Colloid Supplementation during Induction of Anesthesia

Abstract

The present paper puts forward the hypothesis that infusion of colloid during induction will prevent the development of an oxygen debt. The reasoning behind this hypothesis depends on there being a drop in venous tone during induction, as a result of reduced sympathetic drive. The resulting venous relaxation leads to blood volume loss from the arterial side of the circulation into the venous side. The loss of arterial volume is responsible for the reduction in arterial blood pressure. The lowered value of Mean Arterial Pressure (MAP) results in a fall in Cardiac Output (CO) below normal, in the face of little if any change in Systemic Vascular Resistance (SVR). Most clinical assessments to date have emphasised changes in Stroke Volume (SV), whereas the fall in CO is the important variable since it determines Oxygen Delivery to the tissues (DO 2 ). When DO 2 is lower than normal it is responsible for the development of oxygen debt, and this is the main reason for development of the complications commonly found following anesthesia. The present hypothesis is that addition of carefully titrated colloid fluid during induction can be scaled to reduce or prevent the fall in MAP and CO. Although this means the presence of extra fluid in the circulation previous work suggests this will be eliminated readily during recovery. An alternative, giving phenylephrine over the induction period reduces the anesthetic induced venous wall relaxation. Phenylephrine is already being utilised successfully and is likely to be a useful adjunct to colloid supplementation. By maintaining normal or near normal pressure, as assessed prior to induction, and hence sustaining normal blood flow, normal DO 2 will be sustained. Avoidance of an oxygen debt should reduce or even eliminate the complications which result from tissue ischaemia during anesthesia. Vasopressor administration may raise arterial pressure but will worsen the cardiac output and hence increase oxygen debt.

A New Radically Improved Model of the Circulation With Important Clinical Implications

“…The consistent finding during anaesthetic induction of a fall in arterial blood pressure has recently been attributed to a drug induced reduction in venous tone [50,51]. The reasoning given is that with induction of anesthesia an increase occurs in the variation of stroke volume and pulse pressure indicating volume responsiveness due to venous relaxation and not loss of volume.…”

Comparison of efficacy and safety of preemptive infusion protocols of ephedrine and phenylephrine - prevention of hypotension and effects on hemodynamic parameters during spinal anesthesia for caesarean section

“…Acute hypotension reduces cerebral perfusion, which leads to transient ischemia and activates the vomiting center [3][4][5][6]. Fall in CO reduces oxygen delivery to organs and tissues, results in buildup of oxygen debt, causing complications after SA [7,8,9]. Other side effects of hypotension during SA are nausea, vomiting, dizziness, respiratory problems, and fetal acidosis [10,11].…”

Hypertension: A Problem of Organ Blood Flow supply–demand Mismatch

“…Such structures also bring about blood flow homeostasis during stress, hyperosmolarity, emotion, fear and anxiety. In physiological conditions, the aforementioned homeostatic mechanisms will distribute blood flow, and hence oxygen, to organs in proportion to their metabolic demand, which is precisely controlled [ 1 ]. Normally, oxygen delivery exceeds the rate of oxygen consumption (demand) safeguarding capacity within each organ, which can be tapped into as a change in state demands [ 1 ].…”

“…In physiological conditions, the aforementioned homeostatic mechanisms will distribute blood flow, and hence oxygen, to organs in proportion to their metabolic demand, which is precisely controlled [ 1 ]. Normally, oxygen delivery exceeds the rate of oxygen consumption (demand) safeguarding capacity within each organ, which can be tapped into as a change in state demands [ 1 ]. For example, upon ascending to high altitude or during exercise, blood flow is increased to maintain a preferred supply/demand ratio [ 1 ].…”

“…Normally, oxygen delivery exceeds the rate of oxygen consumption (demand) safeguarding capacity within each organ, which can be tapped into as a change in state demands [ 1 ]. For example, upon ascending to high altitude or during exercise, blood flow is increased to maintain a preferred supply/demand ratio [ 1 ]. However, if demand outstrips supply (i.e., a blood flow supply–demand mismatch), then hypoxic-hypoperfusion results.…”