VENTILATORY EFFECTS OF OXYGEN IN THE DOG UNDER THIOPENTONE ANAESTHESIA

The ventilatory effects of prolonged oxygen administration wereexamined in seven dogs during thiopentone anaesthesia. Ventilation,tidal volume (VT), ventilatory rate (f), minute ventilation(VE), inspiratory time (Tl), expiratory time (TE), period (T^tot),Tl/T^tot and mean inspiratory flow (VT/Tl) were measured duringthe inhalation of room air, after 30 min of oxygen inhalation,and finally after a return to breathing room air. Arterial blood-gastensions were measured before and after 5, 10, 20 and 30 minof oxygen administration and 15 min after return to breathingroom air. Oxygen administration produced an immediate, significantand persistent decrease in ventilation, principally from a decreasein ventilatory rate and changes in ventilatory times. This wasin contrast to what occurred in awake animals. Modificationsin ventilatory mechanics or suppression of an hypoxic stimulusto ventilation were probably not involved. Anaesthesia may modifycentrally mediated ventilatory response to hyperoxia.     

VENTILATORY EFFECTS OF OXYGEN-ENRICHED MIXTURES IN THE DOG UNDER ALTHESIN ANAESTHESIA

In six dogs anaesthetized with Althesin, minute ventilation,respiratory rate, tidal volume, Pa_O2 and Pa_CO2 were measuredwhile breathing air (F1_O2 = 0.21), and then after correctionof hypoxaemia (F1_O2 = 0.35), and again while breathing 100%oxygen (F1_O2= 1.00). The administration of 35% oxygen correctedthe hypoxaemia (Pa_O2 = 8.98 ± 0.76 kPa in air; Pa_O2 =16.39 ± 1.59 kPa with 35% oxygen), but produced a significantand sustained depression of ventilation. The administrationof 100% oxygen induced a further significant and sustained decreasein ventilation. It is concluded that hypoxaemia is not necessaryfor the ventilatory depressant action of oxygen in the anaesthetizeddog and that, under Althesin anaesthesia, peripheral arterialchemoreceptors are active up to high Pa_O2 values.     

EFFECT OF FENTANYL ON VENTILATORY RESISTANCES DURING BARBITURATE GENERAL ANAESTHESIA

Fentanyl has been shown to increase the overall resistance toinspiratory flow of the ventilatory system (Rmax). Rmax is thesum of the airway resistance (Raw) and of the non-Newtonianresistance (     

HYPOXIC VENTILATORY DRIVE IN THE DOG UNDER ALTHESIN ANAESTHESIA

Althesin was administered i.v. to eight dogs, using two differentrates of infusion (6.55 +mn; 2.13 µl kg^–1 min and12.80 +mn; 2.00 µl kg^–1 min). Ventilation (T_I, T_E,RR, T_I/T_tot, V_T, V_E, V_T/T_I) and arterial blood-gas tensionswere measured in air and during a 10-min period of 100% oxygenbreathing. For both rates of Althesin infusion the ventilatoryresponse to oxygen was identical: there was significant depressionof ventilation (decrease in V_E and of the ventilatory drive,V_T/T_I) from the 1st min of inhalation lasting up to the 10thmin. This decrease in ventilation was more marked and persistentthan the decrease noticed in the unanaesthetized dog. We concludethat the hypoxic ventilatory drive persists in the dog underAlthesin anaesthesia.     

SOME RESPIRATORY EFFECTS OF HYPERVENTILATION DURING GENERAL ANAESTHESIA

Arterial blood gas tensions and pH were studied serially insix young female patients undergoing general anaesthesia forminor gynaecological surgery. Premedication with atropine andpapaveretum was not associated with any significant change inblood gas tensions or pH. Hyperventilation with 25 per centoxygen during the anaesthetic period was associated with a raisedarterial Po₂ accompanied by a fall in Pco₂ to 30 mm Hg and correspondingelevation in pH. After completion of the anaesthesia a moderatedegree of hypoxaemia was observed but its duration was muchless than that of the accompanying hypercapnia.     

