Endogenous opioids and ventilatory responses to hypercapnia in normal humans.

Though administration of opioid peptides depresses ventilation and ventilatory responsiveness, the role of endogenous opioid peptides in modulating ventilatory responsiveness is not clear. We studied the interaction of endogenous opioids and ventilatory responses in 12 adult male volunteers by relating hypercapnic responsiveness to plasma levels of immunoactive beta-endorphin and by administering the opiate antagonist naloxone. Ventilatory responsiveness to hypercapnia was not altered by pretreatment with naloxone, and this by itself suggests that endogenous opioids have no role in modulating this response. However, there was an inverse relationship between basal levels of immunoactive beta-endorphin in plasma and ventilatory responsiveness to CO2. Furthermore, plasma beta-endorphin levels rose after short-term hypercapnia but only when subjects had been pretreated with naloxone. We conclude that measurement of plasma endorphin levels suggests relationships between endogenous opioid peptides and ventilatory responses to CO2 that are not apparent in studies limited to assessing the effect of naloxone.

Naloxone does not affect ventilatory responses to hypoxia and hypercapnia in rats.

Ventilatory responses (tidal volume, respiratory frequency, and minute ventilation) to steady-state hypoxia and steady-state hypercapnia were measured plethysmographically in awake unrestrained adult rats, before and after subcutaneous injection of placebo (saline) naloxone in doses up to 5.0 mg/kg. Naloxone did not alter the ventilatory responses to hypoxia or hypercapnia.

Endogenous opioids and ventilatory adaptation to prolonged hypoxia in goats.

To investigate whether endogenous opioid peptides mediate time-dependent changes in ventilatory control during prolonged hypoxia, we studied four adult goats at rest during 14 days at simulated high altitude in a hypobaric chamber (PB approximately 450 Torr). Arterial PCO2 fell during the first several hours of hypoxia, remained stable over the next 7 days, and then rose slightly (but without statistical significance) by day 14. Ventilatory responsiveness to CO2 increased during the first week of hypoxia. By day 14, while still greater than control, the ventilatory response to CO2 was less than that observed on day 7. Immunoactive beta-endorphin levels in plasma and CSF did not change during the 14-day period. Administration of naloxone on day 14 did not restore the ventilatory response to CO2 to the level observed during the first week of acclimatization. We conclude that in adult goats, time-dependent changes in ventilatory response to CO2 during acclimatization to prolonged hypoxia are not primarily attributable to alterations in endogenous opioid peptide activity.

Respiratory gas exchange and hemodynamics during lumbar epidural anesthesia: effects of lidocaine with and without epinephrine.

BACKGROUND AND OBJECTIVES: Epinephrine modifies the hemodynamic response to epidural local anesthetic; effects on respiratory gas exchange are not known. We hypothesized that epidural epinephrine would increase oxygen consumption and carbon dioxide production. METHODS: Twelve healthy patients (age, 22 to 46 years) undergoing surgery on the knee were randomly assigned to receive either 2% lidocaine (group L) or 2% lidocaine with epinephrine 5 microg x mL(-1) (group E), approximately 20 mL, over 10 minutes via lumbar epidural catheter. Total-body oxygen consumption (VO2) and carbon dioxide production (VCO2) were determined by indirect calorimetry; hemodynamic measurements were obtained by noninvasive thoracic electrical bioimpedance. Values of VO2, VCO2, heart rate (HR), cardiac index (CI), and mean arterial blood pressure (MAP) were determined every minute and averaged every 5 minutes for 30 minutes. Comparisons were made with analysis of variance (ANOVA) (within groups) and t-tests (between groups). Differences were considered statistically significant if P < .05. RESULTS: VO2 did not change in either group, while VCO2 increased significantly by 22% at 20 minutes in group E. Increases in HR were apparent in both groups, with significantly greater increases in group E (group L, 13%; group E, 21%). CI did not change in group L, but increased by 41% in group E. MAP decreased significantly by 11% in group E, but did not change in group L. CONCLUSIONS: The addition of epinephrine, 5 microg x mL(-1), to the epidural injection of 2% lidocaine is associated with changes not only in hemodynamics, but also in respiratory gas exchange.

Total-body oxygen consumption after isoflurane anesthesia: effects of mild hypothermia and combined epidural-general anesthesia.

