Peak Inspiratory Airway Pressure Research Articles

Transesophageal Echocardiographic Assessment of Pulmonary Arterial and Venous Flow During High-Frequency Jet Ventilation

Study Objective: To evaluate high-frequency jet ventilation (HFJV) effects on pulmonary arterial and venous flow compared to those of intermittent positive-pressure ventilation (IPPV) by using pulsed Doppler transesophageal echocardiography. Design: Prospective clinical study. Setting: University-affiliated hospital operating room. Patients: 13 ASA physical status I and II patients undergoing lower abdominal or lower extremity surgery. Interventions: Patients had total IV anesthesia with propofol and fentanyl. After anesthesia induction, a transesophageal echocardiography probe was inserted into the esophagus. IPPV (TV, 8–10 mL/kg; respiratory rate, 10–12 cycles/min; I/E ratio, 1:2; FIO 2, 1.0) and HFJV (driving pressure, 0.5–0.6 kgf/cm 2; frequency,3 Hz; I/E ratio, 1:1; FIO 2, 1.0) were performed under hemodynamically stable conditions. Measurements: Pulmonary-arterial-flow velocity, pulmonary-venous-flow velocity, left ventricular short-axis view, and airway-pressure curve were recorded simultaneously. Parameters measured were: hemodynamic variables, arterial blood gases, inspiratory airway pressure; [from pulmonary-arterial-flow velocity] pre-ejection period (PEP), acceleration time (AT), right ventricular ejection time (RVET), and their ratios (PEP/AT, AT/RVET); [from pulmonary-venous-flow velocity] time-velocity integral of the first systolic wave (S1), second systolic wave (S2), and diastolic wave (D), and systolic fraction (integral S1 + S2/S1+ S2 + D); [from M-mode] left-ventricular-end systolic volume, left-ventricular-end diastolic volume (LVEDV), stroke volume, cardiac output, and ejection fraction, using Teichholz’s method. Main Results: Peak inspiratory airway pressure during HFJV was significantly lower than that during IPPV. HFJV significantly decreased PEP/AT, correlating positively with pulmonary arterial pressure, and significantly increased AT and AT/RVET, correlating negatively with pulmonary arterial pressure. Systolic fraction, correlating negatively with left atrial pressure, increased significantly during HFJV, as did LVEDV, stroke volume, cardiac output, and ejection fraction. Conclusions: Our results suggest that, in comparison to IPPV, HFJV significantly decreases pulmonary arterial pressure and left atrial pressure, resulting in significant increases in cardiac output and ejection fraction in healthy anesthetized adults.

Significance of cyclic adenosine monophosphate and nitroglycerin in ET-Kyoto solution for lung preservation

Background. We previously demonstrated that the supplement of both dibutyryl cyclic adenosine monophosphate (db-cAMP) and nitroglycerin to the conventional ET-Kyoto solution improved lung preservation significantly. However, the significance of each component in lung preservation remained unclear. We examined the efficacy of the two components on lung preservation in the current study.Methods. Rat lung grafts (eight per group) were studied in an isolated lung perfusion model. Group 1 grafts were flushed and preserved with ET-Kyoto solution containing 2 mmol/L of db-cAMP. Group 2 grafts were flushed and preserved with ET-Kyoto solution containing 100 mg/L of nitroglycerin. In group 3, the grafts were flushed and preserved with ET-Kyoto solution containing neither db-cAMP nor nitroglycerin as control group. After 4-hour cold storage, the lung grafts were reperfused for 50 minutes.Results. The lung grafts in groups 1 and 2 showed significantly better lung function after reperfusion than those in group 3 with regard to arterial oxygen tension, shunt fraction, peak inspiratory airway pressure, mean pulmonary arterial pressure, and pulmonary vascular resistance. The supplementation of db-cAMP improved especially the pulmonary arterial pressure and pulmonary vascular resistance, while the supplementation of nitroglycerin improved especially the oxygenation and airway pressure of the grafts.Conclusions. Both of db-cAMP and nitroglycerin had beneficial effects on lung preservation and are essential to the ET-Kyoto solution. There was a difference between the two components in the effects on preserved lungs.

