Obesity: its relation to anaesthesia

Comparative Analysis of the Usefulness of the GlideScope®, Macintosh, and McCoy Laryngoscopes for Endotracheal Intubation in Patients with Obesity: A Randomized, Clinical Trial

Background

Difficult intubation is dangerous and sometimes fatal, especially in patients with obesity. In difficult intubation cases the best device should be applied to decrease the risk of complications. The current study aimed at comparing laryngoscopes, Macintosh, McCoy, GlideScope^® and devices for intubation purposes.

Methods

A total of 102 patients with obesity and ASA (American society of anesthesiologists) class I or II, and body mass index (BMI) of > 30 kg/m² were selected. After obtaining the informed consent, the patients were divided into 3 groups based on the 3 laryngoscope types. Preoperative airway assessment including the Mallampati score, thyromental distance (TMD), and neck circumference was performed and all the patients were anesthetized based on the same protocol. Subsequently, all of the patients were intubated using a Macintosh, McCoy, or GlideScope^® laryngoscope. Laryngoscopy time, Cormack-Lehane score (1 - 4), and the percentage of glottic opening (POGO; 1 - 100) were evaluated. Data were analyzed using SPSS version 16, and results were considered statistically significant at P ≤ 0.05.

Results

There was no significant difference between demographic characteristics and preoperative airway evaluations. The shortest and longest laryngoscopy time were obtained in the GlideScope^® and McCoy laryngoscope groups, respectively (P = 0.001). The highest Cormack-Lehane score was obtained using the GlideScope^® method (P = 0.04). The POGO was higher and, therefore, more appropriate in the McCoy laryngoscope group (P = 0.009). A direct relationship was observed between neck circumference (P = 0.008), BMI (P = 0.023), Mallampati score (P = 0.000), and laryngoscopy.

Conclusions

In the current study, the shortest and longest intubation time in patients with obesity was observed in the GlideScope^® and the McCoy laryngoscope groups, respectively. Moreover, the direct relationships of BMI and neck circumference with laryngoscopy time were observed in all 3 groups. These results suggested using GlideScope^® in patients with high BMI to reduce laryngoscopy time.

Anesthetic Considerations in Patients Undergoing Bariatric Surgery: A Review Article

Context

This article discusses the anesthetic considerations in patients undergoing bariatric surgery in the preoperative, intraoperative, and postoperative phases of surgery.

Evidence Acquisition

This review includes studies involving obese patients undergoing bariatric surgery. Searches have been conducted in PubMed, MEDLINE, EMBASE, Google Scholar, Scopus, and Cochrane Database of Systematic Review using the terms obese, obesity, bariatric, anesthesia, perioperative, preoperative, perioperative, postoperative, and their combinations.

Results

Obesity is a major worldwide health problem associated with many comorbidities. Bariatric surgery has been proposed as the best alternative treatment for extreme obese patients when all other therapeutic options have failed.

Conclusions

Anesthetists must completely assess the patients before the surgery to identify anesthesia- related potential risk factors and prepare for management during the surgery.

Effect of body mass index in acute respiratory distress syndrome

BACKGROUND

Obesity is associated in healthy subjects with a great reduction in functional residual capacity and with a stiffening of lung and chest wall elastance, which promote alveolar collapse and hypoxaemia. Likewise, obese patients with acute respiratory distress syndrome (ARDS) could present greater derangements of respiratory mechanics than patients of normal weight.

METHODS

One hundred and one ARDS patients were enrolled. Partitioned respiratory mechanics and gas exchange were measured at 5 and 15 cm H2O of PEEP with a tidal volume of 6-8 ml kg(-1) of predicted body weight. At 5 and 45 cm H2O of PEEP, two lung computed tomography scans were performed.

RESULTS

Patients were divided as follows according to BMI: normal weight (BMI≤25 kg m(-2)), overweight (BMI between 25 and 30 kg m(-2)), and obese (BMI>30 kg m(-2)). Obese, overweight, and normal-weight groups presented a similar lung elastance (median [interquartile range], respectively: 17.7 [14.2-24.8], 20.9 [16.1-30.2], and 20.5 [15.2-23.6] cm H2O litre(-1) at 5 cm H2O of PEEP and 19.3 [15.5-26.3], 21.1 [17.4-29.2], and 17.1 [13.4-20.4] cm H2O litre(-1) at 15 cm H2O of PEEP) and chest elastance (respectively: 4.9 [3.1-8.8], 5.9 [3.8-8.7], and 7.8 [3.9-9.8] cm H2O litre(-1) at 5 cm H2O of PEEP and 6.5 [4.5-9.6], 6.6 [4.2-9.2], and 4.9 [2.4-7.6] cm H2O litre(-1) at 15 cm H2O of PEEP). Lung recruitability was not affected by the body weight (15.6 [6.3-23.4], 15.7 [9.8-22.2], and 11.3 [6.2-15.6]% for normal-weight, overweight, and obese groups, respectively). Lung gas volume was significantly lower whereas total superimposed pressure was significantly higher in the obese compared with the normal-weight group (1148 [680-1815] vs 827 [686-1213] ml and 17.4 [15.8-19.3] vs 19.3 [18.6-21.7] cm H2O, respectively).