STUDY OBJECTIVES: To determine the effects of epidural anesthesia and avoidance of intraoperative heat loss on the increase in total-body oxygen consumption in the immediate postoperative period after major intraabdominal surgery. DESIGN: Prospective, randomized (with regard to temperature management) study. SETTING: University medical center. PATIENTS: 24 ASA physical status I, II, and III adults. INTERVENTIONS: All patients received either isoflurane-nitrous oxide (N2O)-opioid general anesthesia or combined epidural-general anesthesia; patients were randomly assigned to active intraoperative warming or routine thermal care. MEASUREMENTS AND MAIN RESULTS: VO2 was measured by indirect calorimetry preoperatively (T0), immediately postoperatively (T1), and 60 to 90 minutes later (T2). For all patients, VO2 was 57 +/- 45% (mean +/- SD) greater at T1 than at T0 (p < 0.05). After isoflurane-N2O-opioid general anesthesia, VO2 increased 15 +/- 20% in normothermic patients (core temperature, 36.4 +/- 0.2 degrees C) compared with 69 +/- 52% in hypothermic patients (35.0 +/- 0.5 degrees C). After combined epidural-general anesthesia, VO2 increased 86 +/- 39% on emergence in normothermic (36.4 +/- 0.2 degrees C) and 58 +/- 11% in hypothermic (35.1 +/- 0.4 degrees C) patients. CONCLUSIONS: Total-body VO2 was increased in the immediate postoperative period. After general anesthesia, the magnitude of the increase in VO2 was significantly less in normothermic patients than in hypothermic patients. After combined epidural-general anesthesia, VO2 was increased in normothermic and in hypothermic patients.

Ventilatory responses to hypercapnia during tetracaine spinal anesthesia.

The effect of spinal anesthesia with hyperbaric tetracaine with epinephrine on resting ventilation and on ventilatory responsiveness to CO2 rebreathing was studied in 10 unpremedicated patients. Resting end-tidal PCO2 (PETCO2) decreased from 37 +/- 3 mmHg (mean +/- SD) to 34 +/- 2 mmHg after induction of spinal anesthesia (p less than 0.05). Minute ventilation (VE) and occlusion pressure (P0.1) at PETCO2 = 55 mmHg increased during spinal anesthesia from 32.0 +/- 12.9 to 40.2 +/- 17.0 l/min and from 5.0 +/- 1.8 to 8.6 +/- 4.7 cmH2O, respectively. The magnitude of the increase in VE during spinal anesthesia correlated inversely with age. Spinal anesthesia was not associated with significant changes in vital capacity, maximal inspiratory pressure, or the slopes of the lines relating VE or P0.1 to PCO2. These results show increased ventilatory responsiveness to CO2 (a parallel leftward shift of the CO2 response curve) with tetracaine spinal anesthesia.

Prophylactic antiemetics for laparoscopic cholecystectomy: a comparison of perphenazine, droperidol plus ondansetron, and droperidol plus metoclopramide.

STUDY OBJECTIVE: To compare the prophylactic administration of ondansetron plus droperidol, droperidol plus metoclopramide, and perphenazine to determine effects on postoperative nausea, vomiting, and sedation after laparoscopic cholecystectomy. DESIGN: Prospective, randomized, double-blind study. SETTING: University medical center. PATIENTS: 212 ASA physical status I and II adults presenting for laparoscopic cholecystectomy. INTERVENTIONS: Patients were randomly assigned to receive one of three prophylactic antiemetic drug combinations: ondansetron 4 mg plus droperidol 0.625 mg (Group OD), droperidol 0.625 mg plus metoclopramide 10 mg (Group DM), or perphenazine 5 mg (Group P). Study drugs were administered intravenously after induction of general anesthesia. MEASUREMENTS AND MAIN RESULTS: The groups were similar with respect to gender, age, weight, duration of surgery, numbers of patients receiving intraoperative atropine or ephedrine, number admitted overnight, and time to discharge home. Patients in Group P used lower total doses of opioids than did patients in Group OD. There were no significant differences in postoperative nausea, pain, or sedation scores, in numbers of patients requiring antiemetics (Group OD, 13 of 66; Group DM, 15 of 66; Group P, 14 of 68), or in numbers of patients vomiting, either in hospital or during the first postoperative day. CONCLUSIONS: These three drug regimens are equivalent for antiemetic prophylaxis before laparoscopic cholecystectomy.

Automated ST-segment analysis during cesarean delivery: effects of ECG filtering modality.

