Perioperative Pulmonary Atelectasis: Part II. Clinical Implications

The development of pulmonary atelectasis is common in the surgical patient. Pulmonary atelectasis can cause various degrees of gas exchange and respiratory mechanics impairment during and after surgery. In its most serious presentations, lung collapse could contribute to postoperative respiratory insufficiency, pneumonia, and worse overall clinical outcomes. A specific risk assessment is critical to allow clinicians to optimally choose the anesthetic technique, prepare appropriate monitoring, adapt the perioperative plan, and ensure the patient's safety. Bedside diagnosis and management have benefited from recent imaging advancements such as lung ultrasound and electrical impedance tomography, and monitoring such as esophageal manometry. Therapeutic management includes a broad range of interventions aimed at promoting lung recruitment. During general anesthesia, these strategies have consistently demonstrated their effectiveness in improving intraoperative oxygenation and respiratory compliance. Yet these same intraoperative strategies may fail to affect additional postoperative pulmonary outcomes. Specific attention to the postoperative period may be key for such outcome impact of lung expansion. Interventions such as noninvasive positive pressure ventilatory support may be beneficial in specific patients at high risk for pulmonary atelectasis (e.g., obese) or those with clinical presentations consistent with lung collapse (e.g., postoperative hypoxemia after abdominal and cardiothoracic surgeries). Preoperative interventions may open new opportunities to minimize perioperative lung collapse and prevent pulmonary complications. Knowledge of pathophysiologic mechanisms of atelectasis and their consequences in the healthy and diseased lung should provide the basis for current practice and help to stratify and match the intensity of selected interventions to clinical conditions.

Improving the utility of high-resolution manometry for the diagnosis of defecatory disorders in women with chronic constipation

BACKGROUND

We compared the utility of existing and modified versions of high-resolution manometry for diagnosing defecatory disorders (DD).

METHODS

In 64 healthy and 136 constipated women, we compared left lateral (LL) and seated manometry, and analyzed with existing (ManoView™) and new methods, for discriminating between constipated patients with normal and prolonged rectal balloon expulsion time (BET). In both positions, the rectoanal gradient (RAG) and, for the new analysis, the pressure topography pattern during evacuation were used to discriminate between constipated patients without and with DD.

KEY RESULTS

The BET was prolonged, suggestive of a DD, in 52 patients (38%). During evacuation, rectoanal pressures and the RAG were greater in the seated than the LL position (P≤.001). The new analysis identified 4 rectoanal pressure patterns. In the seated position, the BET was associated with the pattern (P=.0001), being prolonged in, respectively, 45%, 15%, 53%, and 0% of patients with minimal change, anal relaxation, paradoxical contraction, and transmission. Within each pattern, the RAG was greater (ie, less negative, P<.0001) in patients with a normal than a prolonged BET. Compared to the ManoView™ RAG in the LL position, the integrated analysis (ie, pattern and new RAG) in the LL position (P<.01) and the seated ManoView™ gradient (P=.02) were more effective for discriminating between constipated patients without and with DD.

CONCLUSIONS & INFERENCES

Anorectal HRM ideally should be performed in the more physiological seated position and analyzed by a two-tier approach, which incorporates the overall pattern followed by the rectoanal gradient. These findings reinforce the utility of manometry for diagnosing DD.

Comparison of venous sinus manometry gradients obtained while awake and under general anesthesia before venous sinus stenting

Introduction

Venous sinus stenting is a popular treatment strategy for patients with high venous sinus pressure gradients across a site of outflow obstruction. Little is known about the effect of anesthesia on venous sinus pressure measurements.

Objective

To compare venous manometry performed in patients under general anesthesia and while awake.

Methods

A prospective database was accessed to retrospectively identify patients who had undergone venous sinus stenting. Pressure gradients were compared between those patients who underwent manometry while awake and before stenting under general anesthesia.

Results

Thirty patients with both general anesthesia and awake pressure recordings were identified. Pressure measurements were highly variable but overall were higher under general anesthesia by an average of 5.8 mm Hg (1.7; p=0.002). A significant difference between awake and general anesthesia pressure measurements was detected in the sigmoid sinus (5.8 mm Hg (2.0); p=0.005) and the jugular vein (8.1 mm Hg (3.9); p=0.040). Only 11/30 (36.7%) pressure gradients remained within 5 mm Hg of the original awake gradient when repeated under general anesthesia; 9/30 (30%) patients had gradients that were at least 10 mm Hg different across procedures.

Conclusions

Calculated pressure gradients were markedly affected by anesthesia. These findings suggest that candidacy for stenting should be determined with venous manometry while patients are awake owing to the unpredictable and highly variable effect of general anesthesia on pressure measurements and an apparent tendency to underestimate the degree of venous outflow obstruction.

