Circulatory changes during continuous epidural blockade

Comparison between the effects of epidural lidocaine, tramadol, and lidocaine-tramadol on postoperative pain in cats undergoing elective orchiectomy

BACKGROUND

In veterinary clinical practice, orchiectomy is one of the most common surgical procedures for cats and is performed mainly in young animals. The purpose of this study was to compare three different epidural (EP) analgesic protocols used in cats undergoing orchiectomy in order to determine which protocol resulted in superior outcomes in terms of perioperative analgesia. Twenty-one client-owned male cats were premedicated with a combination of dexmedetomidine (10 µg/kg) and midazolam (0.2 mg/kg) injected intramuscularly. Anesthesia was induced intravenously with propofol. Cats were randomly divided in three treatment groups of seven animals each: Group L received EP lidocaine (2 mg/kg), Group T received EP tramadol (1 mg/kg), and Group LT received EP lidocaine (2 mg/kg) plus tramadol (1 mg/kg). The post-operative pain level was assessed using two different scales: the Glasgow Composite Measure Pain Scale-Feline (CMPS-F) and the Feline Grimace Scale (FGS). Rescue analgesia was administered when the CMPS-F total score was ≥5 or the FGS total score was ≥4.

RESULTS

No adverse effects related to tramadol or lidocaine were observed. Based on post-operative pain assessments, significant differences between groups were observed according to both pain scoring systems. In particular, in Group LT, the CMPS-F and FGS scores decreased significantly in the first six hours following castration.

CONCLUSIONS

Based on our results, EP lidocaine plus tramadol provided the best post-operative analgesic effects in cats submitted to orchiectomy lasting 6 h and could also be a choice to consider for longer surgical procedures.

Comparison of Mean Arterial Blood Pressure and Heart Rate Changes in Response to Three Different Randomized Isotonic Crystalloid Boluses in Hypotensive Anesthetized Dogs

The aim of this prospective, randomized, nonblinded, controlled clinical trial was to compare mean arterial blood pressure (MAP) and heart rate (HR) during an intravenous bolus of three different balanced isotonic crystalloid solutions in euvolemic, anesthetized dogs with hypotension. Thirty healthy dogs (American Society of Anesthesiologists Physical Status I–II) weighing at least 15 kg that presented for elective orthopedic or dental surgical procedures at the Ryan Veterinary Hospital for Small Animals of the University of Pennsylvania were included in this study. Anesthetized hypotensive patients (defined as a MAP ≤ 65 mmHg), were administered an infusion of Lactated Ringer’s solution (LRS), Plasma-Lyte (PLYTE) or Canadian Plasma-Lyte (PLYTECA), selected at random. The infusion was administered over 15 min via a volumetric fluid pump. Differences in oscillometric MAP and HR between time points and across treatments were evaluated by mANOVA. Intravenous isotonic crystalloid infusions over 15 min did not significantly change MAP or HR in hypotensive dogs under general anesthesia. Neither LRS, PLYTE nor PLYTECA exacerbated hypotension or caused tachycardia.

Effects of epidural anaesthesia on intestinal oxygenation in pigs

BACKGROUND

Perioperative intestinal hypoperfusion is a major contributing factor leading to organ dysfunction. It can be caused by stress as a result of surgical manipulation or hypoxia. Additionally, anaesthesia can affect intestinal oxygenation. This animal study was designed to assess the effects of reduced regional sympathetic nervous activity induced by thoracic epidural anaesthesia on intestinal oxygenation.

METHODS

After ethical approval, 16 anaesthetized and acutely instrumented pigs were randomly assigned to two groups (epidural anaesthesia alone vs epidural anaesthesia plus volume loading). The epidural anaesthesia aimed for a T5-T12 block. Measurements were at baseline and after 1 and 2 h.

RESULTS

Epidural anaesthesia was associated with a decrease in mean arterial blood pressure and pronounced mesenteric vasodilatation. Mesenteric blood flow did not change. Intestinal oxygen uptake, mucosal tissue oxygen partial pressure and tissue carbon dioxide partial pressure remained unchanged.

CONCLUSIONS

Despite marked systemic hypotension, epidural anaesthesia did not affect intestinal oxygenation. There was no benefit obtained from volume loading.