Abdominal wall lift versus carbon dioxide insufflation for laparoscopic resection of ovarian tumors

Study Objective: To evaluate and compare changes in pulmonary mechanics and stress hormone responses between abdominal wall lift (gasless) and carbon dioxide (CO 2) insufflation laparoscopic surgery during controlled general anesthesia. Design: Prospective, randomized clinical study. Setting: Operating rooms at a university medical center. Patients: 12 ASA physical status I and II female patients undergoing laparoscopic resection of ovarian tumors. Interventions: Patients were divided into two groups of six each: the abdominal wall lift group and the CO 2 pneumoperitoneum laparoscopic group. Following induction of anesthesia, patients were paralyzed and the trachea was intubated. Anesthesia was maintained with isoflurane and nitrous oxide (N 2O) in oxygen. Throughout the procedure, patients were mechanically ventilated with a tidal volume of 10 ml/kg and a respiratory rate of 10 breaths per minute. Measurements and Main Results: During the laparoscopic procedure, arterial blood gases, acid-base balance, pulmonary mechanics, stress-related hormones, and urine output were measured and recorded. In the CO 2 pneumoperitoneum group, arterial CO 2 tension increased (p <0.01), dynamic pulmonary compliance decreased (p <0.01), peak inspiratory airway pressure increased (p <0.01), and plasma epinephrine (p <0.05), norepinephrine (p <0.05), dopamine (p <0.01), and antidiuretic hormones (p <0.05) increased significantly during the laparoscopic procedure as compared to the abdominal lift group. Adrenocorticotropic hormone and cortisol increased as compared to baseline value in both groups (p <0.05). Urine output was significantly less (p <0.01) in the CO 2 pneumoperitoneum group than in the abdominal wall lift group. Conclusions: Abdominal wall lift laparoscopic surgery is physiologically superior to CO 2 pneumoperitoneum laparoscopic surgery as seen during the conditions of this study. Abdominal wall lift laparoscopic surgery provides normal acid-base balance and a lesser degree of hormonal stress responses, it maintains urine output, and it avoids derangement of pulmonary mechanics.

Acute lung injury after tracheal instillation of acidified soya-based or Enfalac formula or human breast milk in rabbits.

The aim of this study was to compare the severity of the acute lung injury after tracheal instillation of acidified soya-based or Enfalac infant formula, or human breast milk (HBM) in anesthetized rabbits. Alveolar-arterial oxygen tension gradient (A-aDO2) and dynamic compliance were measured before (baseline) and hourly for four hours after tracheal instillation of 0.8 ml x kg(-1) soya-based or Enfalac infant formula or HBM (all acidified to pH 1.8 with hydrochloric acid) or no fluid (control) in 24 anesthetized and tracheotomized adult rabbits. The A-aDO2, the difference between alveolar and arterial oxygen tensions, was corrected for barometric pressure and carbon dioxide tension. Dynamic compliance was the ratio of the expired tidal volume to the peak inspiratory airway pressure, normalized to body weight. Baseline A-aDO2 and dynamic compliance were similar among the four groups. In the control rabbits, A-aDO2 remained unchanged throughout the four hours, whereas mean A-aDO2 increased 180 mm Hg in the soya-based group (P < 0.0025) and 350 and 275 mm Hg in the Enfalac and HBM groups respectively (P < 0.0002). The order of the A-aDO2 post-instillation was Enfalac approximately/= HBM > soya > control (P < 0.0002). Dynamic compliance decreased 10-12% in the control rabbits during the four post-instillation measurements compared with baseline (P < 0.033), decreased 20% in the soya-based group (P < 0.0002) and 40-50% in the Enfalac and HBM groups (P < 0.0002). The severity of the acute lung injury after intratracheal instillation of infant feeds in a volume of 0.8 ml x kg(-1) and at pH 1.8 in rabbits depends in part, on the type of feed: Enfalac approximately/= HBM > soya > control.

Effects of Pneumoperitoneum and Posture on Ventilation Monitored with Continuous Spirometry under General Anesthesia

