The prone position is associated with a decrease in respiratory system compliance in healthy anaesthetized infants

Ten healthy (ASA I or II) anaesthetized infants undergoing clubfoot surgery were studied. General anaesthesia included rocuronium, nitrous oxide and isoflurane. Volume controlled ventilation (12 ml.kg-1) was delivered via a coaxial Mapleson-D (Bain) system and a Datex AS/3 ventilator. Pulmonary mechanics were measured sequentially in the supine and prone positions using a Bicore CP-100 pulmonary function monitor. Subjects had a mean age of 6 (+/- 2) months and a mean weight of 8.3 (+/- 1.4) kg. Dynamic compliance (CDYN) and static compliance (CSTAT) were both significantly lower in the prone position than in the supine position (P < 0.0005). Mean CDYN decreased from 14.9 +/- 4.9 ml.cmH2O-1 (supine) to 11.6 +/- 3.5 ml.cmH2O-1 (prone). Mean CSTAT decreased from 10.2 +/- 2.8 ml.cmH2O-1 (supine) to 8.9 +/- 2.3 ml.cmH2O-1 (prone). No clinically significant differences in gas exchange were noted, however, on repositioning.     

Inhaled and intravenous corticosteroids both attenuate chlorine gas-induced lung injury in pigs

BACKGROUND: The accidental release of chlorine gas is a constant threat in urban areas. The purpose of this randomized, blinded, controlled experiment was to examine the effects of post-injury administration of inhaled or intravenous corticosteroid in chlorine gas-injured pigs followed for 23 h. METHODS: Anaesthetized, ventilated pigs (n = 24) in the prone position were exposed to chlorine gas (400 parts per million in air) (1160 mg/m3) for 15 min, then randomly allocated to receive inhaled budesonide (BUD) and intravenous placebo, intravenous betamethasone (BETA) and inhaled placebo or inhaled and intravenous placebo. Haemodynamics, gas exchange and lung mechanics were evaluated for 23 h after exposure to chlorine gas. RESULTS: Airway and pulmonary artery pressures increased and arterial oxygenation fell sharply (from 13.5 +/- 0.8 to 6.7 +/- 0.9 kPa, P < 0.001) after chlorine gas exposure. These immediate changes were followed by a gradual improvement over 5-7 h to a stable level of dysfunction for the rest of the experiment in placebo animals. Arterial oxygen tension, pulmonary vascular resistance and airway pressure recovered faster and more completely in the budesonide and betamethasone groups than in the placebo group (P < 0.01). Lung wet weight to dry weight ratios were greater in the placebo group than in the budesonide and betamethasone groups (6.34 +/- 0.59 vs. 5.56 +/- 0.38 and 5.53 +/- 0.54, respectively, P < 0.05). There was a trend towards lower histological injury scores compared with placebo in animals that received budesonide (P = 0.05) or betamethasone (P = 0.07). CONCLUSION: Treatment of chlorine gas lung injury with nebulized budesonide or intravenous betamethasone had similar positive effects on recovery of lung function.     

Oxygenation and cerebral perfusion pressure improved in the prone position

BACKGROUND: Treatment of patients in the prone position is a well-established method to improve oxygenation in general intensive care unit (ICU) practice. This method is rarely used in a neurosurgical ICU, considering the risk of intracranial hypertension. The aim of this study was to analyse the effect of prone position on intracranial pressure (ICP), cerebral perfusion pressure (CPP) and systemic oxygenation in patients with reduced intracranial compliance. We hypothesize that the beneficial effects of prone position can outweigh the hazardous effects on the intracranial pressure. METHODS: Eight patients with traumatic brain injury or subarachnoid hemorrhage (SAH) were studied in the supine and prone posture. Hemodynamics, arterial oxygenation, respiratory mechanics, ICP and CPP were continuously measured. RESULTS: A significant improvement in PaO(2) was observed in the prone position, from 12.6 +/- 1.4 kPa to 15.7 +/- 3.2 kPa (P= 0.02). Both intracranial pressure and mean arterial pressure increased in the prone position, from 12 +/- 6 to 15 +/- 4 mmHg (P= 0.03) and from 78 +/- 8 to 88 +/- 8 mmHg (P= 0.005), respectively. Arterial pressure increased to a greater extent than ICP, resulting in improved CPP, from 66 +/- 7 to 73 +/- 8 mmHg (P= 0.03) in the prone position. CONCLUSIONS: The prone position can be used to improve the oxygenation as well as CPP in patients with traumatic brain injury or SAH. However, this method results in raised ICP, and should be used cautiously in patients with reduced intracranial compliance.     

