Mechanical ventilation. American College of Chest Physicians' Consensus Conference

Awakening and Breathing Coordination: A Mixed-Methods Analysis of Determinants of Implementation

Rationale: Routine spontaneous awakening and breathing trial coordination (SAT/SBT) improves outcomes for mechanically ventilated patients, but adherence varies. Understanding barriers to and facilitators of consistent daily use of SAT/SBT (implementation determinants) can guide the development of implementation strategies to increase adherence to these evidence-based interventions. Objectives: We conducted an explanatory, sequential mixed-methods study to measure variation in the routine daily use of SAT/SBT and to identify implementation determinants that might explain variation in SAT/SBT use across 15 intensive care units (ICUs) in urban and rural locations within an integrated, community-based health system. Methods: We described the patient population and measured adherence to daily use of coordinated SAT/SBT from January to June 2021, selecting four sites with varied adherence levels for semistructured field interviews. We conducted key informant interviews with critical care nurses, respiratory therapists, and physicians/advanced practice clinicians (n = 55) from these four sites between October and December 2021 and performed content analysis to identify implementation determinants of SAT/SBT use. Results: The 15 sites had 1,901 ICU admissions receiving invasive mechanical ventilation (IMV) for ⩾24 hours during the measurement period. The mean IMV patient age was 58 years, and the median IMV duration was 5.3 days (interquartile range, 2.5-11.9). Coordinated SAT/SBT adherence (within 2 h) was estimated at 21% systemwide (site range, 9-68%). ICU clinicians were generally familiar with SAT/SBT but varied in their knowledge and beliefs about what constituted an evidence-based SAT/SBT. Clinicians reported that SAT/SBT coordination was difficult in the context of existing ICU workflows, and existing protocols did not explicitly define how coordination should be performed. The lack of an agreed-upon system-level measure for tracking daily use of SAT/SBT led to uncertainty regarding what constituted adherence. The effects of the COVID-19 pandemic increased clinician workloads, impacting performance. Conclusions: Coordinated SAT/SBT adherence varied substantially across 15 ICUs within an integrated, community-based health system. Implementation strategies that address barriers identified by this study, including knowledge deficits, challenges regarding workflow coordination, and the lack of performance measurement, should be tested in future hybrid implementation-effectiveness trials to increase adherence to daily use of coordinated SAT/SBT and minimize harm related to the prolonged use of mechanical ventilation and sedation.

Automated detection and classification of patient-ventilator asynchrony by means of machine learning and simulated data

BACKGROUND AND OBJECTIVE

Mechanical ventilation is a lifesaving treatment for critically ill patients in an Intensive Care Unit (ICU) or during surgery. However, one potential harm of mechanical ventilation is related to patient-ventilator asynchrony (PVA). PVA can cause discomfort to the patient, damage to the lungs, and an increase in the length of stay in the ICU and on the ventilator. Therefore, automated detection algorithms are being developed to detect and classify PVAs, with the goal of optimizing mechanical ventilation. However, the development of these algorithms often requires large labeled datasets; these are generally difficult to obtain, as their collection and labeling is a time-consuming and labor-intensive task, which needs to be performed by clinical experts.

METHODS

In this work, we aimed to develop a computer algorithm for the automatic detection and classification of PVA. The algorithm employs a neural network for the detection of the breath of the patient. The development of the algorithm was aided by simulations from a recently published model of the patient-ventilator interaction.

RESULTS

The proposed method was effective, providing an algorithm with reliable detection and classification results of over 90% accuracy. Besides presenting a detection and classification algorithm for a variety of PVAs, here we show that using simulated data in combination with clinical data increases the variability in the training dataset, leading to a gain in performance and generalizability.

CONCLUSIONS

In the future, these algorithms can be utilized to gain a better understanding of the clinical impact of PVAs and help clinicians to better monitor their ventilation strategies.

Fasting practices of enteral nutrition delivery for airway procedures in critically ill adult patients: A scoping review

BACKGROUND

There is limited understanding of fasting practices and reported safety concerns for airway procedures in critically ill adults.

OBJECTIVE

To describe fasting practices including safety concerns for airway procedures in critically ill adult patients in the reported literature.

INCLUSION CRITERIA

Studies conducted in adult critically ill patients receiving enteral nutrition (EN) and undergoing an airway procedure (endotracheal intubation, endotracheal extubation, and tracheostomy) were included if EN fasting practices and/or prespecified nutrition and clinical outcomes were reported.

METHODS

A scoping review using the Joanna Briggs Institute methodology was conducted. MEDLINE, Embase, and CINAHL were searched from 2000 to January 19, 2022. Results are presented via narrative synthesis.

RESULTS

Fourteen studies were included, with only one randomised control trial (RCT). Twelve studies reported on fasting practices with varied EN fasting durations (0-34 h) and two reported data on nutrition adequacy. Three studies investigated continued EN in one study arm and four studies minimised fasting duration by including gastric suctioning prior to the airway procedure. Safety concerns primarily related to aspiration events (61%) were reported in nine studies.

CONCLUSION

In the reported literature, there is wide variation in EN fasting practices for airway procedures in critically ill patients with limited evidence to inform practice.

Associating local strains to global pressure-volume mouse lung mechanics using digital image correlation

Pulmonary diseases alter lung mechanical properties, can cause loss of function, and necessitate use of mechanical ventilation, which can be detrimental. Investigations of lung tissue (local) scale mechanical properties are sparse compared to that of the whole organ (global) level, despite connections between regional strain injury and ventilation. We examine ex vivo mouse lung mechanics by investigating strain values, local compliance, tissue surface heterogeneity, and strain evolutionary behavior for various inflation rates and volumes. A custom electromechanical, pressure-volume ventilator is coupled with digital image correlation to measure regional lung strains and associate local to global mechanics by analyzing novel pressure-strain evolutionary measures. Mean strains at 5 breaths per minute (BPM) for applied volumes of 0.3, 0.5, and 0.7 ml are 5.0, 7.8, and 11.3%, respectively, and 4.7, 8.8, and 12.2% for 20 BPM. Similarly, maximum strains among all rate and volume combinations range 10.7%-22.4%. Strain values (mean, range, mode, and maximum) at peak inflation often exhibit significant volume dependencies. Additionally, select evolutionary behavior (e.g., local lung compliance quantification) and tissue heterogeneity show significant volume dependence. Rate dependencies are generally found to be insignificant; however, strain values and surface lobe heterogeneity tend to increase with increasing rates. By quantifying strain evolutionary behavior in relation to pressure-volume measures, we associate time-continuous local to global mouse lung mechanics for the first time and further examine the role of volume and rate dependency. The interplay of multiscale deformations evaluated in this work can offer insights for clinical applications, such as ventilator-induced lung injury.

