Surgical Treatment of Patients with Sacroiliac Joint Syndrome: Comparative Study of Two Implants. / Operative Behandlung von Patienten mit Iliosakralgelenksyndrom: Vergleichsstudie zweier Implantate.

The treatment of patients with ISJ dysfunction is difficult due to the multifactorial causes of pain and various problems in clarification. Treatment includes physical therapy, corticosteroids, prolotherapy, radiofrequency denervation and sacroiliac joint fusion. A new option for the surgical treatment of ISG dysfunction is the Torpedo implant system. For a safe fusion, only 2 implants are needed, which are available in lengths of 30-50 mm. The new implant system has been tested in pilot studies for efficacy and biocompatibility with good results. For further documentation for the Torpedo implant system, a comparative study against the iFuse system was carried out.Two different implants were used: Group 1: Deltacor Torpedo, Group 2: iFuse implants (Si-Bone). The data generated during admission and subsequent check-ups (VAS, ODI, opioid use) were entered into an evaluation file set up for this purpose. Follow-up appointments were set at 1 month, 3, 6 and 12 months postoperatively.The data of 65 patients were evaluated comparatively. In all comparisons, only very small effect sizes were found with regard to the differences in the decrease in pain intensities, so that equivalent effectiveness of the two methods could initially be postulated from a clinical point of view. Most patients in both groups reported taking opioids to treat pain before surgery. According to the decrease in pain intensity, opioid treatment could be discontinued in some patients after the operation. After 12 months, the number of patients treated with opioids decreases to 23% in group 1 and to 17% in group 2. The success of the fusions with the two methods can also be proven by image documentation, from which the position of the implants can also be clearly recognised. In no case was there any loosening.Overall, the evaluation of this study allows the conclusion that both implant systems can be successfully used for the treatment of patients with ISJ syndrome. The present results should be confirmed in further comparative studies with the proposed evaluation methods.

Effects of lung protective mechanical ventilation associated with permissive respiratory acidosis on regional extra-pulmonary blood flow in experimental ARDS.

BACKGROUND: Lung protective mechanical ventilation with limited peak inspiratory pressure has been shown to affect cardiac output in patients with ARDS. However, little is known about the impact of lung protective mechanical ventilation on regional perfusion, especially when associated with moderate permissive respiratory acidosis. We hypothesized that lung protective mechanical ventilation with limited peak inspiratory pressure and moderate respiratory acidosis results in an increased cardiac output but unequal distribution of blood flow to the different organs of pigs with oleic-acid induced ARDS. METHODS: Twelve pigs were enrolled, 3 died during instrumentation and induction of lung injury. Thus, 9 animals received pressure controlled mechanical ventilation with a PEEP of 5 cmH2O and limited peak inspiratory pressure (17 ± 4 cmH2O) versus increased peak inspiratory pressure (23 ± 6 cmH2O) in a crossover-randomized design and were analyzed. The sequence of limited versus increased peak inspiratory pressure was randomized using sealed envelopes. Systemic and regional hemodynamics were determined by double indicator dilution technique and colored microspheres, respectively. The paired student t-test and the Wilcoxon test were used to compare normally and not normally distributed data, respectively. RESULTS: Mechanical ventilation with limited inspiratory pressure resulted in moderate hypercapnia and respiratory acidosis (PaCO2 71 ± 12 vs. 46 ± 9 mmHg, and pH 7.27 ± 0.05 vs. 7.38 ± 0.04, p < 0.001, respectively), increased cardiac output (140 ± 32 vs. 110 ± 22 ml/min/kg, p<0.05) and regional blood flow in the myocardium, brain and spinal cord, adrenal and thyroid glands, the mucosal layers of the esophagus and jejunum, the muscularis layers of the esophagus and duodenum, and the gall and urinary bladders. Perfusion of kidneys, pancreas, spleen, hepatic arterial bed, and the mucosal and muscularis blood flow to the other evaluated intestinal regions remained unchanged. CONCLUSIONS: In this porcine model of ARDS mechanical ventilation with limited peak inspiratory pressure resulting in moderate respiratory acidosis was associated with an increase in cardiac output. However, the better systemic blood flow was not uniformly directed to the different organs. This observation may be of clinical interest in patients, e.g. with cardiac, renal and cerebral pathologies.

