The effects of abdominal opening on respiratory mechanics during general anesthesia in normal and morbidly obese patients: a comparative study

Static respiratory mechanics are unaltered in males and females with obesity

We tested the hypothesis that independent of the obesity-related shift in lung volume subdivisions, obesity would not reduce the interrelationships of expiratory flow, lung volume, and static lung elastic recoil pressure in males and females. Simultaneous measurements of expiratory flow, volume, and transpulmonary pressure were continuously recorded while flow-volume loops of varying expiratory efforts were performed in a pressure-corrected, volume-displacement body plethysmograph in males and females with obesity. Static compliance curves were collected using the occlusion technique. Flow-volume, static pressure-volume, and static pressure-flow relationships were examined. Isovolume pressure-flow curves were constructed for the determination of the critical pressure for maximal flow. Data were compared with that collected in lean males and females. Individuals with obesity displayed a notable decrease in functional residual capacity. The interrelationships of flow, lung volume, static elastic recoil pressure, and the minimum pressure required for maximal expiratory flow in males and females with obesity were not different from that in lean males and females (all P > 0.05). Obesity does not alter the interrelationships of flow-volume-pressure of the lung in adult males and females (all P > 0.05). We further explored potential sex differences in static mechanics independent of obesity and observed that females have lower maximal expiratory flow due to a combination of smaller lungs and greater upstream flow resistance compared with males (all P ≤ 0.05).NEW & NOTEWORTHY The potential influence of obesity on the interrelationships between maximal expiratory flow, lung volume, and static lung elastic recoil pressure is unclear. These data show that the presence of obesity does not alter the relationship of flow and pressure across the mid-expiratory range in males and females. In addition, independent of obesity, females have smaller lungs and greater upstream flow resistance, which contributes to reduced maximal flow, when compared with males.

Laparoscopic versus open obesity surgery: a meta-analysis of pulmonary complications

The clinical effects of laparoscopy in the pulmonary function of obese patients have been poorly investigated in the past. A systematic review was undertaken, with the objective to identify published evidence on pulmonary complications in laparoscopic surgery in the obese. Outcome measures included pulmonary morbidity, pulmonary infection and mortality. The random effects model was used to calculate combined overall effect sizes of pooled data. Data are presented as the odds ratio (OR) with 95% confidence interval (CI). A total of 6 randomized and 14 observational studies were included, which reported data on 185,328 patients. Pulmonary complications occurred in 1.6% of laparoscopic and in 3.6% of open procedures (OR 0.45, 95% CI 0.34-0.60). Pneumonia was reported in 0.5% and in 1.1%, respectively (OR 0.45, 95% CI 0.40-0.51). Available evidence suggests lower pulmonary morbidity for laparoscopic surgery in obese patients; further quality studies are however necessary to consolidate these findings.

Pulmonary mechanical responses to intestinal ischaemia-reperfusion and endotoxin preconditioning

During intestinal ischaemia-reperfusion, endotoxin can be translocated. Pretreatment with sublethal doses of endotoxin develops tolerance to ischaemia-reperfusion in different organs; however, the tolerance to intestinal ischaemia-reperfusion in the lung has rarely been investigated. Our aim was to study the role of endotoxin pretreatment in the mechanical responses and inflammatory activation induced by intestinal ischaemia-reperfusion in the lung. Wistar rats were preconditioned with a sublethal dose of endotoxin on day -3 or -1. On day 0, anesthetized, paralyzed and mechanically ventilated rats were subjected to a 60-min occlusion of the superior mesenteric artery and a subsequent 240-min reperfusion. The low-frequency forced oscillation technique was employed to characterize the separate mechanical responses of the airways and respiratory tissues. Intestinal ischaemia-reperfusion caused a significant decrease in airway resistance and increases in tissue resistance and elastance, nitric oxide synthase and myeloperoxidase activities. Pretreatment with endotoxin modified both the pulmonary mechanical responses and the inflammatory markers in the lung during intestinal ischaemia-reperfusion. We conclude that endotoxin or the endotoxin-induced processes (and humoral mediators) have significant roles in the pathomechanism of the remote pulmonary effect of intestinal ischaemia-reperfusion.