CONCLUSIONS

Obese ARDS patients do not present higher chest wall elastance and lung recruitability.

Effect of bispectral index monitoring on desflurane consumption and recovery time in morbidly obese patients undergoing laparoscopic sleeve gastrectomy

BACKGROUND

Morbid obesity magnifies the importance of the fat-blood solubility coefficient of the anesthetic in its relation to emergence and recovery. Using bispectral index (BIS) monitoring for the titration of the administration of inhaled anesthetics such as desflurane may permit a less consumption and more rapid recovery from desflurane anesthesia in morbidly obese patients, which enables earlier maintenance of a patent airway, better protection against aspiration, and better oxygenation.

OBJECTIVE

The aim of this study was to investigate the effect of BIS monitoring on postoperative extubation and recovery times, and intraoperative desflurane consumption in morbidly obese patients undergoing laparoscopic sleeve gastrectomy under general anesthesia using desflurane for maintenance.

PATIENTS AND METHODS

Forty morbidly obese patients were randomly enrolled in this study and divided into two groups of 20 patients each: Non-BIS group and BIS group. End-tidal desflurane concentration, mean blood pressure, and heart rate were regularly recorded. Recovery times (eye opening to verbal commands, time to extubation, and orientation to time, place, and person) and the time to achieve a modified Aldrete score of ≥ 9 were recorded by blinded study anesthesia nurse. Desflurane consumption was calculated in milliliters through gas usage option of Datex-Ohmeda S/5 anesthesia machine.

RESULTS

The mean end-tidal concentrations of desflurane were significantly decreased in the BIS group compared to the non-BIS group (P < 0.05). The mean desflurane consumption and cost were significantly lower in the BIS group (124.8 ± 5.1 ml/patient) compared to the non-BIS group (150.6 ± 6.5 ml/patient) (P < 0.05). Recovery times were significantly shorter in the BIS group versus non-BIS group (P < 0.05).

CONCLUSION

The use of BIS monitoring was effective in reducing intraoperative desflurane requirement (cost) and in shortening early recovery times after laparoscopic sleeve gastrectomy in morbidly obese patients without compromising the hemodynamic stability, adequacy of anesthesia, or patient outcome.

Morbidly obese parturient: Challenges for the anaesthesiologist, including managing the difficult airway in obstetrics. What is new?

The purpose of this article is to review the fundamental aspects of obesity, pregnancy and a combination of both. The scientific aim is to understand the physiological changes, pathological clinical presentations and application of technical skills and pharmacological knowledge on this unique clinical condition. The goal of this presentation is to define the difficult airway, highlight the main reasons for difficult or failed intubation and propose a practical approach to management Throughout the review, an important component is the necessity for team work between the anaesthesiologist and the obstetrician. Certain protocols are recommended to meet the anaesthetic challenges and finally concluding with “what is new?” in obstetric anaesthesia.

Difficult airway management and the novice physician

Background:

Selection of the ideal airway device in patients with difficult airways (DA) or potentially difficult airways remains controversial, especially, for a novice anesthesia physician (NP) who must deviate from conventional direct laryngoscopy with a rigid laryngoscope following a failed intubation and employ one of the several alternative devices. The author determines and compares tracheal intubation success rates, times to success and complications of a novice physician using four alternative airway devices in 20 obese (BMI more than 27.5) patients who may be more difficult to intubate than normal weight patients.

Materials and Methods:

In this prospective randomized experimental study the author investigates a novice physician's use of the Bullard™, Fiberoptic™, Fastrach™ and Trachlight™ comparing reliability, rapidity and safety of orotracheal intubations. Following induction of anesthesia the NP was allowed up to a maximum of two attempts per device at oral intubation. Mean intubation times plus/minus SD, per cent success rates and postoperative complications were evaluated for each device.

Results:

The Fastrach™ was successful 100% of the time on the first attempt requiring a mean time of 55 seconds plus/minus 6.6. All intubations were unsuccessful following two attempts with the Fiberoptic™. A success rate of 20% (one of five) was achieved with the Trachlight™ on first attempt after 95 seconds. The Bullard™ was successful in 40 % (two of five) of the patients after a mean time 60 seconds plus/minus five, but was the only device to result in mild oral discomfort one day post operatively.

Conclusions:

In the hands of a novice physician managing a difficult or potentially difficult airway, often encountered in obese patients, the Fastrach™ demonstrated the highest success rate.

Disrupted sleep and delayed recovery from chronic peripheral neuropathy are distinct phenotypes in a rat model of metabolic syndrome

BACKGROUND

Sleep apnea, hypertension, atherosclerosis, and obesity are features of metabolic syndrome associated with decreased restorative sleep and increased pain. These traits are relevant for anesthesiology because they confer increased risks of a negative anesthetic outcome. This study tested the one-tailed hypothesis that rats bred for low intrinsic aerobic capacity have enhanced nociception and disordered sleep.

