Post-pandemic acute respiratory distress syndrome: A New Global Definition with extension to lower-resource regions

Acute respiratory distress syndrome (ARDS), first described in 1967, is characterized by acute respiratory failure causing profound hypoxemia, decreased pulmonary compliance, and bilateral CXR infiltrates. After several descriptions, the Berlin definition was adopted in 2012, which established three categories of severity according to hypoxemia (mild, moderate and severe), specified temporal aspects for diagnosis, and incorporated the use of non-invasive ventilation. The COVID-19 pandemic led to changes in ARDS management, focusing on continuous monitoring of oxygenation and on utilization of high-flow oxygen therapy and lung ultrasound. In 2021, a New Global Definition based on the Berlin definition of ARDS was proposed, which included a category for non-intubated patients, considered the use of SpO2, and established no particular requirement for oxygenation support in regions with limited resources. Although debates persist, the continuous evolution seeks to adapt to clinical and epidemiological needs, and to the search of personalized treatments.

Airway and Transpulmonary Driving Pressure by End-Inspiratory Holds During Pressure Support Ventilation

BACKGROUND

The precision of quasi-static airway driving pressure (ΔP) assessed in pressure support ventilation (PSV) as a surrogate of tidal lung stress is debatable because persistent muscular activity frequently alters the readability of end-inspiratory holds. In this study, we used strict criteria to discard excessive muscular activity during holds and assessed the accuracy of ΔP in predicting global lung stress in PSV. Additionally, we explored whether the physiological effects of high PEEP differed according to the response of respiratory system compliance (CRS).

METHODS

Adults with ARDS undergoing PSV were enrolled. An esophageal catheter was inserted to calculate lung stress through transpulmonary driving pressure (ΔPL). ΔP and ΔPL were assessed in PSV at PEEP 5, 10, and 15 cm H2O by end-inspiratory holds. CRS was calculated as tidal volume (VT)/ΔP. We analyzed the effects of high PEEP on pressure-time product per minute (PTPmin), airway pressure at 100 ms (P0.1), and VT over PTP per breath (VT/PTPbr) in subjects with increased versus decreased CRS at high PEEP.

RESULTS

Eighteen subjects and 162 end-inspiratory holds were analyzed; 51/162 (31.5%) of the holds had ΔPL ≥ 12 cm H2O. Significant association between ΔP and ΔPL was found at all PEEP levels (P < .001). ΔP had excellent precision to predict ΔPL, with 15 cm H2O being identified as the best threshold for detecting ΔPL ≥ 12 cm H2O (area under the receiver operating characteristics 0.99 [95% CI 0.98-1.00]). CRS changes from low to high PEEP corresponded well with lung compliance changes (R2 0.91, P < .001) When CRS increased, a significant improvement of PTPmin and VT/PTPbr was found, without changes in P0.1. No benefits were observed when CRS decreased.

CONCLUSIONS

In subjects with ARDS undergoing PSV, high ΔP assessed by readable end-inspiratory holds accurately detected potentially dangerous thresholds of ΔPL. Using ΔP to assess changes in CRS induced by PEEP during assisted ventilation may inform whether higher PEEP could be beneficial.

Behavior of Endotracheal Tube Cuff Pressure During a Routine Control Maneuver With Different Manometers

BACKGROUND

The main functions of the endotracheal tube (ETT) cuff are to prevent aspiration and to allow pressurization of the respiratory system. For this purpose, it is essential to maintain adequate pressure inside the cuff, thus reducing the risks for the patient. It is regularly checked using a manometer and is considered the best alternative. The objective of this study was to evaluate the cuff pressure behavior of different ETTs during the simulation of an inflation maneuver using different manometers.

METHODS

A bench study was performed. Four brands of 8-mm internal diameter single lumen with a Murphy eye ETT with cuff and 3 different brands of manometers were used. In addition, a pulmonary mechanics monitor was connected to the inside of the cuff through the body of the distal end of the ETT.

RESULTS

A total of 528 measurements were made on the 4 ETTs. During the complete procedure (connection and disconnection), there was a significant pressure drop of 7 ± 1.4 cm H2O from the initial pressure (Pinitial) (P < .001), of which 6 ± 1.4 cm H2O was lost during connection (difference between Pinitial and Pconnection). The Preconnection value was 19.1 ± 1.6 cm H2O, showing a significant total pressure drop of 11 ± 1.6 cm H2O (difference between Pinitial and Preconnection) (P < .001). The Pfinal mean was 29.6 ± 1.3 cm H2O. Significant differences were found between manometers according to the time of measurement. A similar phenomenon was evidenced when analyzing different ETTs.

