Anaesthesia and Intensive Care

Weaning patients from mechanical ventilation in the intensive care unit can be difficult. In patients requiring prolonged ventilatory support it has been demonstrated that conventional weaning criteria are frequently incorrect. In this group measurement of respiratory work may be of benefit. Until recently, estimation of the work of breathing in patients receiving mechanical ventilation was logistically difficult. The availability of a computerized bedside monitoring device potentially allows easier estimation of the work of breathing at the bedside. The results of preliminary studies utilizing such monitoring are provocative: they highlight the phenomenon of nosocomial respiratory failure and challenge our clinical ability to determine patient workloads and timing of extubation. The potential benefits of work of breathing measurement, in particular the avoidance of respiratory muscle fatigue, earlier extubation, reduced duration of mechanical ventilation, reduction in ICU and hospital length of stay, and most importantly, a reduction in patient morbidity are yet to be demonstrated and concerns still exist about the monitor's accuracy.

The aim of this systematic review was to assess the effects of nonsteroidal anti-inflammatory drugs (NSAIDs) on postoperative renal function. Eight randomized placebo-controlled double-blinded trials (n=345) were identified from searches of MEDLINE, EMBASE and the Cochrane Controlled Trials Register databases. The summary effect size and 95% confidence intervals (95%CI) were calculated by a weighted mean difference analysis using a random-effects model. The NSAIDs (diclofenac, ketorolac, indomethacin, ibuprofen) were used for up to three days after surgery. There were no reported cases of postoperative renal failure requiring dialysis. NSAIDs reduced creatinine clearance by 22 ml.min⁻¹ (95%CI: 7 to 37), sodium output by 54 mmol.day⁻¹ (95%CI: 5 to 103) and potassium output by 38 mmol.day⁻¹ (95%CI: 19 to 56) on Day 1 but not on Day 2. Serum creatinine increased on Day 2 by 15μmol.l⁻¹ (95%CI: 2 to 28). Urine volume did not change significantly at any time. There was therefore a clinically unimportant transient reduction in renal function. NSAIDs should not be withheld from patients with normal preoperative renal function because of concerns about postoperative renal impairment.

This study was performed to assess the changes in pulmonary mechanics before and after tracheostomy in patients with prolonged mechanical ventilation and to detect pre-tracheostomy physiologic factors that predict the outcome of weaning from mechanical ventilation. Pulmonary mechanics were recorded before and after tracheostomy in 20 patients. Work of breathing, mean airway resistance and pressure/time product showed no significant differences after tracheostomy. Peak inspiratory pressure was significantly reduced (pre 33.4±11.8 vs post 28.6±9.2 mmHg). There was no difference in age or duration of mechanical ventilation between two different groups according to the outcome (weaned and not-weaned). Pre-tracheostomy intrinsic positive end expiratory pressure (PEEPi) was significantly lower in the weaned group (1.1±1.6 vs 2.7±1.4 mmHg). A significant difference was also found in pre-tracheostomy compliance (C_static) (47.3±36.9 vs 28.8±16.5 ml/cmH₂O). We concluded that tracheostomy changed pulmonary mechanics very little except for a fall in peak inspiratory pressure. Patients who had better underlying lung mechanics (higher C_static and lower PEEP_i) had better chances of weaning from mechanical ventilation after tracheostomy.

This study assessed the agreement between three methods of cardiac output (CO) measurement, thermodilution, the current clinical standard, and two transoesophageal echocardiographic techniques. Measurements were performed in 37 patients using thermodilution, continuous wave Doppler across the aortic valve and pulsed wave Doppler positioned in the left ventricular outflow tract. The aortic valve area was measured by direct planimetry, and the left ventricular outflow tract area was calculated from its diameter. Weighted least products regression analysis was employed to detect bias, and standard deviation of the difference (SDdiff) was calculated. There was no fixed bias but there was proportional bias between continuous wave Doppler and thermodilution methods (SDdiff 0.92 l/min). There was fixed bias but not proportional bias between pulsed wave and thermodilution methods (SDdiff 1.1 l/min). There was neither fixed nor proportional bias between pulsed wave and continuous wave Doppler methods (SDdiff 1.1 l/min). The transoesophageal Doppler methods described can be clinical alternatives to thermodilution cardiac output measurement.

