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Background We previously reported that there were no differences between the lung-protective actions of pressure-controlled inverse ratio ventilation and volume control ventilation based on the changes in serum cytokine levels. Dead space represents a ventilation-perfusion mismatch, and can enable us to understand the heterogeneity and elapsed time changes in ventilation-perfusion mismatch. Methods This study was a secondary analysis of a randomized controlled trial of patients who underwent robot-assisted laparoscopic radical prostatectomy. The inspiratory to expiratory ratio was adjusted individually by observing the expiratory flow-time wave in the pressure-controlled inverse ratio ventilation group (n = 14) and was set to 1:2 in the volume-control ventilation group (n = 13). Using volumetric capnography, the physiological dead space was divided into three dead space components: airway, alveolar, and shunt dead space. The influence of pressure-controlled inverse ratio ventilation and time factor on the changes in each dead space component rate was analyzed using the Mann-Whitney U test and Wilcoxon’s signed rank test. Results The physiological dead space and shunt dead space rate were decreased in the pressure-controlled inverse ratio ventilation group compared with those in the volume control ventilation group (p < 0.001 and p = 0.003, respectively), and both dead space rates increased with time in both groups. The airway dead space rate increased with time, but the difference between the groups was not significant. There were no significant changes in the alveolar dead space rate. Conclusions Pressure-controlled inverse ratio ventilation reduced the physiological dead space rate, suggesting an improvement in the total ventilation/perfusion mismatch due to improved inflation of the alveoli affected by heterogeneous expansion disorder without hyperinflation of the normal alveoli. However, the shunt dead space rate increased with time, suggesting that atelectasis developed with time in both groups.

Background and Aims: Induction of general anaesthesia is associated with development of atelectasis in the lungs, which may further lead to postoperative pulmonary complications. Inverse ratio ventilation (IRV) has shown to improve oxygenation and minimise further lung injury in patients with acute respiratory distress syndrome. We evaluated the safety and effectiveness of IRV on intraoperative respiratory mechanics and postoperative pulmonary function tests (PFTs). Methods: In a prospective, controlled study, 128 consecutive patients with normal preoperative PFTs who underwent elective laparoscopic cholecystectomy were randomised into IRV and conventional ventilation groups. Initially, all patients were ventilated with settings of tidal volume 8 mL/kg, respiratory rate 12/min, inspiratory/expiratory ratio (I: E) = 1:2, positive end expiratory pressure = 0. Once the pneumoperitoneum was created, the conventional group patients were continued to be ventilated with same settings. However, in the IRV group, I: E ratio was changed to 2:1. Peak pressure (Ppeak), Plateau pressure (Pplat) and lung compliance were measured. Haemodynamic parameters and arterial blood gas values were also measured. PFTs were repeated in postoperative period. Statistical tool included Chi-square test. Results: There was no significant difference in PFTs in patients who underwent IRV as compared to conventional ventilation [forced vital capacity (FVC) 2.52 ± 0.13 versus 2.63 ± 0.16, P = 0.28]. The Ppeak (cmH2O) and Pplat (cmH2O) were statistically lower in IRV patients [Ppeak 21.4 ± 3.4 versus 22.4 ± 4.2, P = 0.003] [Pplat 18.7 ± 2.4 versus 19.9.4 ± 3.2, P = 0.008]. There was no significant difference in lung compliance and oxygenation intraoperatively. Conclusion: Intraoperative IRV led to reduced airway pressures; however, it did not prevent deterioration of PFTs in postoperative period.

Objective To investigate the effects of inverse ratio ventilation combined with lung-protective ventilation on pulmonary function and inflammatory factors in severe burn patients undergoing surgery. Populations and Methods: Eighty patients with severe burns undergoing elective surgery were divided randomly into two groups: control (CG, n = 40) and experiment (EG, n = 40). The CG had conventional ventilation, whereas the EG were ventilated with tidal volume (TV) of 6–8 ml/kg, I (inspiration): E (expiration) of 2:1, and positive end-expiratory pressure (PEEP) 5 cm H2O. The following variables were evaluated before (T0), 1 h after start of surgery (T1) and after surgery (T2): oxygenation index (OI), partial pressure of carbon dioxide (PaCO2), TV, peak airway pressure (Ppeak), mean airway pressure (Pmean), PEEP, pulmonary dynamic compliance (Cdyn), alveolar–arterial difference of oxygen partial pressure D(A-a)O2, lactic acid (Lac), interleukin (IL)-6 and IL-10, and lung complications. Results: At T1 and T2 time points, the OI, Pmean and Cdyn were significantly greater in the EG than in the CG while the TV, Ppeak, D(A-a)O2, IL-6 and IL-10 were significantly smaller in the EG than in the CG. At the end of the surgery, the Lac was significantly smaller in the EG than in the CG (1.28 ± 0.19 vs. 1.40 ± 0.23 mmol/L). Twenty-four hours after the surgery, significantly more patients had hypoxemia (27.5 vs. 10.0%), increased expectoration (45.0 vs. 22.5%), increased lung texture or exudation (37.5 vs. 17.5%) in the CG than in the EG. Conclusions: Inverse ratio ventilation combined with lung-protective ventilation can reduce Ppeak, increase Pmean and Cdyn, improve the pulmonary oxygenation function, and decrease ILs in severe burn surgery patients.

Background Expiratory flow-initiated pressure-controlled inverse ratio ventilation (EF-initiated PC-IRV) reduces physiological dead space. We hypothesised that EF-initiated PC-IRV would be lung protective compared with volume-controlled ventilation (VCV). Methods Twenty-eight men undergoing robot-assisted laparoscopic radical prostatectomy were enrolled in this randomised controlled trial. The EF-initiated PC-IRV group (n = 14) used pressure-controlled ventilation with the volume guaranteed mode. The inspiratory to expiratory (I:E) ratio was individually adjusted by observing the expiratory flow-time wave. The VCV group (n = 14) used the volume control mode with a 1:2 I:E ratio. The Mann–Whitney U test was used to compare differences in the serum cytokine levels. Results There were no significant differences in serum IL-6 between the EF-initiated PC-IRV (median 34 pg ml-1 (IQR 20.5 to 63.5)) and VCV (31 pg ml-1 (24.5 to 59)) groups (P = 0.84). The physiological dead space rate (physiological dead space/expired tidal volume) was significantly reduced in the EF-initiated PC-IRV group as compared with that in the VCV group (0.31 ± 0.06 vs 0.4 ± 0.07; PPP = 0.62). Two patients in the VCV group had permissive hypercapnia with low forced vital capacity (% predicted). Conclusions There were no differences in the lung-protective properties between the two ventilatory strategies. However, EF-initiated PC-IRV reduced physiological dead space rate; thus, it may be useful for reducing the ventilatory volume that is necessary to maintain normocapnia in patients with low forced vital capacity (% predicted) during robot-assisted laparoscopic radical prostatectomy.

