Hemodynamic consequences of auto-PEEP

Guide to Lung-Protective Ventilation in Cardiac Patients

The incidence of acute respiratory insufficiency has continued to increase among patients admitted to modern-day cardiovascular intensive care units. Positive pressure ventilation (PPV) remains the mainstay of treatment for these patients. Alterations in intrathoracic pressure during PPV has distinct effects on both the right and left ventricles, affecting cardiovascular performance. Lung-protective ventilation (LPV) minimizes the risk of further lung injury through ventilator-induced lung injury and, hence, an understanding of LPV and its cardiopulmonary interactions is beneficial for cardiologists.

Lazarus Phenomenon or the Return from the Afterlife-What We Know about Auto Resuscitation

Autoresuscitation is a phenomenon of the heart during which it can resume its spontaneous activity and generate circulation. It was described for the first time by K. Linko in 1982 as a recovery after discontinued cardiopulmonary resuscitation (CPR). J.G. Bray named the recovery from death the Lazarus phenomenon in 1993. It is based on a biblical story of Jesus' resurrection of Lazarus four days after confirmation of his death. Up to the end of 2022, 76 cases (coming from 27 countries) of spontaneous recovery after death were reported; among them, 10 occurred in children. The youngest patient was 9 months old, and the oldest was 97 years old. The longest resuscitation lasted 90 min, but the shortest was 6 min. Cardiac arrest occurred in and out of the hospital. The majority of the patients suffered from many diseases. In most cases of the Lazarus phenomenon, the observed rhythms at cardiac arrest were non-shockable (Asystole, PEA). Survival time after death ranged from minutes to hours, days, and even months. Six patients with the Lazarus phenomenon reached full recovery without neurological impairment. Some of the causes leading to autoresuscitation presented here are hyperventilation and alkalosis, auto-PEEP, delayed drug action, hypothermia, intoxication, metabolic disorders (hyperkalemia), and unobserved minimal vital signs. To avoid Lazarus Syndrome, it is recommended that the patient be monitored for 10 min after discontinuing CPR. Knowledge about this phenomenon should be disseminated in the medical community in order to improve the reporting of such cases. The probability of autoresuscitation among older people is possible.

Positive end expiratory pressure and respiratory system resistance between self-inflating bag and T-piece resuscitator in a cadaveric piglet lung model

INTRODUCTION

In neonatal resuscitation, T-piece resuscitator (TPR) are used widely, but the evidence is limited for their use in infants born at term gestation. The aim of this study was to compare the delivered positive end expiratory pressure (PEEP) and respiratory system resistance (Rrs) using TPR and self-inflating bag (SIB) in a cadaveric piglet model.

METHODS

Cadaveric newborn piglets were tracheotomised, intubated (cuffed tube) and leak tested. Static lung compliance was measured. Positive pressure ventilation was applied by TPR and SIB in a randomized sequence with varying, inflations per minute (40, 60 and 80 min) and peak inspiratory pressures (18 and 30 cmH₂O). PEEP was constant at 5 cmH₂O. The lungs were washed with saline and static lung compliance was re-measured; ventilation sequences were repeated. Lung inflation data for the respiratory mechanics were measured using a respiratory function monitor and digitally recorded for both pre and post-lung wash inflation sequences. A paired sample t-test was used to compare the mean and standard deviation.

RESULTS

The mean difference in PEEP (TPR vs. SIB) was statistically significant at higher inflation rates of 60 and 80 bpm. At normal lung compliance, mean difference was 1.231 (p = 0.000) and 2.099 (p = 0.000) with PIP of 18 and 30 cmH₂O respectively. Significantly higher Rrs were observed when using a TPR with higher inflation rates of 60 and 80 bpm at varying lung compliance.

CONCLUSION

TPR is associated with significantly higher PEEP in a compliant lung model, which is probably related to the resistance of the TPR circuit. The effect of inadvertent PEEP on lung mechanics and hemodynamics need to be examined in humans. Further studies are needed to assess devices used to provide PEEP (TPR, SIB with PEEP valve, Anaesthetic bag with flow valve) during resuscitation of the newborn.