Impact of alveolar recruitment maneuver in the postoperative period of videolaparoscopic bariatric surgery

BACKGROUND AND OBJECTIVES

Pulmonary complications in bariatric surgery are common and, therefore, alveolar recruitment maneuvers (ARM) have been used to prevent or reduce them in the postoperative period (POP). The aim of this study was to evaluate the impact of ARM performed intraoperatively in patients undergoing bariatric surgery by videolaparoscopy in the incidence of postoperative pulmonary complications.

METHODS

Randomized clinical trial with 30 patients divided into control group (CG) and experimental group (EG), with analysis of spirometric, ventilatory, hemodynamic, and radiographic variables. ARM was performed in EG with positive end expiratory pressure of 30 cmH₂O and inspiratory plateau pressure of 45 cmH₂O for 2 minutes after pneumoperitoneum deflation.

RESULTS

We observed a significant decrease in spirometric values (p ≤ 0.001) and higher incidence of pulmonary complications on chest radiograph (p=0.02) in CG, as well as significant improvement in dyspnoea Borg scale (p ≤ 0.001) in EG.

CONCLUSIONS

We conclude that ARM is a safe and effective technique when used for prevention of pulmonary complications in patients undergoing bariatric surgery, resulting in more favorable radiological and spirometric findings in the experimental group compared to the control group in the PO.

[The role of respiratory physiotherapy in the lung function of obese patients undergoing bariatric surgery. A review]

INTRODUCTION

Obesity, considered a new worldwide epidemic, is characterised by excess adipose tissue and contributes to a series of chronic diseases and increased mortality. Obesity associated to surgical procedure in these patients makes respiratory physiotherapy a must to recover lung function and prevent postoperative pulmonary complications.

AIMS

To assess the effects of respiratory physiotherapy on the lung function of obese patients undergoing weight loss surgery.

MATERIAL AND METHODS

We conducted a literature review October 2008-June 2009 of data which had been published over the last thirty years and which was available on the Medline, Pubmed ans Scielo databases.

CONCLUSION

Pre- and postoperative respiratory physiotherapy is vital for patients undergoing weight loss surgery irrespective of technique used, as it can prevent pulmonary complications inherent in the surgical procedure and aid lung function recovery.

Effects of positive end-expiratory pressure on respiratory function and hemodynamics in patients with acute respiratory failure with and without intra-abdominal hypertension: a pilot study

INTRODUCTION

To investigate the effects of positive end-expiratory pressure (PEEP) on respiratory function and hemodynamics in patients with acute lung injury (ALI) or acute respiratory distress syndrome (ARDS) with normal intra-abdominal pressure (IAP < 12 mmHg) and with intra-abdominal hypertension (IAH, defined as IAP >or= 12 mmHg) during lung protective ventilation and a decremental PEEP, a prospective, observational clinical pilot study was performed.

METHODS

Twenty patients with ALI/ARDS with normal IAP or IAH treated in the surgical intensive care unit in a university hospital were studied. The mean IAP in patients with IAH and normal IAP was 16 +/- 3 mmHg and 8 +/- 3 mmHg, respectively (P < 0.001). At different PEEP levels (5, 10, 15, 20 cmH2O) we measured respiratory mechanics, partitioned into its lung and chest wall components, alveolar recruitment, gas-exchange, hemodynamics, extravascular lung water index (EVLWI) and intrathoracic blood volume index (ITBVI).

RESULTS

We found that ALI/ARDS patients with IAH, as compared to those with normal IAP, were characterized by: a) no differences in gas-exchange, respiratory mechanics, partitioned into its lung and chest wall components, as well as hemodynamics and EVLWI/ITBVI; b) decreased elastance of the respiratory system and the lung, but no differences in alveolar recruitment and oxygenation or hemodynamics, when PEEP was increased at 10 and 15cmH2O; c) at higher levels of PEEP, EVLWI was lower in ALI/ARDS patients with IAH as compared with those with normal IAP.

CONCLUSIONS

IAH, within the limits of IAP measured in the present study, does not affect interpretation of respiratory mechanics, alveolar recruitment and hemodynamics.