High peak airway pressure (Ppeak) and high end-tidal carbon dioxide tension (PETCO2) are the common problems encountered in the obese patients undergoing gynecological laparoscopy with conventional volume-controlled ventilation. This study was designed to investigate whether volume-controlled inverse ratio ventilation (IRV) with inspiratory to expiratory (I:E) ratio of 2:1 could reduce Ppeak or the plateau pressure (Pplat), improve oxygenation, and alleviate lung injury in patients with normal lungs.Sixty obese patients undergoing gynecological laparoscopy were enrolled in this study. After tracheal intubation, the patients were randomly divided into the IRV group (n = 30) and control group (n = 30). They were ventilated with an actual tidal volume of 8 mL/kg, respiratory rate of 12 breaths/min, zero positive end-expiratory pressure and I:E of 1:2 or 2:1. Arterial blood samples, hemodynamic parameters, and respiratory mechanics were recorded before and during pneumoperitoneum. The concentrations of tumor necrosis factor-α, and interleukins 6 and 8 in bronchoalveolar lavage fluid were measured immediately before and 60 minutes after onset of CO2 pneumoperitoneum.IRV significantly increased arterial partial pressure of oxygen, mean airway pressure, and dynamic compliance of respiratory system with concomitant significant decreases in Ppeak and Pplat compared to conventional ventilation with I:E of 1:2 (p0.05). Additionally, the levels of tumor necrosis factor-α, and interleukins 6 and 8 were significantly lower than those in control group (p0.05).Volume-controlled IRV not only reduces Ppeak, Pplat, and the release of inflammatory cytokines, but also increases mean airway pressure, and improves oxygenation and dynamic compliance of respiratory system in obese patients undergoing gynecologic laparoscopy without adverse respiratory and hemodynamic effects. It is superior to conventional ratio ventilation in terms of oxygenation, respiratory mechanics and inflammatory cytokine in obese patients undergoing gynecologic laparoscopy.

Background: Studies have shown that pressure-controlled ventilation improves alveolar gas distribution. And inverse ratio ventilation has advantages of improving oxygenation in acute respiratory distress syndrome (ARDS) patients. However, the effects that pressure-controlled inverse ration ventilation in patients undergoes endotracheal intubation general anesthesia have not been assessed. Objective: To investigate whether pressure-controlled inverse ratio ventilation (PIV) would improve ventilatory and oxygenation parameters as well as lung function compared to conventional ventilation in patients undergoing open abdominal surgery. Interventions: In the conventional ventilation (CV) group, the ventilation strategy involved zero end-expiratory pressure and volume-controlled ventilation. In the pressure-controlled inverse ratio ventilation (PIV) group, the strategy involved P high starting at 7 cm H2O, P low starting at 4 cm H2O, T high at 4 s, T low at 2 s, and an inspiratory-to-expiratory time ratio of 2:1. The ΔP value was adjusted according to VT. Pressure levels were increased by 2 cm H2O until a maximal VT was observed. Inspired oxygen fraction (FIO2) was 1.0 and tidal volume (VT) was 6 mL/kg in both groups. Main Outcome Measures: The primary outcome is pulmonary function tests. Hemodynamic, ventilatory and oxygenation parameters were measured; visual analog scale (VAS) scores, and nausea and vomiting scores were also measured. Results: The PIV group tolerated pressure-controlled inverse ratio ventilation without significant hemodynamic instability. Mean airway pressure and static compliance were significantly higher in the PIV group than those in CV group (P P 2 h was well tolerated and improved respiratory compliance and lung function on the first postoperative day.

Aim: To observe the 28 and 90 days mortality associated with prone position and assist control-pressure control (with inverse ratio) ventilation (ACPC-IRV). Materials and Methods: All patients who were admitted to our medical Intensive Care Unit (ICU) who are positive for H1N1 viral infection with severe acute respiratory distress syndrome (ARDS) and requiring invasive mechanical ventilation in prone position were included in our prospective observational study. Six patients who are positive for H1N1 required invasive ventilation in prone position. These patients were planned to ventilate in prone for 16 h and in supine for 8 h daily until P/F ratio >150 with FiO 2 of 0.6 or less and positive end-expiratory pressure 2 O. Results: At admission, among these six patients the mean tidal volume generated was about 376.6 ml which was in the range of 6-8 ml/kg predicted body weight. The mean lung injury score was 3.79, mean PaO 2 /FiO 2 ratio was 52.66 and mean oxygenation index was 29.83. The mean duration of ventilation was 9.4 days (225.6 h). The ICU length of stay was 11.16 days. There was no mortality at 28 and 90 days. Conclusion: Early prone combined with ACPC-IRV in H1N1 patients having severe ARDS can be used as a rescue therapy and it should be confirmed by large observational studies.

Acute respiratory distress syndrome (ARDS) is characterized by severe impairment of gas exchange. Hypoxemia is mainly due to intrapulmonary shunt, whereas increased alveolar dead space explains the alteration of CO2 clearance. Assessment of the severity of gas exchange impairment is a requisite for the characterization of the syndrome and the evaluation of its severity. Confounding factors linked to hemodynamic status can greatly influence the relationship between the severity of lung injury and the degree of hypoxemia and/or the effects of ventilator settings on gas exchange. Apart from situations of rescue treatment, targeting optimal gas exchange in ARDS has become less of a priority compared with prevention of injury. A complex question for clinicians is to understand when improvement in oxygenation and alveolar ventilation is related to a lower degree or risk of injury for the lungs. In this regard, a full understanding of gas exchange mechanism in ARDS is imperative for individualized symptomatic support of patients with ARDS.

