Inadvertent subdural spread complicating cervical epidural steroid injection with local anaesthetic agent.

Although cervical epidural steroid injection with local anaesthetic is considered a safe technique and widely practiced, complications may occur. We report a patient experiencing unexpected delayed high block, moderate hypotension and unconsciousness eight to ten minutes after an apparently normal cervical epidural steroid injection. The most probable diagnosis was a subdural block. Anatomical peculiarities of the epidural and subdural space in the cervical region increase the risk of subdural spread during cervical epidural injection. Fluoroscopic guidance is important during cervical epidural injection to increase certainty of correct needle placement, thus minimizing the risk of complications.

A clinical evaluation of platelet function, haemolysis and oxygen transfer during cardiopulmonary bypass comparing the Quantum HF-6700 to the HF-5700 hollow fibre membrane oxygenator.

The continued improvement of oxygenators is an important aspect of patient safety during cardiopulmonary bypass (CPB). The purpose of this study was to compare the Bard William Harvey HF-5700 oxygenator to the upgraded Bard Quantum HF-6700, which has recently been introduced into clinical practice. No clinical evaluation of this device has been published to date. The two oxygenators differ principally in that the Quantum has a smaller priming volume, achieved at the expense of a smaller membrane surface area which could result in sub-optimal gas exchange characteristics, increased haemolysis and increased platelet dysfunction during CPB. Twenty adult patients undergoing elective, first time coronary artery bypass grafting (CABG) were randomly assigned either to the HF-5700 (n=10) or to the HF-6700 (n=10) group. One patient underwent mitral valve repair in addition to CABG and was excluded from further study. There were no statistically significant differences in either preoperative or operative parameters between the two groups. Samples were obtained at the start of CPB, at 30 min, 60 min, at the end of CPB and at 1 h following termination of CPB. No significant differences between the two groups were found in oxygen transfer, haemolysis (plasma haptoglobin levels) or platelet function (a novel platelet activating factor (PAF)-induced platelet activation test) at any of the time points during CPB. It was concluded that the Quantum HF-6700 matches the HF-5700 for the parameters studied, whilst having the advantage of requiring a smaller priming volume.

A new technique for measuring cardiac output and shunt fraction during venovenous extracorporeal membrane oxygenation.

A new indicator dilution technique is described for measuring cardiac output and shunt fraction in patients undergoing venovenous extracorporeal membrane oxygenation (ECMO). Shunt fraction is the proportion of the ECMO pump flow which recirculates through the ECMO circuit (passing directly from the inflow cannula to the outflow cannula) instead of flowing through the pulmonary and systemic circulations. The indicator is an isotonic (150 mmol/l) solution of lithium chloride which is injected into the ECMO flow returning to the patient. Two lithium sensors are used simultaneously to record the resulting lithium dilution curves in arterial blood and in the blood in the ECMO circuit. Cardiac output and shunt fraction are derived from these curves. The techniques, which is simple and safe, provides measurements that allow optimal adjustment of ECMO flow and cardiovascular support.

In vitro evaluation of a new lithium dilution method of measuring cardiac output and shunt fraction in patients undergoing venovenous extracorporeal membrane oxygenation.

