The aim of this study was to evaluate the correlation of commonly used oxygenation indices with venous admixture (Qs/Qt) in anaesthetised horses under different infusion rates of dobutamine. Six female horses were anaesthetised with acepromazine, xylazine, diazepam, ketamine, and isoflurane, and then intubated and mechanically ventilated with 100% O2. A Swan-Ganz catheter was introduced into the left jugular vein and its tip advanced into the pulmonary artery. Horses received different standardised rates of dobutamine.For each horse, eight samples of arterial and mixed venous blood were simultaneously obtained at fixed times. Arterial and venous haemoglobin (Hb) concentration and O2 saturation, arterial oxygen partial pressure (PaO2), venous oxygen partial pressure (PvO2), and barometric pressure were measured. Arterial (CaO2), mixed venous (CvO2), and capillary (Cc'O2) oxygen contents were calculated using standard formulae. The correlations between F-shunt, arterial oxygen tension to fraction of inspired oxygen ratio (PaO2/FiO2), arterial to alveolar oxygen tension ratio (PaO2/PAO2), alveolar to arterial oxygen tension difference (P[A - a]O2), and respiratory index (P[A - a]O2/PaO2) were tested with linear regression analysis. The goodness-of-fit for each calculated formula was evaluated by means of the coefficient of determination (r2). The agreement between Qs/Qt and F-shunt was analysed with the Bland-Altman test.All tested oxygen tension-based indices were weakly correlated (r2 < 0.2) with the Qs/Qt, whereas F-shunt showed a stronger correlation (r2 = 0.73). F-shunt also showed substantial agreement with Qs/Qt independent of the dobutamine infusion rate. F-shunt better correlated with Qs/Qt than other oxygen indices in isoflurane-anaesthetised horses under different infusion rates of dobutamine

Abstract BACKGROUND:: Guidelines suggest a plateau pressure (PPLAT) of 30 cm H2O or less for patients with acute respiratory distress syndrome, but ventilation may still be injurious despite adhering to this guideline. The shape of the curve plotting airway pressure versus time (STRESS INDEX) may identify injurious ventilation. The authors assessed accuracy of PPLAT and STRESS INDEX to identify morphological indexes of injurious ventilation. METHODS:: Indexes of lung aeration (computerized tomography) associated with injurious ventilation were used as a "reference standard." Threshold values of PPLAT and STRESS INDEX were determined assessing the receiver-operating characteristics ("training set," N = 30). Accuracy of these values was assessed in a second group of patients ("validation set," N = 20). PPLAT and STRESS INDEX were partitioned between respiratory system (PPLAT,RS and STRESS INDEX,RS) and lung (PPLAT,l and STRESS INDEX,L; esophageal pressure; "physiological set," N = 50). RESULTS:: Sensitivity and specificity of PPLAT of greater than 30 cm H2O were 0.06 (95% CI, 0.002-0.30) and 1.0 (95% CI, 0.87-1.00). PPLAT of greater than 25 cm H2O and a STRESS INDEX of greater than 1.05 best identified morphological markers of injurious ventilation. Sensitivity and specificity of these values were 0.75 (95% CI, 0.35-0.97) and 0.75 (95% CI, 0.43-0.95) for PPLAT greater than 25 cm H2O versus 0.88 (95% CI, 0.47-1.00) and 0.50 (95% CI, 0.21-0.79) for STRESS INDEX greater than 1.05. PPLAT,RS did not correlate with PPLAT,L (R = 0.0099); STRESS INDEX,RS and STRESS INDEX,L were correlated (R = 0.762). CONCLUSIONS:: The best threshold values for discriminating morphological indexes associated with injurious ventilation were PPLAT,RS greater than 25 cm H2O and STRESS INDEX,RS greater than 1.05. Although a substantial discrepancy between PPLAT,RS and PPLAT,L occurs, STRESS INDEX,RS reflects STRESS INDEX,L.

