Ozan Akça

Postoperative pain and subcutaneous oxygen tension

Surgical patients randomly assigned to standard pain control had postoperative subcutaneous oxygen partial pressures that were significantly less than patients given better pain treatment. Our data suggest that control of postoperative pain is a major determinant of surgical-wound infection and should be given the same consideration as maintaining adequate vascular volume and normothermia.

Aggressive warming reduces blood loss during hip arthroplasty.

We evaluated the effects of aggressive warming and maintenance of normothermia on surgical blood loss and allogeneic transfusion requirement. We randomly assigned 150 patients undergoing total hip arthroplasty with spinal anesthesia to aggressive warming (to maintain a tympanic membrane temperature of 36.5°C) or conventional warming (36°C). Autologous and allogeneic blood were given to maintain a priori designated hematocrits. Blood loss was determined by a blinded investigator based on sponge weight and scavenged cells; postoperative loss was determined from drain output. Results were analyzed on an intention-to-treat basis. Average intraoperative core temperatures were warmer in the patients assigned to aggressive warming (36.5° ± 0.3° vs 36.1° ± 0.3°C, P < 0.001). Mean arterial pressure was similar in each group preoperatively, but was greater intraoperatively in the conventionally warmed patients: 86 ± 12 vs 80 ± 9 mm Hg, P < 0.001. Intraoperative blood loss was significantly greater in the conventional warming (618 mL; interquartile range, 480–864 mL) than the aggressive warming group (488 mL; interquartile range, 368–721 mL;P = 0.002), whereas postoperative blood loss did not differ in the two groups. Total blood loss during surgery and over the first two postoperative days was also significantly greater in the conventional warming group (1678 mL; interquartile range, 1366–1965 mL) than in the aggressively warmed group (1,531 mL; interquartile range, 1055–1746 mL, P = 0.031). A total of 40 conventionally warmed patients required 86 units of allogeneic red blood cells, whereas 29 aggressively warmed patients required 62 units (P = 0.051 and 0.061, respectively). We conclude that aggressive intraoperative warming reduces blood loss during hip arthroplasty. Implications Aggressive warming better maintained core temperature (36.5° vs 36.1°C) and slightly decreased intraoperative blood pressure. Aggressive warming also decreased blood loss by approximately 200 mL. Aggressive warming may thus, be beneficial in patients undergoing hip arthroplasty.

Ondansetron is no More Effective than Supplemental Intraoperative Oxygen for Prevention of Postoperative Nausea and Vomiting

Supplemental oxygen maintained during and for 2 h after colon resection halves the incidence of nausea and vomiting. Whether supplemental oxygen restricted to the intraoperative period is sufficient remains unknown. Similarly, the relative efficacy of supplemental oxygen and ondansetron is unknown. We tested the hypothesis that intraoperative supplemental oxygen reduces the incidence of postoperative nausea and vomiting. Patients (n = 240) undergoing gynecological laparoscopy were given a standardized isoflurane anesthetic. After induction, they were randomly assigned to the following three groups: routine oxygen administration with 30% oxygen, balance nitrogen (30% Oxygen group), supplemental oxygen administration with 80% oxygen, balance nitrogen (80% Oxygen group), and Ondansetron 8 mg (immediately after induction), combined with 30% oxygen, balance nitrogen (Ondansetron group). The overall incidence of nausea and/or vomiting during the initial 24 postoperative h was 44% in the patients assigned to 30% oxygen and 30% in the Ondansetron group, but only 22% in those given 80% oxygen. The incidence was thus halved by supplemental oxygen and was significantly less than with 30% oxygen. There were, however, no significant differences between the 30% oxygen and ondansetron groups, or between the ondansetron and 80% oxygen groups. We conclude that supplemental oxygen effectively prevents postoperative nausea and vomiting after gynecological laparoscopic surgery; furthermore, ondansetron is no more effective than supplemental oxygen. IMPLICATIONS Supplemental oxygen reduces the risk of postoperative nausea and vomiting (PONV) as well or better than 8 mg of ondansetron. Because oxygen is inexpensive and essentially risk-free, supplemental oxygen is a preferable method of reducing PONV.

