Effect of a 2-h hyperglycemic-hyperinsulinemic glucose clamp to promote glucose storage on endurance exercise performance.

Carbohydrate stores within muscle are considered essential as a fuel for prolonged endurance exercise, and regimes for enhancing such stores have proved successful in aiding performance. This study explored the effects of a hyperglycaemic-hyperinsulinemic clamp performed 18 h previously on subsequent prolonged endurance performance in cycling. Seven male subjects, accustomed to prolonged endurance cycling, performed 90 min of cycling at ~65% VO(2max) followed by a 16-km time trial 18 h after a 2-h hyperglycemic-hyperinsulinemic clamp (HCC). Hyperglycemia (10 mM) with insulin infused at 300 mU/m(2)/min over a 2-h period resulted in a total glucose uptake of 275 g (assessed by the area under the curve) of which glucose storage accounted for about 73% (i.e. 198 g). Patterns of substrate oxidation during 90-min exercise at 65% VO(2max) were not altered by HCC. Blood glucose and plasma insulin concentrations were higher during exercise after HCC compared with control (p < 0.05) while plasma NEFA was similar. Exercise performance was improved by 49 s and power output was 10-11% higher during the time trial (p < 0.05) after HCC. These data suggest that carbohydrate loading 18 h previously by means of a 2-h HCC improves cycling performance by 3.3% without any change in pattern of substrate oxidation.

Distribution of blood flow and ventilation in the lung: gravity is not the only factor.

Current textbooks in anaesthesia describe how gravity affects the regional distribution of ventilation and blood flow in the lung, in terms of vertical gradients of pleural pressure and pulmonary vascular pressures. This concept fails to explain some of the clinical features of disturbed lung function. Evidence now suggests that gravity has a less important role in the variation of regional distribution than structural features of the airways and blood vessels. We review more recent studies that used a variety of methods: external radioactive counters, measurements using inhaled and injected particles, and computer tomography scans. These give a higher spatial resolution of regional blood flow and ventilation. The matching between ventilation and blood flow in these small units of lung is considered; the effects of microgravity, increased gravity, and different postures are reviewed, and the application of these findings to conditions such as acute lung injury is discussed. Down to the scale of the acinus, there is considerable heterogeneity in the distribution of both ventilation and blood flow. However, the matching of blood flow with ventilation is well maintained and may result from a common pattern of asymmetric branching of the airways and blood vessels. Disruption of this pattern may explain impaired gas exchange after acute lung injury and explain how the prone position improves gas exchange.

Estimation of errors in determining intrathoracic blood volume using thermal dilution in pigs with acute lung injury and haemorrhage.

BACKGROUND: Global end diastolic volume (GEDV) has a constant and predictable relationship to intrathoracic blood volume (ITBV). The present study assesses the difference between ITBV derived from GEDV and ITBV measured directly in pigs with acute lung injury (ALI) and mild haemorrhage. METHODS: We caused ALI in 12 anaesthetized pigs by i.v. injection of oleic acid and removed 10% of estimated blood volume. EVLW, GEDV, ITBV (COLD; Pulsion Medical Systems), Pa(o(2))/Fi(o(2)), lung compliance and haemodynamic variables were measured at baseline (time 0) and at 30 and 120 min. All animals were volume-resuscitated, followed by measurements at 180 min. A linear equation estimated from the 44 pairs of ITBV and GEDV values in 11 animals was applied iteratively to the four GEDV measurements in the 12th animal, enabling 48 comparisons between measured (ITBVm) and derived ITBV (ITBVd) to be made. RESULTS: Increase in extravascular lung water index (EVLWi) was associated with significant pulmonary hypertension, worsening of oxygenation and compliance (repeated measures ANOVA; P<0.05). There was good within-subject correlation and agreement between ITBV(m) and ITBV(d) (r=0.72, mean bias 0.8 ml; sd 32 ml). Mean error in deriving ITBV from GEDV was 4.5%. (sd 4.2%; range 0.05-19%). There were no significant differences in errors in the presence of small (up to 10%) deficits in blood volume (F=1.0; P=0.41). CONCLUSIONS: ITBV estimated by thermodilution alone is comparable to measurements made by the thermo-dye dilution technique in the presence of pulmonary hypertension and mild deficits in total blood volume.

