Pressure-controlled Inverse Ratio Ventilation Research Articles

Features of Mechanical Lung Ventilation During Robot-Assisted Radical Prostatectomy in Patients with Different Body Mass Index

The aim of the study. To evaluate effects of carboxyperitoneum and steep Trendenburg position on respiratory biomechanics and gas exchange indicators in patients with different body mass index (BMI) during robotic-assisted radical prostatectomy (RRP). To develop an algorithm for choosing the optimal mechanical lung ventilation (MLV) regimen. Materials and methods. The study included 141 patients with verified prostate cancer who were candidates for RPR. Participants were divided into 2 groups based on BMI: group I included 88 patients with BMI30 kg/m2, group II — 53 patients with BMI30 kg/m2. Indicators of respiratory biomechanics and gas exchange during ventilation in various modes (Volume Controlled Ventilation (VCV), Pressure Controlled Ventilation (PCV), Pressure Controlled– Inverse Ratio Ventilation (PC-IRV) were analyzed in each group at 5 consecutive stages of the procedure.Results. The key parameters evidencing the effectiveness and safety of MLV during RRP procedure did not vary significantly under various ventilation regimens in the group of patients with a BMI30 kg/m2. Whilst in obese patients the use of VCV mode resulted in a significant increase of airway peak pressure (Ppeak) already at the stage of placing them into a steep Trendelenburg position (35°), thus endangering with the development of ventilator-induced lung injury. Increased Ppeak was also accompanied by the drop in oxygen saturation and significantly lower SpO₂ values, starting from the stage of applying carboxyperitoneum and until the end of surgical intervention.Conclusion. In non-obese patients, there’s no particular ventilator regimen that is crucial for achieving the safety and effectiveness of RRP anesthesia management, all regimens can be used. In patients with BMI30 kg/m2 PCV regimen and PC-IRV with inhalation/exhalation ratio of 1.5:1 can be considered as the optimal strategy for MLV during anesthesia for RRP surgery.

Effects of volume-targeted pressure-controlled inverse ratio ventilation on functional residual capacity and dead space in obese patients undergoing robot-assisted laparoscopic radical prostatectomy.

The effect of inverse inspiration:expiration (I:E) ratio on functional residual capacity (FRC) during pneumoperitoneum is unclear. We hypothesised that volume-targeted pressure-controlled inverse ratio ventilation (vtPC-IRV) would increase FRC by increasing the level of auto-PEEP in low respiratory compliance situations. During robot-assisted laparoscopic radical prostatectomy, 20 obese patients were sequentially ventilated with four different settings for 30 min in each setting: (1) control, I:E ratio of 1:2 and baseline airway pressure (BAP) of 5 cm H2O; (2) IRV2, I:E ratio of 2:1 and BAP off; (3) IRV3, I:E ratio of 3:1 and BAP off; and (4) IRV4, I:E ratio of 4:1 and BAP off. The changes in FRC were identified and compared among these settings. The FRC significantly increased as the I:E ratio increased. The FRC values expressed as median (inter-quartile range) during control, IRV2, IRV3, and IRV4 were 1149 (898-1386), 1485 (1018-1717), 1602 (1209-1775), and 1757 (1337-1955) ml, respectively. Auto-PEEP increased significantly as the I:E ratio increased and correlated with FRC (rho=0.303; P=0.006). Shunt and physiological dead space were significantly lower in all IRV groups than in the control group; however, there were no significant differences among the IRV groups. vtPC-IRV with shortened expiratory time and increased auto-PEEP effectively increases FRC during robot-assisted laparoscopic radical prostatectomy in obese patients. FRC increases progressively as the I:E ratio increases from 1:2 to 4:1; however, an I:E ratio higher than 2:1 does not further improve the dead space. UMIN000038989.

Changes in dead space components during pressure-controlled inverse ratio ventilation: A secondary analysis of a randomized trial.

BackgroundWe 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.MethodsThis 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.ResultsThe 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.ConclusionsPressure-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.

Lung-protective properties of expiratory flow-initiated pressure-controlled inverse ratio ventilation: A randomised controlled trial.

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). 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. 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; P<0.001). The physiological dead space rate was negatively correlated with the forced vital capacity (% predicted) in the VCV group (r = -0.85, P<0.001), but not in the EF-initiated PC-IRV group (r = 0.15, P = 0.62). Two patients in the VCV group had permissive hypercapnia with low forced vital capacity (% predicted). 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.

