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Observations on cardiogenic shock

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MacKenzieGJ_1965_v1redux.pdf (24.92Mb)
MackenzieGJ_1965_v2redux.pdf (25.10Mb)
Date
1965
Author
Mackenzie, Gordon James
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Abstract
 
 
The circulatory, arterial blood gas tension and metabolic changes following acute myocardial infarction have been studied serially in patients with and without cardiogenic shock. The effects of oxygen administration on these changes has been investigated. Follow-up studies have been undertaken following recovery from shock and at various stages of convalescence in most patients. Cardiogenic shock has been shown to be associated with a severe impairment of left ventricular function with a reduced cardiac output and markedly reduced stroke volume* an elevated central venous pressure and an inadequate compensatory increase in systemic vascular resistance. These circulatory changes were accompanied by a very considerable degree of arterial blood hypoxaemia, as well as a metabolic acidosis, lactic acidaemia and hyperglycaemia. In uncomplicated acute myocardial infarction the circulatory changes were found to be highly variable. The cardiac output and stroke volume varied from normal to very low values. The systemic vascular resistance varied between high and low values, resulting in the maintenance of the blood pressure at moderate to normal levels. Uncomplicated acute myocardial infarction was accompanied by only a mild degree of arterial blood hypoxaemia and a complete lack of metabolic disturbance. The patients without shock showed a normal rise in arterial blood oxygen tension when breathing oxygen. In contrast, those with shock showed a relatively small increase of arterial blood oxygen tension following oxygen therapy. This impaired response has been shown to be due to the shunting of about 25% of the cardiac output through vessels inaccessible to pulmonary gas exchange. These patients are therefore in urgent need of oxygen and this must be given in as high a concentration as possible. The circulatory effects of oxygen therapy in patients with uncomplicated myocardial infarction are similar to those found in normal subjects - that is, a fall in heart rate and cardiac output with a slight increase in systemic vascular resistance and arterial blood pressure. It is possible that the poor and variable response of arterial blood oxygenation in cases of cardiogenic shock accounts for the less marked and equally variable circulatory response to such therapy. Recovery from cardiogenic shock was found to be associated with a reduction in tachycardia and central venous pressure with an increase in blood pressure* stroke volume and cardiac output and only small variable changes in systemic vascular resistance. The arterial hypoxacmia, metaoolic acidosis and lactic acicaemia progressively declined with recovery. Progressive recovery from uncomplicated acute myocardial infarction was associated with a reduction in central venous pressure and an increase in strrke volume. There was a progressive increase in the arterial blood oxygen tension levels towards normal with increasing recovery. The pathophysiological and therapeutic implications of these findings are discussed.
 
URI
http://hdl.handle.net/1842/35048
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