Roberto Marcolin

Relationships between lung computed tomographic density, gas exchange, and PEEP in acute respiratory failure.

Twenty-two patients with acute respiratory failure underwent lung computed tomography (CT) and physiological measurements at 5, 10, and 15 cm H2O positive end-expiratory pressure (PEEP) to investigate the relationship between morphology and function. Lung densities were primarily concentrated in the dependent regions. From the frequency distribution of CT numbers (difference in xray attenuation between water and lung) and lung gas volume measurements the authors obtained a quantitative estimate of normally inflated, poorly inflated, and non-inflated lung tissue weight. This estimated average lung weight was increased twofold nbove normal and excess lung weight correlated with the mean pulmonary artery pressure (P < 0.01). Venous admixture correlated with the non-inflated tissue mass (P < 0.01). Increasing PEEP caused progressive clearing of radiographic densities and increased the mass of normally inflated tissue (anatomic recruitment), while reducing venous admixture. The cardiac index decreased after increasing PEEP while oxygen delivery was unchanged. The authors conclude that CT scan lung density and oxygen exchange efficiency are correlated; the main effect of augmenting PEEP is to recruit perfused alveolar units that were previously collapsed.

Morphological response to positive end expiratory pressure in acute respiratory failure. Computerized tomography study

SummaryTen patients with acute respiratory failure (ARF), (4 pneumonia, 4 sepsis, 2 polytrauma), underwent computerized tomography (CT) of the lungs, (apex, hilum, base), at 5, 10, 15 cm H2O positive end expiratory pressure (PEEP). The ARF lungs, on CT scan, appeared as a patchwork of normal and dense areas with generally well defined boundaries. Most of the densities were found in the dependent regions. The areas of density were correlated with PaO2 (r=0.51). The PEEP increase resulted in a significant expansion of total cross-sectional lung surface area. The dense areas decreased significantly at the hilum and base when increasing PEEP while the changes at the apex were not significant. The changes of density with PEEP were highly correlated with the changes in oxygenation (r=0.91). In the individual patient, however, the modifications of gas exchange can not be entirely predicted from morphological changes, possibly due to a diversion of pulmonary blood flow.

The role of total static lung compliance in the management of severe ARDS unresponsive to conventional treatment

A group of 36 patients with severe adult respiratory distress syndrome (ARDS) meeting previously established blood gas criteria (mortality rate 90%) became candidates for possible extracorporeal respiratory support [low frequency positive pressure ventilation with extracorporeal CO2 removal (LFPPV-ECCO2R)]. Before connecting the patients to bypass we first switched the patients from conventional mechanical ventilation with positive end expiratory pressure (PEEP) to pressure controlled inverted ratio ventilation (PC-IRV), and then when feasible, to spontaneous breathing with continuous positive airways pressure (CPAP). Forty eight hours after the patients had entered the treatment protocol, only 19 out of the 36 patients in fact required LFPPV-ECCO2R, while 5 were still on PC-IRV, and 12 were on CPAP. The overall mortality rate of the entire population was 23%. The only predictive value of success or failure of a particular treatment mode was total static lung compliance (TSLC). No patients with a TSLC lower than 25 ml (cm H2O)-1 tolerated either PC-IRV or CPAP, while all patients with a TSLC higher than 30 ml (cm H2O)-1 were successfully treated with CPAP. Borderline patients (TSLC between 25 and 30 ml (cm H2O)-1) had to be treated with PC-IRV for more than 48 h, or were then placed on LFPPV-ECCO2R if Paco2 rose prohibitively. We conclude that TSLC is a most useful measurement in deciding on the best management of patients with severe ARDS, unresponsive to conventional treatment.

Mean airway pressure vs. positive end-expiratory pressure during mechanical ventilation

To investigate the effects of both positive end-expiratory pressure (PEEP) and mean airway pressure (Paw) on gas exchange, we used lung lavage to induce severe respiratory insufficiency in six lambs. The animals were then mechanically ventilated at constant tidal volume, respiratory rate, and inspired O2 fraction. PEEP levels were varied −5, +5 and +10 cm H2O around the pressure (Pflex) corresponding to a major change in slope of the inspiratory limb of the respiratory volume-pressure curve. In each animal the effects of the three PEEP levels were studied at two Paw levels, differing by 5 cm H2O.Increasing Paw significantly improved PaO2 and reduced venous admixture. A 5-cm H2O PEEP increase from +5 to +10 did not affect oxygenation; however, oxygenation was significantly better when PEEP was greater than Pflex. Both PaCO2 and anatomic dead space were higher at higher PEEP, and decreased with increasing Paw. Hence, Paw was a major determinant of oxygenation, although a PEEP greater than Pflex appeared necessary to optimize oxygenation at a constant Paw.

