Difficult airways present a clinical challenge for anaesthetists. The Truphatek Truview EVO2© (Truphatek International Ltd, Netanya, Israel) is a new laryngoscope blade used for endotracheal intubation that could be used where there is difficulty in visualizing the laryngeal inlet.

Twenty anaesthetists (12 trainees and eight consultants) compared the Truphatek Truview EVO2© with a conventional Macintosh size 3 blade. The Trucorp Airsim Bronchi© (Trucorp Ltd, Belfast, Northern Ireland, UK) manikin was intubated under normal conditions and under simulated difficult conditions such as tongue inflation and neck rigidity. In each scenario, the Cormack–Lehane grade, time needed for successful intubation, perceived difficulty of tracheal intubation and personal preference of blade were compared. The results were analysed with t-test (time of intubation), Wilcoxon signed-rank sum (Cormack–Lehane grade, ease of manoeuvre, preferred blade) and analysis of variance with Bonferroni correction (augmentation of difficulties in different scenarios).

The Truview EVO2 blade allowed the best laryngeal view as judged by the Cormack–Lehane grade (P < 0.05) in two separate situations: under simulated tongue inflation and under simulated neck rigidity. However, this blade did not reduce the intubation time or the ease of tracheal tube placement with respect to conventional Macintosh blade.

Compared with the classical Macintosh blade, the Truview EVO2 blade allowed a better view of the larynx, but did not facilitate endotracheal intubation in any of the difficult scenarios created with the adjustable manikin and in most scenarios in fact prolonged the intubation time.

Combined spinal-epidural analgesia is effective in labour analgesia. Nitric oxide may play important roles in pregnancy and labour and is probably affected by labour pain. The aim of the present study was to explore the alteration in serum levels of nitric oxide metabolites, i.e. nitrate and nitrite, during labour with or without combined spinal-epidural analgesia.

Fifty pregnant women were recruited at the cervical dilatation of 3∼4 cm, 25 received combined spinal-epidural analgesia and 25 served as control. Twenty in the combined spinal-epidural analgesia group and 19 in the control group finished data collection and were included in the analysis. Blood samples were taken at study entry, full cervical dilation and 2 h after delivery. Total serum level of nitrite and nitrate was measured with enzymatic conversion and followed by Griess reaction. Visual analogue pain scores and mean blood pressure were monitored.

After analgesia, pain score and mean blood pressure were significantly lower in the combined spinal-epidural analgesia group than in the control group (P < 0.05). Serum levels of nitric oxide metabolites were not significantly different at study entry (P > 0.05) but significantly different at full cervical dilation and 2 h after delivery (P < 0.05 for both) between the control group and the combined spinal-epidural analgesia group. Serum levels of nitric oxide metabolites decreased significantly at full cervical dilation and 2 h after delivery compared with study entry in the control group (P < 0.05) and this decrease was almost abolished in the combined spinal-epidural analgesia group (P > 0.05).

Combined spinal-epidural analgesia provided effective analgesia and abolished the decrease in nitric oxide metabolites during active labour.

To determine the efficacy and safety of intravenous postoperative morphine titration in the elderly compared with younger patients.

In the post-anaesthesia care unit, patients complaining of pain received morphine until adequate pain relief. Intravenous morphine was titrated as 3 mg boluses in young (age ⩽65 yr) and 2 mg in elderly patients (>65 yr) every 5 min.

We studied 350 young and 68 elderly patients. There were no significant differences between the two age groups for pain intensity at the onset of titration (numerical rating scale, 7.4 ± 1.7 in young vs. 7.5 ± 1.7 in elderly patients), area under the curve of numerical rating scale vs. morphine boluses (97.7 ± 59.6 vs. 98.2 ± 62), number of boluses required to obtain pain relief (3 ± 1.3 vs. 3 ± 1.3), percentage of titration failures (10% vs. 9%) and incidence of excessive sedation (18% vs. 21%). Renal clearance was significantly reduced in elderly compared with young patients (55 ± 21 vs. 85 ± 15 mL min−1; P < 0.0001).

Using lower bolus doses, pain relief in the immediate postoperative period with morphine was as efficacious and safe in elderly patients as in younger patients. The decrease in renal clearance of morphine in the elderly justifies the reduction of intravenous morphine boluses for the treatment of postoperative pain.

To measure the prevalence of postoperative pain, an assessment was made of 1490 surgical inpatients who were receiving postoperative pain treatment according to an acute pain protocol.