Management of Respiratory Failure: Ventilator Management 101 and Noninvasive Ventilation

Mechanical ventilation is a lifesaving therapy for critically ill patients with respiratory failure, but like all treatments, it has the potential to cause harm if not administered appropriately. This review aims to give an overview of the basic principles of invasive and noninvasive mechanical ventilation. Topics covered include modes of mechanical ventilation, respiratory mechanics and ventilator waveform interpretation, strategies for initial ventilator settings, indications and contraindications for noninvasive ventilation, and the effect of the ventilator on kidney function.

Complications associated with long-term positive-pressure ventilation in dogs and cats: 67 cases

OBJECTIVES

To determine the complications associated with positive-pressure ventilation (PPV) in dogs and cats.

DESIGN

Retrospective study from October 2009 to September 2013.

SETTING

University Teaching Hospital.

ANIMALS

Fifty-eight dogs and 9 cats.

MEASUREMENTS AND MAIN RESULTS

Medical records were retrospectively reviewed; signalment, complications associated with PPV, duration of PPV, and outcome were recorded. Complications most commonly recorded during PPV included hypothermia 41/67 (61%), hypotension 39/67 (58%), cardiac arrhythmias 33/67 (49%), a positive fluid balance 31/67 (46%), oral lesions 25/67 (37%), and corneal ulcerations 24/67 (36%). A definition of ventilator-associated events (VAE) extrapolated from the Center of Disease Control's criteria was applied to 21 cases that received PPV for at least 4 days in this study. Ventilator-associated conditions occurred in 5 of 21 (24%) of cases with infection-related ventilator-associated conditions and ventilator-associated pneumonia identified in 3 of 21 (14%) cases.

CONCLUSIONS

Complications are common and diverse in dogs and cats receiving long-term PPV and emphasizes the importance of intensive, continuous patient monitoring and appropriate nursing care protocols. Many of the complications identified could be serious without intervention and suggests that appropriate equipment alarms could improve patient safety. Development of veterinary specific surveillance tools such as the VAE criteria would aid future investigations and allow for effective multicenter studies.

Pressure support ventilation in intensive care patients receiving prolonged invasive ventilation

Background: To our knowledge, the use and management of pressure support ventilation (PSV) in patients receiving prolonged (≥ 7 days) invasive mechanical ventilation has not previously been described. Objective: To collect and analyse data on the use and management of PSV in critically ill patients receiving prolonged ventilation. Design, setting and participants: We performed a multicentre retrospective observational study in Australia, with a focus on PSV in patients ventilated for ≥ 7 days. Main outcome measures: We obtained detailed data on ventilator management twice daily (8am and 8pm moments) for the first 7 days of ventilation. Results: Among 143 consecutive patients, 90/142 (63.4%) had received PSV by Day 7, and PSV accounted for 40.5% (784/1935) of ventilation moments. The most common pressure support level was 10 cmH2O (352/780) observations [45.1%]) with little variation over time, and 37 of 114 patients (32.4%) had no change in pressure support. Mean tidal volume during PSV was 8.3 (7.0-9.5) mL/kg predicted bodyweight (PBW) compared with 7.5 (7.0-8.3) mL/kg PBW during mandatory ventilation (P < 0.001). For 74.6% (247/331) of moments, despite a tidal volume of more than 8 mL/kg PBW, the pressure support level was not changed. Among 122 patients exposed to PSV, 97 (79.5%) received likely over-assistance according to rapid shallow breathing index criteria. Of 784 PSV moments, 411 (52.4%) were also likely over-assisted according to rapid shallow breathing index criteria, and 269/346 (77.7%) having no subsequent adjustment of pressure support. Conclusions: In patients receiving prolonged ventilation, almost two-thirds received PSV, which accounted for 40.5% of mechanical ventilation time. Half of the PSV-treated patients were exposed to high tidal volume and two-thirds to likely over-assistance. These observations provide evidence that can be used to inform interventional studies of PSV management.

Concept design of the physical structure for ICU ventilators for COVID-19 pandemic

A new disease known as COVID-19 caused by the SARS CoV2 virus has engulfed the entire world and led to a global pandemic situation. Till December 9, 2020, the disease has infected 68 million people worldwide and more than 1.56 million people have been killed. The origin of the COVID-19 disease has been traced back to the bats, but the intermediary contact is unknown. The disease spreads by respiratory droplets and contaminated surfaces. In most cases, the virus shows mild symptoms such as fever, fatigue, dyspnea, cough, etc. which may become severe if appropriate precautions are not adhered to. For people with comorbidities (usually elderly) the disease may turn deadly and cause pneumonia, Acute Respiratory Distress Syndrome (ARDS), and multi-organ failure, thereby affecting a person's ability to perform normal breathing which may put them on ventilator support. The virus causes Acute Respiratory Distress Syndrome (ARDS) that can lead to multi-organ failure in the most severe form. A patient suffering from ARDS must be put on a mechanical ventilator. These assistive devices help patients with respiratory disorders perform normal breathing. Presently nearly sixty thousand COVID-19 patients are in critical condition worldwide, fighting for survival requiring ventilator support. In India, the number stands close to eight thousand such individuals especially when the second wave of COVID-19 is expected to spread globally with initial signs arising from European and Middle East countries. With a large number of patients requiring ventilators, it puts a huge strain on the already weak health infrastructure of the developing countries. This is where some manufacturing and automobile companies have stepped in to help hospitals by developing ventilators at a faster rate and lower costs without comprising on the quality with the support of different government initiatives. This paper aims to study the basic requirements to be considered while designing the physical structure of an elementary level ICU ventilator for the hospital environment. The challenges related to research in electronic wiring of a mechanical ventilator, the overall structural design, and surrounding base could be appropriately done for different loads by simulating the conditions on tools like ANSYS software with accurate dimensions which could improve their future designs.

A Simple Ventilator Designed To Be Used in Shortage Crises: Construction and Verification Testing

Background

The COVID-19 pandemic has demonstrated the possibility of severe ventilator shortages in the near future.

Objective

We aimed to develop an acute shortage ventilator.

Methods

The ventilator was designed to mechanically compress a self-inflating bag resuscitator, using a modified ventilator patient circuit, which is controlled by a microcontroller and an optional laptop. It was designed to operate in both volume-controlled mode and pressure-controlled assist modes. We tested the ventilator in 4 modes using an artificial lung while measuring the volume, flow, and pressure delivered over time by the ventilator.

