Association of Mechanical Energy and Power with Postoperative Pulmonary Complications in Lung Resection Surgery: A Post Hoc Analysis of Randomized Clinical Trial Data

BACKGROUND

Mechanical power (MP), the rate of mechanical energy (ME) delivery, is a recently introduced unifying ventilator parameter consisting of tidal volume, airway pressures, and respiratory rates, which predicts pulmonary complications in several clinical contexts. However, ME has not been previously studied in the perioperative context, and neither parameter has been studied in the context of thoracic surgery utilizing one-lung ventilation.

METHODS

The relationships between ME variables and postoperative pulmonary complications were evaluated in this post hoc analysis of data from a multicenter randomized clinical trial of lung resection surgery conducted between 2020 and 2021 (n = 1,170). Time-weighted average MP and ME (the area under the MP time curve) were obtained for individual patients. The primary analysis was the association of time-weighted average MP and ME with pulmonary complications within 7 postoperative days. Multivariable logistic regression was performed to examine the relationships between energy variables and the primary outcome.

RESULTS

In 1,055 patients analyzed, pulmonary complications occurred in 41% (431 of 1,055). The median (interquartile ranges) ME and time-weighted average MP in patients who developed postoperative pulmonary complications versus those who did not were 1,146 (811 to 1,530) J versus 924 (730 to 1,240) J (P < 0.001), and 6.9 (5.5 to 8.7) J/min versus 6.7 (5.2 to 8.5) J/min (P = 0.091), respectively. ME was independently associated with postoperative pulmonary complications (ORadjusted, 1.44 [95% CI, 1.16 to 1.80]; P = 0.001). However, the association between time-weighted average MP and postoperative pulmonary complications was time-dependent, and time-weighted average MP was significantly associated with postoperative pulmonary complications in cases utilizing longer periods of mechanical ventilation (210 min or greater; ORadjusted, 1.46 [95% CI, 1.11 to 1.93]; P = 0.007). Normalization of ME and time-weighted average MP either to predicted body weight or to respiratory system compliance did not alter these associations.

CONCLUSIONS

ME and, in cases requiring longer periods of mechanical ventilation, MP were independently associated with postoperative pulmonary complications in thoracic surgery.

EDITOR’S PERSPECTIVE

Five-Year Sustained Impact of a Thoracic Enhanced Recovery After Surgery Program

BACKGROUND

Our thoracic enhanced recovery program (ERP) decreased the use of postoperative morphine equivalents and hospital costs 1 year after implementation at our tertiary center. The sustainability and potential increasing benefit of this program were evaluated.

METHODS

From 2015 to 2021, we prospectively analyzed the outcomes of patients who underwent elective pleural, pulmonary, or mediastinal operations at our institution. Patients were separated on the basis of the incision (video-assisted thoracoscopic surgery [VATS] or thoracotomy). The ERP protocol was initiated on May 1, 2016, and includes preoperative education, carbohydrate loading, opioid-sparing analgesia, conservative fluid management, protective ventilation, and early ambulation. Outcomes of patients before (2015, pre-VATS and pre-thoracotomy) and after (May 1, 2016, to December 31, 2021, ERP-VATS and ERP-thoracotomy) ERP implementation were compared.

RESULTS

The cohort included 1079 patients (pre-ERP era, n = 224 [21%]; ERP era, n = 855 [79%]). There was a median reduction of 1.5 hospital days per patient for ERP-thoracotomy and 1 hospital day per patient for ERP-VATS. Median postoperative morphine equivalents decreased in both groups (125 vs 45 mg, in ERP-thoracotomy; 84 vs 23 mg, ERP-VATS; P < .001), as did total admission cost ($32,118 vs $23,775, ERP-thoracotomy; $17,367 vs $11,560, ERP-VATS; P < .001). Median total fluid balance during the hospital stay decreased significantly. Rates of postoperative atrial fibrillation and urinary retention decreased across both subgroups.

CONCLUSIONS

ERP for thoracic surgery is sustainable and has been demonstrated to improve patient outcomes, to decrease opioid use, and to lower hospital costs. Therefore, it has the potential to become the standard of care.

Acute Respiratory Failure Complicating Endoscopic Sleeve Gastroplasty: A Case Report

Endoscopic sleeve gastroplasty (ESG) is a safe and minimally invasive procedure for the treatment of obesity. We report the case of a patient with obesity who underwent ESG complicated by postprocedural respiratory failure. During the procedure, she developed a Pao2/fraction of inspired oxygen (Fio2) ratio that necessitated postoperative mechanical ventilation. Chest radiography demonstrated massively dilated loops of bowel, cephalad displacement of both hemidiaphragms, lung volume reduction, and atelectasis. With absorption of luminal carbon dioxide, she was weaned from mechanical ventilation to supplemental oxygen, and she recovered completely. This case highlights postoperative respiratory failure associated with mechanical loading of the respiratory system following ESG.

