The effect of hyperoxia on cerebral blood flow: a study in healthy volunteers using magnetic resonance phase-contrast angiography.

A small decrease in cerebral blood flow (approximately 10%) in response to 100% oxygen (O2) administration is well recognized. This observation was based on human volunteer studies, which employed a nitrous oxide washout method for the measurement of cerebral blood flow. Because this method is now appreciated to be subject to potential errors we have examined the cerebral blood flow response to 100% oxygen using a magnetic resonance imaging technique to quantify changes in carotid and basilar artery flow. The study, was performed in 12 normal male subjects aged 23-42 years. We report decreases in cerebral blood flow ranging from 9 to 31% with a mean value of over 20%. The decrease in cerebral blood flow was greater in seven young subjects (aged 23-26 years) with decreases in cerebral blood flow of 19.3-31.4% (mean 26.8%). In five older subjects (aged 32-42 years), decreases in CBF were smaller (mean 16. 2%). The administration of 100% O2 was accompanied by a small decrease in end-tidal CO2 (3.7-7.1%), insufficient to explain the changes in cerebral blood flow. We conclude that the decrease in cerebral blood flow in response to O2 administration is greater than previously described and appears to be greater in young adults.

Use of single-slice thick slab phase-contrast angiography for the diagnosis of dural venous sinus thrombosis.

The aim of this study was to examine the reliability of single-slice phase-contrast angiography (SSPCA) as a rapid technique for the investigation of suspected dural venous sinus occlusion. Images were obtained on 25 normal volunteers to document the accuracy of SSPCA in the demonstration of slow flow states. Normal volunteers were imaged using sagittal and coronal SSPCA (slice thickness 13 cm, matrix 256 x 256, TR 14 ms, TE 7 ms, flip angle 20 degrees, peak velocity encoding rate 30 cm/s). Sinus patency and flow rate were confirmed by measurement of flow in the superior sagittal and transverse sinuses using quantified single-slice phase difference images. Imaging was performed in 50 patients undergoing routine brain scans in order to determine the optimal slice orientation for clinical use. Twenty-one patients with suspected dural venous sinus thrombosis were also investigated with SSPCA and the diagnosis confirmed by one or more alternative imaging techniques. Imaging time was 29 s per acquisition and image quality was good in all cases. Variations in dural sinus patency and flow in normal volunteers were accurately predicted by SSPCA (kappa = 0.92). Use of a single angulated slice (130 mm thick, para-sagittal image angled 30 degrees towards coronal and 30 degrees towards transverse) provided sufficient separation of right- and left-sided venous structures to allow use of a single projection. The presence and extent of sinus occlusions in 14 patients and the absence of thrombosis in 7 were accurately identified by SSPCA. Sensitivity and specificity in this limited study were both 100%. The SSPCA technique takes less than 30 s and provides a reliable and rapid technique for the diagnosis of dural venous sinus thrombosis.

Anatomical variation of cerebral venous drainage: the theoretical effect on jugular bulb blood samples.

Recent studies have demonstrated significant variation in bilateral jugular venous oxygen saturation measurements which may be of clinical significance. We have therefore measured variations in normal dural sinus venous drainage to assess the possible effects of normal anatomical variations on measured jugular venous oxygen saturation. Normal volunteers (n = 25) were imaged using magnetic resonance venography to demonstrate variations in venous anatomy. Flow was measured in the superior sagittal sinus and bilaterally in the transverse sinus, sigmoid sinus proximal to the jugular bulb and proximal jugular vein using phase difference magnetic resonance imaging. Examination of magnetic resonance venogram images showed considerable variability in the symmetry of transverse sinus flow. Complete absence of one transverse sinus was seen in four cases and significant asymmetry in the size of the transverse sinuses was present in 13. Quantitative flow studies demonstrated that the ratio of superior sagittal sinus to combined jugular bulb flow showed remarkably little variation (0.46 +/- 0.06). Measurements of transverse sinus flow showed significant asymmetry (< 40% of superior sagittal sinus flow in one transverse sinus) in 21 of 25 volunteers. The effect of the observed asymmetry on jugular venous oxygen saturation was modelled based on the assumption of either a supratentorial or infratentorial lesion. This model predicted significant asymmetry in jugular venous oxygen saturation measurements (> 10%) in 65% of cases with a supratentorial lesion which is in close agreement with clinical observations. This study suggests that normal variations in venous drainage may account for observed asymmetry in jugular venous oxygen saturation measurements.