CONCLUSIONS

Significant pressure changes occur secondary to ETT cuff measurement, which has important implications for patient safety.

Ventilatory Parameters in Obstetric Patients With COVID-19 and Impact of Delivery: A Multicenter Prospective Cohort Study

BACKGROUND

Current evidence on obstetric patients requiring advanced ventilatory support and impact of delivery on ventilatory parameters is retrospective, scarce, and controversial.

RESEARCH QUESTION

What are the ventilatory parameters for obstetric patients with COVID-19 and how does delivery impact them? What are the risk factors for invasive mechanical ventilation (IMV) and for maternal, fetal, and neonatal mortality?

STUDY DESIGN AND METHODS

Prospective, multicenter, cohort study including pregnant and postpartum patients with COVID-19 requiring advanced ventilatory support in the ICU.

RESULTS

Ninety-one patients were admitted to 21 ICUs at 29.2 ± 4.9 weeks; 63 patients (69%) delivered in ICU. Maximal ventilatory support was as follows: IMV, 69 patients (76%); high-flow nasal cannula, 20 patients (22%); and noninvasive mechanical ventilation, 2 patients (2%). Sequential Organ Failure Assessment during the first 24 h (SOFA₂₄) score was the only risk factor for IMV (OR, 1.97; 95% CI, 1.29-2.99; P = .001). Respiratory parameters at IMV onset for pregnant patients were: mean ± SD plateau pressure (PP), 24.3 ± 4.5 cm H₂O; mean ± SD driving pressure (DP), 12.5 ± 3.3 cm H₂O; median static compliance (SC), 31 mL/cm H₂O (interquartile range [IQR], 26-40 mL/cm H₂O); and median Pao₂ to Fio₂ ratio, 142 (IQR, 110-176). Respiratory parameters before (< 2 h) and after (≤ 2 h and 24 h) delivery were, respectively: mean ± SD PP, 25.6 ± 6.6 cm H₂O, 24 ± 6.7 cm H₂O, and 24.6 ± 5.2 cm H₂O (P = .59); mean ± SD DP, 13.6 ± 4.2 cm H₂O, 12.9 ± 3.9 cm H₂O, and 13 ± 4.4 cm H₂O (P = .69); median SC, 28 mL/cm H₂O (IQR, 22.5-39 mL/cm H₂O), 30 mL/cm H₂O (IQR, 24.5-44 mL/cm H₂O), and 30 mL/cm H₂O (IQR, 24.5-44 mL/cm H₂O; P = .058); and Pao₂ to Fio₂ ratio, 134 (IQR, 100-230), 168 (IQR, 136-185), and 192 (IQR, 132-232.5; P = .022). Reasons for induced delivery were as follows: maternal, 43 of 71 patients (60.5%); maternal and fetal, 21 of 71 patients (29.5%); and fetal, 7 of 71 patients (9.9%). Fourteen patients (22.2%) continued pregnancy after ICU discharge. Risk factors for maternal mortality were BMI (OR, 1.10; 95% CI, 1.006-1.204; P = .037) and comorbidities (OR, 4.15; 95% CI, 1.212-14.20; P = .023). Risk factors for fetal or neonatal mortality were gestational age at delivery (OR, 0.67; 95% CI, 0.52-0.86; P = .002) and SOFA₂₄ score (OR, 1.53; 95% CI, 1.13-2.08; P = .006).

INTERPRETATION

Contrary to expectations, pregnant patient lung mechanics were similar to those of the general population with COVID-19 in the ICU. Delivery was induced mainly for maternal reasons, but did not change ventilatory parameters other than Pao₂ to Fio₂ ratio. SOFA₂₄ score was the only risk factor for IMV. Maternal mortality was associated independently with BMI and comorbidities. Risk factors for fetal and neonatal mortality were SOFA₂₄ score and gestational age at delivery.

