Five algorithms that calculate cardiac output from the arterial waveform: a comparison with Doppler ultrasound.

BACKGROUND: Different mathematical approaches are used to calculate arterial pulse pressure wave analysis (PPWA) cardiac output. The CardioQ-Combi is a research oesophageal Doppler (COODM) monitor that includes these five fundamental PPWA algorithms. We compared these PPWA cardiac output readings to COODM and suprasternal USCOM Doppler (COUS) over a range of cardiac output values induced by dopamine infusion in patients undergoing major surgery. USCOM acted as a control. METHODS: Serial sets of cardiac output data were recorded at regular intervals as cardiac output increased. Formulae included: cardiac output calculated form systemic vascular resistance (COMAP), pulse pressure (COPP), Liljestrand-Zander formula (COLZ), alternating current power (COAC) and systolic area with Kouchoukos correction (COSA). The reference method for comparisons was COODM. Statistical methods included: Scatter plots (correlation), Bland-Altman (agreement) and concordance (trending) and polar (trending). RESULTS: From 20 patients 255 sets of cardiac output comparative data were collected. Mean cardiac output for each method ranged between 5.0 and 5.5 litre min(-1). For comparisons between COUS and the five PPWA algorithms with COODM: Correlation was best with COUS (R(2)=0.81) followed by COLZ (R(2)=0.72). Bias ranged between 0.1 and 0.5 litre min(-1). Percentage error was lowest with COUS (26.4%) followed by COLZ (35.2%), others (40.7 to 56.3%). Concordance was best with COUS (92%), followed by COLZ (71%), others (64 to 66%). Polar analysis (mean(standard deviation)) were best with COUS (-2.7 (21.1)), followed by COLZ (+4.7 (26.6). CONCLUSIONS: The Liljestrand-Zander PPWA formula was most reliable compared with oesophageal Doppler in major surgical patients under general anaesthesia, but not better than USCOM.

An assessment of two Doppler-based monitors to track cardiac output changes in anaesthetised patients undergoing major surgery.

Minimally-invasive cardiac output (CO) monitoring to follow changes in CO would be helpful in anaesthesia practice. Two Doppler systems marketed for this purpose include the CardioQ (Deltex Medical Group, Chichester, United Kingdom), which uses an oesophageal probe, and the USCOM (USCOM Ltd., Sydney, NSW, Australia), which uses a hand-held probe. The aim of the study was to assess the ability of these two methods to track CO during major surgery and to determine their relationship. Twenty patients, age 58 (26 to 81) years, (m/f) 15/5, requiring abdominal surgery were studied. The surgical procedures lasted between 128 and 408 minutes and a total of 285 data pairs (8 to 22 per case) were collected. Time plots showed good tracking ability across a wide range of CO in most patients. Correlation between the two devices was excellent in 14 patients (R² >0.85), good in another four (R² >0.64) and poor in two. Regression line data supported the hypothesis that CardioQ under-reads at low CO and over-reads at high CO in respect to the USCOM. However, the precision between the two CO readings was poor with wide limits of agreement and a percentage error of ± 37%. These findings indicate that these devices individually track changes in CO in many patients but cannot be relied upon to provide the same values.

Study to determine the repeatability of supra-sternal Doppler (ultrasound cardiac output monitor) during general anaesthesia: effects of scan quality, flow volume, and increasing age.

BACKGROUND: The ultrasound cardiac output monitor (USCOM) is a continuous wave Doppler system designed to measure cardiac output (CO) non-invasively and intermittently either from the pulmonary or from the aortic valve. USCOM scan quality is critical to obtaining reliable data and during anaesthesia it is said to deteriorate with increasing age. The aim of this study was to investigate the effect of age on supra-sternal USCOM scan repeatability during anaesthesia. METHODS: We performed a series of 6 USCOM scans in 180 patients of all ages after induction for routine surgery. A 12-point Cattermole (CS) score and 10-point insonation (IS) score were used to evaluate scan quality and ease of insonation. The coefficients of variation (CVs) of USCOM variables [CO, peak velocity, stroke volume index (SVI) and the corrected flow time] were derived from the series of six readings. RESULTS: In >95% of young patients (age <50 yr), it was easy to obtain a good-quality USCOM scan (CS>8). In these patients, repeatability of serial readings was good with CVs<5% and precision of less than ±10%. In older patients (>50 yr), scan quality and ease of insonation declined, with >25% of patients >60 yr having unreliable USCOM scans (CS<5). In these patients, the CV was >5-10%. In several elderly patients (>65 yr), we failed to locate the USCOM signal. Average scan time increased with age (30 to >60 s). SVI was also strongly correlated with scan quality (R(2)=0.77). CONCLUSIONS: Increasing age has a significant effect on USCOM scan quality and data reliability.

