Lower pulmonary diffusing capacity in the prone vs. supine posture

Comparison of hemodynamic and respiratory outcomes between two surgical positions for percutaneous nephrolithotomy: a prospective, randomized clinical trial

INTRODUCTION

Percutaneous nephrolithotomy (PCNL) has become the gold standard for the treatment of large and complex kidney stones.

OBJECTIVES

The objective of this study is to evaluate the efficacy and safety of percutaneous nephrolithotomy (PCNL) for patients in the flank position versus prone position.

METHODS

In our prospective randomized trial, 60 patients who would undergo fluoroscopy and ultrasound-guided PCNL in prone or flank position were divided into two groups. Demographic features, hemodynamics, respiratory and metabolic parameters, postoperative pain scores, analgesic requirements, amount of fluid given, blood loss and transfusion, duration of operation and hospital stay, and perioperative complications were compared.

RESULTS

PaO2, SaO2, SpO2 and Oxygen Reserve İndex (ORi) at the 60th minute of the operation and in the postoperative period, Pleth Variability index (PVi) at the 60th minute of the operation, driving pressure in all time periods and the amount of bleeding during the operation were determined to be statistically significantly higher in the prone group. There was no difference between the groups in terms of other parameters. Was found to be statistically significantly higher in the prone group.

CONCLUSIONS

Due to our results the flank position can be preferred in PCNL operations, considering that the position should be chosen according to the surgeon's experience, the patient's anatomical and physiological data, positive effects on respiratory parameters and bleeding, and the operation time can be shortened as the experience increases.

An Observational Pilot Study on Supine Percutaneous Nephrolithotomy: Initial Experience at a Single-Centre

Objective To assess the surgical outcome of supine percutaneous nephrolithotomy (PCNL) in patients with co-morbidities. Materials and methods We retrospectively reviewed the data of 15 patients who underwent supine PCNL at our centre from September 2019 to May 2021. Preoperatively, a complete examination of the patients, along with biochemical and radiological investigations, was done. The data, which included patient demographics, comorbidities, complexity of renal calculi, complications, and stone clearance rate, were collected from the patients' medical records. Results Patients aged between 31 and 70 years were included in the study. The mean (SD) BMI was 26.01 (2.31). Twelve patients (80%) were overweight with a BMI of 25.3 to 29.3 kg/m². The most common comorbidities were diabetes (33.3%) and hypertension (26.7%). In our study, six patients were American Society of Anesthesiologists (ASA) grade 3 (40%), followed by grade 2 in five patients (33.3%), grade 4, and grade 1 in two patients (13.3%) each. The Guy's Stone score was one in nine patients (60%) and two in six patients (40%). Complete clearance was achieved in 13 (86.7%) patients. Two patients (13.3%) had a stone clearance of more than 80%. Data analysis showed that 14 patients (93.3%) had no perioperative complications. Postoperative abdominal distension was noted in one patient (6.7%), which was managed conservatively (Clavien-Dindo grade 1). We did not encounter any cases of organ injury following supine PCNL. Postoperatively, none of our patients received blood transfusions. Conclusion Our study shows that supine PCNL is a good surgical option, especially for high-risk patients with good stone clearance and low complication rates.

Using hyperpolarized 129Xe gas-exchange MRI to model the regional airspace, membrane, and capillary contributions to diffusing capacity

