Design and development of an affordable multi-mode small animal ventilator.

To examine the hypothesis that a decelerating inspiratory flow waveform is responsible for improvements in gas exchange during pressure control ventilation for acute lung injury. Prospective, controlled, crossover study. Twenty-five patients with acute lung injury requiring mechanical ventilation with a positive-end expiratory pressure > or = 10 cm H2O, ventilator frequency of > or = 8 bpm, inspired oxygen concentration of > or = 0.50, peak inspiratory pressure > or = 40 cm H2O, and requiring sedation and paralysis were studied. Patients were ventilated at a tidal volume of 10 mliters/kg, respiratory frequency was set to maintain a pH > 7.30 and PaCO2 < 50 mm Hg, and positive end-expiratory pressure (PEEP) set to maintain Pao2 > 70 mm Hg or Sao2 > 93% with an Fio2 < or = 0.50. In random sequence, ventilator mode was changed from volume control with a square flow waveform, pressure control ventilation with a decelerating flow waveform, or volume control ventilation with a decelerating flow waveform. Tidal volume, minute ventilation, and airway pressures were continuously measured at the proximal airway. After 2 hours of ventilation in each mode, arterial and mixed venous blood gases were drawn and cardiac output determined by thermodilution. Dead space to tidal volume ratio was determined from mixed expired gas concentrations and Paco2. During volume control ventilation with a square flow waveform, Pao2 was decreased (75 +/- 11 mm Hg vs. 85 +/- 9 mm Hg and 89 +/- 12 mm Hg), p < 0.05, and peak inspiratory pressure was increased (50 +/- 9 cm H2O vs. 42 +/- 7 cm H2O and 39 +/- 9 cm H2O) p < 0.05 compared to volume control with a decelerating flow waveform and pressure control ventilation. Mean airway pressure was also lower with volume control with a square flow waveform (17 +/- 4 cm H2O vs. 20 +/- 4 cm H2O and 21 +/- 3 cm H2O) compared to volume control with a decelerating flow waveform and pressure control ventilation. There were no differences in hemodynamic parameters. Both pressure control ventilation and volume control ventilation with a decelerating flow waveform provided better oxygenation at a lower peak inspiratory pressure and higher mean airway pressure compared to volume control ventilation with a square flow waveform. The results of our study suggest that the reported advantages of pressure control ventilation over volume control ventilation with a square flow waveform can be accomplished with volume control ventilation with a decelerating flow waveform.

Cardiorespiratory Effects of Pressure-controlled Ventilation With and Without Inverse Ratio in the Adult Respiratory Distress Syndrome

BACKGROUND: Since the late 1960s, mechanical ventilation has been accomplished primarily using volume controlled ventilation(VCV). While VCV allows a set tidal volume to be guaranteed, VCV could bring about excessive airway pressures that may be lead to barotrauma in the patients with acute lung injury. With the increment of knowledge related to ventilator-induced lung injury, pressure controlled ventilation(PCV) has been frequenfly applied to these patients. But, PCV has a disadvantage of variable tidal volume delivery as pulinonary impedance changes. Since the concept of combining the positive attributes of VCV and PCV(dual control ventilation, DCV) was described firstly in 1992, a few DCV modes were introduced. Pressure-regulated volume control(PRVC) mode, a kind of DCV, is pressure-limited, time-cycled ventilation that uses tidal volume as a feedback control for continuously adjusting the pressure limit. However, no clinical studies were published on the efficacy of PRVC until now. This investigation studied the efficacy of PRVC in the patients with unstable respiratory mechanics. METHODS: The subjects were 8 mechanically ventilated patients(M: F= 6 : 2, 56+/-26 years) who showed unstable respiratory mechanics, which was defined by the coefficients of variation of peak inspiratory pressure for 15 minutes greater than 10% under VCV, or the coefficients of variation of tidal volume greater than 10% under PCV. The study was consisited of 3 modes application with VCV, PCV and PRVC for 15 minutes by random order. To obtain same tidal volume, inspiratory pressure setting was adjusted in PCV. Respiratory parameters were measured by pulmonary monitor(CP-100 pulmonary monitor, Bicore, Irvine, CA, USA). RESULTS: 1) Mean tidal volumes(VT) in each mode were not different(VCV, 431+/-102ml ; PCV, 417+/-99ml; PRVC, 414+/-97ml) 2) The coefficient of variation(CV) of VT were 5.2+/-3.9% in VCV, 15.2+/-7.5% in PCV and 19.3+/-10.0% in PRVC. The CV of VT in PCV and PRVC were significantly greater than that in VCV(p<0.01). 3) Mean peak inspiratory pressure(PIP) in VCV(31.0+/-6.9cm HD) was higher than PIP in PCV(26.0+/-6.5cm H20) or PRVC(27.0+/-6.4cm HD)(p<0.05). 4) The CV of PIP were 13.9+/-3.7% in VCV, 4.9+/-2.6% in PVC and 12.2+/-7.0% in PRVC. The CV of PIP in VCV and PRVC were greater than that in PCV(p<0.01). CONCLUSIONS: Because of wide fluctuations of VT and PIP, PRVC mode did not seem to have advantages compared to VCV or PCV in the patients with unstable respiratory mechanics.

