Artefactual 'hypotension' from shivering

Intrathecal Meperidine Plus Lidocaine for Prevention of Shivering during Cesarean Section

Background

Shivering related to spinal anesthesia may interfere with monitoring and is uncomfortable. The aim of the present study was to investigate low-dose intrathecal meperidine for the prevention of shivering after induction of spinal anesthesia in parturients with cesarean section.

Methods

This was a prospective randomized, double-blind, placebo-controlled trial including 100 parturients, of American Society of Anesthesiologists (ASA) physical status I or II, scheduled for elective cesarean section under spinal anesthesia who were randomly assigned to a meperidine (0.2 mg/kg) plus hyperbaric lidocaine (5%, 75 mg, n = 50; group M) group or a placebo plus hyperbaric lidocaine (5%, 75 mg, n = 50; group L) group. Demographic and surgical data, adverse events, and the mean intensity for each parturient were assessed during the entire study period by a blinded observer.

Results

There were no significant differences between the two study groups regarding the demographic and surgical data (P > 0.05). The incidence of shivering during the entire study period significantly decreased in the group of parturients who received intrathecal meperidine (P = 0.04). There were no significant differences in nausea and vomiting between the two groups.

Conclusions

Low-dose intrathecal meperidine (10 mg) is safe and effective in reducing the incidence and severity of shivering associated with spinal anesthesia in parturients with cesarean section.

Effect of active warming on shivering during spinal anesthesia

BACKGROUND

Hypothermia is considered one of the reasons for intraoperative shivering. The purpose of this study is to assess whether active warming can prevent hypothermia and shivering in young adults under spinal anesthesia.

METHODS

Fifty male patients scheduled for an elective operation on lower extremity under spinal anesthesia were randomly assigned into the warming group (n = 25) and the control group (n = 25). The active warming was performed using a forced air-warming device, a warmed blanket and warmed fluid. Axillary and tympanic temperatures, shivering degree, thermal discomfort, and anesthetic level were checked every 10 minutes after intrathecal injection of local anesthetics.

RESULTS

Patients' characteristics and anesthetic levels were comparable between the groups. Axillary and tympanic temperatures were maintained higher in the warming group than the control group 10 minutes and 20 minutes after intrathecal injection respectively. The lowest temperature in operating room was higher in the warming group (36.3 +/- 0.5degrees C) compared with the control group (35.7 +/- 0.5degrees C) (P < 0.05). Incidences of intraoperative shivering and thermal discomfort were lower in the warming group.

CONCLUSIONS

We conclude that intraoperative active warming can prevent hypothermia and shivering during spinal anesthesia.

Postoperative shivering in children: a review on pharmacologic prevention and treatment

Postoperative shivering consists of muscular tremor and rigidity. It is often associated with body heat loss, although hypothermia alone does not fully explain the occurrence of shivering. Shivering is self-limiting, never becomes chronic, and is rarely associated with major morbidity. However, it affects the comfort of the patients, and may sometimes lead to more serious complications. The efficacy of a great variety of pharmacologic interventions to prevent shivering and to treat established symptoms has been tested in randomized controlled trials. These can be gathered systematically; recommendations on prevention and treatment can then be based on the strongest evidence. Unfortunately all these trials have been performed in adults. Thus, recommendations for the control of postoperative shivering in children have to be extrapolated from adult data. In adults, a systematic review strongly suggests that simple measurements are efficacious for both prevention and treatment. For prevention, extrapolation of these adult data indicates that three children have to receive intravenous clonidine 1.5 micro g/kg during anesthesia for one not to shiver, when they would have done so had they not received clonidine. For this degree of efficacy, the expected incidence of shivering (baseline risk) has to be high (approximately 50%). For treatment, extrapolation from adult data indicates that less than two children need to receive intravenous meperidine (pethidine) 0.35 mg/kg, or clonidine 1.5 micro g/kg for one to stop shivering five minutes after drug administration, when they would not have done so had they not received one of these drugs. Since the treatment of established shivering is efficacious, simple, inexpensive, and relatively safe, and since prevention is only efficacious if the baseline risk is very high, we recommend the 'wait and see' strategy.

