OXYGEN AND ANAEMIA: THEIR EFFECTS IN MICE, ON INDUCTION TIME AND SURVIVAL TIME WITH HALOTHANE ANAESTHESIA

This paper reports the results of five studies on female miceto investigate the effects of halothane anaesthesia in air and100 per cent oxygen on induction time, survival time and sensitivityto halothane, in bled and unbled mice. Studies on the effectof anaemia on induction time and survival time showed that reductionsof haemoglobin content significantly reduced induction timesin mice anaesthetized with 10 per cent halothane in air and100 per cent oxygen (2 1./min), but did not significandy affectthe survival times in the same groups of mice. The use of 100per cent oxygen instead of air as the anaesthetic vehicle causeda highly significant increase in induction times and survivaltimes in both bled and unbled mice. Toxicity studies to determinethe halothane concentrations required to kill 50 per cent and99 per cent of mice in 30 minutes were used to confirm the resultsof the above survival studies. One study showed that in unbledmice, the mice were significantly more sensitive to halothane/airanaesthesia than to halothane/100 per cent oxygen anaesthesia.Other studies showed that a mean haemoglobin reduction of 31per cent did not significandy affect the mouse sensitivity tohalothane/100 per cent oxygen anaesthesia, but a reduction of45 per cent significantly increased the sensitivity of the bledmice to halothane/100 per cent oxygen. Body weight was shownto have a highly significant effect on induction time and survivaltime with 10 per cent halothane/100 per cent oxygen, but a non-significanteffect with 10 per cent halothane/air.     

Spinal anaesthesia for minor paediatric surgery

Our recent experience using spinal anaesthesia for paediatric surgical procedures is reviewed. In 1984, 30 patients aged seven weeks to 13 years were anaesthetised in this manner. Lumbar puncture failed in four of 34 patients, 12 required sedation during the operative course and 11 required light general anaesthesia to complete these procedures. Tetracaine one per cent or bupivacaine 0.75 per cent were the drugs used. During the procedure and depending on their age, the patients were either sedated or were distracted with the use of Disney cartoons played on a video cassette recorder. There were no significant intraoperative or postoperative complications.     

Induction reflex actions with intravenous nalbuphine as an adjunct to isoflurane

Ninety unpremedicated patients undergoing mask anaesthesia were assigned to one of three groups according to the volatile anaesthetic and the acute intravenous premedication administered. Group I received saline placebo as premedication and halothane by inhalation. Group II received saline placebo and isoflurane by inhalation. Group III received nalbuphine 0.1 mg.kg-1 IV as premedication and isoflurance by inhalation. Mean time to loss of consciousness (71 sec) did not differ among groups. The dosage of thiopentone required to induce loss of consciousness was decreased by 15 per cent (from 3.9 to 3.3 mg.kg-1) by nalbuphine premedication (P less than 0.05), and time to induction of surgical anaesthesia using isoflurane was decreased by 15 per cent (P less than 0.05). The incidence of reflex actions (coughing, laryngospasm, breath holding, hiccoughs and movement) during induction was no different in the saline-premedicated halothane or isoflurane groups. Acute intravenous nalbuphine premedication decreased significantly the incidence of reflex actions during induction of isoflurane anaesthesia from 77 per cent to 37 per cent (P less than 0.02). Desaturation episodes (SaO2 less than 90 per cent) were more frequent with isoflurane inductions compared with halothane (55 per cent vs 17 per cent, P less than 0.01). Apnoeic episodes accounted for the majority of desaturations associated with nalbuphine premedication, while excitatory reflexes (coughing and laryngospasm) accounted for more desaturations with isoflurane alone.     