Background: The normal inspiratory to expiratory ratio is 1:2.However, the duration of inspiration can be increased voluntarily till the ratio becomes 2:1.This is called as inverse ratio breathing. The effects of inverse ratio ventilation have been studied on patients with respiratory failure and Acute Respiratory Distress Syndrome. No studies have been carried out to study the effects of inverse ratio breathing in voluntarily breathing individuals. Hence this study was carried out to find the immediate effects of inverse ratio breathing versus diaphragmatic breathing on inspiratory vital capacity and thoracic expansion. Methods: 30 healthy adult females in the age group 20-25 years were included in the study. Inspiratory vital capacity and thoracic expansion at 2nd, 4th and 6th intercostal space was measured using a digital spirometer and an inelastic inch tape respectively. Diaphragmatic breathing was administered for one minute and the same parameters were measured again. A washout period of one day was given and same outcome measures were measured before and after individuals performed inverse ratio breathing with the help of a visual feedback video for one minute. Results: Data was analysed using Wilcoxon test. There was extremely significant difference between the mean increase in the inspiratory vital capacity and thoracic expansion at the 2nd, 4th and 6th intercostals space after inverse ratio breathing as compared to diaphragmatic breathing (p < 0.0001). Conclusion: Inspiratory vital capacity and thoracic expansion increase significantly after inverse ratio breathing.

We report a case of 27-year-old male with lung contusions related acute respiratory distress syndrome (ARDS) managed by ARDSNet guidelines and additional hypothermia. On 4th day, post trauma partial pressure of oxygen dropped to 38 mm of mercury (Hg), not improving even on high positive end-expiratory pressure of 18 cm water (H2O), inverse ratio ventilation and fraction of inspired oxygen of 1. Extracorporeal membrane oxygenation was ruled out due to the risk of hemorrhage from trauma sites. Thereafter, hypothermia along with muscle paralysis was considered to reduce total body oxygen consumption. Patient's condition improved under hypothermia, and he was extubated and taken up for fracture fixation surgeries and discharged later in stable condition.

Background: Hypoxemia is the most common complication during one-lung ventilation (OLV). Inverse ratio ventilation (IRV) may lead to intrinsic positive end-expiratory pressure (PEEP) and improve oxygenation in acute respiratory distress syndrome, so we investigated whether volume-controlled IRV with external PEEP could improve hypoxemia, reduce the risk of acute lung injury during OLV. Methods: Sixty patients undergoing one-lung ventilation for open thoracoctomy were randomly divided into IRV group and control group (n = 30). All patients were initially ventilated with a tidal volume of 8 mL/kg, an inspiratory: expiratory (I:E) ratio of 1:2 and a respiratory rate of 12 breaths/min in 100% oxygen without PEEP. During OLV, lungs were ventilated either with I:E of 2:1 (IRV group) or 1:2 (control group) with an actual tidal volume (VT) 7 mL/kg, respiratory rate 12 breaths/min, external PEEP of 5 cm H2O. Arterial blood was collected respectively to analyze blood gas before and during OLV. Meanwhile, hemodynamic and respiratory mechanics were monitored. The concentrations of IL-1β, IL-6 and IL-8 in bronchoalveolar lavage fluid (BALF) were measured before and during OLV. Results: Compared to the control group, partial pressure of arterial oxygen (PaO2 ), mean airway pressure and dynamic compliance (CL) were significantly higher in IRV group during OLV (P < 0.05). However, plateau pressure (Pplat) and levels of IL-1β, IL-6 and IL-8 in BALF were lower in IRV group than those in control group (P < 0.05). Conclusion: IRV (I:E = 2:1) applying PEEP could improve hypoxemia, promote oxygenation, and improve dynamic compliance of respiratory system, moreover reduce Pplat and the release of inflammatory cytokines in patients during one-lung ventilation. It is superior to conventional ventilation with PEEP during one-lung ventilation.

To the Editor: I read with interest the findings on the influence of inspiration to expiration ratio on cyclic recruitment and derecruitment of atelectasis in a saline lavage model of acute respiratory distress syndrome (ARDS) (1). The main conclusion of this study is that “inverse ratio ventilation minimizes cyclic recruitment and derecruitment of atelectasis in an experimental model of surfactant-depleted pigs”. The experiments were conducted at a respiratory rate of 6 breaths per minute (or even 5 according to Figure 2). Here, for example, the expiratory phase of the respiratory cycle could last up to 8 s when inspiration to expiration ratio is 1:4 (or 8 s inspiration could be observed in I:E of 4:1). These settings were chosen in order “to provoke maximal cyclical recruitment and derecruitment”. According to Table 3 and to the average weight of the piglets, the tidal volume used ranged between 17 (ARDS I:E 1:1) and 22 ml/kg (Baseline). An FIO2 of 1.0 was used for all measurements “for the direct comparison of PaO2 oscillations between the different I:E ratios”. As can be seen in Figure 3B, at an I:E of 1:1, this FIO2 led to a mean PaO2/FIO2 greater than 300 Torr in 6 of the 8 animals studied, and in 2 of these PaO2/FIO2 was even greater than 400 Torr; average PaO2/FIO2 was 318 Torr in this condition (Table 1), not fulfilling the diagnostic criteria for mild ARDS (2). Exploring very low respiratory rates is interesting at a proof of principle level (3, 4), but for the study of the influence of I:E ratios on atelectasis in ARDS, more clinically relevant conditions should be used (5), or the conclusions drawn may be of little clinical relevance. In the experimental conditions considered in this article (1) lung mechanics and physiology would inevitably be very different from a clinical scenario, where greater respiratory rates, lower tidal volumes, lower airway pressures, lower mean PaO2/FIO2 would be used. It is possible that the oscillating PaO2 signal may not be detectable when all these parameters are set to more clinical or physiological values; if so, the interest in inverting the I:E ratio to reduce atelectasis may not be as exciting, especially considering its associated known costs of reducing cardiac output, overdistending the lung and increasing the risk of inflammation. Of note, and based on my personal experience in using the PaO2 sensor employed in the study, I find hard to understand the remarkably constant standard deviation values presented in Table 1 (17.3 Torr for PaO2 oscillations, and 21.1 Torr for mean PaO2/FIO2). Despite the above limitation, the study (1) presents interesting results on the dependency of cyclical recruitment and derecruitment on ventilation timing in ARDS, which deserve further attention.

Recent recognition that artificial ventilation may cause damage to the acutely injured lung has caused renewed interest in ventilation techniques that minimise this potential harm. Many ventilation techniques have proved beneficial in small trials of very specific patient groups, but most have subsequently failed to translate into improved patient outcome in larger trials. An exception to this is 'protective ventilation' using reduced tidal volumes (to lower airway pressure) and increased PEEP (to reduce pulmonary collapse). Results of trials of protective ventilation have been encouraging, and the technique should now be adopted more widely. High frequency ventilation, inverse ratio ventilation, prone positioning and inhaled nitric oxide are all techniques that may be considered when, in spite of optimal artificial ventilation, the patient's gas exchange remains dangerously poor. Under these circumstances, the choice of technique is dependent on their availability, local expertise and individual patient needs.

