Anaesthesia and Intensive Care

Vasopressin (antidiuretic hormone) is emerging as a potentially major advance in the treatment of a variety of shock states. Increasing interest in the clinical use of vasopressin has resulted from the recognition of its importance in the endogenous response to shock and from advances in understanding of its mechanism of action. From animal models of shock, vasopressin has been shown to produce greater blood flow diversion from non-vital to vital organ beds (particularly the brain) than does adrenaline. Although vasopressin has similar direct actions to the catecholamines, it may uniquely also inhibit some of the pathologic vasodilator processes that occur in shock states.

There is current interest in the use of vasopressin in the treatment of shock due to ventricular fibrillation, hypovolaemia, sepsis and cardiopulmonary bypass. This article reviews the physiology and pharmacology of vasopressin and all of the relevant animal and human clinical literature on its use in the treatment of shock following a MEDLINE (1966–2000) search.

To investigate the prevalence and clinical relevance of functional iron deficiency in the critically ill, we performed a prospective observational study in a university hospital general intensive care unit. We collected patient demographics, severity of illness data, haematological and biochemical variables in 51 consecutive admissions. We recorded episodes of culture-positive infection.

Functional iron deficiency (FID), measured by red cell hypochromasia on flow cytometry, was present in 35% of patients at admission to intensive care. FID patients were of similar age, diagnosis, APACHE score, sequential organ failure assessment (SOFA) score, haemoglobin, serum B12, folate and ferritin to patients without FID. However, patients with FID had a prolonged intensive care stay compared with non-FID patients (P<0.001) and increased time to hospital discharge (P=0.09). Duration of intensive care stay correlated with severity of FID (r=0.33, P<0.02). Systemic inflammatory response syndrome (SIRS) was present for longer in those with FID (P<0.02). Overall mortality did not differ between groups. No difference was seen in the incidence of positive cultures between those with FID (9/18 patients) and those without FID (15/33 patients). FID was independently associated only with abnormal white blood cell count (WBC <4 or >11x10⁹.l^-1) at admission to ICU, P=0.007, but not with positive cultures.

There is a high prevalence of FID in intensive care, associated with an increased duration of stay and duration of SIRS. We have been unable to demonstrate a link with infection, either as a predisposing factor or as an acute response.

We investigated whether red cell 2,3-diphosphoglycerate (2,3-DPG) concentrations are reduced in critical illness, whether acidaemia, hypophosphataemia or anaemia influence 2,3-DPG, and whether there is any net effect on in vivo P50.

Twenty healthy, non-smoking, male volunteers were compared with 20 male intensive care patients with APACHE 2 scores >20 on the preceding day. Those transfused in this time were excluded. Venous red cell 2,3-DPG concentrations were measured in both groups. In the patient group, routine multichannel biochemical profile and arterial blood gas analysis were also performed and in vivo P50 calculated.

The mean 2,3-DPG concentration was significantly lower in the patient group than in the controls (4.2±1.3 mmol/l vs 4.9±0.5 mmol/l, P=0.016). The patients were well oxygenated (lowest arterial PO₂=75 mm Hg) and showed a tendency to acidaemia (median pH 7.37, range 7.06 to 7.48) and anaemia (median haemoglobin concentration 113 g/l, range 89 to 154 g/l). By linear regression of patient data, pH had a significant effect on 2,3-DPG concentrations (r=0.6, P=0.011). Haemoglobin and phosphate concentrations did not, but there were few abnormal phosphate values. There was no correlation between 2,3-DPG concentrations and in vivo P50 (r² ≤0.08).

We conclude that 2,3-DPG concentrations were reduced in a broad group of critically ill patients. Although this would normally reduce the P50, the reduction was primarily linked with acidaemia, which increases the P50. Overall, there was no net effect on the P50 and thus no affinity-related decrease in tissue oxygenation.

We studied the effects of nimodipine on brain tissue lactate and malondialdehyde (MDA) levels one hour after experimental head trauma in 25 New Zealand rabbits. Group 1(n=5) was the sham operated group. Group 2 (n=10) received head trauma without treatment and in group 3 (n=10) nimodipine was administered for 30 minutes intravenously (2 μg/kg/min) immediately after head trauma. In groups 2 and 3, tissue samples from the non-traumatized side was named as “a” and traumatized side as “b”. The lactate and malondialdehyde contents were significantly higher in groups 2a, 2b, 3a and 3b when compared with to group 1 (P<0.05). The differences between non-treated groups (2a, 2b) and nimodipine treated groups (3a, 3b) were not significant (P>0.05). The differences between the traumatized sides (2b, 3b) and non-traumatized sides (2a, 3a) were significant (P<0.05). These results demonstrated that nimodipine is ineffective in suppressing the increase of tissue lactate and malondialdehyde levels in the early period of experimental head trauma.

Moderate haemodilution enhances coagulability in vitro and in vivo as measured by thrombelastography (TEG). The mechanism has never been established. We have conducted an in vitro study to determine whether the effect can be moderated or prevented when the reduction in antithrombin III caused by dilution is prevented by supplementation.

