Abstract
BackgroundABGs are performed in acute conditions as the reference method for assessing the acid-base status of blood. Hyperventilation and breath-holding are common ventilatory changes that occur around the time of sampling, rapidly altering the ‘true’ status of the blood. This is particularly relevant in emergency medicine patients without permanent arterial catheters, where the pain and anxiety of arterial punctures can cause ventilatory changes. This study aimed to determine whether peripheral venous values could be a more reliable measure of blood gases following acute changes in ventilation.MethodsTo allow for characterisation of ventilatory changes typical of acutely ill patients, but without the confounding influence of perfusion or metabolic disturbances, 30 patients scheduled for elective surgery were studied in a prospective observational study. Following anaesthesia, and before the start of the surgery, ventilator settings were altered to achieve a + 100% or − 60% change in alveolar ventilation (‘hyper-’ or ‘hypoventilation’), changes consistent with the anticipation of a painful arterial puncture commonly encountered in the emergency room. Blood samples were drawn simultaneously from indwelling arterial and peripheral venous catheters at baseline, and at 15, 30, 45, 60, 90 and 120 s following the ventilatory change. Comparisons between the timed arterial (or venous) samples were done using repeated-measures ANOVA, with post-hoc analysis using Bonferroni’s correction.ResultsArterial blood pH and PCO2 changed rapidly within the first 15–30s after both hyper- and hypoventilation, plateauing at around 60s (∆pH = ±0.036 and ∆PCO2 = ±0.64 kPa (4.7 mmHg), respectively), with peripheral venous values remaining relatively constant until 60s, and changing minimally thereafter. Mean arterial changes were significantly different at 30s (P < 0.001) when compared to baseline, in response to both hyper- and hypoventilation.ConclusionThis study has shown that substantial differences in arterial and peripheral venous acid-base status can be due to acute changes in ventilation, commonly seen in the ER over the 30s necessary to sample arterial blood. If changes are transient, peripheral venous blood may provide a more reliable description of acid-base status.
Highlights
In emergency or intensive care medicine, blood gas analysis is used to monitor the acid-base and oxygenation status of the patient
This study investigates the acute response of end-tidal CO2 (EtCO2) and, simultaneous arterial and peripheral venous acid-base status, following standardised changes in ventilation, with responses to both an increase and decrease in ventilation being examined
From their results we approximated the changes from baseline for Partial pressure of carbon dioxide (PCO2) in both arterial and venous blood respectively, following voluntary hyperventilation
Summary
In emergency or intensive care medicine, blood gas analysis is used to monitor the acid-base and oxygenation status of the patient. Small disturbances around the time of sampling could induce acute transient changes in ventilation and misrepresentation of the acid-base status. Such transient changes could be due to anxiety or fear of the needle prior to puncture [1], resulting in hyperventilation or breath holding. Hyperventilation and breath-holding are common ventilatory changes that occur around the time of sampling, rapidly altering the ‘true’ status of the blood. This is relevant in emergency medicine patients without permanent arterial catheters, where the pain and anxiety of arterial punctures can cause ventilatory changes. This study aimed to determine whether peripheral venous values could be a more reliable measure of blood gases following acute changes in ventilation
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More From: Scandinavian Journal of Trauma, Resuscitation and Emergency Medicine
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