Respiratory function and cardiorespiratory response to exercise in obesity

Perianesthesia respiratory care of the bariatric patient

Our nation's obesity problem has reached epidemic proportions and is only projected to worsen. The morbidly obese patient is at risk for experiencing a multitude of health-related conditions. Morbidly obese patients are presenting for surgery at an increasing rate, especially with the growing popularity of weight-loss surgery. Therefore the perianesthesia nurse has to remain informed of optimal care strategies for this sometimes challenging population. The obese patient presents with distinct respiratory care considerations of which the perianesthesia nurse must be knowledgeable. This review article will specifically focus on the respiratory care of the bariatric patient presenting for surgery.

[Cardiopulmonary function and exercise capacity in patients with morbid obesity]

INTRODUCTION AND OBJECTIVES

The effect of obesity on cardiac function is still under discussion. The objective of this study was to assess cardiopulmonary capacity in morbidly obese patients. Patients and method. A symptom-limited cardiopulmonary exercise stress test was carried out in 31 morbidly obese patients (BMI 50 9 kg/m2) and 30 normal controls (BMI 24 2 kg/m2. Cardiovascular function was evaluated using the oxygen pulse (oxygen uptake/heart rate).

RESULTS

There were no differences in age, sex and height between both groups. During the effort the obese subjects presented greater oxygen uptake, heart rate, systolic arterial pressure and minute ventilation and shorter test duration than control group (14 3 vs 27 4 min; p < 0.001). Oxygen pulse values were higher in obese patients. However, after oxygen uptake indexation by fat free mass, these differences disappeared, suggesting a similar cardiovascular function. At the end of the exercise, the control group reached 96% of their age-predicted maximal heart rate and their respiratory exchange ratio was 1 0.2. Obese patients only reached 86% and 0.87 0.2, respectively.

CONCLUSIONS

Due to their need of more energy output to move total body mass morbidly obese patients have a reduced exercise capacity. They finish the test having done a submaximal exercise. However, during this effort they show a normal cardiopulmonar capacity.

Physical activity, energy expenditure and intake in 11 to 12 years old Japanese prepubertal obese boys

The purpose of this study is to find out the differences in physical activity (PA), energy expenditure (EE) and energy intake (EI) under free-living conditions between Japanese prepubertal obese and nonobese boys. The subjects were 15 prepubertal obese boys (Age: 11.7+/-0.4 years old, Body fat: 35.2+/-1.6%) who do not have obese parents and siblings and 15 prepubertal nonobese boys (Age: 11.8+/-0.4 years old, Body fat: 18.5+/-0.8%). We assessed their daily PA by heart rate (HR) monitoring, pedometer step counts (PSC) and time for sedentary activities (SA). We also examined calculated EE from HR-VO(2) regression, EI and percentage of macronutrient EI. Results are as follows: Percentage of body fat had significant correlation with weight, BMI, time for SA, percentage EI of protein (positive, p<0.001), VO(2max), VO(2max) per body weight, VO(2max) per LBM, PSC, TEE per body weight, TEI per body weight (negative, p<0.001), percentage of EI of carbohydrate (negative, p<0.01). The values of the obese were significantly lower in total EE per body weight and in total EI per body weight. EI from dinner was significantly higher in the obese group. The values of the obese were significantly higher in percentage EI from protein and that from carbohydrate. The results of this study showed prepubertal obese boys who do not have obese parents and siblings have low PA and spend much time for sedentary activities. Obese boys consume higher percentage energy of protein and lower percentage of carbohydrate though differences in EE and EI were found only in total EE per body weight and total EI per body weight between obese boys and nonobese boys.

Upper airway diseases and airway management: a synopsis

This article summarizes some of the more important upper airway conditions likely to affect airway management. A number of upper airway conditions may present difficult challenges to the anesthesiologist. For instance, infected airway structures may lead to partial airway obstruction, stridor, or even complete airway obstruction. Partial airway obstruction may be mild, as in snoring or nasal congestion, or may be more severe, perhaps requiring the use of airway adjuncts, such as a nasopharyngeal airway. Complete airway obstruction is usually managed by prompt intubation, but surgical airways are sometimes needed as a last resort.

