Frank S. Rutledge

Hematocrit modifies the circulatory control of systemic and myocardial oxygen utilization in septic sheep

ObjectiveTo describe the relationship be tween hematocrit and oxygen utilization before and ofter the onset of a hyperdynamic septic state. DesignProspective, observational study. SettingLaboratory of a large university-affiliated medical school. SubjectsThirty mature sheep, each weighing 30 to 40 kg (0.9 to 1.1 m2 body surface area). InterventionsAfter baseline measurements, cecal ligation and perforation were used to establish an intra-abdominal source of infection. The abdominal wound was closed and animals were studied on the second postoperative day. An increase in cardiac output of ≥30% was used to arbitrarily define the onset of sepsis. Repeat measurements were performed and the animal was killed. ResultsThe circulatory response to this septic insult included an increase in both cardiac index (change, baseline to sepsis, Δ +2.24 ± 0.75 L/min/m2; p <.01) and myocardial blood flows (Δ +76.4 ± 56 mL/100 g/min; p < .01). We found a negative correlation between the hematocrit and cardiac index (r2 = .21; p < .01) during the septic study, and noted that the amount (p < .01) of this correlation was significantly greater in the septic than the nonseptic study. Concurrently, the negative correlation observed between hematocrit and whole-body oxygen extraction (r2 = .21;p < .01) was significantly lower (p < .01) across the range of hematocrit values examined during the septic study vs. the similar relationship in the nonseptic study (r2 = .27;p < .01). The increase in myocardial oxygen consumption paralleled the relationship between cardiac work and hematocrit in the septic study, and was accompanied by incresases in both myocardial blood flows (r2 = .25; p < .01) and myocardial oxygen extraction (r2 = .35;p<.01). ConclusionsThe normal circulatory compensation to anemia in hyperdynamic sepsis includes increases in cardiac index and whole-body oxygen extraction, although greater reliance is likely placed on the use of systemic flow reserve to maintain tissue oxygen uptake in septic vs. healthy study conditions. Furthermore, increased reliance on myocardial oxygen extraction in sepsis suggests that the normal flow-reserve supporting myocardial oxygen availability may be limited in this syndrome. (Crit Care Med 1994; 22:470–479)

PRESSURE ULCER PREVENTION WITH LOW-AIR-LOSS BEDS. REPLY

In Reply. —Thank you for allowing us to respond to concerns expressed by Dr Verdery regarding our article, which examined the clinical utility and cost-effectiveness of an air suspension bed in the prevention of pressure ulcers. First, he was concerned about the lack of blinding in the diagnosis and categorization of stage I ulcers. As stated in our methods, blinding was impossible. Therefore, we instituted a process to minimize this bias as much as possible. Specifically, with detection and staging of a pressure ulcer by the study nurse, our hospitals skin care team was consulted. The consultant dermatologist then independently addressed the issue of presence or absence of pressure ulcers and staged them when applicable. Our interrater agreement was good (κ>0.80). Second, Verdery noted we had not mentioned whether a specific treatment protocol was instituted. The studys objective was to address prevention, not treatment. Thus, treatment of established ulcers was