Ventilation in patients with intra-abdominal hypertension: what every critical care physician needs to know

Transpulmonary pressure monitoring in critically ill patients: pros and cons

The use of transpulmonary pressure monitoring based on measurement of esophageal pressure has contributed importantly to the personalization of mechanical ventilation based on respiratory pathophysiology in critically ill patients. However, esophageal pressure monitoring is still underused in the clinical practice. This technique allows partitioning of the respiratory mechanics between the lungs and the chest wall, provides information on lung recruitment and risk of barotrauma, and helps titrating mechanical ventilation settings in patients with respiratory failure. In assisted ventilation modes and during non-invasive respiratory support, esophageal pressure monitoring provides important information on the inspiratory effort and work of breathing. Nonetheless, several controversies persist on technical aspects, interpretation and clinical decision-making based on values derived from this monitoring technique. The aim of this review is to summarize the physiological bases of esophageal pressure monitoring, discussing the pros and cons of its clinical applications and different interpretations in critically ill patients undergoing invasive and non-invasive respiratory support.

Individualized positive end-expiratory pressure reduces driving pressure in obese patients during laparoscopic surgery under pneumoperitoneum: a randomized clinical trial

Introduction

During pneumoperitoneum (PNP), airway driving pressure (ΔPRS) increases due to the stiffness of the chest wall and cephalic shift of the diaphragm, which favors atelectasis. In addition, depending on the mechanical power (MP) formulas, they may lead to different interpretations.

Methods

Patients >18 years of age with body mass index >35 kg/m2 were included in a single-center randomized controlled trial during their admission for bariatric surgery by abdominal laparoscopy. Intra-abdominal pressure was set at 15 mmHg at the pneumoperitoneum time point (PNP). After the recruitment maneuver, the lowest respiratory system elastance (ERS) was detected during the positive end-expiratory pressure (PEEP) step-wise decrement. Patients were randomized to the 1) CTRL group: ventilated with PEEP of 5 cmH2O and 2) PEEPIND group: ventilated with PEEP value associated with ERS that is 5% higher than its lowest level. Respiratory system mechanics and mean arterial pressure (MAP) were assessed at the PNP, 5 min after randomization (T1), and at the end of the ventilation protocol (T2); arterial blood gas was assessed at PNP and T2. ΔPRS was the primary outcome. Three MP formulas were used: MPA, which computes static PEEP × volume, elastic, and resistive components; MPB, which computes only the elastic component; and MPC, which computes static PEEP × volume, elastic, and resistive components without inspiratory holds.

Results

Twenty-eight patients were assessed for eligibility: eight were not included and 20 patients were randomized and allocated to CTRL and PEEPIND groups (n = 10/group). The PEEPIND ventilator strategy reduced ΔPRS when compared with the CTRL group (PEEPIND, 13 ± 2 cmH2O; CTRL, 22 ± 4 cmH2O; p < 0.001). Oxygenation improved in the PEEPIND group when compared with the CTRL group (p = 0.029), whereas MAP was comparable between the PEEPIND and CTRL groups. At the end of surgery, MPA and MPB were correlated in both the CTRL (rho = 0.71, p = 0.019) and PEEPIND (rho = 0.84, p = 0.020) groups but showed different bias (CTRL, -1.9 J/min; PEEPIND, +10.0 J/min). At the end of the surgery, MPA and MPC were correlated in both the CTRL (rho = 0.71, p = 0.019) and PEEPIND (rho = 0.84, p = 0.020) groups but showed different bias (CTRL, -1.9 J/min; PEEPIND, +10.0 J/min).

Conclusion

Individualized PEEP was associated with a reduction in ΔPRS and an improvement in oxygenation with comparable MAP. The MP, which solely computes the elastic component, better reflected the improvement in ΔPRS observed in the individualized PEEP group.

Clinical Trial Registration

The protocol was registered at the Brazilian Registry of Clinical Trials (U1111-1220-7296).

Designing a bi-layer multifunctional hydrogel patch based on polyvinyl alcohol, quaternized chitosan and gallic acid for abdominal wall defect repair

In abdominal wall defect repair, surgical site infection (SSI) remains the primary cause of failure, while complications like visceral adhesions present significant challenges following patch implantation. We designed a Janus multifunctional hydrogel patch (JMP) with antibacterial, anti-inflammatory, and anti-adhesive properties. The patch comprises two distinct layers: a pro-healing layer and an anti-adhesion layer. The pro-healing layer was created by a simple mixture of polyvinyl alcohol (PVA), quaternized chitosan (QCS), and gallic acid (GA), crosslinked to form PVA/QCS/GA (PQG) hydrogels through GA's self-assembly effect and hydrogen bonding. Additionally, the PVA anti-adhesive layer was constructed using a drying-assisted salting method, providing a smooth and dense physical barrier to prevent visceral adhesion while offering essential mechanical support to the abdominal wall. The hydrogel patch demonstrates widely adjustable mechanical properties, exceptional biocompatibility, and potent antimicrobial properties, along with a sustained and stable release of antioxidants. In rat models of skin and abdominal wall defects, the JMP effectively promoted tissue healing by controlling infection, inhibiting inflammation, stimulating neovascularization, and successfully preventing the formation of visceral adhesions. These compelling results highlight the JMP's potential to improve the success rate of abdominal wall defect repair and reduce surgical complications.

Individualised flow-controlled ventilation reduces applied mechanical power and improves ventilation efficiency in a porcine intra-abdominal hypertension model

BACKGROUND

Aim of this study was to evaluate feasibility and effects of individualised flow-controlled ventilation (FCV), based on compliance guided pressure settings, compared to standard of pressure-controlled ventilation (PCV) in a porcine intra-abdominal hypertension (IAH) model. The primary aim of this study was to investigate oxygenation. Secondary aims were to assess respiratory and metabolic variables and lung tissue aeration.

METHODS

Pigs were randomly assigned to FCV (n = 9) and PCV (n = 9). IAH was induced by insufflation of air into the abdomen to induce IAH grades ranging from 0 to 3. At each IAH grade FCV was undertaken using compliance guided pressure settings, or PCV (n = 9) was undertaken with the positive end-expiratory pressure titrated for maximum compliance and the peak pressure set to achieve a tidal volume of 7 ml/kg. Gas exchange, ventilator settings and derived formulas were recorded at two timepoints for each grade of IAH. Lung aeration was assessed by a computed tomography scan at IAH grade 3.

RESULTS

All 18 pigs (median weight 54 kg [IQR 51-67]) completed the observation period of 4 h. Oxygenation was comparable at each IAH grade, but a significantly lower minute volume was required to secure normocapnia in FCV at all IAH grades (7.6 vs. 14.4, MD - 6.8 (95% CI - 8.5 to - 5.2) l/min; p < 0.001). There was also a significant reduction of applied mechanical power being most evident at IAH grade 3 (25.9 vs. 57.6, MD - 31.7 (95% CI - 39.7 to - 23.7) J/min; p < 0.001). Analysis of Hounsfield unit distribution of the computed tomography scans revealed a significant reduction in non- (5 vs. 8, MD - 3 (95% CI - 6 to 0) %; p = 0.032) and poorly-aerated lung tissue (7 vs. 15, MD - 6 (95% CI - 13 to - 3) %, p = 0.002) for FCV. Concomitantly, normally-aerated lung tissue was significantly increased (84 vs. 76, MD 8 (95% CI 2 to 15) %; p = 0.011).

CONCLUSIONS

Individualised FCV showed similar oxygenation but required a significantly lower minute volume for CO2-removal, which led to a remarkable reduction of applied mechanical power. Additionally, there was a shift from non- and poorly-aerated lung tissue to normally-aerated lung tissue in FCV compared to PCV.