Blood from 20 volunteers was divided into four samples. One sample was not diluted and served as control (C). Another was diluted (by 20%) with saline (S). The third was diluted by 20% with saline plus two units of antithrombin (AT III) (SA). The fourth remained undiluted, with two units of added AT III (CA). Coagulation was measured in all four samples using the TEG. In a separate laboratory study, the levels of AT III were measured in control samples and compared with levels after 20% dilution, and 20% dilution with two units of AT III added to the diluent.

Enhanced coagulation was demonstrated in saline-diluted samples (S) by shortening of r- and k-times, and increased alpha angle. In the SA samples, r-time shortening was prevented; k-time shortening and alpha-angle increase persisted, but to a reduced degree (difference from saline-only dilution P<0.051). There were no differences between samples C and CA. A predictable drop of AT III (24.2%) occurred with saline dilution, while AT III levels in the AT III/Saline group were similar to the undiluted control.

Haemodilution-induced coagulation enhancement is attenuated, but not prevented, if AT III levels are maintained in the normal range. This is in keeping with the established concept of an antithrombin threshold preventing positive coagulation feedback into the intrinsic pathway.

We aimed to establish the frequency and nature of drug administration error in anaesthesia (a significant subset of error in medicine) at two hospitals.

Anaesthetists were asked to return a study form anonymously for every anaesthetic, indicating whether or not a drug administration error or pre-error (defined as any incident with potential to become an error) had occurred. Further details were sought if the response was affirmative.

From 10806 anaesthetics, 7794 study forms were returned, representing response rates of 80% from Hospital A and 57% from Hospital B (72% overall). The frequency (95% confidence intervals) of drug administration error, of any type, per anaesthetic was 0.0075 (0.006 to 0.009), of IV bolus errors was 0.005 (0.0035 to 0.006) and of pre-errors was 0.004 (0.003 to 0.005), with no significant difference between hospitals. Overall, one drug administration error was reported for every 133 anaesthetics. The two largest individual categories of error involved incorrect doses (20%) and substitutions (20%) with IV boluses of drug. Of the IV bolus substitutions, 69% occurred between different pharmacological classes. One patient was aware while under muscle relaxation, and two required prolonged ventilation. In addition, 47 transient physiological effects were reported, of which five required intervention.

We conclude that drug administration error during anaesthesia is considerably more frequent than previously reported.

Intraoperative hypotension is a common and sometimes deleterious event in elderly patients undergoing spinal anaesthesia for repair of hip fractures. The synergism between intrathecal opioids and local anaesthetics may allow a reduction in the dose of local anaesthetic and reduce hypotension, while still maintaining adequate anaesthesia. We studied 42 elderly patients having insertion of a Richards pin and plate and compared 7.5 mg hyperbaric bupivacaine with added fentanyl 20 μg (group BF) to 12.5 mg hyperbaric bupivacaine alone (group B). Hypotension was defined as a fall in systolic blood pressure to less than 75% baseline or less than 90 mmHg and occurred with an overall incidence of 59.5%. There was no difference in the incidence or severity of hypotension between the two groups. Two patients from group B and one from group BF experienced mild discomfort. Pruritus was more common in group BF.

In a prospective, randomized study, the effect of age on recovery from remifentanil anaesthesia was evaluated. Twenty consecutive patients classified as ASA 1 and 2 and having elective laparotomy were recruited to one of two groups based on age (Group 1 age <60 y and Group 2 age >60 y). Remifentanil boluses and infusion were used for induction and maintenance of anaesthesia. Dosage was titrated against clinical response to perioperative stimulation and the infusion was terminated at the end of the operation. Time intervals between termination of remifentanil infusion and 1) spontaneous respiration, 2) adequate respiration, 3) eye opening, 4) limb movement, 5) extubation, 6) Aldrete score >9, 7) discharge to recovery room and 8) discharge to the ward were recorded. Patient controlled analgesia with morphine was used for postoperative pain control.

Student's t test was used to compare the differences in these time intervals between Groups 1 and 2. AP value <0.05 was taken as significant. We found that the younger age group regained spontaneous respiration (0.8±0.7 min vs 3.2±3.6 min), adequate respiration (3.4±3.7 min vs 7.6±5.8 min), opened their eyes (0.9±1.0 min vs 3.6±4.4 min), had their endotracheal tubes removed (5.0±4.6 min vs 9.0±6.5 min) and were discharged to recovery room (8.8±4.3 min vs 14.5±7.1 min) earlier than their older counterparts. In conclusion, age was a co-variate for recovery from remifentanil anaesthesia.

In this prospective, randomized controlled trial, changes in endotracheal tube cuff pressure were studied in 60 patients undergoing elective surgery under general anaesthesia with nitrous oxide and oxygen. The cuffs were inflated with either air or distilled water. The mean pressure in the air-filled cuffs increased steadily throughout the procedure, reaching 47.5±7.3 cmH₂O at one hour compared with 31.6±2.4 cmH₂O mean pressure in the water-filled cuffs. The pressure and the rate of rise in cuff pressure were significantly lower (P<0.05) in the water-filled cuffs throughout the hour of study. When an endotracheal tube cuff is distended with water, the rise in cuff pressure during nitrous oxide anaesthesia is lower than that of an air-filled cuff.