Hyperpolarized ¹²⁹Xe MRI has emerged as a novel means to evaluate pulmonary function via 3D mapping of ventilation, interstitial barrier uptake, and RBC transfer. However, the physiological interpretation of these measurements has yet to be firmly established. Here, we propose a model that uses the three components of ¹²⁹Xe gas-exchange MRI to estimate accessible alveolar volume (V_A), membrane conductance, and capillary blood volume contributions to DL_CO. ¹²⁹Xe ventilated volume (VV) was related to V_A by a scaling factor k_V = 1.47 with 95% confidence interval [1.42, 1.52], relative ¹²⁹Xe barrier uptake (normalized by the healthy reference value) was used to estimate the membrane-specific conductance coefficient k_B = 10.6 [8.6, 13.6] mL/min/mmHg/L, whereas normalized RBC transfer was used to calculate the capillary blood volume-specific conductance coefficient k_R = 13.6 [11.4, 16.7] mL/min/mmHg/L. In this way, the barrier and RBC transfer per unit volume determined the transfer coefficient K_CO, which was then multiplied by image-estimated V_A to obtain DL_CO. The model was built on a cohort of 41 healthy subjects and 101 patients with pulmonary disorders. The resulting ¹²⁹Xe-derived DL_CO correlated strongly (R² = 0.75, P < 0.001) with the measured values, a finding that was preserved within each individual disease cohort. The ability to use ¹²⁹Xe MRI measures of ventilation, barrier uptake, and RBC transfer to estimate each of the underlying constituents of DL_CO clarifies the interpretation of these images while enabling their use to monitor these aspects of gas exchange independently and regionally.NEW & NOTEWORTHY The diffusing capacity for carbon monoxide (DL_CO) is perhaps one of the most comprehensive physiological measures used in pulmonary medicine. Here, we spatially resolve and estimate its key components-accessible alveolar volume, membrane, and capillary blood volume conductances-using hyperpolarized ¹²⁹Xe MRI of ventilation, interstitial barrier uptake, and red blood cell transfer. This image-derived DL_CO correlates strongly with measured values in 142 subjects with a broad range of pulmonary disorders.

Observational prospective study for surgical outcome and anesthetic feasibility of tubeless and totally tubeless supine PCNL: A single centre initial experience

OBJECTIVE

To evaluate surgical outcome and spinal anesthetic feasibility of supine percutaneous nephrolithotomy (PCNL) by tubeless and totally tubeless method.

MATERIAL AND METHODS

This observational study included a totally 53 patients. Initial diagnosis of renal stone was based on urinary ultrasonography, kidney, ureter and bladder X-ray, and later confirmed by computed tomography urography. PCNL was done with the patient in Galdakao-modified supine Valdivia position. Nephrostomy was not done using tubeless method, while in totally tubeless method instead of insertion of double j stent, ureteral catheterization was done and the ureter catheter was kept for <24 hours. During postprocedural period, patients were observed for development of fever, perinephric collection, need for blood transfusion and duration of hospital stay.

RESULTS

Patients aged between 14 and 75 years were included in the study. Out of totally 53 patients, supine tubeless PCNL was done in 23 patients while 30 were operated using totally tubeless method. Twenty-nine patients were induced by spinal anesthesia and 24 by general anesthesia. Stone sizes were found to be in the range of 1.4cm to 5.1 cm. Forty-six (86.7%) patients were managed by inferior calyceal puncture. Three patients required double puncture in whom 2 had developed perinephric collection. Complete stone clearance achieved in 49 (92.4%) patients. Four patients developed fever and 2 cases required one unit blood transfusion postoperatively.

CONCLUSION

Tubeless and totally tubeless supine PCNL is technically feasible with good surgical outcomes and can be done under spinal and general anesthesia in properly selected patients.

The effect of body position on pulmonary function: a systematic review

BACKGROUND

Pulmonary function tests (PFTs) are routinely performed in the upright position due to measurement devices and patient comfort. This systematic review investigated the influence of body position on lung function in healthy persons and specific patient groups.

METHODS

A search to identify English-language papers published from 1/1998-12/2017 was conducted using MEDLINE and Google Scholar with key words: body position, lung function, lung mechanics, lung volume, position change, positioning, posture, pulmonary function testing, sitting, standing, supine, ventilation, and ventilatory change. Studies that were quasi-experimental, pre-post intervention; compared ≥2 positions, including sitting or standing; and assessed lung function in non-mechanically ventilated subjects aged ≥18 years were included. Primary outcome measures were forced expiratory volume in 1 s (FEV1), forced vital capacity (FVC, FEV1/FVC), vital capacity (VC), functional residual capacity (FRC), maximal expiratory pressure (PEmax), maximal inspiratory pressure (PImax), peak expiratory flow (PEF), total lung capacity (TLC), residual volume (RV), and diffusing capacity of the lungs for carbon monoxide (DLCO). Standing, sitting, supine, and right- and left-side lying positions were studied.