Intrathecal fentanyl added to intrathecal bupivacaine for day case surgery: a randomized study

BACKGROUND AND OBJECTIVE

The implication of intrathecal lidocaine in neurological toxicity has made intrathecal bupivacaine the commonly used drug for local anaesthesia in ambulatory surgery. However, in high doses intrathecal bupivacaine may produce a high level of sensory and motor block, and arterial hypotension; discharge from hospital may be delayed. Intrathecal opioids added to low-dose local anaesthetics produce a synergistic effect without increasing the sympathetic block or delaying discharge. The aim of our study was to identify the minimum effective dose of intrathecal fentanyl that in combination with low-dose intrathecal bupivacaine would provide adequate surgical conditions without prolonging recovery.

METHODS

A prospective, single, blind, randomized study was conducted in 45 adult males scheduled for minor urological procedures using intrathecal anaesthesia on a day care basis. Patients were randomly assigned to one of three groups (n = 15 each). They received bupivacaine 0.17% 5 mg--with either fentanyl 7.5 microg (fenta-7.5), 10 microg (fenta-10) or 12.5 microg (fenta-12.5) intrathecally in a total volume of 3 mL. The quality of anaesthesia, haemodynamic stability, time to two-segment and S2 regression, time to micturition, and time to discharge were assessed.

RESULTS

The time to two-segment regression and S2 regression with fenta-12.5 was significantly longer than with fenta-7.5 and fenta-10 (P < 0.01). Fenta-7.5 had a significantly higher number of failed blocks (four patients) compared with fenta-12.5 (P < 0.05). The time out of bed, time to micturition and time to discharge were significantly longer with fenta-10 and fenta-12.5 compared with fenta-7.5, and also with fenta-12.5 compared with fenta-10 (P < 0.01). Haemodynamic stability did not differ for all the drug combinations.

CONCLUSIONS

Fentanyl 12.5 microg added to low-dose bupivacaine (5 mg) intrathecally provides better surgical anaesthesia and increased reliability of block than intrathecal fentanyl 7.5 or 10 microg. Haemodynamic stability was the same for all dose combinations used.

Important physical principles in anaesthesiology

The aim of this Review is to introduce anaesthesiologists to the basic physical principles that are important for their work. A better understanding of the underlying processes during anaesthesia is required for greater safety and efficiency. Relevant physical quantities are presented along with the area of anaesthesiology where they are used. This approach provides better targeting to the needs of practising anaesthesiologists. This text has been a part of a specialist course in anaesthesiology at the University of Ljubljana for some years. Current results show that both the students and the specialist anaesthesiologists now show a better understanding of the underlying physical principles required for their work and are more successful in fulfilling the needs of their practical work.

High-dose midazolam and the attenuation of the contractile response to vasoconstrictors in coronary artery segments

BACKGROUND AND OBJECTIVE

Benzodiazepines may cause hypotension and are reported to interfere with smooth vascular muscle activity. The aim was to elucidate the influence of three different benzodiazepines on the vascular reactivity of coronary arteries.

METHODS

Using the model of isolated vessels, we studied the impact of midazolam (0.15, 1.5, 15 microg mL(-1)), diazepam (0.1, 1.0, 10 microg mL(-1)) and flunitrazepam (0.01, 0.1, 1.0 microg mL(-1)) on the contractile responses to histamine (2 x 10(-5) mol L(-1)) and serotonin (3 x 10(-5) mol L(-1)) in isolated intact and denuded coronary arteries.

RESULTS

Midazolam significantly attenuated the contractile response when administered in high concentrations (15 microg mL(-1)). This effect was more pronounced in intact than in denuded preparations (histamine: -22.7 versus -7.3%, P = 0.0079; serotonin: -47.1 versus -15.9%, P < 0.0001). Diazepam and flunitrazepam exerted no significant effects on the vascular tone of coronary arteries.

CONCLUSIONS

Midazolam, but not diazepam or flunitrazepam, attenuates the contractile responses to vasoconstrictors in concentrations beyond those used in clinical practice. This effect is in part mediated by endothelial factors.

