The physiology of ventilation

The diffusion of gases brings the partial pressures of O2 and CO2 in blood and alveolar gas to an equilibrium at the pulmonary blood-gas barrier. Alveolar PCO2 (PACO2) dependson the balance between the amount of CO2 being added by pulmonary blood and the amount being eliminated by alveolar ventilation (V\u2d9 A). In steady-state conditions, CO2 output equals CO2 elimination, but during nonsteadystate conditions, phase issues and impaired tissue CO2 clearance make CO2 output less predictable. Lung heterogeneity creates regional differences in CO2 concentration, and sequential emptying raises the alveolar plateau and steepens the expired CO2 slope in expiratory capnograms. Lung areas that are ventilated but not perfused form part of the dead space. Alveolar dead space is potentially large in pulmonary embolism, COPD, and all forms of ARDS. When PEEP recruits collapsed lung units, resulting in improved oxygenation, alveolar dead space may decrease; however, when PEEP induces overdistention, alveolar dead space tends to increase. Measuring physiologic dead space and alveolar ejection volume at admission or examining the trend during mechanical ventilation might provide useful information on outcomes of critically ill patients with ARDS

Titration of High Frequency Percussive Ventilation by means of real-time monitoring of the viscoelastic respiratory system properties and endotracheal tubes pressure drop.

2012/2013The use of High Frequency Percussive Ventilation (HFPV) is still debated although this type of non-conventional ventilation has proven effective and safe in patients with acute respiratory failure. In the clinical practice, HFPV is not an intuitive ventilatory modality and the absence of real-time delivered volume monitoring produces disaffection among the physicians. Avoiding the "volutrauma" is the cornerstone of the "protective ventilation strategy", which assumes a constant monitoring of inspiratory volume delivered to the patient. Currently the system capable of delivering HFPV is the VDR-4® (Volumetric Diffusive Respirator), which provides only analog airway pressure waveform and digital output of peak and the mean airway pressure. The latter is involved in the determination of oxygenation and hemodynamics, irrespective of the mode of ventilation. At the present time, the mean airway pressure, together with gas exchange analysis, are the only parameters that indirectly guide the physician in assessing the clinical effectiveness of HFPV. Till now, flow, volume and pressure curves generated by HFPV have never been studied in relation to the specific patients respiratory mechanics. The real-time examination of these parameters could allow the physicians to analyze and understand elements of respiratory system mechanics as compliance (Crs), resistance (Rrs), inertance (Irs) and of patient-ventilator interaction. The mechanical effects are complex and result from interactions between ventilator settings and patient’s respiratory system impedance. The aim of this doctoral thesis was to acquire and study volume and respiratory parameters during HFPV in order to explain this complex patients-machine interaction and transfer the results in clinical practice.XXVI Ciclo195

Pressure-flow breath representation eases asynchrony identification in mechanically ventilated patients

Breathing asynchronies are mismatches between the requests of mechanically ventilated subjects and the support provided by mechanical ventilators. The most widespread technique in identifying these pathological conditions is the visual analysis of the intra-tracheal pressure and flow time-trends. This work considers a recently introduced pressure-flow representation technique and investigates whether it can help nurses in the early detection of anomalies that can represent asynchronies. Twenty subjects—ten Intensive Care Unit (ICU) nurses and ten persons inexperienced in medical practice—were asked to find asynchronies in 200 breaths pre-labeled by three experts. The new representation increases significantly the detection capability of the subjects—average sensitivity soared from 0.622 to 0.905—while decreasing the classification time—from 1107.0 to 567.1 s on average—at the price of a not statistically significant rise in the number of wrong identifications—specificity average descended from 0.589 to 0.52. Moreover, the differences in experience between the nurse group and the inexperienced group do not affect the sensitivity, specificity, or classification times. The pressure-flow diagram significantly increases sensitivity and decreases the response time of early asynchrony detection performed by nurses. Moreover, the data suggest that operator experience does not affect the identification results. This outcome leads us to believe that, in emergency contexts with a shortage of nurses, intensive care nurses can be supplemented, for the sole identification of possible respiratory asynchronies, by inexperienced staff

Acute myocardial infarction in non-cardiac critically ill patients: a clinical-pathological study.