Ventilatory modes employing different inspiratory flow patterns and inspiratory to expiratory ratios may alter lung strain in acute lung injury patients. To determine whether variations in lung strain existed between pressure-controlled, volume-controlled, and pressure-controlled inverse ratio modes of ventilation, we randomly applied each for 30 minutes in 18 acute lung injury patients, keeping tidal volume, respiratory rate, fractional inspired oxygen, and total positive end-expiratory pressure constant. After each mode, a multiple linear regression analysis of dynamic airway pressure and airflow was performed with a volume-dependent single compartment model of the equation of motion, and an index of nonlinear elastic behavior was calculated. In five additional patients, concurrent dynamic computerized axial tomography scanning at juxtadiaphragmatic and subcarinal levels was added. Although static mechanics, oxygenation, and hemodynamics were no different between pressure-controlled, volume-controlled, and pressure-controlled inverse ratio ventilation, we found significant differences in nonlinear behavior. This was least with pressure-controlled followed by volume-controlled ventilation, and pressure-controlled inverse ratio ventilation had the greatest nonlinear elastic behavior. Dynamic computerized axial tomography analysis revealed more overinflated units in the left subcarinal slice with pressure-controlled inverse ratio ventilation. Ventilator flow pattern and inspiratory to expiratory ratio independently influence lung strain in acute lung injury; however, further studies are needed to determine the biologic significance.

OBJECTIVE Cyclic recruitment and derecruitment of atelectasis can occur during mechanical ventilation, especially in injured lungs. Experimentally, cyclic recruitment and derecruitment can be quantified by respiration-dependent changes in PaO2 (ΔPaO2), reflecting the varying intrapulmonary shunt fraction within the respiratory cycle. This study investigated the effect of inspiration to expiration ratio upon ΔPaO2 and Horowitz index. DESIGN Prospective randomized study. SETTING Laboratory investigation. SUBJECTS Piglets, average weight 30 ± 2 kg. INTERVENTIONS At respiratory rate 6 breaths/min, end-inspiratory pressure (Pendinsp) 40 cm H2O, positive end-expiratory pressure 5 cm H2O, and FIO2 1.0, measurements were performed at randomly set inspiration to expiration ratios during baseline healthy and mild surfactant depletion injury. Lung damage was titrated by repetitive surfactant washout to induce maximal cyclic recruitment and derecruitment as measured by multifrequency phase fluorimetry. Regional ventilation distribution was evaluated by electrical impedance tomography. Step changes in airway pressure from 5 to 40 cm H2O and vice versa were performed after lavage to calculate PO2-based recruitment and derecruitment time constants (TAU). MEASUREMENTS AND MAIN RESULTS In baseline healthy, cyclic recruitment and derecruitment could not be provoked, whereas in model acute respiratory distress syndrome, the highest ΔPaO2 were routinely detected at an inspiration to expiration ratio of 1:4 (range, 52-277 torr [6.9-36.9 kPa]). Shorter expiration time reduced cyclic recruitment and derecruitment significantly (158 ± 85 torr [21.1 ± 11.3 kPa] [inspiration to expiration ratio, 1:4]; 25 ± 12 torr [3.3 ± 1.6 kPa] [inspiration to expiration ratio, 4:1]; p < 0.0001), whereas the PaO2/FIO2 ratio increased (267 ± 50 [inspiration to expiration ratio, 1:4]; 424 ± 53 [inspiration to expiration ratio, 4:1]; p < 0.0001). Correspondingly, regional ventilation redistributed toward dependent lung regions (p < 0.0001). Recruitment was much faster (TAU: fast 1.6 s [78%]; slow 9.2 s) than derecruitment (TAU: fast 3.1 s [87%]; slow 17.7 s) (p = 0.0078). CONCLUSIONS Inverse ratio ventilation minimizes cyclic recruitment and derecruitment of atelectasis in an experimental model of surfactant-depleted pigs. Time constants for recruitment and derecruitment, and regional ventilation distribution, reflect these findings and highlight the time dependency of cyclic recruitment and derecruitment.

Several methods of ventilation have previously been shown to reduce intraoperative atelectasis and alveolar to arterial oxygen gradient (A-a DO2) in healthy patients. This study was designed to show firstly the relative intra-operative benefit and secondly if any method had an effect on atelectasis postoperatively. Using a factorial design we randomized 24 patients to each of the four ventilatory interventions (manual inflations, large tidal volumes, PEEP, and pressure control inverse ratio ventilation (IRV)). The A-a DO2 was used as the measure of atelectasis and data collected intra- and postoperatively for 24 hours. The mean pre-induction A-a DO2 was 80 mmHg. This study demonstrated that PEEP and IRV were most effective in reducing intraoperative A-a DO2 (P2. No method had any effect on postoperative A-a DO2.

One of the many challenges in the management of the patient with adult respiratory distress syndrome is optimal application of mechanical ventilation. Pressure controlled-inverse ratio ventilation has surfaced as a possible alternative to conventional ventilation for patients affected by this condition. In pressure controlled-inverse ratio ventilation, the conventional inspiratory-to-expiratory ratio is reversed, allowing the inspiratory phase to lengthen with an accompanying increase in mean airway pressure. When carefully applied, mean airway pressure adjustments can be manipulated without increases in positive end-expiratory pressure and peak airway pressure, thus minimizing the risk of alveolar rupture and worsening of lung injury.

In the fluid-filled lungs of early adult respiratory distress syndrome (ARDS) the dependent parts are compressed and atelectatic; whereas, the nondependent areas remain aerated and functional. Ventilating these considerably restricted lungs carries the risk of overinflation and ventilatory-induced lung injury (baro-volutrauma). The consequences for adjusting mechanical ventilation are: 1) reducing tidal volumes in order to avoid alveolar hyperinflation and excessive alveolar pressures; 2) considering permissive hypercapnia if adequate CO2 elimination cannot be maintained; 3) keeping open the unstable alveoli by positive end-expiratory pressure (PEEP) (external or intrinsic). However, the large variations in regional lung compliance make it improbable that an optimal external PEEP level beneficial for the whole lung will be found; 4) using intrinsic PEEP in the inverse ratio ventilation (IRV) mode which varies with differences in regional ventilatory kinetics. No clinical study has yet convincingly demonstrated the benefit of IRV compared to conventional ventilation, controlled clinical long-term trials are not yet available; and 5) using superimposed spontaneous breathing which may be considerably more effective in opening up collapsed alveoli, combined with intentional intrinsic PEEP this is achieved in airway pressure release ventilation (APRV). Other new principles of mechanical ventilation, such as "proportional assist ventilation" or "tracheal gas insufflation" must still be considered as experimental.