Measurements of pain (scores from 0 to 100 on a visual analogue scale) were obtained three times a day on the day before surgery and on days 0–4 postoperatively; mean pain intensity scores were calculated. Patients were classified as having no pain (score 0–5), mild pain (score 6–40), moderate pain (score 41–74) or severe pain (score 75–100).

Moderate or severe pain was reported by 41% of the patients on day 0, 30% on days 1 and 19%, 16% and 14% on days 2, 3 and 4. The prevalence of moderate or severe pain in the abdominal surgery group was high on postoperative days 0–1 (30–55%). A high prevalence of moderate or severe pain was found during the whole of days 1–4 in the extremity surgery group (20–71%) and in the back/spinal surgery group (30–64%).

We conclude that despite an acute pain protocol, postoperative pain treatment was unsatisfactory, especially after intermediate and major surgical procedures on an extremity or on the spine.

Major gynaecological abdominal surgery is associated with moderate to severe postoperative pain, hyperalgesia and the need for multimodal analgesia to reduce high morphine consumption. A low-dose ketamine regimen appears to prevent postoperative hyperalgesia. We examined the potential beneficial effect of ketamine on postoperative pain management and cognitive function.

Ninety patients were included in this double-blind, randomized, placebo-controlled study to test the efficacy and adverse effects of ketamine (as an intraoperative bolus of 0.15 mg kg−1, followed postoperatively by ketamine 0.5 mg per morphine 1 mg in a patient-controlled analgesia device). All patients received additionally ketoprofen. The main end-point was morphine consumption over the first 24 h. Secondary efficacy and safety end-points were morphine consumption during the titration period and during the patient-controlled analgesia period (48 h), the number of morphine-related adverse effects and the results of psychometric tests.

Ketamine, in combination with morphine and ketoprofen, did not improve postoperative pain scales and did not reduce morphine consumption and the incidence of morphine-related adverse effects. Ketamine did not modify mood, cognitive and memory functioning.

Adding a low dose of ketamine to an efficacious multimodal analgesic regimen did not improve analgesia after gynaecological surgery. Although this combination appears to be safe, the lack of benefit suggests that a low dose of ketamine should not be used for routine care.

Levosimendan has a cardioprotective action by inducing coronary vasodilatation and preconditioning by opening KATP channels. The aim of this study was to determine whether levosimendan enhances myocardial damage during hypothermic ischaemia and reperfusion in isolated rat hearts.

Twenty-one male Wistar rats were divided into three groups. After surgical preparation, coronary circulation was started by retrograde aortic perfusion using Krebs–Henseleit buffer solution and lasted 15 min. After perfusion Group 1 (control; n = 7) received no further treatment. In Group 2 (non-treated; n = 7), hearts were arrested with cold cardioplegic solution after perfusion and subjected to 60 min of hypothermic global ischaemia followed by 30 min reperfusion. In Group 3 (levosimendan treated; n = 7), levosimendan was added to the buffer solution during perfusion and the hearts were arrested with cold cardioplegic solution and subjected to 60 min of hypothermic global ischaemia followed by 30 min reperfusion. At the end of the reperfusion period, the hearts were prepared for biochemical assays and for histological analysis.

Tissue malondialdehyde levels were significantly lower in the levosimendan-treated group than in the non-treated group (P = 0.019). The tissue Na+–K+ ATPase activity was significantly decreased in the non-treated group than in the levosimendan-treated group (P = 0.027). Tissue myeloperoxidase (MPO) enzyme activity was significantly higher in the non-treated group than in the levosimendan-treated group (P = 0.004). Electron microscopic examination of the hearts showed cardiomyocytic degeneration at the myofibril, mitochondria and sarcoplasmic reticulum in both non-treated and levosimendan-treated groups. The severity of these findings was more extensive in the non-treated group.

Treatment with levosimendan provided better cardioprotection with cold cardioplegic arrest followed by global hypothermic ischaemia in isolated rat hearts.

Failed intubation is an important cause of anaesthetic-related maternal mortality. The purpose of this study was to determine the ability to predict difficult visualization of the larynx from the following preoperative airway predictive indices, in isolation and combination: modified Mallampati test, the ratio of height to thyromental distance and the Upper-Lip-Bite test.

We collected data on 400 consecutive parturients scheduled for elective Caesarean delivery under general anaesthesia requiring endotracheal intubation and then assessed all three factors before surgery. An experienced anaesthesiologist, not apprised of the recorded preoperative airway assessment, performed the laryngoscopy and grading (as per Cormack and Lehane’s classification). Sensitivity, specificity and positive predictive value for each airway predictor in isolation and in combination were determined.