Clinical implications of preoperative echocardiographic findings on cardiovascular outcomes following vascular surgery: An observational trial

INTRODUCTION

Peripheral artery disease and cardiac disease are often comorbid conditions. Echocardiography is a diagnostic tool that can be performed preoperatively to risk stratify patients by a functional cardiac test. We hypothesized that ventricular dysfunction and valvular lesions were associated with an increased incidence of expanded major adverse cardiac events (Expanded MACE).

METHODS AND MATERIALS

Retrospective cohort study from 2011 to 2020 including all patients from a major academic center who had vascular surgery and an echocardiographic study within two years of the index procedure.

RESULTS

813 patients were included in the study; a majority had a history of smoking (86%), an ASA score of 3 (65%), and were male (68%). Carotid endarterectomy was the most common surgery (24%) and the least common surgery was open abdominal aortic aneurysm repair (5%). We found no significant association between the echocardiographic findings of left ventricular dysfunction, right ventricular dysfunction, or valvular lesions and the postoperative development of Expanded MACE.

CONCLUSIONS

The preoperative echocardiographic findings of left ventricular dysfunction, right ventricular dysfunction and moderate to severe valvular lesions were not predictive of an increased incidence of postoperative Expanded MACE. We identified a significant association between RV dysfunction and post-operative dialysis that should be interpreted carefully due to the small number of outcomes. The transition from open to endovascular surgery and advances in perioperative management may have led to improved cardiovascular outcomes.

TRIAL REGISTRATION

Trial Registration: NCT04836702 (clinicaltrials.gov). https://www.google.com/search?client=firefox-b-d&q=NCT04836702.

Enhanced Recovery Protocol Associated With Decreased 3-Month Opioid Use After Thoracic Surgery

BACKGROUND

Enhanced recovery protocols (ERPs) have been shown to decrease inhospital opioid use after thoracic surgery. However, the impact on opioid use after discharge has not been reported. We hypothesized that prolonged opioid use would decrease after implementation of a comprehensive ERP.

METHODS

Records from all patients undergoing elective pulmonary, pleural, and mediastinal operations at a single institution (2015-2018) were abstracted from a prospective ERP database and The Society of Thoracic Surgeons institutional database. Records were reviewed for documentation of opioid use at 3-month and 6-month postoperative visits. Patients with preoperative chronic opioid use were excluded. Univariate analysis compared patients with and patients without 3-month opioid use, and a multivariable logistic regression evaluated independent predictors of prolonged opioid use.

RESULTS

A total of 499 patients was included: 160 pre-ERP, and 339 post-ERP. Three-month opioid use rates were decreased after implementation of an ERP (44% vs 30%, P = .01); 6-month opioid use rates were not significantly different (25% vs 18%, P = .10). Univariate analysis demonstrated increased 3-month opioid use rates among patients with preoperative tobacco use (38% vs 27%, P = .05) and chronic pain disorder (88% vs 32%, P < .01), with no impact from surgical incision (video-assisted thoracoscopic surgery 33%; open 37%, P = .49). On multivariable analysis, participation in an ERP was independently associated with decreased opioid use at 3 months (odds ratio 0.53; 95% CI, 0.31-0.89; P = .02).

CONCLUSIONS

There is a high burden of prolonged opioid use after elective thoracic surgery. Participation in a comprehensive ERP is associated with decreased opioid use 3 months postoperatively.

Driving pressure-guided ventilation and postoperative pulmonary complications in thoracic surgery: a multicentre randomised clinical trial

BACKGROUND

Airway driving pressure, easily measured as plateau pressure minus PEEP, is a surrogate for alveolar stress and strain. However, the effect of its targeted reduction remains unclear.

METHODS

In this multicentre trial, patients undergoing lung resection surgery were randomised to either a driving pressure group (n=650) receiving an alveolar recruitment/individualised PEEP to deliver the lowest driving pressure or to a conventional protective ventilation group (n=650) with fixed PEEP of 5 cm H₂O. The primary outcome was a composite of pulmonary complications within 7 days postoperatively.

RESULTS

The modified intention-to-treat analysis included 1170 patients (mean [standard deviation, sd]; age, 63 [10] yr; 47% female). The mean driving pressure was 7.1 cm H₂O in the driving pressure group vs 9.2 cm H₂O in the protective ventilation group (mean difference [95% confidence interval, CI]; -2.1 [-2.4 to -1.9] cm H₂O; P<0.001). The incidence of pulmonary complications was not different between the two groups: driving pressure group (233/576, 40.5%) vs protective ventilation group (254/594, 42.8%) (risk difference -2.3%; 95% CI, -8.0% to 3.3%; P=0.42). Intraoperatively, lung compliance (mean [sd], 42.7 [12.4] vs 33.5 [11.1] ml cm H₂O^-1; P<0.001) and Pa_o2 (median [inter-quartile range], 21.5 [14.5 to 30.4] vs 19.5 [13.5 to 29.1] kPa; P=0.03) were higher and the need for rescue ventilation was less frequent (6.8% vs 10.8%; P=0.02) in the driving pressure group.

