Increase In Mean Airway Pressure Research Articles

Factors associated with renal oxygen extraction in mechanically ventilated children after the Norwood operation: insights from high fidelity haemodynamic data.

Maintaining the adequacy of systemic oxygen delivery is of utmost importance, particularly in critically ill children. Renal oxygen extraction can be utilised as metric of the balance between systemic oxygen delivery and oxygen consumption. The primary aim of this study was to determine what clinical factors are associated with renal oxygen extraction in children after Norwood procedure. Mechanically ventilated children who underwent Norwood procedure from 1 September, 2022 to 1 March, 2023 were identified as these patients had data collected and stored with high fidelity by the T3 software. Data regarding haemodynamic values, fluid balance, and airway pressure were collected and analysed using Bayesian regression to determine the association of the individual metrics with renal oxygen extraction. A total of 27,270 datapoints were included in the final analyses. The resulting top two models explained had nearly 80% probability of being true and explained over 90% of the variance in renal oxygen extraction. The coefficients for each variable retained in the best were -1.70 for milrinone, -19.05 for epinephrine, 0.129 for mean airway pressure, -0.063 for mean arterial pressure, 0.111 for central venous pressure, 0.093 for arterial saturation, 0.006 for heart rate, -0.025 for respiratory rate, 0.366 for systemic vascular resistance, and -0.032 for systemic blood flow. Increased milrinone, epinephrine, mean arterial pressure, and systemic blood flow were associated with decreased (improved) renal oxygen extraction, while increased mean airway pressure, central venous pressure, arterial saturation, and systemic vascular resistance were associated with increased (worsened) renal oxygen extraction.

Airway pressure release ventilation (APRV) versus pressure support ventilation (PSV)-A prospective intervention trial comparing haemodynamic parameters in intensive care patients.

Assisted mechanical ventilation may alter the pressure profile in the thorax compared to normal breathing, which can affect the blood flow to and from the heart. Studies suggest that in patients with severe lung disease, airway pressure release ventilation (APRV) may be haemodynamically beneficial compared to other ventilator settings. The primary aim of this study was to investigate if APRV affects cardiac index in intubated intensive care patients without severe lung disease when compared to pressure support ventilation (PSV). The secondary aim comprised potential changes in other haemodynamic and ventilatory parameters. Twenty patients were enrolled in the intensive care unit (ICU) at Sahlgrenska University Hospital. Eligible patients met the inclusion criteria; 18 years of age or above, intubated and mechanically ventilated, triggering and stable on PSV mode, with indwelling haemodynamic monitoring via a pulse-induced continuous cardiac output (PiCCO) catheter. The study protocol started with a 30-min interval on PSV mode, followed by a 30-min interval on APRV mode, and finally a 30-min interval back on PSV mode. At the end of each interval, PiCCO outputs, ventilator outputs, arterial and venous blood gas analyses, heart rate and central venous pressure were recorded and compared between modes. There was no significant difference in cardiac index (3.42 vs. 3.39 L/min/m2) between PSV and APRV, but a significant increase in central venous pressure (+1.0 mmHg, p = .027). Furthermore, we found a significant reduction in peak airway pressure (-3.16 cmH2O, p < .01) and an increase in mean airway pressure (+2.1 cmH2O, p < .01). No statistically significant change was found in oxygenation index (partial pressure of O2 [pO2]/fraction of inspired oxygen) nor in other secondary outcomes when comparing PSV and APRV. There was no significant association between global end-diastolic volume index and cardiac index (R2 = 0.0089) or central venous pressure (R2 = 0.278). All parameters returned to baseline after switching the ventilator mode back to PSV. We could not detect any changes in cardiac index in ICU patients without severe lung disease during APRV compared to PSV mode, despite lower peak airwaypressure and increasedmean airway pressure.

Nasal High-Flow (NHF) Improves Ventilation in Patients with Interstitial Lung Disease (ILD)-A Physiological Study.

Acute hypercapnic respiratory failure has a poor prognosis in patients with interstitial lung disease (ILD). Recent data demonstrated a positive effect of nasal high-flow (NHF) in patients with acute hypoxemic respiratory failure. Preliminary data also show benefits in several hypercapnic chronic lung diseases. The aim of this study was to characterize flow-dependent changes in mean airway pressure, breathing volumes, and breathing frequency and decreases in PCO2. Mean airway pressure was measured in the nasopharyngeal space. To evaluate breathing volumes, a polysomnographic device was used (16 patients). All subjects received 20, 30, 40, and 50 L/min and-to illustrate the effects-nCPAP and nBiPAP. Capillary blood gas analyses were performed in 25 hypercapnic ILD subjects before and 5 h after the use of NHF. Additionally, comfort and dyspnea during the use of NHF were surveyed. NHF resulted in a small flow-dependent increase in mean airway pressure. Tidal volume was unchanged and breathing rate decreased. The calculated minute volume decreased by 20 and 30 L/min NHF breathing. In spite of this fact, hypercapnia decreased at a flow rate of 24 L/min. Additionally, an improvement in dyspnea was observed. NHF leads to a reduction in paCO2. This is most likely achieved by a washout of the respiratory tract and a reduction in functional dead space. NHF enhances the effectiveness of breathing in ILD patients by the reduction in respiratory rate. In summary, NHF works as an effective ventilatory support device in hypercapnic ILD patients.