Results

The ventilator was successful in reaching the desired tidal volume and respiratory rates specified in national emergency use resuscitator system guidelines. The ventilator responded to simulated spontaneous breathing.

Conclusions

The key design goals were achieved. We developed a simple device with high performance for short-term use, made primarily from common hospital parts and generally available nonmedical components to avoid any compatibility or safety issues with the patient, and at low cost, with a unit cost per ventilator is less than $400 US excluding the patient circuit parts, that can be easily manufactured.

Audit of low tidal volume ventilation in patients with hypoxic respiratory failure in a tertiary Australian intensive care unit

A low tidal volume ventilation (LTVV) strategy improves outcomes in patients with acute respiratory distress syndrome (ARDS). Subsequently, a LTVV strategy has become the standard of care for patients receiving mechanical ventilation. This strategy is poorly adhered to within intensive care units (ICUs). A retrospective analysis was conducted of prescribed tidal volumes in mechanically ventilated patients with hypoxic respiratory failure between April 2013 and March 2017. Data collection included the establishment of a new data-entry box for patient height in March 2016, aimed at assisting the calculation of LTVV. We reviewed 836 ICU admissions, comprising 19,884 hours of ventilation. A total of 92% of admissions lacked patient height recording. When height was recorded, 54% of hours of ventilation were LTVV adherent. Non-LTVV hours for both groups involved higher tidal volumes (38%) rather than lower tidal volumes (8%). Non-LTVV-adherent hours were significantly (P<0.001) more likely to be associated with patient mortality than LTVV-adherent hours were. For all hours of ventilation, mean tidal volume before March 2016 was significantly higher (496 (standard deviation (SD) 101) ml, compared to after March 2016 (451 (SD 107) ml, P<0.001, 95% confidence interval for true difference in means 42 to 48 ml). However, this trend gradually reversed over time. There was a clinician preference for multiples of 50 ml. There was poor adherence to LTVV strategy in patients with hypoxic respiratory failure, which was associated with an increase in patient mortality. An electronic medical record intervention was successful in producing change, but this was not sustainable over time. Clinician ventilation prescribing habits were based on numerical simplicity rather than evidence-based practice.

Construction and Performance Testing of a Fast-Assembly COVID-19 (FALCON) Emergency Ventilator in a Model of Normal and Low-Pulmonary Compliance Conditions

INTRODUCTION

The COVID-19 pandemic has revealed an immense, unmet and international need for available ventilators. Both clinical and engineering groups around the globe have responded through the development of "homemade" or do-it-yourself (DIY) ventilators. Several designs have been prototyped, tested, and shared over the internet. However, many open source DIY ventilators require extensive familiarity with microcontroller programming and electronics assembly, which many healthcare providers may lack. In light of this, we designed and bench tested a low-cost, pressure-controlled mechanical ventilator that is "plug and play" by design, where no end-user microcontroller programming is required. This Fast-AssembLy COVID-Nineteen (FALCON) emergency prototype ventilator can be rapidly assembled and could be readily modified and improved upon to potentially provide a ventilatory option when no other is present, especially in low- and middle-income countries.

HYPOTHESIS

We anticipated that a minimal component prototype ventilator could be easily assembled that could reproduce pressure/flow waveforms and tidal volumes similar to a hospital grade ventilator (Engström CarestationTM).

MATERIALS AND METHODS

We benched-tested our prototype ventilator using an artificial test lung under 36 test conditions with varying respiratory rates, peak inspiratory pressures (PIP), positive end expiratory pressures (PEEP), and artificial lung compliances. Pressure and flow waveforms were recorded, and tidal volumes calculated with prototype ventilator performance compared to a hospital-grade ventilator (Engström CarestationTM) under identical test conditions.

RESULTS

Pressure and flow waveforms produced by the prototype ventilator were highly similar to the CarestationTM. The ventilator generated consistent PIP/PEEP, with tidal volume ranges similar to the CarestationTM. The FALCON prototype was tested continuously for a 5-day period without failure or significant changes in delivered PIP/PEEP.

CONCLUSION

The FALCON prototype ventilator is an inexpensive and easily-assembled "plug and play" emergency ventilator design. The FALCON ventilator is currently a non-certified prototype that, following further appropriate validation and testing, might eventually be used as a life-saving emergency device in extraordinary circumstances when more sophisticated forms of ventilation are unavailable.

The predictive value of brain natriuretic peptide or N-terminal pro-brain natriuretic peptide for weaning outcome in mechanical ventilation patients: Evidence from SROC

OBJECTIVE

Mechanical ventilation is an important treatment for critically ill patients. Physicians generally perform a spontaneous breathing trial (SBT) to determine whether the patients can be weaned from mechanical ventilation, but almost 17% of the patients who pass the SBT still require respiratory support. Cardiac dysfunction is an important cause of weaning failure. The use of brain natriuretic peptide or N-terminal pro-BNP is a simple method to assess cardiac function. We performed a systematic review of investigations of brain natriuretic peptide or N-terminal pro-BNP as predictors of weaning from mechanical ventilation.

DATA SOURCES

PubMed (1950 to December 2020), Cochrane, and Embase (1974 to December 2020), and some Chinese databases for additional articles (China Biology Medicine (CBM), China Science and Technology Journal Database (CSTJ), and Wanfang Data and China National Knowledge Infrastructure (CNKI)).

STUDY SELECTION

We systematically searched observation studies investigating the predictive value of brain natriuretic peptide or N-terminal pro-brain natriuretic peptide in weaning outcome of patients with mechanical ventilation.

DATA EXTRACTION

Two independent reviewers extracted data. The differences are resolved through consultation.

DATA SYNTHESIS

We included 18 articles with 1416 patients and extracted six index tests with pooled sensitivity and specificity for each index test. For the BNP change rate predicting weaning success, the pooled sensitivity was 89% (83%-94%) and the pooled specificity was 82% (72%-89%) with the highest pooled AUC of 0.9511.

CONCLUSIONS

The brain natriuretic peptide change rate is a reliable predictor of weaning outcome from mechanical ventilation.

Management of respiratory complications and rehabilitation in individuals with muscular dystrophies: 1st Consensus Conference report from UILDM - Italian Muscular Dystrophy Association (Milan, January 25-26, 2019)

Respiratory complications are common in the patient with muscular dystrophy. The periodic clinical and instrumental respiratory evaluation is extremely important. Despite the presence in the literature of updated guidelines, patient associations often report lack of knowledge of these pathologies, particularly in peripheral hospitals. The purpose of this work, inspired by the Italian Muscular Dystrophy Association (UILDM) is to improve management of respiratory problems necessary for the management of these patients complex. To this end, the main items that the specialist can meet in the follow-up of these pathologies have been analyzed and discussed, among which the respiratory basal evaluation, the criteria of adaptation to non-invasive ventilation, management of bronchial secretions, situations of respiratory emergency, indications for tracheostomy and the subject of advance directives of treatment (DAT).