CONCLUSIONS

In lung resection surgery, a driving pressure-guided ventilation improved pulmonary mechanics intraoperatively, but did not reduce the incidence of postoperative pulmonary complications compared with a conventional protective ventilation.

CLINICAL TRIAL REGISTRATION

NCT04260451.

Peripheral Cardiopulmonary Bypass in Two Patients With Symptomatic Tracheal Masses: Perioperative Challenges

Tracheal tumors or masses causing critical airway obstruction require resection for symptom relief. However, the location and extent of these tumors or masses often preclude conventional general anesthesia and tracheal intubation. Peripheral cardiopulmonary bypass often is required before anesthetizing these patients. Herein, two cases of patients with tracheal masses, in whom awake peripheral cardiopulmonary bypass was instituted, are reported. The first case was that of an obese male child weighing 102 kg, with tracheal rhinoscleroma, who developed Harlequin, or north-south, syndrome after institution of femorofemoral venoarterial partial cardiopulmonary bypass. The second case was that of a female patient with adenoid cystic carcinoma of the trachea causing near-total central airway occlusion. She had severe pulmonary artery hypertension, which prevented the use of venovenous bypass. Instead, femoral vein-axillary artery venoarterial bypass was established to avoid Harlequin syndrome. Some of the challenges encountered were the development of Harlequin syndrome with risk of myocardial and cerebral ischemia, type and conduct of extracorporeal bypass, choice of monitoring sites, and provision of regional anesthesia for peripheral extracorporeal cannulations. Management of such patients needs frequent troubleshooting and multidisciplinary coordination for a successful surgical outcome.

Is less really more? Reexamining video-assisted thoracoscopic versus open lobectomy in the setting of an enhanced recovery protocol

OBJECTIVES

Video-assisted thoracoscopic surgery lobectomy has been associated with improved pain, length of stay, and outcomes compared with open lobectomy. However, enhanced recovery protocols improve outcomes after both procedures. We aimed to compare video-assisted thoracoscopic surgery and open lobectomy in the setting of a comprehensive enhanced recovery protocol.

METHODS

All patients undergoing lobectomy for lung cancer at a single institution since the adoption of an enhanced recovery protocol (May 2016 to December 2018) were stratified by video-assisted thoracoscopic surgery versus open status and compared. Demographics and outcomes, including length of stay, daily pain scores, and short-term operative complications, were compared using standard univariate statistics and multivariable models.

RESULTS

A total of 130 patients underwent lobectomy, including 71 (54.6%) undergoing video-assisted thoracoscopic surgery and 59 (45.4%) undergoing open surgery. Video-assisted thoracoscopic surgery versus open cases exhibited similar length of stay (median 4 days for both, P = .07), opioid requirement (33.2 vs 30.8 mg morphine equivalents, P = .86), and pain scores at 0, 1, 2, and 3 days after surgery (4.3 vs 2.8, P = .12; 4.4 vs 3.7, P = .27; 3.9 vs 3.5, P = .83; and 3.4 vs 3.5, P = .98, respectively). Patients undergoing video-assisted thoracoscopic surgery lobectomy exhibited lower rates of readmission (1.4% vs 17.0%, P < .01), postoperative transfusion requirement (0% vs 10.2%, P < .01), and pneumonia (1.4% vs 10.2%, P = .05). After risk adjustment, an open procedure (vs video-assisted thoracoscopic surgery status) did not significantly affect the length of stay (effect 0.18; P = .10) or overall complication rate (odds ratio, 1.9; P = .12).

CONCLUSIONS

In the setting of a comprehensive enhanced recovery protocol, patients undergoing video-assisted thoracoscopic surgery versus open lobectomy exhibited similar short-term outcomes. Surgical incision may have less impact on outcomes in the setting of a comprehensive thoracic enhanced recovery protocol.

Lung Isolation in the Patient With a Difficult Airway

One-lung ventilation is routinely used to facilitate exposure for thoracic surgical procedures and can be achieved via several lung isolation techniques. The optimal method for lung isolation depends on a number of factors that include (1) the indication for lung isolation, (2) anatomic features of the upper and lower airway, (3) availability of equipment and devices, and (4) the anesthesiologist's proficiency and preferences. Though double-lumen endobronchial tubes (DLTs) are most commonly utilized to achieve lung isolation, the use of endobronchial blockers offer advantages in patients with challenging airway anatomy. Anesthesiologists should be familiar with existing alternatives to the DLT for lung isolation and alternative techniques for DLT placement in the patient with a difficult airway. Newer technologies such as videolaryngoscopy with or without adjunctive fiberoptic bronchoscopy may facilitate intubation and lung isolation in difficult airway management.