Management of Neuromuscular Blocking Agents in Critically Ill Patients with Lung Diseases

The use of neuromuscular blocking agents (NMBAs) is common in the intensive care unit (ICU). NMBAs have been used in critically ill patients with lung diseases to optimize mechanical ventilation, prevent spontaneous respiratory efforts, reduce the work of breathing and oxygen consumption, and avoid patient-ventilator asynchrony. In patients with acute respiratory distress syndrome (ARDS), NMBAs reduce the risk of barotrauma and improve oxygenation. Nevertheless, current guidelines and evidence are contrasting regarding the routine use of NMBAs. In status asthmaticus and acute exacerbation of chronic obstructive pulmonary disease, NMBAs are used in specific conditions to ameliorate patient-ventilator synchronism and oxygenation, although their routine use is controversial. Indeed, the use of NMBAs has decreased over the last decade due to potential adverse effects, such as immobilization, venous thrombosis, patient awareness during paralysis, development of critical illness myopathy, autonomic interactions, ICU-acquired weakness, and residual paralysis after cessation of NMBAs use. The aim of this review is to highlight current knowledge and synthesize the evidence for the effects of NMBAs for critically ill patients with lung diseases, focusing on patient-ventilator asynchrony, ARDS, status asthmaticus, and chronic obstructive pulmonary disease.

Impact of a positive end-expiratory pressure strategy on oxygenation, respiratory compliance, and hemodynamics during laparoscopic surgery in non-obese patients: a systematic review and meta-analysis of randomized controlled trials

BACKGROUND

Higher positive end-expiratory pressure (PEEP) during laparoscopic surgery may increase oxygenation and respiratory compliance. This meta-analysis aimed to compare the impact of different intraoperative PEEP strategies on arterial oxygenation, compliance, and hemodynamics during laparoscopic surgery in non-obese patients.

METHODS

We searched RCTs in PubMed, Cochrane Library, Web of Science, and Google Scholar from January 2012 to April 2022 comparing the different intraoperative PEEP (Low PEEP (LPEEP): 0-4 mbar; Moderate PEEP (MPEEP): 5-8 mbar; high PEEP (HPEEP): >8 mbar; individualized PEEP - iPEEP) on arterial oxygenation, respiratory compliance (Cdyn), mean arterial pressure (MAP), and heart rate (HR). We calculated mean differences (MD) with 95% confidence intervals (CI), and predictive intervals (PI) using random-effects models. The Cochrane Bias Risk Assessment Tool was applied.

RESULTS

21 RCTs (n = 1554) met the inclusion criteria. HPEEP vs. LPEEP increased PaO2 (+ 29.38 [16.20; 42.56] mmHg, p < 0.0001) or PaO2/FiO2 (+ 36.7 [+ 2.23; +71.70] mmHg, p = 0.04). HPEEP vs. MPEEP increased PaO2 (+ 22.00 [+ 1.11; +42.88] mmHg, p = 0.04) or PaO2/FiO2 (+ 42.7 [+ 2.74; +82.67] mmHg, p = 0.04). iPEEP vs. MPEEP increased PaO2/FiO2 (+ 115.2 [+ 87.21; +143.20] mmHg, p < 0.001). MPEEP vs. LPEP, and HPEEP vs. MPEEP increased PaO2 or PaO2/FiO2 significantly with different heterogeneity. HPEEP vs. LPEEP increased Cdyn (+ 7.87 [+ 1.49; +14.25] ml/mbar, p = 0.02). MPEEP vs. LPEEP, and HPEEP vs. MPEEP did not impact Cdyn (p = 0.14 and 0.38, respectively). iPEEP vs. LPEEP decreased driving pressure (-4.13 [-2.63; -5.63] mbar, p < 0.001). No significant differences in MAP or HR were found between any subgroups.

CONCLUSION

HPEEP and iPEEP during PNP in non-obese patients could promote oxygenation and increase Cdyn without clinically significant changes in MAP and HR. MPEEP could be insufficient to increase respiratory compliance and improve oxygenation. LPEEP may lead to decreased respiratory compliance and worsened oxygenation.

PROSPERO REGISTRATION

CRD42022362379; registered October 09, 2022.

Abdominal compartment syndrome in critically ill patients

Intra-abdominal hypertension can have severe consequences, including abdominal compartment syndrome, which can contribute to multi-organ failure. An increase in intra-abdominal hypertension is influenced by factors such as diminished abdominal wall compliance, increased intraluminal content, and certain systemic conditions. Regular measurement of intra-abdominal pressure is essential, and particular attention must be paid to patient positioning. Nonsurgical treatments, such as decompression of intraluminal content using a nasogastric tube, percutaneous drainage, and fluid balance optimization, play crucial roles. Additionally, point-of-care ultrasonography aids in the diagnosis and treatment of intra-abdominal hypertension. Emphasizing the importance of regular measurements, timely decompressive laparotomy is a definitive, but complex, treatment option. Balancing the urgency of surgical intervention against potential postoperative complications is challenging.

Effects of changes in trunk inclination on ventilatory efficiency in ARDS patients: quasi-experimental study

BACKGROUND

Trunk inclination from semirecumbent head-upright to supine-flat positioning reduces driving pressure and increases respiratory system compliance in patients with acute respiratory distress syndrome (ARDS). These effects are associated with an improved ventilatory ratio and reduction in the partial pressure of carbon dioxide (PaCO2). However, these physiological effects have not been completely studied, and their mechanisms have not yet been elucidated. Therefore, this study aimed to evaluate the effects of a change in trunk inclination from semirecumbent (45°) to supine-flat (10°) on physiological dead space and ventilation distribution in different lung regions.

RESULTS

Twenty-two ARDS patients on pressure-controlled ventilation underwent three 60-min steps in which trunk inclination was changed from 45° (baseline) to 10° (intervention) and back to 45° (control) in the last step. Tunk inclination from a semirecumbent (45°) to a supine-flat (10°) position resulted in a higher tidal volume [371 (± 76) vs. 433 (± 84) mL (P < 0.001)] and respiratory system compliance [34 (± 10) to 41 (± 12) mL/cmH2O (P < 0.001)]. The CO2 exhaled per minute improved from 191 mL/min (± 34) to 227 mL/min (± 38) (P < 0.001). Accordingly, Bohr's dead space ratio decreased from 0.49 (± 0.07) to 0.41 (± 0.06) (p < 0.001), and PaCO2 decreased from 43 (± 5) to 36 (± 4) mmHg (p < 0.001). In addition, the impedance ratio, which divides the ventilation activity of the ventral region by the dorsal region ventilation activity in tidal images, dropped from 1.27 (0.83-1.78) to 0.86 (0.51-1.33) (p < 0.001). These results, calculated from functional EIT images, indicated further ventilation activity in the dorsal lung regions. These effects rapidly reversed once the patient was repositioned at 45°.

CONCLUSIONS

A change in trunk inclination from a semirecumbent (45 degrees) to a supine-flat position (10 degrees) improved Bohr's dead space ratio and reduced PaCO2 in patients with ARDS. This effect is associated with an increase in tidal volume and respiratory system compliance, along with further favourable impedance ventilation distribution toward the dorsal lung regions. This study highlights the importance of considering trunk inclination as a modifiable determinant of physiological parameters. The angle of trunk inclination is essential information that must be reported in ARDS patients.

Sánchez-Margallo F, Eugenia Candanosa-Aranda I, Poelaert J, Castellanos G, L. N. G. Malbrain M. The pathophysiological impact of intra-abdominal hypertension in pigs

BACKGROUND

Intra-abdominal hypertension and abdominal compartment syndrome are common with clinically significant consequences. We investigated the pathophysiological effects of raised IAP as part of a more extensive exploratory animal study. The study design included both pneumoperitoneum and mechanical intestinal obstruction models.

METHODS

Forty-nine female swine were divided into six groups: a control group (Cr; n = 5), three pneumoperitoneum groups with IAPs of 20mmHg (Pn20; n = 10), 30mmHg (Pn30; n = 10), 40mmHg (Pn40; n = 10), and two mechanical intestinal occlusion groups with IAPs of 20mmHg (MIO20; n = 9) and 30mmHg (MIO30; n = 5).