Extracorporeal membrane oxygenation for interhospital transfer of severe acute respiratory distress syndrome patients: 5-year experience.

Purpose Transfer of severely hypoxic patients is a high-risk procedure. Extracorporeal Membrane Oxygenation (ECMO) allows safe transport of these patients to tertiary care institutions. Our ECMO transportation program was instituted in 2004; here we report results after 5 years of activity. Methods This is a clinical observational study. Criteria for ECMO center activation were: potentially reversibile respiratory failure, PaO2 <50 mmHg with FiO2 >0.6 for >12 hours, PEEP >5 cmH20, Lung Injury Score (LIS) ≥3 or respiratory acidosis with pH <7.2, no intracranial bleeding, and no absolute contraindication to anticoagulation. If eligible, a skilled crew applied ECMO at the referral hospital. Transportation was performed with a specially equipped ambulance. Results Sixteen patients were possible candidates for ECMO transfer. Two patients were excluded while 14 (mean±SD, age 35.4±18.6, SOFA 8.4±3.7, Oxygenation Index 43.7±13.4) were transported to our institution (distance covered 102±114 km, global duration of transport 589±186 minutes). Two patients improved after iNO-trial and were transferred and subsequently managed without ECMO. The remaining 12 patients were transferred on veno-venous ECMO with extracorporeal blood flow 2.7±1 L·min−1, gas flow 3.8±1.8 L·min−1, and FiO2 1. Data were recorded 30 minutes before and 60 minutes after initiation of ECMO. ECMO improved PCO2 (75±23 vs. 53±9 mmHg, p<0.01) thus improving pH (7.28±0.13 vs. 7.39±0.05, p<0.01) and allowing a reduction in respiratory rate (35±14 vs. 10±4 breaths/min, p<0.01), minute ventilation (10.1±3.8 vs. 3.7±1.7 L·min−1, p<0.01), and mean airway pressure (26±6.5 vs. 22±5 cmH2O, p<0.01). No major clinical or technical complications were observed. Conclusions ECMO effectively enabled high-risk ground transfer of severely hypoxic patients.

Effects of Sigh on Regional Lung Strain and Ventilation Heterogeneity in Acute Respiratory Failure Patients Undergoing Assisted Mechanical Ventilation

Objective:In acute respiratory failure patients undergoing pressure support ventilation, a short cyclic recruitment maneuver (Sigh) might induce reaeration of collapsed lung regions, possibly decreasing regional lung strain and improving the homogeneity of ventilation distribution. We aimed to describe the regional effects of different Sigh rates on reaeration, strain, and ventilation heterogeneity, as measured by thoracic electrical impedance tomography. Design:Prospective, randomized, cross-over study. Setting:General ICU of a single university-affiliated hospital. Patients:We enrolled 20 critically ill patients intubated and mechanically ventilated with PaO2/FIO2 up to 300 mm Hg and positive end-expiratory pressure at least 5 cm H2O (15 with acute respiratory distress syndrome), undergoing pressure support ventilation as per clinical decision. Interventions:Sigh was added to pressure support ventilation as a 35 cm H2O continuous positive airway pressure period lasting 3–4 seconds at different rates (no-Sigh vs 0.5, 1, and 2 Sigh(s)/min). All study phases were randomly performed and lasted 20 minutes. Measurements and Main Results:In the last minutes of each phase, we measured arterial blood gases, changes in end-expiratory lung volume of nondependent and dependent regions, tidal volume reaching nondependent and dependent lung (Vtnondep and Vtdep), dynamic intratidal ventilation heterogeneity, defined as the average ratio of Vt reaching nondependent/Vt reaching dependent lung regions along inspiration (VtHit). With Sigh, oxygenation improved (p < 0.001 vs no-Sigh), end-expiratory lung volume of nondependent and dependent regions increased (p < 0.01 vs no-Sigh), Vtnondep showed a trend to reduction, and Vtdep significantly decreased (p = 0.11 and p < 0.01 vs no-Sigh, respectively). VtHit decreased only when Sigh was delivered at 0.5/min (p < 0.05 vs no-Sigh), while it did not vary during the other two phases. Conclusions:Sigh decreases regional lung strain and intratidal ventilation heterogeneity. Our study generates the hypothesis that in ventilated acute respiratory failure patients, Sigh may enhance regional lung protection.

