Complementary methods to investigate the development of clogging within a horizontal sub-surface flow tertiary treatment wetland.

A combination of experimental methods was applied at a clogged, horizontal subsurface flow (HSSF) municipal wastewater tertiary treatment wetland (TW) in the UK, to quantify the extent of surface and subsurface clogging which had resulted in undesirable surface flow. The three dimensional hydraulic conductivity profile was determined, using a purpose made device which recreates the constant head permeameter test in-situ. The hydrodynamic pathways were investigated by performing dye tracing tests with Rhodamine WT and a novel multi-channel, data-logging, flow through Fluorimeter which allows synchronous measurements to be taken from a matrix of sampling points. Hydraulic conductivity varied in all planes, with the lowest measurement of 0.1md(-1) corresponding to the surface layer at the inlet, and the maximum measurement of 1550md(-1) located at a 0.4m depth at the outlet. According to dye tracing results, the region where the overland flow ceased received five times the average flow, which then vertically short-circuited below the rhizosphere. The tracer break-through curve obtained from the outlet showed that this preferential flow-path accounted for approximately 80% of the flow overall and arrived 8h before a distinctly separate secondary flow-path. The overall volumetric efficiency of the clogged system was 71% and the hydrology was simulated using a dual-path, dead-zone storage model. It is concluded that uneven inlet distribution, continuous surface loading and high rhizosphere resistance is responsible for the clog formation observed in this system. The average inlet hydraulic conductivity was 2md(-1), suggesting that current European design guidelines, which predict that the system will reach an equilibrium hydraulic conductivity of 86md(-1), do not adequately describe the hydrology of mature systems.

Vascular trauma associated with routine spinal anaesthesia.

Samples of cerebrospinal fluid obtained from 130 patients undergoing spinal anaesthesia were examined microscopically. Subarachnoid puncture was performed using either a 25G Whitacre or 25G Quincke spinal needle. Two samples were collected from each patient and the red blood cell count of the second sample collected was taken as a measure of the vascular trauma associated with the procedure. Red blood cells were seen in 50 (38%) of these samples, of which 18 (14%) contained > 100 red blood cells.mm-3. Paraesthesia was felt by 11 (8.5%) patients and the occurrence of paraesthesia was associated with significantly raised red blood cell counts (p < 0.0001). There was also a correlation between the number of needle passes made at lumbar puncture and the red blood cell count in the sample (p < 0. 0001). Neither spinal needle type nor antiplatelet drug therapy influenced red blood cell counts (p = 0.66 and 0.37, respectively). These findings suggest that routine spinal anaesthesia is often complicated by minor degrees of vascular trauma, especially when paraesthesiae or technical difficulty occur at subarachnoid puncture.

Meeting the standards for interhospital transfer of adults with severe head injury in the United Kingdom.

In December 1996, the Association of Anaesthetists of Great Britain and Ireland produced a series of recommendations outlining the safe conduct of interhospital transfers for patients with acute head injuries. We assessed the current ability of UK hospitals to implement these recommendations and opinions on the formation of transfer teams, using a postal questionnaire. This was sent to all Royal College of Anaesthetists tutors, 268 of whom replied (94% response rate). Of the hospitals surveyed, 208 received adult head-injury patients but did not have on-site neurosurgical facilities. In 171 (86.8%) of these hospitals, senior house officers could be expected to accompany the patient during subsequent transfer. The majority of hospitals (192, 92.3%) were able to monitor ECG, pulse oximetry and blood pressure during the journey, but only 97 (46.6%) had facilities to monitor end tidal carbon dioxide levels. As a result of the anaesthetist's involvement in the transfer, emergency operating could be delayed in 169 (81.3%) hospitals. One hundred and fifty-eight (76%) respondents thought that the formation of transfer teams to transport critically ill patients would have some merit. Hospitals are responding to the published guidelines, but improvements are still needed in levels of equipment and insurance provision, along with the identification of a designated consultant at each hospital with responsibility for transfers.

Extraction of nitric oxide and nitrogen dioxide from an oxygen carrier using molecular sieve 5A.

Nitric oxide (NO) is effective in the management of pulmonary hypertension and shunt-related hypoxia. Nitrogen dioxide (NO2) is formed when the gas is delivered with oxygen. Both oxides of nitrogen have well recognized adverse effects. The scavenging properties of several forms of soda lime have been investigated. A gas flow containing NO 70 ppm and NO2 5 ppm in oxygen was introduced into a vertically mounted Waters' canister containing: (i) 125 g of molecular sieve 5A (a calcium aluminosilicate zeolite) and (ii) 135 g of soda lime containing a potassium permanganate marker. NO and NO2 concentrations were measured at hourly intervals at the entry and exit points using an electrochemical analyser. Extraction ratios (gradient/ inlet x 100) were calculated for a 24-h period. High extraction ratios (in excess of 90%) of NO and NO2 were observed with both compounds for up to 1 h but these declined rapidly after this time with soda lime. In contrast, the molecular sieve produced extraction ratios in excess of 98% for both gases over the 24-h period. We conclude that the molecular seive 5A is a highly effective scavenger of NO and NO2.