AWARENESS DURING OPERATIVE OBSTETRICS UNDER GENERAL ANAESTHESIA

Two techniques of anaesthesia have been compared. The first(control group) consisting of premedication with hyoscine 0.6mg, induction with thiopentone 250 mg and suxamethonium 100mg, and maintenance with 67 per cent nitrous oxide with oxygen(using a Howells ventilator) and a suxamethonium infusion. Inthe study group exactly the same technique was used with theaddition of methoxyflurane (0.1 per cent) after delivery ofthe infant by elective or emergency section or vaginally, orthroughout the operation of postpartum sterilization. Attentionhas been focused on the incidence of awareness and dreamingduring operation. It has been demonstrated that the introductionof methoxyflurane into the standard technique, in the mannerdescribed, results in a marked reduction in the incidence ofawareness and a marked and significant reduction in the incidenceof unpleasant dreams. Some of the implications of this modificationare discussed.     

EFFECTS OF SOUNDS PRESENTED DURING GENERAL ANAESTHESIA ON POSTOPERATIVE COURSE

In a double-blind, randomized study, patients undergoing cholecystectomywere administered one of four different sounds during generalanaesthesia: positive suggestions, nonsense suggestions, seasidesounds or sounds from the operating theatre. The effect of thesesounds on the postoperative course was examined to assess intraoperativeauditory registration. No differences were found between thefour groups in postoperative variables.     

COMPARISON OF THE EFFECTS OF SPINAL ANAESTHESIA AND GENERAL ANAESTHESIA ON POSTOPERATIVE OXYGENATION AND PERIOPERATIVE MORTALITY

One hundred patients presenting for surgical treatment of fracturedneck of femur were allocated to receive either spinal (SAB)or general (GA) anaesthesia. Before operation, the mean Pao₂was 9.04 kPa. There was a significant decrease in Pao₁ of 0.68kPa in GA group at 1 h after operation, while blood-gas valueswere unchanged in SAB group. Eight patients (15.7%) in GA groupand five patients (10.2%) in SAB group died within 4 weeks ofsurgery. The difference was not statistically significant. ^* Present address: Department of Anaesthetics, The General Hospital,Gwendolen Road, Leicester LE5 4PW.     

BLOOD LOSS DURING CAESAREAN SECTION UNDER GENERAL ANAESTHESIA

Blood loss during Caesarean section has been measured in 121patients using a haemoglobin dilution method. The results havebeen analysed in an attempt to determine the importance on bloodloss of age, parity, previous Caesarean section, placental site,size of baby, length of operation, and surgical experience.The only statistically significant factors increasing bloodloss were (a) multipara undergoing their first Caesarean section(particularly emergency section) and (b) a low anterior placenta.Heavy blood loss, especially in patients with a low haemoglobin,was associated with an increased incidence of postoperativepyrexia.     

PREMEDICATION WITH LORAZEPAM FOR BRONCHOSCOPY UNDER GENERAL ANAESTHESIA

Lorazepam 3 or 4 mg i.m. was given to 100 patients as premedicationbefore bronchoscopy under thiopentone-suxamethonium anaesthesia.Forty-nine of the patients assessed as anxious received orallorazepam as preoperative night sedation also. Lorazepam wasan effective night sedative. Forty-two of the 49 patients sleptwell and were calm and co-operative in the morning. Followingthe i.m. injection of lorazepam, 64% of patients had completelack of recall for 4–10 h following premedication. Only5% recalled correctly a simple objective test of memory initiatedin the anaesthetic room. The frequency of recall was higherin those who consumed alcohol regularly and in females. Therewas one case of awareness during bronchoscopy in a patient whoreceived only a small dose of lorazepam (2.8 mg per 70 kg).Side-effects were minimal and patient acceptance was impressive.These results show an advance on previous studies using pethidineand diazepam. Further improvement is needed, particularly inadjusting the dose of lorazepam to body weight and to factorssuch as age, sex and alcohol intake.     

HAEMODYNAMIC EFFECTS OF OXPRENOLOL AND PRACTOLOL IN DOGS UNDER HALOTHANE ANAESTHESIA

The effects of beta-adrenergic blockade produced by either oxprenololor practolol in dogs anaesthetized with nitrous oxide and halothanewere studied. The main changes were a fall in cardiac output,heart rate and stroke work index, and an increase in centralvenous pressure. These changes were more marked with practololthan with oxprenolol but this difference was probably due toa higher degree of beta-adrenergic stimulation during the controlperiod in the dogs receiving practolol. The changes seen could,in the main, be attributed solely to beta-blockade. The possibilitythat the drugs are also direct myocardial depressants couldnot be ruled out as in some dogs showing no evidence of beta-stimulationin the control period negative inotropic effects were producedby both drugs.     

