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.     

Prospective,randomized, controlled evaluation of the preventive effects of positive end-expiratory pressure on patient oxygenation during one-lung ventilation

BACKGROUND AND OBJECTIVE: This prospective, randomized, controlled study evaluated the effects on oxygenation by applying a selective and patient-specific value of positive end-expiratory pressure (PEEP) to the dependent lung during one-lung ventilation. METHODS: Fifty patients undergoing thoracic surgery under combined epidural/general anaesthesia were randomly allocated to receive zero PEEP (Group ZEEP, n = 22), or the preventive application of PEEP, optimized on the best thoracopulmonary compliance (Group PEEP, n = 28). Patients' lungs were mechanically ventilated with the same setting during two- and one-lung ventilation (FiO2 = 0.5; VT = 9mL kg(-1), inspiratory :expiratory time = 1 : 1, inspiratory pause = 10%). RESULTS: Lung-chest wall compliance decreased in both groups during one-lung ventilation, but patients of Group PEEP had 10% higher values than patients with no end-expiratory pressure (ZEEP) applied--Group ZEEP (P < 0.05). During closed chest one-lung ventilation, the PaO2 : FiO2 ratio was lower in Group PEEP (232 +/- 88) than in Group ZEEP (339 +/- 97) (P < 0.05); but no further differences were reported throughout the study. No differences were reported between the two groups in the need for 100% oxygen ventilation (10 patients of Group ZEEP (45%) and 14 patients of Group PEEP (50%) (P = 0.78)) or re-inflation of the operated lung during surgery (two patients of Group ZEEP (9%) and three patients of Group PEEP (10%) (P = 0.78)). Postanaesthesia care unit discharge required 48 min (25th-75th percentiles: 32-58 min) in Group PEEP and 45 min (30-57 min) in Group ZEEP (P = 0.60). CONCLUSIONS: The selective application of PEEP to the dependent, non-operated lung increases the lung-chest wall compliance during one-lung ventilation, but does not improve patient oxygenation.     

Effect of respiratory care on pulmonary function in patients after cardiopulmonary bypass

BACKGROUND: Respiratory failure after cardiopulmonary bypass (CPB) remains one of the major complications after cardiac surgery. This study was designed to evaluate effects of respiratory care after CPB on pulmonary function. METHODS: Eighteen patients scheduled for cardiac surgery were investigated. Preoperative respiratory functions (%VC, FEV1.0%, V25/Ht, FRC-CC, deltaN2) were measured in all the patients. Both induction and maintenance of anesthesia were performed using propofol, midazolam, fentanyl, and vecuronium bromide. All the patients were ventilated using volume controlled ventilation by setting FIO2 at 0.5, the respiratory frequency at 15 x min(-1), the tidal volume at 6-10 ml x kg(-1) adjusted to maintain PaCO2 between 30 to 40 mmHg, and the peak airway pressures below 40 cmH2O, PEEP of 0 cmH2O. From 1 hour after the operation, the patients were randomly divided into 2 groups: group A, ventilated artificially with PEEP of 5 cmH2O and group B, ventilated with PEEP adjusted to the patient's lower inflection point (LIP) obtained by the pressure-volume curve. PaO2, Qs/Qt and FRC were measured after induction of anesthesia, just after surgery, 1 hour after surgery and 1 hour after artificial ventilation with PEEP. The values of the LIP were obtained from the P-V curves with the constant-flow methods before and after surgery. RESULTS: PaO2 and FRC decreased and Qs/Qt increased significantly after the surgery in all the patients. One hour after artificial ventilation with PEEP, PaO2 increased and Qs/Qt decreased significantly compared with the values after operation. However, there was no significant difference in the magnitude of these changes among the different groups. The changes in PaO2 and Qs/Qt were not correlated with the changes in FRC and preoperative respiratory functions. The LIP tended to increase after surgery in 2 groups. CONCLUSIONS: Although pulmonary function deteriorated after CPB. PEEP could improve oxygenation in all the patients. There were no significant differences in the degree of these improvements between patients receiving PEEP of 5 cmH2O and patients with PEEP adjusted to their LIP. There was no significant relationship between preoperative pulmonary function and changes in oxygenation after CPB.     

