John Norman

Effectiveness of appropriately trained nurses in preoperative assessment: randomised controlled equivalence/non-inferiority trial

Abstract Objective: To determine whether preoperative assessments carried out by appropriately trained nurses are inferior in quality to those carried out by preregistration house officers. Design: Randomised controlled equivalence/non-inferiority trial. Setting: Four NHS hospitals in three trusts. Three of the four were teaching hospitals. Participants: All patients attending for assessment before general anaesthesia for general, vascular, urological, or breast surgery between April 1998 and March 1999. Intervention: Assessment by one of three appropriately trained nurses or by one of several preregistration house officers. Main outcome measures: History taken, physical examination, and investigations ordered. Measures evaluated by a specialist registrar in anaesthetics and placed in four categories: correct, overassessment, underassessment not affecting management, and underassessment possibly affecting management (primary outcome). Results: 1907 patients were randomised, and 1874 completed the study; 926 were assessed by house officers and 948 by nurses. Overall 121/948 (13%) assessments carried out by nurses were judged to have possibly affected management compared with 138/926 (15%) of those performed by house officers. Nurses were judged to be non-inferior to house officers in assessment, although there was variation among them in terms of the quality of history taking. The house officers ordered considerably more unnecessary tests than the nurses (218/926 (24%) v 129/948 (14%). Conclusions: There is no reason to inhibit the development of nurse led preoperative assessment provided that the nurses involved receive adequate training. However, house officers will continue to require experience in preoperative assessment.

Pre‐oxygenation–how long?

Pre‐oxygenation was studied in 12 fit volunteers and 20 patients using an oxygen flow of 8 litres/minute delivered from a standard anaesthetic machine via a Magill or Bain breathing attachment. End‐tidal nitrogen concentrations of 4% or less were achieved within 3 minutes; the fastest times were achieved using the Magill breathing System when the reservoir bag was filled with oxygen prior to application to the face. Gas‐tight fits of face masks on patients were found to be essential.

Rebreathing with the Magill attachment

The occurrence of rebreathing in anaesthetic circuits has been studied by a number of authors ; the behaviour of semi-closed circuits during spontaneous ventilation being first subjected to analysis by Wynne in 1941 1. In 1954 Mapleson2 predicted that, for the Magill attachment, rebreathing of alveolar gas would not occur if the fresh gas flow rate equalled or exceeded the alveolar ventilation. He also predicted that there would be no rebreathing of any gas either alheolar or deadspace gas if the fresh gas flow rate equalled or exceeded the minute volume. Since the former prediction was based on the assumption that there would be no mixing of alveolar, deadspace and fresh gas in the apparatus or conducting airways, Mapleson suggested that, in clinical practice, the fresh gas flow rate should always exceed the minute volume. Woolmer & Lind3 and Bracken & Sanderson4 using model systems confirmed that where the fresh gas flow rate exceeded the minute volume there was no rebreathing. Similar results have been found during studies on anaesthetised patientss.6. Kain & Nunn7 have recently determined the lowest fresh gas flow rate that could be used without the occurrence of rebreathing in anaesthetised patients. They detected the occurrence of rebreathing by an increase in alveolar (end-tidal) carbon dioxide concentration and by an increase in the expired minute volume two obvious effects of the re-inhalation of expired carbon dioxide. Using this method of assessment these authors found that rebreathing did not occur until the fresh gas flow rate was less than the minute volume: on occasion the fresh gas flow rate could be reduced to less than half the minute volume before rebreathing occurred. Although the presence of rebreathing is usually revealed by changes produced by the re-inhalation of carbon dioxide it must be remembered that rebreathing also causes a fall in the inspired oxygen concentrations. The fall in the inspired oxygen concentration and the rise in alveolar carbon dioxide concentration will lead to a fall in the alveolar oxygen concentration. However, Kain & Nunn found that as the fresh gas flow rate was

Respiratory depression after morphine in the elderly

The effects of intravenous morphine (10 mg/70 kg) on the ventilatory response to CO2 were studied in two groups of subjects, young (18‐29 years) and old (66‐85 years), prior to elective surgery. In both groups morphine caused a signijcant depression of respiration as judged by a reduction in the slope of the CO2 response curve. a reduction in the calculated ventilation at an end tidal CO2 tension of 7.3 kPa, a rise in resting end tidal CO2 and a rise in the CO2 threshold. There were no significant differences between the two groups in the changes produced by the drug, suggesting that acute respiratory depression after a single intravenous injection of morphine is similar in old and young people.

A comparison of midazolam and temazepam for premedication of day case patients

One hundred patients who underwent day case surgery took part in a randomised double‐blind comparison between midazolam 15 mg and temazepam 20 mg orally as premedicants. Postoperative recovery was studied using tests of psychomotor function. Midazolam produced a similar degree of anxiolysis to temazepam and a greater incidence of drowsiness. Recovery was similar after either premedicant and psychomotor function was still depressed 4 hours postoperatively (p < 0.001). Nearly 90% of patients felt that they had benefitted from either premedicant. We conclude that midazolam is a suitable drug for premedication in day case surgery.

