Under open lung conditions inverse ratio ventilation causes intrinsic PEEP and hemodynamic impairment

Effects of inverse ratio ventilation combined with lung protective ventilation on pulmonary function in patients with severe burns for surgery

Objective

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

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

Background

Expiratory flow-initiated pressure-controlled inverse ratio ventilation (EF-initiated PC-IRV) reduces physiological dead space. We hypothesised that EF-initiated PC-IRV would be lung protective compared with volume-controlled ventilation (VCV).

Methods

Twenty-eight men undergoing robot-assisted laparoscopic radical prostatectomy were enrolled in this randomised controlled trial. The EF-initiated PC-IRV group (n = 14) used pressure-controlled ventilation with the volume guaranteed mode. The inspiratory to expiratory (I:E) ratio was individually adjusted by observing the expiratory flow-time wave. The VCV group (n = 14) used the volume control mode with a 1:2 I:E ratio. The Mann–Whitney U test was used to compare differences in the serum cytokine levels.

Results

There were no significant differences in serum IL-6 between the EF-initiated PC-IRV (median 34 pg ml^-1 (IQR 20.5 to 63.5)) and VCV (31 pg ml^-1 (24.5 to 59)) groups (P = 0.84). The physiological dead space rate (physiological dead space/expired tidal volume) was significantly reduced in the EF-initiated PC-IRV group as compared with that in the VCV group (0.31 ± 0.06 vs 0.4 ± 0.07; 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).

Conclusions

There were no differences in the lung-protective properties between the two ventilatory strategies. However, EF-initiated PC-IRV reduced physiological dead space rate; thus, it may be useful for reducing the ventilatory volume that is necessary to maintain normocapnia in patients with low forced vital capacity (% predicted) during robot-assisted laparoscopic radical prostatectomy.

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

BACKGROUND

Pressure-controlled inverse inspiratory to expiratory ratio ventilation (PC-IRV) is thought to be beneficial for reducing the dead space volume.

OBJECTIVE

To investigate the effects of PC-IRV on the components of dead space during robot-assisted laparoscopic radical prostatectomy (RLRP).

DESIGN

A randomised crossover study of three different ventilator modes.

SETTING

A single university hospital from September 2014 to April 2015.

PATIENTS

Twenty consecutive study participants undergoing RLRP.

INTERVENTIONS

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.

MAIN OUTCOME MEASURES

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.

RESULTS

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.

CONCLUSION

PC-IRV with the inspiratory to expiratory ratio individually adjusted by the expiratory flow-time wave decreased VDphys/VTE in patients undergoing RLRP.

TRIAL REGISTRATION

University Hospital Medical Information Network in Japan 000014004.

Effect of Manual Hyperinflation on Hemodynamics, Gas Exchange, and Respiratory Mechanics in Ventilated Patients

The authors investigated the effect of manual hyperinflation (MHI) with set parameters applied to patients on mechanical ventilation on hemodynamics, respiratory mechanics, and gas exchange. Sixteen critically ill patients post-septic shock, with acute lung injury, were studied. Heart rate, arterial pressure, and mean pulmonary artery pressure were recorded every minute. Pulmonary artery occlusion pressure, cardiac output, arterial blood gases, and dynamic compliance (Cdyn) were recorded pre- and post-MHI. From this, systemic vascular resistance index (SVRI), cardiac index, oxygen delivery, and partial pressure of oxygen: fraction of inspired oxygen (PaO2:FiO2) ratio were calculated. There were significant increases in SVRI ( P < 0.05) post-MHI and diastolic arterial pressure ( P < 0.01) during MHI. Cdyn increased post-MHI ( P < 0.01) and was sustained at 20 minutes post-MHI ( P < 0.01). Subjects with an intrapulmonary cause of lung disease had a significant decrease ( P = 0.02) in PaO2:FiO2, and those with extrapulmonary causes of lung disease had a significant increase ( P < 0.001) in PaO2:FiO2 post-MHI. In critically ill patients, MHI resulted in an improvement in lung mechanics and an improvement in gas exchange in patients with lung disease due to extrapulmonary events and did not result in impairment of the cardiovascular system.

Manual hyperinflation causes norepinephrine release

OBJECTIVE

To measure hemodynamics and plasma catecholamines during manual hyperinflation (MHI) in ventilated patients.

METHODS

MHI was performed with a Mapleson "C" circuit, 2l-reservoir bag; peak inspiratory pressure was standardized to 35 mL water; and positive expiratory-end pressure of 5 mL water was administered to seven mechanically ventilated patients with septic (6) and cardiogenic (1) shock (67.2 +/- 5.2 years, Acute Physiology Assessment and Chronic Health Evaluation II score 22.1 +/- 3.1). Diastolic (DAP) and mean arterial pressure (MAP), continuous cardiac index, pulmonary artery occlusion pressure, dynamic compliance, plasma norepinephrine and epinephrine, and arterial blood gases were recorded, and systemic vascular resistance index (SVRI) and oxygenation ratio were calculated.

RESULTS

There were no significant changes in pulmonary artery occlusion pressure, mean arterial pressure, or PaO2/FiO2. There were significant increases in SVRI (P < .001), DAP (P < .001), dynamic compliance (P < .01), and plasma norepinephrine (P < .001) and a decrease in cardiac index (P < .05) after MHI.

CONCLUSIONS

The increases in DAP, SVRI, and plasma norepinephrine suggest a sympathetic vasoconstrictive response during the application of MHI.