We report out initial experience with intraoperative transoesophageal echocardiography (TOE) in 200 patients undergoing repair of congenital heart disease. Complications associated with probe insertion precluded a full study in 11 patients (5.5%) and included airway obstruction (n=6), inability to pass the probe (n=4) and vascular compression (n=1). The preoperative diagnosis was confirmed by TOE in 176 of 189 cases (93%) with minor variances in 12 (6.3%) and one major variance (additional large muscular ventricular septal defect (VSD)). Unexpected abnormalities not diagnosed preoperatively were found at surgery in four cases (2%) and were all of trivial operative significance. Postoperative studies showed no residual defect in 96 (51%) and trivial or mild residual defects in 72 patients (38%). There were moderate or severe residual defects in 21 cases (11%). Ten cases (5.3%) returned to bypass for further surgery, with eight achieving complete or adequate amelioration. In six of the 10 cases, return to bypass was prompted by the TOE examination alone. There was one re-operation in the postoperative period for a VSD patch dehiscence. Routine TOE offers significant advantages in the management of patients undergoing repair of congenital heart disease, particularly in postoperative assessment. Careful monitoring of perfusion and ventilation is required, particularly during probe insertion in children weighing 5 kg or less.

Percutaneous dilatational tracheostomy is frequently performed as an alternative to traditional surgical open tracheostomy with many reported benefits. Despite its relative safety and widespread acceptance, complications can be associated with the procedure itself or long-term. We present four cases where there was difficulty with decannulation because of exuberant obstructive granulation tissue. In each case, the percutaneous tracheostomy involved the cricoid cartilage.

We have investigated, in a prospective double-blind study, recovery from anaesthesia induced by two admixtures of propofol and thiopentone and compared it with a third group of patients who received propofol and lignocaine. Ninety unpremedicated ASA 1 or 2 patients scheduled for elective gynaecological laparoscopy as a daycase procedure were randomly allocated to receive one of three different mixtures for induction of anaesthesia as part of a standardized anaesthetic: Group P₅₀: propofol 1% 10 ml/thiopentone 2.5% 10 ml, Group P₇₅: propofol 1% 15 ml/thiopentone 2.5% 5 ml, Group P₁₀₀: propofol 1% 20 ml/lignocaine 1% 4 ml. Recovery from anaesthesia was assessed for up to four hours post-induction by critical flicker fusion threshold and best post-box toy completion time. Comparison was made with preoperative baseline performance. There was no significant difference in postoperative recovery between the three groups with either assessment but no group returned to their mean preoperative performance levels within the first four hours post-induction. Nor was there any difference between the groups with respect to postoperative analgesia or anti-emetic administration. Utilizing the most sensitive end-point, a sample of nearly 1000 patients in each group would be required to confirm the observed difference with a power of 0.8 based on the data from this study. In comparison with lignocaine, the addition of thiopentone to propofol does not delay recovery from anaesthesia and does not increase postoperative analgesic or anti-emetic requirements.

This double-blind, randomized study of analgesia after caesarean section compared patient controlled epidural analgesia with pethidine (15 mg of a 0.25% solution and a 10 minute lockout period) versus a single bolus of epidural morphine 4 mg. Data were collected on 78 patients at 2, 6, 8, and 24 hours postoperatively and analysed using the Wilcoxon rank sum test. Satisfactory analgesia and nausea/vomiting during the first twenty-four hours did not differ between the two groups. The incidence of pruritus (P<0.001) was lower in the pethidine group at 2, 6, and 8 hours, with no difference by 24 hours. Therefore PCEA pethidine provides a useful alternative to single-dose morphine after caesarean section, particularly in those patients who have suffered severe morphine-induced pruritus previously.