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 (PaO(2)) 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 gases were measured during two-lung ventilation and one-lung ventilation before, during, and after the application of 5 cm H(2)O 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) PaO(2) 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 H(2)O PEEP. The mean plateau end-expiratory pressure increased from 4.2 to 6.8 cm H(2)O with the application of 5 cm H(2)O PEEP and decreased to 4.5 cm H(2)O when 5 cm H(2)O PEEP was removed. Six patients showed a clinically useful (> 20%) increase in PaO(2) with 5 cm H(2)O PEEP, and nine patients had a greater than 20% decrease in PaO(2). The change in PaO(2) with the application of 5 cm H(2)O 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 PaO(2) 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 PaO(2) when 5 cm H(2)O PEEP was applied. CONCLUSIONS: The effects of the application of external 5 cm H(2)O PEEP on oxygenation during one-lung ventilation correspond to individual changes in the relation between the plateau end-expiratory pressure and the inflection point of the static compliance curve. When the application of PEEP causes the end-expiratory pressure to increase from a low level toward the inflection point, oxygenation is likely to improve. Conversely, if the addition of PEEP causes an increased inflation of the ventilated lung that raises the equilibrium end-expiratory pressure beyond the inflection point, oxygenation is likely to deteriorate.     

Correlation between extravascular lung water and oxygenation in ALI/ARDS patients in septic shock: possible role in the development of atelectasis?

This study aimed to evaluate the relationship between PaO2/FiO2 ratio and extravascular lung water in septic shock-induced acute respiratory distress syndrome in a prospective observational clinical trial. Twenty-three patients suffering from sepsis induced acute respiratory distress syndrome were recruited. All patients were ventilated in pressure control/support mode. Haemodynamic parameters were determined by arterial thermodilution (PiCCO) eight hourly for 72 hours. At the same time blood gas analyses were done and respiratory parameters were also recorded. Data are presented as mean +/-SD. For statistical analysis Pearson's correlation test, and analysis of variance (ANOVA) was used respectively. Significant negative correlation was found between extravascular lung water and PaO2/FiO2 (r = -0.355, P < 0.001), and significant positive correlation was shown between extravascular lung water and PEEP (r=0.557, P<0.001). A post-hoc analysis was performed when "low" PEEP: < 10 cmH2O and "high" PEEP: (10 cmH2O PEEP was applied, and neither the oxygenation, nor the driving pressure or the PaCO2 differed significantly, but the extravascular lung water showed significant difference when "high" or "low" PEEP was applied (13+/-5 vs 9+/-2 ml/kg respectively, P=0.001). This study found significant negative correlation between extravascular lung water and PaO2/FiO2. The mechanism by which extravascular lung water affects oxygenation is unknown but the significant positive correlation between PEEP and extravascular lung water shown in this trial suggests that the latter may have a role in the development of alveolar atelectasis.     

Effects of lung recruitment maneuver and positive end-expiratory pressure on lung volume,respiratory mechanics and alveolar gas mixing in patients ventilated after cardiac surgery

