Context Although there is now substantial evidence that pulmonary artery (PA) catheterization does not reduce mortality in critically ill patients, it is unknown whether national utilization has decreased in response. Objective To determine trends in PA catheterization use in the United States. Design, Setting, and Participants A time trend analysis on national estimates of PA catheterization utilization from 1993-2004 using data from all US states contributing to the Nationwide Inpatient Sample. Hospital admissions for those participants aged 18 years or older were assessed, with primary analysis focused on admissions with a medical diagnosis related group and a secondary analysis focused on surgical admissions. PA catheterization was identified by 5 International Classification of Diseases, Ninth Revision procedure codes describing PA or wedge-pressure monitoring, measurement of mixed venous blood gases, or monitoring of cardiac output by oxygen consumption or other technique. Main Outcome Measure Annual PA catheterization use per 1000 medical admissions. Results Between 1993 and 2004, PA catheterization use decreased by 65% from 5.66 to 1.99 per 1000 medical admissions (risk ratio [RR], 0.35; 95% confidence interval [CI], 0.29-0.42). Among patients who died during hospitalization, a group whose disease severity may be consistent across time, the relative decline was similar, decreasing from 54.7 to 18.1 per 1000 deaths (RR, 0.33; 95% CI, 0.28-0.38). A significant change in trend occurred following a 1996 study that suggested increased mortality with PA catheterization. The decline in utilization was similar in surgical patients (RR, 0.37; 95% Cl, 0.25-0.49). Among common diagnoses associated with PA catheterization, the decline was most prominent for myocardial infarction, which decreased by 81% (RR, 0.19; 95% Cl, 0.15-0.23), and least prominent for septicemia, which decreased by 54% (RR, 0.46; 95% Cl, 0.38-0.54). Sensitivity analyses suggested findings were not due to artifact of changing procedure coding practice. Conclusion Use of the PA catheter, previously a hallmark of critical care practice, has decreased in the United States during the last decade, possibly due to growing evidence that this invasive procedure does not reduce mortality.

Trends in the Use of the pulmonary artery catheter in the United states, 1993-2004. Commentary

Background Studies of pulmonary denitrogenation (pre-oxygenation) in obstetric populations have shown high flow nasal oxygen therapy (HFNO) is inferior to facemask techniques. HFNO achieves median end-tidal oxygen fraction (FE′O2) of 0.87 after 3 min. As HFNO prolongs safe apnoea times through apnoeic oxygenation, we postulated that HFNO would still extend safe apnoeic times despite the lower FE′O2 after pre-oxygenation. Methods The Interdisciplinary Collaboration in Systems Medicine simulation suite, a highly integrated, high-fidelity model of the human respiratory and cardiovascular systems, was used to study the effect of varying FE′O2 (60%, 70%, 80%, and 90%) on the duration of safe apnoea times using HFNO and facemask techniques (with the airway open and obstructed). The study population consisted of validated models of pregnant women in active labour and not in labour with BMI of 24, 35, 40, 45, and 50 kg m−2. Results HFNO provided longer safe apnoeic times in all models, with all FE′O2 values. Labour and increased BMI reduced this effect, in particular a BMI of 50 kg m−2 reduced the improvement in apnoea time to 1.8–8.5 min (depending on the FE′O2), compared with an improvement of more than 60 min in the subject with BMI 24 kg m−2. Conclusions Despite generating lower FE′O2, HFNO provides longer safe apnoea times in pregnant subjects in labour. Care should be taken when used in patients with BMI ≥50 kg m−2 as the extension of the safe apnoea time is limited.

Effect of variable pre-oxygenation endpoints on safe apnoea time using high flow nasal oxygen for women in labour: a modelling investigation.

Background Monitoring oxygen consumption (VO2) is neither recommended nor included in peri-operative haemodynamic algorithms aiming at optimising oxygen delivery (DO2) in major abdominal surgery. Estimates of peri-operative VO2 changes are uncertain in earlier publications and have limited generalisability in the current high-risk surgical population. In a prospective non-interventional observational study in elderly patients undergoing major abdominal procedures, we investigated the change of VO2 after induction of anaesthesia and secondarily, the further changes during and after surgery in relation to DO2 and estimated oxygen extraction ratio (O2ER) by routine monitoring. Methods VO2 was determined by indirect calorimetry (QuarkRMR) in 20 patients more than 65 years (ASA II to IV), scheduled for elective open upper abdominal surgery with combined epidural and general anaesthesia. Data were collected during 20-minute periods pre-operatively and after anaesthesia induction, with subsequent measurements during surgery and postoperatively. Simultaneously, DO2 was monitored using LiDCOplus. The O2ER was estimated from arterial-central venous oxygen content calculation. Mixed models were used to analyse the peri-operative changes. Results VO2 decreased after induction of anaesthesia by a mean of 34% (95% CI, 28 to 39). After 2 h of surgery, VO2 was reduced by 24% (95% CI, 20 to 27) compared with the awake baseline measurements. Pre-operative mean DO2 was 440 (95% CI, 396 to 483) ml min m and decreased by a mean of 37% (95% CI, 30 to 43) during anaesthesia. The estimated O2ER did not change intra-operatively 0.24 (95% CI, 0.21 to 0.26) but increased postoperatively to 0.31 (95% CI, 0.27 to 0.36). The changes of VO2 were parallel with changes of DO2 and O2ER in the intra-operative period. Conclusion General anaesthesia reduced VO2 by approximately a third in elderly patients undergoing major abdominal surgery. Parallel changes of intra-operative VO2 and delivery were demonstrated while oxygen extraction was low. The relevance of these changes needs further assessment in relation to outcomes and haemodynamic interventions. Trial registration Clinicaltrials.gov NCT03355118.