Inverse ratio ventilation (IRV) is commonly used in clinical practice. Several studies have used IRV in order to recruit collapsed alveoli. In a randomised trial in twelve surfactant depleted piglets, the lungs were ventilated with sufficient positive end-expiratory pressure (PEEP) to prevent end-expiratory collapse, and the effects of increased inspiration-to-expiration (I:E ratio) were evaluated. Pressure regulated ventilation (with I:E of 1:1, constant tidal volume and decelerating inspiratory flow) was used at 30 breaths per minute (bpm). I:E ratios of 1.5:1, 2.3:1 and 4:1 were applied sequentially. When the I:E ratio was increased, external PEEP had to be reduced in order to keep total PEEP constant. Functional residual capacity, airway pressures, gas exchange, extrathermal volume and hemodynamics were measured. With I:E ratios above 2:1 intrinsic PEEP was generated and with concomitant decrease in cardiac index. PaO2 was not affected, but oxygen delivery was reduced. It is concluded that I:E ratios of 2:1, or above, generate increased intrinsic PEEP with compromised hemodynamics.

Background Pressure-controlled (PCV) and pressure-controlled inverse ratio ventilation (PCIRV) have been proposed instead of volume-controlled conventional ratio ventilation (VC) with positive end-expiratory pressure (PEEP) for patients with adult respiratory distress syndrome (ARDS). The advantages advocated with the use of PCIRV are to decrease airway pressures and to improve gas exchange. However, most studies did not compare PCIRV and VC while keeping both the level of ventilation and end-expiratory alveolar pressure (total-PEEP) constant. Methods Nine patients with moderate to severe ARDS (lung injury score 2.83 +/- 0.18) had their lungs ventilated with VC, PCV with a conventional ratio (I:E 1:2; PC 1/2), and PCIRV (I:E 2:1 and 3:1; PC 2/1 and PC 3/1, respectively). Ventilator settings were adjusted to keep tidal volume, respiratory rate, FIo2, and total-PEEP constant in every mode. With each mode, a complete set of ventilatory, hemodynamic, and gas exchange parameters was obtained after 30 min. Results In PC 3/1, the data obtained could not be strictly compared to the other modes because total-PEEP was higher despite external-PEEP being set at zero. For the other modes (VC, PC 1/2, and PC 2/1), despite differences in peak airway pressures, no difference was noted for end-inspiratory and end-expiratory static airway pressures (which better reflect alveolar pressures) nor for lung and respiratory system compliance. Arterial oxygenation deteriorated slightly with PC 2/1 despite a higher mean airway pressure, whereas alveolar ventilation tended to be slightly, but not significantly, improved (lower PaCo2). A decrease in systolic and mean arterial pressure also was observed with PC 2/1 without other significant hemodynamic change. Conclusions In this prospective controlled study, no short-term beneficial effect of PCV or PCIRV could be demonstrated over conventional VC with PEEP in patients with ARDS.

This article reviews adult respiratory distress syndrome as it is associated with multiple organ dysfunction and systemic inflammatory response. The pathophysiology of adult respiratory distress syndrome is discussed and related to the clinical presentation. Included in the clinical presentation is a discussion of respiratory and hemodynamic alterations, lung mechanics, and oxygen delivery and consumption alterations. Conventional therapeutic modalities for treatment of adult respiratory distress syndrome are reviewed in addition to new ventilatory approaches. New approaches to ventilation and oxygenation included in this article are pressure control ventilation, inverse ratio ventilation, permissive hypercapnia, and extracorporeal therapy. New pharmacologic therapy for the treatment of adult respiratory distress syndrome is also reviewed in this article.

Positive pressure ventilation influences hemodynamics and impairs renal function. The effects of inverse ratio ventilation (IRV) on hormonal response and renal function need to be investigated because this represents a highly invasive form of positive pressure ventilation.Ten male patients were treated postoperatively for 60 min using five different ventilation modes. At the end of these periods, hemodynamics, urine production, fractional excretion of sodium (FESo), as well as the hormones, atrial natriuretic peptide (ANP), renin, angiotensin II, aldosterone, and antidiuretic hormone (ADH), were measured in plasma.Central venous pressure (CVP), ADH, and renin with a positive end-expiratory pressure (PEEP) of 15 cm H(2)O and an inspiration/expiration ratio (I:E) of 1:2 revealed significant increases from baseline, whereas CVP, renin, and FESo showed an increase with an PEEP of 15 cm H(2)O and an I:E ratio of 2:1. Urine production significantly decreased with an PEEP of 15 cm H(2)O and an I:E ratio of 2:1.IRV with PEEP induced clear effects on hemodynamics and hormonal responses (renin) as well as a decrease in urine production in patients with healthy renal and pulmonary systems after an operation. However, all parameters apart from FESo and renin remained within the normal range. Whether pathological values are also observed after longer periods of positive pressure ventilation shall be the subject of other studies.

Background There are no guidelines on ventilation modes in morbidly obese patients. We investigated the effects of volume-controlled (VCV) and pressure-controlled ventilation (PCV) on gas exchange, respiratory mechanics, and cardiovascular responses in laparoscopic gastric banding procedures. Methods After Institutional Review Board approval, 24 adult consenting patients scheduled for laparoscopic gastric banding were studied. Anesthesia was standardized using remifentanil, propofol, rocuronium, and sevoflurane. All patients started with VCV with a tidal volume of 10 ml kg(-1) ideal body weight, respiratory rate adjusted to obtain an end-tidal carbon dioxide of 35-40 mmHg, positive end-expiratory pressure of 5 cmH(2)O, an inspiratory pause of 10% and an inspiratory/expiratory ratio of 1:2. Fifteen minutes after pneumoperitoneum, the patients were randomly allocated to two groups. In Group VCV (n=12), ventilation was with the same parameters. In Group PCV (n=12), the airway pressure was set to provide a tidal volume of 10 ml kg(-1) ideal body weight without exceeding 35 cm H2O. Respiratory rate was adjusted to keep an end-tidal carbon dioxide of 35-40 mmHg. Arterial blood samples were drawn after surgical positioning and 15 min after allocation. Analysis of variance (ANOVA) was used for statistical analysis. Results With constant minute ventilation, VCV generates equal airway pressures and cardiovascular effects with a lower Pa-CO2 as compared to PCV (42.5 (5.2) mmHg versus 48.9 (4.3) mmHg, p < 0.01 ANOVA). Arterial oxygenation remained unchanged. Conclusion VCV and PCV appear to be an equally suited ventilatory technique for laparoscopic procedures in morbidly obese patients. Carbon dioxide elimination is more efficient when using VCV.