In situ prone ESWL for the treatment of lower ureteral stones: Experience with 28 patients

Twenty-eight patients with lower ureteral stones underwent in situ extracorporeal shock wave lithotripsy (ESWL) in the prone position over the period of 7 months between March 1990 and September 1990. For stone disintegration the spark gap shock wave lithotripter Tripter XI (Direx) was used. Satisfactory disintegration was achieved in 93 per cent of patients. The stone-free rate at 12 weeks was 82 per cent, and 11 per cent had residual fragments less than or equal to 4 mm in diameter. Twenty-one per cent of patients required repeat treatments. For only 2 patients general anaesthesia was required (7 per cent). There were no remarkable complications except for haemospermia which resolved spontaneously 15 days after treatment. It was concluded that in situ prone ESWL is an effective and safe procedure for the treatment of lower ureteral stones.     

Groin hernia repair in Scotland

BACKGROUND: The use of mesh for groin hernia repair has dramatically changed the way this common operation is performed. The aim of this study was to survey the methods of groin hernia repair in Scotland and to assess patient satisfaction with the operation. METHODS: Between 1 April 1998 and 31 March 1999 all patients who underwent groin hernia repair in the National Health Service in Scotland were identified. As well as looking at the type of hernia repair performed and postoperative morbidity, patients were sent a Short Form-36 about 3 months after the operation to assess satisfaction and return to normal activity. RESULTS: Information was obtained on 5506 (97 per cent) of patients who underwent groin hernia repair during the study period. Eighty-five per cent of patients had an open mesh repair and 4 per cent had a laparoscopic repair. Most operations (85 per cent) were performed using general anaesthesia on an inpatient basis (78 per cent), and 8 per cent were for repair of a recurrent hernia. Potentially serious intraoperative complications were rare (seven patients), although they were significantly (P < 0. 001) more likely to be associated with a laparoscopic approach or repair of a femoral hernia: relative risk compared with open inguinal hernia repair 33 (95 per cent confidence interval (c.i.) 6-197) and 22 (95 per cent c.i. 3-152) respectively. Wound complications were common and 10 per cent of patients required a district nurse to attend the wound. Patients expressed a high degree of satisfaction; 94 per cent would recommend the same operation to someone else if required. CONCLUSION: An open mesh repair using general anaesthesia has become the repair of choice for a groin hernia in Scotland. Despite a high incidence of wound complications, patients are satisfied with this operation.     

FACTORS INFLUENCING THE ARTERIAL OXYGEN TENSION DURING HALOTHANE ANAESTHESIA WITH SPONTANEOUS RESPIRATION

Factors influencing oxygenation of the arterial blood were studied,during routine anaesthesia, in thirty-six patients anaesthetizedwith halothane and allowed to breathe spontaneously, with amean minute volume of 5 l./min. There was evidence of an unsteadyrespiratory state during the first hour of anaesthesia. Oxygenconsumption was 87 per cent of basal. Physiological deadspaceamounted to 33 per cent of the expired tidal volume (all patientsintubated). At high levels of inspired oxygen concentration,the mean alveolar-arterial Po, gradient was 184 mm Hg, correspondingto a shunt of 14 per cent of pulmonary bloodflow. At lower levelsof alveolar Po₂, the alveolar-arterial Po, gradient diminishedbut was above the value which would be caused by a shunt of14 per cent. This was probably due to uneven ventilation perfusionratios (maldistribution) corresponding to a calculated venousadmixture rising as high as 30 per cent. It is concluded that,to ensure the maintenance of a normal arterial Poa in the majorityof patients, the alveolar Po, is required to be as high as 200mm Hg and this needs an inspired oxygen concentration of 35per cent under the conditions investigated in this study.     

Conscious-sedation analgesia during craniotomy for intractable epilepsy: a review of 354 consecutive cases

The perioperative records of 354 consecutive patients undergoing craniotomy for surgical treatment of intractable epilepsy performed with conscious-sedation analgesia were reviewed retrospectively. There was no perioperative morbidity or mortality identified which could be attributed to the anaesthetic technique. The technique was not suitable for seven patients, in whom general anaesthesia was induced. The most frequent intraoperative problems were convulsions (16 per cent) and nausea and vomiting (eight per cent). Less frequent problems included excessive sedation (three per cent), "tight brain" (1.4 per cent) and local anaesthetic toxicity (two per cent). This study confirms that conscious-sedation analgesia provides suitable conditions for craniotomies when brain mapping is required.     