Mechanical LUCAS resuscitation is effective, reduces physical workload and improves mental performance of helicopter teams.

BACKGROUND: Physical and mental workload during cardiopulmonary resuscitation (CPR) is challenging under extreme working conditions. We hypothesized that the mechanical chest-compression device Lund University Cardiac Assist System (LUCAS) increases the effectiveness of CPR, decreases the physical workload and improves the mental performance of the emergency medical service (EMS) staff during simulated emergency helicopter flights. METHODS: During simulated helicopter flights, 12 EMS teams performed manual or LUCAS-CPR on a manikin at random order. Compression depth, rate, overall time of compressions, application of drugs and defibrillation were recorded to test the quality of CPR. Heart rate monitoring of EMS members was used as a surrogate of physical workload. Cognitive performance was evaluated shortly after each flight by a questionnaire and a memory test about medical and extraneous items presented to the teams during the flights. RESULTS: Overall times of chest-compressions were similar, compression rate (101.7±9.6/min) was lower and compressions were deeper (3.9±0.2cm) with LUCAS as compared to manual CPR (113.3±19.3/min and 3.7±0.4cm) (P<0.01, respectively). Heart rates of the EMS staff were increased after manual as compared to mechanical CPR (100.1±21.0 vs. 80.4±11.3, P<0.01). Results of the questionnaire (93.6±6.9% vs. 87.0±7.3% correct answers, P<0.01) and memory test (22.4±15.4% vs. 11.3±7.5%, P<0.02) were significantly better after LUCAS resuscitation. Dosing of drugs, application intervals and rate of correct handling of drugs and defibrillation were not different between LUCAS or manual CPR. CONCLUSIONS: During simulated helicopter flights LUCAS-CPR improved the efficacy of chest-compressions, was physically less demanding and provided enhanced cognitive performance of the EMS team as compared to manual CPR.

Incidence and prognosis of dysnatraemia in critically ill patients: analysis of a large prevalence study.

BACKGROUND: The objective of this study is to assess the impact of dysnatraemia on mortality among intensive care unit (ICU) patients in a large, international cohort. MATERIAL AND METHODS: Analysis of the Extended Prevalence of Infection in Intensive Care (EPIC II) study, a 1-day (8 May 2007) worldwide multicenter, prospective point prevalence study. Hyponatraemia was categorized as mild (130-134 mM/L), moderate (125-129 mM/L) or severe (< 125 mM/L). Hypernatraemia was also categorized as mild (146-150 mM/L), moderate (151-155 mM/L) or severe (> 155 mM/L). Patients with normal serum sodium (135-145 mM/L) constituted the reference group. The main outcome was hospital mortality. Analysis was conducted separately for patients admitted on the study day (25.8%) and those already present on the ICU (74.2%). RESULTS: Serum sodium was measured in 13 276 of the 13 796 patients (96.2%). A total of 3815 patients (28.7%) had dysnatraemia: 12.9% with hyponatraemia and 15.8% with hypernatraemia. The prevalence of dysnatraemia was significantly greater in patients already present on the ICU prior to the study day than for those just admitted (13.1% vs. 12.3% for hyponatraemia and 17.1% vs. 12.1% for hypernatraemia, both P < 0.001). Hospital mortality rates were higher in patients with dysnatraemia than in those with normal sodium levels and were directly related to the severity of hypo- and hypernatraemia. This association between dysnatraemia and mortality was similar in infected and noninfected patients (P = 0.061). CONCLUSIONS: Dysnatraemia is more frequent during the ICU stay than on the day of admission. Dysnatraemia in the ICU - even mild - is an independent predictor of increased hospital mortality.