Background: in patients admitted to the Intensive Care Unit (ICU) for non cardiac disease, the diagnosis of acute coronary syndromes can be challenging. The aim of the study was to define the rate of discrepancies concerning the diagnosis of acute myocardial infarction and to evaluate the presence of risk factors that could be helpful in identifying patients at higher risk of missed diagnosis. Methods: we compared clinical and autopsy records of 600 critically ill patients who died in our ICU in a 10-years period. We identified patients in whom acute myocardial infarction was reported as the cause of death on the clinical records or was discovered only at post-mortem examination. These subjects were subsequently divided into two Groups: patients in Group 1 underwent diagnostic evaluation for acute myocardial infarction whereas those in Group 2 were not investigated for. Results: In Group 1, a definite clinical diagnosis was reached in 11 patients (14,7%) but remained undetermined in 37 patients (48%). The diagnosis was totally missed in 8 patients in Group 1 (10,6%) and in 20 patients of Group 2 (26,6%). The diagnostic discrepancy was higher in septic patients, in whom the correct diagnosis of acute myocardial infarction was established at a rate lower than 50% in respect to non-septic patients. Conclusions: Our experience strengthens the role of post-mortem examination as a source of feed-back of the overall diagnostic and therapeutic approach especially in septic patients, where the diagnostic error is more frequent

Postoperative analgesia after pulmonary resection with a focus on video-assisted thoracoscopic surgery

Video-assisted thoracoscopic surgery is a widespread technique that has been linked to improved postoperative respiratory function, reduced hospital length of stay and a higher level of tolerability for the patients. Acute postoperative pain is of considerable significance, and the late development of neuropathic pain syndrome is also an issue. As anaesthesiologists, we have investigated the available evidence to optimize postoperative pain management. An opioid-sparing multimodal approach is highly recommended. Loco-regional techniques such as the thoracic epidural and peripheral blocks can be performed. Several adjuvants have been employed with varying degrees of success both intravenously and in combination with local anesthetics. Opioids with different pharmacodynamic and pharmacokinetic profiles can be used, either through continuous infusion or on demand. Non-opioid analgesics are also beneficial. Finally, perioperative gabapentinoids may be implemented to prevent the onset of chronic neuropathic pain

Effect of external PEEP in patients under controlled mechanical ventilation with an auto-PEEP of 5 cmH2O or higher.

In some patients with auto-positive end-expiratory pressure (auto-PEEP), application of PEEP lower than auto-PEEP maintains a constant total PEEP, therefore reducing the inspiratory threshold load without detrimental cardiovascular or respiratory effects. We refer to these patients as complete PEEP-absorbers. Conversely, adverse effects of PEEP application could occur in patients with auto-PEEP when the total PEEP rises as a consequence. From a pathophysiological perspective, all subjects with flow limitation are expected to be complete PEEP-absorbers, whereas PEEP should increase total PEEP in all other patients. This study aimed to empirically assess the extent to which flow limitation alone explains a complete PEEP-absorber behavior (i.e., absence of further hyperinflation with PEEP), and to identify other factors associated with it.One hundred patients with auto-PEEP of at least 5 cmH2O at zero end-expiratory pressure (ZEEP) during controlled mechanical ventilation were enrolled. Total PEEP (i.e., end-expiratory plateau pressure) was measured both at ZEEP and after applied PEEP equal to 80 % of auto-PEEP measured at ZEEP. All measurements were repeated three times, and the average value was used for analysis.Forty-seven percent of the patients suffered from chronic pulmonary disease and 52 % from acute pulmonary disease; 61 % showed flow limitation at ZEEP, assessed by manual compression of the abdomen. The mean total PEEP was 7 ± 2 cmH2O at ZEEP and 9 ± 2 cmH2O after the application of PEEP (p < 0.001). Thirty-three percent of the patients were complete PEEP-absorbers. Multiple logistic regression was used to predict the behavior of complete PEEP-absorber. The best model included a respiratory rate lower than 20 breaths/min and the presence of flow limitation. The predictive ability of the model was excellent, with an overoptimism-corrected area under the receiver operating characteristics curve of 0.89 (95 % CI 0.80-0.97).Expiratory flow limitation was associated with both high and complete PEEP-absorber behavior, but setting a relatively high respiratory rate on the ventilator can prevent from observing complete PEEP-absorption. Therefore, the effect of PEEP application in patients with auto-PEEP can be accurately predicted at the bedside by measuring the respiratory rate and observing the flow-volume loop during manual compression of the abdomen