Combining partial liquid ventilation and prone position in experimental acute lung injury.

BACKGROUND: Partial liquid ventilation (PLV) and prone position can improve arterial oxygen tension (PaO2) in acute lung injury (ALI). The authors evaluated additive effects of these techniques in a saline lung lavage model of ALI. METHODS: ALI was induced in 20 medium-sized pigs (29.2+/-2.5 kg body weight). Gas exchange and hemodynamic parameters were determined in both supine and prone position in all animals. Thereafter, one group was assigned to PLV with two sequential doses of 15 ml/kg of perfluorocarbon (n = 10); the second group was assigned to gaseous ventilation (n = 10). Gas-exchange and hemodynamic parameters were determined at corresponding time points in both groups in prone and supine position. RESULTS: In the PLV group, positioning the animals prone resulted in an increase of PaO2 prior to PLV and during PLV with both doses of perfluorocarbon when compared to ALI. PLV in supine position was only effective if 30 ml/kg of perfluorocarbon was applied. In the gaseous ventilation group, PaO2 increased reproducibly compared with ALI when the animals were turned prone. A significant additive improvement of arterial oxygenation was observed during combined therapy with 30 ml/kg of perfluorocarbon and prone position in the PLV group compared with either therapy alone. CONCLUSIONS: The authors conclude that combining PLV with prone position exerts additive effects on pulmonary gas exchange in a saline lung lavage model of ALI in medium-sized pigs.     

Milrinone improves lung compliance in patients receiving mechanical ventilation for cardiogenic pulmonary edema

BACKGROUND: Cardiogenic pulmonary edema is a frequent cause of respiratory failure. We investigated whether milrinone improved lung compliance. METHODS: We selected 10 patients with respiratory failure due to severe cardiogenic pulmonary edema to receive mechanical ventilation. Patients were administered a bolus injection of milrinone (50 microg kg-1) over 10 min, followed by continuous intravenous infusion (0.5 microg kg-1 min-1). Lung compliance, blood gas values, hemodynamic parameters, and sample plasma milrinone levels were assessed over 120 min after the onset of the continuous infusion of milrinone. RESULTS: Ten min following milrinone infusion, dynamic compliance (Cdyn) and static compliance (Cst) increased from 37 +/- 12 to 42 +/- 12 ml cmH2O-1 and from 40 +/- 13 to 45 +/- 12 ml cmH2O-1, respectively (P < 0.01). Plasma milrinone levels reached a therapeutic level for vasodilator and positive inotropic effect at 10 min after milrinone infusion. A significant decrease in mean pulmonary artery pressure and pulmonary artery wedge pressure occurred simultaneously with an increase in respiratory system compliance. However, an increase in cardiac index was observed later than these changes. There were significant correlations between the mean pulmonary artery pressure and Cdyn (r = -0.39, P < 0.01) and Cst (r = -0.38, P < 0.01). CONCLUSIONS: Milrinone-induced improvement in lung compliance along with an improvement of hemodynamics was found together with an inverse relationship between compliance and mean pulmonary artery pressure.     

Prone position improves gas exchange – but how?

* Mechanically ventilated patients with severe acute lung insufficiencies dramatically improve their gas exchange when treated in the prone position. * ventilation heterogeneity is greater in the supine then in the prone position during CMV. * the dominant dorsal Q while supine is not turned into a dominant ventral Q in the prone position. * in the presence of an abdominal distension, the prone position more clearly improves gas exchange than at normal abdominal pressures. * CPAP enhances the dominant dorsal lung perfusion while supine. In the prone position lung perfusion is more uniform. * V/Q matching is improved in the prone position during CMV.     