METHODS

Rats were developed from a breeding strategy that selected for low aerobic capacity runners (LCR) and high aerobic capacity runners (HCR). Four phenotypes were quantified. Rats underwent von Frey sensory testing (n = 12), thermal nociceptive testing (n = 12), electrographic recordings of sleep and wakefulness (n = 16), and thermal nociceptive testing (n = 14) before and for 6 weeks after a unilateral chronic neuropathy of the sciatic nerve.

RESULTS

Paw withdrawal latency to a thermal nociceptive stimulus was significantly (P < 0.01) lower in LCR than HCR rats. There were also significant differences in sleep, with LCR rats spending significantly (P < 0.01) more time awake (18%) and less time in nonrapid eye movement sleep (-19%) than HCR rats. Nonrapid eye movement sleep episodes were of shorter duration (-34%) in LCR than HCR rats. Rapid eye movement sleep of LCR rats was significantly more fragmented than rapid eye movement sleep of HCR rats. LCR rats required 2 weeks longer than HCR rats to recover from peripheral neuropathy.

CONCLUSIONS

Rodents with low aerobic capacity exhibit features homologous to human metabolic syndrome. This rodent model offers a novel tool for characterizing the mechanisms through which low aerobic function and obesity might confer increased risks for anesthesia.

Local anesthetic hernia repair in overweight and obese patients

BACKGROUND

Inguinal hernia repair under local anesthesia (LA) has many advantages and is associated with high patient satisfaction. However, there are concerns of exceeding the maximum safe dose of LA agents in overweight and obese patients. The aim of the present study was to establish whether inguinal hernia repair could be safely performed under LA in overweight and obese patients.

METHODS

Patients who underwent elective LA hernia repair under a single consultant surgeon were studied retrospectively. Each patient received the same LA mixture developed at our hospital specifically for hernia repair. The mixture includes lignocaine and bupivocaine, both with adrenaline, made up to a volume of 100 ml with saline. Data were collected by case note review, and by postal and telephone surveys.

RESULTS

A total of 125 patients who underwent LA hernia repair, in whom body mass index (BMI) was measured, were studied. Based on the World Health Organization (WHO) classification, there were 35 (28%) normal weight patients and 63 (72%) overweight (BMI>or=25<30) or obese (BMI>or=30) patients. The median BMI was 27 (range 19-38). The mean volumes of LA mixture used for each group were 58 ml and 62 ml, respectively. High day case rates of 91% and 84% were obtained for the two groups, respectively. Complications included three wound hematomas and three simple wound infections, with no significant differences between groups. One patient developed a recurrent hernia (<1%).

CONCLUSIONS

Local anesthetic inguinal hernia repair in the obese is safe and well tolerated. Use of a large volume local anesthetic mixture is recommended in overweight and obese patients.

Choice of volatile anesthetic for the morbidly obese patient: sevoflurane or desflurane

STUDY OBJECTIVE

Morbid obesity is associated with significant comorbidities. Desflurane has a low fat-blood solubility coefficient and may be better suited in this population to achieve a rapid emergence; however, sevoflurane has favorable cardiorespiratory properties that might also prove advantageous in the morbidly obese (MO) patient. This study used careful drug titration to determine if emergence differences between sevoflurane and desflurane could be minimized in MO patients.

DESIGN

A randomized, prospective blinded study to determine the emergence profiles of desflurane and sevoflurane in MO patients when anesthetic drug titration is used.

SETTING

Operating room of the VA Medical Center, Milwaukee, Wis.

PATIENTS

Forty American Society of Anesthesiologists II and III, MO patients (body mass index > or = 35 kg/m2), who were scheduled for elective surgery predicted to last for more than 2 hours, were studied.

INTERVENTIONS

Patients were induced with fentanyl, midazolam, and propofol and maintained with desflurane or sevoflurane, mixed in air and oxygen. Intraoperative bispectral index (BIS) was targeted to 45 to 50 and to 60 in the last 15 minutes of surgery.

MEASUREMENTS

Intraoperative anesthetic concentration, BIS, and hemodynamics were recorded. During emergence, time to follow command and extubation were noted, with assessments of cognitive function via the Mini-Mental Status Test and psychomotor performance via the Digit Symbol Substitution Test. A blinded observer recorded key recovery events.

MAIN RESULTS

Demographic data (age, 61 [36-83] years; body mass index, 38 [35-47] kg/m2), surgical procedures, length of anesthesia (approximately 3.5 hours), adjuvant drugs, and intraoperative BIS, heart rate, and mean arterial pressure were not significantly different. Hemodynamics, time to follow commands and to extubation, and results of Digit Symbol Substitution Test and Mini-Mental Status Test did not differ between anesthetic groups during recovery.

CONCLUSIONS

There were no differences in emergence and recovery profiles in MO patients receiving desflurane or sevoflurane when anesthetic concentration was carefully titrated.