Complications Associated With the Anesthesia Transport of Pediatric Patients: An Analysis of the Wake Up Safe Database

BACKGROUND

Transporting patients under anesthesia care incurs numerous potential risks, especially for those with critical illness. The purpose of this study is to identify and report all pediatric anesthesia transport-associated adverse events from a preexisting database of perioperative adverse events.

METHODS

An extract of the Wake Up Safe database was obtained on December 14, 2017, and screened for anesthesia transport-associated complications. This was defined as events occurring during or immediately after transport or movement of a pediatric patient during or in proximity to their care by anesthesiologists, including repositioning and transfer to recovery or an inpatient unit, if the cause was noted to be associated with anesthesia or handover. Events were excluded if the narrative clearly states that an event was ongoing and not impacted by anesthesia transport, such as a patient who develops cardiac arrest that then requires emergent transfer to the operating room. The search methodology included specific existing data elements that indicate transport of the patient, handover or intensive care status preoperatively as well as a free-text search of the narrative for fragments of words indicating movement. Screened events were reviewed by 3 anesthesiologists for inclusion, and all data elements were extracted for analysis.

RESULTS

Of 2971 events in the database extract, 63.8% met screening criteria and 5.0% (148 events) were related to transport. Events were primarily respiratory in nature. Nearly 40% of all reported events occurred in infants age ≤6 months. A total of 59.7% of events were at least somewhat preventable and 36.4% were associated with patient harm, usually temporary. Of the 86 reported cardiac arrests, 50 (58.1%) had respiratory causes, of which 74% related to anesthesia or perioperative team factors. Respiratory events occurred at all stages of care, with 21.4% during preoperative transport and 75.5% postoperatively. Ninety-three percent of unplanned extubations occurred in patients 6 months and younger. Ten medication events were noted, 2 of which resulted in cardiac arrest. Root causes in all events related primarily to provider and patient factors, with occasional references to verbal miscommunication.

CONCLUSIONS

Five percent of reported pediatric anesthesia adverse events are associated with transport. Learning points highlight the risk of emergence from anesthesia during transport to recovery or intensive care unit (ICU). ICU patients undergoing anesthesia transport face risks relating to transitions in providers, equipment, sedation, and physical positioning. Sedation and neuromuscular blockade may be necessary for transport in some patients but has been associated with adverse events in others.

Could the loss of diaphragm thickness measured by computer tomography predict the rate of reintubation?

Background

Diaphragm function loss is very common in the intensive care unit (ICU) and can predict the success of weaning. However, whether diaphragm thickness loss during mechanical ventilation (MV) as measured by computed tomography (CT) can predict the rate of reintubation remains unclear. Therefore, we hypothesized that a loss of diaphragm thickness would impact the outcome of weaning.

Methods

A retrospective study was performed on patients who received MV in the ICU of West China Hospital, Sichuan University. The diaphragm thickness of each patient on the CT scans within 48 hours after MV and 24 hours before weaning were measured by at least two independent investigators. The primary outcome was the rate of reintubation, and the second outcomes included hospital mortality and the length of ICU stay (ICU LOS) after extubation.

Results

A total of 145 patients were included in the analysis. According to the receiver operating characteristic curve, all patients were divided into two groups (less or more than 1.55 mm diaphragm thickness loss in reintubation). As a result, less loss of diaphragm thickness was a protective factor for the rate of reintubation [33% vs. 12%; adjusted odds ratio (aOR) 0.001; 95% confidence interval (CI), 0.001–0.271; P=0.018] and hospital mortality (18% vs. 4%; aOR 0.001; 95% CI, 0.001–0.035; P=0.007). However, no significant difference was found in the ICU LOS after extubation between the two groups.

Conclusions

Less diaphragm thickness loss was related to a lower rate of reintubation and hospital mortality.

Misrepresenting "Usual Care" in Research: An Ethical and Scientific Error

Comparative effectiveness studies, referred to here as "usual-care" trials, seek to compare current medical practices for the same medical condition. Such studies are presumed to be safe and involve only minimal risks. However, that presumption may be flawed if the trial design contains "unusual" care, resulting in potential risks to subjects and inaccurately informed consent. Three case studies described here did not rely on clinical evidence to ascertain contemporaneous practice. As a result, the investigators drew inaccurate conclusions, misinformed research participants, and subjects' safety was compromised. Before approving usual-care protocols, IRBs and scientific review committees should evaluate the quality and completeness of information documenting usual-care practices. Guidance from governmental oversight agencies regarding evidence-based documentation of current clinical practice could prevent similar occurrences in future usual-care trials. Accurate information is necessary to ensure that trials comply with government regulations that require minimizing research risks to subjects and accurate informed consent documents.

Effects of fluid balance on prognosis of acute respiratory distress syndrome patients secondary to sepsis

BACKGROUND

Fluid management is crucial to acute respiratory distress syndrome (ARDS) secondary to sepsis. However, choices of fluid resuscitation strategies and fluid input volumes remain a thorny problem. Our study aimed to elucidate the relationship between fluid balance and prognosis of ARDS patients secondary to sepsis.

METHODS

Our study included 322 sepsis patients from Ruijin Hospital between 2014 and 2018, and 84 patients were diagnosed as ARDS within 72 hours after onset of sepsis according to Berlin ARDS Definition.

RESULTS

Among the 322 sepsis patients, 84 (26.1%) were complicated with ARDS within 72 hours. ARDS patients had a lower oxygenation index (PaO₂/FiO₂ 166.4±71.0 vs. 255.0±91.2, P<0.05), longer duration of mechanical ventilation (11 [6-24] days vs. 0 [0-0] days, P<0.05) than those without ARDS. Sepsis patients with ARDS showed daily positive net fluid balance during seven days compared with those without ARDS who showed daily negative net fluid balance since the second day with significant statistical differences. Among the 84 sepsis patients with ARDS, 58 (69.0%) died. Mean daily fluid input volumes were much lower in survivors than in non-survivors (43.2±16.7 mL/kg vs. 51.0±25.2 mL/kg, P<0.05) while output volumes were much higher in survivors (45.2±19.8 mL/kg vs. 40.2±22.7 mL/kg, P<0.05). Using binary logistic regression analysis, we found that the mean daily fluid balance was independently associated with mortality of sepsis patients complicating with ARDS (P<0.05).

