Oxygenation Impairment during Anesthesia: Influence of Age and Body Weight.

WHAT WE ALREADY KNOW ABOUT THIS TOPIC: During anesthesia oxygenation is impaired, especially in the elderly or obese, but the mechanisms are uncertain. WHAT THIS ARTICLE TELLS US THAT IS NEW: Pooled data were examined from 80 patients studied with multiple inert gas elimination technique and computed tomography. Oxygenation was impaired by anesthesia, more so with greater age or body mass index. The key contributors were low ventilation/perfusion ratio (likely airway closure) in the elderly and shunt (atelectasis) in the obese. BACKGROUND: Anesthesia is increasingly common in elderly and overweight patients and prompted the current study to explore mechanisms of age- and weight-dependent worsening of arterial oxygen tension (PaO2). METHODS: This is a primary analysis of pooled data in patients with (1) American Society of Anesthesiologists (ASA) classification of 1; (2) normal forced vital capacity; (3) preoxygenation with an inspired oxygen fraction (FIO2) more than 0.8 and ventilated with FIO2 0.3 to 0.4; (4) measurements done during anesthesia before surgery. Eighty patients (21 women and 59 men, aged 19 to 69 yr, body mass index up to 30 kg/m2) were studied with multiple inert gas elimination technique to assess shunt and perfusion of poorly ventilated regions (low ventilation/perfusion ratio [(Equation is included in full-text article.)]) and computed tomography to assess atelectasis. RESULTS: PaO2/FIO2 was lower during anesthesia than awake (368; 291 to 470 [median; quartiles] vs. 441; 397 to 462 mm Hg; P = 0.003) and fell with increasing age and body mass index. Log shunt was best related to a quadratic function of age with largest shunt at 45 yr (r2 =0.17, P = 0.001). Log shunt was linearly related to body mass index (r2 = 0.15, P < 0.001). A multiple regression analysis including age, age2, and body mass index strengthened the association further (r2 = 0.27). Shunt was highly associated to atelectasis (r2 = 0.58, P < 0.001). Log low (Equation is included in full-text article.)showed a linear relation to age (r2 = 0.14, P = 0.001). CONCLUSIONS: PaO2/FIO2 ratio was impaired during anesthesia, and the impairment increased with age and body mass index. Shunt was related to atelectasis and was a more important cause of oxygenation impairment in middle-aged patients, whereas low(Equation is included in full-text article.), likely caused by airway closure, was more important in elderly patients. Shunt but not low(Equation is included in full-text article.)increased with increasing body mass index. Thus, increasing age and body mass index impaired gas exchange by different mechanisms during anesthesia.

Positive End-expiratory Pressure Alone Minimizes Atelectasis Formation in Nonabdominal Surgery: A Randomized Controlled Trial.

BACKGROUND: Various methods for protective ventilation are increasingly being recommended for patients undergoing general anesthesia. However, the importance of each individual component is still unclear. In particular, the perioperative use of positive end-expiratory pressure (PEEP) remains controversial. The authors tested the hypothesis that PEEP alone would be sufficient to limit atelectasis formation during nonabdominal surgery. METHODS: This was a randomized controlled evaluator-blinded study. Twenty-four healthy patients undergoing general anesthesia were randomized to receive either mechanical ventilation with PEEP 7 or 9 cm H2O depending on body mass index (n = 12) or zero PEEP (n = 12). No recruitment maneuvers were used. The primary outcome was atelectasis area as studied by computed tomography in a transverse scan near the diaphragm, at the end of surgery, before emergence. Oxygenation was evaluated by measuring blood gases and calculating the ratio of arterial oxygen partial pressure to inspired oxygen fraction (PaO2/FIO2 ratio). RESULTS: At the end of surgery, the median (range) atelectasis area, expressed as percentage of the total lung area, was 1.8 (0.3 to 9.9) in the PEEP group and 4.6 (1.0 to 10.2) in the zero PEEP group. The difference in medians was 2.8% (95% CI, 1.7 to 5.7%; P = 0.002). Oxygenation and carbon dioxide elimination were maintained in the PEEP group, but both deteriorated in the zero PEEP group. CONCLUSIONS: During nonabdominal surgery, adequate PEEP is sufficient to minimize atelectasis in healthy lungs and thereby maintain oxygenation. Thus, routine recruitment maneuvers seem unnecessary, and the authors suggest that they should only be utilized when clearly indicated. VISUAL ABSTRACT: An online visual overview is available for this article at http://links.lww.com/ALN/B728.