OBJECTIVE: To evaluate, in vitro, a method of measuring cardiac output and shunt fraction during venovenous extracorporeal membrane oxygenation (ECMO). DESIGN: Experimental study using an in vitro model. SETTING: A teaching hospital. MODEL: An ECMO circuit was set up in parallel with a patient circuit consisting of tubing through which saline was circulated from a 50-L reservoir by a pump which was set at 3 L/min to represent cardiac output. A second pump in the ECMO circuit drew saline from the patient circuit and passed it through a membrane oxygenator. The flow from the membrane oxygenator either returned directly to the patient circuit or was diverted, via a third pump, back into the ECMO circuit, thereby producing a shunt. INTERVENTIONS: By adjusting the flow rates of the second (ECMO) and third (shunt) pumps, three shunt fractions of 12%, 25%, and 50% were produced at three different ECMO flow rates. Lithium chloride (0.15 mmol) was injected just downstream of the membrane oxygenator; the lithium ion concentration-time curves were recorded simultaneously in the flow returning to the saline reservoir and in the flow just upstream of the membrane oxygenator using lithium selective electrodes. MEASUREMENTS AND MAIN RESULTS: Nine pairs of curves were recorded, one pair for each combination of ECMO and shunt flow rates. Analysis of these curves allowed shunt flow and "cardiac output" to be calculated and compared with the flow rates delivered by the pumps. Mean "cardiac output" derived from the lithium dilution curves was 2.98 +/- 0.18 (SD) L/min, compared with a delivered pump flow of 3 L/min. Measured shunt flow = 0.008 + 1.09 x actual shunt flow (R = 0.997). CONCLUSIONS: This method would allow cardiac output and shunt flow to be measured in patients undergoing venovenous ECMO. It could result in better patient management and improved cannula design.

Relative changes in cerebral blood flow during cardiac operations using xenon-133 clearance versus transcranial Doppler sonography.

BACKGROUND: Changes in cerebral blood flow (CBF) during cardiac operations have implications in terms of postoperative neurologic and neuropsychological dysfunction. Current techniques of CBF measurement are cumbersome and invasive. Transcranial Doppler sonography offers a noninvasive means of assessing changes in CBF. The aim of this study was validation of this technique with existing methods of CBF measurement during cardiac operations. METHODS: We compared the changes in CBF using xenon-133 clearance with changes in middle cerebral artery velocity by transcranial Doppler sonography (VMCA) using pH-stat and alpha-stat acid-base management during cardiopulmonary bypass. Measurements were taken (1) before bypass, (2) at 28 degrees C on bypass, (3) at 37 degrees C on bypass, and (4) after bypass. Relative changes in CBF and VMCA, calculated as the percent change from the prebypass baseline value normalized to 100%, were used in this analysis. RESULTS: During the hypothermic phase of cardiopulmonary bypass, CBF and VMCA increased by 45.9% and 51.8%, respectively (p < 0.001), during pH-stat acid-base management but decreased by only 26.4% and 22.4%, respectively (p < 0.0001), during alpha-stat acid-base management. Linear regression analysis of the absolute changes in CBF (mL . 100 g-1 . min-1) and VMCA (cm/s) showed a significant correlation (r = 0.60; r2 = 0.36; p < 0.0001), but a better correlation was obtained when relative changes in CBF and VMCA were compared (r = 0.89; r2 = 0.79; p < 0.0001). CONCLUSIONS: Measurements of VMCA, expressed as relative changes of a pre-cardiopulmonary bypass level (using the noninvasive transcranial Doppler sonographic technique), can be used to examine CBF changes during cardiopulmonary bypass.

Alpha-stat acid-base regulation during cardiopulmonary bypass improves neuropsychologic outcome in patients undergoing coronary artery bypass grafting.