Effects of sustained post-traumatic shock and initial fluid resuscitation on extravascular lung water content and pulmonary vascular pressures in a porcine model of shock.

BACKGROUND: The temporal evolution of lung injury following post-traumatic shock is poorly understood. In the present study we have tested the hypothesis that manifestations of pulmonary vascular dysfunction may be demonstrable within the first hour after the onset of shock. METHODS: Twenty-nine anaesthetized pigs (mean weight 27.4 kg; (SD) 3.2) were randomly allocated to three groups: control (C, n=9), shock resuscitated with either NaCl 0.9% (S, n=10), or 4% gelatine (G, n=10). Shock was maintained for 1 h followed by fluid resuscitation with either normal saline or 4% gelatine solution. Cardiac output (CO), mean arterial pressure (MAP), mixed venous saturation (Sv(O(2))), blood lactate concentration, mean pulmonary artery pressure (MPAP), MPAP/MAP, pulmonary vascular resistance (PVR), extravascular lung water index (EVLWi), Pa(O(2))/FI(O(2)), venous admixture (Q(.)(S)/Q(.)(T)), and dynamic lung compliance (C(dyn)) were measured at baseline, beginning of shock phase, end of shock phase, and post-resuscitation. RESULTS: At the end of volume resuscitation CO was restored to control values in both shock groups. MAP remained significantly below control values (95% CI: C=70-95, S=28-52, G=45-69 mm Hg) in both shock groups. MPAP/MAP was significantly greater in both shock groups at the end of the shock phase (95% CI; C=0.15-0.24, S=0.28-0.38, G=0.32-0.42) and at the post-resuscitation phase (95% CI: C=0.12-0.30, S=0.43-0.61, G=0.32-0.49) indicating the presence of relative pulmonary hypertension. This was associated with a significant increase in PVR in Group S (F=3.9; P<0.05). There were no significant changes in Pa(O(2))/FI(O(2)), Q(.)(S)/Q(.)(T), EVLWi, or C(dyn). In a small cohort of animals a measurable increase in EVLWi (>30%) and reduction in C(dyn) (>10%) were observed. CONCLUSIONS: Pulmonary vascular injury manifesting as relative pulmonary hypertension and increased PVR may occur within the first hour after the onset of shock. These changes may not be accompanied by overt changes in oxygenation, compliance, or EVLWi. Br J Anaesth 2003; 91: 224-32

Effect of changes in arterial-mixed venous oxygen content difference (C(a-v)O2) on indices of pulmonary oxygen transfer in a model ARDS lung.

Many indices are used to quantify pulmonary oxygen transfer. Indices that use only measurements from arterial blood and inspired gas assume a constant C(a-v)O2. Though variations in C(a-v)O2 are recognized, indices such as PaO2/FIO2 remain popular and are often considered the best measure of pulmonary oxygen transfer in critically ill patients. This study estimated the effect of within-subject variations in C(a-v)O2 and FIO2 on venous admixture (Qs/Qt), the calculated oxygen content difference between end-capillary and arterial blood (Cc'O2-CaO2), the alveolar-arterial oxygen tension gradient (P(A-a)O2) and PaO2/FIO2, using a validated lung model of acute respiratory distress syndrome (ARDS). All four indices showed changes with FIO2 and C(a-v)O2, although the magnitude of changes in Qs/Qt was clinically unimportant (<2%). The other three indices showed larger variations that may potentially be misleading. At an FlO2 of 0.7, PaO2 /FIO2 varied between 18 and 10 kPa and at an FIO2 of 0.9 the ratio varied between 22 and 8 kPa. These changes, which were unrelated to underlying lung pathology, are sufficiently large to result in misclassification on the gas exchange scale suggested by the American European Consensus Conference on ARDS. This study shows there is no reliable alternative to Qs/Qt to quantify pulmonary oxygen transfer in critically ill patients.