Changing Default Ventilator Settings on Anesthesia Machines Improves Adherence to Lung-Protective Ventilation Measures

Perioperative lung-protective ventilation (LPV) can reduce perioperative pulmonary morbidity. We hypothesized that modifying default anesthesia machine ventilator settings would increase the use of intraoperative LPV. Default tidal volume settings on our anesthesia machines were decreased from 600 to 400 mL, and default positive end-expiratory pressure was increased from 0 to 5 cm H2O. This modification increased mean positive end-expiratory pressure from 3.1 to 5.0 cm H2O and decreased mean tidal volume from 8.2 to 6.7 mL/kg predicted body weight. Notably, increased adherence to LPV from 1.6% to 23.0% occurred quickly with the rate of increase more than doubling from 1.8% to 3.9% per year.

Management of 1-Lung Ventilation-Variation and Trends in Clinical Practice: A Report From the Multicenter Perioperative Outcomes Group

BACKGROUND

Lung-protective ventilation (LPV) has been demonstrated to improve clinical outcomes in surgical patients. There are very limited data on the current use of LPV for patients undergoing 1-lung ventilation (1LV) despite evidence that 1LV may be a particularly important setting for its use. In this multicenter study, we report trends in ventilation practice for patients undergoing 1LV.

METHODS

The Multicenter Perioperative Outcomes Group database was used to identify patients undergoing 1LV. We retrieved and calculated median initial and overall tidal volume (VT) for the cohort and for high-risk subgroups (female sex, obesity [body mass index >30 kg/m], and short stature), percentage of patients receiving positive end-expiratory pressure (PEEP) ≥5 cm H2O, LPV during 1LV (VT ≤ 6 mL/kg predicted body weight [PBW] and PEEP ≥5 cm H2O), and ventilator driving pressure (ΔP; plateau airway pressure - PEEP).

RESULTS

Data from 5609 patients across 4 institutions were included in the analysis. Median VT was calculated for each case and since the data were normally distributed, the mean is reported for the entire cohort and subgroups. Mean of median VT during 1LV for the cohort was 6.49 ± 1.82 mL/kg PBW. VT (mL/kg PBW) for high-risk subgroups was significantly higher; 6.86 ± 1.97 for body mass index ≥30 kg/m, 7.05 ± 1.92 for female patients, and 7.33 ± 2.01 for short stature patients. Mean of the median VT declined significantly over the study period (from 6.88 to 5.72; P < .001), and the proportion of patients receiving LPV increased significantly over the study period (from 9.1% to 54.6%; P < .001). These changes coincided with a significant decrease in ΔP during the study period, from 19.4 cm H2O during period 1 to 17.3 cm H2O in period 12 (P = .003).

CONCLUSIONS

Despite a growing awareness of the importance of protective ventilation, a large proportion of patients undergoing 1LV continue to receive VT PEEP levels outside of recommended thresholds. Moreover, VT remains higher and LPV less common in high-risk subgroups, potentially placing them at elevated risk for iatrogenic lung injury.

Intraoperative Lung-Protective Ventilation Trends and Practice Patterns: A Report from the Multicenter Perioperative Outcomes Group

BACKGROUND

The use of an intraoperative lung-protective ventilation strategy through tidal volume (TV) size reduction and positive end-expiratory pressure (PEEP) has been increasingly investigated. In this article, we describe the current intraoperative lung-protective ventilation practice patterns and trends.

METHODS

By using the Multicenter Perioperative Outcomes Group database, we identified all general endotracheal anesthetics from January 2008 through December 2013 at 10 institutions. The following data were calculated: (1) percentage of patients receiving TV > 10 mL/kg predicted body weight (PBW); (2) median initial and overall TV in mL/kg PBW and; (3) percentage of patients receiving PEEP ≥ 5 cm H2O. The data were analyzed at 3-month intervals. Interinstitutional variability was assessed.

RESULTS

A total of 330,823 patients met our inclusion criteria for this study. During the study period, the percentage of patients receiving TV > 10 mL/kg PBW was reduced for all patients (26% to 14%) and in the subpopulations of obese (41% to 25%), short stature (52% to 36%), and females (39% to 24%; all P values <0.001). There was a significant reduction in TV size (8.90-8.20 mL/kg PBW, P < 0.001). There was also a statistically significant but clinically irrelevant difference between initial and overall TV size (8.65 vs 8.63 mL/kg PBW, P < 0.001). Use of PEEP ≥ 5 cm H2O increased during the study period (25%-45%, P < 0.001). TV usage showed significant interinstitutional variability (P < 0.001).

CONCLUSIONS

Although decreasing, a significant percentage of patients are ventilated with TV > 10 mL/kg PBW, especially if they are female, obese, or of short stature. The use of PEEP ≥ 5 cm H2O has increased significantly. Creating awareness of contemporary practice patterns and demonstrating the efficacy of lung-protective ventilation are still needed to optimize intraoperative ventilation.