Sinus venous thrombosis: a differential diagnosis of postpartum headache.

In this report, we describe a patient who developed severe headache following epidural analgesia for labor and delivery. Although the epidural puncture had been reported to be uneventful, headache was initially suspected to result from an accidental dural puncture. After the headache worsened, a sinus venous thrombosis was suspected and subsequently confirmed by magnetic resonance imaging. This case highlights the difficulty of differential diagnosis of headache in the postnatal period in patients after EDA and stresses the necessity of considering alternative pathologies.

Effects of spontaneous breathing during airway pressure release ventilation on cerebral and spinal cord perfusion in experimental acute lung injury.

BACKGROUND: Systemic-blood flow, cerebral-blood flow, and spinal cord blood flow can be affected by mechanical ventilation. We investigated the effect of spontaneous breathing on cerebral and spinal blood flow during airway pressure release ventilation (APRV) with and without spontaneous breathing. METHODS: Twelve pigs with oleic-acid-induced lung injury were ventilated with APRV with or without spontaneous breathing in random order. Without spontaneous breathing, either the upper airway pressure limit of mechanical ventilation or the ventilator rate was increased to maintain pH and PaCO2 constant. Systemic hemodynamic parameters were determined by the double indicator dilution method, cerebral and spinal cord blood flow was measured with colored microspheres. STATISTICS: ANOVA+Newmann-Keuls-test. RESULTS: As compared with APRV without spontaneous breathing and high tidal volume (V(T)) spontaneous breathing during APRV showed higher systemic blood flow and perfusion of the basal ganglia, frontal lobe, hippocampus, brain stem, temporal lobe, thalamus (all P<0.001), cerebellum, spinal cord (all P<0.01), and the central cortical region (P<0.05). During APRV without spontaneous breathing and low V(T) blood flow was lower in the basal ganglia, frontal lobe, hippocampus (all P<0.01), and temporal lobe (P<0.05) whereas perfusion of the thalamus, central cortical region, brain stem, cerebellum, and spinal cord were not different compared with APRV with spontaneous breathing. CONCLUSIONS: In parallel with higher systemic blood flow regional cerebral and spinal cord blood flow were also higher when spontaneous breathing was maintained during APRV. The higher regional blood flow by maintaining spontaneous breathing was more pronounced when compared with full ventilatory support using high V(T).

Partial amniotic carbon dioxide insufflation (PACI) during minimally invasive fetoscopic surgery: early clinical experience in humans.

BACKGROUND: The technical performance of minimally invasive fetoscopic surgery may be severely hindered by poor visualization of intra-amniotic contents. Partial amniotic carbon dioxide insufflation (PACI) allows the visual limitations of operating within the fluid environment to be overcome. PATIENTS AND METHODS: When amniotic fluid exchange failed to improve fetoscopic visualization, PACI was attempted during 37 fetoscopic procedures between 17 + 5 and 33 + 2 weeks of gestation. PACI was attempted with filtered carbon dioxide using a commercially available insufflator via one to three trocars that were percutaneously introduced into the amniotic cavity. The maximum pressure during PACI was limited by the maximum insufflation pressure (30 mmHg) generated by the insufflator. Improvement of fetoscopic visualization as well as technical, maternal, and fetal safety aspects surrounding PACI were analyzed. RESULTS: PACI could successfully be instituted in 36 of the 37 procedures. In one case, when in the presence of increased uterine tone the opening pressure exceeded the maximum insufflation pressure of the insufflator, the strategy was abandoned. In all cases where PACI could be instituted successfully, the approach offered far superior visualization of the fetoscopic procedure than would have been possible within amniotic fluid. Acute or chronic maternal or fetal complications were observed in only one case (intraoperative membrane rupture). CONCLUSION: PACI greatly improves fetal visualization during fetoscopic interventions when fetoscopy within fluid meets with difficulties. Continued assessment of its benefits, risks, and safety margins at specialist centers is required.