Purpose: To assess whether partitioning the elastance of the respiratory system (E (RS)) between lung (E (L)) and chest wall (E (CW)) elastance in order to target values of end-inspiratory transpulmonary pressure (PPLAT(L)) close to its upper physiological limit (25 cmH(2)O) may optimize oxygenation allowing conventional treatment in patients with influenza A (H1N1)-associated ARDS referred for extracorporeal membrane oxygenation (ECMO). METHODS: Prospective data collection of patients with influenza A (H1N1)-associated ARDS referred for ECMO (October 2009-January 2010). Esophageal pressure was used to (a) partition respiratory mechanics between lung and chest wall, (b) titrate positive end-expiratory pressure (PEEP) to target the upper physiological limit of PPLAT(L) (25 cmH(2)O). RESULTS: Fourteen patients were referred for ECMO. In seven patients PPLAT(L) was 27.2 ± 1.2 cmH(2)O; all these patients underwent ECMO. In the other seven patients, PPLAT(L) was 16.6 ± 2.9 cmH(2)O. Raising PEEP (from 17.9 ± 1.2 to 22.3 ± 1.4 cmH(2)O, P = 0.0001) to approach the upper physiological limit of transpulmonary pressure (PPLAT(L) = 25.3 ± 1.7 cm H(2)O) improved oxygenation index (from 37.4 ± 3.7 to 16.5 ± 1.4, P = 0.0001) allowing patients to be treated with conventional ventilation. CONCLUSIONS: Abnormalities of chest wall mechanics may be present in some patients with influenza A (H1N1)-associated ARDS. These abnormalities may not be inferred from measurements of end-inspiratory plateau pressure of the respiratory system (PPLAT(RS)). In these patients, titrating PEEP to PPLAT(RS) may overestimate the incidence of hypoxemia refractory to conventional ventilation leading to inappropriate use of ECMO.

Many potential donor lungs deteriorate between the time of brain death and evaluation for transplantation suitability, possibly because of the ventilatory strategy used after brain death. OBJECTIVE: To test whether a lung protective strategy increases the number of lungs available for transplantation. DESIGN, SETTING, AND PATIENTS: Multicenter randomized controlled trial of patients with beating hearts who were potential organ donors conducted at 12 European intensive care units from September 2004 to May 2009 in the Protective Ventilatory Strategy in Potential Lung Donors Study. Interventions Potential donors were randomized to the conventional ventilatory strategy (with tidal volumes of 10-12 mL/kg of predicted body weight, positive end-expiratory pressure [PEEP] of 3-5 cm H(2)O, apnea tests performed by disconnecting the ventilator, and open circuit for airway suction) or the protective ventilatory strategy (with tidal volumes of 6-8 mL/kg of predicted body weight, PEEP of 8-10 cm H(2)O, apnea tests performed by using continuous positive airway pressure, and closed circuit for airway suction). MAIN OUTCOME MEASURES: The number of organ donors meeting eligibility criteria for harvesting, number of lungs harvested, and 6-month survival of lung transplant recipients. RESULTS: The trial was stopped after enrolling 118 patients (59 in the conventional ventilatory strategy and 59 in the protective ventilatory strategy) because of termination of funding. The number of patients who met lung donor eligibility criteria after the 6-hour observation period was 32 (54%) in the conventional strategy vs 56 (95%) in the protective strategy (difference of 41% [95% confidence interval {CI}, 26.5% to 54.8%]; P <.001). The number of patients in whom lungs were harvested was 16 (27%) in the conventional strategy vs 32 (54%) in the protective strategy (difference of 27% [95% CI, 10.0% to 44.5%]; P = .004). Six-month survival rates did not differ between recipients who received lungs from donors ventilated with the conventional strategy compared with the protective strategy (11/16 [69%] vs 24/32 [75%], respectively; difference of 6% [95% CI, -22% to 32%]). CONCLUSION: Use of a lung protective strategy in potential organ donors with brain death increased the number of eligible and harvested lungs compared with a conventional strategy.

