Reintubation Rate and Mortality After Emergent Airway Management Outside the Operating Room

BACKGROUND

Little is known about reintubations outside of the operating room. The objective of this study was to evaluate the reintubation rate and mortality after emergent airway management outside operating room (OR), including intensive care unit (ICU) and nonICU settings.

METHODS

A retrospective cohort study. The primary outcome measures were reintubation rate and mortality. Secondary outcome measures were location and indication for intubation, time until reintubation, total intubated days, ICU-stay, hospital-stay, 30-day in-hospital mortality, and overall in-hospital mortality.

RESULTS

A total of 336 outside-OR intubations were performed in 275 patients. Of those 275 patients, 51 (18.5%) were reintubated during the same hospital admission. (41%) of the reintubations occurred in a non-ICU setting. Reintubations occurred after up to 30-days after extubation. Most frequently between 7 and 30 days (32.8%, n = 20). Most of the reintubated patients were reintubated just once (56.9%; n = 29), but some were reintubated 2 times (29.4%; n = 15) or over 3 times (13.7%; n = 7). Reintubated patients had significant longer total ICU-stay (24 ± 3 days vs 12 ± 1 day, p < .001), hospital stay (37 ± 3 vs18 ± 1, p < .001), and total intubation days (8 ± 1 vs 7 ± 0.6, P < .02). The 30-day in-hospital mortality in reintubated patients was 13.7% (n = 7) compared to nonreintubated patients 35.9% (n = 80; P = .002).

CONCLUSION

Reintubation was associated with a significant increase in hospital and ICU stay. The higher mortality rate among nonreintubated patients may indicate survival bias, in that severely sick patients did not survive long enough to attempt extubation.

Propofol Infusions and Their Role for Patients Undergoing Surgery for Head and Neck Squamous Cell Carcinoma

PURPOSE

Propofol infusions may improve survival for patients undergoing surgery for various types of cancer. However, propofol has not been shown to improve survival for all cancer types. The purpose of this retrospective study was to investigate whether propofol infusions during surgery for head and neck squamous cell carcinoma (HNSCC) improved survival.

METHODS

A retrospective analysis was performed on all patients undergoing surgery for HNSCC with neck dissection at one institution between June 15, 2017, and April 28, 2021. The primary analysis was performed as a cohort study, with one cohort receiving a propofol infusion and the other cohort not receiving a propofol infusion. A second analysis was performed as a case-control study with matching by cancer staging, human papillomavirus (HPV)/p16 status, pathology margin status, surgical duration within 90 minutes, American Society of Anesthesiologists (ASA) status, and Charlson Comorbidity Index (CCI) within a score of 1. Cases included patients who received a propofol infusion, and controls were patients who did not receive a propofol infusion.

RESULTS

For the primary analysis, there was no statistically significant difference in age (p=0.650), BMI (p=0.956), sex (p=0.069), and CCI (p=0.351), but there was a statistically significant difference in ASA status (p=0.003). The time exposed to sevoflurane (MAC >0.3) was significantly higher in the no-propofol group (p<0.001). The duration of surgery was significantly longer in the propofol patient group compared to the no-propofol group (p=0.013). The length of hospital stay was roughly two days longer for the propofol group (p=0.029). There was no difference in survival for patients who did not receive propofol versus those who did (p=0.247), even after adjusting for HPV/p16 tumor marker status (p=0.223). When patients were matched in a case-control approach, there were no differences in age (p=0.956), BMI (p=0.828), CCI (p=1.000), or ASA status (p=1.000). The death rate was not significant between the cases and controls (p=0.311).

CONCLUSIONS

This data suggests that propofol may not influence survival in patients with HNSCC. Larger studies are necessary to better characterize the effect of propofol infusions on patients with HNSCC.

Pain, Analgesic Use, and Patient Satisfaction With Spinal Versus General Anesthesia for Hip Fracture Surgery : A Randomized Clinical Trial

BACKGROUND

The REGAIN (Regional versus General Anesthesia for Promoting Independence after Hip Fracture) trial found similar ambulation and survival at 60 days with spinal versus general anesthesia for hip fracture surgery. Trial outcomes evaluating pain, prescription analgesic use, and patient satisfaction have not yet been reported.

OBJECTIVE

To compare pain, analgesic use, and satisfaction after hip fracture surgery with spinal versus general anesthesia.

DESIGN

Preplanned secondary analysis of a pragmatic randomized trial. (ClinicalTrials.gov: NCT02507505).