Effect of pressure-controlled inverse ratio ventilation on dead space during robot-assisted laparoscopic radical prostatectomy: A randomised crossover study of three different ventilator modes.

Pressure-controlled inverse inspiratory to expiratory ratio ventilation (PC-IRV) is thought to be beneficial for reducing the dead space volume. To investigate the effects of PC-IRV on the components of dead space during robot-assisted laparoscopic radical prostatectomy (RLRP). A randomised crossover study of three different ventilator modes. A single university hospital from September 2014 to April 2015. Twenty consecutive study participants undergoing RLRP. Patients were ventilated sequentially with three different modes in random order for 30 min: volume control ventilation (VCV; inspiratory to expiratory ratio 0.5), pressure control ventilation (PCV; inspiratory to expiratory ratio 0.5) and PC-IRV. Inverse inspiratory to expiratory ratio was adjusted individually by observing the expiratory flow-time wave to prevent the risk of dynamic pulmonary hyperinflation. The primary outcome included physiological dead space (VDphys), airway dead space (VDaw), alveolar dead space (VDalv) and shunt dead space (VDshunt). VDphys was calculated by Enghoff's method. We also analysed respiratory dead space (VDresp) and VDaw using a novel analytical method. Then, VDalv and VDshunt were calculated by VDalv = VDresp - VDaw and VDshunt = VDphys - VDresp, respectively. The VDphys/expired tidal volume (VTE) ratio in PC-IRV (29.2 ± 4.7%) was significantly reduced compared with that in VCV (43 ± 8.5%) and in PCV (35.9 ± 3.9%). The VDshunt/VTE in PC-IRV was significantly smaller than that in VCV and PCV. VDaw/VTE in PC-IRV was also significantly smaller than that in VCV but not that in PCV. There was no significant change in VDalv/VTE. PC-IRV with the inspiratory to expiratory ratio individually adjusted by the expiratory flow-time wave decreased VDphys/VTE in patients undergoing RLRP. University Hospital Medical Information Network in Japan 000014004.

The effect of pressure-controlled inverse ratio ventilation on lung protection in obese patients undergoing gynecological laparoscopic surgery.

To examine the effects of pressure-controlled inverse ratio ventilation (PCIRV) and volume-control ventilation (VCV) on arterial oxygenation, pulmonary function, hemodynamics, levels of surfactant protein A (SP-A), and tumor necrosis factor-α (TNF-α) in obese patients undergoing gynecological laparoscopic surgery. Sixty patients, body mass index (BMI) ≥30kg/m2, scheduled for elective gynecological laparoscopic surgery were enrolled in the study. Patients were randomly allocated to receive either PCIRV with an inspiratory-expiratory (I:E) ratio of 1.5:1 (PCIRV group n=30) or VCV with an I:E ratio of 1:2 (VCV group n=30). Ventilation variables, viz. tidal volume (V T), dynamic respiratory-system compliance (C RS), driving pressure (ΔP=V T/C RS), arterial blood oxygen partial pressure/fraction of inspiration oxygen (PaO2/FiO2) and arterial blood carbon dioxide partial pressure (PaCO2), were measured. Hemodynamic variables, viz. mean arterial pressure (MAP), heart rate (HR), and serum levels of SP-A and TNF-α, were also measured. When compared to patients in the VCV group, patients in the PCIRV group had higher V T, dynamic CRS, and PaO2/FiO2, and lower ΔP and PaCO2 at 20 and 60min after the start of pneumoperitoneum (p<0.05). Patients in the PCIRV group had lower SP-A and TNF-α levels at 24 and 48h after surgery than those in the VCV group (p<0.05). In obese patients undergoing gynecological laparoscopic surgery, PCIRV can improve ventilation, promote gas exchange and oxygenation, and is associated with decreased levels of SP-A and TNF-α. These effects demonstrate improved lung protection provided by PCIRV in this patient population.

Pressure-controlled inverse ratio ventilation as a rescue therapy for severe acute respiratory distress syndrome.