RESULTS

There were significant changes (p<0.05) noted in all organ systems, most notably systolic blood pressure (SBP) (p<0.001), cardiac index (CI) (p = 0.003), stroke volume index (SVI) (p<0.001), mean pulmonary airway pressure (MPP) (p<0.001), compliance (p<0.001), pO2 (p = 0.003), bicarbonate (p = 0.041), hemoglobin (p = 0.012), lipase (p = 0.041), total bilirubin (p = 0.041), gastric pH (p<0.001), calculated glomerular filtration rate (GFR) (p<0.001), and urine output (p<0.001). SVV increased progressively as the IAP increased with no obvious changes in intravascular volume status. There were no significant differences between the models regarding their impact on cardiovascular, respiratory, renal and gastrointestinal systems. However, significant differences were noted between the two models at 30mmHg, with MIO30 showing worse metabolic and hematological parameters, and Pn30 and Pn40 showing a more rapid rise in creatinine.

CONCLUSIONS

This study identified and quantified the impact of intra-abdominal hypertension at different pressures on several organ systems and highlighted the significance of even short-lived elevations. Two models of intra-abdominal pressure were used, with a mechanical obstruction model showing more rapid changes in metabolic and haematological changes. These may represent different underlying cellular and vascular pathophysiological processes, but this remains unclear.

Intra-abdominal hypertension and abdominal compartment syndrome in acute pancreatitis

Intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) are underrecognized entities in patients of acute pancreatitis (AP). IAH develops in 30% to 60% and ACS in 15% to 30% of all AP patients and they are markers of severe disease with high morbidity and mortality. The detrimental effect of increased IAP has been recognized in several organ systems, including the central nervous system, cardiovascular, respiratory, renal and gastrointestinal systems. The pathophysiology of IAH/ACS development in patients with AP is multifactorial. Pathogenetic mechanisms include over-zealous fluid management, visceral edema, ileus, peripancreatic fluid collections, ascites and retroperitoneal edema. Laboratory and imaging markers are neither sensitive nor specific enough to detect IAH/ACS and intra-abdominal pressure (IAP) monitoring is vital for early diagnosis and the management of patients of AP with IAH/ACS. The treatment of IAH/ACS requires a multi-modality approach with both medical and surgical attention. Medical management consists of nasogastric/rectal decompression, prokinetics, fluid management and diuretics or hemodialysis. If conservative management is not effective, percutaneous drainage of fluid collection or ascites is necessary. Despite medical management, if IAP worsens, surgical decompression is warranted. The review discusses the relevance of IAH/ACS in patients of AP and its management.

The First 24 Hours: Burn Shock Resuscitation and Early Complications

Resuscitation is required for the management of patients with severe thermal injury. Some of the initial pathophysiologic events following burn injury include an exaggerated inflammatory state, injury to the endothelium, and increased capillary permeability, which all culminate in shock. Understanding these processes is critical to the effective management of patients with burn injuries. Formulas predicting fluid requirements during burn resuscitation have evolved over the past century in response to clinical experience and research efforts. Modern resuscitation features individualized fluid titration and monitoring along with colloid-based adjuncts. Despite these developments, complications from over-resuscitation still occur.

The spine intra-abdominal pressure (SIAP) trial. A prospective, observational, single arm, monocenter study looking at the evolutions of the IAP prior, during and after spine surgery

BACKGROUND AND AIMS

Both anaesthesiologists and spine surgeons consider the intra-abdominal pressure (IAP) as an important peri-operative factor affected by patient positioning. We assessed the change in IAP caused by using a thoraco pelvic support (inflatable prone support, IPS) with the subject under general anesthesia. The IAP was measured before, during and immediately after surgery.

METHODS

The Spine Intra-Abdominal Pressure study (SIAP trial) is a prospective, single-arm, monocenter, observational study looking at changes in IAP prior, during and after spine surgery. The objective is to assess the change in IAP, measured via an indwelling urinary catheter, using the inflatable prone support (IPS) device during prone positioning of patients in spinal surgery.

RESULTS

Forty (40) subjects requiring elective lumbar spine surgery in prone position were enrolled after providing informed consent. The inflation of the IPS results in a significant decrease of IAP (from a median of 9.2 mmHg to 6.46 mmHg (p < 0.001)) in patients undergoing spine surgery in prone position. This decrease in IAP was maintained throughout the procedure despite the discontinuation of muscle relaxants. No serious adverse events or unexpected adverse events occurred.

CONCLUSION

The use of the thoraco-pelvic support IPS device was able to significantly lower the IAP during spine surgery.

Modified Chevrel technique for abdominal closure in critically ill patients with abdominal hypertension and limited options for closure

Abdominal compartment syndrome is a potentially life-threatening condition seen in critically ill patients, and most often caused by acute pancreatitis, postoperative abdominal vascular thrombosis or mesenteric ischemia. A decompressive laparotomy is sometimes required, often resulting in hernias, and subsequent definitive wall closure is challenging.

AIM

This study aims to describe short term results after a modified Chevrel technique for midline laparotomies in patients witch abdominal hypertension.

MATERIALS AND METHODS

We performed a modified Chevrel as an abdominal closure technique in 9 patients between January 2016 and January 2022. All patients presented varying degrees of abdominal hypertension.

RESULTS

Nine patients were treated with new technique (6 male and 3 female), all of whom had conditions that precluded unfolding the contralateral side as a means for closure. The reasons for this were diverse, including presence of ileostomies, intraabdominal drainages, Kher tubes or an inverted T scar from previous transplant. The use of mesh was initially dismissed in 8 of the patients (88,9%) because they required subsequent abdominal surgeries or active infection. None of the patients developed a hernia, although two died 6 months after the procedure. Only one patient developed bulging. A decrease in intrabdominal pressure was achieved in all patients.

CONCLUSION

The modified Chevrel technique can be used as a closure option for midline laparotomies in cases where the entire abdominal wall cannot be used.

Prevalence and Risk Factors of Enteral Feeding Intolerance in Critically Ill Patients and the Effectiveness of Preventive Treatments: A Prospective Study

Background

Feeding intolerance (FI) is a prevalent cause of enteral nutrition (EN) disruption. Factors that can prevent FI are poorly described.

Objectives

To determine the prevalence and risk factors associated with FI in critically ill patients and the effectiveness of preventive treatments.

Patients and Methods

This prospective observational study included critically ill patients admitted to the ICU of a general hospital who received EN through a nasogastric or nasointestinal tube from March 2020 to October 2021. Independent sample t-test, repeated measurement analysis of variance, and multivariate analysis were used to explore independent risk factors and the efficacy of preventive treatments.

Results

The study included 200 critically ill patients (mean age: 59.1 ± 17.8 years), of whom 131 were male. Most patients (58.50%) developed FI after a median EN duration of 2 days. The independent risk factors for FI were fasting for >3 days, high APACHE II score, and acute gastrointestinal injury (AGI) grade I before EN (P < 0.05). During EN, whole protein was found to be an independent preventive treatment that significantly decreased FI (P < 0.05), while before EN, early use of enema and gastric motility drugs in patients with abdominal distention/constipation significantly decreased FI (for both, P < 0.05). The preventive treatment group had significantly higher intake of the nutrient solution and significantly shorter invasive mechanical ventilation duration than the without preventive treatment group (for both, P < 0.05).

Conclusion

In ICU patients receiving nasogastric or nasointestinal tube feeding, FI was frequent, occurred early, and was more frequent in patients with fasting >3 days, a high APACHE II score, and an AGI grade before EN. Preventive treatments can reduce FI prevalence and result in patients consuming more nutrient solutions and having shorter invasive mechanical ventilation duration.

Chinese Clinical Trial Registry Registration no

ChiCTR-DOD-16008532.

