Supplemental intravenous crystalloid administration does not reduce the risk of surgical wound infection

Wound perfusion and oxygenation are important determinants of the development of postoperative wound infections. Supplemental fluid administration significantly increases tissue oxygenation in surrogate wounds in the subcutaneous tissue of the upper arm in perioperative surgical patients. We tested the hypothesis that supplemental fluid administration during and after elective colon resections decreases the incidence of postoperative wound infections. Patients undergoing open colon resection were randomly assigned to small-volume (n = 124, 8 mL.kg(-1).h(-1)) or large-volume (n = 129, 16-18 mL.kg(-1).h(-1)) fluid management. Our major outcomes were two distinct criteria for diagnosis of surgical wound infections: 1) purulent exudate combined with a culture positive for pathogenic bacteria, and 2) Center for Disease Control criteria for diagnosis of surgical wound infections. All wound infections diagnosed using either criterion by a blinded observer in the 15 days after surgery were considered in the analysis. Wound healing was evaluated with the ASEPSIS scoring system. Of the patients given small fluid administration, 14 had surgical wound infections; 11 given large fluid therapy had infections, P = 0.46. ASEPSIS wound-healing scores were similar in both groups: 7 +/- 16 (small volume) versus 8 +/- 14 (large volume), P = 0.70. Our results suggest that supplemental hydration in the range tested does not impact wound infection rate.     

Mild hypercapnia increases subcutaneous and colonic oxygen tension in patients given 80% inspired oxygen during abdominal surgery

BACKGROUND: Supplemental perioperative oxygen increases tissue oxygen tension and decreases incidence of wound infection in colorectal surgery patients. Mild intraoperative hypercapnia also increases subcutaneous tissue oxygen tension. However, the effect of hypercapnia in patients already receiving supplemental oxygen is unknown, as is the effect of mild hypercapnia on intestinal oxygenation in humans-although the intestines are presumably the tissue of interest for colon surgeries. The authors tested the hypothesis that mild intraoperative hypercapnia increases both subcutaneous tissue and intramural intestinal oxygen tension in patients given supplemental oxygen. METHODS: Patients undergoing elective colon resection were randomly assigned to normocapnia (n = 15, end-tidal carbon dioxide tension 35 mmHg) or mild hypercapnia (n = 15, end-tidal carbon dioxide tension 50 mmHg). Intraoperative inspired oxygen concentration was 80%. The authors measured subcutaneous tissue oxygen tension in the right upper arm and intramural oxygen tension in the left colon. Measurements were averaged over time within each patient and, subsequently, among patients. Data were compared with chi-square, unpaired t, or Mann-Whitney rank sum tests; P < 0.05 was significant. RESULTS: Morphometric characteristics and other possible confounding factors were similar in the groups. Intraoperative tissue oxygen tension in hypercapnic patients was significantly greater in the arm (mean +/- SD: 116 +/- 29 mmHg vs. 84 +/- 25 mmHg; P = 0.006) and colon (median [interquartile range]: 107 [81-129] vs. 53 [41-104] mmHg; P = 0.020). CONCLUSIONS: During supplemental oxygen administration, mild intraoperative hypercapnia increased tissue oxygen tension in the arm and colon. Previous work suggests that improved tissue oxygenation will reduce infection risk via the proposed pathomechanism, although only an outcome study can confirm this.     

Obesity decreases perioperative tissue oxygenation

BACKGROUND: Obesity is an important risk factor for surgical site infections. The incidence of surgical wound infections is directly related to tissue perfusion and oxygenation. Fat tissue mass expands without a concomitant increase in blood flow per cell, which might result in a relative hypoperfusion with decreased tissue oxygenation. Consequently, the authors tested the hypotheses that perioperative tissue oxygen tension is reduced in obese surgical patients. Furthermore, they compared the effect of supplemental oxygen administration on tissue oxygenation in obese and nonobese patients. METHODS: Forty-six patients undergoing major abdominal surgery were assigned to one of two groups according to their body mass index: body mass index less than 30 kg/m2 (nonobese) or 30 kg/m2 or greater (obese). Intraoperative oxygen administration was adjusted to arterial oxygen tensions of approximately 150 mmHg and approximately 300 mmHg in random order. Anesthesia technique and perioperative fluid management were standardized. Subcutaneous tissue oxygen tension was measured with a polarographic electrode positioned within a subcutaneous tonometer in the lateral upper arm during surgery, in the recovery room, and on the first postoperative day. Postoperative tissue oxygen was also measured adjacent to the wound. Data were compared with unpaired two-tailed t tests and Wilcoxon rank sum test; P < 0.05 was considered statistically significant. RESULTS: Intraoperative subcutaneous tissue oxygen tension was significantly less in the obese patients at baseline (36 vs. 57 mmHg; P = 0.002) and with supplemental oxygen administration (47 vs. 76 mmHg; P = 0.014). Immediate postoperative tissue oxygen tension was also significantly less in subcutaneous tissue of the upper arm (43 vs. 54 mmHg; P = 0.011) as well as near the incision (42 vs. 62 mmHg; P = 0.012) in obese patients. In contrast, tissue oxygen tension was comparable in each group on the first postoperative morning. CONCLUSION: Wound and tissue hypoxia were common in obese patients in the perioperative period and most pronounced during surgery. Even with supplemental oxygen tissue, oxygen tension in obese patients was reduced to levels that are associated with a substantial increase in infection risk.     