Body mass index and physical function in older women

OBJECTIVE

We modified existing standardized measurement tools in the Physical Performance Test and tasks from the Frailty and Injuries: Cooperative Studies of Intervention Technique Study to evaluate physical function in older women. Our objectives were (1) to characterize physical function themes based on combinations of tasks (deriving factors or components) and (2) to quantify the correlation between derived factors and body mass index (BMI).

RESEARCH METHODS AND PROCEDURES

Nutrition risk screens from enrollees in a Medicare-managed risk program served as the sampling frame. To obtain adequate representation for a range of BMI, a random sample was obtained of 90 women from the following BMI strata: BMI, 22 to <27 kg/m(2); BMI, 27 to <30 kg/m(2); and BMI, > or =30 kg/m(2). Subjects were asked to perform a series of 18 functional tasks during a home visit.

RESULTS

The mean age was similar in the three BMI groups with an overall mean age of 71 +/- 4.9 years (SD). Factors characterized by lower-body function, upper-body function, coordination, and strength were responsible for 30%, 11%, 9%, and 9% of the variance in task scores, respectively. BMI, controlling for age, explained 5%, 14%, 3%, and 0% of the variation in these factors, respectively. Higher BMI is associated significantly with poorer upper- and lower-body function but is not associated significantly to strength or coordination.

DISCUSSION

Higher BMI seems to differentially impede specific aspects of physical function, especially upper-body function, and to a lesser extent, lower-body function. BMI does not seem to be associated with levels of coordination or strength. Better understanding of how BMI impacts physical function will aid in the design of interventions to promote independent living in elderly, obese women.

The effects of mild obesity on lung function

Lung volumes and blood gas tensions were measured in 144 males awaiting coronary artery surgery. Patients were divided into three groups according to their body mass index. Functional residual capacity (FRC), expiratory reserve volume (ERV) and arterial oxygen tension (PaO2) were reduced in the 91 patients with Grade I obesity (mean +/- SD weight, 81.1 +/- 9.0 kg) compared with the results obtained in the 28 patients of normal weight (Grade 0, 70.8 +/- 8.8 kg). The magnitude of the reduction was greater in the Grade II obesity patients (90.1 +/- 8.8 kg, n = 25). Mean values were: FRC 3.45, 3.17, 2.66 l; ERV 1.10, 0.77, 0.59 l and PaO2 11.05, 10.47, 9.99 kPa in patients with Grades 0, I and II obesity respectively. The alveolar-arterial oxygen difference (A-aPO2) was significantly higher in the obese patients. Mean A-aPO2 was 2.47, 3.14 and 3.88 kPa in patients with Grades 0, I and II, respectively. We conclude that obesity, even when mild, significantly impairs lung function.

Adverse effect of additional weight on exercise against gravity in patients with chronic obstructive airways disease

The effects of an acute, artificially simulated increase in body weight on exercise performance were examined in 14 patients of normal weight (mean (SD) body mass index 22.3 (2.7)), age 61 (8) years) with chronic obstructive airways disease (FEV1 1.2 (0.5) 1; vital capacity (VC) 2.9 (0.6) 1), and in six normal subjects with similar age and sex distribution. The patients performed a six minute walking test and a symptom limited step climbing test both with and without an additional 10 kg weight (two leaded aprons). The normal subjects performed a step test with and without the additional weight. Ventilation (VE) and oxygen consumption (VO2) were measured during step climbing. Resting spirometric values were not altered by the additional weight. In the patients the median number of steps climbed fell from 67.5 when they were unweighted to 44.5 when they were weighted. Mean VE and VO2 were increased during weighted step climbing by 14% and 13% but the maximum levels of VE and VO2 achieved were similar during unweighted and weighted exercise (VE 36.8 (8.6) and 37.3 (10.2) 1 min-1, VO2 1.35 (0.3) and 1.41 (0.4) 1 min-1 respectively). The normal subjects were readily able to complete 150 steps both with and without the additional weight. In the patients the six minute walking distance fell only slightly with the extra weight, from 554 (SD 61) to 540 (62) m. A subsidiary study was carried out in six healthy younger subjects in which VE and VO2 were measured during a 5.6 km/h six minute treadmill walk at zero incline. The additional weight did not alter VE or VO2 during exercise. In conclusion, a small acute increase in body weight substantially worsened the already reduced "uphill" exercise performance in patients with chronic obstructive airways disease because of its effect on ventilation and oxygen consumption. These results suggest that modest weight loss might benefit patients with chronic obstructive airways disease even though they may be only slightly above their ideal body weight.