RESULTS

Forty-three studies met inclusion criteria. The study populations included healthy subjects (29 studies), lung disease (nine), heart disease (four), spinal cord injury (SCI, seven), neuromuscular diseases (three), and obesity (four). In most studies involving healthy subjects or patients with lung, heart, neuromuscular disease, or obesity, FEV1, FVC, FRC, PEmax, PImax, and/or PEF values were higher in more erect positions. For subjects with tetraplegic SCI, FVC and FEV1 were higher in supine vs. sitting. In healthy subjects, DLCO was higher in the supine vs. sitting, and in sitting vs. side-lying positions. In patients with chronic heart failure, the effect of position on DLCO varied.

CONCLUSIONS

Body position influences the results of PFTs, but the optimal position and magnitude of the benefit varies between study populations. PFTs are routinely performed in the sitting position. We recommend the supine position should be considered in addition to sitting for PFTs in patients with SCI and neuromuscular disease. When treating patients with heart, lung, SCI, neuromuscular disease, or obesity, one should take into consideration that pulmonary physiology and function are influenced by body position.

Systemic Oxygen Transport with Rest, Exercise, and Hypoxia: A Comparison of Humans, Rats, and Mice

The objective of this article is to compare and contrast the known characteristics of the systemic O₂ transport of humans, rats, and mice at rest and during exercise in normoxia and hypoxia. This analysis should help understand when rodent O₂ transport findings can-and cannot-be applied to human responses to similar conditions. The O₂ -transport system was analyzed as composed of four linked conductances: ventilation, alveolo-capillary diffusion, circulatory convection, and tissue capillary-cell diffusion. While the mechanisms of O₂ transport are similar in the three species, the quantitative differences are naturally large. There are abundant data on total O₂ consumption and on ventilatory and pulmonary diffusive conductances under resting conditions in the three species; however, there is much less available information on pulmonary gas exchange, circulatory O₂ convection, and tissue O₂ diffusion in mice. The scarcity of data largely derives from the difficulty of obtaining blood samples in these small animals and highlights the need for additional research in this area. In spite of the large quantitative differences in absolute and mass-specific O₂ flux, available evidence indicates that resting alveolar and arterial and venous blood PO₂ values under normoxia are similar in the three species. Additionally, at least in rats, alveolar and arterial blood PO₂ under hypoxia and exercise remain closer to the resting values than those observed in humans. This is achieved by a greater ventilatory response, coupled with a closer value of arterial to alveolar PO₂ , suggesting a greater efficacy of gas exchange in the rats. © 2018 American Physiological Society. Compr Physiol 8:1537-1573, 2018.

Modelling the effect of gravity on inert-gas washout outputs

Multiple-breath washout (MBW) is a pulmonary function test (PFT) that is used to infer lung function through measurement of ventilation heterogeneity (VH). However, the body position that a test is taken in may also influence VH, due to the "Slinky" effect of gravity on the lungs. In healthy subjects this has minimal effect, but in unhealthy groups, PFT outputs have been seen to change drastically with body position. In this study, we used a combined computational and clinical approach to better understand the response of outputs from the MBW to body position. A patient-specific model of the MBW was developed, then validated against clinically measured washout data, as well as broader results in the literature. This model was then used to compare changes in MBW outputs with respect to body position, showing that output changes sensitively predict regional airway size differences between lobes. We then highlight cases in which body position effects may bias MBW outputs, leading to elevated or masked responses to bronchoconstriction. We close by placing this result in context with broader clinical practice, and showing how it can help improve interpretation of test outputs.