Acute liver injury in COVID-19 patients hospitalized in the intensive care unit: Narrative review

In recent years, humanity has been confronted with a global pandemic due to coronavirus disease 2019 (COVID-19), which has caused an unprecedented health and economic crisis worldwide. Apart from the respiratory symptoms, which are considered the principal manifestations of COVID-19, it has been recognized that COVID-19 constitutes a systemic inflammatory process affecting multiple organ systems. Across the spectrum of organ involvement in COVID-19, acute liver injury (ALI) has been gradually gaining increasing attention by the international scientific community. COVID-19 associated liver impairment can affect a considerable proportion of COVID-19 patients and seems to correlate with the severity of the disease course. Indeed, COVID-19 patients hospitalized in the intensive care unit (ICU) run a greater risk of developing ALI due to the severity of their clinical condition and in the context of multi-organ failure. The putative pathophysiological mechanisms of COVID-19 induced ALI in ICU patients remain poorly understood and appear to be multifactorial in nature. Several theories have been proposed to explain the occurrence of ALI in the ICU setting, such as hypoperfusion and ischemia due to hemodynamic instability, passive liver congestion as a result of congestive heart failure, ischemia-reperfusion injury, hypoxia due to respiratory failure, mechanical ventilation itself, sepsis and septic shock, cytokine storm, endotheliitis with concomitant coagulopathy, drug-induced liver injury, parenteral nutrition and direct cytopathic viral effect. It should be noted that no specific therapy for COVID-19 induced ALI exists. Therefore, the therapeutic approach lies in preventive measures and is exclusively supportive once ALI ensues. The aim of the current review is to scrutinize the existing evidence on COVID-19 associated ALI in ICU patients, explore its clinical implications, shed light on the underlying pathophysiological mechanisms and propose potential therapeutic approaches. Ongoing research on the particular scientific field will further elucidate the pathophysiology behind ALI and address unresolved issues, in the hope of mitigating the tremendous health consequences imposed by COVID-19 on ICU patients.

Ten rules for optimizing ventilatory settings and targets in post-cardiac arrest patients

Cardiac arrest (CA) is a major cause of morbidity and mortality frequently associated with neurological and systemic involvement. Supportive therapeutic strategies such as mechanical ventilation, hemodynamic settings, and temperature management have been implemented in the last decade in post-CA patients, aiming at protecting both the brain and the lungs and preventing systemic complications. A lung-protective ventilator strategy is currently the standard of care among critically ill patients since it demonstrated beneficial effects on mortality, ventilator-free days, and other clinical outcomes. The role of protective and personalized mechanical ventilation setting in patients without acute respiratory distress syndrome and after CA is becoming more evident. The individual effect of different parameters of lung-protective ventilation, including mechanical power as well as the optimal oxygen and carbon dioxide targets, on clinical outcomes is a matter of debate in post-CA patients. The management of hemodynamics and temperature in post-CA patients represents critical steps for obtaining clinical improvement. The aim of this review is to summarize and discuss current evidence on how to optimize mechanical ventilation in post-CA patients. We will provide ten tips and key insights to apply a lung-protective ventilator strategy in post-CA patients, considering the interplay between the lungs and other systems and organs, including the brain.

Prolonged prone position in pregnant woman with COVID-19 pneumonia

The manuscript describes a case report of 2 prolonged prone position cycles (72 h each) of a coronavirus disease 2019 pneumonia in an intubated pregnant woman (at 22 weeks of gestational age), being successfully discharged from intensive care unit after 20 days. There were no signs of fetal sufferance at daily obstetric monitoring during prone position, and the fetus was born fully vital and without consequences.

At our knowledge, this is the first case of prolonged prone position in a pregnant woman, and we feel that our manuscript could be a valuable contribution to the literature and help intensivists in providing intensive care in these patients, confirming that prone position seems to be a valid therapeutic choice, limiting maternal and fetal hypoxia, and reducing their morbidity, even if the oculate risk/benefit should be performed. Further studies are however necessary to increase the knowledge and the good management of COVID-19 in pregnancy.

Chest wall loading in the ICU: pushes, weights, and positions

Clinicians monitor mechanical ventilatory support using airway pressures—primarily the plateau and driving pressure, which are considered by many to determine the safety of the applied tidal volume. These airway pressures are influenced not only by the ventilator prescription, but also by the mechanical properties of the respiratory system, which consists of the series-coupled lung and chest wall. Actively limiting chest wall expansion through external compression of the rib cage or abdomen is seldom performed in the ICU. Recent literature describing the respiratory mechanics of patients with late-stage, unresolving, ARDS, however, has raised awareness of the potential diagnostic (and perhaps therapeutic) value of this unfamiliar and somewhat counterintuitive practice. In these patients, interventions that reduce resting lung volume, such as loading the chest wall through application of external weights or manual pressure, or placing the torso in a more horizontal position, have unexpectedly improved tidal compliance of the lung and integrated respiratory system by reducing previously undetected end-tidal hyperinflation. In this interpretive review, we first describe underappreciated lung and chest wall interactions that are clinically relevant to both normal individuals and to the acutely ill who receive ventilatory support. We then apply these physiologic principles, in addition to published clinical observation, to illustrate the utility of chest wall modification for the purposes of detecting end-tidal hyperinflation in everyday practice.

Capillary leak syndrome: A rare cause of acute respiratory distress syndrome

Capillary leak syndrome (CLS) is a rare clinical syndrome associated with significant morbidity and mortality. Intensive care and supportive therapy constitute the mainstay of the treatment, along with judicious use of crystalloids and colloids such as dextran and starch during the leak phase. The advantages of proning, steroids, and intravenous immunoglobins are worth contemplating in patients with such a presentation. Extracorporeal membrane oxygenation appears to be an excellent strategy to surmount the impediments of the leak and post leak phase of CLS, especially in patients with severe or refractory hypoxemia.

Physiological and Pathophysiological Consequences of Mechanical Ventilation

Mechanical ventilation is a life-support system used to ensure blood gas exchange and to assist the respiratory muscles in ventilating the lung during the acute phase of lung disease or following surgery. Positive-pressure mechanical ventilation differs considerably from normal physiologic breathing. This may lead to several negative physiological consequences, both on the lungs and on peripheral organs. First, hemodynamic changes can affect cardiovascular performance, cerebral perfusion pressure (CPP), and drainage of renal veins. Second, the negative effect of mechanical ventilation (compression stress) on the alveolar-capillary membrane and extracellular matrix may cause local and systemic inflammation, promoting lung and peripheral-organ injury. Third, intra-abdominal hypertension may further impair lung and peripheral-organ function during controlled and assisted ventilation. Mechanical ventilation should be optimized and personalized in each patient according to individual clinical needs. Multiple parameters must be adjusted appropriately to minimize ventilator-induced lung injury (VILI), including: inspiratory stress (the respiratory system inspiratory plateau pressure); dynamic strain (the ratio between tidal volume and the end-expiratory lung volume, or inspiratory capacity); static strain (the end-expiratory lung volume determined by positive end-expiratory pressure [PEEP]); driving pressure (the difference between the respiratory system inspiratory plateau pressure and PEEP); and mechanical power (the amount of mechanical energy imparted as a function of respiratory rate). More recently, patient self-inflicted lung injury (P-SILI) has been proposed as a potential mechanism promoting VILI. In the present chapter, we will discuss the physiological and pathophysiological consequences of mechanical ventilation and how to personalize mechanical ventilation parameters.

Evaluation of Esophageal Pressures in Mechanically Ventilated Obese Patients

BACKGROUND

Patients who are obese are at risk for developing high pleural pressure, which leads to alveolar collapse. Esophageal pressure (P_es) can be used as a surrogate for pleural pressure and can be used to guide PEEP titration. Although recent clinical data on P_es-guided PEEP has shown no benefit, its utility in the subgroup of patients who are obese has not been studied.

METHODS

The Medical Information Mart for Intensive Care-III critical care database was queried to gather data on P_es in subjects on mechanical ventilation. P_es in obese and non-obese groups were compared, and a subgroup analysis was performed in subjects with class III obesity. Thereafter, empirical and P_es-guided PEEP protocols of a recently published trial were theoretically applied to the obese group and ventilator outcomes were compared.