Airway management after failure to intubate by direct laryngoscopy: outcomes in a large teaching hospital

PURPOSE

The purpose of this single-centre database review was to establish the incidence of failure to intubate by direct laryngoscopy, to measure morbidity and mortality associated with this event, and to examine the use and efficacy of alternative airway devices.

METHODS

Difficult intubation via direct laryngoscopy at Mayo Clinic Rochester is recorded in an electronic database using a functional classification: 0 = no difficulty; 1 = mild to moderate difficulty; and 2 = severe difficulty often requiring a change in intubation technique. Using this database, the total number of intubations was determined for a selected review period and the incidence of failure to intubate by direct laryngoscopy was established. Abstraction of chart data allowed for determination of associated morbidity and mortality, success of alternative airway devices, and case cancellation rate.

RESULTS

During the period from August 1, 2001 through December 31, 2002, 37,482 patients underwent general anesthesia with attempted direct laryngoscopy. One hundred sixty-one patients (0.43%) could not be intubated by direct laryngoscopy alone. Morbidity associated with difficult intubation included soft tissue/dental damage (n = 8), intraoperative cardiac arrest (n = 1), and possible aspiration (n = 1). Three patients required intensive care unit admission. There was no associated mortality. The most commonly used alternative airway device was the flexible fibreoptic scope. Five case cancellations resulted from failure to intubate with alternative devices.

CONCLUSION

The rate of unexpected failure to intubate by direct laryngoscopy is essentially unchanged from earlier studies. While morbidity was low, continued education and early use of alternative difficult airway devices may further limit complications associated with this event.

The lateral recumbent head-down position decreases the incidence of epidural venous puncture during catheter insertion in obese parturients

PURPOSE

The unintentional and unrecognized cannulation of an extradural vein is a potentially serious complication of an epidural anesthetic. The present study was undertaken to assess the incidence of blood vessel puncture related to epidural catheterization in three different body positions, in a cohort of morbidly obese parturients, following the completion of a similar study published in 2001 from which such parturients were excluded.

METHODS

The study was conducted in 450 (three groups of 150) morbidly obese, obstetric patients undergoing continuous epidural analgesia during labour. Epidural catheterization was performed on patients randomized to the sitting, lateral recumbent horizontal, or lateral recumbent head-down position.

RESULTS

There was a lower incidence of vessel cannulation when this procedure was performed in the lateral recumbent head-down position [1.3%; body mass index (BMI): 37.0] than in the lateral recumbent horizontal [12.9%; BMI: 38.0] and in the sitting position [12.0%; BMI: 38.0]. The incidence of accidental subarachnoid puncture was 2%, 1.3% and 2% respectively, in these same positions.

CONCLUSION

Adoption of the lateral recumbent head-down position for the performance of lumbar epidural blockade, in labour at term, reduces the incidence of lumbar epidural venous puncture in these obese parturients.

Childhood obesity: a challenge for the anaesthetist?

The definition of childhood obesity has not been standardized in the past, making studies difficult to compare. In spite of this, the increase in the incidence of childhood obesity is evident and has now reached epidemic proportions. Obese children experience few of the medical complications seen in obese adults. Respiratory physiology appears to be most affected, the degree of which is determined by the level of obesity. Although there is a considerable amount of information on the anaesthetic management of the obese adult, very little has been written concerning the obese child. There is less pathology in the obese child when compared with the adult but some evidence shows a higher likelihood of a critical incident occurring when anaesthetizing such children. This shows that we need to be as worried about anaesthetizing the obese child as we are for the obese adult. This concern should increase with increasing body mass index.

Morbid obesity and tracheal intubation

The tracheas of obese patients may be more difficult to intubate than those of normal-weight patients. We studied 100 morbidly obese patients (body mass index >40 kg/m(2)) to identify which factors complicate direct laryngoscopy and tracheal intubation. Preoperative measurements (height, weight, neck circumference, width of mouth opening, sternomental distance, and thyromental distance) and Mallampati score were recorded. The view during direct laryngoscopy was graded, and the number of attempts at tracheal intubation was recorded. Neither absolute obesity nor body mass index was associated with intubation difficulties. Large neck circumference and high Mallampati score were the only predictors of potential intubation problems. Because in all but one patient the trachea was intubated successfully by direct laryngoscopy, the neck circumference that requires an intervention such as fiberoptic bronchoscopy to establish an airway remains unknown. We conclude that obesity alone is not predictive of tracheal intubation difficulties.

IMPLICATIONS

In 100 morbidly obese patients, neither obesity nor body mass index predicted problems with tracheal intubation. However, a high Mallampati score (greater-than-or-equal to 3) and large neck circumference may increase the potential for difficult laryngoscopy and intubation.