Difficult laryngoscopy (Grade 3 or 4) occurred in 35 patients (8.75%). The ratio of height to thyromental distance had a higher sensitivity, positive predictive value and fewer false negatives than the other variables tested. The ratio of height to thyromental distance of 21.24 provided the best cut-off point for predicting subsequent difficult laryngoscopy. The odds ratio (95% CI) of the ratio of height to thyromental distance, Mallampati class and the Upper-Lip-Bite test were 127.8 (44.8–364.5), 49.8 (20.3–121.8) and 6.6 (2.29–19.30), respectively.

The ratio of height to thyromental distance may prove a useful screening test for predicting difficult laryngoscopy in obstetric population.

Because patients who are to undergo surgery must give their consent to planned postoperative care, clear and complete information on postoperative pain management should be given. The aim of this quality-of-care study was to evaluate by inquiry the impact of written information describing postoperative pain management on the quality and type of information retained, and patient participation in discussing and agreeing to the postoperative pain management programme during the presurgical anaesthesiology consultation.

Prospective before and after interventional surveys, each lasting 3 weeks and conducted at a 6-month interval (time required to prepare the written information), used a standardized anonymous questionnaire given to patients after the anaesthesiology consultation. Questions requiring a ‘yes’ or ‘no’ response assessed the quality of information and what information was retained by the patient, the extent of the patient’s interaction during the discussion with the anaesthesiologist and his/her agreement with the postoperative pain management programme.

Among the 180 before-group patients included, 16.7% reported receiving verbal information during the anaesthesiology consultation, none retained all seven principal side-effects of morphine, 14.4% considered the information to be thorough, 20.6% understood it, 16.7% claimed that it had helped them participate in the discussion and 14.4% concurred with the postoperative pain management programme. Compared to the before inquiry, significantly higher percentages of the 107 after-group patients (given written information before the anaesthesiology consultation) responded as having received verbal information during the anaesthesiology consultation (57.0%), retained morphine’s main side-effects (12.1%), deemed the information thorough (58.9%) and understandable (53.3%), had participated in the discussion (47.7%) and agreed with the postoperative pain management programme (51.4%).

Written information on postoperative pain management distributed before the presurgical anaesthesiology consultation improved the quality of information retained, facilitated discussion with the anaesthesiologist and patient agreement with the postoperative pain management programme.

Previous studies have demonstrated an increased perioperative opioid requirement during inflammatory disease. To evaluate the influence of the inflammatory process, we studied in the same patient the sufentanil requirement during procedures that occur during two distinct phases of ulcerative colitis with different inflammatory profiles: (1) left colectomy for major colitis unresponsive to medical treatment during acute inflammation and (2) coloprotectomy with ileoanal anastomosis, three months after recovery of the acute inflammatory episode.

Sixteen patients with clinical and histological evidence of ulcerative colitis scheduled for colectomy with ileoanal anastomosis were included. For each surgical procedure, anaesthesia was induced with sufentanil 0.5 μg kg−1 and propofol 2 mg kg−1. Patients were ventilated with 50% nitrous oxide and oxygen, and tidal volume was adjusted to keep end-tidal CO2 at 30 mmHg. Anaesthesia was maintained with end-tidal isoflurane at 0.5%. Analgesia was achieved with continuous infusion of sufentanil at 0.3 μg kg−1 h−1. Additional boluses of sufentanil and increases in infusion rates were used when haemodynamic variables increased to more than 20% of preoperative values. Sufentanil consumption during surgery was analysed by Wilcoxon signed rank sum test. P < 0.05 was considered significant.

Total intra-operative sufentanil requirement was significantly larger during colectomy performed for acute inflammatory colitis than during ileoanal anastomosis performed after the inflammatory process (1.24 ± 0.48 μg kg−1 h−1 vs. 0.62 ± 0.3 μg kg−1 h−1; P < 0.05).

For the same patient, inflammatory status influences opioid requirements during surgery for ulcerative colitis.

To improve heat transfer, the Medivance Arctic Sun® Temperature Management System (Medivance, Inc., Louisville, CO, USA) features an adhesive, water-conditioned, highly conductive hydrogel pad for intimate skin contact. This study measured and compared the heat transfer coefficient (h), i.e. heat transfer efficiency, of this pad (hPAD), in a heated model and in nine volunteers’ thighs; and of 10°C water (hWATER) in 33 head-out immersions by 11 volunteers.