Analysis of the effects of the alveolar recruitment maneuver on blood oxygenation during bariatric surgery

BACKGROUND AND METHDS: Alveolar recruitment maneuver (ARM) is indicated in the treatment of intraoperative atelectasis. The objective of the present study was to compare two techniques of ARM using the response of the PaO2/FiO2 ratio and [PaO2 + PaCO2] in patients with grade III obesity.

METHODS

This was an open prospective study with adult patients with grade III obesity who underwent bariatric surgery under volume-controlled mechanical ventilation with positive end-expiratory pressure (PEEP) of 5 cmH2O, divided in three groups: G CONT: PEEP of 5 cmH2O; G ARM10/15/20 after suture of the aponeurosis: progressive increase in PEEP to 10, 15, and 20 cmH2O with a 40-second pause and maintaining each level of PEEP for 2 minutes; and G ARM30 after suture of the aponeurosis: sudden increase in PEEP to 30 cmH2O with a 40-second pause and maintaining a PEEP of 30 for 2 minutes. Heart rate, mean arterial pressure, systolic and diastolic blood pressure, mean (P AW) and plateau (P PLAT) airways pressure, partial pressure of oxygen (PaO2), partial pressure of carbon dioxide (PaCO2), PaO2/FiO2 ratio (inspired fraction of oxygen), and [PaO2 + PaCO2] were analyzed.

RESULTS

The following parameters showed statistically significant differences among the study groups: P PLAT, P AW, PaO2, PaO2/FiO2 ratio, and [PaO2 + PaCO2] (p < 0.0001). Comparing the groups two by two, the following parameters showed statistically significant differences: for P PLAT and P AW: G CONT x G2ARM10/15/20 and G CONT x G ARM30; and for PaO2/FiO2 ratio and [PaO2 + PaCO2]: G CONT x G ARM30.

CONCLUSIONS

Alveolar recruitment maneuver with sudden increase of PEEP to 30 cmH2O showed a better response of the PaO2/FiO2 ratio.

Anesthetic complications of gross obesity

PURPOSE OF REVIEW

The number of obese patients undergoing anesthesia and surgery is increasing. This article aims to present recent achievements in the management of gross and morbidly obese patients in order to improve safety.

RECENT FINDINGS

Current investigations have demonstrated that the type of anesthesia (total intravenous anesthesia or volatile) and the anesthetics used have an important influence on the perioperative period, especially on postanesthesia recovery and respiratory failure during the postoperative period. These findings were compared with previous publications. Practical advice is also presented for performing successful intubation and mechanical ventilation in the morbidly obese patient, as well as describing drug dosage and administration.

SUMMARY

The progress in anesthesia techniques and modern drugs allows for safe management of obese patients, with mortality decreasing in this group of patients.

Pulmonary function is better preserved in pigs when acute normovolemic hemodilution is achieved with hydroxyethyl starch versus lactated Ringer's solution

Acute normovolemic hemodilution (ANH) has been proposed to decrease the need for allogenic blood transfusion. Consequently, great amounts of fluids are necessary to maintain hemodynamics during and after blood removal. The aim of this experiment was to evaluate the oxygenation, respiratory compliance, and lung structure during ANH performed with lactated Ringer's solution and hydroxyethyl starch (HES). Gas exchange, extravascular lung water, intrathoracic blood volume, serum osmolality, respiratory mechanics, and optical and electronic microscopy of lung biopsies were evaluated. Animals were randomized into three groups: CTL (control, n = 9), HES (HES 6% 200/0.5, n = 9), and LR (lactated Ringer's solution, n = 9). Animals in groups HES and LR underwent ANH to reach a preestablished hematocrit of around 15%. The removed blood was replaced with HES in a proportion of 1:1 and with lactated Ringer's solution 3:1. The LR group demonstrated a tendency for a marked time-dependence decrease in compliance (P = 0.013 in T2; P = 0.008 in T3) and in Pao2/fraction of inspired oxygen (Fio2) ratio (P = 0.033 in T2) as well as an increase in (A-a) Grad O2 (P = 0.037 in T2). Extravascular lung water and intrathoracic blood volume did not present any significant variation among the groups. In contrast, serum osmolality presented a significant decline in animals hemodiluted with lactated Ringer's solution. Optical and electronic microscopy of lungs biopsies revealed moderate to serious collapses and basement membrane enlargement in LR group. In this kind of experimental model, ANH with 6% HES (200/0.5) seems to preserve lung structure better as evidenced by maintenance of oxygenation indexes and respiratory compliance when compared with that in the Ringer's solution hemodiluted group.