Background : To evaluate the effects of pneumoperitoneum and posture on total respiratory compliance, peak inspiratory airway pressure and inspiratory minute ventilation during laparoscopic pneumoperitoneum and pelviscopic surgery we monitored continuously with continuous spirometry. Methods : 20 patients were anesthetized and paralyzed, tracheally intubated and mechanically ventilated at te rate of 12/min and at a tidal volume of 10 ml/kg. Measurements were made before surgery, just before insufflation and 5, 10, 20, 30, 60 min after insufflation under position changed (10o reverse Trendelenburg position in laparoscopic cholecystectomy; group C, 10o Trendelenburg and lithotomy position in pelviscopic surgery; group P), and 5, 10 min after deflation under horizontal position. Compliance, peak inspiratory airway pressure and inspiratory minute volume were monitored continuously with side stream spirometry. Results : Compliance of respiratory system decreased 39.8% and 39.1%, peak inspiratory pressure increased 43.5% and 61.3%, inspiratory minute volume decreased 10.9% and 9.1% under pneumoperitoneum in group C and group P. Conclusion : Increased intrabdominal pressure and posture during laparoscopic cholecystectomy and pelviscopic surgery cause significant decreased respiratory compliance and inspiratory minute volume and a significant increased airway pressure. On-line monitoring of respiratory volume, pressure and compliance may be helpful during general anesthesia to avoid the potential harmful effects of increased airway pressure occurring with increased intra-abdominal pressure. (Korean J Anesthesiol 1999; 36: 33∼40)

Changes of Peak Inspiratory Airway Pressure and Compliance during One-Lung Ventilation Using Double Lumen Tube and Univent Tube

Changes of Peak Inspiratory Airway Pressure and Compliance during One-Lung Ventilation Using Double Lumen Tube and Univent Tube

Experimental studies on lung mechanics, gas exchange and oxygen delivery under open lung conditions Mechanical ventilation with decelerating versus constant inspiratory flow

The treatment of patients with acute respiratory failure poses an ever‐present clinical challenge since conventional ventilation sometimes causes further impairment of lung function. Thus, it is important to identify characteristics of different ventilatory patterns and ventilatory strategies that affect airway pressures, lung volumes, pulmonary gas exchange and hemodynamics. In order to mimic acute respiratory failure in the patient, we have used an experimental animal injury model, characterized by highly unstable alveoli.The basic prerequisite for this thesis was a positive end‐expiratory pressure (PEEP) sufficient to keep the lung open throughout the whole ventilatory cycle. Different inspiratory flow patterns were studied by using a successful recruitment procedure together with ventilation performed using PEEP levels below, at, and above the inflection‐point pressure. To elucidate the effect of prolonged inspiration time, sufficient PEEP was supplied to prevent end‐expiratory collapse already during the reference mode with an inspiration/expiration ratio (I:E ratio) of 1:1. When an I:E ratio of 2:1 or above was used, both studies (one with mean airway pressure constant and the other with total PEEP constant) showed impaired hemodynamics, but displayed unaffected arterial oxygen tension. Decelerating inspiratory flow delivers the major part of the tidal volume during early inspiration under sustained constant inspiratory pressure. This reduces serial dead space and improves alveolar ventilation. In all studies, decelerating inspiratory flow showed increased carbon dioxide elimination, i.e. improved alveolar ventilation, but decelerating inspiratory flow was found to be no better for alveolar recruitment or in oxygenation.In an attempt to explain radiological observations when studying the relationship of pulmonary radiological appearance to end‐expiratory pressure, Staubs' concept of quantal alveolar behavior was used. This states that the individual alveolus fills essentially independently of its neighbors and has a propensity to be either air‐filled and expanded, or completely fluid‐filled and collapsed. Stepwise sequential deflation of the lung from full expansion, followed by stepwise inflation of the lung, produced a pressure/attenuation loop. This hysteresis phenomenon implies that the attenuation of the lung relates to the set PEEP, but also to the immediately preceding structural status. For identical end‐expiratory pressures the attenuation on the hysteresis down‐slope invariably had a higher value than that of the up‐slope. Thus, the pressure at which alveolar collapse takes place differs from that of expansion.In conclusion, ventilation with decelerating inspiratory flow revealed lower peak inspiratory and higher mean airway pressure than did constant inspiratory flow. No differences in end‐inspiratory pressure were seen. Decelerating inspiratory flow delivers the major part of the tidal volume during early inspiration, which reduces serial dead space and improves alveolar ventilation. The decelerating inspiratory flow was found to be no better than constant inspiratory flow for alveolar recruitment or oxygenation. When the lung was ventilated with PEEP sufficient to prevent end‐expiratory collapse, an inspiration‐to‐expiration ratio at and above 2:1 impaired hemodynamics. Our results suggest that, in order to obtain and maintain open lung conditions, the lung must be recruited and PEEP reduced to the level just above the alveolar collapse pressure.