SETTING

46 U.S. and Canadian hospitals.

PARTICIPANTS

Patients aged 50 years or older undergoing hip fracture surgery.

INTERVENTION

Spinal or general anesthesia.

MEASUREMENTS

Pain on postoperative days 1 through 3; 60-, 180-, and 365-day pain and prescription analgesic use; and satisfaction with care.

RESULTS

A total of 1600 patients were enrolled. The average age was 78 years, and 77% were women. A total of 73.5% (1050 of 1428) of patients reported severe pain during the first 24 hours after surgery. Worst pain over the first 24 hours after surgery was greater with spinal anesthesia (rated from 0 [no pain] to 10 [worst pain imaginable]; mean difference, 0.40 [95% CI, 0.12 to 0.68]). Pain did not differ across groups at other time points. Prescription analgesic use at 60 days occurred in 25% (141 of 563) and 18.8% (108 of 574) of patients assigned to spinal and general anesthesia, respectively (relative risk, 1.33 [CI, 1.06 to 1.65]). Satisfaction was similar across groups.

LIMITATION

Missing outcome data and multiple outcomes assessed.

CONCLUSION

Severe pain is common after hip fracture. Spinal anesthesia was associated with more pain in the first 24 hours after surgery and more prescription analgesic use at 60 days compared with general anesthesia.

PRIMARY FUNDING SOURCE

Patient-Centered Outcomes Research Institute.

Abstract P187: Testing Of A Long-term Implantable Blood Pressure Waveform Monitoring System

The long-term Implantable Blood Pressure Waveform Monitoring System consists of a miniature applanation tonometer sensor head connected to a battery powered electronics module via a flexible lead. The BP Sensor continuously monitors the arterial BP waveform with data transmitted to a smart phone for real-time data analysis and display. Key data can be transmitted via the cellular network to a central monitoring station for advanced analysis by a computer and clinician. The BP Sensor has been evaluated for safety, accuracy, stability, and reliability for up to 10 months surrounding the external carotid arteries of large canine. Serial ultrasound studies of the artery-sensor interface shows normal artery shape, diameter, and blood flow velocity. BP Sensor performance remained stable for ~ 60 days between calibrations and correlated with reference BP waveform measurement (± 2.5 mm Hg). The BP Sensor head has a novel design that securely couples the diaphragm to the outside wall of a peripheral artery in optimal alignment with minimal flattening (~ 15 %). The Figure below shows the BP Sensor output signal’s detailed BP waveform four months after implantation. The waveform shows subtle and consistent fluctuations in the peaks and valleys of the BP waveform due to positive pressure mechanical ventilation with a respiratory rate of 14 breaths per minute. This is a significant observation which indicates that the BP Sensor has very good sensitivity (± 1 mm Hg) in the normal hemodynamic range (reference BP ~100/60). The real-time and recorded BP Sensor waveform data will be used to make a diagnosis and adjust medication in a more timely and effective manor, leading to improved clinical outcomes.

Continuation of Angiotensin-Converting Enzyme Inhibitors on the Day of Surgery Is Not Associated With Increased Risk of Hypotension Upon Induction of General Anesthesia in Elective Noncardiac Surgeries

OBJECTIVE

The aim of this study was to find out whether the preoperative continuation of angiotensin-converting enzyme inhibitor (ACE-I) or angiotensin II receptor blocker (ARB) treatment is associated with intraoperative hypotension immediately after induction of general anesthesia in elective noncardiac surgeries.

DESIGN

Retrospective cohort study.

SETTING

Single institutional university hospital.

PARTICIPANTS

Four hundred patients who underwent elective noncardiac surgery under general anesthesia, with ACE-I or ARB on their list of preoperative home medications, were included.

INTERVENTION

Preoperative ACE-I and ARB use was evaluated, and patients were divided into an ACE-I/ARB group versus non-ACE-I/ARB group.

MEASUREMENTS

The primary outcome measure was intraoperative hypotension after induction of general anesthesia. The secondary outcome measure was preoperative medication use, medications taken the morning of surgery, induction medication and dosage, and vasopressor medication use during induction.

RESULTS

Three hundred forty-nine patients were included for final analysis. The mean admission American Society of Anesthesiologists status was 2.7 ± 0.5, age 65 ± 11 years, and body mass index 31 ± 6.9 kg/m². There were no statistically significant changes between the no ACE-I/ARB group and the ACE-I/ARB group in systolic blood pressure (p = 0.853), diastolic blood pressure (p = 0.357), and heart rate (p = 0.220) change over the 15 minutes. There was no statistical difference in induction medication dose (propofol, fentanyl, and rocuronium) and pressor use (p = 0.137) for hypotension between the 2 groups. Statistically significant hypotension (p < 0.001) occurred in both groups equally over 15 minutes.

