Meta-analysis of the association between obstructive sleep apnoea and postoperative outcome

BACKGROUND

Obstructive sleep apnoea (OSA) is often undiagnosed before elective surgery and may predispose patients to perioperative complications.

METHODS

A literature search of PubMed-Medline, Web of Science, Scopus, EMBASE, Cochrane Database of Systematic Reviews, and Cochrane Central Register of Controlled Trials up to November 2010 was conducted. Our search was restricted to cohort or case-control studies in adults diagnosed with OSA by screening questionnaire, oximetry, or polysomnography. Studies without controls, involving upper airway surgery, and with OSA diagnosed by ICD-9 codes alone were excluded. The primary postoperative outcomes were desaturation, acute respiratory failure (ARF), reintubation, myocardial infarction/ischaemia, arrhythmias, cardiac arrest, intensive care unit (ICU) transfer, and length of stay.

RESULTS

Thirteen studies were included in the final analysis (n=3942). OSA was associated with significantly higher odds of any postoperative cardiac events [45/1195 (3.76%) vs 24/1420 (1.69%); odds ratio (OR) 2.07; 95% confidence interval (CI) 1.23-3.50, P=0.007] and ARF [33/1680 (1.96%) vs 24/3421 (0.70%); OR 2.43, 95% CI 1.34-4.39, P=0.003]. Effects were not heterogeneous for these outcomes (I(2)=0-15%, P>0.3). OSA was also significantly associated with higher odds of desaturation [189/1764 (10.71%) vs 105/1881 (5.58%); OR 2.27, 95% CI 1.20-4.26, P=0.01] and ICU transfer [105/2062 (5.09%) vs 58/3681 (1.57%), respectively; OR 2.81, 95% CI 1.46-5.43, P=0.002]. Both outcomes showed a significant degree of heterogeneity of the effect among studies (I(2)=57-68%, P<0.02). Subgroup analyses had similar conclusions as main analyses.

CONCLUSIONS

The incidence of postoperative desaturation, respiratory failure, postoperative cardiac events, and ICU transfers was higher in patients with OSA.

Noninvasive proportional assist ventilation for acute respiratory insufficiency. Comparison with pressure support ventilation

Noninvasive positive pressure ventilation (NPPV) is usually applied using pressure support ventilation (PSV). Proportional assist ventilation (PAV) is a newer mode that delivers assisted ventilation in proportion to patient effort. We hypothesized that PAV for NPPV would support gas exchange and avoid intubation as well as PSV and be more comfortable and tolerable for patients. Adult patients with acute respiratory insufficiency were randomized to receive NPPV with PAV delivered using the Respironics Vision ventilator or PSV using a Puritan-Bennett 7200ae critical care ventilator. Each mode was adjusted to relieve dyspnea and improve gas exchange until patients met weaning or intubation criteria, died, or refused to continue. Twenty-one and 23 patients were entered into the PAV and PSV groups, respectively, and had similar diagnoses and baseline characteristics, although pH was slightly lower in the PAV group (7.30 versus 7.35, p = 0.02). Mortality and intubation rates were similar, but refusal rate was lower, reduction in respiratory rate was more rapid, and there were fewer complications in the PAV group. We conclude that use of the PAV mode is feasible for noninvasive therapy of acute respiratory insufficiency. Compared with PSV delivered with the Puritan-Bennett 7200ae, PAV is associated with more rapid improvements in some physiologic variables and is better tolerated.

Postoperative complications in patients with obstructive sleep apnea syndrome undergoing hip or knee replacement: a case-control study

OBJECTIVE

To identify and assess the impact of postoperative complications in patients with unrecognized or known obstructive sleep apnea syndrome (OSAS) undergoing hip replacement or knee replacement compared with control patients undergoing similar operations. Although OSAS is a risk factor for perioperative morbidity, data quantifying the magnitude of the problem in patients undergoing non-upper airway operations are limited.

