A novel capnogram analysis to guide ventilation during cardiopulmonary resuscitation: clinical and experimental observations.

BACKGROUND: Cardiopulmonary resuscitation (CPR) decreases lung volume below the functional residual capacity and can generate intrathoracic airway closure. Conversely, large insufflations can induce thoracic distension and jeopardize circulation. The capnogram (CO2 signal) obtained during continuous chest compressions can reflect intrathoracic airway closure, and we hypothesized here that it can also indicate thoracic distension. OBJECTIVES: To test whether a specific capnogram may identify thoracic distension during CPR and to assess the impact of thoracic distension on gas exchange and hemodynamics. METHODS: (1) In out-of-hospital cardiac arrest patients, we identified on capnograms three patterns: intrathoracic airway closure, thoracic distension or regular pattern. An algorithm was designed to identify them automatically. (2) To link CO2 patterns with ventilation, we conducted three experiments: (i) reproducing the CO2 patterns in human cadavers, (ii) assessing the influence of tidal volume and respiratory mechanics on thoracic distension using a mechanical lung model and (iii) exploring the impact of thoracic distension patterns on different circulation parameters during CPR on a pig model. MEASUREMENTS AND MAIN RESULTS: (1) Clinical data: 202 capnograms were collected. Intrathoracic airway closure was present in 35%, thoracic distension in 22% and regular pattern in 43%. (2) Experiments: (i) Higher insufflated volumes reproduced thoracic distension CO2 patterns in 5 cadavers. (ii) In the mechanical lung model, thoracic distension patterns were associated with higher volumes and longer time constants. (iii) In six pigs during CPR with various tidal volumes, a CO2 pattern of thoracic distension, but not tidal volume per se, was associated with a significant decrease in blood pressure and cerebral perfusion. CONCLUSIONS: During CPR, capnograms reflecting intrathoracic airway closure, thoracic distension or regular pattern can be identified. In the animal experiment, a thoracic distension pattern on the capnogram is associated with a negative impact of ventilation on blood pressure and cerebral perfusion during CPR, not predicted by tidal volume per se.

The other face of advanced paternal age: a scoping review of its terminological, social, public health, psychological, ethical and regulatory aspects.

BACKGROUND: There is a global tendency for parents to conceive children later in life. The maternal dimension of the postponement transition has been thoroughly studied, but interest in the paternal side is more recent. For the moment, most literature reviews on the topic have focused on the consequences of advanced paternal age (APA) on fertility, pregnancy and the health of the child. OBJECTIVE AND RATIONALE: The present review seeks to move the focus away from the biological and medical dimensions of APA and synthesise the knowledge of the other face of APA. SEARCH METHODS: We used the scoping review methodology. Searches of interdisciplinary articles databases were performed with keywords pertaining to APA and its dimensions outside of biology and medicine. We included scientific articles, original research, essays, commentaries and editorials in the sample. The final sample of 177 documents was analysed with qualitative thematic analysis. OUTCOMES: We identified six themes highlighting the interdisciplinary nature of APA research. The 'terminological aspects' highlight the lack of consensus on the definition of APA and the strategies developed to offer alternatives. The 'social aspects' focus on the postponement transition towards reproducing later in life and its cultural dimensions. The 'public health aspects' refer to attempts to analyse APA as a problem with wider health and economic implications. The 'psychological aspects' focus on the consequences of APA and older fatherhood on psychological characteristics of the child. The 'ethical aspects' reflect on issues of APA emerging at the intersection of parental autonomy, children's welfare and social responsibility. The 'regulatory aspects' group different suggestions to collectively approach the implications of APA. Our results show that the field of APA is still in the making and that evidence is lacking to fully address the issues of APA. The review suggests promising avenues of research such as introducing the voice of fathers of advanced age into the research agenda. WIDER IMPLICATIONS: The results of this review will be useful for developing policies and preconception health interventions that consider and include prospective fathers of advanced age.

A proposed lung ultrasound and phenotypic algorithm for the care of COVID-19 patients with acute respiratory failure.