To evaluate in a lung model the effects of expiratory-phase tracheal gas insufflation (expiratory-phase TGI) with both volume and pressure control ventilation, and tidal volume-adjusted continuous flow TGI (volume-adjusted TGI) on system pressures and volumes. Single-compartment lung model. Research laboratory in a university medical center. Expiratory-phase TGI was established, using a solenoid valve activated by the ventilator. Volume-adjusted TGI was applied by reducing tidal volume (VT) by the product of TGI flow and inspiratory time. Ventilation was provided with pressure control of 20 cm H2O or volume control ventilation with VT similar to that with pressure control ventilation. A rate of 15 breaths/min and positive end-expiratory pressure (PEEP) of 10 cm H2O were used throughout. Inspiratory time periods of 1.0, 1.5, 2.0, and 2.5 secs were used with TGI flows of 0, 4, 8, and 12 L/min. Lung model compliance (mL/cm H2O) and resistance (cm H2O/L/sec) combinations of 20/20, 20/5, and 50/20 were used. In expiratory-phase TGI with pressure control ventilation, peak alveolar pressure remained constant, PEEP increased (p < .01) and VT decreased (p < .01). In expiratory-phase TGI with volume control ventilation and volume-adjusted TGI, there were significant increases in peak alveolar pressure and PEEP (p < .01). Readjustment of VT in volume-adjusted TGI was impossible with longer inspiratory time (> or = 2 secs) and higher TGI flows (> or = 8 L/min). The marked increases in system pressures and volumes observed with continuous-flow TGI can be avoided with expiratory-phase TGI and volume-adjusted TGI.

Electrical Impedance Tomography to Set Positive End Expiratory Pressure During Pediatric Extracorporeal Membrane Oxygenation for Respiratory Failure... Is it Feasible?

Objective To explore the effects of two different modes for one-lung ventilation on airway pressure and oxidative stress factors during thoracoscopic radical resection of right lung cancer. Methods Sixty-two patients who needed one-lung ventilation after thoracoscopic radical resection of right lung cancer were divided into volume-controlled ventilation (VCV) group and pressure-controlled ventilation (PCV) group by random number table.VCV was used in both groups during dual lung ventilation.In VCV group, tidal volume was 6 ml/kg, positive end-expiratory pressure was 0 cmH2O (1 cmH2O=0.098 kPa). In PCV group, VCV mode was firstly used to regulate airway pressure to tidal volume at 6 ml/kg, then PCV mode was used, positive end-expiratory pressure was 0 cmH2O, and ventilation frequency was adjusted to maintain the value of end-tidal carbon dioxide partial pressure at 30-45 mmHg (1 mmHg=0.133 kPa). Radial artery blood was collected for blood gas analysis at 10 minutes (T1) before dual lung ventilation and 30 minutes (T2), 60 minutes (T3) and 120 minutes (T4) after one-lung ventilation.Malondialdehyde (MDA) and superoxide dismutase (SOD) in radial artery blood serum were measured at T1, T3 and T4 time points in the two groups. Results There was no significant difference in hemodynamic parameters between the two groups at different time points.At T3 and T4, the peak airway pressures of PCV group were (22.00±4.44) and (21.68±4.55) cmH2O, which were significantly lower than those of VCV group [(25.00±4.14), (25.00±4.03) cmH2O]. At T3 and T4, MDA of PCV group was (6.64±2.15), (7.11±1.50) μmol/L, which was significantly lower than that of VCV group [(7.31±2.09), (8.00±1.83) μmol/L], and SOD of PCV group was (39.42±15.36), (37.49±13.02) U/ml, which was significantly higher than that of VCV group [(35.94±8.47), (31.72±7.83) U/ml]. There was no significant difference in arterial partial pressure of oxygen and carbon dioxide between the two groups during one-lung ventilation. Conclusions PCV in thoracoscopic radical resection of lung cancer is helpful to reduce peak airway pressure and levels of oxidative stress factors, which may be helpful to reduce airway injury. Key words: One-lung ventilation; Volume-controlled ventilation; Pressure-controlled ventilation; Blood gas analysis; Oxidative stress mediators