BACKGROUND: It is unclear whether positive end-expiratory pressure (PEEP) is needed to maintain the improved oxygenation and lung volume achieved after a lung recruitment maneuver in patients ventilated after cardiac surgery performed in the cardiopulmonary bypass (CPB). METHODS: A prospective, randomized, controlled study in a university hospital intensive care unit. Sixteen patients who had undergone cardiac surgery in CPB were studied during the recovery phase while still being mechanically ventilated with an inspired fraction of oxygen (FiO2) 1.0. Eight patients were randomized to lung recruitment (two 20-s inflations to 45 cmH2O), after which PEEP was set and kept for 2.5 h at 1 cmH2O above the pressure at the lower inflexion point (14+/-3 cmH2O, mean +/-SD) obtained from a static pressure-volume (PV) curve (PEEP group). The remaining eight patients were randomized to a recruitment maneuver only (ZEEP group). End-expiratory lung volume (EELV), series dead space, ventilation homogeneity, hemodynamics and PaO2 (oxygenation) were measured every 30 min during a 3-h period. PV curves were obtained at baseline, after 2.5 h, and in the PEEP group at 3 h. RESULTS: In the ZEEP group all measures were unchanged. In the PEEP group the EELV increased with 1220+/-254 ml (P<0.001) and PaO2 with 16+/-16 kPa (P<0.05) after lung recruitment. When PEEP was discontinued EELV decreased but PaO2 was maintained. The PV curve at 2.5 h coincided with the curve obtained at 3 h, and both curves were both steeper than and located above the baseline curve. CONCLUSIONS: Positive end-expiratory pressure is required after a lung recruitment maneuver in patients ventilated with high FiO2 after cardiac surgery to maintain lung volumes and the improved oxygenation.     

The effects of the alveolar recruitment maneuver and positive end-expiratory pressure on arterial oxygenation during laparoscopic bariatric surgery

Abnormalities in gas exchange that occur during anesthesia are mostly caused by atelectasis, and these alterations are more pronounced in morbidly obese than in normal weight subjects. Sustained lung insufflation is capable of recruiting the collapsed areas and improving oxygenation in healthy patients of normal weight. We tested the effect of this ventilatory strategy on arterial oxygenation (Pao2) in patients undergoing laparoscopic bariatric surgery. After pneumoperitoneum was accomplished, the recruitment group received up to 4 sustained lung inflations with peak inspiratory pressures up to 50 cm H2O, which was followed by ventilation with 12 cm H2O positive end-expiratory pressure (PEEP). The patient's lungs in the control group were ventilated in a standard fashion with PEEP of 4 cm H2O. Variables related to gas exchange, respiratory mechanics, and hemodynamics were compared between recruitment and control groups. We found that alveolar recruitment effectively increased intraoperative Pao2 and temporarily increased respiratory system dynamic compliance (both P < 0.01). The effects of alveolar recruitment on oxygenation lasted as long as the trachea was intubated, and lungs were ventilated with high PEEP, but soon after tracheal extubation, all the beneficial effects on oxygenation disappeared. The mean number of vasopressor treatments given during surgery was larger in the recruitment group compared with the control group (3.0 versus 0.8; P = 0.04). In conclusion, our data suggest that the use of alveolar recruitment may be an effective mode of improving intraoperative oxygenation in morbidly obese patients. Our results showed the effect to be short lived and associated with more frequent intraoperative use of vasopressors.     

全麻中低潮气量机械通气对病人肺泡不张发生的影响

目的 探讨全麻中低潮气量（VT）机械通气对病人肺泡不张发生的影响。方法 择期全麻下行开颅手术病人16例。ASAⅠ级或Ⅱ级，心功能Ⅰ级或Ⅱ级，年龄20-50岁，随机分为2组，每组8例，常规VT（10 ml／kg）组（TV组）和低VT（6 ml／kg）组（LV组）。分别于气管插管后10 min和手术结束后10min采用移动CT行全肺扫描，计算膈上1 cm层面肺不张面积和百分比，同时行动脉血气分析，记录动脉血二氧化碳分压（PaCO2），并计算肺泡．动脉血氧分压差[P（A-a），O2]、氧合指数（PaO2／FiO2）及呼吸指数（RI）。结果 气管插管后10 min和手术结束后10 min时2组病人肺泡不张的发生率、面积、百分比、P（A-a）O2、PaCO2、PaO2／FiO2及RI组内、组间差异均无统计学意义（P〉0．05）。结论 低VT （6 ml／kg）机械通气不增加全麻下开颅手术病人肺泡不张的发生。     

