Effects of the Beach Chair Position, Positive End-expiratory Pressure, and Pneumoperitoneum on Respiratory Function in Morbidly Obese Patients during Anesthesia and Paralysis

Background: The authors studied the effects of the beach chair (BC) position, 10 cm H2O positive end-expiratory pressure (PEEP), and pneumoperitoneum on respiratory function in morbidly obese patients undergoing laparoscopic gastric banding.

Methods: The authors studied 20 patients (body mass index 42 +/- 5 kg/m2) during the supine and BC positions, before and after pneumoperitoneum was instituted (13.6 +/- 1.2 mmHg). PEEP was applied during each combination of position and pneumoperitoneum. The authors measured elastance (E,rs) of the respiratory system, end-expiratory lung volume (helium technique), and arterial oxygen tension. Pressure-volume curves were also taken (occlusion technique). Patients were paralyzed during total intravenous anesthesia. Tidal volume (10.5 +/- 1 ml/kg ideal body weight) and respiratory rate (11 +/- 1 breaths/min) were kept constant throughout.

Results: In the supine position, respiratory function was abnormal: E,rs was 21.71 +/- 5.26 cm H2O/l, and end-expiratory lung volume was 0.46 +/- 0.1 l. Both the BC position and PEEP improved E,rs (P < 0.01). End-expiratory lung volume almost doubled (0.83 +/- 0.3 and 0.85 +/- 0.3 l, BC and PEEP, respectively; P < 0.01 vs. supine zero end-expiratory pressure), with no evidence of lung recruitment (0.04 +/- 0.1 l in the supine and 0.07 +/- 0.2 in the BC position). PEEP was associated with higher airway pressures than the BC position (22.1 +/- 2.01 vs. 13.8 +/- 1.8 cm H2O; P < 0.01). Pneumoperitoneum further worsened E,rs (31.59 +/- 6.73; P < 0.01) and end-expiratory lung volume (0.35 +/- 0.1 l; P < 0.01). Changes of lung volume correlated with changes of oxygenation (linear regression, R2 = 0.524, P < 0.001) so that during pneumoperitoneum, only the combination of the BC position and PEEP improved oxygenation.     

Set Positive End-expiratory Pressure during Protective Ventilation Affects Lung Injury

Background: The most appropriate method of determining positive end-expiratory pressure (PEEP) level during a lung protective ventilatory strategy has not been established.

Methods: In a lavage-injured sheep acute respiratory distress syndrome model, the authors compared the effects of three approaches to determining PEEP level after a recruitment maneuver: (1) 2 cm H2O above the lower inflection point on the inflation pressure-volume curve, (2) at the point of maximum curvature on the deflation pressure-volume curve, and (3) at the PEEP level that maintained target arterial oxygen partial pressure at a fraction of inspired oxygen of 0.5.

Results: Positive end-expiratory pressure set 2 cm H2O above the lower inflection point resulted in the least injury over the course of the study. PEEP based on adequate arterial oxygen partial pressure/fraction of inspired oxygen ratios had to be increased over time and resulted in higher mRNA levels for interleukin-8 and interleukin-1[beta] and greater tissue inflammation when compared with the other approaches. PEEP at the point of maximum curvature could not maintain eucapneia even at an increased ventilatory rate.     

Hemodynamic Benefit of Positive End-expiratory Pressure during Acute Descending Aortic Occlusion

Background: Acute aortic occlusion in vascular surgery patients abruptly increases arterial resistance and blood pressure, which, in turn, makes subsequent volume expansion during cross-clamp application difficult. The use of vasodilatory drugs or volatile anesthetic agents to attenuate this response may have persistent detrimental effects after clamp removal. Another potential therapy that produces rapid effects on myocardial loading conditions is positive end-expiratory pressure (PEEP). In a porcine model of acute aortic clamping, the hemodynamic consequences of 15 cm H2O PEEP with and without plasma volume expansion were studied.