Thoracic sympathetic block reduces respiratory system compliance

CONTEXT AND OBJECTIVE

Thoracic epidural anesthesia (TEA) following thoracic surgery presents known analgesic and respiratory benefits. However, intraoperative thoracic sympathetic block may trigger airway hyperreactivity. This study weighed up these beneficial and undesirable effects on intraoperative respiratory mechanics.

DESIGN AND SETTING

Randomized, double-blind clinical study at a tertiary public hospital.

METHODS

Nineteen patients scheduled for partial lung resection were distributed using a random number table into groups receiving active TEA (15 ml 0.5% bupivacaine, n = 9) or placebo (15 ml 0.9% saline, n = 10) solutions that also contained 1:200,000 epinephrine and 2 mg morphine. Under general anesthesia, flows and airway and esophageal pressures were recorded. Pressure-volume curves, lower inflection points (LIP), resistance and compliance at 10 ml/kg tidal volume were established for respiratory system, chest wall and lungs. Students t test was performed, including confidence intervals (CI).

RESULTS

Bupivacaine rose 5 +/- 1 dermatomes upwards and 6 +/- 1 downwards. LIP was higher in the bupivacaine group (6.2 +/- 2.3 versus 3.6 +/- 0.6 cmH2O, p = 0.016, CI = -3.4 to -1.8). Respiratory system and lung compliance were higher in the placebo group (respectively 73.3 +/- 10.6 versus 51.9 +/- 15.5, p = 0.003, CI = 19.1 to 23.7; 127.2 +/- 31.7 versus 70.2 +/- 23.1 ml/cmH2O, p < 0.001, CI = 61 to 53). Resistance and chest wall compliance showed no difference.

CONCLUSION

TEA decreased respiratory system compliance by reducing its lung component. Resistance was unaffected. Under TEA, positive end-expiratory pressure and recruitment maneuvers are advisable.

Effect of vital capacity manoeuvres on arterial oxygenation in morbidly obese patients undergoing open bariatric surgery

BACKGROUND

Arterial oxygenation may be compromised in morbidly obese patients undergoing bariatric surgery. The aim of this study was to evaluate the effect of a vital capacity manoeuvre (VCM), followed by ventilation with positive end-expiratory pressure (PEEP), on arterial oxygenation in morbidly obese patients undergoing open bariatric surgery.

METHODS

Fifty-two morbidly obese patients (body mass index >40 kg m-2) undergoing open bariatric surgery were enrolled in this prospective and randomized study. Anaesthesia and surgical techniques were standardized. Patients were ventilated with a tidal volume of 10 mL kg-1 of ideal body weight, a mixture of oxygen and nitrous oxide (FiO2 = 40%) and respiratory rate was adjusted to maintain end-tidal carbon dioxide at a level of 30-35 mmHg. After abdominal opening, patients in Group 1 had a PEEP of 8 cm H2O applied and patients in Group 2 had a VCM followed by PEEP of 8 cm H2O. This manoeuvre was defined as lung inflation by a positive inspiratory pressure of 40 cm H2O maintained for 15 s. PEEP was maintained until extubation in the two groups. Haemodynamics, ventilatory and arterial oxygenation parameters were measured at the following times: T0 = before application of VCM and/or PEEP, T1 = 5 min after VCM and/or PEEP and T2 = before abdominal closure.