Pulmonary complications are the most common clinical manifestations of coronavirus disease (COVID-19). From recent clinical observation, two phenotypes have emerged: a low elastance or L-type and a high elastance or H-type. Clinical presentation, pathophysiology, pulmonary mechanics, radiological and ultrasound findings of these two phenotypes are different. Consequently, the therapeutic approach also varies between the two. We propose a management algorithm that combines the respiratory rate and oxygenation index with bedside lung ultrasound examination and monitoring that could help determine earlier the requirement for intubation and other surveillance of COVID-19 patients with respiratory failure.

RéSUMé: Les complications pulmonaires du coronavirus (COVID-19) constituent ses manifestations cliniques les plus fréquentes. De récentes observations cliniques ont fait émerger deux phénotypes : le phénotype à élastance faible ou type L (low), et le phénotype à élastance élevée, ou type H (high). La présentation clinique, la physiopathologie, les mécanismes pulmonaires, ainsi que les observations radiologiques et échographiques de ces deux différents phénotypes sont différents. L'approche thérapeutique variera par conséquent selon le phénotype des patients atteints de COVID-19 souffrant d'insuffisance respiratoire.

Gastric insufflation during cardiopulmonary resuscitation: A study in human cadavers.

INTRODUCTION: Bag-valve-mask ventilation is the first-line ventilation method during cardiopulmonary resuscitation (CPR). Risks include excessive volume delivery and gastric insufflation, the latter increasing the risk of pneumonia. The efficacy of ventilation can also be reduced by airway closure. We hypothesized that continuous chest compression (CC) could limit the risk of gastric insufflation compared to the recommended 30:2 interrupted CC strategy. This experimental study was performed in human "Thiel" cadavers to assess the respective impact of discontinuous vs. continuous chest compressions on gastric insufflation and ventilation during CPR. METHODS: The 30:2 interrupted CC technique was compared to continuous CC in 5 non-intubated cadavers over a 6 min-period. Flow and Airway Pressure were measured at the mask. A percutaneous gastrostomy allowed measuring the cumulative gastric insufflated volume. Two additional cadavers were equipped with esophageal and gastric catheters instead of the gastrostomy. RESULTS: For the 7 cadavers studied (4 women) median age of death was 79 [74-84] years. After 6 min of CPR, the cumulative gastric insufflation measured in 5 cadavers was markedly reduced during continuous CC compared to the interrupted CC strategy: (1.0 [0.8-4.1] vs. 5.9 [4.0-5.6] L; p < 0.05) while expired minute ventilation was slightly higher during continuous than interrupted CC (1.9 [1.4-2.8] vs. 1.6 [1.1-2.7] L/min; P < 0.05). In 2 additional cadavers, the progressive rise in baseline gastric pressure was lower during continuous CC than interrupted CC (1 and 2 cmH2O vs. 12 and 5.8 cmH2O). CONCLUSION: Continuous CC significantly reduces the volume of gas insufflated in the stomach compared to the recommended 30:2 interrupted CC strategy. Ventilation actually delivered to the lung is also slightly increased by the strategy.

Intrathoracic Airway Closure Impacts CO2 Signal and Delivered Ventilation during Cardiopulmonary Resuscitation.

RATIONALE: End-tidal CO2 (EtCO2) is used to monitor cardiopulmonary resuscitation (CPR), but it can be affected by intrathoracic airway closure. Chest compressions induce oscillations in expired CO2, and this could reflect variable degrees of airway patency. OBJECTIVES: To understand the impact of airway closure during CPR, and the relationship between the capnogram shape, airway closure, and delivered ventilation. METHODS: This study had three parts: 1) a clinical study analyzing capnograms after intubation in patients with out-of-hospital cardiac arrest receiving continuous chest compressions, 2) a bench model, and 3) experiments with human cadavers. For 2 and 3, a constant CO2 flow was added in the lung to simulate CO2 production. Capnograms similar to clinical recordings were obtained and different ventilator settings tested. EtCO2 was compared with alveolar CO2 (bench). An airway opening index was used to quantify chest compression-induced expired CO2 oscillations in all three clinical and experimental settings. MEASUREMENTS AND MAIN RESULTS: A total of 89 patients were analyzed (mean age, 69 ± 15 yr; 23% female; 12% of hospital admission survival): capnograms exhibited various degrees of oscillations, quantified by the opening index. CO2 value varied considerably across oscillations related to consecutive chest compressions. In bench and cadavers, similar capnograms were reproduced with different degrees of airway closure. Differences in airway patency were associated with huge changes in delivered ventilation. The opening index and delivered ventilation increased with positive end-expiratory pressure, without affecting intrathoracic pressure. Maximal EtCO2 recorded between ventilator breaths reflected alveolar CO2 (bench). CONCLUSIONS: During chest compressions, intrathoracic airway patency greatly affects the delivered ventilation. The expired CO2 signal can reflect CPR effectiveness but is also dependent on airway patency. The maximal EtCO2 recorded between consecutive ventilator breaths best reflects alveolar CO2.