Methods: Forty anesthetized pigs underwent 30-min occlusion of the abdominal aorta 1 cm above the origin of the celiac artery. Animals were randomly divided into four treatment groups (n = 10 each) to receive 15 cm H2O PEEP or zero end-expiratory pressure (ZEEP) with or without plasma volume expansion using 6% hetastarch (10 ml/kg) during cross-clamp application. Mean aortic pressure was measured with a transducer-tipped catheter placed in the ascending aorta; stroke volume was calculated using thermodilution cardiac output. End-expiratory pressure was discontinued upon aortic declamping, and animals were studied over the ensuing 30-min period.

Results: Aortic occlusion doubled systemic vascular resistance in all groups. Mean aortic blood pressure increased significantly in both ZEEP groups at 1 and 5 min but not in animals treated with 15 cm H2O PEEP. The application of PEEP with aortic cross-clamping reduced cardiac output and stroke volume by nearly 50%. Cardiac output and stroke volume increased after volume expansion regardless of end-expiratory pressure. After aortic declamping, aortic blood pressure decreased in all groups but was significantly greater in the PEEP + volume group than in either ZEEP group. Similarly, 5 min after declamping, stroke volume was greatest in the PEEP + volume animals.     

Bariatric Surgery Improves Urinary Incontinence but Not Anorectal Function in Obese Women

Background

While the association between obesity and urinary incontinence (UI) in women has been clearly documented, the relationship with anal incontinence (AI) is less well defined; moreover, while bariatric surgery has been shown to improve UI, its effect on AI is still unclear.

Methods

A total of 32 obese women were studied by means of PFDI-20 and PFIQ-7 questionnaires and anorectal manometry before and after bariatric surgery and compared with 71 non-obese women.

Results

Obese women showed worse overall questionnaire results (OR 5.18 for PFDI-20 and 2.66 for PFIQ-7). Whereas obese women showed worse results for urinary sub-items and a higher urge UI incidence (43.8 vs 18.3 %, p?=?0.013), they did not show worsening in colorecto-anal symptoms. Post-operatively, median PFDI-20 total score did not change (24.2 vs 26.6, p?=?ns), while there was an improvement in urinary score (14.6 vs 8.3, p?<?0.001); median PFIQ-7 improved (4.8 vs 0.0, p?=?0.044), but while the urinary score improved (2.4 vs 0.0, p?=?0.033), the colorecto-anal score did not change significantly. Although after surgery urge UI decreased from 43.8 to 15.6 % (p?=?0.029), the incidence of any AI increased from 28.1 to 40.6 % (p?=?ns) and flatus incontinence increased from 18.8 to 37.5 % (p?=?ns). Anorectal manometry did not show significant changes after surgery.

Conclusions

Obese women had worse questionnaire results, but while showing a higher incidence of UI, they did not experience anorectal function worsening. After bariatric surgery, there was a slight improvement in PFD symptoms related to UI, but anorectal function did not change significantly and flatus incontinence increased.     

Relation of the Static Compliance Curve and Positive End-expiratory Pressure to Oxygenation during One-lung Ventilation

Background : Positive end-expiratory pressure (PEEP) is commonly applied to the ventilated lung to try to improve oxygenation during one-lung ventilation but is an unreliable therapy and occasionally causes arterial oxygen partial pressure (Pao2) to decrease further. The current study examined whether the effects of PEEP on oxygenation depend on the static compliance curve of the lung to which it is applied.

Methods : Forty-two adults undergoing thoracic surgery were studied during stable, open-chest, one-lung ventilation. Arterial blood gasses were measured during two-lung ventilation and one-lung ventilation before, during, and after the application of 5 cm H2O PEEP to the ventilated lung. The plateau end-expiratory pressure and static compliance curve of the ventilated lung were measured with and without applied PEEP, and the lower inflection point was determined from the compliance curve.

Results : Mean (+/- SD) Pao2 values, with a fraction of inspired oxygen of 1.0, were not different during one-lung ventilation before (192 +/- 91 mmHg), during (190 +/- 90), or after ( 205 +/- 79) the addition of 5 cm H2O PEEP. The mean plateau end-expiratory pressure increased from 4.2 to 6.8 cm H2O with the application of 5 cm H2O PEEP and decreased to 4.5 cm H2O when 5 cm H2O PEEP was removed. Six patients showed a clinically useful (> 20%) increase in Pao2 with 5 cm H2O PEEP, and nine patients had a greater than 20% decrease in Pao2. The change in Pao2 with the application of 5 cm H2O PEEP correlated in an inverse fashion with the change in the gradient between the end-expiratory pressure and the pressure at the lower inflection point (r = 0.76). The subgroup of patients with a Pao2 during two-lung ventilation that was less than the mean (365 mmHg) and an end-expiratory pressure during one-lung ventilation without applied PEEP less than the mean were more likely to have an increase in Pao2 when 5 cm H2O PEEP was applied.     