DAY CASE ANORECTAL SURGERY

All patients referred to the University Department of Surgery, Wellington Hospital, Wellington, New Zealand, with minor anorectal conditions requiring surgery were considered for day case surgery. Eighty-three per cent of the patients were found suitable for day surgery. One hundred patients underwent 103 procedures under general anaesthesia. Admission to hospital from the day care facility was required for four patients; two for bleeding, one for pain and one for drowsiness. One patient required readmission due to inability to cope at home. Twenty-six per cent reported severe pain. Eighty-nine per cent found day surgery to be convenient and preferable to inpatient surgery. Eleven per cent found day surgery inconvenient and would prefer inpatient surgery in future. It is suggested that many anorectal procedures can be performed on a day case basis in selected patients, with safety and convenience. It is well tolerated and accepted.     

Anticonvulsant therapy increases fentanyl requirements during anaesthesia for craniotomy

This study was designed to determine whether patients receiving chronic anticonvulsant therapy demonstrate an altered requirement for fentanyl during anaesthesia. Sixty-one patients undergoing craniotomy were studied; 20 controls (MED = 0) who had never received anticonvulsants and 41 epileptics in whom therapeutic plasma concentrations of either one (MED = 1), two (MED = 2), or three (MED = 3) different anticonvulsants were documented. During anaesthesia with 60-70 per cent N2O in O2 and 0.2 per cent isoflurane, a maintenance dose (MD) of fentanyl was administered using a continuous variable-rate IV fentanyl infusion, supplemented by intermittent 50 micrograms IV boluses. In order to define the minimal dosage of fentanyl required, the MD was titrated according to increases or decreases in the heart rate and/or mean arterial pressure exceeding 15 per cent of baseline ward values. A progressively higher fentanyl MD was required in the epileptic patients (MED = 1-4.3 +/- 0.5 microgram.kg-1.hr-1; MED = 2-5.4 +/- 0.6; MED = 3-7.6 +/- 0.6) compared with the control MD (MED = 0-2.6 +/- 0.5) (P less than 0.001). These findings indicate that there appears to be a dose-effect relationship between the number of anticonvulsants received and the maintenance dose of fentanyl required during balanced anaesthesia.     

Changes in myocardial oxygen consumption,efficiency and haemodynamics when systemic pressure is increased during morphine and added halothane anaesthesia in dogs

Depression of left ventricular function by the combination of halothane anaesthesia and increased ventricular afterload may undesirably reduce stroke volume and increase myocardial oxygen consumption by increasing ventricular wall stress. To investigate this possibility we studied six dogs instrumented to measure systemic and left ventricular pressures, ascending aortic and left anterior descending coronary artery flows and external left ventricular diameters. We sampled arterial and coronary sinus blood gases and oxygen contents. During morphine anaesthesia (4mg·kg^-1 intravenously with hourly supplements of 0.1 mg·kg^-1) and during added halothane anaesthesia (1.5 per cent end tidal) we measured systemic pressure, heart rate, stroke volume, stroke work, cardiac output, left ventricular end diastolic pressure and diameter and myocardial oxygen consumption. After infusing phenylephrine (0.02 mg/ml) to increase systolic pressure to 23.28 kPa (175 torr) we repeated measurements in both groups. We found that added halothane depressed systemic pressures (52 per cent), stroke volume (30 per cent), and myocardial oxygen consumption (46 per cent) compared to morphine alone. When afterload was increased with phenylephrine, stroke volume (20 per cent), cardiac output (25 per cent) and myocardial efficiency (47 per cent) were further depressed during added halothane anaesthesia compared to control halothane anaesthesia. Left ventricular end diastolic diameter (5 per cent) and pressure (320 per cent) were significantly increased by added afterload, compared to the control added halothane state. Conversely, increased afterload produced few changes during morphine anaesthesia alone. However, at comparable systemic pressures, myocardial oxygen consumption was similar during both anaesthetic states. We conclude that during added halothane anaesthesia increased afterload decreases stroke volume and myocardial efficiency. Cardiac output is reduced without increased myocardial oxygen consumption compared to morphine anaesthesia at comparable afterload states. In patients with already compromised cardiac output, further depression of stroke volume by increased ventricular afterload during halothane anaesthesia may be deleterious.     