Epidemiology of Weaning From Invasive Mechanical Ventilation in Subjects With COVID-19

BACKGROUND

Patients requiring mechanical ventilation due to COVID-19 have different characteristics of evolution and outcome compared to the general ICU population. Although early weaning from mechanical ventilation is associated with improved outcomes, inadequate identification of patients unable to be weaned may lead to extubation failure and increased days on mechanical ventilation. Outcomes related to mechanical ventilation weaning in this population are scare and inconclusive. Therefore, the objective of this study was to describe the characteristics of mechanical ventilation weaning in subjects with acute respiratory failure induced by COVID-19.

METHODS

This was a multi-center, prospective cohort study. We included adult subjects requiring at least 12 h of mechanical ventilation due to COVID-19 infection admitted to any participating ICUs. Characteristics of the mechanical ventilation weaning and extubation process, as well as clinical results, were the primary outcome variables. Weaning types were defined according to previously described and internationally recognized categories.

RESULTS

Three hundred twenty-six subjects from 8 ICUs were included. A spontaneous breathing trial (SBT) was not performed in 52.1% of subjects. One hundred twenty-eight subjects were extubated, and 29.7% required re-intubation. All the subjects included could be classified by Weaning according to a New Definition (WIND) classification (group 0 = 52.1%, group 1 = 28.5%, group 2 = 8.0%, and group 3 = 11.3%) with statistically significant differences in duration of mechanical ventilation (P < .001) and ICU length of stay (P < .001) between groups.

CONCLUSIONS

The mechanical ventilation weaning process in subjects with COVID-19 was negatively affected by the disease, with many subjects never completing an SBT. Even though temporal variables were modified, the clinical outcomes in each weaning group were similar to those previously reported.

Performance of Invasive Mode in Different Heated Humidification Systems With High-Flow Nasal Cannula

BACKGROUND

Oxygen therapy via high-flow nasal cannula generates physiologic changes that impact ventilatory variables of patients. However, we know that there are detrimental effects on airway mucosa related to inhalation of gases. The objective of this study was to evaluate the performance in terms of absolute humidity, relative humidity, and temperature of different brands of heated humidifiers and circuits in the invasive mode during the use of high-flow oxygen therapy in flows between 30 and 100 L/min.

METHODS

A prospective observational study conducted at the Sanatorio Anchorena equipment analysis laboratory; September 5 to October 20, 2019.

RESULTS

A statistically significant interaction was found among the programmed flows and the different combinations of devices and circuits for the delivery of absolute humidity (P < .001). An effect of flow on delivered absolute humidity was found, regardless of the equipment and circuit combination (P < .001). However, in the invasive mode, the combination of the Fisher&Paykel MR850 heated humidifier with the Medtronic-Dar circuit, the Intersurgical circuit, and the AquaVENT circuit always reached or achieved absolute humidity values > 33 mg/L, even at flows up to 100 L/min. The combination of the Flexicare FL9000 heated humidifier with the Fisher&Paykel RT202 circuit, the Fisher&Paykel Evaqua 2 circuit, the Flexicare circuit, the AquaVENT circuit, and the GGM circuit achieved similar results. The mean (SD) of absolute humidity delivered in the invasive mode (36.2 ± 5.9 mg/L) was higher compared with the noninvasive mode (26.8 ± 7.2 mg/L) (P < .001), regardless of circuit and programmed flows.

CONCLUSIONS

When heated humidifiers were used in the invasive mode for high-flow oxygen therapy, absolute humidity depended not only on the heated humidifiers and the combination of circuits but also on the programmed flow, especially at flows > 50 L/min. Moreover, the heated humidifiers exhibited different behaviors, in some cases inefficient, in delivering adequate humidification. However, some equipment improved performance when set to the invasive mode.

High-Flow Nasal Cannula and Standard Oxygen in Acute Hypoxemic Respiratory Failure Due to COVID-19

BACKGROUND

The evidence regarding benefits of high-flow nasal cannula (HFNC) in patients with COVID-19 is controversial. The aim of this study was to evaluate the impact of HFNC in comparison with standard oxygen therapy on the frequency of endotracheal intubation at 28 d in subjects with acute hypoxemic respiratory failure (AHRF) secondary to SARS-CoV-2 infection.

METHODS

A retrospective, age- and sex-matched-paired, cohort study was conducted in subjects with moderate-to-severe AHRF. Intervention group was treated with HFNC, and control group was treated with standard oxygen therapy. Baseline characteristics and clinical evolution were analyzed. Mantel-Haenszel test was used for categorical variables. Paired samples Wilcoxon test was used for quantitative variables. Multivariate analysis was performed using conditional multiple logistic regression.