USE OF CONTINUOUS POSITIVE AIRWAY PRESSURE IN PAEDIATRIC DENTAL EXTRACTION UNDER GENERAL ANAESTHESIA

In a controlled prospective study, we studied 150 grade ASAl children undergoing outpatient dental extraction under inhalationanaesthesia with a T-piece system allocated to three equal groups:a control group (0 cm H₂O CPAP), and two study groups receiving2.5 or 5 cm H₂O of CPAP via a nasal mask. We found that theincidence and severity of oxygen desaturation were reduced significantlyin the 5-cm H₂O CPAP group. Present address: Department of Anaesthesia, Hull Royal Infirmary,Hull.     

COMPARISON OF ATRACURIUM AND VECURONIUM DURING ANAESTHESIA FOR LAPAROSCOPY

Atracurium 0.3 mg kg^–1 and vecuronium 0.06 mg kg^–1were compared directly in a double-blind randomized trial duringanaesthesia for laparoscopy in 57 healthy young women. The effectsof the drugs were monitored using a portable electromyograph.Both drugs provided adequate intubating conditions at 3 min,and prompt antagonism of paralysis after administration of neostigmine,but recovery was significantly faster with vecuronium (meantime to 20% recovery of control electromyographic response:vecuronium 15.1 min; atracurium 20.6 min (P < 0.001)). Atracuriumcaused a higher frequency of clinically observed allergoid reactions(21%) compared with vecuronium (3%).     

COMPARISON OF THE EFFECTS OF ATROPINE AND GLYCOPYRROLATE ON COGNITIVE FUNCTION FOLLOWING GENERAL ANAESTHESIA

Tests of orientation, concentration and shortterm visual memorywere used to assess 72 patients 1 day before, and 2 days after,elective major surgery. Patients were premedicated with papaveretumand either atropine or glycopyrrolate, before receiving a standardgeneral anaesthetic. Those who had received atropine showedsignificant postoperative short-term memory deficit (P< 0.01),but no change in orientation or concentration. Those who hadbeen given glycopyrrolate showed no significant cognitive changesafter surgery. As glycopyrrolate does not cross the blood-brainbarrier freely, these findings support the involvement of centralcholinergic mechanisms in the deterioration of cognitive functionin the postoperative period.     

CARDIAC ARRHYTHMIAS DURING ANAESTHESIA FOR LAPAROSCOPY

Fifty-six patients undergoing elective laparoscopy were allocatedrandomly to two groups. Group H received alcuronium and wereventilated artificially using 0.5% halothane and nitrous oxidein oxygen. Group E breathed spontaneously a mixture of enfluraneand nitrous oxide in oxygen. Arterial pressure, heart rate,tidal volume, respiratory rate and end-tidal carbon dioxidetension (PE_CO²) were monitored. The electrocardiogram (ECG)was recorded continuously using mogni-rir tape, from beforeinduction until the patient left the insufflated carbon dioxidehad been removed from the abdomen. Spontaneous ventilation withenflurane anaesthesia is a simple and safe technique for routinelaparoscopy, providing the intra-abdominal pressure does notexceed 25 mm Hg     

THE EFFECTS OF PREMEDICATION WITH PENTAZOCINE AND PETHIDINE ON RESPIRATION DURING GENERAL ANAESTHESIA

A comparison of the respiratory depressant effects of intravenousinjection of pentazocine (30 mg) or pethidine (30 mg) was undertakenin anaesthetized patients using a spirometric technique, aftereach patient had received a pre-anaesthetic medication of eitherpentazocine (40 mg) or pethidine (100 mg) by intramuscular injection.Results from four groups of patients were compared. Pentazocinegiven intravenously after either pethidine or pentazocine premedication,produced essentially the same degree of respiratory depression.Pethidine following premedication with pentazocine also producedan approximately similar degree of depression, but pethidineafter pethidine premedication produced a cumulative and significantlygreater degree of respiratory depression than that seen in theother three treatment groups.