The pharmacokinetics of paracetamol in adults after cardiac surgery have not been described. Twenty patients were randomized to receive either paracetamol 2 g through a nasogastric tube and as a suppository eight hours later or vice versa. Arterial blood samples were taken at 0.5, one, two, four, six and eight hours after dosing. Each patient was studied for 16 h. There were 16 males and three females. One patient was excluded because of sampling errors. The mean age was 59 (SD 8) years and the mean weight 84kg (16).

The time-concentration profiles for each individual were used to estimate pharmacokinetic parameters using a non-linear mixed effects model (NONMEM). Population parameter estimates with coefficient of variation (CV%), standardized to a 70 kg person, for a one-compartment model with first order input, lag time and first order elimination were volume of distribution 127 l (28) and clearance 26.4 l/h (29) Rectal paracetamol had an absorption half-life (T_abs) of 2.02 h (31) with a lag time of 0.28h. The absorption half-life for the oral preparation was 1.49h (81) with a lag time of 0.17h. The relative bioavailability of the rectal compared to the oral formulation was 0.98 (18).

Concentrations after either nasogastric or rectal paracetamol 2g were below a target concentration of 10 mg/l, which is associated with analgesia. Absorption after nasogastric administration was slow compared to healthy adults (T_abs 0.06 to 0.7h) and the bioavailability was half that expected, due to nasogastric loss. Parameter estimates had large variability. Paracetamol is unlikely to have useful clinical impact in the majority of patients when standard doses (6 g/day) are given on day 1 after cardiac surgery.

We have examined whether propofol activates complement. In the first study, blood was mixed with saline, propofol or the lipid solvent for propofol, and the activated complement 3 (C3a) and 4 (C4a) concentrations in the supernatant were assayed. In the second study, blood and propofol were mixed with various levels of nafamostat mesilate (anti-complement agent) up to 0.3 mmol/l and the C3a was assayed. In the third study, the time course of plasma C3a concentration in patients during propofol anaesthesia was examined. The results showed that the lipid solvent activated complement and produced similar levels of C3a to propofol, probably via both the classical and alternative pathways. This activation was not inhibited by any of the nafamostat concentrations used. There was no significant change in plasma C3a concentration during propofol anaesthesia. These results suggest that C3a is generated by the lipid solvent, but its accumulation during propofol anaesthesia is minimal.

We conducted a randomized, crossover study of 60 paralysed anaesthetized adult patients to compare ease of insertion for the reinforced (RLMA) and standard laryngeal mask airway (LMA). We also test the hypothesis that oropharyngeal leak pressure (OLP) and intracuff pressure (ICP) vary with head and neck position for the two devices. OLP and ICP were documented in four head and neck positions (neutral first, then flexion, extension and rotation in random order) for each device. The size 5 was used for all patients and the ICP was set at 60 cm H₂O in the neutral position. The first time insertion success rates were similar (LMA: 60/60 v RLMA; 59/60), but insertion time was slightly less for the LMA (6 v 8 s, P=0.004). Compared with the neutral position, OLP for the LMA was higher in flexion (21 v 28 cm H₂O, P<0.0001) and rotation (21 v 23 cm H₂O, P<0.0001), but lower in extension (21 v 14 cm H₂O, P<0.0001). Compared with the neutral position, OLP for the RLMA was higher in flexion (19 v 27 cm H₂O, P<0.0001), similar in rotation (20 v 19 cm H₂O), but lower in extension (27 v 14 cm H₂O, P<0.0001). The difference in OLP between flexion and extension was 13 and 14 cm H₂O for the RLMA and LMA respectively. OLP was slightly higher for the LMA compared with the RLMA when the head was in neutral (P<0.0001) and rotation (P<0.0001), but was similar during flexion and extension. There was a significant positive correlation between ICP and OLP for the LMA (P<0.0001) and RLMA (P<0.0001). We conclude that ease of insertion is similar for the RLMA and LMA. OLP is higher with head/neck flexion and lower with extension for both devices and is associated with a similar change in ICP. We recommend assessing the efficacy of seal for all head and neck positions likely to be encountered prior to the start of surgery.