Nitric acid (HNO3) is frequently used as a solvent, pickling agent, for etching, and as a cleanser. HNO3 fumes may also contain a mixture of HNO3 with various oxides of nitrogen (NO, NO2) [1]. Accidental spillage of HNO3 generates nitrogen oxides that cause chemical pneumonitis when inhaled. In mild cases, there may be no symptoms during the first few hours after exposure, or the typical symptoms of pulmonary edema can appear within 3-24 hours. However, in cases of prolonged exposure, progressive pulmonary edema develops instantaneously, and patients may not survive for more than 24 hours [2]. Treatment of massive pulmonary edema due to increased microvascular permeability is multimodal and comprises mechanical ventilation with positive end expiratory pressure (PEEP), inverse ratio ventilation, replacement of surfactant, and extracorporeal membrane oxygenation (ECMO) [3]. In this report, we describe a case of intravenous anesthesia of nitric acid inhalation injury for ECMO. A 42-year-old man was accidentally exposed to a toxic mixture for approximately 5 min. He worked for an electroplating factory and was exposed to nitric acid. Initially, he experienced a mild oropharyngeal irritation. But approximately 1 h later, dyspnea developed, and he was admitted to the emergency department due to dyspnea at rest and cyanosis 2.5 h after the inhalation. On arrival, he was conscious and well oriented. Expiratory stridor, intercostal muscle retraction, and a frothy secretion from the nose and mouth were noticed. Blood pressure (BP) was 140/74 mmHg with heart rate (HR) of 134/min and respiratory rate of 28/min. Arterial blood gas analysis (ABGA) showed hypoxemia (pH, 7.34; PaCO2, 38.5 mmHg; PaO2, 60.6 mmHg; HCO3-, 18.9 mmol/L; SaO2, 87.9%). A chest radiograph showed pulmonary edema with confluent alveolar-infiltration densities. Although mechanical ventilation was applied with PEEP at 10 cmH2O on 100% inhaled oxygen, the impaired oxygenation worsened. At 4 h after exposure, despite mechanical ventilation with PEEP at 10 cmH2O and FiO2 of 1.0, ABGA showed pH, 7.09; PaCO2, 108.1 mmHg; PaO2, 43.6 mmHg; HCO3-, 31.8 mmol/L; SaO2, 58.5%. As the patient's respiratory situation did not improve, twin pulse extracorporeal life support system (T-PLS®, NewHeartbio, Seoul, Korea) was started. ECMO was set to 3.0 L/min through the femoral artery and vein. Two h later, blood gases improved temporarily (pH, 7.324; PaCO2, 49.5 mmHg; PaO2, 85.8 mmHg; HCO3-, 25.2 mmol/L, SaO2 95.5%), but the pulmonary edema on a chest radiograph worsened. Another 2 h later, because the femoral venous catheter was inadequate to provide sufficient venous drainage, the venous cannulas were attempted to change from the left femoral vein to the right internal jugular vein. On arrival in the operating room, BP was 100/70 mmHg, HR was 110/min, and SpO2 was 100%. The intravenous infusion of 2 µg/kg/min midazolam was discontinued and propofol was infused at 2 mg/kg/h. A wire-reinforced endotracheal tube was placed after administration of 0.6 mg/kg rocuronium. Central venous pressure was maintained at 13-15 cmH2O. ABGA at FiO2 of 0.6 showed pH, 7.298; PO2, 175.9 mmHg; PCO2, 50.4 mmHg; SaO2, 99.4%; HCO3-, 24.1 mmol/L. Approximately 30 min after the propofol infusion, BP decreased to 80/60 mmHg and HR increased to 150/min. Phenylephrine (100 µg) was injected and infused continuously. But, the patient became refractory to the infusion of phenylephrine. ABGA at FiO2 of 0.6 showed pH, 7.271; PO2, 108.7 mmHg; PCO2, 47.4 mmHg; SaO2, 97.1%; HCO3-, 21.3 mmol/L. SBP ranged from 40-60 mmHg, so 8 mg ephedrine and 100 µg epinephrine were injected. Dopamine (3-15 µg/kg/min), dobutamine (3-20 µg/kg/min), and epinephrine (0.05-1 µg/kg/min) were infused. During the hypotensive period, SpO2 was maintained at 50-80% and ECMO flow was maintained at 3.5-6.0 L/min. At 1 hr after the catecholamine infusion, BP was 95/70 mmHg with HR of 175/min. ABGA with FiO2 of 1.0 showed pH, 7.221; PO2, 49.6 mmHg; PCO2, 57.6 mmHg; SaO2, 75%; HCO3-, 23.1 mmol/L. After the right internal jugular vein was accessed for cannulation, the ECMO venous drainage became sufficient. He was transferred to the ICU on 100% oxygen with ambu bagging. Postoperative ABGA with FiO2 of 1.0 showed pH, 7.25; PO2, 57 mmHg; PCO2, 51.9 mmHg; SaO2, 84 %; HCO3-, 22.6 mmol/L. A chest radiograph revealed bilateral interstitial edema in both lungs (Fig. 1). Transthoracic echocardiography showed preserved LV systolic function. A pulmonary artery catheter was placed postoperatively, and the cardiac index was 3.7 L/min/m2. On the seventh postoperative day, the patient was weaned from ECMO. Three weeks after ECMO weaning, he was discharged from the hospital without serious pulmonary or neurological complications. ABGA showed pH, 7.438; PO2, 97.8 mmHg; PCO2, 43.2 mmHg; SaO2, 97.9%; HCO3-, 28.6 mmol/L. Fig. 1 After extracorporeal membrane oxygenation is applied, a chest radiograph demonstrates diffuse interstitial infiltrates and ground glass opacities in both lungs. ECMO by means of peripheral cannulation is an established therapeutic strategy in patients with cardiopulmonary failure and has been used successfully to manage acute reversible pulmonary failure [4]. Surgical procedures during ECMO have been performed in some patients, but no reports are available about applying ECMO under general anesthesia. Considering our patient's pulmonary status, we performed intravenous anesthesia with propofol rather than volatile anesthetics. Propofol is a hypnotic agent whose pharmacological properties make it extremely well suited to sedation and anesthesia. Because of its high potency and the respiratory and cardiovascular complications that can result, propofol should only be used when strict precautionary measures are observed. In our patient, BP decreased to 80/40 mmHg 30 min after the propofol infusion, and HR increased to 150/min but did not improve for about 1 h. In addition to chemical pneumonitis, we assumed that propofol induced the hypotension and tachycardia. Propofol has been reported to stimulate nitric oxide (NO) activity and showed a concentration-dependent increase in NO production by neutrophils [5]. It can be hypothesized that severe hypotension occurs during anesthesia. The implication for NO produced during nitric acid exposure and propofol infusion worsened the hypotension in this case. In conclusion, we experienced unexpected hypotension and tachycardia during propofol infusion for ECMO cannulation in a patient with a nitric acid inhalation injury. We suggest that anesthesiologists should be aware of the clinical features of nitric acid inhalation injury and the effect on possible hemodynamic derangement with use of the intravenous anesthetic such as propofol.