Managing obesity in patients with comorbidities

Type 2 diabetes, cardiovascular disease, and hypertension are comorbities associated with obesity. Treatment and prevention strategies for these comorbidities of obesity are often assumed to be the same-weight loss. Although many persons may lose weight initially, recidivism is a major concern. Therefore, medical nutrition therapy for obese persons with comorbidities should be refocused from weight loss to attaining and maintaining metabolic parameters--normal blood glucose levels, optimal lipid levels, and blood pressure levels within normal limits. Moderate weight loss is only one lifestyle strategy that can be recommended. Research has also supported other lifestyle strategies, including becoming more physically fit. In type 2 diabetes, a restricted energy diet even without weight loss, spacing of meals throughout the day, and fat intake modifications have been shown to improve glycemia. Dyslipidemia can be improved by reducing or changing the fat content of the diet. Blood pressure levels can be reduced by a diet high in fruits and vegetables and low in fat. Research is underway to determine if weight loss can prevent chronic disease; however, once comorbidities are present, lifestyle strategies should be directed toward the improvement of metabolic parameters associated with the comorbidity.

Caring for patients with morbid obesity in hospital

Caring for the patient with morbid obesity may require adaptation of routine nursing care; however, as with all patients, care should be tailored to individual needs. This article aims to highlight the specific needs of patients with morbid obesity and discusses ways of addressing these needs. The activities of living model is commonly used to assess, plan, implement and evaluate nursing care. This model, used to identify the potential needs of a patient with obesity, will provide the framework for the article. Documentation of procedures used for patient care, e.g. lifting and bathing, must be made in the patient's care plan enabling other nurses caring for the patient to identify quickly the most appropriate and safe way to care for the patient.

Effects of PEEP on respiratory mechanics are tidal volume and frequency dependent

How the effects of frequency, tidal volume (VT) and PEEP interact to determine the mechanical properties of the respiratory system is unclear. Airway flow and airway and esophageal pressures were measured in ten intubated, anesthetized/paralyzed patients during mechanical ventilation at 10-30 breaths/min and VT of 250-800 ml. From these measurements, Fourier transformation was used to calculate elastance (E) and resistance (R) of the total respiratory system (subscript rs), lungs (subscript L) and chest wall (subscript cw) at 5, 10 and 0 cm PEEP. As PEEP increased from 0-5 cmH2O, all elastances and resistances decreased (P < 0.05). Increasing PEEP to 10 cmH2O decreased EL, Rrs, and RL further (P < 0.05). The changes in Ers, EL, Rrs and RL caused by PEEP were less (P < 0.05) as VT increased, while changes in Rrs, RL and Ers were less (P < 0.05) as frequency increased. VT dependences in Ers and Rrs were enhanced (P < 0.05) at 0 cmH2O PEEP. The ratio of EL to chest wall elastance was not affected by PEEP (P > 0.05), but increased (P < 0.05) with increasing VT at 5 and 10 cmH2O PEEP. We conclude that it is critical to standardize ventilatory parameters when comparing groups of patients or testing clinical intervention efficacy and that the differential effects on the lungs and chest wall must be considered in optimizing the application of PEEP.

Prone positioning improves pulmonary function in obese patients during general anesthesia

We investigated the effects of prone position on functional residual capacity (FRC), the mechanical properties (compliance and resistance) of the total respiratory system, lung and chest wall, and the gas exchange in 10 anesthetized and paralyzed obese (body mass index more than 30 kg/m2) patients, undergoing elective surgery. We used the esophageal balloon technique together with rapid airway occlusions during constant inspiratory flow to partition the mechanics of the respiratory system into its pulmonary and chest wall components. FRC was measured by the helium dilution technique. Measurements were taken in the supine position and after 15-30 min of prone position maintaining the same respiratory pattern (tidal volume 12 mL/kg ideal body weight, respiratory rate 14 breaths/ min, fraction of inspired oxygen [FIO2]0.4). We found that FRC and lung compliance significantly (P < 0.01) increased from the supine to prone position (0.894 +/- 0.327 L vs 1.980 +/- 0.856 L and 91.4 +/- 55.2 mL/cm H2O vs 109.6 +/- 52.4 mL/cm H2O, respectively). On the contrary, the prone position reduced chest wall compliance (199.5 +/- 58.7 mL/cm H2O vs 160.5 +/- 45.4 mL/cm H2O, P < 0.01), thus total respiratory system compliance did not change. Resistance of the total respiratory system, lung, and chest wall were not modified on turning the patients prone. The increase in FRC and lung compliance was paralleled by a significant (P < 0.01) improvement of PaO2 from supine to prone position (130 +/- 31 vs 181 +/- 28 mm Hg, P < 0.01), while PaCO2 was unchanged. We conclude that, in anesthetized and paralyzed obese subjects, the prone position improves pulmonary function, increasing FRC, lung compliance, and oxygenation.

Total respiratory system, lung, and chest wall mechanics in sedated-paralyzed postoperative morbidly obese patients

OBJECTIVE

To study the relative contribution of the lung and the chest wall on the total respiratory system mechanics, gas exchange, and work of breathing in sedated-paralyzed normal subjects and morbidly obese patients, in the postoperative period.

SETTING

Policlinico Hospital, University of Milan, Italy.

