Mike Paech

Avoidance of nitrous oxide for patients undergoing major surgery: a randomized controlled trial.

Background: Nitrous oxide is widely used in anesthesia, often administered at an inspired concentration around 70%. Although nitrous oxide interferes with vitamin B12, folate metabolism, and deoxyribonucleic acid synthesis and prevents the use of high inspired oxygen concentrations, the consequences of these effects are unclear. Methods: Patients having major surgery expected to last at least 2 h were randomly assigned to nitrous oxide–free (80% oxygen, 20% nitrogen) or nitrous oxide–based (70% N2O, 30% oxygen) anesthesia. Patients and observers were blind to group identity. The primary endpoint was duration of hospital stay. Secondary endpoints included duration of intensive care stay and postoperative complications; the latter included severe nausea and vomiting, and the following major complications: pneumonia, pneumothorax, pulmonary embolism, wound infection, myocardial infarction, venous thromboembolism, stroke, awareness, and death within 30 days of surgery. Results: Of 3,187 eligible patients, 2,050 consenting patients were recruited. Patients in the nitrous oxide–free group had significantly lower rates of major complications (odds ratio, 0.71; 95% confidence interval, 0.56–0.89; P = 0.003) and severe nausea and vomiting (odds ratio, 0.40; 95% confidence interval, 0.31–0.51; P < 0.001), but median duration of hospital stay did not differ substantially between groups (7.0 vs. 7.1 days; P = 0.06). Among patients admitted to the intensive care unit postoperatively, those in the nitrous oxide–free group were more likely to be discharged from the unit on any given day than those in the nitrous oxide group (hazard ratio, 1.35; 95% confidence interval, 1.05–1.73; P = 0.02). Conclusions: Avoidance of nitrous oxide and the concomitant increase in inspired oxygen concentration decreases the incidence of complications after major surgery, but does not significantly affect the duration of hospital stay. The routine use of nitrous oxide in patients undergoing major surgery should be questioned.

Guidelines for the management of hypertensive disorders of pregnancy 2008

This is the Executive Summary of updated guidelines developed by the Society of Obstetric Medicine of Australia and New Zealand for the management of hypertensive diseases of pregnancy. They address a number of challenging areas including the definition of severe hypertension, the use of automated blood pressure monitors, the definition of non‐proteinuric pre‐eclampsia and measuring proteinuria. Controversial management issues are addressed such as the treatment of severe hypertension and other significant manifestations of pre‐eclampsia, the role of expectant management in pre‐eclampsia remote from term, thromboprophylaxis, appropriate fluid therapy, the role of prophylactic magnesium sulfate and anaesthetic issues for women with pre‐eclampsia. The guidelines stress the need for experienced team management for women with pre‐eclampsia and mandatory hospital protocols for treatment of hypertension and eclampsia. New areas addressed in the guidelines include recommended protocols for maternal and fetal investigation of women with hypertension, preconception management for women at risk of pre‐eclampsia, auditing outcomes in women with hypertensive diseases of pregnancy and long‐term screening for women with previous pre‐eclampsia.

Complications of obstetric epidural analgesia and anaesthesia: a prospective analysis of 10,995 cases.

Although epidural anaesthesia and analgesia are widely used in obstetrics, there are no large contemporary prospective series detailing associated complications. Prospective data was collected on all obstetric epidural blocks performed for labour and delivery in a single institution between July 1989 and August 1994. A data entry sheet was compiled and entered onto a computer database. Confidence intervals for proportions were calculated using standard methods. Information from 10 995 epidural blocks was analysed. Epidural analgesia in labour was the primary indication in 7648, and anaesthesia for caesarean section in 3311. Minor complications included failed or abandoned insertion (incidence 0.5%), reinsertion of the epidural catheter (5%), and inadequate anaesthesia (1.7%) or analgesia (0.9%). Three percent were associated with venous puncture and 0.6% with accidental dural puncture. Maternal mortality was zero. Unexpectedly high blocks occurred on eight occasions (0.07%), two requiring intubation and ventilation. Three women (0.06%) experienced mild respiratory depression after postoperative epidural opioid. There was no major local anaesthetic toxicity or neurological deficit. The incidence of potentially life-threatening morbidity was thus 0.02% although in both cases outcome was good. The only persisting complication was neurological, an apparent epidural catheter-induced traumatic mononeuropathy.