Prognosis after simple incision and drainage for a first-episode acute pilonidal abscess

During a 3-year period 73 patients were treated consecutively for a first-episode acute pilonidal abscess with simple incision and drainage under local anaesthesia. In all cases the treatment relieved symptoms and all patients returned to work immediately after treatment. Healing per primam occurred in 42 patients (58 per cent; 95 per cent confidence limits: 45-69) within 10 weeks after treatment. These patients had significantly fewer pits and lateral tracts compared with patients who developed excessive granulation tissue after incision and who required definitive surgical treatment later. Nine patients (21 per cent; 95 per cent confidence limits: 10-37) with healing per primam developed recurrence of their pilonidal disease during the prospective follow-up period (median follow-up period was 60 months, range 36-84 months). Actuarial analysis of the data revealed a constant cure rate of 76 per cent (95 per cent confidence limits: 57-95) after 18 months.     

Duration of intradermal anaesthesia with mixtures of bupivacaine and lidocaine

In a double-blind trial on 20 human volunteers, the duration of intradermal anaesthesia with bupivacaine 0.25 per cent was compared with duration with a mixture of bupivacaine 0.25 per cent and carbonated lidocaine 1.0 per cent and with a mixture of bupivacaine 0.25 per cent and lidocaine hydrochloride 1.0 per cent. The duration of intradermal anaesthesia produced by bupivacaine mixed with carbonated lidocaine was 114 ± 56 (mean ± 1 SD) minutes and was not significantly shorter than the duration of the bupivacaine alone, at 125 ± 70 minutes, or duration with the mixture of bupivacaine and lidocaine hydrochloride, which was 112 ± 41 minutes. These results indicate that the mixture of bupivacaine with either carbonated lidocaine or lidocaine hydrochloride may be used for local anaesthesia without significant shortening of the duration of action.     

STUDIES OF ANAESTHESIA IN RELATION TO HYPERTENSION IH: PULMONARY GAS EXCHANGE DURING SPONTANEOUS VENTILATION

Ventilation, pulmonary gas exchanges and oxygen transport werestudied in a group of treated and untreated hypertensive elderlypatients, before, during and after nitrous oxide-halothane anaesthesiawith spontaneous ventilation. During anaesthesia minute andalveolar ventilation were depressed (— 30 per cent) outof proportion to the decrease in oxygen uptake (-18 per cent)and carbon dioxide production (— 19 per cent), and moderatehypercapnia ensued (mean Paoo3 50.3 mm Hg). All these variablesreturned to the pre-anaesthetic levels within 1 hour of terminatinganaesthesia. VD/VT was increased following induction of anaesthesiaas a result of decreased tidal volumes (— 47 per cent),but did not change progressively during the course of anaesthesia.Total deadspace (VD) was reduced by an average of 44 ml as aresult of intubation. Based on measurements of arterial Poaand the alveolar-arterial Poj difference, mean pulmonary venousadmixture was 10.4 per cent before anaesthesia, 10.9 per centduring anaesthesia but before surgery, 13.1 per cent after surgery,and 15.6 per cent 1 hour after the termination of anaesthesia.Although the average postoperative arterial Poa was slightlylower ( - 7.4 rnm Hg) than before anaesthesia, the differencewas due to many factors, and no evidence of a deteriorationin the over-all pulmonary gas exchange could be found. The conceptof "airway closure" in the supine elderly subject as a causefor the increased pulmonary venous admixture at rest is discussed.Impairment of pulmonary function during anaesthesia in hypertensiveelderly patients causes less concern than the severe changesin cardiovascular function ^*Present address: Hospital Notre Dame, Montreal133, P.Q., Canada     

Where there is no anaesthetist...