Comparison of Effects of Volume-Controlled and Pressure-Controlled Ventilation during Laparoscopic Surgeries in Birat Medical College Teaching Hospital

Introduction: The pneumoperitoneum created during laparoscopic surgery has numerous effects on the patient ranging from respiratory to hemodynamics. The two common methods of ventilator are volume control and pressure control. The volume control method has been commonly used during general anesthesia. Pressure control method has been used in intensive care unit for improving the respiratory mechanics.&#x0D; Objective: The study aims to compare the effects of pressure control to volume control ventilation in patients undergoing laparoscopic surgery. The hypothesis of the study is that pressure control method improves the respiratory mechanics by decreasing the peak airway pressure and increasing the lung compliance.&#x0D; Methodology: The total of 100 patients who underwent laparoscopic surgery were undertaken for this study. The 50 in each group (PCV and VCV) were allotted randomly. As per predicted body weight, the tidal volume was adjusted to 8 ml/kg, for both the modes of ventilation, peep 5 mm of Hg with fio2 of 100% and I:E-1:2,. The variations in peak airway pressure, mean airway pressure, lung compliance, SPO2 and hemodynamic parameters were observed at baseline (T1), at pneumoperitoneum (T2), after 10 minutes of pneumoperitonium (T3) and at 20 minutes after pneumoperitonium (T4).&#x0D; Results: The pressure control group on comparison to volume control mode group showed significant decrease in peak airway pressure while increase in mean airway pressure and increase in lung compliance at different points of pneumoperitoneum. However there was no significant change in hemodynamics between the two groups in patient undergoing laparoscopic surgery.&#x0D; Conclusion: We conclude that respiratory mechanics improve when the patient is on pressure control ventilation in compared to volume control method of ventilation. Whereas there is no difference in hemodynamic parameters between the two methods.&#x0D;

A S tudy of the Effectiveness of Lidocaine to Treat S evere P ulmonary Vascular Constriction induced by Protamine

Abstract Background: Protamine neutralises heparin after separation from cardiopulmonary bypass. This study aimed to evaluate the effects of lidocaine on protamine induced pulmonary vascular constriction in paediatric cardiothoracic surgery. Methods: This was a single-centre, prospective, double-blind and randomised study conducted among eighty pediatric patients with acyanotic congenital cardiac disease, scheduled for elective on-pump cardiac surgery under general anaesthesia. In the study, the participants were divided into four groups: Group NPHL- nonpulmonary hypertension with lidocaine preconditioning, group NPHS- nonpulmonary hypertension with normal saline (as placebo), group PHL- pulmonary hypertension with lidocaine preconditioning, and group PHS- pulmonary hypertension with normal saline (as placebo). Results: Pulmonary vasoconstriction occurred in 11.25% of cases after protamine administration. Both the NPHS and PHS groups exhibited an increase in mean airway pressure (Paw), Respiratory index (RI), alveolar-arterial oxygen difference (A-aDO2), pulmonary artery pressure (PAP) and decreased dynamic pulmonary compliance (Cydn) and oxygen index (OI) after protamine administration. However, these changes were not observed in the NPHL and PHL groups with lidocaine preconditioning. Plasma levels of TXB2 in the NPHS and PHS groups were higher than the NPHL and PHL groups, but 6-keto-PGF1 alpha levels were lower in the NPHS and PHS groups than in the NPHL and PHL groups. Conclusion: In congenital heart disease, repair without cardiopulmonary bypass is not possible in most cases. Prior to reversing heparin with protamine, preconditioning lidocaine reverses protamine-induced pulmonary vasoconstriction and improves lung function.

Development and Evaluation of an Automated Manual Resuscitator-Based Emergency Ventilator-Alternative.