Background In patients with acute respiratory distress syndrome, whether inverse ratio ventilation differs from high positive end-expiratory pressure (PEEP) for gas exchange under a similar mean airway pressure has not been adequately examined. The authors used arterial oxygenation, gastric intramucosal partial pressure of carbon dioxide (PiCO(2)), and pH (pHi) to assess whether pressure-controlled inverse ratio ventilation (PC-IRV) offers more benefits than pressure-controlled ventilation (PCV) with PEEP. Methods Seventeen acute respiratory distress syndrome patients were enrolled and underwent mechanical ventilation with a PCV inspiratory-to-expiratory ratio of 1:2, followed by PC-IRV 1:1 initially. Then, they were randomly assigned to receive PC-IRV 2:1, then 4:1 or 4:1, and then 2:1, alternately. The baseline setting of PCV 1:2 was repeated between the settings of PC-IRV 2:1 and 4:1. Mean airway pressure and tidal volume were kept constant by adjusting the levels of peak inspiratory pressure and applied PEEP. In each ventilatory mode, hemodynamics, pulmonary mechanics, arterial and mixed venous blood gas analysis, PiCO(2), and pHi were measured after a 1-h period of stabilization. Results With a constant mean airway pressure, PC-IRV 2:1 and 4:1 decreased arterial and mixed venous oxygenation as compared with baseline PCV 1:2. Neither the global oxygenation indices with oxygen delivery and uptake nor PiCO(2) and pHi were improved by PC-IRV. During PC-IRV, applied PEEP was lower, and auto-PEEP was higher. Conclusion When substituting inverse ratio ventilation for applied PEEP to keep mean airway pressure constant, PC-IRV does not contribute more to better gas exchange and gastric intramucosal PiCO(2) and pHi than does PCV 1:2 for acute respiratory distress syndrome patients, regardless of the inspiratory-to-expiratory ratios.

Continuous as well as cyclic (with each expiration) lung collapse in acute respiratory failure can be reduced by positive end-expiratory pressure (PEEP) or short expiration times, as in inverse ratio ventilation (IRV). In 20 pigs with oleic acid-induced lung edema, we compared the effects of a PEEP of 20 cm H(2)O with IRV, using an inspiratory-to-expiratory ratio of 3:1 without external PEEP. During IRV, expiration times of 0.5 or 1.0 s were obtained with respiratory rates of 30 breaths/min or 15 breaths/min, respectively. In 15 animals, ventilation-perfusion relationships were studied through the multiple inert gas elimination technique, and lung morphology was studied with computed tomography. In another five pigs, blood flow distribution was studied with perfusion scintigraphy. All three ventilatory modes had similar effects on mean arterial blood pressure, cardiac output, oxygen delivery, and mean airway pressure. PEEP reduced shunt and improved oxygenation to a greater extent than the two modes of IRV, although there was a large variation within each group. The improvement, irrespective of which ventilatory mode was superior in a particular pig, was caused by greater and more even aeration of the lung, whereas the perfusion distribution with PEEP was the same as with IRV. Thus, the strategy of stabilizing the lungs through short expiration times, as in IRV, did not offer any advantages in our lung injury model.

Although pressure controlled-inverse ratio ventilation (PC-IRV) has been used successfully in the treatment of respiratory failure, it has not been applied to the treatment of respiratory dysfunction during anaesthesia. With PC-IRV the inspiratory wave form is fundamentally altered so that inspiratory time is prolonged (inverse I:E), inspiratory flow rate is low, and the peak inspiratory pressure is limited. Positive end-expiratory pressure (PEEP) can be applied and the mean airway pressure is higher than with conventional ventilation. To assess the clinical efficacy of this new mode of ventilation we studied ten patients having lower abdominal gynaecologic surgery in the Trendelenburg position under general anaesthesia. Pulmonary O2 exchange was determined during four steady states: awake control(AC), after 30 and 60 min of PC-IRV during surgery, and at the end of surgery. Patients’ lungs were ventilated with air/O2 by a Siemens 900C servo ventilator in the PC-IRV mode with an I:E ratio of 2:1 and 5 cm H2O of PEEP. TheFiO2 was controlled at 0.5 and arterial blood gases were used to calculate the oxygen tension-based indices of gas exchange. There were significant increases of(A-a) DO2 at 30 and 60 min (41 and 43%). These changes were less than those reported in a previous study using conventional tidal volume ventilation (7.5 ml · kg−1) and were similar to those in patients whose lungs were ventilated with high tidal volumes (12.7 ml · kg−1). Thus, in this clinical model of compromised gas exchange, arterial oxygenation was better with PC-IRV than with conventional ventilation, but not better than with large tidal volume ventilation.

Inverse ratio ventilation (IRV) has been reported to improve oxygenation at lower peak airway pressures in patients with respiratory failure. Therefore we hypothesised that IRV might also improve oxygen exchange during anaesthesia. Conventional ratio ventilation (CRV) and IRV were compared in 24 low-risk surgical patients who were paralysed and whose lungs were ventilated with air/O2 by a non-rebreathing circuit and a Siemens 900-C servo ventilator. Two levels of time-cycled IRV (I:E ratios of 60/40 and 77/23) were bracketed by control periods with CRV (I:E ratio of 35/65). Inspired O2 fraction, O2 uptake and CO2 elimination, arterial blood gases, pulmonary ventilation and mechanics, heart rate and blood pressure were measured. From these data alveolar and dead space ventilation and four oxygen tension-based indices of gas exchange were calculated. During IRV, mean airway pressure (mean AWP) was increased but there were no changes in oxygen exchange indices, pulmonary mechanics, HR or BP. A sub-set of the sample with moderately impaired oxygen exchange, defined as the upper quartile for (A-a)DO2, was examined separately with identical results. Multivariate models were tested to identify variables which predicted O2 exchange during CRV. Patient age was the only predictor consistently significant in all models. We conclude that age is an important determinant of impaired pulmonary oxygen exchange during anaesthesia, and that increasing mean AWP by TC-IRV has no beneficial effects on pulmonary mechanics or gas exchange.

