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Biomedical subjects

R N Sladen

Publications and source records attributed to R N Sladen.

At least 37 records · Page 2Linked to original sources
PubMed1997

Conventional modes of mechanical ventilation.

The conventional modes of mechanical ventilation are volume-preset techniques that offer full or partial ventilatory support to the patient with respiratory insufficiency. The mode of ventilation is the aggregate of the mechanisms for initiation, limitation, and cycling of the ventilator. An understanding of the function of the ventilator during the phases of the respiratory cycle helps the clinician to choose the most appropriate mode of ventilation for the patient.

Humans↗
PubMed1996

Temperature monitoring.

Central temperature is usually tightly regulated in human beings. Anesthesia alters the normal thermoregulatory controls of the body. Intraoperatively, mild degrees of hypothermia may provide some cerebral protection. However, the risk of organ dysfunction and shivering require that the anesthesiologist be prepared to treat severe hypothermia. Appropriate measures such as warning the operating room and using forced air blankets can prevent both intraoperative hypothermia and postoperative shivering. The use of temperature measurement is not limited to the operative and immediate recovery periods. Anesthesiologists practicing in intensive care units and in pain clinics use temperature monitoring as a diagnostic tool in a variety of situations.

Anesthesia Recovery Period↗
PubMed1995

Defining the relationship of oxygen delivery and consumption: use of biologic system models.

To determine the most appropriate mathematical description of the relationship between oxygen consumption and oxygen delivery, we compared the statistical validity of a piecewise linear model to two different biologic system models--Michaelis-Menten (MM) kinetics (used for enzyme systems) and the exponential dose-response relationship (used to describe drug administration and induced response). Nine rabbits underwent five incremental steps of normovolemic hemodilution to progressively decrease DO2. VO2 was measured concurrently by a metabolic gas monitor. All three models (piecewise linear, Michaelis-Menten, and exponential) provided a very close population curve fit to the data points (r2 = 0.88, 0.91, and 0.92). However, there were significant differences in maximum predicted VO2 (VO2max)--6.8, 9.9, 7.2 ml O2.kg-1.min-1 (P < 0.0002)--and a wide range in the model-specific parameters for individual rabbits (critical DO2 6.5-11.8 ml O2.kg-1.min-1, Km 4.2-11.4 ml O2.kg-1.min-1, and kappa 0.12-0.23 ml O2-1.kg.min). In the curvilinear models, average and population parameters were not significantly different. However, in the piecewise linear model, population critical DO2 (10.9 ml O2.kg-1.min-1) was 30% more than the average critical DO2 (8.4 ml O2.kg-1.min-1) for the nine rabbits (P < 0.005). VO2max values predicted by the piecewise linear and exponential dose-response model were more consistent with those in previous publications than was the higher VO2max predicted by the MM model. The difference in the average versus population critical DO2 in the piecewise linear model meant that population modeling was inaccurate because it yielded a critical DO2 higher than that demonstrated by eight of nine individual rabbits.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1995

Comparison of vecuronium and meperidine on the clinical and metabolic effects of shivering after hypothermic cardiopulmonary bypass.

The use of vecuronium and meperidine on the clinical and metabolic effects of shivering in mechanically ventilated patients after hypothermic cardiopulmonary bypass (CPB) was compared. Twenty adult male patients undergoing cardiac surgery were randomized to meperidine, 25 to 75 mg (n = 10), or vecuronium, 0.1 microgram/kg (n = 10), for the treatment of shivering during postoperative rewarming. Vecuronium was continued as an infusion at 1.0 microgram/kg/min for 4 hours. Meperidine abolished shivering in 50% of patients with a 60% recurrence within 2 hours and did not correct acute respiratory acidosis when it occurred. Vecuronium uniformly abolished shivering, corrected acute respiratory acidosis, and improved mixed venous oxygen saturation (20% v 4%), decreased oxygen consumption (-32% v -7%) and decreased end-tidal carbon dioxide (-21% v -5%) significantly more than meperidine (p < 0.005). Meperidine administration caused a significant decline in systolic blood pressure (121.9 +/- 10.6 mmHg to 106.9 +/- 8.5 mmHg, p = < 0.02). The authors conclude that, during rewarming after hypothermic CPB, muscle relaxation with vecuronium reverses both the clinical and metabolic effects of shivering more reliably and effectively than repeated boluses of meperidine, and with greater hemodynamic stability. Control can be maintained by continuous infusion of vecuronium with concomitant sedation for up to 4 hours without prolonging intubation time.