PurposeLow tidal volume ventilation improves the outcomes of acute respiratory distress syndrome (ARDS). However, no studies have investigated the use of a rescue therapy involving mechanical ventilation when low tidal volume ventilation cannot maintain homeostasis. Inverse ratio ventilation (IRV) is one candidate for such rescue therapy, but the roles and effects of IRV as a rescue therapy remain unknown.MethodsWe undertook a retrospective review of the medical records of patients with ARDS who received IRV in our hospital from January 2007 to May 2014. Gas exchange, ventilation, and outcome data were collected and analyzed.ResultsPressure-controlled IRV was used for 13 patients during the study period. Volume-controlled IRV was not used. IRV was initiated on 4.4 ventilation days when gas exchange could not be maintained. IRV significantly improved the PaO2/FiO2 from 76 ± 27 to 208 ± 91 mmHg without circulatory impairment. The mean duration of IRV was 10.5 days, and all survivors were weaned from mechanical ventilation and discharged. The 90-day mortality rate was 38.5 %. Univariate analysis showed that the duration of IRV was associated with the 90-day mortality rate. No patients were diagnosed with pneumothorax.ConclusionsPressure-controlled IRV provided acceptable gas exchange without apparent complications and served as a successful bridge to conventional treatment when used as a rescue therapy for moderate to severe ARDS.

Comparison of Pressure-controlled Inverse Ratio Ventilation versus Pressure-controlled Ventilation in Laparoscopic Cholecystectomy with LMA

Comparison of Pressure-controlled Inverse Ratio Ventilation versus Pressure-controlled Ventilation in Laparoscopic Cholecystectomy with LMA

Pressure-Controlled Inverse Ratio Ventilation during General Anesthesia for Open Abdominal Surgery Improves Postoperative Pulmonary Function

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.

Prone position and pressure control inverse ratio ventilation in H1N1 patients with severe acute respiratory distress syndrome.

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 FiO2 of 0.6 or less and positive end-expiratory pressure <10 cm of H2 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 PaO2 /FiO2 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.

Pressure-Controlled vs Volume-Controlled Ventilation in Acute Respiratory Failure: A Physiology-Based Narrative and Systematic Review

Mechanical ventilation is a cornerstone in the management of acute respiratory failure. Both volume-targeted and pressure-targeted ventilations are used, the latter modes being increasingly used. We provide a narrative review of the physiologic principles of these two types of breath delivery, performed a literature search, and analyzed published comparisons between modes. We performed a systematic review and meta-analysis to determine whether pressure control-continuous mandatory ventilation (PC-CMV) or pressure control-inverse ratio ventilation (PC-IRV) has demonstrated advantages over volume control-continuous mandatory ventilation (VC-CMV). The Cochrane tool for risk of bias was used for methodologic quality. We also introduced physiologic criteria as quality indicators for selecting the studies. Outcomes included compliance, gas exchange, hemodynamics, work of breathing, and clinical outcomes. Analyses were completed with RevMan5 using random effects models. Thirty-four studies met inclusion criteria, many being at high risk of bias. Comparisons of PC-CMV/PC-IRV and VC-CMV did not show any difference for compliance or gas exchange, even when looking at PC-IRV. Calculating the oxygenation index suggested a poorer effect for PC-IRV. There was no difference between modes in terms of hemodynamics, work of breathing, or clinical outcomes. The two modes have different working principles but clinical available data do not suggest any difference in the outcomes. We included all identified trials, enhancing generalizability, and attempted to include only sufficient quality physiologic studies. However, included trials were small and varied considerably in quality. These data should help to open the choice of ventilation of patients with acute respiratory failure.

Pressure-controlled inverse ratio ventilation using laryngeal mask airway in gynecological laparoscopy

Background:It is well documented that pressure-controlled ventilation (PCV) improves oxygenation and ventilation compared to volume-controlled ventilation and reduces peak airway pressure in gynecological laparoscopy. PCV with moderately inversed inspiratory–expiratory (I: E) ratio can successfully recruit collapsed alveoli and has been proved to be beneficial in intensive care. We tested the hypothesis that altering the I: E ratio to 1.5:1 in PCV improves ventilation during gynecological laparoscopy using laryngeal mask airway (LMA).Objective:To study pressure-controlled inverse ratio ventilation (PCIRV) with I: E ratio 1.5:1 as against PCV with I: E ratio 1:2 in gynecological laparoscopy with LMA using noninvasive parameters.Materials and Methods:Intraoperative hemodynamics and side-stream spirometry recordings were noted in 20 consecutive patients undergoing major gynecological laparoscopy with LMA. Flexible LMA or LMA supreme were used depending on normal body mass index (BMI) or high BMI, respectively.Results:Reversing the I: E ratio to 1.5:1 increased the tidal volume, mean airway pressures, and dynamic lung compliance significantly, all indicating better oxygenation at comparable peak airway pressures as against PCV with I: E ratio 1:2. There was no change in the end-tidal carbon dioxide. There was no auto-positive end expiratory pressure (PEEP) or change in the hemodynamics.Conclusion:Reversal of I: E ratio with PCV can be beneficially used with LMA in laparoscopy.

