Postoperative orthostatic intolerance following fast-track unicompartmental knee arthroplasty: incidence and hemodynamics-a prospective observational cohort study.

BACKGROUND: Early postoperative mobilization is essential for early functional recovery but can be inhibited by postoperative orthostatic intolerance (OI). Postoperative OI is common after major surgery, such as total knee arthroplasty (TKA). However, limited data are available after less extensive surgery, such as unicompartmental knee arthroplasty (UKA). We, therefore, investigated the incidence of OI as well as cardiovascular and tissue oxygenation responses during early mobilization after UKA. METHODS: This prospective single-centre observational study included 32 patients undergoing primary UKA. Incidence of OI and cardiovascular and tissue oxygenation responses during mobilization were evaluated preoperatively, at 6 and 24 h after surgery. Perioperative fluid balance, bleeding, surgery duration, postoperative hemoglobin, pain during mobilization and opioid usage were recorded. RESULTS: During mobilization at 6 h after surgery, 4 (14%, 95%CI 4-33%) patients experienced OI; however, no patients terminated the mobilization procedure prematurely. Dizziness and feeling of heat were the most common symptoms. OI was associated with attenuated systolic and mean arterial blood pressure responses in the sitting position (all p < 0.05). At 24 h after surgery, 24 (75%) patients had already been discharged, including three of the four patients with early OI. Only five patients were available for measurements, two of whom experienced OI; one terminated the mobilization procedure due to intolerable symptoms. We observed no statistically significant differences in perioperative fluid balance, bleeding, surgery duration, postoperative hemoglobin, pain, or opioid usage between orthostatic intolerant and tolerant patients. CONCLUSIONS: The incidence of orthostatic intolerance after fast-track unicompartmental knee arthroplasty is low (~ 15%) and is associated with decreased orthostatic pressure responses. Compared to the previously described orthostatic intolerance incidence of ~ 40% following total knee arthroplasty, early orthostatic intolerance is uncommon after unicompartmental knee arthroplasty, suggesting a procedure-specific component. TRIAL REGISTRATION: Prospectively registered at ClinicalTrials.gov; registration number: NCT04195360, registration date: 13.12.2019.

Orthostatic intolerance after acute mild hypovolemia: incidence, pathophysiologic hemodynamics, and heart-rate variability analysis-a prospective observational cohort study.

PURPOSE: Early postoperative mobilization can be hindered by orthostatic intolerance (OI). Postoperative OI has multifactorial pathogenesis, possibly involving both postoperative hypovolemia and autonomic dysfunction. We aimed to investigate the effect of mild acute blood loss from blood donation simulating postoperative hypovolemia, on both autonomic function and OI, thus eliminating confounding perioperative factors such as inflammation, residual anesthesia, pain, and opioids. METHODS: This prospective observational cohort study included 26 blood donors. Continuous electrocardiogram data were collected during mobilization and night sleep, both before and after blood donation. A Valsalva maneuver and a standardized mobilization procedure were performed immediately before and after blood donation, during which cardiovascular and tissue oxygenation variables were continuously measured by LiDCOrapid™ and Massimo Root™, respectively. The incidence of OI, hemodynamic responses during mobilization and Valsalva maneuver, as well as heart rate variability (HRV) responses during mobilization and sleep were compared before and 15 min after blood donation. RESULTS: Prior to blood donation, no donors experienced OI during mobilization. After blood donation, 6/26 (23%; 95% CI, 9 to 44) donors experienced at least one OI symptom. Three out of 26 donors (12%; 95% CI, 2 to 30) terminated the mobilization procedure prematurely because of severe OI symptoms. Cardiovascular and cerebral tissue oxygenation responses were reduced in patients with severe OI. After blood loss, HRV indices of total autonomic power remained unchanged but increased sympathetic and decreased parasympathetic outflow was observed during mobilization, but also during sleep, indicating a prolonged autonomic effect of hypovolemia. CONCLUSION: We describe a specific hypovolemic component of postoperative OI, independent of postoperative autonomic dysfunction, inflammation, opioids, and pain. STUDY REGISTRATION: ClinicalTrials.gov (NCT04499664); registered 5 August 2020.

RéSUMé: OBJECTIF: La mobilisation postopératoire précoce peut être entravée par une intolérance orthostatique (IO). L'IO postopératoire a une pathogenèse multifactorielle, impliquant peut-être à la fois une hypovolémie postopératoire et un dysfonctionnement autonome. Notre objectif était d'étudier l'effet d'une légère perte de sang aiguë due au don de sang simulant une hypovolémie postopératoire, à la fois sur la fonction autonome et sur l'IO, éliminant ainsi les facteurs périopératoires confondants tels que l'inflammation, l'anesthésie résiduelle, la douleur et les opioïdes. MéTHODE: Cette étude de cohorte observationnelle prospective comprenait 26 personnes ayant donné leur sang. Des données d'électrocardiogramme continu ont été recueillies pendant la mobilisation et le sommeil nocturne, avant et après le don de sang. Une manœuvre de Valsalva et une procédure de mobilisation standardisée ont été réalisées immédiatement avant et après le don de sang, au cours desquelles les variables d'oxygénation cardiovasculaire et tissulaire ont été mesurées en continu avec les moniteurs LiDCOrapid™ et Massimo Root™, respectivement. L'incidence d'IO, les réponses hémodynamiques pendant la mobilisation et la manœuvre de Valsalva, ainsi que les réponses de variabilité de la fréquence cardiaque (VFC) pendant la mobilisation et le sommeil ont été comparées avant et 15 minutes après le don de sang. RéSULTATS: Avant le don de sang, aucune personne ayant fait un don de sang n'a ressenti d'IO pendant la mobilisation. Après le don de sang, 6/26 (23 %; IC 95 %, 9 à 44) des donneurs et donneuses ont manifesté au moins un symptôme d'IO. Trois personnes sur 26 (12 %; IC 95 %, 2 à 30) ont interrompu prématurément la procédure de mobilisation en raison de symptômes graves d'IO. Les réponses d'oxygénation des tissus cardiovasculaires et cérébraux ont été réduites chez les personnes atteintes d'IO sévère. Après la perte de sang, les indices de VFC de la puissance totale autonome sont demeurés inchangés, mais une augmentation du flux sympathique et une diminution du flux parasympathique ont été observées pendant la mobilisation, mais également pendant le sommeil, indiquant un effet autonome prolongé de l'hypovolémie. CONCLUSION: Nous décrivons une composante spécifique hypovolémique de l'IO postopératoire, indépendante du dysfonctionnement autonome postopératoire, de l'inflammation, des opioïdes et de la douleur. ENREGISTREMENT DE L'éTUDE: www.ClinicalTrials.gov (NCT04499664); enregistrée le 5 août 2020.