RESULTS

Eighty-four subjects were included. The median time from admission to progression of oxygen therapy to FIO2 ≥ 0.5 or HFNC was 1 (interquartile range [IQR] 0-3) d. PaO2 /FIO2 at the time of oxygen therapy progression showed a median of 150.5 (IQR 100.0-170.0) for the entire sample and was lower in HFNC group compared with control group (median 135 [IQR 96-162] vs median 158 [IQR 132-174], respectively, P = .02). Endotracheal intubation at 28 d was observed in 54.8% HFNC and 73.8% standard oxygen (unadjusted odds ratio 0.38 [95% CI 0.13-1.07], P = .069). In the multivariate analysis, presence of dyspnea at hospital admission, Sequential Organ Failure Assessment score, and PaO2 /FIO2 at time of progression of oxygen therapy to FIO2 ≥ 0.5 was identified as confounding factors for the association between the intervention group and the outcome. Use of HFNC was not an independent predictor of endotracheal intubation frequency after adjusting confounders (odds ratio 0.26 [95% CI 0.04-1.51], P = .13).

CONCLUSIONS

In this study, HFNC therapy in subjects with AHRF secondary to COVID-19 was not an independent predictor of endotracheal intubation, compared with standard oxygen therapy, after adjusting for confounders.

Epidemiology of mechanical ventilation in Argentina. The EpVAr multicenter observational study

OBJETIVE

To describe mechanical ventilation (MV) practices in Argentina, and to explore factors associated with ICU mortality in this population.

DESIGN

A prospective, multicenter, observational study was carried out.

SETTING

Intensive Care.

PATIENTS

We enrolled patients above 18 years old admitted to any of the participating ICUs requiring invasive MV for at least 12 h since the admission to the healthcare institution, including MV initiation in emergency department, operating room or other hospitals.

INTERVENTIONS

None.

VARIABLES

All variables were classified into three categories: variables related to demographic and clinical factors before the MV, factors related to the first day on MV, and factors related to events happening during the MV (complications and weaning from MV). Mechanical ventilation weaning and mortality were classified according to WIND.

RESULTS

The primary analysis included 950 patients. The main indication for MV was acute respiratory failure (58% of patients). Initial ventilation mode was volume control-continuous mandatory ventilation in 75% of cases. ICU and hospital mortality were 44.6% and 47.9% respectively. The variables identified as independent predictors of mortality in ICU were age (OR 3.48 IC 95% 1.22-11.66; p = 0.028), failure to implement NIV before MV (OR 2.76 IC 95% 1.02-7.10; p = 0.038), diagnosis of sepsis (OR 2.46 IC 95% 1.09-5.47; p = 0.027) and extubation failure (OR 4.50 IC 95% 2.05-9.90; p < 0.001).

CONCLUSIONS

The present study allowed us to describe the characteristics and clinical course of the patients who received mechanical ventilation in Argentina, finding as the main result that mortality was higher than that reported in international studies.

Geoeconomic variations in epidemiology, ventilation management, and outcomes in invasively ventilated intensive care unit patients without acute respiratory distress syndrome: a pooled analysis of four observational studies

Background

Geoeconomic variations in epidemiology, the practice of ventilation, and outcome in invasively ventilated intensive care unit (ICU) patients without acute respiratory distress syndrome (ARDS) remain unexplored. In this analysis we aim to address these gaps using individual patient data of four large observational studies.

Methods

In this pooled analysis we harmonised individual patient data from the ERICC, LUNG SAFE, PRoVENT, and PRoVENT-iMiC prospective observational studies, which were conducted from June, 2011, to December, 2018, in 534 ICUs in 54 countries. We used the 2016 World Bank classification to define two geoeconomic regions: middle-income countries (MICs) and high-income countries (HICs). ARDS was defined according to the Berlin criteria. Descriptive statistics were used to compare patients in MICs versus HICs. The primary outcome was the use of low tidal volume ventilation (LTVV) for the first 3 days of mechanical ventilation. Secondary outcomes were key ventilation parameters (tidal volume size, positive end-expiratory pressure, fraction of inspired oxygen, peak pressure, plateau pressure, driving pressure, and respiratory rate), patient characteristics, the risk for and actual development of acute respiratory distress syndrome after the first day of ventilation, duration of ventilation, ICU length of stay, and ICU mortality.