Quantitative evaluation of the echo intensity of the median nerve and flexor muscles of the forearm in the young and the elderly.

OBJECTIVES: Musculoskeletal structures often appear brighter on imaging in the elderly, which makes it difficult to accurately delineate a peripheral nerve during ultrasound-guided regional anaesthetic procedures. The echo intensity of skeletal muscles is significantly increased in the elderly. However, there are no data comparing the echo intensity of peripheral nerves in the young and the elderly, which this study was designed to evaluate. METHODS: 13 healthy, young volunteers (aged <30 years) and 11 elderly patients (aged >60 years) who were scheduled to undergo orthopaedic lower limb surgery were recruited. The settings of the ultrasound system were standardised and a high-frequency linear array transducer was used for the scan. A transverse scan of the median nerve (MN) and the flexor muscles (FMs) at the left mid-forearm was performed and three video loops of the ultrasound scan were recorded for each subject. Still images were captured from the video loops and normalised. Computer-assisted greyscale analysis was then performed on these images to determine the echo intensity of the MN and the FMs of the forearm. RESULTS: The echo intensity of the MN and FMs of the mid-forearm was significantly increased in the elderly (p<0.005). There was also a reduction in contrast between the MN and the adjoining FM in the elderly (p = 0.04). CONCLUSION: Under the conditions of this study, the MN and the FMs in the forearm appeared significantly brighter than those in the young, and there was a loss of contrast between these structures in sonograms of the elderly.

Fentanyl dosage and timing when inserting the laryngeal mask airway.

The study objective was to show that fentanyl given five minutes prior to induction improved insertion conditions for the Classic Laryngeal Mask Airway. Previous work had shown fentanyl at 90 seconds to be unpredictable. A probit analysis design was used in which success/failure rates of different doses of fentanyl were measured and dose-response curves drawn from which the ED50 and ED95 with 95% confidence intervals were determined. Adult Chinese patients with American Society of Anesthesiologists physical status classification I or II and requiring anaesthesia for minor surgery with a laryngeal mask were recruited. They were randomly assigned to one of six dosage groups: 0.25, 0.5, 1.0, 1.5, 2.0 and 3.0 microg x kg1. Fentanyl was given prior to propofol 25 mg x kg(-1), and insertion was assessed 90 seconds later using six categories of patient response. Ninety-six patients, aged 18 to 63 years, were studied. The six dosage groups were similar As the fentanyl dose increased, fewer patients responded to insertion (P < 0.01). Dose-responses could be predicted for all categories, except resistance to insertion and laryngospasm. Probit analysis predicted an ED50 of 0.5 microg x kg(-1) and ED, of 7.5 microg x kg(-1) for ideal insertion conditions (i.e., no swallowing, gagging, body movement or laryngospasm). Commonly used fentanyl doses of 1 to 2 microg x kg(-1) only prevented patients responding to insertion in 70 to 80% of cases. When using propofol 2.5 mg x kg(-1), administering fentanyl five minutes before laryngeal mask insertion does not provide ideal insertion conditions in 95% of cases unless excessively large doses are used. An ideal dose of fentanyl that produces optimum insertion conditions could not be determined.

Surgical emphysema as a cause of severe hypercapnia during laparoscopic surgery.

Surgical emphysema is a well-recognised complication of laparoscopic surgery, but its impact on end-tidal carbon dioxide levels and carbon dioxide elimination is seldom reported and may not be fully appreciated by anaesthetists. Four cases are presented where extensive surgical emphysema occurred during laparoscopic surgery. The visual display of the anaesthetic record using the software program Monitor showed substantial rises in end-tidal carbon dioxide levels and allowed calculation of the carbon dioxide elimination, which increased two- to three-fold above normal levels. Having a visual record of carbon dioxide changes facilitated the recognition of surgical emphysema in three out of the four cases. Strategies such as estimating and tracking changes in carbon dioxide elimination from the minute ventilation and end-tidal carbon dioxide levels may assist in early identification, and palpating for surgical emphysema is recommended during laparoscopy if other causes of increased carbon dioxide levels are excluded.