How Ventilation Is Delivered During Cardiopulmonary Resuscitation: An International Survey.

BACKGROUND: Recommendations regarding ventilation during cardiopulmonary resuscitation (CPR) are based on a low level of scientific evidence. We hypothesized that practices about ventilation during CPR might be heterogeneous and may differ worldwide. To address this question, we surveyed physicians from several countries on their practices during CPR. METHODS: We used a Web-based opinion survey. Links to the survey were sent by e-mail newsletters and displayed on the Web sites of medical societies involved in CPR practice from December 2013 to March 2014. RESULTS: 1,328 surveys were opened, and 548 were completed (41%). Responses came from 54 countries, but 64% came from 6 countries. Responders were mostly physicians (89%). From this group, 97% declared following specific CPR guidelines. Regarding practices, 28% declared always or frequently adopting only continuous chest compressions without additional ventilation. With regard to mechanical chest compression devices, 38% responded that such devices were available to them; when used, 28% declared always or frequently experiencing problems with ventilation such as frequent alarms. During bag-mask ventilation in intubated patients, 18% declared stopping chest compression during insufflation, and 39% applied > 10 breaths/min, which conflicts with international CPR guidelines. When a ventilator was used, the volume controlled mode was the most common strategy cited, but there was heterogeneity regarding ventilator settings for PEEP, trigger, FIO2 , and breathing frequency. SpO2 and end-tidal CO2 were the 2 most monitored variables cited. CONCLUSIONS: Physicians indicated heterogeneous practices that often differ significantly from international CPR guidelines. This may reflect the low level of evidence and a lack of detailed recommendations concerning ventilation during CPR.

A new physiological model for studying the effect of chest compression and ventilation during cardiopulmonary resuscitation: The Thiel cadaver.

BACKGROUND: Studying ventilation and intrathoracic pressure (ITP) induced by chest compressions (CC) during Cardio Pulmonary Resuscitation is challenging and important aspects such as airway closure have been mostly ignored. We hypothesized that Thiel Embalmed Cadavers could constitute an appropriate model. METHODS: We assessed respiratory mechanics and ITP during CC in 11 cadavers, and we compared it to measurements obtained in 9 out-of-hospital cardiac arrest patients and to predicted values from a bench model. An oesophageal catheter was inserted to assess chest wall compliance, and ITP variation (ΔITP). Airway pressure variation (ΔPaw) at airway opening and ΔITP generated by CC were measured at decremental positive end expiratory pressure (PEEP) to test its impact on flow and ΔPaw. The patient's data were derived from flow and airway pressure captured via the ventilator during resuscitation. RESULTS: Resistance and Compliance of the respiratory system were comparable to those of the out-of-hospital cardiac arrest patients (CRSTEC 42 ±â€¯12 vs CRSPAT 37.3 ±â€¯10.9 mL/cmH2O and ResTEC 17.5 ±â€¯7.5 vs ResPAT 20.2 ±â€¯5.3 cmH2O/L/sec), and remained stable over time. During CC, ΔITP varied from 32 ±â€¯12 cmH2O to 69 ±â€¯14 cmH2O with manual and automatic CC respectively. Transmission of ΔITP at the airway opening was significantly affected by PEEP, suggesting dynamic small airway closure at low lung volumes. This phenomenon was similarly observed in patients. CONCLUSION: Respiratory mechanics and dynamic pressures during CC of cadavers behave as predicted by a theoretical model and similarly to patients. The Thiel model is a suitable to assess ITP variations induced by ventilation during CC.