Iloprost inhalation redistributes pulmonary perfusion and decreases arterial oxygenation in healthy volunteers

Background: Previous studies have shown that ventilation–perfusion matching is improved in the prone as compared with that in the supine position. Regional differences in the regulation of vascular tone may explain this. We have recently demonstrated higher production of nitric oxide in dorsal compared with ventral human lung tissue. The purpose of the present study was to investigate regional differences in actions by another vasoactive mediator, namely prostacyclin. The effects on gas exchange and regional pulmonary perfusion in different body positions were investigated at increased prostacyclin levels by inhalation of a synthetic prostacyclin analogue and decreased prostacyclin levels by unselective cyclooxygenase (COX) inhibition. Methods: In 19 volunteers, regional pulmonary perfusion in the prone and supine position was assessed by single photon emission computed tomography using ^99mTc macro‐aggregated albumin before and after inhalation of iloprost, a stable prostacyclin analogue, or an intravenous infusion of a non‐selective COX inhibitor, diclofenac. In addition, gas distribution was assessed in seven subjects using ^99mTc‐labelled ultra‐fine carbon particles before and after iloprost inhalation in the supine position. Results: Iloprost inhalation decreased arterial PaO₂ in both prone (from 14.2±0.5 to 11.7±1.7 kPa, P<0.01) and supine (from 13.7±1.4 to 10.9±2.1 kPa, P<0.01) positions. Iloprost inhalation redistributed lung perfusion from non‐dependent to dependent lung regions in both prone and supine positions, while ventilation in the supine position was distributed in the opposite direction. No significant effects of non‐selective COX inhibition were found in this study. Conclusions: Iloprost inhalation decreases arterial oxygenation and results in a more gravity‐dependent pulmonary perfusion in both supine and prone positions in healthy humans.     

Prone positioning improves oxygenation in post-traumatic lung injury--a prospective randomized trial

BACKGROUND: In a prospective randomized trial the effect of prone positioning on the duration of mechanical ventilation was evaluated in multiple trauma patients and was compared with patients ventilated in supine position. METHOD: Multiple trauma patients of the intensive care units of two university hospitals were considered eligible if they met the criteria for acute lung injury or the acute respiratory distress syndrome. Patients in the prone group (N = 21) were kept prone for at least eight hours and a maximum of 23 hours per day. Prone positioning was continued until a PaO2:FiO2 ratio of more than 300 was present in prone as well as supine position over a period of 48 hours. Patients in the supine group (N = 19) were positioned according to standard care guidelines. RESULTS: The duration of ventilatory support did not differ significantly (30 +/- 17 days in the prone group and 33 +/- 23 days in the supine group). Worst case analysis (death and deterioration of gas exchange) displayed ventilatory support for 41 +/- 29 days in the prone group and 61 +/- 35 days in the supine group (p = 0.06). The PaO2:FiO2 ratio increased significantly more in the prone group in the first four days (p = 0.03). The prevalence of Acute Respiratory Distress Syndrome (ARDS) following acute lung injury (p = 0.03) and the prevalence of pneumonia (p = 0.048) were reduced also. One patient in the prone and three patients in the supine group died due to multi organ failure (p = 0.27). CONCLUSIONS: Intermittent prone positioning was not able to reduce the duration of mechanical ventilation in this limited number of patients. However the oxygenation improved significantly over the first four days of treatment, and the prevalence of ARDS and pneumonia were reduced.     

Effects of pneumoperitoneum and reverse Trendelenburg position on cardiopulmonary function in morbidly obese patients receiving laparoscopic gastric banding

We prospectively evaluated the effects of pneumoperitoneum and reverse Trendelenburg position on cardiopulmonary function in 20 ASA physical status II-III morbidly obese patients (body mass index > 35 kg m(-2)) undergoing laparoscopic gastric banding. After general anaesthesia was induced, patients' lungs were ventilated using intermittent positive pressure ventilation (at measurement times, the following parameters were used: tidal volume 12 mL kg(-1) ideal body weight, respiratory rate of 12 bpm, an inspiratory to expiratory time ratio of 1:2). Haemodynamic variables, blood gas parameters, and lung/chest compliance were recorded: in the supine position, after induction of general anaesthesia (T0, baseline) and induction of pneumoperitoneum (T1); after placing the patient in a 25 degree reverse Trendelenburg position (T2); during the surgical time (T3); before deflating the abdomen (T4); after pneumoperitoneum resolution (T5), and before the end of anaesthesia, with the patient supine (T6). The PaO2, PaO2/FiO2 ratio, and lung/chest compliance decreased during the study. After the pneumoperitoneum had been resolved, lung/chest compliance but not oxygenation parameters returned to baseline values. The arterial to end-tidal CO2 tension difference progressively increased from 0.38+/-0.3 kPa (2.85+/-2.25 mmHg) (T0) to 0.63+/-0.3 kPa (4.73+/-2.25 mmHg) (T6). In morbidly obese patients, undergoing laparoscopic gastric banding, a CO2 pneumoperitoneum markedly affected gas exchange and lung/chest compliance, while positioning the patient in a 25 degree reverse Trendelenburg position had no beneficial effects.     