Fiberoptic intubation: an overview and update

Fiberoptic intubation (FOI) is an effective technique for establishing airway access in patients with both anticipated and unanticipated difficult airways. First described in the late 1960s, this approach can facilitate airway management in a variety of clinical scenarios given proper patient preparation and technique. This paper seeks to review the pertinent technology, clinical techniques, and indications for and complications of its use. The role of FOI in airway management algorithms is discussed. Evidence is presented comparing FOI to other techniques with regard to difficult airway management. In addition, we have reviewed the literature on training processes and skill development in FOI.

Ventricular assist devices and increased blood product utilization for cardiac transplantation

BACKGROUND AND AIM OF STUDY

The purpose of this study was to examine whether blood product utilization, one-year cell-mediated rejection rates, and mid-term survival significantly differ for ventricular assist device (VAD patients compared to non-VAD (NVAD) patients following cardiac transplantation.

METHODS

From July 2004 to August 2011, 79 patients underwent cardiac transplantation at a single institution. Following exclusion of patients bridged to transplantation with VADs other than the HeartMate II® LVAD (n = 10), patients were stratified by VAD presence at transplantation: VAD patients (n = 35, age: 54.0 [48.0-59.0] years) vs. NVAD patients (n = 34, age: 52.5 [42.8-59.3] years). The primary outcomes of interest were blood product transfusion requirements, one-year cell-mediated rejection rates, and mid-term survival post-transplantation.

RESULTS

Preoperative patient characteristics were similar for VAD and NVAD patients. NVAD patients presented with higher median preoperative creatinine levels compared to VAD patients (1.3 [1.1-1.6] vs. 1.1 [0.9-1.4], p = 0.004). VAD patients accrued higher intraoperative transfusion of all blood products (all p ≤ 0.001) compared to NVAD patients. The incidence of clinically significant cell-mediated rejection within the first posttransplant year was higher in VAD compared to NVAD patients (66.7% vs. 33.3%, p = 0.02). During a median follow-up period of 3.2 (2.0, 6.3) years, VAD patients demonstrated an increased postoperative mortality that did not reach statistical significance (20.0% vs. 8.8%, p = 0.20).

CONCLUSIONS

During the initial era as a bridge to transplantation, the HeartMate II® LVAD significantly increased blood product utilization and one-year cell-mediated rejection rates for cardiac transplantation. Further study is warranted to optimize anticoagulation strategies and to define causal relationships between these factors for the current era of cardiac transplantation.

Special article: the endothelial glycocalyx: emerging concepts in pulmonary edema and acute lung injury

The endothelial glycocalyx is a dynamic layer of macromolecules at the luminal surface of vascular endothelium that is involved in fluid homeostasis and regulation. Its role in vascular permeability and edema formation is emerging but is still not well understood. In this special article, we highlight key concepts of endothelial dysfunction with regards to the glycocalyx and provide new insights into the glycocalyx as a mediator of processes central to the development of pulmonary edema and lung injury.

Anesthetic management for esophageal resection

Surgical resection remains a standard treatment option for localized esophageal cancer. Surgical approaches to esophagectomy include transhiatal and transthoracic techniques as well as minimally invasive techniques that have been developed to reduce the morbidities associated with laparotomy and thoracotomy incisions. The perioperative mortality for esophagectomy remains high with cardiopulmonary and anastomotic complications as the most frequent and serious morbidities. This article reviews the management of patients presenting for esophagectomy, with a focus on evidence-based anesthetic and perioperative approaches for improving outcomes.

Anesthetic management of the patient with dilated cardiomyopathy undergoing pulmonary resection surgery: a case-based discussion

Interactions between the cardiovascular and respiratory systems are complex and profound. General anesthesia, muscle relaxation, and positive-pressure ventilation all impose physiological effects on cardiovascular function. In patients presenting for pulmonary resection, additional effects resulting from positioning, 1-lung ventilation, surgical procedures, and contraction of the pulmonary vascular bed may impose an additional physiological burden. For most patients with adequate pulmonary and cardiovascular reserve, these effects are well tolerated. However, the cardiothoracic anesthesiologist may be asked to provide anesthetic care for patients with significantly reduced cardiac function who require potentially curative pulmonary resection for lung cancer. These patients present a major perioperative challenge and a thoughtful approach to intraoperative management is required. The authors review a case of a patient with severely impaired biventricular function who presented for elective pulmonary lobectomy in an attempt to effect a curative resection of lung cancer and present a discussion of physiological and pathophysiological considerations for clinical management.

Approaches to refractory hypoxemia in acute respiratory distress syndrome: current understanding, evidence, and debate

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) cause substantial morbidity and mortality despite our improved understanding of lung injury, advancements in the application of lung-protective ventilation, and strategies to prevent ventilator-induced lung injury. Severe refractory hypoxemia may develop in a subset of patients with severe ARDS. We review several approaches referred to as "rescue" therapies for severe hypoxemia, including lung-recruitment maneuvers, ventilation modes, prone positioning, inhaled vasodilator therapy, and the use of extracorporeal membrane oxygenation. Each shows evidence for improving oxygenation, though each has associated risks, and no single therapy has proven superior in the management of severe hypoxemia. Importantly, increased survival with these strategies has not been clearly established.