Aerosolized Vasodilators for the Treatment of Pulmonary Hypertension in Cardiac Surgical Patients: A Systematic Review and Meta-analysis.

BACKGROUND: In cardiac surgery, pulmonary hypertension is an important prognostic factor for which several treatments have been suggested over time. In this systematic review and meta-analysis, we compared the efficacy of inhaled aerosolized vasodilators to intravenously administered agents and to placebo in the treatment of pulmonary hypertension during cardiac surgery. We searched MEDLINE, CENTRAL, EMBASE, Web of Science, and clinicaltrials.gov databases from inception to October 2015. The incidence of mortality was assessed as the primary outcome. Secondary outcomes included length of stay in hospital and in the intensive care unit, and evaluation of the hemodynamic profile. METHODS: Of the 2897 citations identified, 10 studies were included comprising a total of 434 patients. RESULTS: Inhaled aerosolized agents were associated with a significant decrease in pulmonary vascular resistance (-41.36 dyne·s/cm, P= .03) and a significant increase in mean arterial pressure (8.24 mm Hg, P= .02) and right ventricular ejection fraction (7.29%, P< .0001) when compared to intravenously administered agents. No significant hemodynamically meaningful differences were observed between inhaled agents and placebo; however, an increase in length of stay in the intensive care unit was shown with the use of inhaled aerosolized agents (0.66 days, P= .01). No other differences were observed for either comparison. CONCLUSIONS: The administration of inhaled aerosolized vasodilators for the treatment of pulmonary hypertension during cardiac surgery is associated with improved right ventricular performance when compared to intravenously administered agents. This review does not support any benefit compared to placebo on major outcomes. Further investigation is warranted in this area of research and should focus on clinically significant outcomes.

Comparison of inhaled milrinone, nitric oxide and prostacyclin in acute respiratory distress syndrome.

AIM: To evaluate the safety and efficacy of inhaled milrinone in acute respiratory distress syndrome (ARDS). METHODS: Open-label prospective cross-over pilot study where fifteen adult patients with hypoxemic failure meeting standard ARDS criteria and monitored with a pulmonary artery catheter were recruited in an academic 24-bed medico-surgical intensive care unit. Random sequential administration of iNO (20 ppm) or nebulized epoprostenol (10 µg/mL) was done in all patients. Thereafter, inhaled milrinone (1 mg/mL) alone followed by inhaled milrinone in association with inhaled nitric oxide (iNO) was administered. A jet nebulization device synchronized with the mechanical ventilation was use to administrate the epoprostenol and the milrinone. Hemodynamic measurements and partial pressure of arterial oxygen (PaO2) were recorded before and after each inhaled therapy administration. RESULTS: The majority of ARDS were of pulmonary cause (n = 13) and pneumonia (n = 7) was the leading underlying initial disease. Other pulmonary causes of ARDS were: Post cardiopulmonary bypass (n = 2), smoke inhalation injury (n = 1), thoracic trauma and pulmonary contusions (n = 2) and aspiration (n = 1). Two patients had an extra pulmonary cause of ARDS: A polytrauma patient and an intra-abdominal abscess Inhaled nitric oxide, epoprostenol, inhaled milrinone and the combination of inhaled milrinone and iNO had no impact on systemic hemodynamics. No significant adverse events related to study medications were observed. The median increase of PaO2 from baseline was 8.8 mmHg [interquartile range (IQR) = 16.3], 6.0 mmHg (IQR = 18.4), 6 mmHg (IQR = 15.8) and 9.2 mmHg (IQR = 20.2) respectively with iNO, epoprostenol, inhaled milrinone, and iNO added to milrinone. Only iNO and the combination of inhaled milrinone and iNO had a statistically significant effect on PaO2. CONCLUSION: When comparing the effects of inhaled NO, milrinone and epoprostenol, only NO significantly improved oxygenation. Inhaled milrinone appeared safe but failed to improve oxygenation in ARDS.

Nasal high-flow therapy for type II respiratory failure in COPD: A report of four cases.

Herein we present a report of four cases of severe type II respiratory failure that had contraindications both to conventional non-invasive ventilation and to endotracheal intubation. In all four cases, we successfully used a high-flow nasal oxygen device as a rescue device, with very reassuring outcomes.