低潮气量联合不同阶段呼气末正压通气对老年患者开腹术后肺功能的影响

目的观察术中低潮气量联合不同阶段呼气末正压通气(positive end expiratory pressure,PEEP)对老年患者开腹术后肺功能及并发症的影响。方法选择择期全麻下行开腹手术的老年患者60例,男21例,女39例,年龄≥65岁,ASAⅠ或Ⅱ级,随机分为三组,每组20例。A组手术开始后1h联合PEEP 10cm H_2O持续1h,B组术毕拔除气管导管前1h联合PEEP 10cm H_2O持续1h,C组手术全程联合PEEP 10cm H_2O。分别于术前、术后1、24h行血气分析测PaCO_2、PaO_2和A-aDO_2,计算氧合指数。记录术前、术后24、72h的气道分泌物评分。结果与术前比较,术后1h三组PaCO_2明显升高,B组PaO_2明显下降,A组A-aDO_2明显升高(P0.05);术后24hB组、C组PaCO_2明显升高,B组氧合指数明显下降(P0.05)。与术后1h比较,术后24hA组PaCO_2明显下降,A组A-aDO_2明显下降(P0.05)。术后三组气道分泌物评分差异无统计学意义。结论术中低潮气量联合不同阶段PEEP能够改善术后肺的氧合功能,但对术后肺部并发症无明显影响。     

Prevention of atelectasis formation during the induction of general anesthesia in morbidly obese patients

Atelectasis caused by general anesthesia is increased in morbidly obese patients. We have shown that application of positive end-expiratory pressure (PEEP) during the induction of anesthesia prevents atelectasis formation in nonobese patients. We therefore studied the efficacy of PEEP in morbidly obese patients to prevent atelectasis. Twenty-three adult morbidly obese patients (body mass index >35 kg/m(2)) were randomly assigned to one of two groups. In the PEEP group, patients breathed 100% oxygen (5 min) with a continuous positive airway pressure of 10 cm H(2)O and, after the induction, mechanical ventilation via a face mask with a PEEP of 10 cm H(2)O. In the control group, the same induction was applied but without continuous positive airway pressure or PEEP. Atelectasis, determined by computed tomography, and blood gas analysis were measured twice: before the induction and directly after intubation. After endotracheal intubation, patients of the control group showed an increase in the amount of atelectasis, which was much larger than in the PEEP group (10.4% +/- 4.8% in control group versus 1.7% +/- 1.3% in PEEP group; P < 0.001). After intubation with a fraction of inspired oxygen of 1.0, PaO(2) was significantly higher in the PEEP group compared with the control group (457 +/- 130 mm Hg versus 315 +/- 100 mm Hg, respectively; P = 0.035) We conclude that in morbidly obese patients, atelectasis formation is largely prevented by PEEP applied during the anesthetic induction and is associated with a better oxygenation. IMPLICATIONS: Application of positive end-expiratory pressure during induction of general anesthesia in morbidly obese patients prevents atelectasis formation and improves oxygenation. Therefore, this technique should be considered for anesthesia induction in morbidly obese patients.     

Effects of the alveolar recruitment manoeuver and PEEP on arterial oxygenation in anesthetized obese patients