Use of extracorporeal respiratory support during pregnancy: a case report and literature review

We describe the case of a 25 year-old woman at 27 weeks of gestation who was admitted to our intensive care unit (ICU) for acute respiratory distress syndrome (ARDS) caused by pandemic 2009 H1N1 influenza A. She presented with septic shock and refractory hypoxemia unresponsive to rescue therapies such as recruitment maneuvers, prone positioning, and nitric oxide inhalation. Extracorporeal membrane oxygenation (ECMO) for respiratory support was instituted, and the patients clinical conditions progressively improved: she was extubated after 16 days and discharged from the ICU 3 days later. No fetal complications were observed. At 38 weeks of gestation she gave birth to a healthy baby.

Venous admixture (Qva/Q) and true shunt (Qs/Qt) in ARF patients: Effects of PEEP at constant FIO2

Venous admixture (Qva/Q) in ARF patients is due to both true right to left shunt (Qs/Qt: perfusion of truly unventilated areas) and to maldistribution ((Qva-Qs)/Qt: effects of unevenness of ventilation/perfusion ratio). Using the retention rate of sulphur hexafluoride we determined the effects of PEEP on Qs/Qt and (Qva-Qs)/Qt at a constant FIO2 for each patient (0.57±0.19 SD, range 0.4–0.95). Eleven patients with ARF (treated either by CPPV or CPAP) were studied on 16 occasions. Each measurement was repeated at two levels of PEEP, 5 cm H2O below and 5 cm H2O above the patients clinically determined PEEP level. The increase in PEEP resulted in: — a decrease in Qva/Q (from 0.37±0.13 to 0.27±0.12,p<0.01); — a parallel decrease in Qs/Qt (from 0.29±0.16 to 0.22±0.14,p<0.01); there was a positive correlation between Qva/Q and Qs/Qt changes (r=0.53,p<0.05). No significant variation was demonstrated in (Qva-Qs)/Qt (from 0.074±0.045 to 0.054±0.048). On the other hand there was a negative correlation between the fraction of Qva/Q due to the maldistribution and FIO2: (Qva-Qs)/Qva=0.75–0.86 FIO2 (r=0.74,p<0.01). We conclude that: PEEP decreased Qva/Q mainly through changes in Qs/Qt but did not have a definite effect on (Qva-Qs)/Qt. Maldistribution was responsible for a significant portion of Qva/Q in those ARF patients tolerating a relatively low FIO2 (0.4–0.6).

Extra-corporeal life support for near-fatal multi-drug intoxication: a case report

IntroductionSevere mixed β-blocker and calcium channel blocker intoxication presents a significant risk for patient mortality. Although treatment is well-established, it sporadically fails to support the patient through massive overdoses, thus requiring non-conventional treatments. We report the use of extra-corporeal life support in a patient with refractory hemodynamic impairment due to multi-drug intoxication. Although sometimes used in clinical practice, extra-corporeal membrane oxygenation for intoxications has rarely been reported.Case presentationA 36-year-old Caucasian man presented to our hospital with refractory hypotension, severe cardiac insufficiency and multi-organ failure due to mixed intoxication with atenolol, nifedipine, Lacidipine and sertraline. Together with standard treatment, we performed extra-corporeal membrane oxygenation to overcome refractory cardiogenic shock and lead the patient to achieve a full recovery.ConclusionStandard of care for β-blocker and calcium channel blocker intoxication is well-defined and condensed into protocols of treatment. Although aimed at clearing the noxious agents from the patients system, standard measures may fail to provide adequate hemodynamic support to allow recovery. In selected cases, extra-corporeal membrane oxygenation could be considered a bridge to drug clearance while preventing multi-organ failure due to profound shock.

Percutaneous Cannulation: Indication, Technique, and Complications

Vascular access to systemic circulation is the key point for ECMO institution. In the pioneering years, the surgical approach was the rule both for central and peripheral cannulation in V-A or V-V ECMO. In the early 1990s, the availability of new thin-walled spring-wired reinforced cannulas opened the era of percutaneous cannulation technique, which shortly became the first choice for ECMO peripheral cannulation. Benefits of percutaneous cannulation versus the surgical technique are a reduced procedural time, decreased bleeding complications, and easy decannulation without the need of vessel repair. Percutaneous placement of cannulas can be done at any bedside in the hospital, intensive care unit, emergency room, and catheterization laboratory or intraoperatively. We will review cannula implantation and explantation techniques for V-V and V-A ECMO and discuss the vascular complications that can ensue during and after the procedure and their possible solutions.