Browsing by Author "Coetzee, J. F."

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    Anaesthetic induction with propofol: How much? How fast? How slow? What determines anesthetic induction dose? It’s the Front-End Kinetics, Doctor!
    (Medpharm Publications, 2019) Coetzee, J. F.
    ENGLISH ABSTRACT: It has long been realised that linear dosing according to total body weight (TBW) results in overdosing obese patients and under-dosing small children. Injected drug doses calculated on a mg.kg-1 body weight basis work well only for patients of normal habitus. As long ago as 1969, in a study of induction doses of thiopentone,  ulfsohn and Joshi2 concluded that thiopentone was better administered according to lean body mass (LBM) than to TBW. They reasoned that endomorphic somatotypes required less thiopentone than mesomorphs and ectomorphs of the same TBW, because they had less LBM. They pointed out that there is a strong association between LBM, cardiac output and basal metabolic rate, and suggested that the LBM contained the “pharmacologically active mass”. Obese patients can perhaps be loosely regarded as ordinary individuals entrapped in a cocoon of fat into which hardly any injected drug is distributed. However the LBM of obese persons also increases as they accumulate fat, mainly due to increased muscle mass, as well as  enlargement of other organs and blood volume. The dilemma is that LBM does not increase at the same rate as the increase in fat. Thus, although we know that they need more drug than normal-weight patients, how much more is often uncertain.
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    Anaesthetic management of a three-month-old baby for cervical limited dorsal myeloschisis repair using propofol and alfentanil infusions guided by pharmacokinetic simulation software : case report
    (Medpharm Publications, 2019) Coetzee, E.; Gray, R.; Hollmann, C.; Enslin, N. J. M.; Coetzee, J. F.
    ENGLISH ABSTRACT: We present an uncommon case of limited dorsal myeloschisis in a 3-month-old infant requiring repair guided by intraoperative neuromonitoring (IONM) and therefore avoidance of volatile anaesthetic agents. The case presented challenges in positioning, airway management, a lack of age appropriate pharmacokinetic models in target-controlled infusion (TCI) syringe pumps and unavailability of remifentanil, considered to be an essential drug in this setting. We overcame these challenges using manually controlled infusions of propofol and alfentanil guided by pharmacokinetic simulation software (Stelsim).
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    Blood pressure measurement in obese patients : non-invasive proximal forearm versus direct intra-arterial measurements
    (Taylor & Francis Group, 2018) Verkhovsky, A.; Smit, M.; Levin, A.; Coetzee, J. F.
    Background: In obesity, accurate perioperative blood pressure measurement using upper arm, non-invasive blood pressure (NIBP) is technically challenging. Proximal forearm NIBP may be an acceptable substitute. Mean arterial blood pressures (MAP) estimated by proximal forearm NIBP were compared with direct intra-arterial measurements. It was hypothesised that the measurement techniques would be interchangeable if between-technique MAP differed ≤ 20% and MAP ratios were < 1.2 and > 0.8. Method: A total of 30 adults with body mass index ≥ 30 kg/m2 in whom perioperative intra-arterial blood pressure measurement was considered mandatory were enrolled. MAP measurements using the two techniques were obtained at three random intervals in each patient. Bland–Altman analyses were employed. Results: Forearm mean NIBP MAP overestimated mean intra-arterial MAP by 2.2 (SD 8.1; range from 23.8 to –19.4 mmHg; p = 0.011, 95% CI 3.9 to 0.5). However, Bland–Altman analyses revealed a wide dispersion with several MAP differences and MAP ratios exceeding the pre-specified bounds for interchangeability. Conclusion: Forearm NIBP could not be considered interchangeable with direct intra-arterial MAP measurements in obese patients.
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    Induction of anaesthesia with propofol according to the adjusted ideal body mass in obese and nonobese patients : an observational study
    (Taylor & Francis Group, 2019) Smith, F. J.; Jurgens, F. X.; Coetzee, J. F.; Becker, P. J.