Volunteer studies had ethical approval and written informed consent. Calibrated heat flux transducers measured heat flux (W m−2). Temperature gradient (ΔT) was measured between skin and pad or water temperatures. Temperature gradient was changed through the pad’s water temperature controller or by skin cooling on immersion.

The heat transfer coefficient is the slope of W m−2/ΔT: its unit is W m−2 °C−1. Average with (95% CI) was: model, hPAD = 110.4 (107.8–113.1), R2 = 0.99, n = 45; volunteers, hPAD = 109.8 (95.5–124.1), R2 = 0.83, n = 51; and water immersion, hWATER = 107.1 (98.1–116), R2 = 0.86, n = 94.

The heat transfer coefficient for the pad was the same in the model and volunteers, and equivalent to hWATER. Therefore, for the same ΔT and heat transfer area, the Arctic Sun’s heat transfer rate would equal water immersion. This has important implications for body cooling/rewarming rates.

We have investigated whether, after major abdominal surgery, the addition of remifentanil to tramadol for intravenous patient-controlled analgesia improved analgesia and lowered pain scores, compared to a patient-controlled analgesia containing only tramadol.

Sixty-two patients were allocated randomly to receive an intravenous patient-controlled analgesia with tramadol alone (T), or tramadol plus remifentanil (TR), in a double-blind randomized study. Whenever patients complained of pain, they were allowed to use bolus doses of tramadol (0.2 mg kg−1) or tramadol (0.2 mg kg−1) plus remifentanil (0.2 μg kg−1) mixture every 10 min without a time limit and background infusion. Discomfort, sedation, pain scores, total and bolus patient-controlled analgesia tramadol consumption, and side-effects were recorded for up to 24 h after the start of patient-controlled analgesia.

Pain scores at rest were statistically significantly lower in the TR group at 6, 12 and 24 h than in T group (P < 0.05). Pain scores at movement and patient comfort scores were also found to be significantly lower in the TR group at 2, 6, 12 and 24 h than in the T group (P < 0.05). Although the TR group consumed less tramadol, there were no statistically significant differences in the cumulative tramadol consumptions between the groups at any time. However, the number of patients requiring rescue analgesia and average supplementary doses used was significantly higher in the T group than in the TR group (P < 0.05).

After major abdominal surgery, adding remifentanil (0.2 μg kg−1) to tramadol (0.2 mg kg−1), with 10-min lockout times, for patient-controlled analgesia offered better postoperative pain relief and patient comfort, without causing any sedation or respiratory depression.

Elderly patients with heart failure undergoing urgent major surgery suffer substantial cardiac morbidity and mortality. Levosimendan, a novel calcium sensitizer, enhances myocardial contractility while simultaneously having vasodilatory and cardioprotective properties. This could be advantageous in perioperative management of heart failure patients.

Ten consecutive patients with symptomatic heart failure and left ventricular ejection fraction <35% undergoing urgent hip fracture repair were studied. Levosimendan was administered with an infusion rate of 0.1 μg kg−1 min−1 in a total dose of 12.5 mg starting a minimum of 2 h prior to surgery. Haemodynamic parameters were obtained at baseline and at 4, 8, 12, 16, 20, 24, 28, 36 and 48 h after start of levosimendan. B-type natriuretic peptide was measured on admission and after 48 h.

Patients were 86 ± 7 yr (mean ± SD) of age. Levosimendan significantly increased cardiac index from 2.4 ± 0.3 L min−1 m−2 at baseline to 3.2 ± 0.6 L min−1 m−2 after 24 h by increases in stroke volume index (baseline 27 ± 5 mL m−2, after 24 h 37 ± 10 mL m−2, P < 0.05). Systemic vascular resistance index significantly decreased from 2718 ± 841 to 1964 ± 385 dyn s cm−5 m−2 within 24 h. Haemodynamic changes exerted by levosimendan persisted up to 48 h. B-type natriuretic peptide plasma concentrations decreased from 1143 ± 792 to 935 ± 724 ng L−1 after 48 h (P = 0.006).

In patients with heart failure, preoperative start of levosimendan infusion improves intraoperative and postoperative haemodynamics. These findings suggest that levosimendan is a useful drug for preoperative optimization of cardiac function in high-risk patients undergoing major surgery.

The available data provide inconsistent results on the efficacy of small-dose remifentanil attenuating the cardiovascular response to intubation in children. Therefore, this randomized double-blind study was designed to assess the ability of different small doses of remifentanil on the cardiovascular intubation response in children, with the aim of determining the optimal dose of remifentanil for this purpose.