Mass casualty incidents such as those that are being experienced during the novel coronavirus disease (COVID-19) pandemic can overwhelm local healthcare systems, where the number of casualties exceeds local resources and capabilities in a short period of time. The influx of patients with lung function deterioration as a result of COVID-19 has strained traditional ventilator supplies. To bridge the gap during ventilator shortages and to help clinicians triage patients, manual resuscitator devices can be used to deliver respirations to a patient requiring breathing support. Bag-valve mask (BVM) devices are ubiquitous in ambulances and healthcare environments, however require a medical professional to be present and constantly applying compression to provide the patient with respirations.We developed an automated manual resuscitator-based emergency ventilator-alternative (AMREV) that provides automated compressions of a BVM in a repetitive manner and is broadly compatible with commercially-available BVM devices approximately 5 inches (128 mm) in diameter. The AMREV device relieves the medical professional from providing manual breathing support and allows for hands-free operation of the BVM. The AMREV supports the following treatment parameters: 1) adjustable tidal volume (VT), 2) positive end-expiratory pressure (PEEP) (intrinsic and/or external), 3) 1:1 inspiratory: expiratory ratio, and 4) a controllable respiratory rate between 10-30 breaths per minute.The relationship between the inherent resistance and compliance of the lung and the delivered breaths was assessed for the AMREV device. Adjustable VT of 110-700 ml was achieved within the range of simulated lung states. A linear increase in mean airway pressure (Paw), from 10-40 cmH2O was observed, as the resistance and compliance on the lung model moved from normal to severe simulated disease states. The AMREV functioned continuously for seven days with less than 3.2% variation in delivered VT and Paw. Additionally, the AMREV device was compatible with seven commercially-available BVM setups and delivered consistent VT and Paw within 10% between models.This automated BVM-based emergency-use resuscitator can provide consistent positive pressure, volume-controlled ventilation over an extended duration when a traditional ventilator is not available. True ventilator shortages may lead to manual resuscitators devices such as the AMREV being the only option for some healthcare systems during the COVID-19 pandemic.

Characteristics of Pediatric Ventilator-Associated Events Reported to the National Healthcare Safety Network, 2019

Background: Mechanical ventilation is a life-saving measure for patients with respiratory failure; however, these patients are at high risk for complications and poor outcomes. Surveillance for ventilator-associated events (VAEs) via the CDC NHSN began in 2013 in adult patient care locations in hospitals. Pediatric ventilator-associated event (PedVAE) surveillance began in January 2019. The PedVAE definition is based on increases in mean airway pressure (MAP) or fraction of inspired oxygen (FiO2). We summarized the first 9 months of PedVAE data reported to the NHSN. Methods: Neonatal and pediatric locations of US acute-care hospitals, long-term acute-care hospitals, and inpatient rehabilitation facilities were eligible to participate in PedVAE surveillance as of January 1, 2019. When submitting PedVAEs to the NHSN, facilities may also optionally report information about antimicrobials, pathogens, and clinical events associated with PedVAEs. We analyzed PedVAE data from January through September 2019 submitted by facilities participating in surveillance according to the NHSN protocol. We calculated pooled mean incidence rates (no. events per 1,000 ventilator days) for neonatal and pediatric intensive care units (NICUs and PICUs), and we describe characteristics of PedVAEs. Results: Overall, 205 PedVAEs were reported: 111 events from 147 NICUs in 140 facilities and 94 events from 117 PICUs in 85 facilities. The pooled mean incidence was 1.61 events per 1,000 ventilator days in level 2 and 3 NICUs, 1.09 events per 1,000 ventilator days in level III NICUs, and 1.25 events per 1,000 ventilator days in PICUs. Of 205 PedVAEs, 133 (65%) met only the MAP criterion, 65 (32%) met only the FiO2 criterion, and 7 (3%) met both. Optional data on antimicrobials, pathogens, and clinical events were reported for 74 of 205 PedVAEs (36%). Among these 74 events, antimicrobial administration was common (50 of 74, 68%). By contrast, a minority had a pathogen reported (21 of 74, 28%). Of 74 PedVAEs, 60 were associated with a clinical event (80%), although only 15 (20%) were reported to be associated with a clinical infection. Of 74 PedVAEs, 4 (5%) were associated with mechanical ventilation weaning. Conclusions: PedVAE incidence rates are low in NICUs and PICUs. Most PedVAEs appear to be associated with clinical events. Although a minority of PedVAEs were associated with infections or pathogens, antimicrobial administration was reported for &gt;60%. Further evaluation of the clinical correlates of PedVAEs can inform development of effective prevention and antimicrobial stewardship in mechanically ventilated children.Funding: NoneDisclosures: Cheri Grigg, Centers for Disease Control and Prevention

Inflammatory lung injury in rabbits: effects of high-frequency oscillatory ventilation in the prone position.