METHODS

In ten normal subjects (normal) and ten morbidly obese patients (obese), we partitioned the total respiratory mechanics (rs) into its lung (L) and chest wall (w) components using the esophageal balloon technique together with airway occlusion technique, during constant flow inflation. We measured, after abdominal surgery, static respiratory system compliance (Cst,rs), lung compliance (Cst,L), chest wall compliance (Cst,w), total lung (Rmax,L) and chest wall (Rmax,w) resistance. Rmax,L includes airway (Rmin,L) and "additional" lung resistance (DR,L). DR,L represents the component due to viscoelastic phenomena of the lung tissue and time constant inequalities (pendelluft). Functional residual capacity (FRC) was measured by helium dilution technique.

RESULTS

We found that morbidly obese patients compared with normal subjects are characterized by the following: (1) reduced Cst,rs (p < 0.01), due to lower Cst,L (55.3 +/- 15.3 mL x cm H2O-1 vs 106.6 +/- 31.7 mL x cm H2O-1; p < 0.01) and Cst,w (112.4 +/- 47.4 mL x cm H2O-1 vs 190.7 +/- 45.1 mL x cm H2O-1; p < 0.01); (2) increased Rmin,L (4.7 +/- 3.1 mL x cm H2O x L-1 x s; vs 1.0 +/- 0.8 mL x cm H2O x L-1 x s; p < 0.01) and DR,L (4.9 +/- 2.6 mL x cm H2O x L-1 x s; vs 1.5 +/- 0.8 mL x cm H2O x L-1 x s; p < 0.01); (3) reduced FRC (0.665 +/- 0.191 L vs 1.691 +/- 0.325 L; p < 0.01); (4) increased work performed to inflate both the lung (0.91 +/- 0.25 J/L vs 0.34 +/- 0.08 J/L; p < 0.01) and the chest wall (0.39 +/- 0.13 J/L vs 0.18 +/- 0.04 J/L; p < 0.01); and (5) a reduced pulmonary oxygenation index (PaO2/PAO2 ratio).

CONCLUSION

Sedated-paralyzed morbidly obese patients, compared with normal subjects, are characterized by marked derangements in lung and chest wall mechanics and reduced lung volume after abdominal surgery. These alterations may account for impaired arterial oxygenation in the postoperative period.

The laryngeal mask airway: its features, effects and role

The laryngeal mask airway was designed as a new concept in airway management and has been gaining a firm position in anaesthetic practice. Numerous articles and letters about the device have been published in the last decade, but few large controlled trials have been performed. Despite widespread use, the definitive role of the laryngeal mask has yet to be established. In some situations, such as after failed tracheal intubation or in anaesthesia for patients undergoing laparoscopic or oral surgery, its use is controversial. There are a number of unresolved issues, for example the effect of the laryngeal mask on regurgitation and whether or not cricoid pressure prevents placement of the mask. We review the techniques of insertion, details of misplacement, and complications associated with the use of the laryngeal mask. We discuss the features and physiological effects of the device, including the changes in intra-cuff pressure during anaesthesia and effects on blood pressure, heart rate and intra-ocular pressure. We then attempt to clarify the role of the laryngeal mask in airway management during anaesthesia, based on the current knowledge, by discussing the advantages and disadvantages as well as the indications and contraindications of its use. Lastly we describe the use of the laryngeal mask in circumstances other than airway maintenance during anaesthesia: fibreoptic bronchoscopy, tracheal intubation through the mask and its use in cardiopulmonary resuscitation.

Continuous spinal anaesthesia for caesarean section in the morbidly obese

The use of a continuous spinal anaesthetic technique for the caesarean delivery of three morbidly obese patients is described and the advantages discussed.

Obesity as a predictor of severity in acute pancreatitis

In order to determine whether the presence of obesity, defined as increased body mass index, would serve as a predictor of severity in acute pancreatitis, we have reviewed the medical records of 27 patients with severe acute pancreatitis. All patients had at least four positive Ranson's signs; all but three patients had at least five Ranson's signs. When the 13 patients with a fatal outcome were compared with the 14 who lived, neither obesity nor respiratory failure was an independent predictor of death. However, when the 27 patients were analyzed on the basis of whether they were obese (15 patients) or not obese (12 patients), obesity was an independent predictor of respiratory failure. Obesity was not a predictor of renal failure, pancreatic necrosis, or need for surgery. We suggest that obese patients with severe acute pancreatitis require close monitoring for the development of respiratory failure.

Acid aspiration prophylaxis in morbidly obese patients: famotidine vs. ranitidine

Famotidine and ranitidine were compared as agents for the prevention of acid aspiration syndrome in 32 morbidly obese patients undergoing vertical banded gastroplasty. Single-dose oral famotidine or double-dose oral ranitidine were administered on a random basis before surgery. Gastric contents were aspirated through a gastric tube, manually aided by the surgeon with the abdomen open. Mean (SD) gastric volumes were 13.8 ml (6.7) and 12.1 ml (13.0) for the famotidine and ranitidine groups, respectively. Mean (SD) gastric pH values were 6.2 (1.5) and 6.8 (1.5), respectively. There were no significant differences between the groups and no patient was considered 'at risk' (pH less than 2.5 and gastric volume greater than 25 ml). We conclude that single-dose oral famotidine and double-dose oral ranitidine are equally effective for preventing acid aspiration syndrome in morbidly obese patients.