Reply

Chef du Service de Reanimation, Polyvalente Hopital des Diaconesses, Paris, France (Kalfon).Professor of Anesthesia and Critical Care, Chef de l'Unite de Reanimation Chirurgicale, Hopital de la Pitie-Salpetriere, Universite Paris VI, Paris, France (Rouby).jjrouby.pitie@invivo.edu.In Reply:-The letters from Oppenheim and Pizov and from Findlay et al. indicate an important potential drawback of expiratory washout: auto-PEEP resulting in an increase in inspiratory plateau airway pressure, which may reintroduce a risk of lung barotrauma.Different solutions exist to overcome EWO-induced auto-PEEP. As suggested by Findlay et al., one is to deliver EWO during pressure-controlled ventilation. [1]In such circumstances, because EWO-induced increase in airway pressure automatically results in a decrease in the tidal volume, the lack of EWO-induced auto-PEEP is associated with a reduction in the efficiency of EWO on CO2elimination. In Findlay's study, a 6 l/min EWO flow delivered during pressure-controlled ventilation was associated with a modest reduction in PaCO2(-14%). [1]As a consequence, this technique for counteracting EWO-induced auto-PEEP appears to have serious limitations. It is more simple and efficient to reduce the PEEP level. In a recent study, [2]we could demonstrate in a series of patients with ARDS that inspiratory plateau airway pressure, mean airway pressure, and consequently arterial oxygenation and pulmonary shunt could be maintained constant when the PEEP level was reduced of an amount equal to EWO-induced auto-PEEP. In this study wherein a 15 l/min EWO flow was used, PaCO2could be reduced by 26% if compared with control values without EWO. [22]As emphasized by Findlay et al., it is technically possible to measure EWO-induced auto-PEEP by synchronizing suppression of EWO and occlusion of the expiratory valve. [1]This technical option, already present in prototypes, should be available on any medical device providing EWO and should be considered as a critical element of safety. Findlay et al. have outlined an important limitation of our study, although the indication for EWO was unquestionnable-severe ARDS with lung hyperdensities involving 50% of the lung parenchyma, low respiratory compliance, and profound hypercarbia with acid-base compromise resulting in increased pulmonary artery pressure [3]-the technical conditions of EWO administration were not optimized. EWO-induced auto-PEEP should have been counterbalanced by a concomittant reduction in PEEP, a technique that does not compromise CO2elimination and arterial oxygenation. [2]We agree with Findlay et al. that our study should not bias intensivists against the use of EWO in patients with severe ARDS.Another solution proposed by Oppenheim and Pizov to limit the auto-PEEP resulting from tracheal gas insufflation is to replace oxygen by helium. In an interesting study, [4]these authors have demonstrated that helium is more effective than oxygen for improving CO sub 2 elimination and limiting auto-PEEP. However, helium does not totally avoid the increase in peak inspiratory airway pressure and therefore appears less effective than decreasing PEEP. In addition, its high cost and the risk of decreasing FIO2and worsening arterial oxygenation in patients with ARDS render problematic its routine use in clinical practice.Although we agree that EWO is a peculiar mode of tracheal gas insufflation, we think that it should be clearly individualized from a semantic point of view. The administration of an intratracheal gas flow during inspiration-inspiratory bypass-increases tidal volume and therefore cannot be considered as a new mode of CO2elimination. In contrast, EWO that removes the carbon dioxide-laden gas occupying the instrumental dead space without inducing major changes in tidal volume appears as an original technique for enhancing CO2clearance in patients treated by permissive hypercapnia. In our opinion, EWO rather than inspiratory bypass or continuous tracheal gas insufflation could be clinically used in the near future if technical problems related to the measurement of auto-PEEP are solved by manufacturers of ICU ventilators.Pierre Kalfon, M.D.Chef du Service de Reanimation; Polyvalente Hopital des Diaconesses; Paris, FranceJean-Jacques Rouby, M.D., Ph.D.Professor of Anesthesia and Critical Care; Chef de l'Unite de Reanimation Chirurgicale; Hopital de la Pitie-Salpetriere; Universite Paris VI; Paris, Francejjrouby.pitie@invivo.edu(Accepted for publication November 18, 1997.)