Pseudomeningocele: an unusual cause of intraoperative tracheal compression and expiratory obstruction

Cerebrospinal fluid leak resulting from spine surgery has been associated with postoperative upper airway obstruction and the need for emergent airway management. We report a case of a known pseudomeningocele resulting in acute intraoperative compression of the intrathoracic trachea and an unexpected variable expiratory obstruction.

Inadvertent intrathecal injection of labetalol in a patient undergoing post-partum tubal ligation

After receiving a continuous spinal anesthetic for labor following an inadvertent dural puncture with a 17-gauge epidural needle, a morbidly obese parturient underwent post-partum tubal ligation 12 h after vaginal delivery. The patient received a total of 2 mL of 0.75% hyperbaric bupivacaine for the surgery. In response to moderate hypertension the patient received intravenous labetalol hydrochloride 20 mg. She subsequently was inadvertently administered approximately 15 mg of labetalol through the spinal catheter. The spinal catheter was removed immediately after the procedure. She suffered no apparent adverse neurologic effects.

A retinoic acid-induced clonal cell line derived from multipotential P19 embryonal carcinoma cells expresses smooth muscle characteristics

Despite intense interest in understanding the differentiation of vascular smooth muscle, very little is known about the cellular and molecular mechanisms that control differentiation of this cell type. Progress in this field has been hampered by the lack of an inducible in vitro system for study of the early steps of smooth muscle differentiation. In this study, we describe a model system in which multipotential mouse P19 embryonal carcinoma cells (P19s) can be induced to express multiple characteristics of differentiated smooth muscle. Treatment of P19s with retinoic acid was associated with profound changes in cell morphology and with the appearance at high frequency of smooth muscle alpha-actin-positive cells that were absent or present at extremely low frequency in parental P19s. A clonal line derived from retinoic acid-treated P19s (9E11G) stably expressed multiple characteristics of differentiated smooth muscle, including smooth muscle-specific isoforms of alpha-actin and myosin heavy chain, as well as functional responses to the contractile agonists phenylephrine, angiotensin II, ATP, bradykinin, histamine, platelet-derived growth factor (PDGF)-AA, and PDGF-BB. Additionally, 9E11G cells expressed transcripts for MHox, a muscle homeobox gene expressed in smooth, cardiac, and skeletal muscles, but not the skeletal muscle-specific regulatory factors, MyoD and myogenin. Results demonstrate that retinoic acid treatment of multipotential P19 cells is associated with formation of cell lines that stably express multiple properties of differentiated smooth muscle.(ABSTRACT TRUNCATED AT 250 WORDS)

Nuclear proteins bind a cis-acting element in the smooth muscle alpha-actin promoter

Identification of the regulators of smooth muscle cell (SMC) gene expression is critical to understanding SMC differentiation and alterations in SMC phenotype in vascular disease. Previous studies revealed positive transcriptional activity within the chicken smooth muscle (SM) alpha-actin promoter region from -209 to -257. In the present study, transient transfections of wild-type and mutant chicken SM alpha-actin promoter/reporter gene constructs into rat aortic SMC demonstrated that the positive transcriptional activity of this region was abolished with a two base pair mutation in a conserved sequence motif at -225 to -233 (TGTTTATC to TACTTATC). Electrophoretic mobility shift assays revealed that nuclear factors bound promoter fragments containing this sequence and that specific mutations in the TGTTTATC motif abolished nuclear factor binding. Studies thus provide evidence for binding of a nuclear factor to a positive cis-acting element within the SM alpha-actin promoter. Further characterization of this factor may contribute to a better understanding of the molecular mechanisms that regulate differentiation of SMC in vascular disease.

The smooth muscle alpha-actin gene promoter is differentially regulated in smooth muscle versus non-smooth muscle cells

To identify potential regulators of smooth muscle cell (SMC) differentiation, we studied the molecular mechanisms that control the tissue-specific transcriptional expression of SM alpha-actin, the most abundant protein in fully differentiated SMCs. A construct containing the region from -1 to -125 of the promoter (p125CAT) had high transcriptional activity in SMCs (57-fold > promoterless) and endothelial cells (ECs) (18-fold) but not in skeletal myoblasts or myotubes. Mutation of either of two highly conserved CC(AT-rich)6GG (CArG) motifs at -62 and -112 abolished the activity of p125CAT in SMCs but had no effect in ECs. In contrast, high transcriptional activity in skeletal myotubes, which also express SM alpha-actin, required at least 271 base pairs of the promoter (-1 to > or = -271). Constructs containing 547 base pairs or more of the promoter were transcriptionally active in SMCs and skeletal myotubes but had no activity in skeletal myoblasts or ECs, cell types that do not express SM alpha-actin. Electrophoretic mobility shift assays provided evidence for binding of a unique serum response factor-containing complex of factors to the CArG box elements in SMCs. Results indicate that: 1) transcriptional expression of SM alpha-actin in SMCs requires the interaction of the CArG boxes with SMC nucleoprotein(s); 2) expression of SM alpha-actin in skeletal myotubes requires different cis-elements and trans-factors than in SMCs; and 3) negative-acting cis-elements are important in restricting transcription in cells that do not express SM alpha-actin.