Acidosis, Respiratory↗
PubMed1994

Rewarming and sweating during cardiopulmonary bypass.

The hypothesis was tested that facial sweating at the end of cardiopulmonary bypass (CPB) is a thermoregulatory phenomenon. Twenty-two patients undergoing cardiac surgery with fentanyl anesthesia were studied. Nasopharyngeal temperature, nasal skin temperature, rectal temperature, and mean skin temperature were monitored for 90 minutes after the start of rewarming on CPB. Calf-toe and forehead-nose skin temperature gradients were followed as a measure of peripheral and facial thermoregulatory vasoactive responses. Facial sweating was defined as grade 1 (noticeable) or grade 2 (obvious droplets). Fourteen patients (64%) sweated during rewarming at the end of CPB. In 11 cases the onset of sweating was preceded by a dramatic increase in nasal skin temperature (mean +/- SEM, 4.6 +/- 0.3 degrees C in 5 min), suggesting facial vasodilation. The maximum rate of increase (degree C/5 min) in nasal skin temperature was significantly greater in patients who sweated than in those who did not, 4.1 +/- 0.4 degrees C versus 2.6 +/- 0.3 degrees C (P < 0.015). There was no difference in the age, weight, or BSA between patients who sweated during CPB and those who did not. The nasopharyngeal temperature threshold for the onset of sweating was not elevated (grade 1, 36.4 +/- 0.5 degrees C; grade 2, 37.6 +/- 0.4 degrees C), but there was a 5 to 6 degrees C interpatient variation. It was concluded that facial sweating during rewarming on CPB is typical of a thermoregulatory response. Absence of sweating in one third of patients may be due to pharmacokinetic or pharmacodynamic differences in the response to anesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1992

The effect of the extended (3-year) anesthesia curriculum on anesthesia subspecialty education.

The purpose of this study was to determine the effect of lengthening the anesthesia residency by the American Board of Anesthesiology on the education of anesthesia subspecialists. A survey of anesthesia residency programs was conducted from 1987 to 1991. The most frequent subspecialty practice in the clinical anesthesia (CA) 3 year is cardiovascular anesthesia. However, the percentage of CA3 residents spending extended time (greater than or equal to 6 months) in subspecialty education has significantly decreased. For example, the percentage of CA3 residents spending 12 months in subspecialty education has decreased 83%. There appears to be a slight increase in the number of CA4 or PGY5 residents (fellows) electing subspecialty practice. It is concluded that the 3-year curriculum has produced a negative impact on the education of anesthesia subspecialists.

Anesthesiology↗
PubMed1992

Use of patient-controlled analgesia to compare the efficacy of epidural to intravenous fentanyl administration.

Fentanyl, unlike morphine, is highly lipophilic and rapidly diffuses out of the epidural space. Respiratory depression is, therefore, unlikely when fentanyl is given epidurally. However, much of fentanyl's analgesic effect is mediated by systemic rather than spinal receptor binding. To test this hypothesis, we performed a prospective, double-blind, cross-over study comparing epidural and intravenous (IV) administration of fentanyl in 16 patients for the first 12 h after lower abdominal or lower extremity surgery. To allow direct comparison of these two routes of administration, patient-controlled analgesia was used so patients could self-titrate their analgesia. Patients were randomized to receive fentanyl initially by an epidural (group A, n = 8) or IV (group B, n = 8) catheter for 6 h, after which they were crossed-over to the alternate route by means of a hidden three-way stopcock. The degree of analgesia was subjectively evaluated by a visual analogue scale, and by an observer rating patient's comfort and sedation. Cumulative dosage of fentanyl was recorded, and plasma fentanyl concentrations were measured. The onset of analgesia and increase in plasma fentanyl concentrations were more rapid with intravenous fentanyl. However, after 60 min, analgesia (visual analogue scale 2-4 cm) or plasma fentanyl concentrations (0.3-0.7 ng/mL) did not differ between the two routes of administration. There were also no significant differences in the cumulative dosage of fentanyl within each group (epidural vs IV) or between the groups. Thus, the analgesic effects of epidural fentanyl appear largely mediated by systemic absorption. Intravenous fentanyl achieves a similar degree of analgesia and a more rapid onset of effect without the need for epidural catheterization.