Cardiopulmonary Critical Care is a conveniently small textbook that discusses clinically relevant physiology and treatment of cardiac and pulmonary derangements in intensve care unit patients. I appreciate the compact size of this textbook because my stamina for lifting heavy, more comprehensive textbooks is yielding to the electronic medium. By restricting discussions to cardiac and pulmonary areas, I found that this compact textbook comprehensively covered topics such as advanced ventilator modes and techniques, the variety of new drugs available to treat cardiac and hypertensive disorders, and the unique problems encountered in cardiac and thoracic surgical and trauma patients. As pointed out by its editors, the book is designed for '... clinicians with intermittent responsibilities for critically ill patients in a world of competing demands.' With this goal in mind, I wonder whether this type of clinician will spend much time with the discussions of respiratory and cardiac physiology that are found at the beginning of the textbook. Some of these discussions are quite basic and are readily found in surgical, internal medicine, and anesthesiology textbooks, as well as in most critical care textbooks. Examples include discussions of acid–base abnormalities, oxygen transport, and lung mechanics. I am convinced, however, that intermittent critical care physicians will find the discussions of newer and increasingly popular medications and treatment approaches very practical. When, for example, should vasopressin be used for hypotension? When should a patient with acute lung injury be placed in the prone position? Should lipid-lowering therapy be used in the immediate period after a patient presents with an acute coronary syndrome? The discussions of these topics are well referenced. The authors clearly state when there is controversy and when supporting literature is lacking. Critical care medicine has seen an explosion in new ventilator technologies. With the exception of pulmonary and critical care specialists, it is not unusual for physicians to be overwhelmed with advanced ventilator terminology and techniques. I found that the chapters on mechanical ventilation, including modes of ventilation, weaning from mechanical ventilation, and the use of noninvasive ventilation, were lucidly written and well referenced. The serious reader of these chapters will find the basics of volume and pressure targeted modes (traditional and untraditional), auto-PEEP (auto positive end-expiratory pressure), and weaning techniques clearly presented with clarifying illustrations. Discussions of advanced ventilator management including lung protective strategies, airway pressure release ventilation, and pressure control inverse ratio ventilation will be useful to the advanced critical care practitioner. I appreciated the sections on postoperative care of cardiac and thoracic surgical and trauma patients. Although the physiology of these patients' derangements is well understood by most practitioners of critical care medicine, the unique problems with these perioperative patients and practice preferences of cardiothoracic surgeons and anesthesiologists may be poorly understood by physicians whose training did not span these disciplines. The chapters discuss the basics of care for these patients but they also include unique issues such as the use of independent lung ventilation, epidural and intrathecal narcotic administration, and management of injury to the recurrent laryngeal nerve. A table outlining complications of common and unusual thoracic surgical procedures will be useful to nonsurgical physicians who care for these patients. A small section is dedicated to the use of portable ultrasonography to assist vascular access to the internal jugular vein – a cutting edge technology that is experiencing increasing application. Unfortunately, more studies documenting the safety and efficacy of portable ultrasound for vascular procedures are needed, but I believe that this technology will become standard soon. I hope that future editions of this book will provide even more detailed information to validate and describe this important adjunct to vascular catheterization.

Reperfusion injury is one of the major causes of early morbidity and mortality after lung transplantation. Features of thi s syndrome are pulmonary edema, reduction of compliance, and impaired gas exchange, and these occur in about 20% of all lung transplant recipients. Usual treatment includes prolonged mechanical ventilation with elevated positive end-expiratory airway pressure (PEEP), enhanced mean airway pressure with high oxygen content (Fio2), and, in severe cases, inverse ratio ventilation and extracorporeal membrane oxygenation. We report on the successful treatment with nebulized synthetic surfactant (Exosurf; Wellcome, Burgwedel, Germany) of a patient in whom reperfusion injury developed 5 hours after right lung transplantation. Right lung transplantation was done in a 26-year-old woman who had sarcoidosis with terminal interstitial lung disease and recurrent failure of the right side of the heart. The patient had been dependent on continuous oxygen insufllation for 30 months before transplantation. Pulmonary hypertension was present with a mean pulmonary artery pressure of 50 mm Hg.

Pressure controlled inverse ratio ventilation (PCIRV) is often used as the initial therapeutic manoeuvre to improve oxygenation in severe adult respiratory distress syndrome (ARDS). When this alone fails, however, there is no consensus as to which therapy to resort to. We have used combined high frequency ventilation (CHFV) along with kinetic therapy (KT) to treat three patients with ARDS and resistant hypoxia. The basis for this treatment was our previous clinical observation that the two techniques together produced a greater improvement in oxygenation than either used alone. In CHFV a Monsoon jet ventilator was used to superimpose high frequency jet ventilation (rate 300 cycles min−1, inspiratory time 0.3, driving pressure 1 bar) on pressure controlled ventilation (rate 10 breaths min−1, inspiratory pressure 30 mbar). At the same time patients were positioned on a kinetic therapy pressure relief low air-loss bed (KCI) and rotated through a total angle of 90°. ThreePaO2/FIO2 values for each patient are shown in Table 14 and these correspond to (a) PCIRV alone (b) after 1 h of combined therapy and (c) after 24 h of combined therapy. The combination of CHFV with kinetic therapy produced improvement in oxygenation in all patients. Each of these individual therapies is believed to act through a different physiological mechanism.1 2 It is possible that the two together may, therefore, produce greater improvement than either therapy applied on its own. The number of such cases that present to one institution limits our small study, but we believe the significant improvement in oxygenation warrants further investigation.

In acute respiratory distress syndrome (ARDS) change from supine (SP) to prone position can improve gas exchange by recruiting alveoli situated in dorsal dependent regions and by alteration of ventilation/perfusion ratio. The aim of this study was to investigate the effect of prone position (PP) after application of high fractional inspired oxygen (hFiO2), inverse ratio ventilation (IRV), positive end exspiratory pressure (PEEP)as well as kinetic therapy (KT) and hemofiltration (HF) did not lead to a breakthrough in treatment of severe ARDS.