CONCLUSIONS

Early negative fluid balance is independently associated with a better prognosis of sepsis patients complicated with ARDS.

Can we predict patients that will not benefit from invasive mechanical ventilation? A novel scoring system in intensive care: the IMV Mortality Prediction Score (IMPRES)

Background/aim

The present study aimed to define the clinical and laboratory criteria for predicting patients that will not benefit from invasive mechanical ventilation (IMV) treatment and determine the prediction of mortality and prognosis of these critical ill patients.

Materials and methods

The study was designed as an observational, multicenter, prospective, and cross-sectional clinical study. It was conducted by 75 researchers at 41 centers in intensive care units (ICUs) located in various geographical areas of Turkey. It included a total of 1463 ICU patients who were receiving invasive mechanical ventilation (IMV) treatment. A total of 158 parameters were examined via logistic regression analysis to identify independent risk factors for mortality; using these data, the IMV Mortality Prediction Score (IMPRES) scoring system was developed.

Results

The following cut-off scores were used to indicate mortality risk: <2, low risk; 2–5, moderate risk; 5.1–8, high risk; >8, very high risk. There was a 26.8% mortality rate among the 254 patients who had a total IMPRES score of lower than 2. The mortality rate was 93.3% for patients with total IMPRES scores of greater than 8 (P < 0.001).

Conclusion

The present study included a large number of patients from various geographical areas of the country who were admitted to various types of ICUs, had diverse diagnoses and comorbidities, were intubated with various indications in either urgent or elective settings, and were followed by physicians from various specialties. Therefore, our data are more general and can be applied to a broader population. This study devised a new scoring system for decision-making for critically ill patients as to whether they need to be intubated or not and presents a rapid and accurate prediction of mortality and prognosis prior to ICU admission using simple clinical data.

Formal guidelines: management of acute respiratory distress syndrome

Fifteen recommendations and a therapeutic algorithm regarding the management of acute respiratory distress syndrome (ARDS) at the early phase in adults are proposed. The Grade of Recommendation Assessment, Development and Evaluation (GRADE) methodology has been followed. Four recommendations (low tidal volume, plateau pressure limitation, no oscillatory ventilation, and prone position) had a high level of proof (GRADE 1 + or 1 -); four (high positive end-expiratory pressure [PEEP] in moderate and severe ARDS, muscle relaxants, recruitment maneuvers, and venovenous extracorporeal membrane oxygenation [ECMO]) a low level of proof (GRADE 2 + or 2 -); seven (surveillance, tidal volume for non ARDS mechanically ventilated patients, tidal volume limitation in the presence of low plateau pressure, PEEP > 5 cmH2O, high PEEP in the absence of deleterious effect, pressure mode allowing spontaneous ventilation after the acute phase, and nitric oxide) corresponded to a level of proof that did not allow use of the GRADE classification and were expert opinions. Lastly, for three aspects of ARDS management (driving pressure, early spontaneous ventilation, and extracorporeal carbon dioxide removal), the experts concluded that no sound recommendation was possible given current knowledge. The recommendations and the therapeutic algorithm were approved by the experts with strong agreement.

Formal guidelines: management of acute respiratory distress syndrome

Fifteen recommendations and a therapeutic algorithm regarding the management of acute respiratory distress syndrome (ARDS) at the early phase in adults are proposed. The Grade of Recommendation Assessment, Development and Evaluation (GRADE) methodology has been followed. Four recommendations (low tidal volume, plateau pressure limitation, no oscillatory ventilation, and prone position) had a high level of proof (GRADE 1 + or 1 −); four (high positive end-expiratory pressure [PEEP] in moderate and severe ARDS, muscle relaxants, recruitment maneuvers, and venovenous extracorporeal membrane oxygenation [ECMO]) a low level of proof (GRADE 2 + or 2 −); seven (surveillance, tidal volume for non ARDS mechanically ventilated patients, tidal volume limitation in the presence of low plateau pressure, PEEP > 5 cmH2O, high PEEP in the absence of deleterious effect, pressure mode allowing spontaneous ventilation after the acute phase, and nitric oxide) corresponded to a level of proof that did not allow use of the GRADE classification and were expert opinions. Lastly, for three aspects of ARDS management (driving pressure, early spontaneous ventilation, and extracorporeal carbon dioxide removal), the experts concluded that no sound recommendation was possible given current knowledge. The recommendations and the therapeutic algorithm were approved by the experts with strong agreement.

Changes in ventilator settings and ventilation-induced lung injury in burn patients-A systematic review

OBJECTIVE

Ventilation strategies aiming at prevention of ventilator-induced lung injury (VILI), including low tidal volumes (V_T) and use of positive end-expiratory pressures (PEEP) are increasingly used in critically ill patients. It is uncertain whether ventilation practices changed in a similar way in burn patients. Our objective was to describe applied ventilator settings and their relation to development of VILI in burn patients.

DATA SOURCES

Systematic search of the literature in PubMed and EMBASE using MeSH, EMTREE terms and keywords referring to burn or inhalation injury and mechanical ventilation.

STUDY SELECTION

Studies reporting ventilator settings in adult or pediatric burn or inhalation injury patients receiving mechanical ventilation during the ICU stay.

DATA EXTRACTION

Two authors independently screened abstracts of identified studies for eligibility and performed data extraction.

DATA SYNTHESIS

The search identified 35 eligible studies. V_T declined from 14 ml/kg in studies performed before to around 8 ml/kg predicted body weight in studies performed after 2006. Low-PEEP levels (<10 cmH₂O) were reported in 70% of studies, with no changes over time. Peak inspiratory pressure (PIP) values above 35 cmH₂O were frequently reported. Nevertheless, 75% of the studies conducted in the last decade used limited maximum airway pressures (≤35 cmH₂O) compared to 45% of studies conducted prior to 2006. Occurrence of barotrauma, reported in 45% of the studies, ranged from 0 to 29%, and was more frequent in patients ventilated with higher compared to lower airway pressures.

CONCLUSION

This systematic review shows noticeable trends of ventilatory management in burn patients that mirrors those in critically ill non-burn patients. Variability in available ventilator data precluded us from drawing firm conclusions on the association between ventilator settings and the occurrence of VILI in burn patients.