RESULTS

A total of 105 subjects were included in the study. The average end-expiratory P_es in the obese group was 18.8 ± 5 cm H₂O compared with 16.8 ± 4.8 cm H₂O in the non-obese group (P < .05). If P_es-guided PEEP protocol was to be applied to those in the obese group, then the PEEP setting would be significantly higher than empirical PEEP setting. These findings were accentuated in the subgroup of subjects with class III obesity.

CONCLUSIONS

Individualization of PEEP with P_es guidance may have a role in patients who are obese.

Gut Microbiota Was Involved in the Process of Liver Injury During Intra-Abdominal Hypertension

Background: Intestinal damage caused by intra-abdominal hypertension (IAH) and abdominal compartment syndrome (ACS) can lead to the ectopic gut microbiota, which can contribute to liver injury via portal veins. Therefore, it is speculated that gut microbiota disorder caused by IAH/ACS may result in liver injury. The relationship between gut microbiota and IAH/ACS-related liver injury was investigated in this study.

Methods: A model of IAH was established in rats, and 16S rRNA sequencing was analyzed for gut microbiota in the feces of rats. The elimination of gut microbiota was completed by antibiotics gavage, and fecal microbiota transplantation (FMT) was used to change the composition of gut microbiota in rats.

Results: In addition to the traditional cause of liver blood vessel compression, liver injury caused by IAH was also associated with gut microbiota dysbiosis. Gut microbiota clearance can relieve liver injury caused by IAH, while FMT from IAH-intervened rats can aggravate IAH-related liver injury.

Conclusion: The gut microbiota was one of the most important factors contributing to the IAH-related liver injury, and the JNK/p38 signaling pathway was activated in this process.

Computed tomographic assessment of lung aeration at different positive end-expiratory pressures in a porcine model of intra-abdominal hypertension and lung injury

Background

Intra-abdominal hypertension (IAH) is common in critically ill patients and is associated with increased morbidity and mortality. High positive end-expiratory pressures (PEEP) can reverse lung volume and oxygenation decline caused by IAH, but its impact on alveolar overdistension is less clear. We aimed to find a PEEP range that would be high enough to reduce atelectasis, while low enough to minimize alveolar overdistention in the presence of IAH and lung injury.

Methods

Five anesthetized pigs received standardized anesthesia and mechanical ventilation. Peritoneal insufflation of air was used to generate intra-abdominal pressure of 27 cmH₂O. Lung injury was created by intravenous oleic acid. PEEP levels of 5, 12, 17, 22, and 27 cmH₂O were applied. We performed computed tomography and measured arterial oxygen levels, respiratory mechanics, and cardiac output 5 min after each new PEEP level. The proportion of overdistended, normally aerated, poorly aerated, and non-aerated atelectatic lung tissue was calculated based on Hounsfield units.

Results

PEEP decreased the proportion of poorly aerated and atelectatic lung, while increasing normally aerated lung. Overdistension increased with each incremental increase in applied PEEP. “Best PEEP” (respiratory mechanics or oxygenation) was higher than the “optimal CT inflation PEEP range” (difference between lower inflection points of atelectatic and overdistended lung) in healthy and injured lungs.

Conclusions

Our findings in a large animal model suggest that titrating a PEEP to respiratory mechanics or oxygenation in the presence of IAH is associated with increased alveolar overdistension.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40635-021-00416-5.

Personalized mechanical ventilation in acute respiratory distress syndrome

A personalized mechanical ventilation approach for patients with adult respiratory distress syndrome (ARDS) based on lung physiology and morphology, ARDS etiology, lung imaging, and biological phenotypes may improve ventilation practice and outcome. However, additional research is warranted before personalized mechanical ventilation strategies can be applied at the bedside. Ventilatory parameters should be titrated based on close monitoring of targeted physiologic variables and individualized goals. Although low tidal volume (VT) is a standard of care, further individualization of VT may necessitate the evaluation of lung volume reserve (e.g., inspiratory capacity). Low driving pressures provide a target for clinicians to adjust VT and possibly to optimize positive end-expiratory pressure (PEEP), while maintaining plateau pressures below safety thresholds. Esophageal pressure monitoring allows estimation of transpulmonary pressure, but its use requires technical skill and correct physiologic interpretation for clinical application at the bedside. Mechanical power considers ventilatory parameters as a whole in the optimization of ventilation setting, but further studies are necessary to assess its clinical relevance. The identification of recruitability in patients with ARDS is essential to titrate and individualize PEEP. To define gas-exchange targets for individual patients, clinicians should consider issues related to oxygen transport and dead space. In this review, we discuss the rationale for personalized approaches to mechanical ventilation for patients with ARDS, the role of lung imaging, phenotype identification, physiologically based individualized approaches to ventilation, and a future research agenda.

Measurement of Electrical Impedance Tomography-Based Regional Ventilation Delay for Individualized Titration of End-Expiratory Pressure

RATIONALE

Individualized positive end-expiratory pressure (PEEP) titration might be beneficial in preventing tidal recruitment. To detect tidal recruitment by electrical impedance tomography (EIT), the time disparity between the regional ventilation curves (regional ventilation delay inhomogeneity [RVDI]) can be measured during controlled mechanical ventilation when applying a slow inflation of 12 mL/kg of body weight (BW). However, repeated large slow inflations may result in high end-inspiratory pressure (P_EI), which might limit the clinical applicability of this method. We hypothesized that PEEP levels that minimize tidal recruitment can also be derived from EIT-based RVDI through the use of reduced slow inflation volumes.

METHODS

Decremental PEEP trials were performed in 15 lung-injured pigs. The PEEP level that minimized tidal recruitment was estimated from EIT-based RVDI measurement during slow inflations of 12, 9, 7.5, or 6 mL/kg BW. We compared RVDI and P_EI values resulting from different slow inflation volumes and estimated individualized PEEP levels.

RESULTS

RVDI values from slow inflations of 12 and 9 mL/kg BW showed excellent linear correlation (R² = 0.87, p < 0.001). Correlations decreased for RVDI values from inflations of 7.5 (R² = 0.68, p < 0.001) and 6 (R² = 0.42, p < 0.001) mL/kg BW. Individualized PEEP levels estimated from 12 and 9 mL/kg BW were comparable (bias -0.3 cm H₂O ± 1.2 cm H₂O). Bias and scatter increased with further reduction in slow inflation volumes (for 7.5 mL/kg BW, bias 0 ± 3.2 cm H₂O; for 6 mL/kg BW, bias 1.2 ± 4.0 cm H₂O). P_EI resulting from 9 mL/kg BW inflations were comparable with P_EI during regular tidal volumes.

CONCLUSIONS

PEEP titration to minimize tidal recruitment can be individualized according to EIT-based measurement of the time disparity of regional ventilation courses during slow inflations with low inflation volumes_. This sufficiently decreases P_EI and may reduce potential clinical risks.

Abdominal compartment syndrome in burns patients: Introduction of an evidence-based management guideline and algorithm

ABSTRACT

Abdominal compartment syndrome is a serious potential complication of burn injury, and carries high morbidity and mortality. Although there are generalised published guidelines on managing the condition, to date no management algorithm has yet been published tailored specifically to the burn injury patient. We set out to examine the literature on the subject in order to produce an evidence based management guideline, with the aim of improving outcomes for these patients. The guideline covers early detection and assessment of the condition as well as optimum medical, surgical and postoperative management. We believe that this guideline provides a much needed benchmark for managing burns patients with raised intra-abdominal pressure, as well as providing a template for further research and improvements in care.

Abdominal compartment syndrome among surgical patients

Abdominal compartment syndrome (ACS) develops when organ failure arises secondary to an increase in intraabdominal pressure. The abdominal pressure is determined by multiple factors such as blood pressure, abdominal compliance, and other factors that exert a constant pressure within the abdominal cavity. Several conditions in the critically ill may increase abdominal pressure compromising organ perfusion that may lead to renal and respiratory dysfunction. Among surgical and trauma patients, aggressive fluid resuscitation is the most commonly reported risk factor to develop ACS. Other conditions that have also been identified as risk factors are ascites, hemoperitoneum, bowel distention, and large tumors. All patients with abdominal trauma possess a higher risk of developing intra-abdominal hypertension (IAH). Certain surgical interventions are reported to have a higher risk to develop IAH such as damage control surgery, abdominal aortic aneurysm repair, and liver transplantation among others. Close monitoring of organ function and intra-abdominal pressure (IAP) allows clinicians to diagnose ACS rapidly and intervene with target-specific management to reduce IAP. Surgical decompression followed by temporary abdominal closure should be considered in all patients with signs of organ dysfunction. There is still a great need for more studies to determine the adequate timing for interventions to improve patient outcomes.