ABSTRACTObjective:To compare the effects that prone and supine positioning during high-frequency oscillatory ventilation (HFOV) have on oxygenation and lung inflammation, histological injury, and oxidative stress in a rabbit model of acute lung injury (ALI). Methods:Thirty male Norfolk white rabbits were induced to ALI by tracheal saline lavage (30 mL/kg, 38°C). The injury was induced during conventional mechanical ventilation, and ALI was considered confirmed when a PaO2/FiO2 ratio < 100 mmHg was reached. Rabbits were randomly divided into two groups: HFOV in the supine position (SP group, n = 15); and HFOV with prone positioning (PP group, n = 15). For HFOV, the mean airway pressure was initially set at 16 cmH2O. At 30, 60, and 90 min after the start of the HFOV protocol, the mean airway pressure was reduced to 14, 12, and 10 cmH2O, respectively. At 120 min, the animals were returned to or remained in the supine position for an extra 30 min. We evaluated oxygenation indices and histological lung injury scores, as well as TNF-α levels in BAL fluid and lung tissue. Results:After ALI induction, all of the animals showed significant hypoxemia, decreased respiratory system compliance, decreased oxygenation, and increased mean airway pressure in comparison with the baseline values. There were no statistically significant differences between the two groups, at any of the time points evaluated, in terms of the PaO2 or oxygenation index. However, TNF-α levels in BAL fluid were significantly lower in the PP group than in the SP group, as were histological lung injury scores. Conclusions:Prone positioning appears to attenuate inflammatory and histological lung injury during HFOV in rabbits with ALI.

Retrospective Application of New Pediatric Ventilator-Associated Pneumonia Criteria Identifies a High-Risk Population.

To promote standardization, the Centers for Disease Control and Prevention introduced a new ventilator-associated pneumonia classification, which was modified for pediatrics (pediatric ventilator-associated pneumonia according to proposed criteria [PVAP]). We evaluated the frequency of PVAP in a cohort of children diagnosed with ventilator-associated pneumonia according to traditional criteria and compared their strength of association with clinically relevant outcomes. Retrospective cohort study. Tertiary care pediatric hospital. Critically ill children (0-18 yr) diagnosed with ventilator-associated pneumonia between January 2006 and December 2015 were identified from an infection control database. Patients were excluded if on high frequency ventilation, extracorporeal membrane oxygenation, or reintubated 24 hours following extubation. None. Patients were assessed for PVAP diagnosis. Primary outcome was the proportion of subjects diagnosed with PVAP. Secondary outcomes included association with intervals of care. Two hundred seventy-seven children who had been diagnosed with ventilator-associated pneumonia were eligible for review; 46 were excluded for being ventilated under 48 hours (n = 16), on high frequency ventilation (n = 12), on extracorporeal membrane oxygenation (n = 8), ineligible bacteria isolated from culture (n = 8), and other causes (n = 4). ICU admission diagnoses included congenital heart disease (47%), neurological (16%), trauma (7%), respiratory (7%), posttransplant (4%), neuromuscular (3%), and cardiomyopathy (3%). Only 16% of subjects (n = 45) met the new PVAP definition, with 18% (n = 49) having any ventilator-associated condition. Failure to fulfill new definitions was based on inadequate increase in mean airway pressure in 90% or FIO2 in 92%. PVAP was associated with prolonged ventilation (median [interquartile range], 29 d [13-51 d] vs 16 d [8-34.5 d]; p = 0.002), ICU (median [interquartile range], 40 d [20-100 d] vs 25 d [14-61 d]; p = 0.004) and hospital length of stay (median [interquartile range], 81 d [40-182 d] vs 54 d [31-108 d]; p = 0.04), and death (33% vs 16%; p = 0.008). Few children with ventilator-associated pneumonia diagnosis met the proposed PVAP criteria. PVAP was associated with increased morbidity and mortality. This work suggests that additional study is required before new definitions for ventilator-associated pneumonia are introduced for children.

Effectiveness of nasal highflow in hypercapnic COPD patients is flow and leakage dependent