Positive end-expiratory pressure applied to the dependent lung during one-lung ventilation improves oxygenation and respiratory mechanics in patients with high FEV1

BACKGROUND AND OBJECTIVE: The aim of this study was to test the efficacy of positive end-expiratory pressure (PEEP) to the dependent lung during one-lung ventilation, taking into consideration underlying lung function in order to select responders to PEEP. METHODS: Forty-six patients undergoing open-chest thoracic surgical procedures were studied in an operating room of a university hospital. Patients were randomized to receive zero end-expiratory pressure (ZEEP) or 10 cmH2O of PEEP to the dependent lung during one-lung ventilation in lateral decubitus. The patients were stratified according to preoperative forced expiratory volume in 1 s (FEV1) as an indicator of lung function (below or above 72%). Oxygenation was measured in the supine position, in the lateral decubitus with an open chest, and after 20 min of ZEEP or PEEP. The respiratory system pressure-volume curve of the dependent hemithorax was measured in supine and open-chest lateral decubitus positions with a super-syringe. RESULTS: Application of 10 cmH2O of PEEP resulted in a significant increase in PaO2 (P < 0.05). This did not occur in ZEEP group, considered as a time matched control. PEEP improved oxygenation only in patients with high FEV1 (from 11.6+/-4.8 to 15.3+/-7.1 kPa, P < 0.05). There was no significant change in the low FEV1 group. Dependent hemithorax compliance decreased in lateral decubitus, more in patients with high FEV1 (P < 0.05). PEEP improved compliance to a greater extent in patients with high FEV1 (from 33.6+/-3.6 to 48.4+/-3.9 mLcmH2O(-1), P < 0.05). CONCLUSIONS: During one-lung ventilation in lateral decubitus, PEEP applied to the dependent lung significantly improves oxygenation and respiratory mechanics in patients with rather normal lungs as assessed by high FEV1.     

Bronchoscopic surfactant administration preserves gas exchange and pulmonary compliance after single lung transplantation in dogs

BACKGROUND: Surfactant abnormalities have been implicated in reperfusion injury and respiratory failure in lung transplantation. METHODS: We investigated the efficacy of bronchoscopic administration of a bovine natural lung surfactant extract (Alveofact) to improve gas exchange and lung mechanics after heterologous left lung transplantation in foxhounds (+4 degrees C ischemia for 24 hours, conservation with Euro-Collins solution). Animals received either no surfactant therapy (untreated controls, n = 6) or 50 mg/kg body weight (prior to explantation, only graft) and 200 mg/kg body weight Alveofact (immediately after reperfusion, both lungs, n = 6). After lung transplantation, separate but synchronized ventilation of each lung was performed in a volume-controlled, pressure-limited mode for 12 hours, with the animals prone. Small catheters were inserted into the pulmonary veins of both the graft and the recipient's native lung for separate blood gas analysis. In the control group, marked protein leakage, influx of neutrophils into the alveolar space, and pulmonary edema formation (extravascular lung water; wet/dry ratio) were encountered in the transplanted lung but only to a very minor extent in the recipient's native lung. RESULTS: Lung compliance values and arterial oxygenation progressively deteriorated in the transplanted but not in the native lungs. Pulmonary hemodynamics did not change significantly. Surfactant administration did not significantly influence the development of reperfusion edema, protein leakage, and neutrophil influx into the grafts. However, surfactant restored the surface activity and the gas exchange (PaO2/FIO2 of 201.2 +/- 20.2 mm Hg vs 119.8 +/- 21.7 mm Hg in controls; P <.05) in the transplanted lungs, and compliance was markedly improved in the surfactant-treated animals (18.8 +/- 1.8 mL/mbar vs 11.5 +/- 1.6 mL/mbar in the controls; P <.05). CONCLUSION: Bronchoscopic surfactant administration does not prevent leukocyte influx or vascular leakage but does protect against respiratory failure and improves lung mechanics in single lung transplantation in dogs.     