    ENGLISH ABSTRACT: Obesity changes body composition including fat free mass (FFM), regarded as the “pharmacologically active mass”. Scaling drug doses to obese patients by total body mass (TBM) results in overdose. We aimed to determine the success rate of inducing anaesthesia in normal, overweight and obese patients with propofol, using an adjusted body mass scalar (ABM), which embodies the increased FFM of obese patients. Methods: Ninety-six patients were divided into three groups according to body mass index (BMI): normal, overweight and obese. Propofol 2 mg/kg ABM was administered according to the equation: ABM = IBM + 0.4(TBM – IBM), where IBM = ideal body mass. Induction success was assessed clinically and by electroencephalographic spectral entropy. Results: The groups were similar regarding gender, age, height and IBM. One patient was morbidly obese (BMI = 44). State entropy (SE) decreased to < 60 in 33/33, 28/29 and 33/34 patients in the normal-weight, overweight and obese groups respectively, an overall success rate of 97.5% (95% confidence interval 92.7% to 99.4%). Median lowest achieved SE values and median times that SE remained < 60 did not differ between groups, however the individual values ranged widely in all three groups. Induction failed in the two patients whose SE did not decrease to < 60 (one overweight and one obese). Conclusions: The ABM-based propofol induction dose has a high success rate in normal, overweight and obese patients. Further studies are required to determine the feasibility among morbidly obese patients.
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    Intra-ocular concentration-time relationships of subconjunctivally administered gentamicin
    (Health & Medical Publishing Group, 1991) Van Rooyen, M. M. B.; Coetzee, J. F.; Du Toit, D. F.; Van Jaarsveld, P. P.
    Eighty-nine patients scheduled for cataract removal or lens implantation were divided randomly into three groups. Each received 5, 10 or 20 mg gentamicin subconjunctivally at times varying between 0,2 and 19 hours pre-operatively. At surgery a sample of aqueous humour was obtained and analysed for gentamicin concentration. The data for each group were subjected to non-linear regression analysis to fit an open one-compartment pharmacokinetic model with first-order kinetics. A statistically acceptable fit was obtained. The average values of the pharmacokinetic parameters obtained from the single doses were used to simulate multiple-dose kinetics. The average target intra-ocular gentamicin concentrations and dosage interval were specified in the computer program, which subsequently allowed calculation of the dose required. This allowed the construction of a simple linear nomogram that can be used to read off the dose needed for handling specific clinical situations.
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    We have to flap our wings or fall to the ground : the experiences of medical students on a longitudinal integrated clinical model
    (Health & Medical Publishing Group, 2015) Voss, M.; Coetzee, J. F.; Conradie, H.; Van Schalkwyk, S. C.
    Background. In 2011, Stellenbosch University introduced a district hospital-based longitudinal integrated model for final-year students as part of its rural clinical school. The present study is an analysis of students’ experiences during the first 3 years of the programme. Methods. All 13 students who started the programme between 2011 and 2013 were interviewed. Thematic networks linking recurrent issues were developed and transcripts were analysed against this framework using ATLAS.ti. Results. Two major themes emerged. These were ‘preparation for being a doctor’ and ‘academic/exam preparation’. Students were overwhelmingly positive about the working atmosphere and their preparation for clinical practice and felt that their learning had been facilitated by the flexibility of the programme and the requirement to take responsibility. This contrasted with their academic (‘book’) learning, which was characterised by uncertainty about expectations, particularly regarding exams and parity with learning at the central teaching hospital. The flexibility of the integrated approach was seen as a problematic lack of structure when it came to academic learning. Negative academic emotions were compounded by some frustration about administrative issues early in the programme. Conclusions. The district hospital-based longitudinal integrated model has great potential as a teaching platform for final-year students; however, students remain concerned about academic learning. Potential strategies to reduce student anxiety include more opportunities for dialogue between rural students and specialist teaching platforms, clearly communicated expectations – both about what the students can expect from the programme and about what is expected from them – and administrative excellence.