Intraabdominal Surgery and Anesthesia Management.

Inspired Oxygenation in Surgical Patients During General Anesthesia With Controlled Ventilation: A Concept of Atelectasis. By Bendixen HH, Hedley-Whyte J, and Laver MB. New Engl J Med 1963; 269:991-996. Reprinted with permission. ABSTRACT: The purpose of this study was to determine if the pattern of ventilation, by itself, influences oxygenation during anesthesia and surgery and examine the hypothesis that progressive pulmonary atelectasis may occur during constant ventilation whenever periodic hyperventilation is lacking, but is reversible by passive hyperinflation of the lungs. Eighteen surgical patients, ranging in age from 24 to 87 yr, without known pulmonary disease, were studied during intraabdominal procedures and one radical mastectomy. Although ventilation remained constant, changes occurred in arterial oxygen tension and in total pulmonary compliance, with an average fall of 22% in oxygen tension and 15% in total pulmonary compliance. This fall in oxygen tension supports the hypothesis that progressive mechanical atelectasis may lead to increased venous admixture to arterial blood. The influence of the ventilator pattern on atelectasis and shunting is further illustrated by the reversibility of the fall in oxygen tension that follows hyperinflation. A relation between the degree of ventilation and the magnitude of fall in arterial oxygen tension was found, where large tidal volumes appear to protect against falls in oxygen tension, while shallow tidal volumes lead to atelectasis and increased shunting with impaired oxygenation.

Continuous High-Frequency Oscillation Therapy in Invasively Ventilated Pediatric Subjects in the Critical Care Setting.

BACKGROUND: Continuous high-frequency oscillation (CHFO) creates a pressure gradient in the small airways that accelerates expiratory flow. The intended use of CHFO therapy is to facilitate secretion removal and treat atelectasis. Our objective was to assess the feasibility, safety, and efficacy of CHFO in the mechanically ventilated pediatric population. METHODS: After institutional review board approval, we retrospectively reviewed medical records of mechanically ventilated children treated with CHFO (the MetaNeb system) at our institution from July 1, 2007 through August 31, 2012. Patients supported with extracorporeal membrane oxygenation were excluded. We evaluated changes in ventilator settings in subjects with ventilator data documented within 6 h pre- and post-treatment. We evaluated arterial blood gas (ABG) results for individual treatments, comparing ABG results within 8 h pre-therapy to ABG results within 3 h post-treatment. Oxygen index and PaO2 /FIO2 were calculated. Demographic data, blood pressure, heart rate, and development of new air leak while being treated with CHFO were recorded. Pre- and post-CHFO measurements were compared using Wilcoxon signed-rank testing. RESULTS: Our cohort included 59 invasively ventilated subjects. Median age was 2 y (range 1 month to 19 y), and median weight was 14 kg (2-81 kg). We evaluated data on 528 total treatments (range per subject 1-39 treatments). Peak inspiratory pressure significantly decreased with CHFO, whereas other parameters, including PaCO2 and breathing frequency, remained stable. There was no significant change in systolic blood pressure, diastolic blood pressure, or heart rate following treatment with CHFO. One subject (2%) developed a clinically insignificant pneumothorax during CHFO. CONCLUSIONS: CHFO is feasible and seems safe in our cohort of mechanically ventilated pediatric subjects. The rate of pneumothorax was consistent with that seen in similar pediatric ICU populations. These preliminary results suggest that CHFO may be beneficial by improving lung compliance in pediatric subjects with secretion-induced atelectasis. Prospective clinical studies are needed to further evaluate the clinical efficacy and safety of CHFO in children receiving invasive mechanical ventilation.

PREOXYGENATION: COULD SAFETY MEASURE BE MADE LESS DANGEROUS?.