In an unselected series of 254 operations representing a wide range of surgical, obstetric and gynaecological procedures carried out on the small Pacific island of Tuvalu, the majority (85 per cent) involved the lower half of the body. In all cases but one anaesthesia was administered by a non-specialist. In operations below the level of the diaphragm epidural anaesthesia was usually used with a success rate of 96 per cent. In the upper half of the body ketamine was used where local or regional block was insufficient. Only one operation was performed under general inhalation anaesthesia. The overall postoperative mortality rate was 0.4 per cent and the morbidity rate was 13 per cent. Only two minor complications were attributed to the anaesthetic method used. In situations where anaesthetists are not available, epidural and ketamine anaesthesia in the hands of non-specialists are safe and practical options to general inhalation anaesthesia and are appropriate for most surgical procedures.     

Obstetrical epidural anaesthesia in a Canadian outpost hospital

The number of parturients receiving epidural anaesthesia in university medical centres is increasing. This trend is not paralleled in rural hospitals. Obstetrical epidural anaesthesia as provided in a 40-bed, remote hospital is reviewed for the ten-year period from January 1974 to December 1983. Charts were reviewed retrospectively for 116 patients undergoing epidural blockade. The indications, complication rates, as well as infant outcomes were noted. Seven per cent of all parturients received epidural anaesthetics. Ninety per cent of this group received systemic sedation or narcotics prior to epidural catheter insertion. Nineteen patients (16.3 per cent) experienced a major complication, including four dural punctures (3.4 per cent), ten episodes of significant hypotension (8.6 per cent), blood vessel puncture during catheter insertion in four patients (3.4 per cent), and transient paresthesia in one patient (0.8 per cent). Considerations for the provision of epidural anaesthesia in a remote hospital are discussed.     

Atracurium versus vecuronium: a comparison of recovery in outpatient arthroscopy

Atracurium 0.5 mg.kg-1 and vecuronium 0.1 mg.kg-1 were compared as neuromuscular relaxants for outpatient arthroscopy of the knee under general anaesthesia. In 40 unpremedicated patients divided at random into two groups, anaesthesia was induced with methohexitone, atracurium (Group A) or vecuronium (Group B), three per cent isoflurane prior to intubation and 0.9 per cent during maintenance with nitrous oxide 66 per cent in oxygen. Neuromuscular function was recorded by a Datex Relaxograph. Recovery was assessed by the time the patients took to open their eyes, to be able to answer five questions correctly, the time to recovery of ocular balance (Maddox Wing test) and by comparing pre- and postoperative performance of a paper and pencil test (the p-deletion test). Recovery tests showed no significant differences between groups. After three hours all the patients were fit for discharge. The patients were interviewed one month after the procedure. All were satisfied with their anaesthetic. "Full recovery" took 1.5 days with a range of 1 h-7 days. The only significant difference (p less than 0.01) between the groups was the need for pharmacological reversal of residual paralysis. In a procedure with a mean duration of 45.6 minutes, and using isoflurane, all but one patient (95 per cent) in the atracurium group required neostigmine versus nine patients in the vecuronium group (45 per cent).     

The locked knee

Fifty patients presenting themselves with a locked knee were investigated prospectively by examination under anaesthesia and arthroscopy. Definite abnormality was found in 92 per cent. Torn menisci were present in 68 per cent and isolated ruptures of the cruciate ligament in 10 per cent. Loose bodies were found in 3 patients, degenerative changes alone in 2 patients and a pathological medial synovial shelf in 1 patient. No abnormality was demonstrated in 8 per cent. Sixteen per cent of the knees remained locked following the induction of anaesthesia. This study demonstrates that a true mechanical block is not necessarily present and that the position of an unstable meniscal fragment is not consistently related to the fixed position of the knee under anaesthetic. There were no clinical features that allowed the normal knees to be distinguished preoperatively from those with internal derangement. It is proposed that these patients should be managed by prompt examination under anaesthesia, arthroscopy and definitive surgery.     