PATIENTS AND METHODS

This retrospective, case-control study from a single academic medical institution included patients diagnosed as having OSAS between January 1995 and December 1998 and undergoing hip or knee replacement within 3 years before or anytime after their OSAS diagnosis. Patients with OSAS were subcategorized as having the diagnosis either before or after the surgery and also, regardless of time of diagnosis, by whether they were using continuous positive airway pressure (CPAP) prior to hospitalization. Matched controls were patients without OSAS undergoing the same operation. Interventions were defined specifically as administration of a particular treatment in the context of each complication, eg, supplemental oxygen, implementation of additional monitoring such as oximetry for hypoxemia, or transfer to the intensive care unit (ICU) for cardiac ischemia concerns. Postoperative complications were assessed for all patients in the different categories and included respiratory events such as hypoxemia, acute hypercapnia, and episodes of delirium. Serious complications were noted separately, including unplanned ICU days, reintubations, and cardiac events. The length of hospital stay was also tabulated.

RESULTS

There were 101 patients with the diagnosis of OSAS in this study and 101 matched controls. Thirty-six patients had their joint replacement before OSAS was diagnosed, and 65 had surgery after OSAS was diagnosed. Of the latter 65 patients, only 33 were using CPAP at home preoperatively. Complications were noted in 39 patients (39%) in the OSAS group and 18 patients (18%) in the control group (P=.001). Serious complications occurred in 24 patients (24%) in the OSAS group compared with 9 patients (9%) in the control group (P=.004). Hospital stay was significantly longer for the OSAS patients at a mean +/- SD of 6.8 +/- 2.8 days compared with 5.1 +/- 4.1 days for the control patients (P<.007).

CONCLUSION

Adverse postoperative outcomes occurred at a higher rate in patients with a diagnosis of OSAS undergoing hip or knee replacement compared with a group of matched control patients.

Noninvasive ventilation

Noninvasive ventilation refers to the delivery of assisted ventilatory support without the use of an endotracheal tube. Noninvasive positive pressure ventilation (NPPV) can be delivered by using a volume-controlled ventilator, a pressure-controlled ventilator, a bilevel positive airway pressure ventilator, or a continuous positive airway pressure device. During the past decade, there has been a resurgence in the use of noninvasive ventilation, fueled by advances in technology and clinical trials evaluating its use. Several manufacturers produce portable devices that are simple to operate. This review describes the equipment, techniques, and complications associated with NPPV and also the indications for both short-term and long-term applications. NPPV clearly represents an important addition to the techniques available to manage patients with respiratory failure. Future clinical trials evaluating its many clinical applications will help to define populations of patients most apt to benefit from this type of treatment.

Indications for positive airway pressure treatment of adult obstructive sleep apnea patients: a consensus statement

We developed a short-length document that clearly delineates a prudent approach to and criteria for reimbursement of positive airway pressure (PAP) costs for the treatment of obstructive sleep apnea (OSA). Treatment modalities for OSA with PAP include continuous positive airway pressure, bilevel or variable PAP, and autotitrating PAP. This guidance on the appropriate criteria for PAP use in OSA is based on widely acknowledged peer-reviewed studies and widely accepted clinical practice. These criteria reflect current opinion on the appropriate clinical management of OSA in lieu of data pending from the Sleep Heart Health Study and upcoming outcome studies. This document is not intended to provide a complete review and analysis of the OSA clinical literature. The key to the success of this document is to foster consensus within and outside the clinical sleep community by providing a common sense and easily understood approach to the treatment of OSA with PAP.

Efficacy of nocturnal nasal ventilation in stable, severe chronic obstructive pulmonary disease during a 3-month controlled trial

OBJECTIVE

To evaluate the efficacy of nocturnal nasal ventilation (NNV) in patients with rigidly defined, severe but stable chronic obstructive pulmonary disease (COPD) and hypercapnia.

DESIGN

By randomization, eligible patients were assigned to an active or a sham treatment arm. Data from these two groups were analyzed statistically.