Aged↗
PubMed1992

Postoperative hypertension: a multicenter, prospective, randomized comparison between intravenous nicardipine and sodium nitroprusside.

OBJECTIVE: To compare the efficacy and safety of iv nicardipine with sodium nitroprusside in the treatment of postoperative hypertension after both cardiac and noncardiac surgery. DESIGN: Multicenter, prospective, randomized, open-label study. SETTING: Six tertiary referral medical centers (recovery rooms and surgical ICUs). PATIENTS: A total of 139 patients with postoperative hypertension: i.v. nicardipine (n = 71), sodium nitroprusside (n = 68). INTERVENTION: Administration of i.v. nicardipine or sodium nitroprusside. MEASUREMENTS: Vital signs (BP, heart rate), hemodynamic variables, medication dosage, total number of dose changes, and time to achieve BP control were recorded. MAIN RESULTS: Both medications were equally effective in reducing BP in both the cardiac and noncardiac surgical groups. Under the conditions of the study, i.v. nicardipine controlled hypertension more rapidly than sodium nitroprusside (i.v. nicardipine 14.0 +/- 1.0 mins and sodium nitroprusside 30.4 +/- 3.5 mins, p = .0029). The total number of dose changes required to achieve therapeutic BP response was significantly less in the i.v. nicardipine-treated patients (i.v. nicardipine 1.5 +/- 0.2 vs. sodium nitroprusside 5.1 +/- 1.4, p < .05). Adverse effects were observed with both drugs (i.v. nicardipine 7% [5/71] and sodium nitroprusside 18% [12/68] [NS]). CONCLUSIONS: Intravenous nicardipine is as effective as sodium nitroprusside in the therapy of postoperative hypertension. Specific advantages have been identified. The use of i.v. nicardipine should be considered in the therapy of postoperative hypertension.

Aged↗
PubMed1990

Labetalol for the control of elevated blood pressure following coronary artery bypass grafting.

In a multicenter study, the efficacy and safety of intravenous (IV) labetalol for the control of elevated blood pressure were studied in the intensive care unit (ICU) in 65 patients within 4 hours following coronary artery bypass grafting (CABG). Patients with pre-existing ventricular dysfunction, bradycardia, bronchospastic disease, or postoperative complications were excluded. All patients were monitored with a thermodilution pulmonary artery catheter. Entry criteria were a systolic blood pressure (SBP) greater than 140 mm Hg or diastolic blood pressure (DBP) greater than 90 mm Hg for at least five minutes. Intravenous labetalol was loaded incrementally (5, 10, 20, and 40 mg at 10-minute intervals) to a maximum cumulative dose of 75 mg, until either SBP decreased 10% or DBP decreased 10% and was less than 90 mm Hg. Responders were entered into a 6-hour maintenance period, and received 5 to 40 mg of IV labetalol every 10 minutes as needed for blood pressure control. Hemodynamic data and temperature were recorded at baseline, just before each dose of labetalol during the loading period, and at the end of the maintenance period. Alternative therapy was given in the case of nonresponse or adverse events. Intravenous labetalol successfully controlled post-CABG hypertension in 55 of 65 patients (85%); of these, 46 responded to 35 mg or less. Although 28 patients required no further labetalol in the maintenance period, in the others dosage varied from 5 to 400 mg. Reductions in SBP and DBP were associated with moderate reductions in pulse pressure (SBP-DBP) and heart rate (HR). Cardiac index decreased by 18.5%, with a 12.5% decrease in stroke index and 8.1% decrease in HR. Systemic vascular resistance did not increase significantly. Four patients (6%) developed hypotension related to IV labetalol. There was one death due to perioperative myocardial infarction, which was unrelated to labetalol use. The mechanism of action of IV labetalol in controlling hypertension after CABG surgery seems to be moderate negative inotropy and chronotropy. Its alpha-blocking effects seem to be important in preventing reflex vasoconstriction. This is directly opposite to the primary vasodilator effect found when IV labetalol is used to control nonsurgical hypertension. Because of these actions, labetalol should be avoided or used with caution in patients with preoperative and postoperative cardiac dysfunction. In patients with normal left ventricular function, IV labetalol appears to be a safe, effective agent in controlling post-CABG hypertension, with the added potential benefit of enhanced myocardial oxygen balance.

Analysis of Variance↗
PubMed1990

Nicardipine infusion for postoperative hypertension after surgery of the head and neck.