Intraoperative mechanical ventilation practices can lead to ventilator-induced lung injury (VILI) and postoperative pulmonary complications in healthy lungs. Mechanical power (MP) has been developed as a new concept in reducing the risk of postoperative pulmonary complications as it considers all respiratory mechanics that cause VILI. The most commonly used intraoperative modes are volume control ventilation (VCV) and pressure control ventilation (PCV). In this study, VCV and PCV modes were compared in terms of respiratory mechanics in patients operated in the supine and prone positions. The patients were divided into 4 groups (80 patients), volume control supine and prone, pressure control supine and prone with 20 patients each. MP, respiratory rate, positive end-expiratory pressure, tidal volume, peak pressure, plato pressure, driving pressure, inspiratory time, height, age, gender, body mass index, and predictive body weight data of the patients included in the groups have been obtained from "electronic data pool" with Structured Query Language queries. The supine and prone MP values of the VCV group were statistically significantly lower than the PCV group (P values were 0.010 and 0.001, respectively). Supine and prone MP values of the VCV group were calculated significantly lower than the PCV group. Intraoperative PCV may be considered disadvantageous regarding the risk of VILI in the supine and prone positions.

Airway access for mechanical ventilation can be obtained by: orotracheal intubation, nasotracheal intubation, cricothyrotomy, ortracheostomy. Laryngeal mask and Combitube are devices that can be used in patients with difficult access to the airways (“not ventilate not intubate” situation). Mechanical ventilation is are source focused on healthcare of patients with compromised pulmonary gas exchange, whether caused by structural lung disease or conditions that result in alveolar hypoventilation. There are currently many options for ventilation support, but three of them are the most frequently used: volume controlled ventilation (VCV), pressure controlled ventilation (PCV) and pressure support ventilation (PSV). VCV guarantees tidal volume, but generates higher mean airway pressures, as a consequence of an initial peak pressure; PCV does not generate pressure peak, occurring lower medium pressures, but does not guarantee tidal volume. VCV and PCV allow assisted or controlled ventilation. PSV requires initial patient’s inspiratory stimulus, only functioning on assisted ventilation, and also does not guarantee tidal volume. For most patients VCV and PCV can be used at the beginning of assisted ventilation. There is no demonstration of superiority of one over the other, provided that their limitations are respected. Positive end expiratory pressure (PEEP) and continuous positive airway pressure (CPAP) promote increases in functional residual capacity, resulting in improved blood oxygenation and reduced inspiratory effort. Both PEEP and CPAP promote these benefits through alveolar opening, when totally closed or only partially opened, and redistributing liquid eventually present in alveoli. The strategy of daily interruption of sedation helps reducing mechanical ventilation duration and intensive care unit length of stay. Patients on prolonged mechanical ventilation require gradual process of weaning from mechanical ventilation.