Objective-To evaluate the effectiveness of reduction of inspired oxygen fraction (Fio(2)) or application of positive end-expiratory pressure (PEEP) after an alveolar recruitment maneuver (ARM) in minimizing anesthesia-induced atelectasis in dogs. Animals-30 healthy female dogs. Procedures-During anesthesia and neuromuscular blockade, dogs were mechanically ventilated under baseline conditions (tidal volume, 12 mL/kg; inspiratory-to-expiratory ratio, 1:2; Fio(2), 1; and zero end-expiratory pressure [ZEEP]). After 40 minutes, lungs were inflated (airway pressure, 40 cm H(2)O) for 20 seconds. Dogs were then exposed to baseline conditions (ZEEP100 group), baseline conditions with Fio(2) reduced to 0.4 (ZEEP40 group), or baseline conditions with PEEP at 5 cm H(2)O (PEEP100 group; 10 dogs/group). For each dog, arterial blood gas variables and respiratory system mechanics were evaluated and CT scans of the thorax were obtained before and at 5 (T5) and 30 (T30) minutes after the ARM. Results-Compared with pre-ARM findings, atelectasis decreased and Pao(2):Fio(2) ratio increased at T5 in all groups. At T30, atelectasis and oxygenation returned to pre-ARM findings in the ZEEP100 group but remained similar to T5 findings in the other groups. At T5 and T30, lung static compliance in the PEEP100 group was higher than values in the other groups. Conclusions and Clinical Relevance-Application of airway pressure of 40 cm H(2)O for 20 seconds followed by Fio(2) reduction to 0.4 or ventilation with PEEP (5 cm H(2)O) was effective in diminishing anesthesia-induced atelectasis and maintaining lung function in dogs, compared with the effects of mechanical ventilation providing an Fio(2) of 1.

To evaluate the effects of 10 cm H(2)O of positive end-expiratory pressure (PEEP) on lung aeration and gas exchange in mechanically ventilated sheep during general anesthesia induced and maintained with propofol. ANIMALS: 10 healthy adult Bergamasca sheep. PROCEDURES: Sheep were sedated with diazepam (0.4 mg/kg, IV). Anesthesia was induced with propofol (5 mg/kg, IV) and maintained with propofol via constant rate infusion (0.4 mg/kg/min). Muscular paralysis was induced by administration of vecuronium (25 microg/kg, bolus IV) to facilitate mechanical ventilation. After intubation, sheep were positioned in right lateral recumbency and mechanically ventilated with pure oxygen and zero end-expiratory pressure (ZEEP). After 60 minutes, 10 cm H(2)O of PEEP was applied for 20 minutes. Spiral computed tomography of the thorax was performed, and data were recorded for hemodynamic and gas exchange variables and indicators of respiratory mechanics after 15 (T(15)), 30 (T(30)), and 60 (T(60)) minutes of ZEEP and after 20 minutes of PEEP (T(PEEP)). Computed tomography images were analyzed to determine the extent of atelectasis before and after PEEP application. RESULTS: At T(PEEP), the volume of poorly aerated and atelectatic compartments was significantly smaller than at T(15), T(30), and T(60), which indicated that there was PEEP-induced alveolar recruitment and clearance of anesthesia-induced atelectasis. Arterial oxygenation and static respiratory system compliance were significantly improved by use of PEEP. CONCLUSIONS AND CLINICAL RELEVANCE: Pulmonary atelectasis can develop in anesthetized and mechanically ventilated sheep breathing pure oxygen; application of 10 cm H(2)O of PEEP significantly improved lung aeration and gas exchange.

Background: The authors tested the hypothesis that during laparoscopic surgery, Trendelenburg position and pneumoperitoneum may worsen chest wall elastance, concomitantly decreasing transpulmonary pressure, and that a protective ventilator strategy applied after pneumoperitoneum induction, by increasing transpulmonary pressure, would result in alveolar recruitment and improvement in respiratory mechanics and gas exchange. Methods: In 29 consecutive patients, a recruiting maneuver followed by positive end-expiratory pressure 5 cm H2O maintained until the end of surgery was applied after pneumoperitoneum induction. Respiratory mechanics, gas exchange, blood pressure, and cardiac index were measured before (TBSL) and after pneumoperitoneum with zero positive end-expiratory pressure (TpreOLS), after recruitment with positive end-expiratory pressure (TpostOLS), and after peritoneum desufflation with positive end-expiratory pressure (Tend). Results: Esophageal pressure was used for partitioning respiratory mechanics between lung and chest wall (data are mean ± SD): on TpreOLS, chest wall elastance and elastance of the lung (EL) increased (8.2 ± 0.9 vs. 6.2 ± 1.2 cm H2O/L, respectively, on TBSL; P = 0.00016; and 11.69 ± 1.68 vs. 9.61 ± 1.52 cm H2O/L on TBSL; P = 0.0007). On TpostOLS, both chest wall elastance and EL decreased (5.2 ± 1.2 and 8.62 ± 1.03 cm H2O/L, respectively; P = 0.00015 vs. TpreOLS), and PaO2/inspiratory oxygen fraction improved (491 ± 107 vs. 425 ± 97 on TpreOLS; P = 0.008) remaining stable thereafter. Recruited volume (the difference in lung volume for the same static airway pressure) was 194 ± 80 ml. PplatRS remained stable while inspiratory transpulmonary pressure increased (11.65 + 1.37 cm H2O vs. 9.21 + 2.03 on TpreOLS; P = 0.007). All respiratory mechanics parameters remained stable after abdominal desufflation. Hemodynamic parameters remained stable throughout the study. Conclusions: In patients submitted to laparoscopic surgery in Trendelenburg position, an open lung strategy applied after pneumoperitoneum induction increased transpulmonary pressure and led to alveolar recruitment and improvement of chest wall elastance, EL, and gas exchange.