A technique that may improve the reliability of endobronchial blocker positioning during adult one-lung anaesthesia.

We describe a novel technique, previously applied to small children, for adult one-lung anaesthesia in which a single-lumen endotracheal tube is used with an endobronchial balloon blocker The main aims of the technique are to reduce the likelihood of cephalad displacement of the balloon into the trachea and to facilitate directional placement of the endobronchial balloon. We present five illustrative cases of one-lung anaesthesia in patients of adult size, in which the endotracheal tube-endobronchial balloon technique was considered preferable to the use of a double-lumen tube technique. The situations included difficult intubation, need for postoperative ventilation, a tortuous trachea and an unexpected need to perform one-lung anaesthesia. The technique involved deliberate placement of the endotracheal tube tip near the carina to block cephalad dislodgement of the blocker The chance of the balloon blocking the endotracheal tube tip could be further reduced by having the intraluminal endobronchial balloon blocker emerge through the Murphy eye.

Evaluation of an uncalibrated arterial pulse contour cardiac output monitoring system in cirrhotic patients undergoing liver surgery.

BACKGROUND: The pulmonary artery catheter is invasive and may cause serious complications. A safe method of cardiac output (CO) measurement is needed. We have assessed the accuracy and reliability of a recently marketed self-calibrating arterial pulse contour CO monitoring system (FloTrac/Vigileo) in end-stage liver failure patients undergoing liver transplant. The pattern of alterations known as cirrhotic cardiomyopathy, and the transplant procedure itself, provided an evaluation under varying clinical conditions. METHODS: The cardiac index was measured simultaneously by thermodilution (CI(TD): mean of four readings) using a pulmonary artery catheter and pulse contour analysis (CI(V): mean value computed by the FloTrac/Vigileo over the same time period). Readings were made at 10 time-points during liver transplant surgery (T1-T5) and on the intensive care unit (T6-T10). CI(V) was computed using the latest Vigileo software version 01.10. RESULTS: A total of 290 paired readings from 29 patients were collected. Mean (SD) CI(TD) was 5.2 (1.3) and CI(V) was 3.9 (0.9) litre min(-1) m(-2), with a corrected for repeated measures bias between readings of 1.3 (0.2) litre min(-1) m(-2) and 95% limits of agreement of -1.5 (0.2) to 4.1 (0.3) litre min(-1) m(-2). The percentage error (2SD(Bias)/meanCI(TD)) was 54%, which exceeded a 30% limit of acceptance. Low peripheral resistance and increasing bias were related (r=0.69; P<0.001). The Vigileo system failed to reliably trend CI data, with a concordance compared with thermodilution below an acceptable level (at best 68% of sequential readings). CONCLUSIONS: In cirrhotic patients with hyperdynamic circulation, the Vigileo system showed a degree of error and unreliability higher than that considered acceptable for clinical purposes.

Fentanyl dose-response curves when inserting the LMA Classic laryngeal mask airway.

Probit analysis was used to predict an optimal dose of fentanyl, co-administered with propofol 2.5 mg.kg(-1), when inserting the laryngeal mask airway. In all, 21 male and 54 female healthy Chinese patients, aged 18-63 years, requiring anaesthesia for minor surgery were recruited. They were assigned to one of five groups: placebo, 0.5, 1.0, 1.5 and 2.0 microg.kg(-1). Insertion was performed 90 s after administration and insertion conditions assessed using a six-category score. Dose-response curves could only be drawn for swallowing and movement categories, and only the ED(50) could be predicted with certainty. To provide optimal conditions in over 95% of patients, fentanyl doses well above the clinical range were required. A standard fentanyl dose of 1 mug.kg(-1), co-administered with propofol 2.5 mg.kg(-1), provided optimal conditions in 65% of cases. Ninety seconds may have been insufficient time for fentanyl to reach its peak effect.

Right upper lobe collapse secondary to an anomalous bronchus after endotracheal intubation for routine surgery.

Perioperative hypoxaemia is a common but serious problem with well recognised causes. However, an anomalous bronchus causing lobar collapse as a cause is seldom mentioned. A healthy young male patient was anaesthetised for a knee operation. He required re-intubation immediately postoperatively for hypoxia. He was found to have right upper lobe collapse. Fibreoptic examination of the trachea demonstrated an anomalous bronchus as the cause. Intra-operatively, the endotracheal tube had been inserted too deeply and the bronchial orifice had been obstructed by the tip. It took several hours for the lung to re-expand. Greater awareness of this potential complication is needed.