BackgroundNasal Highflow (NHF) delivers a humidified and heated airflow via nasal prongs. Current data provide evidence for efficacy of NHF in patients with hypoxemic respiratory failure. Preliminary data suggest that NHF may decrease hypercapnia in hypercapnic respiratory failure. The aim of this study was to evaluate the mechanism of NHF mediated PCO2 reduction in patients with chronic obstructive pulmonary disease (COPD).MethodsIn 36 hypercapnic COPD patients (PCO2 > 45 mmHg), hypercapnia was evaluated by capillary gas sampling 1 h after NHF breathing under four conditions A to D with different flow rates and different degrees of leakage (A = 20 L/min, low leakage, two prongs, both inside; B = 40 L/min, low leakage, two prongs, both inside; C = 40 L/min, high leakage, two prongs, one outside and open; D = 40 L/min, high leakage, two prongs, one outside and closed). Under identical conditions, mean airway pressure was measured in the hypopharynx of 10 COPD patients.ResultsHypercapnia significantly decreased in all patients. In patients with capillary PCO2 > 55 mmHg (n = 26), PCO2 additionally decreased significantly by increased leakage and/or flow rate in comparison to lower leakage/ flow rate conditions (A = 94.2 ± 8.2%; B = 93.5 ± 4.4%; C = 90.5 ± 7.2%; D = 86.8 ± 3.8%). The highest mean airway pressure was observed in patients breathing under condition B (2.3 ± 1.6 mbar; p < 0.05).ConclusionsThis study demonstrates effective PCO2 reduction with NHF therapy in stable hypercapnic COPD patients. This effect does not correlate with an increase in mean airway pressure but with increased leakage and airflow, indicating airway wash out and reduction of functional dead space as important mechanisms of NHF therapy. These results may be useful when considering NHF treatment in hypercapnic COPD patients.Trial registrationClinical Trials: NCT02504814; First posted July 22, 2015.

To study the efficacy of non-invasive ventilation in severe bronchiolitis

Objectives: Bronchiolitis is the most common lower respiratory tract infection in infancy and about 6-15% of patients of acute bronchiolitis require ventilatory support. Non Invasive Ventilation by increasing Mean Airway Pressure reduces airway resistance and recruits non-functional respiratory units to improve oxygenation. The objective of this study is to determine the effectiveness of Non Invasive Ventilation in patients of severe acute bronchiolitis. Methods: The present observational descriptive study was conducted in the department of Paediatrics, Dr. B.C. Roy Post Graduate Institute of Paediatric sciences, Kolkata, India. Those patients fulfilling the criteria for severe Acute Bronchiolitis according to Bronchiolitis Scoring System were included in this study. 76 patients were studied during the 1 year period from April 2014 to March 2015. Results: A success rate of 72.4% has been observed in this study. Mean duration of Non Invasive Ventilation in patients where it was successful was 32.5±15.3 hours. Abnormalities in pH and PCO2 improved over a period of 6 hours. Conclusion: Non Invasive Ventilation was found effective in 72.4% of patients of severe bronchiolitis. Abnormalities in pH & PCO2 were also improved over 6 hours. Thus, it is an effective, safe and cost effective modality of treatment of severe bronchiolitis.

Acute Respiratory Distress Syndrome and Lung Protection

Hypoxemic respiratory failure, frequently termed acute respiratory distress syndrome (ARDS), is 1 of the classic problems confronting the clinician using mechanical ventilation. Multiple trials over recent decades have identified the manipulation of mean airway pressure as the essential intervention to improve oxygenation. The easiest method to increase mean airway pressure (that the clinician can titrate) is increasing the positive end-expiratory pressure (PEEP). We have also learned that alveolar pressure rises with a consistent tidal volume and increasing PEEP. Key studies reviewed in the last column identify the value of reducing tidal volume and maintaining static alveolar pressure, measured as plateau pressure less than 30 cm H2O. If tidal volume is reduced, patients may develop a degree of hypercarbia because of reduced minute ventilation (defined as respiratory rate tidal volume). In general, reduced minute ventilation will cause the pH to decrease. Most critical care providers would accept a pH as low as 7.20 reflecting reduced minute ventilation and respiratory acidosis. Clinician must strike a balance between adequate ventilation and acid/base protection for the patient and the need to increase mean airway pressure while avoiding excessive airway pressure through the increase in PEEP with a reduction in the tidal volume. The articles discussed in this column describe current definitions for ARDS, review important comanagement strategies, and present physiologic causes for injury to the lungs by mechanical ventilation as reflected in the failure of recent trials involving high-frequency oscillatory ventilation (HFOV).

Quantifying the Amount of Bleeding and Associated Changes in Intra-Abdominal Pressure and Mean Airway Pressure in Patients Undergoing Lumbar Fixation Surgeries: A Comparison of Three Positioning Systems.

Study DesignProspective, randomised controlled, single centre study of 45 patients posted for two level lumbar fixation surgery in the prone position.PurposeTo compare intra-abdominal pressure (IAP), mean airway pressure mean airway pressure and blood loss during the spine surgery in prone position using three different positioning systems.Overview of LiteratureStudies have correlated IAP with the amount of perioperative bleeding. However, IAP and airway pressures while assessing the bleeding comparing two or more prone positioning systems are unclear.MethodsThis prospective study was conducted on a cohort of 45 patients scheduled for two-level lumbar fixation. Patients were randomly allocated to a spine table, Wilson's frame, and thermomodulated pads. Bladder pressure as an indicator of IAP, mean and peak airway pressures, and blood loss were monitored.ResultsIAP increased whenever patient position was changed to prone .The increase in pressure was more in the Wilson's frame group but was statistically significant only on prolonged positioning. Adopting the prone position always increased the mean airway pressure, but the increased was significant only in the Wilson's frame group. Mean airway pressure decreased in the spine table group and was statistically significant. The blood loss in the spine table group was significantly less as compared to the other groups.ConclusionsPositioning on a spine table results in less blood loss and low mean airway pressure. The Wilson's frame results in high IAP, increased mean airway pressure, and more blood loss. The thermomodulated frame increases mean airway pressure and produces a moderate increase in IAP and airway pressure.