STUDY OBJECTIVES: To determine the effect of different electrocardiographic (ECG) filtering modalities on ST-segment changes during cesarean delivery. We compared the use of narrow and standard bandwidth ECG filtering modes in assessing ECG-detected ischemic changes in healthy patients undergoing routine, elective cesarean delivery. DESIGN: Prospective, nonrandomized clinical trial. SETTING: Academic medical center. PATIENTS: 20 healthy parturients undergoing elective cesarean delivery with regional anesthesia. INTERVENTION: Continuous 5-lead ECG monitoring was performed in all 20 study parturients. The same incoming ECG signal was divided by a special cable and displayed on two Marquette 7010 monitors. Leads I, II, and V5 were analyzed. One of the monitors filtered the signal with a 0.07 to 100 Hz filter (DIAG), the other with a 0.3 to 40 Hz filter (MON). The ST segment was analyzed continuously by electronic comparison with a template established as a baseline at the beginning of the case. This continuous output was led in digital form every 15 seconds to an IBM PC computer for data analysis. MEASUREMENTS AND MAIN RESULTS: In each of the leads analyzed, the mean MON versus DIAG different showed a bias, with MON showing consistently lower (ie, more negative) readings than DIAG. Using different criteria for ST depression (> 0.25, > 0.5, or > 1.0mm), we categorized patients as showing more ST depression on either MON or DIAG. With the 0.25 mm criterion, ST depression was identified significantly more often in MON then DIAG in leads H and V5 (p < 0.05). Using the other criteria, the differences were similar, but were not statistically significant. In general, very few instances of ST depression were identified in lead I. No patient had sequelae indicative of intraoperative myocardial ischemia, such as chest pain, dyspnea, persistent ectopy, or hemodynamic instability. CONCLUSIONS: In patients at low risk for myocardial ischemia, narrow bandwidth (monitor mode) ECG filtering reveals greater degrees of ST-segment depression than does standard (diagnostic mode) ECG filtering. Studies examining ST-segment phenomena would be facilitated by including a description of the ECG filtering-technique.

Effects of alkalinization of lidocaine on the pain of skin infiltration and intravenous catheterization.

STUDY OBJECTIVE: To test the hypothesis that alkalinization of lidocaine decreases the pain of skin infiltration in surgical patients. DESIGN: Double-blind, randomized, prospective study. SETTING: Preoperative holding units, Brigham and Women's Hospital. PATIENTS: 184 adult surgical patients. INTERVENTIONS: We compared the efficacy of 1% lidocaine with and without 0.1 mEq/ml of sodium bicarbonate (NaHCO3) for relief of pain of (1) skin infiltration and (2) intravenous (i.v.) catheterization prior to surgery. MEASUREMENTS AND MAIN RESULTS: Patients evaluated the intensity of pain using a 100 mm visual analog scale (VAS). There were no differences between study groups (lidocaine with NaHCO3, n = 89; lidocaine alone, n = 95) with respect to site of catheterization or catheter gauge used. Lidocaine plus NaHCO3 caused significantly less pain on skin infiltration (median VAS = 4; range = 0 to 51) than did lidocaine alone (VAS = 8; range = 0 to 48; p < 0.008). Pain of i.v. catheterization also did not differ between groups. There was a weak correlation between catheter gauge and pain of i.v. catheterization (r = -0.19; p = 0.01). CONCLUSIONS: Pain resulting from skin infiltration of lidocaine solutions can be diminished by adding NaHCO3. However, catheter size is more important than the presence or absence of NaHCO3 in determining the pain of i.v. catheterization.

Respiratory effects of spinal anesthesia: resting ventilation and single-breath CO2 response.

The effects of spinal anesthesia with bupivacaine or lidocaine on resting pulmonary ventilation and on the response to the single-breath carbon dioxide test were studied in 11 unpremedicated patients. Resting end-tidal PCO2 decreased from 34.8 +/- 4.5 (mean +/- SD) to 31.6 +/- 4.6 mm Hg after induction of spinal anesthesia (P = 0.002). The decrease in end-tidal PCO2 correlated negatively with patient age (r = -0.67, P = 0.02) and positively with spinal analgesic level (r = 0.58, P = 0.06). Breath-to-breath variability of ventilation increased during spinal anesthesia. Spinal anesthesia was not associated with statistically significant changes in tidal volume, respiratory rate, minute ventilation, mean inspiratory flow rate, inspiratory duty cycle duration, or the response to the single-breath CO2 test.

Recurrence of pulsus alternans after fentanyl injection in a patient with aortic stenosis and congestive heart failure.

Following aortic valve replacement in a patient with aortic stenosis and cardiac failure, marked pulsus alternans recurred immediately after intravenous injection of 0.5 mg fentanyl, without concomitant changes in heart rate, mean left atrial pressure, or the electrocardiogram. Pulsus alternans is known to occur in association with heart failure and aortic stenosis, but has not been reported previously in response to anaesthetic drugs. Mechanisms of pulsus alternans are discussed, and the possible contributory role of fentanyl is considered.

