Anaesthesia and Intensive Care

Intensive care units are complex, dynamic patient management environments. Incidents and accidents can be caused by human error, by problems inherent in complex systems, or by a combination of these. Study objectives were to develop and evaluate an incident reporting system. A report form was designed eliciting a description of the incident, contextual information and contributing factors. Staff group sessions using open-ended questions, observations in the workplace and a review of earlier narratives were used to develop the report form. Three intensive care units participated in a two-month evaluation study. Feedback questionnaires were used to assess staff attitudes and understanding, project design and organization. These demonstrated a positive attitude and good understanding by more than 90% participants. Errors in communication, technique, problem recognition and charting were the predisposing factors most commonly chosen in the 128 incidents reported. It was concluded that incident monitoring may be a suitable technique for improving patient safety in intensive care.

The AIMS-ICU project is a national study set up to develop, introduce and evaluate an anonymous voluntary incident reporting system for intensive care. ICU staff members reported events which could have reduced, or did reduce, the safety margin for the patient. Seven ICUs contributed 536 reports, which identified 610 incidents involving the airway (20%), procedures (23%), drugs (28%), patient environment (21%), and ICU management (9%). Incidents were detected most frequently by rechecking the patient or the equipment, or by prior experience. No ill effects or only minor ones were experienced by most patients (short-term 76%, long-term 92%) as a result of the incident. Multiple contributing factors were identified, 33% system-based and 66% human factor-based. Incident monitoring promises to be a useful technique for improving patient safety in the ICU, when sufficient data have been collected to allow analysis of sets of incidents in defined “clinical situations”.

Sixty-one consecutive patients in the Intensive Care Unit requiring central venous lines (CVC) for five or more days were randomized to receive either a standard triple lumen CVC (STD/CVC) or a silver sulphadiazine and chlorhexidine impregnated CVC (SSD/CVC). Data from the 54 patients who completed the trial show a reduced infection rate (positive tip culture) in the SSD/CVC group (4 out of 28) compared to the STD/CVC group (10 out of 26) (P<0.05).

In addition, the new Fibrin Analysing System (FAS) brush was evaluated and used to determine the presence of infection in all the CVCs (STD/CVC and SSD/CVC combined, n=54) at day 3 (i.e. early warning of CVC colonization/infection) and at the time of removal of the CVC. The FAS brush was able to detect an infected CVC on only one occasion on day 3 out of the 14 CVC tips which were later found to be colonized/infected at the time of removal. The sensitivity of the FAS brush in detecting colonized/infected CVCs at the time of CVC removal compared with CVC tip culture was 21% with a specificity of 100%. These findings would currently not support the routine use of the FAS brush in determining CVC infection/colonization.

The arterial blood gas chemistry was measured continuously in ten patients during primary cemented total hip replacement in order to define more precisely the patterns of changes in blood gases during various stages of the operation. All ten patients demonstrated significant drops in P_aO₂ after femoral cement implantation and nine of the ten after acetabular cement implanation. The mean drop in P_aO₂ following acetabular cement expressed as mean ± SD was 18±8 mmHg (16±6%) (P<0.05) and femoral cement application was 25±11 mmHg (23±9%) (P<0.05). For changes in P_aO₂ there were corresponding drops in SpO₂ in all patients with the femoral cement and in eight patients with the acetabular cement. The mean drop in SpO₂ following the application of acetabular and femoral cements respectively were 1.7±1.5% and 3±2.45%. No changes in blood P_aO₂ were observed during dislocation of the hip joint or reaming of acetabulum and femur. In vitro studies revealed no effect of the liquid monomer or the cured cement on the performance of the Clark electrode of the sensor. We suggest that significant drops in P_aO₂ occur with both acetabular and femoral cement implantation and that the derangements in blood P_aO₂ last longer than detected by pulse oximetry following cement implantation.

Twenty-one patients who underwent cardiac valvular replacement procedures were studied to determine the peri-operative changes of plasma endothelin-1 (ET-1) concentration and disposition of ET-1 in the pulmonary and systemic vasculature between patients with elevated (over 20 mmHg) mean pulmonary artery pressure and patients with normal pulmonary artery pressure. The overall profile alterations of plasma ET- 1 concentration did not differ between the two groups of patients. The plasma ET- 1 levels in the pulmonary artery and right atrium were significantly higher in patients with high pulmonary artery pressure than in patients with normal pulmonary artery pressure. Before cardiopulmonary bypass, significant pulmonary extraction of the plasma ET- 1 existed in patients with high pulmonary artery pressure but the pulmonary extraction was not seen after bypass. There was no transpulmonary difference of the plasma ET- 1 concentration in patients with normal pulmonary artery pressure either before or after bypass. The high levels of ET- 1 in the pulmonary circuit and the pulmonary extraction of the ET- 1 in patients with high pulmonary artery pressure might be a protective mechanism for rheumatic valvular patients with elevated pulmonary artery pressure.

Seven out of eight piglets which were susceptible to malignant hyperthermia (MHS) died when subjected to a heat challenge which was well tolerated by controls. The piglets which succumbed developed the classical clinical and biochemical changes of malignant hyperthermia before they died. These results show that overheating alone can trigger malignant hyperthermia in susceptible animals. Because the biochemical basis of malignant hyperthermia is similar in both humans and pigs, these observations suggest that overheating can also trigger malignant hyperthermia in humans. The susceptibility to overheating in malignant hyperthermia susceptible humans and animals probably explains why the myopathy which predisposes to this condition has also been reported to predispose to heat-stroke and the sudden infant death syndrome. In view of this, particular care to prevent overheating should be taken in infants of parents who are susceptible to malignant hyperthermia.