Difficult and failed intubation in obstetric anaesthesia: an observational study of airway management and complications associated with general anaesthesia for caesarean section

BACKGROUND Recent developments in anaesthesia and patient demographics have potentially changed the practice of obstetric general anaesthesia. There are few contemporary data on Australasian practice of general anaesthesia for caesarean section, especially relating to airway management, anaesthetic techniques and complications. METHODS Using a standardised case record form, a prospective observational study was conducted during 2005-06 in 13 maternity hospitals dealing with approximately 49 500 deliveries per annum. Patient demographics, airway management, anaesthetic techniques and major complications were evaluated in those given general anaesthesia. RESULTS Data were obtained from 1095 women receiving general anaesthesia for caesarean section, 47% of which were classified as category 1 and 18% as category 4. Tracheal intubation was planned in all cases with rapid-sequence induction used in 97%. A grade 3 or 4 laryngoscopic view was obtained in 3.6 and 0.6% of cases respectively, with 3.3% considered a difficult intubation. There were four failed intubations (0.4%, 95% CI 0.01-0.9%), of which three were subsequently managed using a laryngeal mask airway. Antacid prophylaxis was used in 94% of elective cases and 64% of emergencies. Regurgitation of gastric contents was noted in eight cases (0.7%, 95% CI 0.2-1.2%), with one confirmed case of aspiration (0.1%, 95% CI 0.002-0.5%). There were no cases of serious airway-related morbidity. CONCLUSIONS General anaesthesia is most commonly used in emergency situations. Tracheal intubation after rapid-sequence induction remains the predominant approach to airway management in Australasia. The incidence of failed intubation is consistent with previous studies. Aspiration prophylaxis is not routinely used for emergency surgery.

A randomized, placebo-controlled trial of preoperative oral pregabalin for postoperative pain relief after minor gynecological surgery.

BACKGROUND:Although pregabalin shows efficacy against neuropathic pain, very limited evidence supports postoperative analgesic efficacy. Our study objective was to investigate analgesic efficacy in an ambulatory day surgical population experiencing acute visceral pain. The null hypothesis was that there was no significant difference in pain relief between pregabalin and placebo. METHODS:A randomized, double-blind, parallel-group, placebo-controlled trial was performed in 90 women having minor gynecological surgery involving the uterus. Patients received either oral pregabalin 100 mg (Group PG) or placebo (Group C) approximately 1 h before surgery. The primary outcome was pain score in the recovery unit and patients were followed for 24 h. RESULTS:There was no significant difference between groups for pain experienced in the recovery room (median, interquartile range 16, 0–36 vs 10, 6.5–36 for Groups PG and C, respectively, P = 0.80) or thereafter; nor for recovery room fentanyl requirement (42% Group PG versus 27% Group C, P = 0.12) or the quality of recovery at 24 h postoperatively (median, interquartile range score 17, 17–18 Group PG versus 18, 16.5–18 Group C, P = 0.75). The incidence of posthospital discharge light-headedness, visual disturbance, and difficulty with walking was significantly higher in the pregabalin group. CONCLUSIONS:A single preoperative dose of 100 mg pregabalin does not reduce acute pain or improve recovery after minor surgery involving only the uterus.