O-079 Nasal Continuous Positive Airway Pressure And Cardiac Function In Preterm Infants With Lung Disease

<h3>Introduction</h3> Previous studies of infants on ventilatory support suggest that right ventricular output (RVO) decreases with increasing mean airway pressure. This may be due to increased pressure in the thoracic cavity. We investigated changes in cardiac output (CO) at different levels of nasal continuous positive airway pressure (nCPAP) in preterm infants with evolving chronic lung disease. <h3>Methods</h3> We studied infants between 28 and 34 weeks corrected gestational age, a minimum of two weeks old, treated with nCPAP of 5 to 7 cm H₂O, with an O₂ requirement of 25–40%, in whom written parental consent was obtained. Infants with significant cardiac shunts were excluded. Infants were randomly assigned to nCPAP levels of 4, 6, and 8 cm H₂O for 15 min each. Right and left ventricular output, left pulmonary artery flow, superior vena cava flow, heart rate and blood pressure were measured after each change with a Vivid-I ultrasound machine by a single examiner (FB) blinded to nCPAP levels. <h3>Results</h3> Thirty infants with a median (IQR) gestational age of 25.9 (25.6–26.8) weeks and a birth weight of 0.78 (0.66–0.94) kg were studied at a median age of 43 (24–53) days. There were no significant differences in any cardiovascular parameters at different levels of nCPAP. <h3>Discussion</h3> We conclude that nCPAP levels between 4 and 8 cm H₂O did not have an effect on CO in our study population of stable preterm infants with evolving chronic lung disease.

Moderately high frequency ventilation with a conventional ventilator allows reduction of tidal volume without increasing mean airway pressure.

BackgroundThe aim of this study was to explore if positive-pressure ventilation delivered by a conventional ICU ventilator at a moderately high frequency (HFPPV) allows a safe reduction of tidal volume (VT) below 6 mL/kg in a porcine model of severe acute respiratory distress syndrome (ARDS) and at a lower mean airway pressure than high-frequency oscillatory ventilation (HFOV).MethodsThis is a prospective study. In eight pigs (median weight 34 [29,36] kg), ARDS was induced by pulmonary lavage and injurious ventilation. The animals were ventilated with a randomized sequence of respiratory rates: 30, 60, 90, 120, 150, followed by HFOV at 5 Hz. At each step, VT was adjusted to allow partial pressure of arterial carbon dioxide (PaCO2) to stabilize between 57 and 63 mmHg. Data are shown as median [P25th,P75th].ResultsAfter lung injury, the PaO2/FiO2 (P/F) ratio was 92 [63,118] mmHg, pulmonary shunt 26 [17,31]%, and static compliance 11 [8,14] mL/cmH2O. Positive end-expiratory pressure (PEEP) was 14 [10,17] cmH2O. At 30 breaths/min, VT was higher than 6 (7.5 [6.8,10.2]) mL/kg, but at all higher frequencies, VT could be reduced and PaCO2 maintained, leading to reductions in plateau pressures and driving pressures. For frequencies of 60 to 150/min, VT progressively fell from 5.2 [5.1,5.9] to 3.8 [3.7,4.2] mL/kg (p < 0.001). There were no detrimental effects in terms of lung mechanics, auto-PEEP generation, hemodynamics, or gas exchange. Mean airway pressure was maintained constant and was increased only during HFOV.ConclusionsDuring protective mechanical ventilation, HFPPV delivered by a conventional ventilator in a severe ARDS swine model safely allows further tidal volume reductions. This strategy also allowed decreasing airway pressures while maintaining stable PaCO2 levels.