Forty-three Acute Pain Service units in Australia and New Zealand were surveyed regarding data they collected on their daily rounds. The survey sought to determine what data each unit actually collected and what they considered to be a set of data that would be an acceptable minimal standard for the purpose of audit. The scoring or scaling mechanisms that were used in auditing the various parameters were also ascertained in an attempt to derive a consistent means of comparing data from the various Acute Pain Service groups. The Acute Pain Special Interest Group is currently developing suggestions for a standard data set and associated scoring mechanisms in line with the results of this survey.

Administration of suxamethonium to patients with critical illness polyneuropathy may produce life-threatening hyper-kalaemia. A questionnaire to assess the awareness of this problem was sent to all UK intensive care units. A clinical scenario suggestive of critical illness polyneuropathy was accompanied by a list of possible drugs used to facilitate endotracheal intubation. Most respondents (68.7%) chose suxamethonium while 20.4% avoided any muscle relaxant. This result suggests a worrying lack of appreciation of the dangers of suxamethonium use in critical illness polyneuropathy.

This report describes the perioperative management of an adrenergic crisis occurring following insufflation of the peritoneum for planned laparoscopic surgery for phaechromocytoma. Despite preoperative alpha and beta adrenergic blockade, the occurrence of acute severe hypertension, mydriasis and pulmonary oedema prior to direct surgical manipulation caused the procedure to be abandoned. The severity of the event was unusual and most likely contributed to by haemorrhagic necrosis of the tumour releasing catecholamines. Serum levels of noradrenaline and adrenaline at the time were 744,600 and 166, 940 pg.ml⁻¹ respectively. Treatment included bolus doses of esmolol, nicardipine and urapidil (an α₁ adrenergic antagonist) by constant intravenous infusion and mechanical ventilation. Postoperative cerebral CT scan was normal. An abdominal CT showed central haemorrhagic necrosis of the tumour. Two weeks later, open surgical removal of the phaeochromocytoma was successfully performed under general anaesthesia. Induction of pneumoperitoneum for laparoscopy may be particularly hazardous in a patient with a phaeochromocytoma.

We present a case of recovery from fulminant hepatic failure secondary to high serum levels of fluconazole precipitated by amphotericin B induced renal dysfunction. Fluconazole dose adjustment or alternative antifungal treatment should be considered in patients with impaired renal function.

A 15-year-old female survived a total of 65 minutes cardiac arrest following ingestion of verapamil and selective serotonin re-uptake inhibitors. We consider that the lack of neurological damage, despite evidence of significant renal and myocardial injury, may be related to the possible neuroprotective effect of a large dose of verapamil

Effective humidification is sometimes difficult to achieve in children when normal mechanisms are bypassed by having a tracheostomy in situ. The humidification options available in the paediatric population are heat and moisture exchangers (HMEs) and heated humidifiers, both of which are reviewed and discussed. In some circumstances the humidification achieved with HMEs is inadequate. We outline the hospital and subsequent home management of two infants, both with tracheostomies in situ, who unsuccessfully trialed HMEs and subsequently achieved effective humidification with heated humidifiers. We propose that heated humidifiers would help more tracheostomized infants who are suffering from similar problems.

Epidural abscess is a rare complication of epidural block and occasionally presents in the post partum period. A case is described where a thoracolumbar abscess presented with backache and headache 10 days after an apparently uneventful block for labour and caesarean section. The abscess was treated medically with a satisfactory outcome. The literature is reviewed in order to assess several recent reports of infectious complications of epidural block in obstetric patients.