Contour analysis of the photoplethysmographic pulse measured at the finger

Analysis of the contour of the peripheral pulse to assess arterial properties was first described in the nineteenth century. With the recognition of the importance of arterial stiffness there has been a resurgence of interest in pulse wave analysis, particularly the analysis of the radial pressure pulse acquired using a tonometer. An alternative technique utilizes a volume pulse. This may conveniently be acquired optically from a finger (digital volume pulse). Although less widely used, this technique deserves further consideration because of its simplicity and ease of use. As with the pressure pulse, the contour of the digital volume pulse is sensitive to changes in arterial tone induced by vasoactive drugs and is influenced by ageing and large artery stiffness. Measurements taken directly from the digital volume pulse or from its second derivative can be used to assess these properties. This review describes the background to digital volume pulse contour analysis, how the technique relates to contour analysis of the pressure pulse, and current and future applications.

Implantable telemetric pressure measurement

Highly miniaturised implantable pressure sensors can be used for wireless monitoring of different therapeutic procedures. This article presents an outlook on the market potential of these systems.

Report from the meeting: Gastrointestinal Tonometry: State of the Art. 22nd-23rd May 1998, London, UK

Gastrointestinal (GI) tonometry, the only clinically available method for the accurate diagnosis of compromised GI blood flow, has been shown to be a sensitive predictor of increased morbidity, mortality and prolonged hospitalization. The recent introduction of the Tonocap, as a means of performing automated air tonometry, has simplified the application of GI tonometry in the clinical setting. Despite this the utility of GI tonometry remains controversial. The GI Tonometry: State of the Art meeting brought together a group of clinicians with a proven track record of research, clinical interest and expertise in this field. The aim of the meeting was to come to a consensus regarding certain issues such as the past and future roles of GI tonometry and standards for its correct usage and interpretation. Finally suggestions as to further research and clinical evaluation were made within a broader discussion regarding the complexities of applying the principles of evidence-based medicine to the introduction of a new piece of medical technology.

The changing use of esophageal manometry in clinical practice

OBJECTIVE

Clinical practice guidelines now advise against the use of esophageal manometry in the early evaluation of unexplained chest pain. We examined data from patients referred for manometric evaluation over a 10-yr period (1987-1996) to see if clinicians were changing practice patterns and whether manometric diagnoses were affected by the changes.

METHODS

Principal indications for the procedure and manometric findings were extracted from a review of 1162 subjects referred to a single clinical laboratory. The tracings were analyzed using a standardized classification method and categorized according to a pathophysiology-based scheme. Referral indications and manometric diagnoses were compared for the first and second 5-yr periods of study.

RESULTS

Chest pain as a referral indication declined from the first to the second half of the study period (odds ratio, 0.44; p < 0.0001), whereas dysphagia and preoperative evaluations became more common (odds ratio, 1.3; p < 0.05; odds ratio, 13.7; p < 0.0001, respectively). Similarly, hypermotility disorders decreased in frequency (odds ratio, 0.63; p = 0.0001), whereas hypomotility disorders increased (odds ratio, 1.6; p < 0.01). The decrease in hypermotility disorders was solely related to a decrease in nonspecific spastic disorders, including nutcracker esophagus (odds ratio, 0.58; p < 0.0001); the proportion of diagnoses of achalasia and diffuse esophageal spasm remained stable.

CONCLUSIONS

These data show that practice patterns are already following current guidelines. They also reflect the disillusionment of clinicians with the poor specificity of manometry in chest pain management, the increasing popularity of antireflux surgery, yet the ongoing observation that nonspecific spastic disorders are closely associated with unexplained chest pain and may have a still-undefined pathogenetic role.

Current advances in rhinomanometry

Current advances in rhinomanometry were reviewed in this paper. Active posterior rhinomanometry with a "head-out" body plethysmography may be the least invasive method currently available for measuring nasal patency. In general, active anterior rhinomanometry with a face mask or a nasal nozzle has been employed in various studies throughout the world. Nasal resistance as calculated from the equation R = 0.78 (delta P/V)1.33 at any points on a pressure/flow curve, or averaged nasal resistance may be the most suitable expression for nasal patency. Values for nasal resistance at delta P 100 Pa in Japanese patients or delta P 150 Pa in Caucasians have been widely employed as standard objective data for nasal obstruction, although rhinomanometric results sometimes do not agree with subjective evaluation of nasal obstruction. Nasal airflow acceleration or peak flow index during nasal breathing at rest can be applied as warranted to confirm an objective diagnosis of symptomatic nasal obstruction. Further, nationality and anthropological characteristics can be related to the severity and type of stuffiness.

Rhinomanometry 1988: practice and trends

This report discusses characteristics and measurement of transnasal pressures and flow of respiratory air, indices of nasal airway patency, and components of contemporary rhinomanometric systems. Sources of error that can result from mucovascular fluctuation and from the use of face masks and nasal nozzles are delineated. Useful adjuncts to rhinomanometry include microcomputation and plethysmography. State-of-the-art transducers and microcircuitry and reliability and economy. Aerodynamic parameters closely correlated with chronic obstructive nasal symptoms have yet to be determined. Nevertheless, resistance calculated from concomitant measurements of transnasal pressure and flow, as recommended by the International Committee on Standardization of Rhinomanometry, provides a practical index of nasal patency and aids the exchange of rhinological information.