Video assisted thoracoscopic surgery (VATS) for pneumothorax: a reason for unscheduled surgery?

Timing of urgent surgery, with full schedules and the businesslike attitude of operating room management, can lead to animated discussions, affecting quality of care and job satisfaction. No publication appears to address the timing of definitive care for a stable, spontaneous, pneumothorax (SP) by unscheduled, or urgent, video assisted thoracoscopic surgery (VATS). We reviewed the literature and describe our series of 38 patients with SP and VATS. Of 185 patients with SP, 38 were presented for VATS. Of these 29% were unscheduled. Average time between diagnosis of SP and VATS was 11 days, with four days between decision for VATS and its execution. Post-operative antibiotics were prescribed to 37% of patients. There was a correlation between chest drain time in situ and infective signs (p = 0.001, rho = 0.654) as well as proven infections (p = 0.05, rho = 0.386), but not between for scheduled and unscheduled procedures. In conclusion, our case series and review did not identify reasons why VATS for SP should be performed as an urgent procedure, though we support more rapid planning.

Effect of non-steady-state perfusion on xenon-133 cerebral blood flow measurements: an analytical study.

Activation studies employing the noninvasive xenon-133 technique are widely used to investigate the cerebral circulation. Typical examples are the investigation of hemispheral specialization of higher cortical function with cognitive activation or the assessment of the hemodynamic reserve in occlusive cerebrovascular disease by CO2 inhalation. Traditionally, in studies using this technique, there is the requirement of a circulatory steady state during the measurement. Due to limitations in the duration of the stimulus or habituation to the stimulus, the basic assumption is often violated. In this study we investigated with the aid of a computer model to what extent blood flow measurement results are affected by non-steady-state blood flow. The findings indicate that cortical activation need not extend throughout the whole measurement to be detectable. Maintenance of activation for at least 5 min is sufficient for a successful measurement. In addition, the results show that the activation should be fully established when the measurement starts to achieve maximal sensitivity. Delay in activating the circulation will result in attenuated responses, especially if the stimulus is delayed beyond 2 min.

Estimation of total systemic arterial compliance in humans.

Systemic arterial compliance, a major component of aortic input impedance, was determined in 10 patients with congestive heart failure secondary to idiopathic dilated cardiomyopathy and 11 age-matched control subjects found free of detectable cardiovascular disease. Total arterial compliance was determined from high-fidelity ascending aortic pressure and velocity recordings using 1) the traditional monoexponential aortic diastolic pressure decay and 2) the direct solution of the equation, which describes the three-element windkessel model of the arterial system. Resting values for total arterial compliance (x10(-3) cm5/dyn) derived from method 1 were significantly correlated with compliance derived from method 2 (r = 0.89, P less than 0.01). However, method 1 values (control mean 1.15 +/- 0.27, heart failure mean 1.18 +/- 0.54) were consistently and significantly lower (P less than 0.001) than method 2 values (control mean 1.59 +/- 0.50, heart failure mean 1.38 +/- 0.60). Resting total arterial compliance in heart-failure patients was not significantly different from control subjects. Total arterial compliance did not significantly change with exercise in either group despite increases in arterial pressure. However, nitroprusside administration in the heart-failure group increased total arterial compliance both at rest and on exercise compared with the unmedicated state. These different methodological approaches to the estimation of total arterial compliance in humans resulted in significantly different absolute values for compliance, although both methods provided concordant results with respect to the response of arterial compliance to physiological and pharmacological interventions.(ABSTRACT TRUNCATED AT 250 WORDS)

Training needs and qualifications of anaesthesiologists not exposed to ALS.

OBJECTIVES: To establish which needs exist for specific training in Advanced Cardiac Life Support (ALS) in anaesthesiology residents and interns not exposed to structured ALS courses. METHODS: 48 residents, and seven interns accepted for training in anaesthesiology, were tested in a spontaneous, blind, cross-sectional, prospective assessment using a recording manikin with validated scoring system, a questionnaire, and 35 multiple-choice questions. RESULTS: 65% admitted not having had any CPR training within the last 2 years. The answers were correct in 55 +/- 14% of the cases, increasing significantly with the length of training (P = 0.001). One-rescuer CPR skills were inadequate: only 13% (n = 7) of participants scored within acceptable limits when using the Berden Scoring system (Berden et al., Resuscitation 1992;13:31-41), which assigned weighted error points to BLS skills. No correlation with skill was noted with increased length of residency, confidence, ER or ICU experience, or participation in CPR-incidents. CONCLUSIONS: Anaesthesiology residents and interns were not able to demonstrate BLS skills properly even while in training and did not recognize this themselves. CPR-related knowledge is poor and increases only incidentally over the years of residency even though participants were frequently confronted with seminars and resuscitation situations, and see protocols daily. The use of multiple-choice questions and the Berden scoring system avoids difficulties in evaluating case-scenario type of tests. We suggest that trainees are motivated to take part in standardized, intensive, recognised ALS courses which emphasize BLS skills and require (re)certification.

Arterial tonometry: review and analysis.

A review is presented of the field of arterial tonometry and of the problems involved with its application. A second generation model is developed which interprets most of the difficulties encountered in previous experimental work. The model also identifies barriers that must be overcome to allow tonometry to become a practical technique for obtaining measurement of continuous, absolute blood pressure. Problems addressed include those of calibration, positioning sensitivity, design standardization, material properties and vascular loading characteristics. Theoretical and experimental studies provide support for the application of basic biomechanical concepts for solution of these problems and suggest required design features.