Introduction: Evaluation and comparison of two modes of mechanical ventilation – volume control and pressure control in spine surgery in prone position in terms of respiratory mechanics (peak airway pressure [PAP], plateau pressure, lung compliance, dead space and oxygenation), hemodynamic parameters (heart rate and blood pressure), pulmonary function tests (vital capacity, peak expiratory flow rate, forced expiratory volume in first second). Materials and Methods: After obtaining approval from institutional ethics committee, the present prospective, randomized, single-blind study was conducted in 50 adult patients of either sex, American Society of Anesthesiologists I or II undergoing thoracic or lumbar spine surgery in prone position. Standard anesthesia protocols comprising of thiopentone, fentanyl and vecuronium were followed. Patients in volume control ventilation (VCV) group (n = 25) were ventilated with volume control mode with tidal volume (TV) = 7 ml/kg, positive end expiratory pressure = 5 cm H2O, I:E = 1:2 and respiratory rate varied to keep Et CO2 = 35–40 mmHg, FiO2 = 0.4. While in pressure controlled ventilation (PCV) mode (n = 25) patients were ventilated with similar settings except peak inspiratory pressure was adjusted to determine TV = 7 ml/kg. Pulmonary function tests were measured pre-operatively and post-operatively. Respiratory mechanics (PAP, lung compliance) and hemodynamic parameters were measured pre-, intra-, and post-operatively. Results: The demographic profile and surgical characteristics were similar between the groups. Peak inspiratory pressure was higher in VCV (20 vs. 18) and dynamic compliance low in VCV (31.3 vs. 35.93). Other parameters like dead space, minute ventilation, EtCO2 and oxygenation were comparable in the two groups. Postoperative PFT decreased in both groups but were comparable. Conclusion: This study found that intraoperative respiratory mechanisms were better maintained with PCV mode than VCV in patients undergoing thoracolumbar spine surgery in prone position although both offered similar pulmonary functions. Therefore, pressure mode can be a better alternative for ventilator strategy.

In this randomized prospective study, peak airway pressure (PAP) and gastric insufflation were compared between volume control ventilation (VCV) and pressure control ventilation (PCV) using size-1 laryngeal mask airway (LMA) in babies weighing 2.5-5 kg. Forty ASA I and II children, weighing 2.5-5 kg, undergoing elective infraumbilical surgeries (duration < 60 min) were randomized to two groups of 20 each to receive either PCV or VCV. Patients at risk of aspiration, difficult airway and upper respiratory tract infection, and poor lung compliance were excluded. Anesthesia technique included sevoflurane/O(2)/N(2)O without neuromuscular blockade. PAP in PCV and tidal volume in VCV modes were changed to achieve adequate ventilation (P(E)CO(2) of 5-5.4 kPa). PAP was maintained below 20 cm H(2)O. Chi-squared test, Mann-Whitney U-test and Wilcoxon W-test were applied; P < 0.05 was considered significant. Mean PAP (cm H(2)O) was 12.2 ± 1.09 in PCV and 13.60 ± 0.94 in VCV groups (P = 0.000). The confidence interval of mean difference of PAP varied from 0.79 to 2.10. Significant increases in abdominal circumference were observed in both groups: PCV: 0.94 ± 1.04 cm and VCV: 2.2 ± 1.3 cm; (P = 0.000). The SpO(2) and hemodynamic variables did not differ between the groups. One patient in VCV group (with PAP = 14 cm H(2)O) could not be ventilated to the target P(E)CO(2), and the LMA had to be replaced with tracheal tube. In conclusion, PCV should be the preferred mode to provide positive pressure ventilatio (PPV), when using the size-1 cLMA in babies weighing 2.5-5 kg, in view of less gastric insufflation associated with it for surgeries of brief duration. More studies are required to validate the clinical significance of these two modes of ventilation in longer procedures, in this subpopulation.

The Effects of Flexible Bronchoscopy on Mechanical Ventilation in a Pediatric Lung Model