BACKGROUND: Diminished functional residual capacity and pulmonary collapse during general anesthesia lead to alterations in respiratory mechanics and gas exchange. Such phenomena are more pronounced in obese patients. We recently demonstrated the beneficial effects of the alveolar recruitment strategy on oxygenation in anesthetized patients of normal body mass index (BMI). The aim of the present study was to evaluate whether obese patients also benefit from the alveolar recruitment strategy and to determine the level of positive end-expiratory pressure (PEEP) that prevents recollapse in obese patients. METHODS: Three groups of 30 patients each were studied: patients with normal BMI (control group) and obese patients to whom we applied PEEP at 5 and 10 cm H2O (obese-5 and obese-10 groups, respectively) after the recruitment maneuver. We studied respiratory mechanics (respiratory distensibility, airway pressures and flow volume) and arterial oxygenation (PaO2) before and after the recruitment. RESULTS: PaO2 at baseline was higher in the control group (174 +/- 44 mm Hg) than in either the obese-5 or obese-10 group (108 +/- 24 and 114 +/- 22 mm Hg, respectively, p < 0.001). Oxygenation improved in all groups after recruitment (p < 0.001), and PaO2 in the obese-10 group was similar to that of the control group (218 +/- 25 mm Hg and 259 +/- 80 mm Hg, respectively, p > 0.05). Oxygenation in the obese-5 group, however, was worse (153 +/- 41 mm Hg) than that of either of the other groups (p < 0.001). CONCLUSIONS: We conclude that the alveolar recruitment strategy was effective for increasing PaO2 in anesthetized patients, regardless of body mass. The oxygenation of obese patients receiving the higher level of PEEP was similar to that of non-obese patients.     

Arterial oxygenation during one lung ventilation in obese patients

To test the hypothesis that arterial oxygenation during one lung ventilation (OLV) is impaired more in obese patients than in non-obese control patients, we performed consecutive measurements of arterial oxygen tension (PaO2) during OLV in 48 patients scheduled for pulmonary lobectomy. Minimum value of PaO2 during OLV was significantly less in 16 obese patients [body mass index (BMI) > 25] compared to 32 control patients (BMI < 25). Moreover, PaO2 value of left lung ventilation was significantly less than the value of right lung ventilation in obese patients while the difference was not statistically significant in the control group.     

Oxygen in air (FiO2 0.4) improves gas exchange in young healthy patients during general anesthesia

PURPOSE: One hundred percent O(2) is used routinely for preoxygenation and induction of anesthesia. The higher the O(2) concentration the faster is the development of atelectasis, an important cause of impaired pulmonary gas exchange during general anesthesia (GA). We evaluated the effect of ventilation with 0.4 FiO(2) in air, 0.4 FiO(2) in N(2)O and 100% O(2) following intubation on the development of impaired gas exchange. METHODS: Twenty-seven patients aged 18-40 yr, undergoing elective laparoscopic cholecystectomy were administered 100% O(2) for preoxygenation (three minutes) and ventilation by mask (two minutes). Following intubation these patients were randomly divided into three groups of nine each and ventilated either with 0.4 FiO(2) in air, 0.4 FiO(2) in N(2)O or 100% O(2). Arterial blood gases were obtained before preoxygenation and 30 min following intubation for PaO(2) analysis. Subsequently PaO(2)/FiO(2) ratios were calculated. Results were analyzed with Student's t test and one-way ANOVA. P value of < or = 0.05 was considered significant. RESULTS: Ventilation of the lungs with O(2) in air (FiO(2) 0.4) significantly improved the PaO(2)/FiO(2) ratio from baseline, while 0.4 FiO(2) in N(2)O or 100% O(2) worsened the ratio (558 +/- 47 vs 472 +/- 28, 365 +/- 34 vs 472 +/- 22 and 351 +/- 23 vs 477 +/- 28 respectively; P < 0.05). CONCLUSION: Ventilation of lungs with O(2) in air (FiO(2) 0.4) improves gas exchange in young healthy patients during GA.     

High frequency oscillatory ventilation in burn patients with the acute respiratory distress syndrome