Thresholds for premature ventricular contractions in frog hearts exposed to lithotripter fields.

Piezoelectrically generated lithotripter shocks were shown to produce premature ventricular contractions of the frog heart. Anesthetized grass frogs, Rana pipiens, were studied following implantation of an aortic catheter and EKG leads. The most sensitive phase of the heart cycle for the generation of premature ventricular contractions with lithotripter shocks at 30 MPa peak pressure was found to be the T-P segment. During this phase of the heart cycle, the minimum peak-positive pressure shock wave necessary to produce a premature ventricular contraction in a frog heart was between 5 MPa and 10 MPa.

Theoretical and experimental analysis of right ventricular bypass and univentricular circulatory support.

In this paper we examine the dynamic coupling between cardiac pump events and vascular arterial-venous factors that regulate the rate of blood flow around the circulation. A series of experiments were designed to test the feasibility of maintaining vascular and pulmonary function in the absence of the right heart and to characterize the physiologic and hemodynamic consequence of such an exclusion. Theoretical analysis of the cardiovascular system (excluding neuro-humoral factors) using both lumped time invariant and distributed compartmental mathematical equivalent representations, demonstrated that a change in cardiac output (Q) has an inverse-linear effect on venous and direct-linear effect on arterial pressure. A single blood-pump, in a form of a mechanical substitute or the biologic left-heart, alone can support the circulation. Cardiac output reserve is limited (50 percent of normal) because of the rapidly diminishing pulmonary venous-pressure as outflow is increased, irrespective of the pump's specific characteristics. Experiments in animals combined with mock-circulatory studies and computer modeling confirm that near normal flow can be sustained by increasing the stressed blood volume or reducing selectively the systemic venous compliance (i.e., inflatable pressure suit, venous constriction, intra-abdominal compression maneuvers, etc.). The right heart is not essential for normal pulmonary circulation but serves to maintain low systemic venous pressure and relatively high left-heart flow reserve. Purely mechanical properties of the vascular system determine the control and stability of the circulation.

Shape of the left ventricle and its computer modelling.

A simple computer program was made to draw different left ventricle shapes in order to support the theory of elongation and to get a visual presentation of the shape of the left ventricle. Experimental data, obtained from echocardiography and Simpson's rule, were used for this program. The results yielded different shapes under different physiological circumstances, indicating the sensitivity of the method. It was concluded that these figures (shapes) support the use of elongation as a shape index.

Differentiation of intramyocardial fluid pressure from fiber stress.

To characterize the complex force field generated in the ventricular myocardium, intramyocardial pressure (IMP) measurement is used as an indirect means of assessing the distribution of regional wall stress. To resolve the long term confusion associated with this measurement, IMP is divided into its two dominant components: intramyocardial fluid pressure (IFP) and intramyocardial fiber stress (IFS). The intramyocardial response to regional and global contractile function is examined in terms of changes in the magnitude and transmural gradient of IMP recording. The experimental results support the theoretical concept proposed where the hydraulic properties of the myocardium proved to have an influence on cardiac function. To gain a deeper understanding of myocardial function, cellular and subcellular components must be considered.

A perspective on myocardial contractility.

Myocardial contractile properties form the cornerstone of the heart's ability to pump blood. Efforts have been made to characterize these properties via classic elasticity theory concepts, which can lead to spurious results, as demonstrated by experiments measuring intramyocardial pressure. Two ways out of these difficulties are identified. One is to start at the cellular level, the other at the chamber level. The latter allows separation of ventricle (source) and arterial (load) effects on measured pressure and flow, distinct from previous definitions of ventricular contractility which tended to lump the two.

The changing view of the heart through the centuries.

In human perception, the heart was not always part of the blood circulating system. It was later included as a suction pump until Harvey argued that the heart is actually a compression pump, the central organ of the circulation, and the only organ responsible for the motion of blood. Considered initially as an autonomous pump, the heart gradually became viewed as subservient to the needs of the peripheral organs it perfuses. Constant properties assigned to the heart had to be replaced, one after another, by adjustable parameters. Even the adequacy of the heart as the sole pump has been doubted, an issue that resurfaces today.

Human circulatory system model based on Frank's mechanism.

A new analytical model of the left ventricle as a pump, developed from isolated canine experiments, was adapted to describe each of the four heart chambers in a complete human circulatory system model. Each chamber is embodied as a volume and time dependent isovolumic pressure source, after Otto Frank's classic experiments. Analytical results show that a small set of equations is sufficient to describe the main features of the heart as a pump, including isovolumic and ejecting beats for a wide range of ventricular and circulation conditions. This model allows interactive teaching of cardiovascular system dynamics. Computed results demonstrate that, with additional experiments, a quantitative description of the human circulation for research purposes may emerge from this approach.

The left ventricular ejection effect.

A recently developed model of the left ventricle, based on experimental data, has been shown to exhibit the main features of the heart's ability to pump. Two special cases during blood ejection, termed pressure deactivation and hyperactivation, were identified. This study proposes an 'ejection effect' correction to the model that addresses deactivation, hyperactivation and adjusts the shape of the computed ventricular ejection curve in late systole. Also, a new approach based on new animal experiments is proposed to identify the ejection effect mechanism(s).