Intra-abdominal hypertension and abdominal compartment syndrome: a current review

PURPOSE OF REVIEW

Intra-abdominal hypertension (IAH) and its deleterious effects are present in at least one-third of ICU patients. Increased recognition of IAH has led to significant reduction in the incidence of abdominal compartment syndrome (ACS). Many questions remain regarding what therapeutic interventions truly reduce morbidity and mortality associated with IAH/ACS. Recent research sheds new light on the effects of IAH in individual organ systems and unique disease states. This paper will review recent research in IAH/ACS recognition, treatment, and management.

RECENT FINDINGS

Recent research on IAH/ACS includes an improved understanding of the prevalence of IAH/ACS and confirmation of its independent association with organ failure. Specifically, new research adds clarity to the effects of IAH/ACS on individual organ systems and specific disease states. These results combine to improve the clinical ability to diagnose, monitor, and treat IAH/ACS.

SUMMARY

There is significant research on the broad impact of IAH/ACS in the ICU setting. Focus on IAH/ACS has gone beyond the purview of intensivists and surgeons to include outstanding work by specialists in multiple sub-specialties. These advances have generated improvements in current treatment algorithms. We review recent IAH/ACS literature and have categorized the most pertinent results into organ system-specific contributions.

Intra-abdominal hypertension and hypoxic respiratory failure together predict adverse outcome - A sub-analysis of a prospective cohort

PURPOSE

To assess whether the combination of intra-abdominal hypertension (IAH, intra-abdominal pressure ≥ 12 mmHg) and hypoxic respiratory failure (HRF, PaO2/FiO2 ratio < 300 mmHg) in patients receiving invasive ventilation is an independent risk factor for 90- and 28-day mortality as well as ICU- and ventilation-free days.

METHODS

Mechanically ventilated patients who had blood gas analyses performed and intra-abdominal pressure measured, were included from a prospective cohort. Subgroups were defined by the absence (Group 1) or the presence of either IAH (Group 2) or HRF (Group 3) or both (Group 4). Mixed-effects regression analysis was performed.

RESULTS

Ninety-day mortality increased from 16% (Group 1, n = 50) to 30% (Group 2, n = 20) and 27% (Group 3, n = 100) to 49% (Group 4, n = 142), log-rank test p < 0.001. The combination of IAH and HRF was associated with increased 90- and 28-day mortality as well as with fewer ICU- and ventilation-free days. The association with 90-day mortality was no longer present after adjustment for independent variables. However, the association with 28-day mortality, ICU- and ventilation-free days persisted after adjusting for independent variables.

CONCLUSIONS

In our sub-analysis, the combination of IAH and HRF was not independently associated with 90-day mortality but independently increased the odds of 28-day mortality, and reduced the number of ICU- and ventilation-free days.

The Correlation between Head of Bed Angle and Intra-Abdominal Pressure of Intubated Patients; a Pre-Post Clinical Trial

INTRODUCTION

The recommended position for measuring Intra-Abdominal Pressure (IAP) is the supine position. However, patients put in this position are prone to Ventilator-associated pneumonia. This study was done to evaluate the relationship between bed head angle and IAP measurements of intubated patients in the intensive care unit.

METHODS

In this clinical trial, seventy-six critically ill patients under mechanical ventilation were enrolled. IAP measurement was performed every 8 hours for 24 hours using the KORN method in three different degrees of the head of bed (HOB) elevation (0 ° , 15 ° , and 30 ° ). Bland-Altman analysis was performed to identify the bias and limits of agreement among the three HOBs. According to World Society of the Abdominal Compartment Syndrome (WSACS), we can consider two IAP techniques equivalent if a bias of <1 mmHg and limits of agreement of - 4 to +4 were found between them. Data were analyzed using SPSS statistical software (v. 19), and the significance level was considered as 0.05.

RESULTS

The prevalence of intra-abdominal hypertension was 18.42%. Mean ± standard deviation (SD) of IAP were 8.44 ± 4.02 mmHg for HOB angle 0°, 9.58 ± 4.52 for HOB angle 15 ° , and 11.10 ± 4.73 for HOB angle 30^o (p = 0.0001). The IAP measurement bias between HOB angle 0°and HOB angle 15° was 1.13 mmHg. This bias was 2.66 mmHg between HOB angle 0° and HOB angle 30°.

CONCLUSION

Elevation of HOB angle from 0 to 30 degree significantly increases IAP. It seems that the measurement of IAP at HOB angle 15° was more reliable than 30°.

The Nature of Recruitment and De-Recruitment and Its Implications for Management of ARDS

Recruitment maneuvers in ARDS are used to improve oxygenation and lung mechanics by applying high airway pressures to reopen collapsed or obstructed peripheral airways and alveoli. In the early 1990s, recruitment maneuvers became a central feature of a variant form of lung-protective ventilation known as open-lung ventilation. This strategy is based on the belief that repetitive opening and closing of distal airspaces induces shear injury and therefore contributes both to ventilator-induced lung injury and ARDS-associated mortality. However, the largest multi-center randomized controlled trial of open-lung ventilation in moderate to severe ARDS reported that recruitment maneuver plateau pressures of 50-60 cm H₂O were associated with significantly higher mortality compared to traditional lung-protective ventilation. Despite being based on well conducted preclinical and clinical recruitment maneuver studies, the higher mortality associated with the open-lung ventilation strategy requires re-examining the assumptions and conclusions drawn from those previous studies. This narrative review examines the evidence used to design recruitment maneuver strategies. We also review the radiologic, rheologic, and histopathologic evidence regarding the nature of lung injury and the phenomena of recruitment and de-recruitment as it informs our perceptions of recruitment potential in ARDS. Major lung-protective ventilation clinical trial data and other clinical data are also examined to assess the practical necessity of recruitment maneuvers in ARDS and whether a subset of cases might benefit from pursuing recruitment maneuver therapy. Finally, a less a radical approach to recruitment maneuvers is offered that might achieve the goals of recruitment maneuvers with less risk of harm.

Impact of Different Positive End-Expiratory Pressures on Lung Mechanics in the Setting of Moderately Elevated Intra-Abdominal Pressure and Acute Lung Injury in a Porcine Model

The effects of a moderately elevated intra-abdominal pressure (IAP) on lung mechanics in acute respiratory distress syndrome (ARDS) have still not been fully analyzed. Moreover, the optimal positive end-expiratory pressure (PEEP) in elevated IAP and ARDS is unclear. In this paper, 18 pigs under general anesthesia received a double hit lung injury. After saline lung lavage and 2 h of injurious mechanical ventilation to induce an acute lung injury (ALI), an intra-abdominal balloon was filled until an IAP of 10 mmHg was generated. Animals were randomly assigned to one of three groups (group A = PEEP 5, B = PEEP 10 and C = PEEP 15 cmH₂O) and ventilated for 6 h. We measured end-expiratory lung volume (EELV) per kg bodyweight, driving pressure (ΔP), transpulmonary pressure (ΔP_L), static lung compliance (C_stat), oxygenation (P/F ratio) and cardiac index (CI). In group A, we found increases in ΔP (22 ± 1 vs. 28 ± 2 cmH₂O; p = 0.006) and ΔP_L (16 ± 1 vs. 22 ± 2 cmH₂O; p = 0.007), with no change in EELV/kg (15 ± 1 vs. 14 ± 1 mL/kg) when comparing hours 0 and 6. In group B, there was no change in ΔP (26 ± 2 vs. 25 ± 2 cmH₂O), ΔP_L (19 ± 2 vs. 18 ± 2 cmH₂O), C_stat (21 ± 3 vs. 21 ± 2 cmH₂O/mL) or EELV/kg (12 ± 2 vs. 13 ± 3 mL/kg). ΔP and ΔP_L were significantly lower after 6 h when comparing between group C and A (21 ± 1 vs. 28 ± 2 cmH₂O; p = 0.020) and (14 ± 1 vs. 22 ± 2 cmH₂O; p = 0.013)). The EELV/kg increased over time in group C (13 ± 1 vs. 19 ± 2 mL/kg; p = 0.034). The P/F ratio increased in all groups over time. CI decreased in groups B and C. The global lung injury score did not significantly differ between groups (A: 0.25 ± 0.05, B: 0.21 ± 0.02, C: 0.22 ± 0.03). In this model of ALI, elevated IAP, ΔP and ΔP_L increased further over time in the group with a PEEP of 5 cmH₂O applied over 6 h. This was not the case in the groups with a PEEP of 10 and 15 cmH₂O. Although ΔP and ΔP_L were significantly lower after 6 hours in group C compared to group A, we could not show significant differences in histological lung injury score.