Postoperative myocardial damage in patients with coronary artery disease undergoing major non cardiac surgery.

A prospective study was carried out in a group of 50 patients with coronary artery disease, presenting for major non-cardiac surgery, to investigate the timing and incidence of further perioperative myocardial damage. A standardised anaesthetic was used. A standard 12-lead ECG was taken immediately before surgery and at 24, 48, and 72 hr after the start of anaesthesia. Blood samples were taken immediately preoperatively and at 6, 24, 48, and 72 hr after anaesthesia for total CK and CK-MB assay. Thirty-three patients (66%) showed ECG evidence suggestive of further infarction, and of these, two (4%) died in the immediate perioperative period. The first ECG change occurred in 27/31 (87%) by 24 hr, in 3/31 (10%) by 48 hr, and 1/31 (3%) by 72 hr. Twenty-nine patients (58%) including the two deaths showed CK-MB enzyme changes. The first elevation in CK-MB was nil at 6 hr and 72 hr, with 23/27 (85%) at 24 hr, and 4/27 (15%) at 48 hr. In 22/50 (44%) ECG and enzymes were correlative. Goldman and Cooperman risk indices were calculated for each patient. The Cooperman risk index was superior to the Goldman scale in the correlation of observed with predicted myocardial morbidity. Patients with ECG changes only before surgery were just as liable to further myocardial damage as those patients with ECG changes and a documented history of a previous infarct and/or symptoms. Myocardial damage is maximal in the first 24 hr after surgery, and may not be adequately predicted by current risk indices.RésuméNous avons entrepris une étude prospective de I’incidence et de l’histoire naturelle de nouvelle lésion myocardique survenant en période périopératoire chez 50 coronariens lors d’une intervention chirurgicale majeure autre que cardiaque. L’anesthésie se déroulait de façon conventionnelle mais on faisait un ECG à 12 dérivations juste avant et 24, 48, et 72 h après le début de l’anesthésie. On prélevait du sang au mêmes moments de même qu’à 6 h après le début de l’anesthésie afin de mesurer les CK totales et la fraction CK-MB. Trentetrois patients (66%) ont présenté à l’ECG une évidence d’infarctus nouveau et deux d’entre eux (4%) sont décédés en péri-opératoire immédiat. Les premiers signes électrocardiographiques d’infarctus étaient présents à 24 h chez 27/31 patients (87%), à 48 h chez 3/31 (10%) et à 72 h chez 1/31 (3%). Chez vingtneuf patients (58%), dont ceux qui sont décédés, il y eu augmentation des CK-MB qui s’est d’abord manifesté chez les survivants à 24 h dans 23/27 cas (85%) et à 48 h dans 4/27 cas (15%). Vingtdeux patients (44%) eurent à la fois une altération électrocardiographique et une augmentation des CK-MB. On a calculé les scores de risque de Cooperman et de Goldman et le premier prédisait mieux que le second la morbidité myocardique observée. La présence d’une histoire de problème cardiaque n’alourdissait pas le pronostic sombre d’un ECG préopératoire anormal. Le myocarde est maximalement à risque en deça de 24 h d’une intervention chirurgicale et les scores de risque le sousestiment souvent.

Early postoperative myocardial morbidity in patients with coronary artery disease undergoing major non-cardiac surgery: correlation with perioperative ischaemia