Gas exchange during exercise in obese children

Twenty-three obese children, aged 9 to 14 years, ranging in percentage overweight from 26% to 83% (median 51.6% +/- 16.3%), and 37 normal-weight children, matched for sex, age and height, performed a maximal exercise test on a treadmill. Cardiorespiratory performance was assessed by determination of the ventilatory anaerobic threshold (VAT) expressed in ml O2/min per kg and as a percent of maximal oxygen uptake (% VO2max). VAT and VO2max related to body weight were significantly lower (P less than 0.01) in the obese than in the normal-weight children. VAT % VO2max was similar in the two groups. A significant correlation was found between VAT and VO2max both in the obese (r = 0.85) and in the control groups (r = 0.79). The habitual level of physical activity was lower in the obese subjects compared to the control subjects (P less than 0.001). In conclusion our study shows that physical fitness of overweight children is quantitatively lowered and that it can be assessed by VAT. VAT does not require a maximal test and is particularly useful in the ergometric study of subjects with exercise intolerance.

Sex differences in awake ventilatory drive and abnormal breathing during sleep in eucapnic obesity

We studied hypoxic and hypercapnic ventilatory drives in 22 eucapnic obese subjects (14 female and eight male subjects) referred for weight reduction therapy and 23 normal subjects (eight female and 15 male subjects). In the female subjects, both occlusion pressure, currently used as an indicator of ventilatory drive, and ventilatory responses to hypoxia, as well as occlusion pressure response to hypercapnia, were significantly greater in the obese than in the normal subjects; however, no significant differences in these responses between male obese and male normal subjects were observed, except for the hypoxic occlusion pressure response. We also studied disordered breathing during sleep in the obese subjects, and male predominance in abnormal breathing and oxygen desaturation was noted. These results showed that obese female subjects increased their hypoxic and hypercapnic chemosensitivities against their body mass loading, which was not evident in obese male subjects. The relatively depressed chemosensitivities of the latter may be related to disordered breathing and oxygen desaturation during sleep.

Cardiorespiratory function during exercise in obese children

Fifteen obese children, aged 4 to 16 years and ranging in body weight from 27.3 to 95 kg (median 67.5) and percentage overweight from 22 to 127% (median 40), underwent graded exercise testing on a treadmill and were compared with healthy peers of comparable age. Cardiorespiratory performance capacity was assessed by determination of the ventilatory threshold. This was defined as the highest oxygen uptake at which the pulmonary ventilation stops to increase linearly with increasing exercise intensity. The ventilatory threshold, expressed as ml O2/min/kg, was significantly (p less than 0.05) lower than in normal children and averaged 70.6 +/- 13.5% of the normal mean value, matched for age. The habitual level of physical activity, assessed by a questionnaire, was 27% lower (p less than 0.01) in the obese children compared to healthy controls. As the ventilatory threshold was strikingly lower and also exceeded sooner in the majority of the obese children, compared with normal controls, it may be assumed that obese children avoid moderate or strenuous exercise, because of the higher degree of effort needed. This may contribute to the maintenance of overweight.