Airway Pressure Changes During One-Lung Ventilation

This investigation analyzed the changes in inspiratory airway pressures during transition from two-lung to one-lung ventilation in patients tracheally intubated with a double-lumen endotracheal tube (DLT) using a classical method of intubation without fiberoptic bronchoscopy. All patients were anesthetized in a standardized fashion. Ventilation was accomplished with the Siemens 900 constant-flow mechanical ventilator (Solna, Sweden). Peak (Ppeak) and plateau (Pplateau) inspiratory airway pressures were recorded with an on-line respiratory monitor before and after clamping the tracheal limb of the DLT. The position of the DLTs was evaluated by fiberoptic bronchoscopy with the patient in supine position. Of the 51 intubations, the DLT was malpositioned in 15 cases (29.5%). Ppeak and Pplateau increased significantly when switched from two-lung ventilation to one-lung ventilation in both correctly and incorrectly positioned DLTs. When the DLT was in a correct position, Ppeak increased by a mean of 55.1% and Pplateau increased by a mean of 41.9%. When the DLT was malpositioned, this increase was significantly larger (74.9% and 68.8%, respectively). Three tests commonly used as markers of malpositioned DLTs were evaluated based on the data of this study, and it was established that, although the pressure differences related to position are statistically significant, as a single value, they cannot be used for clinical decision making. (Anesth Analg 1997;84:1034-7)

Airway pressure changes during one-lung ventilation.

This investigation analyzed the changes in inspiratory airway pressures during transition from two-lung to one-lung ventilation in patients tracheally intubated with a double-lumen endotracheal tube (DLT) using a classical method of intubation without fiberoptic bronchoscopy. All patients were anesthetized in a standardized fashion. Ventilation was accomplished with the Siemens 900 constant-flow mechanical ventilator (Solna, Sweden). Peak (Ppeak) and plateau (Pplateau) inspiratory airway pressures were recorded with an on-line respiratory monitor before and after clamping the tracheal limb of the DLT. The position of the DLTs was evaluated by fiberoptic bronchoscopy with the patient in supine position. Of the 51 intubations, the DLT was malpositioned in 15 cases (29.5%). Ppeak and Pplateau increased significantly when switched from two-lung ventilation to one-lung ventilation in both correctly and incorrectly positioned DLTs. When the DLT was in a correct position, Ppeak increased by a mean of 55.1% and Pplateau increased by a mean of 41.9%. When the DLT was malpositioned, this increase was significantly larger (74.9% and 68.8%, respectively). Three tests commonly used as markers of malpositioned DLTs were evaluated based on the data of this study, and it was established that, although the pressure differences related to position are statistically significant, as a single value, they cannot be used for clinical decision making.

Retrograde Fiberoptic Intubation

Retrograde Fiberoptic Intubation

APACHE II score is better than weaning indices in predicting prolonged mechanical ventilator dependence

Spontaneous minute ventilation (VE), peak inspiratory airway pressure (Plmax), rapid shallow breathing index (f/vT), relative inspiratory effect (RIE), and the P(A-a)O2, blood urea nitrogen and gender score (A + B + G) are used in predicting weaning success. Some patients are transferred from intensive care to subacute care facilities when prolonged mechanical ventilation (MV) is anticipated. This prospective. observational study compares the role of weaning indices versus APACHE II score in identifying patients requiring prolonged MV.

HIGH-INFLATION PRESSURE AND POSITIVE END-EXPIRATORY: Injurious to the Lung? No

Survival rates in ARDS with conventional ventilation using high oxygen fractions and low PEEP levels have been reported to be less than 10%. In three prospective evaluations of ARDS in the 1980s, mortality rates remained greater than 60%. Early studies using high-level PEEP therapy in severe ARDS by Douglas, Downs, Kirby, and Civetta showed improved survival rates with ranges between 60% and 80%. In 1979 Gallagher reviewed 59 patients with ARDS who were treated with PEEP greater than 15 cm H2O titrated to improve FRC by achieving an intrapulmonary shunt fraction of 15%. The overall survival was 65%, with only 5% of the patients dying secondary to respiratory failure. In the more recent study by Miller in trauma patients and later by DiRusso in a variety of surgical patients, the overall mortality rate for those patients receiving PEEP greater than 15 cm H2O was 20% to 30%. Of the 14 patients who died, only seven (10% of the total) succumbed to respiratory failure. The remaining patients died from the primary underlying disease with normal oxygenation or after significant weaning from high PEEP levels. By using a goal-oriented approach to the management of patients with severe ARDS, we have found that high-level PEEP therapy was effective in lowering the intrapulmonary shunt and improving the SaO2 at acceptable levels of inspired oxygen. All of these patients were ventilated with traditional high tidal volumes (10 to 15 mL/kg) and therefore exhibited high peak inspiratory airway pressures. This support method did not seem to cause lung injury or an excessive amount of barotrauma in these patients, but in fact, was associated with a lower mortality rate (30%) than reported in other studies of patients with lesser degrees of lung oxygenation dysfunction and extrapulmonary organ system dysfunction. Currently available information indicates that increases in mean airway pressure (induced with PEEP or other modes of ventilatory support to restore losses in FRC that occur during ARDS) and limiting exposure to toxic concentrations of oxygen minimize ventilator-induced secondary lung injury and maximize chances for survival. Arbitrary limitations of peak inspiratory or end-expiratory airway pressure or mandatory tidal volume in patients with severe ARDS seem to be unfounded. Failure to achieve adequate physiologic end-points in these patients may increase morbidity and mortality rates.