CONCLUSION

Continuation of ACE-I/ARB on the day of surgery was not associated with increased risk of intraoperative hypotension upon induction and within 15 minutes of general anesthesia in elective noncardiac surgeries.

Subchronic administration of (R,S)-ketamine induces ketamine ring hydroxylation in Wistar rats

Subchronic administration of (R,S)-ketamine, (R,S)-Ket, is used in the treatment of neuropathic pain, in particular Complex Regional Pain Syndrome, but the effect of this protocol on the metabolism of (R,S)-Ket is unknown. In this study, daily administration of a low dose of (R,S)-Ket for 14-days to Wistar rats was conducted to determine the impact of sub-chronic dosing on the pharmacokinetics of (R,S)-Ket and its major metabolites. The data indicate that, relative to a single administration of (R,S)-Ket, subchronic administration resulted in increased clearance of (R,S)-Ket and the N-demethylated metabolite norketamine measured as elimination half-life (t1/2) and decreased plasma concentrations of these compounds. Subchronic administration produced a slight decrease in t1/2 and an increase in plasma concentration of the major metabolite, (2S,6S;2R,6R)-hydroxynorketamine, and produced significant increases in the plasma concentrations of the (2S,6R;2R,6S)-hydroxynorketamine and (2S,4R;2R,4S)-hydroxynorketamine metabolites. The metabolism of (R,S)-Ket predominately occurs via two microsomal enzyme-mediated pathways: (R,S)-Ket⇒(R,S)-norketamine⇒(2S,6S;2R,6R)-hydroxynorketamine and (2S,4R;2R,4S)-hydroxynorketamine and the (R,S)-Ket⇒(2S,6R;2R,6S)-hydroxyketamine⇒(2S,6R;2R,6S)-hydroxynorketamine and (2S,6S;2R,6R)-hydroxynorketamine. The results indicate that the activity of both metabolic pathways are increased by subchronic administration of (R,S)-Ket producing new metabolite patterns and potential differences in clinical effects.

Ultrasound-Guided Out-of-Plane vs. In-Plane Interscalene Catheters: A Randomized, Prospective Study

BACKGROUND

Continuous interscalene blocks provide excellent analgesia after shoulder surgery. Although the safety of the ultrasound-guided in-plane approach has been touted, technical and patient factors can limit this approach. We developed a caudad-to-cephalad out-of-plane approach and hypothesized that it would decrease pain ratings due to better catheter alignment with the brachial plexus compared to the in-plane technique in a randomized, controlled study.

OBJECTIVES

To compare an out-of-plane interscalene catheter technique to the in-plane technique in a randomized clinical trial.

PATIENTS AND METHODS

Eighty-four patients undergoing open shoulder surgery were randomized to either the in-plane or out-of-plane ultrasound-guided continuous interscalene technique. The primary outcome was VAS pain rating at 24 hours. Secondary outcomes included pain ratings in the recovery room and at 48 hours, morphine consumption, the incidence of catheter dislodgments, procedure time, and block difficulty. Procedural data and all pain ratings were collected by blinded observers.

RESULTS

There were no differences in the primary outcome of median VAS pain rating at 24 hours between the out-of-plane and in-plane groups (1.50; IQR, [0 - 4.38] vs. 1.25; IQR, [0 - 3.75]; P = 0.57). There were also no differences, respectively, between out-of-plane and in-plane median PACU pain ratings (1.0; IQR, [0 - 3.5] vs. 0.25; IQR, [0 - 2.5]; P = 0.08) and median 48-hour pain ratings (1.25; IQR, [1.25 - 2.63] vs. 0.50; IQR, [0 - 1.88]; P = 0.30). There were no differences in any other secondary endpoint.

CONCLUSIONS

Our out-of-plane technique did not provide superior analgesia to the in-plane technique. It did not increase the number of complications. Our technique is an acceptable alternative in situations where the in-plane technique is difficult to perform.