OBJECTIVE: To evaluate the effectiveness of reduction of inspired oxygen fraction (Fio(2)) or application of positive end-expiratory pressure (PEEP) after an alveolar recruitment maneuver (ARM) in minimizing anesthesia-induced atelectasis in dogs. ANIMALS: 30 healthy female dogs. PROCEDURES: During anesthesia and neuromuscular blockade, dogs were mechanically ventilated under baseline conditions (tidal volume, 12 mL/kg; inspiratory-to-expiratory ratio, 1:2; Fio(2), 1; and zero end-expiratory pressure [ZEEP]). After 40 minutes, lungs were inflated (airway pressure, 40 cm H(2)O) for 20 seconds. Dogs were then exposed to baseline conditions (ZEEP100 group), baseline conditions with Fio(2) reduced to 0.4 (ZEEP40 group), or baseline conditions with PEEP at 5 cm H(2)O (PEEP100 group; 10 dogs/group). For each dog, arterial blood gas variables and respiratory system mechanics were evaluated and CT scans of the thorax were obtained before and at 5 (T5) and 30 (T30) minutes after the ARM. RESULTS: Compared with pre-ARM findings, atelectasis decreased and Pao(2):Fio(2) ratio increased at T5 in all groups. At T30, atelectasis and oxygenation returned to pre-ARM findings in the ZEEP100 group but remained similar to T5 findings in the other groups. At T5 and T30, lung static compliance in the PEEP100 group was higher than values in the other groups. CONCLUSIONS AND CLINICAL RELEVANCE: Application of airway pressure of 40 cm H(2)O for 20 seconds followed by Fio(2) reduction to 0.4 or ventilation with PEEP (5 cm H(2)O) was effective in diminishing anesthesia-induced atelectasis and maintaining lung function in dogs, compared with the effects of mechanical ventilation providing an Fio(2) of 1.

Objective To compare the effects of two fractions of inspired oxygen (FiO 2) (0.4 and 1) on lung aeration and gas exchange during general anaesthesia in cats.Study design Randomized, blinded, controlled study.Animals Thirty healthy, mixed breed, client owned female cats.Materials and methods Cats were premedicated intramuscularly with acepromazine (0.03 mg kg -1) and medetomidine (0.015 mg kg -1). Anaesthesia was induced with propofol (5 mg kg -1) and, after orotracheal intubation, maintained with isoflurane carried by either 100% oxygen (G100, n = 15) or an oxygen-air mixture with 40% oxygen (G40, n = 15). All cats were placed in dorsal recumbency and breathed spontaneously throughout the entire procedure. Following surgery (ovariectomy), a spiral computed tomography (CT) of the thorax was performed, arterial oxygen (PaO 2) and carbon dioxide (PaCO 2) tensions were measured and alveolar-arterial gradient of oxygen [P(A-a)O 2] calculated. The CT images were analysed for lung aeration by the analysis of radiograph attenuations (Hounsfield units, HU), according to the following classification: hyperinflated area (-1000 to -900 HU), normally aerated area (-900 to -500 HU), poorly aerated area (-500 to -100 HU) and non-aerated area (-100 to +100 HU). The groups were compared using one-way anova.Results Compared to G100, the normally-aerated lung area was significantly greater and the poorly-aerated and non-aerated areas were significantly smaller in G40. PaCO 2 was similar in both groups. PaO 2 and P(A-a)O 2 were significantly higher in G100. In both groups, pulmonary atelectasis developed preferentially in the caudal lung fields.Conclusion In cats anaesthetised with isoflurane, the administration of an FiO 2 of >0.9 significantly impaired lung aeration and gas exchange as compared to an FiO 2 of 0.4.Clinical relevance An FiO 2 of 0.4 may better preserve lung aeration and gas exchange in anaesthetised spontaneously breathing cats but monitoring is essential to ensure oxygenation is adequate