Optimising mechanical ventilation through model-based methods and automation

Mechanical ventilation (MV) is a core life-support therapy for patients suffering from respiratory failure or acute respiratory distress syndrome (ARDS). Respiratory failure is a secondary outcome of a range of injuries and diseases, and results in almost half of all intensive care unit (ICU) patients receiving some form of MV. Funding the increasing demand for ICU is a major issue and MV, in particular, can double the cost per day due to significant patient variability, over-sedation, and the large amount of clinician time required for patient management. Reducing cost in this area requires both a decrease in the average duration of MV by improving care, and a reduction in clinical workload. Both could be achieved by safely automating all or part of MV care via model-based dynamic systems modelling and control methods are ideally suited to address these problems. This paper presents common lung models, and provides a vision for a more automated future and explores predictive capacity of some current models. This vision includes the use of model-based methods to gain real-time insight to patient condition, improve safety through the forward prediction of outcomes to changes in MV, and develop virtual patients for in-silico design and testing of clinical protocols. Finally, the use of dynamic systems models and system identification to guide therapy for improved personalised control of oxygenation and MV therapy in the ICU will be considered. Such methods are a major part of the future of medicine, which includes greater personalisation and predictive capacity to both optimise care and reduce costs. This review thus presents the state of the art in how dynamic systems and control methods can be applied to transform this core area of ICU medicine.

Predictive Virtual Patient Modelling of Mechanical Ventilation: Impact of Recruitment Function

Mechanical ventilation is a life-support therapy for intensive care patients suffering from respiratory failure. To reduce the current rate of ventilator-induced lung injury requires ventilator settings that are patient-, time-, and disease-specific. A common lung protective strategy is to optimise the level of positive end-expiratory pressure (PEEP) through a recruitment manoeuvre to prevent alveolar collapse at the end of expiration and to improve gas exchange through recruitment of additional alveoli. However, this process can subject parts of the lung to excessively high pressures or volumes. This research significantly extends and more robustly validates a previously developed pulmonary mechanics model to predict lung mechanics throughout recruitment manoeuvres. In particular, the process of recruitment is more thoroughly investigated and the impact of the inclusion of expiratory data when estimating peak inspiratory pressure is assessed. Data from the McREM trial and CURE pilot trial were used to test model predictive capability and assumptions. For PEEP changes of up to and including 14 cmH₂O, the parabolic model was shown to improve peak inspiratory pressure prediction resulting in less than 10% absolute error in the CURE cohort and 16% in the McREM cohort. The parabolic model also better captured expiratory mechanics than the exponential model for both cohorts.

Biomedical engineer's guide to the clinical aspects of intensive care mechanical ventilation

Background

Mechanical ventilation is an essential therapy to support critically ill respiratory failure patients. Current standards of care consist of generalised approaches, such as the use of positive end expiratory pressure to inspired oxygen fraction (PEEP–FiO₂) tables, which fail to account for the inter- and intra-patient variability between and within patients. The benefits of higher or lower tidal volume, PEEP, and other settings are highly debated and no consensus has been reached. Moreover, clinicians implicitly account for patient-specific factors such as disease condition and progression as they manually titrate ventilator settings. Hence, care is highly variable and potentially often non-optimal. These conditions create a situation that could benefit greatly from an engineered approach. The overall goal is a review of ventilation that is accessible to both clinicians and engineers, to bridge the divide between the two fields and enable collaboration to improve patient care and outcomes. This review does not take the form of a typical systematic review. Instead, it defines the standard terminology and introduces key clinical and biomedical measurements before introducing the key clinical studies and their influence in clinical practice which in turn flows into the needs and requirements around how biomedical engineering research can play a role in improving care. Given the significant clinical research to date and its impact on this complex area of care, this review thus provides a tutorial introduction around the review of the state of the art relevant to a biomedical engineering perspective.

Discussion

This review presents the significant clinical aspects and variables of ventilation management, the potential risks associated with suboptimal ventilation management, and a review of the major recent attempts to improve ventilation in the context of these variables. The unique aspect of this review is a focus on these key elements relevant to engineering new approaches. In particular, the need for ventilation strategies which consider, and directly account for, the significant differences in patient condition, disease etiology, and progression within patients is demonstrated with the subsequent requirement for optimal ventilation strategies to titrate for patient- and time-specific conditions.

Conclusion

Engineered, protective lung strategies that can directly account for and manage inter- and intra-patient variability thus offer great potential to improve both individual care, as well as cohort clinical outcomes.

Predictors of early weaning failure from mechanical ventilation in critically ill patients after emergency gastrointestinal surgery: A retrospective study

Mechanical ventilation (MV) is the most common therapeutic modality used for critically ill patients. However, prolonged MV is associated with high morbidity and mortality. Therefore, it is important to avoid both premature extubation and unnecessary prolongation of MV. Although some studies have determined the predictors of early weaning success and failure, only a few have investigated these factors in critically ill surgical patients who require postoperative MV. The aim of this study was to evaluate predictors of early weaning failure from MV in critically ill patients who had undergone emergency gastrointestinal (GI) surgery.The medical records of 3327 adult patients who underwent emergency GI surgery between January 2007 and December 2016 were reviewed retrospectively. Clinical and laboratory parameters before surgery and within 2 days postsurgery were investigated.This study included 387 adult patients who required postoperative MV. A low platelet count (adjusted odds ratio [OR]: 0.995; 95% confidence interval [CI]: 0.991-1.000; P = .03), an elevated delta neutrophil index (DNI; adjusted OR: 1.025; 95% CI: 1.005-1.046; P = .016), a delayed spontaneous breathing trial (SBT; adjusted OR: 14.152; 95% CI: 6.571-30.483; P < .001), and the presence of postoperative shock (adjusted OR: 2.436; 95% CI: 1.138-5.216; P = .022) were shown to predict early weaning failure from MV in the study population.Delayed SBT, a low platelet count, an elevated DNI, and the presence of postoperative shock are independent predictors of early weaning failure from MV in critically ill patients after emergency GI surgery.

A virtual patient model for mechanical ventilation

BACKGROUND AND OBJECTIVES

Mechanical ventilation (MV) is a primary therapy for patients with acute respiratory failure. However, poorly selected ventilator settings can cause further lung damage due to heterogeneity of healthy and damaged alveoli. Varying positive-end-expiratory-pressure (PEEP) to a point of minimum elastance is a lung protective ventilator strategy. However, even low levels of PEEP can lead to ventilator induced lung injury for individuals with highly inflamed pulmonary tissue. Hence, models that could accurately predict peak inspiratory pressures after changes to PEEP could improve clinician confidence in attempting potentially beneficial treatment strategies.