Mild Hypercapnia Increases Subcutaneous and Colonic Oxygen Tension in Patients Given 80% Inspired Oxygen during Abdominal Surgery

Background: Supplemental perioperative oxygen increases tissue oxygen tension and decreases incidence of wound infection in colorectal surgery patients. Mild intraoperative hypercapnia also increases subcutaneous tissue oxygen tension. However, the effect of hypercapnia in patients already receiving supplemental oxygen is unknown, as is the effect of mild hypercapnia on intestinal oxygenation in humans-although the intestines are presumably the tissue of interest for colon surgeries. The authors tested the hypothesis that mild intraoperative hypercapnia increases both subcutaneous tissue and intramural intestinal oxygen tension in patients given supplemental oxygen.

Methods: Patients undergoing elective colon resection were randomly assigned to normocapnia (n = 15, end-tidal carbon dioxide tension 35 mmHg) or mild hypercapnia (n = 15, end-tidal carbon dioxide tension 50 mmHg). Intraoperative inspired oxygen concentration was 80%. The authors measured subcutaneous tissue oxygen tension in the right upper arm and intramural oxygen tension in the left colon. Measurements were averaged over time within each patient and, subsequently, among patients. Data were compared with chi-square, unpaired t, or Mann-Whitney rank sum tests; P < 0.05 was significant.

Results: Morphometric characteristics and other possible confounding factors were similar in the groups. Intraoperative tissue oxygen tension in hypercapnic patients was significantly greater in the arm (mean +/- SD: 116 +/- 29 mmHg vs. 84 +/- 25 mmHg; P = 0.006) and colon (median [interquartile range]: 107 [81-129] vs. 53 [41-104] mmHg; P = 0.020).     

The influence of 2 surgical bandage systems on wound tissue oxygen tension

HYPOTHESIS: Local wound heating improves tissue oxygen tension in postoperative patients. SETTING: University hospital. PATIENTS: Forty normothermic and well-hydrated patients recovering from elective open abdominal surgery. INTERVENTIONS: A comparison between an experimental bandage system (Warm-Up; Augustine Medical Inc, Eden Prairie, Minn) and conventional gauze covered with elastic adhesive (Medipore Dress-it; 3M, St Paul, Minn). The experimental system is heated to 38 degrees C and does not touch the wound. MAIN OUTCOME MEASURES: Subcutaneous tissue oxygen tension was measured postoperatively and on the first postoperative day. In a subgroup, we also evaluated the effects of bandage pressure per se on tissue oxygen. RESULTS: Initial postoperative tissue oxygen tensions were approximately 30 mm Hg greater with the experimental bandage, even before warming. Subcutaneous oxygen tension during heating remained significantly greater in patients with the warmed bandage than the conventional elastic bandage (116 +/- 40 vs 85 +/- 34 mm Hg, respectively) while the patients were breathing approximately 50% oxygen. The difference was smaller on the first postoperative day, but still statistically significant (82 +/- 30 vs 65 +/- 22 mm Hg, respectively). In the subgroup analysis, tissue oxygen tension increased significantly by 12 +/- 4 mm Hg when the heating bandage was substituted for a conventional bandage (P<.001). CONCLUSION: In normothermic and well-hydrated surgical patients, much benefit from the heating bandage system appears to result from pressure relief. These data suggest that relieving wound pressure markedly improves tissue perfusion and oxygenation.     