MATERIAL AND METHODS

Initially, 35 patients with severe COPD (forced expiratory volume in 1 second [FEV1] of less than 40% predicted) and daytime hypercapnia (arterial carbon dioxide tension [PaCO2] of more than 45 mm Hg) were enrolled in a 3-month NNV trial. After a minimal observation period of 6 weeks, 13 patients were judged to be clinically stable and were randomized to NNV (N = 7) or sham (N = 6) treatment, consisting of nightly use of a bilevel positive airway pressure (PAP) device set to deliver an inspiratory pressure of either 10 or 0 cm of water (H2O). The device was used in the spontaneous or timed mode and set to a minimal expiratory pressure of 2 cm H2O. Patients underwent extensive physiologic testing including polysomnography and were introduced to the bilevel PAP system during a 2.5-day hospital stay.

RESULTS

The NNV and sham treatment groups were similar in mean age (71.0 versus 66.5 years), PaCO2 (54.7 versus 48.5 mm Hg), and FEV1 (0.62 versus 0.72 L). Only four of seven patients in the NNV group were still using the bilevel PAP device at the completion of the trial, as opposed to all six patients in the sham group. Only one patient had a substantial reduction in PaCO2 - from 50 mm Hg at baseline to 43 mm Hg after 3 months of NNV. He declined further NNV treatment with bilevel PAP. Sham treatment did not lower PaCO2. Lung function, nocturnal oxygen saturation, and sleep efficiency remained unchanged in both groups.

CONCLUSION

Disabled but clinically stable patients with COPD and hypercapnia do not readily accept and are unlikely to benefit from NNV.

Severe hypercapnia after low-flow oxygen therapy in patients with neuromuscular disease and diaphragmatic dysfunction

OBJECTIVE

To increase the general awareness of the possible exacerbation of hypercapnia by the administration of low-flow oxygen in patients with neuromuscular disorders.

DESIGN

We retrospectively reviewed the medical records of 118 consecutive adult patients with a diagnosis of neuromuscular disease who underwent phrenic nerve conduction studies during a 5-year period, and we analyzed pulmonary function data for 8 patients who underwent arterial blood gas studies before and after the administration of low-flow oxygen.

MATERIAL AND METHODS

In the eight patients with neuromuscular disease and diaphragmatic dysfunction (three with polymyositis, three with amyotrophic lateral sclerosis or nonspecific motor neuron disease, and one each with inflammatory motor neuropathy and chronic poliomyelitis), we analyzed the response of the arterial carbon dioxide tension (PaCO2) after low-flow supplemental oxygen therapy (0.5 to 2 L/min). Linear analysis was used to attempt to find correlations between respiratory variables and the PaCO2 response after oxygen therapy.

RESULTS

For the overall study group, the mean PaCO2 increased 28.2 +/- 23.3 torr after low-flow oxygen treatment; in five patients, it increased by 27 torr or more. Four patients who were subsequently treated with nocturnal assisted ventilation were able to use supplemental oxygen during the day with less severe hypercapnia. Statistical analysis failed to reveal specific correlations between increased PaCO2 values after oxygen therapy and any respiratory variables.

CONCLUSION

In patients with neuromuscular disease and diaphragmatic dysfunction, even low-flow supplemental oxygen should be administered with caution, and assisted ventilation should be strongly considered as an initial intervention.

The practice of critical care medicine. A national survey report. ACCP Council on Critical Care

Aggressive reimbursement reform has been an imposing directive for care providers of ICU medicine. Timely knowledge of actual care routines obtained from a large sample of actively practicing physicians should be mandatory when developing any guidelines or practice standards. A questionnaire was therefore designed by the steering committee of the ACCP Council on Critical Care and sent to its members. The 1,294 responses were analyzed for demographics of the individual practitioner, local aspects of ICU staffing and policies, reimbursement, and a specific practice issue, nutrition. The typical respondent was aged 41 to 50 (41 percent), was a pulmonary subspecialist (68 percent), was not critical care certified (55 percent), worked 25 to 50 percent of his or her total time in the ICU (40 percent), and would continue ICU practice despite poor reimbursement (82 percent). Physicians practiced within a group (53 percent), in a 100- to 500-bed hospital (69 percent), with house staff available (60 percent), and predominantly cared for Medicare patients (55 percent). The following data may allow better judgments to be made pertaining to the implementation of care policies in the current ICU environment.

