Noninvasive monitoring in the patient with heart disease
Nonpolluted or noninvasive are terms that were coined to describe things we had taken for granted, not requiring a defining term. For many decades it was unnecessary to describe monitoring as noninvasive. Then invasive methods were introduced and became commonplace. But now the terms invasive and noninvasive no longer suffice since we must deal with a spectrum ranging from noninvasive to highly invasive1 with several intermediate gradations of invasiveness (Table). Only noninvasive techniques as defined here will be discussed.
Inspection is probably the oldest and most respected of noninvasive monitoring techniques. Universally observed are the traditional eye signs, capillary filling after blanching the skin, the color of the conjuctival membrane, which we check for engorgement, blanching or a blue tint secondary to venous congestion, or arterial hypoxemia. The patient with heart disease might also be checked for distension of neck veins. The novice might be surprised to see distended neck veins after induction of anesthesia even in patients without heart disease. This change is similar to the general dilatation of the veins during sleep and anesthesia and a slightly elevated right atrial pressure commonly observed with the major inhalation anesthetics. Redistribution of blood within the body that occurs with sleep and anesthesia could be observed even more clearly with the help of infrared photography, a gentle and noninvasive technique, but one not used for clinical monitoring.
One of the most important signs observed by inspection, one not easily recorded mechanically or electronically, is the pattern of respiration in a . . .