Objective To compare the pressure-controlled ventilation (PCV) and volume-controlled ventilation (VCV) in the patients undergoing spinal surgery in prone position supported by a Wilson frame.Methods Forty patients,of ASA physical status Ⅰ or Ⅱ,aged 30-64 yr,with body mass index ＜ 30 kg/m2,scheduled for elective spinal surgery in prone position supported by a Wilson frame under general anesthesia,were randomly allocated to receive mechanical ventilation using either VCV (n =20) or PCV (n =20) mode.Endotracheal intubation and mechanical ventilation were performed after induction of anesthesia.The tidal volume (VT) was set at 10 ml/kg according to the ideal body weight in group VCV.The maximal inspiratory pressure of the anesthesia machine was adjusted to maintain the VT at 10 ml/kg in group P.Both ventilation modes were required to maintain PET CO2 within the normal range.VT,respiratory rate,minute ventilation (MV),dynamic lung compliance (Cdyn),peak and mean airway pressure (Ppeak,Pmean),mean arterial pressure (MAP) and HR were recorded at 10 min after the patients were turned to supine position and at 30 min after the patients were turned to prone position after intubation.Arterial blood samples were collected for blood gas analysis,and oxygenation index(OI) and physiologic dead space fraction (VD/VT) were calculated.Results Compared with those at 10 min after turning to supine position,Ppeak was significantly increased and Cdyn,VT and MV were decreased at 30 min after turning to prone position in both groups.Compared with group VCV,Ppeak was significantly decreased,respiratory rate and Cdyn were increased,and no significant change was found in VT,MV,OI,VD/VT,Pmean,MAP and HR in PCV group.Conclusion Compared with VCV,PCV can improve the ventilatory efficacy and reduce the influence of prone position on respiratory dynamics in the patients undergoing spinal surgery in prone position supported by a Wilson frame. Key words: Respiration, artificial ; Prone position ; Wilson frame

Lung protective (LP) mechanical ventilation (MV) protocols are well-defined, recommended, and frequently translated to burn patients with ARDS. Less is known about application and suitability of these protocols in burn patients who do not develop ARDS but who nevertheless require MV. The purpose of this study was to examine the use of LPMV strategies in burn patients without ARDS. Retrospective review of all patients requiring MV admitted to an adult regional ABA-verified burn center between 14/11/15 and 23/4/17. Our MV protocol was a low tidal volume (Vt), plateau pressure (Pplat) limited, positive end-expiratory pressure (PEEP) directed strategy defined by the ARDS Network (ARDSNet). Values are shown as the mean ± SD or median (1st, 3rd quartiles) as appropriate. We screened 92 patients who required MV and excluded the following: admission > 24h post burn (n=8), < 48h of MV (n=29), use of comfort measures < 24 h (n=6), ARDS (n=9), non-burn diagnosis (n=18), and burn < 1% TBSA without an inhalation injury (INH), (n=20), leaving a study population of 20 subjects. Characteristics were age 51 ± 15 yr, 20% female, %TBSA burn 35 ± 23, % BSA full thickness burn 7 (0,29), and 45% with INH. Duration of MV was 16 ± 9 days. Mortality was 25%. Volume controlled ventilation (VCV), pressure controlled ventilation (PCV), and pressure support ventilation (PSV) were used for a median of 28%, 1%, and 61% of all MV time, respectively. On VCV, Vt and Pplat were 6.5 ± 0.8 ml/kg and 22.3 ± 4.2 cm H2O, respectively. On PCV, Vt was 6.7 ± 0.9 ml/kg while on PSV it was 8.3 ± 2 ml/kg. Across all modes of MV, PaCO2 and pH were 42 ± 5 and 7.4 (7.35,7.41), respectively. FiO2 was 0.4 (0.4, 0.5), and PEEP was set at 8.5 ± 2.4 cm H2O, which was 1.7 (0.6, 2.6) cmH2O higher than ARDSNet recommended (p=0.3). No patients required “rescue” with unconventional MV. No significant differences in mode of MV, minute ventilation (min vent), Vt, Pplat, FiO2, or PEEP were identified between those with INH (n=9) and without INH (No INH, n=11) over the entire course of MV. In the 1st 96 hours of MV, VCV was used for 70% and 73% of all ventilation hours in INH and No INH, respectively while INH spent a greater proportion of ventilation time on PCV (17%) than No INH (4%). Subjects with INH tended to have a higher min vent [11 ± 2 L/min vs 10 ± 2 L/min, p=0.43], a higher PEEP setting [10 ± 4 cm H2O vs 8 ± 3 cm H2O, p=0.13] and a lower PaO2/FiO2 [205 ± 65 vs 273 ± 79, p=0.05] during the 1st 96 h of MV. Although a small number of patients were studied, the ARDSNet protocol was applied and targets were met even when there was an inhalation injury. A larger prospective observational study would be required to confirm these observations. This study may help to guide use of MV in burn patients.