Postoperative nausea and vomiting (PONV) has many causes, including anaesthetic drugs. Choice of induction agent may affect the incidence of PONV, though the evidence is conflicting. We have analysed our database of outcome after surgery. Data on 4173 patients were analysed using multivariate logistic regression, with an overall incidence of PONV 21.3%. Propofol, when compared to thiopentone for induction of anaesthesia, resulted in an 18% reduction in PONV (OR=0.82, P=0.03). The likely postoperative benefits of propofol may outweigh concerns about its additional cost.

The efficacy of EMLA^® cream combined with glyceryl trinitrate (GTN) ointment was assessed by a double-blind prospective study. Adult female patients were randomly allocated to receive either EMLA 1 ml or 2 ml combined with GTN 2 mg, or EMLA 2 ml only. The difference in pain scores between the three groups was not statistically significant. When GTN was used with EMLA, the quality of the veins was superior and aided intravenous cannulation. There were no significant side-effects.

It is concluded that if GTN is used with EMLA, the dose of EMLA can be reduced and intravenous cannulation is technically easier compared with EMLA alone.

A randomized, prospective, blind trial was conducted comparing caudal epidural blockade (caudal block) with subcutaneous ring block of the penis (penile ring block) in fifty healthy boys between two and twelve years of age undergoing elective circumcision. Subjects receiving caudal block had a longer duration of analgesia (P=0.003), and took longer to first micturition (P=0.04) but there was no difference in time taken to awaken from anaesthesia or spontaneously walk unaided. There was an 8% failure rate with the penile ring block but no local or systemic complications related to either block and a very low incidence of vomiting. It is concluded that both techniques are effective. Caudal block is more reliable and produces a longer duration of analgesia but penile ring block is inherently safer and has a lower incidence of adverse effects.

Marlex mesh interposition as part of staged abdominal repair (M-STAR) was used on 68 occasions to reduce pressure during abdominal closure (46), facilitate multiple laparotomies (15), both indications (4) or defect repair (3), in 66 critical care admissions (median \APACHE-II=21). Physiological data before and after M-STAR performed for intra-abdominal pressure were retrospectively available on 33/36 ventilated occasions. Compliance improved (median Vt/[Paw-PEEP] 22.6 vs 30.3 ml/cm H₂O, P<0.0001), but efficiency of oxygenation (median P_aO₂/FiO₂ 136 vs 175 mmHg) and ventilation (median VE/P_aCO₂ 243 vs 289 ml/min/mmHg) were unchanged. Heart rate fell (median 130 to 110, P=0.01), blood pressure and inotrope dose did not change. Urine flow increased (median 60 to 110 ml/h, P=0.007) but there was no clear trend in six-hourly serum creatinine. Seven bowel fistulae and three dehiscences occurred. Thirty-five patients survived critical care after 2–7 (median 2) M-STAR related operations and 3–63 (median 20) days. Thirty-one hospital survivors used 19–158 (median 47) hospital days; one patient was still in hospital at 39 months. Five patients died 1–55 months after hospital discharge. At follow-up 1–39 (median 7.5) months after critical care there were two fistulae, five stitch sinuses and five incisional hernias in the 27 survivors. M-STAR facilitates critical care and repeat laparotomy with acceptable surgical sequelae.

Physiological deadspace fraction of tidal volume (V_D/V_T), arterial to end-tidal carbon dioxide tension differences [P(a-é)CO₂], arterial oxygen tension (PaO₂) and respiratory system compliance were studied in twenty patients with patent ductus ateriosus scheduled for multiple ligation and transfixation through posterolateral thoracotomy under general anaesthesia with controlled ventilation. The study period was divided into six stages: stage 1—supine posture under anaesthesia, stage 2—lateral posture before start of surgery, stage 3—after chest opening before lung manipulation, stage 4—after ductus ligation and lung re-expansion before chest closure, stage 5—lateral posture, chest closed, stage 6—supine stage before reversal.

There was a significant (P<0.01) increase of V_D/V_T on attaining the lateral posture. The fraction decreased significantly (P<0.05) on opening of the chest (stage 3) and subsequently increased at stage 4. There was no significant change in mean P(a-é)CO₂ at various stages of thoracotomy. PaO₂ fell significantly on opening of the chest and was lowest before chest closure (stage 4). P_aO₂ increased following chest closure but was still significantly lower than the pre-surgical supine stage. Respiratory system compliance was lowest at stage 4.

Changes in deadspace fraction V_D /V_T do not correspond favourably to arterial oxygen tensions during posterolateral thoractomy.

The efficacy and potency of Commonwealth Serum Laboratories (CSL) snake antivenoms in neutralizing the procoagulant action of Australian snake venoms was studied in vitro. The procoagulant action of venoms from Tiger, Brown and Taipan Snakes were measured in pooled canine or pooled human plasma. Mixtures of the venoms and their appropriate antivenoms, ranging from 0.1 to 15 times the recommended neutralizing dose of antivenom were then added to pooled canine or pooled human plasma and the efficacy and potency of the antivenoms in preventing the procoagulant action was measured. Neutralization was achieved by the addition of the appropriate antivenom in concentrations of 0.5 (Taipan), 10 (Tiger), 10 (Gwardar), 15 (Dugite) and an estimated 20 (Common Brown) times the dose expected. Similar results were obtained in canine and human plasma. The potency of Tiger and especially Brown Snake antivenom is substantially lower (10–20 times) than that predicted by CSL. These findings support an increase in the dose of antivenom to be used for the treatment of Tiger and especially Brown Snake envenomation complicated by coagulopathy. The in vitro canine model may be suitable for studying the procoagulant effects of Australian snake venoms.