Factors Affecting Lung Function: A Review of the Literature

Lung function reference values are traditionally based on anthropometric factors, such as weight, height, sex, and age. FVC and FEV₁ decline with age, while volumes and capacities, such as RV and FRC, increase. TLC, VC, RV, FVC and FEV₁ are affected by height, since they are proportional to body size. This means that a tall individual will experience greater decrease in lung volumes as they get older. Some variables, such as FRC and ERV, decline exponentially with an increase in weight, to the extent that tidal volume in morbidly obese patients can be close to that of RV. Men have longer airways than women, causing greater specific resistance in the respiratory tract. The increased work of breathing to increase ventilation among women means that their consumption of oxygen is higher than men under similar conditions of physical intensity. Lung volumes are higher when the subject is standing than in other positions. DLCO is significantly higher in supine positions than in sitting or standing positions, but the difference between sitting and standing positions is not significant. Anthropometric characteristics are insufficient to explain differences in lung function between different ethnic groups, underlining the importance of considering other factors in addition to the conventional anthropometric measurements.

Positioning for percutaneous nephrolithotomy

PURPOSE OF THE REVIEW

To highlight the progressive evolution of the issue of patient positioning for percutaneous nephrolithotomy (PNL), explain the history of the prone and supine positions, report respective advantages and drawbacks, critically interpret the past and current literature supporting such arguments, identify the best candidates for each position, and reflect on the future evolution of the two approaches.

RECENT FINDINGS

Positioning for PNL has become a matter of debate during the last decade. The traditional prone PNL position - most widely performed with good success and few complications, and exhibiting essentially no limits except for the treatment of pelvic kidneys - is nowadays flanked mainly by the supine and supine-modified positions, equally effective and probably safer from an anesthesiological point of view. Of course, both approaches have a number of advantages and drawbacks, accurately reported and critically sieved.

SUMMARY

The current challenge for endourologists is to be able to perform PNL in both prone and supine positions to perfectly tailor the procedure on any patient with any stone burden, including increasingly challenging cases and medically high-risk patients, according to the patient's best interest. Intensive training and experience is especially needed for supine PNL, still less popular and underperformed worldwide.

VIDEO ABSTRACT

http://links.lww.com/COU/A8.

Percutaneous nephrolithotomy in the oblique supine lithotomy position and prone position: a comparative study

OBJECTIVES

To compare the safety, efficacy, and complications of percutaneous nephrolithotomy (PCNL) in the oblique supine lithotomy position vs the prone position in a randomized comparative study.

PATIENTS AND METHODS

The study included 101 and 102 patients in the oblique supine lithotomy position and prone position, respectively. Inclusion criteria were renal and upper ureteral stones. Exclusion criteria were uncorrectable bleeding disorders, active urinary tract infection, and pregnancy.

RESULTS

Both the groups were comparable regarding the male/female ratio, stone size, and site. No significant differences were found in terms of the stone-free rate, blood transfusion rate, and complication rates. Significant differences were reported in mean hemoglobin loss (-1.03 and -2.18 g/dL), mean operative time (86.16 and 111.7 minutes), and mean hospital stay (49.88 and 81.2 hours) in the supine and prone positions, respectively, and anesthesiological parameters (the mean blood pressure decreased by 2 and 14.06 mm Hg, the mean heart rate changed by -0.82 and +13.28 beat/minute, and the peak air way pressure changed by +1.08 cm H2O and +7.56 cm H2O in the supine and prone positions, respectively).

CONCLUSIONS

PCNL in both positions was equally successful with no significant differences in complications. PCNL in the oblique supine lithotomy position was superior to PCNL in the prone position regarding operative time, hospital stay, and effects on respiratory and cardiovascular status, making it more comfortable for patients and anesthesiologists. Morbidly obese patients, patients with cardiologic disorders, and patients with pulmonary obstructive airway disease need further studies to show if they would benefit from these differences. Additionally, it is more comfortable for the surgeon with little challenges added in the initial puncture.

[Learning of percutaneous nephrolithotomy in supine position. An observational multicenter study]

OBJECTIVE

To prospectively study the post-operative results and complications of percutaneous nephrolithotomy (PNL) in supine position to assess difficulty of learning it and how experience affects the results. To establish a relative comparison with the data published in the literature on the prone position.

MATERIAL AND METHODS

A prospective observational multicenter study on PNL in Valdivia position or in its Galdakao variant was performed. Demographic variables and specific variables related to the lithiasis were collected. Technical aspects, surgery time, success rate and complications according to the Clavien-Dindo classifications were assessed.