Airway Occlusion Pressure to Titrate Positive End-expiratory Pressure in Patients with Dynamic Hyperinflation

Background: Although the use of external positive end-expiratory pressure (PEEP) is recommended for patients with intrinsic PEEP, no simple method exists for bedside titration. We hypothesized that the occlusion pressure, measured from airway pressure during the phase of ventilator triggering (P0.1t), could help to indicate the effects of PEEP on the work of breathing (WOB).

Methods: Twenty patients under assisted ventilation with chronic obstructive pulmonary disease were studied with 0, 5, and 10 cm H2O of PEEP while ventilated with a fixed level of pressure support.

Results: PEEP 5 significantly reduced intrinsic PEEP (mean +/- SD, 5.2 +/- 2.4 cm H2O at PEEP 0 to 3.6 +/- 1.9 at PEEP 5;P < 0.001), WOB per min (12.6 +/- 6.7 J/min to 9.1 +/- 5.9 J/min;P = 0.003), WOB per liter (1.2 +/- 0.4 J/l to 0.8 +/- 0.4 J/l;P < 0.001), pressure time product of the diaphragm (216 +/- 86 cm H2O [middle dot] s-1 [middle dot] min-1 to 155 +/- 179 cm H2O [middle dot] s-1 [middle dot] min-1;P = 0.001) and P0.1t (3.3 +/- 1.5 cm H2O to 2.3 +/- 1.4 cm H2O;P = 0.002). At PEEP 10, no further significant reduction in muscle effort nor in P0.1t (2.5 +/- 2.1 cm H2O) occurred, and transpulmonary pressure indicated an increase in end-expiratory lung volume. Significant correlations were found between WOB per min and P0.1t at the three levels of PEEP (P < 0.001), and between the changes in P0.1tversus the changes in WOB per min (P < 0.005), indicating that P0.1t and WOB changed in the same direction. A decrease in P0.1 with PEEP indicated a decrease in intrinsic PEEP with a specificity of 71% and a sensitivity of 88% and a decrease in WOB with a specificity of 86% and a sensitivity of 91%.     

Recruitment Maneuvers after a Positive End-expiratory Pressure Trial Do Not Induce Sustained Effects in Early Adult Respiratory Distress Syndrome

Background: Recruitment maneuvers performed in early adult respiratory distress syndrome remain a matter of dispute in patients ventilated with low tidal volumes and high levels of positive end-expiratory pressure (PEEP). In this prospective, randomized controlled study the authors evaluated the impact of recruitment maneuvers after a PEEP trial on oxygenation and venous admixture (Qs/Qt) in patients with early extrapulmonary adult respiratory distress syndrome.

Methods: After a PEEP trial 30 consecutive patients ventilated with low tidal volumes and high levels of PEEP were randomly assigned to either undergo a recruitment maneuver or not. Data were recorded at baseline, 3 min after the recruitment maneuver, and 30 min after baseline. Recruitment maneuvers were performed with a sustained inflation of 50 cm H2O maintained for 30 s.

Results: Compared with baseline the ratio of the arterial oxygen partial pressure to the fraction of inspired oxygen (Pao2/Fio2) and Qs/Qt improved significantly at 3 min after the recruitment maneuver (Pao2/Fio2, 139 +/- 46 mm Hg versus 246 +/- 111 mm Hg, P < 0.001; Qs/Qt, 30.8 +/- 5.8% versus 21.5 +/- 9.7%, P < 0.005), but baseline values were reached again within 30 min. No significant differences in Pao2/Fio2 and Qs/Qt were detected between the recruitment maneuver group and the control group at baseline and after 30 min (recruitment maneuver group [n = 15]: Pao2/Fio2, 139 +/- 46 mm Hg versus 138 +/- 39 mm Hg; Qs/Qt, 30.8 +/- 5.8% versus 29.2 +/- 7.4%; control group: [n = 15]: Pao2/Fio2, 145 +/- 33 mm Hg versus 155 +/- 52 mm Hg; Qs/Qt, 30.2 +/- 8.5% versus 28.1 +/- 5.4%).     