BACKGROUND: High frequency oscillatory ventilation (HFOV) improves gas exchange while providing lung protective effects during the ventilation of patients with the acute respiratory distress syndrome (ARDS). The purpose of this study was to review our experience with HFOV in adult burn patients with oxygenation failure secondary to ARDS. METHODS: Retrospective cohort review of all burn patients treated with HFOV at a regional adult burn center. RESULTS: All values are reported as the mean +/- standard deviation (S.D.). HFOV was used on 28 occasions in 25 patients (age 44 +/- 16 years, %TBSA burns 40 +/- 15, and a 28% incidence of inhalation injury) who had severe oxygenation failure from ARDS (PaO2/FiO2 ratio 98 +/- 26, and oxygenation index (OI) (FiO2 x 100 x mean airway pressure/PaO2) 27 +/- 10) following 4.8 +/- 4.4 days of conventional mechanical ventilation (CMV). After switching from CMV to HFOV, there were significant improvements in the PaO(2)/FiO2 ratio within 1h and in the oxygenation index within 24 h. The duration of HFOV was 6.1 +/- 5.8 days. HFOV was continued during 26 surgeries for 14 patients where a mean of 18 +/- 9% TBSA burns were excised and closed. The only complications related to HFOV were three episodes of severe hypercapnia. In-hospital mortality was 32%. CONCLUSIONS: HFOV was safe, and was highly effective in correcting oxygenation failure associated with ARDS in burn patients, and can be successfully used as an intra-operative ventilation modality for burn patients.     

Epidural block does not worsen oxygenation during one-lung ventilation for lung resections under isoflurane/nitrous oxide anaesthesia

BACKGROUND AND OBJECTIVES: The aim of this prospective, randomized, controlled clinical study was to evaluate the effects of thoracic epidural anaesthesia combined with isoflurane/nitrous oxide anaesthesia on intraoperative oxygenation during one-lung ventilation for lung resections. METHODS: Forty patients were randomly allocated to receive general anaesthesia maintained with isoflurane/nitrous oxide (group General, n = 20) or the same anaesthetic combined with thoracic epidural anaesthesia (group Integrated, n = 20). All patients were mechanically ventilated with the same settings (FiO2 = 0.5; VT = 9 mL kg(-1); inspiratory: expiratory time = 1:1; inspiratory pause = 10%). Effects on oxygenation were evaluated by determining the changes in PaO2/FiO2 ratio at 10, 30, 45 and 60 min of one-lung ventilation as compared to values obtained after induction of anaesthesia (supine, two-lung ventilation). RESULTS: The PaO2/FiO2 ratio was decreased in both groups during one-lung ventilation until the end of surgery. No differences were found at any observation time between the groups. Ventilation with 100% oxygen because of SpO2 decrease <92% was required in nine patients of group General (45%) and in eight patients of group Integrated (40%) (P = 0.64). Manual re-inflation of the operated lung was required in one patient of group General only (P = 0.99). Heart rate was lower in group Integrated than in group General throughout the study. No differences between the two groups in mean arterial pressure were observed. CONCLUSIONS: Adding a thoracic epidural block to isoflurane/nitrous oxide anaesthesia during one-lung ventilation for lung resections does not result in clinically relevant detrimental effects on intraoperative oxygenation.     

Effect of PEEP on regional ventilation during laparoscopic surgery monitored by electrical impedance tomography

Background: Anesthesia per se and pneumoperitoneum during laparoscopic surgery lead to atelectasis and impairment of oxygenation. We hypothesized that a ventilation with positive end‐expiratory pressure (PEEP) during general anesthesia and laparoscopic surgery leads to a more homogeneous ventilation distribution as determined by electrical impedance tomography (EIT). Furthermore, we supposed that PEEP ventilation in lung‐healthy patients would improve the parameters of oxygenation and respiratory compliance. Methods: Thirty‐two patients scheduled to undergo laparoscopic cholecystectomy were randomly assigned to be ventilated with ZEEP (0 cmH₂O) or with PEEP (10 cmH₂O) and a subsequent recruitment maneuver. Differences in regional ventilation were analyzed by the EIT‐based center‐of‐ventilation index (COV), which quantifies the distribution of ventilation and indicates ventilation shifts. Results: Higher amount of ventilation was examined in the dorsal parts of the lungs in the PEEP group. Throughout the application of PEEP, a lower shift of ventilation was found, whereas after the induction of anesthesia, a remarkable ventral shift of ventilation in ZEEP‐ventilated patients (COV: ZEEP, 40.6 ± 2.4%; PEEP, 46.5 ± 3.5%; P<0.001) was observed. Compared with the PEEP group, ZEEP caused a ventral misalignment of ventilation during pneumoperitoneum (COV: ZEEP, 41.6 ± 2.4%; PEEP, 44 ± 2.7%; P=0.013). Throughout the study, there were significant differences in the parameters of oxygenation and respiratory compliance with improved values in PEEP‐ventilated patients. Conclusion: The effect of anesthesia, pneumoperitoneum, and different PEEP levels can be evaluated by EIT‐based COV monitoring. An initial recruitment maneuver and a PEEP of 10 cmH₂O preserved homogeneous regional ventilation during laparoscopic surgery in most, but not all, patients and improved oxygenation and respiratory compliance.     