Additional pulmonary surgery in a previously pneumonectomized patient requires apnea during surgical manipulation of the surviving lung. We report on a novel approach to manage the intraoperative apnea period, combining apneic oxygenation and minimally invasive, low flow extracorporeal CO2 removal. A 69-year-old man previously submitted to left pneumonectomy was scheduled for wedge resection of a single right upper lobe lesion. During the intraoperative apnea period, oxygenation was maintained through apneic oxygenation with continuous positive airway pressure (CPAP) of 5 cmH2O and inspiratory oxygen fraction (FiO2) of 1 and respiratory acidosis was prevented through extracorporeal CO2 removal, performed with the Decap® system (Hemodec, Salerno, Italy), a veno¬venous pump-driven extracorporeal circuit including a neonatal membrane lung. The extracorporeal circuit was connected to the right femoral vein, accessed via a 14 Fr double lumen catheter. The blood flow through the circuit was 350 mL/min and the sweep flow of oxygen through the membrane lung was 8 L/min. The intraoperative apnea period lasted 13 minutes. Our approach allowed maintaining normocapnia (PaCO2 38,5 and 40 mmHg before and at the end of the apnea period, respectively), preserving oxygenation (P/F ratio 378, 191, 198 and 200 after 3, 6, 9 and 12 min of apnea, respectively). Our report suggests that the minimally invasive CO2 removal associated with apneic oxygenation is an useful technique for managing anesthesiological situations requiring moderate apnea periods.

The aim of this study was to evaluate the influence of abdominal surgery on atelectasis formation in healthy dogs. After the induction of general anesthesia (GA), 20 dogs, scheduled for elective ovariohysterectomy, were positioned in dorsal recumbency: 10 dogs underwent immediate surgery (S group), while 10 dogs (NS group) were maintained under anesthesia for 60 min before surgery. In both groups, a helical computed tomography (CT) scan of the thorax and an arterial blood gas analysis were performed 60 min after the induction of GA. Lung aeration was estimated by analyzing the radiographic attenuation of the CT images. The atelectasic and poorly aerated lung compartments were significantly larger, and the normally aerated lung compartment was smaller in the S group compared to the NS group. The PaO2 was similar in both groups. Abdominal surgery significantly increases pulmonary atelectasis in healthy dogs under GA

The aim of this study was to evaluate the influence of abdominal surgery on atelectasis formation in healthy dogs. After the induction of general anesthesia (GA), 20 dogs, scheduled for elective ovariohysterectomy, were positioned in dorsal recumbency: 10 dogs underwent immediate surgery (S group), while 10 dogs (NS group) were maintained under anesthesia for 60 min before surgery. In both groups, a helical computed tomography (CT) scan of the thorax and an arterial blood gas analysis were performed 60 min after the induction of GA. Lung aeration was estimated by analyzing the radiographic attenuation of the CT images. The atelectasic and poorly aerated lung compartments were significantly larger, and the normally aerated lung compartment was smaller in the S group compared to the NS group. The PaO2 was similar in both groups. Abdominal surgery significantly increases pulmonary atelectasis in healthy dogs under GA.