A Comparison of Epidural Ropivacaine Infusion Alone and in Combination with 1, 2, and 4 [micro sign]g/mL Fentanyl for Seventy-Two Hours of Postoperative Analgesia After Major Abdominal Surgery

UNLABELLED Our aim in this prospective, randomized, double-blinded study was to compare the analgesic effectiveness and side effects of epidural infusions with ropivacaine 2 mg/mL alone (Group R; n = 60) and in combination with fentanyl 1 microg/mL (R1F; n = 59), 2 microg/mL (R2F; n = 62), and 4 microg/mL (R4F; n = 63) for up to 72 h after major abdominal surgery. Effective epidural neural blockade was established before surgery; postoperatively, the infusion rate was titrated to a maximum of 14 mL/h for analgesia. No additional analgesics other than acetaminophen were permitted during the infusion. The median of individual visual analog scale score with coughing were <20 mm for all groups (0 = no pain, 100 = worst pain) and was significantly lower (P < 0.01) for Group R4F at rest and with coughing (compared with Group R). Infusions were discontinued due to inability to control pain in significantly fewer patients in Group R4F (16%) than the other groups (34% to 39%; P < 0.01). For all groups, >90% of patients had no detectable motor block after 24 h. Hypotension, nausea, and pruritus were more common with the larger dose of fentanyl. We conclude that, after major abdominal surgery, an epidural infusion of ropivacaine 2 mg/mL with fentanyl 4 microg/mL provided significantly more effective pain relief over a 3-day period than ropivacaine alone or ropivacaine with lower concentrations of fentanyl. IMPLICATIONS Postoperative epidural analgesic infusions are widely used, but there is little information regarding optimal strengths of opioid with local anesthetic. In this blinded, prospective study, we compared four different epidural infusion solutions for efficacy and side effects over a clinically useful postoperative period and conclude that an epidural infusion of ropivacaine 2 mg/mL with fentanyl 4 microg/mL was most effective.

Neuraxial Drug Administration A Review of Treatment Options for Anaesthesia and Analgesia

Neuraxial drug administration describes techniques that deliver drugs in close proximity to the spinal cord, i.e. intrathecally into the CSF or epidurally into the fatty tissues surrounding the dura, by injection or infusion. This approach was initially developed in the form of spinal anaesthesia over 100 years ago. Since then, neuraxial drug administration has evolved and now includes a wide range of techniques to administer a large number of different drugs to provide anaesthesia, but also analgesia and treatment of spasticity in a variety of acute and chronic settings.This review concentrates on the pharmacological agents used and the clinical basis behind currently utilised approaches to neuraxial drug administration. With regard to local anaesthetics, the main focus is on the development of the enantiomer-specific compounds ropivacaine and levobupivacaine, which provide similar efficacy to bupivacaine with a reduced risk of severe cardiotoxicity. Opioids are the other group of drugs widely used neuraxially, in particular to provide analgesia alone or more commonly in combination with other agents. The physicochemical properties of the various opioids explain the main differences in efficacy and safety between these drugs when used intrathecally, of which morphine, fentanyl and sufentanil are most commonly used. Another group of drugs including clonidine, dexmedetomidine and epinephrine (adrenaline) provide neuraxial analgesia via α-adrenergic receptors and are used mainly as adjuvants to local anaesthetics and opioids. Furthermore, intrathecal baclofen is in routine clinical use to treat spasticity in a number of neurological conditions.Beside these established approaches, a wide range of other drugs have been assessed for neuraxial administration to provide analgesia; however, most are in various early stages of investigation and are not used routinely. These drugs include neostigmine, ketamine, midazolam and adenosine, and the conotoxin ziconotide. The latter is possibly the most unusual compound here; it has recently gained registration for intrathecal use in specific chronic pain conditions.