The therapy of postoperative hypertension (POH) after head and neck surgery was evaluated in a prospective, randomized, double-blind trial. Nicardipine hydrochloride, a Ca channel-blocker for iv use, was compared with placebo. Patients were initially randomized to receive nicardipine infusion or placebo. Those not responding to placebo were given nicardipine infusion on an open basis. Hypertension was significantly better controlled in patients treated with nicardipine infusion compared with placebo (83% vs. 22%, p less than .002). Subsequently, six (86%) of seven of the placebo failures were successfully treated with nicardipine. There were no significant complications in either group. We conclude that the titratable infusion of nicardipine is an effective and safe method for the control of POH after surgery of the head and neck. Further studies are now warranted comparing nicardipine with other drugs currently used to treat this condition.

Blood Pressure↗
PubMed1990

Colorimetric end-tidal carbon dioxide monitoring for tracheal intubation.

We evaluated a colorimetric end-tidal carbon dioxide (ETCO2) detector (FEF end-tidal carbon dioxide detector, Fenem, New York, N.Y.) during 62 intubations in anesthetized patients who were hemodynamically stable. The intubations were performed during a drill that simulates difficult tracheal intubation and therefore is associated with an increased risk of esophageal intubation. Each intubation attempt was monitored by two anesthesiologists and a research assistant who together used chest auscultation, colorimetric ETCO2, and capnography to confirm tracheal intubation and detect esophageal intubation. The reliability of the monitors was compared with capnography. Colorimetric ETCO2 confirmed tracheal intubations and detected esophageal intubations 100% of the time, as judged by capnography. There were no false-positive or false-negative decisions based on endotracheal tube position; however, one equivocal color change occurred, which was caused by failure to inflate the endotracheal tube cuff. Colorimetric ETCO2 monitoring confirmed tracheal intubation more rapidly than did chest auscultation (P less than 0.001) or capnography (P less than 0.05), and detected esophageal intubation more rapidly than did chest auscultation (P less than 0.05) and as rapidly as capnography did. Confirmation of tracheal intubation was achieved earlier than detection of esophageal intubation with all three monitors (P less than 0.05). We conclude that colorimetric ETCO2 monitoring is a safe, reliable, rapid, simple, and portable method for determining endotracheal tube position for patients who are hemodynamically stable and should be recommended where capnography is not available.

Carbon Dioxide↗
PubMed1989

Blood conservation in cardiac surgery. Preliminary results with an institutional commitment.

To evaluate the effect of blood conservation in cardiac surgery, use of blood products was analyzed in patients undergoing CABG before and after implementation of blood conservation techniques. Age, sex, coronary anatomy, ejection fraction, cardiopulmonary bypass time, and the preoperative hematocrit, platelet count, and clotting studies were similar in both groups. Methods of blood conservation included autologous transfusion of blood withdrawn before bypass, autotransfusion of shed mediastinal blood, strict protocols for transfusion, and acceptance of normovolemic anemia. With blood conservation, 25.5% of patients received no transfusions and 54.9% received blood only. Significant reductions (p less than 0.001) were achieved in the transfusion of blood from 6.8 +/- 2.4 to 2.3 +/- 2.6 units per patient and of plasma from 2.5 +/- 2.2 to 0.6 +/- 2.0 units per patient. Reductions in the use of platelets and cryoprecipitate were substantial, although not significant. Total donor exposure was reduced significantly from 13.1 +/- 7.3 to 4.3 +/- 6.7 donors per patient. The postoperative hematocrit was significantly lower and remained so at discharge. However, 30 days later there was no difference. This reduction in transfusion requirements decreased costs and donor exposure.

Aged↗
PubMed1987

Hematologic effects of cardiac and noncardiac surgery.

The intraoperative and postoperative changes in number and type of WBCs in patients undergoing cardiac surgery were studied. These changes were then compared with those that occurred in patients undergoing four noncardiac surgical procedures (abdominal vascular reconstruction, thoracotomy, cholecystectomy, and carotid thromboendarterectomy). Both cardiac surgery and abdominal vascular surgery resulted in a marked increase in bands and decrease in lymphocytes. Thoracotomy and cholecystectomy resulted in similar but smaller changes. Carotid thromboendarterectomy did not produce hematologic changes. We conclude that the hematologic changes that occur with cardiac surgery are primarily a result of the stress and trauma of major surgery rather than a result of cardiopulmonary bypass itself.

Adult↗