RESULTS

Patients in the two groups were comparable regarding patient characteristics, surgical, haemodynamic and ventilatory parameters. In Group 1, arterial oxygen partial pressure (PaO2) and arterial haemoglobin oxygen saturation (SaO2) were significantly increased and alveolar-arterial oxygen pressure gradient (A-aDO2) decreased at T2 when compared with T0 and T1. In Group 2, PaO2 and SaO2 were significantly increased and A-aDO2 decreased at T1 and T2 when compared with T0. Arterial oxygenation parameters at T1 and T2 were significantly improved in Group 2 when compared with Group 1.

CONCLUSION

The addition of VCM to PEEP improves intraoperative arterial oxygenation in morbidly obese patients undergoing open bariatric surgery.

Positive end-expiratory pressure optimization using electric impedance tomography in morbidly obese patients during laparoscopic gastric bypass surgery

BACKGROUND

Morbidly obese patients have an increased risk for peri-operative lung complications and develop a decrease in functional residual capacity (FRC). Electric impedance tomography (EIT) can be used for continuous, fast-response measurement of lung volume changes. This method was used to optimize positive end-expiratory pressure (PEEP) to maintain FRC.

METHODS

Fifteen patients with a body mass index of 49 +/- 8 kg/m(2) were studied during anaesthesia for laparoscopic gastric bypass surgery. Before induction, 16 electrodes were placed around the thorax to monitor ventilation-induced impedance changes. Calibration of the electric impedance tomograph against lung volume changes was made by increasing the tidal volume in steps of 200 ml. PEEP was titrated stepwise to maintain a horizontal baseline of the EIT curve, corresponding to a stable FRC. Absolute FRC was measured with a nitrogen wash-out/wash-in technique. Cardiac output was measured with an oesophageal Doppler method. Volume expanders, 1 +/- 0.5 l, were given to prevent PEEP-induced haemodynamic impairment.

RESULTS

Impedance changes closely followed tidal volume changes (R(2) > 0.95). The optimal PEEP level was 15 +/- 1 cmH(2)O, and FRC at this PEEP level was 1706 +/- 447 ml before and 2210 +/- 540 ml after surgery (P < 0.01). The cardiac index increased significantly from 2.6 +/- 0.5 before to 3.1 +/- 0.8 l/min/m(2) after surgery, and the alveolar dead space decreased. P(a)O2/F(i)O2, shunt and compliance remained unchanged.

CONCLUSION

EIT enables rapid assessment of lung volume changes in morbidly obese patients, and optimization of PEEP. High PEEP levels need to be used to maintain a normal FRC and to minimize shunt. Volume loading prevents circulatory depression in spite of a high PEEP level.

Illustrations of Inhaled Anesthetic Uptake, Including Intertissue Diffusion to and from Fat

Although several mathematical and computer simulations of inhaled anesthetic pharmacokinetics have been devised, their complexity sometimes limits an intuitive appreciation of the interactions produced by the determinants of kinetics. In this essay, we illustrate the factors that govern inhaled anesthetic pharmacokinetics with drawings that consider delivery of anesthetic by ventilation to the lungs and dispersion of the anesthetic to tissue depots by the circulation. The illustrations incorporate the effects of both blood flow and blood solubility as determinants of the extent of dispersion. They incorporate tissue volume and solubility as determinants of the capacity of the tissue depots. Capacity to hold (take up) anesthetic is depicted by areas representing specific tissues, and the extent of anesthetic movement is depicted by the length and breadth of arrows to and from the areas depicting capacity. The illustrations incorporate increasingly important elements to kinetics, such as obesity. Obesity increases the depots available for storage of anesthetic, including anesthetic that reaches fat by intertissue diffusion. Such anesthetic returns to the circulation to delay recovery in healthy and obese patients, particularly with more soluble anesthetics. However, the increased anesthetic in fat occurs at a lower partial pressure and thus might not influence emergence materially. We hope that these illustrations will allow anesthesia practitioners to appreciate the interactions of the factors that govern inhaled anesthetic pharmacokinetics.