"Shoulder pain and limitation of motion in a young girl: think different"

Background Primary Synovial Chondromatosis (PSC) is a rare benign tumor of the synovial membrane in which cartilage metaplasia produces calcific loose bodies within the articular space. Only a few cases are reported in the pediatric population and its etiology remains unknown. This condition typically affects large weight-bearing joints with pain, swelling and decrease range of motion. Due to its slow progressions, delayed diagnosis is frequent and differential diagnosis should consider other chronic arthritis and malignancies. While arthroscopic removal of loose bodies is the current treatment up to now, the association of partial or complete synovectomy is debated. Case presentation We report about a 14-year-old girl with a long-lasting right shoulder pain, especially during movements or exercise, localized tenderness and hypotonia of the glenohumeral joint. No previous trauma was mentioned. Blood exams, Mantoux test and plain radiography of the right shoulder were unremarkable. Ultrasound imaging revealed echogenic and calcified bodies stretching the glenohumeral joint and dislocating the long head of biceps tendon. Magnetic resonance showed a "rice-grain" pattern of the right shoulder. From an arthroscopic surgery, multiple loose white bodies were removed within the synovial membrane, and synovial chondromatosis was confirmed by histological analysis. At one month follow up visit, the patient completely recovered without pain. Conclusion Synovial chondromatosis is a very uncommon cause of mono articular pain in children, especially when it affects shoulder. Pediatricians should keep in mind this condition to avoid delayed diagnosis and treatment, even in consideration of the low risk of malignant transformation. Through this case, we would highlight common diagnostic pitfalls and treatment of synovial chondromatosis

High-Flow Nasal Interface Improves Oxygenation in Patients Undergoing Bronchoscopy

During bronchoscopy hypoxemia is commonly found and oxygen supply can be delivered by interfaces fed with high gas flows. Recently, the high-flow nasal cannula (HFNC) has been introduced for oxygen therapy in adults, but they have not been used so far during bronchoscopy in adults. Forty-five patients were randomly assigned to 3 groups receiving oxygen: 40 L/min through a Venturi mask (V40, N = 15), nasal cannula (N40, N = 15), and 60 L/min through a nasal cannula (N60, N = 15) during bronchoscopy. Gas exchange and circulatory variables were sampled before (FiO2 = 0.21), at the end of bronchoscopy (FiO2 = 0.5), and thereafter (V40, FiO2 = 0.35). In 8 healthy volunteers oxygen was randomly delivered according to V40, N40, and N60 settings, and airway pressure was measured. At the end of bronchoscopy, N60 presented higher PaO2, PaO2/FiO2, and SpO2 than V40 and N40 that did not differ between them. In the volunteers (N60) median airway pressure amounted to 3.6 cmH2O. Under a flow rate of 40 L/min both the Venturi mask and HFNC behaved similarly, but nasal cannula associated with a 60 L/min flow produced the better results, thus indicating its use in mild respiratory dysfunctions

State-of-the-Art Sensor Technology in Spain: Invasive and Non-Invasive Techniques for Monitoring Respiratory Variables

The interest in measuring physiological parameters (especially arterial blood gases) has grown progressively in parallel to the development of new technologies. Physiological parameters were first measured invasively and at discrete time points; however, it was clearly desirable to measure them continuously and non-invasively. The development of intensive care units promoted the use of ventilators via oral intubation ventilators via oral intubation and mechanical respiratory variables were progressively studied. Later, the knowledge gained in the hospital was applied to out-of-hospital management. In the present paper we review the invasive and non-invasive techniques for monitoring respiratory variables