The importance of medical education in the changing field of pain medicine

Suffering chronic pain is a global epidemic that requires a closer look on how we are educating trainees to become more effective in pain management. The vast majority of medical professionals will encounter treatment of pain throughout their career. Our current system for educating these medical professionals is flawed in a number of ways. Improving pain education will narrow the gap between over and under treatment of acute and chronic pain. Reviews have demonstrated dissatisfaction among practitioners throughout the world on how pain education is currently conducted. Changing the educational process will require support from several areas: medical educators, clinicians, policymakers, administrators and several other organizations.

Postoperative epidural analgesia following radical retropubic prostatectomy: outcome assessment

BACKGROUND AND OBJECTIVES

We retrospectively examined the effects of epidural analgesia on patients undergoing radical retropubic prostatectomy (RRP).

METHODS

Patients (203) underwent radical retropubic prostatectomy under either general or epidural anesthesia alone or a combined general epidural technique. Of those, 143 had an epidural catheter placed and underwent radical retropubic prostatectomy under general anesthesia followed by postoperative epidural analgesia (Group E+G). Twenty-eight patients had the operation under epidural anesthesia followed by epidural analgesia in the postoperative period (Group E). Thirty-two patients had general anesthesia for the operation and postoperative systemic analgesia (Group G).

RESULTS

There were no significant differences between the groups with respect to age, height, weight, ASA status, or operation time. The length of postoperative hospital stay was significantly longer in the general anesthesia group patients as compared to the other two groups (P < 0.05). Intraoperative blood loss and blood replacement were significantly higher in the general anesthesia group (P < 0.001). There were no significant differences between the groups with respect to return of bowel function postoperatively, or incidence of complications.

CONCLUSIONS

Epidural anesthesia and analgesia following radical retropubic prostatectomy have demonstrated a number of beneficial effects. These include decreased blood loss and shorter hospital stay.

Transdermal fentanyl system plus im ketorolac for the treatment of postoperative pain

PURPOSE

To assess the safety and efficacy of transdermal fentanyl plus im ketorolac vs im ketorolac alone in the treatment of postoperative pain.

METHODS

Ninety-two patients scheduled for surgery involving moderate to severe postoperative pain were randomized to one of two groups. Group A (n = 46) received an active fentanyl patch and group P (n = 46) received a placebo patch. Patches remained in place for 24 hr. Each patient received intraoperative ketorolac, 60 mg im. Patients were monitored for 36 hr postoperatively and the groups were analyzed for ketorolac usage, pain scores, vital signs, serum fentanyl concentrations, and adverse events. Intramuscular ketorolac was available on demand.

RESULTS

Group A had lower pain scores at 8.12, 16 and 24 hr after patch placement (P < 0.05). Group A had lower heart rates, lower respiratory rates and fewer dropouts due to inadequate pain relief (4.3% vs 21.7% P < 0.05). Group A patients also used less ketorolac than group P patients (P < 0.05). The incidence of pruritus was higher in group A patients (19% vs 2%, P < 0.05), while the incidence of nausea and vomiting was not different between the two groups. Transdermal fentanyl was adequate "stand-alone" analgesia in only 23.8% of group A patients while 93.7% of the remaining group A patients receiving a combination of transdermal fentanyl and ketorolac had adequate pain relief.

CONCLUSION

The transdermal fentanyl delivery system plus ketorolac im was more effective in controlling post-operative pain than ketorolac im alone. The two treatment modalities were comparable in safety with no difference in serious adverse events.

Sevoflurane versus isoflurane for maintenance of anesthesia: are serum inorganic fluoride ion concentrations of concern?

Sevoflurane administration can result in increased serum inorganic fluoride ion concentrations, which have been associated with inhibition of renal concentrating ability. We measured serum fluoride levels, renal function, and recovery variables as a function of time in ASA grade I-III patients administered general anesthesia with isoflurane or sevoflurane for at least 1 h. Fifty patients were exposed to sevoflurane (< or = 2.4% inspired concentration) or isoflurane (< or = 1.9% inspired concentration) for maintenance of anesthesia as part of a multicenter trial. Blood was collected for determination of serum fluoride ion concentration, electrolytes, blood urea nitrogen, and creatinine at various time points pre- and postoperatively. Mean serum fluoride levels were significantly increased in sevoflurane versus isoflurane groups at all time points; the mean peak serum levels were 28.2 +/- 14 mumol/L at 1 h for sevoflurane and 5.08 +/- 4.35 mumol/L at 12 h for isoflurane. Sevoflurane-mediated increases in serum fluoride levels peaked at 1 h and, in general, decreased rapidly after discontinuation of the anesthesia. Three of 24 patients exposed to sevoflurane had one or more fluoride levels > 50 mumol/L. One of these patients had a serum inorganic fluoride ion level > 50 mumol/L at 12 h after sevoflurane, and an additional patient had fluoride levels > 33 mumol/L for up to 24 h after sevoflurane discontinuation. Those two patients also demonstrated an increase in serum blood urea nitrogen and creatinine at 24 h after sevoflurane administration compared with baseline. The elimination half-life of serum fluoride ion was 21.6 h. The results of this study suggest the possibility of sevoflurane induced nephrotoxicity.