Pulmonary complications of orthotopic liver transplantation

We retrospectively reviewed the pulmonary complications and associated morbidity and mortality of 44 consecutive patients who underwent 52 orthotopic liver transplantations (OLTs) at the Mayo Clinic during 1987. All survivors participated in follow-up for 1 year after OLT. Of the five deaths in the study group, three were associated with pulmonary infections. On postoperative chest roentgenograms, 24 cases of pulmonary infiltrates were noted; 12 were caused by infections. Ten opportunistic pulmonary infections developed in nine patients: four cytomegalovirus, three Pneumocystis carinii pneumonia, and one each of Cryptococcus, Aspergillus, and Candida. All except one of the opportunistic infections were diagnosed after the sixth postoperative week. Fiberoptic bronchoscopy was helpful for diagnosing opportunistic pulmonary infections in six patients. One Aspergillus pulmonary infection was diagnosed by transthoracic needle aspiration. Bacterial pneumonia occurred in five patients. Preoperative pulmonary function tests, performed in 40 patients, revealed a restrictive ventilatory defect in 28% and impaired gas transfer in 52%. Pleural effusion was present in 18% of patients preoperatively and in 77% during the first week after OLT. Preoperative severity of liver disease and results of arterial blood gas determinations, pulmonary function tests, and chest roentgenography were not associated with postoperative mortality and pulmonary infections. Infectious and noninfectious pulmonary complications are common in liver transplant recipients. Attempts to decrease the frequency and severity of pulmonary complications by early diagnosis and effective treatment may diminish the morbidity and mortality associated with OLT.

Desmoplastic malignant mesothelioma masquerading as sclerosing mediastinitis: a diagnostic dilemma

A 48-year-old woman presented with dyspnea, chest discomfort, and left vocal cord paralysis that developed 2 months after a flu-like illness. Radiographic examination showed prominence of mediastinal soft tissues and an ill-defined left upper lobe infiltrate. Dense mediastinal sclerosis was found at thoracotomy, and biopsy samples taken from the sclerotic areas showed densely hyalinized fibrotic tissue. Necrotizing granulomas containing organisms resembling Histoplasma capsulatum were present within mediastinal lymph nodes. Based on these findings, a diagnosis of sclerosing mediastinitis was made. During the next year, the patient's respiratory function deteriorated, and biopsy samples taken during a second thoracotomy 1 year later were again interpreted as sclerosing mediastinitis. The patient died postoperatively; at autopsy, the sclerotic mass involving the mediastinum was composed of a mixture of dense fibrosis and sarcomatous tissue. The final diagnosis was localized mediastinal desmoplastic malignant mesothelioma. We report it here because of its unusual clinical presentation, which mimicked sclerosing mediastinitis.

Lipoprotein analysis in the evaluation of chest pain in the emergency department

Apolipoproteins were measured in a prospective blinded fashion in blood specimens from patients with chest pain in the emergency department. A definitive diagnosis for the chest pain (non-cardiac-related in 32% and angina or myocardial infarction in 68%) was available in 136 of the 162 patients originally enrolled in the study. Logistic regression and multivariate analysis failed to show any usefulness of apolipoprotein determinations in distinguishing patients with cardiac ischemia from those without it. The clinician's initial impression of the chest pain, the electrocardiogram, a history of previous angina, myocardial infarction, or peripheral atherosclerosis, and male sex were strongly associated with the final diagnosis. We conclude that, although apolipoprotein analysis has proved useful in epidemiologic studies, the most reliable indicators of ischemic pain remain the medical history, the electrocardiogram, and the clinician's overall initial impression.