Invasive mechanical ventilation in the emergency department

Emergency department (ED) lenght of stay of the patients requiring admission to the intensive care units has increased gradually in recent years. Mechanical ventilation is an integral part of critical care and mechanically ventilated patients have to be managed and monitored by emergency physicians for longer than expected in EDs. This early period of care has significant impact on the outcomes of these patients. Therefore, emergency physicians should have comprehensive knowledge of mechanical ventilation. This review will summarize the current literature of the basic concepts, appropriate clinical applications, monitoring parameters, components and mechanisms of mechanical ventilation in the ED.

Circulatory Collapse due to Hyperinflation in a Patient with Tracheobronchomalacia: A Case Report and Brief Review

We present a case of repeated cardiac arrests derived from dynamic hyperinflation in a patient with severe tracheobronchomalacia. Mechanical ventilation led to auto-PEEP with hemodynamic impairment and pulseless electric activity. Adjusted ventilation settings, deep sedation, and muscle paralysis followed by acute stenting of the affected collapsing airways restored ventilation and prevented recurrent circulatory collapse. We briefly review the pathophysiology and treatment options in patients with dynamic hyperinflation.

Rescue therapeutic strategy combining ultra-protective mechanical ventilation with extracorporeal CO2 removal membrane in near-fatal asthma with severe pulmonary barotraumas: A case report

RATIONALE

Mechanical ventilation of severe acute asthma is still considered a challenging issue, mainly because of the gas trapping phenomenon with the potential for life-threatening barotraumatic pulmonary complications.

PATIENT CONCERNS

Herein, we describe 2 consecutive cases of near-fatal asthma for whom the recommended protective mechanical ventilation approach using low tidal volume of 6 mL/kg and small levels of PEEP was rapidly compromised by giant pneumomediastinum with extensive subcutaneousemphysema.

DIAGNOSES

Near fatal asthma.

INTERVENTION

A rescue therapeutic strategy combining extracorporeal CO2 removal membrane with ultra-protective extremely low tidal volume (3 mL/kg) ventilation was applied.

OUTCOMES

Both patients survived hospital discharge.

LESSONS

These 2 cases indicate that ECCO2R associated with ultra-protective ventilation could be an alternative to surgery in case of life-threatening barotrauma occurring under mechanical ventilation.

Monitoring of total positive end-expiratory pressure during mechanical ventilation by artificial neural networks

Ventilation treatment of acute lung injury (ALI) requires the application of positive airway pressure at the end of expiration (PEEP_app) to avoid lung collapse. However, the total pressure exerted on the alveolar walls (PEEP_tot) is the sum of PEEP_app and intrinsic PEEP (PEEP_i), a hidden component. To measure PEEP_tot, ventilation must be discontinued with an end-expiratory hold maneuver (EEHM). We hypothesized that artificial neural networks (ANN) could estimate the PEEP_tot from flow and pressure tracings during ongoing mechanical ventilation. Ten pigs were mechanically ventilated, and the time constant of their respiratory system (τ_RS) was measured. We shortened their expiratory time (TE) according to multiples of τ_RS, obtaining different respiratory patterns (R_pat). Pressure (P_AW) and flow (V'_AW) at the airway opening during ongoing mechanical ventilation were simultaneously recorded, with and without the addition of external resistance. The last breath of each R_pat included an EEHM, which was used to compute the reference PEEP_tot. The entire protocol was repeated after the induction of ALI with i.v. injection of oleic acid, and 382 tracings were obtained. The ANN had to extract the PEEP_tot, from the tracings without an EEHM. ANN agreement with reference PEEP_tot was assessed with the Bland-Altman method. Bland Altman analysis of estimation error by ANN showed -0.40 ± 2.84 (expressed as bias ± precision) and ±5.58 as limits of agreement (data expressed as cmH₂O). The ANNs estimated the PEEP_tot well at different levels of PEEP_app under dynamic conditions, opening up new possibilities in monitoring PEEP_i in critically ill patients who require ventilator treatment.

Starling curves and central venous pressure

Recent studies challenge the utility of central venous pressure monitoring as a surrogate for cardiac preload. Starting with Starling’s original studies on the regulation of cardiac output, this review traces the history of the experiments that elucidated the role of central venous pressure in circulatory physiology. Central venous pressure is an important physiologic parameter, but it is not an independent variable that determines cardiac output.