Neuropsychologic impairment in patients undergoing cardiopulmonary bypass may be associated with cerebral blood flow changes arising from different management protocols for carbon dioxide tension during bypass. Seventy patients having coronary artery bypass grafting were randomized to either pH-stat or alpha-stat acid-base management during cardiopulmonary bypass with a membrane oxygenator. In each patient, cerebral blood flow (xenon 133 clearance), middle cerebral artery blood flow velocity (transcranial Doppler sonography), and cerebral oxygen metabolism (cerebral metabolic rate and cerebral extraction ratio) were measured during four phases of the operation: before bypass, during bypass (at hypothermia and at normothermia), and after bypass. A battery, of neuropsychologic tests were also conducted before and 6 weeks after the operation. During hypothermic (28 degrees C) bypass, cerebral blood flow was significantly (p < 0.001) greater in the pH-stat group (41 mlx100 gm(-1)xmin(-1); 95% confidence interval 39 to 43 mlx100 gm(-1)xmin(-1)) than in the alpha-stat group (24 mlx100 gm(-1)xmin(-1); confidence interval 22 to 26 mlx100 gm(-1)xmin(-1)) at constant pressure and How. Arterial carbon dioxide tensions were 41 mm Hg (40 to 41 mm Hg) and 26 mm Hg (25 to 27 mm Hg), respectively; pH was 7.36 (7.34 to 7.38) and 7.53 (7.51 to 7.55), respectively. Middle cerebral artery flow velocity was significantly (p < 0.05) reduced in the alpha-stat group to 87% (77% to 96%) of the prebypass value, whereas it was significantly (p < 0.05) increased (152%; 141% to 162%) in the pH-stat group. Cerebral extraction ratio for oxygen demonstrated relative cerebral hyperemia during hypothermic (28 degrees C) bypass in both the pH-stat and alpha-stat groups (0.12 [0.11 to 0.14] and 0.25 [0.22 to 0.28], respectively); however, hyperemia was significantly more pronounced in the pH-stat group, indicating greater disruption in cerebral autoregulation. Neuropsychologic impairment criteria of deterioration in results of three or more tests revealed that a significantly (Fisher's exact test, p = 0.02) higher proportion of patients in the pH-stat group fared poorly than in the alpha-stat group at 6 weeks (17/35, 48.6% [32% to 65.1%], and 7/35, 20% [6.7% to 33.2.2%], respectively). In conclusion, patients receiving alpha-stat management had less disruption of cerebral autoregulation during cardiopulmonary bypass, accompanied by a reduced incidence of postoperative cerebral dysfunction.

Irradiated polyglactin 910: a new synthetic absorbable suture.

Two hundred and thirty-six patients had a variety of skin and mucosal wounds sutured with a new rapidly absorbed suture material (irradiated polyglactin 910). No wound complications could be attributed to the material. These included 62 patients with scalp wounds, taking part in a comparative trial with traditional interrupted, monofilament, non-absorbable suturing. No difference in the cosmetic result could be detected three months later. The irradiated polyglactin disappeared from the wound surface spontaneously and suture removal was not normally required. Irradiated polyglactin 910 is suitable for closure of wounds where rapid suture absorption is desirable, particularly for wounds in the scalp, scrotum, and perineum and is an ideal material for mucocutaneous anastomosis at stoma surgery. Loss of suture strength is so rapid that suture removal is unnecessary, eliminating the need for further medical or paramedical care. As absorption is by hydrolysis rather than enzymatic digestion, stitch abscesses are not seen.

Myelination of a key relay zone in the hippocampal formation occurs in the human brain during childhood, adolescence, and adulthood.

BACKGROUND: A previous study demonstrated that myelination of the superior medullary lamina along the surface of the parahippocampal gyrus is occurring in human brain during adolescence. To further investigate whether postnatal increases of myelination may continue during the second decade and possibly even longer, the extent of myelination in this region has been analyzed in 164 psychiatrically normal individuals aged newborn to 76 years. METHODS: Cross sections of the hippocampal formation with adjoining hippocampal gyrus were analyzed on a blinded basis using either a global rating scale or measurements of the area of myelin staining. RESULTS: A curvilinear increase in the extent of myelination between the first and sixth decades of life (r = .71 and r = .67, respectively) was observed. When the area of myelination was expressed relative to brain weight, there was a twofold increase between the first and second decades and an additional increase of 60% between the fourth and sixth decades. Female subjects showed a significantly greater degree of myelin staining than did male subjects during the interval of ages 6 to 29 years; however, after the third decade, there were no gender differences in the area of myelin staining. CONCLUSIONS: The increased staining of myelin during the first and second decades principally occurred in the subicular region and adjacent portions of the presubiculum. During the fourth through sixth decades, however, it extended to progressively more lateral locations along the surface of the presubiculum. The precise origin(s) of the axons showing progressive myelination is unknown; however, the axons in the subiculum may include some perforant path fibers, while those found in the presubiculum may include cingulum bundle projections. Overall, our data are consistent with the idea that both early and late postnatal increases of myelination occur in a key corticolimbic relay area of the human brain and underscore the importance of applying a neurodevelopmental perspective to the study of psychopathology during childhood, adolescence, and even adulthood.