As a part of a study assessing early postoperative myocardial morbidity in 50 patients with active coronary artery disease undergoing major non-cardiac surgery, the ECG was monitored continuously for 24 hr after the onset of anaesthesia, using a frequency modulated (FM) Holter monitor. Concurrent automated blood pressure and pulse were measured non-invasively at three-minute intervals during anaesthesia and subsequently at five-minute intervals. Thirty patients were monitored with two-site ECG recordings, from modified V1 and V5 (Group A). Twenty patients had seventeen-site ECG monitoring, multiplexing a four by four array of precordial electrodes onto one channel of the frequency modulated recorder (Group B). Tapes were analyzed for noise, supraventricular and ventricular dysrythmias, runs of tacky- and bradycardia, and ST segment changes. These data were correlated with serial standard 12-lead ECGs and CK-MB assay in the 72 hr after surgery. Seven tapes from Group A could not be analyzed. Change (>1 mm) on ST monitoring from both Groups A (14/23), B (14/20), correlated with serial 12-lead ECG and/or CK-MB changes. The majority of first ST change 19/28 (70%) occurred after anaesthesia. In 14/28 (50%) ST change occurred during episodes of tachycardia and elevated blood pressure (>20% above baseline). Nine patients (9/23) in Group A had no ST change; however, six had serial 12-lead ECG and/or CK-MB changes. Six patients (6/20) in Group B had no ST changes, and none of these patients had any change of serial 12-lead ECGs or CK-MB assay. No patient complained of chest pain during the Holter monitoring period. Continual monitoring of heart rate and blood pressure and accurate ST monitoring are essential to detect and treat perioperative myocardial ischemia. A multiple-lead precordial system is substantially more sensitive than traditional two-lead ECG holter monitoring in detecting myocardial ischaemia.RésuméAu cours d’une étude de la morbidité myocardique postopératoire chez 50 candidats à une chirurgie non cardiaque atteints de maladie coronarienne, nous avons enregistré l’ECG avec un moniteur Holter à modulation de fréquence (FM) de façon continue pendant 24 h à partir de l’induction de l’anesthésie. On mesurait aussi le pouls et la pression artérielle par oscillométrie aux trois minutes pendant l’intervention chirurgicale et aux cinq minutes par la suite. Chez 30 patients, on monitora l’équivalent de V1 et V5 (groupe A) alors que chez 20 autres on avait 17 électrodes précordiales arrangées en une matrice de 4 × 4 que l’on multiplexait sur un canal du Holter FM (groupe B). Nous avons analysé les enregistrements en fonction du niveau d’interférence, des dysrythmies ventriculaires et supraventri-culaires, des episodes de tachy ou de bradycardie et des modifications des segments ST. On mis toute cette information en parallèle avec des ECG à 12 dérivations et des analyses des niveaux de CK-MB répétés pendant les 72 h suivant l’interven tion. Sept enregistrements du groupe A étaient inutilisables. Les modifications du segment ST de plus de 1 mm survenues chez 14 patients de chaque groupe étaient en corrélation avec les trouvailles à l’ECG 12 dérivations et les niveaux de CK-MB. Dixneuf des 28 épisodes d’altération du segment ST survinrent après l’anesthésie et 14 d’entreeux accompagnait une poussée de tachycardie et d’hypertension (> 120% de la valeur contrôle). Neuf des vingt-trois patients du groupe A avaient des segments ST normaux pourtant, six d’entreeux virent changer leur ECG 12 dérivations et/ou leur niveau de CK-MB. Des six patients du groupe B dont les segments ST restèrent inchangés, aucun ne démontra de changement électrocardiographique ou enzymatique. Par ailleurs aucun patient ne se plaint d’angine pendant la période de Holter. La mesure fréquente du pouls et de la pression artérielle et un monitorage précis et continu des segments ST est essentiel à la détection (et au traitement) de l’ischémie périopératoire. Un système ECG à multiples dérivations précordiales est à cet égard beaucoup plus sensible que les deux dérivations utilisées traditionnellement dans le monitorage Holter.

Co-axial breathing systems

USA MUsJu&seiis 021 14, were the preliminary findings reported at the surgical forum. We then reported that soon after delivery blood gastrin levels dropped considerably to reach the prepregnant values. Such a dramatic drop was surprising to us, considering that the stress of labour by releasing adrenaline can indirectly increase gastrin level^.^.^ The other exciting aspects of the earlier study regarding vasoactive intestinal polypeptides led us to present it as an abstract in the surgical forum. The control group of individuals in the present study were the same as the previous study; since 1976 we have repeatedly evaluated our control gastrin data for clinical purposes and have found no appreciable changes in their plasma levels and we, therefore, elected to present our original data as controls. We have, nonetheless, evaluated 33 new patients in the perigestational period in the present study. We demonstrated that, during labour. gastrin levcls are high but the lcvcl Rq/erences

Fluid-loading and cardiopulmonary by-pass. A study of renal function.

The incidence of acute renal failure following cardiopulmonary by-pass (CPB) varies widely between 2 and 15%.’-’ A retrospective study from this hospital showed that the incidence of renal dysfunction in 428 patients following open heart surgery was 31%.* The mortality in these patients with renal dysfunction was 45%, although the deaths were not necessarily due to renal failure. It has been suggested that the following factors predispose to the development of poor post-operative renal function : a perfusion time of more than 60 minutes, low flow during perfusion; a mean arterial pressure during perfusion of less than 60 mmHg; haemolysis during perfusion; mitral valve disease; Fallot’s tetralogy and previous renal impairment. The first four factors are concerned with the perfusion itself and suggest that measures likely to improve renal perfusion and urine production may prevent post-operative renal failure. Fluid loading, diuretic agents and sympathetic blockade have been used for this purpose, but there is very little information about the effects of these measures on renal function during perfusion. This study was designed to determine the effect of administering a fluid load of 20 ml/kg of Hartmann’s Ringer lactate solution before perfusion on renal function during by-pass.

APPARATUS FOR RECORDING ELECTROCARDIOGRAMS, INCORPORATING AUTOMATIC SEARCH AND HIGH-SPEED PLAYBACK

Abstract An apparatus for recording the electrocardiogram on tape, which permits the rapid automatic search for and playback of cardiac arrhythmias is described. The equipment is being used to evaluate methods of suppressing cardiac arrhythmias.