Anaesthesia for day case surgery: a survey of adult clinical practice in the UK

BACKGROUND AND OBJECTIVE

In October 2000, we conducted a national postal survey of consultant day case anaesthetists in the UK to explore the range and variation in the practice of anaesthetizing a patient for day case surgery (paediatrics, urology and orthopaedics). The survey was carried out as part of a larger study that comprised a major two-centre randomized controlled trial designed to investigate the costs and outcome of several anaesthetic techniques during day care surgery in paediatric and adult patients (cost-effectiveness study of anaesthesia in day case surgery). We report the findings of this national survey of adult urology and orthopaedic day case anaesthetic practice in the UK.

METHODS

The survey used a structured postal questionnaire and collected data on the duration of the surgical procedure; the use of premedication; the anaesthetic agents used for induction and maintenance; the fresh gas flows used for anaesthesia; the use of antiemetics; and the administration of local anaesthesia and analgesia.

RESULTS

The overall response rate for the survey was 74% (63% for urology, 67% for orthopaedics). The survey indicated the following practice in adult urology and adult orthopaedic day case surgery: 6 and 12% used premedication; propofol was the preferred induction agent (96 and 97%) and isoflurane the preferred maintenance agent (56 and 58%); 32 and 41% used prophylactic antiemetics; 86 and 93% used a laryngeal mask.

CONCLUSIONS

This survey identifies the variation in current clinical practice in adult day surgery anaesthesia in the UK and discusses this variation in the context of current published evidence.

Effect of dexamethasone on motor brachial plexus block with bupivacaine and with bupivacaine-loaded microspheres in a sheep model

BACKGROUND AND OBJECTIVE

It has been suggested that dexamethasone potentiates the sensory block produced by bupivacaine when both drugs are loaded in microspheres. The aim of the study was to evaluate the effect of dexamethasone on the brachial plexus block obtained with plain bupivacaine and bupivacaine-loaded microspheres.

METHODS

Dexamethasone alone (Group 5) or added to plain bupivacaine (75 mg) with (Groups 3 and 4) and without pH correction (Group 2) was compared with plain bupivacaine (75 mg; Group 1). The effect of a small dose of dexamethasone (0.42 mg) was then evaluated on the brachial plexus block obtained with bupivacaine (750 mg) as bupivacaine-loaded microspheres (Group 6). Dexamethasone was added either in the suspending medium (Group 7) or incorporated with bupivacaine into microspheres (Group 8). The motor block was evaluated in a plexus brachial sheep model.

RESULTS

Dexamethasone alone did not produce any motor block. When added to plain bupivacaine without pH correction, complete motor block could not be obtained. When the pH was corrected, addition of dexamethasone to plain bupivacaine seemed to delay the onset of motor block and did not prolong its duration, and it had no effect on the pharmacokinetics of bupivacaine. With bupivacaine-loaded microspheres, the duration of complete motor block was reduced when a small dose of dexamethasone was added in the suspending medium. However, the duration of motor block was significantly prolonged when dexamethasone was incorporated with bupivacaine into microspheres.

CONCLUSIONS

Despite the delayed onset of motor block, the incorporation of dexamethasone in bupivacaine-loaded microspheres dramatically increases the duration of action (700 +/- 485-5160 +/- 2136 min), which could be clinically relevant when such a drug-delivery system will be available.

Haemodynamic response to a small intravenous bolus injection of epinephrine in cardiac surgical patients

BACKGROUND AND OBJECTIVE

The aim was to study the rapid changes in cardiac output and systemic vascular resistance produced by intravenous epinephrine (5 microg) on a beat-by-beat basis.

METHODS

Ten patients were studied during cardiac surgery. Radial or brachial arterial pressure was recorded continuously during intravenous administration of epinephrine (5 microg). Cardiac output and systemic vascular resistance were derived for each beat using arterial pulse contour analysis calibrated by lithium indicator dilution. In each patient a further dose of epinephrine (5 microg) was administered during cardiopulmonary bypass with the blood flow kept constant so that changes in arterial pressure corresponded to changes in systemic vascular resistance.