Interobserver variation in the chest radiograph component of the lung injury score.

The lung injury score is a semi-quantitative system used in the definition and grading of the acute respiratory distress syndrome. It is composed of two, three or four equally weighted components. One component is derived from the chest radiograph, which may contribute up to 50% of the total score. A score of 1 is awarded for each quadrant on the chest radiograph which contains alveolar consolidation. We examined the interobserver variation between two anaesthetists, two radiologists and two critical care physicians who scored blindly 100 chest radiographs from patients with adult respiratory distress syndrome. There was very good agreement between the two radiologists in the total scores (kappa 0.97) and in individual scores in each of the 4 quadrants (kappa 0.97-1.0). The agreement between anaesthetists and radiologists was only fair for the total score (kappa 0.37-0.42), but moderate to good for individual quadrant scores (kappa 0.43-0.73). The agreement between the two anaesthetists was moderate for individual quadrant scores (kappa 0.44-0.60), but only fair for total score (kappa 0.34). There was poor agreement between the two critical care physicians for total score (kappa 0.05) and for individual quadrant scores (kappa 0.04-0.20). Agreement between the physicians and other observers was poor to fair for the total score (kappa 0.12-0.32) and poor to moderate for the individual quadrant scores (kappa 0.15-0.63). Both anaesthetists and physician 2 underestimated the overall chest scores (median scores 2, 3 and 1 respectively) in comparison to the radiologists (median scores 3.5). Physician 1 significantly overscored (median score 4). The chest radiograph component of the lung injury score can be consistently assessed by radiologists, but significant variations may be introduced when assessed by other clinicians. This has significant implications for the use of the lung injury score in studies of adult respiratory distress syndrome and other studies which incorporate radiographic appearances in the definition.

Haemodynamic and oxygen transport response during exchange transfusion for severe falciparum malaria.

We describe the haemodynamic and oxygen transport response in a patient undergoing exchange transfusion for severe falciparum malaria. We found that exchange transfusion produced a significant increase in left ventricular stroke work index, systemic oxygen delivery and oxygen consumption. This potentially beneficial effect of exchange transfusion has not been reported previously.

A comparison of arterial lines and insertion techniques in critically ill patients.

We compared three arterial line insertion techniques and two types of arterial catheters in 69 critically ill patients. Use of the direct-puncture technique (method A) was associated with a significantly higher failure rate (23%) than use of a catheter with a separate guide wire (method B, 'classical' Seldinger technique, p < 0.001) or a catheter with an integral guide wire (method C, 'modified' Seldinger technique, p < 0.02). Operators randomly allocated to using method A took significantly longer to perform the procedure than those using method C (p < 0.01), used significantly more catheters (p < 0.0001) and made significantly more punctures in achieving a successful insertion than those using either methods B (p < 0.001) or C (p < 0.001). Both catheter types B and C (polyurethane) were significantly less likely to block, thus requiring less likely to block, thus requiring re-insertion, than catheter type A (Teflon) (p < 0.02, p < 0.01 respectively). We recommend the use of a 'classical' Seldinger technique (method B) for arterial line insertion in critically ill patients and the use of a polyurethane catheter, in preference to Teflon, to maximise catheter life after insertion.

The need for quality control in measurement of mixed venous oxygen saturation.

