LITERATURE REVIEW Carol L. Lake, MD, Editor

Lim KH, Connolly M, Rose D, Siegman F, Jacobowitz I, Acinapura A, Cunningham JN Jr: Prevention of reperfusion injury of the ischemic spinal cord: Use of recombinant superoxide dis- mutase. Ann Thorac Surg 42:282-286, 1986

The mechanisms of paraplegia after sur- gery of the thoracic or abdominal aorta include interruption of intercostal arteries or ischemia of the spinal cord from hypotension or prolonged aortic occlusion. In the absence of anatomic disruption of circulation, agents or manuevers minimizing reperfusion injury may have poten- tial benefits. Such an agent is superoxide dismu- tase, a scavenger of the oxygen free radicals generated during ischemia that secondarily com- pound the ischemic injury. In canine experiments of aortic crossclamping for ten minutes after the immediate disappearance of somatosensory evoked potentials, superoxide dismutase, either 25,000 or 50,000 units injected intraaortically prior to declamping followed by intraaortic infu- sions of 5,000 or 10,000 U/min for ten minutes after declamping, significantly reduced the inci- dence of neurological deficit. Thus, free radical scavengers may extend the safe period of surgical aortic occlusion.

Musha H, Murayama M, Ito H et al: Estimation of autonomic nervous tone by evaluat- ing minimal hourly heart rate. Respir Circ 34:1003-1007,1986

These investigators evaluated the minimal hourly heart rate in healthy elderly and healthy young volunteers, joggers, and elderly proprano- lol-treated hypertensive subjects using Holter ECG recordings. Aging appeared to reduce both sympathetic and vagal tone, as demonstrated by a higher minimal hourly heart rate at nights in the elderly than in the young subjects, with less difference in the daytime. Vagal tone normally predominated at night and sympathetic tone during the day. Sympathetic tone in the joggers and young healthy subjects was similar, with the

lower heart rate of the joggers attributable to predominant vagal tone.

Similar findings were noted by others (de Marneffe M, Jacobs P, Haardt R, Englert M: Variations of normal sinus node function in rela- tion to age: Role of autonomic influence. Eur Heart J 7:662-672, 1986) who suggested that parasympathetic activity, predominant in the young, decreased with age to produce equilibra- tion between parasympathetic and sympathetic activity in older individuals. The intrinsic elec- trophysiological properties of the sinus node (such as the maximal corrected sinus node recov- ery time, mean sinus cycle length, and sinoatrial conduction time) decrease with aging.

Ellmauer S, Brandt L: The influence of barbiturates on the hemodynamics during extra- corporeal circulation. Thiopental vs methohexi- tal. Anaesthesist 35:414-418, 1986.

The effects of thiopental, 3 mg/kg or 6 mg/kg, were compared with methohexital, 1 or 2 mg/kg, during cardiopulmonary bypass in 40 New York Heart Association group II or III patients developing hypertension (mean arterial pressure over 80 mm Hg) during coronary artery bypass grafting. Induction and maintenance anesthetic agents included fentanyl, 0.1 mg/kg, hypnomidate, 0.1 mg/kg, pancuronium, 0.1 mg/ kg, and isoflurane. During hypothermic (28°C) bypass, administration of thiopental caused a transient increase of systemic vascular resistance (SVR) 30 seconds after injection followed by a decrease to 67% (6 mg/kg) or 56% (3 mg/kg) of control. SVR returned to control values within five minutes. Methohexital also decreased SVR but without a biphasic response.

Flancbaum L, Wright J, Siegel JH: Emer- gency surgery in patients with post-traumatic myocardial contusion. J Trauma 26795-801, 1986

Cardiac contusion demonstrates a spec- trum of abnormalities from subclinical ventricu-

./ournal of Cardiothoracic Anesthesia, Vol 1, No 2 (April), 1987: pp 17 l- 175 171