Effects of alterations in pulmonary function and sleep variables on survival in patients with amyotrophic lateral sclerosis

Breathing abnormalities and nocturnal hypoventilation occur in patients with amyotrophic lateral sclerosis (ALS). A prospective study was undertaken to determine the relationship of pulmonary function test abnormalities with quality of sleep and survival in 21 patients with ALS. Results of spirometry including determination of maximal respiratory pressures and arterial blood gases were compared with several formal polysomnographic variables and then also with 18-month survival. The patients had mild to moderate pulmonary function deficits, but the quality of sleep was best related to age (mean age, 58.5 years). The results of pulmonary function tests and arterial blood gas measurements did not correlate well with the presence of nocturnal breathing events or survival time, but the maximal inspiratory pressure was 86% sensitive for predicting the presence of a nocturnal oxygen saturation nadir of 80% or less and 100% sensitive for predicting 18-month survival. Although obstructive breathing events occurred, the primary explanation for the decline in nocturnal oxygen saturation was hypoventilation. We conclude that routine pulmonary function tests may be useful for screening for reductions in nocturnal oxygen saturation and also may have prognostic value. Further studies may determine whether treatment of nocturnal hypoventilation will have an effect on survival in patients with ALS who have breathing impairment.

Nocturnal nasal ventilation for treatment of patients with hypercapnic respiratory failure

We reviewed the Mayo Clinic experience with nocturnal nasal ventilation (NNV) and retrospectively assessed the clinical benefits, patient compliance, and complications. NNV had been instituted in 26 patients with daytime hypercapnia and nocturnal hypoventilation due to neuromuscular diseases or chronic obstructive pulmonary disease. After initiation of NNV, 21 of 26 patients continued to use this treatment regularly (81% compliance rate) and considered their life-style improved. In this subset of patients, the arterial partial pressure of carbon dioxide during unassisted breathing decreased from 64 +/- 13 to 51 +/- 7 mm Hg, and the arterial partial pressure of oxygen increased from 58 +/- 12 to 68 +/- 8 mm Hg. No significant change was noted in the forced vital capacity or maximal respiratory pressures. Four of the five patients in whom NNV had been discontinued cited discomfort related to the mask or severity and poor prognosis of the underlying illness as reasons for cessation of treatment. We conclude that NNV is well tolerated by most patients and may improve alveolar ventilation and arterial oxygenation in patients with chronic respiratory failure.

Radiology in the intensive-care unit

Portable chest radiography is an essential component of clinical patient management in the intensive-care unit. With routine use of this procedure, unexpected cardiopulmonary abnormalities are frequently detected, and malposition or complications of intravascular devices and endotracheal, thoracostomy, or nasogastric tubes are also commonly found. The pulmonary parenchyma may be assessed for changes of acute lung injury, cardiogenic edema, areas of pneumonitis, atelectasis, or other abnormal collections of fluid or air. In mechanically ventilated patients, barotrauma occurs frequently and may be manifested by subtle intrathoracic collections of air. Technical factors may limit the resolution of the anteroposterior chest radiograph obtained at the bedside, but crucial clinical information is often gained. Portable chest radiographic findings, the role of computed tomography and ultrasonography, and interventional radiologic procedures pertinent to patients in the intensive-care unit are reviewed.

Metered dose inhalers for bronchodilator delivery in intubated, mechanically ventilated patients

We determined the relative efficacy of two bronchodilator aerosol delivery methods in 18 intubated mechanically ventilated patients with airways obstruction. Two treatment arms, consisting of albuterol 270 micrograms (three puffs) from a metered dose inhaler and albuterol 2.5 mg from a saline solution nebulized with an updraft inhaler, were compared in a single blind, randomized crossover design. Pulmonary function was evaluated using an interrupter technique. Changes in passive expiratory flow at respiratory system recoil pressures between 6 and 10 cm H2O provided the therapeutic endpoints. Paired measurements were made before and 30 minutes after drug delivery. The MDI and NEB resulted in similar improvements in iso-recoil flow (mean increase for both groups = 0.1 L/s). Treatment sequence, severity of obstruction, and bronchodilator responsiveness had no effect on relative efficacy. Albuterol caused a small but significant increase in heart rate that was similar following both delivery methods. We conclude that bronchodilator aerosol delivery with metered dose inhalers provides a viable alternative to nebulizer therapy in intubated mechanically ventilated patients and may result in a cost savings to hospitals and patients.