Hyperperfusion and cerebral dysfunction. Effect of differing acid-base management during cardiopulmonary bypass.

Alterations in cerebral blood flow (CBF) occurring during cardiopulmonary bypass (CPB), which are thought to be responsible for increased morbidity, are probably related to changes in arterial carbon dioxide during acid-base management. In this study, 70 patients undergoing elective coronary artery bypass surgery (CABS) were randomised to one of two differing, but widely practised, cardiopulmonary bypass acid-base protocols; pH-stat and alpha-stat. Cerebral blood flow was measured during surgery using the xenon-133 isotope clearance technique. Cerebral oxygen metabolism was measured as the cerebral metabolic rate for oxygen (CMRO2) and matching of the cerebral blood flow to oxygen demand as the cerebral extraction ratio for oxygen (CERO2). Detailed neuropsychological tests were conducted in all patients before surgery and repeated at 6 weeks after surgery for assessment of changes in cognitive function. During hypothermic (28 degrees C) CPB, CBF was significantly greater (P < 0.001) in the pH-stat group (41 ml/100 g per min; 95% confidence intervals (CI), 39-43) than in the alpha-stat group (24 ml/100 g per min; 95% CI, 22-26). The cerebral extraction ratio for oxygen indicated a degree of mismatch of cerebral perfusion and demand during CPB in both pH-stat and alpha-stat groups (0.12; 95% CI, 0.11-0.14 and 0.25; 95% CI, 0.22-0.28, respectively). This mismatch was far more pronounced in the pH-stat group than in the alpha-stat group, indicating greater disruption in cerebral autoregulation in the former group.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of differing acid-base regulation on cerebral blood flow autoregulation during cardiopulmonary bypass.

Cerebral dysfunction following cardiopulmonary bypass may be aggravated by altered autoregulation of cerebral blood flow. We have used trans-cranial Doppler to measure middle cerebral artery blood flow velocity during cardiopulmonary bypass managed by either pH-stat or alpha-stat acid-base protocols. Fourteen patients were studied, 7 in each group. During bypass at 28 degrees C, patients underwent incremental alterations in mean arterial pressure from 20-90 mmHg, maintaining systemic perfusion flow at 1.75 L/min per m2. The cerebral extraction ratio of oxygen was measured to indicate matching of cerebral blood flow to demand. The pH-stat group showed a pressure passive cerebral circulation with significant (r = 0.999, P less than 0.05) increase in blood flow velocity with increasing arterial pressure. This also occurred in alpha-stat group during the pressure range of 20-50 mmHg (r = 0.951, P less than 0.05). During the pressure range of 50-90 mmHg in alpha-stat group the change in flow velocity (0.16 cm/sec per mmHg) was significantly (P less than 0.05) less than that in pH-stat group (0.58 cm/second per mmHg). The cerebral extraction ratio of oxygen was less depressed in the alpha-stat group than in the pH-stat group, indicating more appropriate matching of cerebral blood flow and tissue demand. These results suggest that, during alpha-stat managed cardiopulmonary bypass, cerebral blood flow velocity is less subject to wide pressure alteration than pH-stat.

Effect of propofol anesthesia on baroreflex activity in humans.