Cardiopulmonary critical care

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.

Book reviews

This is a pocket-sized 192-page book with full colour illustrations which, as the introduction states, is designed to serve as both a self-assessment book and a reference manual. It seems to have an unrealistically wide target audience as it claims to be aimed at senior medical students, intensive care specialists and surgeons! There are 272 questions which vary in format with multiple-choice, data analysis, radiology interpretation and short answer questions. A selection of material from a wide range of specialties is covered, including neonatal intensive care, general medicine and surgery, trauma, radiology, anaesthesia, bacteriology, physiology and pharmacology. Each page contains 2–3 questions with the answers including a comprehensive discussion on the following page. The illustrations are well presented and there is a wide range of interesting and relevant clinical material. Whilst reading through the book I found it difficult to imagine who would find it useful. Some of the questions were quite specialised and there appeared to be a surgical bias with a number of questions relating to the interpretation of endoscopic, surgical and CT scan appearances. I found an irritating number of mistakes within the text such as an incorrect anion gap equation and an incorrect ventilator waveform for pressure control inverse ratio ventilation. Although I found a few useful tips for the management of various ICU complications, the text and index were not comprehensive enough to be the useful reference manual as stated in the introduction. Overall, whilst some of the material in the book will be helpful for teaching material, I think that the content is both too wide ranging and specialised to be useful for those preparing for examinations which include intensive care.

Improving oxygenation when conventional ventilation fails: a case study

Long periods of significant hypoxia do not disqualify a patient from becoming an organ donor. As the management of organ donor patients becomes more complex, recovery coordinators often have to change their thinking and resort to nonconventional means of management. This case study presents a hypoxic donor and how using pressure-control inverse ratio ventilation improved oxygenation in this donor. Before changing ventilator modes, the transplant surgeons were concerned about the long periods of hypoxia the patient had experienced during her hospitalization. After making the change, improving oxygenation, and demonstrating an improved oxygen state, 4 organs were recovered and subsequently transplanted. All the recovered organs functioned immediately after transplantation without any signs of poor performance. Although this treatment modality is not available at every institution, it can be used to improve oxygenation problems in organ donors.

The outcome of early pressure-controlled inverse ratio ventilation on patients with severe acute respiratory distress syndrome in surgical intensive care unit

Background: Pressure-controlled inverse ratio ventilation (PC-IRV) was used in patients with acute respiratory distress syndrome (ARDS) after failed volume-cycled conventional ratio ventilation (VC-CRV). The aim of this study was to evaluate the outcome of early PC-IRV in severe ARDS. Methods: Twenty patients with severe ARDS were switched from VC-CRV to PC-IRV if they failed to maintain SaO 2 >90% by the following criteria: peak inspiratory pressure (PIP) >35 cm H 2O, FIO 2 = 60%, and positive end-expiratory pressure (PEEP) 10 cm H 2O. Results: The values of PIP, mean airway pressure, minute volumes, and lung injury score in VC-CRV were 43.9 ± 8.0 cm H 2O, 19.5 ± 6.4 cm H 2O, 11.0 ± 2.1 L/min, and 2.8 ± 0.2 respectively. In PC-IRV, the corresponding data were 31.8 ± 5.1 cm H 2O, 25.4 ± 4.6 cm H 2O, 8.3 ± 0.9 L/min, and 2.5 ± 0.4. All of these parameters were significantly different. Fifteen patients (75%) survived their intensive care unit stay. Conclusions: Early PC-IRV in severe ARDS improves oxygenation, facilitates tapering of high fraction of inspiratory oxygen, and decreases high PEEP or PIP, and then results in the improvement of the patient’s outcome.