Postoperative wound oxygen tension with epidural or intravenous analgesia: a prospective,randomized, single-blind clinical trial

BACKGROUND: Adequate tissue oxygen tension is an essential requirement for surgical-wound healing. The authors tested the hypothesis that epidural anesthesia and analgesia increases wound tissue oxygen tension compared with intravenous morphine analgesia. METHODS: In a prospective, randomized, blind clinical study, the authors allocated patients having major abdominal surgery (n = 32) to receive combined general and epidural anesthesia with postoperative patient-controlled epidural analgesia (epidural group, n = 16), or general anesthesia alone with postoperative patient-controlled intravenous analgesia (intravenous group, n = 16). An oxygen sensor and a temperature sensor were placed subcutaneously in the wound before closure. Wound oxygen tension (P(w)O(2)) and temperature were measured continuously for 24 h. Other variables affecting wound tissue oxygenation and visual analogue scale (VAS) pain scores were also documented. RESULTS: Despite epidural patients having lower body temperatures at the end of surgery (35.7 +/- 0.3) versus 36.3 +/- 0.5 degrees C, = 0.004), they had significantly higher mean P(w)O(2) over the 24 h period, compared with the intravenous group (64.4 +/- 14 vs. 50.7 +/- 15) mmHg, mean (SD), 95% CI difference, -22 to -5, = 0.002). Area under the P(w)O(2) -24 h time curve was also significantly higher in the epidural group (930 +/- 278 vs. 749 +/- 257) mmHg x h, 95% CI difference -344 to -18, = 0.03). VAS pain scores at rest and moving were significantly lower in the epidural group at all times. CONCLUSION: Epidural anesthesia and postoperative analgesia for major abdominal surgery increases wound tissue oxygen tension compared with general anesthesia and intravenous morphine analgesia.     

Supplemental oxygen and carbon dioxide each increase subcutaneous and intestinal intramural oxygenation

Oxidative killing by neutrophils, a primary defense against surgical pathogens, is directly related to tissue oxygenation. We tested the hypothesis that supplemental inspired oxygen or mild hypercapnia (end-tidal PCO2 of 50 mm Hg) improves intestinal oxygenation. Pigs (25 +/- 2.5 kg) were used in 2 studies in random order: 1) Oxygen Study: 30% versus 100% inspired oxygen concentration at an end-tidal PCO2 of 40 mm Hg, and 2) Carbon Dioxide Study: end-tidal PCO2 of 30 mm Hg versus 50 mm Hg with 30% oxygen. Within each study, treatment order was randomized. Treatments were maintained for 1.5 h; measurements were averaged over the final hour. A tonometer inserted in the subcutaneous tissue of the left upper foreleg measured subcutaneous oxygen tension. Tonometers inserted into the intestinal wall measured intestinal intramural oxygen tension from the small and large intestines. Oxygen 100% administration doubled subcutaneous oxygen partial pressure (PO2) (57 +/- 10 to 107 +/- 48 mm Hg, P = 0.006) and large intestine intramural PO2 (53 +/- 14 to 118 +/- 72 mm Hg, P = 0.014); intramural PO2 increased 40% in the small intestine (37 +/- 10 to 52 +/- 25 mm Hg, P = 0.004). An end-tidal PCO2 of 50 mm Hg increased large intestinal PO2 approximately 16% (49 +/- 10 to 57 +/- 12 mm Hg, P = 0.039), whereas intramural PO2 increased by 45% in the small intestine (31 +/- 12 to 44 +/- 16 mm Hg, P = 0.002). Supplemental oxygen and mild hypercapnia each increased subcutaneous and intramural tissue PO2, with supplemental oxygen being most effective.     

Postoperative Wound Oxygen Tension with Epidural or Intravenous Analgesia: A Prospective, Randomized, Single-blind Clinical Trial

Background: Adequate tissue oxygen tension is an essential requirement for surgical-wound healing. The authors tested the hypothesis that epidural anesthesia and analgesia increases wound tissue oxygen tension compared with intravenous morphine analgesia.

Methods: In a prospective, randomized, blind clinical study, the authors allocated patients having major abdominal surgery (n = 32) to receive combined general and epidural anesthesia with postoperative patient-controlled epidural analgesia (epidural group, n = 16), or general anesthesia alone with postoperative patient-controlled intravenous analgesia (intravenous group, n = 16). An oxygen sensor and a temperature sensor were placed subcutaneously in the wound before closure. Wound oxygen tension (Pwo2) and temperature were measured continuously for 24 h. Other variables affecting wound tissue oxygenation and visual analogue scale (VAS) pain scores were also documented.

Results: Despite epidural patients having lower body temperatures at the end of surgery (35.7 +/- 0.3) versus 36.3 +/- 0.5 [degrees]C, P = 0.004), they had significantly higher mean Pwo2 over the 24 h period, compared with the intravenous group (64.4 +/- 14 vs. 50.7 +/- 15) mmHg, mean (SD), 95% CI difference, -22 to -5, P = 0.002). Area under the Pwo2 -24 h time curve was also significantly higher in the epidural group (930 +/- 278 vs. 749 +/- 257) mmHg x h, 95% CI difference -344 to -18, P = 0.03). VAS pain scores at rest and moving were significantly lower in the epidural group at all times.     