A survey of Chinese herbal medicine intake amongst preoperative patients in Hong Kong.

We have surveyed, by means of a questionnaire, the preoperative use of traditional Chinese medicines in 259 adult Chinese patients admitted to a Hong Kong teaching hospital. The spectrum and use of herbal remedies differed from that reported by Western sources. Of those patients surveyed 90% used Chinese herbs on a regular daily basis in traditional soups and teas while 44% had consulted a traditional Chinese medicine practitioner in the last twelve months prior to admission, but mainly for health promotion (59%) and minor ailments (30%). Only 25% sought advice for their current illness and 13% were taking regular traditional Chinese medicines prior to admission. The ingredients were difficult to identify. Patients with cancer were more likely to use ling zhi (odds ratio 5.4). Female patients with reproductive problems were more likely to visit a traditional Chinese medical practitioner (odds ratio 2.6) and use ginseng (odds ratio 5.1). The anaesthetic implications of preoperative traditional Chinese medicine in keeping with Hong Kong practices need to be investigated, and appropriate anaesthetic guidelines should be developed.

Differences in the single-oral-dose pharmacokinetics and urinary excretion of paracetamol and its conjugates between Hong Kong Chinese and Caucasian subjects.

BACKGROUND AND OBJECTIVES: The present study was conducted to determine if ethnic differences exist for single oral dose pharmacokinetics of paracetamol and its conjugates between Hong Kong Chinese and Caucasian subjects. METHODS: Twenty healthy Chinese (n = 11) and Caucasian (n = 9) subjects, aged 21-44 years, 11 male and nine female, were given oral paracetamol syrup 20 mg/kg, following an overnight fast. Paracetamol and its metabolites (glucuronide, sulphate, cysteine and mercapturic acid conjugates) were measured in serial plasma samples (0.25, 0.5, 0.75, 1.0, 1.5, 2, 3,...,12, 24 h) and urine collections (0-24 h) by high-performance liquid chromatography. RESULTS: In Chinese subjects, the (mean range) peak plasma concentration of paracetamol was 23.8 mug/mL (17.9-32.3) and time to attain this peak 0.66 h (0.5-0.75). This was lower (P < 0.015) at 18.7 microg/mL (14.4-22.9) and achieved later (P < 0.033) at 1.06 h (0.5-2.0) in Caucasians. In Chinese subjects, plasma levels of glucuronide were lower, sulphate higher and cysteine conjugates significantly lower than in Caucasians (P < 0.05). Chinese subjects excreted 6% more sulphate and 5% less glucuronide. They also excreted significantly less mercapturic acid conjugates (P < 0.001). DISCUSSION AND CONCLUSION: Chinese subjects show more rapid absorption of paracetamol, a tendency to produce less glucuronide but more sulphate conjugates and reduced production of cysteine and mercapturic acid conjugates. The latter may help to protect against hepatotoxicity following paracetamol overdose.

Pre-operative hepatitis in a woman treated with Chinese medicines.

A 37-year-old Hong Kong Chinese female with cervical cancer was scheduled for radical hysterectomy and lymphadenectomy. Her past health was good. Pre-operatively, she was found to have a fatty liver, prolonged prothrombin time and abnormal liver function tests. Surgery was not postponed and she was anaesthetised uneventfully, using a general anaesthetic technique. The procedure lasted 4 h. Postoperatively, she developed a large pelvic haematoma and a wound infection. Her coagulation and liver function tests gradually returned to normal. No obvious medical cause for her liver dysfunction could be found. However, it emerged that she had received a 6-week course of traditional Chinese medicines prior to admission. The prescriptions contained over 60 different ingredients, some of which were known to be hepatotoxic, cytotoxic or to cause bleeding. This was the most likely explanation for her liver dysfunction.

General anaesthesia in a child with Larsen syndrome.

Larsen syndrome is a rare congenital connective tissue disorder which is characterized by multiple dislocations of major joints, typical facial appearance, cervical spine narrowing and instability and respiratory difficulties secondary to laryngotracheomalacia. A case of general anaesthesia for laparoscopic hernia repair in a male child aged 16 months with this syndrome is presented. Anaesthesia was well tolerated though intubation proved difficult. Cervical spine instability and postoperative respiratory complications are potential problems.

The influence of baricity on the haemodynamic effects of intrathecal bupivacaine 0.5%.