Previous studies have shown that infusions of propofol, a new intravenous anesthetic, were associated with decreased arterial pressure and slow heart rates. To evaluate the role of baroreflex mechanisms in sustaining these conditions, the effects of two infusion rates of propofol (54 and 108 micrograms.kg-1.min-1) to supplement 66% nitrous oxide in oxygen anesthesia were studied in twelve ASA class I patients having a mean age of 34 years. Baroreflex control of heart rate was studied by perturbing the patients' arterial pressure with phenylephrine or sodium nitroprusside. Valsalva maneuvers were used to assess the response of the systemic arterial system. Steady state anesthesia at both infusion rates was not associated with decreased sensitivity of the baroreflex control of heart rate, but resetting of the reflex occurred to allow lower arterial pressures for a given heart rate than in the awake state. During propofol infusions at either rate, the diastolic pressure overshoot normally associated with the relief of raised airway pressure in the Valsalva maneuver was significantly reduced. It is concluded that propofol/nitrous oxide anesthesia is not associated with impairment of baroreflex sensitivity, but that central sympatholytic and/or vagotonic mechanisms enable low heart rates to be sustained despite decreased arterial pressures.

An evaluation of six disposable heat and moisture exchangers.

Six disposable heat and moisture exchangers were tested on patients undergoing anaesthesia requiring mechanical ventilation. Inspiratory humidity and temperature were monitored to find the steady-state values reached with each device together with the times taken for these to be achieved. The exchangers were tested in a non-rebreathing T-piece circuit and in a conventional circle system with a fresh gas flow of 6 l/min: the Siemens 150 provided 28 and 32 mg of water/litre of inspired gas (at about 30 degrees C) in 10 and 5 min respectively, but is rather heavy and bulky. The Portex Humidvent provided 25 and 30 mg/l, and although taking longer to reach steady state (27 and 15 min respectively) is small, light and cheap. The Siemens 151 provided 25 and 27 mg/l in 18 and 10 min respectively, but is heavier than the Portex exchanger. The performances of these three devices were not significantly different from each other in either study (P less than 0.05). For the T-piece system the Pall and Engstrom exchangers were the next most efficient. The Pall device provided 18 and 23 mg/l (in 18 and 8 min respectively) and the Engstrom provided 20 and 23 mg/l (in 19 and 10 min respectively). In the circle system, there were no significant differences between the performances of the Portex, Siemens 151, Pall and Engstrom exchangers. The Pall is also a very effective bacterial filter and has been found to be satisfactory in the intensive care setting. The Terumo appeared to perform no better than a circle system with catheter mount (13 mg/l at 27 degrees C). It would seem that more complex humidification equipment is not necessary during anaesthesia if an efficient heat and moisture exchanger is used.

Haemodynamic effects of a prolonged infusion of propofol as a supplement to nitrous oxide anaesthesia. Studies in association with peripheral arterial surgery.

The haemodynamic effects of propofol at two infusion rates (54-65 and 108-130 micrograms kg-1 min-1) have been studied during peripheral arterial surgery in eight elderly patients premedicated with morphine sulphate 0.15 mg kg-1. The haemodynamic response to laryngoscopy and intubation was partially suppressed: neither arterial pressure nor heart rate exceeded awake values. During stable anaesthesia at the lower infusion rate before surgery, systolic (SAP) and diastolic (DAP) arterial pressures were significantly decreased from awake values (SAP: -47%; DAP: -46%) as a result of decreases in cardiac output (-32%) and systemic vascular resistance (SVR) (-9%). During surgery, with either spontaneous (SV) or intermittent positive pressure (IPPV) ventilation, both infusion rates were associated with decreases in arterial pressures when compared with the awake state. Cardiac output was decreased (SV: -35%, IPPV: -36%) and SVR increased (SV: +22%, IPPV: +45%) at the lower infusion rate; similar changes were observed during the faster infusion rate.

Dose requirements of propofol by infusion during nitrous oxide anaesthesia in man. II: Patients premedicated with lorazepam.