The aim of this study was to evaluate the influence of a recruiting maneuver (RM) on the effects of PEEP on lung function in healthy horses under general anaesthesia. Fifteen horses were sedated with acepromazine (0.02 mg kg-1 IV) and detomidine (0.005 mg kg-1 IV), general anaesthesia was intravenously induced with midazolam (0.1 mg kg-1) and ketamine (2.2 mg kg-1) and maintained with isoflurane in 100% oxygen. After intubation all horses lungs were mechanically ventilated in a volume controlled mode: Vt (12 ml kg-1) and I:E (1:2) were unchanged during the study while RR was titrated to maintain the PE’CO2 between 40 and 45 mmHg. Three different ventilatory strategies were applied in all horses during the same anaesthetic episode: zero PEEP (ZEEP), 10 cmH2O of PEEP (PEEP) and a RM followed by the application of 10 cmH2O of PEEP (RMPEEP). The RM was performed applying 50 cmH2O for 20 seconds to the respiratory system. Thirty minutes after each ventilatory strategy was initiated, HR and MAP were recorded, an arterial blood sample was collected [PaO2, P(A-a)O2], static compliance of the respiratory system (CRSstat) and the PEEP recruited lung volume (RLV) (Grasso S et al 2005) were calculated. Data were compared with the ANOVA test (P<0.05). The PaO2 and Crsstat were higher while P(A-a)O2 lower at RMPEEP (60.7 ± 6.8 kPa, 473.5 ± 89.1 ml cmH2O-1 and 23.8 ± 7.5 kPa) compared to ZEEP (40.8 ± 16.9 kPa, 339.7 ± 81.9 ml cmH2O-1 and 44.5 ± 16.8 kPa) and PEEP (41.2 ± 17.8 mmHg, 360.9 ± 54.9 ml cmH2O-1 and 44.4 ± 17.6 mmHg). The RLV was larger at RMPEEP (5.5 ± 2.4 L) than at PEEP (2.6 ± 1.6 L). A RM significantly improved the effects of 10 cmH2O of PEEP on lung function in horses under general anaesthesia.

Objective: The Acute Respiratory Distress Syndrome Network protocol recommends limiting tidal volume and plateau pressure; it also recommends increasing respiratory rate to prevent hypercapnia. We tested a strategy that combines the low tidal volume with lower respiratory rates and minimally invasive CO2 removal. Subjects: Ten lung-damaged pigs (instilled hydrochloride). Interventions: Two conditions randomly applied in a crossover fashion: the Acute Respiratory Distress Syndrome Network protocol and the Acute Respiratory Distress Syndrome Network protocol plus lower respiratory rate plus minimally invasive Co2 removal. A similar arterial Co2 partial pressure was targeted in the two conditions. Measurements and Main Results: Physiological parameters, computed tomography scans, plasma and bronchoalveolar lavage concentrations of interleukin-1[beta], interleukin-6, interleukin-8, interleukin-10, interleukin-18, and tumor necrosis factor-[alpha]. During the lower respiratory rate condition, respiratory rate was reduced from 30.5 +/- 3.8 to 14.2 +/- 3.5 (p < 0.01) breaths/min and minute ventilation from 10.4 +/- 1.6 to 4.9 +/- 1.7 L/min (p < 0.01). The extracorporeal device removed 38.9% +/- 6.1% (79.9 +/- 18.4 mL/min) of CO2 production. During the lower respiratory rate condition, interleukin-6, interleukin-8, and tumor necrosis factor-[alpha] concentrations were significantly lower in plasma; interleukin-6 and tumor necrosis factor-[alpha] concentrations were lower in bronchoalveolar lavage, whereas the concentrations of the other cytokines remained unchanged. Conclusion: The strategy of lower respiratory rate plus minimally invasive extracorporeal CO2 removal was feasible and safe and, as compared with the Acute Respiratory Distress Syndrome Network protocol, reduced the concentrations of some, but not all, of the tested cytokines without affecting respiratory mechanics, gas exchange, and hemodynamics.