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Introduction: Airway pressure release ventilation (APRV) has been used extensively in adult patients with acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). Purported advantages of APRV include increase in mean airway pressure (MAP), decrease in peak inspiratory pressures (PIP), and ability to spontaneously ventilate. It has not been studied extensively in pediatrics especially in the infant population with ALI/ARDS. We demonstrate two patients in which the APRV strategy was used to improve refractory hypoxemia (patient 1) and perform lung recruitment while on extra-corporeal membrane oxygenation (ECMO) (patient 2). Methods: Retrospective review of two patients’ charts; one in the Neonatal ICU and another in the Pediatric ICU. The patient’s ventilator modes, settings, blood gas measurements and radiographic imaging were analyzed. Results: Two patients’ charts were reviewed in whom APRV was used for refractory hypoxemia and to perform lung recruitment. Patient 1 was a 6 month old 3.9 kg ex-24 week preemie with recurrent bouts of necrotizing enterocolitis requiring bowel resection, status post stricturoplasty who was kept intubated post-op and returned to the NICU. During the procedure her PIP was 21 mm Hg, positive end expiratory pressure (PEEP) of 4, rate of 16 bpm, and FiO2 of 38% with SpO2 of 100% that delivered a MAP of 10.4 mm Hg. Venous blood gas at the end of the case demonstrated a pH 7.36, pCO2 45, pO2 37, HCO3 25, Lactate 1.9. Initially in the NICU her ventilator was set in pressure cycled assist controlled (PC/AC) with a rate of PIP 19, PEEP of 5, rate, rate of 33 bpm, PIP and FiO2 21% with SpO2 of 95% that delivered a MAP of 7 mm Hg. Over the next 26 hours she developed progressive hypoxemia requiring up titration in her PIP (26 mm Hg), PEEP (7 mm Hg) and FiO2 (85%) delivering a MAP of 12 mm Hg with SpO2 of 80–85%. Chest x-ray demonstrated a right upper lobe atelectasis along with low lung volumes. She was switched to APRV with a pressure high (PHIGH) of 25 mm Hg, pressure low (PLOW) of 0 mm Hg, time high (THIGH) of 2 seconds and time low (TLOW) of 0.2 seconds with MAP of 22 mm Hg, FiO2 40% with SpO2 97%. Chest radiography demonstrated improved aeration within approximately 1 hour of APRV initiation. She subsequently self extubated after 47 hours on APRV to 2 liters nasal cannula and remained extubated. Patient 2 was a 1 month old 5 kg male with a giant omphalocele who developed renal failure, volume overload and progressive respiratory failure requiring endotracheal intubation and eventual veno-venous (VV) ECMO. He was kept on rest lung settings PIP 25 mm Hg, PEEP 9 mm Hg, FiO2 40% and rate of 10 with a MAP of 11 mm Hg. He was on full VV-ECMO support with a flow of 760 mL/min and sweep gas of 0.8 L/min. His chest x-rays demonstrated bilaterally opacified lung fields with no expiratory tidal volumes. He was placed on APRV on post-ECMO day 6 at settings of pressure high (PHIGH) of 20 mm Hg, pressure low (PLOW) of 2 mm Hg, time high (THIGH) of 4 seconds and time low (TLOW) of 0.35 seconds with MAP of 18 mm Hg, while still on ECMO support. His lungs began to show aeration and evidence of recruitment at 12 hours on APRV with marked improvement in his lung aeration. He continued on APRV for 48 hours and then was transitioned to conventional ventilation. Conclusions: APRV is a useful ventilator strategy in cases of refractory hypoxemia and de-recruited lungs. We demonstrate the safe use of APRV in two patients less than 1 year of age with improvement in oxygenation and lung recruitment. Advantages of APRV were mentioned above. The disadvantages include air trapping and CO2 retention. While the disadvantages can be mostly mitigated with titration of the APRV settings, additional studies are needed to demonstrate efficacy and safety along with formulation of age appropriate pressure and time settings.

Effects of a 1:1 Inspiratory to Expiratory Ratio on Respiratory Mechanics and Oxygenation during One-Lung Ventilation in the Lateral Decubitus Position

Prolonged inspiratory to expiratory (I:E) ratio ventilation may have both positive and negative effects on respiratory mechanics and oxygenation during one-lung ventilation (OLV), but definitive information is currently lacking. We therefore compared the effects of volume-controlled ventilation with I:E ratios of 1:1 and 1:2 on respiratory mechanics and oxygenation during OLV. Fifty-six patients undergoing thoracoscopic lobectomy were randomly assigned volume-controlled ventilation with an I:E ratio of 1:1 (group 1:1, n=28) or 1:2 (group 1:2, n=28) during OLV. Arterial and central venous blood gas analyses and respiratory variables were recorded 15 minutes into two-lung ventilation, at 30 and 60 minutes during OLV, and 15 minutes after two-lung ventilation was re-initiated. Peak and plateau airway pressures in cmH2O [standard deviation] during OLV were significantly lower in group 1:1 than in group 1:2 (P <0.01) (19 [3] and 23 [4]; 16 [3] and 19 [5], respectively). The arterial to end-tidal carbon dioxide tension difference was significantly lower in group 1:1 than in group 1:2 (P <0.01), (0.5 [0.3] and 1.1 [0.5]). There were no significant differences in PaO2 during OLV between the two groups (OLV30, P=0.856; OLV60, P=0.473). In summary, volume-controlled ventilation with an I:E ratio of 1:1 reduced peak and plateau airway pressures improved dynamic compliance and efficiency of alveolar ventilation, but it did not improve arterial oxygenation in a substantial manner. Furthermore, the associated increase in mean airway pressure might have reduced cardiac output, resulting in a lower central venous oxygen saturation.