Introduction The SARS-CoV-2 pandemic has created a sudden lack of ventilators. DuplicARⓇ is a novel device that allows simultaneous and independent ventilation of two subjects with a single ventilator. The aims of this study are (a) to determine the efficacy of DuplicARⓇ to independently regulate the peak and positive-end expiratory pressures in each subject, both under pressure-controlled ventilation and volume-controlled ventilation and (b) to determine the ventilation mode in which DuplicARⓇ presents the best performance and safety. Materials and Methods Two test lungs are connected to a single ventilator using DuplicARⓇ. Three experimental stages are established: (1) two identical subjects, (2) two subjects with the same weight but different lung compliance, and (3) two subjects with different weights and lung compliances. In each stage, the test lungs are ventilated in two ventilation modes. The positive-end expiratory pressure requirements are increased successively in one of the subjects. The goal is to achieve a tidal volume of 7 ml/kg for each subject in all different stages through manipulation of the ventilator and the DuplicARⓇ controllers. Results DuplicARⓇ allows adequate ventilation of two subjects with different weights and/or lung compliances and/or PEEP requirements. This is achieved by adjusting the total tidal volume for both subjects (in volume-controlled ventilation) or the highest peak pressure needed (in pressure-controlled ventilation) along with the basal positive-end expiratory pressure on the ventilator and simultaneously manipulating the DuplicARⓇ controllers to decrease the tidal volume or the peak pressure in the subject that needs less and/or to increase the positive-end expiratory pressure in the subject that needs more. While ventilatory goals can be achieved in any of the ventilation modes, DuplicARⓇ performs better in pressure-controlled ventilation, as changes experienced in the variables of one subject do not modify the other one. Conclusions DuplicARⓇ is an effective tool to manage the peak inspiratory pressure and the positive-end expiratory pressure independently in two subjects connected to a single ventilator. The driving pressure can be adjusted to meet the requirements of subjects with different weights and lung compliances. Pressure-controlled ventilation has advantages over volume-controlled ventilation and is therefore the recommended ventilation mode.

Background and Aim:Mechanical ventilation is essential for supporting patients’ respiratory function when they are under general anesthesia. For cats with limited lung capacity, the different effects of volume-controlled ventilation (VCV) and pressure-controlled ventilation (PCV) on respiratory function remain elusive. The objective of the present study was to compare the efficacy of VCV and PCV in cats under general anesthesia using a cuffed endotracheal tube (ETT).Materials and Methods:Twelve healthy cats were randomly allocated to either a VCV or PCV group. Five tidal volumes (6, 8, 10, 12, and 14 mL/kg) were randomly applied to assess the efficacy of VCV, and respiratory rates were adjusted to achieve a minute ventilation of 100 mL/kg/min. Peak inspiratory pressures (4, 5, 6, 7, and 8 mmHg) were randomly applied to assess the efficacy of PCV, and respiratory rates were adjusted to achieve a minute ventilation of 100 mL/kg/min. Blood pressure, gas leakages, and end-tidal CO2 were recorded from 60 trials for airway control during the use of VCV or PCV. Data were compared using Fisher’s exact test with a significance level of p<0.05.Results:Leakages did not differ between VCV (1/60 events) and PCV (0/60 events; p=0.500). Hypercapnia was identified when using VCV (6/60 events) less frequently than when using PCV (7/60 events; p=0.762), but did not reach statistical significance. Hypotension (mean arterial blood pressure <60 mmHg) occurred less frequently with VCV (0/60 events) than with PCV (9/60 events; p=0.003). Moreover, VCV provided a significantly lower work of breathing (151.10±65.40 cmH2O mL) compared with PCV (187.84±89.72 cmH2O mL; p<0.05).Conclusion:VCV in cats using a cuffed ETT causes less hypotension than PCV. It should be noted that VCV provides a more stable tidal volume compared with PCV, resulting in a more stable minute volume. Nonetheless, VCV should not be used in patients with an airway obstruction because higher peak airway pressure may occur and lead to lung injury.