Modeling intra-abdominal volume and respiratory driving pressure during pneumoperitoneum insufflation-a patient-level data meta-analysis

During pneumoperitoneum, intra-abdominal pressure (IAP) is usually kept at 12-14 mmHg. There is no clinical benefit in IAP increments if they do not increase intra-abdominal volume IAV. We aimed to estimate IAV (ΔIAV) and respiratory driving pressure changes (ΔP_RS) in relation to changes in IAP (ΔIAP). We carried out a patient-level meta-analysis of 204 adult patients with available data on IAV and ΔP_RS during pneumoperitoneum from three trials assessing the effect of IAP on postoperative recovery and airway pressure during laparoscopic surgery under general anesthesia. The primary endpoint was ΔIAV, and the secondary endpoint was ΔP_RS. The endpoints' response to ΔIAP was modeled using mixed multivariable Bayesian regression to estimate which mathematical function best fitted it. IAP values on the pressure-volume (PV) curve where the endpoint rate of change according to IAP decreased were identified. Abdomino-thoracic transmission (ATT) rate, that is, the rate ΔP_RS change to ΔIAP was also estimated. The best-fitting function was sigmoid logistic and linear for IAV and ΔP_RS response, respectively. Increments in IAV reached a plateau at 6.0 [95%CI 5.9-6.2] L. ΔIAV for each ΔIAP decreased at IAP ranging from 9.8 [95%CI 9.7-9.9] to 12.2 [12.0-12.3] mmHg. ATT rate was 0.65 [95%CI 0.62-0.68]. One mmHg of IAP raised ΔP_RS 0.88 cmH₂O. During pneumoperitoneum, IAP has a nonlinear relationship with IAV and a linear one with ΔP_RS. IAP should be set below the point where IAV gains diminish.NEW & NOTEWORTHY We found that intra-abdominal volume changes related to intra-abdominal pressure increase reached a plateau with diminishing gains in commonly used pneumoperitoneum pressure ranges. We also found a linear relationship between intra-abdominal pressure and respiratory driving pressure, a known marker of postoperative pulmonary complications.

Do we have the guts to go? The abdominal compartment, intra-abdominal hypertension, the human microbiome and exploration class space missions

Humans are destined to explore space, yet critical illness and injury may be catastrophically limiting for extraterrestrial travel. Humans are superorganisms living in symbiosis with their microbiomes, whose genetic diversity dwarfs that of humans. Symbiosis is critical and imbalances are associated with disease, occurring within hours of serious illness and injury. There are many characteristics of space flight that negatively influence the microbiome, especially deep space itself, with its increased radiation and absence of gravity. Prolonged weightlessness causes many physiologic changes that are detrimental; some resemble aging and will adversely affect the ability to tolerate critical illness or injury and subsequent treatment. Critical illness-induced intra-abdominal hypertension (IAH) may induce malperfusion of both the viscera and microbiome, with potentially catastrophic effects. Evidence from animal models confirms profound IAH effects on the gut, namely ischemia and disruption of barrier function, mechanistically linking IAH to resultant organ dysfunction. Therefore, a pathologic dysbiome, space-induced immune dysfunction and a diminished cardiorespiratory reserve with exacerbated susceptibility to IAH, imply that a space-deconditioned astronaut will be vulnerable to IAH-induced gut malperfusion. This sets the stage for severe gut ischemia and massive biomediator generation in an astronaut with reduced cardiorespiratory/immunological capacity. Fortunately, experiments in weightless analogue environments suggest that IAH may be ameliorated by conformational abdominal wall changes and a resetting of thoracoabdominal mechanics. Thus, review of the interactions of physiologic changes with prolonged weightlessness and IAH is required to identify appropriate questions for planning exploration class space surgical care.

Do we have the guts to go? The abdominal compartment, intra-abdominal hypertension, the human microbiome and exploration class space missions

Humans are destined to explore space, yet critical illness and injury may be catastrophically limiting for extraterrestrial travel. Humans are superorganisms living in symbiosis with their microbiomes, whose genetic diversity dwarfs that of humans. Symbiosis is critical and imbalances are associated with disease, occurring within hours of serious illness and injury. There are many characteristics of space flight that negatively influence the microbiome, especially deep space itself, with its increased radiation and absence of gravity. Prolonged weightlessness causes many physiologic changes that are detrimental; some resemble aging and will adversely affect the ability to tolerate critical illness or injury and subsequent treatment. Critical illness-induced intra-abdominal hypertension (IAH) may induce malperfusion of both the viscera and microbiome, with potentially catastrophic effects. Evidence from animal models confirms profound IAH effects on the gut, namely ischemia and disruption of barrier function, mechanistically linking IAH to resultant organ dysfunction. Therefore, a pathologic dysbiome, space-induced immune dysfunction and a diminished cardiorespiratory reserve with exacerbated susceptibility to IAH, imply that a space-deconditioned astronaut will be vulnerable to IAH-induced gut malperfusion. This sets the stage for severe gut ischemia and massive biomediator generation in an astronaut with reduced cardiorespiratory/immunological capacity. Fortunately, experiments in weightless analogue environments suggest that IAH may be ameliorated by conformational abdominal wall changes and a resetting of thoracoabdominal mechanics. Thus, review of the interactions of physiologic changes with prolonged weightlessness and IAH is required to identify appropriate questions for planning exploration class space surgical care.

[Abdominal Emergencies in The View of an Intensivist - Intra-abdominal Hypertension and Abdominal Compartment Syndrome]

In critically ill patients an intra-abdominal hypertension is a common phenomenon. An IAH is defined as an IAP persistent ≥ 12 mmHg, an abdominal compartment syndrome is defined as an IAP persistent ≥ 20 mmHg in combination with new organ failure. The bladder pressure serves as a surrogate parameter for the IAP. The bladder pressure should be measured in a standardized manner. The therapy of IAH should be individualized.

A Comparative Evaluation of the Effect of Prone Positioning Methods on Blood Loss and Intra-Abdominal Pressure in Obese Patients Undergoing Spinal Surgery

Background Improper prone positioning of obese patients for spine surgery can increase the intra-abdominal pressure (IAP), resulting in increased bleeding from epidural venous plexus. The choice of prone positioning frame can be an important determinant of the IAP.

Materials and Methods This prospective, randomized study was performed on obese patients (body mass index ≥ 30) scheduled for lumbar laminectomy. After administration of general anesthesia, patients were positioned prone either on Wilson’s frame (group W), or on horizontal bolsters (group H). IAP was recorded at three intervals: (1) in supine position, (2) 10 minutes after prone positioning, and (3) in prone position at the end of surgery. Intraoperative blood loss was measured quantitatively and assessed subjectively by the surgeon.