Combining Partial Liquid Ventilation and Prone Position in Experimental Acute Lung Injury

Background: Partial liquid ventilation (PLV) and prone position can improve arterial oxygen tension (PaO2) in acute lung injury (ALI). The authors evaluated additive effects of these techniques in a saline lung lavage model of ALI.

Methods: ALI was induced in 20 medium-sized pigs (29.2 +/- 2.5 kg body weight). Gas exchange and hemodynamic parameters were determined in both supine and prone position in all animals. Thereafter, one group was assigned to PLV with two sequential doses of 15 ml/kg of perfluorocarbon (n = 10); the second group was assigned to gaseous ventilation (n = 10). Gas-exchange and hemodynamic parameters were determined at corresponding time points in both groups in prone and supine position.

Results: In the PLV group, positioning the animals prone resulted in an increase of PaO2 prior to PLV and during PLV with both doses of perfluorocarbon when compared to ALI. PLV in supine position was only effective if 30 ml/kg of perfluorocarbon was applied. In the gaseous ventilation group, PaO2 increased reproducibly compared with ALI when the animals were turned prone. A significant additive improvement of arterial oxygenation was observed during combined therapy with 30 ml/kg of perfluorocarbon and prone position in the PLV group compared with either therapy alone.     

Administration of aerosolized terbutaline and budesonide reduces chlorine gas-induced acute lung injury

BACKGROUND: The pathophysiology and treatment of chlorine gas-induced acute lung injury is poorly characterized and based on anecdotal data. This study aimed to assess the effects of aerosolized beta-2 adrenergic agonist and corticosteroid therapy on chlorine gas-induced lung injury. METHODS: Anesthetized, ventilated pigs were exposed to chlorine gas (400 parts per million for 20 minutes), then assigned randomly 30 minutes later to receive aerosolized terbutaline, budesonide, terbutaline followed by budesonide or placebo (6 pigs in each group). Hemodynamics, gas exchange, and lung mechanics were evaluated for another 5 hours. RESULTS: All the animals demonstrated an immediate increase in airway and pulmonary artery pressure as well as sharp drops in arterial oxygen tension (PaO2) and lung compliance (CL). Recovery of PaO2 and CL was greatest in the terbutaline plus budesonide group, but therapy with terbutaline and budesonide alone also was associated with significant improvement in PaO2 and CL, as compared with placebo. CONCLUSIONS: Treatment of acute chlorine gas lung injury with aerosolized terbutaline followed by aerosolized budesonide improved lung function. Combined treatment was more effective than treatment with either drug alone.     

Effect of PEEP and inhaled nitric oxide on pulmonary gas exchange during gaseous and partial liquid ventilation with small volumes of perfluorocarbon

BACKGROUND: Partial liquid ventilation, positive end-expiratory pressure (PEEP) and inhaled nitric oxide (NO) can improve ventilation/perfusion mismatch in acute lung injury (ALI). The aim of the present study was to compare gas exchange and hemodynamics in experimental ALI during gaseous and partial liquid ventilation at two different levels of PEEP, with and without the inhalation of nitric oxide. METHODS: Seven pigs (24+/-2 kg BW) were surfactant-depleted by repeated lung lavage with saline. Gas exchange and hemodynamic parameters were assessed in all animals during gaseous and subsequent partial liquid ventilation at two levels of PEEP (5 and 15 cmH2O) and intermittent inhalation of 10 ppm NO. RESULTS: Arterial oxygenation increased significantly with a simultaneous decrease in cardiac output when PEEP 15 cmH2O was applied during gaseous and partial liquid ventilation. All other hemodynamic parameters revealed no relevant changes. Inhalation of NO and instillation of perfluorocarbon had no additive effects on pulmonary gas exchange when compared to PEEP 15 cmH2O alone. CONCLUSION: In experimental lung injury, improvements in gas exchange are most distinct during mechanical ventilation with PEEP 15 cmH2O without significantly impairing hemodynamics. Partial liquid ventilation and inhaled NO did not cause an additive increase of PaO2.     