General anaesthetic management for laser resection of central airway lesions in 85 procedures

The perioperative course of 41 patients undergoing 85 endoscopic laser resections of central airway lesions under general anaesthesia was reviewed. The CO2 laser was used in 60 procedures and the Nd:YAG in 25. Intravenous anaesthesia and Venturi ventilation were utilized for 65 resections; 20 procedures involved predominantly inhalation anaesthesia via the ventilating bronchoscope. Significant intraoperative complications included arterial desaturation (SaO2 less than 90 per cent) in 26 per cent of procedures, and refractory hypertension requiring vasodilator therapy in 19 per cent. Intravenous anaesthesia was associated with a longer duration of recovery room care and a higher incidence of postoperative respiratory complications (delayed extubation, recovery room re-intubation and ventilation, and post-extubation stridor). Inhalation anaesthesia appeared to simplify the intraoperative management and decrease the incidence, duration and severity of immediate postoperative respiratory complications.     

Effects of dose and concentration of rectal methohexitone for induction of anaesthesia in children

To investigate the effect of dose and concentration of rectal methohexitone for induction of anaesthesia, 60 children (ASA physical status 1 or 2) undergoing outpatient surgery were studied. Each child was randomly assigned to receive one of three rectal solutions (each containing atropine 0.02 mg X kg-1): Group A - ten per cent methohexitone, 25 mg X kg-1 (n = 20); Group B - ten per cent methohexitone, 15 mg X kg-1 (n = 20); or Group C - one per cent methohexitone, 15 mg X kg-1 (n = 20). After induction of anaesthesia, or a maximum period of 20 minutes following rectal administration of methohexitone, halothane, nitrous oxide, and oxygen were administered by mask. The time to induction of anaesthesia, complications, postanaesthetic recovery scores, and recovery time did not differ significantly among the three groups. The incidence of failed inductions did not differ significantly between Group A (zero per cent) and Group C (ten per cent) but both were significantly less than Group B (45 per cent) (p less than 0.05). Heart rate increased significantly between 10 and 30 minutes after rectal administration of methohexitone and atropine. The authors conclude that ten per cent rectal methohexitone 25 mg X kg-1 and one per cent rectal methohexitone 15 mg X kg-1 are equally effective for induction of anaesthesia in children and both are significantly more effective than ten per cent methohexitone 15 mg X kg-1.     

The effect of pH adjustment of bupi-vacaine on onset and duration of epidural anaesthesia for Caesarean section

Previous studies have reported that elevation of the pH of local anaesthetics results in more rapid onset of action, with enhanced quality and duration of block. This study investigated the effect of pH adjustment of 0.5 per cent bupivacaine immediately prior to epidural anaesthesia for Caesarean section. Addition of 0.1 ml of 8.4 per cent sodium bicarbonate to 20 ml of 0.5 per cent bupivacaine consistently raised the pH of the local anaesthetic from 5.49 to 7.04 (mean values). One hundred patients, presenting for elective Caesarean section under epidural anaesthesia participated in the study. Forty patients received epidural anaesthesia, using pH-adjusted 0.5 per cent bupivacaine, in a dosage adequate to produce block to the T4 level. A control group of 40 patients received the standard commercial preparation of 0.5 per cent bupivacaine. A further ten patients in each group received epidural anaesthesia using 0.5 per cent bupivacaine with the addition of 1:400,000 epinephrine, to study the effect of epinephrine on pH adjustment of the local anaesthetic. Elevation of the pH of the local anaesthetic significantly increased the speed of onset of action from 6.4 minutes to 3.2 minutes and the time to peak effect from 24.8 minutes to 18.1 minutes, while the duration of anaesthesia was increased from 124.8 minutes to 147.3 minutes. The time to S2 segment blockade was also shortened from 13.5 to 8.6 minutes. Addition of 1:400,000 epinephrine to the local anaesthetic did not influence the effect of pH adjustment. Maternal and umbilical cord plasma levels of bupivacaine were not affected by pH adjustment of the local anaesthetic, while MV/UV and UA/UV ratios were unaltered.