Anesthesia in the obese patient: Pharmacokinetic considerations

The prevalence of obesity has increased 15% up to 20% and represents an important challenge for the anesthesiologist in drug-dosing management. The aim of this work is to provide an overview on physiological changes and pharmacokinetic implications of obesity for the anesthesiologist. Obesity increases both fat and lean masses; however, the percentage of fat tissue increases more than does the lean mass, affecting the apparent volume of distribution of anesthetic drugs according to their lipid solubility. Benzodiazepine loading doses should be adjusted on actual weight, and maintenance doses should be adjusted on ideal body weight. Thiopental sodium and propofol dosages are calculated on total body weight (TBW). The loading dose of lipophilic opioids is based on TBW, whereas maintenance dosages should be cautiously reduced because of the higher sensitivity of the obese patient to their depressant effects. Pharmacokinetic parameters of muscle relaxants are minimally affected by obesity, and their dosage is based on ideal rather than TBW. Inhalation anesthetics with very low lipid solubility, such as sevoflurane and desflurane, allow for quick modification of the anesthetic plan during surgery and rapid emergence at the end of surgery, hence representing very flexible anesthetic drugs for use in this patient population. Drug dosing is generally based on the volume of distribution for the loading dose and on the clearance for maintenance. In the obese patient, the volume of distribution is increased if the drug is distributed both in lean and fat tissues whereas the anesthetic drug clearance is usually normal or increased.

Body Fat Accumulation and Postoperative Complications after Abdominal Surgery

The contribution of subcutaneous or intra-abdominal fat (SCF, IAF) accumulation to postoperative mortality or morbidity after elective gastric or colorectal cancer surgery was studied. One hundred thirty-nine patients who underwent gastric or colorectal cancer surgery were investigated. Data were collected on the following preoperative comorbid conditions: lung dysfunction, cardiovascular dysfunction, liver dysfunction, or diabetes mellitus (DM). The IAF and SCF areas were determined at the umbilical level by preoperative CT scanning. We investigated whether IAF or SCF was independently associated with postoperative mortality or morbidity. The mortality rate was 0.7 per cent (1/139). Nineteen (14%) of 139 patients had medical complications (pneumonitis or arrhythmia) and 27 (19%) had surgery-related complications (anastomotic leakage, intra-abdominal collections, or abdominal wound infection) postoperatively. Age (≥70 years), lung dysfunction, cardiovascular dysfunction, and IAF were significantly associated with medical complications, and surgical site (gastric/colorectal), DM, body mass index, IAF, and SCF were significant for surgery-related complications by univariate analysis. Multilogistic regression analysis showed that age, cardiovascular dysfunction, and IAF were significant for medical complications, and surgical site, DM, and SCF were independently related with surgery-related complications. Body fat accumulation is independently associated with postoperative morbidity after gastric or colorectal surgery, and assaying it may be useful for predicting postoperative complications.

Respiratory mechanics in morbid obese patients with chronic obstructive pulmonary disease and hypertension during pneumoperitoneum

BACKGROUND AND OBJECTIVE

To evaluate the effects of pneumoperitoneum and the reverse Trendelenburg position on respiratory mechanics and blood-gases in morbid obese patients with chronic obstructive pulmonary disease and hypertension.

METHODS

Sixteen morbid obese patients with chronic obstructive pulmonary disease and hypertension were studied. Mean arterial pressure, heart rate, respiratory resistance, dynamic respiratory compliance and peak inspiratory pressures were measured at four time points: 5 min after induction of anaesthesia (T1), 5 min after insufflation of the peritoneum (T2), 5 min after adoption of a 20 degrees reverse Trendelenburg position (T3), and 5 min after deflation of the peritoneum (T4). Arterial blood-gas status was measured at the same measuring points.

RESULTS

Respiratory compliance was 40 +/- 12, 28 +/- 8, 32 +/- 8 and 37 +/- 11 mL cm H2O(-1) in T1, T2, T3 and T4, respectively. The changes were significant at T2, T3 and T4. Airway resistance and peak inspiratory pressures showed comparable changes throughout the study with that of respiratory compliance. Haemodynamic measurements showed no clinically significant changes in this study.

CONCLUSIONS

In morbid obese patients with chronic obstructive pulmonary disease and hypertension, a 20 degrees reverse Trendelenburg position improved respiratory mechanics and oxygenation without any apparent adverse effects on haemodynamics during laparoscopic gastric banding surgery.