Effects of spinal anaesthesia versus epidural anaesthesia for caesarean section on postoperative analgesic consumption and postoperative pain.

BACKGROUND AND OBJECTIVE: Regional anaesthesia is commonly used for elective caesarean section. The aim of this study was to investigate whether there is a positive effect of either spinal or epidural anaesthesia on postoperative analgesic requirements and pain relief. METHODS: The analgesic effect of either spinal or epidural induction of perispinal anaesthesia have been compared in 132 women (ASA I or II) scheduled for elective caesarean section, all having epidural catheterization for perioperative anaesthesia and postoperative analgesia. The patients were randomized into two groups. To achieve a sensory block height to the level of the sixth thoracic dermatome, the parturients received isobaric bupivacaine 0.5% and 5 microg sufentanil intrathecally or ropivacaine 0.75% and 10 microg sufentanil epidurally. For postoperative analgesia, all patients used patient-controlled epidural analgesia at identical settings [bolus of ropivacaine 0.133% (11-15 mg according to patient's height), lock-out time 1 h]. Intraoperative and postoperative pain was recorded using a visual analogue pain score as well as analgesic requirements over the first 24 h after surgery. RESULTS: One hundred and twenty-five patients completed the study. There were no differences in patient-controlled epidural analgesic requirements between groups. During surgery, the pain score on a visual analogue scale was more intense with epidural anaesthesia than with spinal anaesthesia (P < 0.05). For the whole 24 h observation period, the area under the curve for pain was lower with spinal anaesthesia (P < 0.0005). At almost all postoperative time points, visual analogue scale scores at rest and during mobilization were lower with spinal anaesthesia (P < 0.05), which was accompanied by less motor blockade and lower frequency of adverse effects. More patients with epidural anaesthesia received supplemental analgesic medication. CONCLUSION: In parturients undergoing elective caesarean section, postoperative use of epidural ropivacaine via patient-controlled epidural analgesia is similar after spinal and epidural anaesthesia. Spinal anaesthesia is, however, accompanied with less postoperative pain, use of additional analgesics and side-effects.

Spontaneous breathing during airway pressure release ventilation in experimental lung injury: effects on hepatic blood flow.

OBJECTIVE: Positive pressure ventilation can affect systemic haemodynamics and regional blood flow distribution with negative effects on hepatic blood flow. We hypothesized that spontaneous breathing (SB) with airway pressure release ventilation (APRV) provides better systemic and hepatic blood flow than APRV without SB. DESIGN: Animal study with a randomized cross-over design. SETTING: Animal laboratory of Bonn University Hospital. SUBJECTS: Twelve pigs with oleic-acid-induced lung injury. INTERVENTIONS: APRV with or without SB in random order. Without SB, either the upper airway pressure limit or the ventilator rate was increased to maintain constant pH and PaCO2. MEASUREMENTS AND RESULTS: Systemic haemodynamics were determined by double-indicator dilution, organ blood flow by coloured microspheres. Systemic blood flow was best during APRV with SB. During APRV with SB blood flow (ml g(-1) min(-1)) was 0.91+/-0.26 (hepatic arterial), 0.29+/-0.05 (stomach), 0.64+/-0.08 (duodenum), 0.62+/-0.10 (jejunum), 0.53+/-0.07 (ileum), 0.53+/-0.07 (colon), 0.46+/-0.09 (pancreas) and 3.59+/-0.55 (spleen). During APRV without SB applying high P(aw) it decreased to 0.13+/-0.01 (stomach), 0.37+/-0.03 (duodenum), 0.29+/-0.03 (jejunum), 0.31+/-0.05 (ileum), 0.32+/-0.03 (colon) and 0.23+/-0.04 (pancreas) p<0.01, respectively. During APRV without SB applying same Paw limits it decreased to 0.18+/-0.03 (stomach, p<0.01), 0.47+/-0.06 (duodenum, p<0.05), 0.38+/-0.05 (jejunum, p<0.01), 0.36+/-0.03 (ileum, p<0.05), 0.39+/-0.05 (colon, p<0.05), and 0.27+/-0.04 (pancreas, p<0.01). Arterial liver blood flow did not change significantly when SB was abolished (0.55+/-0.11 and 0.63+/-0.11, respectively). CONCLUSIONS: Maintaining SB during APRV was associated with better systemic and pre-portal organ blood flow. Improvement in hepatic arterial blood flow was not significant.