Findings

Of the 7608 patients included in the original studies, this analysis included 3852 patients without ARDS, of whom 2345 were from MICs and 1507 were from HICs. Patients in MICs were younger, shorter and with a slightly lower body-mass index, more often had diabetes and active cancer, but less often chronic obstructive pulmonary disease and heart failure than patients from HICs. Sequential organ failure assessment scores were similar in MICs and HICs. Use of LTVV in MICs and HICs was comparable (42·4% vs 44·2%; absolute difference –1·69 [–9·58 to 6·11] p=0·67; data available in 3174 [82%] of 3852 patients). The median applied positive end expiratory pressure was lower in MICs than in HICs (5 [IQR 5–8] vs 6 [5–8] cm H₂O; p=0·0011). ICU mortality was higher in MICs than in HICs (30·5% vs 19·9%; p=0·0004; adjusted effect 16·41% [95% CI 9·52–23·52]; p<0·0001) and was inversely associated with gross domestic product (adjusted odds ratio for a US$10 000 increase per capita 0·80 [95% CI 0·75–0·86]; p<0·0001).

Interpretation

Despite similar disease severity and ventilation management, ICU mortality in patients without ARDS is higher in MICs than in HICs, with a strong association with country-level economic status.

Funding

No funding.

[Comparison between the first and second COVID-19 wave of patients who required invasive mechanical ventilation in an intensive care unit in Argentina]

INTRODUCTION

the information regarding characteristics and ventilatory results comparing the first (W1) and the second wave (W2) in Argentina are limited. The main objective of this study was to describe general characteristics and ventilatory variables in COVID-19 patients who required invasive mechanical ventilation (IMV) and compare differences between waves. Secondarily, factors associated with mortality in intensive care unit (ICU) were studied.

METHODS

We conducted a prospective observational cohort study that included patients older than 18 years infected with SARS-CoV-2 consecutively admitted to ICU with IMV between August 1, 2020, and June 30, 2021. We included 412 patients.

RESULTS

We found statistically significant differences (p < 0.001) in age [W1 64(55-72) vs W2 59 (50-66) years], presence of COPD [W1 n = 42 (19.8%) vs. W2 n = 13(6.3%)], plateau pressure [W1 27(25-30) cm H2O vsW2 24 (22-27) cmH2O], driving pressure (ΔP) [W1 15 (13-17) cmH2O vs. W2 12 (11-14) cm H2O] compliance [W1 40 mL/cmH2O (32-46) vs. W2 = 33 mL/cm H2O (27-40)]; reintubation [W1 30.4% (n = 63/207) vs. W2 13.7% (n = 28/205)]. We identified as independent factors associated with mortality the following variables: age [OR 1.07(95% CI 1.05-1.09)], the ΔP in the first 24 hours [OR 1.19(95% CI 1.10-1.28)] and W2 [OR 1.81 (95% IC1.12-2.93); p = 0.015.

DISCUSSION

During W2 the patients were younger. It was possible to achieve ventilatory mechanics more adjusted to a protective ventilation strategy. In conclusion, in the patients studied, age and ΔP were independent predictors of mortality.

Characteristics and outcomes of patients infected with nCoV19 requiring invasive mechanical ventilation in Argentina

Objective

A novel coronavirus emerged this year as a cause of viral pneumonia. The main characteristics of the virus are rapid transmission, high contagion capacity and potential severity. The objective of this case series study is to describe the clinical characteristics of patients with confirmed coronavirus disease (COVID-19) admitted to different intensive care units in Argentina for mechanical ventilation.

Methods

A descriptive, prospective, multicenter case series study was conducted between April 1 and May 8, 2020. Data from patients older than 18 years who were admitted to the intensive care unit for mechanical ventilation for acute respiratory failure with a positive diagnosis of COVID-19 were included.

Results

The variables for 47 patients from 31 intensive care units were recorded: 78.7% were men (median age of 61 years), with a SAPS II score of 43 and a Charlson index score of 3. The initial ventilatory mode was volume control - continuous mandatory ventilation with a tidal volume less than 8mL/kg in 100% of cases, with a median positive end-expiratory pressure of 10.5cmH₂O. At the end of the study, 29 patients died, 8 were discharged, and 10 remained hospitalized. The SAPS II score was higher among patients who died (p = 0.046). Charlson comorbidity index was associated with higher mortality (OR = 2.27, 95% CI 1.13 - 4.55, p = 0.02).