Obesity Decreases Perioperative Tissue Oxygenation

Background: Obesity is an important risk factor for surgical site infections. The incidence of surgical wound infections is directly related to tissue perfusion and oxygenation. Fat tissue mass expands without a concomitant increase in blood flow per cell, which might result in a relative hypoperfusion with decreased tissue oxygenation. Consequently, the authors tested the hypotheses that perioperative tissue oxygen tension is reduced in obese surgical patients. Furthermore, they compared the effect of supplemental oxygen administration on tissue oxygenation in obese and nonobese patients.

Methods: Forty-six patients undergoing major abdominal surgery were assigned to one of two groups according to their body mass index: body mass index less than 30 kg/m2 (nonobese) or 30 kg/m2 or greater (obese). Intraoperative oxygen administration was adjusted to arterial oxygen tensions of approximately 150 mmHg and approximately 300 mmHg in random order. Anesthesia technique and perioperative fluid management were standardized. Subcutaneous tissue oxygen tension was measured with a polarographic electrode positioned within a subcutaneous tonometer in the lateral upper arm during surgery, in the recovery room, and on the first postoperative day. Postoperative tissue oxygen was also measured adjacent to the wound. Data were compared with unpaired two-tailed t tests and Wilcoxon rank sum test; P < 0.05 was considered statistically significant.

Results: Intraoperative subcutaneous tissue oxygen tension was significantly less in the obese patients at baseline (36 vs. 57 mmHg; P = 0.002) and with supplemental oxygen administration (47 vs. 76 mmHg; P = 0.014). Immediate postoperative tissue oxygen tension was also significantly less in subcutaneous tissue of the upper arm (43 vs. 54 mmHg; P = 0.011) as well as near the incision (42 vs. 62 mmHg; P = 0.012) in obese patients. In contrast, tissue oxygen tension was comparable in each group on the first postoperative morning.     

Tissue oxygen tension during regional low-flow perfusion in neonates

OBJECTIVE: We examined cerebral cortical and peripheral organ tissue Po(2) values in a neonatal piglet model of regional low-flow perfusion. METHODS: Twenty-one neonatal piglets were placed on cardiopulmonary bypass, were cooled to 18 degrees C, then underwent either deep hypothermic circulatory arrest or regional low-flow perfusion at 20 or 40 mL/(kg x min) for 90 minutes. Regional low-flow perfusion was carried out by advancing the aortic cannula into the proximal innominate artery. Tissue mean Po(2) and Po(2) distribution were measured in the cerebral cortex, liver, small bowel, and skeletal muscle through the principle of oxygen-dependent quenching of phosphorescence. Measured quantities were compared by analysis of variance or the Fisher exact test. RESULTS: During regional low-flow perfusion, axillary and femoral arterial pressures, respectively, were 55 +/- 15 and 8 +/- 4 mm Hg at 40 mL/(kg x min) and 37 +/- 10 mm Hg (P =.04) and 17 +/- 5 mm Hg (P =.08) at 20 mL/(kg x min). Venous saturations were 95% +/- 6% at 40 mL/(kg x min) and 84% +/- 6% at 20 mL/(kg x min) (P =.03 at 15, 30, and 45 minutes). Cortical Po(2) was similar to prebypass values during regional low-flow perfusion at 40 mL/(kg x min) (53 +/- 5 mm Hg) but declined during reperfusion and recovery. Cortical Po(2) was lower than before bypass during low-flow perfusion at 20 mL/(kg x min) (38 +/- 7 mm Hg) but increased during reperfusion. Po(2) in liver and bowel was less than 10 mm Hg during low-flow perfusion at both 20 and 40 mL/(kg x min). Fraction of oxygen distribution with Po(2) lower than 15 mm Hg was less during perfusion at 40 mL/(kg x min) than at 20 mL/(kg x min) (P =.001). Three of 6 piglets that received a 40-mL/(kg x min) flow rate had significant upper torso edema, metabolic acidosis, and an unstable recovery period, whereas zero of 6 piglets that received a 20-mL/(kg x min) flow rate did. CONCLUSIONS: In a piglet model, regional low-flow perfusion at 20 mL/(kg x min) resulted in lower cortical tissue oxygenation but better recovery than did perfusion at 40 mL/(kg x min). Neither flow rate adequately oxygenated organs in the lower torso.     