Encouraging early clinical experience with deliberately delayed temporary fetoscopic tracheal occlusion for the prenatal treatment of life-threatening right and left congenital diaphragmatic hernias.

OBJECTIVE: In order to assess the effect of deliberately delayed percutaneous fetoscopic tracheal occlusion on survival of fetuses with life-threatening congenital diaphragmatic hernia. METHODS: Eight fetuses with life-threatening congenital diaphragmatic hernia underwent fetoscopic tracheal balloon occlusion between 29 + 0 and 32 + 4 weeks of gestation. Delayed occlusion was chosen in order to minimize potentially negative pulmonary effects from premature delivery as a result of fetal surgery. In addition, we wanted to become able to provide all available postnatal intensive care treatment means in these patients. RESULTS: Six of the 8 fetuses survived to discharge from hospital. CONCLUSION: Delayed fetoscopic tracheal balloon occlusion may be rewarded with lung growth sufficient to allow survival of fetuses with life-threatening congenital diaphragmatic hernia.

The effects of mechanical ventilation on the gut and abdomen.

PURPOSE OF REVIEW: Mechanical ventilation generates an increase in airway pressure and, therefore, in intrathoracic pressure, which may decrease systemic and intraabdominal organ perfusion. Critically ill patients rarely die of hypoxia and/or hypercarbia but commonly develop a systemic inflammatory response that culminates in multiple-organ dysfunction syndrome and death. In the pathogeneses of this syndrome the gastrointestinal tract and liver have received considerable attention. RECENT FINDINGS: Mechanical ventilation with high positive end-expiratory pressure has been found to decrease splanchnic perfusion. Hepatic arterial buffer response is preserved and an increased hepatic arterial blood flow will compensate the decrease in portal blood flow. Despite an increased cardiac output with an acute moderate increase in arterial PCO2 during protective ventilation it cannot be expected that splanchnic and gut perfusion is improved. In the absence of a significant rise in intraabdominal pressure without impairment in cardiovascular function, splanchnic and gastrointestinal function remained unchanged during short periods of prone positioning. Spontaneous breathing during ventilator support improves systemic blood flow and gastrointestinal and splanchnic perfusion. SUMMARY: In critically ill patients mechanical ventilation should be adjusted to avoid conditions known to be associated with decreased gastrointestinal and splanchnic perfusion.

Effects of spontaneous breathing during airway pressure release ventilation on respiratory work and muscle blood flow in experimental lung injury.