Development of theory-based knowledge translation interventions to facilitate the implementation of evidence-based guidelines on the early management of adults with traumatic spinal cord injury.

RATIONALE: Optimal, early management following a spinal cord injury (SCI) can limit individuals' disabilities and costs related to their care. Several knowledge syntheses were recently published to guide health care professionals with regard to early interventions in SCI patients. However, no knowledge translation (KT) intervention, selected according to a behaviour change theory, has been proposed to facilitate the use of SCI guidelines in an acute care setting. OBJECTIVES: To develop theory-informed KT interventions to promote the application of evidence-based recommendations on the acute care management of SCI patients. METHODS: The first four phases of the knowledge-to-action model were used to establish the study design. Knowledge selection was based on the Grading of Recommendations Assessment, Development and Evaluation system. Knowledge adaptation to the local context was sourced from the ADAPTE process. The theoretical domains framework oriented the selection and development of the interventions based on an assessment of barriers and enablers to knowledge application. RESULTS: Twenty-nine recommendations were chosen and operationalized in measurable clinical indicators. Barriers related to knowledge, skills, perceived capacities, beliefs about consequences, social influences, and the environmental context and resources theoretical domains were identified. The mapping of behaviour change techniques associated with those barriers led to the development of an online educational curriculum, interdisciplinary clinical pathways as well as policies and procedures. CONCLUSIONS: This research project allowed us developing KT interventions according to a thorough behavioural change methodology. Exposure to the generated interventions will support health care professionals in providing the best care to SCI patients.

Effect of ventilatory variability on occurrence of central apneas.

OBJECTIVE: To compare the influence of 2 ventilation strategies on the occurrence of central apneas. METHODS: This was a prospective, comparative, crossover study with 14 unsedated subjects undergoing weaning from mechanical ventilation in the medical ICU of Hôpital du Sacré-Cœur, Montréal, Québec, Canada. The subjects were ventilated alternately in neurally adjusted ventilatory assist (NAVA) and pressure support ventilation (PSV) modes. Inspiratory flow/time and pressure/time waveforms and diaphragmatic electrical activity were used to detect central apneas. Ventilatory variability and breathing pattern were evaluated in both modes. Breathing patterns just before central apneas, and associations between apneas and sleep patterns (electroencephalogram) were studied. RESULTS: Switching from PSV to NAVA did not change mean minute ventilation, tidal volume, or breathing frequency. However, tidal volume variability, defined as the coefficient of variability (standard error/mean), was significantly greater with NAVA than with PSV (17.2 ± 8 vs 10.3 ± 4, P = .045). NAVA induced a greater decrease in central apneas, compared to PSV (to 0 with NAVA vs 10.5 ± 11 with PSV, P = .005). Central apneas during PSV were detected only during non-rapid-eye-movement sleep. CONCLUSIONS: NAVA was associated with increased ventilatory variability, compared to constant-level PSV. With NAVA the absence of over-assistance during sleep coincided with absence of central apneas, suggesting that load capacity and/or neuromechanical coupling were improved by NAVA and that this improvement decreased or abolished central apneas.

Clinical review: Update on neurally adjusted ventilatory assist--report of a round-table conference.

Conventional mechanical ventilators rely on pneumatic pressure and flow sensors and controllers to detect breaths. New modes of mechanical ventilation have been developed to better match the assistance delivered by the ventilator to the patient's needs. Among these modes, neurally adjusted ventilatory assist (NAVA) delivers a pressure that is directly proportional to the integral of the electrical activity of the diaphragm recorded continuously through an esophageal probe. In clinical settings, NAVA has been chiefly compared with pressure-support ventilation, one of the most popular modes used during the weaning phase, which delivers a constant pressure from breath to breath. Comparisons with proportional-assist ventilation, which has numerous similarities, are lacking. Because of the constant level of assistance, pressure-support ventilation reduces the natural variability of the breathing pattern and can be associated with asynchrony and/or overinflation. The ability of NAVA to circumvent these limitations has been addressed in clinical studies and is discussed in this report. Although the underlying concept is fascinating, several important questions regarding the clinical applications of NAVA remain unanswered. Among these questions, determining the optimal NAVA settings according to the patient's ventilatory needs and/or acceptable level of work of breathing is a key issue. In this report, based on an investigator-initiated round table, we review the most recent literature on this topic and discuss the theoretical advantages and disadvantages of NAVA compared with other modes, as well as the risks and limitations of NAVA.