What constitutes an effective but safe initial dose of lidocaine to test a thoracic epidural catheter?

To investigate the effects of age and dose on the spread of thoracic epidural anesthesia, we placed thoracic epidural catheters in 50 surgical patients divided into groups by age (Group I [young], 18-51 yr; Group II [old], 56-80 yr) and randomly assigned patients to receive either 5 mL (A) or 9 mL (B) of 2% lidocaine (plain) injected via the epidural catheter. Hemodynamic variables were measured (heart rate, mean arterial blood pressure, noninvasive impedance cardiac index) at baseline and every 5 min for 30 min. Detectable blockade occurred within 8 min after injection of 3 + 2 mL or 3 + 6 mL in 48 of 50 patients. Maximum spread of analgesia to pinprick occurred 15-23 min after completion of local anesthetic injection and was significantly different between age and volume groups by two-way analysis of variance (Group IA [young 5], 10.9 +/- 4.0 dermatomes; Group IIB [young 9], 13.9 +/- 4.5 dermatomes; Group IIA [old 5], 14.1 +/- 5.6 dermatomes; and Group IIB [old 9], 17.4 +/- 5.1 dermatomes). Minor decreases in mean arterial blood pressure (8%-17%) and heart rate (4%-11%) were noted. Two patients in the Old 9 group required IV ephedrine or ephedrine/atropine to treat hypotension and bradycardia. We conclude that given the rapid onset (3-8 min), extensive spread (11-14 dermatomal segments), and consistent hemodynamic stability, thoracic epidural anesthesia should be initiated with lidocaine 100 mg (5 mL 2% lidocaine) to establish proper location of the catheter in the epidural space in both younger and older patients.

Epidural anesthesia enhances sympathetic nerve activity in the unanesthetized segments in cats

To evaluate compensatory sympathetic excitation during epidural anesthesia, we measured cardiac and renal sympathetic nerve activity during thoracic or lumbar epidural anesthesia in cats. Thirteen cats were divided into three groups: five cats received thoracic epidural anesthesia, five received lumbar epidural anesthesia, and three received lumbar epidural anesthesia after the carotid sinus and vagoaortic nerves were severed (denervated lumbar group). Heart rate (HR), mean arterial pressure (MAP), and cardiac and renal sympathetic nerve activity were measured repeatedly after administration of a single dose of 0.1 mL/kg of 1% lidocaine via the epidural catheter. Epidural solution spread from a median of C-8 to T-6 in the thoracic epidural group, T-8 to L-3 in the lumbar epidural group, and T-7 to L-3 in the denervated lumbar group. During thoracic epidural anesthesia, HR, MAP, and cardiac sympathetic nerve activity decreased, while renal nerve activity increased. Similarly, HR, MAP, and renal sympathetic nerve activity decreased during lumbar epidural anesthesia, and cardiac activity increased. In the denervated lumbar group, HR, MAP, and renal sympathetic nerve activity decreased but cardiac activity remained unchanged. Sympathetic nerve activity in corresponding unanesthetized segments increased during thoracic or lumbar epidural anesthesia in association with significant decreases in MAP and HR. After severance of the carotid sinus and vagoaortic nerves, the absence of sympathetic excitation in the unanesthetized segments during lumbar epidural anesthesia suggests that the compensatory response is produced by the baroreceptor reflex response to anesthesia-induced hypotension.

Effect of epidural block on the lag time of pulse oximeter response

Thirty-six healthy patients, ASA 1, aged 16-41 years, scheduled for elective plastic surgery were studied to determine if thoracocervical or lumbar epidural blocks affected the lag time of the pulse oximeter response. Patients were allocated to receive thoracocervical epidural block (n = 20) (group 1) (lignocaine 1%) or lumbar epidural block (n = 16) (group 2) (lignocaine 1.5%). Epidural block was performed with a 17-gauge Tuohy needle inserted in the midline between C7-T2 vertebrae in group 1 and between L1-S1 in group 2 and an epidural catheter was introduced. Arterial oxygen saturation (SpO2) was measured continuously using a Datex pulse oximeter. The lag time of the pulse oximeter response was measured while breathing oxygen (100%) after breath-holding. Values were obtained 10 min before and 5, 10, 15, 20, 30, and 40 min after epidural injection of a test dose. There was a progressive decrease in the lag time of the pulse oximeter response so that by 30 min after epidural injection the mean (SD) value had decreased from 29 (6.1) to 14 (3.4) in Group 1 and 41 (12.8) to 23 (7.9) s in group 2 (p < 0.01).

