Anesthesia and the cardiovascular system
Surgical procedures and anesthesia confront the cardiovascular system with a triple threat: trauma, blood loss, and depressant drugs. Trauma triggers a cascade of hormones; if that were not enough, the surgeon might constrict the vena cava, compress a lung, trigger reflexes, and handle the gut, causing sequestration of fluid in traumatized tissue. Exposed pleural and peritoneal lining lets water evaporate, not to mention blood loss and the potential of small clots. To this onslaught, anesthesia adds depressant drugs, induces ventilation/perfusion mismatches with mechanical ventilation (which turns respiratory mechanics upside-down by imposing positive pressure during inhalation), and then infuses cold solutions that are never quite the same as the real thing. Aware of all of these factors, the anesthesiologist appreciates the stresses imposed on the patient and does his or her best to keep the system as close as possible to “how Mother Nature intended it.” To that end, we must have a firm grasp of physiology. Let’s start with the most visible outward sign of the cardiovascular system: blood pressure.