RESULTS

When the patients were not on cardiopulmonary bypass, the epinephrine produced an initial increase in systemic vascular resistance to 129 +/- 15% (mean +/- SD) of control, followed by a more prolonged reduction to 57 +/- 13% of control. Cardiac output showed a small initial reduction coincident with the increase in systemic vascular resistance, followed by an increase to 152 +/- 24% of control. During cardiopulmonary bypass, the changes produced by epinephrine on systemic vascular resistance were qualitatively similar but smaller in amplitude, probably because of a greater volume of dilution in the bypass circuit.

CONCLUSIONS

Small bolus doses of epinephrine produce an initial increase in systemic vascular resistance followed by a much greater reduction that may cause hypotension.

Anaesthesia for day case surgery: a survey of paediatric clinical practice in the UK

BACKGROUND AND OBJECTIVE

In October 2000, we conducted a national postal survey of day case consultant anaesthetists in the UK to explore the range and variation in practice of anaesthetizing a patient for day case surgery (paediatrics, urology and orthopaedics). This paper reports the findings of this national survey of paediatric day case anaesthetic practice carried out as part of a major two-centre randomized controlled trial designed to investigate the costs and outcome of several anaesthetic techniques during day care surgery in paediatric and adult patients (cost-effectiveness study of anaesthesia in day case surgery).

METHODS

The survey used a structured postal questionnaire and collected data on the duration of surgical procedure; the use of premedication; the anaesthetic agents used for induction and maintenance; the fresh gas flow rates used for general anaesthesia; the use of antiemetics; and the administration of local anaesthesia and analgesia.

RESULTS

The overall response rate for the survey was 74 and 63% for the paediatric section of the survey. Respondents indicated that 19% used premedication, 63% used propofol for induction, 54% used isoflurane for maintenance, 24% used prophylactic antiemetics and 85%, used a laryngeal mask. The findings of this national survey are discussed and compared with published evidence.

CONCLUSIONS

This survey identifies the variation in clinical practice in paediatric day surgery anaesthesia in the UK.

Recollection of dreams after short general anaesthesia: influence on patient anxiety and satisfaction

BACKGROUND AND OBJECTIVE

We ascertained whether dreams during short general anaesthesia influence subsequent patient satisfaction and anxiety.

METHODS

Fifty female patients were randomized into two groups to test for a difference between intravenous and inhalational anaesthesias. In Group Propo, anaesthesia was induced and maintained with propofol; in Group Metho-Iso, anaesthesia was induced with methohexital and maintained with isoflurane. Satisfaction and anxiety with anaesthesia were evaluated using a visual analogue scale from 0 to 100. Dream incidence rate, satisfaction and anxiety were assessed from immediately after waking until 3 months later.

RESULTS

Seventeen patients (34%) dreamed during anaesthesia. There were no significant differences in satisfaction or anxiety after anaesthesia between the dreaming and non-dreaming patients (satisfaction, 92.3 +/- 21.6 versus 92.1 +/- 21.6; anxiety, 21.1 +/- 21.1 versus 30.3 +/- 32.1), or between Group Propo and Group Metho-Iso (satisfaction, 94.4 +/- 19.3 versus 90.0 +/- 23.4; anxiety, 26.0 +/- 27.6 versus 28.4 +/- 30.7). There was no significant difference in the incidence rate of dreaming with the type of anaesthesia used (Group Propo, 11 patients; Group Metho-Iso, 6 patients).

CONCLUSIONS

Dreaming during general anaesthesia is common but does not influence satisfaction or anxiety after anaesthesia.

Control of shivering under regional anesthesia in obstetric patients with tramadol

PURPOSE

Tramadol in a dose of 1 mg x kg(-1) iv is effective in the treatment of shivering after general anesthesia. The current study aimed to investigate (1) whether tramadol was equally effective for shivering under regional anesthesia in obstetric patients and (2) whether effective treatment could be achieved with lower doses.