Analysis of pain management in critically ill patients

We analyzed the adequacy of pain control for 17 trauma patients during the initial part of their stay in the intensive care unit, and assessed reasons for inadequate analgesia, if it occurred. Patients, and physicians, and nurses were interviewed. A verbal pain intensity scale was used to determine whether patients received adequate analgesia. Patients were asked if the pain hindered their activities, and whether they requested pain medication from their caregivers. Caregivers were questioned whether patients received adequate analgesia. Prescribed morphine regimens and the amount of narcotic administered were analyzed. Twenty-seven percent of patients rated pain intensity as moderate and 47% as severe. Ninety-five percent of housestaff and 81% of nurses reported the patients received adequate pain control. Forty-seven percent of the patients who had moderate or severe pain asked their physician for more pain medication, and 65% asked the nurse. Thirteen residents did not order a larger dose of morphine due to concern about respiratory depression or hypotension. Morphine dosages ranged from 1-8 mg intravenously every 1-2 hours as necessary. Nurses administered less than the maximum amount ordered 58% of the time. The mean dosing interval was 2.3 hours. Barriers to adequate pain management were disparity in the perception of pain between patients and caregivers; patients not requesting more analgesia despite despite the presence of moderate to severe pain; and physician and nurse concerns about patients' adverse physiologic response to increased dosages.

Pain perception and serum beta-endorphin in trauma patients

Acute traumatic injury engenders the production of beta-endorphin (BE) and other endogenous opioids. Elevated BE concentration putatively correlates with pain perception in trauma patients. The authors examined traumatic injury severity, pain perception, and BE concentration in patients admitted to an urban trauma center. Brief rating instruments for pain and unpleasantness were administered, and blood was drawn for BE analysis in 48 trauma admissions and 33 age-, gender-, and race-matched control subjects for comparison. The authors found no correlation between severity of pain perception and BE, but a significant correlation was found between BE and patient body weight (P < 0.05), physician pain rating (P < 0.01), and Injury Severity Score (P < 0.001). The results suggest that past findings associating trauma pain perception and BE concentration are spurious.

Clinical pharmacokinetics of propofol given as a constant-rate infusion and in combination with epidural blockade

STUDY OBJECTIVES

To investigate the pharmacokinetics of propofol in combination with epidural anesthesia or with intravenous (i.v.) alfentanil infusion, and to investigate the clinical feasibility of this anesthetic technique in lower abdominal surgery.

DESIGN

Randomized, open clinical study.

SETTING

Operating theaters and postanesthesia recovery unit at the department of gynecology of a university medical center.

PATIENTS

20 healthy, consenting ASA physical status I and II adult female patients undergoing lower abdominal surgery.

INTERVENTIONS

A total i.v. anesthetic technique was used in all patients. In Group 1, a continuous infusion of propofol was combined with an epidural block with bupivacaine. Group 2 patients received a combination of propofol and alfentanil infusions.

MEASUREMENTS AND MAIN RESULTS

The pharmacokinetics of propofol are best fitted to a two-compartment open model and were similar in both patient groups. Propofol blood clearance was 29.8 +/- 6.51 ml/min/kg, and volume of distribution was 3.60 +/- 1.34 L/kg, resulting in a blood elimination half-life of 144 +/- 46 minutes. The entire period of anesthesia was stable in the alfentanil group. In the epidural group, the initial period of anesthesia was too light as judged by the autonomic response to tracheal intubation, which also correlated in time to a lower propofol blood concentration than was seen in the alfentanil group. No evidence was found that an epidural block induced a change in propofol kinetics, apart from the lower blood concentration during the initial period of anesthesia.

CONCLUSIONS

We could not show any statistically significant influence of an epidural blockade on the pharmacokinetic parameters of propofol. Nevertheless, the concentration-time profile changed during infusion, rendering the described infusion regimen, in combination with epidural anesthesia, unsatisfactory for adequate hypnosis. The propofol infusion regimen combined with alfentanil provided immediate and stable blood concentrations that were adequate for surgery.