Evaluation of a recruitment maneuver with positive inspiratory pressure and high PEEP in patients with severe ARDS

BACKGROUND: To evaluate the effect of a recruitment maneuver (RM) with constant positive inspiratory pressure and high positive end-expiratory pressure (PEEP) on oxygenation and static compliance (Cs) in patients with severe acute respiratory distress syndrome (ARDS). METHODS: Eight patients with ARDS ventilated with lung-protective strategy and an arterial partial pressure of oxygen to inspired oxygen fraction ratio (PaO2/FIO2) < or =100 mmHg regardless of PEEP were prospectively studied. The RM was performed in pressure-controlled ventilation at FIO2 of 1.0 until PaO2 reached 250 mmHg or a maximal plateau pressure/PEEP of 60/45 cmH2O was achieved. The RM was performed with stepwise increases of 5 cmH2O of PEEP every 2 min and thereafter with stepwise decreases of 2 cmH2O of PEEP every 2 min until a drop in PaO2 >10% below the recruitment PEEP level. Data was collected before (preRM), during and after 30 min (posRM). RESULTS: The PaO2/FIO2 increased from 83 +/- 22 mmHg preRM to 118 +/- 32 mmHg posRM (P = 0.001). The Cs increased from 28 +/- 10 ml cmH2O(-1) preRM to 35 +/- 12 ml cmH2O(-1) posRM (P = 0.025). The PEEP was 12 +/- 3 cmH2O preRM and was set at 15 +/- 4 cmH2O posRM (P = 0.025). The PEEP of recruitment was 36 +/- 9 cmH2O and the collapsing PEEP was 13 +/- 4 cmH2O. The PaO2 of recruitment was 225 +/- 105 mmHg, with five patients reaching a PaO2 > or = 250 mmHg. The FIO2 decreased from 0.76 +/- 0.16 preRM to 0.63 +/- 0.15 posRM (P = 0.001). No major complications were detected. CONCLUSION: Recruitment maneuver was safe and useful to improve oxygenation and Cs in patients with severe ARDS ventilated with lung-protective strategy.     

Pressure control inverse ratio ventilation in the treatment of adult respiratory distress syndrome in patients with blunt chest trauma.

The objective of this study was to evaluate the efficacy of pressure control inverse ratio ventilation (PCIRV) in improving oxygenation in trauma patients with adult respiratory distress syndrome (ARDS) and to assess the potential risks associated with this form of treatment. This was a cohort study assessing the trends in hemodynamic and ventilatory parameters after the initiation of PCIRV, conducted at a community Level I trauma center intensive care unit. The study comprised 15 trauma patients developing severe, progressive ARDS [two or more of the following criteria: positive end-expiratory pressure (PEEP) >10 cm H2O; arterial partial pressure of oxygen divided by fraction of inspired oxygen (PaO2:FiO2) ratio <150; and peak inspiratory pressure (PIP) >45 cm H2O]: ten due to blunt chest injuries, three due to sepsis, and two due to fat emboli syndrome. PCIRV was initiated. Main outcome measures were PIP, PEEP (total, auto), oxygen saturation, cardiac index, oxygen delivery, PaO2:FiO2 ratio, compliance, evidence of complications of PCIRV, and mortality. Within 24 hours of conversion to PCIRV, the patients stabilized and the mean PaO2:FiO2 ratio rose from 96.3+/-57.8 to 146.8+/-91.1 (P<0.05) and PIP fell from 47.9+/-13.8 to 38.8+/-8.4 cm H2O; auto-PEEP increased from 0.5+/-1.9 to 7.5+/-5.6 cm H2O (P<0.05); oxygen delivery index remained stable (563+/-152 to 497+/-175 mL/min/m2); three patients developed evidence of barotrauma, one patient developed critical illness polyneuropathy, and two patients died (13%). PCIRV is an effective salvage mode of ventilation in patients with severe ARDS, but it is not without complications. Auto-PEEP levels and cardiac index should be monitored to ensure tissue oxygen delivery is maintained.     