Hemodynamics during laparoscopic surgery in pregnancy.

IMPLICATIONS: During laparoscopic cholecystectomy in four pregnant women, we observed hemodynamic changes similar to those in nonpregnant patients (i.e., decreases in cardiac index together with increases in mean arterial blood pressure and systemic vascular resistance).

Ventilatory responses to hypercapnia during bupivacaine spinal anesthesia.

The effect of spinal anesthesia with isobaric 0.5% bupivacaine on ventilatory responsiveness to CO2 rebreathing was studied in ten unpremedicated patients. Minute ventilation (VE) at end-tidal PCO2 = 55 mm Hg increased from 18.7 +/- 6.7 L/min (mean +/- SD) to 22.3 +/- 10.1 L/min after induction of spinal anesthesia (P less than 0.05). Occlusion pressure (P0.1) at PCO2 = 55 mm Hg also increased, from 3.8 +/- 1.5 to 5.0 +/- 1.7 cm H2O (P less than 0.05). Spinal anesthesia was not associated with significant changes in vital capacity, maximal inspiratory pressure, resting end-tidal PCO2, or the slopes or intercepts of the lines relating VE or P0.1 to PCO2. These results show an increased ventilatory responsiveness to CO2 with bupivacaine spinal anesthesia.

Laparoscopic cholecystectomy during pregnancy. Review of anesthetic management, surgical considerations.

BACKGROUND: We present our experience with laparoscopic cholecystectomy in pregnant patients, with consideration of the physiological changes of pregnancy affecting anesthetic and surgical management. METHODS: We reviewed the medical records of all pregnant patients undergoing laparoscopic surgery at Brigham and Women's Hospital between January 1, 1991 and April 30, 1995. RESULTS: Laparoscopic cholecystectomy was performed without complication in ten patients (gestational age 9-30 weeks). Details of anesthetic and surgical management are described. The anesthetic and surgical implications of pregnancy-associated physiological changes in the gastrointestinal, respiratory, cardiovascular, and central nervous system are reviewed. CONCLUSIONS: With appropriate attention to the altered physiology of pregnancy, laparoscopic cholecystectomy can be performed safely and effectively during pregnancy.

Electrocardiographic R-wave changes during cardiac surgery.

The diagnostic accuracy of exercise electrocardiography has been improved by incorporation of R-wave gain factor to correct the measured ST-segment changes. If marked changes in R-wave amplitude occur in individual patients during cardiac operations, a similar gain factor correction may improve the intraoperative diagnosis of myocardial ischemia. This investigation was designed to determine the frequency and magnitude of intraoperative V5 R-wave amplitude changes during cardiac operations. Electrocardiograms were recorded from 83 patients while patients were awake, anesthetized (baseline), after placement of the Favaloro and Canadian sternal retractors, and at end-operation. Compared with baseline values, placement of the Canadian sternal retractor was associated with a reduction in V5 R-wave amplitude from 15 +/- 1 to 10 +/- 1 mm (mean +/- SEM), in V5 S-wave amplitude from 3.5 +/- 0.4 to 1.7 +/- 0.3 mm, and in absolute ST-segment deviation from 0.50 +/- 0.04 to 0.39 +/- 0.05 mm. Changes in V5 R-wave amplitude were correlated with changes in ST-segment deviation in patients with baseline ST-segment deviations greater than or equal to 0.5 mm (r = 0.55, P = 0.0004, n = 37). Changes associated with the Favaloro retractor and the respiratory cycle were less marked. However, the V5 R-wave amplitude was decreased from 15 +/- 1 to 9 +/- 1 mm at end-operation. In conclusion, sternal spreading with the Canadian retractor was associated with marked reductions in V5 R- and S-wave amplitudes and ST-segment deviations. Marked changes in V5 R-wave amplitude persisted after sternal closure.(ABSTRACT TRUNCATED AT 250 WORDS)

Linking mass spectrometers to provide continuing monitoring during system failure.

Although multipatient monitoring with a time-shared mass spectrometer provides considerable cost advantages, failure of one component in a shared system can disrupt gas monitoring at all sites. We describe a simple method for linking two central mass spectrometer systems to provide continual monitoring during failure of one unit, without the need for time-consuming reconfiguration of individual patient sample line and display connections.

Prophylactic antiemetics for laparoscopic cholecystectomy: ondansetron versus droperidol plus metoclopramide.