Thoracic epidural anesthesia increases tissue oxygenation during major abdominal surgery

Intraoperative surgical stress may markedly increase adrenergic nerve activity and plasma catecholamine concentrations, which causes peripheral vasoconstriction and decreased tissue oxygen partial pressure possibly leading to tissue hypoxia. Tissue hypoxia is associated with an increased incidence of surgical wound infections. Thoracic epidural anesthesia blocks afferent neural stimuli and inhibits efferent sympathetic outflow in response to painful stimuli. Consequently, we tested the hypothesis that supplemental thoracic epidural anesthesia during major abdominal surgery improves tissue perfusion and subcutaneous oxygen tension. Thirty patients were randomly assigned to two groups: general (n = 15) or combined general and epidural anesthesia (n = 15). Anesthesia technique and fluid management were standardized. Subcutaneous tissue oxygen tension was measured continuously in the upper arm with a Clark type electrode. Data were compared with unpaired, two-tailed t-tests, Wilcoxon's ranked sum test, or repeated-measures analysis of variance and Scheffé F tests as appropriate; P < 0.05 was considered statistically significant. After 60 min, intraoperative tissue oxygen tension was significantly larger during combined anesthesia than during general anesthesia (54.3 +/- 7.4 mm Hg versus 42.1 +/- 8.6 mm Hg; P = 0.0002). Subcutaneous tissue oxygen tension remained significantly higher in the combined general/epidural anesthesia group throughout the observation period. Hemodynamic responses and global oxygen variables were similar in the groups. Thoracic epidural anesthesia improved intraoperative tissue oxygen tension outside the area of the epidural block. Thus, our results give evidence that supplemental neural nociceptive block blunts generalized vasoconstriction caused by surgical stress and adrenergic responses. IMPLICATIONS: Thoracic epidural anesthesia blunts the decrease of subcutaneous tissue oxygen tension caused by surgical stress and adrenergic vasoconstriction during major abdominal surgery. Consequently, combined general and epidural anesthesia helps to provide sufficient tissue oxygenation.     

Modified Glenn connection for acutely ischemic right ventricular failure reverses secondary left ventricular dysfunction.

BACKGROUND: Right heart failure after cardiopulmonary bypass can result in severe hemodynamic compromise with high mortality, but the underlying mechanisms remain poorly understood. After ischemia-induced right ventricular failure, alterations in the interventricular septal position decrease left ventricular compliance and limit filling but may also distort left ventricular geometry and compromise contractility and relaxation. This study investigated the effect of acute isolated right ventricular ischemia on biventricular performance and interaction and the response of subsequent right ventricular unloading by use of a modified Glenn shunt. METHODS: In 8 pigs isolated right ventricular ischemic failure was induced by means of selective coronary ligation. A modified Glenn circuit was then established by a superior vena cava-pulmonary artery connection. Ventricular performance was determined by conductance catheter-derived right ventricular pressure-volume loops and left ventricular pressure-segment length loops. Hemodynamic data at baseline, after right ventricular ischemia, and after institution of the Glenn circuit were obtained during inflow occlusion, and the load-independent contractile indices were derived. RESULTS: Right ventricular free-wall ischemia resulted in acute right ventricular dilation (118 +/- 81 mL vs 169 +/- 70 mL, P =.0008) and impairment of left ventricular contractility indicated by the reduced end-systolic pressure-volume relation slope (50.0 +/- 19 mm Hg/mm vs 18.9 +/- 8 mm Hg/mm, P =.002) and preload recruitable stroke work index slope (69.6 +/- 26 erg x cm(-3) x 10(3) vs 39.7 +/- 13 erg x cm(-3) x 10(3), P =.003). In addition, left ventricular relaxation (tau) was significantly prolonged (33.3 +/- 10 ms vs 53.0 +/- 16 ms, P =.012). Right ventricular unloading with the Glenn shunt reduced right ventricular dilation and significantly improved left ventricular contraction, end-systolic pressure-volume relation slope (18.9 +/- 8 mm Hg/mm vs 35.8 +/- 18 mm Hg/mm, P =.002), preload recruitable stroke work index slope (39.7 +/- 26 erg x cm(-3) x 10(3) vs 63.0 +/- 22 erg x cm(-3) x 10(3), P =.003), and diastolic performance (tau 53.0 +/- 16 ms vs 43.5 +/- 13 ms, P =.001). CONCLUSIONS: Right ventricular ischemia-induced dilation resulted in acute impairment of left ventricular contractility and relaxation. A modified Glenn shunt attenuated the left ventricular dysfunction by limiting right ventricular dilation and restoring left ventricular cavity geometry.     