Clinical complications of obesity

The development of important respiratory disorders and significant hypertension in association with increasing body weight is not widely recognized. Altered respiratory function results from a combination of mechanical impedance to breathing exerted by thoracic and abdominal fat and a ventilation-perfusion mismatch. Sleep-disordered breathing with periods of hypoventilation, with or without apnoeic episodes, may commonly occur in patients with extreme obesity. Nocturnal hypercapnia and hypoxia in such patients may lead to a decrease in ventilatory drive, abnormal central respiratory control and possibly, in time, the development of the obese-hypoventilation syndrome. Respiratory abnormalities should be suspected in obese patients with a history of restlessness at night, loud snoring and daytime somnolence. Treatment is substantial weight reduction, but short-term measures include the use of compressed air via nasal cannulae for obstructive apnoea, and drugs which alter sleep pattern or stimulate respiration. The alterations in endocrine function, which accompany weight gain, may contribute to an increase in blood pressure and there appears to be a relationship between plasma insulin and catecholamine concentrations, fat cell size and the development of hypertension. The confirmation of a raised blood pressure requires that readings be taken with an adequately sized arm-cuff. In many instances endocrine function becomes normal with weight loss, and there is a corresponding decrease in blood pressure. The ideal management for an obese hypertensive patient is the combination of a suitable calorie-restricted diet with a programme of physical exercise.

Nocturnal hypoxia and prolactin secretion in obese women

Respiration during sleep was studied in six obese women who had impaired prolactin response to insulin induced hypoglycaemia (non-responders), six obese women with a normal prolactin response to hypoglycaemia (responders), and six lean women. Sleep apnoea did not occur in any subject. All the obese women showed a decrease in haemoglobin oxygen saturation when asleep, which occurred predominantly during periods of rapid eye movement sleep. That the fall in oxygen saturation was significantly greater (p less than 0.05) in the obese non-responders suggests that central as well as mechanical factors may be important for the genesis of nocturnal hypoxia and is evidence for a disturbance of central nervous function in some obese women.

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.

Lateral thoracotomy and one-lung anesthesia in patients with morbid obesity

Between May, 1980, and October, 1981, 22 morbidly obese patients ranging in weight from 93.4 to 236.8 kg (average, 145.2 kg) underwent transthoracic gastric stapling. Fourteen of these operations were performed using endobronchial intubation and selective collapse of the left lung to facilitate surgical exposure. The patients were compared with 22 consecutive patients treated by trans-abdominal gastric stapling during the same period. None of the 44 patients had evidence of chronic alveolar hypoventilation (pickwickian syndrome). In terms of operating time, blood loss, duration of intubation, and hospital stay, the two groups did not differ significantly. Despite marked shunting during one-lung ventilation, satisfactory arterial oxygen tension (PaO2) could be demonstrated on 100% oxygen for all thoracotomy patients (PaO2 range, 67 to 230 torr; mean, 132.3 torr). In fact, except for a lower PaO2 during one-lung anesthesia, the thoracotomy patients were indistinguishable from the laparotomy patients in terms of perioperative respiratory function. Pain, sedation, and positioning led to significant decreases in vital capacity and one-second forced expiratory volume in both groups on the first post-operative day, and in the thoracotomy group on the second day. There were only two wound infections in the thoracotomy group, as opposed to six infections with two dehiscences in the laparotomy group. It is concluded that lateral thoracotomy with or without one-lung anesthesia can be performed safely in massively obese patients--at least in those without preexisting alveolar hypoventilation syndrome.

Meperidine infusion for postoperative analgesia in grossly obese patients

Postoperative analgesia was provided to nine grossly obese patients with a continuous intravenous meperidine infusion. The narcotic was infused at an initial rate of 1.3 mg . min-1 for 45 minutes, then 0.7 mg . min-1 for 30 minutes followed by 0.5 mg . min-1 for the next 24 hours. Pain was assessed at hourly intervals, serial blood samples were taken for measurement of plasma meperidine concentrations, and respiratory function was assessed by serial measurement of vital capacity and arterial blood gas analysis. Analgesia was gradual in onset and from six hours after commencement of the infusion, seven of the patients suffered little or no pain. Plasma meperidine concentrations reached a peak of 0.33 +/- 0.05 microgram . ml-1 at one hour decreased gradually after three hours. Surprisingly, there was poor correlation between analgesia and plasma meperidine concentration. All patients breathed spontaneously and maintained satisfactory blood gas tensions. However, there was a marked reduction in postoperative vital capacity. Thus meperidine administered by continuous intravenous infusion can provide good postoperative analgesia in the obese patient without producing respiratory depression. However, the lack of correlation between analgesia and plasma narcotic concentration suggests that further study is required before intravenous regimes can be prescribed by application of pharmacokinetic principles.