The Effects of Neuromuscular Block on Peak Airway Pressure and Abdominal Elastance During Pneumoperitoneum

Administration of muscle relaxants is considered as necessary to prevent high intraabdominal and peak inspiratory pressures induced by pneumoperitoneum during laparoscopy. In the present study, we hypothesized that neuromuscular block does not alter pulmonary or abdominal elastic properties in pigs receiving general anesthesia. To test this hypothesis, changes in peak airway pressure and abdominal elastance during intraabdominal CO(2), insufflation from 0 to 15 mm Hg were recorded in anesthetized pigs, with or without muscle relaxants. A 100% increase in peak inspiratory airway pressure was obtained. This was unaffected by neuromuscular block induced by atracurium (13.2 +/- 5.0 mm Hg vs 25.0 +/- 4.8 mm Hg for the control group and 12.6 +/- 5.0 mm Hg vs 23.5 +/- 6.2 mm Hg for the paralyzed group). Abdominal pressure/volume relationships were independent of muscle relaxant administration (calculated elastance was 3.98 +/- 1.56 mm Hg/L without muscle relaxant vs 3.86 +/- 1.37 mmHg/L in the atracurium group). We conclude that high peak inspiratory airway pressures and intraabdominal pressures during laparoscopy are not affected by neuromuscular block. These findings also question the necessity of muscle relaxants in clinical anesthetic practice during laparoscopic surgery.

The Effects of Neuromuscular Block on Peak Airway Pressure and Abdominal Elastance During Pneumoperitoneum

Administration of muscle relaxants is considered as necessary to prevent high intraabdominal and peak inspiratory pressures induced by pneumoperitoneum during laparoscopy.In the present study, we hypothesized that neuromuscular block does not alter pulmonary or abdominal elastic properties in pigs receiving general anesthesia. To test this hypothesis, changes in peak airway pressure and abdominal elastance during intraabdominal CO2 insufflation from 0 to 15 mm Hg were recorded in anesthetized pigs, with or without muscle relaxants. A 100% increase in peak inspiratory airway pressure was obtained. This was unaffected by neuromuscular block induced by atracurium (13.2 +/- 5.0 mm Hg vs 25.0 +/- 4.8 mm Hg for the control group and 12.6 +/- 5.0 mm Hg vs 23.5 +/- 6.2 mm Hg for the paralyzed group). Abdominal pressure/volume relationships were independent of muscle relaxant administration (calculated elastance was 3.98 +/- 1.56 mm Hg/L without muscle relaxant vs 3.86 +/- 1.37 mm Hg/L in the atracurium group). We conclude that high peak inspiratory airway pressures and intraabdominal pressures during laparoscopy are not affected by neuromuscular block. These findings also question the necessity of muscle relaxants in clinical anesthetic practice during laparoscopic surgery. (Anesth Analg 1996;82:525-7)

Effect of pneumoperitoneum on interatrial pressure gradient during laparoscopic cholecystectomy.

Alterations of the left atrial/right atrial pressure gradient were determined using a Swan-Ganz thermodilution catheter in 20 patients who underwent laparoscopic cholecystectomy with 12 mmHg pneumoperitoneum (LAP) and 13 patients who underwent minilaparotomy cholecystectomy (MINI). Right and left atrial pressures were both elevated by pneumoperitoneum. A diminished or reversed left/right interatrial pressure gradient was recognized during pneumoperitoneum in 4 of the 20 patients (20%) in the LAP group, whereas it was not recognized during operation in any of the 13 patients in the MINI group. Evaluation of the elevation of intrathoracic pressure during pneumoperitoneum using peak inspiratory airway pressure or pulmonary arterial pressure could not predict the occurrence of this paradoxical interatrial pressure gradient.