Peri-operative oxygen consumption revisited: An observational study in elderly patients undergoing major abdominal surgery

Hypoxaemia during general anaesthesia can cause harm. Apnoeic oxygenation extends safe apnoea time, reducing risk during airway management. We hypothesised that low-flow nasal oxygenation (LFNO) would extend safe apnoea time similarly to high-flow nasal oxygenation (HFNO), whilst allowing face-mask preoxygenation and rescue.A high-fidelity, computational, physiological model was used to examine the progression of hypoxaemia during apnoea in virtual models of pregnant women in and out of labour, with BMI of 24-50 kg m-2. Subjects were preoxygenated with oxygen 100% to reach end-tidal oxygen fraction (FE'O2) of 60%, 70%, 80%, or 90%. When apnoea started, HFNO or LFNO was commenced. To simulate varying degrees of effectiveness of LFNO, periglottic oxygen fraction (FgO2) of 21%, 60%, or 100% was configured. HFNO provided FgO2 100% and oscillating positive pharyngeal pressure.Application of LFNO (FgO2 100%) after optimal preoxygenation (FE'O2 90%) resulted in similar or longer safe apnoea times than HFNO FE'O2 80% in all subjects in labour. For BMI of 24, the time to reach SaO2 90% with LFNO was 25.4 min (FE'O2 90%/FgO2 100%) vs 25.4 min with HFNO (FE'O2 80%). For BMI of 50, the time was 9.9 min with LFNO (FE'O2 90%/FgO2 100%) vs 4.3 min with HFNO (FE'O2 80%). A similar finding was seen in subjects with BMI ≥40 kg m-2 not in labour.There is likely to be clinical benefit to using LFNO, given that LFNO and HFNO extend safe apnoea time similarly, particularly when BMI ≥40 kg m-2. Additional benefits to LFNO include the facilitation of rescue face-mask ventilation and ability to monitor FE'O2 during preoxygenation. 

Comparison of apnoeic oxygen techniques in term pregnant subjects: a computational modelling study.

Systemic oxygen delivery (DO2) is a more comprehensive marker of patient status than arterial oxygen saturation (SaO2), and DO2 in the range of 330–500 mL min−1 is reportedly adequate during anaesthesia. We measured DO2 during one-lung ventilation (OLV) for thoracic surgery—where the risk of pulmonary shunt is significant, and hypoxia occurs frequently—and compared sevoflurane and propofol, the two most commonly used anaesthetics in terms of DO2. Sevoflurane impairs hypoxic pulmonary vasoconstriction. Thus, our hypothesis was that propofol-based anaesthesia would show a higher DO2 value than sevoflurane-based anaesthesia. This was a double-blinded randomised controlled trial conducted at a university hospital from 2017 to 2018. The study population consisted of patients scheduled for lobectomy under OLV (N = 120). Sevoflurane or propofol was titrated to a bispectral index of 40–50. Haemodynamic variables were measured during two-lung ventilation (TLV) and OLV at 15 and 45 min (OLV15 and OLV45, respectively) using oesophageal Doppler monitoring. The mean DO2 (mL min−1) was not different between the sevoflurane and propofol anaesthesia groups (TLV: 680 vs. 706; OLV15: 685 vs. 703; OLV45: 759 vs. 782, respectively). SaO2 was not correlated with DO2 (r = 0.09, p = 0.100). Patients with SaO2 97%) showed inadequate DO2 (14% of measurements < 500 mL min−1). In conclusion, DO2 did not significantly differ between sevoflurane and propofol. SaO2 was not correlated with DO2 and was not informative regarding whether the patients were receiving an adequate oxygen supply. DO2 may provide additional information on patient status, which may be especially important when patients show a low SaO2.

Systemic Oxygen Delivery during One-Lung Ventilation: Comparison between Propofol and Sevoflurane Anaesthesia in a Randomised Controlled Trial.

Background Increased oxygen extraction, the ratio of consumption to delivery, has been associated with poor outcome after surgery Oxygen consumption (VO2) can change in several ways in the perioperative period, but is seldom monitored directly in routine care This study investigates the effects of general anaesthesia on VO2 Methods We searched PubMed, EMBASE, and Cochrane Library 1946-2018 for studies including VO2 measurements before and after anaesthesia induction Quality was assessed by Cochrane risk of bias tool and NIH Quality Assessment tool for before-and-after studies Changes in VO2 after anaesthesia induction were pooled in a random effects model meta-analysis with standardized mean differences transformed to absolute changes of VO2 Changes in VO2 after surgical incision and after recovery from anaesthesia were analysed as secondary outcomes in the included studies Results Twenty-four studies including 453 patients were analysed for VO2 changes induced by anaesthesia Studies were published during 1969-2000 and mean age of patients ranged 28-70 years VO2 decreased after anaesthesia induction by -65 (-75; -55, 95% CI) mL min-1 and indexed VO2 (VO2I) by -33 (-38; -28, 95% CI) mL min-1 m-2  After surgical incision and in the post-operative period VO2 increased again Heterogeneity was considerable among the studies and the overall quality of evidence was very low Conclusions General anaesthesia probably reduces oxygen consumption but the effect estimate is uncertain Given the limited generalizability and low quality of the available evidence, new studies in modern perioperative settings and in today's older high-risk surgical patient populations are needed

Sofia Vadman

Papers

The effects of general anaesthesia on oxygen consumption: A meta-analysis guiding future studies on perioperative oxygen transport