Abstract Objective – To evaluate the feasibility and efficacy of noninvasive continuous positive airway pressure (CPAP) administered with a pediatric helmet in healthy dogs recovering from general anesthesia. Design – Randomized, cross-over, clinical study. Setting – University teaching hospital Animals – Fifteen healthy female, client-owned dogs recovering from general anesthesia following elective ovariohysterectomy. Interventions – All dogs received the same standardized anesthetic protocol (acepromazine, morphine, propofol, and isoflurane in oxygen). After extubation, a pediatric helmet was placed on all dogs and connected to a venturi valve supplied with medical air. In all patients, the gas flow was set to 50 L/minute and the FiO2 to 0.21. Dogs received the following sequence of treatments, each lasting 20 minutes: 0 CPAP (pre-CPAP), CPAP of 5 cm H2O (CPAP), and again 0 CPAP (post-CPAP). Measurements and Main Result – During the entire study, the following data were collected: pressure and FiO2 inside the helmet, mean arterial pressure, respiratory rate, heart rate, sedation score (0 = awake, 10 = deep sedation), and tolerance to the helmet (0 = excellent, 4 = poor). At the end of each phase, an arterial blood sample was sampled. As compared with the pre-CPAP and the post-CPAP periods, during the CPAP period, the PaCO2, alveolar-arterial oxygen gradient (P[A−a]O2), and respiratory rate significantly decreased. The PaO2 was higher at CPAP (105.6±4.0mmHg) compared with pre-CPAP (80.6±6.9mmHg) and post-CPAP (86.7 ± 5.8 mm Hg). Tolerance and sedation scores during the CPAP period were not different from those in the pre-CPAP and post-CPAP periods. Conclusions – Noninvasive CPAP applied through a helmet is a feasible and effective supportive technique in dogs recovering from general anesthesia.

RATIONALE: In the presence of increased chest wall elastance, the airway pressure does not reflect the lung-distending (transpulmonary) pressure. OBJECTIVE: To compare the physiological effects of a conventional open lung approach titrated for an end-inspiratory airway opening plateau pressure (30 cm H2O) with a transpulmonary open lung approach titrated for a elastance-derived end-inspiratory plateau transpulmonary pressure (26 cm H2O), in a pig model of acute respiratory distress syndrome (HCl inhalation) and reversible chest wall mechanical impairment (chest wall and abdomen restriction). METHODS: In eight pigs, physiological parameters and computed tomography were recorded under three conditions: 1) conventional open lung approach, normal chest wall; 2) conventional open lung approach, stiff chest wall; and 3) transpulmonary open lung approach, stiff chest wall. MEASUREMENTS AND MAIN RESULTS: As compared with the normal chest wall condition, at end-expiration non aerated lung tissue weight was increased by 116 ± 68 % during the conventional open lung approach and by 28 ± 41 % during the transpulmonary open lung approach (p < .01), whereas cardiac output was decreased by 27 ± 19 % and 22 ± 14 %, respectively (p = not significant). CONCLUSION: In this model, the end-inspiratory transpulmonary open lung approach minimized the impact of chest wall stiffening on alveolar recruitment without causing hemodynamic impairment.

Current evidence on epidemiology and outcomes of invasively mechanically ventilated intensive care unit (ICU) patients is predominantly gathered in resource-rich settings. Patient casemix and patterns of critical illnesses, and probably also ventilation practices are likely to be different in resource-limited settings. We aim to investigate the epidemiological characteristics, ventilation practices and clinical outcomes of patients receiving mechanical ventilation in ICUs in Asia.

This report summarizes current physiological and technical knowledge on esophageal pressure (Pes) measurements in patients receiving mechanical ventilation. The respiratory changes in Pes are representative of changes in pleural pressure. The difference between airway pressure (Paw) and Pes is a valid estimate of transpulmonary pressure. Pes helps determine what fraction of Paw is applied to overcome lung and chest wall elastance. Pes is usually measured via a catheter with an air-filled thin-walled latex balloon inserted nasally or orally. To validate Pes measurement, a dynamic occlusion test measures the ratio of change in Pes to change in Paw during inspiratory efforts against a closed airway. A ratio close to unity indicates that the system provides a valid measurement. Provided transpulmonary pressure is the lung-distending pressure, and that chest wall elastance may vary among individuals, a physiologically based ventilator strategy should take the transpulmonary pressure into account. For monitoring purposes, clinicians rely mostly on Paw and flow waveforms. However, these measurements may mask profound patient-ventilator asynchrony and do not allow respiratory muscle effort assessment. Pes also permits the measurement of transmural vascular pressures during both passive and active breathing. Pes measurements have enhanced our understanding of the pathophysiology of acute lung injury, patient-ventilator interaction, and weaning failure. The use of Pes for positive end-expiratory pressure titration may help improve oxygenation and compliance. Pes measurements make it feasible to individualize the level of muscle effort during mechanical ventilation and weaning. The time is now right to apply the knowledge obtained with Pes to improve the management of critically ill and ventilator-dependent patients.