Ethyl pyruvate preserves cardiac function and attenuates oxidative injury after prolonged myocardial ischemia

OBJECTIVE: Myocardial injury and dysfunction following ischemia are mediated in part by reactive oxygen species. Pyruvate, a key glycolytic intermediary, is an effective free radical scavenger but unfortunately is limited by aqueous instability. The ester derivative, ethyl pyruvate, is stable in solution and should function as an antioxidant and energy precursor. This study sought to evaluate ethyl pyruvate as a myocardial protective agent in a rat model of ischemia-reperfusion injury. METHODS: Rats underwent 30-minute ischemia and 30-minute reperfusion of the left anterior descending coronary artery territory. Immediately prior to both ischemia and reperfusion, animals received an intravenous bolus of either ethyl pyruvate (n = 26) or vehicle control (n = 26). Myocardial high-energy phosphate levels were determined by adenosine triphosphate assay, oxidative injury was measured by lipid peroxidation assay, infarct size was quantified by triphenyltetrazolium chloride staining, and cardiac function was assessed in vivo. RESULTS: Ethyl pyruvate administration significantly increased myocardial adenosine triphosphate levels compared with control (87.6 +/- 29.2 nmol/g vs 10.0 +/- 2.4 nmol/g, P =.03). In ischemic myocardium, ethyl pyruvate reduced oxidative injury compared with control (63.8 +/- 3.3 nmol/g vs 89.5 +/- 3.0 nmol/g, P <.001). Ethyl pyruvate diminished infarct size as a percentage of area at risk (25.3% +/- 1.5% vs 33.6% +/- 2.1%, P =.005). Ethyl pyruvate improved myocardial function compared with control (maximum pressure: 86.6 +/- 2.9 mm Hg vs 73.5 +/- 2.5 mm Hg, P <.001; maximum rate of pressure rise: 3518 +/- 243 mm Hg/s vs 2703 +/- 175 mm Hg/s, P =.005; maximal rate of ventricular systolic volume ejection: 3097 +/- 479 microL/s vs 2120 +/- 287 microL/s, P =.04; ejection fraction: 41.9% +/- 3.8% vs 31.4% +/- 4.1%, P =.03; cardiac output: 26.7 +/- 0.9 mL/min vs 22.7 +/- 1.3 mL/min, P =.01; and end-systolic pressure-volume relationship slope: 1.09 +/- 0.22 vs 0.59 +/- 0.2, P =.02). CONCLUSIONS: In this study of myocardial ischemia-reperfusion injury, ethyl pyruvate enhanced myocardial adenosine triphosphate levels, attenuated myocardial oxidative injury, decreased infarct size, and preserved cardiac function.     

Hypercapnia improves tissue oxygenation in morbidly obese surgical patients

Risk of wound infection is increased in morbidly obese surgical patients, in part because a major determinant of wound infection risk, tissue oxygenation, is marginal. Unlike in lean patients, supplemental inspired oxygen (Fio2) only slightly improves tissue oxygenation in obese patients. Mild hypercapnia improves tissue oxygenation in lean patients but has not been evaluated in obese patients. We thus tested the hypothesis that mild hypercapnia markedly improves tissue oxygenation in morbidly obese patients given Fio2 80% during major abdominal surgery. Thirty obese patients (body mass index 61.5 +/- 17 kg/m2) scheduled for open gastric bypass were randomly assigned to normocapnia (n = 15, end-tidal Pco2 35 mm Hg) or hypercapnia (n = 15, end-tidal Pco2 50 mm Hg); Fio2 was 80%. Anesthetic management and other confounding factors were controlled. Tissue oxygen tension was measured subcutaneously at the upper arm using a polarographic probe in a silastic tonometer. Demographic characteristics, cardiovascular measurements, and Pao2 (222 +/- 48 versus 230 +/- 68 mm Hg in normocapnic versus hypercapnic; mean +/- sd; P = 0.705) were comparable in the groups. Tissue oxygen tension, however, was greater in hypercapnic than in normocapnic patients (78 +/- 31 versus 56 +/- 13 mm Hg; P = 0.029). Mild hypercapnia increased tissue oxygenation by an amount believed to be clinically important and could potentially reduce the risk of surgical wound infection in morbidly obese patients.     