METHODS

This study develops and validates a physiologically relevant respiratory model that captures elastance and resistance via basis functions within a well-validated single compartment lung model. The model can be personalised using information available at a low PEEP to predict lung mechanics at a higher PEEP. Proof of concept validation is undertaken with data from four patients and eight recruitment manoeuvre arms.

RESULTS

Results show low error when predicting upwards over the clinically relevant pressure range, with the model able to predict peak inspiratory pressure with less than 10% error over 90% of the range of PEEP changes up to 12 cmH₂O.

CONCLUSIONS

The results provide an in-silico model-based means of predicting clinically relevant responses to changes in MV therapy, which is the foundation of a first virtual patient for MV.

Estimation of Arterial Carbon Dioxide Based on End-Tidal Gas Pressure and Oxygen Saturation

Arterial blood gas (ABG) analysis is the traditional method for measuring the partial pressure of carbon dioxide. In mechanically ventilated patients a continuous noninvasive monitoring of carbon dioxide would obviously be attractive. In the current study, we present a novel formula for noninvasive estimation of arterial carbon dioxide. Eighty-one datasets were collected from 19 anesthetized and mechanically ventilated pigs. Eleven animals were mechanically ventilated without interventions. In the remaining eight pigs the partial pressure of carbon dioxide was manipulated. The new formula (Formula 1) is PaCO₂ = PETCO₂ + k(PETO₂ − PaO₂) where PaO₂ was calculated from the oxygen saturation. We tested the agreements of this novel formula and compared it to a traditional method using the baseline PaCO₂ − ETCO₂ gap added to subsequently measured, end-tidal carbon dioxide levels (Formula 2). The mean difference between PaCO₂ and calculated carbon dioxide (Formula 1) was 0.16 kPa (±SE 1.17). The mean difference between PaCO₂ and carbon dioxide with Formula 2 was 0.66 kPa (±SE 0.18). With a mixed linear model excluding cases with cardiorespiratory collapse, there was a significant difference between formulae (p < 0.001), as well as significant interaction between formulae and time (p < 0.001). In this preliminary animal study, this novel formula appears to have a reasonable agreement with PaCO₂ values measured with ABG analysis, but needs further validation in human patients.

TRPV4 inhibition attenuates stretch-induced inflammatory cellular responses and lung barrier dysfunction during mechanical ventilation

Mechanical ventilation is an important tool for supporting critically ill patients but may also exert pathological forces on lung cells leading to Ventilator-Induced Lung Injury (VILI). We hypothesised that inhibition of the force-sensitive transient receptor potential vanilloid (TRPV4) ion channel may attenuate the negative effects of mechanical ventilation. Mechanical stretch increased intracellular Ca²⁺ influx and induced release of pro-inflammatory cytokines in lung epithelial cells that was partially blocked by about 30% with the selective TRPV4 inhibitor GSK2193874, but nearly completely blocked with the pan-calcium channel blocker ruthenium red, suggesting the involvement of more than one calcium channel in the response to mechanical stress. Mechanical stretch also induced the release of pro-inflammatory cytokines from M1 macrophages, but in contrast this was entirely dependent upon TRPV4. In a murine ventilation model, TRPV4 inhibition attenuated both pulmonary barrier permeability increase and pro-inflammatory cytokines release due to high tidal volume ventilation. Taken together, these data suggest TRPV4 inhibitors may have utility as a prophylactic pharmacological treatment to improve the negative pathological stretch-response of lung cells during ventilation and potentially support patients receiving mechanical ventilation.

Ventilator-induced lung injury during controlled ventilation in patients with acute respiratory distress syndrome: less is probably better

INTRODUCTION

Mechanical ventilation is required to support respiratory function in the acute respiratory distress syndrome (ARDS), but it may promote lung damage, a phenomenon known as ventilator-induced lung injury (VILI). Areas covered: Several mechanisms of VILI have been described, such as: inspiratory and/or expiratory stress inducing overdistension (volutrauma); interfaces between collapsed or edema-filled alveoli with surrounding open alveoli, acting as stress raisers; alveoli that repetitively open and close during tidal breathing (atelectrauma); and peripheral airway dynamics. In this review, we discuss: the definition and classification of ARDS; ventilatory parameters that act as VILI determinants (tidal volume, respiratory rate, positive end-expiratory pressure, peak, plateau, driving and transpulmonary pressures, energy, mechanical power, and intensity); and the roles of prone positioning and muscle paralysis. We seek to provide an up-to-date overview of the evidence in the field from a clinical perspective. Expert commentary: To prevent VILI, mechanical ventilation strategies should minimize inspiratory/expiratory stress, dynamic/static strain, energy, mechanical power, and intensity, as well as mitigate the hemodynamic consequences of positive-pressure ventilation. In patients with moderate to severe ARDS, prone positioning can reduce lung damage and improve survival. Overall, volutrauma seems to be more harmful than atelectrauma. Extracorporeal support should be considered in selected cases.

Patient-Ventilator Dyssynchrony

In mechanically ventilated patients, assisted mechanical ventilation (MV) is employed early, following the acute phase of critical illness, in order to eliminate the detrimental effects of controlled MV, most notably the development of ventilator-induced diaphragmatic dysfunction. Nevertheless, the benefits of assisted MV are often counteracted by the development of patient-ventilator dyssynchrony. Patient-ventilator dyssynchrony occurs when either the initiation and/or termination of mechanical breath is not in time agreement with the initiation and termination of neural inspiration, respectively, or if the magnitude of mechanical assist does not respond to the patient's respiratory demand. As patient-ventilator dyssynchrony has been associated with several adverse effects and can adversely influence patient outcome, every effort should be made to recognize and correct this occurrence at bedside. To detect patient-ventilator dyssynchronies, the physician should assess patient comfort and carefully inspect the pressure- and flow-time waveforms, available on the ventilator screen of all modern ventilators. Modern ventilators offer several modifiable settings to improve patient-ventilator interaction. New proportional modes of ventilation are also very helpful in improving patient-ventilator interaction.