A comparison of four bedside methods of hemoglobin assessment during cardiac surgery

The purpose of this study was to compare the accuracy of conductivity, adjusted conductivity, photometric, and centrifugation methods of measuring or estimating hemoglobin (Hb) with Coulter measured HB as the reference. These bedside methods were studied in 25 cardiac surgery patients during euvolemia and hemodilution and after salvaged autologous red blood cell transfusion. In vivo patient blood samples were obtained before induction, at the start of cardiopulmonary bypass (CPB), after CPB, and after blood transfusion. In 10 patients, blood was sampled in vitro from units of processed blood. Hb values were determined using conductivity by Stat-Crit, adjusted conductivity by Nova Stat Profile 9, bedside photometry by HemoCue, and centrifugation methods. The calculated bias values of Coulter test method Hb (mean +/- SD) for in vivo patient blood samples (n = 90) were: Stat-Crit = 0.6 +/- 0.8 g/dL; Nova Stat Profile 9 = -0.7 +/- 0.4 g/dL; HemoCue = -0.1 +/- 0.2 g/dL; and centrifuge = 0.1 +/- 0.5 g/dL (P < 0.0001). Hb bias values (g/dL) for in vitro samples (n = 10) obtained from processed blood were Stat-Crit = 5.1 +/- 0.6; Nova Stat Profile 9 = 3.0 +2- 0.6; HemoCue = 0.4 +/- 0.4; and centrifuge = 0.6 +/- 0.3 (P < 0.0001). Hb assessment by different test methods may be significantly affected during hemodilution and after blood transfusion. In vitro conditions exaggerated the inaccuracy of conductivity and adjusted conductivity Hb estimates. The rank order of closest approximation to the Coulter measurement for all in vivo blood samples was provided by bedside photometry, followed by centrifugation, adjusted conductivity, and uncorrected conductivity methods.

Sedative and ventilatory effects of midazolam infusion: effect of flumazenil reversal

The purpose of this study was to evaluate the effects of flumazenil (1 mg i.v.) on the ventilatory response of premedicated patients receiving a continuous infusion of midazolam for sedation. After assessing baseline ventilatory function using a modified Read rebreathing method for determining hypercapnic ventilatory drive, 16 healthy outpatients were administered fentanyl, 50 micrograms i.v., and midazolam 2 mg i.v., followed by a variable-rate midazolam infusion, 0.3-0.5 mg.min-1. Upon termination of the midazolam infusion, serum midazolam concentrations were measured and ventilatory function was reassessed. Then, 10 ml either saline or flumazenil (1 mg) were administered according to a randomized, double-blind protocol. Ventilatory function was subsequently measured at 5 min, 30 min and 60 min intervals after study drug. Compared with the baseline value, midazolam infusion reduced tidal volume and increased respiratory rate and alveolar dead space. However, midazolam did not decrease the slope of the CO2-response curve. Flumazenil reduced the degree of midazolam-induced sedation and the decrease in tidal volume (P < 0.05), but not the change in resting respiratory rate. In some patients, the ventilatory response to hypercarbia actually decreased after flumazenil administration compared with the immediate prereversal (sedated) values. It is concluded that midazolam infusion, 0.43 mg.min-1, did not impair CO2-responsiveness. Flumazenil's effect on central ventilatory drive was more variable than its reversal of midazolam-induced sedation.

