Driving Pressure and Transpulmonary Pressure: How Do We Guide Safe Mechanical Ventilation?

Translational Role of Rodent Models to Study Ventilator-Induced Lung Injury

Mechanical ventilation is an important part of medical care in intensive care units and operating rooms to support respiration. While it is a critical component of medical care, it is well known that mechanical ventilation itself can be injurious to the lungs. Despite a large number of clinical and preclinical studies that have been done so far, there still exists a gap of knowledge regarding how to ventilate patients mechanically without increasing lung injury. Here, we will review what we have learned so far from preclinical and clinical studies and consider how to use preclinical models of ventilation-induced lung injury that better recapitulate the clinical scenarios.

Ventilatory Ratio Threshold for Unassisted Breathing: A Retrospective Exploratory Analysis

BACKGROUND

The ventilatory ratio (VR) is a simple index of ventilatory efficiency and dead space. Because increased dead space and high ventilatory demands impose a limitation to unassisted ventilation, and may predispose patients to injurious strong efforts during assisted ventilation, evaluation of the VR could provide helpful information during weaning. We hypothesize that there is a threshold of VR associated with tolerance of unassisted breathing.

METHODS

In a retrospective analysis, we included subjects ventilated in a control mode for at least 24 h, who were successfully liberated from mechanical ventilation, without use of noninvasive ventilation, and discharged alive from the ICU. We focused on the successful weaning attempts (the last, if more than one was performed) and evaluated the VR at the beginning and at the end of the assisted ventilation period.

RESULTS

We examined 2,000 medical records and included in our analysis 572 subjects (age: 68 y, R_5-95 = 25-85, 68% male) with main admission diagnosis of respiratory failure (23%), sepsis (11%), brain injury (34%), and postoperative (14%). The VR at the beginning and the end of the assisted ventilation period was 1.5 (R_5-95 = 1-2.1) and 1.4 (R_5-95 = 1-2), respectively. The median duration of assisted ventilation in subjects with a VR ≥ 2 at the beginning of the assisted ventilation period was 3 d (R_5-95 = 0-14 d), significantly longer than in those with a VR < 2, 0.5 d (R_5-95 = 0-8 d, P < .001).

CONCLUSIONS

Successful liberation from assisted ventilation was associated with a VR < 2. A VR > 2 was associated with longer duration of weaning. The VR could be used as an additional tool to facilitate the decision-making process during weaning.

Coronavirus Disease (COVID-19) compared with Middle East Respiratory Syndrome (MERS): A Radiological Perspective

BACKGROUND

This study aims to describe the radiological findings in chest radiographs (CXRs) of patients with coronavirus disease (COVID-19) and the Middle East respiratory syndrome (MERS) and compare the radiological patterns of the two diseases.

METHOD

A retrospective cohort study was conducted in a tertiary care hospital in the Southern region of Saudi Arabia. The CXRs were evaluated for the presence and distribution of ground-glass opacities (GGO), consolidation, pleural effusions, pneumothorax, cavitation, and nodules.

RESULTS

A total of 120 CXRs from 15 MERS and six COVID-19 patients were assessed. In the first available CXR, GGO was present in 11 (73%) of the MERS patients (18% located in the middle zones and 67% located peripherally) and in 100% of COVID-19 patients (peripheral and middle zone involvement in all patients). In the first available CXRs, consolidation was present in 10 MERS patients (67%) and all six COVID-19 patients, while it was present in all patients of both groups when all the available CXRs were considered. Confluent consolidation was present in 47% of the MERS patients and 50% of COVID-19 patients. All the fatal cases had confluent consolidation and radiological signs of acute respiratory distress syndrome (ARDS). Pneumothorax was present in 13% of patients, with 100% mortality, and pleural effusion was present in 47% of patients, with 57% mortality. Lung nodules were present in one patient of each group.

CONCLUSION

COVID-19 patients showed earlier development of GGO and consolidation with greater involvement of the middle and peripheral lung zones. Confluent consolidation and ARDS-like radiological findings were associated with high mortality. Pneumothorax and pleural effusions were more frequent in MERS patients, with high associated mortality.

Oesophageal balloon positioning by echocardiography to guide positive pressure ventilation

Understanding the respiratory mechanics of ARDS patients is crucial to avoid ventilator-induced lung injury (VILI), and this is much more challenging if not only lung compliance is altered but the whole compliance of the respiratory system is abnormal, as in obese patients. We face this problem daily in the ICU, and to optimize ventilation, we estimate respiratory mechanics using an oesophageal balloon. The balloon position is crucial to assess reliable values. In the present technical note, we describe the use of echocardiography to confirm the correct position of this instrument.