Klinische Aspekte des akuten Lungenversagens des Erwachsenen (ARDS)

Acute respiratory distress syndrome (ARDS) is rare but beset with a high mortality rate. In recent years, however, a trend towards higher survival rates has been observed. High inspiratory oxygen concentrations, large tidal volumes, and high peak inspiratory airway pressures applied during mechanical ventilation have been identified as harmful to the lung and can contribute to the progression of ARDS. This had led to reconsideration of the sequelae of ventilatory therapy. Mechanical ventilation and other adjunctive strategies in ARDS have changed from the conventional approach aiming at normalisation of physiological ventilatory parameters to an elaborated approach that intends to protect the ventilated lung, prevent oxygen toxicity, recruit the infiltrated atelectatic and consolidated lung and reduce the anatomical and alveolar dead space. This new approach consists of various forms of pressure-controlled mechanical ventilation with PEEP and permissive hypercapnia, body position changes, and inhalation of nitric oxide. Should these procedures fail to improve impaired gas exchange, extracorporeal membrane oxygenation is an additional therapeutic option. None of these therapeutic procedures, however, has been tested against traditional standard treatment in a classical randomised controlled trial. The following review focuses on the latest insights into the pathophysiology, diagnosis, and treatment of ARDS.

Change of the Peak Inspiratory Airway Pressure and Exhaled Volume during One Lung Ventilation

Change of the Peak Inspiratory Airway Pressure and Exhaled Volume during One Lung Ventilation

Large Tidal Volume Ventilation Does Not Improve Oxygenation in Morbidly Obese Patients During Anesthesia

Eight morbidly obese patients (body mass index [BMI] = 46) were studied during general anesthesia and controlled mechanical ventilation. To evaluate the effect of large tidal volume ventilation on oxygenation and ventilation, the baseline 13 mL/kg tidal volume (VT) (calculated by the ideal body weight) was increased in 3 mL/kg volume increments to 22 mL/kg, while ventilatory rate (RR) and inspiratory time (TI) were kept constant. Each volume increment was maintained for 15 min. Gas exchange was assessed by measuring the arterial blood oxygen tensions, and calculating the indices of alveolar-arterial oxygen tension difference [P(A-a)O2] and arterial/alveolar oxygen tension ratio (a/A). Peak inspiratory airway pressure (Ppeak), end-inspiratory airway pressure (Pplateau), and compliance of the respiratory system (CRS) were recorded using the Capnomac Ultima (Datex, Helsinki, Finland) on-line respiratory monitor. Increasing tidal volumes to 22 mL/kg increased the recorded Ppeak (26.3 +/- 4.1 vs 37.9 +/- 3.2 cm H2O, P < 0.008), Pplateau (21.5 +/- 3.6 vs 27.7 +/- 4.3 cm H2O, P < 0.01), and CRS (39.8 +/- 7.7 vs 48.5 +/- 8.3 mL/cm H2O) significantly without improving arterial oxygen tension and resulted in severe hypocapnia. Since changes in arterial oxygenation were small and not statistically significant, mechanical ventilation of morbidly obese patients with large VTS seems to offer no advantage to smaller (13 mL/kg ideal body weight) VTS.

Airway anesthesia during positive and negative inspiratory pressure breathing in man

We have measured the effects of airway anesthesia (aerosolized 5% lidocaine) on the respiratory pattern during positive or negative inspiratory pressure in 8 resting subjects. The subjects breathed through a 600 ml dead space (peak inspiratory airway pressure, Paw = −2 cmH 2O ) without or with negative (approx. −5 or −10 cmH 2O) or positive (approx. +5 or +10 cmH 2O) inspiratory pressure, provided by a laminar flow resistance or a positive pressure source, respectively. Control measurements were performed before and after measurements with airway anesthesia. Measurements included tidal volume, respiratory frequency, ventilation, inspiratory and expiratory duration, occlusion pressure (P 0.1) and end-tidal P CO 2 . None of the parameters measured was significantly altered by airway anesthesia, which was effective in suppressing the cough reflex. We conclude that information from lung afferents that are suppressed with the elimination of the cough reflex is not important for the breathing pattern during resting ventilation with elevated tidal volume (dead space load) and with positive or negative inspiratory pressure.