Changes in arterial-mixed venous oxygen content difference (CaO2 - CvO2) and the effect on shunt calculations in critically ill patients.

Many commonly used indices of pulmonary oxygen transfer assume that CaO2 - CvO2 is constant. We studied changes in CaO2 - CvO2 in critically ill patients to determine the effect on calculated shunt of assuming a fixed CaO2 - CvO2. Two hundred pairs of arterial and mixed venous blood gas measurements were obtained retrospectively from 43 patients, each providing four or five pairs from a period of 48 h. CaO2 - CvO2 range from 13 to 74 ml l-1. The mean within-patient sd was 6.8 ml l-1 and the overall between-patient sd was 10.9 ml l-1. Our results show that assuming a fixed CaO2 - CvO2 leads to errors in quantifying pulmonary oxygen transfer.

Subcutaneous morphine for postoperative analgesia.

OBJECTIVE: a. To confirm the efficacy of subcutaneous morphine infusion for postoperative analgesia and compare this effect with three-hourly subcutaneous bolus injections of morphine. b. To evaluate the suitability of a simple micro-infusion set to deliver subcutaneous infusion, as conventional infusion pumps are expensive and not readily available. SETTING: Double blind, prospective controlled clinical trial. PATIENTS: 21 patients belonging to the American Society of Anaesthesiologists' (ASA) classes I or II, who underwent major elective abdominal surgery were studied in an intensive care unit. INTERVENTION: All patients were given loading doses of morphine intravenously (iv) followed by subcutaneous (sc) infusion in two groups and three-hourly sc bolus injections in the third group. The doses were titrated on an individual basis. The infusion was delivered by a power driven pump in one group and by a microinfusion set in the other. Those with significant pain during this regime were given morphine supplements intravenously. MEASUREMENT: Pain scoring was done hourly using a modified verbal rating scale. The percentage of patients who required intravenous supplements in each group was compared to draw statistical conclusions. RESULTS: 1. Subcutaneous infusion provided adequate analgesia in 86% of the patients studied. 2. There was no significant difference between the groups in terms of additional iv supplement requirement. 3. The microinfusion set required frequent readjustments to maintain constant flow. CONCLUSIONS: Intermittent subcutaneous bolus injections of morphine given through an indwelling butterfly needle is a simple, safe, and effective method for postoperative analgesia after major abdominal surgery. Simple infusion sets are not suitable to deliver subcutaneous infusions, and the need for infusion pumps makes the infusion technique unsuitable for routine use in wards.

Effects of transcutaneous needle stimulation on the immune response in rabbits.

Studies in the field of neuroimmunomodulation have shown that endorphins such as methionine-encephalin may have an immunomodulatory role. This study was undertaken to test whether transcutaneous needle stimulation, which is known to release such peptides from the central neurones, has an effect on immune response in rabbits. Twelve healthy rabbits, in three similar subgroups, were exposed to pathogenic Escherichia coli and their immune response was studied under different experimental conditions. Our results show that needle stimulation causes a reversal of stress induced suppression of antibody production. Further studies are necessary to evaluate any therapeutic uses these observations may have in humans.

Chronic pain syndrome should be recognized as a separate clinical entity.

Chronic pain is a relatively new concept in our understanding of pain. It is rarely recognised or diagnosed as a separate clinical entity in Sri Lanka. Thus the extent of this problem is not known. The case histories of two patients with the chronic pain syndrome are presented, with a brief review of the theoretical aspects of chronic pain. Trends in the management of chronic pain are summarized. Unfortunately, organized treatment programmes for chronic pain are unavailable in Sri Lanka.