Prone position in mechanically ventilated patients with reduced intracranial compliance

BACKGROUND: Prone position has been used for several years to treat acute lung insufficiency, but in previous studies patients with unstable intracranial pressure (ICP) are mostly excluded. The aim of this study was to investigate if prone position is a safe and useful treatment in patients with reduced intracranial compliance. METHODS: A consecutive, prospective pilot study of 11 patients admitted to the neuro intensive care unit (NICU) due to traumatic brain injury or intracerebral haemorrhage. ICP, cerebral perfusion pressure (CPP), heart rate (HR), mean arterial blood pressure (MABP), arterial partial pressure of oxygen (PaO(2)), arterial partial pressure of carbon dioxide (PaCO(2)), arterial oxygen saturation (SaO(2)) and respiratory system compliance were measured before, three times during and two times after the patients were placed in the prone position. RESULTS: No significant changes were demonstrated in ICP, CPP or MABP. PaO(2) and SaO(2) were significantly increased in the prone position. HR was significantly increased in the prone position and after 10 min in the supine post-prone position and the respiratory system compliance was increased after 1 h in the supine post-prone position. CONCLUSION: Turning NICU patients from the supine to the prone position did not influence ICP, CPP or MABP, but significantly improved patient PaO(2), SaO(2) and respiratory system compliance.     

Prone positioning and inhaled nitric oxide: synergistic therapies for acute respiratory distress syndrome

BACKGROUND: Inhaled nitric oxide (INO) and prone positioning have both been advocated as methods to improve oxygenation in patients with acute respiratory distress syndrome (ARDS). This study was designed to evaluate the relative contributions of INO and prone positioning alone and in combination on gas exchange in trauma patients with ARDS. METHODS: Sixteen patients meeting the consensus definition of ARDS were studied. Patients received mechanical ventilation in the supine position, mechanical ventilation plus INO at 1 part per million in the supine position, mechanical ventilation in the PP, and mechanical ventilation in the prone positioning plus INO at 1 part per million. A stabilization period of 1 hour was allowed at each condition. After stabilization,hemodynamic and gas exchange variables were measured. RESULTS: INO and prone positioning both increased PaO2/FIO2 compared with ventilation in the supine position. PaO2/FIO2 increased by 14% during use of INO, and 10 of 16 patients (62%) responded to INO in the supine position. PaO2/FIO2 increased by 33%, and 14 of 16 patients (87.5%) responded to the prone position.The combination of INO and prone positioning resulted in an improvement in PaO2/FIO2 in 15 of 16 patients(94%), with a mean increase in PaO2/FIO2 of 59%. Pulmonary vascular resistance was reduced during use of INO, with a greater reduction in pulmonary vascular resistance seen with INO plus prone positioning (175 +/- 36 dynes x s/cm5 vs. 134 +/- 28 dynes x s/cm5) compared with INO in the supine position (164 +/- 48 dynes x s/cm5 vs.138 +/- 44 dynes x s/cm5). There were no significant hemodynamic effects of INO or prone positioning and no complications were seen during this relative short duration of study. CONCLUSIONS: INO and prone positioning can contribute to improved oxygenation in patients with ARDS. The two therapies in combination are synergistic and may be important adjuncts to mechanical ventilation in the ARDS patient with refractory hypoxemia.     

Pulmonary effects of body position, PEEP, and surfactant depletion in dogs

The influence of position (sphinx, lateral, supine), surfactant depletion, and different positive end-expiratory pressure (PEEP) on functional residual capacity (FRC), series dead space (VdS) and compliance of the respiratory system (Crs) were evaluated in five dogs. Ventilation homogeneity as measured by an index (multiple breath alveolar mixing efficiency), oxygenation, and cardiovascular hemodynamics were additionally examined. The dogs were anesthetized with halothane, paralyzed, and mechanically ventilated. FRC and VdS were found to be notably large in dogs, 45 +/- 8 ml/kg and 6 +/- 1 ml/kg, respectively. FRC and ventilation homogeneity were improved in the sphinx position (prone position with upright head). Surfactant depletion by lung lavage with 37 degrees C saline caused an immediate and stable decrease in FRC, Crs, and oxygenation (P less than 0.05, respectively) for about 5 h without marked effects on the circulatory system. FRC and VdS increased with increasing PEEP. At the highest PEEP, 10 cmH2O (1 kPa), Crs decreased (P less than 0.05) and ventilation became more uneven, indicating alveolar overdistension.     