Sleep quality in mechanically ventilated patients: comparison between NAVA and PSV modes.

BACKGROUND: Mechanical ventilation seems to occupy a major source in alteration in the quality and quantity of sleep among patients in intensive care. Quality of sleep is negatively affected with frequent patient-ventilator asynchronies and more specifically with modes of ventilation. The quality of sleep among ventilated patients seems to be related in part to the alteration between the capacities of the ventilator to meet patient demand. The objective of this study was to compare the impact of two modes of ventilation and patient-ventilator interaction on sleep architecture. METHODS: Prospective, comparative crossover study in 14 conscious, nonsedated, mechanically ventilated adults, during weaning in a university hospital medical intensive care unit. Patients were successively ventilated in a random ordered cross-over sequence with neurally adjusted ventilatory assist (NAVA) and pressure support ventilation (PSV). Sleep polysomnography was performed during four 4-hour periods, two with each mode in random order. RESULTS: The tracings of the flow, airway pressure, and electrical activity of the diaphragm were used to diagnose central apneas and ineffective efforts. The main abnormalities were a low percentage of rapid eye movement (REM) sleep, for a median (25th-75th percentiles) of 11.5% (range, 8-20%) of total sleep, and a highly fragmented sleep with 25 arousals and awakenings per hour of sleep. Proportions of REM sleep duration were different in the two ventilatory modes (4.5% (range, 3-11%) in PSV and 16.5% (range, 13-29%) during NAVA (p = 0.001)), as well as the fragmentation index, with 40 ± 20 arousals and awakenings per hour in PSV and 16 ± 9 during NAVA (p = 0.001). There were large differences in ineffective efforts (24 ± 23 per hour of sleep in PSV, and 0 during NAVA) and episodes of central apnea (10.5 ± 11 in PSV vs. 0 during NAVA). Minute ventilation was similar in both modes. CONCLUSIONS: NAVA improves the quality of sleep over PSV in terms of REM sleep, fragmentation index, and ineffective efforts in a nonsedated adult population.

Preliminary evaluation of a new index to predict the outcome of a spontaneous breathing trial.

BACKGROUND: The available predictors of spontaneous-breathing-trial (SBT) success/failure lack accuracy. We devised a new index, the CORE index (compliance, oxygenation, respiration, and effort). OBJECTIVE: To compare the CORE index to the CROP index (compliance, rate, oxygenation, and pressure), airway-occlusion pressure 0.1 s after the start of inspiratory flow (P(0.1)), and rapid shallow breathing index (RSBI) for predicting SBT success/failure in a critical care environment. METHODS: With 47 mechanically ventilated patients recovering from respiratory failure, of various causes, we prospectively examined the SBT success/failure prediction accuracy and calculated receiver operating characteristic curves, sensitivity, specificity, and likelihood ratios of CORE, CROP, P(0.1), and RSBI. RESULTS: The specificities were CORE 0.95, P(0.1) 0.70, CROP 0.70, and RSBI 0.65. The sensitivities were CORE 1.00, CROP 1.00, P(0.1) 0.93, and RSBI 0.89. The areas under the receiver operating characteristic curve were CORE 1.00 (95% CI 0.92-1.00), CROP 0.91 (95% CI 0.79-0.97), P(0.1) 0.81 (95% CI 0.67-0.91), and RSBI 0.77 (95% CI 0.62-0.88). The positive likelihood ratios were CORE 20.0, CROP 3.3, P(0.1) 3.1, and RSBI 2.5. The negative likelihood ratios were CORE 0.0, CROP 0.0, P(0.1) 0.1, and RSBI 0.2. CONCLUSIONS: The CORE index was the most accurate predictor of SBT success/failure.

Diaphragmatic electromyography during cryoballoon ablation: a novel concept in the prevention of phrenic nerve palsy.