While providing reserve time for dificult airway management, preoxygenation with pure oxygen increases the risk of pulmonary complications due to absorption atelectases. The authors explored when it could be appropriate to prevent atelectases by preoxygenation with decreased FiO2. ASA I-II elective gynecological surgery patients were randomized among five groups (n = 22 each) with preoxygenation using FiO2 100, 70, 60, 60% + PEEP 5 mbar and 50%. Even FiO2 70% led to decrease. in safe apnea time (i.e. time interval to Sp²O2 95%) by two, while FiO2 50% - by more than three times. Furthermore, in five similar additional groups of women with same techniques ofpreoxygenation (n = 10 each) it was shown that for FiO2 5 70% very fast pattern of SpO2 fall after the first change ofpulseoxymeter figure (100% by 99%) is typical: interval to SpO2 90% was less than 1 min, while for FiO2 100% it lasts for 200 s. Since critical problem is "Cannot intubate, cannot ventilate", the authors tried to focus on the difficultfacemask ventilation prognosis. In the group of 71 elective general surgery patients (31 males, 40 females, ASA I-III) original prognostic model based on seven simple bedside tests (removable dentures, beard, snoring, Mallampati class 2-4, age > 50 y.o., BM > 30 kg/m², sternomental distance < 12 cm) demonstrated the reliability of difficult facemask ventilation negative prognosis of 97,5%. The authors suggest that only in patients with reliable prognosis of easy facemask ventilation prevention ofpulmonary complications by preoxygenation with FiO2 50-60% could be safely recommended.

Hints for cyclical recruitment of atelectasis during ongoing mechanical ventilation in lavage and oleic acid lung injury detected by SpO2 oscillations and electrical impedance tomography.

PURPOSE OF THE STUDY: Detection of cyclical recruitment of atelectasis after induction of lavage (LAV) or oleic acid injury (OAI) in mechanically ventilated pigs. Primary hypothesis is that oxygen oscillations within the respiratory cycle can be detected by SpO2 recordings (direct hint). SpO2 oscillations reflect shunt oscillations that can only be explained by cyclical recruitment of atelectasis. Secondary hypothesis is that electrical impedance tomography (EIT) depicts specific regional changes of lung aeration and of pulmonary mechanical properties (indirect hint). MATERIALS AND METHODS: Three groups (each n = 7) of mechanically ventilated pigs were investigated applying above mentioned methods before and repeatedly after induction of lung injury: (1) sham treated animals (SHAM), (2) LAV, and (3) OAI. RESULTS: Early oxygen oscillations occurred in the LAV group (mean calculated amplitude: 73.8 mmHg reflecting shunt oscillation of 11.2% in mean). In the OAI group oxygen oscillations occurred hours after induction of lung injury (mean calculated amplitude: 57.1 mmHg reflecting shunt oscillations of 8.4% in mean). The SHAM group had no relevant oxygen oscillations (<30 mmHg, shunt oscillations < 1.5%). Synchronously to oxygen oscillations, EIT depicted (1) a decrease of ventilation in dorsal areas, (2) an increase in ventral areas, (3) a decrease of especially dependent expiratory impedance, 3) an increase in late inspiratory flow especially in the dependant areas, (4) an increase in the speed of peak expiratory flow (PEF), and (5) a decrease of dorsal late expiratory flow. CONCLUSIONS: SpO2 and EIT recordings detect events that are interpreted as cyclical recruitment of atelectasis.

A fibre optic oxygen sensor that detects rapid PO2 changes under simulated conditions of cyclical atelectasis in vitro.

Two challenges in the management of Acute Respiratory Distress Syndrome are the difficulty in diagnosing cyclical atelectasis, and in individualising mechanical ventilation therapy in real-time. Commercial optical oxygen sensors can detect [Formula: see text] oscillations associated with cyclical atelectasis, but are not accurate at saturation levels below 90%, and contain a toxic fluorophore. We present a computer-controlled test rig, together with an in-house constructed ultra-rapid sensor to test the limitations of these sensors when exposed to rapidly changing [Formula: see text] in blood in vitro. We tested the sensors' responses to simulated respiratory rates between 10 and 60 breaths per minute. Our sensor was able to detect the whole amplitude of the imposed [Formula: see text] oscillations, even at the highest respiratory rate. We also examined our sensor's resistance to clot formation by continuous in vivo deployment in non-heparinised flowing animal blood for 24h, after which no adsorption of organic material on the sensor's surface was detectable by scanning electron microscopy.