Results A total of 60 patients were enrolled with 30 patients in each group. IAP in supine position was similar in both groups. However, IAP 10 minutes after prone positioning was significantly higher at 11.44 ± 1.61 mm Hg in group W as compared to 9.56 ± 1.92 mm Hg in group H (p = 0.001). Similarly, IAP of 12.24 ± 1.45 mm Hg in group W, measured on completion of surgery was significantly higher than 9.96 ± 2.35 mm Hg in group H (p = 0.001). Mean total blood loss of 440.40 ± 176.98 mL in group W was significantly higher than 317.20 ± 91.04 mL in group H (p = 0.003).

Conclusion Obese patients positioned prone on Wilson’s frame had significantly higher IAP and blood loss compared to patients positioned on horizontal bolsters.

Prospective Observational Study to Evaluate the Effect of Different Levels of Positive End-Expiratory Pressure on Lung Mechanics in Patients with and without Acute Respiratory Distress Syndrome

Background: The optimal level of positive end-expiratory pressure is still under debate. There are scare data examining the association of PEEP with transpulmonary pressure (TPP), end-expiratory lung volume (EELV) and intraabdominal pressure in ventilated patients with and without ARDS. Methods: We analyzed lung mechanics in 3 patient groups: group A, patients with ARDS; group B, obese patients (body mass index (BMI) > 30 kg/m²) and group C, a control group. Three levels of PEEP (5, 10, 15 cm H₂O) were used to investigate the consequences for lung mechanics. Results: Fifty patients were included, 22 in group A, 18 in group B (BMI 38 ± 2 kg/m²) and 10 in group C. At baseline, oxygenation showed no differences between the groups. Driving pressure (ΔP) and transpulmonary pressure (ΔP_L) was higher in group B than in groups A and C at a PEEP of 5 cm H₂O (ΔP A: 15 ± 1, B: 18 ± 1, C: 14 ± 1 cm H₂O; ΔP_L A: 10 ± 1, B: 13 ± 1, C: 9 ± 0 cm H₂O). Peak inspiratory pressure (P_insp) rose in all groups as PEEP increased, but the resulting driving pressure and transpulmonary pressure were reduced, whereas EELV increased. Conclusion: Measuring EELV or TPP allows a personalized approach to lung-protective ventilation.

Comparison of the proximal and distal approaches for axillary vein catheterization under ultrasound guidance (PANDA) in cardiac surgery patients susceptible to bleeding: a randomized controlled trial

BACKGROUND

The present study aimed at comparing the success rate and safety of proximal versus distal approach for ultrasound (US)-guided axillary vein catheterization (AVC) in cardiac surgery patients susceptible to bleeding.

METHODS

In this single-center randomized controlled trial, cardiac surgery patients susceptible to bleeding and requiring AVC were randomized to either the proximal or distal approach group for US-guided AVC. Patients susceptible to bleeding were defined as those who received oral antiplatelet drugs or anticoagulants for at least 3 days. Success rate, catheterization time, number of attempts, and mechanical complications within 24 h were recorded for each procedure.

RESULTS

A total of 198 patients underwent randomization: 99 patients each to the proximal and distal groups. The proximal group had the higher first puncture success rate (75.8% vs. 51.5%, p < 0.001) and site success rate (93.9% vs. 83.8%, p = 0.04) than the distal group. However, the overall success rates between the two groups were similar (99.0% vs. 99.0%; p = 1.00). Moreover, the proximal group had fewer average number of attempts (p < 0.01), less access time (p < 0.001), and less successful cannulation time (p < 0.001). There was no significant difference in complications between the two groups, such as major bleeding, minor bleeding, arterial puncture, pneumothorax, nerve injuries, and catheter misplacements.

CONCLUSIONS

For cardiac surgery patients susceptible to bleeding, both proximal and distal approaches for US-guided AVC can be considered as feasible and safe methods of central venous cannulation. In terms of the first puncture success rate and cannulation time, the proximal approach is superior to the distal approach. Trial registration Clinicaltrials.gov, NCT03395691. Registered January 10, 2018, https://clinicaltrials.gov/ct2/show/NCT03395691?cond=NCT03395691&draw=1&rank=1 .

Abdominal compartment syndrome and intra-abdominal hypertension

PURPOSE OF REVIEW

Abdominal compartment syndrome (ACS) is a severe complication resulting from an acute and sustained increase in intra-abdominal pressure (IAP), causing significant morbidity and mortality. Although prospective double-blinded, randomized trials, and evidence-based analysis are lacking there is new evidence that still demonstrates high morbidity and mortality in critically ill populations because of intra-abdominal hypertension (IAH) in the 21st century. The objective of this review is to alert the health professional about this important diagnosis and to highlight the latest updates proposed by the World Abdominal Compartment Society.

RECENT FINDINGS

The present article reviews the clinical conditions of ACS and IAH and the latest updates from pathophysiology to the new management flowchart resulting from the implantation of point-of-care ultrasound in the monitoring and assistance of medical treatment of IAH/ACS.

SUMMARY

The present review emphasizes the importance of IAH in daily clinical practice and brings new WSACS updates on monitoring and treatment.

Individualized Positive End-expiratory Pressure and Regional Gas Exchange in Porcine Lung Injury

Background

In acute respiratory failure elevated intraabdominal pressure aggravates lung collapse, tidal recruitment, and ventilation inhomogeneity. Low positive end-expiratory pressure (PEEP) may promote lung collapse and intrapulmonary shunting, whereas high PEEP may increase dead space by inspiratory overdistension. The authors hypothesized that an electrical impedance tomography–guided PEEP approach minimizing tidal recruitment improves regional ventilation and perfusion matching when compared to a table-based low PEEP/no recruitment and an oxygenation-guided high PEEP/full recruitment strategy in a hybrid model of lung injury and elevated intraabdominal pressure.

Methods

In 15 pigs with oleic acid–induced lung injury intraabdominal pressure was increased by intraabdominal saline infusion. PEEP was set in randomized order: (1) guided by a PEEP/inspired oxygen fraction table, without recruitment maneuver; (2) minimizing tidal recruitment guided by electrical impedance tomography after a recruitment maneuver; and (3) maximizing oxygenation after a recruitment maneuver. Single photon emission computed tomography was used to analyze regional ventilation, perfusion, and aeration. Primary outcome measures were differences in PEEP levels and regional ventilation/perfusion matching.

Results

Resulting PEEP levels were different (mean ± SD) with (1) table PEEP: 11 ± 3 cm H2O; (2) minimal tidal recruitment PEEP: 22 ± 3 cm H2O; and (3) maximal oxygenation PEEP: 25 ± 4 cm H2O; P &lt; 0.001. Table PEEP without recruitment maneuver caused highest lung collapse (28 ± 11% vs. 5 ± 5% vs. 4 ± 4%; P &lt; 0.001), shunt perfusion (3.2 ± 0.8 l/min vs. 1.0 ± 0.8 l/min vs. 0.7 ± 0.6 l/min; P &lt; 0.001) and dead space ventilation (2.9 ± 1.0 l/min vs. 1.5 ± 0.7 l/min vs. 1.7 ± 0.8 l/min; P &lt; 0.001). Although resulting in different PEEP levels, minimal tidal recruitment and maximal oxygenation PEEP, both following a recruitment maneuver, had similar effects on regional ventilation/perfusion matching.

Conclusions

When compared to table PEEP without a recruitment maneuver, both minimal tidal recruitment PEEP and maximal oxygenation PEEP following a recruitment maneuver decreased shunting and dead space ventilation, and the effects of minimal tidal recruitment PEEP and maximal oxygenation PEEP were comparable.

Editor’s Perspective

What We Already Know about This Topic

What This Article Tells Us That Is New

A Clinician's Guide to Management of Intra-abdominal Hypertension and Abdominal Compartment Syndrome in Critically Ill Patients

This article is one of ten reviews selected from the Annual Update in Intensive Care and Emergency Medicine 2020. Other selected articles can be found online at https://www.biomedcentral.com/collections/annualupdate2020. Further information about the Annual Update in Intensive Care and Emergency Medicine is available from http://www.springer.com/series/8901.