Hospital anaesthesia and general practice

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Medical evaluation and treatment of the obese patient with cardiovascular disease

The incidence of coronary artery disease only weakly correlates with the percent of excess body weight; however, obesity in humans is not a homogeneous condition. Classification of obesity based on anatomic distribution of body fat allows for identification of a group of patients at increased risk for cardiovascular disease. Abdominal (upper body) obesity, measured as the waist/hip ratio, is a strong independent risk factor of cardiovascular disease and should be used to assess a subgroup in need of medical weight loss treatment. A focus on dietary fat intake and the magnitude of overeating "caloric intake" are central to the pathogenesis of cardiovascular disease observed in the obese person. Identification of the process of overeating (magnitude of recent weight gain, episodes of weight cycling) is important in the design of successful medical nutrition treatment programs. A nutrition/medical history that includes age of obesity onset and duration of obesity provides additional criteria for assessment of risk of disease. Childhood-onset obesity and prolonged obesity (greater than 15 years) has been associated with increased cardiovascular disease risk. Recently, grades of obesity based on body mass index have provided a valuable marker for treatment. Each reduction in obesity grade (equal to delta 5 body mass index or delta 11.6 kg) is associated with a decrease in risk of medical illness. The new focus of obesity treatment should be to decrease body weight in 10% to 15% increments (equal to 1 grade) with emphasis on reducing the risk of medical illness and treatment intensity (e.g., number of existing medical visits, hospitalization).(ABSTRACT TRUNCATED AT 250 WORDS)

The relation of body weight to length of stay and charges for hospital services for patients undergoing elective surgery: a study of two procedures

We studied the relation of body weight to lengths of stay and total charges for all patients hospitalized at the Brigham and Women's Hospital for total knee replacement and total hip replacement during a 12-month period. Patients with moderate obesity (actual body weight 141-170 per cent of ideal) had lengths of stay and total charges similar to normal weight patients (body weight 100-110 per cent ideal). However, patients who were extremely overweight (body weight greater than or equal to 188 per cent ideal) had mean lengths of stay 35 per cent longer (28.9 days vs 21.5) and total charges 30 per cent higher ($25,692 vs $19,576) than patients with normal weight. Those who were extremely underweight (body weight less than or equal to 75 per cent ideal) had mean lengths of stay 40 per cent longer (30.1 days vs 21.5) and total charges 35 per cent higher ($26,447 vs $19,576).

Unilateral pulmonary oedema/atelectasis in the lateral decubitus position

An obese male patient developed hypoxia, hyercarbia and radiological signs of pulmonary oedema/atelectasis in the dependent lung after surgery in the lateral decubitus position. This appears to have been due to ventilation-perfusion mismatch, although other factors were considered. The patient recovered following 36 hours of intermittent positive pressure ventilation of the lungs.

[Per- and post-operative gas exchange: isocapnic hyperventilation versus normoventilation]

The effects of isocapnic hyperventilation (A) and normoventilation (B) on PaCO2, PaO2 and A-aDO2 were compared in 102 patients undergoing elective surgery, randomized into two comparable groups A and B. Cases for thoracic, high abdominal and intracranial surgery were excluded, as well as patients with clinically evident pulmonary pathology. A volumetric ventilator was used in association with three different breathing systems (A: Bain system and circle system without CO2 absorption; B: circle system with CO2 absorption). The groups were comparable, except for percentage of overweight: 75% in group A and 56% in group B. Overweight was defined as weight above the mean ideal weight of 100%, and obesity as a weight above 120% the mean ideal weight. Blood gases were sampled 1) preoperatively, 2) 15 min and 3) 60 min after the beginning of mechanical ventilation, 4) postoperatively, 90 min after extubation, without supplemental oxygen. The preoperative mean PaO2 values were 79 +/- 11.4 mmHg (A) and 82.5 +/- 13.2 mmHg (B); the PaCO2 were 37.2 +/- 3.7 mmHg (A) and 37.2 +/- 3.8 mmHg (B). During surgery, PaO2 was distinctly higher (p less than 0.01) in group A than in group B (on average 15-20 mmHg higher), indicating the favourable effect of great tidal volumes on gas exchange. Correspondingly, the A-aDO2 was less increased in group A than in group B (p less than 0.01). At 15 min, 33% of the patients were hypocapnic (PaCO2 less than 35 mmHg): one case in group A and three in group B could be classed as severe hypocapnia (PaCO2 = 25-30 mmHg).(ABSTRACT TRUNCATED AT 250 WORDS)

Multidisciplinary treatment of obesity with a protein-sparing modified fast: results in 668 outpatients

Six hundred sixty-eight obese outpatients, 71 per cent (+/- 34) in excess of ideal weight, were enrolled in a multidisciplinary weight control program. The major components of the program included nutrition, education, behavior modification, and exercise. Rapid weight loss was accomplished using a very low calorie (less than 800 kcal) ketogenic diet. Patients adhered to the protein sparing modified fast (PSMF) for 17 +/- 12 weeks and averaged 9 +/- 17 weeks in a refeeding/maintenance program. Mean weight loss was 47 +/- 29 lb (21 +/- 13 kg) at the point of minimum weight and 41 +/- 29 lb (19 +/- 13 kg) at the end of the maintenance period. Systolic and diastolic blood pressure and serum triglycerides fell significantly in men and women. Success in weight loss was greatest in the heaviest patients, those who adhered the longest to the PSMF, and those who stayed the longest in the maintenance program.

