Biomedical subjects
F A Donald
Publications and source records attributed to F A Donald.
Comparison of measured and estimated angles of table tilt at Caesarean section.
BACKGROUND: Lateral maternal tilt reduces aortocaval compression and the consequent cardiovascular instability. METHODS: We measured the angle of table tilt used by 16 anaesthetists during uncomplicated, elective Caesarean section. After initiating anaesthesia, they were asked to position the patient and estimate the angle of tilt, which was then measured. RESULTS: Almost every anaesthetist positioned the patient less than 15 degrees because they overestimated the angle of tilt. When questioned on their knowledge of the current advice for lateral tilt, 11 of the 16 anaesthetists were aware of the 15 degrees recommendation. CONCLUSION: Estimation of the angle of table tilt is unreliable.
Effect on postoperative analgesia of small-dose lysine acetylsalicylate added to prilocaine during intravenous regional anesthesia.
Nonsteroidal antiinflammatory drugs act largely peripherally by blocking the local synthesis of prostaglandins. The aim of this study was to evaluate whether the addition of a small dose of lysine acetylsalicylate (LA) to the prilocaine used for intravenous regional anesthesia (IVRA) would improve the quality of postoperative analgesia. Sixty patients undergoing lower extremity IVRA for foot or ankle surgery were randomly assigned to three double-blind groups: LA-IVRA where 90 mg of LA was mixed with prilocaine 0.5% for IVRA and 1 mL of 0.9% NaCl administered intravenously (IV) through the forearm catheter after tourniquet inflation; LA-IV where 1 mL of 0.9% NaCl was mixed with prilocaine and 90 mg of LA administered IV; and placebo where 1 mL of 0.9% NaCl was administered both with prilocaine for the IVRA and IV. Duration of analgesia (time elapsed between tourniquet release and first injection of morphine, expressed as mean +/- SD) was significantly longer (P < 0.05) in LA-IVRA (387 +/- 216 min) when compared with LA-IV (175 +/- 264 min) and placebo (126 +/- 201 min). Analgesic requirements remained significantly lower in LA-IVRA when compared with placebo only during the first six postoperative hours, LA-IV being in an intermediate position. Pain scores were significantly lower in LA-IVRA during the first postoperative hour when compared with LA-IV and during the first 3 postoperative hours when compared with placebo. We conclude that 90 mg of LA (corresponding to 50 mg of acetylsalicylic acid) added to prilocaine 0.5% during IVRA improves the quality of postoperative analgesia in the early postoperative period.
The effects of solution concentration and epinephrine on lateral distribution of hyperbaric tetracaine spinal anesthesia.
In a search of a differential spinal block between dependent and nondependent sides, we investigated whether the use of a larger concentration of hyperbaric tetracaine (T) and/or the omission of epinephrine (E) would provide differential spread in patients left for 15 min in the lateral decubitus position. Spinal anesthesia was performed in the lateral decubitus position with the operated side dependent in 60 patients scheduled for lower limb surgery. All patients remained lateral for 15 min after spinal injection before being turned supine. They received 12 mg of T in 10% dextrose and E 0.2 mg was added when predicted duration of surgery was more than 90 min. The concentration of T to be used for each patient was randomized. This resulted in four groups of 15 patients: T 0.5% + E (control group), T 1% + E, T 0.5%, and T 1%. A unilateral anesthesia was defined as the presence of an adequate sensory (L-1 or higher) and/or motor (3 degrees) blockade on the dependent side and the absence of one or both modalities on the nondependent side, or as a duration of sensory (regression to L-2) and motor (1 degrees of recovery) blockade 20% longer on the dependent compared to the nondependent side. None of the 60 patients showed unilateral sensory block. A comparable number of patients in all groups showed unilateral motor block: four in T 0.5% + E, two in T 1% + E, four in T 0.5%, and five in T 1%. Likewise, a comparable number of patients in all groups showed a prolonged duration of sensory and motor block, respectively: six and eight in T 0.5% + E, six and nine in T 1% + E, six and eight in T 0.5%, and seven and seven in T 1%. In conclusion, although a preferential distribution of hyperbaric T toward the dependent side in patients of all four groups was noticed, the use of a larger concentration of T, omission of E, or combination of these two factors did not provide a more marked differential spread when compared to the standard solution of T 0.5% + E.
Acute right ventricular failure, pathophysiology and treatment.
Right ventricular (RV) failure is now accepted as a pathophysiological entity. This acceptance has stemmed from the increasing facility of bedside assessment of pump function using thermodilution techniques. The subsequent improvement in the assessment of RV volume changes has allowed existing theories to be confirmed. The anatomical disposition and geometry of the right ventricle allow it to adapt very well to wide variations in preload, but poorly to increases in afterload. In the presence of increased afterload, RV stroke volume decreases linearly with increasing resistance and the ventricle eventually dilates. This dilation is then responsible for further RV failure, due to decreased right coronary artery flow (from systolo-diastolic to diastolic only) at a time when myocardial oxygen consumption is increased. Furthermore, RV dilation shifts the interventricular septum to the left, decreasing left ventricular preload and, hence, the cardiac output. An often lethal vicious circle is induced. The main therapeutic goals aimed at breaking this circle are restoration of adequate oxygen delivery to the myocardium and diminution of RV afterload.
Cardiopulmonary interactions in acute lung injury: clinical and prognostic importance of pulmonary hypertension.
Development of acute lung injury (ALI) in the critically ill is associated with an array of abnormal interactions between the heart and lungs. Of these abnormalities, increased pulmonary vascular resistance (PVR) is common and seems to indicate a worse prognosis than when PVR is normal. Increased pulmonary artery pressure, which follows ALI in humans, has been attributed to many factors. Early in ALI, pulmonary artery hypertension (PAH) is secondary to an imbalance between the release of vasoactive mediators derived from arachidonic acid, endothelium-derived relaxing factor, and other metabolites. As ALI progresses, the combination of mechanical obstruction and severe regional hypoxic pulmonary artery vasoconstriction probably becomes the main factor responsible for PAH. In addition to these elements, in situ and peripherally derived thromboemboli can be seen in ALI, owing to diverse disturbances in the coagulation and fibrinolytic processes. The result is increased workload of the right ventricle which is caused by increased afterload and may induce hemodynamic disturbances that culminate in overt right ventricular failure. However, epidemiologic studies have demonstrated that death following ALI is more often the result of respiratory failure or sepsis. The absence of effective therapy for PAH in ALI might be explained by the pathophysiological and clinical course of the disease. A reasonable conclusion from the contributing elements cited above is that PAH complicating sepsis and trauma is simply a marker of the gravity of the systemic insult that leads to the development of ALI and probably not a separate process.