Objectives: Medical technology is a large and expanding industry. Introducing new medical devices is important but several challenges exist in implementing the optimal method of evaluation. Both objective and subjective measures can be used for evaluation. The former is the mainstay of evaluation, yet subjective assessment is often the basis for the introduction of new medical technology. The aim of this study was to determine the interaction and concordance between objective and subjective assessment of new medical technology.

Methods: This study used both objective performance measures and subjective user perceptions in the evaluation of a new medical device designed to improve the accuracy of gravity-assisted delivery of intravenous fluids, compared with the current, widely used “roller-clamp” device. The concordance of objective and subjective assessments was evaluated using comparative analysis.

Results: Objective assessment of the accuracy of intravenous fluid delivery revealed no difference between the two devices (p = .636). Subjective assessment revealed that the new device was perceived to be significantly more accurate (p = .001). This lack of concordance can be partially explained by both device and demand characteristics.

Conclusions: This case study reveals a significant discordance between the objective and subjective assessments. It provides some explanation for why new medical devices are adopted without objective evidence of benefit. This phenomenon has been termed “persuasive design” and its influence should be controlled for in the evaluation, purchase and introduction of new medical devices. This should help reduce the risk and associated cost of premature introduction.

The terminology used for describing intervention groups in randomised controlled trials (RCT) on the effect of intravenous fluid on outcome in abdominal surgery has been imprecise, and the lack of standardised definitions of the terms ‘standard’, ‘restricted’ and ‘liberal’ has led to some confusion and difficulty in interpreting the literature. The aims of this paper were to clarify these definitions and to use them to perform a meta-analysis of nine RCT on primarily crystalloid-based peri-operative intravenous fluid therapy in 801 patients undergoing elective open abdominal surgery. Patients who received more or less fluids than those who received a ‘balanced’ amount were considered to be in a state of ‘fluid imbalance’. When ‘restricted’ fluid regimens were compared with ‘standard or liberal’ fluid regimens, there was no difference in post-operative complication rates (risk ratio 0·96 (95% CI 0·56, 1·65), P=0·89) or length of hospital stay (weighted mean difference (WMD) −1·77 (95% CI −4·36, 0·81) d, P=0·18). However, when the fluid regimens were reclassified and patients were grouped into those who were managed in a state of fluid ‘balance’ or ‘imbalance’, the former group had significantly fewer complications (risk ratio 0·59 (95% CI 0·44, 0·81), P=0·0008) and a shorter length of stay (WMD −3·44 (95% CI −6·33, −0·54) d, P=0·02) than the latter. Using imprecise terminology, there was no apparent difference between the effects of fluid-restricted and standard or liberal fluid regimens on outcome in patients undergoing elective open abdominal surgery. However, patients managed in a state of fluid balance fared better than those managed in a state of fluid imbalance.

Summary

Background and objective: Cardiopulmonary bypass is associated with changes of intra- and extravascular volume status often resulting in cardiopulmonary dysfunction. The purpose of this prospective double-blind study was to evaluate the influence of different priming solutions of the extracorporeal circuit on intra- and extravascular volume status and haemodynamics in patients undergoing elective mitral valve replacement. Methods: Twenty-two patients with mitral valve insufficiency were randomly allocated into two equal groups. In Group 1 cardiopulmonary bypass was primed with a nearly isooncotic solution consisting of 4% albumin. The second group received a pure crystalloid priming solution. The thermo-dye indicator dilution technique was used for the assessment of cardiac output, central and pulmonary blood volume, right ventricular end-diastolic volume and total blood volume. Results: Patients in the crystalloid group showed increased intraoperative fluid requirements. Significantly more fluid was accumulated in the extravascular space whereas total blood volume was decreased after surgery. Stroke volume index (SVI) was significantly decreased in the immediate postoperative period when compared to baseline. As indicated by the increase in extravascular fluid content after surgery, both colloid and crystalloid priming volumes were transferred to the extravascular space. Conclusion: The use of colloid priming solutions in patients with mitral valve insufficiency leads to less fluid requirements and significantly reduced fluid shift in the interstitium. However, these changes are not associated with changes in haemodynamic parameters or short term outcome.

Summary

Sepsis is associated with a profound intravascular fluid deficit due to vasodilatation, venous pooling and capillary leakage. Fluid therapy is aimed at restoration of intravascular volume status, haemodynamic stability and organ perfusion. Circulatory stability following fluid resuscitation is usually achieved in the septic patient at the expense of tissue oedema formation that may significantly influence vital organ function. The type of fluid therapy, crystalloid or colloid, in sepsis with capillary leakage remains an area of intensive and controversial discussion. The current understanding of the physiology of increased microvascular permeability in health and sepsis is incomplete. Furthermore, there is a lack of appropriate clinical study end-points for fluid resuscitation. This review considers critically the clinical and experimental data analysing the assessment of capillary leakage in sepsis and investigating the effects of different fluid types on increased microvascular permeability in sepsis.

Background and objective: This study was performed to identify risk factors for complications and in-hospital mortality associated with pneumonectomy.

Methods: The influence of fluid balance during anaesthesia was evaluated, taking into account the patient's age, gender and body mass index, smoking habits, history of pulmonary or cardiac disorders, the site of pneumonectomy and duration of anaesthesia. One-hundred-and-seven patients undergoing elective pneumonectomy were included in the study.

Results: A total of 31 patients (29%) suffered from one or more postoperative complications, seven (22.4%) of these had severe dysrhythmias, six (19.6%) had pulmonary complications and three (9.3%) had cardiovascular complications. The overall mortality rate was 10.3%.

Conclusions: Based on logistic regression analysis, our data indicate the following risk factors for postoperative complications: positive fluid balance exceeding 4000 mL during anaesthesia (pulmonary complications and mortality), body mass index < 17 or > 25 kg m−2 (severe dysrhythmias), or history of chronic heart disease (pulmonary complications). Thirteen patients (12.4%) suffered from a fluid balance 4000 ml during anaesthesia. Regression analysis indicated that fluid balance exceeding 4000 mL was associated with a higher risk of postoperative complications than blood loss exceeding 1000 mL and to be the strongest risk factor for postoperative pulmonary complications and in-hospital mortality. Further trials estimating the effect of restrictive fluid regimens and the use of vasopressors for blood pressure control during anaesthesia must be carried out.

Ringer's solution expands blood volume by between 20% and 25% in awake volunteers, but little is known about its volume effect during general anaesthesia. In 35 men with a mean age of 70 years, the power of various intra-operative factors to change blood volume as estimated by the haemoglobin dilution method were analysed by multiple linear regression every 10 min during transurethral resection of the prostate performed under enflurane anaesthesia. The results show that blood volume increased by 60% of the infused Ringer's solution and by 35% of the irrigating fluid absorbed directly into the blood, while it decreased by slightly more than 100% of the bled volume. There was no correlation between systolic pressure and blood volume changes. This suggests that the volume effect of Ringer's solution in the blood is greater than generally believed during general anaesthesia.