Intraoperative hemodynamic, renin, and catecholamine responses after prophylactic and intraoperative administration of intravenous enalaprilat

This study was designed to evaluate effects of enalaprilat, an angiotensin-converting enzyme inhibitor, on hemodynamic and hormonal responses during surgery at endotracheal intubation, incision, and limb-tourniquet inflation. Thirty patients undergoing limb procedures with general anesthesia (N2O/narcotic technique) and a pneumatic tourniquet were randomized to receive either preoperative enalaprilat (1.25 mg intravenously [i.v.] 20 min prior to induction) or intraoperative enalaprilat (0.625 mg i.v. at the onset of tourniquet-associated hypertension), with appropriate placebo controls. Arterial blood pressure and heart rate increased significantly in response to intubation in the placebo group. Although there were no significant differences in catecholamine levels, plasma renin activity was significantly increased at postincision in the preoperative-enalaprilat group versus the placebo group. This suggests that activation of the renin-angiotensin system may play a key role in mediation of intraoperative hemodynamic responses to endotracheal intubation. With respect to tourniquet hypertension, preoperative or intraoperative treatment with enalaprilat reduced neither the pressor response to tourniquet inflation nor the amount of enflurane subsequently required to control arterial blood pressure. These findings suggest that this response is mediated by pain pathways, and may be treated more effectively with anesthesia/analgesia.

Does the use of methylmethacrylate cement in total shoulder replacement induce hemodynamic or pulmonary instability?

STUDY OBJECTIVE

To investigate whether the use of methylmethacrylate cement causes hemodynamic or pulmonary instability during total shoulder replacement surgery.

DESIGN

Prospective, nonrandomized study.

SETTING

Operating room.

PATIENTS

9 ASA physical status I and II patients.

INTERVENTIONS

A 20-gauge radial artery catheter was placed in the wrist opposite the surgical site. Sedation with midazolam was provided, and a pulmonary artery catheter was placed through an 8.5-Fr introducer into the patient's right internal jugular vein.

MEASUREMENTS AND MAIN RESULTS

Before induction of anesthesia, systolic, diastolic, and mean arterial blood pressures; heart rate; central venous pressure; systolic, diastolic, and mean pulmonary artery pressures; pulmonary capillary wedge pressure; and thermodilution cardiac output measurements were obtained. Arterial and mixed venous blood gas samples also were collected and analyzed for calculation of Qs/Qt. These hemodynamic and pulmonary parameters were measured again just before cementing of each prosthesis with methylmethacrylate cement and at 1, 5, 10, and 20 minutes after cementing. There were no statistically significant changes in any of the measured hemodynamic parameters at any time. There was no statistically significant difference in the calculated intrapulmonary shunt fraction.

CONCLUSION

In this study population, the use of methylmethacrylate for total shoulder replacement was not associated with adverse hemodynamic events or increased intrapulmonary shunting.

Fenoldopam infusion for the treatment of postoperative hypertension

STUDY OBJECTIVE

To examine the safety and efficacy of intravenous fenoldopam as compared to placebo for the treatment of postoperative hypertension.

DESIGN

Randomized, placebo-controlled, double-blind study.

SETTING

Community hospital.

PATIENTS

16 ASA I-III hypertensive patients scheduled for noncardiac surgical procedures.

INTERVENTIONS

Treatment with fenoldopam or placebo was initiated immediately after other causes of hypertension had been ruled out. Hypertension was defined as a supine systolic blood pressure (SBP) or diastolic blood pressure (DBP) greater than 20% over the patient's preoperative baseline, which was obtained 6 hours prior to the procedure with the patient lying quietly. The baseline consisted of 3 consecutive blood pressure (BP) measurements obtained at 5-minute intervals and not varying by more than 10%. Fenoldopam or placebo infusion was initiated at 0.1 microgram/kg/min and increased and decreased as necessary until the therapeutic goal BP was reached or treatment failure had occurred. The therapeutic goal BP was a decrease to at least 10% above the preoperative baseline, and failure of treatment was defined as inability to reach this BP level after 15 minutes at 1.5 micrograms/kg/min.

MEASUREMENTS AND MAIN RESULTS

BP and heart rate (HR) data were collected consistently throughout the study and 1 hour after termination of infusion. Laboratory studies and 12-lead electrocardiographic results were obtained at the start of the study and repeated 24 hours after termination of infusion. Blood samples were obtained for the measurement of epinephrine, norepinephrine, and dopamine levels and were analyzed using high-performance liquid chromatography with electrochemical detection. Pretreatment BP measurements were significantly elevated from baseline in both groups. Fenoldopam treatment significantly reduced BP to the therapeutic goal in 8 of 8 patients; placebo reduced BP to this goal in only 4 of 8 patients (p < 0.05). At the end of the titration period, the therapeutic goal BP was not significantly different from baseline in the fenoldopam group. HR was significantly elevated (p < 0.05) at goal in the fenoldopam group as compared with the placebo group. Fenoldopam administration lowered SBP and DBP to goal in a mean time of 28 minutes versus 42.5 minutes in the placebo group. There were no significant differences in catecholamine levels at any of the measurement periods.