Partial liquid ventilation in acute salt water-induced lung injury

BACKGROUND AND OBJECTIVES: Salt-water aspiration results in pulmonary oedema and hypoxia. We tested the hypothesis that partial liquid ventilation has beneficial effects on gas exchange and rate of survival in acute and extended salt water-induced lung injury. METHODS: Anaesthetized, ventilated rats (tidal volume 6 mL kg(-1), PEEP 5 cmH2O) received a tracheal salt-water instillation (3%, 8 mL kg(-1) body weight) and were randomly assigned to three groups (n = 10 per group). While lungs of Group 1 were gas-ventilated, lungs of Group 2 received a single perfluorocarbon instillation (30 min after the injury, 5 mL kg(-1) perfluorocarbon) and lungs of Group 3 received an additional continuous perfluorocarbon application into the treachea (5 mL kg(-1) h(-1)) Arterial blood gases were measured with an intravascular blood gas sensor. RESULTS: Salt-water instillation resulted in a marked decrease in PaO2 values within 30 min (from 432 +/- 65 to 83 +/- 40 mmHg, FiO2 = 1.0, P < 0.01). Arterial oxygenation improved in all three groups irrespective of treatment. We observed no significant differences between groups in peak PaO2 and PaCO2 values. CONCLUSIONS: Our results suggest that partial liquid ventilation has no additional beneficial effects on gas exchange after life-threatening salt water-induced lung injury when compared to conventional gas ventilation with positive end-expiratory pressure.     

Comparison of exogenous surfactant therapy, mechanical ventilation with high end-expiratory pressure and partial liquid ventilation in a model of acute lung injury

We have compared three treatment strategies, that aim to prevent repetitive alveolar collapse, for their effect on gas exchange, lung mechanics, lung injury, protein transfer into the alveoli and surfactant system, in a model of acute lung injury. In adult rats, the lungs were ventilated mechanically with 100% oxygen and a PEEP of 6 cm H2O, and acute lung injury was induced by repeated lung lavage to obtain a PaO2 value < 13 kPa. Animals were then allocated randomly (n = 12 in each group) to receive exogenous surfactant therapy, ventilation with high PEEP (18 cm H2O), partial liquid ventilation or ventilation with low PEEP (8 cm H2O) (ventilated controls). Blood-gas values were measured hourly. At the end of the 4-h study, in six animals per group, pressure-volume curves were constructed and bronchoalveolar lavage (BAL) was performed, whereas in the remaining animals lung injury was assessed. In the ventilated control group, arterial oxygenation did not improve and protein concentration of BAL and conversion of active to non-active surfactant components increased significantly. In the three treatment groups, PaO2 increased rapidly to > 50 kPa and remained stable over the next 4 h. The protein concentration of BAL fluid increased significantly only in the partial liquid ventilation group. Conversion of active to non-active surfactant components increased significantly in the partial liquid ventilation group and in the group ventilated with high PEEP. In the surfactant group and partial liquid ventilation groups, less lung injury was found compared with the ventilated control group and the group ventilated with high PEEP. We conclude that although all three strategies improved PaO2 to > 50 kPa, the impact on protein transfer into the alveoli, surfactant system and lung injury differed markedly.