The Latest in Critical Care, 9/3/23 (Issue #13)

Pulse oximeters overestimated oxygen saturation in darker-skinned patients with Covid, causing treatment delays.

It was a bit of a national and professional embarrassment when after many decades of ubiquitous use of pulse oximetry, calibrated on patients with light skin, someone finally thought to validate it with arterial blood gases in darker-skinned patients in clinical settings — and found pulse oximetry may dangerously overestimate those patients’ arterial oxygen saturation. Not until 2020 did we learn that more than one in six patients who self-identify as Black may have functional saturations of 88% or lower on ABGs, despite pulse oximetry readings of 92-96%.

(Pulse oximetry’s suboptimal performance in darker-skinned patients was recognized inside industry for decades, but was considered within a reasonable margin of error and unlikely to be clinically significant.)

A follow-up study conducted in the early part of pandemic reviewed the cases of about 24,500 patients with pulse oximetry and arterial blood gas tests.

Darker-skinned patients were more likely to have misleadingly normal pulse oximetry readings. Those with falsely high pulse ox readings (of any race) were slightly less likely to receive early treatment for Covid-19, and more likely to be later readmitted to the hospital. There was no clear signal of increased mortality.

FDA has no clear plan to address the issue through regulatory guidance, but recently stated “It is a high priority for the agency to ensure that oximetry device performance is equitable and accurate for all U.S. patients.” Read in JAMA Internal Medicine

Usual sugammadex doses may be inadequate to reverse neuromuscular blockade.

Sugammadex is a reversal agent for neuromuscular blockade induced by rocuronium or vecuronium. It’s often given by anesthesiologists at the end of surgeries in the O.R. to help mechanically ventilated patients more quickly recover spontaneous breathing and be successfully extubated. A train-of-four stimulus is given and (according to the manufacturer), a sugammadex dose of 2 mg/kg should be administered if at least two twitches are present, or 4 mg/kg if there are less than two twitches (and a posttetanic count of more than 0). But like other drugs, metabolism of sugammadex might vary among patients.

Among 97 patients admitted for cardiac surgery and followed prospectively, the sugammadex dose required to achieve a train-of-four ratio of 0.9 or greater varied by a factor of 12x, with some patients requiring almost 6 mg/kg. Even at the same depth of neuromuscular blockade, dosages required for reversal varied significantly. Almost 90% of patients needed less than the manufacturer’s dosing, but 13% required more, and two patients (~2%) required repeated sugammadex dosing for recurrent paralysis.

Authors advocate for use of quantitative twitch monitoring (acceleromyography or electromyography) rather than visual train-of-four twitch monitoring to ensure adequate reversal of neuromuscular blockade. Read in Anesthesiology

Most cancer screening was not proven to reduce all-cause mortality, in a large analysis.

It’s a complex topic, and the widely reported meta-analysis does not claim to rule out benefits of cancer screening. Rather, it showed they were uncertain (except for sigmoidoscopy) and likely absent or very small for prostate, breast, fecal blood, and colonoscopy screenings. We can parse some of the nuances by looking at a large colonoscopy screening trial in NEJM (which showed zero reduction in the 11% all-cause mortality among 28,000 patients invited to be screened, compared to 56,000 uninvited controls, few of whom were ever screened).

“How can anyone say colonoscopy didn’t help when only 42% of the invited patients actually responded and got colonoscopies?” you might ask. That’s a valid point, and the truth is colonoscopy screening did save a tiny number of lives in that trial. The invited group had a 0.28% 10-year rate of death from colorectal cancer, and the uninvited group 0.31%. That’s about eight lives saved out of 28,000 invited (and 11,000 screened). But even had all the 28,000 invited patients been screened, the 10-year risk of death from colorectal cancer was only predicted to be reduced from 0.30% to 0.15% (or 42 lives saved). A 50% relative risk reduction: great for public service announcements, but not enough to significantly reduce all-cause mortality.

Screening has become a sacred ritual in our secular religion of longevity, a modern, slightly more effective version of warding off the evil eye. But the scary truth (known even to the ribbon-peddling nonprofits) is that a large proportion of lethal solid cancers arise quickly, in between screening episodes, and progress aggressively, eliminating any benefits of early detection by screening. Mammography screening for breast cancer has been previously shown not to reduce all-cause mortality, with only small reductions in breast cancer-specific mortality that improved with age.

For the fatalistic, this study may provide a wonderful sense of liberation—they can just get on with their carefree lives, knowing death will come for them someday at its whim. Maybe that will shorten the wait for my screening colonoscopy. Call me superstitious, and pass the Golytely. Read in JAMA Internal Medicine

In the News

BA.2.86, the highly mutated Covid strain of interest, is now in Michigan, New York, Ohio, Texas and Virginia, but there’s no evidence it’s causing any increase in hospitalizations or more severe illness.

CDC is signaling it will recommend the fall booster for everyone — the elderly, sure, but also 25-year-olds and 5-year-olds who appear to be at virtually zero risk for severe disease from the circulating Omicron variants, thanks to its lower virulence and their prior immunity (natural and acquired). There are no randomized trials planned to test the effectiveness of the booster.