Early extubation after coronary artery surgery in efficiently rewarmed patients: a postoperative comparison of opioid anesthesia versus inhalational anesthesia and thoracic epidural analgesia

Twenty-eight patients were studied after uncomplicated aortocoronary bypass surgery with hypothermic cardiopulmonary bypass (CPB). In all patients residual hypothermia was effectively treated by the use of extended rewarming during CPB and postoperatively by an external heat source. This treatment almost eliminated postoperative shivering, and it resulted in the lowering of oxygen uptake, carbon dioxide production, and required ventilatory volumes to stable levels where spontaneous breathing could be used safely. The patients were divided into two groups. In group I (n = 12), intraoperative anesthesia was based on an intravenous (IV) opioid (phenoperidine), which caused persistent respiratory depression and made mechanical ventilation necessary for a mean postoperative time period of 10.7 +/- 3.8 hours even with the rewarming. In group II (n = 16), thoracic epidural analgesia and intraoperative general anesthesia with enflurane were used. In this group, postoperative metabolic and ventilatory requirements were stable and low, finger skin temperature was normalized earlier, systemic vascular resistance was lower, and stroke index was higher. Emergence from anesthesia was uneventful and was achieved early postoperatively in Group II. The patients had good pain relief and were mentally alert. Adequate spontaneous breathing was resumed quickly and endotracheal extubation was performed within the first two postoperative hours (1.6 +/- 0.5 hours). No complications or increased morbidity occurred, and no patient needed to be reintubated in Group II.

Thoracic epidural anesthesia in conscious and anaesthetized rats. Effects on central haemodynamics compared to cardiac beta adrenoceptor and ganglionic blockade

A simple technique for cannulation of the thoracic epidural space in rats was described. 40-50 microliter of epidural bupivacaine 5 mg/ml induced a distribution of sensory analgesia from lower cervical to lower thoracic segments. With this model, effects of thoracic epidural anaesthesia (TEA) on mean arterial pressure (MAP), cardiac output (CO), systemic vascular resistance (SVR), stroke volume (SV), heart rate (HR), central venous pressure (CVP), left ventricular end-diastolic pressure (LVEDP) and maximal increase of pressure in the left ventricle (max dp/dt) were studied in six groups of animals: 1) In conscious animals (n = 10) MAP, CO, SV and HR decreased significantly by 12%, 25%, 10% and 16%, respectively, while SVR increased significantly by 20% during TEA; 2) In chloralose-anaesthetized animals (n = 7) the reduction in CO during TEA was less pronounced and there were no significant changes in SV or SVR; 3) In conscious animals (n = 6) LVEDP, CVP and max dp/dt decreased significantly during TEA; 4) Hexamethonium, when administered to pharmacologically vagotomized conscious animals during TEA (n = 8), induced a significant decrease in SVR (23%) but no change in HR; 5) Changes in haemodynamics after cardiac adrenoceptor blockade with metoprolol, in conscious animals (n = 12), did not differ significantly from those seen during TEA, except for an unchanged SV after metoprolol; 6) 50 microliters of bupivacaine (5 mg/ml) when given i.v. to conscious animals (n = 8) did not affect CO, SV, HR or TPR significantly, while MAP increased slightly but significantly. Thus, in this conscious animal model, TEA almost completely and rather selectively blocked probably mediated by a reflex activation of unblocked sympathetic efferents.(ABSTRACT TRUNCATED AT 250 WORDS)

[Cervical peridural selective sensitive anesthesia in surgery and rehabilitation of the hand]

Active patient participation in the operative and postoperative programme is very important for tenolysis, tendon grafts and joint releases. Different anesthesic means can be used to perform selective sensitive analgesia. Cervical epidural anesthesia was used for fifteen cases of hand surgery. The technique is described, the results are analyzed. Indications and use of cervical epidural anesthesia for hand surgery are discussed.