Dexmedetomidine and Meperidine Additively Reduce the Shivering Threshold in Humans

Background and Purpose— Hypothermia might prove to be therapeutically beneficial in stroke victims; however, even mild hypothermia provokes vigorous shivering. Meperidine and dexmedetomidine each linearly reduce the shivering threshold (triggering core temperature) with minimal sedation. We tested the hypothesis that meperidine and dexmedetomidine synergistically reduce the shivering threshold without producing substantial sedation or respiratory depression. Methods— We studied 10 healthy male volunteers (18 to 40 years) on 4 days: (1) control (no drug); (2) meperidine (target plasma level 0.3 &mgr;g/mL); (3) dexmedetomidine (target plasma level 0.4 ng/mL); and (4) meperidine plus dexmedetomidine (target plasma levels of 0.3 &mgr;g/mL and 0.4 ng/mL, respectively). Lactated Ringer’s solution (≈4°C) was infused through a central venous catheter to decrease tympanic membrane temperature by ≈2.5°C/h; mean skin temperature was maintained at 31°C. An increase in oxygen consumption >25% of baseline identified the shivering threshold. Sedation was evaluated by using the Observer’s Assessment of Sedation/Alertness scale. Two-way repeated-measures ANOVA was used to identify interactions between drugs. Data are presented as mean±SD;P <0.05 was statistically significant. Results— The shivering thresholds on the study days were as follows: control, 36.7±0.3°C; dexmedetomidine, 36.0±0.5°C (P <0.001 from control); meperidine, 35.5±0.6°C (P <0.001); and meperidine plus dexmedetomidine, 34.7±0.6°C (P <0.001). Although meperidine and dexmedetomidine each reduced the shivering threshold, their interaction was not synergistic but additive (P =0.19). There was trivial sedation with either drug alone or in combination. Respiratory rate and end-tidal Pco2 were well preserved on all days. Conclusions— Dexmedetomidine and meperidine additively reduce the shivering threshold; in the small doses tested, the combination produced only mild sedation and no respiratory toxicity.

Comparable Postoperative Pulmonary Atelectasis in Patients Given 30% or 80% Oxygen during and 2 Hours after Colon Resection

BACKGROUND High concentrations of inspired oxygen are associated with pulmonary atelectasis but also provide recognized advantages. Consequently, the appropriate inspired oxygen concentration for general surgical use remains controversial. The authors tested the hypothesis that atelectasis and pulmonary dysfunction on the first postoperative day are comparable in patients given 30% or 80% perioperative oxygen. METHODS Thirty patients aged 18-65 yr were anesthetized with isoflurane and randomly assigned to 30% or 80% oxygen during and for 2 h after colon resection. Chest radiographs and pulmonary function tests (forced vital capacity and forced expiratory volume) were obtained preoperatively and on the first postoperative day. Arterial blood gas measurements were obtained intraoperatively, after 2 h of recovery, and on the first postoperative day. Computed tomography scans of the chest were also obtained on the first postoperative day. RESULTS Postoperative pulmonary mechanical function was significantly reduced compared with preoperative values, but there was no difference between the groups at either time. Arterial gas partial pressures and the alveolar-arterial oxygen difference were also comparable in the two groups. All preoperative chest radiographs were normal. Postoperative radiographs showed atelectasis in 36% of the patients in the 30%-oxygen group and in 44% of those in the 80%-oxygen group. Relatively small amounts of pulmonary atelectasis (expressed as a percentage of total lung volume) were observed on the computed tomography scans, and the percentages (mean +/- SD) did not differ significantly in the patients given 30% oxygen (2.5% +/- 3.2%) or 80% oxygen (3.0% +/- 1.8%). These data provided a 99% chance of detecting a 2% difference in atelectasis volume at an alpha level of 0.05. CONCLUSIONS Lung volumes, the incidence and severity of atelectasis, and alveolar gas exchange were comparable in patients given 30% and 80% perioperative oxygen. The authors conclude that administration of 80% oxygen in the perioperative period does not worsen lung function. Therefore, patients who may benefit from generous oxygen partial pressures should not be denied supplemental perioperative oxygen for fear of causing atelectasis.

Hypercapnia Improves Tissue Oxygenation

Background Wound infections are common, serious, surgical complications. Oxidative killing by neutrophils is the primary defense against surgical pathogens and increasing intraoperative tissue oxygen tension markedly reduces the risk of such infections. Since hypercapnia improves cardiac output and peripheral tissue perfusion, we tested the hypothesis that peripheral tissue oxygenation increases as a function of arterial carbon dioxide tension (Paco2) in anesthetized humans. Methods General anesthesia was induced with propofol and maintained with sevoflurane in 30% oxygen in 10 healthy volunteers. Subcutaneous tissue oxygen tension (Psqo2) was recorded from a subcutaneous tonometer. An oximeter probe on the upper arm measured muscle oxygen saturation. Cardiac output was monitored noninvasively. Paco2 was adjusted to 20, 30, 40, 50, or 60 mmHg in random order with each concentration being maintained for 45 min. Results Increasing Paco2 linearly increased cardiac index and Psqo2: Psqo2 = 35.42 + 0.77 (Paco2), P < 0.001. Conclusions The observed difference in PsqO2 is clinically important because previous work suggests that comparable increases in tissue oxygenation reduced the risk of surgical infection from −8% to 2 to 3%. We conclude that mild intraoperative hypercapnia increased peripheral tissue oxygenation in healthy human subjects, which may improve resistance to surgical wound infections.