Tidal volume in acute respiratory distress syndrome: how best to select it

Mechanical ventilation is the type of organ support most widely provided in the intensive care unit. However, this form of support does not constitute a cure for acute respiratory distress syndrome (ARDS), as it mainly works by buying time for the lungs to heal while contributing to the maintenance of vital gas exchange. Moreover, it can further damage the lung, leading to the development of a particular form of lung injury named ventilator-induced lung injury (VILI). Experimental evidence accumulated over the last 30 years highlighted the factors associated with an injurious form of mechanical ventilation. The present paper illustrates the physiological effects of delivering a tidal volume to the lungs of patients with ARDS, and suggests an approach to tidal volume selection. The relationship between tidal volume and the development of VILI, the so called volotrauma, will be reviewed. The still actual suggestion of a lung-protective ventilatory strategy based on the use of low tidal volumes scaled to the predicted body weight (PBW) will be presented, together with newer strategies such as the use of airway driving pressure as a surrogate for the amount of ventilatable lung tissue or the concept of strain, i.e., the ratio between the tidal volume delivered relative to the resting condition, that is the functional residual capacity (FRC). An ultra-low tidal volume strategy with the use of extracorporeal carbon dioxide removal (ECCO₂R) will be presented and discussed. Eventually, the role of other ventilator-related parameters in the generation of VILI will be considered (namely, plateau pressure, airway driving pressure, respiratory rate (RR), inspiratory flow), and the promising unifying framework of mechanical power will be presented.

The Management of Sepsis: A Practical Review

The incidence of the sepsis syndrome has increased dramatically in the last few decades. During this time we have gained new insights into the pathophysiologic mechanisms leading to organ dysfunction in sepsis and the importance of the host-bacterial interactions in mediating many of these processes. This knowledge has led to new therapeutic approaches and the investigation of a number of novel agents. An assessment of these approaches is presented to aid clinicians in the management of patients with severe sepsis. Criteria used to select studies included their relevance to the management of sepsis and their pertinence to clinicians. Appropriate antibiotic selection and volume resuscitation remain the cornerstone of treatment of septic patients. Hydroxyethyl starch solutions have theoretical advantages over crystalloids; there is, however, no data that the type of resuscitation fluid alters outcome. Vasoactive agents are required in patients who remain hemodynamically unstable or have evidence of tissue hypoxia after adequate volume resuscitation. Although dopamine is widely used, dobutamine and norepinephrine are our vasoactive agents of choice. Dopamine has no proven role in oliguric patients, with early dialysis recommended in patients with acute renal failure. The preferred method of renal replacement therapy remains to be determined. Blood products should be used cautiously in patients with disseminated intravascular coagulation. Therapeutic strategies that interfere with the immune system have not been proven to improve the outcome in unselected groups of patients. However, immunomodulation may prove to have a role in select subgroups of patients. Antibiotic therapy and intensive physiological support continues to be the main approach to the management of patients with severe sepsis. Despite the development of numerous novel therapeutic agents, these drugs have not been demonstrated to improve patient outcome.

Trauma and acute lung injury

Acute lung injury is a serious complication of major trauma occurring as a direct consequence of trauma to the lung or, more commonly, arising indirectly as a consequence of trauma elsewhere to the body. A spectrum of severity exists with acute respiratory distress syndrome (ARDS) defined as the most severe form of injury. The frequency of ARDS with severe trauma is unclear but is believed to occur in approximately 15- 25% of cases, although this is confused by the effects of multiple transfusions and associated injuries including burns and head injury. ARDS from all causes is estimated to occur with a frequency of two to 10 cases per 100 000 population. It causes a huge social and financial impact, with many survivors requiring a prolonged critical care stay and a significant number having a persisting poor quality of life a year after the injury. The mortality is, however, decreasing and stands at approximately 40%. A number of approaches are now recognized that can improve oxygenation and large trials have identified best critical care practice, leading to a reduction in ventilator-induced injury, with associated improvements in outcome.

Lung Protective Ventilation Strategies

While traditional ventilation approaches are appropriate for the patient without significant lung disease and only requiring short-term mechanical ventilatory support, the strategy should be altered for the patient with severe lung disease. Research on the mechanisms of ventilator-induced lung injury has led to the development of mechanical ventilation strategies that imrove patient outcomes. The trend toward using lower tidal volmes, limited airway pressures, and PEEP have produced imroved outcome results. Predictive indices of outcome using laboratory values, biologic markers, and mediators of lung inury are being evaluated for early identification of patients at risk for lung injury. Nonconventional ventilatory approaches, such as noninvasive positive pressure ventilation and high freuency ventilation, as well as adjunctive therapies (inhaled niric oxide and extracorporeal circulation) are being explored as alternatives in ARDS and ALI. While more clinical studies outine outcomes in specific subgroups of patients, the ventilatoy strategy should continually be revised at the bedside.

Impact of invasive ventilation on survival when non-invasive ventilation is ineffective in patients with Duchenne muscular dystrophy: A prospective cohort

BACKGROUND

Many patients with DMD undergo tracheostomy. Tracheostomy is associated with certain complications, however its effect on prognosis is not known.

METHODS

The relationship between type of mechanical ventilation and survival at 12 years was evaluated in a prospective cohort of patients with Duchenne muscular dystrophy followed in a French reference center for Neuromuscular Diseases. Cox proportional-hazards regressions were used to estimate the hazard ratios associated with risk of switching from non-invasive to invasive ventilation, and with risk of death.

RESULTS

One hundred and fifty patients were included. Initial use of invasive ventilation was associated with an episode of acute respiratory failure (p < 0.0001) and with a severe clinical status (p < 0.05). Risk of death was associated with swallowing disorders (2.51, IC [1.12-5.66], p < 0.03) and cardiac failure (p < 0.05) but not with type of mechanical ventilation.

CONCLUSION

Switching to invasive ventilation is appropriate when non-invasive ventilation is ineffective.

Carbon Dioxide and the Heart: Physiology and Clinical Implications

Carbon dioxide (CO2) is an end product of aerobic cellular respiration. In healthy persons, PaCO2 is maintained by physiologic mechanisms within a narrow range (35-45 mm Hg). Both hypercapnia and hypocapnia are encountered in myriad clinical situations. In recent years, the number of hypercapnic patients has increased by the use of smaller tidal volumes to limit lung stretch and injury during mechanical ventilation, so-called permissive hypercapnia. A knowledge and appreciation of the effects of CO2 in the heart are necessary for optimal clinical management in the perioperative and critical care settings. This article reviews, from a historical perspective: (1) the effects of CO2 on coronary blood flow and the mechanisms underlying these effects; (2) the role of endogenously produced CO2 in metabolic control of coronary blood flow and the matching of myocardial oxygen supply to demand; and (3) the direct and reflexogenic actions of CO2 on myocardial contractile function. Clinically relevant issues are addressed, including the role of increased myocardial tissue PCO2 (PmCO2) in the decline in myocardial contractility during coronary hypoperfusion and the increased vulnerability to CO2-induced cardiac depression in patients receiving a β-adrenergic receptor antagonist or with otherwise compromised inotropic reserve. The potential use of real-time measurements of PmO2 to monitor the adequacy of myocardial perfusion in the perioperative period is discussed.