Central haemodynamics and regional blood flows during thoracic epidural analgesia combined with positive pressure ventilation. An experimental study in the pig

Cardiac output, central haemodynamics and regional blood flows were studied in pigs. The microsphere technique was used for blood flow determinations. Measurements were made during spontaneous breathing (SB) and during intermittent positive pressure ventilation with 0.8 kPa (8 cmH2O) positive end-expiratory pressure (8 PEEP) before and during thoracic epidural analgesia (TEA). TEA in the pig caused reduced cardiac output due to reduced heart rate with maintained stroke volume. During TEA there was also a reduction of mean arterial blood pressure which ran almost parallel to the decrease in cardiac output with maintained systemic vascular resistance during SB and at 8 PEEP. The distribution of cardiac output was basically the same during SB and at 8 PEEP as it was before TEA. However, myocardial blood flow and relative perfusion decreased during TEA, both during SB and at 8 PEEP. TEA also reduced spinal cord blood flow within the thoracic region during SB and at 8 PEEP.

Haemodynamic effects of intravenous bupivacaine during high thoracic epidural anaesthesia

Administration of small doses of bupivacaine epidurally at the upper thoracic level will partially block the cardiac sympathetic nerves but not the sympathetic outflow via the adrenals. Local anaesthetics have direct systemic effects on the myocardium and the systemic circulation. The present study aimed to examine the effect of high thoracic epidural anaesthesia (TEA) in elderly patients, and to examine the effect of raising plasma bupivacaine concentrations in these patients, who had earlier had the sympathetic innervation of the heart blocked by thoracic epidural anaesthesia. Fifteen elderly patients scheduled for thoracotomy took part in the study. All received high thoracic epidural anaesthesia including the upper five thoracic dermatomes. When epidural block was established, ten patients received bupivacaine 3 mg/min intravenously for 20 min, while five patients received a corresponding volume of normal saline solution. After TEA was established, heart rate, mean arterial blood pressure and cardiac output decreased. When bupivacaine was given to these patients intravenously during the block, mean arterial blood pressure increased, while cardiac output decreased still more. The mechanisms behind these effects seem to be a direct constriction of the systemic blood vessels and a depressive effect on the myocardium, which was blocked from the influence of the cardiac sympathetic nerves by the high thoracic epidural block.

Circulatory effects of short-term hypercapnia during high thoracic epidural anaesthesia in elderly patients

Circulatory changes and the degree of sympathetic block were evaluated in 15 elderly patients with high thoracic epidural anaesthesia (T1-T5). Bupivacaine 5-6 ml 0.5% was injected via an epidural catheter at the T3-level. The quality of the sympathetic block was determined with the Valsalva manoeuvre. Induced hypercapnia was used to quantify the degree of sympathetic block. Following thoracic epidural anaesthesia (TEA), cardiac output, stroke volume and arterial blood pressure decreased. During hypercapnia, heart rate and arterial blood pressure increased both before and after established TEA. Thus the block of the sympathetic innervation to the heart with a high TEA using 0.5% bupivacaine was not sufficient to prevent mobilization of circulatory reserves during sympathetic stimulation. The most likely explanation is considered to be the lack of neural block of the efferent nerves leading to the adrenal medulla and the peripheral vascular bed.

Circulatory changes during high thoracic epidural anaesthesia--influence of sympathetic block and of systemic effect of the local anaesthetic

Circulatory changes during high thoracic epidural anaesthesia (TEA) were studied in nine healthy volunteers by means of echocardiography and systolic time intervals. The subjects also underwent a physical work test with bicycle ergometry. To evaluate the systemic effect of the local anaesthetic (bupivacaine), the same subjects were investigated 3 weeks later when a corresponding dose of the local anaesthetic was injected intramuscularly instead of epidurally. On the first occasion, after baseline measurements an epidural catheter was inserted at T4 level and 5 ml of 0.5% bupivacaine were injected. This volume led to sensory block within dermatomes T1-T5. On the second occasion all subjects received 8 ml of 0.5% bupivacaine intramuscularly. Heart rate (HR) and systolic blood pressure decreased during TEA, both at rest and during exercise. Following i.m. injection, HR decreased at rest but remained unchanged during exercise. The systolic blood pressure was not affected but the diastolic blood pressure increased during the exercise test. After administration of TEA, stroke volume (SV) decreased 22% and cardiac output (CO) 33%. Following i.m. injection of bupivacaine, SV decreased 8% and CO 20%. The pre-ejection period/left ventricular ejection time ratio increased 23% during TEA and 16% after i.m. injection. The results indicate that the circulatory changes did not seem to be caused entirely by the cardiac sympathetic block, but were due partly to the systemic effect of bupivacaine.