Right ventricular function during high-frequency oscillatory ventilation in adults with acute respiratory distress syndrome

To evaluate the effect of mean airway pressure under high-frequency oscillatory ventilation on right ventricular function. Prospective randomized study. Intensive care unit of a tertiary care hospital. Sixteen consecutive patients within the first 48 hrs of mainly pulmonary acute respiratory distress syndrome. After a 6-hr-period of protective conventional mechanical ventilation, patients were submitted to three 1-hr periods of high-frequency oscillatory ventilation (+5, +10, +15) in a randomized order, with a mean airway pressure level determined by adding 5, 10, or 15 cm H2O to the mean airway pressure recorded during conventional mechanical ventilation. Mean airway pressure was 18±3 cm H2O during conventional mechanical ventilation and was increased until 33±3 cm H2O at high-frequency oscillatory ventilation+15. Right ventricular function was assessed using transesophageal echocardiography. During conventional mechanical ventilation, nine patients presented a right ventricular dysfunction (right ventricular end-diastolic area/left ventricular end-diastolic area ratio>0.6) of whom four patients had a right ventricular failure (right ventricular end-diastolic area/left ventricular end-diastolic area ratio>0.9). High-frequency oscillatory ventilation+10 and +15 further worsened right ventricular function, resulting in about a 40% increase in right ventricular end-diastolic area/left ventricular end-diastolic area ratio and a 30% increase in end-diastolic eccentricity index when compared with conventional mechanical ventilation or high-frequency oscillatory ventilation+5 periods. At high-frequency oscillatory ventilation+15, 15 patients had right ventricular dysfunction and nine had right ventricular failure. High-frequency oscillatory ventilation did not improve oxygenation whatever the mean airway pressure level. A significant redistribution of tidal variation to the posterior parts of the lung was observed on electrical impedance tomography measurements when increasing mean airway pressure. However, this redistribution was not observed in patients who presented a worsening of right ventricular function (right ventricular end-diastolic area/left ventricular end-diastolic area increase>40%) at high-frequency oscillatory ventilation+15. In patients with mainly pulmonary acute respiratory distress syndrome, using high mean airway pressure under high-frequency oscillatory ventilation can worsen right ventricular function when compared with protective conventional mechanical ventilation, notably in patients in whom high-frequency oscillatory ventilation produced less alveolar recruitment of the posterior parts of the lungs. This study highlights the interest of monitoring right ventricular function during high-frequency oscillatory ventilation.

Effects of Airway Pressure Release Ventilation (APRV) on Extravascular Lung Water (EVLW) in Acute Lung Injury and Acute Respiratory Distress Syndrome (ALI/ARDS)

PURPOSE: EVLW plays an important role in the pathophysiology of ALI/ARDS and correlates negatively with oxygenation and mortality. Several studies have shown that the addition of PEEP reduces EVLW in the setting of ALI/ARDS. The mechanism of this benefit is not clearly understood. Our trial is testing the hypothesis that APRV reduces the EVLW (primary endpoint) in ALI/ARDS patients through the increase in mean airway pressure (mPaw) paralleling the improvement in oxygenation (secondary endpoint).

A comparison of pressure‐controlled and volume‐controlled ventilation for laparoscopic cholecystectomy*

The potential advantages of pressure-controlled over volume-controlled ventilation during laparoscopic surgery have yet to be proven. We randomly assigned 42 patients with BMI <30 kg.m(-2) scheduled for laparoscopic cholecystectomy to receive either pressure- or volume-controlled ventilation. Compared with volume-controlled ventilation, pressure-controlled ventilation resulted in a significant decrease in mean (SD) peak airway pressure at 10 min (20.4 (2.7) vs 24.0 (4.7)cmH₂O, p=0.004) and 30 min (20.7 (3.0) vs 23.9 (4.9)cmH₂O, p=0.015) and an increase in mean airway pressure at 10 min (10.5 (0.9) vs 9.6 (1.1)cmH₂O, p=0.007) and 30 min (10.5 (1.1) vs 9.6 (1.2)cmH₂O, p=0.016) after the start of surgery. Gas exchange and haemodynamic stability were similar. We conclude that pressure-controlled ventilation is a safe alternative and offers some advantages to volume-controlled ventilation during laparoscopic cholecystectomy in non-obese patients.