The infusion rate of propofol required to supplement 67% nitrous oxide in oxygen to maintain surgical anaesthesia was determined in 72 patients premedicated with lorazepam. Following an induction dose of propofol 2 mg kg-1, groups of eight patients received an infusion of propofol varying from 60 to 200 micrograms kg-1 min-1. Probit analysis was used to determine the ED50 (130 micrograms kg-1 min-1; 95% confidence limits: 106-167 micrograms kg-1 min-1) and ED95 (348 micrograms kg-1 min-1; 95% confidence limits: 233-1296 micrograms kg-1 min-1) for propofol infusion. Whole blood propofol concentrations at the time of surgical incision correlated strongly with the infusion rate, giving an EC50 value of 2.5 micrograms ml-1, and an EC95 value of 5.92 micrograms ml-1. There was no significant correlation between the rate of infusion of propofol, or the total propofol dose, and the times to response to command, or to recall of birthdate.

Hemodynamic effects of infusions of the emulsion formulation of propofol during nitrous oxide anesthesia in humans.

The hemodynamic response to anesthesia with the aqueous emulsion formulation of propofol was studied in healthy patients (ASA I or II), aged 39-57 yr, premedicated with morphine, 0.15 mg/kg. Anesthesia was induced in all patients with propofol, 2 mg/kg. Subsequently, patients were randomly assigned to two groups and maintained by a continuous intravenous infusion (group 1 received 54 micrograms X kg-1 X min-1, group 2 received 108 micrograms X kg-1 X min-1) to supplement 67% nitrous oxide. Three minutes after induction, systolic arterial pressure (SAP) decreased 28% (P less than 0.01) and was associated with decreased (-12%) cardiac output (Q70) and decreased (-15%) systemic vascular resistance (SVR). The hemodynamic response to tracheal intubation was not obtunded, but peak values of arterial pressures and heart rate did not exceed those recorded awake. Thirty minutes elapsed before repeating measurements prior to the first surgical incision. In group 1, SAP and Q70 decreased to 65% and 68% of awake values and in group 2 to 55% and 74% (P less than 0.05). Mild ventilatory depression persisted for the duration of spontaneous ventilation and was not reduced by the stimulus of surgery, which caused no significant hemodynamic responses in either group. Decreasing arterial PCO2 to the awake value by controlled ventilation increased SVR (P less than 0.05), but the associated increased SAP and decreased Q70 did not reach statistical significance. No patient reported awareness. The infusion of the emulsion formulation of propofol was associated with satisfactory anesthesia and recovery and with hemodynamic effects similar to those recorded with other intravenous anesthetics.

Dose requirements of propofol by infusion during nitrous oxide anaesthesia in man. I: Patients premedicated with morphine sulphate.

The study was performed to determine the ED50 and ED95 of a continuous infusion of the emulsion formulation of propofol during 67% nitrous oxide anaesthesia in 57 patients premedicated with morphine sulphate 0.15 mg kg-1. Anaesthesia was induced with propofol 2 mg kg-1, and maintained before incision with a fixed-rate infusion of propofol to supplement nitrous oxide. The response to the first surgical incision, made at least 30 min after induction of anaesthesia, was observed. The ED50 was 53.5 micrograms kg-1 min-1 and the ED95 was 112.2 micrograms kg-1 min-1. At the time of the first surgical incision, the venous whole blood concentrations of propofol at the ED50 and ED95 infusion rates (EC50 and EC95) were 1.66 micrograms ml-1 and 3.39 micrograms ml-1, respectively. The satisfactory maintenance of anaesthesia provided by nitrous oxide supplemented with propofol was associated with haemodynamic stability and rapid, uncomplicated recovery.

Paediatric retrievals in South Australia.

Since the early 1970s there has been a co-ordinated retrieval service in South Australia for adult, paediatric and neonatal patients. The paediatric service has been mounted from the Adelaide Children's Hospital and to the end of 1983 numbers 379 patients, including 90 patients in 1983. This is now providing a considerable workload on the Anaesthetic and Intensive Care Departments. The records have been entered into a file program in a microcomputer and analysed. The results of this analysis are presented and discussed.