RESULTS

A total of 335 PNL in supine position conducted in 13 Spanish centers were registered from September 2008 to June 2011. The man:woman ratio was 1:1.28 and mean age 51.3+14.5 years. 211 (63%) cases were performed by urologists with experience in >50 cases and 124 (37%) by urologists with less experience. Mean operation time was 113.3 ± 46.4 min, 106.6 ± 38.2 for the experienced ones vs. 124.9 ± 56.2 in the novice ones (P<.002). No difference was detected in the mean size of the lithiasis. However, in the experienced group, there was a greater proportion of coraliform cases and multiple lithiasis than in the novice group (P<.001). Success rate evaluated as total absence of lithiasic residuals was 69.6%, without differences between groups (68.2 vs. 71.8%). In 102 (30.6%) patient had residual lithiasis and 60 (17,9%) required complementary treatment. Relative global success rate was 82.1% and complications rate 25.4%, without detecting differences between groups. However, the novel group had more major complications (P>.001).

CONCLUSION

The PNL in supine position is obtaining rapid and consolidated diffusion in our setting and its effectiveness and safety seems to be equivalent to that described in the literature for PNL in prone position. It is possible to obtain good results with a modest learning curve. The rate of greater complications associated to the procedure decreases with experience.

When prone position is contraindicated or not preferable, can supine percutaneous nephrolithotomy solve the problem?

PURPOSE

To assess safety and efficacy of supine percutaneous nephrolithotomy in patients for whom prone position or general anesthesia is contraindicated or not preferable due to associated comorbidities, overweight or ipsilateral upper ureteric calculi.

MATERIALS AND METHODS

Fifty two patients (37 males and 15 females, mean age 33 ± 10.2 years) were included in this study. Supine position was selected due to anesthetic considerations (preexisting compromised cardiopulmonary status, morbid obesity (body mass index > 40 kg/m²) and/or other associated medical comorbidities), impossible prone position due to bone deformities or associated ipsilateral upper ureteric stone. Regional anesthesia was used in 24 patients while 28 patients underwent general anesthesia. After standard cystoscopy and retrograde ureteropyelography in the dorsal lithotomy position, the position was modified using 3 liters of saline bag below the ipsilateral upper flank. Percutaneous access to the pelvicalyceal system was performed through the posterior axillary line under fluoroscopic guidance.

RESULTS

Successful renal puncture was achieved in all cases. Single access via the lower calyx was the most commonly used access (36 cases). Stone-free rate was 92.3%. Postoperative complications classified according to Clavien Dindo classification included bleeding requiring transfusion (3.8%), prolonged fever (7.7%), deep venous thrombosis (1.9%) [grade II in all] and urinary leakage requiring ureteric stenting (5.8%) [grade IIIa].

CONCLUSIONS

The modified supine position for percutaneous nephrolithotomy is a safe and effective option that offers several advantages with an excellent outcome. It can be performed safely for morbidly obese patients and those with cardiopulmonary compromise.

The Learning Curve for Flank Percutaneous Nephrolithotomy for Kidney Calculi: A Single Surgeon's Experience

Purpose

Percutaneous nephrolithotomy (PCNL) is conventionally conducted in the prone position. However, the prone position increases anesthesia-related morbidity and position changes lengthen the operation time. We report perioperative outcomes and the learning curve for flank PCNL on the basis of a single surgeon's experience.

Materials and Methods

This study investigated 53 cases of flank PCNL performed for renal stones at our institution from April 2008 to September 2010. We compared mean operative time, stone-free rate, drop in hemoglobin level, length of hospital stay, complications, and need for additional procedures after the surgery. The 53 cases were divided into three groups by case number to compare therapeutic effect, stability, and the learning curve for flank position PCNL.

Results

The mean operation time for the 53 patients was 97.3±43.1 minutes. The mean operation time gradually decreased as the surgeon accumulated experience. From the 36th case, the mean operation time showed a statistically significant decrease to 72.2±24.1 minutes (p=0.003). The overall stone-free rate was 64.2% for all procedures (range, 61.1-76.5%). There were no significant differences in the drop in hemoglobin level, stone-free rate, re-treatment, hospital stay, or complication rate. There was no injury to the bowel or renal vessels, and no other major complications occurred.