Effects of Positive End-expiratory Pressure and Different Tidal Volumes on Alveolar Recruitment and Hyperinflation

Background: The morphologic effect of positive end-expiratory pressure (PEEP) and of two tidal volumes were studied by computed tomography to determine whether setting the tidal volume (Vt) at the upper inflection point (UIP) of the pressure-volume (P-V) curve of the respiratory system or 10 ml/kg have different effects on hyperinflation and alveolar recruitment.

Methods: Alveolar recruitment and hyperinflation were quantified by computed tomography in nine patients with the acute respiratory distress syndrome (ARDS). First, end expiration was compared without PEEP and with PEEP set at the lower inflection point of the P-V curve; second, at end inspiration above PEEP, a reduced Vt set at the UIP (rVt) and a standard 10 ml/kg Vt (Vt) ending above the UIP were compared. Three lung zones were defined from computed tomographic densities: hyperdense, normal, and hyperinflated zones.

Results: Positive end-expiratory pressure induced a significant decrease in hyperdensities (from 46.8 +/- 18% to 38 +/- 15.1% of zero end-expiratory pressure (ZEEP) area; P < 0.02) with a concomitant increase in normal zones (from 47.3 +/- 20.9% to 56.5 +/- 13.2% of the ZEEP area; P < 0.05), and a significant increase in hyperinflation (from 8.1 +/- 5.9% to 17.8 +/- 12.7% of ZEEP area; P < 0.01). At end inspiration, a significant increase in hyperinflated areas was observed with Vt compared with rVt (33.4 +/- 17.8 vs. 26.8 +/- 17.3% of ZEEP area; P < 0.05), whereas no significant difference was observed for both normal and hyperdense zones.     

A Comparison of Fat Intake of Normal Weight, Moderately Obese and Severely Obese Subjects

Background: Excess dietary fat has been implicated in the etiology of obesity. Methods: This study examined the fat intake of three weight groups, normal (20.0 < BMI < 27.0), moderately obese (27.1 < BMI < 39.9) and severely obese (BMI > 40.0). Each group contained 50 subjects. Detailed 3-day food records were used to gather the nutritional data. Anthropometric and sociodemographic information was also collected. Results: Overall fat intake was 89±42 g/day or 37 ± 10% of total energy. Total fat (g/1000 kcalories) intake was found to be significantly higher in the obese groups (p < 0.05). Subjects in the moderately and severely obese groups consumed significantly more fat and cholesterol and less carbohydrate than did normal weight subjects. Compared to the normal weight subjects, obese subjects also had higher intakes of saturated, monounsaturated and polyunsaturated fat (as a percentage of dietary energy). There was no difference in energy or protein intake, and P/S ratio among the three groups. BMI was strongly positively correlated with total fat, saturated, monounsaturated, polyunsaturated fat, cholesterol, and protein intake (as g/day only), and negatively correlated with carbohydrate intake and the CHO/FAT ratio. Energy intake was not significantly associated with BMI. Conclusion: A high fat diet may promote obesity, independently of its calorie contribution.     