METHODS

In a randomised, double-blind study, 36 obstetric patients who shivered during Cesarean section under regional anesthesia and who requested anti-shivering treatment were allocated to one of three groups for iv treatment: Group T0.5 received tramadol 0.5 mg x kg(-1) (n = 12), Group T0.25 tramadol 0.25 mg x kg(-1) (n = 13) and Group NS normal saline 0.05 ml x kg(-1) (n = 11). Treatment efficacy was evaluated subjectively by the parturient as no improvement, slight improvement, or marked improvement. The attending anesthesiologist who was blinded also independently noted the time elapsed from treatment to the time shivering subsided. Side effects such as nausea, vomiting or sedation and Apgar scores of the newborn were also noted.

RESULTS

Eighty percent of parturients in Group T0.5 and 92% in Group T0.25 were judged by observers to have shivering controlled compared with 27% in Group NS (P < 0.001). The response rates of Group T0.5 and Group T0.25 were not different. There was no increased incidence of side effects in the treatment groups.

CONCLUSION

We conclude that tramadol iv was effective in the treatment of intraoperative shivering during regional anesthesia for Cesarean section. There was no demonstrable difference in response rate or incidence of side effects between the two doses of 0.5 mg x kg(-1) and 0.25 mg x kg(-1).

Clonidine at induction reduces shivering after general anaesthesia

PURPOSE

Postanaesthetic shivering occurs in 5-65% of patients. In addition to causing discomfort, it is associated with deleterious consequences. Our objective was to investigate the effect of 150 micrograms clonidine, at induction of anaesthesia, on perioperative core and peripheral temperature, incidence of postanaesthetic shivering and patients' perception of cold.

METHODS

Sixty ASA 1 or 2 patients scheduled for elective orthopaedic limb surgery were randomly allocated to group 1, who received 150 micrograms clonidine iv, or group 2, who received a saline bolus iv, before induction. In all patients, anaesthesia was induced with fentanyl and propofol and maintained by spontaneous respiration (via a laryngeal mask airway) of oxygen, nitrous oxide and enflurane. Core (nasopharyngeal) and peripheral (dorsal hand) temperatures were recorded at induction and 15-min intervals. Nurses, unaware of the treatment groups, recorded visible shivering in the recovery room. When cognitive function returned, patients were asked to grade their perception of cold on a 10 cm linear analogue scale, higher scores indicating heat discomfort.

RESULTS

While core temperature decreased and peripheral temperature increased in both groups, there was no difference between the groups at any time. However, there was a lower incidence of shivering in the clonidine group (20% vs 66.7%, P < 0.001). Patients receiving clonidine felt warmer; thermal comfort score (median interquartile range) 5.9 (5.0-7.2) vs 5.0 (4.5-6.0), P < 0.05).

CONCLUSION

Clonidine 150 g iv at induction of anaesthesia reduces the incidence of shivering and patients' subjective perception of cold on emergence from general anaesthesia.

The effect of different end-tidal volatile agent and carbon dioxide concentrations upon the incidence of postoperative shivering

Sixty patients (47 female) undergoing surgical excision of three or more wisdom teeth were randomly allocated into three groups with differing end-tidal carbon dioxide and volatile agent concentrations during maintenance of anaesthesia. The anaesthetic techniques employed were identical in all other respects. All patients were observed for 10 min after arrival in the recovery area to assess the presence and severity of shivering, axillary temperature and oxygen saturation. There were no significant differences in axillary temperatures between groups or between shivering and non-shivering patients, although there was a significant difference (p = 0.001) in duration of anaesthesia between shivering and non-shivering patients. There was no significant difference between groups with respect to the incidence of shivering (p = 0.96).

A comparison of thiopentone and propofol with respect to the incidence of postoperative shivering

One hundred patients (69 female) undergoing surgical excision of three or more wisdom teeth were randomly allocated to receive either thiopentone or propofol for induction of anaesthesia. Other than the induction agent, the anaesthetic regimen was standardised for all cases. All patients were observed for 15 min after entry into the recovery area to assess the presence and intensity of shivering. Twenty-five patients in the thiopentone group (n = 50) and 11 patients in the propofol group shivered postoperatively (p < 0.005). There was no statistically significant difference in axillary temperature between shivering and non-shivering patients. The use of propofol as an induction agent is associated with a lower incidence of postoperative shivering than thiopentone.