One hundred and twenty-four children aged 3–9 yr were randomized to one of four groups to receive the following in a double-blind manner: normal saline (Group 1), remifentanil 0.75 μg kg−1 (Group 2), remifentanil 1 μg kg−1 (Group 3) and remifentanil 1.25 μg kg−1 (Group 4). Non-invasive blood pressure and heart rate were recorded before anaesthesia induction (baseline value), immediately before intubation (postinduction values), at intubation and at 1 min intervals for 5 min after intubation.

Tracheal intubation caused significant increases in systolic blood pressure and heart rate in Groups 1–3 compared with the baseline values. The maximum percent increases of systolic blood pressure and heart rate were 10% and 26% of the baseline values, respectively, in Group 2; 5% and 14% in Group 3; and 1% and 8% in Group 4 compared with 27% and 37% in Group 1. Except for the Group 3 vs. Group 4 comparison, there were significant differences among the four groups in the maximum percent increases of systolic blood pressure and heart rate.

When used as part of anaesthesia induction with propofol and vecuronium in children, bolus administration of remifentanil resulted in a dose-related attenuation of the cardiovascular intubation response.

The inhibition of thermoregulatory control by anaesthesia is manifested by reduced vasoconstriction and shivering thresholds. As intraoperative bleeding can result in haemodynamic changes, including vasoconstriction, we investigated the effect of experimental bleeding on the shivering threshold in rabbits.

Twenty-four rabbits were randomly assigned to one of three treatment strategies: (1) no blood removal (control), (2) 5 mL kg−1 isovolaemic blood removal and (3) 10 mL kg−1 isovolaemic blood removal. After tracheal intubation under isoflurane anaesthesia, anaesthesia was maintained with 50% nitrous oxide in oxygen. The removed blood volume was replaced with the same volume of warm hydroxyethyl starch colloid solution. Oesophageal temperature was measured as a core temperature at 1-min intervals. After blood removal, the animal’s body was cooled at a rate of 2–3°C h−1 by perfusing water at 10°C through a U-shaped thermode positioned in the colon. Hypothermic shivering was evaluated by visual inspection, and the core temperature at which shivering was triggered was identified as the thermoregulatory threshold for this response.

Just before the cooling, the body temperature of the animals was around 38.6°C in all of the three groups. The shivering threshold in the control group was 37.2 ± 0.2°C (mean ± SD). The shivering thresholds in the 5 mL kg−1 (36.9° ± 0.3°C) and 10 mL kg−1 (36.5° ± 0.5°C) blood removal groups were significantly lower and in proportion with the volume of blood removed than that in the control group.

Isovolaemic haemodilution decreased the shivering threshold in rabbits in proportion with the volume of blood removed.

Despite advantages of induction and maintenance of anaesthesia with sevoflurane, postoperative nausea and vomiting occurs frequently. Fentanyl is a commonly used supplement that may contribute to this, although it may alrove analgesia.

This double-blind study examined the incidence and severity of postoperative nausea and vomiting and pain in the first 24 h after sevoflurane anaesthesia in 216 adult day surgery patients. Patients were randomly allocated to either receive or not receive 1 μg kg−1 fentanyl, while a third group received dexamethasone in addition to fentanyl.

Omission of fentanyl did not reduce the overall incidence of postoperative nausea and vomiting, but did reduce the incidence of vomiting and/or moderate to severe nausea prior to discharge from 20% and 17% with fentanyl and fentanyl-dexamethasone, respectively, to 5% (P = 0.013). Antiemetic requirements were reduced from 24% and 31% to 7% (P = 0.0012). Dexamethasone had no significant effect on the incidence or severity of postoperative nausea and vomiting. Combining the two fentanyl groups revealed further significant benefits from the avoidance of opioids, reducing postoperative nausea and vomiting and nausea prior to discharge from 35% and 33% to 22% and 19% (P = 0.049 and P = 0.035), respectively, while nausea in the first 24 h was decreased from 42% to 27% (P = 0.034). Pain severity and analgesic requirements were unaffected by the omission of fentanyl. Fentanyl did reduce minor intraoperative movement but had no sevoflurane-sparing effect and increased respiratory depression, hypotension and bradycardia.

As fentanyl exacerbated postoperative nausea and vomiting without an improvement in postoperative pain and also had adverse cardiorespiratory effects, it appears to be an unnecessary and possibly detrimental supplement to sevoflurane in day surgery.