Effects of posture on blood flow diversion by hypoxic pulmonary vasoconstriction in dogs

We used differential excretion of sulphur hexafluoride from the left and right lung to measure blood flow diversion by hypoxic pulmonary vasoconstriction (HPV) in the prone and supine positions in dogs (n = 9). Gas exchange was assessed using the multiple inert gas elimination technique. Blood flow diversion from the hypoxic (3% oxygen) left lung was mean 70.7 (SD 11.2)% in the supine compared with 57.0 (12.1)% in the prone position (P < 0.02). The supine position was associated with increased perfusion to low VA/Q regions (P < 0.05). The increased flow diversion with hypoxia in the supine position was associated with more ventilation to high VA/Q regions (P < 0.05). We conclude that flow diversion by hypoxic pulmonary vasoconstriction is greater in the supine position. This effect could contribute to the variable response in gas exchange with positioning in patients with ARDS.      

Augmented spontaneous breathing and pulmonary gas exchange during pneumoperitoneum

BACKGROUND AND OBJECTIVE: Ventilation of the lungs with positive end-expiratory pressure during pneumoperitoneum has been shown to improve the arterial partial pressure of oxygen. The implications of spontaneous breathing on pulmonary gas exchange remain unknown in this setting. We therefore sought to examine the influence of pressure-support ventilation with spontaneous breathing on gas exchange during simulated laparoscopy. METHODS: Ten pigs were subjected to pneumoperitoneum at a pressure of 15 cmH2O. Animals received, in a random order, pressure-support and pressure-controlled ventilation for 60 min per mode. Inert gas and haemodynamic measurements were performed before changing to a subsequent mode. RESULTS: Pressure-support ventilation was more efficient than pressure-controlled ventilation regarding perfusion of normal V(A)/Q lung areas (78 +/- 4% vs. 72 +/- 5%) (P < 0.05), alveolar-arterial partial pressure of oxygen difference (9.73 +/- 1.3 vs. 11.2 +/- 1.2 kPa) and arterial partial pressure of oxygen (14.93 +/- 1.6 vs. 13.7 +/- 2.0 kPa) (P < 0.05). CONCLUSIONS: Pressure-support ventilation resulted in significantly better gas exchange than pressure-controlled ventilation in this model of simulated laparoscopy.     

Post-suction recruitment manoeuvre restores lung function in healthy, anaesthetized pigs

Endotracheal suction can cause partial lung collapse and hypoxia and alter lung mechanics. We investigated the effects of adding a recruitment manoeuvre directly after endotracheal suction to restore lung volume in volume-controlled ventilation and pressure-controlled ventilation modes. Five anaesthetized pigs were investigated. The effects of endotracheal suction with or without a recruitment manoeuvre were compared in random order. In volume-controlled ventilation, compliance decreased after suction from 33 +/- 5 to 26 +/- 6 ml x cmH2O(-1) (P<0.05), and 30 minutes later it remained decreased at 25 +/- 6 ml x cmH2O(-1). Venous admixture increased after suction from 5 +/- 2 to 8 +/- 4% (P<0.05), but had recovered at 30 minutes. In pressure-controlled ventilation, compliance decreased after suction from 34 +/- 3 to 25 +/- 7 ml x cmH2O(-1) (P<0.05), and 30 minutes later it remained decreased at 25 +/- 7 ml x cmH2O(-1). Venous admixture increased after suction from 5 +/- 2 to 13 +/- 7% (P<0.05), and had not recovered after 30 minutes, 10 +/- 4%. When a recruitment manoeuvre was applied directly after suction, no negative side-effects were registered in volume-controlled ventilation or pressure-controlled ventilation. We conclude that the impairment of lung mechanics and gas exchange induced by endotracheal suction can be prevented by a simple post-suction recruitment manoeuvre. Further studies are needed to identify a suitable suction recruitment manoeuvre in patients with diseased lungs.