Impact of lung ultrasound on clinical decision making in critically ill patients.

PURPOSE: To assess the impact of lung ultrasound (LU) on clinical decision making in mechanically ventilated critically ill patients. METHODS: One hundred and eighty-nine patients took part in this prospective study. The patients were enrolled in the study when LU was requested by the primary physician for (1) unexplained deterioration of arterial blood gases and (2) a suspected pathologic entity [pneumothorax, significant pleural effusion (including parapneumonic effusion, empyema, or hemothorax), unilateral atelectasis (lobar or total), pneumonia and diffuse interstitial syndrome (pulmonary edema)]. RESULTS: Two hundred and fifty-three LU examinations were performed; 108 studies (42.7%) were performed for unexplained deterioration of arterial blood gases, and 145 (57.3%) for a suspected pathologic entity (60 for pneumothorax, 34 for significant pleural effusion, 22 for diffuse interstitial syndrome, 15 for unilateral lobar or total lung atelectasis, and 14 for pneumonia). The net reclassification index was 85.6%, indicating that LU significantly influenced the decision-making process. The management was changed directly as a result of information provided by the LU in 119 out of 253 cases (47%). In 81 cases, the change in patient management involved invasive interventions (chest tube, bronchoscopy, diagnostic thoracentesis/fluid drainage, continuous venous-venous hemofiltration, abdominal decompression, tracheotomy), and in 38 cases, non-invasive (PEEP change/titration, recruitment maneuver, diuretics, physiotherapy, change in bed position, antibiotics initiation/change). In 53 out of 253 cases (21%), LU revealed findings which supported diagnoses not suspected by the primary physician (7 cases of pneumothorax, 9 of significant pleural effusion, 9 of pneumonia, 16 of unilateral atelectasis, and 12 of diffuse interstitial syndrome). CONCLUSION: Our study shows that LU has a significant impact on decision making and therapeutic management.

Lung collapse in the diving sea lion: hold the nitrogen and save the oxygen.

Lung collapse is considered the primary mechanism that limits nitrogen absorption and decreases the risk of decompression sickness in deep-diving marine mammals. Continuous arterial partial pressure of oxygen profiles in a free-diving female California sea lion (Zalophus californianus) revealed that (i) depth of lung collapse was near 225 m as evidenced by abrupt changes in during descent and ascent, (ii) depth of lung collapse was positively related to maximum dive depth, suggesting that the sea lion increased inhaled air volume in deeper dives and (iii) lung collapse at depth preserved a pulmonary oxygen reservoir that supplemented blood oxygen during ascent so that mean end-of-dive arterial was 74 ± 17 mmHg (greater than 85% haemoglobin saturation). Such information is critical to the understanding and the modelling of both nitrogen and oxygen transport in diving marine mammals.

Assessing the impact of lung hyperinflation maneuver on systemic inflammatory response and lung collapse in patients undergoing surgeries under spontaneous ventilation.

BACKGROUND AND OBJECTIVES: Lung hyperinflation maneuvers (LHM) reverse intraoperative atelectasis; however, they can lead to pulmonary-induced systemic inflammatory response. The objective of this study was to determine the impact of LHM on systemic inflammatory response and lung structure in patients undergoing subarachnoid block. METHODS: After approval by the Ethics Committee of the institution and signing the informed consent, 20 patients undergoing small and medium surgical procedures were randomly separated into two groups: 1) control (CG), and 2) LHM (LHMG). One hour after the spinal anesthesia, LHM was performed in LHMG by applying bilevel positive pressure in the airways (BIPAP) with an expiratory pressure of 20 cmH(2)O and inspiratory pressure of 20 cmH(2)O for 1 to 2 minutes. Blood levels of TNFalpha, IL-1, IL-6, IL-8, IL-10, and IL-12 were determined by flow cytometry at baseline and at 90, 180, and 780 minutes. Lung volumes and weights were determined using CT scans obtained immediately after the surgery. RESULTS: The use of LHM resulted in a reduction in the fraction of non-aerated pulmonary parenchyma (7.5 +/- 4.3%, in the Control Group, vs. 4 +/- 2.1%, in the LHM Group, p = 0.02) without changing pulmonary volumes. A progressive increase in plasma levels of IL-1, IL-6, IL-8, and IL-10, similar in both groups, was observed. Plasma levels of TNFalpha and IL-12 were undetectable during the study. CONCLUSIONS: The use of LHM reduced the incidence of atelectasis, but it did not amplify the inflammatory response in patients with normal lungs undergoing small and medium surgeries under subarachnoid block.