Thoracic surgery requires immobilization of the operating area. Usually, this is achieved with one-lung ventilation (OLV), however this may still lead to some movement. High-frequency jet ventilation (HFJV) may be an alternative way of ventilation in thoracic surgery. The purpose of this study was to determine the effectiveness of HFJV as an alternative option to OLV for thoracic procedures.

Sixty patients were randomized to receive either HFJV (n = 29) or OLV (n = 31) during the operation. During the course of the study 10 patients were excluded (4 patients in HFJV group and 6 patients in OLV group). The following haemodynamic and ventilatory parameters were recorded: heart rate, systolic and mean blood pressure, ventricular stroke volume, cardiac index, systemic vascular resistance, peak inspiratory pressure, oxygen saturation, PaO2 and PaCO2. Overall parameters were documented before the initiation of the chosen mode of ventilation every 15 min during the operation.

Patients in both groups showed comparable cardiovascular function. Mean values of peak inspiratory pressure were significantly higher in the OLV group. Oxygen saturation values were statistically higher in the HFJV group. PaCO2 values were similar in both during surgery, but were higher in the OLV group after awakening. Mean values of shunt fraction were lower in the HFJV group. Lower values of peak inspiratory pressure were therefore associated with higher partial pressure of carbon dioxide levels in the HFJV group. In the OLV group, 44% of patients experienced a postoperative sore throat. Operating conditions were comparable.

HFJV is safe option, comparable to OLV and offers some advantages for open-chest thoracic procedures.

Post-anaesthetic shivering is one of the most common complications, occurring in 5–65% of patients recovering from general anaesthesia and 33% of patients receiving epidural anaesthesia. Our objective was to investigate the efficacy of intraoperative dexmedetomidine infusion on postoperative shivering.

Ninety female patients, ASA I-II, 35–60 yr old, scheduled for elective total abdominal hysterectomy with or without bilateral salpingo-oophorectomy were randomized into two groups. After endotracheal intubation one group received normal saline infusion and the other received dexmedetomidine as a loading dose of 1 μg kg−1 for 10 min followed by a maintenance infusion of 0.4 μg kg−1 h−1. In the recovery room, pain was assessed using a 100 mm visual analogue scale and those patients who had a pain score of more than 40 mm were administered 1 mg kg−1 intramuscular diclofenac sodium. Patients with shivering grades more than 2 were administered 25 mg intravenous meperidine. Patients were protected with passive insulation covers.

Post-anaesthetic shivering was observed in 21 patients in the saline group and in seven patients in the dexmedetomidine group (P = 0.001). Shivering occurred more often in the saline group. The Ramsay Sedation Scores were higher in the dexmedetomidine group during the first postoperative hour. Pain scores were higher in the saline group for 30 min after the operation. The need for intraoperative atropine was higher in the dexmedetomidine group. Intraoperative fentanyl use was higher in the saline group. Perioperative tympanic temperatures were not different between the groups whereas postoperative measurements were lower in the dexmedetomidine group (P < 0.05).

Intraoperative dexmedetomidine infusion may be effective in the prevention of post-anaesthetic shivering.

Partial obstruction of endotracheal tubes due to accumulation of secretions and mucus plugs can increase the tube resistance and subsequently impose increased resistive load on the patient. This study was performed to determine the changes in the resistance of endotracheal tubes of sizes 7.5, 8.0 and 8.5 mm with different degrees and locations of endotracheal tube narrowing.

Reductions of 10%, 25%, 50% and 75% in the endotracheal tube’s cross-sectional areas were created at different sites along the axes of the tube connected to an artificial lung. While ventilating with a constant inspiratory flow, a 1 s end-inspiratory occlusion manoeuvre was applied and the resulting plateau pressure was determined. The resistance was calculated as (peak airway pressure – plateau pressure)/peak inspiratory flow.

Significant increases in the endotracheal tube’s resistances were observed as the tube’s cross-sectional area reduction was increased from 25% to 50% and from 50% to 75% for the 7.5 mm endotracheal tube, from 25% to 50% for the 8.0 mm endotracheal tube, and from 50% to 75% for the 8.5 mm endotracheal tube. Changes of the endotracheal tube resistances were not affected by the site of cross-sectional area reductions along the axes of the tubes.

For endotracheal tubes of sizes 7.5, 8.0 and 8.5 mm, significant changes in the tubes resistances are observed when the partial obstructions of the tubes exceed certain critical values. The location of the partial obstruction did not affect the changes in the endotracheal tube resistances.