小潮气量加低水平呼气末正压通气对腹腔镜手术患者呼吸力学及肺氧合功能的影响

目的探讨小潮气量加低水平呼气末正压（positive end-expiratory pressure,PEEP）机械通气对肺功能正常患者人工气腹期间呼吸力学及肺氧合功能的影响。方法 2009年8月~2010年4月,45例ASAⅠ~Ⅱ级,择期全麻下行腹腔镜手术患者,随机均分为3组,每组15例。麻醉诱导维持用药相同,气管插管后行机械通气,气腹前3组通气参数均设定为潮气量（VT）8 ml/kg,呼吸频率（RR）12次/min,吸呼比（I∶E）=1∶2。气腹后通气参数设定分别为：Ⅰ组VT=6 ml/kg,RR=18次/min,PEEP=5 cm H2O;Ⅱ组VT=10 ml/kg,RR=10次/min,PEEP=0;Ⅲ组（对照组）同气腹前。分别在气管插管后（T0）,手术开始（T1）,气腹5 min（T2）,气腹30 min（T3）,气腹60 min（T4）,拔气管导管前15 min（T5）,拔气管导管后20 min（T6）监测脉搏血氧饱和度（SpO2）、呼气末CO2分压（PETCO2）、气道峰压（Ppeak）、平均气道压（Pmean）,并计算肺动态顺应性（Cdyn）。分别在T0,T3,T4,T6时点抽取动脉血监测血气,并根据动脉血氧分压（PaO2）、动脉血CO2分压（PaCO2）、吸入氧浓度（FiO2）等计算氧合指数、呼吸指数、肺泡动脉血氧分压差（A-aDO2）。结果 3组各时点平均动脉压及心率、PaO2组间比较差异无显著性（P〉0.05）。与T0时相比,Ppeak气腹后升高（P〈0.05）,Ⅱ、Ⅲ组更明显;Pmean气腹后也升高（P〈0.05）,Ⅰ组最明显;Cdyn气腹后明显降低（P〈0.05）,Ⅱ组最明显;PETCO2明显升高（P〈0.05）,Ⅰ组更明显;气腹后pH值明显降低（P〈0.05）,Ⅰ组最明显;Ⅰ、Ⅲ组PaCO2气腹后明显升高（P〈0.05）,Ⅱ组无明显变化（P〉0.05）。与机械通气时（T0、T3、T4）相比,3组A-aDO2拔管后（T6）明显降低（P〈0.05）,Ⅰ组更明显;氧合指数拔管后（T6）明显降低（P〈0.05）,3组组间差异无显著性（P〉0.05）;呼吸指数拔管后明显降低,Ⅰ组最明显（P〈0.05）。结论小潮气量机械通气加低水平呼气末正压可以有效降低术中气道压,改善肺顺应性,增加肺通气效率,可以安全地应用于腹腔镜手术呼吸管理中。     

Spirometric Function Improves in the Morbidly Obese After 1-Year Post-surgery

Background  

Obesity can negatively affect pulmonary function tests, with or without clinical symptoms, but the impact of bariatric weight loss is still debated. Aiming to document such profile in a consecutive homogeneous population, a prospective cohort study was undertaken.     

Mitochondrial Respiratory Capacity and Content Are Normal in Young Insulin-Resistant Obese Humans

Considerable debate exists about whether alterations in mitochondrial respiratory capacity and/or content play a causal role in the development of insulin resistance during obesity. The current study was undertaken to determine whether such alterations are present during the initial stages of insulin resistance in humans. Young (∼23 years) insulin-sensitive lean and insulin-resistant obese men and women were studied. Insulin resistance was confirmed through an intravenous glucose tolerance test. Measures of mitochondrial respiratory capacity and content as well as H₂O₂ emitting potential and the cellular redox environment were performed in permeabilized myofibers and primary myotubes prepared from vastus lateralis muscle biopsy specimens. No differences in mitochondrial respiratory function or content were observed between lean and obese subjects, despite elevations in H₂O₂ emission rates and reductions in cellular glutathione. These findings were apparent in permeabilized myofibers as well as in primary myotubes. The results suggest that reductions in mitochondrial respiratory capacity and content are not required for the initial manifestation of peripheral insulin resistance.     

Roux-en Y Gastric Bypass Surgery Reduces Hedonic Hunger and Improves Dietary Habits in Severely Obese Subjects

Background

Many obese subjects suffer from an increased hedonic drive to consume palatable foods, i.e., hedonic hunger, and often show unfavorable dietary habits. Here, we investigated changes in the hedonic hunger and dietary habits after Roux-en-Y gastric bypass (RYGB) surgery.

Methods

Forty-four severely obese patients were examined before and on average 15.9?±?0.9 months after RYGB surgery with the Power of Food Scale (PFS), a questionnaire that reliably measures an individual’s motivation to consume highly palatable foods but not actual consumptive behavior. Dietary habits were assessed by a food frequency questionnaire.