CONCLUSION

Fenoldopam is an effective drug for reducing BP following hypertensive episodes in the postoperative setting. Fenoldopam use is associated with an increase in HR versus placebo.

The pharmacokinetics of droperidol in anesthetized children

Despite the wide use of droperidol to reduce nausea and vomiting in children, its pharmacokinetics have not been described in pediatric patients. Twelve ASA Class I-II children, undergoing tonsillectomy and adenoidectomy, received standardized anesthesia; none of the children received premedication. After induction of general anesthesia, droperidol (0.05 mg/kg) was injected intravenously as a bolus. Droperidol plasma concentrations were determined by radioimmunoassay. Pharmacokinetic data were analyzed by model-independent methods. The pharmacokinetic parameters (mean +/- SD) for the studied population were elimination half-life: 101.5 +/- 26.4 min, mean residence time: 127.2 +/- 28.6 min, volume of distribution at steady state: 0.58 +/- 0.29 L/kg and clearance: 4.66 +/- 2.28 mL.kg-1 x min-1. The clearance and volume of distribution at steady state values are lower than those reported for the adult population, and they apparently decreased in a parallel fashion. The smaller volume of distribution at steady state is consistent with the lipophilic distribution of droperidol and the reduced content of adipose tissue in children. The elimination half-time and mean residence time values are similar to those reported previously for adults. The relatively short half-life of droperidol for our pediatric population does not explain its extended antiemetic action. It does, however, reaffirm that the pharmacokinetic duration of a drug's action is only one of the determinants of its clinical duration.

Time-course of respiratory depression after an alfentanil infusion-based anesthetic

Postoperative respiratory depression after alfentanil administration has been described in several case reports. The effects of a prolonged alfentanil infusion on the CO2 response curve or cognitive function have not been studied. Twenty-one ASA physical status I or II patients were studied after a prolonged alfentanil infusion (> 90 min) to determine the incidence of postoperative respiratory depression, arterial O2 desaturation, and impairment of cognitive function. Each patient's recovery was observed at 30-min intervals for evidence of respiratory depression (utilizing the Read CO2 rebreathing method), desaturation by pulse oximetry (severe desaturation defined as arterial O2 saturation < 90%), and cognitive function (utilizing Trieger dot and digit substitution tests). Plasma samples were also examined for secondary elevations in alfentanil plasma concentrations. Significant depression of the CO2 response curve and cognitive function was found up to 1 h postoperatively. Arterial O2 desaturation was seen in 11 of 21 patients (52%). No correlation was found between arterial O2 desaturation and cognitive function scores or CO2 rebreathing results. Increased depression of the CO2 response curve was not necessarily associated with severe desaturation episodes. A secondary increase in plasma alfentanil concentration was detected in 5 of the 21 patients (24%), but these patients did not experience further depression of the CO2 response curve. We conclude that prolonged alfentanil administration may result in severe arterial O2 desaturation with significant depression of the hypercapnic respiratory drive during the first hour in the postanesthesia care unit, even though the majority of our patients were easily aroused in response to verbal stimuli.

Do heated humidifiers and heat and moisture exchangers prevent temperature drop during lower abdominal surgery?

STUDY OBJECTIVE

To compare the effects of using a heated humidifier (HH), a heat and moisture exchanger (HME), or no warming device in maintaining body temperature during surgical procedures of 1 to 4 hours' duration.

DESIGN

A randomized, controlled study.

SETTING

Operating room, Thomas Jefferson University Hospital, Philadelphia, PA.

PATIENTS

51 ASA physical status I, II, and III patients, age 16 to 69 years, scheduled for a variety of lower abdominal procedures under general endotracheal anesthesia anticipated to last 1 to 4 hours.

INTERVENTIONS

We randomly assigned patients to receiving an HH, an HME, or no warming device during the procedure. We then measured the patient's sublingual temperature every 5 minutes prior to induction, every 15 minutes intraoperatively, and every 15 minutes postoperatively until he or she was discharged from the postanesthesia care unit, (PACU). We also measured the esophageal temperature every 15 minutes intraoperatively.

MEASUREMENTS AND MAIN RESULTS

Sublingual temperature or esophageal temperature probes placed at the site of maximal heart tones indicated that the patients' temperatures dropped significantly from baseline values in all three groups during the first 60 minutes of surgery, then remained constant during the next 120 minutes of surgery. Patients who had no warming device shivered and felt cold significantly more often than patients in the HH group but not more often than patients in the HME group. There was no difference in shivering between the HH and HME groups. The patients who received an HH tended to have a higher temperature (a mean of 0.5 degrees C) throughout the study, but this did not reach statistical significance.