Better preservation of endothelial function and decreased activation of the fetal renin-angiotensin pathway with the use of pulsatile flow during experimental fetal bypass

OBJECTIVE: Pulsatile flow was shown to overcome the progressive rise in peripheral and placental vascular resistances observed during steady-flow bypass, this rise being counteracted by inhibition of nitric oxide synthase. This study quantifies the release of endothelial vasoactive substances during a 60-minute in utero model of fetal bypass. METHODS: Fetuses were randomly allocated into 1 of 2 groups (steady flow, n = 8, or pulsatile flow, n = 13) and subjected to bypass through central cannulation and perfusion with either a centrifugal or pulsatile (125 beats x min(-1)) blood pump. RESULTS: Lactate concentration was high, starting at fetal exteriorization and increasing during fetal preparation in the 2 groups. Once bypass was established, the rise was significant only in the steady-flow group. Plasma nitric oxide metabolites, similar before bypass, reached higher levels during pulsatile flow at the end of bypass (99+/-9 vs. 82+/-23 micromol x L(-1); P =.037). Levels of urinary nitric oxide metabolites were significantly higher in the pulsatile-flow than in the steady-flow group (764+/-143 vs. 508+/-240 micromol x L(-1); P =.005). Plasma cyclic guanosine monophosphate levels increased after 30 minutes of bypass in the pulsatile-flow group (25+/-18 vs. 12+/-8 pmol x mL(-1); P =.004), and urinary cyclic guanosine monophosphate excretion was higher in the pulsatile-flow group (517+/-450 vs. 118+/-78 pmol x mL(-1); P =.024). Plasma endothelin-1 levels increased in the 2 groups and were higher in the steady-flow group at 30 minutes (27+/-5 vs. 23+/-2 pg x mL(-1); P =.04) and 60 minutes of bypass (39+/-7 vs 32 +/- 6 pg x mL(-1); P =.04). Plasma renin concentration increased significantly during bypass only in the steady-flow group (26+/-10 vs. 57+/-42 in ng A1 x mL(-1) x h(-1); P =.04). CONCLUSIONS: Improved placental and peripheral perfusion during fetal pulsatile-flow bypass may be mediated by preservation of fetal/maternal endothelial nitric oxide biosynthetic mechanisms and/or decreased activation of the fetal renin-angiotensin pathway.     

The effects of epidural and general anesthesia on tissue oxygenation

The risk of wound infections is inversely related to subcutaneous tissue oxygen tension. General anesthesia increases local blood flow by direct vasodilation and central inhibition of thermoregulatory vasoconstriction. Epidural anesthesia can increase perfusion in blocked regions by decreasing sympathetic tone. We therefore tested the hypothesis that epidural anesthesia increases tissue oxygen tension in awake and anesthetized subjects. Fifteen healthy volunteers underwent epidural, general, and combined epidural and general anesthesia. Subcutaneous tissue oxygen tension was measured using tonometers in the lateral upper arm and the lateral thigh. Epidural anesthesia to a T10 level was maintained with 0.75% mepivacaine. General anesthesia was maintained with 1.5% sevoflurane in 30% oxygen; 30% inspired oxygen was given via a sealed facemask during baseline and epidural anesthesia. Baseline subcutaneous tissue oxygen tensions for arm and thigh were 57 +/- 11 and 54 +/- 8 mm Hg, respectively. Epidural anesthesia significantly increased tissue oxygenation in the thigh by 9 mm Hg, to 63 +/- 7 mm Hg, without increasing arm oxygenation. Tissue oxygenation in the arm and thigh were similar during general anesthesia alone, 58 +/- 11 and 63 +/- 12 mm Hg. Arm oxygenation remained unchanged with the addition of epidural anesthesia; however, thigh subcutaneous oxygen partial pressure increased 8 +/- 3 mm Hg, from 63 +/- 12 to 71 +/- 9 mm Hg. Although epidural anesthesia increased tissue oxygenation significantly with and without general anesthesia, the magnitude of this increase might be of marginal clinical importance in regard to surgical wound infections. IMPLICATIONS: Epidural anesthesia significantly increased subcutaneous tissue oxygenation in the thigh both with and without general anesthesia. Although each increase was statistically significant, previous work suggests that the magnitude of these changes is unlikely to markedly reduce the risk of surgical wound infection.     

Intraoperative tissue oximetry in the human gastrointestinal tract

Tissue oxygen tension was measured using a modified Clark oxygen electrode in the gastrointestinal tract of 33 patients undergoing laparatomy. The electrode, which incorporated a thermistor, had a linear response to oxygen tension (r = 0.995, p less than 0.001). The patients were all maintained on an inspired oxygen concentration of 33 +/- 3% and had a mean arterial oxygen tension (PaO2) of 124.9 +/- 31.9 mm Hg. Tissue oxygen tension measurements (mm Hg, mean +/- SD) were recorded from the serosal surfaces of the stomach (46.3 +/- 15.4), mid-ileum (36 +/- 9.7), terminal ileum (33.5 +/- 11.5), cecum (30.3 +/- 7.4), transverse colon (38.5 +/- 10), descending colon (29.3 +/- 11), and sigmoid colon (39.2 +/- 7.7) and tended to increase with increasing PaO2 (r = 0.70, p less than 0.001). Arterial occlusion resulted in a gradual decrease in tissue oxygen tension. It is concluded that intraoperative tissue oxygen tension measurement is feasible, and that the technique may have clinical applications in the assessment of intestinal viability.     