Pressure-controlled inverse ratio ventilation after cardiac surgery

Background and objective Pressure-controlled inverse ratio ventilation was compared with controlled mechanical ventilation in patients after cardiac surgery. Methods Ten patients were ventilated after sternal closure using a Siemens Servo 900C ventilator to a target end-tidal PCO2 of 4.0 kPa. They were randomized to receive controlled mechanical ventilation or pressure-controlled inverse ratio ventilation. CO2-based data were recorded on a laptop personal computer, which together with arterial PCO2 permitted measurement of the respiratory dead space. Once measurements were complete the ventilator was switched to the other mode and new measurements taken. Results PaCO2 and CO2 were virtually the same in both modes. Peak airway pressure (17.2 ± 2.7 vs. 20.8 ± 2.5 cmH2O, P < 0.01) and minute ventilation (4.9 ± 1.1 vs. 5.3 ± 1.1 cmH2O, P < 0.01) were less during pressure-controlled inverse ratio ventilation. Physiological dead space fraction (0.39 ± 0.06 vs. 0.51 ± 0.05, P < 0.001), airway dead space (56 ± 15 vs. 81 ± 15 mL, P < 0.001) and alveolar dead space fraction (0.25 ± 0.07 vs. 0.31 ± 0.09, P < 0.01) were all less during pressure-controlled inverse ratio ventilation. There were no differences in heart rate or mean arterial pressure. Conclusions The prolonged inspiratory period and pressure-controlled flow pattern of pressure-controlled inverse ratio ventilation reduce the alveolar and airway dead spaces, and give lower peak airway pressures, compared with conventional ventilation, in cardiac surgical patients.

Mechanical ventilation in acute respiratory distress syndrome

The acute respiratory distress syndrome occurs commonly in critical care. There is an increasing volume of clinical and experimental evidence that poor ventilatory technique that is injurious to the lungs can propagate the systemic inflammatory response and adversely affect mortality. Many ventilatory techniques have been hypothesized to 'protect' the lungs during mechanical ventilation, including tidal volume limitation, high positive end-expiratory pressure, pressure-controlled inverse ratio ventilation, and prone positioning. Experimental techniques include liquid ventilation, surfactant administration and extracorporeal gas exchange. Despite excellent rationale for their use, few techniques, apart from tidal volume limitation, have been shown to improve survival in randomized controlled trials.

Influence of direct and indirect etiology on acute outcome and 6-month functional recovery in acute respiratory distress syndrome.

To assess the possibility that acute respiratory distress syndrome (ARDS) of pulmonary and nonpulmonary origins represent two distinct syndromes. Analysis of data collected prospectively from an inception cohort of 117 patients with ARDS. Adult intensive care unit (ICU), university/postgraduate hospital. Differences were sought in mortality and 6-month functional outcome between patients developing ARDS due to pulmonary (group 1) and nonpulmonary (group 2) pathology. Group 1 patients displayed a trend toward increased ICU and in-hospital mortality (42.1% vs. 23.2%, p = .10, and 47.4% vs. 27.9%, p = .11, respectively). No difference was found in ICU length of stay (46.3 +/- 4.9 vs. 39.0 +/- 4.8 days for groups 1 and 2, respectively) nor in duration of positive-pressure ventilation (26.2 +/- 4.3 vs. 20.6 +/- 3.2 days). However, the need for pressure-controlled inverse ratio ventilation was significantly greater in group 1 (16.9 +/- 3.2 vs. 9.1 +/- 1.3 days; p = .033). In survivors, reductions in total lung capacity at 6 months (68.1 +/- 4.6 vs. 61.8 +/- 4.6% predicted for groups 1 and 2, respectively; p = .4), accessible lung volume (74.4 +/- 4.4 vs. 68.9 +/- 4.9% predicted; p = .56), and forced expiratory volume (77.8 +/- 2.9 vs. 80.3 +/- 2.4% predicted; p = .57) did not differ between groups. Gas transfer coefficient was well preserved (84.5 +/- 4.6 vs. 86.6 +/- 4.7% predicted; p = .80). These data suggest a trend toward higher mortality and ventilatory requirements in ARDS of direct etiology, generating a hypothesis worthy of further exploration.

Combined high frequency ventilation and kinetic therapy for the management of severe hypoxia in adult respiratory distress syndrome

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.