Two hundred adults undergoing laparoscopic cholecystectomy were enrolled in a prospectively randomized, double-blind investigation comparing ondansetron, 4 mg (Group O) with the combination of droperidol, 0.625 mg, and metoclopramide, 10 mg (Group DM). Antiemetic drugs were administered intravenously (IV) after induction of general anesthesia (propofol, desflurane). Moderate or severe nausea in the postanesthesia care unit was treated with the cross-over drug, i.e., ondansetron for patients in Group DM or droperidol plus metoclopramide for patients in Group O. Data were analyzed using t-tests and chi 2 analyses, with P < 0.05 considered statistically significant. The groups were similar with respect to gender, age, weight, duration of surgery, number receiving intraoperative atropine or ephedrine, number admitted over-night, and time to discharge home. Of 102 patients in Group O, 44 required antiemetics in the postanesthesia care unit, compared with 24 of 98 patients in Group DM (P < 0.01). One patient (in Group DM) was admitted for persistent nausea. In conclusion, droperidol 0.625 mg IV in combination with metoclopramide 10 mg IV was more effective in preventing postoperative nausea than was ondansetron 4 mg IV in patients undergoing laparoscopic cholecystectomy, with no difference in the time to discharge.

Arterial to end-tidal carbon dioxide pressure difference during laparoscopic surgery in pregnancy.

BACKGROUND: There is controversy about whether capnography is adequate to monitor pulmonary ventilation to reduce the risk of significant respiratory acidosis in pregnant patients undergoing laparoscopic surgery. In this prospective study, changes in arterial to end-tidal carbon dioxide pressure difference (PaCO2--PetCO2), induced by carbon dioxide pneumoperitoneum, were determined in pregnant patients undergoing laparoscopic cholecystectomy. METHODS: Eight pregnant women underwent general anesthesia at 17-30 weeks of gestation. Carbon dioxide pnueumoperitoneum was initiated after obtaining arterial blood for gas analysis. Pulmonary ventilation was adjusted to maintain PetCO2 around 32 mmHg during the procedure. Arterial blood gas analysis was performed during insufflation, after the termination of insufflation, after extubation, and in the postoperative period. RESULTS: The mean +/- SD for PaCO2--PetCO2 was 2.4 +/- 1.5 before carbon dioxide pneumoperitoneum, 2.6 +/- 1.2 during, and 1.9 +/- 1.4 mmHg after termination of pneumoperitoneum. PaCO2 and pH during pneumoperitoneum were 35 +/- 1.7 mmHg and 7.41 +/- 0.02, respectively. There were no significant differences in either mean PaCO2--PetCO2 or PaCO2 and pH during various phases of laparoscopy. CONCLUSIONS: Capnography is adequate to guide ventilation during laparoscopic surgery in pregnant patients. Respiratory acidosis did not occur when PetCO2 was maintained at 32 mmHg during carbon dioxide pneumoperitoneum.

Transcutaneous PCO2 monitoring during laparoscopic cholecystectomy in pregnancy.

PURPOSE: Respiratory acidosis during carbon dioxide (CO2) insufflation has been suggested as a cause of spontaneous abortion and preterm labour following laparoscopic cholecystectomy during pregnancy. Capnography may not be adequate as a guide to adjust pulmonary ventilation during laparoscopic surgery and hence arterial carbon dioxide (PaCO2) monitoring has been recommended. We report the feasibility and benefits of transcutaneous carbon dioxide monitoring (PtcCO2) as an approach to optimise ventilation during laparoscopic surgery in pregnancy. METHOD: A healthy parturient received general anaesthesia for laparoscopic cholecystectomy. Pulmonary ventilation was adjusted to maintain end-tidal carbon dioxide (conventional PETCO2) at 32 mmHg during CO2 insufflation. A PtcCO2 monitor was used to trend PaCO2 throughout the procedure. Mechanical ventilation was interrupted every five minutes to obtain an end-tidal PCO2 value at large tidal volume (squeeze PETCO2). RESULTS: The PtcCO2 increased from 39 mmHg before induction to 45 mmHg after CO2 insufflation. This corresponds to an estimated maximum PaCO2 of 39-40 mmHg during insufflation. The PtcCO2 gradually returned to pre-induction baseline values one hour after the termination of CO2 insufflation. Squeeze PETCO2 values approximated PtcCO2 more closely than did conventional PETCO2 values (P < 0.01). CONCLUSION: Continuous PtcCO2 measurements as well as squeeze PETCO2 may be of clinical value in trending and preventing hypercarbia during laparoscopic surgery.