STUDY OBJECTIVES: To evaluate the effects of spontaneous breathing at ambient airway pressure (Paw) and during airway pressure release ventilation (APRV) on respiratory work and respiratory muscle blood flow (RMBF) in experimental lung injury. DESIGN: Prospective experimental study. SETTING: Research laboratory of a university hospital. SUBJECTS: Twelve hemodynamically stable, analgosedated, and tracheotomized domestic pigs. MEASUREMENTS: Respiratory work was estimated by the inspiratory pressure time product (PTPinsp) of esophageal pressure, and RMBF was measured with colored microspheres. Lung injury was induced with IV boli of oleic acid. The first set of measurements was performed before induction of lung injury while pigs were breathing spontaneously at ambient Paw, the second after induction of lung injury while breathing spontaneously at ambient Paw, and the third with lung injury and spontaneous breathing with APRV. RESULTS: After induction of lung injury PTPinsp increased from 138 +/- 14 to 214 +/- 32 cm H2O s/min when pigs breathed spontaneously at ambient Paw (p < 0.05) and returned to 128 +/- 27 cm H2O s/min during APRV. While systemic hemodynamics and blood flow to the psoatic and intercostal muscles did not change, diaphragmatic blood flow increased from 0.34 +/- 0.05 before to 0.54 +/- 0.08 mL/g/min after induction of lung injury and spontaneous breathing at ambient Paw (p < 0.05) and returned to 0.32 +/- 0.05 mL/g/min during APRV (p < 0.05 vs spontaneous breathing at ambient Paw [lung injury]). CONCLUSION: Respiratory work and RMBF are increased in acute lung injury when subjects breathe spontaneously at ambient Paw. Supporting spontaneous breathing with APRV decreases respiratory work and RMBF to physiologic values.

Proportional assist versus pressure support ventilation in patients with acute respiratory failure: cardiorespiratory responses to artificially increased ventilatory demand.

OBJECTIVE: To test the hypothesis that in response to increased ventilatory demand, dynamic inspiratory pressure assistance better compensates for increased workload compared with static pressure support ventilation (PSV). DESIGN: Randomized clinical crossover study. SETTING: General intensive care u nits of a university hospital. PATIENTS: Twelve patients with acute respiratory failure. INTERVENTIONS: Patients received PSV, proportional assist ventilation (PAV), and PAV+ automatic tube compensation (ATC) in random order while maintaining mean inspiratory airway pressure constant. During each setting, ventilatory demand was increased by adding deadspace without ventilator readjustment. MEASUREMENTS AND MAIN RESULTS: Cardiorespiratory, ventilatory, and work of breathing variables were assessed by routine monitoring plus pneumotachography; airway, esophageal, and abdominal pressure measurements; and nitrogen washout. After deadspace addition, tidal volume and end-expiratory lung volume increased similarly in all ventilatory modalities. Ventilator work, peak inspiratory flow, and maximum airway pressure increased significantly during PAV+ATC when compared with PSV after deadspace addition. However, increase in ventilator work did not result in a smaller increase in patients' work of breathing with elevated ventilatory demand during PAV+ATC (PSV 807 +/- 204 mJ/L, PAV 802 +/- 193 mJ/L, and PAV+ATC 715 +/- 202 mJ/L, p = .11). Increase in patients' work of breathing was mainly caused by a significantly higher resistive workload during PAV and PAV+ATC. CONCLUSION: In patients with acute respiratory failure, dynamic inspiratory pressure assistance modalities are not superior to PSV with respect to cardiorespiratory function and inspiratory muscles unloading after increasing ventilatory demand. The latter might be explained by higher peak flows resulting in nonlinearly increased resistive workload that was incompletely compensated by PAV+ATC.

Assisted breathing is better in acute respiratory failure.

PURPOSE OF REVIEW: Mechanical ventilation is usually provided in acute lung injury to ensure alveolar ventilation and reduce the patients' work of breathing without further damaging the lungs by the treatment itself. Although partial ventilatory support modalities were initially developed for weaning from mechanical ventilation, they are increasingly used as primary modes of ventilation, even in patients in the acute phase of pulmonary dysfunction. The aim of this paper is to review the role of spontaneous breathing ventilatory modalities with respect to their physiologic or clinical evidence. RECENT FINDINGS: By allowing patients with acute lung injury to breathe spontaneously, one can expect improvement in gas exchange and in systemic blood flow, on the basis of both experimental and clinical trials. In addition, by increasing end-expiratory lung volume, as will occur when airway pressure release ventilation is used, recruitment of collapsed or consolidated lung is likely to occur, especially in juxtadiaphragmatic lung regions. Until recently, traditional approaches to mechanical ventilatory support of patients with acute lung injury have called for adaptation of the patient to the mechanical ventilator using heavy sedation and administration of neuromuscular blocking agents. Recent investigations have questioned the utility of sedation, muscle paralysis, and mechanical control of ventilation. Further, evidence exists that lowering sedation levels will decrease the duration of mechanical ventilatory support, the length of stay in the intensive care unit, and the overall costs of hospitalization. SUMMARY: On the basis of currently available data, the authors suggest the use of techniques of mechanical ventilatory support that maintain, rather than suppress, spontaneous ventilatory effort, especially in patients with severe pulmonary dysfunction.