Observation of ventilation-induced Spo(2) oscillations in pigs: first step to noninvasive detection of cyclic recruitment of atelectasis?

High arterial partial oxygen pressure (Pao(2)) oscillations within the respiratory cycle were described recently in experimental acute lung injury. This phenomenon has been related to cyclic recruitment of atelectasis and varying pulmonary shunt fractions. Noninvasive detection of Spo(2) (oxygen saturation measured by pulse oximetry) as an indicator of cyclic collapse of atelectasis, instead of recording Pao(2) oscillations, could be of clinical interest in critical care. Spo(2) oscillations were recorded continuously in three different cases of lung damage to demonstrate the technical feasibility of this approach. To deduce Pao(2) from Spo(2), a mathematical model of the hemoglobin dissociation curve including left and right shifts was derived from the literature and adapted to the dynamic changes of oxygenation. Calculated Pao(2) amplitudes (derived from Spo(2) measurements) were compared to simultaneously measured fast changes of Pao(2), using a current standard method (fluorescence quenching of ruthenium). Peripheral hemoglobin saturation was capable to capture changes of Spo(2) within each respiratory cycle. For the first time, Spo(2) oscillations due to cyclic recruitment of atelectasis within a respiratory cycle were determined by photoplethysmography, a technology that can be readily applied noninvasively in clinical routine. A mathematic model to calculate the respective Pao(2) changes was developed and its applicability tested.

Inflammatory response in ventilated left and collapsed right lungs, serum and pleural fluid, in transthoracic esophagectomy for cancer.

INTRODUCTION: Open, right-sided, transthoracic esophagectomy with one-lung ventilation (OLV) triggers a massive inflammatory reaction. The influence of the OLV on the inflammatory cascade is unclear. Data on the inflammatory response in the ventilated left and collapsed right lung, respectively, are scarce. The aim of this study was to analyze this reaction in bronchoalveolar lavage (BAL) fluid from both lungs, the right pleural space and the peripheral blood, and to study its time course. METHODS: Concentrations of interleukin (IL)-6, IL-8, IL-10 and IL-1RA in the BAL fluids from the right and left lungs, respectively, in the peripheral blood and in the right pleural space in patients undergoing transthoracic esophagectomy for cancer, were determined using enzyme-linked immunosorbent assays in 29 patients. RESULTS: Assay of the pro-inflammatory cytokines in the bilateral BAL fluids showed significantly higher concentrations in the ventilated left lung at the time of extubation. The anti-inflammatory response was only seen with respect to IL-1RA, but not IL-10, and was mostly restricted to the ventilated left lung. In the blood, only IL-6, IL-10 and IL-1RA increased, whereas IL-8 showed little change. The response was already observed at the end of surgery, indicating a rapid reaction to the surgical and anesthetic trauma. In the pleural fluid, all cytokine concentrations increased, and the highest values were detected on day one post-surgery, and decreased thereafter. Pulmonary complications or anastomotic leakage were not related to the cytokine concentrations. CONCLUSION: Both the ventilated left and the collapsed right lung showed an inflammatory response. The response was more pronounced on the ventilated left side and the time courses were significantly different. In the blood, the pro-inflammatory IL-6 and both anti-inflammatory cytokines increased early on. All cytokines increased in the pleural cavity. The findings underline the complexity of the inflammatory reaction associated with OLV in transthoracic esophagectomy.