This study compared the haemodynamic effects of subarachnoid block with plain bupivacaine 0.5% (dextrose-free), heavy bupivacaine 0.5% (in dextrose 8%) and a mixture of these two solutions, i.e. bupivacaine 0.5% in dextrose 4%. Thirty-six male patients, aged 55-89 years, undergoing transurethral surgery were recruited. Invasive systolic arterial and central venous pressures were recorded at 5-s intervals after the block was initiated using a computerised data-collection system. The height of sensory blockade was recorded at 5-min intervals. No preload was given and episodes of hypotension were treated with colloid (8 ml x kg(-1)) and, if this was ineffective, a metaraminol infusion. Systolic arterial and central venous pressures decreased in all three groups following block (p < 0.05). These decreases were more rapid in onset in the heavy bupivacaine group compared with plain bupivacaine group (p < 0.005). Patients in the heavy bupivacaine group also had a greater requirement for early treatment of hypotension (< 10 min) and treatment with metaraminol (p < 0.05). The onset of sensory blockade was more rapid in the heavy group compared with the mixed group, although final sensory levels were similar. The onset of haemodynamic and sensory changes are more rapid when using heavy bupivacaine intrathecally. This leads to a higher and earlier incidence of hypotension and requirement for treatment.

A comparison of three fluid-vasopressor regimens used to prevent hypotension during subarachnoid anaesthesia in the elderly.

We aimed to compare the efficacy of fluid preloading with two recently recommended fluid-vasopressor regimens for maintaining blood pressure during subarachnoid anaesthesia in the elderly. Sixty elderly patients requiring surgery for traumatic hip fractures received subarachnoid anaesthesia using 0.05 ml/kg of 0.5% heavy bupivacaine. Hypotension, i.e. systolic arterial pressure < 75% of baseline, was prevented or treated by: A--normal saline 16 ml/kg plus intravenous ephedrine boluses (0.1 mg/kg); B--normal saline 8 ml/kg plus intramuscular depot ephedrine (0.5 mg/kg); or C--Haemaccel 8 ml/kg plus metaraminol infusion. Systolic arterial pressure and heart rate were recorded using custom-written computer software (Monitor, version 1.0). Systolic arterial pressure decreased in all groups after five minutes (P < 0.001). Decreases were greatest in group A (P < 0.05). Heart rate increased by 7% group A and decreased by 9% in group C (P < 0.05). During the first hour, hypotension was present for 47%, 25% and 20% of the time in groups A, B and C respectively and overcorrection of systolic arterial pressure occurred in 19% of the time in group C. We conclude that treatment A was inadequate in preventing hypotension. Treatments B and C were more effective but were associated with an increased heart rate and overcorrection of systolic arterial pressure respectively.

Spectral analysis of sudden bradycardia during intrathecal meperidine anesthesia.

BACKGROUND AND OBJECTIVES: Severe bradycardia occurring suddenly during spinal anesthesia, although rare, is potentially fatal. Bradycardias are more common after intrathecal meperidine. We report two such episodes occurring in elderly male patients undergoing transurethral surgery. METHODS: Subarachnoid block was provided using 50 mg meperidine. Autonomic function was assessed by measuring heart rate (HR) variability using R-R intervals from standard electrocardiographic recordings. Frequency-domain spectra were constructed from 512 heartbeats, and an autoregressive method was used to calculate spectral power. RESULTS: In both patients, bradycardia (HR <50 beats/min) occurred after about 10 minutes and was associated with severe hypotension and a 10- to 100-fold increase in spectral density in both the low (0.04-0.15 Hz), mainly sympathetic, and the high (0.15-0.40 Hz), mainly parasympathetic, frequency bands. These spectral increases were subsequently attenuated by intravenous atropine. Heart rate slowing was noted to be periodic, or oscillatory, in one patient. CONCLUSION: Sudden increases in vagal, or parasympathetic, activity probably accounted for bradycardia.

Anesthesia for a child with complex I respiratory chain enzyme deficiency.

The mitochondrial myopathies are a rare group of conditions affecting the respiratory chain and oxidative phosphorylation. The anesthetic management of a 6-year-old girl with complex I respiratory chain deficiency requiring surgery for a fractured hip is presented and discussed. Potential problems were masseter spasm, tendency to develop lactate acidosis, and malignant hyperthermia susceptibility. These problems were avoided by the use of a laryngeal mask airway, allowing the patient to spontaneously ventilate; caudal analgesia; and maintenance of anesthesia with a proprofol infusion.