Nitrous oxide and long-term morbidity and mortality in the ENIGMA trial

BACKGROUND:There is a plausible pathophysiologic rationale for increased long-term cardiovascular morbidity and mortality in patients receiving significant exposure to nitrous oxide. However, this relationship has not been established clinically. The ENIGMA trial randomized 2050 patients having noncardiac surgery lasting more than 2 hours to nitrous oxide–based or nitrous oxide–free anesthesia. We conducted a follow-up study of the ENIGMA patients to evaluate the risk of cardiovascular events in the longer term. METHODS:The trial case report forms and medical records of all study patients were reviewed. The date and cause of death and occurrence of myocardial infarction or stroke were recorded. A telephone interview was then conducted with all surviving patients. The primary endpoint of the study was survival. RESULTS:The median follow-up time was 3.5 (range: 0 to 5.7) years. Three hundred eighty patients (19%) had died since the index surgery, 91 (4.5%) were recorded as having myocardial infarction, and 44 (2.2%) had a stroke during the entire follow-up period. Nitrous oxide did not significantly increase the risk of death [hazard ratio = 0.98 (95% confidence interval, CI: 0.80 to 1.20; P = 0.82)]. The adjusted odds ratio for myocardial infarction in patients administered nitrous oxide was 1.59 (95% CI: 1.01 to 2.51; P = 0.04) and for stroke was 1.01 (95% CI: 0.55 to 1.87; P = 0.97). CONCLUSIONS:The administration of nitrous oxide was associated with increased long-term risk of myocardial infarction, but not of death or stroke in patients enrolled in the ENIGMA trial. The exact relationship between nitrous oxide administration and serious long-term adverse outcomes will require confirmation by an appropriately designed large randomized controlled trial.

The assessment of postoperative pain by monitoring skin conductance: results of a prospective study*

The number of fluctuations of skin conductance per second correlates with postoperative pain. The aim of this prospective study was to test the cut‐off value for the number of fluctuations of skin conductance per second obtained from a previous study. Seventy‐five patients were asked to quantify their level of pain on a numeric rating scale (0–10) in the recovery room. The number of fluctuations of skin conductance per second was recorded simultaneously. The number of fluctuations of skin conductance per second was different between patients with no (0.07), mild (0.16), moderate (0.28) and severe pain (0.33); p < 0.001. The tested cut‐off value for the number of fluctuations of skin conductance per second (0.1) distinguished a numeric rating scale ≤ 3 from > 3 with 88.5% sensitivity and 67.7% specificity. The number of fluctuations of skin conductance per second may be a useful means of assessing postoperative pain.

Risk factors for severe postoperative nausea and vomiting in a randomized trial of nitrous oxide-based vs nitrous oxide-free anaesthesia

BACKGROUND Refractory postoperative nausea and vomiting (PONV) requiring repeated treatment with antiemetic drugs is a miserable experience for the patient that may substantially increase the cost of care. As risk stratification may aid in prophylaxis and treatment, we explored risk factors for severe PONV in patients enrolled in a large international, randomized controlled trial (the ENIGMA trial). METHODS Two thousand and fifty patients, aged > or =18 yr and undergoing surgery anticipated to exceed 2 h in duration, were recruited. Patients were randomized to nitrous oxide (N(2)O)-based or N(2)O-free anaesthesia. Choice of other anaesthetic, analgesic, and antiemetic drugs was left to the discretion of the anaesthetist. Anaesthetic depth was adjusted according to clinical judgement and, if available, bispectral index (BIS) monitoring. Severe PONV was defined as: (i) two or more episodes of expulsion of gastric contents at least 6 h apart; (ii) received at least three doses of antiemetic medication for treatment of PONV, within 24 h of surgery; or both. We used logistic regression, and classification and regression tree analysis, to define risk factors for severe PONV. RESULTS Three hundred and thirty-three (16.6%) patients experienced severe PONV. Age <55 yr, female sex, abdominal surgery, N(2)O administration, absence of BIS monitoring, and longer duration of anaesthesia were predictors of severe PONV [area under receiver operating characteristic curve=0.70 (95% confidence interval: 0.67-0.73)]. CONCLUSIONS Severe PONV was common and risk factors for it were similar to those reported in other studies that included all patients reporting nausea, vomiting, or both.