The effects of positive expiratory pressure on isovolume flow and dynamic hyperinflation in patients receiving mechanical ventilation

The use of continuous positive airway pressure (CPAP) or positive end-expiratory pressure (PEEP) has been advocated by some to assist in the weaning process of patients receiving mechanical ventilation for respiratory failure. The efficacy of this technique and its effect on respiratory system mechanics are not well understood. The theoretical advantage of CPAP or PEEP during the weaning process can be obliterated if excessive dynamic hyperinflation is induced. A key determinant of the individual response to this proposed weaning technique is the recognition of the presence or absence of expiratory flow limitation. We studied the effect of progressively increased levels of applied PEEP on isovolume expiratory flow and end-expiratory lung volume in seven patients during controlled mechanical ventilation. In the absence of expiratory flow limitation, passive expiratory flow decreased and end-expiratory lung volume increased when any level of PEEP was applied. In contrast, flow-limited patients did not demonstrate a change in isovolume expiratory flow or end-expiratory lung volume until the applied PEEP reduced the driving pressure for expiratory flow below a critical value. All patients demonstrated dynamic hyperinflation during controlled ventilation as evident by the existence of intrinsic PEEP. The nominal value of applied PEEP that caused a reduction in isovolume expiratory flow was unrelated to the initial level of intrinsic PEEP. The clinical implications of these findings with respect to CPAP therapy during weaning from mechanical ventilation are discussed.

Transdiaphragmatic twitch pressure. Effects of lung volume and chest wall shape

The effect of lung volume and thoracoabdominal shape on the transdiaphragmatic twitch pressure (Pdit) amplitude was evaluated in six volunteers during airway occlusion. Twitch stimulation was applied through fine wire electrodes implanted near both phrenic nerves. Stimulations were tolerated with little discomfort and constant phrenic nerve responses were maintained for hours. At FRC the group mean Pdit was 31.4 cm H2O (range, 19 to 36 cm H2O), and its coefficient of variation ranged between 2 and 5% in individual subjects. At 1 L above FRC, the Pdit decreased a mean of 7.8 cm H2O (range, 2.8 to 11.9 cm H2O). This change was caused primarily by a decrease in esophageal pressure amplitude. The shape of the relaxed chest wall was altered by loading the rib cage with a force of 5 to 9 kg. Load and shape had little effect on Pdit independently of lung volume. Our modified technique of phrenic nerve stimulation through small wire electrodes is ideally suited for longitudinal intervention studies in patients. We conclude that the variability of Pdit with shape is small compared with its expected decrease with lung volume.

Transbronchial needle aspiration in the practice of bronchoscopy

We reviewed the records of all patients who underwent bronchoscopy with a flexible fiberoptic instrument and transbronchial needle aspiration (TBNA) at our institution between August 1983 and December 1985. During 85 bronchoscopy sessions, 89 TBNAs were performed in 84 patients. Seventy-three aspirates were obtained from 68 patients who were eventually proved to have a malignant lesion. Of these 68 patients, 25 had positive results of TBNA (37%). Of these 25 patients, 15 had non-small-cell cancers (11 bronchogenic and 4 metastatic from extrapulmonary sites), and 10 had small-cell carcinomas. In patients with a malignant lesion, 23% of the central aspirates (from paratracheal regions or within 2 cm of the carina) and 65% of the distal aspirates (beyond 2 cm from the carina) were positive (a total yield of 34%). Five of the distal aspirates were obtained from peripheral lesions under fluoroscopic guidance, and three were positive for a malignant process. In eight patients, the only malignant finding at bronchoscopy was the aspirate. Two of the eight patients had carcinoma metastatic to the lung, three had small-cell carcinoma, and the other three had bronchogenic carcinoma. In five patients, TBNA obviated more invasive diagnostic measures. We find TBNA to be useful in selected patients. It increases our diagnostic yield for small-cell carcinoma and carcinoma metastatic to the chest. TBNA should be considered when a submucosal process is present, extrinsic compression is evident, or an accessible extrabronchial mass is found radiographically.