Platelet-derived growth factor-BB-induced suppression of smooth muscle cell differentiation

Previously, we demonstrated that treatment of postconfluent quiescent rat aortic smooth muscle cells (SMCs) with platelet-derived growth factor (PDGF)-BB dramatically reduced smooth muscle (SM) alpha-actin synthesis. In the present studies, we focused on the expression of two other SM-specific proteins, SM myosin heavy chain (SM-MHC) and SM alpha-tropomyosin (SM-alpha TM), to determine whether the actions of PDGF-BB were specific to SM alpha-actin or represented a global ability of PDGF-BB to inhibit expression of cell-specific proteins characteristic of differentiated SMCs. SM-MHC and SM-alpha TM expression were assessed by one- or two-dimensional gel electrophoretic analysis of proteins from cells labeled with [35S]methionine, as well as by Northern analysis of mRNA levels. Synthesis of both SM-specific proteins was decreased by 50-70% in PDGF-BB--treated cells as compared with cells treated with PDGF vehicle. Treatment of cells with 10% fetal bovine serum, which produced a mitogenic effect equivalent to that of PDGF-BB, decreased SM-MHC synthesis by 40% but increased SM-alpha TM synthesis. SM-MHC and SM-alpha TM mRNA expression was decreased by 80% at 24 hours in PDGF-BB--treated postconfluent SMCs, whereas treatment with 10% fetal bovine serum did not decrease the expression of SM-alpha TM mRNA but did inhibit SM-MHC mRNA expression by 36%. Consistent with the absence of detectable PDGF alpha-receptors on these cells, PDGF-AA had no effect on either mitogenesis or expression of SM-MHC or SM-alpha TM.(ABSTRACT TRUNCATED AT 250 WORDS)

Elements of the smooth muscle alpha-actin promoter required in cis for transcriptional activation in smooth muscle. Evidence for cell type-specific regulation

To assess the role of cis-acting elements within the smooth muscle alpha-actin gene in smooth muscle cells (SMC), we transfected chicken smooth muscle alpha-actin promoter-chloramphenicol acetyltransferase gene fusion plasmids into SMC derived from rat and chicken aortas. In marked contrast to effects in chicken skeletal myoblasts and fibroblasts, p122CAT (positions -122 to +19), containing two conserved CArG elements, elicited a modest increase in chloramphenicol acetyltransferase reporter activity in chicken SMC. Addition of upstream sequences between -122 and -151 (p151CAT) increased activity in adult chicken SMC. Addition of sequence between positions -151 and -257 (p257CAT) resulted in a 7-fold increase in chloramphenicol acetyltransferase activity over that of p151CAT in rat SMC, but not in chicken SMC. A genomic clone encoding the rat smooth muscle alpha-actin gene was isolated, and the 5'-flanking region was partially characterized. Comparison of primary sequence between rat and chicken promoters showed a conserved E box motif at position -214 in the chicken gene and at position -213 in the rat gene. Results of these studies demonstrate that regions upstream of the conserved CArG elements exert potent regulatory effects on transcription and that SMC require different cis-acting elements than other cell types to transcriptionally regulate this gene.

Platelet-derived growth factor-induced destabilization of smooth muscle alpha-actin mRNA

We have previously shown that treatment of postconfluent, quiescent rat vascular smooth muscle cells (SMC) with platelet-derived growth factor (PDGF) dramatically reduced smooth muscle (SM) alpha-actin synthesis and SM alpha-actin mRNA abundance, suggesting a role for this mitogen in the control of SMC differentiation. In the present studies, we explored the molecular mechanisms whereby PDGF decreases SM alpha-actin mRNA levels. Treatment of postconfluent SMC with both platelet PDGF and recombinant PDGF-BB resulted in a dramatic and concentration-dependent decrease in SM alpha-actin mRNA levels. We observed no differences in efficacy between platelet PDGF and PDGF-BB, indicating that the PDGF-A chain is not required for the effect. The rate of decrease in SM alpha-actin mRNA abundance in PDGF-treated SMC was greater than that observed in cells treated with the transcriptional inhibitor, actinomycin D, with or without PDGF, indicating that PDGF induced a transcriptionally dependent destabilization of the cytosolic SM alpha-actin mRNA pool. This effect appeared selective for SM alpha-actin, in that there was no evidence of a similar change in non-muscle (NM) beta-actin mRNA stability following PDGF treatment. Results of nuclear run-on analyses showed no differences in SM alpha-actin transcription between PDGF- and vehicle-treated SMC at either 4 or 24 hours following treatment, demonstrating that decreases in transcription of the SM alpha-actin gene did not contribute to PDGF-induced changes in SM alpha-actin mRNA abundance. Results of these studies support a possible role for PDGF in regulation of SMC differentiation via a post-transcriptional control mechanism.