BACKGROUND: Hemidiaphragmatic paralysis is the most frequent complication associated with cryoballoon ablation for atrial fibrillation. To date, no preventive strategy has proved effective. OBJECTIVE: We sought to assess the feasibility of diaphragmatic electromyography during cryoballoon ablation, explore the relationship between altered signals and phrenic nerve palsy, and define characteristic changes that herald hemidiaphragmatic paralysis. METHODS: Cryoballoon ablation was performed in the right superior pulmonary vein or superior vena cava in 16 mongrel dogs weighing 37.7 ± 2.4 kg, at sites determined by phrenic nerve capture. During ablation, the phrenic nerve was paced at 60 bpm from the superior vena cava while recording diaphragmatic compound motor action potentials (CMAPs) by esophageal decapolar catheters. Diaphragmatic excursion was monitored by fluoroscopy and abdominal palpation. RESULTS: Before ablation, the CMAP amplitude was 592 (interquartile range 504, 566) µV, initial latency 21.5 ± 4.2 ms, peak latency 64.7 ± 21.1 ms, and duration 101.7 ± 13.3 ms. Hemidiaphragmatic paralysis was obtained in all dogs 62 ± 34 seconds into the cryoapplication. The CMAP amplitude decreased exponentially, with no patterned changes in latencies and duration. Discriminatory analyses by receiver-operating curve characteristics identified a 30% reduction in CMAP amplitude as the most predictive cutoff value for hemidiaphragmatic paralysis (c-statistic 0.965; P<.0001). This criterion presaged diaphragmatic paralysis, as detected by abdominal palpation, by 31 ± 23 seconds. CONCLUSION: Diaphragmatic electromyographic signals could be reliably recorded during cryoballoon ablation. An exponential decrease in CMAP amplitude precedes diaphragmatic paralysis, with a 30% reduction yielding the best discriminatory potential. A promising safety margin was detected, which merits prospective validation.

Patient-ventilator interaction during pressure support ventilation and neurally adjusted ventilatory assist.

OBJECTIVE: To compare the effect of pressure support ventilation and neurally adjusted ventilatory assist on breathing pattern, patient-ventilator synchrony, diaphragm unloading, and gas exchange. Increasing the level of pressure support ventilation can increase tidal volume, reduce respiratory rate, and lead to delayed ventilator triggering and cycling. Neurally adjusted ventilatory assist uses diaphragm electrical activity to control the timing and pressure of assist delivery and is expected to enhance patient-ventilator synchrony. DESIGN: Prospective, comparative, crossover study. SETTING: Adult critical care unit in a tertiary university hospital. PATIENTS: Fourteen nonsedated mechanically ventilated patients (n = 12 with chronic obstructive pulmonary disease). INTERVENTIONS: Patients were ventilated for 10-min periods, using two pressure support ventilation levels (lowest tolerable and +7 cm H2O higher) and two neurally adjusted ventilatory assist levels (same peak pressures and external positive end-expiratory pressure as with pressure support ventilation), delivered in a randomized order. MEASUREMENTS AND MAIN RESULTS: Diaphragm electrical activity, respiratory pressures, air flow, volume, neural and ventilator respiratory rates, and arterial blood gases were measured. Peak pressures were 17 +/- 6 cm H2O and 24 +/- 6 cm H2O and 19 +/- 5 cm H2O and 24 +/- 6 cm H2O with high and low pressure support ventilation and neurally adjusted ventilatory assist, respectively. The breathing pattern was comparable with pressure support ventilation and neurally adjusted ventilatory assist during low assist; during higher assist, larger tidal volumes (p = .003) and lower breathing frequencies (p = .008) were observed with pressure support ventilation. Increasing the assist increased cycling delays only with pressure support ventilation (p = .003). Compared with pressure support ventilation, neurally adjusted ventilatory assist reduced delays of ventilator triggering (p < .001 for low and high assist) and cycling (high assist: p = .004; low assist: p = .04), and abolished wasted inspiratory efforts observed with pressure support ventilation in six subjects. The diaphragm electrical activity and pressure-time product for ventilator triggering were lower with neurally adjusted ventilatory assist (p = .005 and p = .02, respectively; analysis of variance). Arterial blood gases were similar with both modes. CONCLUSIONS: Neurally adjusted ventilatory assist can improve patient-ventilator synchrony by reducing the triggering and cycling delays, especially at higher levels of assist, at the same time preserving breathing and maintaining blood gases.