New physiological insights in ventilation during cardiopulmonary resuscitation.

PURPOSE OF REVIEW: In the setting of cardiopulmonary resuscitation (CPR), classical physiological concept about ventilation become challenging. Ventilation may exert detrimental hemodynamic effects that must be balanced with its expected benefits. The risks of hyperventilation have been thoroughly addressed, even questioning the need for ventilation, emphasizing the need to prioritize chest compression quality. However, ventilation is mandatory for adequate gas exchange as soon as CPR is prolonged. Factors affecting the capability of chest compressions to produce alveolar ventilation are poorly understood. In this review, we discuss the conventional interpretation of interactions between ventilation and circulation, from the perspective of novel physiological observations. RECENT FINDINGS: Many patients with cardiac arrest exhibit 'intrathoracic airway closure.' This phenomenon is associated with lung volume reduction, impedes chest compressions to generate ventilation and overall limits the delivered ventilation. This phenomenon can be reversed by the application of small levels of positive end-expiratory pressure. Also, a novel interpretation of the capnogram can rate the magnitude of this phenomenon, contributing to clarify the physiological meaning of exhaled CO2 and may help assess the real amount of delivered ventilation. SUMMARY: Recent advances in the understanding of ventilatory physiology during CPR shows that capnogram analysis not only provides information on the quality of resuscitation but also on the amount of ventilation produced by chest compressions and on the total amount of ventilation.

Mechanical power of ventilation is associated with mortality in critically ill patients: an analysis of patients in two observational cohorts.

PURPOSE: Mechanical power (MP) may unify variables known to be related to development of ventilator-induced lung injury. The aim of this study is to examine the association between MP and mortality in critically ill patients receiving invasive ventilation for at least 48 h. METHODS: This is an analysis of data stored in the databases of the MIMIC-III and eICU. Critically ill patients receiving invasive ventilation for at least 48 h were included. The exposure of interest was MP. The primary outcome was in-hospital mortality. RESULTS: Data from 8207 patients were analyzed. Median MP during the second 24 h was 21.4 (16.2-28.1) J/min in MIMIC-III and 16.0 (11.7-22.1) J/min in eICU. MP was independently associated with in-hospital mortality [odds ratio per 5 J/min increase (OR) 1.06 (95% confidence interval (CI) 1.01-1.11); p = 0.021 in MIMIC-III, and 1.10 (1.02-1.18); p = 0.010 in eICU]. MP was also associated with ICU mortality, 30-day mortality, and with ventilator-free days, ICU and hospital length of stay. Even at low tidal volume, high MP was associated with in-hospital mortality [OR 1.70 (1.32-2.18); p < 0.001] and other secondary outcomes. Finally, there is a consistent increase in the risk of death with MP higher than 17.0 J/min. CONCLUSION: High MP of ventilation is independently associated with higher in-hospital mortality and several other outcomes in ICU patients receiving invasive ventilation for at least 48 h.

Impact of ventilation strategies during chest compression. An experimental study with clinical observations.

The optimal ventilation strategy during cardiopulmonary resuscitation (CPR) is unknown. Chest compression (CC) generates circulation, while during decompression, thoracic recoil generates negative pressure and venous return. Continuous flow insufflation of oxygen (CFI) allows noninterrupted CC and generates positive airway pressure (Paw). The main objective of this study was to assess the effects of positive Paw compared with the current recommended ventilation strategy on intrathoracic pressure (P(IT)) variations, ventilation, and lung volume. In a mechanical model, allowing compression of the thorax below an equilibrium volume mimicking functional residual capacity (FRC), CC alone or with manual bag ventilation were compared with two levels of Paw with CFI. Lung volume change below FRC at the end of decompression and P(IT), as well as estimated alveolar ventilation, were measured during the bench study. Recordings were obtained in five cardiac arrest patients to confirm the bench findings. Lung volume was continuously below FRC, and as a consequence P(IT) remained negative during decompression in all situations, including with positive Paw. Compared with manual bag or CC alone, CFI with positive Paw limited the fall in lung volume and resulted in larger positive and negative P(IT) variations. Positive Paw with CFI significantly augmented ventilation induced by CC. Recordings in patients confirmed a major loss of lung volume below FRC during CPR, even with positive Paw. Compared with manual bag ventilation, positive Paw associated with CFI limits the loss in lung volume, enhances CC-induced positive P(IT), maintains negative P(IT) during decompression, and generates more alveolar ventilation.

What type of monitoring has been shown to improve outcomes in acutely ill patients?

OBJECTIVE: Lack of evidence that some monitoring systems can improve outcomes has raised doubts about their use in the intensive care unit (ICU). The objective of this study was to determine which monitoring techniques have been shown to improve outcomes in ICU patients. DESIGN: Comprehensive literature review. METHODS: We conducted a highly sensitive search, up to June 2006, in the Cochrane Central Register of Controlled Trials (CENTRAL) and MedLine, for prospective, randomized controlled trials (RCTs) conducted in adult patients in the ICU and the operating room (major surgical procedures) and focusing on the impact of monitoring on outcome. MEASUREMENTS AND RESULTS: Of 4,175 potential articles, 67 evaluated the impact of monitoring in acutely ill adult patients. There were 40 studies related to hemodynamic monitoring, 17 to respiratory monitoring, and 10 to neurological monitoring. Seven studies were classified in two different categories. Positive non-mortality outcomes were observed in 17 of 40 hemodynamic studies, 11 of 17 respiratory, and in all 10 neurological studies. Mortality was evaluated in 31 hemodynamic studies, but a beneficial impact was demonstrated in only 10. For respiratory monitoring, 7 studies evaluated mortality, but only 3 of them showed an improved outcome. We found no neurological monitoring studies that assessed mortality. CONCLUSION: There is no broad evidence that any form of monitoring improves outcomes in the ICU and most commonly used devices have not been evaluated by RCT. This review puts into perspective the recent negative studies on the use of the pulmonary artery catheter in the acutely ill.