Sevoflurane-induced preconditioning protects against cerebral ischemic neuronal damage in rats

In the present study, we tested the ability of sevoflurane to induce early and late preconditioning against ischemic neuronal injury using an in vivo model of global cerebral ischemia in the rat. Seven-minute global ischemia was induced by cardiac arrest, followed by resuscitation and recovery for 7 days. Hippocampal slices were then prepared and the amplitude of extracellularly recorded, orthodromically evoked, CA1 population spikes (neuronal function) was quantified. Rats were preconditioned for 30 min with 1.0 minimum alveolar concentration (MAC) of sevoflurane once or on 4 consecutive days, 15 min (single exposure, early) or 24 h (four exposures, late preconditoning) prior to cardiac arrest. After early or late preconditioning, sevoflurane reduced ischemic neuronal damage from 43 +/- 3% [sham rats, (mean +/- SEM)] to 30 +/- 3% and 35 +/- 4%, respectively. Histopathology demonstrated a preserved morphology of the CA1 region of preconditioned rats, whereas pyknosis was present in control and sham-treated rats. Sevoflurane-induced preconditioning confers neuroprotection during an early as well as late time window.

Exposure to sevoflurane and nitrous oxide during four different methods of anesthetic induction

UNLABELLED The National Institute for Occupational Safety and Health-recommended exposure levels for nitrous oxide exposure are 25 ppm as a time-weighted average over the time of exposure. The exposure limit for halogenated anesthetics (without concomitant nitrous oxide exposure) is 2 ppm. Inhaled sevoflurane provides an alternative to i.v. induction of anesthesia. However, the inadvertent release of anesthetic gases into the room is likely to be greater than that with induction involving i.v. anesthetics. We therefore evaluated anesthesiologist exposure during four different induction techniques. Eighty patients were assigned to one of the induction groups to receive: 1) sevoflurane and nitrous oxide from a rebreathing bag, 2) sevoflurane and nitrous oxide from a circle circuit, 3) propofol 3 mg/kg, and 4) thiopental sodium 5 mg/kg. Anesthesia was maintained with sevoflurane and nitrous oxide via a laryngeal mask. Trace concentrations were measured directly from the breathing zone of the anesthesiologist. During induction, peak concentrations of sevoflurane and nitrous oxide with the two i.v. methods rarely exceeded 2 ppm sevoflurane and 50 ppm nitrous oxide. Concentrations during the two inhalation methods were generally <20 ppm sevoflurane and 100 ppm nitrous oxide. During maintenance, median values were near 2 ppm sevoflurane and 50 ppm nitrous oxide in all groups. Sevoflurane concentrations during inhaled induction frequently exceeded the National Institute for Occupational Safety and Health-recommended exposure ceiling of 2 ppm but mostly remained <20 ppm. Exposure during the maintenance phase of anesthesia also frequently exceeded the 2-ppm ceiling. We conclude that operating room anesthetic vapor concentrations are increased during inhaled inductions and remain increased with laryngeal mask ventilation. IMPLICATIONS We compared waste gas concentrations to sevoflurane and nitrous oxide during four different induction methods. During inhaled induction with a rebreathing bag or a circle circuit system, waste gas concentrations frequently exceed National Institute for Occupational Safety and Health limits of 2 ppm sevoflurane and 50 ppm nitrous oxide. Therefore, we recommend that people at risk (e.g., women of child-bearing age) should pay great attention when using this technique.

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.

Insufficiency in a New Temporal-Artery Thermometer for Adult and Pediatric Patients

SensorTouch™ is a new noninvasive temperature monitor and consists of an infrared scanner that detects the highest temperature on the skin of the forehead, presumably over the temporal artery. The device estimates core temperature (Tcore). We tested the hypothesis that the SensorTouch™ is sufficiently precise and accurate for routine clinical use. We studied adults (n = 15) and children (n = 16) who developed mild fever, a core temperature of at least 37.8°C, after cardiopulmonary bypass. Temperature was recorded at 15-min intervals throughout recovery with the SensorTouch™ thermometer and from the pulmonary artery (adults) or bladder (children). Pulmonary artery (Tcore) and SensorTouch™ (Tst) temperatures correlated poorly in adults: Tcore = 0.7 · Tst + 13, r2 = 0.3. Infrared and pulmonary artery temperatures differed by 1.3 ± 0.6°C; 89% of the adult temperatures thus differed by more than 0.5°C. Bladder and infrared temperatures correlated somewhat better in pediatric patients: Tcore = 0.9 · Tst + 12, r2 = 0.6. Infrared and bladder temperatures in children differed by only 0.3°C, but the sd of the difference was 0.5°C. Thus, 31% of the values in the infants and children differed by more than 0.5°C.