Objective-To evaluate the use of the oxygen content-based index, Fshunt, as an indicator of venous admixture ([Formula: see text]s/[Formula: see text]t) at various fractions of inspired oxygen (Fio(2)s) in anesthetized sheep undergoing Flung or 2-lung ventilation. Animals-6 healthy adult female sheep. Procedures-Sheep were anesthetized and administered 5 different Fio(2)s (0.21, 0.40, 0.60, 0.80, and 1.00) in random order during 2-lung mechanical ventilation. Arterial and mixed venous blood samples were obtained at each Fio(2) after a 15-minute stabilization period. Vital capacity alveolar recruitment maneuvers were performed after blood collection. The previously used Fio(2) sequence was reversed for sample collection during Flung ventilation. Blood samples were analyzed for arterial, pulmonary end-capillary, and mixed venous oxygen content and partial pressure and for hemoglobin concentration. Oxygen hemoglobin saturation, [Formula: see text]s/[Formula: see text]t, Fshunt, and oxygen tension-based indices (OTIs; including Pao(2):Fio(2), alveolar-arterial difference in partial pressure of oxygen [Pao(2) - Pao(2)], [Pao(2) - Pao(2)]:Fio(2), [Pao(2) - Pao(2)]:Pao(2), and Pao(2):Pao(2)) were calculated at each Fio(2); associations were evaluated with linear regression analysis, concordance, and correlation tests. Intermethod agreement between [Formula: see text]s/[Formula: see text]t and Fshunt was tested via Bland-Altman analysis. Results-Strong and significant associations and substantial agreement were detected between Fshunt and [Formula: see text]s/[Formula: see text]t. Relationships between OTIs and [Formula: see text]s/[Formula: see text]t varied, but overall correlations were weak. Conclusions and Clinical Relevance-Whereas OTIs were generally poor indicators of [Formula: see text]s/[Formula: see text]t, Fshunt was a good indicator of [Formula: see text]s/[Formula: see text]t at various Fio(2)s, regardless of the magnitude of [Formula: see text]s/[Formula: see text]t, and could be potentially used as a surrogate for [Formula: see text]s/[Formula: see text]t measurements in healthy sheep.

Objective-To evaluate the use of the oxygen content-based index, Fshunt, as an indicator of venous admixture (Qs/Qt) at various fractions of inspired oxygen (FIO2s) in anesthetized sheep undergoing 1-lung or 2-lung ventilation. Animals-6 healthy adult female sheep. Procedures-Sheep were anesthetized and administered 5 different FIO2s (0.21, 0.40, 0.60, 0.80, and 1.00) in random order during 2-lung mechanical ventilation. Arterial and mixed venous blood samples were obtained at each FIO2 after a 15-minute stabilization period. Vital capacity alveolar recruitment maneuvers were performed after blood collection. The previously used FIO2 sequence was reversed for sample collection during 1-lung ventilation. Blood samples were analyzed for arterial, pulmonary end-capillary, and mixed venous oxygen content and partial pressure and for hemoglobin concentration. Oxygen hemoglobin saturation, Qs/Qt, Fshunt, and oxygen tension-based indices (OTIs; including PaO2:FIO2, alveolar-arterial difference in partial pressure of oxygen [PAO2 -PaO2], [PAO2 -PaO2]:FIO2, [PAO2 -PaO2]:PaO2, and PaO2:PAO2) were calculated at each FIO2; associations were evaluated with linear regression analysis, concordance, and correlation tests. Intermethod agreement between Qs/Qt and Fshunt was tested via Bland-Altman analysis. Results-Strong and significant associations and substantial agreement were detected between Fshunt and Qs/Qt. Relationships between OTIs and Qs/Qt varied, but overall correlations were weak. Conclusions and Clinical Relevance-Whereas OTIs were generally poor indicators of Qs/Qt, Fshunt was a good indicator of Qs/Qt at various FIO2s, regardless of the magnitude of Qs/Qt, and could be potentially used as a surrogate for Qs/Qt measurements in healthy sheep.