Platelet-derived growth factor regulates actin isoform expression and growth state in cultured rat aortic smooth muscle cells

The role of platelet-derived growth factor (PDGF) in the control of smooth muscle cell (SMC) differentiation was explored in vitro by examining its effects on expression of the smooth muscle (SM) specific contractile protein SM alpha actin in cultured rat aortic SMC. Quiescent, postconfluent SMC express maximal levels of alpha actin and responded to human platelet-derived growth factor (partially purified from platelets) by entering the cell cycle and undergoing approximately one synchronous round of DNA synthesis. Concomitantly, these cultures exhibited a marked reduction in alpha actin synthesis. Chronic treatment with PDGF (72 hours at 8 or 12 hour intervals) was associated with a transient increase in thymidine labeling index and a decrease in alpha actin expression. Interestingly, between 48 and 72 hours following initial treatment, thymidine labeling indices returned to near control levels while SM alpha actin expression remained depressed. This effect was reversible; fractional alpha actin synthesis increased immediately after PDGF removal. When subsequently stimulated with 10% fetal bovine serum (FBS), cells chronically pretreated with PDGF entered S phase approximately 4 hours earlier than cells pretreated with PDGF vehicle, consistent with the idea that the maintained suppression of alpha actin synthesis in SMC subjected to chronic PDGF treatment was associated with partial cell cycle transit. Chronic treatment with highly purified recombinant PDGF-BB elicited similar effects on alpha actin synthesis and partial cell cycle transit. Flow cytometric analysis of chronic PDGF-treated SMC demonstrated a 25% increase in forward angle light scatter, an index of cell size. These data implicate a possible role for PDGF in regulation of SMC differentiation and suggest a potentially important role for this mitogen in the phenotypic modulation accompanying SMC growth and in mediation of the cellular hypertrophy associated with cell cycle progression.

Cell cycle versus density dependence of smooth muscle alpha actin expression in cultured rat aortic smooth muscle cells

Cultured smooth muscle cells (SMC) undergo induction of smooth muscle (SM) alpha actin at confluency. Since confluent cells exhibit contact inhibition of growth, this finding suggests that induction of SM alpha actin may be associated with cell cycle withdrawal. This issue was further examined in the present study using fluorescence-activated cell sorting of SMC undergoing induction at confluency and by examination of the effects of FBS and platelet-derived growth factor (PDGF) on SM alpha actin expression in postconfluent SMC cultures that had already undergone induction. Cell sorting was based on DNA content or differential incorporation of bromodeoxyuridine (Budr). The fractional synthesis of SM alpha actin in confluent cells was increased two- to threefold compared with subconfluent log phase cells, but no differences were observed between confluent cycling (Budr+) and noncycling (Budr-) cells. In cultures not exposed to Budr, confluent cycling S + G2 cells exhibited similar induction. These data indicate that cell cycle withdrawal is not a prerequisite for the induction of SM alpha actin synthesis in SMC at confluency. Growth stimulation of postconfluent cultures with either FBS or PDGF resulted in marked repression of SM alpha actin synthesis but the level of repression was not directly related to entry into S phase in that PDGF was a more potent repressor of SM alpha actin synthesis than was FBS despite a lesser mitogenic effect. This differential effect of FBS versus PDGF did not appear to be due to transforming growth factor-beta present in FBS since addition of transforming growth factor-beta had no effect on PDGF-induced repression. Likewise, FBS (0.1-10.0%) failed to inhibit PDGF-induced repression. Taken together these data demonstrate that factors other than replicative frequency govern differentiation of cultured SMC and suggest that an important function of potent growth factors such as PDGF may be the repression of muscle-specific characteristics.

Density-dependent contraction of the endothelial nascent histamine pool by exogenous heparin

The aortic endothelial cell nascent histamine pool has been implicated in the control of vessel wall permeability under conditions of stress and injury. We report the contraction of this histamine pool in low density bovine aortic endothelial cell (BAEC) cultures by exogenous heparin. Untreated BAEC exhibit a decline in histamine content in 3-day cultures with increasing plating density between 1000 and 16,000 cells/cm2. Heparin abolished this density-related difference by effecting a 67% contraction of the histamine pool in the lowest density cultures. This effect was reversible and specific to heparin. At a confluent density, endothelial cells secrete heparin-like glycosaminoglycans which affect smooth muscle and endothelial metabolism. We propose that the metabolic effects of exogenous heparin, and perhaps endogenous heparins, extend to specific modulations of the BAEC nascent histamine pool.