Conclusion

Patients with COVID-19 and on mechanical ventilation in this series presented clinical variables similar to those described to date in other international reports. Our findings provide data that may predict outcomes.

Performance of Different Active Humidification Systems in High-Flow Oxygen Therapy

BACKGROUND

We sought to evaluate the performance in terms of absolute humidity (AH), relative humidity (RH), and temperature of different heated humidifiers (HH) and circuits that are commonly used to deliver high-flow oxygen therapy in conventional ranges (30-60 L/min) and unconventional ranges (70-100 L/min).

METHODS

In this prospective, observational study, an electronic thermohygrometer was used to obtain the required measurements. A mechanical ventilator was used as a source for high-flow nasal cannula oxygen therapy. For active humidification, the following equipment was used: a HH with standard disposable water trap circuit, 3 servo-controlled HH, and 7 circuits with a heated wire. Data on environmental conditions (ie, temperature, RH, AH) were collected from the laboratory during each measurement; the temperature, RH, and AH resulting from the application of 8 flows (30-100 L/min) were also recorded. Variables were compared with analysis of variance for repeated measurements with Tukey post hoc tests. A value of P < .05 was assumed to be significant.

RESULTS

During the study, a statistically significant difference was found in the average AH for each flow for the different devices (P < .005). The highest AH values were recorded with the Fisher & Paykel MR850 and the Medtronic-DAR circuit (AH = 40.8 mg/L with flow of 50 L/min, P < .005), and the lowest AH values were recorded with the Flexicare FL9000 HH and the Flexicare circuit (AH = 11.4 mg/L with 100 L/min flow, P < .005). For flows > 50 L/min, the best performance for all flows in terms of AH was found with the Fisher & Paykel MR850 HH, regardless of the circuit used.

CONCLUSIONS

During oxygen therapy with very high gas flows, HH devices behave differently and in many cases are inefficient in delivering adequate humidification, even at conventional flows. Caution is therefore recommended when selecting the device and flow settings for the implementation of high-flow nasal cannula oxygen therapy.

Complications of Congenital Hernia in Pregnancy: A Case Report

Congenital hernias, frequently misdiagnosed during pregnancy, are potentially fatal and require prompt repair. A pregnant woman with medical history of repaired congenital hernia was admitted with misdiagnosis of preeclampsia. Physical examination and chest x-ray revealed a Bochdalek hernia. Transitory stabilization prompted surgeons to postpone hernia repair, but an urgent thoracotomy was required to relieve a subsequent bowel obstruction that was complicated by an intrathoracic colonic perforation. Emergent cesarean delivery was required with a good maternal and fetal outcome. A multidisciplinary team was present in the operating room. All monitoring catheters were placed in advance in the intensive care unit. During recovery, the patient experienced ventricular fibrillation, presumed to be a manifestation of takotsubo syndrome, which responded favorably to cardiopulmonary resuscitation.

High-flow nasal cannula in the treatment of acute hypoxemic respiratory failure in a pregnant patient: case report

Little evidence exists to support the use of noninvasive mechanical ventilation for acute hypoxemic respiratory failure. However, considering the complications associated with endotracheal intubation, we attempted to implement noninvasive mechanical ventilation in a 24-year-old patient who was 32 weeks pregnant and was admitted to the intensive care unit with acute hypoxemic respiratory failure and sepsis secondary to a urinary tract infection. Lack of tolerance to noninvasive mechanical ventilation led us to use an alternative method to avoid endotracheal intubation. The use of high-flow nasal cannula allowed to overcome this situation, wich supports this technique as a treatment option for critical obstetric patients that is safe for both the mother and fetus.

Effects of High-Flow Nasal Cannula on End-Expiratory Lung Impedance in Semi-Seated Healthy Subjects

BACKGROUND

High-flow nasal cannula (HFNC) enables delivery of humidified gas at high flow while controlling the F_IO2 . Although its use is growing in patients with acute respiratory failure, little is known about the impact of HFNC on lung volume. Therefore, we aimed to assess lung volume changes in healthy subjects at different flows and positions.