We investigated the variability of arterial, mixed venous and peripheral venous oxygen saturation readings in three co-oximeters in regular use on two Intensive Care Units. Over a 2-week period, 96 readings were obtained from each of the following machines; two AVL 912 co-oxylite co-oximeters (Machines A and B, Biomedical Instruments, Graz, Austria) and one IL-282 (Machine C, Instrumentation Laboratories, Lexington, MA, USA). The coefficient of variation in the arterial oxygen saturations was extremely small on all three machines (< 0.43%). The coefficient of variation in the mixed venous samples, however, ranged from 1.96 to 4.61% on machine A, and from 2.73 to 4.71% on machine B, but only from 0.17 to 1.47% on machine C. The variation in mixed venous saturations obtained from a single blood sample repeatedly analysed on machines A and B was large enough to influence clinical management.

Paralytic ileus as a complication of atropine therapy following severe organophosphate poisoning.

A 32-year-old man presented with symptoms of severe organophosphate poisoning and required an atropine infusion for 5 weeks. We believe the development of a paralytic ileus occurred as a rare feature of atropine toxicity when other signs were masked by the underlying condition. The onset of a paralytic ileus coincided with a spontaneous increase in red cell cholinesterase levels and may be an early sign of recovery from organophosphate poisoning.

Malignant astrocytoma of the cervico-medullary junction masquerading as Guillain-Barré syndrome.

Brainstem gliomas are rare primary brain tumours which most commonly occur in the midbrain and pons. Malignant gliomas and tumours at the cervico-medullary junction are particularly unusual. The diagnosis of tumours at this site is particularly difficult using computed tomographic (CT) scanning owing to artifacts around the base of the skull. Intrinsic tumours of the cervico-medullary junction may lead to a dissociated motor deficit and the onset of symptoms can be rapid. We describe a patient in whom an isolated ascending motor deficit in association with a raised cerebrospinal fluid protein and a normal CT scan led to an erroneous diagnosis of Guillain-Barré syndrome. The patient was treated on the intensive care unit for an 8-week period before further investigation demonstrated a malignant glioma of the cervico-medullary junction. We recommend confirmation of the diagnosis of polyradiculopathy by nerve conduction studies wherever possible.

Comparison of the hemodynamic and oxygen transport responses to modified fluid gelatin and hetastarch in critically ill patients: a prospective, randomized trial.

OBJECTIVE: To compare the hemodynamic and oxygen transport responses to a rapid (< 10-min) infusion of 500 mL of modified fluid gelatin (group A) or hydroxyethyl starch (group B) in patients suffering from acute hypovolemia. DESIGN: Prospective, randomized, noncrossover study. SETTING: University hospital, general intensive care unit. PATIENTS: Twenty-eight patients with hypovolemia mechanically ventilated for concurrent acute respiratory failure. INTERVENTIONS: Patients were mechanically ventilated. Pulmonary and femoral artery catheters were used for hemodynamic monitoring. MEASUREMENTS AND MAIN RESULTS: Hemodynamic and oxygen transport variables were determined at baseline, 15 mins, and 30 mins after the infusion of each fluid. In both groups pulmonary artery occlusion pressure, stroke volume, and cardiac index significantly increased. In neither group did heart rate decrease. Oxygen delivery increased significantly in group A patients but not in group B patients. This result was due to greater hemodilution in group B patients. CONCLUSIONS: There are no significant differences in the hemodynamic responses to hydroxyethyl starch or modified fluid gelatin. The hemodynamic and oxygen transport effects of artificial colloid solutions may not be entirely predictable and should be monitored in critically ill patients.

Esmolol in a case of severe tetanus. Adequate haemodynamic control achieved despite markedly elevated catecholamine levels.

A patient with severe tetanus, who had a sympathetic crisis while sedated with 30 mg/h diazepam and 30 mg/h morphine, is described. Satisfactory control of the haemodynamic crisis was achieved with bolus doses of esmolol to a total of 180 mg. A disturbing finding was that although there was adequate control of the tachycardia and hypertension, arterial catecholamine levels remained markedly elevated. Adrenaline levels of 531 pg/ml (normal 10-110 pg/ml) and noradrenaline levels of 1,036 pg/ml (normal 100-500 pg/ml) were recorded when the patient had a systolic arterial pressure of 110 mmHg and a heart rate of 97/min. The implications of this finding are discussed.