Effects of spontaneous breathing during airway pressure release ventilation on intestinal blood flow in experimental lung injury.

BACKGROUND: In critical illness, the gut is susceptible to hypoperfusion and hypoxia. Positive-pressure ventilation can affect systemic hemodynamics and regional blood flow distribution, with potentially deleterious effects on the intestinal circulation. The authors hypothesized that spontaneous breathing (SB) with airway pressure release ventilation (APRV) provides better systemic and intestinal blood flow than APRV without SB. METHODS: Twelve pigs with oleic acid-induced lung injury received APRV with and without SB. When SB was abolished, either the tidal volume or the ventilator rate was increased to maintain pH and arterial carbon dioxide tension constant as compared to APRV with SB. Systemic hemodynamics were determined by double indicator dilution. Blood flow to the intestinal mucosa-submucosa and muscularis-serosa was measured using colored microspheres. RESULTS: Systemic blood flow increased during APRV with SB. During APRV with SB, mucosal-submucosal blood flow (ml. g-1. min-1) was 0.39 +/- 0.21 in the stomach, 0.76 +/- 0.35 in the duodenum, 0.71 +/- 0.35 in the jejunum, 0.71 +/- 0.59 in the ileum, and 0.63 +/- 0.21 in the colon. During APRV without SB and high tidal volumes, it decreased to 0.19 +/- 0.03 in the stomach, 0.42 +/- 0.21 in the duodenum, 0.37 +/- 0.10 in the jejunum, 0.3 +/- 0.14 in the ileum, and 0.41 +/- 0.14 in the colon (P < 0.001, respectively). During APRV without SB and low tidal volumes, the respective mucosal-submucosal blood flows decreased to 0.24 +/- 0.10 (P < 0.01), 0.54 +/- 0.21 (P < 0.05), 0.48 +/- 0.17 (P < 0.01), 0.43 +/- 0.21 (P < 0.01), and 0.50 +/- 0.17 (P < 0.001) as compared to APRV with SB. Muscularis-serosal perfusion decreased during full ventilatory support with high tidal volumes in comparison with APRV with SB. CONCLUSION: Maintaining SB during APRV was associated with better systemic and intestinal blood flows. Improvements were more pronounced in the mucosal-submucosal layer.

Measurement of functional residual capacity by nitrogen washout during partial ventilatory support.

OBJECTIVE: Evaluation of an open circuit multiple breath nitrogen washout (MBNW) technique for measurement of functional residual capacity (FRC) during partial ventilatory support using corrections for gas viscosity, sampling delay time, and re-inspired nitrogen. DESIGN: Measurements in a lung model with known reference volume simulating spontaneous breathing and duplicate measurements in patients breathing spontaneously with partial ventilatory support. SETTING. Experimental laboratory and intensive care units of a university hospital. PATIENTS: Eighteen patients with acute respiratory failure. INTERVENTIONS: Change of FiO(2) from baseline to 1.0. MEASUREMENTS AND MAIN RESULTS: FRC was measured by MBNW during spontaneous breathing with continuous positive airway pressure, pressure support ventilation, proportional assist ventilation, automatic tube compensation, and airway pressure release ventilation. In the lung model, repeated measurements at three volumes were done with all partial ventilatory support modalities, and baseline FiO(2 )was varied with one mode and FRC. The mean of differences between MBNW (FRC(MBNW)) and reference was 28 ml (1.6%), and the 2.SD-interval was 84 ml (4.9%) for all modes. Measurements up to a baseline FiO(2) of 0.8 showed differences of 5 ml (-0.3%) and the 2.SD-interval of 38 ml (2.2%) between reference and FRC(MBNW). In 18 patients, 66 duplicate measurements revealed a mean difference of 30 ml (0.9%) with a coefficient of repeatability of 358 ml (13%) independent of ventilatory mode and chronological order. CONCLUSION: This study suggests that, using corrections for gas viscosity, sampling delay time, and re-inspired nitrogen, FRC can be determined with good repeatability in patients and good accuracy in a lung model during partial ventilatory support.