METHODS

This was a prospective physiological study performed in 16 healthy subjects. The changes in lung volumes were assessed by measuring end-expiratory lung impedance by using electrical impedance tomography. All the subjects successively breathed during 5 min in these following conditions: while in a supine position without HFNC (T0) and 3 measurements in a semi-seated position at 45° without HFNC (T1), and with HFNC at a flow of 30 L/min (T2), and 50 L/min (T3).

RESULTS

Compared with the supine position, the values of end-expiratory lung impedance significantly increased with the subjects in a semi-seated position. End-expiratory lung impedance significantly increased after HFNC initiation in subjects in a semi-seated position and further increased by increasing flow at 50 L/min. When taking the end-expiratory lung impedance measurement in subjects in a semi-seated position (T1) as reference, the differences among the medians of global end-expiratory lung impedance were statistically significant (P < .001), which amounted to 1.05 units in T1; 1.12 units in T2; and 1.44 units in T3 (P < .05 for all comparisons, Wilcoxon test). The breathing frequency did not differ between the supine and semi-seated position (T0 and T1) but significantly decreased after initiation of HFNC and further decreased at high flow. T0 and T1 were not different (P = .13); whereas there was a statistically significant difference among T1, T2, and T3 (P < .05, post hoc test with Bonferroni correction).

CONCLUSIONS

In healthy subjects, the semi-seated position and the use of HFNC increased end-expiratory lung impedance globally. These changes were accompanied by a significant decrease in the breathing frequency.

Mechanical ventilation in critically-ill pregnant women: a case series

BACKGROUND

Approximately 0.1-0.2% of pregnancies are complicated by respiratory failure requiring mechanical ventilatory support, but few data exist to inform clinical management. This study aimed to characterize current practice and the effect of delivery on respiratory function.

METHODS

A retrospective review was performed of pregnant women who received mechanical ventilation for more than 24h, from four intensive care units in institutions with large-volume obstetric units.

RESULTS

Data were collected from 29 patients with a mean gestation at intensive care unit admission of 25.3 ± 6 weeks. Tidal volumes were 7.7 ± 1.7 mL/kg predicted body weight. Estimated respiratory system compliance was reduced, but was higher in four patients ventilated for neurological conditions without lung disease. Three maternal and three neonatal deaths occurred. Ten patients delivered while on ventilatory support: one spontaneous delivery, four for obstetric indications and five for worsening maternal condition. Following delivery of these 10 patients, three demonstrated a greater than 50% decrease in oxygenation index and five a greater than 50% increase in compliance. No characteristics identified which patients may benefit from delivery.

CONCLUSIONS

Review of current practice in four centers suggests that mechanical ventilation in pregnant patients follows usual guidelines applicable to non-pregnant patients. Delivery was associated with modest improvement in maternal respiratory function in some patients. Any potential benefit of delivery in improving maternal physiology must be weighed against the stress of delivery. The risks of premature birth for the fetus must be weighed against continued exposure to maternal hypoxemia and hypotension.

Evaluation of tracheal cuff pressure variation in spontaneously breathing patients

Background:

Most of the studies referring cuff tubes’ issues were conducted on intubated patients. Not much is known about the cuff pressure performance in chronically tracheostomized patients disconnected from mechanical ventilation.

Objective:

To evaluate cuff pressure (CP) variation in tracheostomized, spontaneously breathing patients in a weaning rehabilitation center.

Materials and Methods:

Experimental setup to test instruments in vitro, in which the gauge (TRACOE) performance at different pressure levels was evaluated in six tracheostomy tubes, and a clinical setupin which CP variation over 24 h, every 4 h, and for 6 days was measured in 35 chronically tracheostomized clinically stable, patients who had been disconnected from mechanical ventilation for at least 72 h. The following data were recorded: Tube brand, type, and size; date of the tube placed; the patient's body position; the position of the head; axillary temperature; pulse and respiration rates; blood pressure; and pulse oximetry.

Results:

In vitro difference between the initial pressure (IP) and measured pressure (MP) was statistically significant (P < 0.05). The difference between the IP and MP was significant when selecting for various tube brands (P < 0.05). In the clinical set-up, 207 measurements were performed and the CP was >30 cm H₂O in 6.28% of the recordings, 20-30 cm H₂O in 42.0% of the recordings, and <20 cm H₂O in 51.69% of the recordings.

Conclusion:

The systematic CP measurement in chronically tracheostomized, spontaneously breathing patients showed high variability, which was independent of tube brand, size, type, or time of placement. Consequently, measurements should be made more frequently.