Advantages of autologous blood transfusion in off-pump coronary artery bypass.

BACKGROUND: In this randomized controlled study, we investigated the effects of autologous Hemobag blood transfusion (AHBT) and allogenic blood transfusion (ABT) in off-pump coronary artery bypass (OPCAB) surgery. METHODS: Sixty patients who underwent surgery between February 2008 and August 2008 were randomized into 2 groups. The AHBT group (n = 30) consisted of patients who received autologous Hemobag blood transfusion, and the ABT group (n = 30) consisted of patients who received allogenic blood transfusion. All patients underwent OPCAB via sternotomy. The time to extubation, chest tube drainage volume, postoperative white blood cell counts, amount of blood transfusion, sedimentation rate, C-reactive protein concentration, postoperative temperature, and the presence of atelectasis were recorded in the intensive care unit. RESULTS: Intraoperative bleeding and fluid resuscitation were similar in the 2 groups (P > .05); however, there were significant decreases in postoperative blood loss, extubation period, postoperative white cell counts, sedimentation rate, incidence of atelectasis, C-reactive protein, and fever in the AHBT group compared with the ABT group (P < .05). The rate of atrial fibrillation in the AHBT group tended to be lower than in the ABT group. CONCLUSION: Autologous blood transfusion in OPCAB may be beneficial in certain cardiac surgery patients; however, these beneficial effects require further study to be proved.

The effects of open lung ventilation on respiratory mechanics and haemodynamics in atelectatic infants after cardiopulmonary bypass.

Acute lung injury (ALI) frequently occurs in infants after cardiopulmonary bypass (CPB) surgery and it sometimes develops into acute respiratory distress syndrome in critically ill infants, which can be life threatening. This study investigated the effects of open lung ventilation on the haemodynamics and respiratory mechanics of 64 infants (34 males; 30 females) with a mean +/- SD age of 8.3 +/- 0.3 months who developed ALI following CPB surgery. Open lung ventilation significantly improved the respiratory mechanics and oxygenation parameters of the infants, including the partial pressure of oxygen in arterial blood (PaO(2)), the ratio of PaO(2)/FiO(2) (fraction of inspired oxygen), peak inspiratory pressure, static compliance and airway resistance. It is concluded that open lung ventilation can greatly improve oxygenation and respiratory mechanics in infants with ALI following CPB surgery.

Are selective lung recruitment maneuvers hemodynamically safe in severe hypovolemia? An experimental study in hypovolemic pigs with lobar collapse.

BACKGROUND: We have previously shown, in normovolemic pigs, that a selective lung recruitment maneuver (S-LRM), i.e., insufflation of air-oxygen via a balloon catheter with its tip located in the bronchus of a collapsed lung lobe, effectively improves oxygenation and lung volume without affecting hemodynamics negatively. In this study, we examined the respiratory and circulatory effects of S-LRM during hypovolemia with compromised circulation. METHODS: In eight ventilated (fraction of inspired oxygen, Fio2 1.0) and anesthetized pigs a balloon catheter was inserted in the bronchus of the right lower lung lobe. The lobe was selectively lavaged to create a dense lobar collapse. The pigs were then subjected to S-LRM (40 cm H2O airway pressure for 30 s) at normovolemia, after venesection of 20% and 40% of the blood volume, respectively. Blood gases, compliance of the respiratory system (Crs), vascular pressures, and cardiac output were registered before, during, and after the S-LRM. RESULTS: Pao2, venous admixture, and Crs improved significantly with S-LRM at all three volume levels. No change in hemodynamics with S-LRM occurred in normovolemia and 20% hypovolemia. For 40% hypovolemia, cardiac output was unchanged by S-LRM, whereas minor decreases in mean arterial blood pressure were seen: 48 (37-52) mm Hg (median, 25th and 75th percentiles) 3 min before S-LRM, 40 (35-44) mm Hg at the end of S-LRM (P = 0.0207), and 47 (39-54) mm Hg 3 min after S-LRM. CONCLUSION: A S-LRM effectively improved oxygenation and Crs and had only minor circulatory side effects, even in severe hypovolemia in this animal model of lobar collapse.