Effects of epidural analgesia on plasma catecholamines and cortisol in parturition

To assess the effect of epidural block on plasma catecholamines and cortisol during labour and delivery, plasma epinephrine, norepinephrine and cortisol levels were determined in 26 healthy parturients, all of whom delivered vaginally (18 received an epidural block, eight had meperidine 50 mg intramuscularly). We found a significant drop of plasma epinephrine and cortisol and no significant reduction of plasma norepinephrine 1 h after administration of epidural block compared to preblock values. Observing the data during the whole course of labour in correlation with cervical dilatation, in the control group, where the parturients received meperidine, all hormones rose progressively up to the moment of delivery. One hour after delivery the catecholamines returned to normal levels; cortisol returned more slowly. In the epidural group the increase of plasma epinephrine and cortisol was significantly inhibited but not that of norepinephrine.

Haemodynamics and oxygen consumption in the dog during high epidural block with special reference to the splanchnic region

High epidural block (Th I-IV) with bupivacaine was carried out in 16 dogs. Mean arterial blood pressure decreased to 52% of control value owing to nearly equal decreases in systemic vascular resistance and cardiac output. Portal venous blood flow decreased from 25.8 +/- 8.6 to 16.7 +/- 7.2 ml/kg b.w. X min-1 following epidural block, while hepatic arterial blood flow remained unchanged at 9.1 +/- 3.1 ml/kg b.w. X min-1 owing to a reduction in hepatic arterial resistance of 51%. Hepatic oxygen uptake was maintained during the epidural block through increased oxygen extraction. However, total oxygen uptake decreased by 18% and, in spite of this, arteriovenous oxygen content difference increased by 25%, indicating circulatory depression.

Postoperative pain prevention by continuous epidural infusion. A study of the clinical effects and the plasma concentrations obtained

A method for postoperative pain prevention is described using epidural bupivacaine infused by means of a variable rate peristaltic pump. High plasma concentrations of bupivacaine were found but no serious signs of bupivacaine toxicity were observed and the method proved satisfactory in practice. Theoretical and practical considerations and aspects of clinical management are discussed.

The combination of general anaesthesia and epidural block I: The effects of sequence of induction on haemodynamic variables and blood gas measurements in healthy patients

The haemodynamic effects of epidural block, administered before or after general anaesthesia, were investigated in twelve healthy women scheduled for elective gynaecological surgery. The effects of 10° head down tilt and administration of atropine 0.6 mg intravenously were also determined. Haemodynamic measurements included systolic (SAP), diastolic (DAP) and mean (MAP) arterial pressure, heart rate (HR), cardiac output (CO) and systemic vascular resistance (SVR). In those receiving general anaesthesia first (Group A) (thiopentone/suxamethonium/N2O/O2) significant changes occurred only at the time when epidural block and general anaesthesia were both present: SAP, DAP and MAP (-22%, p < 0.001) were reduced compared to awake control values, however changes in HR, CO and SVR were not significant. In those receiving epidural block first (Group B) (1.5% lignocaine, mean dose 270 mg), MAP was reduced by 20% (p < 0.01) from awake control values after epidural block and there was a further reduction to 35% below control (p < 0.001) when general anaesthesia was induced. These changes were accompanied by a significant reduction in SVR.

Comparison of all variables between Group A and Group B showed no clinically significant differences, indicating that the order of performance of epidural block (before or after general anaesthesia) did not affect haemodynamic variables. Head down tilt resulted in no haemodynamic changes in the presence of general anaesthesia or epidural block alone and only minimal changes when the two were combined. In contrast, intravenous atropine (0.6 mg) resulted in a return of arterial pressures to essentially baseline values in both Group A and Group B (HR increased 84%, p < 0.001; MAP increased 37%, p < 0.001; CO increased 70%, p < 0.001).

Postoperative analgesia

Postoperative analgesia both by drugs and regional techniques is reviewed. In the United Kingdom in the last 25 years or more there has been little advance on either front. Some marginal improvement in regard to drugs might be brought about by better education of both doctors and nurses and better patient contact. Extradural analgesia and intercostal block do not offer a complete solution, though a judicious increase in the use certainly of the former might be beneficial. The problem awaits a radical new approach.