Conclusions

Flank PCNL can be used to remove renal stones effectively while overcoming the disadvantages of the existing prone position PCNL. After 36 cases, the learning curve showed acquisition of surgical competence. The clinical experience reported here suggests that flank PCNL is a safe and feasible technique.

Percutaneous lithotripsy in Valdivia-Galdakao decubitus position: our experience

Percutaneous nephrolithotripsy (PNL) is actually the first therapeutic option to resolve complex renal stones. Our department initiated its experience in 1985 and treated the first 585 patients in ventral decubitus, as the original technique was described. Then, in 1998, the dorsal decubitus was adopted (Valdivia Uria), in which 695 patients were treated. Since 2006 the Valdivia Galdakao variant has been used. The Valdivia Galdakao position is an intermediate dorsal decubitus with extension of its homolateral lower limb and flexion of the contralateral. It is a practical way to place the patient for percutaneous renal surgery, avoiding hyperextensions and hyperflexions that can result in articular damage. It preserves cardiovascular and ventilatory dynamics and allows a better access to the respiratory tract. In this position, the bowel slips away from the puncture area lowering the risk of its damage. A single lumbar and genital sterile surgical field is created allowing antegrade and retrograde simultaneous endoscopic and even laparoscopic access, increasing efficiency and safety of the minimal invasive procedures. Between April 2006 and March 2008, 175 PNLs were performed in our department with the patient in Valdivia Galdakao position. The aim of this article is to describe our experience in this decubitus confirming that the Valdivia Galdakao is a safe, practical and versatile position that should be considered as first choice when a percutaneous renal surgery is indicated.

The effect of posture-induced changes in peripheral nitric oxide uptake on exhaled nitric oxide

Airway and alveolar NO contributions to exhaled NO are being extracted from exhaled NO measurements performed at different flow rates. To test the robustness of this method and the validity of the underlying model, we deliberately induced a change in NO uptake in the peripheral lung compartment by changing body posture between supine and prone. In 10 normal subjects, we measured exhaled NO at target flows ranging from 50 to 350 ml/s in supine and prone postures. Using two common methods, bronchial NO production [Jaw(NO)] and alveolar NO concentration (FANO) were extracted from exhaled NO concentration vs. flow or flow−1 curves. There was no significant Jaw(NO) difference between prone and supine but a significant FANO decrease from prone to supine ranging from 23 to 33% depending on the method used. Total lung capacity was 7% smaller supine than prone ( P = 0.03). Besides this purely volumetric effect, which would tend to increase FANO from prone to supine, the observed degree of FANO decrease from prone to supine suggests a greater opposing effect that could be explained by the increased lung capillary blood volume (Vc) supine vs. prone ( P = 0.002) observed in another set of 11 normal subjects. Taken together with the relative changes of NO and CO transfer factors, this Vc change can be attributed mainly to pulmonary capillary recruitment from prone to supine. Realistic models for exhaled NO simulation should include the possibility that a portion of the pulmonary capillary bed is unavailable for NO uptake, with a maximum capacity of the pulmonary capillary bed in the supine posture.

The effect of conductive ventilation heterogeneity on diffusing capacity measurement

It has long been assumed that the ventilation heterogeneity associated with lung disease could, in itself, affect the measurement of carbon monoxide transfer factor. The aim of this study was to investigate the potential estimation errors of carbon monoxide diffusing capacity (DlCO) measurement that are specifically due to conductive ventilation heterogeneity, i.e., due to a combination of ventilation heterogeneity and flow asynchrony between lung units larger than acini. We induced conductive airway ventilation heterogeneity in 35 never-smoker normal subjects by histamine provocation and related the resulting changes in conductive ventilation heterogeneity (derived from the multiple-breath washout test) to corresponding changes in diffusing capacity, alveolar volume, and inspired vital capacity (derived from the single-breath DlCO method). Average conductive ventilation heterogeneity doubled ( P < 0.001), whereas DlCO decreased by 6% ( P < 0.001), with no correlation between individual data ( P > 0.1). Average inspired vital capacity and alveolar volume both decreased significantly by, respectively, 6 and 3%, and the individual changes in alveolar volume and in conductive ventilation heterogeneity were correlated ( r = −0.46; P = 0.006). These findings can be brought in agreement with recent modeling work, where specific ventilation heterogeneity resulting from different distributions of either inspired volume or end-expiratory lung volume have been shown to affect DlCO estimation errors in opposite ways. Even in the presence of flow asynchrony, these errors appear to largely cancel out in our experimental situation of histamine-induced conductive ventilation heterogeneity. Finally, we also predicted which alternative combination of specific ventilation heterogeneity and flow asynchrony could affect DlCO estimate in a more substantial fashion in diseased lungs, irrespective of any diffusion-dependent effects.

