Patient effort at a glance

A: Patient with little effort. Top: Volume Controlled Ventilation: airway pressure in cmH2O in yellow, constant flow in L/min in pink. Middle: Pressure controlled ventilation: airway pressure in cmH2O in yellow, decelerating flow in L/min in pink. Bottom: Esophageal pressure in cmH2O. B: Patient with high effort. Top: Volume Controlled Ventilation: airway pressure with convex negative deflection during trigger and first half of inspiration (blue arrow). Middle: Pressure controlled ventilation: airway pressure with negative deflection during the trigger (yellow arrow) and slight convex deflection (green arrow), concave deflection in the flow (orange arrow). Bottom: Convex deflection in esophageal pressure (grey arrow).

Different Inspiratory Flow Waveform during Volume-Controlled Ventilation in ARDS Patients

The most used types of mechanical ventilation are volume- and pressure-controlled ventilation, respectively characterized by a square and a decelerating flow waveform. Nowadays, the clinical utility of different inspiratory flow waveforms remains unclear. The aim of this study was to assess the effects of four different inspiratory flow waveforms in ARDS patients. Twenty-eight ARDS patients (PaO2/FiO2 182 ± 40 and PEEP 11.3 ± 2.5 cmH2O) were ventilated in volume-controlled ventilation with four inspiratory flow waveforms: square (SQ), decelerating (DE), sinusoidal (SIN), and trunk descending (TDE). After 30 min in each condition, partitioned respiratory mechanics and gas exchange were collected. The inspiratory peak flow was higher in the DE waveform compared to the other three waveforms, and in SIN compared to the SQ and TDE waveforms, respectively. The mean inspiratory flow was higher in the DE and SIN waveforms compared with TDE and SQ. The inspiratory peak pressure was higher in the SIN and SQ compared to the TDE waveform. Partitioned elastance was similar in the four groups; mechanical power was lower in the TDE waveform, while PaCO2 in DE. No major effect on oxygenation was found. The explored flow waveforms did not provide relevant changes in oxygenation and respiratory mechanics.

Effects of pressure- and volume-controlled ventilation on the work of breathing in cats using a cuffed endotracheal tube

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.

Mechanical ventilation modes utilization. An international survey of clinicians

Background There has been an exponential increase in modes of mechanical ventilation over the last couple decades. With this increase, there have been paucity of evidence of which mode is superior to others or much guidance to use a mode in different disease status causing respiratory failure. Methods: An international survey of six questions was posted on the “society of mechanical ventilation” website and advertised on social media over the period of four months. This is a descriptive study, results are presented in two different ways. First as the total modes used and secondly, per the geographical areas as the preferred mode, mode used mostly in ARDS, COPD, and Spontaneous weaning trials. Results: Conventional older modes, Volume-controlled and Pressure-controlled ventilation were used significantly more in general and in different disease states irrespective of geographical location. Four other modes were used almost equally in all disease states irrespective of geographical location. Pressure support ventilation was the most common mode used during the spontaneous breathing trial. Conclusion: There was large heterogenicity of modes used between clinicians in general, in different disease states and in between different international geographical locations. Mechanical ventilation modes utilization varies widely and remains a personal preference with no consensus between clinicians globally. Keywords: Modes of mechanical ventilation, ARDS, COPD, SBT, survey

COMPARATIVE ANALYSIS OF PRESSURE CONTROLLED AND VOLUME CONTROLLED VENTILATION ON RESPIRATORY MECHANICS, HAEMODYNAMICS AND SYSTEMIC STRESS RESPONSE IN PATIENTS UNDERGOING SURGERY IN PRONE POSITION.

BACKGROUND: General Anaesthesia in prone position is related with increased airway pressure, decreased pulmonary and thoracic compliance. AIM: Comparision of pressure controlled and volume controlled ventilation in patients undergoing lumbar spine surgery in prone position.METHODS: After ethics committee approval & written informed consent, a comparative randomized interventional study was conducted from July-December 2017. Randomization was done using random number tables. Patients of either sex, ASA grade I&II, age 25-55 yrs were included while those with severe pulmonary ,cardiovascular, endocrine disease & BMI> 30kg/m2 were excluded. Patients were randomly assigned to VCV group (n = 30), or PCV group (n = 30). Haemodynamic (HR,SBP,DBP,MAP), Respiratory (P-Peak,P-mean,C-dyn) variables,blood glucose,S.cortisol were measured and ABG analysis was done 10 minutes after intubation (T1), 30 minutes after prone positioning(T2) and 60 minuts after extubation(T3). RESULTS: Demographic parameters , perioperative hemodynamic values were comparable with no significant statistical difference.The P-Peak levels were lower and dynamic compliance was higher in PCV group during both T1 and T2 with p value of less than 0.05 Postoperative PaO2 level was significantly higher in Group PCV compared with Group VCV.The difference between post operative and preoperative serum cortisol and blood glucose levels was significantly less in patients ventilated with PCV mode.CONCLUSION: According to our study,PCV mode is associated with lower P-peak levels during prone position, better oxygenation postoperatively and lesser systemic stress response.We concluded that PCV mode might be more appropriate in prone position surgeries.

Comparison of the effects of volume-controlled ventilation and pressure-controlled ventilation modes on hemodynamics, respiratory mechanics and blood gas parameters in patients undergoing laparoscopic cholecystectomy

Background: This study aimed to compare the changes induced by VCV and PCV modes in hemodynamics, respiration (airway pressures, gas exchange parameters) and metabolism (acid-base balance) in patients undergoing laparoscopic cholecystectomy.Methods: Patients were divided into two randomised groups as volume-controlled ventilation (VCV) group (VC) and pressure-controlled ventilation (PCV) group (PC). The following parameters were recorded at 3 different time points: T1: in supine position 10 minutes after induction of anaesthesia, T2: 15 minutes after CO2 insufflation in inverted Trendelenburg position (head 30 degrees up), T3: 10 minutes after CO2 desufflation. HR, SpO2, SAP (systolic arterial pressure), DAP (diastolic arterial pressure), MAP (mean arterial pressure), PetCO2 (end-tidal carbon dioxide pressure), Ppeak, Pplateau, Pmean, Vt (tidal volume) and compliance with the available data, the cases in both groups Vd, Vd/Vt ratios and P(A-a)O2 were calculated. Arterial blood gas parameters (pH, PaO2, PaCO2, SaO2, P(a-et)CO2) values were recorded.Results: It was found that Ppeak and Pplateau values were significantly higher in the VC group (p<0.05). It was found that compliance was significantly higher in the PC group (p<0.05) (p<0.01). In the postoperative period, it was found that PaO2 values were significantly higher in the PC group compared to the VC group (p<0.05). It was found that the P(A-a)O2 values of the PC group were significantly higher than those of the VC group during the desufflation phase (p<0.05).Conclusions: We think that PCV mode can be a good alternative for the prevention and correction of physiopathological changes due to laparoscopic surgery.