Management of Intraoperative Mechanical Ventilation to Prevent Postoperative Complications after General Anesthesia: A Narrative Review

Mechanical ventilation (MV) is still necessary in many surgical procedures; nonetheless, intraoperative MV is not free from harmful effects. Protective ventilation strategies, which include the combination of low tidal volume and adequate positive end expiratory pressure (PEEP) levels, are usually adopted to minimize the ventilation-induced lung injury and to avoid post-operative pulmonary complications (PPCs). Even so, volutrauma and atelectrauma may co-exist at different levels of tidal volume and PEEP, and therefore, the physiological response to the MV settings should be monitored in each patient. A personalized perioperative approach is gaining relevance in the field of intraoperative MV; in particular, many efforts have been made to individualize PEEP, giving more emphasis on physiological and functional status to the whole body. In this review, we summarized the latest findings about the optimization of PEEP and intraoperative MV in different surgical settings. Starting from a physiological point of view, we described how to approach the individualized MV and monitor the effects of MV on lung function.

The Association of Intraoperative driving pressure with postoperative pulmonary complications in open versus closed abdominal surgery patients - a posthoc propensity score-weighted cohort analysis of the LAS VEGAS study

BACKGROUND

It is uncertain whether the association of the intraoperative driving pressure (ΔP) with postoperative pulmonary complications (PPCs) depends on the surgical approach during abdominal surgery. Our primary objective was to determine and compare the association of time-weighted average ΔP (ΔP_TW) with PPCs. We also tested the association of ΔP_TW with intraoperative adverse events.

METHODS

Posthoc retrospective propensity score-weighted cohort analysis of patients undergoing open or closed abdominal surgery in the 'Local ASsessment of Ventilatory management during General Anaesthesia for Surgery' (LAS VEGAS) study, that included patients in 146 hospitals across 29 countries. The primary endpoint was a composite of PPCs. The secondary endpoint was a composite of intraoperative adverse events.

RESULTS

The analysis included 1128 and 906 patients undergoing open or closed abdominal surgery, respectively. The PPC rate was 5%. ΔP was lower in open abdominal surgery patients, but ΔP_TW was not different between groups. The association of ΔP_TW with PPCs was significant in both groups and had a higher risk ratio in closed compared to open abdominal surgery patients (1.11 [95%CI 1.10 to 1.20], P <  0.001 versus 1.05 [95%CI 1.05 to 1.05], P <  0.001; risk difference 0.05 [95%CI 0.04 to 0.06], P <  0.001). The association of ΔP_TW with intraoperative adverse events was also significant in both groups but had higher odds ratio in closed compared to open abdominal surgery patients (1.13 [95%CI 1.12- to 1.14], P <  0.001 versus 1.07 [95%CI 1.05 to 1.10], P <  0.001; risk difference 0.05 [95%CI 0.030.07], P <  0.001).

CONCLUSIONS

ΔP is associated with PPC and intraoperative adverse events in abdominal surgery, both in open and closed abdominal surgery.

TRIAL REGISTRATION

LAS VEGAS was registered at clinicaltrials.gov (trial identifier NCT01601223 ).

Advances in airway management and mechanical ventilation in inhalation injury

PURPOSE OF REVIEW

Airway management, mechanical ventilation, and treatment of systemic poisoning in burn patients with inhalation injury remains challenging. This review summarizes new concepts as well as open questions.

RECENT FINDINGS

Several life-threatening complications, such as airway patency impairment and respiratory insufficiency, can arise in burn patients and require adequate and timely airway management. However, unnecessary endotracheal intubation should be avoided. Direct visual inspection via nasolaryngoscopy can guide appropriate airway management decisions. In cases of lower airway injury, bronchoscopy is recommended to remove casts and estimate the extent of the injury in intubated patients. Several mechanical ventilation strategies have been studied. An interesting modality might be high-frequency percussive ventilation. However, to date, there is no sound evidence that patients with inhalation injury should be ventilated with modes other than those applied to non-burn patients. In all burn patients exposed to enclosed fire, carbon monoxide as well as cyanide poisoning should be suspected. Carbon monoxide poisoning should be treated with an inspiratory oxygen fraction of 100%, whereas cyanide poisoning should be treated with hydroxocobalamin.

SUMMARY

Burn patients need specialized care that requires specific knowledge about airway management, mechanical ventilation, and carbon monoxide and cyanide poisoning.

The Association Between the Mechanical Ventilator Pressures and Outcomes in a Cohort of Patients with Acute Respiratory Failure

Background

Pressures measured during mechanical ventilation provide important information about the respiratory system mechanics and can help predict outcomes.

Methods

The electronic medical records of patients hospitalized between 2010 and 2016 with sepsis who required mechanical ventilation were reviewed to collect demographic information, clinical information, management requirements, and outcomes, such as mortality, ICU length of stay, and hospital length of stay. Mechanical ventilation pressures were recorded on the second full day of hospitalization.