Lung and 'end organ' injury due to mechanical ventilation in animals: comparison between the prone and supine positions

Introduction

Use of the prone position in patients with acute lung injury improves their oxygenation. Most of these patients die from multisystem organ failure and not from hypoxia, however. Moreover, there is some evidence that the organ failure is caused by increased cell apoptosis. In the present study we therefore examined whether the position of the patients affects histological changes and apoptosis in the lung and 'end organs', including the brain, heart, diaphragm, liver, kidneys and small intestine.

Methods

Ten mechanically ventilated sheep with a tidal volume of 15 ml/kg body weight were studied for 90 minutes. Five sheep were placed in the supine position and five sheep were placed in the prone position during the experiment. Lung changes were analyzed histologically using a semiquantitative scoring system and the extent of apoptosis was investigated with the TUNEL method.

Results

In the supine position intra-alaveolar hemorrhage appeared predominantly in the dorsal areas, while the other histopathologic lesions were homogeneously distributed throughout the lungs. In the prone position, all histological changes were homogeneously distributed. A significantly higher score of lung injury was found in the supine position than in the prone position (4.63 ± 0.58 and 2.17 ± 0.19, respectively) (P < 0.0001). The histopathologic changes were accompanied by increased apoptosis (TUNEL method). In the supine position, the apoptotic index in the lung and in most of the 'end organs' was significantly higher compared with the prone position (all P < 0.005). Interestingly, the apoptotic index was higher in dorsal areas compared with ventral areas in both the prone and supine positions (P < 0.003 and P < 0.02, respectively).

Conclusion

Our results suggest that the prone position appears to reduce the severity and the extent of lung injury, and is associated with decreased apoptosis in the lung and 'end organs'.

Pattern of diffusion disturbance related to clinical diagnosis: The K(CO) has no diagnostic value next to the DL(CO)

AIM OF THE STUDY

The diffusion capacity of the lung for carbon monoxide (DL(CO)) is an important tool in the diagnosis and follow-up of patients with pulmonary diseases. In case of a decreased DL(CO) the K(CO), defined as DL(CO)/V(A) (V(A) is alveolar volume), can differentiate between normal alveolocapillary membrane (normal K(CO)) and abnormal alveolocapillary membrane (low K(CO)). The latter category consists of decreased surface of the membrane, increased thickness or decreased perfusion of ventilated alveoli. The V(A)/TLC (TLC is total lung capacity determined by whole body plethysmography) can partially differentiate between these categories. The aim of this study was to investigate the diagnostic value of the specific diffusion disturbances, which can be constructed by combining the DL(CO), K(CO) and V(A)/TLC.

METHODS

In 460 patients the diagnosis made by clinicians were fitted into five diagnostic categories: asthma, chronic obstructive pulmonary disease (COPD), treatment effects of haematologic malignancies, heart failure and diffuse parenchymal lung diseases (DPLD). These categories were linked to the pattern of diffusion disturbance.

RESULTS

Almost all patients with asthma have a normal DL(CO), most patients in the other groups do not have the expected pattern of diffusion disturbance, especially in the group with DPLD a bad match is observed.

CONCLUSION

In this study the pattern of diffusion disturbance is of limited use in establishing a diagnosis. The use of the K(CO) next to the DL(CO) has no additional diagnostic value. Regional ventilation-perfusion inequality probably forms an important underlying mechanism of decreased DL(CO).