Cardiopulmonary resuscitation during severe hypothermia in pigs: does epinephrine or vasopressin increase coronary perfusion pressure?

The American Heart Association does not recommend epinephrine for management of hypothermic cardiac arrest if body core temperature is below 30 degrees C. Furthermore, the effects of vasopressin administration during hypothermic cardiac arrest are totally unknown. This study was designed to assess the effects of vasopressin and epinephrine on coronary perfusion pressure in a porcine model during hypothermic cardiac arrest cardiopulmonary resuscitation (CPR). Pigs were surface-cooled until their body core temperature was 26 degrees C. After 30 min of untreated cardiac arrest, followed by 3 min of basic life support CPR, 15 animals were randomly assigned to receive, at 5-min intervals, either vasopressin (0.4, 0.4, and 0.8 U/kg; n = 5), epinephrine (45, 45, and 200 microg/kg; n = 5), or saline placebo (n = 5). Compared with epinephrine, mean +/- SEM coronary perfusion pressure was significantly higher (P < 0.05) 90 s and 5 min after the first (35+/-4 vs 22+/-3 mm Hg and 37+/-2 vs 16+/-2 mm Hg) and the second vasopressin administration (40+/-5 vs 26+/-5 mm Hg and 36+/-5 vs 18+/-2 mm Hg, respectively). After the third drug administration, coronary perfusion pressure in the epinephrine group increased dramatically and was comparable to vasopressin. In the saline placebo group, coronary perfusion pressure was significantly lower (P < 0.05) than in the vasopressin and epinephrine groups. Six animals treated with epinephrine or vasopressin had transient return of spontaneous circulation, whereas all placebo animals died (P < 0.05). During CPR in severe hypothermia, administration of both vasopressin and epinephrine resulted in significant increases in coronary perfusion pressure when compared with placebo. IMPLICATIONS: Our study was designed to assess the effects of vasopressin and epinephrine in a porcine model simulating cardiac arrest during severe hypothermia. This study demonstrates that the administration of both emergency drugs results in an increased perfusion pressure in the heart.     

Effects of carbon dioxide pneumoperitoneum on cerebral hemodynamics in pigs.

Previous studies have shown that laparoscopic interventions are associated with increases in intracranial pressure. However, the consequences on cerebral blood flow (CBF) are unknown. This study investigates the effects of carbon dioxide (CO2) pneumoperitoneum on CBF in pigs. Ten pigs (weight, 20-26 kg) were anesthetized with 1.4% isoflurane and fentanyl (1 microg/kg per minute). Mechanical ventilation (fraction of inspired oxygen = 0.4) was set to maintain normocapnia (end-tidal CO2 tension = 35 mm Hg). Arterial and central venous catheters were placed for measurement of mean arterial blood pressure and central venous pressure. Bilateral internal carotid artery blood flow was measured using two transient time flow probes placed around both carotid arteries (with ligated external carotid arteries). Cortical and subcortical cerebral blood flow was measured using laser Doppler flowmetry. Sagittal sinus pressure was measured via a superior sagittal sinus catheter. After baseline measurements, the peritoneal cavity of the animals was insufflated with CO2 to achieve an intraabdominal pressure of 12-mm Hg. After 10 minutes of stable CO2, pneumoperitoneum measurements were repeated. Increases in central venous pressure (6.3 +/- 2.1 to 11.1 +/- 3.0 mm Hg) and sagittal sinus pressure (8.0 +/- 2.8 to 11.9 +/- 3.0 mm Hg) were noted during CO2 pneumoperitoneum (P < .05). Bilateral internal carotid artery blood flow (46.0 +/- 7.4 vs 47.7 +/- 7.1 mL/100g per minute), cortical CBF (263 +/- 115 vs 259 +/- 158 tissue perfusion units), and subcortical CBF (131 +/- 145 vs 133 +/- 149 tissue perfusion units) did not change during CO2 pneumoperitoneum. The current data show that CO2 pneumoperitoneum increases sagittal sinus pressure without changing CBF. Increases in sagittal sinus pressure are likely related to decreases in cerebral venous drainage caused by increases in intraabdominal pressure.