Evaluation of bronchodilator responsiveness in mechanically ventilated patients

Airway pressure, flow, and volume were measured before and after administration of aerosolized metaproterenol during controlled mechanical inflation and stepwise deflation of the relaxed respiratory system in 13 mechanically ventilated patients. An increase in passive expiratory flow at constant respiratory system recoil pressure was considered evidence of bronchodilatation. In 10 patients, at a respiratory system recoil pressure of 6 cm H2O (VP6), expiratory flow increased 21 to 500% above prebronchodilator level. In these 10 dynamically hyperinflated patients, an increase in VP6 was associated with a decrease in peak inspiratory pressure (Ppeak) (mean delta = -4.7 cm H2O) and a decrease in intrinsic positive end-expiratory pressure (Peepi) (mean delta = -2.4 cm H2O). The elastance of the respiratory system was not affected by metaproterenol, and the delta Peepi corresponded to a mean decrease in end-expiratory lung volume of 0.20 L. The results are consistent with predictions based on a single-compartment model. When mean expiratory flow is determined only by the tidal volume and expiratory time, a decrease in airway resistance results in a decrease in lung volume at which patients are ventilated. Therefore, the decrease in Ppeak is caused not only by a decrease in the resistive pressure cost but also by a decrease in the elastic pressure cost of inflating the respiratory system. It is emphasized that Ppeak and Peepi provide valuable information about bronchodilator-induced changes in lung function during controlled mechanical ventilation.

Respiratory system mechanics in ventilated patients: techniques and indications

For the past 50 years, basic research has provided valuable insights into the concepts of respiratory system mechanics, but clinical application in the critical-care arena remains in its infancy. On the basis of the limited information that is available on critically ill patients, we believe that physicians who are responsible for the care of mechanically ventilated patients must understand the mechanical interactions between humans and machines. With measurements of flow, volume, and pressure, a more precise quantitative evaluation of the respiratory system can be obtained than with clinical assessment alone. In this article, we discuss the principles, techniques, and clinical applications of measurements of respiratory system mechanics in ventilated patients and suggest directions for further research that may prove to be clinically relevant.

Brain metastasis in hypernephroma

Of 926 patients with hypernephroma, 36 (3.9%) had metastasis to the brain. The median age at presentation was 61 years (range, 34 to 82). Nineteen patients had a single lesion metastatic to the brain, and 16 of these lesions were supratentorial. In 28% of the patients, computed tomography showed hyperdense lesions before contrast material was injected. All patients, except 2 with incomplete records, had evidence of widespread disease involving bone, liver, or lung. The median time interval between the initial diagnosis and the discovery of brain metastasis was 65.5 weeks (range, 0 to 462), with only 2 patients initially presenting with brain metastasis. Twenty-five of the patients who received only radiation therapy had a median survival of 13 weeks (range, 4 to 146), while 7 selected patients who underwent surgical resection and postoperative radiation had a median survival of 66 weeks (range, 18 to 260). In 5 of the 7 patients, scans demonstrated recurrent tumor from 6 to 23 weeks postoperatively. One patient had a pronounced reduction in the size of the tumor after radiation therapy only. This study shows that brain metastasis is usually a late complication of hypernephroma and is associated with a poor prognosis.

Vinyl chloride cytogenetics

This report presents cytogenetic findings from a group of 209 workers employed for up to 28 years in the manufacture of vinyl chloride monomer at the Texas Division of Dow Chemical U.S.A. Cytogenetic evaluation results from this group were compared to results found in examination of individuals being considered for employment. Statistical analyses were performed on a group basis for chromatid aberrations, chromosome aberrations and proportion of abnormal cells; no statistical difference of significance was found between the two groups. Comparison of these results with reported studies suggests that the level of cytogenetic aberrations in vinyl chloride workers is probably related to the length and level of exposure, and that risk of adverse genetic effect can be avoided in controlled, minimal-exposure environments.