon the pathophysiology of obesity and its impact on clinical management.

RECENT FINDINGS

Obesity continues to be a health epidemic of the industrialized world, and is associated with substantial morbidity and mortality. Chronic obesity results in derangements in cardiovascular, respiratory and metabolic function. Drug administration may be effected depending on the lipophilicity of the molecule administered. The ability to gain vascular access is often impaired because of large body habitus and should be aided with ultrasound guidance. The fidelity of blood pressure monitoring can also be adversely affected, necessitating the use of direct intraarterial monitoring.

SUMMARY

Obesity has pathophysiologic effects upon all major organ systems. A thorough knowledge of these effects and specific intensive care unit-related issues are necessary for clinicians to anticipate common complications and provide timely and effective treatment for the obese intensive care unit patient.

Perioperative considerations for patients with morbid obesity

The anesthetic management of the MO patient requires an important focus on a number of issues beginning with a careful preoperative evaluation and synthesizing pre-existing disease processes with the anesthetic management plan. The common misperception that all MO patients are "full stomach" has been challenged and may be a nonissue. New approaches to pre-oxygenation to lessen the likelihood of desaturation during apnea may be a valuable tool if difficulty is encountered in tracheal intubation. In addition, promising results have been demonstrated with the use of the ILMA for ventilation and for blindly establishing tracheal tube placement. Proper patient positioning is essential to aid in successful intubation when a laryngoscope is employed. Intraoperative anesthetic management can be guided with a processed electroencephalogram monitor to help improve emergence and to enhance wakefulness in the PACU. Careful consideration must be given to postoperative analgesic needs by minimizing the use of opioids and employing nonopioid analgesics including NSAIDs, alpha2-adrenergic agonists, and low doses of ketamine.

Neostigmine-induced reversal of vecuronium in normal weight, overweight and obese female patients

BACKGROUND

The purpose of this study was to compare neostigmine-induced reversal of vecuronium in normal weight, overweight and obese female patients.

METHODS

In total, 15 each of normal weight (18.5<or=BMI<25), overweight (25<or=BMI<30) and obese (BMI>or=30) patients were enrolled. Anaesthesia was induced and maintained with fentanyl, propofol and nitrous oxide. Neuromuscular block was induced with vecuronium 0.1 mg kg(-1) on the basis of the patient's real body weight (RBW) and was monitored using acceleromyographic train-of-four (TOF) of the adductor pollicis. All patients received neostigmine 0.04 mg kg(-1) combined with atropine 0.02 mg kg(-1) at 25% recovery of the first twitch (T1) of TOF and were allowed to recover to a TOF ratio of 0.9.

RESULTS

The time from administration of vecuronium to spontaneous recovery of T1 to 25% of control was significantly longer in the obese [mean (SD, range); 68.4 (16.3, 39.8-110.8) min] and the overweight groups [49.3 (6.2, 39.8-60.8) min] as compared with the normal weight group [41.0 (9.0, 27.5-59.5) min]. The times for facilitated recovery with neostigmine to a TOF ratio of 0.7 did not differ among groups. However, the recovery to a TOF ratio of 0.9 in the obese [25.9 (6.7, 13.5-41.0) min] and the overweight groups [14.6 (7.7, 3.3-28.5) min] were significantly longer than that in the normal weight group [6.9 (2.0, 3.0-10.7) min].

CONCLUSIONS

Early reversal after neostigmine is prompt; however, recovery to a TOF ratio of 0.9 is slow in overweight and obese patients when vecuronium is dosed on the basis of the patient's RBW.

Anesthesia for Pediatric Obesity

This article discusses the unique anesthetic implications of obesity, with an emphasis on children and adolescents. It also touches on the issues surrounding bariatric surgery in the morbidly obese adolescent population. Adolescent bariatric surgery is moving to the forefront as a treatment modality because weight-loss programs alone are not keeping pace with the growth of the problem. Bariatric surgery offers the potential to achieve the weight reductions necessary to reverse the debilitating and costly comorbidities of obesity.

Bariatric Programs in Nursing Homes

The increase in prevalence of obesity in older individuals and the association of obesity with increased morbidity, functional decline, hospitalization, and complications is expected to increase the number of individuals who have obesity requiring nursing home care, particularly subacute and short-term rehabilitation. Providing appropriate nursing home care to residents who have obesity requires environmental modifications, specialized equipment, and staff training. Effective nursing home care of residents who have obesity is interdisciplinary and requires special nursing, medical, nutritional, psychosocial, and rehabilitation considerations.

Anesthetic Management of Patients with Obesity and Sleep Apnea

An increasing number of obese patients in the operating room is inevitable due to the well-known associated chronic health problems such as cardiovascular disease, diabetes mellitus, arthritis and cancer. Further, bariatric surgery is also likely to be increasingly performed. This article discusses the intraoperative issues in the care of patients with obesity, including airway management, pharmacokinetics, perioperative positioning, regional anesthesia, the intensity of monitoring required, laparoscopy, and minimizing hypoxia during anesthesia.

Best practice recommendations for anesthetic perioperative care and pain management in weight loss surgery

OBJECTIVE

To develop evidence-based recommendations that optimize the safety and efficacy of perioperative anesthetic care and pain management in weight loss surgery (WLS) patients.

RESEARCH METHODS AND PROCEDURES

This Task Group examined the scientific literature on anesthetic perioperative care and pain management published in MEDLINE from January 1994 to March 2004. We also reviewed additional data from other sources (e.g., book chapters). The search yielded 195 abstracts, of which 35 references were reviewed in detail. Task Group consensus was used to provide recommendations when evidence in the literature was insufficient.

RESULTS

We developed anesthesia practice and patient safety advisory recommendations for preoperative evaluation, intraoperative management, and postoperative care and pain management of WLS patients. We also provided suggestions related to medical error reduction and systems improvements, credentialing, and future research.

DISCUSSION

Obesity-related comorbidities including obstructive sleep apnea place WLS patients at increased risk for complications perioperatively. Regarding perioperative safety and outcomes, conclusive evidence beyond the accepted standard of care in the reviewed literature is limited. Few reports specifically address the perioperative needs of severely obese patients. In this advisory, we synthesize current knowledge and make best practice recommendations for perioperative care and pain management in WLS patients. These recommendations require periodic review as further medical knowledge and evidence evolve.

The Effects of Cisatracurium on Morbidly Obese Women

There is conflicting evidence on the duration of action of atracurium in obese patients. Cisatracurium is one of the stereoisomers of atracurium. We investigated the neuromuscular effects of cisatracurium in morbidly obese patients. Twenty obese female patients (body mass index >40) were randomized in two groups. Group I (n = 10) received 0.2 mg/kg of cisatracurium on the basis of real body weight (RBW), whereas in Group II (n = 10) the dose was calculated on ideal body weight (IBW). In a control group of 10 normal weight female patients (body mass index 20-24), the dose of cisatracurium was based on RBW. Neuromuscular transmission was monitored using acceleromyography of the adductor pollicis, and anesthesia was induced and maintained with remifentanil and propofol. Onset time was comparable between Group I and the control group (132 s versus 135 s; P = ns). The duration 25% was longer in Group I than in the control group (74.6 min versus 59.1 min; P = 0.01) and in the control group compared with Group II (45.0 min; P = 0.016). In conclusion, the duration of action of cisatracurium was prolonged in morbidly obese patients when dosed according to RBW compared with a control group of normal weight patients. Duration was also prolonged in the control group patients compared with morbidly obese patients to whom the drug was administered on the basis of IBW.