Does obesity affect recovery? A study using intravenous methohexitone and Althesin for short procedures

One hundred and twenty unpremedicated patients, scheduled for minor gynaecological procedures, were randomly allocated to receive Althesin or methohexitone to supplement N2O and O2 anaesthesia. Patients were assessed as thin, medium or fat according to the degree of obesity as measured by skinfold calipers. The range of mean times for the patients to open their eyes was 3.1-4.0 minutes, to be orientated was 4.4-6.7 minutes and to perform a manipulative test was 27.7-32.1 minutes. No statistically significant differences were seen in these indices of recovery whether they received Althesin or methohexitone or whether they were thin, medium or fat. A paper and pencil test was also performed. Induction doses of the intravenous agent were calculated on a body weight basis and increments given only in response to movement. The mean total dose of Althesin was decreased from 1.33 mg total steroid/kg for thin patients to 1.06 mg total steroid/kg for fat patients (p less than 0.01). The mean total dose of methohexitone was decreased from 3.4 mg/kg for thin patients to 2.9 mg/kg for fat patients which was not significant.

Anaesthesia in the morbidly obese. A comparison of anaesthetic and analgesic regimens for upper abdominal surgery

Seventy morbidly obese patients presented for upper abdominal surgery; 17% had pre-existing cardiovascular disease and 23% pre-existing respiratory disease. Twenty-eight patients received general anaesthesia, plus narcotic analgesia postoperatively, and 42 general anaesthesia plus thoracic epidural analgesia intra- and postoperatively. Aspects of anaesthetic management are discussed and compared with previous similar reports. Doses of local anaesthetic for induction of epidural analgesia were less than those for the non-obese but doses of local anaesthetic for maintenance of epidural analgesia were similar to those in non-obese patients. Patients who had thoracic epidural analgesia required less volatile anaesthesia than the group who had general anaesthesia and narcotic analgesics. Postoperative respiratory complications were more common in patients with pre-existing cardiovascular and respiratory disease, and occurred less frequently in patients who had thoracic epidural analgesia.

Treatment of massive obesity by prolonged jaw immobilization for edentulous patients

Twenty massively obese patients who were edentulous in one or both jaws were treated by prolonged jaw immobilization. Dentures were secured under general anaesthesia to the edentulous jaws by various direct wiring methods and the jaws immobilized by interdental wires, where teeth were present, and intermaxillary wires. The wired-in dentures were generally well tolerated with minimal mucosal reaction but with a high incidence of infection around the attachment wires. Patients edentulous in one jaw alone, (11 maxilla, two mandible), managed well and 11 achieved a satisfactory weight loss. The seven patients edentulous in both jaws had considerable difficulty with pain and infection, three having the fixation appliances removed in the immediate post-operative period and only one achieved a satisfactory weight loss. Thus prolonged jaw immobilization is an effective means of treating massively obese patients if they are edentulous in one jaw alone but less so if they are completely edentulous.

Adiposity and the pharmacokinetics of halothane. The effect of adiposity on the maintenance of and recovery from halothane anaesthesia

Thirty fit patients (15-70 years, 46-98 kg) undergoing body-surface operations were selected to include a wide range of adiposity (12-45% of total body weight estimated from measurements of skinfold thickness). They were anaesthetized with halothane and 70% N2O in O2. From measurements of total ventilation (ml min-1 kg-1) and of halothane concentrations in inspired (F1) end-tidal (FE') and 'mixed-spill' (FS) gases, the following parameters were calculated for 5-min intervals from 20 to 40 min after induction; the rate of uptake of halothane per percent inspired concentration (Vha1 ml min-1%-1) and the degree of equilibrium achieved with the inspired concentration, calculated as FE'/F1 expressed as a percentage. Multiple-regression analysis of the results for 19 patients, taking account of the effects of body fat, ventilation, age, and the blood-gas partition coefficient lambda of halothane for the individual patient, showed that Vha1 increased with adiposity (b=0-375, P=0-0019), and with ventilation (b=0-054, P=0-09) but decreased with increasing age (b=-0-258, P=0-006). The time intervals between the end of the anaesthetic and the achievement of four defined levels of recovery (response to painful stimulus obedience to a simple command, response to a question, orientation in time and space), were recorded. Multiple-regression analysis showed that recovery time increased with addiposity, duration of administration and end-tidal concentration at the end of the administration, and decreased with increasing age. All four effects were statistically non-significant at the first levels of recovery but all increased at the later levels and all eventually became significant.