Hemodynamic effects of prenalterol, a beta1-adrenoreceptor agonist, in hypotension induced by high thoracic epidural block in man

The hemodynamic effects of prenalterol, a new beta1-adrenoreceptor agonist, on hypotension induced by a thoracic epidural block extending between T1 and T12 and thereby blocking the cardiac sympathetic supply have been studied in eight patients scheduled for abdominal aortic aneurysm resection. The thoracic epidural block induced a drop in blood pressure, due to a reduction in cardiac output and systemic vascular resistance. Intravenous infusion of 10 mg of prenalterol rapidly and effectively reversed the hypotension by an increase in cardiac output without any effects on systemic vascular resistance or heart rate. The results indicate that prenalterol is a pure beta1 agonist with a marked inotropic but no chronotropic property.

The influence of thoracic epidural analgesia on the circulation at rest and during physical exercise in man

The effects of thoracic epidural analgesia (TEA) on the circulation at rest, during, and after physical exercise were investigated in 10 volunteers. At rest, TEA did not affect oxygen consumption (VO2) or cardiac output (Q), but heart rate (HR) was, increased by 7 beats/min, and stroke volume decreased correspondingly by 13 ml. Systolic arterial blood pressure was slightly reduced, but no other changes in systemic or pulmonary circulatory parameters were produced. TEA did not change VO2 during exercise, a 2.11/min reduction of Q being accompanied by a 4.2% increase of oxygen utilization coefficient. HR showed a relative reduction of about 10%. At moderate work loads during TEA, systemic arterial blood pressures were significantly lower than during control exercise. The resulting rate pressure product (RPP) was markedly reduced, while total peripheral resistance (TPR) remained unchanged. During recovery after the termination of exercise during TEA, VO2, Q, HR, RPP and TPR fell more rapidly towards values obtained at rest. From a clinical point of view the results support the safeness of TEA and also support its use in surgical patients with heart disease.

Cardiovascular effects of epidural analgesia. I. Thoracic epidural analgesia. An experimental study in sheep of the effects on central circulation, regional perfusion and myocardial performance during normoxia, hypoxia and isoproterenol administration

Some circulatory effects of thoracic epidural analgesia (TEA) were investigated in splenectomized, open-chest sheep during normoxia, hypoxia and isoproterenol administration. During normoxia, TEA caused comparatively marked reductions in systemic arterial blood pressure, total peripheral resistance and cardiac output. A fall in heart rate was not compensated for by any rise in stroke volume. Myocardial contractility (LV dd/dt/IP) was not affected by TEA. The proportion of cardiac output diverted to the blocked area was markedly increased. Compensatory vasoconstriction was not observed within the unblocked area in six out of nine animals. Myocardial blood flow showed a pronounced reduction in accordance with the calculated changes of heart work, so that myocardial oxygen extraction remained unchanged. Studies under hypoxia revealed that cardiac responses to hypoxia in the sheep are mediated chiefly by neurogenic factors. TEA abolished the hypoxia-induced rise in heart rate but did not affect the increase in pulmonary vascular resistance caused by hypoxia. The administration of isoproterenol during TEA increased systemic arterial blood pressure, but due to further fall in total peripheral resistance it was not fully normalized. Cardiac output and heart rate increased markedly. Myocardial oxygen consumption and blood flow increased but did not reach control levels.

Thoracic epidural analgesia I-a double-blind study between bupivacaine and etidocaine

A double-blind comparison was made in 40 patients undergoing thoracic epidural analgesia with either bupivacaine 0.5% or etidocaine 1.0%, both with adrenaline 5 mug/ml. All patients were undergoing elective upper abdominal surgery. They were studied both pre- and postoperatively. The parameters measured were: onset time, segmental spread and duration of analgesia; and also systolic blood pressure, heart rate and peak expiratory flow rate. In respect of these parameters, no major differences were found between the two solutions under the conditions of the study. The overall results, however, differ in many respects to those found when these agents are used in lumbar epidural analgesia.

Pulmonary consequences of upper abdominal surgery--therapeutic considerations

Pulmonary complications following abdominal surgery are the largest single cause of morbidity and mortality in the post-operative period. This paper discusses the predisposing factors and clinical features, including the changes in ventilatory function tests. Important concepts in post-operative pain management are outlined, with emphasis on extradural analgesia.