CONCLUSIONS

Results indicate that these warming devices provide little benefit in preventing a temperature drop during procedures of 1 to 4 hours' duration, although patients with an HH tended to have a higher temperature than those with an HME or no device.

A comparison of labetalol and nitroprusside for inducing hypotension during major surgery

The hemodynamic and intrapulmonary shunt effects of intravenous labetalol and nitroprusside were compared during induced hypotension for major spinal surgery. A randomized, double-blind protocol was used in which 20 patients, ASA physical status I or II, received either nitroprusside infusion (n = 10) or labetalol bolus injections of 10 mg every 10 min (n = 10) until mean arterial blood pressure was reduced to 55-60 mm Hg. Pulmonary artery pressures were measured and mixed venous samples obtained via a pulmonary artery catheter. Nitroprusside increased heart rate significantly more than labetalol during the period of hypotension. When compared with prehypotension baseline values, nitroprusside increased heart rate significantly with a concomitant significant decrease in systemic vascular resistance. Cardiac output increased significantly 60 min after hypotension was achieved in patients treated with nitroprusside. Systemic vascular resistance decreased significantly below baseline levels in patients treated with labetalol but without changes in cardiac output, heart rate, or mean pulmonary artery pressure. There was a 122% increase in intrapulmonary shunt with nitroprusside administration, compared with an 11% increase with labetalol. Labetalol was effective for inducing hypotension and was not associated with an increase in heart rate, intrapulmonary shunt, or cardiac output as seen with nitroprusside.

Relationship between arterial carbon dioxide and end-tidal carbon dioxide when a nasal sampling port is used

End-tidal carbon dioxide (ETCO2) values obtained from awake nonintubated patients may prove to be useful in estimating a patient's ventilatory status. This study examined the relationship between arterial carbon dioxide tension (PaCO2) and ETCO2 during the preoperative period in 20 premedicated patients undergoing various surgical procedures. ETCO2 was sampled from a 16-gauge intravenous catheter pierced through one of the two nasal oxygen prongs and measured at various oxygen flow rates (2, 4, and 6 L/min) by an on-line ETCO2 monitor with analog display. Both peak and time-averaged values for ETCO2 were recorded. The results showed that the peak ETCO2 values (mean = 38.8 mm Hg) correlated more closely with the PaCO2 values (mean = 38.8 mm Hg; correlation coefficient r = 0.76) than did the average ETCO2 values irrespective of the oxygen flow rates. The time-averaged PaCO2-ETCO2 difference was significantly greater than the PaCO2-peak ETCO2 difference (P less than 0.001). Values for subgroups within the patient population were also analyzed, and it was shown that patients with minute respiratory rates greater than 20 but less than 30 and patients age 65 years or older did not differ from the overall studied patient population with regard to PaCO2-ETCO2 difference. A small subset of patients with respiratory rates of 30/min or greater (n = 30) did show a significant increase in the PaCO2-ETCO2 difference (P less than 0.001). It was concluded that under the conditions of this study, peak ETCO2 values did correlate with PaCO2 values and were not significantly affected by oxygen flow rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of diazepam and flumazenil on sedation and hypoxic ventilatory response

We evaluated the effects of a benzodiazepine antagonist, flumazenil (Ro 15-1788), 1 mg intravenous, on the hypoxic ventilatory response in 10 healthy patients who had received diazepam 0.97 +/- 0.34 mg/minute (mean +/- SD) for sedation during minor operative procedures. When assessed using a sedation analog scale, flumazenil significantly decreased diazepam-induced sedation. In only two of the five patients with evidence of diazepam-induced depression of the ventilatory response to hypoxia was there significant reversal of this depression after flumazenil administration. Finally, patients in whom the duration of sedation with diazepam was shorter (78 +/- 14 minutes) had a significantly greater decrease in the slope of their hypoxic ventilatory response curve (1.3 +/- 0.8 L.min-1.%sat-1 [-43% from baseline]) than did patients with longer sedation times (145 +/- 37 minutes duration; 2.0 +/- 0.8 L.min-1.%sat-1 [-5% from baseline]). These data suggest that flumazenil, 1 mg intravenous, is only partially effective in reversing diazepam-induced depression of hypoxic ventilatory drive and that tolerance may develop to the respiratory depressant effects of diazepam.