Results

This study included 312 adult patients. The mean age is 59.1 ± 16.3 years; 57.4% were men. The mean BMI was 29.3 ± 10.7. Some patients had pulmonary infections (46.2%), and some patients had extrapulmonary infections (34.9%). The overall mortality was 42.6%. In a multi-variable model that included age, gender, number of comorbidities, APACHE 2 score, and PaO₂/FiO₂ ratio, peak pressure, plateau pressure, driving pressure, and PEEP all predicted mortality when entered into the model separately. There was an increase in peak pressure, plateau pressure, and driving pressure across BMI categories ranging from underweight to obese.

Conclusions

This study demonstrates that ventilator pressure measurements made early during the management of patients with acute respiratory failure requiring mechanical ventilation provide prognostic information regarding outcomes, including mortality. Patients with high mechanical ventilator pressures during the early course of their acute respiratory failure require more attention to identify reversible disease processes when possible. In addition, increased BMIs are associated with increased ventilator pressures, and this increases the complexity of the clinical evaluation in the management of obese patients.

Individualized PEEP to optimise respiratory mechanics during abdominal surgery: a pilot randomised controlled trial

BACKGROUND

Higher intraoperative driving pressures (ΔP) are associated with increased postoperative pulmonary complications (PPC). We hypothesised that dynamic adjustment of PEEP throughout abdominal surgery reduces ΔP, maintains positive end-expiratory transpulmonary pressures (P_{tp_ee}) and increases respiratory system static compliance (C_rs) with PEEP levels that are variable between and within patients.

METHODS

In a prospective multicentre pilot study, adults at moderate/high risk for PPC undergoing elective abdominal surgery were randomised to one of three ventilation protocols: (1) PEEP≤2 cm H₂O, compared with periodic recruitment manoeuvres followed by individualised PEEP to either optimise respiratory system compliance (PEEP_maxCrs) or maintain positive end-expiratory transpulmonary pressure (PEEP_{Ptp_ee}). The composite primary outcome included intraoperative ΔP, P_{tp_ee}, C_rs, and PEEP values (median (interquartile range) and coefficients of variation [CV_PEEP]).

RESULTS

Thirty-seven patients (48.6% female; age range: 47-73 yr) were assigned to control (PEEP≤2 cm H₂O; n=13), PEEP_maxCrs (n=16), or PEEP_{Ptp_ee} (n=8) groups. The PEEP_{Ptp_ee} intervention could not be delivered in two patients. Subjects assigned to PEEP_maxCrs had lower ΔP (median8 cm H₂O [7-10]), compared with the control group (12 cm H₂O [10-15]; P=0.006). PEEP_maxCrs was also associated with higher P_{tp_ee} (2.0 cm H₂O [-0.7 to 4.5] vs controls: -8.3 cm H₂O [-13.0 to -4.0]; P≤0.001) and higher C_rs (47.7 ml cm H₂O [43.2-68.8] vs controls: 39.0 ml cm H₂O [32.9-43.4]; P=0.009). Individualised PEEP (PEEP_maxCrs and PEEP_{Ptp_ee} combined) varied widely (median: 10 cm H₂O [8-15]; CV_PEEP=0.24 [0.14-0.35]), both between, and within, subjects throughout surgery.

CONCLUSIONS

This pilot study suggests that individualised PEEP management strategies applied during abdominal surgery reduce driving pressure, maintain positive P_{tp_ee} and increase static compliance. The wide range of PEEP observed suggests that an individualised approach is required to optimise respiratory mechanics during abdominal surgery.

CLINICAL TRIAL REGISTRATION

NCT02671721.

Intraoperative Anesthetic Management of Patients with Chronic Obstructive Pulmonary Disease to Decrease the Risk of Postoperative Pulmonary Complications after Abdominal Surgery

Patients with chronic obstructive pulmonary disease (COPD) exhibit airflow limitation and suboptimal lung function, and they are at high risk of developing postoperative pulmonary complications (PPCs). We aimed to determine the factors that would decrease PPC risk in patients with COPD. We retrospectively analyzed 419 patients with COPD who were registered in our institutional PPC database and had undergone an abdominal surgery under general anesthesia. PPCs comprised respiratory failure, pleural effusion, atelectasis, respiratory infection, and bronchospasm; the presence or type of PPC was diagnosed by respiratory physicians and recorded in the database before this study. Binary logistic regression was used for statistical analysis. Of the 419 patients, 121 patients (28.8%) experienced 200 PPCs. Multivariable analysis showed three modifiable anesthetic factors that could decrease PPC risk: low tidal volume ventilation, restricted fluid infusion, and sugammadex-induced neuromuscular blockade reversal. We found that the 90-day mortality risk was significantly greater in patients with PPC than in those without PPC (5.8% vs. 1.3%; p = 0.016). Therefore, PPC risk in patients with COPD can be decreased if low tidal volume ventilation, restricted fluid infusion, and sugammadex-induced reversal during abdominal surgery are efficiently managed, as these factors result in decreased postoperative mortality.