Results

After the RYGB procedure, patients showed markedly lower aggregated PFS scores and sub-domain scores related to generally available, physically present, as well as tasted foods than before the surgery (all P?<?0.001). Changes in dietary habits after the surgery were characterized by a more frequent consumption of poultry, fish, eggs, and cooked vegetables (P?<?0.008) and a less frequent consumption of chocolate (P?<?0.048), cakes/biscuits/cookies (P?=?0.09), and fruit juice/soft drinks (P?=?0.08).

Conclusions

Data show a marked reduction of the hedonic drive to consume palatable food and beneficial changes in dietary habits characterized by an increased intake of protein-rich foods and vegetables and a reduced consumption of sugar-containing snacks and beverages after RYGB surgery. Based on these findings, it can be speculated that the reduction of the hedonic drive to consume palatable foods induced by RYGB surgery helps severely obese patients to establish healthier dietary habits.     

Effects of Ventilation with Large Tidal Volumes or Positive End-Expiratory Pressure on Cardiorespiratory Function in Anesthetized Obese Patients

The cardiorespiratory effects of ventilation with large tidal volumes (LTV) or positive end-expiratory pressure (PEEP) were investigated in 10 extremely obese patients during anesthesia for a jejuno-ileal by-pass operation.
Elevation of the tidal volume by 35% and insertion of a dead space (LTV-group: five patients) or applying a PEEP of 1.0 kPa (PEEP-group: five patients) resulted in significant rises in arterial oxygen tensions (Pa_o2) of 87.4% and 72.4%, respectively. The alveolar-arterial oxygen tension differences (P(a-a)_o2) decreased by 29.2% in the LTV-group and 25.6% in the PEEP-group when compared to control values. No significant differences were found between the groups in Pa_o2 or P(A-a)o₂.
PEEP-ventilation caused a maximal increase in compliance of 42.6%, but there was an increase of only 20.8% in the LTV-group.
Stroke index (the impedance cardiography method) decreased by 19.7% in the PEEP-group, whereas no changes occurred in the LTV-group. The decrease in stroke index was probably due to a reduction in venous return, as reflected in the systolic time intervals. In the PEEP-group a prolongation of the pre-ejection period (PEP) was observed, causing an increase in the PEP/LVET-ratio of 41.2%. A 13.8% increase in PEP/LVET-ratio was found in the LTV-group.
In spite of the increased arterial oxygen contents, no improvements in arterial oxygen delivery were found in either of the groups.     

Mechanical Ventilation with Lower Tidal Volumes and Positive End-expiratory Pressure Prevents Alveolar Coagulation in Patients without Lung Injury

Background: Alveolar fibrin deposition is a hallmark of acute lung injury, resulting from activation of coagulation and inhibition of fibrinolysis. Previous studies have shown that mechanical ventilation with high tidal volumes may aggravate lung injury in patients with sepsis and acute lung injury. The authors sought to determine the effects of mechanical ventilation on the alveolar hemostatic balance in patients without preexistent lung injury.

Methods: Patients scheduled for an elective surgical procedure (lasting >= 5 h) were randomly assigned to mechanical ventilation with either higher tidal volumes of 12 ml/kg ideal body weight and no positive end-expiratory pressure (PEEP) or lower tidal volumes of 6 ml/kg and 10 cm H2O PEEP. After induction of anesthesia and 5 h later bronchoalveolar lavage fluid and blood samples were obtained, and markers of coagulation and fibrinolysis were measured.

Results: In contrast to mechanical ventilation with lower tidal volumes and PEEP (n = 21), the use of higher tidal volumes without PEEP (n = 19) caused activation of bronchoalveolar coagulation, as reflected by a marked increase in thrombin-antithrombin complexes, soluble tissue factor, and factor VIIa after 5 h of mechanical ventilation. Mechanical ventilation with higher tidal volumes without PEEP caused an increase in soluble thrombomodulin in lavage fluids and lower levels of bronchoalveolar activated protein C in comparison with lower tidal volumes and PEEP. Bronchoalveolar fibrinolytic activity did not change by either ventilation strategy.