[Refractory hypoxemia treated early by HFO in a severe traumatic brain injury patient]. / Hypoxémie réfractaire traitée précocement par HFO chez un patient traumatisé crânien grave.

A 23-year-old man without previous medical history, was transferred to our surgical intensive care unit for management of a traumatic brain injury (Glasgow Coma Score of 3 on admission). He rapidly presented a refractory hypoxaemia essentially due to posterior alveolar collapse. Severe hypoxaemia and hypercarboxaemia didn't respond to conventional ventilation and complicated the management of the brain injury and the control of intracranial pressure. The introduction of high-frequency oscillatory ventilation permitted a respiratory improvement in 48 hours and a good neurological outcome.

Use of dynamic compliance for open lung positive end-expiratory pressure titration in an experimental study.

OBJECTIVE: We tested whether the continuous monitoring of dynamic compliance could become a useful bedside tool for detecting the beginning of collapse of a fully recruited lung. DESIGN: Prospective laboratory animal investigation. SETTING: Clinical physiology research laboratory, University of Uppsala, Sweden. SUBJECTS: Eight pigs submitted to repeated lung lavages. INTERVENTIONS: Lung recruitment maneuver, the effect of which was confirmed by predefined oxygenation, lung mechanics, and computed tomography scan criteria, was followed by a positive end-expiratory pressure (PEEP) reduction trial in a volume control mode with a tidal volume of 6 mL/kg. Every 10 mins, PEEP was reduced in steps of 2 cm H2O starting from 24 cm H2O. During PEEP reduction, lung collapse was defined by the maximum dynamic compliance value after which a first measurable decrease occurred. Open lung PEEP according to dynamic compliance was then defined as the level of PEEP before the point of collapse. This value was compared with oxygenation (Pao2) and CT scans. MEASUREMENTS AND MAIN RESULTS: Pao2 and dynamic compliance were monitored continuously, whereas computed tomography scans were obtained at the end of each pressure step. Collapse defined by dynamic compliance occurred at a PEEP of 14 cm H2O. This level coincided with the oxygenation-based collapse point when also shunt started to increase and occurred one step before the percentage of nonaerated tissue on the computed tomography exceeded 5%. Open lung PEEP was thus at 16 cm H2O, the level at which oxygenation and computed tomography scan confirmed a fully open, not yet collapsed lung condition. CONCLUSIONS: In this experimental model, the continuous monitoring of dynamic compliance identified the beginning of collapse after lung recruitment. These findings were confirmed by oxygenation and computed tomography scans. This method might become a valuable bedside tool for identifying the level of PEEP that prevents end-expiratory collapse.

Effects of a single-lung recruitment maneuver on the systemic release of inflammatory mediators.

OBJECTIVE: To study the hypothesis, that systemic levels of pro-inflammatory and anti-inflammatory cytokines may be affected by a single recruitment maneuver in mechanically ventilated patients. DESIGN: Prospective, interventional clinical trial. SETTING: Intensive care unit of a university hospital. PATIENTS: Sixteen mechanically ventilated patients with clinical and radiological signs of atelectasis. INTERVENTIONS: A single recruitment maneuver (RM) was performed by elevating the airway pressure to 40 cmH(2)O for 7s. MEASUREMENTS AND MAIN RESULTS: Plasmatic concentrations of interleukin (IL)-1beta, IL-6, IL-8, IL-10, IL-12p70 and tumor necrosis factor (TNF-alpha), arterial blood gases and hemodynamic parameters were measured immediately before and 5-360 min after the RM. The RM caused a minor, nevertheless significant improvement of oxygenation (p = 0.02) and carbon dioxide elimination (p=0.006) as well as a moderate drop of the mean arterial pressure (p=0.025). In contrast, plasma concentrations remained unaffected by the RM in all six mediators measured. CONCLUSION: A single inflation with an airway pressure of 40cmH(2)O for 7 s improved gas exchange only slightly and did not modify systemic levels of inflammatory mediators in mechanically ventilated patients with radiological evidence of atelectasis.