Decreased cardiac index as an indicator of tension pneumothorax in the ventilated patient.

We describe three critically ill patients receiving pressure-controlled ventilation who suffered acute hypotensive episodes associated with the development of tension pneumothoraces. In four documented episodes of tension pneumothorax a major decrease in cardiac index was the most consistently detected abnormality. The expected increases in central venous pressure and heart rate did not occur in three of the episodes in two of the patients, both of whom were receiving inotropic therapy. Any increases in airway pressure could not be assessed on pressure-controlled ventilation. The physiology of tension pneumothorax in the ventilated patient is described and the importance of decreased cardiac index as a haemodynamic indicator of tension pneumothorax is discussed.

A re-evaluation of the ventilator score as an indicator of prognosis in the adult respiratory distress syndrome.

OBJECTIVE: To determine whether the ventilator score of Smith and Gordon (1986) can accurately predict outcome in patients with severe Adult Respiratory Distress Syndrome (ARDS). DESIGN: Retrospective study of data from case records and flow sheets. SETTING: University Hospital Intensive Care Unit. SUBJECTS: Fifty-five patients with severe Adult Respiratory Distress Syndrome. MEASUREMENTS AND MAIN RESULTS: The ventilator score of Smith and Gordon (1986), based on a compound score of the patient's age, alveolar to arterial oxygen tension difference and mean peak airway pressure, was calculated daily for for each patient. In contrast to the original report, a high ventilator score ( greater than 80) had a predictive value for death of only 59%, and a specificity of only 29%. The use of a higher ventilator score ( greater than 100) resulted in a predictive value of only 70% with a specificity of 75%. The use of inverse ratio ventilation was associated with a significant improvement in survival in those patients with ventilator scores greater than 100. This finding has not been reported previously. CONCLUSIONS: The ventilator score does not provide a satisfactory predictor of outcome in ARDS and cannot be used as a prognostic tool. It may have some use as an indicator of the severity of respiratory failure. A ventilator score greater than 100 may be an indication for the institution of inverse ratio ventilation.

Successful use of continuous veno-venous haemofiltration to treat profound fluid retention in severe peripartum cardiomyopathy.

The use of continuous veno-venous haemofiltration after failure of conventional treatment in a patient with severe peripartum cardiomyopathy is described. Treatment with inotropes and diuretics failed to produce a diuresis despite the presence of severe fluid overload. Haemofiltration over a 9-day period allowed removal of 171 of fluid with a concomitant improvement in haemodynamic function and a spontaneous diuresis.

Azygos catheter placement as a cause of failure of dialysis.

Common complications of venous dialysis catheters include sepsis and accidental removal. Angiographic demonstration of dialysis lines is only rarely requested usually to confirm the presence of clot or stenosis as a cause for poor dialysis flow. Poor flow can also be due to inadvertent placement of the catheter in the azygos system. The use of dialysis catheters with a long venous limb which extends beyond the arterial port may predispose to such placement as their lumen is lateral to the central axis of the catheter. In those patients with poor venous access catheter placement under angiographic control may be helpful.

Magnetic resonance imaging of extradural blood patches: appearances from 30 min to 18 h.

We have used magnetic resonance imaging to examine five patients treated with extradural blood patches for persistent post lumbar puncture headache. Images were obtained between 30 min and 18 h after patching. Extradural blood patch injection produced a focal haematoma mass around the injection site which initially compressed the thecal sac and nerve roots. The main bulk of the extradural clot extended only three to five spinal segments from the injection site, although small amounts of blood spread more distally. Spread from the injection site was principally cephalad. Mass effect was present at 30 min and 3 h, but clot resolution had occurred by 7 h, leaving a thick layer of mature clot over the dorsal part of the thecal sac. Eighteen hours after injection only small widely distributed clots, adherent to the thecal sac, were demonstrated. Extensive leakage of blood from the injection site into the subcutaneous tissues was present in all patients.