Effects of spontaneous breathing during airway pressure release ventilation on renal perfusion and function in patients with acute lung injury.

OBJECTIVE: Controlled mechanical ventilation can impair systemic and renal blood flow and function, which may be aggravated by respiratory acidosis. We hypothesized that partial ventilatory support using airway pressure release ventilation (APRV) with spontaneous breathing provides better cardiopulmonary and renal function than full ventilatory support using APRV without spontaneous breathing. DESIGN: Prospective randomized study. SETTING: Intensive care unit of a university hospital. PATIENTS: Twelve patients with acute lung injury (ALI). INTERVENTIONS: Airway pressure release ventilation with and without spontaneous breathing, maintaining either the same minute ventilation (V(E)) or the same airway pressure (Paw) limits. MEASUREMENTS: Systemic hemodynamics were estimated by double-indicator dilution, effective renal blood flow (ERBF) by para-aminohippurate, and glomerular filtration rate (GFR) by inulin clearance. RESULTS: Compared to APRV with spontaneous breathing, cardiac index (CI) was decreased when the upper Paw limit was increased to provide the same V(E) (4.26+/-1.21 l min(-1) m(-2)vs 3.72+/-0.99 l min(-1) m(-2); p<0.05) while CI was increased when Paw limits were held constant (4.91+/-1.41 l min(-1) m(-2); p<0.05). Effective renal blood flow and GFR were higher during APRV with spontaneous breathing (858+/-388 ml min(-1) m(-2) and 94+/-47 ml min(-1) m(-2)) than during APRV without spontaneous breathing and the same V(E) (714+/-236 ml min(-1) m(-2)and 82+/-35 ml min(-1) m(-2)) or the same Paw (675+/-287 ml min(-1) m(-2) and 80+/-41 ml min(-1) m(-2); p<0.05). Urine volume did not change. CONCLUSIONS: Spontaneous breathing during APRV was associated with better renal perfusion and function than APRV without spontaneous breathing applying either the same V(E) or the same Paw limits. Maintaining spontaneous breathing during ventilatory support may, therefore, be advantageous in preventing deterioration of renal function in patients with ALI.

Controlled versus assisted mechanical ventilation.

On the basis of currently available data, it can be suggested that maintained spontaneous breathing during mechanical ventilation should not be suppressed even in patients with severe pulmonary dysfunction if no contraindications, such as increased intracranial pressure, are present. Improvements in pulmonary gas exchange, systemic blood flow, and oxygen supply to tissues, which have been observed when spontaneous breathing was allowed during ventilatory support, are reflected in the clinical improvement in the patient's condition, as indicated by significantly fewer days with ventilation, earlier extubation, and shorter stays in the intensive care unit. The positive effects of spontaneous breathing have been documented only for some of the available partial ventilatory support modalities. If ventilatory modalities are limited to those whose positive effects have been documented, then partial ventilatory support can be used as a primary modality even in patients with severe pulmonary dysfunction. Whereas controlled mechanical ventilation followed by weaning with partial ventilatory support modalities has been the earlier standard in ventilation therapy, this approach should be reconsidered in view of the available data.