Sixty-seven children between one and 15 years of age were randomized to have Laryngeal Mask Airway (LMA) insertion using either the standard technique (Group A) as described by Brain or the “reverse technique” (involving a 180° turn after insertion with the cuff facing the palate) (Group B). A blinded observer using a fibreoptic bronchoscope assessed the final position of the LMA. The LMA had to be placed within 15 seconds for the procedure to be considered “successful”. The success rate using the standard technique was 90.3% (28/31) and 100% (36/36) using the reverse technique (P value 0.06). The 95% confidence interval for the difference in success rates between Group B and A (B-A) was –0.73% to 20.1%. It is our opinion that the reverse technique of insertion of the LMA is an acceptable alternative to the standard technique.

We aimed to assess the reliability of patients as historians in terms of the self assessment of functional capacity and also examined the usefulness of a simple ward exercise tolerance test.

One hundred consecutive elective vascular surgery patients were interviewed preoperatively using a modified Duke Activity Status Index (DASI) questionnaire. To test reliability in reference to an independent observer, the questionnaire concerning the patient was also applied to each patient's closest relative who was blinded to the patient's responses. Patients were then asked to walk up two flights of stairs and the time taken to complete the task or the reason for failing to complete the task was recorded.

The DASI questionnaire was successfully applied to 98 of 100 patients. The average time for completion was five minutes. There was significant correlation between the scores obtained by each patient and that of their closest relative (r=0.883, P<0.01). Mean percentage score was 48.6, range 0 to 100. Fifty-nine of 100 patients selected were able to undergo the simple ward exercise test. DASI scores (mean, SD) were significantly different between those who completed two flights (67.2, 21.5), one flight (45.5, 15.6) or who were unable to climb at all (28.8, 25) (Mann-Whitney U test corrected for multiple comparisons, P<0.05). Patients with higher DASI scores were able to complete the task at a faster rate.

The DASI questionnaire is easy to administer and a useful method for quantifying exercise tolerance. We also demonstrated a high correlation between the responses of patients and relatives.

An analysis of the anaesthesia caseload of the United Nations Military Hospital and its predecessors over the first 12 months of operation from September 1999 has been performed. Most patients were East Timorese civilians or Australian Military personnel. General anaesthesia using the ULCO Portable Field Anaesthesia Machine was most commonly administered.

An analysis was performed of the anaesthesia caseload of the Dili General Hospital for a four-month period from April 21, 2000 to August 20, 2000.

Cardiac output is a major determinant of the rate of uptake of volatile anaesthetic agents. Theoretical work suggests a 30% change in cardiac output will produce a measurable change in end-tidal volatile agent. We present three patients in whom significant changes in haemodynamic parameters, consistent with a large fall in cardiac output, were accompanied by an increase in end-tidal volatile agent concentrations. The changes in end-tidal volatile agent concentrations were comparable in magnitude but in the opposite direction to the changes in end-tidal CO₂. Clinically, an unexplained change in end-tidal concentration of a volatile agent may signify a large change in cardiac output.

A 74-year-old woman was admitted to the intensive care unit (ICU) with respiratory failure. Following intubation and mechanical ventilation, nasogastric enteral feeding was begun. The sensitivity of the glucose oxidase strip method for detecting aspiration of enteral feed has been questioned because the glucose levels in commonly used feeds are similar to those of normal tracheal aspirates. In order to increase the glucose concentration of the feed, 10g of glucose was added to each 500 ml feed carton. Testing oral and tracheal secretions with standard glucose oxidase strips allowed the accurate detection of both pharyngeal regurgitation and tracheal aspiration.

An episode of subclinical aspiration was detected and this was associated with a fall in the PaO₂/FiO₂ ratio. There were no further episodes of aspiration following the introduction of a gastric motility agent, maintaining the patient in the semi-recumbent position and an increase in the positive end expiratory pressure (PEEP).

A 47-year-old woman with Cushing's syndrome suffered a severe anaphylactic reaction on induction of anaesthesia, resulting in circulatory arrest. A spontaneous cardiac output appeared after 25 minutes of chest compression and she regained consciousness three hours later, with no neurological deficit. A Bispectral Index monitor demonstrated values greater than 40 throughout the whole period of resuscitation. Possible implications for this observation are discussed.

We present a case of a ten-month-old boy with Goldenhar's syndrome and significant retrognathia in whom a tracheostomy was performed to relieve upper airway obstruction. Tracheal intubation was facilitated by direct suspension laryngoscopy using a slotted rigid laryngoscope. We propose this technique as an alternative method for tracheal intubation in infants and young children with a difficult airway. The management of the difficult airway in children with Goldenhar's syndrome is discussed.